Sorafenib plus ATRA induces apoptosis in FLT3/ITD cell lines. FLT3/ITD⁺ (Molm14, MV4-11) and FLT3/WT (THP-1, NB4) leukemia cell lines were treated with sorafenib (Soraf, 20 nM) and/or ATRA (100 nM). (A) Expression of caspase 3 and PARP cleavage by western blotting of cell lysates at 24 hours. (B) AnnexinV binding at 48 hours, represented by average of 3 independent experiments. Error bars indicate average ± SD (*P < .05, **P < .01, ***P < .001). (C) CD11b expression by flow cytometry at 72 hours, represented by average of 3 independent experiments. Error bars indicate average ± SD. (D) Cellular morphology at 72 hours by Wright-Giemsa staining, magnification ×50. Increased levels of cell death are observed in sorafenib- and combination-treated FLT3/ITD⁺ cells, whereas evidence of differentiation is apparent in ATRA-treated cells. Red scale bar represents 20 µm. PARP, poly (ADP-ribose) polymerase.