A selective CDK inhibitor; inhibits Cdk1/cyclin B, Cdk2/cyclin A, Cdk2/cyclin E, and Cdk5/p35 (IC50s = 33, 33, 28, and 20 nM, respectively); 90-fold selective for CDKs over ERK1, ERK2, PKC-δ, PKA, CK1, and insulin receptor tyrosine kinase; over 3,000-fold selective over a range of other kinases; antiproliferative (GI50s = 30-1,000 nM); inhibits mitotic division; preferentially arrests cells in G2/M phase