A potent inhibitor of Cdk1, Cdk2, and Cdk9 (IC50s = 16, 6, and 20 nM, respectively); inhibits kinase activity of Cdk5/p25 and GSK3β; induces cell cycle arrest by inhibiting phosphorylation of CDK-dependent substrates; has in vivo antiproliferative activity against a range of tumor cell lines (IC50s ranging from 200-1,700 nM); in vivo oral administration inhibits growth of human tumor xenografts and inhibits cell cycle proteins