ELDR overexpression induces differentiation of THP-1 cells and renders them sensitive to LSD1i/ATRA. (A) Microscopic images of cells from the ELDR-overexpressing THP-1 cell lines ELDR-C1 and ELDR-C3 after treatment with ATRA or vehicle (EtOH) compared with an EV1^ctrl after May Grünwald Giemsa staining. The arrows indicate more differentiated cells. (B) Quantification of 3 independent replicates of experiment as described in panel (A) after May Grünwald Giemsa staining. (C-D) CD11b levels (MFI [mean fluorescence intensity] by flow cytometry) measured after 3 days of incubation of ELDR-overexpressing THP-1 lines ELDR-C1 and ELDR-C3 and the EV1 line with increasing concentrations of ATRA (C) or 10 nM ATRA and increasing concentrations of LSD1i (D). (E) CD11b EC50 values for MFI of the experiments in panels (C-D). (F-H) Growth curves of the ELDR-overexpressing THP-1 cell lines ELDR-C1 and ELDR-C3 in the presence of LSD1i, ATRA, or both. n = 3 biological replicates. The growth curve for EV1 is also revealed as a reference. (I-J) Growth of ELDR-C1 and ELDR-C3 THP-1 lines compared with the EV1 control in the presence of the indicated inhibitors midostaurin (FLT3 inhibitor) and pinometostat (DOT1L inhibitor). n = 3 biological replicates. Data are presented as mean + SD (panel B); ± SD (panels C-D, F-J). ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. P values were calculated using 1-way ANOVA with Dunnett's multiple comparisons test (panel B); 2-way ANOVA with Dunnett's multiple comparisons test (panels C-D); parametric unpaired t test (panels F-J). EtOH, ethanol; ATRA, all-trans retinoic acid; EV1, empty vector 1; LSD1i, lysine specific demethylase 1 inhibitor; FLT3, Fms related receptor tyrosine kinase 3; DOT1L, DOT1 like histone lysine methyltransferase; ns, not significant.