# Patent

## Title
Expression of apoAI and variants thereof using spliceosome mediated RNA trans-splicing

## Abstract

Methods and compositions for generating novel nucleic acid molecules through targeted spliceosome mediated RNA trans-splicing that result in expression of a apoAI protein, an apoAI variant, the preferred embodiment referred to herein as the apoAI Milano variant, a pre-pro-apoAI or an analog of apoAI. The methods and compositions include pre-trans-splicing molecules (PTMs) designed to interact with a target precursor messenger RNA molecule (target pre-mRNA) and mediate a trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule (chimeric RNA) capable of encoding apoAI, the apoAI Milano variant, or an analog of apoAI. The expression of this apoAI protein results in protection against vascular disorders resulting from plaque build up, i.e., atherosclerosis, strokes and heart attacks.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to U.S. Provisional Application Nos. 60/538,796, filed Jan. 23, 2004, and 60/584,280, filed Jun. 30, 2004; is a continuation-in part of U.S. patent application Ser. No. 11/041,155, filed Jan. 21, 2005 and corresponding PCT Application No. US/05/02392 filed Jan. 21, 2005; and is a divisional of Ser. No. 11/141,447 filed May 31, 2005, the disclosures of which are incorporated by reference in their entireties.


1. INTRODUCTION
The present invention provides methods and compositions for generating novel nucleic acid molecules through targeted spliceosome mediated RNA trans-splicing that result in expression of wild type apoAI, apoAI analogues or variants such as, for example, the apoAI Milano variant, or the initial gene product, pre-pro-apoAI. The compositions of the invention include pre-trans-splicing molecules (PTMs) designed to interact with a target precursor messenger RNA molecule (target pre-mRNA) and mediate a trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule (chimeric RNA) capable of encoding the wild type apoAI, apoAI analogues or, variants, such as the Milano variant, or the pre-pro-apoAI. The expression of this protein and incorporation into high density lipoprotein (HDL) results in protection against cardiovascular disorders resulting from plaque build up, i.e., atherosclerosis, strokes and heart attacks.
In particular, the PTMs of the present invention include those genetically engineered to interact with the apoAI target pre-mRNA so as to result in expression of the apoAI Milano variant. In addition, the PTMs of the invention include those genetically engineered to interact with the apoB target pre-mRNA and/or any other selected target pre-mRNAs, so as to result in expression of an apoB/apoAI Milano chimeric protein, thereby reducing apoB expression and producing apoAI Milano function. In addition, the present invention includes the use of other methods such as the trans-splicing of apoAI sequences into highly abundant transcripts, such as albumin pre-messenger RNA to generate increased levels of apoAI. In addition, the present invention includes the use of other methods, such as trans-splicing ribozymes to create apoAI Milano chimeric mRNA and proteins. The compositions of the invention further include recombinant vector systems capable of expressing the PTMs of the invention and cells expressing said PTMs.
The methods of the invention encompass contacting the PTMs of the invention with an apoAI target pre-mRNA, and/or an apoB target pre-mRNA under conditions in which a portion of the PTM is trans-spliced to a portion of the target pre-mRNA to form a mRNA molecule wherein (i) expression of apoAI is substituted with expression of the apoAI Milano variant; (ii) expression of apoB is substituted with expression of an apoB/apoAI Milano chimeric protein and the level of apoB expression is simultaneously reduced and/or (iii) the expression of albumin is substituted with the expression of apoAI or apoAI variant. The methods of the invention also encompass contacting the PTMs of the invention with other target pre-mRNAs, which are highly expressed and encode efficiently secreted liver proteins, under conditions in which a portion of the PTM is trans-spliced to a portion of the target pre-mRNA to form a mRNA molecule wherein expression of the highly expressed protein is substituted with expression of the wild type apoAI, apoAI analogues or Milano variant. The compositions of the present invention may be administered in combination with other cholesterol lowering agents or lipid regulating agents. The methods and compositions of the present invention can be used to prevent or reduce the level of vascular plaque buildup that is normally associated with cardiovascular disease.
The albumin gene is highly expressed in the liver, thereby providing an abundant target pre-mRNA for trans-splicing. The PTMs of the present invention include those genetically engineered to interact with an albumin target pre-mRNA so as to result in expression of wild type apoAI, apoAI analogues or apoAI variants such as the Milano variant. The methods of the invention encompass contacting such PTMs with an albumin target pre-mRNA under conditions in which a portion of the PTM is trans-spliced to a portion of the albumin target pre-mRNA to form a chimeric mRNA molecule wherein expression of albumin is substituted with expression of wild type apoAI, apoAI analogues or apoAI variants such the apoAI Milano variant or pre-pro-apoAI, or an analogue of apoAI.
This application incorporates by reference the Sequence Listing contained in an ASCII text file named “356007.00145_ST25.txt” submitted via EFS-Web. The text file was created on Jun. 22, 2011, and is 16.1 kb.
2. BACKGROUND OF THE INVENTION
2.1. RNA Splicing
DNA sequences in the chromosome are transcribed into pre-mRNAs which contain coding regions (exons) and generally also contain intervening non-coding regions (introns). Introns are removed from pre-mRNAs in a precise process called cis-splicing (Chow et al., 1977, Cell 12:1-8; and Berget, S. M. et al., 1977, Proc. Natl. Acad. Sci. USA 74:3171-3175). Splicing takes place as a coordinated interaction of several small nuclear ribonucleoprotein particles (snRNP's) and many protein factors that assemble to form an enzymatic complex known as the spliceosome (Moore et al., 1993, in The RNA World, R. F. Gestland and J. F. Atkins eds. (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.); Kramer, 1996, Annu. Rev. Biochem., 65:367-404; Staley and Guthrie, 1998, Cell 92:315-326).
In most cases, the splicing reaction occurs within the same pre-mRNA molecule, which is termed cis-splicing. Splicing between two independently transcribed pre-mRNAs is termed trans-splicing. Trans-splicing was first discovered in trypanosomes (Sutton & Boothroyd, 1986, Cell 47:527; Murphy et al., 1986, Cell 47:517) and subsequently in nematodes (Krause & Hirsh, 1987, Cell 49:753); flatworms (Rajkovic et al., 1990, Proc. Natl. Acad. Sci. USA, 87:8879; Davis et al., 1995, J. Biol. Chem. 270:21813) and in plant mitochondria (Malek et al., 1997, Proc. Natl. Acad. Sci. USA 94:553). In the parasite Trypanosoma brucei, all mRNAs acquire a splice leader (SL) RNA at their 5′ termini by trans-splicing. A 5′ leader sequence is also trans-spliced onto some genes in Caenorhabditis elegans. This mechanism is appropriate for adding a single common sequence to many different transcripts.
The mechanism of splice leader trans-splicing, which is nearly identical to that of conventional cis-splicing, proceeds via two phosphoryl transfer reactions. The first causes the formation of a 2′-5′ phosphodiester bond producing a ‘Y’ shaped branched intermediate, equivalent to the lariat intermediate in cis-splicing. The second reaction, exon ligation, proceeds as in conventional cis-splicing. In addition, sequences at the 3′ splice site and some of the snRNPs which catalyze the trans-splicing reaction, closely resemble their counterparts involved in cis-splicing.
Trans-splicing refers to a different process, where an intron of one pre-mRNA interacts with an intron of a second pre-mRNA, enhancing the recombination of splice sites between two conventional pre-mRNAs. This type of trans-splicing was postulated to account for transcripts encoding a human immunoglobulin variable region sequence linked to the endogenous constant region in a transgenic mouse (Shimizu et al., 1989, Proc. Natl. Acad. Sci. USA 86:8020). In addition, trans-splicing of c-myb pre-mRNA has been demonstrated (Vellard, M. et al. Proc. Natl. Acad. Sci., 1992 89:2511-2515) and RNA transcripts from cloned SV40 trans-spliced to each other were detected in cultured cells and nuclear extracts (Eul et al., 1995, EMBO. J. 14:3226). However, naturally occurring trans-splicing of mammalian pre-mRNAs is thought to be a rare event (Flouriot G. et al., 2002 J. Biol. Chem: Finta, C. et al., 2002 J. Biol Chem 277:5882-5890).
In vitro trans-splicing has been used as a model system to examine the mechanism of splicing by several groups (Konarska & Sharp, 1985, Cell 46:165-171 Solnick, 1985, Cell 42:157; Chiara & Reed, 1995, Nature 375:510; Pasman and Garcia-Blanco, 1996, Nucleic Acids Res. 24:1638). Reasonably efficient trans-splicing (30% of cis-spliced analog) was achieved between RNAs capable of base pairing to each other, splicing of RNAs not tethered by base pairing was further diminished by a factor of 10. Other in vitro trans-splicing reactions not requiring obvious RNA-RNA interactions among the substrates were observed by Chiara & Reed (1995, Nature 375:510), Bruzik J. P. & Maniatis, T. (1992, Nature 360:692) and Bruzik J. P. and Maniatis, T., (1995, Proc. Natl. Acad. Sci. USA 92:7056-7059). These reactions occur at relatively low frequencies and require specialized elements, such as a downstream 5′ splice site or exonic splicing enhancers.
In addition to splicing mechanisms involving the binding of multiple proteins to the precursor mRNA which then act to correctly cut and join RNA, a third mechanism involves cutting and joining of the RNA by the intron itself, by what are termed catalytic RNA molecules or ribozymes. The cleavage activity of ribozymes has been targeted to specific RNAs by engineering a discrete “hybridization” region into the ribozyme. Upon hybridization to the target RNA, the catalytic region of the ribozyme cleaves the target. It has been suggested that such ribozyme activity would be useful for the inactivation or cleavage of target RNA in vivo, such as for the treatment of human diseases characterized by production of foreign of aberrant RNA. In such instances small RNA molecules are designed to hybridize to the target RNA and by binding to the target RNA prevent translation of the target RNA or cause destruction of the RNA through activation of nucleases. The use of antisense RNA has also been proposed as an alternative mechanism for targeting and destruction of specific RNAs.
Using the Tetrahymena group I ribozyme, targeted trans-splicing was demonstrated in E. coli. (Sullenger B. A. and Cech. T. R., 1994, Nature 341:619-622), in mouse fibroblasts (Jones, J. T. et al., 1996, Nature Medicine 2:643-648), human fibroblasts (Phylacton, L. A. et al. Nature Genetics 18:378-381) and human erythroid precursors (Lan et al., 1998, Science 280:1593-1596). For a review of clinically relevant technologies to modify RNA see Sullenger and Gilboa, 2002 Nature 418:252-8. The present invention relates to the use of targeted trans-splicing mediated by native mammalian splicing machinery, i.e., spliceosomes, to reprogram or alter the coding sequence of a targeted mRNA.
U.S. Pat. Nos. 6,083,702, 6,013,487 and 6,280,978 describe the use of PTMs to mediate a trans-splicing reaction by contacting a target precursor mRNA to generate novel chimeric RNAs.
2.2. Cardiovascular Disease
Cardiovascular disease (CVD) is the most common cause of death in Western societies, and its prevalence is increasing worldwide. One of the strongest predictors of risk is the plasma concentration of high-density lipoprotein (HDL) or apolipoprotein A-1 (apoAI), the major protein component of HDL, which exhibits an inverse relationship with the development of atherosclerosis and coronary heart disease (Sirtori C R et al., 1999, Atherosclerosis 142:29-40; Genest J 2003, J. Inherit. Metab. Dis. 26:267-287). ApoAI is the major apolipoprotein of HDL and is a relatively abundant plasma protein with a concentration of 1.0-1.5 mg/ml. ApoAI plays an important role in promoting the efflux of excess cholesterol from peripheral cells and tissues for transfer to the liver for excretion, a process called reverse cholesterol transport (RCT). Numerous in vitro and in vivo studies have demonstrated the protective effects of apoAI and HDL against atherosclerosis plaque development (Rubin E M, et al., Nature. 1991, 353:265-7; Plump A S et al., 1994 Proc Natl Acad. Sci. USA 91:9607-11; Paszty C, et al., 1994 J Clin Invest. 94:899-903; Duverger N et al., 1996, Circulation 94:713-7).
ApoAI Milano is one of a number of naturally occurring variants of wild type apoAI. It was first identified in 1980 in an Italian family (Franceschini G et al., 1980, J. Clin. Invest. 66:892-900; Weisgraber K H et al., 1980 J Clin Invest. 66:901-907). To date 40 carriers have been identified and all are heterozygous. These carriers have low plasma HDL-cholesterol levels and moderately elevated levels of triglycerides, a condition that is usually associated with high-risk predictors for coronary heart disease. Despite severe reductions in plasma HDL-cholesterol levels and apoAI concentrations, the affected carriers do not develop coronary artery disease. In fact, infusions of the purified recombinant apoAI Milano or expression of apoAI Milano in rabbits and apoE deficient mice show protection against plaque formation and atherosclerosis (Ameli S et al., 1994, Circulation 90:1935-41; Soma M R et al., 1995 Cir. Res. 76:405-11; Shah P K et al., 1998 Circulation 97:780-5; Franceschini G et al., 1999, Arterioscler Thromb Vasc Biol. 19:1257-1262; Chiesa G et al., 2002, Cir. Res. 90:974-80; Chiesa G and Sirtori C, 2003, Curr. Opin. Lipdol. 14:159-163). Results from clinical trials, however have shown more modest levels of reduction. The degree of plaque reduction may be related to the limited number of doses and amounts of protein administered, and/or its duration in the circulation (pharmacokinetics).
Plasma apoAI is a single polypeptide chain of 243 amino acids, whose primary sequence is known (Brewer et al, 1978, Biochem. Biophys. Res. Commun. 80:623-630). ApoAI is synthesized as a 267 amino acid precursor in the cell. This preproapolipoproteinA-1 is first intracellularly processed by N-terminal cleavage of 18 amino acids to yield proapolipoproteinA-1, and then further cleavage of 6 amino acids in the plasma or the lymph by the activity of specific proteases to yield mature apolipoproteinA-1. The major structural requirement of the apoAI molecule is believed to be the presence of repeat units of 11 or 22 amino acids, presumed to exist in amphipathic helical conformation (Segrest et al., 1974, FEBS Lett 38:247-253). This structure allows for the main biological activities of apoAI, i.e. lipid binding and lecithin:cholesterol acyltransferase (LCAT) activation.
Human apolipoproteinAI Milano (apoAI Milano) is a natural variant of apoAI (Weisgraber et al, 1980, J. Clin. Invest 66:901-907). In apoAI Milano the amino acid Arg173 is replaced by the amino acid Cys 173. Since apoAI Milano contains one Cys residue per polypeptide chain, it may exist in a monomeric, homodimeric, or heterodimeric form. These forms are chemically interchangeable, and the term apoAI Milano does not, in the present context, discriminate between these forms. On the DNA level the variant form results from a C to T substitution in the gene sequence, i.e. the codon CGC changed to TGC, allowing the translation of a Cys instead of Arg at amino acid position 173. However, this variant of apoAI is one of the most interesting variants, in that apoAI Milano subjects are characterized by a remarkable reduction in HDL-cholesterol level, but without an apparent increased risk of arterial disease (Franceschini et al. 1980, J. Clin. Invest 66:892-900).
Another useful variant of apoAI is the Paris variant, where the arginine 151 is replaced with a cysteine.
The systemic infusion of apoAI alone (Miyazaki et al. 1995, Arterioscler Thromb Vasc Biol. 15:1882-1888) or of HDL (Badimon et al, 1989, Lab Invest. 60:455-461 and J Clin Invest. 85:1234-1241, 1990) in experimental animals and initial human clinical studies (Nanjee et al., 1999, Arterioscler Thromb Vasc Biol. 19:979-989 and Eriksson et al. 1999, Circulation 100:594-598) has been shown to exert significant biochemical changes, as well as to reduce the extent and severity of atherosclerotic lesions.
Human gene therapy may provide a superior approach for achieving plaque reduction by providing prolonged and continuous expression of genes such as wild type apoAI, pre-pro-apoAI, apoAI analogues or variants such as the Milano variant. In the case of conventional gene therapy approaches that add back the entire apoAI cDNA, un-regulated expression of this cDNA may lead to toxicity and ectopic gene expression. These problems could be overcome by utilization of spliceosome mediated RNA trans-splicing into albumin and other liver transcripts to express wild type apoAI, apoAI Milano or other useful apoAI variants.
Similarly, spliceosome mediated RNA trans-splicing may be used to simultaneously reduce the expression of apoB, a major component of low-density lipoprotein, and produce HDL, i.e., express apoAI wild type or the Milano variant or convert other expressed proteins such as albumin to produce apoAI function.
3. SUMMARY OF THE INVENTION
The present invention relates to compositions and methods for generating novel nucleic acid molecules through spliceosome-mediated targeted RNA trans-splicing, ribozyme mediated trans-splicing, or other means of converting mRNA. The compositions of the invention include pre-trans-splicing molecules (hereinafter referred to as “PTMs”) designed to interact with a natural target pre-mRNA molecule (hereinafter referred to as “pre-mRNA”) and mediate a spliceosomal trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule (hereinafter referred to as “chimeric RNA”). The methods of the invention encompass contacting the PTMs of the invention with a natural target pre-mRNA under conditions in which a portion of the PTM is spliced to the natural pre-mRNA to form a novel chimeric RNA. The PTMs of the invention are genetically engineered so that the novel chimeric RNA resulting from the trans-splicing reaction may encode a protein that provides health benefits. Generally, the target pre-mRNA is chosen because it is expressed within a specific cell type thereby providing a means for targeting expression of the novel chimeric RNA to a selected cell type. For example, PTMs may be targeted to pre-mRNAs expressed in the liver such as apoAI and/or albumin pre-mRNA.
In particular, the compositions of the invention include pre-trans-splicing molecules (hereinafter referred to as “PTMs”) designed to interact with an apoAI target pre-mRNA molecule (hereinafter referred to as “apoAI pre-mRNA”) and mediate a spliceosomal trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule (hereinafter referred to as “chimeric RNA”).
The compositions of the invention further include PTMs designed to interact with albumin target pre-mRNA molecule (hereinafter referred to as “albumin pre-mRNA”) and mediate a spliceosomal trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule.
The compositions of the invention further include PTMs designed to interact with an apoB target pre-mRNA molecule (hereinafter referred to as “apoB pre-mRNA”) and mediate a spliceosomal trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule.
The compositions of the invention include PTMs designed to interact with an apoAI target pre-mRNA molecule, albumin target pre-mRNA, or an apoB target pre-mRNA or other pre-mRNA targets and mediate a spliceosomal trans-splicing reaction resulting in the generation of a novel chimeric RNA molecule. Such PTMs are designed to produce an apoAI wild-type protein or apoAI variants, including Milano which are useful to protect against atherosclerosis.
The general design, construction and genetic engineering of PTMs and demonstration of their ability to successfully mediate trans-splicing reactions within the cell are described in detail in U.S. Pat. Nos. 6,083,702, 6,013,487 and 6,280,978 as well as patent Ser. Nos. 09/756,095, 09/756,096, 09/756,097 and 09/941,492, the disclosures of which are incorporated by reference in their entirety herein.
The general design, construction and genetic engineering of trans-splicing ribozymes and demonstration of their ability to successfully mediate trans-splicing reactions within the cell are described in detail in and U.S. Pat. Nos. 5,667,969, 5,854,038 and 5,869,254, as well as patent Ser. No. 20030036517, the disclosures of which are incorporated by reference in their entirety herein.
The methods of the invention encompass contacting the PTMs of the invention with an apoAI target pre-mRNA, albumin target pre-mRNA, or apoB target pre-mRNA, or other expressed pre-mRNA targets, under conditions in which a portion of the PTM is spliced to the target pre-mRNA to form a chimeric RNA. The methods of the invention comprise contacting the PTMs of the invention with a cell expressing an apoAI target pre-mRNA, or an apoB target pre-mRNA or other expressed pre-mRNA targets, such as albumin pre-mRNA, under conditions in which the PTM is taken up by the cell and a portion of the PTM is trans-spliced to a portion of the target pre-mRNA to form a novel chimeric RNA molecule that results in expression of the an apoAI Milano or another variants. Alternatively, for example, when targeting the albumin or apoB pre-mRNAs, the novel chimeric RNA may encode a wild type apoAI protein.
Alternatively, nucleic acid molecules encoding the PTMs of the invention may be delivered into a target cell followed by expression of the nucleic acid molecule to form a PTM capable of mediating a trans-splicing reaction. The PTMs of the invention are genetically engineered so that the novel chimeric RNA resulting from the trans-splicing reaction may encode the apoAI Milano variant protein which has been shown to reduce plaque buildup which may be useful in the prevention or treatment of vascular disease. Alternatively, the chimeric mRNA may encode a wild type apoAI protein or apoAI analogues. Thus, the methods and compositions of the invention can be used in gene therapy for the prevention and treatment of vascular disorders resulting from accumulation of plaque which is a risk factor associated with heart attacks and strokes.



4. BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1. Schematic representation of different trans-splicing reactions. (a) trans-splicing reactions between the target 5′ splice site and PTM's 3′ splice site, (b) trans-splicing reactions between the target 3′ splice site and PTM's 5′ splice site and (c) replacement of an internal exon by a double trans-splicing reaction in which the PTM carries both 3′ and 5′ splice sites. BD, binding domain; BP, branch point sequence; PPT, polypyrimidine tract; and ss, splice sites.
FIG. 2. Human apoAI gene and mRNA. The apoAI gene is 1.87 kb long and comprises 4 exons including a non-coding exon 1. The apoAI mRNA is 897 nucleotides long including a 5′ UTR and 3′ UTR. The apoAI amino acid sequence consists of 267 residues including a 24 amino acid signal peptide at the N-terminus and the mature protein is a single polypeptide chain with 243 amino acid residues.
FIG. 3A. Nucleotide and amino acid sequence of wild type apoAI. FIG. 3B. apoAI-Milano variant.
FIG. 3C. Strategy to create apoAI-Milano.
FIG. 4. Target gene and PTM structure. FIG. 4A. Schematic structure of human wild type apoAI full length target gene for in vitro studies. FIG. 4B Schematic structure of human apoAI Milano PTM1 (exon 4).
FIG. 5. Schematic illustration of trans-splicing reaction between apoAI target pre mRNA and PTM.
FIG. 6. ApoB-100 gene and mRNA.
FIG. 7. Schematic structure of ApoB target pre-mRNA.
FIG. 8. Mini-gene target and PTM structure showing a schematic structure of human apoB mini-gene target for in vitro studies and Mini-gene target and PTM structure showing a schematic structure of human apoAIMilano PTM2.
FIG. 9. Schematic illustration of trans-splicing reaction between apoB target pre mRNA and PTM).
FIG. 10. Human Albumin Gene Structure. (See, also Minghetti et al., 1986, J. Biol. Chem. 261:6747-6757).
FIG. 11. Human apoAI.
FIG. 12. Human apoAI Gene and mRNA structural details
FIG. 13. Schematic illustration of human and mouse albumin exon 1/human apoAI trans-spliced cDNAs.
FIG. 14. Nucleotide sequences of human albumin exon 1/human apoAI (wild type) trans-spliced mRNA. Underlined sequence represents human albumin signal peptide; /indicates junction between albumin and apoAI. ATG and stop codon, TGA are indicated in italics.
FIG. 15. Western Analysis of Mouse and Human Alb/apoAI trans-spliced cDNAs in 293 cells.
FIG. 16. Western Analysis of Mouse and Human Alb/apoAI trans-spliced cDNAs in 293 and HepG2 cells.
FIG. 17. Target Construct for Binding Domain Screen. Schematic structure of 5′ GFP-Albln1Ex2 target gene for in vitro studies. Target pre-mRNA construct contains partial coding sequence for GFP fluorescent protein followed by 5′ splice site, albumin intron 1, 3′ acceptor site and albumin exon 2.
FIG. 18. 5′ GFP-Albln1Ex2 Pre-mRNA Target Sequence. Nucleotide sequence of 5′ GFP-Albln1Ex2 gene for in vitro studies. Sequences shown in italics indicate first half of the coding sequence for GFP fluorescent protein followed by human albumin intron 1 and exon 2 sequences (underlined). “/” indicates 5′ and 3′ splice junctions.
FIG. 19. PTM Cassette Used for Binding Domain Screen. Schematic structure of a prototype PTM expression cassette is shown. It consists of a trans-splicing domain (TSD) followed by a 24 nucleotide spacer, a 3′ splice site including the consensus yeast branch point (BP), an extended polypyrimidine tract and the AG splice acceptor site. The TSD was fused to the remaining 3′ GFP coding sequence. In addition, the PTM cassette also contain full length coding sequence for a second fluorescent reporter (DsRed2) and the expression is driven by an internal ribosome entry site (IRES) of the encephalomyocarditis virus (ECMV).
FIG. 20. Binding Domain Screening Strategies. (A) high capacity screen and (B) rational binding domain design strategy.
FIG. 21. Schematic of targeted trans-splicing of human apoAI into albumin target pre-mRNA.
FIG. 22. Schematic of human and mouse apoAI trans-spliced cDNA constructs (test constructs), similar constructs with point (deletion) mutants (negative controls) and wild type human Apo A-I and Milano variants (positive controls).  indicates point mutation (deletion) that result in premature termination. No full-length protein was detected on Western blot.
FIG. 23. SDS gels showing human apoAI expression in 293 cells
FIG. 24. Western blot showing expression and secretion of mature human apoAI protein in 293 cells. Lane 1, mouse Alb-hAI; lane 2, human Alb-hA1; lane 3, wt Apo A-I and lane 4, Milano variant. Upper panel, protein in supernatant and lower panel, protein in cell lysate.
FIG. 25. Cholesterol efflux in 293 cells demonstrating the expression of functional human apoAI protein.
FIG. 26A. Schematic of FACS-based PTM selection strategy.
FIG. 26B. Comparison of high capacity screening (HCS) protocols.
FIG. 27. Schematic of pre-mRNA target used in HCS.
FIG. 28. Schematic of PTM cassette used in HCS. PTM cassette consists of a trans-splice domain including (TSD): variable BDs, short spacer, BP, PPT, 3′ half of the coding sequence for zsG, IRES followed by the full length coding sequence for second reporter DsRedExpress. Abbreviations: 3′zsG, 3′ half of the zsGreen fluorescent protein coding sequence; IRES, internal ribosome entry site, BD, binding domain; BP, branch point; PPT, polypyrimidine trace. SA, splice acceptor site.
FIG. 29. PCR analysis of the mouse albumin binding domain (BD) library.
FIG. 30. High capacity screening (HCS) method and summary of results.
FIG. 31. Trans-splicing efficiency of PTMs selected from HCS.
FIG. 32. Bar graph showing trans-splicing efficiency and GFP fluorescence of various PTMs selected from HCS.
FIG. 33. Schematic showing the human apoAI PTM expression cassette used for proof of principle in vitro studies.
FIG. 34. Schematic diagram of the mouse albumin mini-gene pre-mRNA target.
FIG. 35. Trans-splicing of mAlbPTMs into albumin exon 1 in stable cells.
FIG. 36. Western blot analysis of trans-spliced human apoAI protein.
FIG. 37. PTM-mediated trans-splicing into endogenous albumin exon 1 in mice.
FIG. 38. Schematic diagram showing a human albumin targeting strategy to increase apoAI expression.
FIG. 39 Elimination of albumin sequence in the final trans-spliced product.
FIG. 40 Schematic drawings of mouse albumin-human apoAI (mAlb-hapoAI) cDNA, trans-spliced mRNA, old and new PTM and targets. NCE, non-coding exon; hAI, human apoAI and Ex, exon.
FIG. 41 Trans-splicing between target and PTM plasmids produces functional protein in 293 cells. 293 cells transfected with different concentrations of mAlb-hapoAI cDNA or PTM+target plasmids. 48 hrs post-transfection, media was collected, processed and assayed (efflux potential) for activity as described before.
FIG. 42 Trans-splicing efficiency of the new and old PTMs in 293 cells. 293 cells transfected with different concentrations of PTM+target plasmids. 48 hrs post-transfection, total RNA isolated and trans-splicing efficiency was quantified by qRT-PCR using specific primers.
FIG. 43A RT-PCR results showing the presence of mouse mAlb-hapoAI mRNA
FIG. 43B RT-PCR results showing the presence of trans-spliced mRNA in mice.
FIG. 43C. RT-PCR results showing trans-splicing of human apoAI PTM into endogenous mouse albumin pre-mRNA in mice. MC, minicircles, PL, plasmid DNA; RT, reverse transcription and +/− indicate RT+ and RT− reactions.
FIG. 44A. Western blot analysis of serum samples from mice injected with mAlb-hapoAI cDNA. 20 μl serum passed through Proto-Blue column (to deplete albumin+IgG) and analyzed by Western blot using human apoAI specific antibody. MC, minicircles and PL, plasmid DNA RT.
FIG. 44B. Western blot analysis of serum samples from mice injected with PTM only and PTM+Target plasmids. 20-50 μl serum passed through Proto-Blue column (to deplete albumin+IgG) and analyzed by Western blot using human apoAI specific antibody. MC, minicircles and PL, plasmid DNA.
FIG. 45A. Western blot analysis of serum samples from mice injected with PTM plasmid. 50 μl serum was immunoprecipitated and analyzed by Western blot using human apoAI specific antibody. Arrows indicate 28 kDa human apoAI protein.
FIG. 45B. Western blot analysis of serum samples from mice injected with cDNA plasmid. 10 μl serum was immunoprecipitated and analyzed by Western blot using human apoAI specific antibody.
FIG. 46. HDL analysis of serum samples from mice injected with PTM and mAlb-hapoAI cDNA plasmids.
FIG. 47. Schematic illustration of trans-splicing strategy to increase biological half-life of human apoAI protein. hAI, human apoAI and Ex, exon.
FIG. 48. Schematic illustration of trans-splicing (pro) strategy to improve function. Pro, sequence encoding for pro peptide.
FIG. 49. Schematic illustration of trans-splicing (pre-pro) strategy to improve function. Pre, sequence coding for pre signal peptide; Pro, sequence coding for pro signal peptide.



5. DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to novel compositions comprising pre-trans-splicing molecules (PTMs) and the use of such molecules for generating novel nucleic acid molecules. The PTMs of the invention comprise (i) one or more target binding domains that are designed to specifically bind to a apoAI or apoB target pre-mRNA or other expressed pre-mRNA targets, such as albumin pre-mRNA, (ii) a 3′ splice region that includes a branch point, pyrimidine tract and a 3′ splice acceptor site and/or a 5′ splice donor site; and (iii) additional nucleotide sequences such as those encoding for the wild type apoAI, apoAI analogues or apoAI variants, especially the Milano variant. The PTMs of the invention may further comprise one or more spacer regions that separate the RNA splice site from the target binding domain.
The methods of the invention encompass contacting the PTMs of the invention with apoAI target pre-mRNA, or apoB target pre-mRNA, or other expressed pre-mRNA targets such as albumin target pre-mRNA, under conditions in which a portion of the PTM is trans-spliced to a portion of the target pre-mRNA to form a novel chimeric RNA that results in expression of the apoAI Milano variant or other apoAI variants, wild type apoAI, or an apoB/apoAI Milano chimeric protein, or other chimeric protein encompassing other variants of apoAI.
5.1. Structure of the Pre-Trans-Splicing Molecules
The present invention provides compositions for use in generating novel chimeric nucleic acid molecules through targeted trans-splicing. The PTMs of the invention comprise (i) one or more target binding domains that target binding of the PTM to an apoAI or apoB pre-mRNA or other expressed pre-mRNA targets such as, for example, albumin pre-mRNA (ii) a 3′ splice region that includes a branch point, pyrimidine tract and a 3′ splice acceptor site and/or 5′ splice donor site; and (iii) coding sequences for apoAI Milano, other variants of apoAI or wild type apoAI. The PTMs of the invention may also include at least one of the following features: (a) binding domains targeted to intron sequences in close proximity to the 3′ or 5′ splice signals of the target intron, (b) mini introns, (c) ISAR (intronic splicing activator and repressor)—like cis-acting elements, and/or (d) ribozyme sequences. The PTMs of the invention may further comprise one or more spacer regions to separate the RNA splice site from the target binding domain.
The general design, construction and genetic engineering of such PTMs and demonstration of their ability to mediate successful trans-splicing reactions within the cell are described in detail in U.S. Pat. Nos. 6,083,702, 6,013,487 and 6,280,978 as well as patent application Ser. Nos. 09/941,492, 09/756,095, 09/756,096 and 09/756,097, the disclosures of which are incorporated by reference in their entirety herein.
The target binding domain of the PTM endows the PTM with a binding affinity for the target pre-mRNA, i.e., an apoAI or apoB target pre-mRNA, or other pre-mRNA targets such as, for example, albumin pre-mRNA. As used herein, a target binding domain is defined as any molecule, i.e., nucleotide, protein, chemical compound, etc., that confers specificity of binding and anchors the pre-mRNA closely in space to the PTM so that the spliceosome processing machinery of the nucleus can trans-splice a portion of the PTM to a portion of the pre-mRNA. The target pre-mRNA may be mammalian, such as but not limited to, mouse, rat, bovine, goat, or human pre-RNA.
The target binding domain of the PTM may contain multiple binding domains which are complementary to and in anti-sense orientation to the targeted region of the selected pre-mRNA, i.e., an apoAI, apoB or albumin target pre-mRNA. The target binding domains may comprise up to several thousand nucleotides. In preferred embodiments of the invention the binding domains may comprise at least 10 to 30 and up to several hundred or more nucleotides. The efficiency and/or specificity of the PTM may be increased significantly by increasing the length of the target binding domain. For example, the target binding domain may comprise several hundred nucleotides or more. In addition, although the target binding domain may be “linear” it is understood that the RNA will very likely fold to form a secondary “safety” structure that may sequester the PTM splice site(s) until the PTM encounters it's pre-mRNA target, thereby increasing the specificity of trans-splicing. A second target binding region may be placed at the 3′ end of the molecule and can be incorporated into the PTM of the invention. Absolute complementarily, although preferred, is not required. A sequence “complementary” to a portion of an RNA, as referred to herein, means a sequence having sufficient complementarity to be able to hybridize with the target pre-mRNA, forming a stable duplex. The ability to hybridize will depend on both the degree of complementarity and the length of the nucleic acid (see, for example, Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, 2d Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). Generally, the longer the hybridizing nucleic acid, the more base mismatches with an RNA it may contain and still form a stable duplex. One skilled in the art can ascertain a tolerable degree of mismatch or length of duplex by use of standard procedures to determine the stability of the hybridized complex.
Binding may also be achieved through other mechanisms, for example, through triple helix formation, aptamer interactions, antibody interactions or protein/nucleic acid interactions such as those in which the PTM is engineered to recognize a specific RNA binding protein, i.e., a protein bound to a specific target pre-mRNA. Alternatively, the PTMs of the invention may be designed to recognize secondary structures, such as for example, hairpin structures resulting from intramolecular base pairing between nucleotides within an RNA molecule.
In a specific embodiment of the invention, the target binding domain is complementary and in anti-sense orientation to sequences of the apoAI, apoB, or albumin target pre-mRNA, which hold the PTM in close proximity to the target for trans-splicing. For example, a target binding domain may be defined as any molecule, i.e., nucleotide, protein, chemical compound, etc., that confers specificity of binding and anchors the apoAI, or apoB or albumin pre-mRNA closely in space to the PTM so that the spliceosome processing machinery of the nucleus can trans-splice a portion of the PTM to a portion of the apoAI, or apoB, or albumin pre-mRNA.
The PTM molecule also contains a 3′ splice region that includes a branchpoint sequence and a 3′ splice acceptor AG site and/or a 5′ splice donor site. The 3′ splice region may further comprise a polypyrimidine tract. Consensus sequences for the 5′ splice donor site and the 3′ splice region used in RNA splicing are well known in the art (see, Moore, et al., 1993, The RNA World, Cold Spring Harbor Laboratory Press, p. 303-358). In addition, modified consensus sequences that maintain the ability to function as 5′ donor splice sites and 3′ splice regions may be used in the practice of the invention. Briefly, the 5′ splice site consensus sequence is AG/GURAGU (SEQ ID NO. 1) (where A=adenosine, U=uracil, G=guanine, C=cytosine, R=purine and /=the splice site). The 3′ splice site consists of three separate sequence elements: the branchpoint or branch site, a polypyrimidine tract and the 3′ consensus sequence (YAG). The branch point consensus sequence in mammals is YNYURAC (SEQ ID NO. 2) (Y=pyrimidine; N=any nucleotide). The underlined A is the site of branch formation. A polypyrimidine tract is located between the branch point and the splice site acceptor and is important for efficient branch point utilization and 3′ splice site recognition. Recently, pre-mRNA introns beginning with the dinucleotide AU and ending with the dinucleotide AC have been identified and referred to as U12 introns. U12 intron sequences as well as any sequences that function as splice acceptor/donor sequences may also be used to generate the PTMs of the invention.
A spacer region to separate the RNA splice site from the target binding domain may also be included in the PTM. The spacer region may be designed to include features such as (i) stop codons which would function to block translation of any unspliced PTM and/or (ii) sequences that enhance trans-splicing to the target pre-mRNA.
In a preferred embodiment of the invention, a “safety, stem-loop structure” is also incorporated into the spacer, binding domain, or elsewhere in the PTM to prevent non-specific trans-splicing (Puttaraju et al., 1999 Nat. Biotech, 17:246-252; Mansfield S G et al., 2000, Gene therapy, 7:1885-1895). This is a region of the PTM that covers elements of the 3′ and/or 5′ splice site of the PTM by relatively weak complementarity, preventing non-specific trans-splicing. The PTM is designed in such a way that upon hybridization of the binding/targeting portion(s) of the PTM, the 3′ and/or 5′ splice site is uncovered and becomes fully active.
Such “safety” sequences comprise one or more complementary stretches of cis-sequence (or could be a second, separate, strand of nucleic acid) which binds to one or both sides of the PTM branch point, pyrimidine tract, 3′ splice site and/or 5′ splice site (splicing elements), or could bind to parts of the splicing elements themselves. This “safety” binding prevents the splicing elements from being active (i.e. block U2 snRNP or other splicing factors from attaching to the PTM splice site recognition elements). The binding of the “safety” may be disrupted by the binding of the target binding region of the PTM to the target pre-mRNA, thus exposing and activating the PTM splicing elements (making them available to trans-splice into the target pre-mRNA).
Nucleotide sequences encoding for exon 4, exons 3-4, exons 2-4, or exons 1-4 of the apoAI Milano variant are also included in the PTM of the invention. For example, the nucleotide sequence can include those sequences encoding gene products missing or altered in known genetic diseases. In addition, nucleotide sequences encoding marker proteins or peptides which may be used to identify or image cells may be included in the PTMs of the invention. In yet another embodiment of the invention nucleotide sequences encoding affinity tags such as, HIS tags (6 consecutive histidine residues) (Janknecht, et al., 1991, Proc. Natl. Acad. Sci. USA 88:8972-8976), the C-terminus of glutathione-S-transferase (GST) (Smith and Johnson, 1986, Proc. Natl. Acad. Sci. USA 83:8703-8707) (Pharmacia), FLAG (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys) (Eastman Kodak/IBI, Rochester, N.Y.), or CDC2 PSTAIRE epitope tag can be included in PTM molecules for use in affinity purification.
In a preferred embodiment of the invention, the PTMs of the invention contain apoAI exon 4 with an Arg to Cys substitution at position 173 (hereinafter referred to as “Arg→Cys”), thereby leading to the expression of the apoAI Milano variant protein. A variety of different PTM molecules may be synthesized to substitute (Arg→Cys) at position 173. The PTMs of the invention may contain apoAI exon or exons, which when trans-spliced to the apoAI, or apoB, target pre-mRNA or other pre-mRNA targets, will result in the formation of a composite or chimeric RNA capable of encoding an apoAI Milano variant chimeric protein, or an apoB/apoAI Milano variant protein. The nucleotide sequence of the apoAI gene is known, as well as the mutation leading to expression of the Milano variant and incorporated herein in its entirety (FIG. 3A-B). Likewise, the nucleotide sequence of the apoB gene is known (FIG. 6).
The apoAI exon sequences to be included in the structure of the PTM are designed to include apoAI exon 4 sequences as depicted in FIG. 4. In such an instance, 3′ exon replacement results in the formation of a chimeric RNA molecule that encodes the apoAI Milano variant protein having a Arg→Cys substitution at position 173.
The PTM's of the invention may be engineered to contain a single apoAI exon sequence, multiple apoAI exon sequences, or alternatively the complete set of 4 exon sequences. The number and identity of the apoAI sequences to be used in the PTMs will depend on the type of trans-splicing reaction, i.e., 5′ exon replacement, 3′ exon replacement or internal exon replacement, as well as the pre-mRNA targets.
Specific PTMs of the invention include, but are not limited to, those containing nucleic acids encoding apoAI exon 4 sequences. Such PTMs may be used for mediating a 3′ exon replacement trans-splicing reaction as depicted in FIGS. 5, 9 and 21.
Specific PTMs of the invention include, but are not limited to, those containing nucleic acid sequences encoding apoAI-Milano. Such PTMs may be used for mediating a 5′ exon replacement trans-splicing reaction. These PTMs would contain the N-terminal portion of the coding sequence, including the Milano mutation. In addition, PTMs of the invention may comprise a single apoAI variant exon or any combination of two or more apoAI variant exons.
Further, the PTMs of the invention include, but are not limited to, those containing nucleic acid sequences encoding wild type apoAI and/or apoAI analogues with extended half-life and efficacy.
The present invention further provides PTM molecules wherein the coding region of the PTM is engineered to contain mini-introns. The insertion of mini-introns into the coding sequence of the PTM is designed to increase definition of the exon and enhance recognition of the PTM splice sites. Mini-intron sequences to be inserted into the coding regions of the PTM include small naturally occurring introns or, alternatively, any intron sequences, including synthetic mini-introns, which include 5′ consensus donor sites and 3′ consensus sequences which include a branch point, a 3′ splice site and in some instances a pyrimidine tract.
The mini-intron sequences are preferably between about 60-150 nucleotides in length, however, mini-intron sequences of increased lengths may also be used. In a preferred embodiment of the invention, the mini-intron comprises the 5′ and 3′ end of an endogenous intron. In preferred embodiments of the invention the 5′ intron fragment is about 20 nucleotides in length and the 3′ end is about 40 nucleotides in length.
In a specific embodiment of the invention, an intron of 528 nucleotides comprising the following sequences may be utilized. Sequences of the intron construct are as follows:







5′ fragment sequence:


(SEQ ID NO. 3)


Gtagttcttttgttcttcactattaagaacttaatttggtgtccatgtct


 


ctttttttttctagtttgtagtgctggaaggtatttttggagaaattctt


 


catgagcattaggagaatgtatgggtgtagtgtcttgtataatagaaatt


 


gttccactgataatttactctagttttttatttcctcatattattttcag


 


tggctttttcttccacatctttatattttgcaccacattcaacactgtag


 


cggccgc.


 


3′ fragment sequence:


(SEQ ID NO. 4)


Ccaactatctgaatcatgtgccccttctctgtgaacctctatcataatac


 


ttgtcacactgtattgtaattgctcttttactttcccttgtatcttttgt


 


gcatagcagagtacctgaaacaggaagtattttaaatattttgaatcaaa


 


tgagttaatagaatctttacaaataagaatatacacttctgcttaggatg


 


ataattggaggcaagtgaatcctgagcgtgatttgataatgacctaataa


 


tgatgggttttatttccag.






