Patent Publication Number: US-7595294-B2

Title: Vasoactive intestinal polypeptide pharmaceuticals

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 11/245,499 filed Oct. 7, 2005, which claims benefit of provisional application 60/617,500 filed Oct. 8, 2004. This application is a continuation-in-part of International Application No. PCT/US2005/036235 filed Oct. 7, 2005. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to polypeptide analogs and their synthesis and uses. More particularly, the invention relates to synthetic polypeptide analogs related to vasoactive intestinal polypeptide, and pharmaceutical compositions thereof. 
     BACKGROUND 
     When food is present in the alimentary canal, cells in the gut secrete a hormonal signal (an “incretin”), which sensitizes the pancreas to the presence of glucose and results in a potentiated glucose-dependent insulin secretory response. Such a synergistic response to provide glucose-dependent insulin release (Kieffer T J and Habener, J R (1999) Endocr. Rev. 20, 876-913) is seen for the incretin signals, Glucagon-like Peptide 1 (GLP1) and Glucose-dependent Insulinotropic Peptide (GIP). These incretin signals typically exhibit short duration of action in the body, with GLP1 exhibiting at ½ of approximately 1-2 minutes (Knudsen, L B 2004, J. Med. Chem. 47, 4128-34). GLP1 and GIP are cleaved by an amino peptidase, dipeptidyl peptidase IV (DPPIV) and thus, the naturally occurring native hormone is not generally used in medicinal formulations. A peptide found in the saliva of the Gila Monster (exendin 4, Exenatide, Byetta; Amylin Pharmaceuticals, San Diego, Calif.) was shown to bind to the GLP1 receptor and exhibit potent agonistic activity, thereby imparting a desirable glucose-dependent insulin secretory response (Nielsen L L, Young, A A, Parkes, D G (2004) Regul. Peptides, 117, 77-88). Exenatide and analogs of GLP1 have been administered to patients in need of treatment for type 2 diabetes. 
     Pituitary Adenylate Cyclase-Activating Peptide (PACAP) is a neuromodulatory peptide which stimulates PAC1, VPAC1, and VPAC2 receptors, and is emitted from nerve endings in the pancreas. Receptors of this general class reside in multiple tissues in the body, including in the pancreas (Vaudry D, et al. (2000). Pharmacol Rev 52: 269-324). Administration (infusion) of PACAP to human volunteers or to rodents causes potentiated glucose-dependent insulin secretion, but also results in hyperglycemia (Filipsson K, Tornoe K, Holst J and Ahren B (1997). J Clin Endocrinol Metab 82: 3093-8). In contrast, Vasoactive Intestinal Polypeptide (VIP) activates only the VPAC1 and VPAC2 receptors. In the pancreas, stimulation of the VPAC2 receptors has been shown to provide a potentiated, glucose-dependent insulin release in response to elevated blood glucose levels similar to that of GLP1 or exenatide (Tsutsumi, M., et al. (2002) Diabetes 51, 1453-60). Thus such a stimulus (from PACAP or VPAC agonistic analogs) could be synergistic or alternative to incretin-like signals in stimulating glucose-dependent insulin release, since a similar profile of potentiated insulin secretion results from activation of a second class of receptor. Such an effect would be beneficial in the treatment of metabolic disorders, including Type 2 Diabetes Mellitus (T2DM), metabolic acidosis, insulin resistance and obesity. However, the lack of blood glucose lowering by PACAP in vivo is thought to be related to its ability to cause gluconeogenesis in the liver and release of glucagon. These activities, as well as several side effects, are believed to be caused by activation of PAC1 and VPAC1 receptors. In addition, the naturally occurring native sequence of PACAP and its analogs also are typically short-lived in the body. 
     Although the reptile GLP1 like molecules (exendin-4, heliodermin, heliospectrin) are longer acting than the mammalian incretins, synthetic exendin-4 (Byetta) remains a relatively short acting peptide (t½ 2 hr in man) and there is a medical need for longer-acting peptides that can modulate glucose-dependent insulin secretion. 
     SUMMARY OF THE INVENTION 
     The invention provides synthetic polypeptide analogs of PACAP and Vasoactive Intestinal Polypeptide (VIP), and salts thereof, in which the C-terminus comprises amino acid residues that form an amphipathic α-helix, said residues selected from hydrophilic amino acids (Haa) and lipophilic amino acids (Laa) ordered in the sequence:
 
Haa(Laa Laa Haa Haa) n Laa.
 
     wherein n−1-5. In an embodiment, n=1 or 2. 
     Modifications introduced in the present polypeptide analogs of PACAP and VIP facilitate increased duration of action of therapeutics which activates the PACAP and VIP family of receptors, preferably the VPAC2 receptor. Without being bound to any particular theory, it is believed that an increase in duration of action may be due to the ability of the amphipathic helix in the C-terminal region to interact with the phospholipids of the cell membranes in the body and thereby have a “depoting” effect. Thus, the present peptide analogs are bound to cell membranes and then slowly re-released to the plasma to impart its effect distally. In contrast, if a peptide such as PACAP, VIP or GLP1 is free in the plasma it is rapidly acted upon by proteases or cleared by glomerular filtration (Nestor J J Jr. Improved Duration of Action of Peptide Drugs. In  Peptide - based Drug Design : Taylor M D, Amidon G L, Eds.; American Chemical Society Washington D.C., 1995: 449-471). 
     Therefore, one aspect of the invention provides analogs to PACAP, VIP, and the physiologically active truncated analogs and homologs of same, or salts thereof, in which the C-terminus comprises amino acid residues that form an amphipathic α-helix, the sequence of said residues selected from the native amino acids or selected unnatural amino acids having the ability to stabilize said α-helix. 
     Also provided are pharmaceutical compositions for the delivery of an effective glucose-dependant insulin releasing amount of a polypeptide analog of PACAP, VIP, and the physiologically active truncated analogs and homologs of same, or a salt thereof, in which the C-terminus comprises amino acid residues that form an amphipathic α-helix, said residues selected from hydrophilic amino acids (Haa) and lipophilic amino acids (Laa) ordered in the sequence:
 
Haa(Laa Laa Haa Haa) n Laa;
 
     wherein n=1-5. 
     The invention further provides methods for treating mammalian conditions characterized by high blood glucose, which methods comprise administering to a mammal in need thereof an effective glucose-dependant insulin releasing amount of a polypeptide analog of PACAP, VIP, and the physiologically active truncated analogs and homologs of same, or a salt thereof, in which the C-terminus comprises amino acid that form an amphipathic α-helix, said residues selected from hydrophilic amino acids (Haa) and lipophilic amino acids (Laa) ordered in the following sequence:
 
Haa(Laa Laa Haa Haa) n Laa;
 
     wherein n=1-5. 
     The invention further provides methods for treating mammalian conditions affected by VPAC receptor activation, which methods comprise administering to a mammal in need thereof an effective glucose-dependant insulin releasing amount of a polypeptide analog of PACAP, VIP, and the physiologically active truncated analogs and homologs of same, or a salt thereof, in which the C-terminus comprises amino acid that form an amphipathic α-helix, said residues selected from hydrophilic amino acids (Haa) and lipophilic amino acids (Laa) ordered in the following sequence:
 
Haa(Laa Laa Haa Haa) n Laa;
 
     wherein n=1-5. 
     The invention also includes processes for the solid phase synthesis of polypeptide analogs of PACAP, VIP, and the physiologically active truncated analogs and homologs of same, or a salt thereof, in which the C-terminus comprises amino acid residues that form an amphipathic α-helix, said residues selected from hydrophilic amino acids (Haa), and lipophilic amino acids (Laa) ordered in the following sequence:
 
Haa(Laa Laa Haa Haa) n Laa;
 
     wherein n=1-5. 
     Processes presented herein for preparing polypeptide analogs comprise sequentially coupling protected amino acids on a suitable resin support, removing the side chain and Nα-protecting groups, and cleaving the polypeptide from the resin. 
     The invention also provides DNA sequences, vectors, and plasmids for the recombinant synthesis of polypeptide analogs of PACAP, VIP, and the physiologically active truncated analogs and homologs of same, or a salt thereof, in which the C-terminus comprises amino acid residues that form an amphipathic α-helix, said residues selected from hydrophilic amino acids (Haa) and lipophilic amino acids (Laa) ordered in the sequence:
 
Haa(Laa Laa Haa Haa) n Laa;
 
