Cytotoxicity assay

MTT assay was usually used to measure cell viability and cytotoxicity of anti-cancer drugs. Briefly, leukemia cells were seeded in 96-well plates (1 × 10⁴ cells/well). Then, cells were treated with various concentrations of alantolactone and control group was treated by DMSO. After 72-h treatment of alantolactone, 20 μL MTT solution (5 mg/mL) was added to each well and then incubated in 37 °C, 5 % CO₂ incubator for additional 4 h. After being centrifuged by 1500 rpm for 15 min, all supernatant were removed and 100 μL DMSO was added to each well to dissolve the formazan crystal. Absorbance was measured at 570 nm using a micro-plate reader (synergy H4, BioTek, USA). Then the IC₅₀ value was analyzed by GraphPad Prism 5 project.