Cell viability assay

The MTT assay was performed to determine cell viability according to the manufacture’s procedure. Briefly, the human CML cells K562 and K562-R were incubated with different concentrations of Bcr-Abl tyrosine kinase inhibitors (imatinib, dasatinib and nilotinib) and 10 μM CPT with a density of 1 × 10⁴ cells per well in 100 μL RPMI 1640 medium for 48 h. Then, the cells were subsequently incubated with a final concentration of 5 mg/mL MTT for 4 h and the formazan crystals were dissolved in 150 μL of dimethyl sulfoxide (DMSO). The absorbance was detected at 490 nm using a microplate reader (Thermo Fisher Scientific, Finland). The cell viability of 0 µM served as the control group.