Loss of cell-cycle control, increased resistance to apoptosis, and tumor-induced neovascularization represent major hallmarks of cancer.Cyclin-dependent kinases (CDKs) are serine/threonine kinases that require association with a cyclin regulatory subunit for activation and are required for the correct timing and order of the events of the cell division cycle.Aberrant CDK control and consequent loss of cell-cycle checkpoint function have been directly linked to the molecular pathology of cancer.CDK2 inhibitors containing aminopyrimidines, pyrazoles and indirubins were discovered through high-throughput screening with IC50 values as low as 100 nM.The lead generation and optimization process was supported right from the start by structural biology and computational chemistry efforts.Crystal structures of inhibitors of various scaffolds show that all share a common binding mode featuring two or three hydrogen bonds to the backbone of the kinase hinge region.Further insight into inhibitor/CDK2 interactions was gained from analysis of additional crystal structures supporting the development of a pan-selective CDK inhibitor.The orally bioavailable pan-CDK inhibitor BAY 1000394 selectively binds to and inhibits the activity of CDK1/Cyclin B, CDK2/Cyclin E, CDK3/Cyclin E, CDK4/Cyclin D1, CDK5/p35, CDK7/Cyclin H and CDK9/Cyclin T 1, serine/threonine kinases that play key roles in the regulation of the cell cycle progression and cellular proliferation.Inhibition of these kinases leads to cell cycle arrest during the G1/S transition, thereby leading to an induction of apoptosis, and inhibition of tumor cell proliferation.BAY 1000394 shows high enzymatic and cellular potency in the nM range.The inhibitor is highly efficient in a variety of tumor xenograft models and shows a promising pharmacokinetic profile in vivo.