👤 Francis S Willard

Glucagon-like peptide-1 receptor (GLP-1R)/glucose-dependent insulinotropic peptide receptor (GIPR) agonistic analogs have yielded superior results in enhancing glycemic control and weight management compared to GLP-1R agonism alone. Intriguingly, GIPR agonism appears to induce antiemetic effects, potentially alleviating part of the nausea and vomiting side effects common to GLP-1R agonists like semaglutide. Here, we show in rats and shrews that GIPR agonism blocks emesis and attenuates other malaise behaviors elicited by GLP-1R activation while maintaining reduced food intake and body weight loss and improved glucose tolerance. The GLP-1R/GIPR agonist tirzepatide induced significantly fewer side effects than equipotent doses of semaglutide. These findings underscore the therapeutic potential of combined pharmaceutical strategies activating both incretin systems, leading to enhanced therapeutic index and reduced occurrence of nausea and vomiting for obesity and diabetes treatments. Show less

The incretin peptides glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptors coordinate β cell secretion that is proportional to nutrient intake. This effect permits consistent and restricted glucose excursions across a range of carbohydrate intake. The canonical signaling downstream of ligand-activated incretin receptors involves coupling to Gαs protein and generation of intracellular cAMP. However, recent reports have highlighted the importance of additional signaling nodes engaged by incretin receptors, including other G proteins and β-arrestin proteins. Here, the importance of Gαs signaling was tested in mice with conditional, postdevelopmental β cell deletion of Gnas (encoding Gαs) under physiological and pharmacological conditions. Deletion of Gαs/cAMP signaling induced immediate and profound hyperglycemia that responded minimally to incretin receptor agonists, a sulfonylurea, or bethanechol. While islet area and insulin content were not affected in Gnasβcell-/-, perifusion of isolated islets demonstrated impaired responses to glucose, incretins, acetylcholine, and IBMX In the absence of Gαs, incretin-stimulated insulin secretion was impaired but not absent, with some contribution from Gαq signaling. Collectively, these findings validate a central role for cAMP in mediating incretin signaling, but also demonstrate broad impairment of insulin secretion in the absence of Gαs that causes both fasting hyperglycemia and glucose intolerance. Show less

In response to extracellular ligands, G protein-coupled receptors (GPCRs) undergo conformational changes that induce coupling to intracellular effectors such as heterotrimeric G proteins that trigger various downstream signaling pathways. These events have been shown to be highly regulated by concerted effects of post-translational modifications (PTMs) that occur in a ligand-dependent manner. Most notably, phosphorylation of residues in the C-terminal cytoplasmic tail of GPCRs has been strongly implicated in promoting receptor interactions with β-arrestins (βarrs), which are cytosolic adaptor proteins that modulate G protein coupling, receptor internalization, and perhaps also serve as signaling modules in their own right. Here, we use proteomic methods to identify C-tail residues that are phosphorylated in the glucagon family of class B1 GPCRs (GLP-1R, GCGR, and GIPR) upon agonist addition. We demonstrate that the phosphorylation of GLP-1R and GIPR is a critical determinant in the formation of GPCR-βarr complexes. However, our results suggest that ligand-induced βarr recruitment to GCGR proceeds in a phosphorylation-independent manner. These findings highlight the importance of recognizing phosphorylation as a component in the regulation of class B1 GPCR signaling but also the need to consider how such phenomena may not necessarily yield identical effects on intracellular signaling cascades. Show less

With an increasing prevalence of obesity, there is a need for new therapies to improve body weight management and metabolic health. Multireceptor agonists in development may provide approaches to fulfill this unmet medical need. LY3437943 is a novel triple agonist peptide at the glucagon receptor (GCGR), glucose-dependent insulinotropic polypeptide receptor (GIPR), and glucagon-like peptide-1 receptor (GLP-1R). In vitro, LY3437943 shows balanced GCGR and GLP-1R activity but more GIPR activity. In obese mice, administration of LY3437943 decreased body weight and improved glycemic control. Body weight loss was augmented by the addition of GCGR-mediated increases in energy expenditure to GIPR- and GLP-1R-driven calorie intake reduction. In a phase 1 single ascending dose study, LY3437943 showed a safety and tolerability profile similar to other incretins. Its pharmacokinetic profile supported once-weekly dosing, and a reduction in body weight persisted up to day 43 after a single dose. These findings warrant further clinical assessment of LY3437943. Show less

SignificanceTirzepatide is a dual agonist of the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP-1R), which are incretin receptors that regulate carbohydrate metabolism. This investigational agent has proven superior to selective GLP-1R agonists in clinical trials in subjects with type 2 diabetes mellitus. Intriguingly, although tirzepatide closely resembles native GIP in how it activates the GIPR, it differs markedly from GLP-1 in its activation of the GLP-1R, resulting in less agonist-induced receptor desensitization. We report how cryogenic electron microscopy and molecular dynamics simulations inform the structural basis for the unique pharmacology of tirzepatide. These studies reveal the extent to which fatty acid modification, combined with amino acid sequence, determines the mode of action of a multireceptor agonist. Show less

Tirzepatide (LY3298176) is a dual GIP and GLP-1 receptor agonist under development for the treatment of type 2 diabetes mellitus (T2DM), obesity, and nonalcoholic steatohepatitis. Early phase trials in T2DM indicate that tirzepatide improves clinical outcomes beyond those achieved by a selective GLP-1 receptor agonist. Therefore, we hypothesized that the integrated potency and signaling properties of tirzepatide provide a unique pharmacological profile tailored for improving broad metabolic control. Here, we establish methodology for calculating occupancy of each receptor for clinically efficacious doses of the drug. This analysis reveals a greater degree of engagement of tirzepatide for the GIP receptor than the GLP-1 receptor, corroborating an imbalanced mechanism of action. Pharmacologically, signaling studies demonstrate that tirzepatide mimics the actions of native GIP at the GIP receptor but shows bias at the GLP-1 receptor to favor cAMP generation over β-arrestin recruitment, coincident with a weaker ability to drive GLP-1 receptor internalization compared with GLP-1. Experiments in primary islets reveal β-arrestin1 limits the insulin response to GLP-1, but not GIP or tirzepatide, suggesting that the biased agonism of tirzepatide enhances insulin secretion. Imbalance toward GIP receptor, combined with distinct signaling properties at the GLP-1 receptor, together may account for the promising efficacy of this investigational agent. Show less