Apilimod mesylate is a potent and orally-available inhibitor of the cytokines interleukin-12 (IL-12) and interleukin-23 (IL-23) with the potential to treat certain autoimmune and inflammatory diseases. Apilimod mesylate (STA-5326 mesylate) inhibits IL-12 with IC50 of 1 nM, 1 nM and 2 nM, in IFN-γ/SAC-stimulated human PBMCs, human monocytes and mouse PBMCs, respectively. Apilimod mesylate (STA-5326 mesylate) is also a cell permeable small molecule that specifically inhibits PIKfyve with IC50 of 14 nM.