MDM4 and leukemia: The p53-based therapy relies on drug-induced apoptosis.4 In sharp contrast to Nutlin3a, MMRi64 preferentially induces apoptosis in leukemia/lymphoma cells, probably due to PUMA induction and simultaneous shutdown of pro-growth-arrest p21 (Figures 4 and 5a), and downregulation of Mdm2 and MdmX.