Palbociclib decreases leukemia cell proliferation and attenuates leukemia cell sensitivity to methotrexate. (A-C) Methotrexate dose-response curves for NALM-6 (A), REH (B), and Jurkat (C) leukemia cells in the absence or presence of palbociclib at varying concentrations. Leukemia cell viability was assessed after 48 hours of drug treatment using the CellTiter-Glo luminescent cell viability assay. Error bars represent the mean ± SD of 3 technical replicates. (D-F) Cell cycle analysis of NALM-6 (D), REH (E), and Jurkat (F) leukemia cells cultured in either CSF or regular media with a palbociclib concentration that caused a level of G0/G1 arrest similar to CSF. Leukemia cells were treated with EdU (5-ethynyl 2’-deoxyuridine) for 30 minutes before fixation, permeabilization, staining, and analysis by flow cytometry. Representative flow cytometry histograms for both CSF and the comparable palbociclib dose are shown. AF, Alexa Fluor.