Pharmacological characterization of mono-, dual- and tri-peptidic agonists at GIP and GLP-1 receptors

Glucose-dependent insulinotropic peptide (GIP) is an incretin hormone with physiological roles in adipose tissue, the central nervous system and bone metabolism. While selective ligands for GIP receptor (GIPR) have not been advanced for disease treatment, dual and triple agonists of GIPR, in conjunction with that of glucagon-like peptide-1 (GLP-1) and glucagon receptors, are currently in clinical trials, with an expectation of enhanced efficacy beyond that of GLP-1 receptor (GLP-1R) agonist monotherapy for diabetic patients. Consequently, it is important to understand the pharmacological behavior of such drugs. In this study, we have explored signaling pathway specificity and the potential for biased agonism of mono-, dual- and tri-agonists of GIPR using human embryonic kidney 293 (HEK293) cells recombinantly expressing human GIPR or GLP-1R. Compared to GIP (1-42), the GIPR mono-agonists Pro3GIP and Lys3GIP are biased towards ERK1/2 phosphorylation (pERK1/2) relative to cAMP accumulation at GIPR, whereas the triple agonist at GLP-1R/GCGR/GIPR is biased towards pERK1/2 relative to beta-arrestin2 recruitment. Moreover, the dual GIPR/GLP-1R agonist, LY3298176, is biased towards pERK1/2 relative to cAMP accumulation at both GIPR and GLP-1R compared to their respective endogenous ligands. These data reveal novel pharmacological properties of potential therapeutic agents that may impact on diversity in clinical responses.