Cell viability assay

K562 (2 x 10⁴ cells/well), 32Dp210 (4 x 10⁴ cells/well), and 32Dp210-T315I (4 x 10⁴ cells/well) CML cells were seeded in 96-well plates and treated with PBS (control) or shikonin as indicated. Cell viability was determined by incubation with fresh medium containing 0.5 mg/mL MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide; Sigma] for 4 h at 37 °C. The MTT-containing medium was then removed and DMSO (200 μL) was added to each well. Well absorbance was measured at 570 nm in a microplate spectrophotometer (Bio-Rad, Richmond, CA, USA).