Enitociclib demonstrates cytotoxic activity in KMT2A-r pediatric leukemia cells. (A) Cytotoxicity of 3 CDK9 inhibitors was assessed in MV4-11 and KOPN-8 cells using Alamar blue assay. (B) Cell viability of various leukemia cell lines, patient samples, and healthy controls after 72-hour treatment with enitociclib were measured by Alamar blue assay. Data represented as percent viability normalized to respective DMSO controls. (C) Enitociclib treatment increased apoptosis in a dose-dependent manner in KOPN-8 cells, as measured by annexin V/PI staining. A minimal effect was observed on healthy PBMCs. (D) Enitociclib demonstrates antileukemic activity in an MV4-11 rat model. PI, propidium iodide; QW, once weekly; SD, standard deviation.