The pharmacology of novel illicit synthetic cannabinoids

Herbal smoking mixtures containing illicit synthetic cannabinoids (SCs), originally sold as legal substitutes to cannabis, have become the most rapidly growing class of recreational designer drugs since 2008. Legal restrictions on the first generation SCs created a chemist-driven structural evolution making identification and the study of their pharmacology and toxicology difficult. The consumption of these novel compounds is of major concern as the toxicity seems to be increasing with each new generation of structures. As very little is known about their pharmacological activity, it was pertinent to establish their actions at cannabinoid receptors CB₁ and CB₂. This was done using a high-throughput fluorescent-based plate reader membrane potential assay on AtT20 pituitary tumor cells stably transfected with either rat or human cDNA for CB₁ and human cDNA for CB₂. Relevant off target pathways, specifically the TRP channels, were also tested for activity by measuring the changes in intracellular calcium in a fluorescent-based plate reader assay on HEK293 cells transfected with human TRPA1 or human TRPV1. Approximately 60 SCs were tested and all showed activity at both CB₁ and CB₂ receptors with the majority having high efficacy and potency. Some compounds were up to 1,000 times more potent at CB₁ in comparison to Δ⁹-THC, the main psychoactive ingredient in cannabis. Many also differed from Δ⁹-THC by showing a selectivity for CB₂. The physiological implications of this outcome have yet to be determined but could play a role in toxicity. At the off target pathways only one SC showed partial agonist activity at TRPV1 but 28 showed agonist activity at TRPA1 ranging from partial to full agonists. As these ion channels have been implicated in the cardiovascular system, gastrointestinal system and CNS, their activation could be another mode of toxicity. Finally, a method was developed using reverse phase column chromatography and HPLC/MS/MS to measure endocannabinoid levels in cells lines after a drug stimulation. Preliminary data showed that SCs can affect the endocannabinoid system further proving their lack of specificity.