CDK9 and neuroblastoma: We observed that, in comparison with monoselective inhibitors of CDK9, such as compound 3 (24), which is only able to induce PARP cleavage at high concentrations, CYC065 caused extensive apoptotic cell death at cellular GI50 concentrations in MYCN-amplified NB cells, presumably due to concomitant inhibition of CDK2, itself a major regulator of apoptotic cell death.