BSO

BSO (L-Buthionine-(S,R)-sulfoximine) synergistically enhanced BCNU activity against melanoma cell lines and human tumors. BSO (50 μM) treatment for 48 hr results in a 95% decrease in ZAZ and M14 melanoma cell line GSH levels, and a 60% decrease in GST enzyme activity. GST-μ protein and mRNA levels are significantly reduced in both cell lines. GST-π expression is unaffected. BSO enhancement of alkylator action may be related in part to down regulation of GST.^[1]

The effect of BSO treatment on glutathione content (GSH + GSSG) is determined on cells plated in 24-well plates at the same density as in the thymidine incorporation assay. GSH is measured at time zero, and at 6, 24, 48, and 72 hr by a modified Tietze method. GSH standard curves are obtained by dissolving 5 mg GSH in 25 ml 0.01 N HCl and running determinations on serial dilutions. Cell supernatants are prepared by freezethawing cells resuspended to 10⁷ cells per ml in 0.01 M NaP0₄ + 0.005 M EDTA buffer (pH 7.5) three times, and centrifuging for 30 min at 30,000g at 4℃. GSH levels are determined from the rate of change in optical density at 412 nm, 25℃.

LButhionine-S,R-sulfoximine (L-S,R-BSO) substantially inhibits GSH production at a greater degree and causes a higher toxicity to guinea pigs than mice, implying that mice may have an additional protective mechanism against oxidative stress injury. Indeed, administration of L-S,R-BSO to mice inhibits tissue GSH production while increasing ascorbate levels. L-S,R-BSO also increases tissue ascorbate levels in mice fed a ascorbate and dehydroascorbatefree diet suggesting activation of ascorbate synthesis, which is further confirmed by increased urinary ascorbate excretion.^[2]