CDK9 and cancer: However, its inhibition effect on CDK9 significantly drops (IC50 = 380 nM) under high ATP conditions (ATP concentration = 2 mM), which is the appropriate cellular ATP condition in human, and limited therapeutic capacity was found in a phase I clinical trial.95 Moreover, because of targeting MCL-1 in white blood cells, atuveciclib caused neutropenia as the main adverse event in patients with advanced cancer.95