Agonist‐inverse agonist characterization at CB 1 and CB 2 cannabinoid receptors of L759633, L759656 and AM630

We have tested our prediction that AM630 is a CB 2 cannabinoid receptor ligand and also investigated whether L759633 and L759656, are CB 2 receptor agonists. Binding assays with membranes from CHO cells stably transfected with human CB 1 or CB 2 receptors using [ 3 H]‐CP55940, confirmed the CB 2 ‐selectivity of L759633 and L759656 (CB 2 /CB 1 affinity ratios=163 and 414 respectively) and showed AM630 to have a K i at CB 2 receptors of 31.2 n M and a CB 2 /CB 1 affinity ratio of 165. In CB 2 ‐transfected cells, L759633 and L759656 were potent inhibitors of forskolin‐stimulated cyclic AMP production, with EC 50 values of 8.1 and 3.1 n M respectively and CB 1 /CB 2 EC 50 ratios of >1000 and >3000 respectively. AM630 inhibited [ 35 S]‐GTPγS binding to CB 2 receptor membranes (EC 50 =76.6 n M ), enhanced forskolin‐stimulated cyclic AMP production in CB 2 ‐transfected cells (5.2 fold by 1 μ M ), and antagonized the inhibition of forskolin‐stimulated cyclic AMP production in this cell line induced by CP55940. In CB 1 ‐transfected cells, forskolin‐stimulated cyclic AMP production was significantly inhibited by AM630 (22.6% at 1 μ M and 45.9% at 10 μ M ) and by L759633 at 10 μ M (48%) but not 1 μ M . L759656 (10 μ M ) was not inhibitory. AM630 also produced a slight decrease in the mean inhibitory effect of CP55940 on cyclic AMP production which was not statistically significant. We conclude that AM630 is a CB 2 ‐selective ligand that behaves as an inverse agonist at CB 2 receptors and as a weak partial agonist at CB 1 receptors. L759633 and L759656 are both potent CB 2 ‐selective agonists.British Journal of Pharmacology (1999) 126 , 665–672; doi: 10.1038/sj.bjp.0702351