CDK9 and neoplasm: Given that upregulation of MCL-1 has been documented as a mechanism of resistance to the BCL-2 specific inhibitor venetoclax, and that other CDK inhibitors with activity against CDK9 have been shown preclinically to enhance the anti-tumor effects of BCL-2 inhibition, we next assessed whether systemic administration of the combination of voruciclib and venetoclax causes significantly enhanced tumor growth inhibition versus exposure to either single agent alone.