Differential drug-drug interactions of the synthetic Cannabinoids JWH-018 and JWH-073: implications for drug abuse liability and pain therapy.

Marijuana substitutes often contain blends of multiple psychoactive synthetic cannabinoids (SCBs), including the prevalent SCBs (1-pentyl-1H-indole-3-yl)-1-naphthalenyl-methanone (JWH-018) and (1-butyl-1H-indole-3-yl)-1-naphthalenyl-methanone (JWH-073). Because SCBs are frequently used in combinations, we hypothesized that coadministering multiple SCBs induces synergistic drug-drug interactions. Drug-drug interactions between JWH-018 and JWH-073 were investigated in vivo for Δ(9)-tetrahydrocannabinol (Δ(9)-THC)-like discriminative stimulus effects, analgesia, task disruption, and hypothermia. Combinations (JWH-018:JWH-073) of these drugs were administered to mice in assays of Δ(9)-THC discrimination, tail-immersion, and food-maintained responding, and rectal temperatures were measured. Synergism occurred in the Δ(9)-THC discrimination assay for two constant dose ratio combinations (1:3 and 1:1). A 1:1 and 2:3 dose ratio induced additivity and synergy, respectively, in the tail-immersion assay. Both 1:1 and 2:3 dose ratios were additive for hypothermia, whereas a 1:3 dose ratio induced subadditive suppression of food-maintained responding. In vitro drug-drug interactions were assessed using competition receptor-binding assays employing mouse brain homogenates and cannabinoid 1 receptor (CB1R)-mediated inhibition of adenylyl cyclase activity in Neuro2A wild-type cells. Interestingly, synergy occurred in the competition receptor-binding assay for two dose ratios (1:5 and 1:10), but not in the adenylyl cyclase activity assay (1:5). Altogether, these data indicate that drug-drug interactions between JWH-018 and JWH-073 are effect- and ratio-dependent and may increase the relative potency of marijuana substitutes for subjective Δ(9)-THC-like effects. Combinations may improve the therapeutic profile of cannabinoids, considering that analgesia but not hypothermia or task disruption was potentiated. Importantly, synergy in the competition receptor-binding assay suggests multiple CB1R-SCB binding sites.