Tirzepatide (LY3298176) is a dual GIP and GLP-1 receptor agonist under development for the treatment of type 2 diabetes mellitus (T2DM), obesity, and non-alcoholic 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 (GIPR) than the GLP-1 receptor (GLP-1R), corroborating an imbalanced mechanism of action. Pharmacologically, signaling studies demonstrate that tirzepatide mimics the actions of native GIP at the GIPR but show bias at the GLP-1R to favor cAMP generation over β-arrestin recruitment, coincident with a weaker ability to drive GLP-1R 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 the biased agonism of tirzepatide enhances insulin secretion. Imbalance toward GIPR, combined with distinct signaling properties at the GLP-1R, together may account for the promising efficacy of this new investigational agent.
Francis S. Willard, Jonathan D. Douros, Maria B. N. Gabe, Aaron D. Showalter, David B. Wainscott, Todd M. Suter, Megan E. Capozzi, Wijnand J. C. van der Velden, Cynthia. Stutsman, Guemalli R. Cardona, Shweta Urva, Paul J. Emmerson, Jens J. Holst, David A. D'Alessio, Matthew P. Coghlan, Mette M. Rosenkilde, Jonathan E. Campbell, Kyle W. Sloop
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