Cell viability determination

Cell viability was determined using the CellTiter Non-Radioactive Cell Proliferation Assay (MTT) (Promega) according to the manufacturer's instructions. Briefly, primary AML cells and HL-60 cells were plated into the 96-well plates with a density of 2×10⁴ cells. After transfection, cells were further incubated for 24 h in culture medium containing increasing concentrations of cytarabine (0, 100, 200 and 500 nM). Subsequently, MTT dye (20 μl per well) was added and further incubated for 4 h at 37°C. The formazan precipitate was dissolved using dimethyl sulfoxide (DMSO) (150 μl per well), and the absorbance was measured at 490 nm using an automatic microplate reader (Molecular Device). Each treatment was allocated with 5 replicates. The results were calculated according to a standard curve and expressed as relative to control treatment.