Tunable Biased Signaling of the Angiotensin II Type 1 Receptor for Inotropy via C-Terminal Peptide Engineering and Allosteric Site Targeting

The angiotensin II (AngII) type 1 receptor (AT1R) is a key prototypical G protein-coupled receptor in cardiovascular regulation. Biased agonists activating G protein or β-arrestin pathways offer therapeutic promise, but the molecular determinants of this signaling bias and its physiological implications remain poorly understood. This study profiles AngII analogs with C-terminal Phe⁸ modifications, identifies compounds 11, 12, and 29a as exhibiting differential Gα_q activation while retaining potent β-arrestin recruitment. Notably, 12 with low levels of Gα_q activity, enhances left ventricular ejection fraction with limited pressor responses in normotensive rats. In contrast, other analogs with variably superior Gα_q activity do not promote inotropy. Molecular modeling suggests that the flexible side chain of 12 accesses a deep allosteric pocket within AT1R, driving its unique signaling profile. This study demonstrates that engineering AngII's C-terminus enables selective tuning of AT1R signaling to control arterial versus cardiac responses, providing strategies for developing improved cardiovascular therapeutics.