# Patent

## Title
Constitutively translocating cell line

## Abstract

The present invention relates to agonist-independent methods of screening for compounds that alter GPCR desensitization. Included in the present invention are cell lines containing GRKs, in which GPCRs are desensitized in the absence of agonist; the GRKs may be modified. The present invention relates to methods to determine if a GPCR is expressed at the plasma membrane, and if the GPCR has an affinity for arrestin. Modified GPCRs which have increased arrestin affinity are included in the present invention. These modified GPCRs are useful in methods to screen for compounds that alter desensitization, including both the agonist-independent methods and agonist-dependent methods described herein.

## Background
The present application is a Continuation-In-Part application of International Application No. PCT/US03/14581, filed on May 12, 2003, which claims the benefit of U.S. Provisional Application No. 60/379,986 filed on May 13, 2002; and U.S. Provisional Application No. 60/401,698 filed on Aug. 7, 2002; which are hereby incorporated by reference in their entireties.


FIELD OF THE INVENTION
The present invention relates to methods of assaying GPCR desensitization in a agonist-independent manner, host cells useful in such methods, methods of the identification of compounds that alter GPCR desensitization, the compounds identified, and their use in disease treatment.
BACKGROUND
G protein-coupled receptors (GPCRs) are cell surface proteins that translate hormone or ligand binding into intracellular signals. GPCRs are found in all animals, insects, and plants. GPCR signaling plays a pivotal role in regulating various physiological functions including phototransduction, olfaction, neurotransmission, vascular tone, cardiac output, digestion, pain, and fluid and electrolyte balance. Although they are involved in numerous physiological functions, GPCRs share a number of common structural features. They contain seven membrane domains bridged by alternating intracellular and extracellular loops and an intracellular carboxyl-terminal tail of variable length.
GPCRs have been implicated in a number of disease states, including, but not limited to: cardiac indications such as angina pectoris, essential hypertension, myocardial infarction, supraventricular and ventricular arrhythmias, congestive heart failure, atherosclerosis, renal failure, diabetes, respiratory indications such as asthma, chronic bronchitis, bronchospasm, emphysema, airway obstruction, upper respiratory indications such as rhinitis, seasonal allergies, inflammatory disease, inflammation in response to injury, rheumatoid arthritis, chronic inflammatory bowel disease, glaucoma, hypergastrinemia, gastrointestinal indications such as acid/peptic disorder, erosive esophagitis, gastrointestinal hypersecretion, mastocytosis, gastrointestinal reflux, peptic ulcer, Zollinger-Ellison syndrome, pain, obesity, bulimia nervosa, depression, obsessive-compulsive disorder, organ malformations (for example, cardiac malformations), neurodegenerative diseases such as Parkinson's Disease and Alzheimer's Disease, multiple sclerosis, Epstein-Barr infection and cancer.
The magnitude of the physiological responses controlled by GPCRs is linked to the balance between GPCR signaling and signal termination. The signaling of GPCRs is controlled by a family of intracellular proteins called arresting. Arrestins bind activated GPCRs, including those that have been agonist-activated and especially those that have been phosphorylated by G protein-coupled receptor kinases (GRKs).
Receptors, including GPCRs, have historically been targets for drug discovery and therapeutic agents because they bind ligands, hormones, and drugs with high specificity. Approximately fifty percent of the therapeutic drugs in use today target or interact directly with GPCRs. See e.g., Jurgen Drews, (2000) “Drug Discovery: A Historical Perspective,” Science 287:1960-1964.
There is a need for accurate, easy to interpret methods of detecting G protein-coupled receptor activity and methods of assaying GPCR activity. One method, as disclosed in Barak et al., U.S. Pat. Nos. 5,891,646 and 6,110,693, uses a cell expressing a GPCR and a conjugate of an arrestin and a detectable molecule, the contents of which are incorporated by reference in their entirety.
Although only several hundred human GPCRs are known, it is estimated that upwards of a thousand GPCRs exist in the human genome. Of these known GPCRs, many are orphan receptors that have yet to be associated with a ligand.
The majority of the existing methods for identifying GPCR antagonists are dependent on the presence of agonist. Assays for identifying compounds that prevent the activation of GPCRs typically require that the GPCR is first activated in order to identify interfering compounds. For receptors with known agonists, these agonists are currently used to activate these receptors. However, many GPCRs are orphan receptors with no known ligand or agonist.
The agonist-dependence of GPCR assays continues to be a problem because antagonist discovery for orphan receptors is typically dependent on the prior discovery of agonist or ligand. Agonist-independent methods to screen for compounds that alter GPCR desensitization will (1) eliminate the step of agonist-addition in screening methods, and (2) enable identification of compounds that alter the desensitization of orphan receptors. Agonist-independent methods will eliminate the step of identifying an agonist of an orphan receptor prior to screening for compounds that alter desensitization of the orphan receptor.
SUMMARY
The present invention relates to methods of identifying compounds which alter GPCR internalization.
A first aspect of the present invention is a method of identifying a compound which alters GPCR internalization, including: (a) providing a cell including a GPCR, an arrestin, and a modified GRK, wherein said GPCR is at least partially internalized in an agonist-independent manner upon expression of said GRK; (b) exposing said cell to the compound(s); (c) determining the cellular distribution of the GPCR, arrestin, or modified GRK; and (d) monitoring a difference between (1) the distribution of the GPCR, arrestin, or modified GRK in the cell in the presence of the compound(s) and (2) the distribution of the GPCR, arrestin, or modified GRK in the cell in the absence of the compound(s). An agonist may not be provided in the above method. In the method, a difference between (1) and (2) of step (d) may indicate modulation of GPCR internalization.
The GRK may be over-expressed, its expression may be inducible, and it may include a CAAX motif. The GRK may be GRK1, GRK2, GRK3, GRK4, GRK5, GRK6, or a biologically active fragment thereof.
The GPCR may be modified to have enhanced phosphorylation by a GRK. The GPCR may be β2AR(Y326A), a GPCR listed in FIG. 1A-1C, an orphan GPCR, a modified GPCR, a taste receptor, a Class A GPCR, a Class B GPCR, a mutant GPCR, or a biologically active fragment thereof.
The arrestin may be visual arrestin, cone arrestin, β-arrestin 1, β-arrestin-2, or a biologically active fragment thereof.
The GPCR, GRK, or arrestin may be detectably labeled. A molecule involved in desensitization may be detectably labeled, or a molecule that interacts with a molecule involved in desensitization may be detectably labeled.
In a further aspect, the present invention relates to a method of identifying a compound that alters GPCR phosphorylation, including: (a) providing a cell including a GPCR and a GRK; (b) exposing the cell to the compound(s); and (c) determining whether GRK phosphorylation of the GPCR is altered in the presence of the compound(s).
The cellular distribution of the GPCR or GRK may be determined. A difference may be monitored between (1) the distribution of the GPCR or GRK in the cell in the presence of the compound(s) and (2) the distribution of the GPCR or GRK in the cell in the absence of the compound(s). A difference may be correlated between (1) and (2) to the phosphorylation of the GPCR.
The GRK may not be located in the plasma membrane, indicating that GRK phosphorylation of the GPCR is altered. The phosphorylation state of the GPCR may be determined. The activity of the GRK may be determined. The ability of the GPCR to be internalized may be determined.
In an additional aspect, the present invention relates to a method of determining if a GPCR is expressed at the plasma membrane, including: (a) providing a cell including a GPCR, an arrestin, and a GRK, wherein the arrestin is detectably labeled; (b) determining the cellular distribution of the arrestin; and (c) correlating the cellular distribution of the arrestin to the ability of the GPCR to be expressed at the plasma membrane. The arrestin may be localized in vesicles, pits endosomes, or elsewhere in the desensitization pathway.
Additionally, the present invention relates to a further method of determining if a GPCR is expressed at the plasma membrane, including: (a) providing a cell including a GPCR and a GRK, wherein the GRK is detectably labeled; (b) determining the cellular distribution of the GRK, and (c) correlating the cellular distribution of the GRK to the ability of the GPCR to be expressed at the plasma membrane. The GRK may be localized at the plasma membrane.
In a further aspect, the present invention relates to a method of analyzing the ability of a GPCR to bind arrestin, including: (a) providing a cell including a GPCR, an arrestin, and a GRK, wherein the arrestin is detectably labeled; (b) determining the cellular distribution of the arrestin; and (c) correlating the cellular distribution of the arrestin to the ability of the GPCR to bind arrestin. The arrestin or the GPCR may be localized in vesicles, pits, or endosomes.
In an additional aspect, the present invention relates to a compound identified by a method of the present invention.
In a further aspect, the present invention is related to a method of treating a disease by modulating desensitization of a GPCR in a host cell, including: (a) providing a compound identified by a method of the present invention; and (b) administering the compound to a host.
Another aspect of the invention relates to a host cell including a GPCR and a modified GRK. The GRK may be inducible or over-expressed. The host cell may further include arrestin, wherein the arrestin may be detectably labeled. The GPCR, GRK or another molecule involved in desensitization, or a molecule that interacts with a molecule involved in desensitization may be detectably labeled.
A further aspect of the present invention relates to a method of modifying a nucleic acid encoding a GRK in which a GPCR is constitutively internalized, including: (a) providing a nucleic acid encoding a GRK; (b) mutating the nucleic acid encoding a GRK such that the encoded GRK includes a CAAX motif, wherein the modified GRK phosphorylates a GPCR in the absence of agonist; and (c) expressing the modified GRK in a cell. The nucleic acid encoding a GRK may include SEQ ID No: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, or 34.
The present invention also relates to a kit for identifying a compound that modulates the internalization of a GPCR, including a host cell including a GPCR and a modified GRK.
In a further aspect, the present invention relates to a modified GPCR including a NPXXY motif, and a carboxyl terminal tail, wherein the carboxyl terminal tail includes a putative site of palmitoylation and one or more clusters of phosphorylation, wherein the carboxyl terminal tail includes a retained portion of a carboxyl-terminus region of a first GPCR portion fused to a portion of a carboxyl-terminus from a second GPCR, and wherein the second GPCR includes the one or more clusters of phosphorylation and further includes a second putative site of palmitoylation approximately 10 to 25 amino acid residues downstream of a second NPXXY motif. The first GPCR may be a Class A receptor. The first GPCR may be hGPR3, hGPR6, hGPR12, hSREB2, hSREB3, hGPR8, or hGPR22. The second GPCR may be a Class B receptor. The Class B receptor may be selected from the group consisting of a vasopressin V2 receptor, a neurotensin-1 receptor, a substance P receptor, and an oxytocin receptor.
The present invention relates to a nucleic acid encoding a modified GPCR. Included in the present invention are nucleic acids selected from the group consisting of SEQ ID Nos: 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, and 90. Also included in the present invention are expression vectors including the nucleic acid. Host cells including the expression vector or the nucleic acid are also included.
In a further aspect, the present invention relates to a method of screening compounds for GPCR activity including the steps of: (a) providing a cell that expresses at least one modified GPCR, wherein the cell further includes arrestin conjugated to a detectable molecule; b) exposing the cell to the compound; (c) detecting location of the arrestin within the cell; (d) comparing the location of the arrestin within the cell in the presence of the compound to the location of the arrestin within the cell in the absence of the compound; and (e) correlating a difference between (1) the location of the arrestin within the cell in the presence of the compound and (2) the location of the arrestin within the cell in the absence of the compound. The arrestin may be detected in endosomes, endocytic vesicles, or pits.
A further aspect of the present invention is a kit for identifying a molecule that modulates the activity of a GPCR, including a cell that expresses at least one modified GPCR, wherein the cell further includes a molecule involved in desensitization conjugated to a detectable molecule.



BRIEF DESCRIPTION OF DRAWINGS
The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which:
FIG. 1A-1C is a list of GPCRs that may be used with the present invention.
FIG. 2A-2Q is a list of GRKs that may be used with the present invention. Amino acid and nucleic acid sequences of certain GRKs are shown. The amino acid and nucleic acid sequences of GRK2-C20, a modified GRK, are shown.
FIG. 3A-3BB is a list of GPCRs that have been modified to have enhanced affinity for arrestin. The amino acid and nucleic acid sequences are shown.
FIG. 4 illustrates the agonist-independent translocation of arrestin-GFP to GPCRs in the presence of GRK2-C20.
FIG. 5 illustrates the agonist-independent translocation of arrestin-GFP to GPCRs in the presence of GRK2-C20.
FIG. 6 illustrates the agonist-independent translocation of arrestin-GFP to GPCRs in the presence of GRK2-C20.
FIG. 7 illustrates the agonist-independent translocation of arrestin-GFP to GPCRs in the presence of GRK2-C20.
FIG. 8 demonstrates that losartan, a nonpeptide antagonist/inverse agonist of the AT1AR, inhibits the ligand-independent translocation of arrestinGFP to the AT1AR induced by expression of GRK2-C20. Data plotted are the mean ±SD for a representative experiment performed in triplicate.
FIG. 9 illustrates the percent inhibition of constitutive, GRK2-C20 induced, arrestinGFP translocation to the AT1AR by losartan treatment for 3 hours.
FIG. 10 illustrates the percent inhibition of constitutive, GRK2-C20 induced, arrestinGFP translocation to the AT1AR by losartan treatment for 18 hours.



