IPA-3 is a cell-permeable allosteric inhibitor of PAK1 (tha p21-activated kinase 1) that is non-competitive with respect to ATP binding (IC₅₀ = 2.5 µM). It does not, however, inhibit the activity of PAK1 that has been pre-activated with Cdc42. IPA-3 binds covalently to the PAK1 regulatory domain (apparent Kd = 1.9 uM) and prevents binding to the upstream activator Cdc42. Potential anti-tumor agent.