CDK4 and neoplasm: Like flavopiridol, roscovitine is a broad-range inhibitor that targets CDK1, CDK2, CDK5, CDK7, and CDK9 (with IC50 values between 0.2-0.7 μM) but is a poor inhibitor for CDK4/6 and CDK8 (IC50 > 100 μM).564,586 Roscovitine has been tested across a wide variety of tumor cell lines, where it demonstrates two main effects: cell cycle arrest and initiation of apoptosis.