Psora-4 is a novel, potent and selective small-molecule inhibitor of voltage-gated potassium channels - Kv1.3 with EC₅₀ of 3 nM. It binds preferentially to the C-type inactivated state of the channel, similar to the activity of CP 339818, and displays 17- to 70-fold selectivity over closely-related K_V1 channels (K_V1, K_V2, K_V4 and K_V7); exhibits activity at K_V1.5 (IC₅₀ = 7.7 nM). Suppresses proliferation of human and rat myelin-specific effector memory T cells (EC₅₀ values are 25 and 60 nM respectively).