*4.3. Cell Viability Assay*

Cell viability was assessed using the MTT colorimetric assay. Cells (6 ~ 8 <sup>×</sup> <sup>10</sup><sup>2</sup> cells/well) were seeded into 96-well plates and treated with various concentrations of KJ-28d or a combination of anti-cancer drugs or IR. After 5 days of treatment, 10 µL MTT (0.5 mg/mL) was added, and cells were further incubated for 3 h. After removal of the supernatant, the resultant pellet was dissolved in DMSO. The absorbance of the resultant formazan was measured at 540 nm using a Multiskan EX plate reader (Thermo LabSystems, Waltham, MA, USA).
