Potent and selective CDK inhibitor (Ki values are 1, 2, 3, 46, 171 and 260 nM for CDK4/cyclin D1, CDK1/cyclin B, CDK2/cyclin E, GSK3α, CDK7/cyclin H and GSK3β). Exhibits no effect against a panel of >120 other kinases (Ki > 5,000 nM). Inhibits the proliferation of tumor cell lines independent of multidrug resistant status, or p53 status. Suppresses retinoblastoma protein in tumor cells and xenografts. Also inhibits tumor growth in the HCT116 human colorectal tumor xenograft model in nude mice. Orally bioavailable. Purity 98%. MW (observed): 441.45