In an embodiment of the invention the Tia-1 binding sequences are inserted within 100 nucleotides from the 5′ donor site (Del Gatto-Konczak et al., 2000, Mol. Cell. Biol. 20:6287-6299). In a preferred embodiment of the invention the Tia-1 binding sequences are inserted within 50 nucleotides from the 5′ donor site. In a more preferred embodiment of the invention the Tia-1 sequences are inserted within 20 nucleotides of the 5′ donor site.
The compositions of the invention further comprise PTMs that have been engineered to include cis-acting ribozyme sequences. The inclusion of such sequences is designed to reduce PTM translation in the absence of trans-splicing or to produce a PTM with a specific length or defined end(s). The ribozyme sequences that may be inserted into the PTMs include any sequences that are capable of mediating a cis-acting (self-cleaving) RNA splicing reaction. Such ribozymes include but are not limited to hammerhead, hairpin and hepatitis delta virus ribozymes (see, Chow et al. 1994, J Biol Chem 269:25856-64).
In an embodiment of the invention, splicing enhancers such as, for example, sequences referred to as exonic splicing enhancers may also be included in the PTM design. Transacting splicing factors, namely the serine/arginine-rich (SR) proteins, have been shown to interact with such exonic splicing enhancers and modulate splicing (see, Tacke et al., 1999, Curr. Opin. Cell Biol. 11:358-362; Tian et al., 2001, J. Biological Chemistry 276:33833-33839; Fu, 1995, RNA 1:663-680). Nuclear localization signals may also be included in the PTM molecule (Dingwell and Laskey, 1986, Ann. Rev. Cell Biol. 2:367-390; Dingwell and Laskey, 1991, Trends in Biochem. Sci. 16:478-481). Such nuclear localization signals can be used to enhance the transport of synthetic PTMs into the nucleus where trans-splicing occurs.
Additional features can be added to the PTM molecule either after, or before, the nucleotide sequence encoding a translatable protein, such as polyadenylation signals to modify RNA expression/stability, or 5′ splice sequences to enhance splicing, additional binding regions, “safety”-self complementary regions, additional splice sites, or protective groups to modulate the stability of the molecule and prevent degradation. In addition, stop codons may be included in the PTM structure to prevent translation of unspliced PTMs. Further elements, such as a 3′ hairpin structure, circularized RNA, nucleotide base modification, or synthetic analogs, can be incorporated into PTMs to promote or facilitate nuclear localization and spliceosomal incorporation, and intra-cellular stability.
PTMs may also be generated that require a double-trans-splicing reaction for generation of a chimeric trans-spliced product. Such PTMs could, for example, be used to replace an internal exon or exons which could be used for expression of an apoAI variant protein. PTMs designed to promote two trans-splicing reactions are engineered as described above, however, they contain both 5′ donor sites and 3′ splice acceptor sites. In addition, the PTMs may comprise two or more binding domains and splice regions. The splice regions may be placed between the multiple binding domains and splice sites or alternatively between the multiple binding domains.
Optimal PTMs for wild type apoAI or other pre-mRNA targets, such as albumin pre-mRNA, may be selected by spliceosome-mediated trans-splicing high capacity screen (HCS). Such screens include, but are not limited to, those described in patent application Ser. No. 10/693,192. Briefly, each new PTM library is clonally delivered to target cells by transfection of bacterial protoplasts or viral vectors encoding the PTMs. The 5′ GFP-apoAI, apoB, or albumin targets are transfected using Lipofectamine reagents and the cells analyzed for GFP expression by FACS. Total RNA samples may also be prepared and analyzed for trans-splicing by quantitative real time PCR (qRT-PCR) using target and PTM specific primers for the presence of correctly spliced repaired products and the level of repaired product. Each trans-splicing domain (TSD) and binding domain is engineered with several unique restriction sites, so that when a suitable sequence is identified (based on the level of GFP function and qRT-PCR data), part of or the complete TSD, can be readily subcloned into a PTM cassette to produce PTMs of the invention.
When specific PTMs are to be synthesized in vitro (synthetic PTMs), such PTMs can be modified at the base moiety, sugar moiety, or phosphate backbone, for example, to improve stability of the molecule, hybridization to the target mRNA, transport into the cell, etc. For example, modification of a PTM to reduce the overall charge can enhance the cellular uptake of the molecule. In addition modifications can be made to reduce susceptibility to nuclease or chemical degradation. The nucleic acid molecules may be synthesized in such a way as to be conjugated to another molecule such as a peptides (e.g., for targeting host cell receptors in vivo), or an agent facilitating transport across the cell membrane (see, e.g., Letsinger et al., 1989, Proc. Natl. Acad. Sci. USA 86:6553-6556; Lemaitre et al., 1987, Proc. Natl. Acad. Sci. 84:648-652; PCT Publication No. WO88/09810, published Dec. 15, 1988) or the blood-brain barrier (see, e.g., PCT Publication No. WO89/10134, published Apr. 25, 1988), hybridization-triggered cleavage agents (see, e.g., Krol et al., 1988, BioTechniques 6:958-976) or intercalating agents (see, e.g., Zon, 1988, Pharm. Res. 5:539-549). To this end, the nucleic acid molecules may be conjugated to another molecule, e.g., a peptide, hybridization triggered cross-linking agent, transport agent, hybridization-triggered cleavage agent, etc.
Various other well-known modifications to the nucleic acid molecules can be introduced as a means of increasing intracellular stability and half-life. Possible modifications according to the present invention include, but are not limited to, the addition of flanking sequences of ribonucleotides to the 5′ and/or 3′ ends of the molecule. (See FIG. 47). In some circumstances where increased stability is desired, nucleic acids having modified internucleoside linkages such as 2′-O-methylation may be preferred. Nucleic acids containing modified internucleoside linkages may be synthesized using reagents and methods that are well known in the art (see, Uhlmann et al., 1990, Chem. Rev. 90:543-584; Schneider et al., 1990, Tetrahedron Lett. 31:335 and references cited therein).
The synthetic PTMs of the present invention are preferably modified in such a way as to increase their stability in the cells. Since RNA molecules are sensitive to cleavage by cellular ribonucleases, it may be preferable to use as the competitive inhibitor a chemically modified oligonucleotide (or combination of oligonucleotides) that mimics the action of the RNA binding sequence but is less sensitive to nuclease cleavage. In addition, the synthetic PTMs can be produced as nuclease resistant circular molecules with enhanced stability to prevent degradation by nucleases (Puttaraju et al., 1995, Nucleic Acids Symposium Series No. 33:49-51; Puttaraju et al., 1993, Nucleic Acid Research 21:4253-4258). Other modifications may also be required, for example to enhance binding, to enhance cellular uptake, to improve pharmacology or pharmacokinetics or to improve other pharmaceutically desirable characteristics.
Modifications, which may be made to the structure of the synthetic PTMs include but are not limited to backbone modifications such as use of:
(i) phosphorothioates (X or Y or W or Z═S or any combination of two or more with the remainder as O). e.g. Y═S (Stein, C. A., et al., 1988, Nucleic Acids Res., 16:3209-3221), X═S (Cosstick, R., et al., 1989, Tetrahedron Letters, 30:4693-4696), Y and Z═S (Brill, W. K.-D., et al., 1989, J. Amer. Chem. Soc., 111:2321-2322); (ii) methylphosphonates (e.g. Z=methyl (Miller, P. S., et al., 1980, J. Biol. Chem., 255:9659-9665); (iii) phosphoramidates (Z═N-(alkyl)2 e.g. alkyl methyl, ethyl, butyl) (Z=morpholine or piperazine) (Agrawal, S., et al., 1988, Proc. Natl. Acad. Sci. USA 85:7079-7083) (X or W═NH) (Mag, M., et al., 1988, Nucleic Acids Res., 16:3525-3543); (iv) phosphotriesters (Z═O-alkyl e.g. methyl, ethyl, etc.) (Miller, P. S., et al., 1982, Biochemistry, 21:5468-5474); and (v) phosphorus-free linkages (e.g. carbamate, acetamidate, acetate) (Gait, M. J., et al., 1974, J. Chem. Soc. Perkin 1, 1684-1686; Gait, M. J., et al., 1979, J. Chem. Soc. Perkin 1, 1389-1394).
In addition, sugar modifications may be incorporated into the PTMs of the invention. Such modifications include the use of: (i) 2′-ribonucleosides (R═H); (ii) 2′-O-methylated nucleosides (R═OMe)) (Sproat, B. S., et al., 1989, Nucleic Acids Res., 17:3373-3386); and (iii) 2′-fluoro-2′-riboxynucleosides (R═F) (Krug, A., et al., 1989, Nucleosides and Nucleotides, 8:1473-1483).
Further, base modifications that may be made to the PTMs, including but not limited to use of: (i) pyrimidine derivatives substituted in the 5-position (e.g. methyl, bromo, fluoro etc) or replacing a carbonyl group by an amino group (Piccirilli, J. A., et al., 1990, Nature, 343:33-37); (ii) purine derivatives lacking specific nitrogen atoms (e.g. 7-deaza adenine, hypoxanthine) or functionalized in the 8-position (e.g. 8-azido adenine, 8-bromo adenine) (for a review see Jones, A. S., 1979, Int. J. Biolog. Macromolecules, 1: 194-207).
In addition, the PTMs may be covalently linked to reactive functional groups, such as: (i) psoralens (Miller, P. S., et al., 1988, Nucleic Acids Res., Special Pub. No. 20, 113-114), phenanthrolines (Sun, J-S., et al., 1988, Biochemistry, 27:6039-6045), mustards (Vlassov, V. V., et al., 1988, Gene, 72:313-322) (irreversible cross-linking agents with or without the need for co-reagents); (ii) acridine (intercalating agents) (Helene, C., et al., 1985, Biochimie, 67:777-783); (iii) thiol derivatives (reversible disulphide formation with proteins) (Connolly, B. A., and Newman, P. C., 1989, Nucleic Acids Res., 17:4957-4974); (iv) aldehydes (Schiff's base formation); (v) azido, bromo groups (UV cross-linking); or (vi) ellipticines (photolytic cross-linking) (Perrouault, L., et al., 1990, Nature, 344:358-360).
In an embodiment of the invention, oligonucleotide mimetics in which the sugar and internucleoside linkage, i.e., the backbone of the nucleotide units, are replaced with novel groups can be used. For example, one such oligonucleotide mimetic which has been shown to bind with a higher affinity to DNA and RNA than natural oligonucleotides is referred to as a peptide nucleic acid (PNA) (for review see, Uhlmann, E. 1998, Biol. Chem. 379:1045-52). Thus, PNA may be incorporated into synthetic PTMs to increase their stability and/or binding affinity for the target pre-mRNA.
In another embodiment of the invention synthetic PTMs may covalently linked to lipophilic groups or other reagents capable of improving uptake by cells. For example, the PTM molecules may be covalently linked to: (i) cholesterol (Letsinger, R. L., et al., 1989, Proc. Natl. Acad. Sci. USA 86:6553-6556); (ii) polyamines (Lemaitre, M., et al., 1987, Proc. Natl. Acad. Sci. USA 84:648-652); other soluble polymers (e.g. polyethylene glycol) to improve the efficiently with which the PTMs are delivered to a cell. In addition, combinations of the above identified modifications may be utilized to increase the stability and delivery of PTMs into the target cell. The PTMs of the invention can be used in methods designed to produce a novel chimeric RNA in a target cell.
The methods of the present invention comprise delivering to the target cell a PTM which may be in any form used by one skilled in the art, for example, an RNA molecule, or a DNA vector which is transcribed into a RNA molecule, wherein said PTM binds to a pre-mRNA and mediates a trans-splicing reaction resulting in formation of a chimeric RNA comprising a portion of the PTM molecule spliced to a portion of the pre-mRNA. Furthermore, the invention also encompasses additional methods for modifying or converting mRNAs such as use of trans-splicing ribozymes and other means that are known to skilled practitioners in the field.
In a specific embodiment of the invention, the PTMs of the invention can be used in methods designed to produce a novel chimeric RNA in a target cell so as to result in expression of the apoAI Milano or other variant proteins. The methods of the present invention comprise delivering to a cell a PTM which may be in any form used by one skilled in the art, for example, an RNA molecule, or a DNA vector which is transcribed into a RNA molecule, wherein said PTM binds to a apoAI or apoB pre-mRNA and mediates a trans-splicing reaction resulting in formation of a chimeric RNA comprising the portion of the PTM molecule having the apo-1 Milano mutation spliced to a portion of the pre-mRNA.
In another specific embodiment of the invention, the PTMs of the invention can be used in methods designed to produce a novel chimeric RNA in a target cell so as to result in the substitution of albumin expression with expression of the wild type apoAI, apoAI Milano or other variant proteins. The methods of the present invention comprise delivering to a cell a PTM which may be in any form used by one skilled in the art, for example, an RNA molecule, or a DNA vector which is transcribed into a RNA molecule, wherein said PTM binds to an albumin pre-mRNA and mediates a trans-splicing reaction resulting in formation of a chimeric RNA comprising the portion of the PTM molecule encoding wild type apoAI, or apoAI Milano variant spliced to a portion of the pre-mRNA.
5.2. Synthesis of the Trans-Splicing Molecules
The nucleic acid molecules of the invention can be RNA or DNA or derivatives or modified versions thereof, single-stranded or double-stranded. By nucleic acid is meant a PTM molecule or a nucleic acid molecule encoding a PTM molecule, whether composed of deoxyribonucleotides or ribonucleosides, and whether composed of phosphodiester linkages or modified linkages. The term nucleic acid also specifically includes nucleic acids composed of bases other than the five biologically occurring bases (adenine, guanine, thymine, cytosine and uracil). In addition, the PTMs of the invention may comprise, DNA/RNA, RNA/protein or DNA/RNA/protein chimeric molecules that are designed to enhance the stability of the PTMs.
The PTMs of the invention can be prepared by any method known in the art for the synthesis of nucleic acid molecules. For example, the nucleic acids may be chemically synthesized using commercially available reagents and synthesizers by methods that are well known in the art (see, e.g., Gait, 1985, Oligonucleotide Synthesis: A Practical Approach, IRL Press, Oxford, England).
Alternatively, synthetic PTMs can be generated by in vitro transcription of DNA sequences encoding the PTM of interest. Such DNA sequences can be incorporated into a wide variety of vectors downstream from suitable RNA polymerase promoters such as the T7, SP6, or T3 polymerase promoters. Consensus RNA polymerase promoter sequences include the following:











T7:
TAATACGACTCACTATAGGGAGA
(SEQ ID NO. 5)



 



SP6:
ATTTAGGTGACACTATAGAAGNG
(SEQ ID NO. 6)



 



T3:
AATTAACCCTCACTAAAGGGAGA.
(SEQ ID NO. 7)






