Glutathione S-transferase-activated compounds

A pharmaceutical composition effective in treating MCF-7 cells, which composition comprises at least one compound of of the formula:

• ##STR18## or the amides, esters or salts thereof, wherein:
• L is an electron withdrawing leaving group;
• S.sup.x is S.dbd.O, O.dbd.S.dbd.O, S.dbd.NH, HN.dbd.S.dbd.O, Se.dbd.O, O.dbd.Se.dbd.O, Se.dbd.NH, HN.dbd.Se.dbd.O, S.sup.+ R.sup.4 wherein R.sup.4 is alkyl (1-6C), or O--C.dbd.O or HN--C.dbd.O;
• each R Of R.sup.1, R.sup.2 and R.sup.3 is independently H or a noninterfering substituent;
• n is 0, 1 or 2;
• Y is selected from the group consisting of ##STR19## wherein m is 1 or 2;
• and AA.sub.C is an amino acid selected from the group consisting of:
• glycine, valine, alanine, .beta.-alanine, 4-amino butyric acid, aspartic acid, phenylglycine, histidine, tryptophan, tyrosine, unsubstituted phenylalanine, and phenylalanine substituted in its aromatic ring by one or two substituents selected from the group consisting of halo, OR, SR, and NR.sub.2, wherein R is H or alkyl (1-4C), linked through a peptide bond to the remainder of said compound of formula 1 in admixture with a pharmaceutically acceptable excipient.