D2 Dopamine Receptor G Protein-Biased Partial Agonists Based on Cariprazine

Functionally selective G protein-coupled receptor ligands are valuable tools for deciphering the roles of downstream signaling pathways that potentially contribute to therapeutic effects versus side effects. Recently, we discovered both G(i/o)-biased and beta-arrestin2-biased D-2 receptor agonists based on the Food and Drug Administration (FDA)-approved drug aripiprazole. In this work, based on another FDA-approved drug, cariprazine, we conducted a structure-functional selectivity relationship study and discovered compound 38 (MS1768) as a potent partial agonist that selectively activates the G(i/o) pathway over beta-arrestin2. Unlike the dual D2R/D3R partial agonist cariprazine, compound 38 showed selective agonist activity for D2R over D3R. In fact, compound 38 exhibited potent antagonism of dopamine-stimulated beta-arrestin2 recruitment. In our docking studies, compound 38 directly interacts with S193(5.42) on TM5 but has no interactions with extracellular loop 2, which appears to be in contrast to the binding poses of D2R beta-arrestin2-biased ligands. In in vivo studies, compound 38 showed high D2R receptor occupancy in mice and effectively inhibited phencyclidine-induced hyperlocomotion.