The base in bold is the first base incorporated into RNA during transcription. The underline indicates the minimum sequence required for efficient transcription.
RNAs may be produced in high yield via in vitro transcription using plasmids such as SPS65 and Bluescript (Promega Corporation, Madison, Wis.). In addition, RNA amplification methods such as Q-β amplification can be utilized to produce the PTM of interest.
The PTMs may be purified by any suitable means, as are well known in the art. For example, the PTMs can be purified by gel filtration, affinity or antibody interactions, reverse phase chromatography or gel electrophoresis. Of course, the skilled artisan will recognize that the method of purification will depend in part on the size, charge and shape of the nucleic acid to be purified.
The PTM's of the invention, whether synthesized chemically, in vitro, or in vivo, can be synthesized in the presence of modified or substituted nucleotides to increase stability, uptake or binding of the PTM to a target pre-mRNA. In addition, following synthesis of the PTM, the PTMs may be modified with peptides, chemical agents, antibodies, or nucleic acid molecules, for example, to enhance the physical properties of the PTM molecules. Such modifications are well known to those of skill in the art.
In instances where a nucleic acid molecule encoding a PTM is utilized, cloning techniques known in the art may be used for cloning of the nucleic acid molecule into an expression vector. Methods commonly known in the art of recombinant DNA technology which can be used are described in Ausubel et al. (eds.), 1993, Current Protocols in Molecular Biology, John Wiley & Sons, NY; and Kriegler, 1990, Gene Transfer and Expression, A Laboratory Manual, Stockton Press, NY.
The DNA encoding the PTM of interest may be recombinantly engineered into a variety of host vector systems that also provide for replication of the DNA in large scale and contain the necessary elements for directing the transcription of the PTM. The use of such a construct to transfect target cells in the patient will result in the transcription of sufficient amounts of PTMs that will form complementary base pairs with the endogenously expressed pre-mRNA targets, such as for example, apoAI or apoB pre-mRNA target, and thereby facilitate a trans-splicing reaction between the complexed nucleic acid molecules. For example, a vector can be introduced in vivo such that is taken up by a cell and directs the transcription of the PTM molecule. Such a vector can remain episomal or become chromosomally integrated, as long as it can be transcribed to produce the desired RNA, i.e., PTM. Such vectors can be constructed by recombinant DNA technology methods standard in the art. A vector can also be introduced into a cell ex vivo and the transfected/transduced cells returned to the patient.
Vectors encoding the PTM of interest can be plasmid, viral, or others known in the art, used for replication and expression in mammalian cells. Expression of the sequence encoding the PTM can be regulated by any promoter/enhancer sequences known in the art to act in mammalian, preferably human cells. Such promoters/enhancers can be inducible or constitutive. Such promoters include but are not limited to: the SV40 early promoter region (Benoist, C. and Chambon, P. 1981, Nature 290:304-310), the promoter contained in the 3′ long terminal repeat of Rous sarcoma virus (Yamamoto et al., 1980, Cell 22:787-797), the herpes thymidine kinase promoter (Wagner et al., 1981, Proc. Natl. Acad. Sci. USA 78:1441-1445), the regulatory sequences of the metallothionein gene (Brinster et al., 1982, Nature 296:39-42), the viral CMV promoter, the human chorionic gonadotropin-β promoter (Hollenberg et al., 1994, Mol. Cell. Endocrinology 106:111-119), etc.
In a specific embodiment of the invention, liver specific promoter/enhancer sequences may be used to promote the synthesis of PTMs in liver cells for expression of the apoAI Milano variant protein. Such promoters include, for example, the albumin, transthyretin, CMV enhancers/chicken beta-actin promoter, ApoE enhancer alpha1-antitrypsin promoter and endogenous apoAI or apo-B promoter elements. In addition, the liver-specific microglobulin promoter cassette optimized for apoAI or apo-B gene expression may be used, as well as, post-transcriptional elements such as the wood chuck post-transcriptional regulatory element (WPRE).
Any type of plasmid, cosmid, YAC or viral vector can be used to prepare the recombinant DNA construct which can be introduced directly into the tissue site. Alternatively, viral vectors can be used which selectively infect the desired target cell. Vectors for use in the practice of the invention include any eukaryotic expression vectors, including but not limited to viral expression vectors such as those derived from the class of retroviruses, adenoviruses or adeno-associated viruses.
A number of selection systems can also be used, including but not limited to selection for expression of the herpes simplex virus thymidine kinase, hypoxanthine-guanine phosphoribosyltransterase and adenine phosphoribosyl transferase protein in tk-, hgprt- or aprt-deficient cells, respectively. Also, anti-metabolic resistance can be used as the basis of selection for dihydrofolate transferase (dhfr), which confers resistance to methotrexate; xanthine-guanine phosphoribosyl transferase (gpt), which confers resistance to mycophenolic acid; neomycin (neo), which confers resistance to aminoglycoside G-418; and hygromycin B phosphotransferase (hygro) which confers resistance to hygromycin. In a preferred embodiment of the invention, the cell culture is transformed at a low ratio of vector to cell such that there will be only a single vector, or a limited number of vectors, present in any one cell.
5.3. Uses and Administration of Trans-Splicing Molecules
5.3.1. Use of PTM Molecules for Expression of ApoAI Milano Variants
The compositions and methods of the present invention are designed to substitute apoAI, or apoB expression, or other pre-mRNA targets, such as albumin, with wild-type apoAI, apoAI Milano or other apoAI variant expression. Specifically, targeted trans-splicing, including double-trans-splicing reactions, 3′ exon replacement and/or 5′ exon replacement can be used to substitute apoAI, apoB, or albumin sequences with either wild type apoAI or apoAI Milano sequences resulting in expression of apoAI wild type or Milano variant.
Various delivery systems are known and can be used to transfer the compositions of the invention into cells, e.g. encapsulation in liposomes, microparticles, microcapsules, recombinant cells capable of expressing the composition, receptor-mediated endocytosis (see, e.g., Wu and Wu, 1987, J. Biol. Chem. 262:4429-4432), construction of a nucleic acid as part of a retroviral, adenoviral, adeno-associated viral or other vector, incorporation into a plasmid or mini-circle, injection of DNA, electroporation, calcium phosphate mediated transfection, etc.
The compositions and methods can be used to provide a gene encoding a wild-type apoAI, apoAI Milano, apoB/apoAI wild type or Milano, alb/apoAI wild type or milano chimeric protein to cells of an individual where expression of said gene products reduces plaque formation.
Specifically, the compositions and methods can be used to provide sequences encoding a wild type apoAI, an apoAI Milano variant molecule, or apoB/apoAI or alb/apoAI chimeric protein to cells of an individual to reduce the plaque formation normally associated with vascular disorders leading to heart attacks and stroke.
In a preferred embodiment, nucleic acids comprising a sequence encoding a PTM are administered to promote PTM function, by way of gene delivery and expression into a host cell. In this embodiment of the invention, the nucleic acid mediates an effect by promoting PTM production. Any of the methods for gene delivery into a host cell available in the art can be used according to the present invention. For general reviews of the methods of gene delivery see Strauss, M. and Barranger, J. A., 1997, Concepts in Gene Therapy, by Walter de Gruyter & Co., Berlin; Goldspiel et al., 1993, Clinical Pharmacy 12:488-505; Wu and Wu, 1991, Biotherapy 3:87-95; Tolstoshev, 1993, Ann. Rev. Pharmacol. Toxicol. 33:573-596; Mulligan, 1993, Science 260:926-932; and Morgan and Anderson, 1993, Ann. Rev. Biochem. 62:191-217; 1993, TIBTECH 11(5): 155-215. Exemplary methods are described below.
Delivery of the PTM into a host cell may be either direct, in which case the host is directly exposed to the PTM or PTM encoding nucleic acid molecule, or indirect, in which case, host cells are first transformed with the PTM or PTM encoding nucleic acid molecule in vitro or ex vivo, then transplanted into the host. These two approaches are known, respectively, as in vivo or ex vivo gene delivery.
In a specific embodiment, the nucleic acid is directly administered in vivo, where it is expressed to produce the PTM. This can be accomplished by any of numerous methods known in the art, e.g., by constructing it as part of an appropriate nucleic acid expression vector and administering it so that it becomes intracellular, e.g. by infection using a defective or attenuated retroviral or other viral vector (see U.S. Pat. No. 4,980,286), or by direct injection of naked DNA, or by use of microparticle bombardment (e.g., a gene gun; Biolistic, Dupont, Bio-Rad), or coating with lipids or cell-surface receptors or transfecting agents, encapsulation in liposomes, microparticles, or microcapsules, or by administering it in linkage to a peptide which is known to enter the nucleus, by administering it in linkage to a ligand subject to receptor-mediated endocytosis (see e.g., Wu and Wu, 1987, J. Biol. Chem. 262:4429-4432).
In a specific embodiment, a viral vector that contains the PTM can be used. For example, a retroviral, including lentiviral, vector can be utilized that has been modified to delete retroviral sequences that are not necessary for packaging of the viral genome and integration into host cell DNA (see Miller et al., 1993, Meth. Enzymol. 217:581-599). Alternatively, adenoviral or adeno-associated viral vectors can be used for gene delivery to cells or tissues. (see, Kozarsky and Wilson, 1993, Current Opinion in Genetics and Development 3:499-503 for a review of adenovirus-based gene delivery).
In a preferred embodiment of the invention an adeno-associated viral vector may be used to deliver nucleic acid molecules capable of encoding the PTM. The vector is designed so that, depending on the level of expression desired, the promoter and/or enhancer element of choice may be inserted into the vector.
Another approach to gene delivery into a cell involves transferring a gene to cells in tissue culture by such methods as electroporation, lipofection, calcium phosphate mediated transfection, or viral infection. Usually, the method of transfer includes the transfer of a selectable marker to the cells. The cells are then placed under selection to isolate those cells that have taken up and are expressing the transferred gene. The resulting recombinant cells can be delivered to a host by various methods known in the art. In a preferred embodiment, the cell used for gene delivery is autologous to the host's cell.
In a specific embodiment of the invention, hepatic stem cells, oval cells, or hepatocytes may be removed from a subject and transfected with a nucleic acid molecule capable of encoding a PTM designed to produce, upon trans-splicing, a wild-type apoAI, an apoAI Milano or other apoAI variant protein and/or apoB/apoAI or alb/apoAI chimeric protein. Cells may be further selected, using routine methods known to those of skill in the art, for integration of the nucleic acid molecule into the genome thereby providing a stable cell line expressing the PTM of interest. Such cells are then transplanted into the subject, thereby providing a source of wild type apoAI, or apoAI Milano variant protein.
The present invention also provides for pharmaceutical compositions comprising an effective amount of a PTM or a nucleic acid encoding a PTM, and a pharmaceutically acceptable carrier. In a specific embodiment, the term “pharmaceutically acceptable” means approved by a regulatory agency of the Federal or a state government or listed in the U.S. Pharmacopeia or other generally recognized pharmacopeia for use in animals, and more particularly in humans. The term “carrier” refers to a diluent, adjuvant, excipient, or vehicle with which the therapeutic is administered. Examples of suitable pharmaceutical carriers are described in “Remington's Pharmaceutical sciences” by E. W. Martin.
In specific embodiments, pharmaceutical compositions are administered: to subjects with diseases or disorders involving accumulation of plaque in the vascular system, for example, in hosts where aberrant levels of apoAI and apoB protein are expressed. The activity of the protein encoded for by the chimeric mRNA resulting from the PTM mediated trans-splicing reaction can be readily detected, e.g., by obtaining a host tissue sample (e.g., from biopsy tissue, or a blood sample) and assaying in vitro for mRNA or protein levels or activity of the expressed chimeric mRNA.
In specific embodiments, pharmaceutical compositions are administered in diseases or disorders involving the accumulation of plaque in the vascular system, for example, in hosts where apoAI and/or apoB are aberrantly expressed, or expressed at low levels. Such disorders include but are not limited to vascular disorders that frequently lead to atherosclerosis, heart attacks or strokes.
Many methods standard in the art can be thus employed, including but not limited to immunoassays to detect and/or visualize the protein, i.e., wild type apoAI, apoAI Milano or apoB/apoAI Milano chimeric protein, encoded for by the chimeric mRNA (e.g., Western blot, immunoprecipitation followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, immunocytochemistry, etc.) and/or hybridization assays to detect formation of chimeric mRNA expression by detecting and/or visualizing the presence of chimeric mRNA (e.g., Northern assays, dot blots, in situ hybridization, and Reverse-Transcription PCR, etc.), etc.
In a specific embodiment, it may be desirable to administer the pharmaceutical compositions of the invention locally to the area in need of treatment, i.e., liver tissue. 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 or stent, by means of an endoscope, 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. Other control release drug delivery systems, such as nanoparticles, matrices such as controlled-release polymers, hydrogels.
The PTM will be administered in amounts which are effective to produce the desired effect in the targeted cell. Effective dosages of the PTMs can be determined through procedures well known to those in the art which address such parameters as biological half-life, bioavailability and toxicity. The amount of the composition of the invention which will be effective will depend on the severity of the vascular disorder being treated, and can be determined by standard clinical techniques. Such techniques include analysis of blood samples to determine the level of apoAI or ApoB/apoAI or alb/apoAI chimeric protein expression. In addition, in vitro assays may optionally be employed to help identify optimal dosage ranges.
The present invention also provides a pharmaceutical pack or kit comprising one or more containers filled with one or more of the ingredients of the pharmaceutical compositions of the invention optionally associated with such container(s) can be a notice in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals or biological products, which notice reflects approval by the agency of manufacture, use or sale for human administration.
5.3.2 Trans-Splicing Strategy to Improve Human ApoAI Function and Half-Life