     wherein n=1-5. 
     In addition, the invention provides pharmaceutical compositions and methods for the prevention and treatment of a variety of metabolic disorders, including diabetes, insulin resistance, hyperglycemia, metabolic acidosis and obesity, which are manifested by elevated blood glucose levels, comprising an effective amount of the polypeptide(s) of the invention, or salt thereof, and a pharmaceutically acceptable carrier. In other aspects of the invention, therapeutically effective amounts of metabolic disorder compounds, including insulin, insulin analogs, incretin, incretin analogs, glucagon-like peptide, glucagon-like peptide analogs, glucose dependent insulinotropic peptide analogs, exendin, exendin analogs, sulfonylureas, biguanides, α-glucosidase inhibitors, thiazolidinediones, peroxisome proliferator activated receptor (PPAR) agonists, PPAR antagonists and PPAR partial agonists may be administered in combination with the polypeptides of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A ,  1 B,  1 C,  1 D, and  1 E are lists of exemplary polypeptide analogs according to the invention. Standard nomenclature using single letter abbreviations for amino acids are used. The letter “X” refers to a polyethylene glycol chain having C 10 -C 3000  chain. Preferred polyethylene chains may be linear or branched and will have a molecular weight above 20 kiloDalton. The term “acyl” refers to a C 2 -C 30  acyl chain. This chain may comprise a linear aliphatic chain, a branched aliphatic chain, an aralkyl chain, or an aryl chain containing an acyl moiety. The letter “Z” refers to lysine having a long acyl chain at the epsilon position. The term “hex” refers to hexanoyl. The term “pen” refers to pentanoyl. The terms “lau” refers to lauroyl. The term “myr” refers to myristoyl. The term “ste” refers to stearoyl. The term “pr” refers to propionyl. Arachidoyl refers to a linear C20 fatty acid substituent. 
         FIG. 2  lists other polypeptide and polypeptide analogs. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Abbreviations and Definitions 
     The one- and three-letter abbreviations for the various common nucleotide bases and amino acids are as recommended in Pure Appl. Chem. 31, 639-645 (1972) and 40, 277-290 (1974) and comply with 37 CFR .sctn.1.822 (55 FR 18245, May 1, 1990). The abbreviations represent L-amino acids unless otherwise designated as D- or DL. Certain amino acids, both natural and non-natural, are achiral, e.g., glycine. All peptide sequences are presented with the N-terminal amino acid on the left and the C-terminal amino acid on the right. 
     “Hydrophilic amino acid (Haa)” refers to an amino acid having at least one hydrophilic functional group in addition to those required for peptide bond formation, such as arginine, asparagine, aspartic acid, glutamic acid, glutamine, histidine, lysine, serine, threonine, and their homologs. 
     “Lipophilic amino acid (Laa)” refers to an uncharged, aliphatic or aromatic amino acid, such as isoleucine, leucine, methionine, phenylalanine, tryptophan, tyrosine, valine, and their homologs. 
     In the invention, alanine is classified as “amphiphilic” i.e., capable of acting as either hydrophilic or lipophilic. 
     “Homolog of PACAP or VIP” refers to a polypeptide comprising amino acids in a sequence that is substantially similar to the native sequence of PACAP or VIP, such as at least 50, 60, 70, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% amino acid sequence identity. Homologs presented herein may comprise amino acid substitutions, deletions, and/or insertions relative to the native sequence of PACAP or VIP. Exemplary homologs comprise a span of at least 5, 10, 15, 20, 25, 30, or 35 contiguous amino acids that is identical or substantially similar to the native sequence of PACAP or VIP. 
     “Analogs of PACAP or VIP” refers to a polypeptide comprising: (i) PACAP, VIP, and/or homologs of PACAP or VIP; and (ii) at least one functionality not present in naturally occurring native PACAP and/or VIP. For example, analogs can optionally comprise a functionality within the sidechain of an amino acid or at the amino or carboxyl terminal of the polypeptide. Exemplary functionalities include alkyl-, aryl-, acyl-, keto-, azido-, hydroxyl-, hydrazine, cyano-, halo-, hydrazide, alkenyl, alkynyl, ether, thiol, seleno-, sulfonyl-, borate, boronate, phospho, phosphono, phosphine, heterocyclic, enone, imine, aldehyde, ester, thioacid, hydroxylamine, amino group, or the like or any combination thereof. Other exemplary functionalities that can be introduced include, but are not limited to, amino acids comprising a photoactivatable cross-linker, spin-labeled amino acids, fluorescent amino acids, metal binding amino acids, metal-containing amino acids, radioactive amino acids, amino acids with novel functional groups, amino acids that covalently or noncovalently interact with other molecules, photocaged and/or photoisomerizable amino acids, amino acids comprising biotin or a biotin analogue, glycosylated amino acids such as a sugar substituted serine, other carbohydrate modified amino acids, keto containing amino acids, amino acids comprising polyethylene glycol or polyether, heavy atom substituted amino acids, chemically cleavable and/or photocleavable amino acids, amino acids with an elongated side chains as compared to natural amino acids, e.g., polyethers or long chain hydrocarbons, e.g., greater than about 5 or greater than about 10 carbons, carbon-linked sugar-containing amino acids, redox-active amino acids, amino thioacid containing amino acids, and amino acids comprising one or more toxic moiety. 
     Analogs presented herein may comprise non-natural amino acids based on natural amino acids, such as tyrosine analogs include para-substituted tyrosines, ortho-substituted tyrosines, and meta substituted tyrosines, wherein the substituted tyrosine comprises an acetyl group, a benzoyl group, an amino group, a hydrazine, an hydroxyamine, a thiol group, a carboxy group, an isopropyl group, a methyl group, a C 6 -C 20  straight chain or branched hydrocarbon, a saturated or unsaturated hydrocarbon, an O-methyl group, a polyether group, a nitro group, or the like. Glutamine analogs include, but are not limited to, α-hydroxy derivatives, β-substituted derivatives, cyclic derivatives, and amide substituted glutamine derivatives. Examples of phenylalanine analogs include, but are not limited to, meta-substituted phenylalanines, wherein the substituent comprises a hydroxy group, a methoxy group, a methyl group, an allyl group, an acetyl group, or the like. Specific examples include, but are not limited to, O-methyl-L-tyrosine, an L-3-(2-naphthyl)alanine, a 3-methyl-phenylalanine, an O-4-allyl-L-tyrosine, a 4-propyl-L-tyrosine, a tri-O-acetyl-GlcNAc.beta.-serine, an L-Dopa, a fluorinated phenylalanine, an isopropyl-L-phenylalanine, a p-azido-L-phenylalanine, a p-acyl-L-phenylalanine, a p-benzoyl-L-phenylalanine, an L-phosphoserine, a phosphonoserine, a phosphonotyrosine, a p-iodo-phenylalanine, a p-bromophenylalanine, a p-amino-L-phenylalanine, and an isopropyl-L-phenylalanine, and the like. 
     Generally, analogs are optionally designed or selected to modify the biological properties of the polypeptide, such as to modulate toxicity, biodistribution, solubility, stability, e.g., thermal, hydrolytic, oxidative, resistance to enzymatic degradation, and the like, facility of purification and processing, structural properties, spectroscopic properties, chemical and/or photochemical properties, catalytic activity, redox potential, half-life, ability to react with other molecules, e.g., covalently or noncovalently, and the like. 
     “Physiologically active truncated homolog or analog of PACAP or VIP” refers to a polypeptide having a sequence comprising less than the full complement of amino acids found in PACAP or VIP which, however, elicits a similar physiological response. Representative truncated homologs and/or analogs presented herein comprise at least 5, 10, 15, 20, 25, 30, or 35 contiguous amino acids found in the native sequence of PACAP or VIP. The truncated PACAP or VIP need not be fully homologous with PACAP or VIP to elicit a similar physiological response. PACAP or VIP are preferred, but not exclusive, representatives of this group. 
     “PEG” refers to polyethylene glycol, polypropylene glycol, or polyoxyalkylenes attached to the peptide or protein through a linker functional group. Preferred forms of PEG have a molecular weight of greater than 10,000 Daltons and most preferred forms have a molecular weight of 20,000 Daltons or greater. They may be linear or branched molecules. Polyethyleneglycol chains are functionalized to allow their conjugation to reactive groups on the polypeptide or protein chain. Typical functional groups allow reaction with amino, carboxy or sulfhydryl groups on the peptide through the corresponding carboxy, amino or maleimido groups (and the like) on the polyethylene glycol chain. In an embodiment, PEG comprises a C 10 -C 3000  chain. In another embodiment, PEG has a molecular weight above 40,000 Daltons. PEG as a protein modification is well known in the art and its use is described, for example, in U.S. Pat. Nos. 4,640,835; 4,496,689; 4,301,144; 4,670,417; 4,791,192; and 4,179,337. 
     “Amphipathic α-helix” refers to the secondary structure exhibited by certain polypeptides in which the amino acids assume an α-helical configuration having opposing polar and nonpolar faces oriented along the long axis of the helix. The possibility of α-helical structure in the polypeptide of interest may be explored to some extent by the construction of a “Schiffer-Edmundson wheel” (M. Schiffer and A. B. Edmundson, Biophys. J. 7, 121 (1967), incorporated herein by reference), of the appropriate pitch and noting the segregation of the hydrophilic and lipophilic residues on opposite faces of the cylinder circumscribing the helix. Alternatively, empirical evidence, such as circular dichroism or x-ray diffraction data, may be available indicating the presence of an α-helical region in a given polypeptide. An ideal α-helix has 3.6 amino acid residues per turn with adjacent side chains separated by 100° of arc. 
     Another aspect of protein structure relevant to the invention, and in particular those compounds of the strature corresponding to Formula II, is the use of a polyproline type II helix (Stapley B J and Creamer T P (1999) Protein Sci 8: 587-95) to facilitate the development of the amphiphilic alpha helix described above. Polyproline helices increasingly are recognized as being an important element in protein structure and an important aspect of that helix is its amphiphilic character. Here we make use of such a polyproline type II helix to facilitate that formation of the amphiphilic alpha helix described above to yield potent VPAC2 ligands. A prominent feature of polyproline helices is the very strong preference for Pro residues within the helix and specific amino acids as capping residues at the N-terminus. Some examples of favored capping residues are Gln, Ser, Gly, Asp, Ala, Arg, Lys, Glu (Rucker A L, et al. (2003) Proteins 53: 68-75). 
     Another aspect of the polyproline helix is the resistance to proteolysis that it affords. A number of naturally occurring peptides and proteins have polyproline regions or Pro residues at their C-terminus, where they may also prevent proteolytic digestion. Examples that bind to the GLP1 receptor are Exendin-4, heliodermin, heliospectin. 
     Unless stated otherwise, standard nomenclature using single letter abbreviations for amino acids are used. The letter “X” refers to a polyethylene glycol chain having C 10 -C 3000  chain. Preferred polyethylene chains may be linear or branched and will have a molecular weight above 20 kiloDalton. The term “acyl” refers to a C 2 -C 30  acyl chain. This chain may comprise a linear aliphatic chain, a branched aliphatic chain, an aralkyl chain, or an aryl chain containing an acyl moiety. The letter “Z” refers to lysine having a long acyl chain at the epsilon position. The term “hex” refers to hexanoyl. The term “pen” refers to pentanoyl. The terms “lau” refers to lauroyl. The term “myr” refers to myristoyl. The term “ste” refers to stearoyl. The term “pr” refers to propionyl. Arachidoyl refers to a linear C20 fatty acid substituent. 
     Although it may be apparent to an ordinary person skilled in the art, a PEG entity itself does not have a functional group to be attached to a target molecular, such as a peptide. Therefore, to create PEG attachment, a PEG entity need to be functionalized first, then a functionalized attachment is used to attach the PEG entity to a target molecule, such as a peptide. Site-specific pegylation can be achieved through Cys substitution on a peptide molecular. The target peptide can be synthesized by solid phase synthesis or recombinant means described herein. The invention discloses the combination concept of using acylation on a Lys residue and specific pegylation on at least one Cys residue. Certain Lys residues in disclosed peptide sequences can be substituted to Cys for site-specific pegylation. 
     Polypeptides 
     In an embodiment, polypeptides presented herein comprise truncated portions of PACAP and/or VIP having at least 5, 10, 15, 20, 25, 30, or 35 contiguous amino acids of the native sequence of PACAP or VIP. In another embodiment, the present polypeptides share at least 50, 60, 70, 80, 85, 90, 95, or 99% amino acid sequence identity to the native sequence of PACAP or VIP. In yet another embodiment, the present polypeptides comprise a span of at least 5, 10, 15, 20, 25, 30, or 35 contiguous amino acids of PACAP and/or VIP having at least 50, 60, 70, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100% amino acid sequence identity to the native sequence of PACAP or VIP. 
     Polypeptides presented herein optionally comprise modifications, functionalities, and/or amino acid substitutions which modulate VPAC2 selectivity. Exemplary modifications, functionalities, and/or substitutions include, but are not limited to, C-terminal cationic extensions and/or mutations reported in Gourlet et al. (Peptides 18, 403-8; Xia M, et al. (1997) and J. Pharmacol. Exp. Ther. 281: 629-33 (1997); the contents of both of which are incorporated herein by reference). 
     Modifications at the amino or carboxyl terminus may optionally be introduced into the present polypeptides. For example, the present polypeptides, such as analogs of VIP, can be acylated on the N-terminus by long chain fatty acids to yield polypeptides exhibiting low efficacy, partial agonist and antagonist activity (Gourlet et al., Eur. J. Pharmacol. 354: 105-111 (1998), the contents of which is incorporated herein by reference). Modification of the peptides of this invention with longer chain fatty acids at the N-terminus, similarly will yield antagonists with a prolonged duration of action (Moreno D, et al. (2000) Peptides 21: 1543-9). Other modifications to the N-terminus, such as deletions or incorporation of D-amino acids such as D-Phe also give potent and long acting antagonists when substituted into the compounds of Formulas 1-3. Such antagonists also have commercial utility and are within the scope of this invention. 
     Other exemplary modifications of the present polypeptides, such as analogs of VIP, include acylation with hexanoic acid to yield polypeptides that exhibit increased selectivity towards VPAC2 (Langer et al., Peptides 25: 275-8 (2004), the contents of which is incorporated herein by reference). Thus the length and positioning of such acylation can alter efficacy, and could result in loss of efficacy (antagonistic) or agonistic analogs. Contrary to this unpredictability, polypeptides presented herein have been designed and tested to obtain desired efficacy and activity. 
     Modifications may optionally be introduced within the side chain of at least one amino acid within the present polypeptides to increase duration of action and/or potency. For example, the present polypeptides can optionally comprise at least one amino acid acylated to a functionality in the side chain (i.e., R group). Representative modifications include fatty acid acylation, directly or through linkers, of reactive side chains (such as Lys) at various positions within the polypeptide. Similar modifications have been reported in Kurtzhals et al. where acylation of insulin on LysB 29  resulted in insulin detemir (Kurtzhals et al., (1995) Biochem J. 312, 725-31: and Kurtzhals, P., (2004) Int. J. Obesity 28: Suppl 2, S23-8). Similarly, acylation with long chain fatty acids through linkers (preferably Glu) has resulted in potent and long-acting analogs of GLP1 (Knudsen L B, et al. (2000). J. Med. Chem. 43, 1664-69), but the acylation can result in loss of activity or potent agonists, depending on the length and positioning of the acyl chain(s). Contrary to the unpredictable effects with the introduction of long chain fatty acids, polypeptides presented herein have been designed to incorporate an optimal number, length and positioning of the acyl chains so as to obtain desired activity. Such linkage is demonstrated here for direct acylation to Lys, but linkage through other linkers, such as Glu (Knudsen, L B, et al. (2000)), is also within the scope of the present invention. 
     Another type of modification that can optionally be introduced into the present polypeptides (e.g. within the polypeptide chain or at either the N- or C-terminal) to extend duration of action is PEGylation or incorporation of long-chain polyethylene glycol polymers (PEG). Introduction of PEG or long chain polymers of PEG increases the effective molecular weight of the present polypeptides to prevent rapid filtration into the urine. Any Lys residue in any peptide analog sequence may be conjugated to PEG directly or through a linker to yield a potent and long acting analog. Such linker can be a Glu residue or an acyl residue containing a thiol functional group for linkage to the appropriately modified PEG chain. An alternative method for introducing a PEG chain is to first introduce a Cys residue at the C-terminus or at solvent exposed residues such as replacements for Arg or Lys residues. This Cys residue is then site-specifically attached to a PEG chain containing, for example, a maleimide function. Methods for incorporating PEG or long chain polymers of PEG are well known in the art and described, for example, in Greenwald et al., Adv. Drug Del. Rev. 55: 217-250 (2003), the contents of which is incorporated herein by reference. 
     A more recently reported alternative approach for incorporating PEG or PEG polymers through incorporation of non-natural amino acids can be performed with the present polypeptides. This approach utilizes an evolved tRNA/tRNA synthetase pair and is coded in the expression plasmid by the amber suppressor codon (Deiters, A, et al. (2004). Bio-org. Med. Chem. Lett. 14, 5743-5). For example, p-azidophenylalanine can be incorporated into the present polypeptides and then reacted with a PEG polymer having an acetylene moiety in the presence of a reducing agent and copper ions to facilitate an organic reaction known as “Huisgen [3+2] cycloaddition”. 
     Amphipathic Helix 
     Polypeptides of the present invention comprise amphipathic α-helix corresponding to the formula:
 
