Cytotoxicity analyses were performed using Cell Counting Kit-8 (CCK-8) (Beyotime, China) based on a water-soluble tetrazolium dye (WST-8), which is more sensitive than the conventional 3-(4,5-dimethylthiazol-2-yl)-5-(3- carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS)-based assay. Briefly, serial dilutions of TFS at concentrations of 500/2n μg/L (n=0–6) in triplicate were added to cells cultured on a 96-well plate in M199 supplemented with 5% FBS. At each 24 h period, cell viability following TFS exposure was tested as per the manufacturer’s protocols for CCK-8. Colorimetric absorbance after the mitochondrial enzyme substrate reaction was measured at 450 nm using a microplate reader (ELX800, Gene, Hong Kong, China). As DMSO exhibits no cytotoxicity at doses of up to 0.1% (v/v) (Liu et al., 2020a (link)), TFS-exposed signals were compared to solvent-control signals (DMSO up to 0.001%, v/v).