Albumin is a soluble, monomeric protein that comprises about one-half of the blood serum protein and exhibits a relatively slow clearance profile compared to many plasma proteins. Because of these properties, albumin is an ideal candidate to create chimeric proteins to slow clearance profile of potential therapeutic proteins. The half-life of human serum albumin is  ̃20-22 days. Apolipoprotein AI (apoAI) is the major component of high density lipoprotein (HDL), and there is an inverse correlation between HDL concentration vs. number of cardiovascular incidents. See Sirtori C R et al., 1999, Atherosclerosis 142:29-40; Genest J 2003, J. Inherit. Metab. Dis. 26:267-287; Nissen et al., 2003, JAMA 290, 2292-2300; Brewer B H, 2004, Am Heart J, 148, S14-S18; Brewer B H, 2004, N Engl J Med, 350, 1491-1494, the disclosures of which are hereby incorporated by reference. The half-life of human apoAI protein is  ̃10-times lower than that of the human serum albumin. Thus, by extending the half-life of human apoAI protein by, for example, trans-splicing into albumin exon 13, more benefit would be realized per unit amount of apoAI protein. Accordingly, the methods and nucleic acid molecules of the present invention may be used to increase plasma levels of apoAI and high density lipoprotein for patients with or at risk for atherosclerosis.
In addition, as shown in FIG. 47, the targeting of other albumin introns may be used to increase half-life of human apoAI. For example, PTMs according to the present invention may contain albumin exons 14 and 15, in addition to the majority of the coding sequence for human apoAI. The resulting trans-spliced product, therefore, would contain the entire albumin coding sequence plus the human apoAI coding sequence and may be used to produce an albumin-apoAI chimeric protein with extended half-life and increased efficacy. It will be readily apparent to those skilled in the art that PTMs with other exon combinations may be constructed and used according to the claimed methods and nucleic acid molecules of the present invention. Moreover, the methods and nucleic acid molecules of the claimed invention may include the (a) human apoAI “pro” peptide and (b) “pre-pro” apoAI peptide to improve the function of the trans-spliced human apoAI protein in vivo. The strategy was designed to take advantage of the endogenous native cellular machinery to enhance recognition, processing and secretion of the final trans-spliced protein to the site of action similar to endogenous apoAI protein. This strategy is illustrated in FIGS. 48 and 49.
6. EXAMPLE
Expression of Human Apolipoprotein (Apoa-I)
6.1: Albumin-Human Apoa-I Chimeric Proteins
The present study was undertaken to evaluate the albumin targeting strategy (FIG. 21) for the production of human apoAI protein, a major component of high density lipoprotein (HDL) or other variants and subsequently increase HDL concentration as a treatment for individuals having or at risk for cardio vascular disease (CHD). The rationale for selecting albumin as a target is because of its elevated expression in liver. High albumin pre-mRNA concentration results in abundant targets for trans-splicing. The concept involves targeted trans-splicing of wild type human apoAI or apoAI analogues into albumin pre-mRNA target; and the goal is to increase apoAI expression. This study evaluates the effect of albumin sequence human apoAI protein expression, secretion and function.
The albumin-hapoAI trans-spliced product was evaluated for function in vivo. As used herein with reference to trans-spliced albumin-human apoAI described in this application indicates human apoAI plus 7 nucleotides derived from albumin (mouse or human) target pre-mRNA, and, hereafter referred to as trans-spliced chimeric mRNA or trans-spliced human apoAI protein. Human and mouse versions of the albumin-human apoAI cDNA controls (FIG. 22) to mimic the final trans-spliced mRNA were constructed and tested for expression, processing and function in 293 and hepatoma cells (HepG2). The cDNA constructs were constructed using long complementary oligonucleotides and PCR products consisting of albumin exon 1 and human apoAI exon 3 and 4. Briefly, the coding sequence of mouse and human albumin exon 1 were assembled using the following long oligos: mouse Alb forward primer:
ATGAAGTGGGTAACCTTTCTCCTCCTCCTCTTCGTCTCCGGCTCTGCTTT TTCCAGGGGTGTGTTTCGCCGAGAAGCACCC, (SEQ ID NO. 8)
reverse primer:
GGGTGCTTCTCGGCGAAACACACCCCTGGAAAAAGCAGAGCCGGAGACGA AGAGGAGGAGGAGAAAGGTTACCCACTTCATG, (SEQ ID NO. 9)
and human Alb forward primer:
ATGAAGTGGGTAACCTTTATTTCCCTTCTTTTTCTCTTTAGCTCGGCTTA TTCCAGGGGTGTGTTTCGTCGAGATGCACCC, (SEQ ID NO. 10)
reverse primer:
GGGTGCATCTCGACGAAACACACCCCTGGAATAAGCCGAGCTAAAGAGAA AAAGAAGGGAAATAAAGGTTACCCACTTCATG (SEQ ID NO. 11). The underlined nucleotides indicate the end of albumin exon 1 sequence and 2 “C”s at the 3′ end of the forward primers overlap to human apoAI.
The human apoAI coding sequence was PCR amplified using a cDNA clone (ATCC: clone #MGC-1249) and primers: Apo23 (5′-CCCCAGAGCCCCTGGGATCGAGTG) (SEQ ID NO. 12) and Apo5 (5′-CTAG AAGCTT CCCACTTTGGAAACGTTTAT TCTGAGCACC GG) (SEQ ID NO. 13). The PCR product was blunted at the 5′ end and then digested with Hind III (indicated in bold) restriction enzyme. The resulting product was first ligated with mouse or human albumin exon 1 and then cloned into pcDNA3.1 expression vector (Invitrogen). Expression plasmids containing the entire coding sequence of human apoAI including the signal peptide into pcDNA3.1 to generate wild type human apoAI, and the Milano variant which contains an Arg to Cys substitution at position 173 (R173C) expression plasmids were also constructed as positive controls. The final constructs were verified by sequencing.
6.2: Production, Expression and Secretion of Albumin-Apoa-I Proteins in 293 Cells
The effect of albumin exon 1 sequence on expression and processing of human apoAI protein was evaluated by transfecting human and mouse cDNA plasmids along with a negative (deletion mutant) and a positive control cDNAs (wt apoAI) into 293 cells. After transfection, cells were rinsed 2.times. with serum free DMEM and incubated with serum free advanced DMEM media (Invitrogen). After 48 hrs post-transfection, media was collected, concentrated, analyzed for the expression of human apoAI protein.
Coomassie Blue staining of the gel revealed that both the mouse and the human cDNAs produced the predicted  ̃28 kDa protein band which co-migrated with that of wt apoAI demonstrating good expression, processing and secretion in 293 cells (FIG. 23. lanes 2-3, 6-7). In addition, these data also showed that the level of expression was similar to that of wt apoAI (FIG. 23. lane 4, 8) indicating no adverse effects of albumin sequence on human apoAI expression and processing. On the other hand, no such band was detected in mock transfected cells and in cells that received mouse cDNA with a 2 nucleotide deletion in the signal peptide (FIG. 23. lane 1 and 5).
The identity of the band that was observed in SDS gels as human apoAI was confirmed by Western analysis using a monoclonal human apoAI antibody (Biodesign, Cat. #H45625). About  ̃0.5-10 μg total protein from the supernatant or the total cell lysate from cells transfected with cDNA control constructs, wt apoAI and Milano variant was analyzed on a 12% SDS gel and transferred onto a nylon membrane and incubated with human anti-apoAI antibody. Western results confirmed the production of human apoAI protein with an apparent molecular mass of 28 kDa predicted for the mature protein. Western data also indicated the presence of >90% of the mature human apoAI protein from the cDNAs or wt apoAI in the supernatant compared to a cell lysate demonstrating normal processing and secretion in 293 cells (FIG. 24; compare lanes 1 & 2 with 3). Similar results were also observed with hepatoma (HepG2) cells transfected with cDNA constructs.
6.3: Trans-Spliced Albumin-Human Apoa-I Protein is Functionally Active
The effect of the 7 nucleotides from albumin on human apoAI function was evaluated by measuring ATP-binding cassette transporter protein (ABC1) mediated transfer of cellular cholesterol into apoAI acceptor. The release of radio-labeled cellular cholesterol to lipid free human apoAI was quantified and the efflux values obtained with trans-spliced proteins were compared with those from wt apoAI and negative control samples. Control HeLa and HeLa cells stably transfected with an ABC1 encoding plasmid were grown to near confluency. Cells were then loaded with 1 μCi/ml 3H cholesterol. After equilibrating for 24 hrs, cells were washed 3× with serum free media and incubated with a serial dilution of the media containing the trans-spliced proteins (supernatant from 293 cells transfected w/cDNA constructs, normalized for apoAI protein concentration) or with 10 μg/wild type apoAI protein as positive control. Cells were allowed to efflux for 18 hrs. After the efflux period, medium was collected and an aliquot of the medium was then counted by liquid scintillation counting. The remaining counts in the cell fraction were determined after an over night extraction with isopropanol. The percent efflux was calculated by dividing the counts in the efflux media by the sum of the counts in the media plus the cell fraction. DMEM/BSA media was used as a blank and was subtracted from the radioactive counts obtained in the presence of an acceptor in the efflux media.
The amount of ABC1 mediated efflux observed with trans-spliced proteins (mouse and human proteins) was similar to that of wt apoAI (FIG. 25). The efflux data also demonstrated that the absolute efflux activity observed with the trans-spliced proteins were comparable or slightly better than the wt apoAI protein across the concentration range tested indicating the absence of any major adverse effects due to albumin sequence in the final trans-spliced product on apoAI function. These results provide strong evidence about the effectiveness of the compositions of the present invention for the production of functional biologically active proteins in vivo.
7. EXAMPLE
High Capacity Screens for Isolation of Optimal Binding Domains for Albumin Targets
A high capacity screen (HCS) to identify optimal binding domains for mouse albumin pre-mRNA target was performed as described before (U.S. patent application Ser. No. 10/693,192, filed Oct. 24, 2003) (FIG. 26A) with various modifications (FIG. 26B).
7.1: High Capacity Screen pre-mRNA Target
Mouse albumin intron 1 and exon 2 comprising nucleotides 114 through 877 a total of 763 bp (Ref. seq. NC—000071) (FIG. 18), was PCR amplified using the genomic DNA and primers mAlb15 (5′-CTAG GGATCC GTTTTATGTTTTTTCATCTCTG) (SEQ ID NO. 14) and mAlb8 (5′-CTAG GCGGCCGC_AGGCCTTTGAAATGTTGTTCTCC) (SEQ ID NO. 15). The PCR product was then digested with Bam HI and Not I (indicated in bold) and cloned into an existing HCS target plasmid to generate pc5′ zsG-mIn1-Ex2 plasmid (FIG. 27). Stable cells expressing the 5′ half of the coding sequence for the green fluorescent protein (GFP) (zsGreen from Clontech) coupled to intron 1 and exon 2 of mouse albumin gene was established in 293 cells by transfecting the target plasmid followed by hygromycin selection. After 2 weeks of selection, hygromycin resistant clones were pooled, characterized by RT-PCR and used for HCS.
7.2: Mouse Albumin PTM Binding Domain Library
The mouse albumin sequence comprising intron 1 and exon 2 was PCR amplified using genomic DNA and primers as described above, digested with Bam HI and Not I and ligated to generate a large concatemerized fragment ( ̃0.10 kb). This step was introduced to increase BD complexity. The concatemerized DNA was then fragmented into small pieces by sonication and fractionated on a 3% agarose gel. Fragment size ranging from 50-250 nucleotides were gel purified, ends were repaired using Klenow enzyme and cloned into PTM cassette described before (U.S. patent application Ser. No. 10/693,192, filed Oct. 24, 2003) (FIG. 28).
PCR analysis of the library colonies showed >87% recombination efficiency and produced a complex library with >106 independent clones with BDs varying in size from 50-250 nts (FIG. 29). The primary library was amplified in bacteria and used for screening the optimal BDs by HCS.
7.3: PTM Selection Strategy
Following the FACS-based PTM selection strategy described before (U.S. patent application Ser. No. 10/693,192, filed Oct. 24, 2003), a mouse albumin (mAlb) binding domain (BD) library using the assay cells expressing the 5′ zsG-mIn1-Ex2 pre-mRNA target was tested. Several of the existing steps were modified and several new steps were added as outlined in FIG. 26B.
Briefly, on day 1, COS-7 cells were plated and transfected with 5′ zsG-mIn1-Ex2 target plasmid using Lipo2000 reagent. On day 2,  ̃106 independent PTM clones were delivered to assay cells expressing 5′ zsG-mIn1-Ex2 pre-mRNA as protoplasts. As illustrated in the FIG. 30, cells were sorted after 24 hr by FACS, and cells expressing high GFP and proportionate RFP were collected in 2 fractions i.e., high green (HG) and low green (LG) fractions, instead of a single fraction as previously described. PTMs from the collected cells were rescued by HIRT DNA extraction followed by EcoR V digestion to reduce target plasmid contamination in the final HIRT DNA preparation. About 40 binding domain containing PTMs from LG and HG fractions were initially tested by parallel transfection. Trans-splicing efficiency of these PTMs was assessed by FACS analysis.
As predicted, the percent GFP positive (GFP+) cells and the mean GFP fluorescence were higher in PTMs from the HG fraction compared to the LG fraction in a 2:1 ratio (FIG. 30).
A hundred more BD-containing clones from the HG fraction were isolated and tested by parallel transfection and the results are summarized in FIG. 31. GFP mean fluorescence was used as an indicator for assessing trans-splicing efficiency of the individual PTMs. Based on the GFP mean fluorescence, the trans-splicing efficiency of the majority of the PTMs selected from the HCS were either similar or slightly higher than the rationally designed model PTM (FIG. 31). However, several PTMs with considerably higher (1.5 to 2-fold) trans-splicing compared with the model PTM were present. In the current screen, a ratio of 1:20 of superior PTMs vs. the rest was obtained.
From this step, the top 20 PTMs were selected for further characterization by parallel transfection, followed by molecular analysis using reverse transcription (RT) real time quantitative PCR (RT-qPCR) for specific trans-splicing, and the results are summarized in FIG. 32. Total RNA was isolated and trans-splicing efficiency was measured by RT-qPCR. Target and PTM specific primers were used for measuring specific trans-splicing, and total splicing was measured using primers specific for the 5′ zsG exon as previously described. Based on the qPCR or GFP mean fluorescence values up to  ̃5-10 fold enrichment (after normalization) for trans-splicing efficiency was detected with PTMs selected from the HCS compared to a rationally designed model PTM (FIG. 32). Similar results, i.e. enhancement in trans-splicing efficiency, was observed with the enriched library (LG and HG samples) compared with the starting library, which is consistent with previous screen.
The effect of BD orientation and sequence position on trans-splicing efficiency and specificity was also analyzed. The sequence of random clones from the starting PTM library were compared with the enriched library i.e., PTMs selected after one round of enrichment.
Sequence analysis of the PTMs from the starting library revealed that  ̃51% of the BDs were in correct (antisense) orientation compared to 49% incorrect orientation. The BD size varied from 40 nt and up to 336 nt and also showed good distribution indicating the complexity of the mAlb BD library. In contrast, sequence analysis of the PTMs selected from the enriched library, as expected, showed an increase in correct orientation BDs (88%) and the mean BD length was significantly higher than the starting library, which is consistent with previous work demonstrating that longer BDs are more efficient (Puttaraju et al., 2001). Based on molecular and GFP mean fluorescence values, lead PTMs #88, 97, 143 and 158 were selected for functional studies. n addition to the lead PTMs mentioned above, several PTMs with significantly higher trans-splicing have been selected and compared with model PTMs, e.g., 82, 90, 93, 122, 123 and 152.
