Biased Agonism and Biased Allosteric Modulation at the CB1 Cannabinoid Receptor.

CB1 cannabinoid receptors (CB1Rs) are attractive therapeutic targets for numerous central nervous system disorders. However, clinical application of cannabinoid ligands has been hampered due to their adverse on-target effects. Ligand-biased signalling from, and allosteric modulation of, CB1Rs offer pharmacological approaches that may enable the development of improved CB1R drugs, through modulation of only therapeutically desirable CB1R signalling pathways. There is growing evidence that CB1Rs are subject to ligand-biased signalling and allosterism. Therefore, in the present study, we quantified ligand-biased signalling and allosteric modulation at CB1Rs. Cannabinoid agonists displayed distinct biased signalling profiles at CB1Rs. For instance, whereas 2-AG and WIN55,212-2 showed little preference for inhibition of cAMP and phosphorylation of extracellular signal-regulated kinase 1/2 (pERK1/2), anandamide, methanandamide, CP55940 and HU-210 were biased towards cAMP inhibition. The small molecule allosteric modulator, Org27569, displayed biased allosteric effects by blocking cAMP inhibition mediated by all cannabinoid ligands tested, while having little or no effect on ERK1/2 phosphorylation mediated by a subset of these ligands. Org27569 also displayed negative binding cooperativity with [3H]SR141716A, however it had minimal effects on binding of cannabinoid agonists. Furthermore, we highlight the need to validate the reported allosteric effects of the endogenous ligands lipoxin A4 and pregnenolone at CB1Rs. Pregnenolone but not lipoxin A4 displaced [3H]SR141716A, however, there was no functional interaction between either of these ligands and cannabinoid agonists. This study demonstrates an approach to validate and quantify ligand-biased signalling and allosteric modulation at CB1Rs, revealing ligand-biased “fingerprints” that may ultimately allow the development of improved CB1R-targeted therapies.
The American Society for Pharmacology and Experimental Therapeutics.