In vitro determination of the efficacy of illicit synthetic cannabinoids at CB1receptors

• DOI: 10.1111/bph.14829
• Publication Date: 2019-08-14T17:18:56Z
• Authors: Shivani Sachdev; Kiran Vemuri; Samuel D. Banister; Mitchell Longworth; Michael Kassiou; Marina Santiago; Alexandros Makriy...; Mark Connor
• Keywords: Cannabinoid Receptor Agonists; 0301 basic medicine; Dose-Response Relationship, Drug; Illicit Drugs; Cyclohexanols; 3. Good health; Mice; 03 medical and health sciences; Receptor, Cannabinoid, CB1; Cell Line, Tumor; Animals; Humans; Cannabinoid Receptor Antagonists

Background and PurposeThe morbidity and mortality associated with recreational use of synthetic cannabinoid receptor agonists (SCRAs) may reflect strong activation of CB1receptors and is a major health concern. The properties of SCRA at CB1receptors are not well defined. Here we have developed an assay to determine acute CB1receptor efficacy using receptor depletion with the irreversible CB1receptor antagonist AM6544, with application of the Black and Leff operational model to calculate efficacy.Experimental ApproachReceptor depletion in mouse AtT‐20 pituitary adenoma cells stably expressing human CB1receptors was achieved by pretreatment of cells with AM6544 (10 μM, 60 min). The CB1receptor‐mediated hyperpolarisation of AtT‐20 cells was measured using fluorescence‐based membrane potential dye. From data fit to the operational model, the efficacy (τ) and affinity (KA) parameters were obtained for each drug.Key ResultsAM6544 did not affect the potency or maximal effect of native somatostatin receptor‐induced hyperpolarization. Theτvalue of ∆9‐THC was 80‐fold less than the reference CB receptor agonist CP55940 and 260‐fold less than the highest efficacy SCRA, 5F‐MDMB‐PICA. The operational efficacy of SCRAs ranged from 233 (5F‐MDMB‐PICA) to 28 (AB‐PINACA), with CP55940 in the middle of the efficacy rank order. There was no correlation between theτandKAvalues.Conclusions and ImplicationsAll SCRAs tested showed substantially higher efficacy at CB1receptors than ∆9‐THC, which may contribute to the adverse effects seen with these drugs but not ∆9‐THC.