Haa(Laa Laa Haa Haa) n Laa
 
wherein n, Haa, and Laa are selected from the group of hydrophilic amino acids and the Laa&#39;s are selected from the group of lipophilic amino acids, as defined above. Without being bound to any particular theory, it is believed that the amphipathic helix in the C-terminal region imparts an increase in duration of action of the present polypeptides by interacting with the phospholipids of the cell membranes in the body and thereby have a “depoting” effect. Polypeptides of the present invention comprise a peptide region that is an amphipathic alpha helix, not merely an alpha helix. Without wishing to be bound by any particular theory, the amphipathic alpha helix is believed to facilitate increased interaction with cell membranes and assist in proper placement of C-terminal fatty acyl chain modifications for membrane interaction.
 
     Studies by Eisenberg et al. have combined a hydrophobicity scale with the helical wheel to quantify the concept of amphipathic helices (Nature 299: 371-374 (1982) and Proc. Nat. Acad. Sci. USA 81: 140-144 (1984); the disclosures of which are hereby incorporated by reference). The mean hydrophobic moment is defined as the vector sum of the hydrophobicities of the component amino acids making up the helix. The following hydrophobicities for the amino acids are those reported by Eisenberg et al. as the “consensus” scale: Ile 0.73; Phe 0.61; Val 0.54; Leu 0.53; Trp 0.37; Met 0.26 Ala 0.25; Gly 0.16; Cys 0.04; Tyr 0.02; Pro −0.07; Thr −0.18; Ser −0.26; His −0.40; Glu −0.62; Asn −0.64; Gln −0.69; Asp −0.72; Lys −1.10; Arg −1.76. 
     The hydrophobic moment, μH, for an ideal α-helix having 3.6 residues per turn (or a 100° arc (=360°/3.6) between side chains), may be calculated from:
 
μH=[(ΣH N  sine δ( N− 1) 2 +(ΣH N  COS δ( N− 1)) 2 ] 1/2 ,
 
where H N  is the hydrophobicity value of the N th  amino acid and the sums are taken over the N amino acids in the sequence with periodicity δ=100°. The hydrophobic moment may be expressed as the mean hydrophobic moment per residue by dividing μH by N to obtain &lt;μH&gt;. A value of &lt;μH&gt; at 100°+−0.20° of about 0.20 or greater is suggestive of amphipathic helix formation.
 
     A study by Cornett et al. has further extended the study of amphiphathic α-helices by introducing the “amphipathic index” as a predictor of amphipathicity (J. Mol. Biol., 195: 659-685 (1987); the disclosure of which is hereby incorporated by reference). They concluded that approximately half of all known α-helices are amphipathic, and that the dominant frequency is 97.5° rather than 100°, with the number of residues per turn being closer to 3.7 than 3.6. The basic approach of Eisenberg, et al. is sufficient to classify a given sequence as amphipathic, particularly when one is designing a sequence ab initio to form an amphipathic α-helix. 
     A substitute amphipathic α-helical amino acid sequence may lack homology with the sequence of a given segment of a naturally occurring polypeptide but elicits a similar secondary structure, i.e. an α-helix having opposing polar and nonpolar faces, in the physiological environment. Replacement of the naturally occurring amino acid sequence with an alternative sequence may beneficially affect the physiological activity, stability, or other properties of the altered parent polypeptide. Exemplary reports describing the design and selection of such sequences is provided in J. L. Krstenansky, et al., FEBS Letters 242: 2, 409-413 (1989), and J. P. Segrest, et al. Proteins: Structure, Function, and Genetics 8: 103-117 (1990) among others. 
     Polypeptides of the present invention comprise amphipathic α-helix corresponding to the formula:
 
Haa(Laa Laa Haa Haa) n Laa
 
wherein the Haa&#39;s are selected from the group of hydrophilic amino acids and the Laa&#39;s are selected from the group of lipophilic amino acids, as defined above. Assuming an idealized α-helix in an embodiment where n=2, residues 1, 4, 5, 8, and 9 are distributed along one face (A) of the helix within about a 140° arc of each other, while residues 2, 3, 6, 7, and 10 occupy an opposing 140° arc on the other face (B) of the helix. In an embodiment, all the residues on one face are of the same polarity while all those on the other face are of the opposite polarity, i.e., if face A is all hydrophilic, face B is all lipophilic and vice versa. The skilled artisan will recognize that while the helices of the invention are described by
 
Haa(Laa Laa Haa Haa) n Laa,
 
the reverse sequence,
 
Laa(Haa Haa Laa Laa) n Haa
 
will also meet the residue distribution criteria and is an equivalent descriptor of the helices of the invention.
 
     Alanine may be substituted for either hydrophilic or lipophilic amino acids, since Ala can reside readily on either face of an amphipathic α-helix, although Ala-10 does not form an amphipathic α-helix. Generally, proline, cysteine, and tyrosine are not used; however, their presence and other random errors in the sequence may be tolerated, e.g. a hydrophilic residue on the lipophilic face, as long as the remaining amino acids in the segment substantially conform to the hydrophilic face—lipophilic face division. A convenient method for determining if a sequence is sufficiently amphipathic to be a sequence of this invention is to calculate the mean hydrophobic moment, as defined above. If the peak mean moment per residue at 100°+−20° exceeds about 0.20, then the sequence will form an amphipathic helix and is a sequence of the invention. 
     In applying this concept to PACAP and VIP, it is hypothesized that either or both regions (N-terminal or C-terminal), preferably the C-terminal, may exhibit α-helical secondary structure and could be replaced with a non-homologous sequence having similar structural tendencies, without loss of biological activity or induction of immunoreaction. 
     Pharmaceutical Formulations 
     Polypeptides of the present invention may be administered in any amount to impart beneficial therapeutic effect. In a preferred embodiment, compounds of the present invention are useful in the treatment of elevated blood glucose levels, hyperglycemia, diabetes, including Type 2 Diabetes Mellitus, insulin resistance, metabolic acidosis and obesity. In an embodiment, compounds presented herein impart beneficial activity in the modulation of insulin and/or glucose levels. In an embodiment, the present polypeptides are administered to a patient at concentrations higher or lower than that of other forms of treatment which modulate insulin and/or glucose secretion. In yet another embodiment, the present polypeptides are administered with other compounds to produce a synergistic therapeutic effect. For example, polypeptides of the invention may be administered in conjunction with exendin or exendin analogs. 
     EXAMPLES 
     Example 1 
     Synthetic Analogs 
     Some of the exemplary synthetic polypeptide analogs illustrated in  FIG. 1  are derived from VPAC2 sel UldB (see  FIG. 1 ). Other exemplary synthetic polypeptide analogs illustrated in  FIG. 1  are truncated homologs of VIP (see  FIG. 1 ). 
     In one aspect, the present polypeptide analogs of the physiologically active truncated homologs of VIP, such as those shown in  FIG. 1  as TP 1 to TP 6. Analogs TP 1 to TP 6 have a long acyl residue comprising C12-C24, preferably C16-C24. Analogs TP 7 to TP 12 shown in  FIG. 1  have an acyl residue on the N-terminus comprising C2-C16, preferably C6. Analogs SQNM 10-12 (corresponding to SEQ ID NO: 40-42) shown in  FIG. 2  do not contain acylation at either the C or N-termini. 
     Other representative polypeptide analogs presented herein have amino acid sequences corresponding to general formula (I): 
                            Formula (I)   (SEQ ID NO: 81)                         Acyl-His-Ser-Asp-aa 1 -aa 2 -Phe-Thr-aa 3 -aa 4 -Tyr-aa 5 -           Arg-aa 6 -Baa 1 -Baa 2 -Baa 3 -aa 7 -Ala-aa 8 -Baa 4 -Baa 5 -Tyr-       Leu-aa 9 -aa 10 -aa 11 -aa 12 -aa 13 -aa 14 -aa 15 -aa 16 -Haa-(Laa-       Laa-Haa-Haa) n -Laa-Lys(ε-long acyl)-X            
wherein:
         n=1-5;   each Haa is independently a hydrophilic amino acid;   each Laa is independently a lipophilic amino acid;   acyl is a C 2-16  acyl chain;   long acyl is a C 12-30  acyl chain;   X is OH or NHR1 where R1 is H or lower alkyl, haloalkyl, or Cys(PEG)-X, or PEG;   PEG is a functionalized polyethylene glycol chain of C 10 -C 3000  chain;   aa 1  is Gly or Ala;   aa 2  is Val, Lie, or Leu;   aa 3  is Asp, Arg, Gln, or Glu;   aa 4  is Ser, Asn, Gln, Asp or Glu;   aa 5  is Ser or Thr;   aa 6  is Leu or Tyr;   Baa 1  is Arg or Leu;   Baa 2  is Lys, Leu, or Arg;   Baa 3  is Gln, Lys or Ala;   aa 7  is Met, Leu, Val or Ala   aa 8  is Ala or Val;   Baa 4  is Lys, Arg or Gln;   Baa 5  is Lys, Arg or Gln;   aa 9  is Asn, Gln, Ala or Glu;   aa 10  is Trp, Ala, or Ser;   aa 11  is Ile, Val or Trp;   aa 12  is Leu, Lys, Arg or Gln;   aa 13  is Lys, Arg, Asn, Gln, or Gly;   aa 14  is Ala, Gly, Gln, Lys or Arg;   aa 15  is Lys, Arg, Leu, Ala or absent; and   aa 16  is Lys, Arg, Leu, Ala or absent.
 
