Discovery of a Biased Allosteric Modulator for Cannabinoid 1 Receptor: Preclinical Anti-Glaucoma Efficacy

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 <i>erythro</i>, (±)-<b>9</b> vs <i>threo</i>, (±)-<b>10</b> constitutes the first demonstration of diastereoselective CB1R-allosteric modulator interaction. Of the (±)-<b>9</b> enantiomers, (-)-(<i>S</i>,<i>R</i>)-<b>13</b> evidenced improved potency over GAT211 as a CB1R ago-PAM, whereas (+)-(<i>R</i>,<i>S</i>)-<b>14</b> was a CB1R allosteric agonist biased toward G protein- vs β-arrestin1/2-dependent signaling. (-)-(<i>S</i>,<i>R</i>)-<b>13</b> and (+)-(<i>R</i>,<i>S</i>)-<b>14</b> were devoid of undesirable side effects (triad test), and (+)-(<i>R</i>,<i>S</i>)-<b>14</b> reduced intraocular pressure with an unprecedentedly long duration of action in a murine glaucoma model. (-)-(<i>S</i>,<i>R</i>)-<b>13</b> docked into both a CB1R extracellular PAM and intracellular allosteric-agonist site(s), whereas (+)-(<i>R</i>,<i>S</i>)-<b>14</b> preferentially engaged only the latter. Exploiting G-protein biased CB1R-allosteric modulation can offer safer therapeutic candidates for glaucoma and, potentially, other diseases.