DETAILED DESCRIPTION
In accordance with the present invention there may be employed conventional molecular biology, microbiology, immunology, and recombinant DNA techniques within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Sambrook et al, “Molecular Cloning: A Laboratory Manual” (3rd edition, 2001); “Current Protocols in Molecular Biology” Volumes I-IV [Ausubel, R. M., ed. (2002 and updated bimonthly)]; “Cell Biology: A Laboratory Handbook” Volumes I-III [J. E. Celis, ed. (1994)]; “Current Protocols in Immunology” Volumes I-IV [Coligan, J. E., ed. (2002 and updated bimonthly)]; “Oligonucleotide Synthesis” (M. J. Gait ed. 1984); “Nucleic Acid Hybridization” [B. D. Hames & S. J. Higgins eds. (1985)]; “Transcription And Translation” [B. D. Hames & S. J. Higgins, eds. (1984)]; “Culture of Animal Cells, 4th edition” [R. I Freshney, ed. (2000)]; “Immobilized Cells And Enzymes” [IRL Press, (1986)]; B. Perbal, “A Practical Guide To Molecular Cloning” (1988); Using Antibodies: A Laboratory Manual: Portable Protocol No. I, Harlow, Ed and Lane, David (Cold Spring Harbor Press, 1998); Using Antibodies: A Laboratory Manual, Harlow, Ed and Lane, David (Cold Spring Harbor Press, 1999); “G Protein-Coupled Receptors” [T. Haga, et al., eds. (1999)].
Unless otherwise stated, the following terms used in the specification and claims have the meanings given below:
A “replicon” is any genetic element (e.g., plasmid, chromosome, virus) that functions as an autonomous unit of DNA replication in vivo; i.e., capable of replication under its own control.
A “vector” is a replicon, such as plasmid, phage or cosmid, to which another DNA segment may be attached so as to bring about the replication of the attached segment.
A “DNA molecule” refers to the polymeric form of deoxyribonucleotides (adenine, guanine, thymine, or cytosine) in its either single stranded form, or a double-stranded helix. This term refers only to the primary and secondary structure of the molecule, and does not limit it to any particular tertiary forms. Thus, this term includes double-stranded DNA found, inter alia, in linear DNA molecules (e.g., restriction fragments), viruses, plasmids, and chromosomes. In discussing the structure of particular double-stranded DNA molecules, sequences may be described herein according to the normal convention of giving only the sequence in the 5′ to 3′ direction along the nontranscribed strand of DNA (i.e., the strand having a sequence homologous to the mRNA).
An “origin of replication” refers to those DNA sequences that participate in the initiation of DNA synthesis.
A DNA “coding sequence” is a double-stranded DNA sequence which is transcribed and translated into a polypeptide in vivo when placed under the control of appropriate regulatory sequences. The boundaries of the coding sequence are determined by a start codon at the 5′ (amino) terminus and a translation stop codon at the 3′ (carboxyl) terminus. A coding sequence can include, but is not limited to, prokaryotic sequences, cDNA from eukaryotic mRNA, genomic DNA sequences from eukaryotic (e.g., mammalian) DNA, and even synthetic DNA sequences. A polyadenylation signal and transcription termination sequence will usually be located 3′ to the coding sequence.
Transcriptional and translational control sequences are DNA regulatory sequences, such as promoters, enhancers, polyadenylation signals, terminators, and the like, that provide for the expression of a coding sequence in a host cell.
The expression of a coding sequence in a host cell may be inducible. By inducible, it is meant that the expression can be regulated. For example, the nucleic acid may be present in the cell, but it is not expressed until a necessary signal is provided. Typically, inducible expression of a protein is controlled by a promoter that requires a necessary signal to induce transcription of the protein. However, expression may also be induced by a process or sequence that increases the number of DNA sequences of interest in the cell. Such processes or sequences include origins of replication, as well as the physical addition of DNA to a cell.
A “promoter sequence” is a DNA regulatory region capable of binding RNA polymerase in a cell and initiating transcription of a downstream (3′ direction) coding sequence. For purposes of defining the present invention, the promoter sequence is bounded at its 3′ terminus by the transcription initiation site and extends upstream (5′ direction) to include the minimum number of bases or elements necessary to initiate transcription at levels detectable above background. Within the promoter sequence will be found a transcription initiation site (conveniently defined by mapping with nuclease S1), as well as protein binding domains (consensus sequences) responsible for the binding of RNA polymerase. Eukaryotic promoters will often, but not always, contain “TATA” boxes and “CAT” boxes. Prokaryotic promoters contain Shine-Dalgarno sequences in addition to the −10 and −35 consensus sequences.
An “expression control sequence” is a DNA sequence that controls and regulates the transcription and translation of another DNA sequence. A coding sequence is “under the control” of transcriptional and translational control sequences in a cell when RNA polymerase transcribes the coding sequence into mRNA, which is then translated into the protein encoded by the coding sequence.
A “signal sequence” can be included before the coding sequence. This sequence encodes a signal peptide, N-terminal to the polypeptide, that communicates to the host cell to direct the polypeptide to the cell surface or secrete the polypeptide into the media, and this signal peptide is clipped off by the host cell before the protein leaves the cell. Signal sequences can be found associated with a variety of proteins native to prokaryotes and eukaryotes.
The term “oligonucleotide,” as used herein in referring to the probe of the present invention, is defined as a molecule comprised of two or more ribonucleotides, preferably more than three. Its exact size will depend upon many factors which, in turn, depend upon the ultimate function and use of the oligonucleotide.
The term “primer” as used herein refers to an oligonucleotide, whether occurring naturally as in a purified restriction digest or produced synthetically, which is capable of acting as a point of initiation of synthesis when placed under conditions in which synthesis of a primer extension product, which is complementary to a nucleic acid strand, is induced, i.e., in the presence of nucleotides and an inducing agent such as a DNA polymerase and at a suitable temperature and pH. The primer may be either single-stranded or double-stranded and must be sufficiently long to prime the synthesis of the desired extension product in the presence of the inducing agent. The exact length of the primer will depend upon many factors, including temperature, source of primer and use of the method. For example, for diagnostic applications, depending on the complexity of the target sequence, the oligonucleotide primer typically contains 15-25 or more nucleotides, although it may contain fewer nucleotides.
The primers herein are selected to be “substantially” complementary to different strands of a particular target DNA sequence. This means that the primers must be sufficiently complementary to hybridize with their respective strands. Therefore, the primer sequence need not reflect the exact sequence of the template. For example, a non-complementary nucleotide fragment may be attached to the 5′ end of the primer, with the remainder of the primer sequence being complementary to the strand. Alternatively, non-complementary bases or longer sequences can be interspersed into the primer, provided that the primer sequence has sufficient complementarity with the sequence of the strand to hybridize therewith and thereby form the template for the synthesis of the extension product.
As used herein, the terms “restriction endonucleases” and “restriction enzymes” refer to bacterial enzymes, each of which cut double-stranded DNA at or near a specific nucleotide sequence.
A cell has been “transformed” by exogenous or heterologous DNA when such DNA has been introduced inside the cell. The transforming DNA may or may not be integrated (covalently linked) into chromosomal DNA making up the genome of the cell. In prokaryotes, yeast, and mammalian cells for example, the transforming DNA may be maintained on an episomal element such as a plasmid. With respect to eukaryotic cells, a stably transformed cell is one in which the transforming DNA has become integrated into a chromosome so that it is inherited by daughter cells through chromosome replication. This stability is demonstrated by the ability of the eukaryotic cell to establish cell lines or clones comprised of a population of daughter cells containing the transforming DNA. A “clone” is a population of cells derived from a single cell or common ancestor by mitosis. A “cell line” is a clone of a primary cell that is capable of stable growth in vitro for many generations.
Two DNA sequences are “substantially homologous” when at least about 65% (preferably at least about 80%, and most preferably at least about 90 or 95%) of the nucleotides match over the defined length of the DNA sequences. Sequences that are substantially homologous can be identified by comparing the sequences using standard software available in sequence data banks, or in a Southern hybridization experiment under, for example, stringent conditions as defined for that particular system. Defining appropriate hybridization conditions is within the skill of the art. See, e.g., Maniatis et al., supra; DNA Cloning, Vols. I & II, supra; Nucleic Acid Hybridization, supra.
It should be appreciated that also within the scope of the present invention are DNA sequences encoding the same amino acid sequence as SEQ ID NO: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, and 89, but also those which are degenerate to SEQ ID NO: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, and 90. By “degenerate to” is meant that a different three-letter codon is used to specify a particular amino acid.
“Arrestin” means all types of naturally occurring and engineered variants of arrestin, including, but not limited to, visual arrestin (sometimes referred to as Arrestin 1), cone arrestin (sometimes referred to as arrestin-4), β-arrestin 1 (sometimes referred to as Arrestin 2), and β-arrestin 2 (sometimes referred to as Arrestin 3).
“βARK1” is a GRK termed β-adrenergic receptor kinase 1, also called GRK2.
“βAR” is a GPCR termed a β-adrenergic receptor.
“Internalization” of a GPCR is the translocation of a GPCR from the cell surface membrane to an intracellular vesicular membrane, where it may be inaccessible to substances remaining outside the cell.
“Carboxyl-terminal tail” means the carboxyl-terminal tail of a GPCR following membrane span 7. The carboxyl-terminal tail of many GPCRs begins shortly after the conserved NPXXY motif that marks the end of the seventh transmembrane domain (i.e. what follows the NPXXY motif is the carboxyl-terminal tail of the GPCR). The carboxyl-terminal tail may be relatively long (approximately tens to hundreds of amino acids), relatively short (approximately tens of amino acids), or virtually non-existent (less than approximately ten amino acids). As used herein, “carboxyl-terminal tail” shall mean all three variants (whether relatively long, relatively short, or virtually non-existent), and may or may not contain palmitoylated cysteine residue(s).
“Class A receptors” preferably do not translocate together with arrestin proteins to endocytic vesicles or endosomes in association with arrestin-GFP in HEK-293 cells.
“Class B receptors” preferably do translocate together with arrestin proteins to endocytic vesicles or endosomes associated with arrestin-GFP in HEK-293 cells.
“DACs” mean any desensitization active compounds. Desensitization active compounds are any compounds that influence the GPCR desensitization mechanism by either stimulating or inhibiting the process. DACs may influence the GPCR desensitization pathway by acting on any cellular component of the process, as well as any cellular structure implicated in the process, including but not limited to: arrestins, GRKs, GPCRs, phosphoinositide 3-kinase, AP-2 protein, clathrin, protein phosphatases, and the like. DACs may include, but are not limited to, compounds that inhibit arrestin translocating to a GPCR, compounds that inhibit arrestin binding to a GPCR, compounds that stimulate arrestin translocating to a GPCR, compounds that stimulate arrestin binding to a GPCR, compounds that inhibit GRK phosphorylation of a GPCR, compounds that stimulate GRK phosphorylation of a GPCR, compounds that stimulate or inhibit GRK binding to a GPCR, compounds that inhibit protein phosphatase dephosphorylation of a GPCR, compounds that stimulate protein phosphatase dephosphorylation of a GPCR, compounds that prevent GPCR internalization or recycling to the cell surface, compounds that regulate the release of arrestin from a GPCR, antagonists of a GPCR, inverse agonists and the like. DACs may inhibit or stimulate the GPCR desensitization process and may not bind to the same ligand binding site of the GPCR as traditional agonists and antagonists of the GPCR. DACs may act independently of the GPCR, i.e., they do not have high specificity for one particular GPCR or one particular type of GPCRs. DACs may bind the same site(s) as agonist or antagonist but do not desensitize the receptor (perhaps by not altering the receptor to be properly phosphorylated or bind to arrestin or any other protein). DACs may bind to allosteric sites on the receptor and inhibit or enhance desensitization.
“Detectable molecule” means any molecule capable of detection by spectroscopic, photochemical, biochemical, immunochemical, electrical, radioactive, and optical means, including but not limited to, fluorescence, phosphorescence, and bioluminescence and radioactive decay. Detectable molecules include, but are not limited to, GFP, luciferase, β-galactosidase, rhodamine-conjugated antibody, and the like. Detectable molecules include radioisotopes, epitope tags, affinity labels, enzymes, fluorescent groups, chemiluminescent groups, and the like. Detectable molecules include molecules which are directly or indirectly detected as a function of their interaction with other molecule(s).
“GFP” means Green Fluorescent Protein which refers to various naturally occurring forms of GFP which may be isolated from natural sources or genetically engineered, as well as artificially modified GFPs. GFPs are well known in the art. See, for example, U.S. Pat. Nos. 5,625,048; 5,777,079; and 6,066,476. It is well understood in the art that GFP is readily interchangeable with other fluorescent proteins, isolated from natural sources or genetically engineered, including but not limited to, yellow fluorescent proteins (YFP), red fluorescent proteins (RFP), cyan fluorescent proteins (CFP), blue fluorescent proteins, luciferin, UV excitable fluorescent proteins, or any wave-length in between. As used herein, “GFP” shall mean all fluorescent proteins known in the art.
“Unknown or Orphan Receptor” means a GPCR whose ligands are unknown.
“Downstream” means toward a carboxyl-terminus of an amino acid sequence, with respect to the amino-terminus.
“Upstream” means toward an amino-terminus of an amino acid sequence, with respect to the carboxyl-terminus.
Amino acid substitutions may also be introduced to substitute an amino acid with a particularly preferable property. For example, a Cys may be introduced a potential site in order to allow formation of disulfide bridges with another Cys. A H is may be introduced as a particularly “catalytic” residue (i.e., H is can act as an acid or base and is the most common amino acid in biochemical catalysis). Pro may be introduced because of its particularly planar structure, which induces β-turns in the protein's structure.
Two amino acid sequences are “substantially homologous” when at least about 70% of the amino acid residues (preferably at least about 80%, and most preferably at least about 90 or 95%) are identical, or represent conservative substitutions.
A “heterologous” region of the DNA construct is an identifiable segment of DNA within a larger DNA molecule that is not found in association with the larger molecule in nature. Thus, when the heterologous region encodes a mammalian gene, the gene will usually be flanked by DNA that does not flank the mammalian genomic DNA in the genome of the source organism. Another example of a heterologous coding sequence is a construct where the coding sequence itself is not found in nature (e.g., a cDNA where the genomic coding sequence contains introns, or synthetic sequences having codons different than the native gene). Allelic variations or naturally-occurring mutational events do not give rise to a heterologous region of DNA as defined herein.
The phrase “pharmaceutically acceptable” refers to molecular entities and compositions that are physiologically tolerable and do not typically produce an allergic or similar untoward reaction, such as gastric upset, dizziness and the like, when administered to a human.
The phrase “therapeutically effective amount” is used herein to mean an amount sufficient to prevent, and preferably reduce some feature of pathology such as for example, elevated blood pressure, respiratory output, etc.
A DNA sequence is “operatively linked” to an expression control sequence when the expression control sequence controls and regulates the transcription and translation of that DNA sequence. The term “operatively linked” includes having an appropriate start signal (e.g., ATG) in front of the DNA sequence to be expressed and maintaining the correct reading frame to permit expression of the DNA sequence under the control of the expression control sequence and production of the desired product encoded by the DNA sequence. If a gene that one desires to insert into a recombinant DNA molecule does not contain an appropriate start signal, such a start signal can be inserted in front of the gene.
“Hybridization” means hydrogen bonding, which may be Watson-Crick, Hoogsteen or reversed Hoogsteen hydrogen bonding, between complementary nucleoside or nucleotide bases. For example, adenine (A) and thymine (T) are complementary nucleobases that pair through the formation of hydrogen bonds.
The term “standard hybridization conditions” refers to salt and temperature conditions substantially equivalent to 5×SSC and 65° C. for both hybridization and wash. However, one skilled in the art will appreciate that such “standard hybridization conditions” are dependent on particular conditions including the concentration of sodium and magnesium in the buffer, nucleotide sequence length and concentration, percent mismatch, percent formamide, and the like. Also important in the determination of “standard hybridization conditions” is whether the two sequences hybridizing are RNA-RNA, DNA-DNA or RNA-DNA. Such standard hybridization conditions are easily determined by one skilled in the art according to well known formulae, wherein hybridization is typically 10-20° C. below the predicted or determined Tm with washes of higher stringency, if desired.
By “animal” is meant any member of the animal kingdom including vertebrates (e.g., frogs, salamanders, chickens, or horses) and invertebrates (e.g., worms, etc.). “Animal” is also meant to include “mammals.” Preferred mammals include livestock animals (e.g., ungulates, such as cattle, buffalo, horses, sheep, pigs and goats), as well as rodents (e.g., mice, hamsters, rats and guinea pigs), canines, felines, primates, lupine, camelid, cervidae, rodent, avian and ichthyes.
“Antagonist(s)” include all agents that interfere with wild-type and/or modified GPCR binding to an agonist, wild-type and/or modified GPCR desensitization, wild-type and/or modified GPCR binding arrestin, wild-type and/or modified GPCR endosomal localization, internalization, and the like, including agents that affect the wild-type and/or modified GPCRs as well as agents that affect other proteins involved in wild-type and/or modified GPCR signaling, desensitization, endosomal localization, resensitization, and the like.
“Modified GPCR” means a GPCR that has one or more modifications in the amino acid sequence of its carboxyl-terminal tail. As such, the carboxyl-terminal tail may be modified in whole or in part. These modifications in the amino acid sequence include mutations of one or more amino acids, insertion of one or more amino acids, deletion of one or more amino acids, and substitutions of one or more amino acids in which one or more amino acids are deleted and one or more amino acids are added in place of the deleted amino acids. Such modified GPCRs are described herein, as well as in U.S. Ser. No. 09/993,844, which is incorporated herein by reference in its entirety.
“GPCR” means G protein-coupled receptor and includes GPCRs naturally occurring in nature, as well as GPCRs which have been modified.
“Putative site of palmitoylation” means an expected site of palmitate addition, preferably a cysteine residue. In the GPCRs used in the present invention, the putative site of palmitoylation is preferably 10 to 25, preferably 15 to 20, amino acid residues downstream of the NPXXY motif.
“Clusters of phosphorylation sites” mean clusters of amino acid residues that may be efficiently phosphorylated and thus readily function as phosphorylation sites. The clusters of amino acids occupy two out of two, two out of three, three out of three positions, three out of four positions, four out of four, four out of five positions, five out of five, and the like consecutive amino acid positions in the carboxyl terminal tail of a GPCR. These clusters of phosphorylation sites are preferably clusters of serine (S) and/or threonine (T) residues. Clusters of phosphorylation sites may be substituted, inserted, or added on to a GPCR sequence so that the resulting modified GPCR binds arrestin with sufficient affinity to recruit arrestin into endosomes.
“NPXXY motif” means a conserved amino acid motif that marks the end of the seventh transmembrane domain. The conserved amino acid motif begins most frequently with asparagine and proline followed by two unspecified amino acids and then a tyrosine. The two unspecified amino acids may vary among GPCRs but the overall NPXXY motif is conserved.
“Abnormal GPCR desensitization” and “abnormal desensitization” mean that the GPCR desensitization pathway is disrupted such that the balance between active receptor and desensitized receptor is altered with respect to wild-type conditions. Either there is more active receptor than normal or there is more desensitized receptor than wild-type conditions. Abnormal GPCR desensitization may be the result of a GPCR that is constitutively active or constitutively desensitized, leading to an increase above normal in the signaling of that receptor or a decrease below normal in the signaling of that receptor.
“Biological sample” is intended to include tissues, cells and biological fluids isolated from a subject, as well as tissues, cells and fluids present within a subject; wherein said sample can be blood, serum, a urine sample, a fecal sample, a tumor sample, a cellular wash, an oral sample, sputum, biological fluid, a tissue extract, freshly harvested cells, or cells which have been incubated in tissue culture.
“Concurrent administration,” “administration in combination,” “simultaneous administration,” or “administered simultaneously” mean that the compounds are administered at the same point in time or sufficiently close in time that the results observed are essentially the same as if the two or more compounds were administered at the same point in time.
“Conserved abnormality” means an abnormality in the GPCR pathway, including but not limited to, abnormalities in GPCRs, GRKs, arresting, AP-2 protein, clathrin, protein phosphatase and the like, that may cause abnormal GPCR signaling. This abnormal GPCR signaling may contribute to a GPCR-related disease.
“Desensitized GPCR” means a GPCR that presently does not have ability to respond to agonist and activate conventional G protein signaling.
“Desensitization pathway” means any cellular component of the desensitization process, as well as any cellular structure implicated in the desensitization process and subsequent processes, including but not limited to, arresting, GRKs, GPCRS, AP-2 protein, clathrin, protein phosphatases, and the like. In the methods of assaying of the present invention, the polypeptides may be detected, for example, in the cytoplasm, at a cell membrane, in clathrin-coated pits, in endocytic vesicles, endosomes, any stages in between, and the like.
“GPCR signaling” means GPCR induced activation of G proteins. This may result in, for example, cAMP production.
“G protein-coupled receptor kinase” (GRK) includes any kinase that has the ability to phosphorylate a GPCR. Certain GRKs which may be used in the present invention are listed in FIG. 2A-2Q. Splice variants, biologically active fragments, modified GRKs, and GRKs from animals and other organisms are included.
“Homo sapiens GPCR” means a naturally occurring GPCR in a Homo sapiens. 
“Inverse agonist” means a compound that, upon binding to the GPCR, inhibits the basal intrinsic activity of the GPCR. An inverse agonist is a type of antagonist.
“Modified GRK” means a GRK modified such that it alters desensitization.
“Naturally occurring GPCR” means a GPCR that is present in nature.
“Odorant ligand” means a ligand compound that, upon binding to a receptor, leads to the perception of an odor including a synthetic compound and/or recombinantly produced compound including agonist and antagonist molecules.
“Odorant receptor” means a receptor protein normally found on the surface of olfactory neurons which, when activated (normally by binding an odorant ligand) leads to the perception of an odor.
The term “pharmaceutically acceptable carrier,” as used herein means a pharmaceutically-acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, excipient, solvent or encapsulating material, involved in carrying or transporting a chemical agent.
“Sensitized GPCR” means a GPCR that presently has ability to respond to agonist and activate conventional G protein signaling.
“Modulation” includes at least an up-regulation or down-regulation of the expression, or an increase or decrease in activity of a protein. Modulation of a protein includes the up-regulation, down-regulation, increase or decrease in activity of a protein or compound that regulates a protein. Modulation also includes the regulation of the gene, the mRNA, or any other step in the synthesis of the protein of interest.
An “overexpressed” protein refers to a protein that is expressed at levels greater than wild-type expression levels.
“Modified GRK” means a GRK that has one or more modifications in the amino acid sequence at the C-terminus of the GRK. The modified GRK constitutively localizes to the plasma membrane. Preferably, the GRK is modified by the addition of a CMX motif.
“CAAX” (SEQ ID NO:95) motif means a four amino acid sequence, wherein C is cysteine; A is an aliphatic amino acid; and X is the C-terminal amino acid of the protein.
A “constitutive” activity means an activity that occurs in the absence of agonist. For example, the modified GRK constitutively localizes to the plasma membrane means that the modified GRK localizes to the plasma membrane in the absence of agonist.
“GRK-C20” refers to a modified GRK which has the ability to have a geranylgeranyl group added to it. GRK2-C20 is a GRK2 modified in this manner. Preferably, the GRK-C20 contains a CAAX motif.
The present inventors developed an agonist-independent method to screen for compounds that alter GPCR desensitization. They developed cell lines in which GPCRs are desensitized in the absence of agonist. These cell lines include GRKs, which may be modified. Using these cell lines, they developed methods to screen for compounds that alter GPCR desensitization in the absence of agonist. These methods eliminate the step of agonist addition from the screening method. The elimination of this step (1) creates more efficient screening methods for compounds that alter desensitization of GPCRs with known agonists, and (2) provides screening methods for compounds that alter desensitization of orphan GPCRs, which have no known agonist. They developed methods to determine if a GPCR is expressed at the plasma membrane, and determine if the GPCR has an affinity for arrestin; preferably these methods utilize an orphan GPCR and host cells containing a GRK, wherein the GPCR is at least partially internalized in an agonist-independent manner upon expression of the GRK, thus eliminating the need for agonist addition. They modified GPCRs to increase their affinities for arrestin. These modified GPCRs are useful in the agonist-independent methods to screen for compounds that alter desensitization.
GPCRs and Desensitization
The exposure of a GPCR to agonist produces rapid attenuation of its signaling ability that involves uncoupling of the receptor from its cognate heterotrimeric G-protein. The cellular mechanism mediating agonist-specific or homologous desensitization is a two-step process in which agonist-occupied receptors are phosphorylated by a G protein-coupled receptor kinases (GRKs) and then bind an arrestin protein.
It is known that after agonists bind GPCRs, G-protein coupled receptor kinases (GRKs) phosphorylate intracellular domains of GPCRs. After phosphorylation, an arrestin protein associates with the GRK-phosphorylated receptor and uncouples the receptor from its cognate G protein. The interaction of the arrestin with the phosphorylated GPCR terminates GPCR signaling and produces a non-signaling, desensitized receptor.
The arrestin bound to the desensitized GPCR targets the GPCR to clathrin-coated pits or other cellular machinery for endocytosis (i.e., internalization) by functioning as an adaptor protein, which links the GPCR to components of the endocytic machinery, such as adaptor protein-2 (AP-2) and clathrin. The internalized GPCRs are dephosphorylated and are recycled back to the cell surface resensitized, or are retained within the cell and degraded. The stability of the interaction of arrestin with the GPCR is one factor that dictates the rate of GPCR dephosphorylation, recycling, and resensitization. The involvement of GPCR phosphorylation and dephosphorylation in the desensitization process has been exemplified in U.S. Ser. No. 09/933,844, filed Nov. 5, 2001, the disclosure of which is hereby incorporated by reference in its entirety.
Using methods described herein, the present inventors identified certain GPCRs which do not have an affinity for arrestin. They modified these GPCRs to comprise one or more sites of phosphorylation, preferably clusters of phosphorylation sites, properly positioned in their carboxyl-terminal tail. This modification allows the modified GPCR to form a stable complex with an arrestin that will internalize as a unit into endosomes. These modified GPCRs may be useful in methods of assaying GPCR activity. These modified GPCRs may be useful to identify agonists of the GPCRs. These modified GPCRs may be useful in the agonist-independent screening methods described herein.
Agonist-independent screening methods using GPCRs altered to contain a DRY motif are described in U.S. Ser. No. 10/054,616, which is incorporated herein by reference in its entirety. The alteration of the GPCR is included in that screening process; each GPCR to be utilized must be altered in that manner.