8. EXAMPLE
Trans-Splicing of Human Apolipoprotein ApoAI in Cells
8.1. Human Apolipoprotein (ApoAI) PTM
Detailed structure of a human apolipoproteinAI (apoAI) PTM used in this example to show in vitro proof of principle is shown in FIG. 33. The PTM cassette consists of a trans-splicing domain (TSD) that include unique restriction sites, NheI and SacII, for cloning the lead binding domains (BDs), a 24 nucleotide spacer region, a strong 3′ splice site including the consensus yeast branch point (BP), an extended polypyrimidine tract (19 nucleotides long), a splice acceptor site (CAG dinucleotide) followed by the majority of the coding sequence for wild type human apoAI mRNA from nt 118 through nt 842 (Ref seq. NM—000039 and as shown in FIG. 3A). The PTM cassette also contains the SV40 polyadenylation site and woodchuck hepatitis post-transcriptional regulatory element (WPRE) to enhance the stability of trans-spliced message. The entire cassette is cloned into pcDNA3.1 vector backbone, which contains cytomegalovirus promoter (Invitrogen). In addition, the vector backbone was further modified to include Maz4 (transcriptional pause site) sequence to reduce cryptic cis-splicing between vector ampicillin gene and PTM 3′ splice site. PTMs used for functional studies mAlbPTM97C2 and mAlbPTM158 were generated by cloning 279 bp and 149 bp BD sequence into the PTM cassette between NheI and SacII sites and were verified by sequencing.
8.2 Mouse Albumin Minigene Target pre-mRNA
For demonstrating in vitro apoAI function, a mouse albumin mini-gene target consisting of exon 1, intron 1 and exon 2 was used. A schematic diagram of the pre-mRNA target is shown in FIG. 34. The mouse albumin coordinates are as described in Ref Seq. NC—00071. The mouse albumin Ex1-In1-Ex2 pre-mRNA target (mAlbEx1-In1-Ex2) constructed as follows: an 877 bp fragment corresponding to nucleotides 1 through 877 was PCR amplified using the following mouse genomic DNA and primers: mAlb-Ex1F (5′-ctagGCTAGC ACCTTT CCTATCAACCCCACTAGC) (SEQ ID NO. 16) and mAlb8 (5′-ctagGCGGCCGC AGGCCTTTGAAATGTTGTTCTCC) (SEQ ID NO. 17). These primers contain unique restriction sites at the end of the fragment (indicated in bold). The PCR product was digested with Nhe I and Not I and cloned into inducible expression vector pcDNA5/FRT/TO designed to use with Flip-In T-Rex system (Invitrogen). The final construct (pcDNATOfrt-mAlbEx1-In1-Ex2) contains the following features: CMV promoter, Tet operator, SV40 polyadenylation site and hygromycin selection marker for establishing stable cell lines.
8.3: Generation of a Stable Cell Line Expressing Albumin Target
Using the target plasmid described above, a stable target cell line that expressed the mouse albumin mini-gene target consist of exon 1, intron 1 and exon 2 was generated. Analysis of total RNA from cells transfected with target plasmid (pcDNATOfrt-mAlbEx1-In1-Ex2) by RT-PCR produced the expected cis-spliced product, but no albumin protein. Upon confirming the splicing pattern of mouse albumin mini-gene target pre-mRNA, a stable cell line in Flip-In T-Rex 293 cells was established by transfecting the target plasmid followed by hygromycin selection. After selecting for a period of  ̃0.2 weeks, hygromycin resistant clones were pooled and maintained in hygromycin until used.
8.4: Efficient Trans-splicing of Human ApoAI PTMs
Human apoAI PTMs selected from the HCS showed efficient and accurate trans-splicing to mouse albumin pre-mRNA in stable cells. PTM mediated trans-splicing and production of mouse albumin-human apoAI chimeric mRNA was evaluated by transfecting stable cells with mAlbPTM97C2 and mAlbPTM158, along with a splice mutant lacking the TSD (splice incompetent PTM) and mock transfection. Total RNA isolated from these cells was analyzed by RT-PCR using mouse albumin target and human apoAI PTM specific primers. These primers produced the predicted 390 bp product only in cells that received functional PTMs (FIG. 35, lanes 2-4 and 6). No such product was detected in cells transfected with the splice mutant or in mock transfection (FIG. 35, lane 1 and 5). The PCR product was purified and was directly sequenced, confirming the precise trans-splicing to the predicted splice sites of the PTM and the target pre-mRNA in stable cells (FIG. 35).
Real-time quantitative RT-PCR was used to quantify the fraction of mouse albumin pre-mRNA transcripts converted into chimeric mRNAs by PTMs. Primers for real-time qPCR were designed to discriminate between target exon 1 and trans-spliced mRNAs. Using the protocols described previously, trans-splicing efficiency of mAlbPTM97C2 and mAlbPTM158 was quantified.
Mouse albumin specific PTMs 97C2 and 158 showed a trans-splicing efficiency of 5.6% and 3.45%, respectively. These data confirmed robust trans-splicing between mouse albumin mini-gene target pre-mRNA and PTMs in stable cells.
8.5: Trans-Splicing and Production of Full-Length Protein
The PTM-mediated trans-splicing was assessed for the ability to produce the protein product of trans-splicing human apoAI into mouse albumin pre-mRNA in stable cells. Briefly, assay cells expressing the mouse albumin mini-gene pre-mRNA was transfected with mAlbPTMs (97C2 and 158), trans-spliced cDNA as a positive control, and splice mutant with a point mutation (G>T) at splice junction as a negative control. Cells were washed after 5 hrs with serum free media and incubated with advanced DMEM serum free medium. After 48 hrs, the medium was collected, concentrated and analyzed by Western blot. Production of full-length human apoAI protein was demonstrated using anti-human apoAI antibody as described above.
Accurate trans-splicing between mouse albumin exon 1 and the PTM would result in a 28 kDa albumin-human apoAI chimeric protein. Trans-splicing mediated production of full-length mature human apoAI protein is evident in cells transfected with functional PTMs (97C2 and 158) (FIG. 36, lanes 2-3) but not in controls, i.e., cells transfected with a splice mutant or in mock (FIG. 36, lanes 4-5) and it also co-migrated with the human apoAI protein produced using cDNA control plasmid (FIG. 36, lane 1-3). These studies again confirmed precise trans-splicing between the mouse albumin exon 1 and human apoAI PTMs, resulting in the production of full-length human apoAI protein in stable cells.
9. EXAMPLE
Trans-Splicing to Endogenous Mouse Albumin Pre-mRNA in Mice
The efficacy of the lead PTMs selected from the high capacity screen (HCS) were evaluated in vivo. Fifty micrograms of mAlbPTM97C2 (PTM only) or 20 μg of mouse albumin mini-gene target plus 30 .mu.g of mAlbPTM97C2 plasmids were mixed with jet-PEI-Gal (Q-Biogen) reagent and injected via the tail vein into normal C57BL/6 mice. Liver and serum samples were collected at 24 and 48 hrs time points. Total and poly A mRNA was isolated and analyzed by RT-PCR using mouse albumin exon 1 specific and human apoAI PTM specific primers.
Trans-splicing was detected in a single round in mice that received both mini-gene target plus PTM plasmids, as well as in mice that received PTM only (FIG. 37, lane 3, 8 & 9). Each positive RT-PCR product was purified and sequenced demonstrating the precise trans-splicing of mouse albumin exon 1 into human apoAI coding sequence at the predicted splice sites (FIG. 37, lower panel). These results demonstrated accurate trans-splicing between the PTM and the endogenous albumin pre-mRNA target in mice and further validated albumin targeting strategy in vivo.
FIG. 38 describes a strategy to increase apoAI expression by targeting to human albumin sequences by inclusion of a signal peptide. FIG. 39 describes various means of eliminating albumin sequences in the final trans-spliced product, i.e. to produce a trans-spliced product that is identical to the wild type human apoAI without any albumin sequence.
10. EXAMPLE
In Vitro Trans-Splicing of Human ApoAI into Mouse Albumin Pre-mRNA: Functionality of the Product
The function of the human apoAI protein produced through trans-splicing of human apoAI into mouse albumin pre-mRNA has been evaluated in vitro. This was assessed by measuring, ATP-binding cassette transporter protein (ABC1) mediated, transfer of cellular cholesterol into apoAI acceptor. The release of radio-labeled cellular cholesterol to lipid free human apoAI was quantified and the efflux values obtained with trans-spliced protein were compared with that from wild type human apoAI protein. Human embryonic kidney cells (HEK293) were transfected with mouse albumin PTM (mAlbPTM97C2) containing either: the apoAI natural 3′UTR+bovine growth hormone poly A signal (BGH pA); or WPRE 3′UTR+SV40 poly A signal (SV40 pA) along with mouse albumin mini-gene targets (FIG. 40). 48 hrs post-transfection, supernatant was collected, concentrated and assayed for cholesterol efflux. HeLa cells transfected with ABC1 plasmid and HeLa control cells were grown to near confluency. Cells were then loaded with 1 μCi/ml3H cholesterol. After equilibrating for 24 hrs, the cells were washed and incubated with media containing the trans-spliced human apoAI protein (supernatant from HEK293 cells transfected with PTM+target or cDNA control plasmid that mimics trans-splicing) or with different concentrations (2.5 μg, 5 μg, or 10 μg) of wild type purified apoAI protein as positive control. Cells were then allowed to efflux for 18 hrs. After the efflux period, medium was collected and an aliquot was then counted by liquid scintillation counting. The remaining counts in the cell fraction were determined after an over night extraction with isopropanol. The percent efflux was calculated by dividing the counts in the efflux media by the sum of the counts in the medium plus the cell fraction. DMEM/BSA medium was used as a blank and was subtracted from the radioactive counts obtained in the presence of an acceptor in the efflux media. As shown in FIG. 41, the amount of ABC1-mediated efflux observed with trans-spliced protein was significantly above the background and was similar to that of wt apoAI produced from control cDNA plasmid. The above described results indicate (a) that human apoAI protein produced through trans-splicing is functional and (b) the absence of adverse effects due to albumin sequence in the final trans-spliced mRNA on apoAI function.
Trans-splicing efficiency at the RNA level was quantified by real time RT-PCR (qRT-PCR) and the results are shown in FIG. 42. Based on qRT-PCR results it is clear that both PTMs, i.e., PTM with apoAI natural 3′UTR plus bovine growth hormone (BGH) poly A signal (new PTM) and the PTM with WPRE 3′UTR plus SV40 pA signal (old PTM), showed similar trans-splicing efficiency at the RNA level. The accuracy of trans-splicing was confirmed by direct sequencing of the RT-PCR product.
11. EXAMPLE
In Vivo Trans-Slicing of Human ApoAI into Mouse Albumin Pre-mRNA
Trans-splicing to an endogenous mouse albumin pre-mRNA target has been shown to produce human apoAI protein and HDL in mice. In particular, to verify the efficacy of the lead PTMs selected from high capacity screen (HCS) and to demonstrate trans-splicing of PTM into endogenous mouse albumin target followed by production of human apoAI protein, the following experiment has been performed. Fifty micrograms of: mAlbPTM97C2 (PTM only); 30 μg of PTM+15 μg of mini-gene target (additional target plasmid to increase pre-mRNA concentration); or 20 μg of control cDNA plasmid that mimic trans-spliced mRNA were hydrodynamically injected via the tail vein into normal C57BL/6 mice. Liver and serum samples were collected at 8, 16, 24 and 48 hrs time points. Total and polyA mRNA was isolated and analyzed by end point RT-PCR using mouse albumin exon 1 specific (ACCTTTCTCCTCCTCCTCTTCGT) (SEQ ID NO. 18) and human apoAI PTM specific primers (ACATAGTCTCTGCCGCTGTCTTT) (SEQ ID NO. 19). As shown in FIG. 43A the presence of trans-spliced chimeric mRNA was detected in 11 out of 14 mice that were injected with cDNA control plasmid, indicating good delivery of the plasmid DNA. Next, PTM trans-splicing to endogenous mouse albumin pre-mRNA target was evaluated using the target and PTM specific primers as described above. Trans-splicing between mouse albumin target pre-mRNA and PTM was readily detected in a single round of PCR with 1 μg of total RNA and 25 cycles of amplification. All samples from mice that received both the mini-gene target and the PTM plasmids were positive for trans-splicing (FIG. 43B). In comparison, 10 out of 13 mice were positive for trans-splicing that received the PTM only (FIG. 43C). Each positive RT-PCR product was purified and sequenced demonstrating precise trans-splicing of human apoAI coding sequence into mouse albumin exon 1 at the predicted splice sites. These results demonstrate accurate trans-splicing between the PTM and the endogenous albumin pre-mRNA target in mice and further validate albumin targeting strategy for the production of therapeutic proteins in vivo.
In addition, accurate trans-splicing to the endogenous mouse albumin pre-mRNA target to produce human apoAI protein in mice was demonstrated. Serum samples were collected from mice injected with PTM only, PTM+target and cDNA for the production of human apoAI protein were tested by Western blot. Approximately, 20-50 μl serum was passed through ProteoPrepTM Blue affinity column (Sigma-Aldrich, Product Code PROT BA). This step was introduced to eliminate albumin and IgGs which make up greater than 70% of the proteins in serum and to increase sample loads to better visualize lower abundant proteins. Samples separated by 12% SDS-PAGE were transferred to nitrocellulose membranes and probed with a human specific apoAI monoclonal antibody (Biodesign International, Cat #H45625M). Proteins were visualized by a chemiluminescence kit (Invitrogen, Cat#WB7103). Western blot results indicated the appearance of human apoAI protein as early as 16 hrs post-injection in mice injected with cDNA control plasmids. In this group, 7 out of 14 samples were positive for human apoAI protein. (FIG. 44A). In mice that received both target and PTM, 5 out of 6 samples were positive for human apoAI protein. In mice that received the PTM only (targeting endogenous target), 4 out of 10 samples were positive for human apoAI protein. These results demonstrate the accurate trans-splicing of human apoAI sequence into endogenous mouse albumin exon 1 leading to the production of human apoAI protein (FIG. 44B).
12. EXAMPLE
In Vivo Trans-Splicing of Minicircle Vector DNA for Expression of Human ApoAI Protein
Minicircles are DNA vectors that lack the bacterial DNA sequence that is implicated in the silencing of gene expression in vivo. See, for example, Chen Z Y, He C Y, Ehrhardt A, Kay M A. (2003) DNA vectors devoid of bacterial DNA result in persistent and high-level transgene expression in vivo. Mol. Ther. 8:495-500; Chen Z Y, He C Y, Meuse L, Kay M A. (2004) Silencing of episomal transgene expression by plasmid bacterial DNA elements in vivo. Gene Ther. 11:856-864 the disclosures of which are hereby incorporated by reference.
Minicircles were tested by cloning the mAlbPTM97C2 expression cassette into minicircle vector. Fifty to seventy five micrograms of mAlbPTM97C2 (functional PTM), mAlbPTM97C2-splice mutant (defective PTM) or control cDNA (mimics trans-spliced mRNA) in the form of minicircles were hydrodynamically injected via tail vein into normal C57BL/6 mice. Liver and serum samples were collected at 48 hrs through 4 week time points. RNA analysis by qRT-PCR using mouse albumin exon 1 specific forward primer and human apoAI specific reverse primer confirmed the trans-splicing of mouse albumin PTM into endogenous mouse albumin pre-mRNA target. As shown in Table 1, the results obtained with a splice mutant PTM were similar to background observed in the mock group. The presence of trans-spliced mRNA was readily detected at 4 week post-injection indicating minicircles can be used as a non-viral PTM delivery system.







