In vitro determination of the efficacy of illicit synthetic cannabinoids at CB1 receptors

Shivani Sachdev, Kiran Vemuri, Samuel D. Banister, Mitchell Longworth, Michael Kassiou, Marina Santiago, Alexandros Makriyannis, Mark Connor

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)


Background and Purpose: The morbidity and mortality associated with recreational use of synthetic cannabinoid receptor agonists (SCRAs) may reflect strong activation of CB1 receptors and is a major health concern. The properties of SCRA at CB1 receptors are not well defined. Here we have developed an assay to determine acute CB1 receptor efficacy using receptor depletion with the irreversible CB1 receptor antagonist AM6544, with application of the Black and Leff operational model to calculate efficacy. Experimental Approach: Receptor depletion in mouse AtT-20 pituitary adenoma cells stably expressing human CB 1 receptors was achieved by pretreatment of cells with AM6544 (10 μM, 60 min). The CB 1 receptor-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 Results: AM6544 did not affect the potency or maximal effect of native somatostatin receptor-induced hyperpolarization. The τ value 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 the τ and KA values. Conclusions and Implications: All SCRAs tested showed substantially higher efficacy at CB1 receptors than ∆9-THC, which may contribute to the adverse effects seen with these drugs but not ∆9-THC.

Original languageEnglish
Pages (from-to)4653-4665
Number of pages13
JournalBritish Journal of Pharmacology
Issue number24
Publication statusPublished - 10 Dec 2019


  • synthetic cannabinoids
  • efficacy
  • irreversible antagonist
  • operational model
  • toxicity


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