Cell-permeable cyclin-dependent kinase inhibitor. IC50 values are 0.033, 0.033, 0.028 and 0.020 μM for cdk1/cyclin B, cdk2/cyclin A, cdk2/cyclin E, and cdk5/p35 respectively. Inhibits ERK1 (IC50 = 12.0 μM) and ERK2 (IC50 = 3.1 μM) and is 3000-fold selective over a range of other protein kinases (IC50 > 100 μM). Arrests cell cycle at G2/M boundary (IC50 = 1.25 μM), and induces apoptosis at concentrations > 10 μM.