Intracellular (reduced) GSH levels in ML1 cells. (A) GSH levels in ML1 cells transduced with control vector (GFP) or FLIP_Long (FLIP_Long) after 24 hours of exposure to L-buthionine sulphoximine (BSO) at concentrations of 10 to 200 μM. Test results were expressed as a proportion of baseline (set as 100%, GSH values in each determination were the average of 2 measurements). Shown in the insert is a comparison of GSH levels in wild-type (WT), GFP, and FLIP_Long-transduced ML1 cells. (B) ML1 cells were exposed to BSO, at concentrations of 10 to 200 μM (shown are results with 100 μM) for 24 hours followed by treatment with ATO at 2 to 10 μM as in Figure 6B (shown are results at 5 μM) for 18 hours, and apoptosis was determined. Taken together the data showed that FLIP_Long cells were more resistant to ATO than GFP-transduced cells. GSH depletion by BSO was not effective in enhancing ATO-induced apoptosis in either control-transduced GFP or in FLIP_Long-overexpressing ML1 cells. Results represent the mean plus or minus SE of 3 independent experiments, each carried out in duplicate.