KDM5A inhibition enhanced the differentiation-inducing effect of ATRA at a lower dose. (A)Proliferation assay of NB4 cells treated with 5 μM CPI-455 and/or 0.1 or 0.5 nM ATRA, 10 nM ATRA, or vehicle (dimethyl sulfoxide [DMSO]) for the indicated days. Viable cells were detected by using a trypan blue exclusion assay. Statistical significance was determined by two-way analysis of variance. ****P < .0001, ####P < .0001. (B) CD11b⁺ or CD11c⁺ cells were detected by flow cytometry of NB4 cells treated with 2.5 μM CPI-455 and/or 0.5 nM ATRA, or vehicle (DMSO) for 4 days. ***P < .001, *P < .05 (C) The morphology of NB4 cells treated with 2.5 μM CPI-455 and/or 0.5 nM ATRA, or vehicle (DMSO) for 4 days. Bar = 15 μm. (D) The NBT test of NB4 cells treated with 2.5 μM CPI-455 and/or 0.5 nM ATRA, or vehicle (DMSO) for 3 days. The values represent mean ± standard deviation of the percentages of NBT-positive cells, n = 6. FACS, fluorescence-activated cell sorting.