TOXICITY, SINGLE-STRAND BREAKS, AND 5-HYDROXYMETHYL-2'-DEOXYURIDINE FORMATION IN HUMAN BREAST EPITHELIAL-CELLS TREATED WITH HYDROGEN-PEROXIDE

DNA damage induced by oxidants includes formation of DNA strand breaks as well as oxidative damage to DNA bases. We quantified both forms of DNA damage concurrently in two model human breast epithelial cell lin es treated with hydrogen peroxide to compare the dose-dependent induct ion of each form of DNA damage with growth inhibition. Antioxidant def enses also were quantified. MCF-7 breast cancer cells had relatively h igher levels of non-protein thiols, oxidized glutathione (GSSG) reduct ase, catalase, and superoxide dismutase than did the MCF-IOA line of i mmortalized, but not transformed, human breast epithelial cells. The l evels of antioxidant defenses were not predictive of endogenous oxidat ive DNA damage levels nor of toxicity and DNA damage induced by hydrog en peroxide. The endogenous levels of 5-hydroxymethyl-2'-deoxyuridine were higher in MCF-7 than MCF-10A cells. The cells were treated with 1 0-200 muM hydrogen peroxide for 15 min at 37-degrees-C in complete med ia. Low concentrations of hydrogen peroxide were growth stimulatory to both cell lines. At higher concentrations,growth inhibition by hydrog en peroxide was greater in MCF-7 than in MCF-10A cells. Accordingly, i nduction of both single-strand DNA breaks and 5-hydroxymethyl-2'-deoxy uridine in DNA was greater in MCF-7 than MCF-10A cells. In both cell l ines, the dose-dependent induction of single-strand breaks paralleled growth inhibition more closely than did formation of 5-hydroxymethyl-2 '-deoxyuridine.