provided that if aa 15  or aa 16  is absent, the next amino acid present downstream is the next amino acid in the peptide agonist sequence. In a preferred embodiment, acyl is a C 2-8  acyl chain and long acyl is a C 12-30  acyl chain.
       
     Other representative polypeptide analogs presented herein have amino acid sequences corresponding to general formula (II): 
                            Formula (II)   (SEQ ID NO: 82)                         Acyl-His-Ser-Asp-aa 1 -aa 2 -Phe-Thr-aa 3 -aa 4 -Tyr-aa 5 -           Arg-aa 6 -Baa 1 -Baa 2 -Baa 3 -aa 7 -Ala-aa 8 -Baa 4 -Baa 5 -Tyr-       Leu-aa 9 -aa 10 -aa 11 -aa 12 -aa 13 -aa 14 -aa 15 -aa 16 -Haa-(Laa-       Laa-Haa-Haa) n -Laa-aa 17 -Pro-Pro-Pro-Lys(ε-long       acyl)-X            
wherein:
         n=1-5;   each Haa is independently a hydrophilic amino acid;   each Laa is independently a lipophilic amino acid;   acyl is a C 2-16  acyl chain;   long acyl is a C 12-30  acyl chain;   X is OH or NHR1 where R1 is H or lower alkyl, haloalkyl, or Cys(PEG)-X, or PEG;   PEG is a functionalized polyethylene glycol chain of C 10 -C 3000  chain;   aa 1  is Gly or Ala;   aa 2  is Val, Ile, or Leu;   aa 3  is Asp, Arg, Gln, or Glu;   aa 4  is Ser, Asn, Gln, Asp or Glu;   aa 5  is Ser or Thr;   aa 6  is Leu or Tyr;   Baa 1  is Arg or Leu;   Baa 2  is Lys, Leu, or Arg;   Baa 3  is Gln, Lys or Ala;   aa 7  is Met, Leu, Val or Ala   aa 8  is Ala or Val;   Baa 4  is Lys, Arg or Gln;   Baa 5  is Lys, Arg or Gln;   aa 9  is Asn, Gln, Ala or Glu;   aa 10  is Trp, Ala, or Ser;   aa 11  is Ile, Val or Trp;   aa 12  is Leu, Lys, Arg or Gln;   aa 13  is Lys, Arg, Asn, Gln, or Gly;   aa 14  is Ala, Gly, Gln, Lys or Arg;   aa 15  is Lys, Arg, Leu, Ala or absent;   aa 16  is Lys, Arg, Leu, Ala or absent; and   aa 17  is Gln, Ser, Gly, Asp, Ala, Arg, Lys, Glu, Pro, Asn, Leu, or absent.
 
provided that if aa 15 , aa 16  or aa 17  is absent, the next amino acid present downstream is the next amino acid in the peptide agonist sequence. In a preferred embodiment, acyl is a C 2-8  acyl chain and long acyl is a C 12-30  acyl chain.
       
     Other representative polypeptide analogs presented herein have amino acid sequences corresponding to general formula (III): 
                        Formula (III)           Acyl-His-Ser-Asp-aa 1 -aa 2 -Phe-Thr-aa 3 -aa 4 -Tyr-aa 5 -       Arg-aa 6 -Baa 1 -Baa 2 -Baa 3 -aa 7 -Ala-aa 8 -Baa 4 -Baa 5 -Tyr-       Leu-aa 9 -aa 10 -aa 11 -aa 12 -aa 13 -aa 14 -aa 15 -aa 16 -Haa-(Laa-       Laa-Haa-Haa) n -Laa-aa 17 -Lys(ε-long acyl)-PEG            
wherein:
         n=1-5;   each Haa is independently a hydrophilic amino acid;   each Laa is independently a lipophilic amino acid;   acyl is a C 2-16  acyl chain;   long acyl is a C 12-30  acyl chain;   PEG is a functionalized polyethylene glycol chain of C 10 -C 3000  chain;   aa 1  is Gly or Ala;   aa 2  is Val, Ile, or Leu;   aa 3  is Asp, Arg, Gln, or Glu;   aa 4  is Ser, Asn, Gln, Asp or Glu;   aa 5  is Ser or Thr;   aa 6  is Leu or Tyr;   Baa 1  is Arg or Leu;   Baa 2  is Lys, Leu, or Arg;   Baa 3  is Gln, Lys or Ala;   aa 7  is Met, Leu, Val or Ala;   aa 8  is Ala or Val;   Baa 4  is Lys, Arg or Gln;   Baa 5  is Lys, Arg or Gln;   aa 9  is Asn, Gln, Ala or Glu;   aa 10  is Trp, Ala, or Ser;   aa 11  is Ile, Val or Trp;   aa 12  is Leu, Lys, Arg or Gln;   aa 13  is Lys, Arg, Asn, Gln, or Gly;   aa 14  is Ala, Gly, Gln, Lys or Arg;   aa 15  is Lys, Arg, Leu, Ala or absent;   aa 16  is Lys, Arg, Leu, Ala or absent; and   aa 17  is Gln, Ser, Gly, Asp, Ala, Arg, Lys, Glu, Pro, Asn, Leu, or absent.
 
provided that if aa 15 , aa 16  or aa 17  is absent, the next amino acid present downstream is the next amino acid in the peptide agonist sequence. In a preferred embodiment, acyl is a C 2-8  acyl chain and long acyl is a C 12-30  acyl chain.
       
     The skilled artisan will appreciate that numerous permutations of the polypeptide analogs may be synthesized which will possess the desirable attributes of those described herein provided that an amino acid sequence having a mean hydrophobic moment per residue at 100°+−20° greater than about 0.20 is inserted at positions in the C-terminal region. 
     Example 2 
     Additional Analogs 
     In some embodiments of the invention, representative polypeptide analogs presented herein have the following amino acid sequences: 
                        Formula (IV)           Acyl-aa 1 -aa 2 -aa 3 -aa 4 -aa 5 -aa 6 -Thr-aa 8 -aa 9 -aa 10 -Thr-       aa 12 -aa 13 -aa 14 -aa 15 -aa 16 -aa 17 -Ala-aa 19 -aa 20 -aa 21 -       aa 22 -aa 23 -aa 24 -aa 25 -aa 26 -aa 27 -aa 28 -aa 29 -aa 30 -aa 31 -       aa 32 -aa 33 -aa 34 -aa 35 -aa 36 -aa 37 -aa 38 -aa 39 -aa 40              
wherein:
         aa 1  is: any naturally occurring amino acid, dH, or is absent;   aa 2  is: any naturally occurring amino acid, dA, dS, or Aib;   aa 3  is: Asp or Glu;   aa 4  is: any naturally occurring amino acid, dA, Aib, or NMeA;   aa 5  is: any naturally occurring amino acid, dV, or Aib;   aa 6  is: any naturally occurring amino acid;   aa 8  is: Asp, Glu, Ala, Lys, Leu, Arg, or Tyr;   aa 9  is: Asn, Gln, Asp, or Glu;   aa 10  is: any naturally occurring aromatic amino acid, or Tyr (OMe);   aa 12  is: hR, Orn, Lys (isopropyl), Aib, Cit or any naturally occurring amino acid except Pro;   aa 13  is: Aib, or any naturally occurring amino acid except Pro;   aa 14  is: hR, Orn, Lys (isopropyl), Aib, Cit, or any naturally occurring amino acid except Pro;   aa 15  is: hR, Orn, Lys (isopropyl), Aib, K (Ac), Cit, or any naturally occurring amino acid except Pro;   aa 16  is: hR, Orn, Lys (isopropyl), Cit, or any naturally occurring amino acid except Pro;   aa 17  is: Nle, Aib, or any naturally occurring amino acid except Pro;   aa 19  is: any naturally occurring amino acid except Pro;   aa 20  is: hR, Orn, Lys (isopropyl), Aib, K(Ac), Cit, or any naturally occurring amino acid except Pro;   aa 21  is: hR, Orn, Aib, K(Ac), Cit, or any naturally occurring amino acid except Pro;   aa 22  is: Aib, Tyr (OMe), or any naturally occurring amino acid except Pro;   aa 23  is: Aib, or any naturally occurring amino acid except Pro;   aa 24  is: any naturally occurring amino acid except Pro;   aa 25  is: Aib, or any naturally occurring amino acid except Pro;   aa 26  is: any naturally occurring amino acid except Pro;   aa 27  is: hR, Lys (isopropyl), Orn, dK, or any naturally occurring amino acid except Pro;   aa 28  is: any naturally occurring amino acid, Aib, hR, Cit, Gm, dK, or is absent;   aa 29  is: any naturally occurring amino acid, hR, Orn, Cit, Aib or is absent;   aa 30  is: any naturally occurring amino acid, hR, Orn, Cit, Aib or is absent; and   aa 31  to aa 40  are any naturally occurring amino acid or are absent;
 
