Figure 5 shows that 0.5 mM buthionine sulfoximine (BSO), a known inhibitor of gamma-glutamylcysteine synthetase, (Reliene and Schiestl 2006) increases about 30
times the susceptibility of the parental yeast cells to 3-BP indicating a spectacular synergistic toxic effect. As expected the deletion of the JEN1 gene restores resistance to 3-BP. This shows that BSO acts intracellularly. Notably the cytotoxicity
of doxorubicin shown to be enhanced by BSO has also been reported in multi-drug resistant cells from human breast tumor (Dusre et al. 1989). Figure 6 shows a strong
correlation between the intracellular level of GSH and the sensitivity to 3-bromopyruvate