Synergism of sequential combining decitabine and idarubicin in inducing apoptosis of AML cells and tumor cells of subcutaneous AML mouse model. A, Annexin V and PI staining for apoptosis assay in U937, HEL and SKM-1 cells. Apoptosis was assayed by Annexin V and PI staining and fluorescence-activated cell sorting analysis. The percentage of apoptotic cells (Annexin V and PI positive) was indicated in the histogram. B, The Morphological and ultrastructural changes in apoptosis cells. To compare with the control group, DAC group and IDA group, the tumor cells from subcutaneous AML mouse model treated with DAC followed by IDA some showed the typical characteristic of apoptosis cells which microvilli on cell membrane were disappeared, bubbles exist on nuclear and cell membrane, chromosome condensation and the formation of apoptotic bodies. C, TUNEL assay of tumor tissue from subcutaneous AML mouse model confirmed induction of apoptosis after treatment with DAC alone, IDA alone and DAC followed by IDA. ***p < 0.001, **p < 0.01, *p < 0.05.