provided that if aa 1 , aa 28 , aa 29 , aa 30 , aa 31 , aa 32 , aa 33 , aa 34 , aa 35 , aa 36 , aa 37 , aa 38 , aa 39 , or aa 40  is absent, the next amino acid present downstream is the next amino acid in the peptide agonist sequence;
 
and a C-terminal sequence selected from the group consisting of:
   (a) -Haa-(Laa-Laa-Haa-Haa) n -Laa-Lys(ε-long acyl)-X;   (b) -Haa-(Laa-Laa-Haa-Haa) n -Laa-aa 17 -Pro-Pro-Pro-Lys(ε-long acyl)-X; (SEQ ID NO: 84)   (c) -Haa-(Laa-Laa-Haa-Haa) n -Laa-Lys(s-long acyl)-PEG; and   (d) a polyproline type II helix;
 
wherein:
   n is an integer number from 1 to 3;   each Haa is independently a hydrophilic amino acid;   each Laa is independently a lipophilic amino acid;   acyl is a C 2-16  acyl chain;   long acyl is a C 12-30  acyl chain;   X is OH or NHR1 where R1 is H or lower alkyl, haloalkyl, or PEG.       
     In some embodiments of the invention, representative polypeptide analogs presented herein have the following amino acid sequences: 
                        Formula (V)           Acyl-aa 1 -aa 2 -aa 3 -aa 4 -aa 5 -aa 6 -Thr-aa 8 -aa 9 -aa 10 -Thr-       aa 12 -aa 13 -aa 14 -aa 15 -aa 16 -aa 17 -Ala-aa 19 -aa 20 -aa 21 -       aa 22 -aa 23 -aa 24 -aa 25 -aa 26 -aa 27 -aa 28 -aa 29 -aa 30 -aa 31 -       aa 32 -aa 33 -aa 34 -aa 35 -aa 36 -aa 37 -aa 38 -aa 39 -aa 40              
wherein:
         aa 1  is: His, dH, or is absent;   aa 2  is: dA, Ser, Val, Gly, Thr, Leu, dS, Pro, or Aib;   aa 3  is: Asp or Glu;   aa 4  is: Ala, Ile, Tyr, Phe, Val, Thr, Leu, Trp, Gly, dA, Aib, or NMeA;   aa 5  is: Val, Leu, Phe, Ile, Thr, Tm, Tyr, dV, Aib, or NMeV;   aa 6  is: Phe, Ile, Leu, Thr, Val, Trp, or Tyr;   aa 8  is: Asp, Glu, Ala, Lys, Leu, Arg, or Tyr;   aa 9  is: Asn, Gln, Asp, or Glu;   aa 10  is: Tyr, Trp, or Tyr(OMe);   aa 12  is: Arg, Lys, Glu, hR. Orn, Lys (isopropyl), Aib, Cit, or Ala;   aa 13  is: Leu, Phe, Glu, Ala, or Aib;   aa 14  is: Arg, Leu, Lys, Ala, hR, Orn, Lys (isopropyl), Phe, Gln, Aib, or Cit;   aa 15  is: Lys, Ala, Arg, Glu, Leu, hR. Orn, Lys (isopropyl), Phe, Gln, Aib, K(Ac), or Cit;   aa 16  is: Gln, Lys, Glu, Ala, hR. Orn, Lys (isopropyl), or Cit;   aa 17  is: Val, Ala, Leu, Ile, Met, Nle, Lys, or Aib;   aa 19  is: Val, Ala, Glu, Phe, Gly, His, Ile, Lys, Leu, Met, Asn, Pro, Gln, Arg, Ser, Thr, Trp, Tyr, Cys, or Asp;   aa 20  is: Lys, Gln, hR, Arg, Ser, His, Orn, Lys (isopropyl), Ala, Aib, Trp, Thr, Leu, Ile, Phe, Tyr, Val, K(Ac), or Cit;   aa 21  is: Lys, His, Arg, Ala, Phe, Aib, Leu, Gln, Orn, hR , K(Ac) or Cit;   aa 22  is: Tyr, Trp, Phe, Thr, Leu, Ile, Val, Tyr(OMe), Ala, or Aib;   aa 23  is: Leu, Phe, Ile, Ala, Trp, Thr, Val, or Aib;   aa 24  is: Gln, Glu, or Asn;   aa 25  is: Ser, Asp, Phe, Ile, Leu, Thr, Val, Trp, Gln, Asn, Tyr, Aib, or Glu;   aa 26  is: Ile, Leu, Thr, Val, Trp, Tyr, Phe or Aib   aa 27  is: Lys, hR. Arg, Gln, Ala, Asp, Glu, Phe, Gly, His, Ile, Met, Asn, Pro, Ser, Thr, Val, Trp, Tyr, Lys (isopropyl), Cys, Leu, Orn, or dK;   aa 28  is: Asn, Asp, Gln, Lys, Arg, Aib, Orn, hR, Cit, Pro, dK, or is absent;   aa 29  is: Lys, Ser, Arg, Asn, hR, Ala, Asp, Glu, Phe, Gly, His, Ile, Leu, Met, Pro, Gln, Thr, Val, Trp, Tyr, Cys, Orn, Cit, Aib or is absent;   aa 30  is: Arg, Lys, Ile, Ala, Asp, Glu, Phe, Gly, His, Leu, Met, Asn, Pro, Gln, Ser, Thr, Val, Trp, Tyr, Cys, hR. Cit, Aib, Orn, or is absent;   aa 31  is: Tyr, His, Phe, Thr, Cys, or is absent;   aa 32  is: Ser, Cys, or is absent;   aa 33  is: Trp or is absent;   aa 34  is: Cys or is absent;   aa 35  is: Glu or is absent;   aa 36  is: Pro or is absent;   aa 37  is: Gly or is absent;   aa 38  is: Trp or is absent;   aa 39  is: Cys or is absent; and   aa 40  is: Arg or is absent;
 
provided that if aa 1 , aa 28 , aa 29 , aa 30 , aa 31 , aa 32 , aa 33 , aa 34 , aa 35 , aa 36 , aa 37 , aa 38 , aa 39 , or aa 40  is absent, the next amino acid present downstream is the next amino acid in the peptide agonist sequence;
 
and a C-terminal sequence selected from the group consisting of:
   (a) -Haa-(Laa-Laa-Haa-Haa) n -Laa-Lys(ε-long acyl)-X;   (b) -Haa-(Laa-Laa-Haa-Haa) n -Laa-aa 17 -Pro-Pro-Pro-Lys(ε-long acyl)-X; (SEQ ID NO: 85)   (c) -Haa-(Laa-Laa-Haa-Haa) n -Laa-Lys(s-long acyl)-PEG; and   (d) a polyproline type II helix;
 
wherein:
   n is an integer number from 1 to 3;   each Haa is independently a hydrophilic amino acid;   each Laa is independently a lipophilic amino acid;   acyl is a C 2-16  acyl chain;   long acyl is a C 12-30  acyl chain;   X is OH or NHR1 where R1 is H or lower alkyl, haloalkyl, or PEG.       
     Example 3 
     General Method for Synthesizing Polypeptides 
     The polypeptides of the invention may be synthesized by methods such as those set forth in J. M. Stewart and J. D. Young, Solid Phase Peptide Synthesis, 2nd ed., Pierce Chemical Co., Rockford, Ill. (1984) and J. Meienhofer, Hormonal Proteins and Peptides, Vol. 2, Academic Press, New York, (1973) for solid phase synthesis and E. Schroder and K. Lubke, The Peptides, Vol. 1, Academic Press, New York, (1965) for solution synthesis and Houben-Weyl,  Synthesis of Peptides and Peptidomimetics.  4th ed. Vol E22; M. Goodman, A. Felix, L. Moroder, C. Toniolo, Eds., Thieme: New York, 2004 for general synthesis techniques. Microwave assisted peptide synthesis is an attractive method and will be a particularly effective method of synthesis for the peptides of the invention (Erdelyi M, et al. (2002) Synthesis 1592-6). The disclosures of the foregoing treatises are incorporated by reference herein. 
     In general, these methods involve the sequential addition of protected amino acids to a growing peptide chain. Normally, either the amino or carboxyl group of the first amino acid and any reactive side chain group are protected. This protected amino acid is then either attached to an inert solid support, or utilized in solution, and the next amino acid in the sequence, also suitably protected, is added under conditions amenable to formation of the amide linkage. After all the desired amino acids have been linked in the proper sequence, protecting groups and any solid support are removed to afford the crude polypeptide. The polypeptide is desalted and purified, preferably chromatographically, to yield the final product. 
     A preferred method of preparing the analogs of the physiologically active truncated polypeptides, having fewer than about forty amino acids, involves solid phase peptide synthesis. In this method the α-amino (Nα) functions and any reactive side chains are protected by acid- or base-sensitive groups. The protecting group should be stable to the conditions of peptide linkage formation, while being readily removable without affecting the extant polypeptide chain. Suitable α-amino protecting groups include, but are not limited to t-butoxycarbonyl (Boc), benzyloxycarbonyl (Cbz), o-chlorobenzyloxycarbonyl, biphenylisopropyloxycarbonyl, t-amyloxycarbonyl (Amoc), isobornyloxycarbonyl, α,α-dimethyl-3,5-dimethoxybenzyloxy-carbonyl, o-nitrophenylsulfenyl, 2-cyano-t-butoxycarbonyl, 9-fluorenyl-methoxycarbonyl (Fmoc) and the like, preferably t-butoxycarbonyl (Boc). Suitable side chain protecting groups include, but are not limited to: acetyl, benzyl (Bzl), benzyloxymethyl (Bom), o-bromobenzyloxycarbonyl, t-butyl, t-butyldimethylsilyl, 2-chlorobenzyl (Cl-z), 2,6-dichlorobenzyl, cyclohexyl, cyclopentyl, isopropyl, pivalyl, tetrahydropyran-2-yl, tosyl (Tos), trimethylsilyl, and trityl. 
     In solid phase synthesis, the C-terminal amino acid is first attached to a suitable resin support. Suitable resin supports are those materials which are inert to the reagents and reaction conditions of the stepwise condensation and deprotection reactions, as well as being insoluble in the media used. Examples of commercially available resins include styrene/divinylbenzene resins modified with a reactive group, e.g., chloromethylated co-poly-(styrene-divinylbenzene), hydroxymethylated co-poly-(styrene-divinylbenzene), and the like. Benzylated, hydroxymethylated phenylacetamidomethyl (PAM) resin is preferred. When the C-terminus of the compound is an amide, a preferred resin is p-methylbenzhydrylamino-co-poly(styrene-divinyl-benzene) resin. 
     Attachment to the PAM resin may be accomplished by reaction of the Nα protected amino acid, preferably the Boc-amino acid, as its ammonium, cesium, triethylammonium, 1,5-diazabicyclo-[5.4.0]undec-5-ene, tetramethylammonium, or similar salt in ethanol, acetonitrile, N,N-dimethylformamide (DMF), and the like, preferably the cesium salt in DMF, with the resin at an elevated temperature, for example between about 40° and 60° C., preferably about 50° C., for from about 12 to 72 hours, preferably about 48 hours. 
     The Nα-Boc-amino acid may be attached to the benzhydrylamine resin by means of, for example, an N,N′-diisopropylcarbodiimide (DIC)/1-hydroxybenzotriazole (HOBt) mediated coupling for from about 2 to about 24 hours, preferably about 2 hours at a temperature of between about 10° and 50° C., preferably 25° C. in a solvent such as dichloromethane or dimethylformamide, preferably dichloromethane. 
     The successive coupling of protected amino acids may be carried out by methods well known in the art, typically in an automated peptide synthesizer. Following neutralization with triethylamine or similar base, each protected amino acid is preferably introduced in approximately 1.5 to 2.5 fold molar excess and the coupling carried out in an inert, nonaqueous, polar solvent such as dichloromethane, DMF, or mixtures thereof, preferably in dichloromethane at ambient temperature. Representative coupling agents are N,N′-dicyclohexylcarbodiimide (DCC), N,N′-diisopropyl-carbodiimide (DIC) or other carbodiimide, either alone or in the presence of 1-hydroxybenzotriazole (HOBt), O-acyl ureas, benzotriazol-1-yl-oxytris(pyrrolidino)phosphonium hexafluorophosphate (PyBop), N-hydroxysuccinimide, other N-hydroxyimides, or oximes. Alternatively, protected amino acid active esters (e.g. p-nitrophenyl, pentafluorophenyl and the like) or symmetrical anhydrides may be used. 
     At the end of the solid phase synthesis the fully protected peptide is removed from the resin. When the linkage to the resin support is of the benzyl ester type, cleavage may be effected by means of aminolysis with an alkylamine or fluoroalkylamine for peptides with an alkylamide C-terminus, or by aminolysis with, for example, ammonia/methanol or ammonia/ethanol for peptides with an unsubstituted amide C-terminus, at a temperature between about −10° and 50° C., preferably about 25° C., for between about 12 and 24 hours, preferably about 18 hours. Peptides with a hydroxy C-terminus may be cleaved by HF or other strongly acidic deprotection regimen or by saponification. Alternatively, the peptide may be removed from the resin by transesterification, e.g., with methanol, followed by aminolysis or saponification. The protected peptide may be purified by silica gel chromatography. 
     The side chain protecting groups may be removed from the peptide by treating the aminolysis product with, for example, anhydrous liquid hydrogen fluoride in the presence of anisole or other carbonium ion scavenger, treatment with hydrogen fluoride/pyridine complex, treatment with tris(trifluoroacetyl)boron and trifluoroacetic acid, by reduction with hydrogen and palladium on carbon or polyvinylpyrrolidone, or by reduction with sodium in liquid ammonia, preferably with liquid hydrogen fluoride and anisole at a temperature between about −10° and +10° C., preferably at about 0° C., for between about 15 minutes and 2 hours, preferably about 1.5 hours. 
     For peptides on the benzhydrylamine resin, the resin cleavage and deprotection steps may be combined in a single step utilizing liquid hydrogen fluoride and anisole as described above. 
     The solution may be desalted (e.g. with BioRad AG-3® anion exchange resin) and the peptide purified by a sequence of chromatographic steps employing any or all of the following types: ion exchange on a weakly basic resin in the acetate form; hydrophobic adsorption chromatography on underivatized co-poly(styrene-divinylbenzene), e.g. Amberlite® XAD; silica gel adsorption chromatography; ion exchange chromatography on carboxymethylcellulose; partition chromatography, e.g. on Sephadex® G-25; counter-current distribution; or high performance liquid chromatography (HPLC), especially reversed-phase HPLC on octyl- or octadecylsilylsilica (ODS) bonded phase column packing. 
     Thus, another aspect of the present invention relates to processes for preparing polypeptides and pharmaceutically acceptable salts thereof, which processes comprise sequentially condensing protected amino acids on a suitable resin support, removing the protecting groups and resin support, and purifying the product, to afford analogs of the physiologically active truncated homologs and analogs of PACAP and VIP, preferably of PACAP and VIP in which the amino acids at the C-terminus form an amphipathic α-helical peptide sequence, as defined above. 
     Example 4 
     Exemplary Synthesis and Purification Protocol for a Representative Polypeptide Analog 
     Representative polypeptide analog corresponding to SEQ ID NO: 1 was prepared using the synthetic and purification methods described below. 
     