The present inventors developed agonist-independent screening methods using GRKs, which may be modified. These GRKs phosphorylate GPCRs in the absence of agonist. These phosphorylated GPCRs internalize in the absence of agonist. The present inventors developed agonist-independent methods of screening for antagonists of GPCR internalization utilizing these modified GRKs. These methods do not require the GPCR alterations described in U.S. Ser. No. 10/054,616.
Previously, certain GRKs were shown to constitutively localize in the plasma membrane. Inglese et al constructed GRK2-C20 which was constitutively isoprenylated and localized to the membranes.
The present inventors determined that cellular expression of GRKs that constitutively localize in the plasma membrane results in constitutive desensitization of GPCRs. These GRKs may be over-expressed, their expression may be inducible, the nucleic acids encoding them may be located in a vector or integrated into the genome. The present inventors constructed host cell expressing a GRK that constitutively localizes in the plasma membrane. These host cells may also express arrestin. To these host cells, they introduced a GPCR of interest. Using the GRK-containing cells, they developed methods to determine if a GPCR of interest is expressed at the plasma membrane, analyze the ability of a GPCR to bind arrestin, and detect constitutively desensitized GPCRs. They built upon these desensitization methods and developed agonist-independent methods of identifying compounds that alter GPCR desensitization. These methods are useful for the identification of compounds that alter the internalization of GPCRs, whether the GPCR agonist is known or unknown.
The present inventors also determined that increased expression of wild-type or modified GRKs increased desensitization, irrespective of whether the GRK constitutively localized in the plasma membrane.
The present invention is related to modified GPCRs, polypeptides of modified GPCRs, nucleic acid molecules that encode the modified GPCRs, vectors containing the nucleic acid molecules which encode the modified GPCRs, vectors enabling the nucleic acid construction of the modified GPCRs, and cells containing modified GPCRs. The invention further relates to assay systems using the modified GPCRs, assay systems using the cells containing modified GPCRs, compounds identified using the assay systems, methods of treatment using the compounds identified, methods of disease diagnosis using the assay systems, and kits containing assay reagents of the present invention and cells of the present invention.
Mutations can be made in the GPCR or modified GPCR such that a particular codon is changed to a codon which codes for a different amino acid. Such a mutation is generally made by making the fewest nucleotide changes possible. A substitution mutation of this sort can be made to change an amino acid in the resulting protein in a non-conservative manner (i.e., by changing the codon from an amino acid belonging to a grouping of amino acids having a particular size or characteristic to an amino acid belonging to another grouping) or in a conservative manner (i.e., by changing the codon from an amino acid belonging to a grouping of amino acids having a particular size or characteristic to an amino acid belonging to the same grouping). Such a conservative change generally leads to less change in the structure and function of the resulting protein. A non-conservative change is more likely to alter the structure, activity or function of the resulting protein. The present invention should be considered to include sequences containing conservative changes which do not significantly alter the activity or binding characteristics of the resulting protein.
In a particular embodiment, the modified GPCRs of the present invention include GPCRs that have been modified to have one or more sites of phosphorylation, preferably clusters of phosphorylation sites, properly positioned in its carboxyl-terminal tail. These modified GPCRs recruit arrestin to endosomes within approximately 30 minutes of agonist stimulation. These modified GPCRs recruit arrestin to endosomes in the cells described herein, in which the GPCR is phosphorylated in an agonist-independent manner.
The modified GPCRs of the present invention comprise one or more sites of phosphorylation, preferably one or more clusters of phosphorylation sites, properly positioned in its carboxyl-terminal tail. The present inventors have discovered that GPCRs containing one or more sites of phosphorylation, preferably clusters of phosphorylation sites, properly positioned in its carboxyl-terminal tail have an increased affinity for arrestin and colocalize with arrestin in endosomes upon GPCR phosphorylation, either after stimulation with agonist or in an agonist-independent manner as described herein. The present inventors have also discovered that the one or more sites of phosphorylation, preferably clusters of phosphorylation sites, must be optimally positioned within the GPCR tail for the GPCR to have an increased affinity for arrestin. Therefore, the modified GPCRs may be constructed such that the one or more sites of phosphorylation, preferably clusters of phosphorylation sites, are optimally positioned within the carboxyl-terminal tail. The portions of polypeptides, which are to be fused together to form the modified GPCR, are chosen such that the one or more sites of phosphorylation, preferably clusters of phosphorylation sites, are reliably positioned properly within the carboxyl-terminal tail. In the alternative, the location of discrete point mutations to create the modified GPCR may be chosen so that the one or more sites of phosphorylation, preferably clusters of phosphorylation sites, are properly positioned within the carboxyl-terminal tail.
The present inventors have discovered that the modified GPCRs of the present invention are useful in assays for screening compounds that may alter G protein-coupled receptor (GPCR) activity. Examples of assays in which the present invention may be used include, but are not limited to, those as described in U.S. Pat. Nos. 5,891,646 and 6,110,693, the disclosures of which are hereby incorporated by reference in their entireties. Additional examples of assays in which the present invention may be used include, but are not limited to, assays using Fluorescent Resonance Energy Transfer (FRET) and assays using Bioluminescence Resonance Energy Transfer (BRET) technology as described in Angers, S., Salahpour, A., Joly, E., Hilairet, S., Chelsky, “β2-adrenergic receptor dimerization in living cells using bioluminescence resonance energy transfer (BRET),” Proc. Natl, Acad. Sci. USA 97, 7: 3684-3689.
The present inventors have determined that these modified GPCRs are useful in agonist-independent assays for screening compounds that may alter GPCR internalization. Examples of assays in which the present invention may be used include, but are not limited to, assays described herein.
Methods of Enhancing GPCR Desensitization
Provided in the present invention are methods of enhancing GPCR desensitization. One embodiment is related to the expression of GRKs, which may be modified. The GRKs may be over-expressed or their expression may be inducible. These methods may be used to analyze the desensitization of a GPCR, including a modified GPCR, an orphan GPCR, a taste receptor, a mutant GPCR, the β2AR Y326A GPCR mutant, or another GPCR. Certain GPCRs useful in the present invention are listed in FIG. 1A-1C.
In a preferred embodiment, a cell is provided that contains an expression system and a nucleic acid encoding a GRK. The GRK may be modified such that the expression of the GRK results in constitutive desensitization of the GPCR. The GRK may be over-expressed and its expression may be inducible.
Preferably, host cells are provided which include a GRK, which may be modified, and arrestin. A GPCR is then added to these cells. The agonist-independent desensitization of the GPCR is detected. FIGS. 4, 5, 6, and 7 are examples of this method. Detection methods are described below.
The present invention provides methods of determining if the GPCR of interest is expressed at the plasma membrane. GPCRs expressed at the plasma membrane are useful in the previously mentioned methods of compound identification.
A preferred method of determining if a GPCR of interest is expressed at the plasma membrane includes: (a) providing a cell including a GPCR, an arrestin, and a GRK, wherein the arrestin is detectably labeled; (b) determining the cellular distribution of the arrestin; and (c) correlating the cellular distribution of the arrestin to the ability of the GPCR to be expressed at the plasma membrane.
Preferred embodiments of this aspect of the invention are described in Examples 2, 3, 4, 5, 6, and 7 and illustrated in FIGS. 4, 5, 6, and 7.
Another method of determining if a GPCR of interest is expressed at the plasma membrane includes: (a) providing a cell comprising a GPCR and a GRK, wherein the GRK is detectably labeled; (b) determining the cellular distribution of the GRK; and (c) correlating the cellular distribution of the GRK to the ability of the GPCR to be expressed at the plasma membrane.
The present invention provides methods of analyzing the ability of a GPCR to bind arrestin. GPCRs which bind arrestin are useful in the previously mentioned methods of compound identification.
A preferred method of analyzing the ability of a GPCR to bind arrestin includes: (a) providing a cell including a GPCR, an arrestin, and a GRK, wherein the arrestin is detectably labeled; (b) determining the cellular distribution of the arrestin; and (c) correlating the cellular distribution of the arrestin to the ability of the GPCR to bind arrestin.
Preferred embodiments of this aspect of the invention are described in Examples 2, 3, 4, 5, 6, and 7, and illustrated in FIGS. 4, 5, 6, and 7.
Using this method, certain GPCRs will bind arrestin and desensitize. However, certain GPCRs will not desensitize without modification of the GPCR, as described in U.S. Ser. No. 09/993,844. The present inventors modified several GPCRs, including known and orphan GPCRs, listed in FIG. 3A-3BB. Upon modification, these modified GPCRs constitutively desensitized in the above system.
Modified GPCRs
The present invention is related to modified GPCRs. Modified GPCRs of the present invention may comprise one or more modifications in their carboxyl-terminal tail. These modifications may comprise inserting one or more sites of phosphorylation, preferably clusters of phosphorylation sites, within certain regions of the carboxyl-terminal tail. As such, the carboxyl-terminal tail may be modified in whole or in part. The carboxyl-terminal tail of many GPCRs begins shortly after a conserved NPXXY motif that marks the end of the seventh transmembrane domain (i.e. what follows the NPXXY motif is the carboxyl-terminal tail of the GPCR). The carboxyl-terminal tail of many GPCRs comprises a putative site of palmitoylation approximately 10 to 25 amino acid residues, preferably 15 to 20 amino acid residues, downstream of the NPXXY motif. This site is typically one or more cysteine residues. The carboxyl-terminal tail of a GPCR may be relatively long, relatively short, or virtually non-existent. The present inventors have determined that the carboxyl-terminal tail of a GPCR determines the affinity of arrestin binding.
The present inventors have discovered that specific amino acid motifs in the carboxyl-terminal tail promote formation of a stable GPCR/arrestin complex and thus ultimately may promote recruitment of arrestin to endosomes. These amino acid motifs comprise one or more amino acids, preferably clusters of amino acid residues, that may be efficiently phosphorylated and thus readily function as phosphorylation sites. The clusters of amino acids may occupy two out of two, two out of three, three out of three, three out of four positions, four out of four, four out of five positions, five out of five, and the like consecutive amino acid positions. Accordingly, the clusters of amino acids that promote formation of a stable GPCR/arrestin complex are “clusters of phosphorylation sites.” These clusters of phosphorylation sites are preferably clusters of serine and threonine residues.
GPCRs that form stable complexes with arrestin comprise one or more sites of phosphorylation, preferably clusters of phosphorylation sites. In addition to the presence of the one or more sites of phosphorylation, preferably clusters of phosphorylation sites, it has been discovered that the sites must be properly positioned within the carboxyl-terminal tail to promote formation of a stable GPCR/arrestin complex. To promote formation of a stable GPCR/arrestin complex, the one or more sites of phosphorylation, preferably one or more clusters of phosphorylation, may be approximately 15 to 35 (preferably 15 to 25) amino acid residues downstream of a putative site of palmitoylation of the GPCR. In addition, the one or more sites of phosphorylation, preferably one or more clusters of phosphorylation, may be approximately 20 to 55 (preferably 30 to 45) amino acid residues downstream of the NPXXY motif of the GPCR. GPCRs containing one or more sites of phosphorylation, preferably clusters of phosphorylation sites, properly positioned are typically Class B receptors.
By way of example, it has been discovered that the V2R receptor comprises a cluster of phosphorylation sites (SSS) that promotes formation of a stable GPCR/arrestin complex at 19 amino acid residues downstream of the putative site of palmitoylation and 36 amino acid residues downstream of the NPXXY motif. The NTR-2 receptor comprises a cluster of phosphorylation sites (STS) that promotes formation of a stable GPCR/arrestin complex at 26 amino acid residues downstream of the putative site of palmitoylation and 45 amino acid residues downstream of the NPXXY motif. The oxytocin receptor (OTR) receptor comprises two clusters of phosphorylation sites (SSLST (SEQ ID NO: 91) and STLS (SEQ ID NO: 92)) that promote formation of a stable GPCR/arrestin complex, one at 20 amino acid residues downstream of the putative site of palmitoylation and the other at 29 amino acid residues downstream of the putative site of palmitoylation, and one at 38 amino acid residues downstream of the NPXXY motif and the other at 47 amino acid residues downstream of the NPXXY motif, respectively. The substance P receptor (SPR, also known as the neurokinin-1 receptor) comprises a cluster of phosphorylation sites (TTIST) (SEQ ID NO: 93) that promotes formation of a stable GPCR/arrestin complex at 32 amino acid residues downstream of the putative site of palmitoylation and 50 amino acid residues downstream of the NPXXY motif.
The present inventors have determined that GPCRs that lack one or more sites of phosphorylation, preferably clusters of phosphorylation, properly positioned within the carboxyl terminal tail form GPCR/arrestin complexes that are less stable and dissociate at or near the plasma membrane. These GPCRs are typically Class A receptors, olfactory receptors, taste receptors, and the like. However, the present inventors have discovered that stable GPCR/arrestin complexes may be achieved with GPCRs naturally lacking one or more sites of phosphorylation and having a lower affinity for arrestin by modifying the carboxyl-terminal tails of these receptors. Preferably, the carboxyl-terminal tails are modified to include one or more sites of phosphorylation, preferably one or more clusters of phosphorylation sites, properly positioned within the carboxyl terminal tail.
The present invention includes the polypeptide sequences of these modified GPCRs. The modified GPCRs of the present invention include GPCRs that have been modified to have one or more sites of phosphorylation, preferably one or more clusters of phosphorylation, properly positioned in their carboxyl terminal tails. The polypeptide sequences of the modified GPCRs of the present invention also include sequences having one or more additions, deletions, substitutions, or mutations. These mutations are preferably substitution mutations made in a conservative manner (i.e., by changing the codon from an amino acid belonging to a grouping of amino acids having a particular size or characteristic to an amino acid belonging to the same grouping). Such a conservative change generally leads to less change in the structure and function of the resulting protein. The present invention should be considered to include sequences containing conservative changes which do not significantly alter the activity or binding characteristics of the resulting protein.
The modified GPCRs of the present invention include GPCRs containing a NPXXY motif, a putative site of palmitoylation approximately 10 to 25 amino acid residues (preferably 15 to 20 amino acids) downstream of the NPXXY motif, and a modified carboxyl-terminal tail. The modified carboxyl-terminal tail has one or more sites of phosphorylation, preferably one or more clusters of phosphorylation sites, such that the phosphorylation sites are approximately 15 to 35, preferably 15 to 25, amino acid residues downstream of the putative site of palmitoylation of the modified GPCR. The modified carboxyl-terminal tail may have one or more sites of phosphorylation, preferably one or more clusters of phosphorylation sites, such that the phosphorylation sites are approximately 20 to 55, preferably 30 to 45, amino acid residues downstream of the NPXXY of the modified GPCR.
The present invention further includes isolated nucleic acid molecules that encode modified GPCRs. It should be appreciated that also within the scope of the present invention are DNA sequences encoding modified GPCRs which code for a modified GPCR having the same amino acid sequence as the modified GPCRs, but which are degenerate. By “degenerate to” it is meant that a different three-letter codon is used to specify a particular amino acid.
As one of skill in the art would readily understand, the carboxyl-tail of many GPCRs may be identified by the conserved NPXXY motif that marks the end of the seventh transmembrane domain.
To create a modified GPCR containing a modified carboxyl-terminus region according to the present invention, a GPCR lacking phosphorylation sites or clusters of phosphorylation sites or with a lower or unknown affinity for arrestin may have one or more additions, substitutions, deletions, or mutations of amino acid residues in its carboxyl-terminal tail. These additions, substitutions, deletions, or mutations are performed such that the carboxyl-terminal tail is modified to comprise one or more sites of phosphorylation, preferably clusters of phosphorylation sites. By way of example, discrete point mutations of the amino acid residues may be made to provide a modified GPCR. By way of example three consecutive amino acids may be mutated to serine residues to provide a modified GPCR. These mutations are made such that the one or more sites of phosphorylation, preferably clusters of phosphorylation sites, are properly positioned within the carboxyl terminal tail.
In addition, to create a modified GPCR containing a modified carboxyl-terminal tail region, mutations may be made in a nucleic acid sequence of a GPCR lacking sites of phosphorylation or clusters of phosphorylation sites or with a lower or unknown affinity for arrestin such that a particular codon is changed to a codon which codes for a different amino acid, preferably a serine or threonine. Such a mutation is generally made by making the fewest nucleotide changes possible. A substitution mutation of this sort can be made to change an amino acid in the resulting protein to create one or more sites of phosphorylation, preferably clusters of phosphorylation sites. Also by way of example, discrete point mutations of the nucleic acid sequence may be made. The phosphorylation sites are positioned such that they are located approximately 15 to 35 amino acid residues downstream of the putative site of palmitoylation of the modified GPCR.
Furthermore, to provide modified GPCRs of the present invention, a GPCR lacking properly positioned phosphorylation sites or with a lower or unknown affinity for arrestin may also have its carboxyl-terminal tail, in whole or in part, exchanged with that of a GPCR having properly positioned clusters of phosphorylation sites. The site of exchange may be after or including the conserved NPXXY motif. As an alternative, a putative site of palmitoylation of a GPCR may be identified at approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of the conserved NPXXY motif, and the site of exchange may be after or including the palmitoylated cysteine(s). Preferably, the carboxyl-terminal tail of a GPCR lacking properly positioned clusters of phosphorylation sites or with a lower or unknown affinity for arrestin is exchanged at an amino acid residue in close proximity to a putative site a palmitoylation. More preferably, the carboxyl-terminal tail of a GPCR lacking properly positioned clusters of phosphorylation sites or with a lower or unknown affinity for arrestin is exchanged at a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of the NPXXY motif, such that the palmitoylated cysteine residue is maintained. Exchanging in the preferred manner allows the clusters of phosphorylation sites to be reliably positioned properly within the carboxyl-terminal tail of the modified GPCR. The tails may be exchanged and the modified GPCRs may be constructed accordingly by manipulation of the nucleic acid sequence or the corresponding amino acid sequence.
In a further alternative, the carboxyl-tail of a GPCR, for example a GPCR not containing the NPXXY motif, may be predicted from a hydrophobicity plot and the site of exchange may be selected accordingly. Based on a hydrophobicity plot, one of skill in the art may predict a site where it is expected that the GPCR may anchor in the membrane and then predict where to introduce a putative site of palmitoylation accordingly. Using this technique GPCRs having neither a NPXXY motif nor a putative site of palmitoylation may be modified to create a point of reference (e.g. a putative site of palmitoylation). The introduced putative site of palmitoylation may then be used to position a tail exchange.
The carboxyl-terminal tail used for the exchange may be from a second GPCR having one or more properly positioned clusters of phosphorylation sites and having a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of a NPXXY motif. The tail as identified may be exchanged, after or including the conserved NPXXY motif. As an alternative, a putative site of palmitoylation of a GPCR may be identified at approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of the conserved NPXXY motif, and the tail may be exchanged after or including the palmitoylated cysteine(s). Preferably, the carboxyl-terminal tail of a GPCR having clusters of phosphorylation sites is exchanged at an amino acid residue in close proximity to a putative site of palmitoylation. More preferably, the carboxyl-terminal tail of a GPCR having clusters of phosphorylation sites is exchanged at a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of the NPXXY motif, such that the portion of the carboxyl-terminal tail containing the clusters of phosphorylation sites begins at the amino acid residue immediately downstream of the palmitoylated cysteine residue. Exchanging in the preferred manner allows the clusters of phosphorylation sites to be reliably positioned properly within the carboxyl-terminal tail of the modified GPCR. The carboxyl-terminal tail having clusters of phosphorylation sites used for the exchange may have a detectable molecule conjugated to the carboxyl-terminus. The tails may be exchanged and the modified GPCRs may be constructed accordingly by manipulation of the nucleic acid sequence or the corresponding amino acid sequence.
In addition, the carboxyl-terminal tail portion used for the exchange may originate from a polypeptide synthesized to have an amino acid sequence corresponding to an amino acid sequence from a GPCR having one or more sites of phosphorylation, preferably one or more clusters of phosphorylation sites. The synthesized polypeptide may have a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of a NPXXY motif. The synthesized polypeptide may have one or more additions, substitutions, mutations, or deletions of amino acid residues that does not affect or alter the overall structure and function of the polypeptide.
Furthermore, the carboxyl-terminal tail portion used for the exchange may originate from a naturally occurring polypeptide recognized to have an amino acid sequence corresponding to an amino acid sequence from a GPCR having one or more clusters of phosphorylation sites. The polypeptide may have a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of a NPXXY motif. The polypeptide may have one or more additions, substitutions, mutations, or deletions of amino acid residues that does not affect or alter the overall structure and function of the polypeptide.
A modified GPCR containing a modified carboxyl-terminus region may be created by fusing a first carboxyl-terminal tail portion of a GPCR lacking properly positioned clusters of phosphorylation sites or with a lower or unknown affinity for arrestin with a second carboxyl-terminal tail portion of a GPCR or polypeptide having one or more clusters of phosphorylation sites. The second GPCR or polypeptide used for the exchange may have a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of a NPXXY motif. Accordingly, the modified carboxyl-terminus region of the modified GPCR comprises a portion of a carboxyl-terminal tail from a GPCR lacking properly positioned clusters of phosphorylation sites or with a lower or unknown affinity for arrestin fused to a portion of a carboxyl-terminal tail of a GPCR or polypeptide having clusters of phosphorylation sites. The tail of a GPCR lacking properly positioned clusters of phosphorylation sites may be exchanged after or including the conserved NPXXY motif, and fused to a carboxyl-terminal tail containing clusters of phosphorylation sites, after or including the conserved NPXXY motif. As an alternative, the tail of a GPCR lacking properly positioned clusters of phosphorylation sites may be exchanged after or including the palmitoylated cysteine(s), and fused to a tail containing clusters of phosphorylation sites, after or including the palmitoylated cysteine(s). The tails may be exchanged and the modified GPCRs may be constructed accordingly by manipulation of the nucleic acid sequence or the corresponding amino acid sequence.
In a further alternative, the carboxyl-tail of a GPCR, for example a GPCR not containing the NPXXY motif, may be predicted from a hydrophobicity plot and exchanged accordingly. The site of exchange may be selected according to the hydrophobicity plot. Based on a hydrophobicity plot, one of skill in the art may predict a site where it is expected that the GPCR may anchor in the membrane and then predict where to introduce a putative site of palmitoylation accordingly. Using this technique GPCRs having neither a NPXXY motif nor a putative site of palmitoylation may be modified to create a point of reference (e.g. a putative site of palmitoylation). The introduced putative site of palmitoylation may be then used to position a tail exchange. After introduction of a putative site of palmitoylation, the resulting tail may be fused with a second carboxyl-terminal tail portion of a GPCR or polypeptide having one or more clusters of phosphorylation sites and having a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of a NPXXY motif.
Preferably, the modified carboxyl-terminus region of the modified GPCR is fused at amino acid residues in close proximity to a putative site of palmitoylation. More preferably, the modified carboxyl-terminus region of the modified GPCR is fused such that the portion from the first GPCR with a lower affinity for arrestin comprises amino acid residues from the NPXXY motif through a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of the NPXXY motif and the portion from the second GPCR having clusters of phosphorylation sites and a putative site of palmitoylation approximately 10 to 25 (preferably 15 to 20) amino acid residues downstream of a NPXXY motif comprises amino acid residues beginning with an amino acid residue immediately downstream of the putative site of palmitoylation of the second GPCR extending to the end of the carboxyl-terminus. This fusion is preferred because the clusters of phosphorylation sites are reliably positioned properly within the carboxyl-terminal tail and the modified GPCR maintains its structure and ability to function.
By way of example, a Class A receptor or an orphan receptor may have a portion of its carboxyl-terminal tail exchanged with a portion of a carboxyl-terminal tail from a known Class B receptor. Further, receptors having virtually non-existent carboxyl-terminal tails, for example, olfactory receptors and taste receptors, may have a portion of their carboxyl-terminal tails exchanged with a portion of a carboxyl-terminal tail from a known Class B receptor. The Class B receptor tail used for these exchanges may have a detectable molecule fused to the carboxyl-terminus.
Modified GPCRs may be generated by molecular biological techniques standard in the genetic engineering art, including but not limited to, polymerase chain reaction (PCR), restriction enzymes, expression vectors, plasmids, and the like. By way of example, vectors, such as a pEArrB (enhanced arrestin binding), may be designed to enhance the affinity of a GPCR lacking clusters of phosphorylation sites for arrestin. To form a vector, such as a pEArrB vector, PCR amplified DNA fragments of a GPCR carboxyl-terminus, which forms stable complexes with arrestin, may be digested by appropriate restriction enzymes and cloned into a plasmid. A schematic of one such plasmid is illustrated in FIG. 4A. The DNA of a GPCR, which is to be modified, may also be PCR amplified, digested by restriction enzymes at an appropriate location, and subcloned into the vector, such as pEArrB, as illustrated in FIG. 4B. When expressed, the modified GPCR will contain a polypeptide fused to the carboxyl-terminus. The polypeptide will comprise clusters of phosphorylation sites. Preferably, the polypeptide originates from the GPCR carboxyl-terminus of a receptor that forms stable complexes with arrestin.
Such modified GPCRs may also occur naturally as the result of aberrant gene splicing or single nucleotide polymorphisms. Such naturally occurring modified GPCRs would be predicted to have modified endocytic targeting. These naturally occurring modified GPCRs may be implicated in a number of GPCR-related disease states.
As shown in FIG. 3, the present inventors modified several GPCRs. The β2-adrenergic receptor, dopamine D1A receptor, mu opiod receptor, orphan GPR3, orphan GPR6, orphan GPR12, orphan GPR7, orphan GPR8, orphan GPR55, orphan SREB2, and orphan SREB3 were modified as described herein. These modified GPCRs contain a properly positioned V2R cluster of phosphorylation sites (SSS) within the modified GPCR's tail.
As may be shown by standard receptor binding assays, the modified receptors are essentially indistinguishable from their wild-type counterparts except for an increased affinity for arrestin and thus an increased stability of their complex with arrestin and in their ability to traffic with arrestin and in their ability to recycle and resensitize. For example, the modified receptors are appropriately expressed at the membrane and possess similar affinity for agonists or ligands. However, the modified GPCRs have an increased affinity for arrestin and thus form a more stable complex with arrestin than their wild-type counterparts and may remain bound to arrestin when trafficking to endosomes.
