Hydroxylated metabolites of the synthetic cannabinoid JWH‐018 retain in vitro and in vivo affinity and activity at CB1 cannabinoid receptors

K2 products marketed as “legal marijuana” are a public health concern due to severe adverse effects not commonly observed with marijuana use, including seizures, hallucinations, and panic attacks. JWH‐018 is a synthetic cannabinoid present in most K2 preparations and is structurally dissimilar to Δ 9 ‐THC. Several hydroxylated (‐OH) metabolites of JWH‐018 have been reported in urine of human users. Differences in activity of metabolites may provide a mechanism for the distinct adverse effects of K2. In this study, JWH‐018 and six ‐OH metabolites (M1–M6) were first evaluated by competition receptor and 35 S‐GTPγS binding assays to determine their affinity and intrinsic activity at mouse CB1 cannabinoid receptors (mCB1Rs), respectively. JWH‐018 and M1 were then examined for in vivo activity using the “cannabinoid tetrad” in mice. In vitro studies show that five JWH‐018 ‐OH metabolites retain nanomolar receptor affinity and activate mCB1Rs with equal or greater efficacy than Δ 9 ‐THC. In the tetrad assay, M1 reduces temperature, decreases locomotor activity and increases analgesia and catalepsy CB1R‐dependently in mice. Since hydroxylation of a parent molecule is usually inactivating, these initial results indicate the distinct adverse effects associated with K2 use may be due to retained affinity and activity of JWH‐018 ‐OH metabolites at mCB1Rs. APHL Award (JM); UAMS Pilot Study (PLP); RR020146 (WEF)