The pharmacological basis for nonpeptide agonism of the GLP-1 receptor by orforglipron

Orally bioavailable, synthetic nonpeptide agonists (NPAs) of the glucagon-like peptide-1 receptor (GLP-1R) may offer an effective, scalable pharmacotherapy to address the metabolic disease epidemic. One of the first molecules in the emerging class of GLP-1R NPAs is orforglipron, which is in clinical development for treating type 2 diabetes and obesity. Here, we characterized the pharmacological properties of orforglipron in comparison with peptide-based GLP-1R agonists and other NPAs. Competition binding experiments using either [¹²⁵I]GLP-1(7-36)NH₂ or [³H]orforglipron indicated that orforglipron is a high-affinity [inhibition constant (<i>K</i>_i) = 1 nM], selective ligand of the human GLP-1R. Signal transduction assays showed that orforglipron has low intrinsic efficacy for effector activation and negligible β-arrestin recruitment. To evaluate GLP-1R engagement in vivo, mice expressing the human GLP-1R were administered orforglipron and subjected to a glucose tolerance test. Predicted receptor occupancy was calculated using the receptor <i>K</i>_i value of orforglipron and its unbound concentration in vivo that reduces hyperglycemia. These experiments revealed that low GLP-1R occupancy by orforglipron is sufficient to yield a full biological response. Moreover, in a model where CRISPR-Cas9 gene editing was used to sensitize the rat GLP-1R (<i>Glp1r^S33W</i>) to GLP-1R NPAs, target engagement by orforglipron in the pancreas and brain was consistent with peptide-based GLP-1R agonists. Diet-induced obesity in <i>Glp1r^S33W</i> rats enabled studies showing weight loss in animals orally administered orforglipron versus subcutaneous injection of GLP-1R agonist semaglutide. Furthermore, crossover studies indicated oral orforglipron can sustain efficacy initiated by parenteral semaglutide. The pharmacological properties of orforglipron may inform targeting of other peptide receptors with NPAs.