In vitro determination of the CB1 efficacy of illicit synthetic cannabinoids

Abstract

BACKGROUND AND PURPOSEThe recreational use of synthetic cannabinoid receptor agonists (SCRA) new psychoactive substances is associated with significant morbidity and mortality compared with herbal cannabis. To explore the relationship between SCRA CB1 receptor activity and acute toxicity, we determined the CB1 efficacy of thirteen SCRAs using receptor depletion with the irreversible CB1 antagonist AM6544 followed by curve‐fitting with the Black and Leff operational model. We also investigated the effects of brodifacoum, an anticoagulant associated with a recent outbreak of SCRA poisoning, on the acute signalling of human CB1 receptors.EXPERIMENTAL APPROACHReceptor depletion in mouse AtT‐20 pituitary adenoma cells stably expressing human CB1 was achieved by pre‐treatment of cells with AM6544 (10 μM, 60 mins). The CB1‐mediated hyperpolarisation of AtT‐20 cells was measured using fluorescence‐based membrane potential dye. The efficacy (tau) and affinity (KA) parameters were obtained for each drug by fitting data to the operational model. We next determined the effect of brodifacoum (1 μM, 5 mins) on the hyperpolarization induced by subsequent application of CP55940 or Δ9‐THC.KEY RESULTSThe tau value of Δ9‐THC was 80‐fold less than the reference CB‐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. Application of brodifacoum had no effect on the potency, or the maximal response produced by high efficacy cannabinoid CP55940 or low efficacy phytocannabinoid Δ9‐THC (P<0.05).CONCLUSION AND IMPLICATIONSWe determined the efficacy of a library of the most prevalent SCRAs identified in the new psychoactive substances market since 2008 and found that the SCRAs we tested had up to 300 times the efficacy of Δ9‐THC, which may contribute to the apparently greater toxicity of these drugs. Our data suggests that cannabinoid induced signaling was not affected by brodifacoum, indicating that combining SCRA with brodifacoum is not likely to enhance user experience through interactions with CB1.Support or Funding InformationThis work was supported by NHMRC Project Grant 1107088 awarded to M.K., and M.C. and National Institutes of Health grant P01DA009158 to A.M.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.