These modified GPCRs are useful in assays to screen for an agonist of the GPCR, as well as in agonist-independent assays to identify compounds that alter GPCR desensitization.
Methods of Assaying GPCR Activity Using the Modified GPCRs
The modified GPCRs of the present invention are useful in methods of assaying GPCR activity. The modified GPCRs of the present invention may be used in assays to study GPCRs that have weaker than desired interactions or associations with arrestins and GPCRs that have unknown interactions or associations with arresting. Methods of the present invention that use the modified GPCRs provide a sensitive assay and may provide for enhanced detection, for example, of arrestin/GPCRs in endosomes. The assays using the modified GPCRs of the present invention may be useful for screening compounds and sample solutions for ligands, agonists, antagonists, inverse agonists, desensitization active compounds, and the like. Once identified, these compounds may be useful as drugs capable of modulating GPCR activity and useful in the treatment of one or more of the disease states in which GPCRs have been implicated.
In a preferred assay according to the present invention, cells are provided that express modified GPCRs of the present invention and these cells may further contain a conjugate of an arrestin and a detectable molecule.
Arrestin coupled to a detectable molecule may be detected and monitored as it functions in the GPCR pathway. The location of the arrestin may be detected, for example, evenly distributed in the cell cytoplasm, concentrated at a cell membrane, concentrated in clathrin-coated pits, localized on endosomes, and the like. In response to agonist stimulation, the proximity of arrestin to a GPCR may be monitored, as well as the proximity to any other cell structure. For example, in response to agonist stimulation arrestin may be detected in proximity to GPCRs at a cell membrane, concentrated with GPCRs in clathrin-coated pits, colocalized with a GPCR on endosomes, and the like.
The modified GPCRs of the present invention have an increased affinity for arrestin and provide a stable complex of the GPCR with arrestin, and thereby promote colocalization of the GPCR with arrestin into endosomes. In the methods of assaying of the present invention, arrestin may be detected, for example, in the cytoplasm, concentrated in proximity to GPCRs at a cell membrane, concentrated in proximity to GPCRs in clathrin-coated pits, colocalized with a GPCR on endosomes, and the like. Preferably the arrestin may be detected colocalized with a GPCR on endosomes.
The association of arrestin with a GPCR at a cell membrane may be rapidly detected after agonist addition, for example, approximately 1 second to 2 minutes. The colocalization of arrestin with GPCR on endosomes may be detected within several minutes of agonist addition, for example, approximately 3 to 15 minutes, and may persist for extended periods of time, for example, after 1 hour. The association of arrestin with GPCR on endosomes may give a strong, readily recognizable signal. Under magnification of 40× objective lens, the signal may be doughnut-like in appearance. The signal resulting from the compartmentalization of arrestin and GPCR colocalized in endosomes vesicles is typically easy to detect and may persist for extended periods of time.
A preferred method of assessing GPCR pathway activity of the present invention comprises (a) providing a cell that expresses at least one modified GPCR of the present invention and that further comprises a conjugate of an arrestin and a detectable molecule; (b) inducing translocation of the arrestin; and (c) detecting interaction of the arrestin with the modified GPCR along the translocation pathway.
Interaction of the arrestin with the modified GPCR may be detected, for example, in endosomes, in clathrin-coated pits, concentrated in proximity to a cell membrane, and the like. Preferably, interaction of the arrestin with the modified GPCR is detected in endosomes. Interaction of arrestin with a GPCR in endosomes may be detected within several minutes of agonist addition, for example, approximately 3 to 15 minutes, and may persist for extended periods of time, for example, after 1 hour. The association of arrestin with a GPCR in endosomes may give a strong, readily recognizable signal that persists for extended periods of time.
In a method of screening compounds for GPCR activity of the present invention a cell that expresses at least one modified GPCR is provided. The cell further contains arrestin conjugated to a detectable molecule. The cell is exposed to the compounds to be tested. The location of the arrestin within the cell is detected. The location of the arrestin within the cell in the presence of the compound is compared to the location of the arrestin within the cell in the absence of the compound, and a difference is correlated between (1) the location of the arrestin within the cell in the presence of the compound and (2) the location of the arrestin within the cell in the absence of the compound.
By way of example, compounds and sample solutions may be screened for GPCR agonist activity using the modified GPCRs of the present invention. In this method, cells that express at least one modified GPCR of the present invention and that further comprise a conjugate of an arrestin and a detectable molecule are provided. The cells are exposed to compounds or sample solutions to be tested. It is detected whether interaction of the arrestin with the modified GPCR is increased after exposure to the test compound or solution, an increase in interaction being an indication that the compound or solution has GPCR agonist activity. Interaction of the arrestin with the GPCR may be detected in endosomes, in clathrin-coated pits, in proximity to a cell membrane, and the like. The modified GPCR may also be conjugated to a detectable molecule, preferably at the carboxyl-terminus. As explained above modifications to GPCRs as in the present invention should not affect the GPCRs' natural affinity for agonists or ligands.
Also by way of example, compounds and sample solutions may be screened for GPCR antagonist or inverse agonist activity using the modified GPCRs of the present invention. Cells that express at least one modified GPCR of the present invention and that further comprise a conjugate of an arrestin and a detectable molecule are provided. The cells are exposed to compounds or sample solutions to be tested and to a known agonist for the GPCR. It is detected whether interaction of the arrestin with the modified GPCR is decreased after exposure to the test compound or solution, a decrease in interaction being an indication that the compound or solution has GPCR antagonist or inverse agonist activity. Interaction of the arrestin with the GPCR may be detected in endosomes, in clathrin-coated pits, in proximity to a cell membrane, and the like. The modified GPCR may also be conjugated to a detectable molecule, preferably at the carboxyl-terminus. As explained above modifications to GPCRs as in the present invention should not affect the GPCRs' natural affinity for antagonists or inverse agonists.
Further by way of example, compounds and sample solutions may be screened for GPCR desensitization activity using the modified GPCRs of the present invention. First cells that express at least one first modified GPCR of the present invention and that further comprise a conjugate of an arrestin and a detectable molecule are provided. The first cells are exposed to compounds or sample solutions to be tested and to a known agonist for the first GPCR. It is detected whether interaction of the arrestin with the first modified GPCR is decreased or not increased after exposure to the test compound or solution, a decrease or lack of increase in interaction being an indication that the compound or solution has GPCR desensitization activity. Interaction of the arrestin with the GPCR may be detected in endosomes, in clathrin-coated pits, in proximity to a cell membrane, and the like. Then second cells that express at least one second modified GPCR of the present invention and that further comprise a conjugate of an arrestin and a detectable molecule are provided. The second modified GPCR is not related to the first modified GPCR. The second cells are exposed to the compounds or sample solutions to be tested and to a known agonist for the second GPCR. It is detected whether interaction of the arrestin with the second modified GPCR is decreased or not increased after exposure to the test compound or solution, a decrease or lack of increase in interaction being an indication that the compound or solution has GPCR desensitization activity independent of the GPCR expressed. Interaction of the arrestin with the GPCR may be detected in endosomes, in clathrin-coated pits, in proximity to a cell membrane, and the like.
The methods of assessing GPCR pathway activity of the present invention also include cell-free assays. In cell-free assays of the present invention, a substrate having deposited thereon a modified GPCR of the present invention is provided. A fluid containing a conjugate of an arrestin and a detectable molecule is also provided. Translocation of the arrestin is induced and interaction of the arrestin with the GPCR is detected. The GPCR and arrestin may be obtained from whole cells and used in the cell-free assay after purification. The modified GPCR has arrestin binding sites and agonist binding sites and may be supported in a multilayer or bilayer lipid vesicle. The vesicle supporting the modified GPCR may be deposited on the substrate, and the modified GPCR may be supported in the lipid vesicle and deposited on the substrate such that the arrestin binding sites are exposed to arrestin and the receptor binding sites are accessible to agonists. The substrate may be any artificial substrate on which the GPCR may be deposited, including but not limited to, glass, plastic, diamond, ceramic, semiconductor, silica, fiber optic, diamond, biocompatible monomer, biocompatible polymer, polymer beads (including organic and inorganic polymers), and the like.
The present invention relates to the compounds identified as ligands, agonists, antagonists, inverse agonists, or DACs by the methods of assaying of the present invention. These compounds may be used to treat any one of the disease states in which GPCRs have been implicated. The compounds identified may be administered to a human or a non-human in therapeutically effective doses to treat or ameliorate a condition, disorder, or disease in which GPCRs have been implicated. A therapeutically effective dose refers to that amount of the compound sufficient to result in amelioration of symptoms of such a condition, disorder or disease.
Methods to Identify Compounds that Modulate GPCR Desensitization
The present invention relates to methods of screening for compounds that modulate GPCR desensitization. The methods utilize modified GRKs which constitutively phosphorylate GPCRs, resulting in constitutive desensitization. These may be used to identify compounds that alter the desensitization of GPCRs, even if the GPCR agonist is unknown. Once identified, these compounds may be useful as drugs capable of modulating GPCR activity and useful in the treatment of one or more of the disease states in which GPCRs have been implicated.
In a preferred method according to the present invention, cells are provided that contain an expression system and a nucleic acid encoding a modified GRK, resulting in constitutive desensitization of GPCRs expressed in the cell. These cells may further contain an arrestin conjugated to a GFP.
A preferred method of identifying a compound which inhibits GPCR internalization includes: (a) providing a cell including a GPCR, an arrestin, and a modified GRK; (b) exposing the cell to the compound(s); (c) determining the cellular distribution of the GPCR or arrestin; and (d) correlating a difference between (1) the location of the labeled molecule in the cell in the presence of the compound(s) and (2) the location of the labeled molecule in the cell in the absence of the compound(s) to modulation of GPCR internalization. Non-limiting embodiments of this method are described in FIGS. 4, 5, 6, and 7 and Examples 2, 3, 4, 5, 6, and 7.
The GRK of step (a), as described above, may be GRK 1, 2, 3, 4, 5, 6, or any other GRK, including splice variants, biologically active fragments, or modified GRKs. The GRK may be overexpressed and/or its expression may be inducible. The GRK may include a CAAX motif.
In the above method, agonist may or may not be provided.
Methods of detecting the labeled molecules and determining the cellular distribution of the GPCR or arrestin are described below.
GPCRs useful in the present invention include, but are not limited to GPCRs which have known agonists, GPCRs which do not have known agonists, GPCRs listed in FIG. 1A-1C, GPCRs illustrated in FIGS. 3, 4, 5, 6, and 7, AT1AR, Class A GPCRs, Class B GPCRs, taste receptors, odorant receptors, orphan receptors, modified GPCRs, GPCRs as described in U.S. patent application Ser. Nos. 10/054,616, 09/993,844, 10/095,620, 10/101,235, 09/631,468,10/141,725, 10/161,916, 09/469,554, 09/772,644, 60/393,789, and 60/379,986, which are herein incorporated by reference, or biologically active fragments of the above GPCRs.
Vectors and Nucleic Acids, Host Cells for Protein Expression
The present invention relates to modified GRKs, including GRKs which are over-expressed, or their expression is inducible.
Nucleic acids encoding modified GRKs are provided. The present invention relates to the expression, over-expression, and the inducible expression of these proteins. The expression may be carried out by a suitable expression system contained in a vector, as described below.
One aspect of the present invention relates to the combination of (1) nucleic acids encoding a modified GRK with (2) a system for expression of modified GRKs resulting in constitutive desensitization of GPCRs. This system for expression of modified GRKs may include a promoter or origin of replication.
Another aspect of the present invention relates to modified GPCRs, nucleic acids encoding modified GPCRs, and host cell for modified GPCR expression.
Nucleic acids encoding modified GPCRs are provided. The present invention relates to the expression, over-expression, and the inducible expression of these proteins. The expression may be carried out by a suitable expression system contained in a vector, as described below.
A feature of this invention is the expression of the DNA sequences disclosed herein. As is well known in the art, DNA sequences may be expressed by operatively linking them to an expression control sequence in an appropriate expression vector and employing that expression vector to transform an appropriate unicellular host. The transforming DNA may or may not be integrated (covalently linked) into chromosomal DNA making up the genome of the cell.
Such operative linking of a DNA sequence of this invention to an expression control sequence, of course, includes, if not already part of the DNA sequence, the provision of an initiation codon, ATG, in the correct reading frame upstream of the DNA sequence.
A wide variety of host/expression vector combinations may be employed in expressing the DNA sequences of this invention. Useful expression vectors, for example, may consist of segments of chromosomal, non-chromosomal and synthetic DNA sequences. Suitable vectors include derivatives of SV40 and known bacterial plasmids, e.g., E. coli plasmids col El, pCR1, pBR322, pMB9 and their derivatives, plasmids such as RP4; phage DNAS, e.g., the numerous derivatives of phage A, e.g., NM989, and other phage DNA, e.g., M13 and filamentous single stranded phage DNA; yeast plasmids such as the 2μ plasmid or derivatives thereof; vectors useful in eukaryotic cells, such as vectors useful in insect or mammalian cells; vectors derived from combinations of plasmids and phage DNAs, such as plasmids that have been modified to employ phage DNA or other expression control sequences; and the like.
Any of a wide variety of expression control sequences—sequences that control the expression of a DNA sequence operatively linked to it—may be used in these vectors to express the DNA sequences of this invention. Such useful expression control sequences include, for example, the early or late promoters of SV40, CMV, vaccinia, polyoma or adenovirus, the lac system, the trp system, the TAC system, the TRC system, the LTR system, the major operator and promoter regions of phage λ, the control regions of fd coat protein, the promoter for 3-phosphoglycerate kinase or other glycolytic enzymes, the promoters of acid phosphatase (e.g., Pho5), the promoters of the yeast α-mating factors, and other sequences known to control the expression of genes of prokaryotic or eukaryotic cells or their viruses, and various combinations thereof.
A wide variety of unicellular host cells are also useful in expressing the DNA sequences of this invention. These hosts may include well known eukaryotic and prokaryotic hosts, such as strains of E. coli, Pseudomonas, Bacillus, Streptomyces, fungi such as yeasts, plant cells, nematode cells, and animal cells, such as HEK-293, U20S, CHO, RI. I, B-W and L-M cells, African Green Monkey kidney cells (e.g., COS 1, COS 7, BSC1, BSC40, and BMT10), insect cells (e.g., Sf9), and human cells and plant cells in tissue culture. In one aspect of the present invention, the host cells include a GRK-C20 and an arrestin. In a further aspect of the present invention, the host cells include a GRK-C20, an arrestin, and a GPCR.
It will be understood that not all vectors, expression control sequences and hosts will function equally well to express the DNA sequences of this invention. Neither will all hosts function equally well with the same expression system. However, one skilled in the art will be able to select the proper vectors, expression control sequences, and hosts without undue experimentation to accomplish the desired expression without departing from the scope of this invention. For example, in selecting a vector, the host must be considered because the vector must function in it. The vector's copy number, the ability to control that copy number, and the expression of any other proteins encoded by the vector, such as antibiotic markers, will also be considered.
In selecting an expression control sequence, a variety of factors will normally be considered. These include, for example, the relative strength of the system, its controllability, and its compatibility with the particular DNA sequence or gene to be expressed, particularly as regards potential secondary structures. Suitable unicellular hosts will be selected by consideration of, e.g., their compatibility with the chosen vector, their secretion characteristics, their ability to fold proteins correctly, and their fermentation requirements, as well as the toxicity to the host of the product encoded by the DNA sequences to be expressed, and the ease of purification of the expression products.
Considering these and other factors a person skilled in the art will be able to construct a variety of vector/expression control sequence/host combinations that will express the DNA sequences of this invention on fermentation or in large scale animal culture.
It is further intended that modified GRK analogs may be prepared from nucleotide sequences of the protein complex/subunit derived within the scope of the present invention. Analogs, such as fragments, may be produced, for example, by pepsin digestion of GRK material. Other analogs, such as muteins, can be produced by standard site-directed mutagenesis of GRK coding sequences. Analogs exhibiting “GRK activity” such as small molecules, whether functioning as promoters or inhibitors, may be identified by known in vivo and/or in vitro assays.
As mentioned above, a DNA sequence encoding a modified GRK6 can be prepared synthetically rather than cloned. The DNA sequence can be designed with the appropriate codons for the GRK amino acid sequence. In general, one will select preferred codons for the intended host if the sequence will be used for expression. The complete sequence is assembled from overlapping oligonucleotides prepared by standard methods and assembled into a complete coding sequence. See, e.g., Edge, Nature, 292:756 (1981); Nambair et al., Science, 223:1299 (1984); Jay et al., J. Biol. Chem., 259:6311 (1984).
Synthetic DNA sequences allow convenient construction of genes which will express GRK analogs or “muteins”. Alternatively, DNA encoding muteins can be made by site-directed mutagenesis of native or modified GRK genes or cDNAs, and muteins can be made directly using conventional polypeptide synthesis.
A general method for site-specific incorporation of unnatural amino acids into proteins is described in Christopher J. Noren, Spencer J. Anthony-Cahill, Michael C. Griffith, Peter G. Schultz, Science, 244:182-188 (April 1989). This method may be used to create analogs with unnatural amino acids.
Additional motifs, such as epitope tags or sequences to aid in purification, may be incorporated into the nucleic acids encoding the modified GRKs or modified GPCRs. Preferably, the nucleic acids encoding the motifs may be at the 5′ or 3′ end of the nucleic acid, resulting in the presence of the motif at the N or C terminus of the protein.
The Conjugates
The cells used in the methods of assaying of the present invention may comprise a conjugate of an arrestin protein and a detectable molecule. In the cells and methods of the present invention, the cells may also comprise a conjugate of a modified GPCR of the present invention and a detectable molecule.
All forms of arrestin, naturally occurring and engineered variants, including but not limited to, visual arrestin, cone arrestin, βarrestin 1 and βarrestin 2, may be used in the present invention. The modified GPCRs of the present invention may interact to a detectable level with all forms of arrestin.
Detectable molecules that may be used to conjugate with the arrestin include, but are not limited to, molecules that are detectable by spectroscopic, photochemical, biochemical, immunochemical, electrical, radioactive, and optical means, including but not limited to bioluminescence, phosphorescence, and fluorescence. Detectable molecules include, but are not limited to, GFP, luciferase, β-galactosidase, rhodamine-conjugated antibody, and the like. Detectable molecules include radioisotopes, epitope tags, affinity labels, enzymes, fluorescent groups, chemiluminescent groups, and the like. Detectable molecules include molecules which are directly or indirectly detected as a function of their interaction with other molecule(s). These detectable molecules should be a biologically compatible molecule and should not compromise the ability of the arrestin to interact with the GPCR system and the interaction of the arrestin with the GPCR system must not compromise the ability of the detectable molecule to be detected. Preferred detectable molecules are optically detectable molecules, including optically detectable proteins, such that they may be excited chemically, mechanically, electrically, or radioactively to emit fluorescence, phosphorescence, or bioluminescence. More preferred detectable molecules are inherently fluorescent molecules, such as fluorescent proteins, including, for example, Green Fluorescent Protein (GFP). The detectable molecule may be conjugated to the arrestin protein by methods as described in Barak et al. (U.S. Pat. Nos. 5,891,646 and 6,110,693). The detectable molecule may be conjugated to the arrestin at the front-end, at the back-end, or in the middle.
The GPCR or biologically active fragments thereof may also be conjugated with a detectable molecule. Preferably, the carboxyl-terminus of the GPCR is conjugated with a detectable molecule. A carboxyl-terminal tail conjugated or attached to a detectable molecule can be used in a carboxyl-terminal tail exchange to provide the detectably labeled GPCR.
If the GPCR is conjugated with a detectable molecule, proximity of the GPCR with the arrestin may be readily detected. In addition, if the GPCR is conjugated with a detectable molecule, compartmentalization of the GPCR with the arrestin may be readily confirmed. The detectable molecule used to conjugate with the GPCRs may include those as described above, including, for example, optically detectable molecules, such that they may be excited chemically, mechanically, electrically, or radioactively to emit fluorescence, phosphorescence, or bioluminescence. Preferred optically detectable molecules may be detected by immunofluorescence, luminescence, fluorescence, and phosphorescence.
For example, the GPCRs may be antibody labeled with an antibody conjugated to an immunofluorescence molecule or the GPCRs may be conjugated with a luminescent donor. In particular, the GPCRs may be conjugated with, for example, luciferase, for example, Renilla luciferase, or a rhodamine-conjugated antibody, for example, rhodamine-conjugated anti-HA mouse monoclonal antibody. Preferably, the carboxyl-terminal tail of the GPCR may be conjugated with a luminescent donor, for example, luciferase. The GPCR, preferably the carboxyl-terminal tail, also may be conjugated with GFP as described in L. S. Barak et al. “Internal Trafficking and Surface Mobility of a Functionally Intact β2-Adrenergic Receptor-Green Fluorescent Protein Conjugate”, Mol. Pharm. (1997) 51, 177-184.
Cell Types and Substrates
The cells of the present invention may express at least one modified GPCR of the present invention. The cells may further comprise a conjugate of an arrestin protein and a detectable molecule. Useful cells include eukaryotic and prokaryotic cells, including, but not limited to, bacterial cells, yeast cells, fungal cells, insect cells, nematode cells, plant cells, and animal cells. Suitable animal cells include, but are not limited to, HEK-293 cells, U2OS cells, HeLa cells, COS cells, and various primary mammalian cells. An animal model expressing a conjugate of an arrestin and a detectable molecule throughout its tissues or within a particular organ or tissue type, may also be used.
The cells of the present invention may express one modified protein that results in agonist-independent localization of GPCRs to endocytic vesicles or endosomes.
A substrate may have deposited thereon a plurality of cells of the present invention. The substrate may be any suitable biologically substrate, including but not limited to, glass, plastic, ceramic, semiconductor, silica, fiber optic, diamond, biocompatible monomer, or biocompatible polymer materials.
Methods of Detection
Methods of detecting the intracellular location of the detectably labeled arrestin, the intracellular location of a detectably labeled GPCR, or interaction of the detectably labeled arrestin, or other member of GPCR/arrestin complex with a GPCR or any other cell structure, including for example, the concentration of arrestin or GPCR at a cell membrane, colocalization of arrestin with GPCR in endosomes, and concentration of arrestin or GPCR in clathrin-coated pits, and the like, will vary dependent upon the detectable molecule(s) used.
One skilled in the art readily will be able to devise detection methods suitable for the detectable molecule(s) used. For optically detectable molecules, any optical method may be used where a change in the fluorescence, bioluminescence, or phosphorescence may be measured due to a redistribution or reorientation of emitted light. Such methods include, for example, polarization microscopy, BRET, FRET, evanescent wave excitation microscopy, and standard or confocal microscopy.
In a preferred embodiment arrestin may be conjugated to GFP and the arrestin-GFP conjugate may be detected by confocal microscopy. In another preferred embodiment, arrestin may conjugated to a GFP and the GPCR may be conjugated to an immunofluorescent molecule, and the conjugates may be detected by confocal microscopy. In an additional preferred embodiment, arrestin may conjugated to a GFP and the carboxy-terminus of the GPCR may be conjugated to a luciferase and the conjugates may be detected by bioluminescence resonance emission technology. In a further preferred embodiment arrestin may be conjugated to a luciferase and GPCR may be conjugated to a GFP, and the conjugates may be detected by bioluminescence resonance emission technology. The methods of the present invention are directed to detecting GPCR activity. The methods of the present invention allow enhanced monitoring of the GPCR pathway in real time.
In a preferred embodiment, the localization pattern of the detectable molecule is determined. In a further preferred embodiment, alterations of the localization pattern of the detectable molecule may be determined. The localization pattern may indicate cellular distribution of the detectable molecule. Certain methods of detection are described in U.S. Ser. No. 10/095,620, filed Mar. 12, 2002, which claims priority to U.S. Provisional Patent Application No. 60/275,339, filed Mar. 13, 2001, the contents of which are incorporated by reference in their entirety.
Molecules may also be detected by their interaction with another detectably labeled molecule, such as an antibody.
Disease Treatment
Another aspect of the invention relates to methods of treating a human or non-human subject suffering from a GPCR-related disease, such as cardiovascular disease, heart failure, asthma, nephrogenic diabetes insipidus, or hypertension. For example, compounds which alter AT1AR internalization may be useful to treat diseases and conditions related to AT1AR. Such diseases and conditions related to AT1AR include, but are not limited to: renal disease, diabetes and nephropathy, diabetes mellitus, type 2 diabetes, nephropathy, hypertension, congesive heart failure, endothelial dysfunction, vascular inflammation, and various heart diseases. Such treatment can be performed either by administering to a subject in need of such treatment, an amount of the compounds identified by the present method sufficient to treat the GPCR-related disease, or at least to lessen the symptoms thereof.
Treatment may also be effected by administering to the subject the naked modified nucleic acid sequences of the invention, such as by direct injection, microprojectile bombardment, delivery via liposomes or other vesicles, or by means of a vector which can be administered by one of the foregoing methods. Gene delivery in this manner may be considered gene therapy.
Pharmaceutical Compositions
The preparation of therapeutic compositions which contain polypeptides, analogs or active fragments as active ingredients is well understood in the art. Typically, such compositions are prepared as injectables, either as liquid solutions or suspensions, however, solid forms suitable for solution in, or suspension in, liquid prior to injection can also be prepared. The preparation can also be emulsified. The active therapeutic ingredient is often mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredient. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol, or the like and combinations thereof. In addition, if desired, the composition can contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents which enhance the effectiveness of the active ingredient.
Losartan is a known angiotensin receptor antagonist, of the following formula:




