Cell Counting Kit-8 (CCK-8) Assay

Cells were seeded at a density of 5×10³ cells/well in 96-well cell culture plates and incubated overnight in 100 μL of RPMI 1640 medium. In the following days, DMSO, IH, FZ or IH+FZ at different concentrations were added 4 hours before irradiation (0 Gy, 2 Gy, 4 Gy and 6 Gy) with 6 MV X-rays at a dose rate of 2 Gy/min generated by a linear accelerator (Siemens, Erlangen, Germany). To measure the cell viability at the indicated time point, 10 μL of CCK-8 reagent (Dojindo Laboratories, Kumamoto, Japan) was added to each well, and the cells were incubated at 37°C for 2.5 hours. Optical density (OD) values at a wavelength of 450 nm were measured by a microplate reader (Thermo Fisher Scientific).