Inhibition of the E1 enzyme with PYZD-4409 preferentially induces cell death in malignant cell lines and primary AML cells over normal hematopoietic cells. (A) Myeloma, leukemia, and solid tumor cell lines were treated with increasing concentrations of PYZD-4409 for 72 hours. After incubation, cell growth and viability was measured by the Alamar Blue assay. Data represent the mean percentage ± SD of viable cells relative to control. Representative experiments are shown. (B) Mononuclear cells from patients with AML (n = 2) and the PBSCs of donors for allotransplantation (n = 4) were treated with PYZD-4409 (10μM) for 24 hours and then plated in duplicate for clonogenic growth in media containing 1% methylcellulose and cytokines. The numbers of colonies were counted after incubation for 7 days (AML) or 2 weeks (normal). Data represent the mean percentage ± SD of colonies relative to buffer-treated controls.