Figure 4. Antiproliferative response associated with myeloid differentiation. (A–F). Human acute myeloid leukemia HL-60 cells were treated with 10 μM erlotinib (ERLO), 10 μM gefitinib (GEFI), or an equal volume of DMSO, alone or in combination with 100 nM all-trans retinoic acid (ATRA) or 50 nM 1α,25-hydroxycholecalciferol (VD), for the indicated number of days (7, where not specified), followed by (A, B, E, and F) or alongside with (C and D) the assessment of proliferation (A–D) or cell cycle distribution (E and F) based on the bead-assisted cytofluorometric quantification of cell number (A and B), the CFSE-dependent assessment of replication (C and D), or the analysis of DNA content upon propidium iodide staining (E and F). Representative dot plots, CFSE emission profiles and cell cycle distributions are reported in (A, C, andE), respectively. In (A), the cell:bead (C/B) ratio is reported. In (E), numbers refer to the percentage of cells with a DNA content >2n and <4n (compatible with the S phase of the cell cycle). Quantitative data on the C/B ratio, CFSE fluorescence and distribution in different phases of the cell cycle are reported in (B, D, and F), respectively (means ± SEM; n = 3). ***P < 0.001 (ANOVA plus Dunnett post-hoc test), as compared with DMSO-treated cells; #P < 0.05, ##P < 0.01 (ANOVA plus Bonferroni post-hoc test), as compared with ATRA-treated cells; +++P < 0.001 (ANOVA plus Bonferroni post-hoc test), as compared with VD-treated cells.