TABLE 1







Tram-splicing in mice - qRT-PCR Results












Group
Mouse ID
Weight
Injection remarks
time
nor-TS
















A. Mock
4
21.9
ok
48
h
1.18E+00


B. SM, 50 ug
6
19.2
1.8 ml
48
h
1.48E+00



9
18.6
1.7 ml


2.07E+00



10
19.6
1.7 ml


5.70E+00


B. SM, 50 ug
1
19.4
1.8 ml, slow recovery
4
wk
1.48



2
18.5
1.8 ml, B


2.07



7
18.3
1.8 ml


5.70


C. PTM, 75 ug
11
22.1
1.8 ml, B
48
h
1.89E+00



12
19.7
1.7 ml, Brett tried, Jun completed


9.42E+01



13
21.8
1.8 ml, B



15
16.9
1.6 ml


1.35E+03



16
20.2
1.8 ml


1.29E+02


C. PTM, 75 ug
17
18.3
  1 ml
1
wk
2.18



18
18.5
1.8 ml, B


1.09



19
18.6
1.6 ml


31.50



20
20.1
1.7 ml


188.71



25
20.9
1.8 ml


44.55


C. PTM, 75 ug
21
18.9
1.7 ml
2
wk
47.84



22
17.4
1.6 ml


64.03



23
19.9
1.7 ml



24
20.1
1.7 ml, B several attemps


1.40



28
18.6
1.7 ml, B


C. PTM, 75 ug
26
18.2
1.7 ml, B
4
wk
0.19



27
19.6
1.7 ml


25.92



29
21.3
1.8 ml, B


1.33



30
16.5
1.5 ml


3.93



35
19.4
1.7 ml


7.225


D. mAIb-bAI cDNA, 50 ug
42
18.9
1.7 ml
48
h
1.53E+05



43
18.4
1.7 ml, B


1.25E+05



44
15.4
1.5 ml


8.56E+05



46
20.2
1.8 ml, B
4
wk
9.2E+03



47
22.2
1.8 ml, B 3 hrs later


4.6E+03



48
18.1
1.7 ml


9.8E+01









Western blot analysis of serum samples from mice injected with minicircles encoding the PTM confirmed the production of human apoAI protein through trans-splicing. Ten to fifty micro liter serum samples were immunoprecipitated using human specific apoAI antibody. After elution, samples were concentrated, analyzed on a 12% SDS-PAGE and probed with the same antibody (human specific apoAI antibody) that was used for immunoprecipitation. The blot was developed using an ECL kit (Invitrogen, Cat #WB7104). Western results clearly showed the presence of a 28 kDa protein band that co-migrated with the positive control purified apoAI protein (FIG. 45A). The presence of human apoAI protein was also detected in 4 week serum samples (FIG. 45B). These results not only confirmed the production of human apoAI protein through trans-splicing of PTM into endogenous mouse albumin pre-mRNA target in mice, but also demonstrated the utility of minicircles as a non-viral PTM delivery system.
13. EXAMPLE
In Vivo Trans-Splicing of Human ApoAI PTM into Mouse Albumin Pre-mRNA Increases High-Density Lipoprotein (HDL)
One of the main objectives of the current study is to determine whether production of human apoAI protein through trans-splicing contributes to HDL increase in vivo. To test this, mice were injected with mouse albumin PTM (PTM only) and control cDNA plasmid (mimics trans-spliced mRNA), as described above. Serum samples were collected at different time points (48 hrs through 4 weeks) and total HDL-cholesterol was determined by dextran sulfate precipitation method and the results were compared with controls. Specifically, 12 μl of serum was mixed with 4 μl dextran sulfate precipitation reagent plus 30 μl saline and, after 10 min at room temperature, was centrifuged for 30 min (4° C.) at 12,000 rpm. The clear supernatant (40 μl) was mixed with 169 μl saline and total cholesterol was measured using FPLC. The baseline total HDL-cholesterol in the control group averaged to about 60 mg/dL. At 48 hrs time point,  ̃25% increase in total HDL-cholesterol was observed in the control cDNA group that expresses an mRNA that is identical to trans-spliced mRNA. In contrast, no significant increase was observed in the PTM group at 48 hrs. However, as shown in FIG. 46, significant increases (25-50%) in total HDL-cholesterol was observed in serum samples collected at 1, 2 and 4 week time points in mice treated with PTM only and also mice treated with cDNA. Accordingly, the results presented in this application clearly show: (a) successful and accurate trans-splicing of mouse albumin PTM into mouse albumin target pre-mRNA, (b) production of human apoAI protein through trans-splicing and, most importantly, (c) production of human apoAI protein through trans-splicing in mice leads to significant (25-50%) increase in HDL level over the baseline. Increases in HDL blood levels are associated with reduced risk of cardiovascular disease. Numerous reports have indicated that “increasing the HDL cholesterol level by 1 mg may reduce cardiovascular risk by 2-3 percent (Castelli W P. Cholesterol and lipids in the risk of coronary artery disease—the Framingham Study. Can J Cardiol 1988; 4 [Suppl A]:5-10A; Third Report of the National Cholesterol Education Program [NCEP] Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults [Adult Treatment Panel III]. Final Report. Bethesda [Md.]: National Cholesterol Education Program, National Heart, Lung, and Blood Institute, National Institutes of Health; September 2002. NIH Publication 02-5215. Brewer B H, 2004, Am Heart J, 148, S14-S18; Brewer B H, 2004, N Engl J Med, 350, 1491-1494)
The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and accompanying Figures. Such modifications are intended to fall within the scope of the appended claims. Various references are cited herein, the disclosure of which are incorporated by reference in their entireties.
Sequence CWU 1
57 1 8 RNA Artificial Chemically Synthesized 1 agguragu 8 2 7 RNA Artificial Chemically Synthesized 2 ynyurac 7 3 258 DNA Artificial Chemically Synthesized 3 gtagttcttt tgttcttcac tattaagaac ttaatttggt gtccatgtct cttttttttt 60 ctagtttgta gtgctggaag gtatttttgg agaaattctt acatgagcat taggagaatg 120 tatgggtgta gtgtcttgta taatagaaat tgttccactg ataatttact ctagtttttt 180 atttcctcat attattttca gtggcttttt cttccacatc tttatatttt gcaccacatt 240 caacactgta gcggccgc 258 4 270 DNA Artificial Chemically Synthesized 4 ccaactatct gaatcatgtg ccccttctct gtgaacctct atcataatac ttgtcacact 60 gtattgtaat tgtctctttt actttccctt gtatcttttg tgcatagcag agtacctgaa 120 acaggaagta ttttaaatat tttgaatcaa atgagttaat agaatcttta caaataagaa 180 tatacacttc tgcttaggat gataattgga ggcaagtgaa tcctgagcgt gatttgataa 240 tgacctaata atgatgggtt ttatttccag 270 5 23 DNA Artificial Chemically Synthesized 5 taatacgact cactataggg aga 23 6 23 DNA Artificial Chemically Synthesized 6 atttaggtga cactatagaa gng 23 7 23 DNA Artificial Chemically Synthesized 7 aattaaccct cactaaaggg aga 23 8 81 DNA Artificial Chemically Synthesized 8 atgaagtggg taacctttct cctcctcctc ttcgtctccg gctctgcttt ttccaggggt 60 gtgtttcgcc gagaagcacc c 81 9 82 DNA Artificial Chemically Synthesized 9 gggtgcttct cggcgaaaca cacccctgga aaaagcagag ccggagacga agaggaggag 60 gagaaaggtt acccacttca tg 82 10 81 DNA Artificial Chemically Synthesized 10 atgaagtggg taacctttat ttcccttctt tttctcttta gctcggctta ttccaggggt 60 gtgtttcgtc gagatgcacc c 81 11 82 DNA Artificial Chemically Synthesized 11 gggtgcatct cgacgaaaca cacccctgga ataagccgag ctaaagagaa aaagaaggga 60 aataaaggtt acccacttca tg 82 12 24 DNA Artificial Chemically Synthesized 12 ccccagagcc cctgggatcg agtg 24 13 42 DNA Artificial Chemically Synthesized 13 ctagaagctt cccactttgg aaacgtttat tctgagcacc gg 42 14 32 DNA Artificial Chemically Synthesized 14 ctagggatcc gttttatgtt ttttcatctc tg 32 15 35 DNA Artificial Chemically Synthesized 15 ctaggcggcc gcaggccttt gaaatgttgt tctcc 35 16 34 DNA Artificial Chemically Synthesized 16 ctaggctagc acctttccta tcaaccccac tagc 34 17 35 DNA Artificial Chemically Synthesized 17 ctaggcggcc gcaggccttt gaaatgttgt tctcc 35 18 23 DNA Artificial Chemically Synthesized 18 acctttctcc tcctcctctt cgt 23 19 23 DNA Artificial Chemically Synthesized 19 acatagtctc tgccgctgtc ttt 23 20 897 DNA Artificial Chemically Synthesized 20 agagactgcg agaaggaggt cccccacggc ccttcaggat gaaagctgcg gtgctgacct 60 tggccgtgct cttcctgacg gggagccagg ctcggcattt ctggcagcaa gatgaacccc 120 cccagagccc ctgggatcga gtgaaggacc tggccactgt gtacgtggat gtgctcaaag 180 acagcggcag agactatgtg tcccagtttg aaggctccgc cttgggaaaa cagctaaacc 240 taaagctcct tgacaactgg gacagcgtga cctccacctt cagcaagctg cgcgaacagc 300 tcggccctgt gacccaggag ttctgggata acctggaaaa ggagacagag ggcctgaggc 360 aggagatgag caaggatctg gaggaggtga aggccaaggt gcagccctac ctggacgact 420 tccagaagaa gtggcaggag gagatggagc tctaccgcca gaaggtggag ccgctgcgcg 480 cagagctcca agagggcgcg cgccagaagc tgcacgagct gcaagagaag ctgagcccac 540 tgggcgagga gatgcgcgac cgcgcgcgcg cccatgtgga cgcgctgcgc acgcatctgg 600 ccccctacag cgacgagctg cgccagcgct tggccgcgcg ccttgaggct ctcaaggaga 660 acggcggcgc cagactggcc gagtaccacg ccaaggccac cgagcatctg agcacgctca 720 gcgagaaggc caagcccgcg ctcgaggacc tccgccaagg cctgctgccc gtgctggaga 780 gcttcaaggt cagcttcctg agcgctctcg aggagtacac taagaagctc aacacccagt 840 gaggcgcccg ccgccgcccc ccttcccggt gctcagaata aacgtttcca aagtggg 897 21 38 DNA Artificial Chemically Synthesized 21 ctaggctagc agagactgcg agaaggaggt cccccacg 38 22 6 DNA Artificial Chemically Synthesized 22 gctagc 6 23 6 DNA Artificial Chemically Synthesized 23 aagctt 6 24 42 DNA Artificial Chemically Synthesized 24 ctagaagctt cccactttgg aaacgtttat tctgagcacc gg 42 25 15 DNA Artificial Chemically Synthesized 25 gagatgcgcg accgc 15 26 59 DNA Artificial Chemically Synthesized 26 ctagcacgag ctgcaagaga agctgagccc actgggcgag gagatgtgcg accgcgcgc 59 27 15 DNA Artificial Chemically Synthesized 27 gagatgtgcg accgc 15 28 6 DNA Artificial Chemically Synthesized 28 gctagc 6 29 6 DNA Artificial Chemically Synthesized 29 ccgcgg 6 30 47 DNA Artificial Chemically Synthesized 30 tactaactca attttttttt tttttttttt aattaacagc ccctaaa 47 31 9 DNA Artificial Chemically Synthesized 31 ccggtgagt 9 32 6 DNA Artificial Chemically Synthesized 32 cagaag 6 33 9 DNA Artificial Chemically Synthesized 33 caagtaagg 9 34 6 DNA Artificial Chemically Synthesized 34 tagaag 6 35 9 DNA Artificial Chemically Synthesized 35 aaggtatgg 9 36 6 DNA Artificial Chemically Synthesized 36 gctagc 6 37 6 DNA Artificial Chemically Synthesized 37 ccgcgg 6 38 47 DNA Artificial Chemically Synthesized 38 tactaactca attttttttt tttttttttt aattaacagc ccctaaa 47 39 54 DNA Artificial Chemically Synthesized 39 atgaaagctg cggtgctgac cttggccgtg ctcttcctga cggggagcca ggct 54 40 18 DNA Artificial Chemically Synthesized 40 cggcatttct ggcagcaa 18 41 66 DNA Artificial Chemically Synthesized 41 gatgaacccc cccagagccc ctgggatcga gtgaaggacc tggccactgt gtacgtggat 60 gtgctc 66 42 22 DNA Artificial Chemically Synthesized 42 ccgagaagca cccccccaga gc 22 43 859 DNA Artificial Chemically Synthesized 43 atgaagtggg taacctttat ttcccttctt tttctcttta gctcggctta ttccaggggt 60 gtgtttcgtc gagatgcacc cccccagagc ccctgggatc gagtgaagga cctggccact 120 gtgtacgtgg atgtgctcaa agacagcggc agagactatg tgtcccagtt tgaaggctcc 180 gccttgggaa aacagctaaa cctaaagctc cttgacaact gggacagcgt gacctccacc 240 ttcagcaagc tgcgcgaaca gctcggccct gtgacccagg agttctggga taacctggaa 300 aaggagacag agggcctgag gcaggagatg agcaaggatc tggaggaggt gaaggccaag 360 gtgcagccct acctggacga cttccagaag aagtggcagg aggagatgga gctctaccgc 420 cagaaggtgg agccgctgcg cgcagagctc caagagggcg cgcgccagaa gctgcacgag 480 ctgcaagaga agctgagccc actgggcgag gagatgcgcg accgcgcgcg cgcccatgtg 540 gacgcgctgc gcacgcatct ggccccctac agcgacgagc tgcgccagcg cttggccgcg 600 cgccttgagg ctctcaagga gaacggcggc gccagactgg ccgagtacca cgccaaggcc 660 accgagcatc tgagcacgct cagcgagaag gccaagcccg cgctcgagga cctccgccaa 720 ggcctgctgc ccgtgctgga gagcttcaag gtcagcttcc tgagcgctct cgaggagtac 780 actaagaagc tcaacaccca gtgaggcgcc cgccgccgcc ccccttcccg gtgctcagaa 840 taaacgtttc caaagtggg 859 44 66 DNA Artificial Chemically Synthesized 44 ggaaacagac aagagtgagg ttgctcatcg gtttaaagat ttgggagaag aaaatttcaa 60 agcctt 66 45 209 DNA Artificial Chemically Synthesized 45 atggctcagt caaagcacgg tctaacaaaa gaaatgacaa tgaaataccg tatggaaggg 60 tgcgtcgatg gacataaatt tgtgatcacg ggagagggca ttggatatcc gttcaaaggg 120 aaacaggcta ttaatctgtg tgtggtcgaa ggtggaccat tgccatttgc cgaagacata 180 ttgtcagctg cctttatgta cggaaacag 209 46 700 DNA Artificial Chemically Synthesized 46 gtaagaaatc catttttcta ttgttcaact tttattctat tttcccagta aaataaagtt 60 ttagtaaact ctgcatcttt aaagaattat tttggcattt atttctaaaa tggcatagta 120 ttttgtattt gtgaagtctt acaaggttat cttattaata aaattcaaac atcctaggta 180 aaaaaaaaaa aaggtcagaa ttgtttagtg actgtaattt tcttttgcgc actaaggaaa 240 gtgcaaagta acttagagtg actgaaactt cacagaatag ggttgaagat tgaattcata 300 actatcccaa agacctatcc attgcactat gctttattta aaaaccacaa aacctgtgct 360 gttgatctca taaatagaac ttgtatttat atttattttc attttagtct gtcttcttgg 420 ttgctgttga tagacactaa aagagtatta gatattatct aagtttgaat ataaggctat 480 aaatatttaa taatttttaa aatagtattc ttggtaattg aattattctt ctgtttaaag 540 gcagaagaaa taattgaaca tcatcctgag tttttctgta ggaatcagag cccaatattt 600 tgaaacaaat gcataatcta agtcaaatgg aaagaaatat aaaaagtaac attattactt 660 cttgttttct tcagtattta acaatccttt tttttcttcc 700 47 67 DNA Artificial Chemically Synthesized 47 cttgcccaga caagagtgag gttgctcatc ggtttaaaga tttgggagaa gaaaatttca 60 aagcctt 67 48 79 DNA Artificial Chemically Synthesized 48 atgaagtggg taacctttct cctcctcctc ttcgtctccg gctctgcttt ttccaggggt 60 gtgtttcgcc gagaagcac 79 49 6 DNA Artificial Chemically Synthesized 49 gctagc 6 50 43 DNA Artificial Chemically Synthesized 50 ccgcggacga tctcatattc tatcgtcgaa tactaactca att 43 51 39 DNA Artificial Chemically Synthesized 51 tttttttttt ttttttaatt aacagccccc cagagcccc 39 52 52 DNA Artificial Chemically Synthesized 52 gggtgtgttt cgccgagaag caccccccca gagcccctgg gatcgagtga ag 52 53 54 DNA Artificial Chemically Synthesized 53 aggggtgtgt ttcgccgaga agcacccccc cagagcccct gggatcgagt gaag 54 54 64 DNA Artificial Chemically Synthesized 54 nnnnnnnttt tttccagggg tgtgtttcgc cgagaagcac ccccccagag cccctgggat 60 cgag 64 55 79 DNA Artificial Chemically Synthesized 55 atgaagtggg taacctttat ttcccttctt tttctcttta gctcggctta ttccaggggt 60 gtgtttcgtc gagatgcac 79 56 42 DNA Artificial Chemically Synthesized 56 cggcatttct ggcagcaaga tgaacccccc cagagcccct gg 42 57 81 DNA Artificial Chemically Synthesized 57 atgaaagctg cggtgctgac cttggccgtg ctcttcctga cggggagcca ggctcggcat 60 ttctggcagc aagatgaacc c 81.

## Claims

1. A method for expressing an apoAI polypeptide in a subject comprising administering to said subject a pre-trans-splicing molecule comprising:
(a) one or more target binding domains that target binding of the pre-trans-splicing molecule to human albumin pre-mRNAs expressed within a cell;
(b) a 3′ splice region comprising a branch point and a 3′ splice acceptor site;
(c) a spacer region that separates the 3′ splice region from the target binding domain;
(d) a safety nucleotide sequence comprising one or more complementary sequences that bind to one or more sides of the 5′ splice region; and
(e) a nucleotide sequence to be trans-spliced to the target pre-mRNA wherein said nucleotide sequence encodes an apoAI;
wherein said pre-trans-splicing molecule is recognized by nuclear splicing components within the cell.

2. A method for expressing an apoAI polypeptide in a subject comprising administering to said subject a pre-trans-splicing molecule comprising:
(a) one or more target binding domains that target binding of the pre-trans-splicing molecule to human albumin pre-mRNAs expressed within a cell;
(b) a 5′ splice site;
(c) a spacer region that separates the 5′ splice site from the target binding domain;
(d) a safety nucleotide sequence comprising one or more complementary sequences that bind to one or more sides of the 3′ splice region; and
(e) a nucleotide sequence to be trans-spliced to the target pre-mRNA wherein said nucleotide sequence encodes an apoAI polypeptide;
wherein said pre-trans-splicing molecule is recognized by nuclear splicing components within the cell.

3. The method of claim 1 or 2 wherein the target pre-mRNA expressed within the cell is a human apoAI target.

4. The method of claim 1 or 2 wherein the target pre-mRNA expressed within the cell is a human apoB target.

5. The method of claim 1 or 2 wherein the apoAI polypeptide is a pre-pro-apoAI.

6. The method of claim 1 or 2 wherein the apoAI polypeptide is an apoAI analogue.

7. The method of claim 1 or 2 wherein the target pre-mRNA expressed within the cell is highly expressed and encodes efficiently secreted proteins.

8. The method of claim 1 or 2 wherein the target pre-mRNA is expressed within a liver cell.

9. The method of claim 8 wherein the liver cell is a hepatocyte.