Psora 4 (5-(4-Phenylbutoxy)psoralen) is a selective and potent Kv1.3 blocker, a caloric restriction mimetic with immunosuppressive activity that enhances neural progenitor cell differentiation and maturation.

Kv1.5:7.7 nM （EC50）, myelin-specific effector memory T cells (human):25 nM （EC50）, Kv1.3:3 nM （EC50）, myelin-specific effector memory T cells (rat):60 nM （EC50）

Psora 4 blocks Kv1.3 in a dose-dependent manner by preferentially binding to the C-type inactivation state of the channel with an EC50 value of 3 nM.Psora 4 is the most potent small molecule Kv1.3 blocker known. It is 17- to 70-fold more selective for Kv1.3 than the closely related Kv1 family of channels (Kv1.1, Kv1.2, Kv1.4, and Kv1.7), with the exception of Kv1.5, which is selective for Kv1.5 (EC50 of 7.7 nM).
Psora 4 selectively inhibits the proliferation of human and rat myelin-specific effector memory T cells with EC50 values of 25 and 60 nM, respectively, but does not persistently inhibit peripheral blood naïve and central memory T cells. [1]

In an in vivo rat toxicity assay, 33 mg/kg Psora 4 administered subcutaneously five times daily did not show any signs of acute toxicity. [1]