Involvement of H2O2 and O2- in the cytotoxicity of N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD), a novel insect-derived anti-tumor compound.

We investigated the mechanism underlying the cytotoxicity of N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD) toward MDA-MB-435S, a human breast cancer cell line sensitive to 5-S-GAD. We found that the addition of either catalase or superoxide dismutase (SOD) to a culture medium of MDA-MB-435S cells almost completely abolished the cytotoxic effect of 5-S-GAD, indicating that both hydrogen peroxide (H(2)O(2)) and the superoxide anion (O(2)(-)) are involved in the cytotoxic action of 5-S-GAD. We compared the catalase and SOD levels in MDA-MB-435S and T47D, a cell line resistant to 5-S-GAD, and found that the levels in resistant cells are higher than those in sensitive cells. We concluded that the levels of these enzymes are crucial determinants of the sensitivity or insensitivity of cells to 5-S-GAD.