Buthionine sulfoximine is an analogs of methionine sulfoximine and inhibits gamma-glutamylcysteine synthetase about 20 times more effectively than prothionine sulfoximine and at least 100 times more effectively than methionine sulfoximine.

Treatment of mice bearing HT1080 and HT1080/DR4 xenografts with a continuous i.v infusion of nontoxic doses of D,L-Buthionine-(S,R)-sulfoximine (300 and 600 mg/kg/day) produce a 60% reduction of GSH plasma levels and greater than 95 % reduction in GSH tumor levels in both parental and multidrug-resistant tumors.