OVEREXPRESSION OF STABLY TRANSFECTED HUMAN GLUTATHIONE-S-TRANSFERASE P1-1 PROTECTS AGAINST DNA-DAMAGE BY BENZO[A]PYRENE DIOL-EPOXIDE IN HUMAN T47D CELLS

The (+)-anti enantiomer of benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) is a potent mutagenic and carcinogenic metabolite of benzo[a]p yrene (BP), and a major fraction is conjugated with glutathione in viv o. The chemopreventive role of glutathione S-transferases (GSTs) in pr otecting against covalent modification of DNA and other cellular macro molecules by BPDE was modeled in human T47D and MCF-7 cell lines previ ously stably transfected with human GST pi 1 (hGSTP1). Cells were expo sed to [H-3]BPDE (30-600 nM). Dose-response experiments indicated that the high level of expression of hGSTP1-1 in the T47D pi cell line (44 11 +/- 183 milliunits mg of cytosolic protein, using 1-Cl-2,4-dinitrob enzene as substrate), resulted in 70-90% reduction in the covalent H-3 -adduct formation in DNA or RNA isolated from the GSTP1-transfected T4 7D ir cell line. The lower level of hGSTP1-1 expression in the transfe cted MCF-7 cell line (91 milliunits/mg) provided only marginal protect ion against [H-3]BPDE adduct formation and did not affect sensitivity to BPDE-induced cytotoxicity. Protection against BPDE-induced cytotoxi city was observed only in the T47D pi cell line, which had an IC50 val ue 5.8-fold greater than that of the T47Dneo control cell line. Measur ement of glutathione conjugates of BPDE indicated that the total conju gation was 5-fold higher in the GST pi-transfected T47D line, most of which was exported into the culture medium over the 20-min exposure pe riod. These results indicate that hGSTP1-1 protects effectively agains t DNA and RNA modification by BPDE, but moderate to high level express ion may be required for strong protection against BPDE-induced genotox icity and cytotoxicity.