K2 and several similar purported "incense products" spiked with synthetic
cannabinoids are abused as cannabis substitutes. We hypothesized that metabolism of
JWH-073, a prevalent
cannabinoid found in K2, contributes to toxicity associated with K2 use. Competition receptor binding studies and
G-protein activation assays, both performed by employing mouse brain homogenates, were used to determine the affinity and intrinsic activity, respectively, of potential monohydroxylated (M1, M3-M5) and monocarboxylated (M6) metabolites at
cannabinoid 1 receptors (CB1Rs). Surprisingly, M1, M4 and M5 retain nanomolar affinity for CB1Rs, while M3 displays micromolar affinity and M6 does not bind to CB1Rs.
JWH-073 displays equivalent efficacy to that of the CB1R full agonist
CP-55,940, while M1, M3, and M5 act as CB1R partial agonists, and M4 shows little or no intrinsic activity. Further in vitro investigation by Schild analysis revealed that M4 acts as a competitive neutral CB1R antagonist (K(b)∼40nM). In agreement with in vitro studies, M4 also demonstrates CB1R antagonism in vivo by blunting
cannabinoid-
induced hypothermia in mice. Interestingly, M4 does not block agonist-mediated responses of other measures in the
cannabinoid tetrad (e.g., locomotor suppression,
catalepsy or
analgesia). Finally, also as predicted by in vitro results, M1 exhibits agonist activity in vivo by inducing significant
hypothermia and suppression of locomotor activity in mice. In conclusion, the present study indicates that further work examining the physiological effects of synthetic
cannabinoid metabolism is warranted. Such a complex mix of metabolically produced CB1R
ligands may contribute to the adverse effect profile of JWH-073-containing products.