Figure 3: Effect of perifosine (PER) and N-acetyl-cysteine (NAC) on total glutathione (GSH) levels (a), glutathione disulfide (GSSG) levels (b), percentage glutathione disulfide (%GSSG) levels (c), and cytotoxicity (d) in head and neck cancer cells. Cells were treated with 5  M PER (FaDu and Cal-27) or 10  M PER (SCC-25) for 24 hours with or without treatment with 20 mM NAC for 1 hour before and during PER exposure. (a)–(c) Cells were harvested for glutathione analysis using the spectrophotometric recycling assay. Error bars represent 1SD of experiments. (d) Cells were analyzed for clonogenic survival and the data were normalized to control (CON). Error bars represent 1SD of experiments performed on different days with at least 2 cloning dishes taken from 1 treatment dish. *, versus control; , versus respective treatment without NAC.