MTS assays

Cells were seeded in a 96-well plate (0.5 × 10⁴ cells/well). After 24 h of incubation, an apoptosis inhibitor (Z-VAD-FMK (25 µM) (Selleckchem, Houston, TX, USA)), a ferroptosis inhibitor (ferrostatin-1 (1 µM) (Sigma-Aldrich)), and an antioxidant N-acetylcysteine (NAC (1 mM)) were added to the cells, and the plate was incubated for 1 h. Then, we added aqueous solutions of STS or sodium thiosulfate (FUJIFILM Wako Pure Chemical Corporation) at different concentrations. After incubation for 48 h, 20 µL of MTS solution [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt] (Promega, Madison, WI, USA) was added to each well, and the plate containing the cells was incubated. Cell viability was measured as being directly correlated to the determined values at absorbance of 620 and 460 nm (BioRad, iMARK™, Hercules, CA, USA).