TP53 and B-cell chronic lymphocytic leukemia: Flavopiridol is a synthetic flavone which broadly inhibits cyclin dependent kinases (CDK); down-regulates expression of anti-apoptotic proteins such as Mcl-1 and X-linked inactivator of apoptosis (XIAP); decreases phosphorylation and transcriptional activity of RNA polymerase II, resulting in decreased gene transcription; and induces apoptosis distally to p53 by activating caspase 3 in primary CLL cells.