Cyclin-dependent kinase inhibitor. IC50 values are 6, 6, 9, > 10,000, and 6 nM for cdc2/cyclin B, cdk2/cyclin A, cdk2/cyclin E, cdk4/cyclin D1 and cdk5-p35 respectively. Selective over a range of other protein kinases (IC50 > 10,000 nM). Shown to have antiproliferative properties, mediated by p42/p44 MAPK.