Similarities and differences upon binding of naturally occurring Δ9-tetrahydrocannabinol-derivatives to cannabinoid CB1 and CB2 receptors.

We have here assessed, using D9-tetrahydrocannabinol (D9-THC) for comparison, the, effect of Δ9-tetrahydrocannabinolic acid (D9-THCA) and of Δ9- Δ9-, tetrahydrocannabivarin (D9-THCV) that is mediated by human versions of CB1, CB2, and CB1-CB2 receptor functional units, expressed in a heterologous system. Binding, to the CB1 and CB2 receptors was addressed in living cells by means of a, homogeneous assay. A biphasic competition curve for the binding to the CB2 receptor, was obtained for D9-THCV in cells expressing the two receptors. Signaling studies, included cAMP level determination, activation of the mitogen-activated protein kinase, pathway and s-arrestin recruitment. The signaling of D9-THCA and D9-THCV via, individual receptors or receptor heteromers disclosed differential bias, i.e. the bias for, a given phytocannabinoid depended on the receptor (CB1, CB2 or CB1-CB2) and on, the compound used as reference to calculate the bias factor (D9-THC, a selective, agonist or a non-selective agonist). These results are consistent with different binding, modes leading to differential functional selectivity depending on the agonist structure, and the state (monomeric or heteromeric) of the cannabinoid receptor. In addition, on, studying Gi-coupling, we showed that D9-THCV and D9-THCA were able to revert the, effect of a selective CB2 receptor agonist, but only D9-THCV, and not D9-THCA, reverted the effect of arachidonyl-2'-chloroethylamide (ACEA, 100nM) a selective, agonist of the CB1 receptor. Overall, these results indicate that cannabinoids may have, a variety of binding modes that results in qualitatively different effects depending on the, signaling pathway engaged upon cannabinoid receptor activation.