Chirality of novel bitopic agonists determine unique pharmacology at the dopamine 2 and 3 receptors

The dopamine 2 and 3 receptors (D 2 R and D 3 R) are well‐characterized targets for neuropsychiatric disorders. D 2 R/D 3 R agonists are used as add‐on therapies for Parkinson’s disease (PD) and have been studied for other motor‐associated disorders. Selectively targeting D 3 R over D 2 R is attractive for two reasons: i) restricted tissue distribution of D 3 R compared to D 2 R exhibits potential for lesser side‐effects; ii) there is evidence for dominant role of D 3 R over D 2 R for neuroprotective and neurorestorative actions of dopaminergic agonists used for the treatment of PD. However, lack of highly selective D 3 R agonists has made it difficult to separate the D 3 R vs. D 2 R physiological effects. Indeed, the development of highly selective D 3 R agonists has remained a challenge due to their 78% sequence identity in the transmembrane domain. To improve the outlook of D 3 R agonist‐based medication development, based on a potent D 3 R‐selective agonist PF592,379, we have designed, synthesized, and pharmacologically characterized bitopic ligands with a secondary pharmacophore tethered to the PF592,379 primary pharmacophore by a linker. Using BRET based functional assays that measure G‐protein activation and β‐arrestin recruitment, we characterized these bitopic ligands at both D 3 R and D 2 R. We found that the addition of secondary pharmacophore to the PF592,379 scaffold improved potency at D 3 R in G‐protein activation with maximal efficacy similar or higher than that of the parent compound. In contrast, the potencies at D 3 R in recruitment of β‐arrestin remained the same. Some of these compounds also showed modest D 3 R over D 2 R selectivity. Interestingly, certain combinations of secondary pharmacophores and linkers resulted in G‐protein signaling bias at either D 3 R or D 2 R but not both, resulting in receptor‐selective bias. We also found that given the same ligand structure, chirality can confer subtype selectivity and promote G‐protein bias. Together, our novel bitopic D 3 R agonists based on PF592,379 scaffold provide novel tools to further probe unique pharmacology at D 3 R and evaluate the therapeutic potential of targeting D 3 R vs. D 2 R for PD. Support or Funding Information National Institute on Drug Abuse – Intramural Research Program, National Institutes of Health