Figure 4: Effect of inhibitors of glutathione and thioredoxin metabolism on perifosine (PER) toxicity in head and neck cancer cells. (a) Cal-27 and SCC-25 cells were treated with 5 M PER (Cal-27) or 10 M PER (SCC-25) for 24 hours with or without treatment with 1 mM buthionine sulfoximine (BSO) for 1 hour before and during PER exposure. (b)-(c) Cells were treated as stated above and harvested for total glutathione (GSH) levels (b), and percentage glutathione disulfide (%GSSG) levels (c) using the spectrophotometric recycling assay. Error bars represent ± 1SD of experiments. (d) Cal-27 and SCC-25 cells were treated with 5 M PER (Cal-27) or 10 M PER (SCC-25) for 24 hour with or without treatment with 0.5 M Auranofin (AUR) for 1 hour before and during PER exposure. Clonogenic cell survival data were normalized to control (CON). Error bars represent ± 1SD of experiments performed on different days with at least 4 cloning dishes taken from 1 treatment dish. *, versus control; , versus respective treatment without BSO or AUR.