Discovery of a Biased Allosteric Modulator for Cannabinoid 1 Receptor: Preclinical Anti-Glaucoma Efficacy
Sumanta Garai, Luciana M. Leo, Anna-Maria Szczesniak, Dow P. Hurst, Peter C. Schaffer, Ayat Zagzoog, Tallan Black, Jeffrey R. Deschamps, Elke Miess, Stefan Schulz, David R. Janero, Alex Straiker, Roger G. Pertwee, Mary E. Abood, Melanie E. M. Kelly, Patricia H. Reggio, Robert B. Laprairie, Ganesh A. Thakur
Abstract
We apply the magic methyl effect to improve the potency/efficacy of GAT211, the prototypic 2-phenylindole-based cannabinoid type-1 receptor (CB1R) agonist-positive allosteric modulator (ago-PAM). Introducing a methyl group at the α-position of nitro group generated two diastereomers, the greater potency and efficacy of erythro, (±)-9 vs threo, (±)-10 constitutes the first demonstration of diastereoselective CB1R-allosteric modulator interaction. Of the (±)-9 enantiomers, (−)-(S,R)-13 evidenced improved potency over GAT211 as a CB1R ago-PAM, whereas (+)-(R,S)-14 was a CB1R allosteric agonist biased toward G protein- vs β-arrestin1/2-dependent signaling. (−)-(S,R)-13 and (+)-(R,S)-14 were devoid of undesirable side effects (triad test), and (+)-(R,S)-14 reduced intraocular pressure with an unprecedentedly long duration of action in a murine glaucoma model. (−)-(S,R)-13 docked into both a CB1R extracellular PAM and intracellular allosteric-agonist site(s), whereas (+)-(R,S)-14 preferentially engaged only the latter. Exploiting G-protein biased CB1R-allosteric modulation can offer safer therapeutic candidates for glaucoma and, potentially, other diseases.