Selective inhibitor of γ-glutamyl cysteine synthetase, an enzyme in the glutathione, q.v., biosynthetic pathway. BSO-mediated depletion of intracellular glutathione has been associated with increased sensitivity of tumor cells to antineoplastic agents. Prepn: K. Hayashi, Chem. Pharm. Bull. 8, 177 (1960). Synthesis and in vitro and in vivo enzyme inhibition: O. W. Griffith, A. Meister, J. Biol. Chem. 254, 7758 (1979). Mechanism of action and metabolism in animals O. W. Griffith, ibid. 257, 13704 (1982). Chemosensitization by BSO of melphalan-resistant murine leukemia cells in vivo: S. Somfai-Relle et al., Biochem. Pharmacol. 33, 485 (1984); R. A. Kramer et al., Cancer Res. 47, 1593 (1987). Enhanced melphalan, q.v., cytotoxicity in human cancer cells in vitro: J. A. Green et al., ibid. 44, 5427 (1984); and in mice bearing human tumor xenografts: H. S. Friedman et al., J. Natl. Cancer Inst. 81, 524 (1989).