BTZ resistance is conferred by increases in GSH. (A-B) U266/BR (A) and RPMI8226/BR (B) cells were left untreated (CTL) and treated with (1) 2.5 μM GO-203 alone each day for 72 hours, (2) 20 (U266/BR) or 16 (RPMI8226/BR) nM BTZ for 24 hours, or (3) GO-203 for 48 hours combined with BTZ during an additional 24 hours. GO-203/BTZ-treated cells were also incubated in the presence of 5 mM NAC for 72 hours. Lysates were subjected to immunoblot analysis with the indicated antibodies. (C-D) The indicated drug-naïve and BTZ-resistant cells were analyzed for GSH levels. The results (mean ± SD of 3 determinations) are expressed as μM GSH per 106 cells. (E-F) U266/BR (E) and RPMI8226/BR (F) cells were treated as described in panels A and B and were analyzed for relative GSH levels (mean ± SD of 3 determinations) as compared with that obtained with control cells. BR, BTZ-resistant cells; DN, drug-naïve cells.