The present invention describes a new use of losartan: losartan is useful in methods of altering arrestin translocation to the AT1AR receptor (FIGS. 8-9). This method my be used to treat a patient by administering an effective amount of losartan to a patient in need thereof.

A GPCR agonist, antagonist, or DAC obtained by the methods disclosed herein can be formulated into the therapeutic composition as neutralized pharmaceutically acceptable salt forms. Pharmaceutically acceptable salts include the acid addition salts (formed with the free amino groups of the polypeptide or antibody) and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed from the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, 2-ethylamino ethanol, histidine, procaine, and the like.
The therapeutic compositions are conventionally administered intravenously, as by injection of a unit dose, for example. The term “unit dose” when used in reference to a therapeutic composition of the present invention refers to physically discrete units suitable as unitary dosage for humans, each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect in association with the required diluent (i.e., carrier, or vehicle).
The data obtained from the cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage of such compositions lies preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For any composition used in the method of the invention, the therapeutically effective dose can be estimated initially from cell culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range which includes the IC50 (i.e., the concentration of the test composition which achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography.
The compositions are administered in a manner compatible with the dosage formulation, and in a therapeutically effective amount. The quantity to be administered depends on the subject to be treated, capacity of the subject's immune system to utilize the active ingredient, and degree of modulation of GPCR activity desired. Precise amounts of active ingredient required to be administered depend on the judgment of the practitioner and are peculiar to each individual. However, suitable dosages may range from about 0.001 to 30, preferably about 0.01 to about 25, and more preferably about 0.1 to 20 milligrams of active ingredient per kilogram body weight of individual per day and depend on the route of administration. Suitable regimes for initial administration and booster shots are also variable, but are typified by an initial administration followed by repeated doses at one or more hour intervals by a subsequent injection or other administration. Alternatively, continuous intravenous infusion sufficient to maintain concentrations of ten nanomolar to ten micromolar in the blood are contemplated.
The skilled artisan will appreciate that certain factors may influence the dosage required to effectively treat a subject, including but not limited to, the severity of the disease or condition, disorder, or disease, previous treatments, the general health and/or age of the subject, and other diseases present. Moreover, treatment of a subject with a therapeutically effective amount of the composition(s) can include a single treatment or, preferably, can include a series of treatments. In a preferred example, a subject is treated with the composition in the range of between about 0.1 to 20 mg/kg body weight, one time per week for between about 1 to 10 weeks, preferably between 2 to 8 weeks, more preferably between about 3 to 7 weeks, and even more preferably for about 4, 5, or 6 weeks. It will also be appreciated that the effective dosage of the composition used for treatment may increase or decrease over the course of a particular treatment. Changes in dosage may result and become apparent from the results of diagnostic assays as described herein.
The therapeutic compositions may further include an effective amount of the GPCR agonist, antagonist, or DAC and one or more of the following active ingredients: an antibiotic, a steroid, and the like.
The term “prodrug” indicates a therapeutic agent that is prepared in an inactive form that is converted to an active form (i.e., drug) within the body or cells thereof by the action of endogenous enzymes or other chemicals and/or conditions. In particular, prodrug versions of the oligonucleotides of the invention can be prepared as SATE ((S-acetyl-2-thioethyl) phosphate) derivatives according to the methods disclosed for example in WO 93/24510 and in WO 94/26764.
The term “pharmaceutically acceptable salts” refers to physiologically and pharmaceutically acceptable salts of the compounds of the invention: i.e., salts that retain the desired biological activity of the parent compound and do not impart undesired toxicological effects thereto. The compounds for modulating any of the disclosed genes, gene transcripts or proteins encoded thereby include antisense compounds as well as other modulatory compounds.
Pharmaceutically acceptable base addition salts for use with antisense as well as other modulatory compounds are formed with metals or amines, such as alkali and alkaline earth metals or organic amines. Examples of metals used as cations are sodium, potassium, magnesium, calcium, and the like. Examples of suitable amines are N,N′-dibenzylethylenediamine, chloroprocaine, choline, diethanolamine, dicyclohexylamine, ethylenediamine, N-methylglucamine, and procaine (see, e.g., Berge et al., “Pharmaceutical Salts,” J. Pharma. Sci., 1977, 66: 1-19). The base addition salts of acidic compounds are prepared by contacting the free acid form with a sufficient amount of the desired base to produce the salt in the conventional manner. The free acid form may be regenerated by contacting the salt form with an acid and isolating the free acid in the conventional manner. The free acid forms differ from their respective salt forms somewhat in certain physical properties such as solubility in polar solvents, but otherwise the salts are equivalent to their respective free acid for purposes of the present invention. As used herein, a pharmaceutical addition salt includes a pharmaceutically acceptable salt of an acid form of one of the components of the compositions of the invention. These include organic or inorganic acid salts of the amines. Preferred acid salts are the hydrochlorides, acetates, salicylates, nitrates and phosphates. Other suitable pharmaceutically acceptable salts are known in the art and include basic salts of a variety of inorganic and organic acids, such as, for example, with inorganic acids (e.g., hydrochloric acid, hydrobromic acid, sulfuric acid or phosphoric acid); with organic carboxylic, sulfonic, sulfo- or phospho-acids or N-substituted sulfamic acids, for example acetic acid, propionic acid, glycolic acid, succinic acid, maleic acid, hydroxymaleic acid, methylmaleic acid, fumaric acid, malic acid, tartaric acid, lactic acid, oxalic acid, gluconic acid, glucaric acid, glucuronic acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, salicylic acid, 4-aminosalicylic acid, 2-phenoxybenzoic acid, 2-acetoxybenzoic acid, embonic acid, nicotinic acid or isonicotinic acid; and with amino acids, such as the 20 alpha-amino acids involved in the synthesis of proteins in nature, for example glutamic acid or aspartic acid, and also with phenylacetic acid, methanesulfonic acid, ethanesulfonic acid, 2-hydroxyethanesulfonic acid, ethane-1,2-disulfonic acid, benzenesulfonic acid, 4-methylbenzenesulfonic acid, naphthalene-2-sulfonic acid, naphthalene-1,5-disulfonic acid, 2- or 3-phosphoglycerate, glucose-6-phosphate, N-cyclohexylsulfamic acid (with the formation of cyclamates), or with other acid organic compounds, such as ascorbic acid.
Pharmaceutically acceptable salts of compounds may also be prepared with a pharmaceutically acceptable cation. Suitable pharmaceutically acceptable cations are well known in the art and include alkaline, alkaline earth, ammonium and quaternary ammonium cations. Carbonates or hydrogen carbonates are also possible.
For oligonucleotides, preferred examples of pharmaceutically acceptable salts include but are not limited to (a) salts formed with cations such as sodium, potassium, ammonium, magnesium, calcium, polyamines such as spermine and spermidine, etc.; (b) acid addition salts formed with inorganic acids, for example hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid and the like; (c) salts formed with organic acids such as, for example, acetic acid, oxalic acid, tartaric acid, succinic acid, maleic acid, fumaric acid, gluconic acid, citric acid, malic acid, ascorbic acid, benzoic acid, tannic acid, palmitic acid, alginic acid, polyglutamic acid, naphthalenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, naphthalenedisulfonic acid, polygalacturonic acid, and the like; and (d) salts formed from elemental anions such as chlorine, bromine, and iodine.
The antisense compounds and other modulatory compounds described herein can be utilized in pharmaceutical compositions by adding an effective amount of an antisense compound or other modulatory compound to a suitable pharmaceutically acceptable diluent or carrier. Use of the compounds and methods of the invention may also be useful prophylactically.
The antisense compounds of the invention are useful for research and diagnostics, because these compounds hybridize to nucleic acids encoding a gene identified using the systematic discovery technique or a mRNA transcript thereof. Such hybridization allows the use of sandwich and other assays to easily be constructed to exploit this fact. Hybridization of the antisense oligonucleotides of the invention with a nucleic acid encoding a gene or gene transcript identified by a systematic discovery method can be detected by means known in the art. Such means may include, for example, conjugation of an enzyme to the oligonucleotide, radiolabelling of the oligonucleotide or any other suitable detection means. Kits using such detection means for detecting the level of a transcript of a gene in a sample may also be prepared.
The present invention also includes pharmaceutical antisense compositions and formulations which include the antisense compounds and other modulatory compounds and compositions of the invention. The pharmaceutical compositions of the present invention may be administered in a number of ways depending upon whether local or systemic treatment is desired and upon the area to be treated.
In certain embodiments, it may be desirable to administer the pharmaceutical compositions of the invention locally to the area in need of treatment. This may be achieved by, for example, and not by way of limitation, local infusion during surgery, topical application, e.g., in conjunction with a wound dressing after surgery, by injection, by means of a catheter, by means of a suppository, or by means of an implant, said implant being of a porous, non-porous, or gelatinous material, including membranes, such as sialastic membranes, or fibers. In one embodiment, administration can be by direct injection at the site (or former site) of a malignant tumor or neoplastic or pre-neoplastic tissue.
For topical application, the compositions may be combined with a carrier so that an effective dosage is delivered, based on the desired activity.
Pharmaceutical compositions and formulations for topical administration may include transdermal patches, ointments, lotions, creams, gels, drops, suppositories, sprays, liquids and powders. Conventional pharmaceutical carriers, aqueous, powder or oily bases, thickeners and the like may be necessary or desirable.
For oral administration, the pharmaceutical compositions may take the form of, for example, tablets or capsules prepared by conventional means with pharmaceutically acceptable excipients such as binding agents (e.g., pregelatinised maize starch, polyvinylpyrrolidone or hydroxypropyl methylcellulose); fillers (e.g., lactose, microcrystalline cellulose or calcium hydrogen phosphate); lubricants (e.g., magnesium stearate, talc or silica); disintegrants (e.g., potato starch or sodium starch glycolate); or wetting agents (e.g., sodium lauryl sulphate). The tablets may be coated by methods well known in the art. Liquid preparations for oral administration may take the form of, for example, solutions, syrups or suspensions, or they may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may be prepared by conventional means with pharmaceutically acceptable additives such as suspending agents (e.g., sorbitol syrup, cellulose derivatives or hydrogenated edible fats); emulsifying agents (e.g., lecithin or acacia); non-aqueous vehicles (e.g., almond oil, oily esters, ethyl alcohol or fractionated vegetable oils); and preservatives (e.g., methyl or propyl-p-hydroxybenzoates or sorbic acid). The preparations may also contain buffer, salts, flavoring, coloring and sweetening agents as appropriate.
Preparations for oral administration may be suitably formulated to give controlled release of the active composition.
The compositions may be formulated for parenteral administration by injection, e.g., by bolus injection or continuous infusion. Formulations for injection may be presented in unit dosage form, e.g., in ampules or in multi-dose containers, with an added preservative. The compositions may take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. Alternatively, the active ingredient may be in powder form for constitution with a suitable vehicle, e.g., sterile pyrogen-free water, before use.
For administration by inhalation, the compositions for use according to the present invention are conveniently delivered in the form of an aerosol spray, presentation from pressurized packs or a nebulizer, with the use of a suitable propellant, e.g., dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol, the dosage unit may be determined by providing a valve to deliver a metered amount. Capsules and cartridges of, e.g., gelatin for use in an inhaler or insufflator may be formulated containing a powder mix of the composition and a suitable powder base such as lactose or starch.
The compositions may also be formulated as a depot preparation. Such long acting formulations may be administered by implantation (for example subcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the compositions may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt.
The compositions may, if desired, be presented in a pack or dispenser device that may contain one or more unit dosage forms containing the active ingredient. The pack may for example comprise metal or plastic foil, such as a blister pack. The pack or dispenser device may be accompanied by instructions for administration.
Pharmaceutical compositions (e.g., gene, gene transcript or protein product modulatory agents as described herein) of the present invention include, but are not limited to, solutions, emulsions, and liposome-containing formulations. These compositions may be generated from a variety of components that include, but are not limited to, preformed liquids, self-emulsifying solids and self-emulsifying semisolids.
The pharmaceutical formulations of the present invention, which may conveniently be presented in unit dosage form, may be prepared according to conventional techniques well known in the pharmaceutical industry. Such techniques include the step of bringing into association the active ingredients with the pharmaceutical carrier(s) or excipient(s). In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredients with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product.
In one embodiment of the present invention, the pharmaceutical compositions may be formulated and used as foams. Pharmaceutical foams include formulations such as, but not limited to, emulsions, microemulsions, creams, jellies and liposomes. While basically similar in nature, these formulations vary in the components and the consistency of the final product. The preparation of such compositions and formulations is generally known to those skilled in the pharmaceutical and formulation arts and may be applied to the formulation of the compositions of the present invention.
The compositions of the present invention may be prepared and formulated as emulsions. Emulsions are typically heterogenous systems of one liquid dispersed in another in the form of droplets usually exceeding 0.1 m in diameter. See, e.g., Idson, in Pharmaceutical Dosage Forms v. 1, p. 199 (Lieberman, Rieger and Banker (Eds.), 1988, Marcel Dekker, Inc., New York); Rosoff, in Pharmaceutical Dosage Forms, v. 1, p. 245; Block in Pharmaceutical Dosage Forms, v. 2, p. 335; Higuchi et al., in Remington's Pharmaceutical Sciences 301 (Mack Publishing Co., Easton, Pa., 1985). Emulsions are often biphasic systems comprising of two immiscible liquid phases intimately mixed and dispersed with each other. In general, emulsions may be either water-in-oil (w/o) or of the oil-in-water (o/w) variety. When an aqueous phase is finely divided into and dispersed as minute droplets into a bulk oily phase, the resulting composition is called a water-in-oil (w/o) emulsion. Alternatively, when an oily phase is finely divided into and dispersed as minute droplets into a bulk aqueous phase the resulting composition is called an oil-in-water (o/w) emulsion. Emulsions may contain additional components in addition to the dispersed phases and the active drug which may be present as a solution in either the aqueous phase, oily phase or itself as a separate phase.
Pharmaceutical excipients such as emulsifiers, stabilizers, dyes, and anti-oxidants may also be present in emulsions as needed. Pharmaceutical emulsions may also be multiple emulsions that are comprised of more than two phases such as, for example, in the case of oil-in-water-in-oil (o/w/o) and water-in-oil-in-water (w/o/w) emulsions. Such complex formulations often provide certain advantages that simple binary emulsions do not. Multiple emulsions in which individual oil droplets of an o/w emulsion enclose small water droplets constitute a w/o/w emulsion. Likewise a system of oil droplets enclosed in globules of water stabilized in an oily continuous provides an o/w/o emulsion.
Emulsions are characterized by little or no thermodynamic stability. Often, the dispersed or discontinuous phase of the emulsion is well dispersed into the external or continuous phase and maintained in this form through the means of emulsifiers or the viscosity of the formulation. Either of the phases of the emulsion may be a semisolid or a solid, as is the case of emulsion-style ointment bases and creams. Other means of stabilizing emulsions entail the use of emulsifiers that may be incorporated into either phase of the emulsion. Emulsifiers may broadly be classified into four categories: synthetic surfactants, naturally occurring emulsifiers, absorption bases, and finely dispersed solids (Idson, in Pharmaceutical Dosage Forms v. 1, p. 199 (Lieberman, Rieger and Banker (Eds.), 1988, Marcel Dekker, Inc., New York).
Synthetic surfactants, also known as surface active agents, have found wide applicability in the formulation of emulsions and have been reviewed in the literature (Rieger, in Pharmaceutical Dosage Forms, v. 1, p. 285; Idson, in Pharmaceutical Dosage Forms, v. 1, p. 199). Surfactants are typically amphiphilic and comprise a hydrophilic and a hydrophobic portion. The ratio of the hydrophilic to the hydrophobic nature of the surfactant has been termed the hydrophile/lipophile balance (HLB) and is a valuable tool in categorizing and selecting surfactants in the preparation of formulations. Surfactants may be classified into different classes based on the nature of the hydrophilic group: nonionic, anionic, cationic and amphoteric (Rieger, in Pharmaceutical Dosage Forms).
Naturally occurring emulsifiers used in emulsion formulations include lanolin, beeswax, phosphatides, lecithin and acacia. Absorption bases possess hydrophilic properties such that they can soak up water to form w/o emulsions yet retain their semisolid consistencies, such as anhydrous lanolin and hydrophilic petrolatum. Finely divided solids have also been used as good emulsifiers, especially in combination with surfactants and in viscous preparations. These include polar inorganic solids, such as heavy metal hydroxides, non-swelling clays (e.g., bentonite, aftapulgite, hectorite, kaolin, montmorillonite, colloidal aluminum silicate and colloidal magnesium aluminum silicate), pigments and nonpolar solids (e.g., carbon or glyceryl tristearate).
A large variety of non-emulsifying materials are also included in emulsion formulations and contribute to the properties of emulsions. These include fats, oils, waxes, fatty acids, fatty alcohols, fatty esters, humectants, hydrophilic colloids, preservatives and antioxidants (Block, in Pharmaceutical Dosage Forms, v. 1 p. 385 (Lieberman, Rieger and Banker (Eds.), 1988, Marcel Dekker, Inc., New York)).
Hydrophilic colloids or hydrocolloids include naturally occurring gums and synthetic polymers, such as polysaccharides (e.g., acacia, agar, alginic acid, carrageenan, guar gum, karaya gum, and tragacanth), cellulose derivatives (e.g., carboxymethylcellulose and carboxypropylcellulose), and synthetic polymers (e.g., carbomers, cellulose ethers, and carboxyvinyl polymers). These disperse or swell in water to form colloidal solutions that stabilize emulsions by forming strong interfacial films around the dispersed-phase droplets and by increasing the viscosity of the external phase.
Since emulsions often contain a number of ingredients such as carbohydrates, proteins, sterols and phosphatides that may readily support the growth of microbes, these formulations often incorporate preservatives. Commonly used preservatives included in emulsion formulations include methyl paraben, propyl paraben, quaternary ammonium salts, benzalkonium chloride, esters of p-hydroxybenzoic acid, and boric acid. Antioxidants are also commonly added to emulsion formulations to prevent deterioration of the formulation. Antioxidants used may be free radical scavengers (e.g., tocopherols, alkyl gallates, butylated hydroxyanisole, butylated hydroxytoluene) or reducing agents (e.g., ascorbic acid and sodium metabisulfite), and antioxidant synergists (e.g., citric acid, tartaric acid, and lecithin).
The application of emulsion formulations via dermatological, oral and parenteral routes and methods for their manufacture have been reviewed in the literature (Idson, in Pharmaceutical Dosage Forms, v. 1, p. 199). Emulsion formulations for oral delivery have been very widely used because of reasons of ease of formulation, efficacy from an absorption and bioavailability standpoint. (Rosoff, in Pharmaceutical Dosage Forms, v. 1, p. 245 (Lieberman, Rieger and Banker (Eds.), 1988, Marcel Dekker, Inc., New York); Idson, in Pharmaceutical Dosage Forms). Mineral-oil base laxatives, oil-soluble vitamins and high fat nutritive preparations are among the materials that have commonly been administered orally as o/w emulsions.
In one embodiment of the present invention, the compositions of oligonucleotides and nucleic acids are formulated as microemulsions. A microemulsion may be defined as a system of water, oil and amphiphile which is a single optically isotropic and thermodynamically stable liquid solution (Rosoff, in Pharmaceutical Dosage Forms, v. 1, p. 245). Typically microemulsions are systems that are prepared by first dispersing an oil in an aqueous surfactant solution and then adding a sufficient amount of a fourth component, generally an intermediate chain-length alcohol to form a transparent system. Therefore, microemulsions have also been described as thermodynamically stable, isotropically clear dispersions of two immiscible liquids that are stabilized by interfacial films of surface-active molecules (Leung and Shah, in Controlled Release of Drugs: Polymers and Aggregate Systems, 185-215 (Rosoff, M., Ed., 1989, VCH Publishers, New York). Microemulsions commonly are prepared via a combination of three to five components that include oil, water, surfactant, cosurfactant and electrolyte. Whether the microemulsion is of the water-in-oil (w/o) or an oil-in-water (o/w) type is dependent on the properties of the oil and surfactant used and on the structure and geometric packing of the polar heads and hydrocarbon tails of the surfactant molecules (Schott, in Remington's Pharmaceutical Sciences, 271 (Mack Publishing Co., Easton, Pa., 1985).
Surfactants used in the preparation of microemulsions include, but are not limited to, ionic surfactants, non-ionic surfactants, Brij 96, polyoxyethylene oleyl ethers, polyglycerol fatty acid esters, tetraglycerol monolaurate (ML310), tetraglycerol monooleate (MO310), hexaglycerol monooleate (PO310), hexaglycerol pentaoleate (PO500), decaglycerol monocaprate (MCA750), decaglycerol monooleate (MO750), decaglycerol sequioleate (SO750), decaglycerol decaoleate (DAO750), alone or in combination with co-surfactants. The co-surfactant, usually a short-chain alcohol such as ethanol, 1-propanol, and 1-butanol, serves to increase the interfacial fluidity by penetrating into the surfactant film and consequently creating a disordered film because of the void space generated among surfactant molecules.
Microemulsions may, however, be prepared without the use of co-surfactants and alcohol-free self-emulsifying microemulsion systems are known in the art. The aqueous phase may typically be, but is not limited to, water, an aqueous solution of the drug, glycerol, PEG300, PEG400, polyglycerols, propylene glycols, and derivatives of ethylene glycol. The oil phase may include, but is not limited to, materials such as Captex 300, Captex 355, Capmul MCM, fatty acid esters, medium chain (C8-C12) mono-, di-, and tri-glycerides, polyoxyethylated glyceryl fatty acid esters, fatty alcohols, polyglycolized glycerides, saturated polyglycolized C8-C10 glycerides, vegetable oils and silicone oil.
Microemulsions are particularly of interest from the standpoint of drug solubilization and the enhanced absorption of drugs. Lipid based microemulsions (both o/w and w/o) have been proposed to enhance the oral bioavailability of drugs, including peptides (Constantinides et al., Pharm. Res., 1994, 11:1385-90; Ritschel, Meth. Find. Exp. Clin. Pharmacol., 1993, 13: 205). Microemulsions afford advantages of improved drug solubilization, protection of drug from enzymatic hydrolysis, possible enhancement of drug absorption due to surfactant-induced alterations in membrane fluidity and permeability, ease of preparation, ease of oral administration over solid dosage forms, improved clinical potency, and decreased toxicity (Constantinides et al., 1994; Ho et al., J. Pharm. Sci., 1996, 85: 138-143). Often microemulsions may form spontaneously when their components are brought together at ambient temperature. This may be particularly advantageous when formulating thermolabile drugs, peptides or oligonucleotides. Microemulsions have also been effective in the transdermal delivery of active components in both cosmetic and pharmaceutical applications. It is expected that the microemulsion compositions and formulations of the present invention will facilitate the increased systemic absorption of oligonucleotides and nucleic acids and other active agents from the gastrointestinal tract, as well as improve the local cellular uptake of oligonucleotides and nucleic acids and other active agents within the gastrointestinal tract, vagina, buccal cavity and other areas of administration.
Microemulsions of the present invention may also contain additional components and additives such as sorbitan monostearate (Grill 3), Labrasol, and penetration enhancers to improve the properties of the formulation and to enhance the absorption of the oligonucleotides and nucleic acids of the present invention. Penetration enhancers used in the microemulsions of the present invention may be classified as belonging to one of five broad categories—surfactants, fatty acids, bile salts, chelating agents, and non-chelating non-surfactants (Lee et al., Crit. Rev. Therap. Drug Carrier Systems, 1991, p. 92). Each of these classes has been discussed above.
There are many organized surfactant structures besides microemulsions that have been studied and used for the formulation of drugs. These include monolayers, micelles, bilayers and vesicles. Vesicles, such as liposomes, are useful because of their specificity and the duration of action. As used in the present invention, the term “liposome” means a vesicle composed of amphiphilic lipids arranged in a spherical bilayer or bilayers.
Liposomes are unilamellar or multilamellar vesicles which have a membrane formed from a lipophilic material and an aqueous interior. The aqueous portion contains the composition to be delivered. Cationic liposomes possess the advantage of being able to fuse to the cell wall. Non-cationic liposomes, although not able to fuse as efficiently with the cell wall, are taken up by macrophages in vivo. Selection of the appropriate liposome depending on the agent to be encapsulated would be evident given what is known in the art.
In order to cross intact mammalian skin, lipid vesicles must pass through a series of fine pores, each with a diameter less than 50 nm, under the influence of a suitable transdermal gradient. Therefore, it is desirable to use a liposome which is highly deformable and able to pass through such fine pores.
Further advantages of liposomes include: (a) liposomes obtained from natural phospholipids are biocompatible and biodegradable; (b) liposomes can incorporate a wide range of water and lipid soluble drugs; (c) liposomes can protect encapsulated drugs in their internal compartments from metabolism and degradation (Rosoff, in Pharmaceutical Dosage Forms). Important considerations in the preparation of liposome formulations are the lipid surface charge, vesicle size and the aqueous volume of the liposomes.
Liposomes are useful for the transfer and delivery of active ingredients to the site of action. Because the liposomal membrane is structurally similar to biological membranes, when liposomes are applied to a tissue, the liposomes start to merge with the cellular membranes. As the merging of the liposome and cell progresses, the liposomal contents are emptied into the cell where the active agent may act.
Another embodiment also contemplates the use of liposomes for topical administration. Such advantages include reduced side-effects related to high systemic absorption of the administered drug, increased accumulation of the administered drug at the desired target, and the ability to administer a wide variety of drugs, both hydrophilic and hydrophobic, into the skin. Several reports have detailed the ability of liposomes to deliver agents including high-molecular weight DNA into the skin. Compounds including analgesics, antibodies, hormones and high-molecular weight DNAs have been administered to the skin. The majority of applications resulted in the targeting of the upper epidermis.
Liposomes fall into two broad classes. Cationic liposomes are positively charged liposomes which interact with the negatively charged DNA molecules to form a stable complex. The positively charged DNA/liposome complex binds to the negatively charged cell surface and is internalized in an endosome. Due to the acidic pH within the endosome, the liposomes are ruptured, releasing their contents into the cell cytoplasm (Wang et al., Biochem. Biophys. Res. Comm., 1987, 147:980-985).
Liposomes which are pH-sensitive or negatively-charged, entrap DNA rather than complex with it. Since both the DNA and the lipid are similarly charged, repulsion rather than complex formation occurs. Nevertheless, some DNA is entrapped within the aqueous interior of these liposomes. pH-sensitive liposomes have been used to deliver DNA encoding the thymidine kinase gene to cell monolayers in culture. Expression of the exogenous gene was detected in the target cells (Zhou et al., J. Controlled Release, 1992, 19: 269-74).
Another contemplated liposomal composition includes phospholipids other than naturally-derived phosphatidylcholine. Neutral liposome compositions, for example, can be formed from dimyristoyl phosphatidylcholine (DMPC) or dipalmitoyl phosphatidylcholine (DPPC). Anionic liposome compositions generally are formed from dimyristoyl phosphatidylglycerol, while anionic fusogenic liposomes are formed primarily from dioleoyl phosphatidylethanolamine (DOPE). Another type of liposomal composition is formed from phosphatidylcholine (PC) such as, for example, soybean PC, and egg PC. Another type is formed from mixtures of phospholipid and/or phosphatidylcholine and/or cholesterol.
“Sterically stabilized” liposomes, which refers to liposomes comprising one or more specialized lipids that, when incorporated into liposomes, result in enhanced circulation lifetimes relative to liposomes lacking such specialized lipids are also contemplated. Examples of sterically stabilized liposomes are those in which part of the vesicle-forming lipid portion of the liposome (A) comprises one or more glycolipids, such as monosialoganglioside GM1, or (B) is derivatized with one or more hydrophilic polymers, such as a polyethylene glycol (PEG) moiety. While not wishing to be bound by any particular theory, it is thought in the art that, at least for sterically stabilized liposomes containing gangliosides, sphingomyelin, or PEG-derivatized lipids, the enhanced circulation half-life of these sterically stabilized liposomes derives from a reduced uptake into cells of the reticuloendothelial system (RES) (Allen et al., FEBS Lett., 1987, 223: 42; Wu et al., Can. Res., 1993, 53: 3765).
