Discovery of a cannabinoid CB2 receptor fluorescent probe based on a pyridin-2-yl-benzyl-imidazolidine-2,4-dione scaffold

Abstract

Cannabinoid receptor type 2 (CB2R) agonists have therapeutic potential for the treatment of (neuro)inflammatory diseases. Fluorescent probes enable the detection of CB2R in relevant cell types and serve as a chemical tool in cellular target engagement studies. Here, we report the structure-based design and synthesis of a new CB2R selective fluorescent probe. Based on the cryo-EM structure of LEI-102 in complex with the CB2R, we synthesized 5-fluoropyridin-2-yl-benzyl-imidazolidine-2,4-dione analogues in which we introduced a variety of linkers and fluorophores. Molecular pharmacological characterization showed that compound 22 containing a Cy5-fluorophore with an alkyl-spacer was the most potent probe with a pKi of 6.2 ± 0.6. It was selective over the cannabinoid CB1 receptor and behaved as an inverse agonist (EC50 5.3 ± 0.1, Emax -63% ± 6). Probe 22 may serve as a chemical tool in target and lead validation studies for the CB2R.