CSF attenuates leukemia cell sensitivity to methotrexate. (A-C) Methotrexate dose-response curves for NALM-6 (A), REH (B), and Jurkat (C) leukemia cells in either regular media or CSF. Leukemia cell viability was assessed after 48 hours of drug treatment using the CellTiter-Glo luminescent cell viability assay, which quantitates adenosine triphosphate as an indicator of viable and metabolically active cells. Error bars represent the mean ± SD of 3 technical replicates. LogIC50 and bottom values with confidence intervals were calculated from the dose-response curves and are shown in the supplemental Table. (D-F) Methotrexate dose-response curves for NALM-6 (D), REH (E), and Jurkat (F) leukemia cells cultured in regular media after 48 hours of preculture in either regular media or CSF. 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.