Edited leukemia cells display increased sensitivity to DOT1L inhibition. (A) Bar graph represents the mean number of colonies generated per 5000 or 10⁴ seeded cells after 12 to 14 days in the presence of increasing concentrations of EPZ004777 or vehicle (DMSO). Data from 4 (MPAL) and 3 (AML) independent experiments performed in duplicate were pooled together (IC₅₀ values: MV4-11, 10 nM; MPAL/AML, 51/11 nM; K562, >50 µM). (B) Images show representative morphologies of colonies displaying decreased density after drug treatment. Scale bars define 100 µm. (C) MV4-11 and leukemic cells (n [MPAL] = 4; n [AML] = 3) were analyzed by flow cytometry for cell surface expression of CD14 after incubation with 10 µM EPZ04777 (black line) or DMSO (gray line) in CFC assays. (D) Representative qPCR analyses of MLL target genes show decreasing levels relative to DMSO treatment. Shown are representative data from 1 of 4 (MPAL) and 3 (AML) independent experiments. *P < .05 was considered statistically significant. Error bars indicate SEM.