title: Allosteric ligands of the glucagon-like peptide 1 receptor (GLP-1R) differentially modulate endogenous and exogenous peptide responses in a pathway-selective manner: implications for drug screening.
abstract: The glucagon-like peptide-1 (GLP-1) receptor is a key regulator of insulin secretion and a major therapeutic target for treatment of diabetes. However, GLP-1 receptor function is complex, with multiple endogenous peptides that can interact with the receptor, including full-length (1-37) and truncated (7-37) forms of GLP-1 that can each exist in an amidated form and the related peptide oxyntomodulin. We have investigated two GLP-1 receptor allosteric modulators, Novo Nordisk compound 2 (6,7-dichloro2-methylsulfonyl-3-tert-butylaminoquinoxaline) and quercetin, and their ability to modify binding and signaling (cAMP formation, intracellular Ca(2+) mobilization, and extracellular signal-regulated kinase 1/2 phosphorylation) of each of the naturally occurring endogenous peptide agonists, as well as the clinically used peptide mimetic exendin-4. We identified and quantified stimulus bias across multiple endogenous peptides, with response profiles for truncated GLP-1 peptides distinct from those of either the full-length GLP-1 peptides or oxyntomodulin, the first demonstration of such behavior at the GLP-1 receptor. Compound 2 selectively augmented cAMP signaling but did so in a peptide-agonist dependent manner having greatest effect on oxyntomodulin, weaker effect on truncated GLP-1 peptides, and negligible effect on other peptide responses; these effects were principally driven by parallel changes in peptide agonist affinity. In contrast, quercetin selectively modulated calcium signaling but with effects only on truncated GLP-1 peptides or exendin and not oxyntomodulin or full-length peptides. These data have significant implications for how GLP-1 receptor targeted drugs are screened and developed, whereas the allosterically driven, agonist-selective, stimulus bias highlights the potential for distinct clinical efficacy depending on the properties of individual drugs.
authors.affiliation: Drug Discovery Biology Laboratory, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology, Monash University, Parkville, Victoria, Australia.
authors.forename: Cassandra
authors.initials: C
authors.lastname: Koole
authors.forename: Denise
authors.initials: D
authors.lastname: Wootten
authors.forename: John
authors.initials: J
authors.lastname: Simms
authors.forename: Celine
authors.initials: C
authors.lastname: Valant
authors.forename: Rohan
authors.initials: R
authors.lastname: Sridhar
authors.forename: Owen L
authors.initials: OL
authors.lastname: Woodman
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Miller
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Summers
authors.forename: Arthur
authors.initials: A
authors.lastname: Christopoulos
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Sexton
mesh_terms: D000818:Animals; D006224:Cricetinae; D004353:Drug Evaluation, Preclinical; D000077270:Exenatide; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D008024:Ligands; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D053772:Oxyntomodulin; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D018027:Receptors, Glucagon; D015398:Signal Transduction / Q000502:physiology; D014688:Venoms
chemical_list: D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D008024:Ligands; D053772:Oxyntomodulin; D010455:Peptides; D018027:Receptors, Glucagon; D014688:Venoms; D052216:Glucagon-Like Peptide 1; D000077270:Exenatide; D048052:Mitogen-Activated Protein Kinase 3