Kenpaullone is a potent inhibitor of CDK1/cyclin B and GSK-3β, with IC₅₀s of 0.4 μM and 23 nM, and also inhibits CDK2/cyclin A, CDK2/cyclin E, and CDK5/p25 with IC₅₀s of 0.68 μM, 7.5 μM, 0.85 μM, respectively. IC50 & Target: IC50: 0.4 μM (CDK1/cyclin B), 0.68 μM (CDK2/cyclin A), 7.5 μM (CDK2/cyclin E), 0.85 μM (CDK5/p25)^[1], 23 nM (GSK-3β)^[2] In Vitro: Kenpaullone shows much less effect on c-src (IC₅₀, 15 μM), casein kinase 2 (IC₅₀, 20 μM), erk 1 (IC₅₀, 20 μM), and erk 2 (IC₅₀, 9 μM). Kenpaullone acts by competitive inhibition of ATP binding, and the apparent K_i is 2.5 μM. Kenpaullone can inhibit the growth of tumor cells in culture (mean GI₅₀, 43 μM) and causes altered cell cycle progression most clearly revealed under conditions of recovery from serum starvation^[1]. Kenpaullone demonstrates a wide range of biological utility, extending from maintenance of pancreatic β cell survival and proliferation to the induction of apoptosis in cancer cells^[2].