2.8. Cell Proliferation Assay
Cell viability was tested by an MTS assay (Promega, WA, USA). Cells were seeded in 96-well plates and then treated with the indicated concentrations of compounds for 72 h. Then, 20 µL of MTS was added and incubated at 37 °C for 1-2 h. The absorbance at 490 nm was measured by a SpectraMax 190 plate reader, and the IC50 value was calculated using GraphPad Prism. In the drug combination assay, the CI value was calculated by Calcusyn software.