CDK9 and cancer: In another study, Polier et al. initially showed that wogonin and flavones are inhibitors of cyclin-dependent kinase 9 (CDK9) and can effectively block phosphorylation of the carboxy-terminal domain of RNA polymerase II at Ser2, which in turn reduces RNA synthesis and subsequent downregulation of antiapoptotic protein myeloid cell leukemia 1 (Mcl-1), leading to significant apoptosis in a variety of human cancer cells [49].