A Ligand-Triggered Receptor Conformation Enables the Design of Selective Agonists for the Dopamine 3 Receptor (D3R) Using a Bitopic Strategy

Abstract While G protein-coupled receptors (GPCRs) represent the largest drug target family, designing subtype-selective molecules is still a challenge, especially to distinguish among closely related subtypes. One of the most challenging cases is the distinction between dopamine D2R and D3R, pivotal receptors in motor functions and cognition, and targets of Parkinson’s disease treatments, schizophrenia, or substance use disorders. Attempts to design D3R-selective molecules with ligands binding toward the first transmembrane helix (the most sequence-diverse and conformationally flexible segment in GPCRs but rarely participating in ligand binding) allowed us to discover a ligand-induced ordering of TM1 unique to D3R, yielding an unexploited selectivity site for drug development. Using rational bitopic drug design and the ligand-triggered conformation of the D3R we designed, synthesized, and characterized the most selective D3R agonists to date, >100,000-fold more selective than available ligands. More specifically, we report D3R partial agonists AB12-82 (6d) and AB13-73A (11), with >575,000- and >750,000-fold subtype selectivity, picomolar potency, and 85% and 49% efficacy, respectively. We also present the most selective full agonists reported to date, AB13-08 (4b) and AB13-46A (9), presenting low and subnanomolar potencies with >2,800- and 6,300-fold selectivity for D3R. Overall, we introduce a first-in-class pharmacological toolbox to dissect the (patho)-physiology of D3R, open new avenues for the design of improved neurotherapeutics, and show that using ligand-induced TM1 reorganizations might represent a promising strategy for the design of subtype-selective molecules in other GPCRs.