       
         
           
               
               
            
               
                 (SEQ ID NO: 1) 
                   
               
            
           
           
               
               
            
               
                 Pentanoyl-His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr- 
                   
               
               
                 Thr-Arg-Leu-Arg-Lys-Gln-Val-Ala-Ala-Lys-Lys-Tyr- 
               
               
                 Leu-Asn-Trp-Ile-Lys-Lys-Ala-Lys-Arg-Glu-Leu-Leu- 
               
               
                 Glu-Lys-Leu-Lys(epsilon stearoyl)-NH 2   
               
            
           
         
       
     
     Generally, the peptide was synthesized on Fmoc-Rink-Amide-PEG resin via Fmoc chemistry. Protecting groups used for amino acid side chain functional groups are: t-Butyl group for Glu, Tyr, Thr, Asp and Ser; Boc group for Lys and Trp; Pbf group for Arg; Trt group for Asn and His. N-alpha Fmoc protected amino acids were purchased from EMD Biosciences (San Diego, Calif.). Reagents for coupling and cleavage were purchased from Aldrich (St. Louis, Mo.). Solvents were purchased from Fisher Scientific (Fairlawn, N.J.). 
     Generally, the synthetic protocol involved assembly of the peptide chain on resin by repetitive removal of the Fmoc protecting group and coupling of protected amino acid. For the synthesis, Dde-Lys(Fmoc)-OH was coupled onto the Rink Amide resin first. The Fmoc protecting group was then removed by 20% piperidine in DMF. Stearic acid was coupled onto the side chain of Lys using HBTU, HOBt and NMM. The Dde group was removed by 2% hydrazine in DMF and the next Fmoc protected amino acid was coupled. HBTU and HOBt were used as coupling reagent and NMM was used as base. After removal of last Fmoc protecting group, valeric acid (4 equivalents) was coupled to the amino terminus with DIC (4 equivalents) and HOBt (4 equivalents). The peptide resin was treated with cocktail 1 for cleavage and removal of the side chain protecting groups. Crude peptide was precipitated from cold ether and collected by filtration. 
     Purification of crude peptide was achieved via RP-HPLC using 20 mm×250 mm column from Waters (Milford, Mass.). Peptide was purified using TFA Buffer. A linear gradient of 35% to 55% acetonitrile in 60 minutes was used. Pooled fractions were lyophilized. The peptide identity was verified by mass spectrometry analysis and amino acid analysis. The peptide purity was determined by analytical HPLC column (C 18 column, 4.6×250 mm, manufactured by Supelco (St. Louis, Mo.)) chromatography. 
     The above procedure can be summarized in the following step wise protocol:
         Step 1. Resin swelling: Fmoc-Rink-Amide-PEG resin was swelled in DCM for 30 minutes (10 ml/g resin)   Step 2. Deprotection:
           a. 20% piperidine/DMF solution (10 ml/g resin) was added to the resin;   b. Solution stirred for 30 minutes (timing was started when all the resin was free floating in the reaction vessel); and   c. Solution was drained.   
           Step 3. Washing: Resin was washed with DMF (10 ml/g resin) five times. The ninhydrin test was performed and appeared positive.   Step 4. Coupling:
           a. Fmoc-AA-OH (3 equivalents calculated relative to resin loading) and HOBt (3 equivalents relative to resin loading) was weighed into a plastic bottle.   b. Solids were dissolved with DMF (5 ml/g resin).   c. HBTU (3 equivalents relative to resin loading) was added to the mixture, followed by the addition of NMM (6 equivalents relative to resin loading).   d. Mixture was added to the resin.   e. Mixture was bubbled (or stirred) gently for 10-60 minutes until a negative ninhydrin test on a small sample of resin was obtained.   
           Step 5. Washing: Resin was washed three times with DMF.   Step 6. Steps 2-5 were repeated until the peptide was assembled.   Step 7. N-terminal Fmoc Deprotection: Step 2 was repeated.   Step 8. Washing and Drying:
           a. After the final coupling, resin was washed three times with DMF, one time with MeOH, three times with DCM, and three times with MeOH.   b. Resin was dried under vacuum (e.g., water aspirator) for 2 hours and high vacuum (oil pump) for a minimum of 12 hours.   
           Step 9. Cleavage:
           a. Dry resin was placed in a plastic bottle and the cleavage cocktail was added. The mixture was shaken at room temperature for 2.5 hours.   b. The resin was removed by filtration under reduced pressure. The resin was washed twice with TFA. Filtrates were combined and an 8-10 fold volume of cold ether was added to obtain a precipitate.   c. Crude peptides were isolated by filtration and then washed twice with cold ether.   
               

     The following chemicals and solvents were used in the synthetic protocol described above: NMM (N-Methylmorpholine); HBTU (2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium Hexafluorophosphate); HOBt (1-Hydroxybenzotriazole); DMF (Dimethylformamide); DCM (Dichloromethane); Methanol; Diethylether; Piperidine; Tis (Triisopropylsilane); Thioanisole; Phenol; EDT (1,2-Ethanedithiol); Trifluoroacetic acid Cocktail 1: TFA/Thioanisole/Phenol/H 2 O/EDT (87.5/5/2.5/2.5/2.5 v/v/); TFA buffer: A (0.1% TFA in water); and TFA buffer B (0.1% TFA in Acetonitrile). 
     Other representative polypeptide analogs were prepared in a manner similar to that described above. Listed below in TABLE 1 are chemical properties of exemplary polypeptide analogs of the invention. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Properties of Exemplary Polypeptide Analogs 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 Molecular Weight 
               
               
                   
                   
                   
                 Based on 
               
               
                 Name of 
                 Amino 
                 Purity Based on RP- 
                 Electrospray 
               
               
                 Analog 
                 Acid Sequence 
                 HPLC Chromatogram 
                 Mass Spectrometry 
               
               
                   
               
               
                 TP-103 
                 SEQ ID NO: 2 
                 96.9% 
                 5267.2 a.m.u. 
               
               
                 TP-104 
                 SEQ ID NO: 3 
                 95.5% 
                 4756.7 a.m.u. 
               
               
                 TP-105 
                 SEQ ID NO: 4 
                 96.1% 
                 5183.3 a.m.u. 
               
               
                 TP-106 
                 SEQ ID NO: 5 
                 95.2% 
                 4784.8 a.m.u. 
               
               
                 TP-107 
                 SEQ ID NO: 6 
                 99.6% 
                 4955.1 a.m.u. 
               
               
                 TP-108 
                 SEQ ID NO: 7 
                 91.5% 
                 5172.4 a.m.u. 
               
