Two affinity sites of cannabinoid CB2 receptor identified by a novel homogeneous binding assay.

Cannabinoid receptors are G-protein-coupled receptors with potential in a variety of diseases. There are two different cannabinoid receptors types; ligands for type 2 (CB2R) show more promise than those for type 1 (CB1R) as they lack psychotropic actions. However, the lipophilic nature of CB2R ligands and the complex pharmacology of these receptors are delaying the translational success of medications targeting the endocannabinoid system. We here report the discovery and synthesis of a fluorophore-labeled high-affinity and CB2R-selective ligand that may be used in nonradioactive binding assays. The novel fluorophore-conjugated compound was useful for pharmacological characterization of CB2R by using a time-resolved fluorescence resonance energy transfer (TR-FRET) assay. This methodology does not require radiolabelled compounds and may be undertaken in homogeneous conditions and in living cells. TR-FRET assays disclosed a previously unreported second affinity site and showed conformational changes in CB2R forming receptor heteromers with another G-protein-coupled receptor.
The American Society for Pharmacology and Experimental Therapeutics.