Detection of cannabinoid receptor type 2 in native cells and zebrafish with a highly potent, cell-permeable fluorescent probe

Despite its essential role in the (patho)physiology of several diseases, CB(2)R tissue expression profiles and signaling mechanisms are not yet fully understood. We report the development of a highly potent, fluorescent CB(2)R agonist probe employing structure-based reverse design. It commences with a highly potent, preclinically validated ligand, which is conjugated to a silicon-rhodamine fluorophore, enabling cell permeability. The probe is the first to preserve interspecies affinity and selectivity for both mouse and human CB(2)R. Extensive cross-validation (FACS, TR-FRET and confocal microscopy) set the stage for CB(2)R detection in endogenously expressing living cells along with zebrafish larvae. Together, these findings will benefit clinical translatability of CB(2)R based drugs.