LY320135, a novel cannabinoid CB1 receptor antagonist, unmasks coupling of the CB1 receptor to stimulation of cAMP accumulation

LY320135 is a selective antagonist for the brain CB1 receptor, having greater than 70-fold higher affinity for the CB1 than the peripheral CB2 receptor. The K-i values for LY320135 at the CB1 and CB2 receptors, transfected and stably expressed in cell lines, were 224 nM and >10 mu M, respectively. Similar K-i values were measured in binding studies performed on cerebellum and spleen membrane preparations endogenously expressing the CB1 (203 nM) and CB2 (>10 mu M) receptors, respectively. LY320135 functionally reversed anandamide-mediated adenylate cyclase inhibition in Chinese hamster ovary (CHO) cells stably expressing the CB1 receptor. Pertussis toxin treatment of CHO cells expressing the CB1 receptor attenuated the anandamide-mediated inhibition of adenylate cyclase and unmasked a stimulatory effect of anandamide on adenylate cyclase. The stimulatory component was blocked with LY320135. This compound also blocked WIN 55212-2-mediated inhibition of N-type calcium channels and activation of inwardly rectifying potassium channels in N18 and AtT-20-CB2 cells, respectively. LY320135 is a promising lead compound for the further development of novel, potent and selective cannabinoid antagonists of novel structure.