Cellular Assay to Study β-Arrestin Recruitment by the Cannabinoid Receptors 1 and 2

Cannabinoid receptor 1 (CB₁R) and cannabinoid receptor 2 (CB₂R) are G protein-coupled receptors (GPCRs) that activate a variety of pathways upon activation by (partial) agonists including the G protein pathway and the recruitment of β-arrestins. Differences in the activation level of these pathways lead to biased signaling. Here, we describe a detailed protocol to characterize the potency and efficacy of ligands to induce or inhibit β-arrestin recruitment to the human CB₁R and CB₂R using the PathHunter^® assay. This is a cellular assay that uses a β-galactosidase complementation system which has a chemiluminescent read-out and can be performed in 384-well plates. We have successfully used this assay to characterize a set of reference ligands (both agonists, antagonists, and an inverse agonist) on human CB₁R and CB₂R, of which some examples will be presented here.