               
                   
               
            
           
         
       
     
     Example 5 
     Recombinant Synthesis of the Polypeptides 
     Alternatively, the polypeptides of the present invention may be prepared by cloning and expression of a gene encoding for the desired polypeptide. In this process, a plasmid containing the desired DNA sequence is prepared and inserted into an appropriate host microorganism, typically a bacteria, such as  E. coli , or a yeast, such as  Saccharomyces cerevisiae , inducing the host microorganism to produce multiple copies of the plasmid, and so of the cDNA encoding for the polypeptide analogs of the invention. 
     First, a synthetic gene coding for the selected PACAP or VIP analog is designed with convenient restriction enzyme cleavage sites to facilitate subsequent alterations. Polymerase chain reaction (PCR), as taught by Mullis in U.S. Pat. Nos. 4,683,195 and 4,683,202, incorporated herein by reference, may be used to amplify the sequence. 
     The amplified synthetic gene may be isolated and ligated to a suitable plasmid, such as a Trp LE plasmid, into which four copies of the gene may be inserted in tandem. Preparation of Trp LE plasmids is described in U.S. Pat. No. 4,738,921 and European Patent Publication No. 0212532, incorporated herein by reference. Trp LE plasmids generally produce 8-10 times more protein than Trp E plasmids. The multi-copy gene may then be expressed in an appropriate host, such as  E. coli  or  S. cerevisiae.    
     Trp LE 18 Prot (Ile3, Pro5) may be used as an expression vector in the present invention. Trp LE 18 Prot (Ile3, Pro5) contains the following elements: a pBR322 fragment (EcoRI-BamHI) containing the ampicillin resistant gene and the plasmid origin of replication; an EcoRI-SacII fragment containing the trp promoter and the trpE gene; an HIV protease (Ile3, Pro5) gene fragment (SacII-HindIII); a bGRF gene fragment (HindIII-BamHI); and a transcription terminator from  E. coli  rpoc gene. The HIV protease and bGRF gene fragments are not critical and may be replaced with other coding sequences, if desired. 
     The expressed multimeric fusion proteins then accumulate intracellularly into stable inclusion bodies and may be separated by centrifugation from the rest of the cellular protein. VIP and PACAP related peptides do not denature so purification is straightforward through a combined ion exchange concentration/purification protocol followed by “polishing” on preparative reversed-phase high performance chromatography using a aqueous to aqueous-organic buffer gradient using 0.1% trifluoroacetic acid or 0.4M NH 4 OAc (pH 4) as the pH modifier. The organic modifier used may be any of a number of water miscible solvents, for example acetonitrile, n-propanol, isopropanol, and the like, preferably n-propanol. The isolated fusion protein is converted to the monomeric PACAP or VIP analog by acylation with activated fatty acids and may be purified by cation exchange and/or reverse phase HPLC. The precise protocol is dependent on the particular sequence being synthesized. Typically the free amino terminus is less reactive than a Lys side chain, so differential acylation is straightforward. Alternatively, a fragment of the final sequence may be prepared in this way with subsequent condensation with a synthetically produced fragment containing the N- or C-terminal modifications. Chemical or “native” conjugations may be used (Dawson, P. E.; Muir, T. W.; Clark-Lewis, I.; Kent, S. B. Science 1994, 266, (5186), 776-9; Nilsson, B. L.; Soellner, M. B.; Raines, R. T.  Annu Rev Biophys Biomol Struct  2005, 34, 91-118.). 
     Alternative methods of cloning, amplification, expression, and purification will be apparent to the skilled artisan. Representative methods are disclosed in Maniatis, et al., Molecular Cloning, a Laboratory Manual, 3rd Ed., Cold Spring Harbor Laboratory (2001), incorporated herein by reference. 
     Example 6 
     In Vitro Bioassay with Islet Cell Static Cultures 
     The following exemplary in vitro bioassay was conducted to evaluate the ability of representative polypeptide analogs to modulate insulin secretion. 
     Islet isolation. Rat islets were harvested (Sweet I R, et al. (2004) Biochem. Biophys. Res. Commun. 314, 976-983) from male Fisher rats weighing about 250 g and which were anesthetized by intraperitoneal injection of sodium pentobarbital (35 mg/230 g rat). Generally, the islets were prepared by injecting collagenase (10 mL of 0.23 mg/mL Liberase, Roche Molecular Biochemicals, Indianapolis, Ind.) into the pancreatic duct of the partially dissected pancreas and surgically removing it. All procedures were approved by the Institutional Animal Care and Use Committee at the University of Washington. 
     The pancreata were placed into 15 mL conical tubes containing 5 mL of 0.23 mg/mL Liberase and incubated at 37° C. for 30 min. The digestate was then filtered through a 400-micrometer stainless steel screen, rinsed with Hanks&#39; buffered salt solution, and purified in a gradient solution of Optiprep (Nycomed, Oslo, Norway). Islets were cultured for 18-24 h prior to performing the assay in RPMI Media 1640 supplemented with 10% (v/v) heat inactivated fetal bovine serum (FBS), antibiotic-antimycotic (100 U/mL penicillin, 100 lg/mL streptomycin, and 0.25 lg/mL amphotericin B), 2 mM glutamine (all from Gibco-BRL, Grand Island, N.Y.), and 1 mM beta mercaptoethanol. 
     Bioassay. Islets were picked under a microscope and placed into 10 ml 3 mM Krebs Ringer Buffer (KRB) solution for washing. Islets were incubated in 3 mM glucose KRB for 60 min and then groups of 10 islets per well were placed into 200 μl media in a 96-well plate. The islets were incubated for 120 min under control or treatment conditions, and supernatants were collected. A typical set of conditions tested 3 mM glucose (resting control), 16 mM glucose (testing control), 16 mM glucose+10 nm GLP1, 16 mM glucose+10 nM Exendin-4, 16 mM glucose+50 nM test peptide. The buffer conditions were KRB with 0.1% BSA, 20 mM HEPES and the assay was performed in quadruplicate. Supernatants were evaluated for insulin content using a commercial insulin enzyme-linked immunosorbent (ELISA) assay per manufacturer&#39;s directions. 
     Results of Bioassay. TABLE 2 illustrates the insulin secretion obtained in the above assay for analog TP-106, which exhibited maximal activity in this assay at a concentration of 200 nM. For comparison, Exendin 4 was tested in this assay and showed maximal activity at 10 nM. TP-106 is a highly hydrophobic analog, designed to depot in the site of sc injection and therefore the effective concentration of TP-106 is expected to be much lower than the nominal concentration (200 nM). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Results of Islet Cell Static Culture Bioassay with TP-106 
               
            
           
           
               
               
               
            
               
                   
                 Insulin secreted 
                 Standard 
               
               
                   
                 (ng/100 islets/min) 
                 Deviation 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 3 mM glucose 
                 0.01 
                 0.00 
               
               
                 16 mM glucose 
                 1.38 
                 0.17 
               
               
                 Exendin 4 + 16 mM glucose 
                 4.82 
                 0.20 
               
               
                 50 nM TP-106 + 16 mM glucose 
                 2.72 
                 0.60 
               
               
                 200 nM TP-106 + 16 mM glucose 
                 5.20 
                 0.50 
               
               
                 16 mM glucose + 16 mM glucose 
                 1.58 
                 0.05 
               
               
                   
               
            
           
         
       
     
     The islet cell static culture assay described above was performed on additional exemplary polypeptide analogs. TP-107 exhibited maximal activity in this assay at a concentration of 100 nM. For comparison, Exendin 4 was tested in this assay and showed maximal activity at 10 nM. Presented peptides were designed to bind to serum albumin and thus, the concentration of free peptide to impart insulin activity is expected to be much lower and therefore the analog more potent than indicated in this in vitro assay. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Results of Islet Cell Static Culture Bioassay with TP-107 and TP-108 
               
            
           
           
               
               
               
            
               
                   
                 Average 
                   
               
               
                   
                 Insulin secreted 
                 Standard 
               
               
                   
                 (ng/100 islets/min) 
                 Deviation 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 3 mM glucose 
                 0.14 
                 0.00 
               
               
                 16 mM glucose 
                 3.65 
                 0.80 
               
               
                 10 nM Exendin 4 + 16 mM glucose 
                 6.75 
                 1.15 
               
               
                 10 nM PACAP + 16 mM glucose 
                 6.07 
                 1.67 
               
               
                 10 nM TP-107 + 16 mM glucose 
                 2.89 
                 0.21 
               
               
                 100 nM TP-107 + 16 mM glucose 
                 6.10 
                 1.55 
               
               
                 1 uM TP-107 + 16 mM glucose 
                 6.07 
                 0.90 
               
               
                 100 nM TP-108 + 16 mM glucose 
                 4.10 
                 1.21 
               
               
                 1 uM TP-108 + 16 mM glucose 
                 5.65 
                 0.13 
               
               
                   
               
            
           
         
       
     
     Example 7 
     In Vivo Bioassay 
     The following exemplary in vivo assay was conducted to evaluate the ability of representative polypeptide analogs to modulate insulin secretion. 
     Tested Study Groups. Naïve, 8 weeks old female db/db mice were acclimated for one week, during which period animals were handled periodically to allow them to be acclimated to experiment procedures. Study groups contained 6 mice per group and were administered with one of the following by intraperitoneal injection: 
     (1) Vehicle control; 
     (2) Positive control (exendin-4 or other standard treatment); 
     (3) Polypeptide Analog at high dose; or 
     (4) Polypeptide Analog at low dose. 
     A small volume of blood was taken from a cut at the tip of tail for blood sampling. Blood glucose levels were determined on a commercial, hand-held glucose meter. On Day 1, animals were injected with polypeptide analogs and controls in the morning. Blood samples were taken and analyzed immediately before injection and at 2, 4, 8, 14, and 24 hours after injection. Animals were allowed to feed, ad libitem, throughout the assay (Tsutsumi et al., Diabetes 51:1453-60 (2002)). 
     TABLE 4 lists a representative sampling of the data obtained from the in vivo assay described above. As shown below, TP-106 exhibited statistically significant activity (e.g., reduced plasma glucose) at a high dose 2 hr after injection and maintains activity at 4 hrs post dosing. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Results of In Vivo Assay with TP-103 and TP-106 
               
               
                 Mean Blood Glucose Levels (mmol/L) 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 0 hr 
                 2 hr 
                 4 hr 
                 8 hr 
                 14 hr 
                 24 hr 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Vehicle 
                 23.9 
                 21.9 
                 18.3 
                 27.3 
                 22.5 
                 23.5 
               
               
                   
                 s.d.* = 1.33 
                 s.d. = 1.22 
                 s.d. = 1.01 
                 s.d. = 1.52 
                 s.d. = 1.25 
                 s.d. = 1.31 
               
               
                 TP-103 Low dose 
                 22.9 
                 20.5 
                 17.6 
                 26.4 
                 24.6 
                 21.4 
               
               
                   
                 s.d. = 1.27 
                 s.d. = 1.14 
                 s.d. = 0.98 
                 s.d. = 1.47 
                 s.d. = 1.37 
                 s.d. = 1.19 
               
               
                 TP-103 High dose 
                 20.7 
                 17.3 
                 16.9 
                 23.4 
                 23.7 
                 25.0 
               
               
                   
                 s.d. = 1.15 
                 s.d. = 0.96 
                 s.d. = 0.94 
                 s.d. = 1.30 
                 s.d. = 1.31 
                 s.d. = 1.39 
               