Many liposomes comprising lipids derivatized with one or more hydrophilic polymers, and methods of preparation thereof, are known in the art. See, e.g., Sunamoto et al. (Bull. Chem. Soc. Jpn., 1980, 53: 2778) described liposomes comprising a nonionic detergent, 2C12 15G, that contains a PEG moiety. Illum et al. (FEBS Lett., 1984, 167: 79) noted that hydrophilic coating of polystyrene particles with polymeric glycols results in significantly enhanced blood half-lives. Synthetic phospholipids modified by the attachment of carboxylic groups of polyalkylene glycols (e.g., PEG) are described by Sears (U.S. Pat. Nos. 4,426,330 and 4,534,899). Klibanov et al. (FEBS Lett., 1990, 268: 235) described experiments demonstrating that liposomes comprising phosphatidylethanolamine (PE) derivatized with PEG or PEG stearate have significant increases in blood circulation half-lives. Blume et al. (Biochimica et Biophysica Acta, 1990, 1029: 91) extended such observations to other PEG-derivatized phospholipids, e.g., DSPE-PEG, formed from the combination of distearoylphosphatidylethanolamine (DSPE) and PEG. Liposomes having covalently bound PEG moieties on their external surface are described in European Patent No. EP 0 445 131 B1 and WO 90/04384 to Fisher. Liposome compositions containing 1-20 mole percent of PE derivatized with PEG, and methods of use thereof, are described by, e.g., Woodle et al. (U.S. Pat. Nos. 5,013,556 and 5,356,633) and Martin et al. (U.S. Pat. No. 5,213,804 and European Patent No. EP 0 496 813 B1). Liposomes comprising a number of other lipid-polymer conjugates are disclosed in WO 91/05545 and U.S. Pat. No. 5,225,212 (both to Martin et al.) and in WO 94/20073 (Zalipsky et al.). Liposomes comprising PEG-modified ceramide lipids are described in WO 96/10391 (Choi et al.). U.S. Pat. No. 5,540,935 (Miyazaki et al.) and U.S. Pat. No. 5,556,948 (Tagawa et al.) describe PEG-containing liposomes that can be further derivatized with functional moieties on their surfaces.
Methods of encapsulating nucleic acids in liposomes is also known in the art. See, WO 96/40062 to Thierry et al. discloses methods for encapsulating high molecular weight nucleic acids in liposomes. U.S. Pat. No. 5,264,221 to Tagawa et al. discloses protein-bonded liposomes and asserts that the contents of such liposomes may include an antisense RNA. U.S. Pat. No. 5,665,710 to Rahman et al. describes certain methods of encapsulating oligodeoxynucleotides in liposomes.
Surfactants find wide application in formulations such as emulsions (including microemulsions) and liposomes. The most common way of classifying and ranking the properties of the many different types of surfactants, both natural and synthetic, is by the use of the hydrophile/lipophile balance (HLB). The nature of the hydrophilic group (also known as the “head”) provides the most useful means for categorizing the different surfactants used in formulations (Rieger, in Pharmaceutical Dosage Forms, p. 285 (Marcel Dekker, Inc., New York, N.Y., 1988, p. 285)).
If the surfactant molecule is not ionized, it is classified as a nonionic surfactant. Nonionic surfactants find wide application in pharmaceutical and cosmetic products and are usable over a wide range of pH values. In general their HLB values range from 2 to about 18 depending on their structure. Nonionic surfactants include nonionic esters such as ethylene glycol esters, propylene glycol esters, glyceryl esters, polyglyceryl esters, sorbitan esters, sucrose esters, and ethoxylated esters. Nonionic alkanolamides and ethers such as fatty alcohol ethoxylates, propoxylated alcohols, and ethoxylated/propoxylated block polymers are also included in this class. The polyoxyethylene surfactants are the most popular members of the nonionic surfactant class.
If the surfactant molecule carries a negative charge when it is dissolved or dispersed in water, the surfactant is classified as anionic. Anionic surfactants include carboxylates such as soaps, acyl lactylates, acyl amides of amino acids, esters of sulfuric acid such as alkyl sulfates and ethoxylated alkyl sulfates, sulfonates such as alkyl benzene sulfonates, acyl isethionates, acyl taurates and sulfosuccinates, and phosphates. The most important members of the anionic surfactant class are the alkyl sulfates and the soaps.
If the surfactant molecule carries a positive charge when it is dissolved or dispersed in water, the surfactant is classified as cationic. Cationic surfactants include quaternary ammonium salts and ethoxylated amines. The quaternary ammonium salts are the most used members of this class.
If the surfactant molecule has the ability to carry either a positive or negative charge, the surfactant is classified as amphoteric. Amphoteric surfactants include acrylic acid derivatives, substituted alkylamides, N-alkylbetaines and phosphatides.
The use of surfactants in drug products, formulations and in emulsions has been reviewed (Rieger, in Pharmaceutical Dosage Forms, 285 (Marcel Dekker, Inc., New York, N.Y., 1988).
In one embodiment, the present invention employs various penetration enhancers to effect the efficient delivery of nucleic acids and other agents, particularly oligonucleotides, to the skin of animals. Most drugs are present in solution in both ionized and nonionized forms. However, usually only lipid soluble or lipophilic drugs readily cross cell membranes. It has been discovered that even non-lipophilic drugs may cross cell membranes if the membrane to be crossed is treated with a penetration enhancer. In addition to aiding the diffusion of non-lipophilic drugs across cell membranes, penetration enhancers also enhance the permeability of lipophilic drugs.
Penetration enhancers may be classified as belonging to one of five broad categories, i.e., surfactants, fatty acids, bile salts, chelating agents, and non-chelating non-surfactants (Lee et al., Critical Reviews in Therapeutic Drug Carrier Systems, 1991, p. 92). Each of the above mentioned classes of penetration enhancers are described below in greater detail.
Another embodiment of the invention contemplates pharmaceutical compositions comprising surfactants. Surfactants (or “surface-active agents”) are chemical entities which, when dissolved in an aqueous solution, reduce the surface tension of the solution or the interfacial tension between the aqueous solution and another liquid, with the result that absorption of oligonucleotides through the mucosa is enhanced. In addition to bile salts and fatty acids, these penetration enhancers include, for example, sodium lauryl sulfate, polyoxyethylene-9-lauryl ether and polyoxyethylene-20-cetyl ether) (Lee et al., Crit. Rev. Therap. Drug Carrier Systems, 1991, 92); and perfluorochemical emulsions, such as FC-43 (Takahashi et al., J. Pharm. Pharmacol., 1988, 40: 252).
Another embodiment contemplates the use of various fatty acids and their derivatives to act as penetration enhancers include, for example, oleic acid, lauric acid, capric acid (n-decanoic acid), myristic acid, palmitic acid, stearic acid, linoleic acid, linolenic acid, dicaprate, tricaprate, monoolein (1-monooleoyl-rac-glycerol), dilaurin, caprylic acid, arachidonic acid, glycerol 1-monocaprate, 1-dodecylazacycloheptan-2-one, acylcarnitines, acylcholines, C1-10 alkyl esters thereof (e.g., methyl, isopropyl and t-butyl), and mono- and di-glycerides thereof (i.e., oleate, laurate, caprate, myristate, palmitate, stearate, linoleate, and the like) (Lee et al., 1991; Muranishi, Crit. Rev. Therap. Drug Carrier Systems, 1990, 7: 1-33; El Hariri et al., J. Pharm. Pharmacol., 1992, 44: 651-4).
The compositions comprising the active agents of the invention may further comprise bile salts. The physiological role of bile includes the facilitation of dispersion and absorption of lipids and fat-soluble vitamins (Brunton, Chapter 38 in: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 9th Ed., Hardman et al. Eds., McGraw-Hill, N.Y., 1996, pp. 934-935). Various natural bile salts, and their synthetic derivatives, act as penetration enhancers. Thus, the term “bile salts” includes any of the naturally occurring components of bile as well as any of their synthetic derivatives. The bile salts of the invention include, for example, cholic acid (or its pharmaceutically acceptable sodium salt, sodium cholate), dehydrocholic acid (sodium dehydrocholate), deoxycholic acid (sodium deoxycholate), glucholic acid (sodium glucholate), glycholic acid (sodium glycocholate), glycodeoxycholic acid (sodium glycodeoxycholate), taurocholic acid (sodium taurocholate), taurodeoxycholic acid (sodium taurodeoxycholate), chenodeoxycholic acid (sodium chenodeoxycholate), ursodeoxycholic acid (UDCA), sodium tauro-24,25-dihydro-fusidate (STDHF), sodium glycodihydrofusidate and polyoxyethylene-9-lauryl ether (POE) (Lee et al., 1991; Swinyard, Chapter 39 In: Remington's Pharmaceutical Sciences, 18th Ed., Gennaro, ed., Mack Publishing Co., Easton, Pa., 1990, pages 782-783; Muranishi, 1990; Yamamoto et al., J. Pharm. Exp. Ther., 1992, 263: 25; Yamashita et al., J. Pharm. Sci., 1990, 79: 579-83).
The invention further contemplates compositions comprising chelating agents. Chelating agents can be defined as compounds that remove metallic ions from solution by forming complexes therewith, with the result that absorption of oligonucleotides through the mucosa is enhanced. With regards to their use as penetration enhancers for use when the active agent is an antisense agent, chelating agents have the added advantage of also serving as DNase inhibitors, as most characterized DNA nucleases require a divalent metal ion for catalysis and are thus inhibited by chelating agents (Jarrett, J. Chromatogr., 1993, 618: 315-39). Chelating agents of the invention include but are not limited to disodium ethylenediaminetetraacetate (EDTA), citric acid, salicylates (e.g., sodium salicylate, 5-methoxysalicylate and homovanilate), N-acyl derivatives of collagen, laureth-9 and N-amino acyl derivatives of beta-diketones (enamines) (Lee et al., 1991; Muranishi, 1990; Buur et al., J. Control Rel., 1990, 14: 43-51).
The invention also contemplates pharmaceutical compositions comprising active agents and non-chelating non-surfactants. Non-chelating non-surfactant penetration enhancing compounds can be defined as compounds that demonstrate insignificant activity as chelating agents or as surfactants, but that nonetheless enhance absorption of oligonucleotides through the alimentary mucosa (Muranishi, 1990). This class of penetration enhancers include, for example, unsaturated cyclic ureas, 1-alkyl- and 1-alkenylazacyclo-alkanone derivatives (Lee et al., 1991); and non-steroidal anti-inflammatory agents such as diclofenac sodium, indomethacin and phenylbutazone (Yamashita et al., J. Pharm. Pharmacol., 1987, 39: 621-6).
For pharmaceutical compositions comprising oligonucleotides, agents that enhance uptake of oligonucleotides at the cellular level may also be added to the pharmaceutical and other compositions of the present invention. For example, cationic lipids, such as lipofectin (Junichi et al., U.S. Pat. No. 5,705,188), cationic glycerol derivatives, and polycationic molecules, such as polylysine (Lollo et al., PCT Application WO 97/30731), are also known to enhance the cellular uptake of oligonucleotides.
Other agents may be utilized to enhance the penetration of the administered nucleic acids, including glycols such as ethylene glycol and propylene glycol, pyrrols such as 2-pyrrol, azones, and terpenes (e.g., limonene and menthone).
Certain compositions of the present invention also incorporate carrier compounds in the formulation. As used herein, “carrier compound” or “carrier” can refer to a nucleic acid, or analog thereof, which is inert (i.e., does not possess biological activity per se) but is recognized as a nucleic acid by in vivo processes that reduce the bioavailability of a nucleic acid having biological activity by, for example, degrading the biologically active nucleic acid or promoting its removal from circulation. The coadministration of a nucleic acid and a carrier compound, typically with an excess of the latter substance, can result in a substantial reduction of the amount of nucleic acid recovered in the liver, kidney or other extracirculatory reservoirs, presumably due to competition between the carrier compound and the nucleic acid for a common receptor. For example, the recovery of a partially phosphorothioate oligonucleotide in hepatic tissue can be reduced when it is coadministered with polyinosinic acid, dextran sulfate, polycytidic acid or 4-acetamido-4′-isothiocyano-stilbene-2,2′-disulfonic acid (Miyao et al., Antisense Res. Dev., 1995, 5: 115-121; Takakura et al., Antisense & Nucl. Acid Drug Dev., 1996, 6: 177-183).
The pharmaceutical compositions disclosed herein may also comprise an excipients. In contrast to carrier compounds described above, these excipients include a pharmaceutically acceptable solvent, suspending agent or any other pharmacologically inert vehicle for delivering one or more nucleic acids or other active agents to an animal. The excipient may be liquid or solid and is selected, with the planned manner of administration in mind, so as to provide for the desired bulk, consistency, etc., when combined with a nucleic acid or other active agent and the other components of a given pharmaceutical composition. Typical pharmaceutical carriers include, but are not limited to, binding agents (e.g., pregelatinized maize starch, polyvinylpyrrolidone or hydroxypropyl methylcellulose, etc.); fillers (e.g., lactose and other sugars, microcrystalline cellulose, pectin, gelatin, calcium sulfate, ethyl cellulose, polyacrylates or calcium hydrogen phosphate, etc.); lubricants (e.g., magnesium stearate, talc, silica, colloidal silicon dioxide, stearic acid, metallic stearates, hydrogenated vegetable oils, corn starch, polyethylene glycols, sodium benzoate, sodium acetate, etc.); disintegrants (e.g., starch, sodium starch glycolate, etc.); and wetting agents (e.g., sodium lauryl sulphate, etc.).
Pharmaceutically acceptable organic or inorganic excipients suitable for non-parenteral administration which do not deleteriously react with nucleic acids can also be used to formulate the compositions of the present invention. Suitable pharmaceutically acceptable carriers include, but are not limited to, water, salt solutions, alcohols, polyethylene glycols, gelatin, lactose, amylose, magnesium stearate, talc, silicic acid, viscous paraffin, hydroxymethylcellulose, polyvinylpyrrolidone and the like.
Formulations for topical administration of nucleic acids and other contemplated active agents may include sterile and non-sterile aqueous solutions, non-aqueous solutions in common solvents such as alcohols, or solutions of the nucleic acids in liquid or solid oil bases. The solutions may also contain buffers, diluents and other suitable additives. Pharmaceutically acceptable organic or inorganic excipients suitable for non-parenteral administration which do not deleteriously react with nucleic acids or other contemplated active agents can be used.
The compositions of the present invention may additionally contain other adjunct components conventionally found in pharmaceutical compositions, at their art-established usage levels. Thus, for example, the compositions may contain additional, compatible, pharmaceutically-active materials such as, e.g., antipruritics, astringents, local anesthetics or anti-inflammatory agents, or may contain additional materials useful in physically formulating various dosage forms of the compositions of the present invention, such as dyes, flavoring agents, preservatives, antioxidants, opacifiers, thickening agents and stabilizers. However, such materials, when added, should not unduly interfere with the biological activities of the components of the compositions of the present invention. The formulations can be sterilized and, if desired, mixed with auxiliary agents, e.g., lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salts for influencing osmotic pressure, buffers, colorings, flavorings and/or aromatic substances and the like which do not deleteriously interact with the nucleic acid(s) of the formulation.
Aqueous suspensions may contain substances which increase the viscosity of the suspension including, for example, sodium carboxymethylcellulose, sorbitol and/or dextran. The suspension may also contain stabilizers.
Test Kits
In a further embodiment of this invention, commercial test kits including an assay system for screening potential drugs effective to modulate the activity of the GPCR may be prepared. The test kits may include cells, nucleic acids, or proteins described herein. The test kits may be used to carry out any of the methods described herein. A GPCR of interest may be introduced into host cells of the test kit. The test kit may be useful for determining if the GPCR is expressed at the plasma membrane, if the phosphorylated or unphosphorylated GPCR binds arrestin, or if the phosphorylated or unphosphorylated GPCR is internalized. The test kit may be useful for the identification of compounds that alter the desensitization of the GPCR of interest.
The GPCR may be introduced into a test system, and the prospective drug may also be introduced into the resulting cell culture, and the culture thereafter examined to observe any changes in the GPCR activity (e.g., signaling, recycling, affinity for arrestin, and the like) in the cells.
The following examples are presented in order to more fully illustrate the preferred embodiments of the invention. They should in no way be construed, however, as limiting the broad scope of the invention.
EXAMPLES
Example 1
Experimental Procedures
The present inventors subcloned the Bovine GRK2-C20 cDNA (Inglese et al., Nature 1992) into the expression vector pcDNA3.1zeo+ (Invitrogen). Expression of this cDNA produces GRK2 with a CAAX motif (where C is cysteine, A is a small aliphatic residue, and X is an uncharged amino acid) added to the carboxyl terminus. The specific CAAX motif added to the end of GRK2, CVLL (SEQ ID NO: 94), directs the geranylgeranylation (C20 isoprenylation) of this protein. The enzyme-directed covalent attachment of the 20 carbon geranylgeranyl lipid group to the carboxyl terminus of GRK2 allows it to be localized at the plasma membrane (Inglese et al., Nature 1992).
Cell Culture
Human embryonic kidney (HEK-293) cells were purchased from the American Type Culture Collection (ATCC) and grown in Eagle's minimum essential medium (EMEM) supplemented with 10% (v/v) heat-inactivated fetal calf serum and gentamicin (100 μg/ml). HEK-293 cells stably expressing arrestin-GFP (HEK293-ArrGFP) were generated by standard procedures using G418 selection (0.4 mg/ml). HEK-293 cells were transiently transfected with arrestin-GFP, the GPCR of interest, and GRK2-C20. For control experiments performed in parallel, HEK-293 cells were transiently transfected with arrestin-GFP, the GPCR of interest, and no GRK2-C20. HEK293 cells were transiently transfected with arrestin-GFP, the GPCR of interest and GRK2-C20. For control experiments performed in parallel, the HEK293 cells were transiently transfected with arrestin-GFP were transiently transfected with the GPCR of interest and no GRK2-C20. All transfections were performed by the calcium phosphate coprecipitation method as previously described (Oakley et al., 1999). Following the transfection, cells were maintained in the culture medium (EMEM supplemented with 10% FCS and 10 μg/ml gentamycin) for approximately 24 hours. The cells were then plated on 35 mm glass bottom dishes (MatTek) and incubated for an additional 16-24 hours. Transfected GPCRs included both known GPCRs (receptors for which the natural ligand is know) and orphan GPCRs (receptors for which the natural ligand has not yet been identified).
Confocal Microscopy
Transfected HEK-293 cells were plated on 35 mm glass bottom dishes (MatTek) and cultured overnight. The next day, the medium was removed and replaced with serum-free medium supplemented with 10 mM HEPES for an additional 1 hour incubation at 37° C. The distribution of arrestin-GFP was then assessed using a Zeiss laser scanning confocal microscope (LSM 5 Pascal). Images were acquired with a 63× oil objective from live cells using single line excitation (488 nm) and a LP505 emission filter.
Example 2
Agonist-Independent Desensitization of Known GPCRs Upon Expression of a Modified GRK
The present inventors determined that overexpression of the GRK2-C20, which is expressed at the plasma membrane (Inglese et al., Nature 1992), in a cell line expressing arrestin-GFP promoted the binding of arrestin-GFP to GPCRs in the absence of added ligand.
The HEK293 cells transiently transfected with arrestin-GFP were transiently transfected with the GPCR of interest and with or without GRK2-C20. Using confocal microscopy, the distribution of the arrestin-GFP was determined. The localization of the arrestin-GFP at clathrin coated pits, endocytic vesicles, endosomes, or other stages in the desensitization pathway indicated arrestin-GFP binding to the GPCR. Thus, GPCR desensitization, visualized by the binding of arrestin-GFP to the GPCRs, was analyzed.
In the absence of added agonist, arrestin-GFP localized in small puncta (presumably clathrin coated pits) at the plasma membrane in cells expressing GRK2-C20 and either the cannabinoid type 2 receptor (CB2R) (FIG. 4). Moreover, in the absence of added agonist, arrestin-GFP localized in endocytic vesicles in cells expressing GRK2-C20 and either the angiotensin II type IA receptor (AT1AR), vasopressin V2 receptor (V2R), (FIG. 4) or neurokinin-1/substance P receptor (NK-1 or SPR). In control cells expressing each of the receptors (CB2R, AT1AR, V2R, or SPR) but lacking GRK2-C20, arrestin-GFP was diffusely expressed in the cytoplasm and did not localize to any significant extent in pits at the plasma membrane or vesicles inside the cell (FIG. 4).
Example 3
Agonist-Independent Desensitization of Orphan GPCRs Upon Expression of a Modified GRK
The present inventors determined that overexpression of the GRK2-C20, which is expressed at the plasma membrane (Inglese et al., Nature 1992), in a cell line expressing arrestin-GFP promoted the binding of arrestin-GFP to GPCRs in the absence of added ligand.
As above, the HEK293 cells transiently transfected with arrestin-GFP were transiently transfected with the GPCR of interest and with or without GRK2-C20. Using confocal microscopy, the distribution of the arrestin-GFP was determined. The localization of the arrestin-GFP at clathrin coated pits, endocytic vesicles, endosomes, or other stages in the desensitization pathway indicated arrestin-GFP binding to the GPCR. Thus, GPCR desensitization, visualized by the binding of arrestin-GFP to the GPCRs, was analyzed.
In the absence of added agonist, arrestin-GFP localized in small puncta (presumably clathrin coated pits) at the plasma membrane in cells expressing the orphan receptor GPR55 (FIG. 7). In control cells expressing GPR55 but lacking GRK2-C20, arrestin-GFP was diffusely expressed in the cytoplasm and did not localize to any significant extent in pits at the plasma membrane or vesicles inside the cell (FIG. 7). Other orphan GPCRs are described below.
Example 4
Method of Analyzing the Ability of a GPCR to Bind Arrestin
The present inventors developed a method to determine if a GPCR of interest is expressed at the plasma membrane. Preferably, the expression of orphan GPCRs may be analyzed in host cells in which GPCRs desensitize in an agonist-independent manner, as described herein.
As above, the HEK293 cells transiently transfected with arrestin-GFP were transiently transfected with the GPCR of interest and with or without GRK2-C20. Using confocal microscopy, the distribution of the arrestin-GFP was determined. The localization of the arrestin-GFP at clathrin coated pits, endocytic vesicles, endosomes, or other stages in the desensitization pathway indicated arrestin-GFP binding to the GPCR. Thus, GPCR desensitization, visualized by the binding of arrestin-GFP to the GPCRs, was analyzed.
Certain GPCRs, as described above, localized in clathrin coated pits, endocytic vesicles, endosomes, or other stages in the desensitization pathway. This localization indicated that the GPCRs had the ability to bind arrestin, because arrestin binding is requisite for subsequent localization in the desensitization pathway. A GPCR that does not bind arrestin would not enter or localize in the desensitization pathway. GPCRs that do not bind arrestin may be altered such that they do bind arrestin. The present inventors modified certain GPCRs to enhance arrestin affinity, as described below.
Example 5
Method of Increasing the Ability of a GPCR to Bind Arrestin
The present inventors modified GPCRs to enhance their binding to arrestin. These modifications are described in U.S. Ser. No. 09/993,844. GPCRs were modified at their C-terminal tails to be better phosphorylated by GRKs. These modified and phosphorylated GPCRs then had enhanced binding to arrestin. They demonstrated increased internalization. The letter E (for enhanced phosphorylation) is added to the end of the name of the GPCR which has been modified in this manner.
Modified GPCR constructs were generated by polymerase chain reaction following standard protocols and contain the HA epitope. Chimeric receptors were constructed in which the carboxyl-terminal tails of the GPCR and V2R were exchanged (FIG. 3A-3BB), one for the other, after the putative sites of palmitoylation. Sequences of the DNA constructs were confirmed by DNA sequencing.
The nucleic acids of the GPCR of interest were PCR-amplified with primers that introduced a Not I restriction enzyme site (gcggccgc) immediately after the codon for a cysteine residue (a putative site of palmitoylation) 10 to 25 amino acids (preferably 15 to 20) downstream of the NPXXY that is to be fused to the V2R carboxyl terminus. The amplified receptor DNA fragment was then subcloned into the pEArrB-1 vector (described in U.S. patent application Ser. No. 09/993,844) using the Not I restriction enzyme site and an additional restriction enzyme site upstream of the receptor atg start codon. When expressed, the modified GPCR will contain a 31 amino acid peptide fused to the receptor carboxyl terminus. The first two amino acids will be Ala residues contributed by the Not I site, and the last 29 amino acids will be from the V2R carboxyl terminus.
The present inventors modified the carboxyl-terminal tails of the following receptors as described above and in the U.S. patent application Ser. No. 09/993,844: the β2-adrenergic receptor (β2ARE), dopamine D1A receptor (D1ARE), mu opiod receptor (MORE), orphan GPR3 (GPR3E), orphan GPR6 (GPR6E), orphan GPR12 (GPR12E), orphan GPR7 (GPR7E), orphan GPR8 (GPR8E), orphan GPR55 (GPR55E), orphan SREB2 (SREB2E), and orphan SREB3 (SREB3E). The “E” stands for “enhanced arrestin binding”. In the absence of added agonist, arrestin-GFP localized in endocytic vesicles for each of the modified GPCRs listed above when co-expressed with GRK2-C20 (FIGS. 4, 5, 6, and 7). For some of these modified receptors (such as orphan GPR6E), a small but significant amount of arrestin-GFP was observed to localize in intracellular vesicles in the control cells lacking the GRK2-C20 (FIG. 5). However, overexpression of GRK2-C20 with these receptors promoted a marked increase in this response (FIG. 5). The amino acid and nucleic acid sequences of these modified GPCRs, the wild-type sequences, and sequences of HA-tagged modified GPCRs are shown in FIG. 3A-3BB and in SEQ ID Nos: 35-90.
Example 6
Method of Determining if a GPCR of interest is Expressed at the Plasma Membrane
The present inventors developed a method to determine if a GPCR of interest is expressed at the plasma membrane.
The HEK293 cells transiently transfected with arrestin-GFP were transiently transfected with the GPCR of interest and with or without GRK2-C20. Using confocal microscopy, the distribution of the arrestin-GFP was determined. The localization of the arrestin-GFP at clathrin coated pits, endocytic vesicles, endosomes, or other stages in the desensitization pathway indicated arrestin-GFP binding to the GPCR. Thus, GPCR desensitization, visualized by the binding of arrestin-GFP to the GPCRs, was analyzed.
Certain GPCRs, as described above, localized in clathrin coated pits, endocytic vesicles, endosomes, or other stages in the desensitization pathway. This localization indicated that the GPCRs were expressed at the plasma membrane, because plasma membrane expression is requisite for subsequent localization in the desensitization pathway. A GPCR that was not expressed at the plasma membrane would not localize in the desensitization pathway. GPCRs that do not express at the plasma membrane may be altered such that they do express at the plasma membrane. For example, the expression of the GPCR may be altered, the amino acid sequence of the GPCR may be altered, or the GPCR may be introduced into another host cell.
Example 7
Monitoring Desensitization of GPCR Mutants
Desensitization may be monitored in cells including GPCR mutants. The desensitization of the GPCR mutant may be dependent on GRK overexpression.
A vector including the human β2AR-E-Y326A containing a point mutation, the Tyrosine residue 326 converted to Alanine, will be transfected into cells expressing arrestin-GFP and a GRK, which may be modified. The “E” indicates that the GPCR has been modified, as described above. The Y326A mutation causes the GPCR to be dependent on overexpressed GRK for phosphorylation and subsequent desensitization. The β2AR-Y326A will desensitize in the absence of agonist upon expression of GRK-C20. The expression of the GRK may be altered, including methods of altering the amount of GRK nucleic acids in the cell using an inducible promoter, replication controlling machinery such as the origin of replication, or manually altering the amount of vector in the cells.
The cells will be seeded in 96 well or higher density plates and incubated overnight. The next morning the activator of the inducible system or vehicle only will be added to the wells to induce overexpression of the GRK or modified GRK. Agonist will be added to cells expressing the GRK (not the modified GRK).
Compounds of interest will then be added to the wells to see if they alter the internalization of arrestin-GFP. The cells will then be fixed with 2% paraformaldehyde and the amount of arrestin-GFP translocation will be measured using image analysis systems.
Example 8
Nonpeptide Antagonist/Inverse GPCR Agonist Inhibits Constitutive Translocation of ArrestinGFP Induced by Expression of GRK2-C20
U2OS cells stably expressing arrestinGFP and the angiotensin II type 1A receptor (AT1 AR) were transiently transduced with human GRK2-C20 using a baculovirus expression system. A range of GRK2-C20 expression levels was obtained by using varying amounts (serial dilution) of the GRK2-C20 baculovirus. As shown by the black bars in FIG. 8, addition of GRK2-C20 promotes ligand-independent translocation of arrestinGFP to the AT1AR. A maximum arrestinGFP translocation response of 305±25 Fgrains and a minimum of 77±13 Fgrains was achieved with the 1:4 and 1:256 dilutions, respectively, of GRK2-C20 baculovirus. In the absence of added GRK2-C20 (none), no translocation was observed (18±3 Fgrains).
To test whether the ligand-independent arrestinGFP translocation could be blocked by an antagonist/inverse agonist of the AT1AR, the cells were treated with losartan. Losartan is a nonpeptide molecule that functions as an antagonist/inverse agonist of the AT1AR. Losartan (1 μM final concentration) was added to the cells either immediately after transduction for an 18 hour incubation or 15 hours after transduction for a 3 hour incubation. At the end of the incubation, the cells were analyzed for arrestinGFP translocation using the INCell Analyzer system.
As shown in FIGS. 8, 9, and 10, losartan treatment blocks the ligand-independent translocation of arrestinGFP to the AT1AR induced by expression of GRK2-C20. The most dramatic effect was observed after an 18 hour incubation with losartan (FIGS. 8 and 10). At the lower levels of GRK2-C20 expression (1:64, 1:128, and 1:256 dilutions), this treatment paradigm results in the inhibition of greater than 90% of the ligand-independent translocation of arrestinGFP to the AT1AR.
While the invention has been described and illustrated herein by references to various specific material, procedures and examples, it is understood that the invention is not restricted to the particular material combinations of material, and procedures selected for that purpose. Numerous variations of such details can be implied as will be appreciated by those skilled in the art.
The following is a list of documents related to the above disclosure and particularly to the experimental procedures and discussions. The following documents, as well as any documents referenced in the foregoing text, should be considered as incorporated by reference in their entirety.

