title: Discovery of dual-action membrane-anchored modulators of incretin receptors.
abstract: BACKGROUND
  The glucose-dependent insulinotropic polypeptide (GIP) and the glucagon-like peptide-1 (GLP-1) receptors are considered complementary therapeutic targets for type 2 diabetes. Using recombinant membrane-tethered ligand (MTL) technology, the present study focused on defining optimized modulators of these receptors, as well as exploring how local anchoring influences soluble peptide function.
  
  
  RESULTS
  Serial substitution of residue 7 in membrane-tethered GIP (tGIP) led to a wide range of activities at the GIP receptor, with [G(7)]tGIP showing enhanced efficacy compared to the wild type construct. In contrast, introduction of G(7) into the related ligands, tGLP-1 and tethered exendin-4 (tEXE4), did not affect signaling at the cognate GLP-1 receptor. Both soluble and tethered GIP and GLP-1 were selective activators of their respective receptors. Although soluble EXE4 is highly selective for the GLP-1 receptor, unexpectedly, tethered EXE4 was found to be a potent activator of both the GLP-1 and GIP receptors. Diverging from the pharmacological properties of soluble and tethered GIP, the newly identified GIP-R agonists, (i.e. [G(7)]tGIP and tEXE4) failed to trigger cognate receptor endocytosis. In an attempt to recapitulate the dual agonism observed with tEXE4, we conjugated soluble EXE4 to a lipid moiety. Not only did this soluble peptide activate both the GLP-1 and GIP receptors but, when added to receptor expressing cells, the activity persists despite serial washes.
  
  
  CONCLUSIONS
  These findings suggest that conversion of a recombinant MTL to a soluble membrane anchored equivalent offers a means to prolong ligand function, as well as to design agonists that can simultaneously act on more than one therapeutic target.
authors.affiliation: Molecular Cardiology Research Institute, Tufts Medical Center, Tufts University School of Medicine, Boston, Massachusetts, United States of America.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Fortin
authors.forename: Daniel
authors.initials: D
authors.lastname: Chinnapen
authors.forename: Martin
authors.initials: M
authors.lastname: Beinborn
authors.forename: Wayne
authors.initials: W
authors.lastname: Lencer
authors.forename: Alan S
authors.initials: AS
authors.lastname: Kopin
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D000077270:Exenatide; D005749:Gastric Inhibitory Polypeptide / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D054795:Incretins / Q000494:pharmacology; D018613:Microscopy, Confocal; D010455:Peptides / Q000494:pharmacology; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism*; D018027:Receptors, Glucagon / Q000378:metabolism; D014688:Venoms / Q000494:pharmacology
chemical_list: C000593833:GLP1R protein, human; D000067757:Glucagon-Like Peptide-1 Receptor; D054795:Incretins; D010455:Peptides; D011964:Receptors, Gastrointestinal Hormone; D018027:Receptors, Glucagon; D014688:Venoms; D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1; D000077270:Exenatide; C041086:gastric inhibitory polypeptide receptor