               
                 TP-106 Low dose 
                 23.9 
                 20.5 
                 16.1 
                 24.0 
                 28.2 
                 23.2 
               
               
                   
                 s.d. = 1.33 
                 s.d. = 1.14 
                 s.d. = 0.89 
                 s.d. = 1.33 
                 s.d. = 1.57 
                 s.d. = 1.29 
               
               
                 TP-106 High dose 
                 21.8 
                 13.4 
                 14.7 
                 25.1 
                 26.3 
                 21.2 
               
               
                   
                 s.d. = 1.21 
                 s.d. = 0.75 
                 s.d. = 0.82 
                 s.d. = 1.39 
                 s.d. = 1.46 
                 s.d. = 1.18 
               
               
                   
               
               
                 *s.d. = standard deviation 
               
            
           
         
       
     
     Example 8 
     Uses of the Invention 
     The polypeptides of the present invention are useful for the prevention and treatment of a variety of metabolic disorders. In particular, the compounds of the present invention are indicated for the prophylaxis and therapeutic treatment of elevated blood glucose levels, hyperglycemia, diabetes, including Type 2 Diabetes Mellitus, Maturity Onset Diabetes of the Young (MODY), Metabolic Syndrome, insulin resistance, metabolic acidosis and obesity. 
     The polypeptides of the present invention are useful for the prevention and treatment of a variety of inflammatory disorders, defined broadly. In particular the compounds of the present invention are indicated for the prophylaxis and therapeutic treatment of asthma (Linden A, et al. (2003). Thorax 58: 217-21), cardioprotection during ischemia (Kalfin, et al. (1994). J Pharmacol Exp Ther 1268: 952-8; Das, et al. (1998). Ann NY Acad Sci 865: 297-308), primary pulmonary hypertension (Petkov V, et al. (2003). J Clin Invest 111: 1339-46), and the like. 
     In another embodiment, the polypeptides of the invention may be administered in combination with other compounds useful in the treatment of metabolic disorders. For example, the polypeptides of the invention may be administered with one or more of the following compounds used in the treatment of metabolic disorders, including but not limited to insulin, insulin analogs, incretin, incretin analogs, glucagon-like peptide, glucagon-like peptide analogs, glucose dependent insulinotropic peptide analogs, exendin, exendin analogs, sulfonylureas, biguanides, α-glucosidase inhibitors, thiazolidinediones, peroxisome proliferator activated receptor (PPAR, of which includes agents acting on the α, β, or γ subtypes of PPAR receptors and/or those agent acting on multiple subtypes of the PPAR receptors) agonists, PPAR antagonists and PPAR partial agonists may be administered in combination with the polypeptides of the present invention. 
     In other contemplated disease applications, the peptides of the invention can be used advantageously in coordination with pharmaceuticals currently applied for that disease. Particularly beneficial are combination drug formulations containing mixtures of the active pharmaceutical ingredients with excipients. For example, in asthma, the VPAC2 agonists can used in combination with inhaled formulations containing bronchodilators, beta 2 adrenoceptor agonists, inhaled corticosteroids, anti-inflammatory steroids, leukotriene modifiers, leukotriene receptor antagonists, chemokine modifiers, chemokine receptor antagonists, cromolyn, nedocromil, xanthines, anticholinergic agents, immune modulating agents, other known anti-asthma medications, and the like. Additional agents in development (Corry D B and Kheradmand F (2006) J Allergy Clin Immunol 117 (2 Suppl): S461-47) may also be beneficial when used in combination with VPAC2 agonists. 
     VPAC2 combination treatments may make use of currently applied therapeutics for treatment of pulmonary hypertension, as well. Thus a VPAC2 agonist may be utilized in combination with nitric oxide donors, prostacyclins, endothelin antagonists, adrenoceptor blockers, phosphodiesterases inhibitors, ion channel blockers and other vasodilators (Levy J H (2005) Tex Heart Inst J 32: 467-71; Haj R M, et al. (2006) Curr Opin Anesthesiol 19: 88-95). 
     Representative delivery regimens include oral, parenteral (including subcutaneous, intramuscular and intravenous injection), rectal, buccal (including sublingual), transdermal, inhalation and intranasal. An attractive and widely used method for delivery of peptides entails subcutaneous injection of a controlled release injectable formulation. Preferred administration routes for the application of the peptides of the invention are subcutaneous, intranasal and inhalation administration. 
     The selection of the exact dose and composition and the most appropriate delivery regimen will be influenced by, inter alia, the pharmacological properties of the selected polypeptide, the nature and severity of the condition being treated, and the physical condition and mental acuity of the recipient. Additionally, the route of administration will result in differential amounts of absorbed material. Bioavailabilities for administration of peptides through different routes are particularly variable, with amounts from less than 1% to near 100% being seen. Typically, bioavailability from routes other than intravenous injection are 50% or less. 
     In general, the polypeptides of the invention, or salts thereof, are administered in amounts between about 0.1 and 60 μg/kg body weight per day, preferably from about 0.1 to about 1 μg/kg body weight per day, by subcutaneous injection. For a 50 kg human female subject, the daily dose of active ingredient is from about 5 to about 1000 μg, preferably from about 5 to about 500 μg by subcutaneous injection. Different doses will be needed, depending on the route of administration and the applicable bioavailability observed. By inhalation, the daily dose is from 100 to about 5,000 μg, twice daily. In other mammals, such as horses, dogs, and cattle, higher doses may be required. This dosage may be delivered in a conventional pharmaceutical composition by a single administration, by multiple applications, or via controlled release, as needed to achieve the most effective results, preferably one or more times daily by injection. 
     Pharmaceutically acceptable salts retain the desired biological activity of the parent polypeptide without toxic side effects. Examples of such salts are (a) acid addition salts formed with inorganic acids, for example hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid and the like; and salts formed with organic acids such as, for example, acetic acid, oxalic acid, tartaric acid, succinic acid, maleic acid, fumaric acid, gluconic acid, citric acid, malic acid, ascorbic acid, benzoic acid, tannic acid, pamoic acid, alginic acid, polyglutamic acid, naphthalenesulfonic acids, naphthalene disulfonic acids, polygalacturonic acid and the like; (b) base addition salts formed with polyvalent metal cations such as zinc, calcium, bismuth, barium, magnesium, aluminum, copper, cobalt, nickel, cadmium, and the like; or with an organic cation formed from N,N′-dibenzylethylenediamine or ethylenediamine; or (c) combinations of (a) and (b), e.g., a zinc tannate salt and the like. 
     A further aspect of the present invention relates to pharmaceutical compositions comprising as an active ingredient a polypeptide of the present invention, or pharmaceutically acceptable salt thereof, in admixture with a pharmaceutically acceptable, non-toxic carrier. As mentioned above, such compositions may be prepared for parenteral (subcutaneous, intramuscular or intravenous) administration, particularly in the form of liquid solutions or suspensions; for oral or buccal administration, particularly in the form of tablets or capsules; for intranasal administration, particularly in the form of powders, nasal drops or aerosols; for inhalation, particularly in the form of liquid solutions or dry powders with excipients, defined broadly; and for rectal or transdermal administration. 
     The compositions may conveniently be administered in unit dosage form and may be prepared by any of the methods well-known in the pharmaceutical art, for example as described in Remington&#39;s Pharmaceutical Sciences, 17th ed., Mack Publishing Company, Easton, Pa., (1985), incorporated herein by reference. Formulations for parenteral administration may contain as excipients sterile water or saline, alkylene glycols such as propylene glycol, polyalkylene glycols such as polyethylene glycol, oils of vegetable origin, hydrogenated naphthalenes, serum albumin nanoparticles (as used in Abraxane™, American Pharmaceutical Partners, Inc. Schaumburg Ill.), and the like. For oral administration, the formulation can be enhanced by the addition of bile salts or acylcarnitines. Formulations for nasal administration may be solid and may contain excipients, for example, lactose or dextran, or may be aqueous or oily solutions for use in the form of nasal drops or metered spray. For buccal administration typical excipients include sugars, calcium stearate, magnesium stearate, pregelatinated starch, and the like. 
     When formulated for nasal administration, the absorption across the nasal mucous membrane may be enhanced by surfactant acids, such as for example, glycocholic acid, cholic acid, taurocholic acid, ethocholic acid, deoxycholic acid, chenodeoxycholic acid, dehydrocholic acid, glycodeoxycholic acid, cyclodextrins and the like in an amount in the range between about 0.2 and 15 weight percent, preferably between about 0.5 and 4 weight percent, most preferably about 2 weight percent. An additional class of absorption enhancers exhibiting greater efficacy with decreased irritation is the class of alkyl maltosides, such as tetradecylmaltoside (Arnold, J J, et al. (2004). J Pharm. Sci. 93, 2205-13, and references therein, all of which are hereby incorporated by reference). 
     When formulated for delivery by inhalation, a number of formulations offer advantages. Adsorption of the active peptide to readily dispersed solids such as diketopiperazines (for example Technosphere particles; Pfutzner A and Forst T (2005). Expert Opin Drug Deliv 2: 1097-106.) or similar structures gives a formulation which results in a rapid initial uptake of the therapeutic agent. Lyophylized powders, especially glassy particles, containing the active peptide and an excipient are useful for delivery to the lung with good bioavailability, for example, see Exubera® (inhaled insulin by Pfizer and Aventis Pharmaceuticals Inc.). Additional systems for delivery of polypeptides by inhalation (Mandal T K (2005) Am J Health Syst Pharm 62: 1359-64) are well known in the art and are incorporated into this invention. 
     Delivery of the compounds of the present invention to the subject over prolonged periods of time, for example, for periods of one week to one year, may be accomplished by a single administration of a controlled release system containing sufficient active ingredient for the desired release period. Various controlled release systems, such as monolithic or reservoir-type microcapsules, depot implants, osmotic pumps, vesicles, micelles, liposomes, transdermal patches, iontophoretic devices and alternative injectable dosage forms may be utilized for this purpose. Localization at the site to which delivery of the active ingredient is desired is an additional feature of some controlled release devices, which may prove beneficial in the treatment of certain disorders. 
     One form of controlled release formulation contains the polypeptide or its salt dispersed or encapsulated in a slowly degrading, non-toxic, non-antigenic polymer such as copoly(lactic/glycolic) acid, as described in the pioneering work of Kent, Lewis, Sanders, and Tice, U.S. Pat. No. 4,675,189, incorporated by reference herein. The compounds or, preferably, their relatively insoluble salts, may also be formulated in cholesterol or other lipid matrix pellets, or silastomer matrix implants. Additional slow release, depot implant or injectable formulations will be apparent to the skilled artisan. See, for example, Sustained and Controlled Release Drug Delivery Systems, J. R. Robinson ed., Marcel Dekker, Inc., New York, 1978, and R. W. Baker, Controlled Release of Biologically Active Agents, John Wiley &amp; Sons, New York, 1987, incorporated by reference herein. 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each independent publication or patent application was specifically and individually indicated to be incorporated by reference. 
     While the examples and discussion given above are intended to illustrate the synthesis and testing of representative compounds of the invention, it will be understood that it is capable of further modifications and should not be construed as limiting the scope of the appended claims.