Cytotoxicity and Synergy Assessment

Cytotoxicity was evaluated by tetrazolium-based 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) kit (Promega Corporation, Madison, WI, USA) as described previously [22 (link)]. The cell viability in terms of cellular ATP content was evaluated by an ATP-lite assay kit (PerkinElmer Life Sciences, Boston, MA, USA) [23 (link)]. The drug interaction for the UVC/WFA combined treatment was analyzed as previously described [24 (link)]. In brief, the formula for determining the synergy (α), i.e., additive, synergistic, or antagonistic for α = 1, >1, and <1, respectively, was listed as follows: α = survival fraction (SF) for UVC alone treatment × SF for WFA alone treatment/SF for UVC/WFA combined treatment. Cells were photographed at 100× magnification for morphology analysis.