    Attramadal, H., Arriza, J. L., Aoki, C., Dawson, T. M., Codina, J., Kwatra, M. M., Snyder, S. H., Caron, M. G. & Lefkowitz, R. J. (1992) J. Biol. Chem. 267, 17882-17890
    Barak, L. S., Oakley, R. H., Laporte, S. A. and Caron, M. G. (2001) Proc. Natl. Acad. Sci. USA 98, 93-98
    Barak, L. S., Warabi, K., Feng, X., Caron, M. G. & Kwatra, M. M. (1999) J. Biol. Chem. 274, 7565-7569
    Barak, L. S., Ferguson, S. S., Zhang, J. & Caron, M. G. (1997) J. Biol. Chem. 272, 27497-27500
    Barak, L. S., Ferguson, S. S., Zhang, J., Martenson, C., Meyer, T. &
    Caron, M. G. (1997) Mol. Pharmacol. 51, 177-184
    Barak, L. S., Menard, L., Ferguson, S. S., Colapietro, A. M. & Caron, M. G. (1995) Biochemistry 34, 15407-15414
    Ferguson, S. S., Barak, L. S., Zhang, J. & Caron, M. G. (1996) Can. J. Physiol. Pharmacol. 74, 1095-1110
    Ferguson, S. S., Menard, L., Barak, L. S., Koch, W. J., Colapietro, A. M. & Caron, M. G. (1995) J. Biol. Chem. 270, 24782-24789
    Inglese, J., Koch, W. J., Caron, M. G., Lefkowitz, R. J. (1992) Nature 359:147-150
    Kim, K.-M., Valenzano, K. J., Robinson, S. R., Yao, W. D., Barak, L. S., Caron, M. G. (2001) J. Biol. Chem. 276: 37409-37414
    Laporte, S. A., Oakley, R. H., Holt, J. A., Barak, L. S. & Caron, M. G. (2000) J. Biol. Chem. 275, 23120-23126
    Laporte, S. A., Oakley, R. H., Zhang, J., Holt, J. A., Ferguson, S. S., Caron, M. G. & Barak, L. S. (1999) Proc. Natl. Acad. Sci. USA 96, 3712-3717
    Menard, L., Ferguson, S. S., Zhang, J., Lin, F. T., Lefkowitz, R. J., Caron, M. G. & Barak, L. S. (1997) Mol. Pharmacol. 51, 800-808
    Mhaouty-Kodja, S., Barak, L. S., Scheer, A., Abuin, L., Diviani, D., Caron, M. G. & Cotecchia, S. (1999) Mol. Pharmacol. 55, 339-347
    Oakley, R. H., Laporte, S. A., Holt, J. A., Barak, L. S., Caron, M. G. (2001). J. Biol. Chem. 276: 19452-19460
    Oakley, R. H., Laporte, S. A., Holt, J. A., Caron, M. G. & Barak, L. S. (2000) J. Biol. Chem. 275, 17201-17210
    Oakley, R. H., Laporte, S. A., Holt, J. A., Barak, L. S. & Caron, M. G. (1999) J. Biol. Chem. 274, 32248-32257
    Zhang, J., Barak, L. S., Anborgh, P. H., Laporte, S. A., Caron, M. G. & Ferguson, S. S. (1999) J. Biol. Chem. 274, 10999-11006
    Zhang, J., Barak, L. S., Winkler, K. E., Caron, M. G. & Ferguson, S. S. (1997) J. Biol. Chem. 272, 27005-27014

