Characterization of Novel Cannabinoid Receptor 2-Selective Agonists at the Biochemical and Cellular Levels: Leads for Therapeutic Agents

Putative cannabinoid receptor 2 (CB2)-selective agonists were identified from a library of commercially available compounds via inhibition of cAMP accumulation in high throughput screening. Binding affinity and receptor subtype selectivity were assessed using heterologous competition binding assays against the known cannabinoid orthosteric ligand CP55940. Test compounds ASX0152383 and CSC003141 preferentially bound to CB2, with no detection of binding to CB1 up to 1 mM. CMB038865 exhibited nearly 100-fold selectivity for CB1 over CB2, while CZ000026 bound non-preferentially to both receptors in the low micromolar range. To determine the extent of G protein coupling, GTPγS binding assays were performed. Dose-dependent increases in binding of the nonhydrolyzable GTP analog to Gα subunits were induced by all test compounds. G protein-mediated MAPK signaling downstream of high affinity compounds was assessed by measuring ERK1/2 phosphorylation in the presence and absence of pertussis toxin (PTX). Activation induced by ASX015283 agonism at CB2 resulted in ERK 1/2 phosphorylation which was abrogated by PTX, indicating Gi/o protein-dependence. Interestingly, CMB038865 agonism at CB1 resulted in low levels of ERK phosphorylation and signaling was not abrogated by PTX. However, CMB038865 agonism at CB2 resulted in robust levels of ERK phosphorylation in a PTX-sensitive manner, indicative of Gi/o protein-dependent signaling. These results indicate CMB038865 is a partially selective CB1 agonist potentially biased towards G protein signaling pathways, while ASX015283 and CSC003141 are CB2-selective agonists that may possess therapeutic potential for the treatment of chronic pain and inflammation without the psychoactive effects concomitant with activation of CB1 receptors in the central nervous system