Characterization of peripheral human cannabinoid receptor (hCB2) expression and pharmacology using a novel radioligand, [35S]Sch225336

Studies to characterize the endogenous expression and pharmacology of peripheral human cannabinoid receptor (hCB2) have been hampered by the dearth of authentic anti-hCB2 antibodies and the lack of radioligands with CB2 selectivity. We recently described a novel CB2 inverse agonist, N-[1(S)-[4-[[4- methoxy2-[(4-methoxyphenyl) sulfonyl] phenyl] sulfonyl] phenyl] ethyl] methane-sulfonamide (Sch225336), that binds hCB2 with high affinity and excellent selectivity versus hCB1. The precursor primary amine of Sch225336 was prepared and reacted directly with [S-35] mesyl chloride ( synthesized from commercially obtained [S-35] methane sulfonic acid) to generate [S-35] Sch225336. [ 35S] Sch225336 has high specific activity (> 1400 Ci/mmol) and affinity for hCB2( 65 pM). Using [S-35] Sch225336, we assayed hemopoietic cells and cell lines to quantitate the expression and pharmacology of hCB2. Lastly, we used [S-35] Sch225336 for detailed autoradiographic analysis of CB2 in lymphoid tissues. Based on these data, we conclude that [S-35] Sch225336 represents a unique radioligand for the study of CB2 endogenously expressed in blood cells and tissues.