Concurrent CDK7 and CDK9 Blockade Sustains Transcriptional Shutdown and Suppresses Oncogenic Dependencies in Cancer

CDK7 supports transcriptional initiation and promoter escape, whereas CDK9 promotes productive elongation. Because inhibition of a single node can be partially buffered by transcriptional plasticity, we tested whether co-targeting CDK7 and CDK9 enforces a deeper and more durable transcriptional shutdown with improved antitumor activity.

By combining genetic and pharmacological perturbations across breast and ovarian cancer models, we found that dual CDK7–CDK9 knockout caused the strongest suppression of proliferation and nascent RNA synthesis, accompanied by greater loss of RNAPII phosphorylation and pronounced depletion of MYC and MCL1, compared with single knockouts. Pharmacological co-inhibition phenocopied these effects, producing rapid EU suppression that preceded decreases in EdU incorporation and cell number, preventing adaptation to single treatments and yielding deeper pathway inhibition than either monotherapy.