## Claims

1. A method of identifying a compound which alters G protein-coupled receptor (GPCR) internalization, comprising:
a) providing a cell comprising a CPCR, an arrestin, and a modified G protein-coupled receptor kinase (GRK) comprising one or more modifications in the amino acid sequence of the four C-terminal amino acids of the GRK as compared to a wild type GRK, wherein said GPCR is at least partially internalized in an agonist-independent manner upon expression of said modified GRK;
b) exposing said cell to the compound(s);
c) determining the cellular distribution of the GPCR, arrestin, or modified GRK, wherein said modified GRK alters GPCR desensitization in the absence of an agonist as compared to a wild type GRK; and
d) monitoring a difference between (1) the distribution of the GPCR, arrestin, or modified GRK in the cell in the presence of the compound(s) and (2) the distribution of the GPCR, arrestin, or modified GRK in the cell in the absence of the compound(s).

2. The method of claim 1, wherein the expression of the modified GRK of step (a) is inducible.

3. The method of claim 1, wherein the modified GRK comprises a CAAX (SEQ ID NO:95) motif, wherein C is cysteine, A is an aliphatic amino acid, and X is the wild type C-terminal amino acid of GRK.

4. The method of claim 1, wherein the GPCR comprises one or more modifications in the amino acid sequence of its carboxy-terminal tail, to have enhanced phosphorylation by the modified GRK as compared to a wild type GPCR.

5. The method of claim 1, wherein the CPCR is (β2AR(Y326A).

6. The method of claim 1, wherein the GPCR is a GPCR listed in FIG. 1, an orphan GPCR, a taste receptor, a Class A GPCR, a Class B GPCR, a mutant GPCR, or a biologically active fragment thereof.

7. The method of claim 1, wherein the modified or wild type GRK is GRK1, GRK2, GRK3, GRK4, GRK5, GRK6, or a biologically active fragment thereof.

8. The method of claim 1, wherein the GPCR, GRK, or arrestin is detectably labeled.

9. The method of claim 1, wherein a molecule involved in GPCR desensitization is detectably labeled, or a molecule that interacts with a molecule involved in GPCR desensitization is detectably labeled.

10. The method of claim 1, wherein the arrestin is visual arrestin, cone arrestin, β-arrestin 1, β-arrestin 2, or a biologically active fragment thereof.

11. The method of claim 1, wherein an agonist of said GPCR is not provided.

12. The method of claim 1, wherein a difference between (1) and (2) of step (d) indicates modulation of GPCR internalization.

13. The method of claim 1, wherein the GPCR is AT1AR.

14. The method of claim 3, wherein said CAAX motif is CVLL (SEQ ID NO:94).