PSB-SB-487
# PSB-SB-487

PSB-SB-487 is a coumarin derivative which is an antagonist at the former orphan receptor GPR55. Unlike older GPR55 antagonists such as O-1918, PSB-SB-487 has good selectivity over the related receptor GPR18, with an $IC_{50}$ of 113nM at GPR55 vs 12500nM at GPR18. However it has poorer selectivity over other related receptors, acting as a weak antagonist at $CB_1$ with a Ki of 1170nM, and a partial agonist at $CB_2$ with a Ki of 292nM.

