A synthetic amino acid. Buthionine sulfoximine irreversibly inhibits gamma-glutamylcysteine synthetase, thereby depleting cells of glutathione, a metabolite that plays a critical role in protecting cells against oxidative stress, and resulting in free radical-induced apoptosis. Elevated glutathione levels are associated with tumor cell resistance to alkylating agents and platinum compounds. By depleting cells of glutathione, this agent may enhance the in vitro and in vivo cytotoxicities of various chemotherapeutic agents in drug-resistant tumors. Buthionine sulfoximine may also exhibit antiangiogenesis activity. or A drug used to treat chronic myelogenous leukemia (CML). It is also used with other drugs to prepare patients with CML for a stem cell transplant. It is also being studied in the treatment of other types of cancer. Busulfex attaches to DNA in cells and may kill cancer cells. It is a type of alkylating agent. Also called busulfan and Myleran.