CDK9 and prostate cancer: We hypothesized that CDK9 inhibition affects O-GlcNAcylation of CDK9 because combined inhibition of OGT and CDK9 is toxic to prostate cancer cells [23], OGT inhibition decreases phosphorylation of CDK9 [46] and CDK9 is known to be O-GlcNAcylated [13].