Xenobiotic metabolizing and antioxidant enzymes in normal and neoplastic human breast tissue

Glutathione levels in human tumors

This review summarizes clinical studies in which glutathione was measured in tumor tissue from patients with brain, breast, gastrointestinal, gynecological, head and neck and lung cancer. Glutathione tends to be elevated in breast, ovarian, head and neck, and lung cancer and lower in brain and liver tumors compared to disease-free tissue. Cervical, colorectal, gastric, and esophageal cancers show both higher and lower levels of tumor glutathione. Some studies show an inverse relationship between patient survival and tumor glutathione. Based on this survey, we recommend approaches that may improve the clinical value of glutathione as a biomarker.

Estrogen-induced breast cancer: alterations in breast morphology and oxidative stress as a function of estrogen exposure

Epidemiological evidence indicates that prolonged lifetime exposure to estrogen is associated with elevated breast cancer risk in women. Oxidative stress and estrogen receptor-associated proliferative changes are suggested to play important roles in estrogen-induced breast carcinogenesis. In the present study, we investigated changes in breast morphology and oxidative stress following estrogen exposure. Female ACI rats were treated with 17beta-estradiol (E(2), 3 mg, s.c.) for either 7, 15, 120 or 240 days. Animals were euthanized, tissues were excised, and portions of the tissues were either fixed in 10% buffered formalin or snap-frozen in liquid nitrogen. Paraffin-embedded tissues were examined for histopathologic changes. Proliferative changes appeared in the breast after 7 days of E(2) exposure. Atypical ductal proliferation and significant reduction in stromal fat were observed following 120 days of E(2) exposure. Both in situ and invasive carcinomas were observed in the majority of the mammary glands from rats treated with E(2) for 240 days. Palpable breast tumors were observed in 82% of E(2)-treated rats after 228 days, with the first palpable tumor appearing after 128 days. No morphological changes were observed in the livers, kidneys, lungs or brains of rats treated with E(2) for 240 days compared to controls. Furthermore, 8-isoprostane (8-isoPGF(2alpha)) levels as well as the activities of antioxidant enzymes, such as glutathione peroxidase, superoxide dismutase and catalase, were quantified in the breast tissues of rats treated with E(2) for 7, 15, 120 and 240 days and compared to activity levels in age-matched controls. 8-isoPGF(2alpha) levels displayed time-dependent increases upon E(2) treatment and were significantly higher than control levels at the 15, 120 and 240 day time-points. 8-isoPGF(2alpha) observed in E(2)-induced mammary tumors were significantly higher than levels found in control mammary tissue from age-matched animals. Similarly, alterations in glutathione peroxidase and superoxide dismutase activities were detected in both mammary and tumor tissue from E(2)-treated rats. Taken together, our data reveal that proliferative changes in the breast tissue of ACI rats are associated with increases in 8-isoPGF(2alpha) formation as well as changes in the activities of antioxidant enzymes. These oxidative changes appear to be a function of E(2) exposure and occur prior to tumor development.

Identification of a novel putative non-selenocysteine containing phospholipid hydroperoxide glutathione peroxidase (NPGPx) essential for alleviating oxidative stress generated from polyunsaturated fatty acids in breast cancer cells

A dramatic reduction in the expression of a novel phospholipid hydroperoxide glutathione peroxidase (PHGPx), which incorporates cysteine instead of selenocysteine in the conserved catalytic motif was observed in a microarray analysis using cDNAs amplified from mRNA of Brca1-null mouse embryonic fibroblasts. This non-selenocysteine PHGPx named NPGPx is a cytoplasmic protein with molecular mass of approximately 22 kDa and has little detectable glutathione peroxidase activity in vitro. Ectopic expression of NPGPx in Brca1-null cells that were sensitive to oxidative stress induced by hydrogen peroxide conferred a similar resistance level to that of the wild-type cells, suggesting the importance of this protein in reducing oxidative stress. Expression of NPGPx was found in many tissues, including developing mammary gland. However, the majority of breast cancer cell lines studied (11 of 12) expressed very low or undetectable levels of NPGPx irrespective of BRCA1 status. Re-expression of NPGPx in breast cancer lines, MCF-7 and HCC1937, which have very little or no endogenous NPGPx, induced resistance to eicosapentaenoic acid (an omega-3 type of polyunsaturated fatty acid)-mediated cell death. Conversely, inhibition of the expression of NPGPx by the specific small interfering RNA in HS578T breast cancer cells that originally express substantial amounts of endogenous NPGPx increased their sensitivity to eicosapentaenoic acid-mediated cell death. Thus, NPGPx plays an essential role in breast cancer cells in alleviating oxidative stress generated from polyunsaturated fatty acid metabolism.

CYP3A4, CYP2C9 and CYP2B6 expression and ifosfamide turnover in breast cancer tissue microsomes

Ifosfamide is a prodrug that requires bioactivation by cytochrome P450 for antitumour activity. Up to now, little is known, to what extent in addition to the liver the ifosfamide metabolism may occur intratumorally. For this purpose, we investigated the expression of CYP3A4, CYP2C9 and CYP2B6 in breast cancer tissue using Western Blotting. Ifosfamide turnover was determined by detection of metabolites of the ifosfamide 4-hydroxylation and N-dechloroethylation in tumour microsomal incubations using HPLC/UV and LC/MS. The results demonstrate that all mammary tumours (n=11) reveal CYP3A4 expression; contents varied from 0.5 to 63 pmol mg(protein)(-1). CYP2C9 (n=9) was present in all tested breast tumour samples, too, while CYP2B6 (n=10) protein could not be detected. All measured breast cancer microsomes (n=4) showed an ifosfamide N-dechloroethylation capacity in the range from 0.04 to 0.21 pmol min(-1) mg(protein)(-1), while metabolites of the 4-hydroxylation could not be determined. In conclusion, the detected presence of CYP3A4 and CYP2C9 in breast tumours offers the possibility of intratumoral turnover of ifosfamide. For the first time in the literature, we could demonstrate a turnover of ifosfamide by microsomal preparations from human breast cancer tissue. A calculated modulation of intratumoral ifosfamide turnover could considerably influence its therapeutic efficiency.

Activation of the antitumor agent aminoflavone (NSC 686288) is mediated by induction of tumor cell cytochrome P450 1A1/1A2

The present studies were performed to elucidate the mechanism of cytotoxicity of the aminoflavone analog (5-amino-2,3-fluorophenyl)-6,8-difluoro-7-methyl-4H-1-benzopyran-4-one (AF; NSC 686288), a novel flavone with potent in vitro and in vivo antiproliferative activity against a number of human tumor cell lines and with a unique pattern of antiproliferative activity in the National Cancer Institute tumor cell line screen. AF was extensively metabolized by cytochrome P450 (P450) 1A1 and 1A2 to several metabolites, one of which was identified by mass spectrometry as a potentially reactive hydroxylamine. Radiolabeled AF was converted by rat and human microsomes, by recombinant CYP1A1 and CYP1A2, and by sensitive human tumor cell lines to species that covalently bound macromolecules. Treatment of sensitive human MCF7 cells with AF resulted in increased CYP1A1 mRNA and CYP1A1/1A2 protein followed by covalent binding of an AF metabolite to DNA, phosphorylation and stabilization of p53, and increased expression of the p53 transcriptional target p21. Covalent binding of the AF metabolite was increased by pretreatment with the CYP1A inducer 3-methylcholanthrene and decreased by coincubation with the CYP1A inhibitor alpha-naphthoflavone. In contrast, induction of CYP1A1 and covalent binding of the AF metabolite did not occur in AF-resistant M14-MEL cells. These observations suggest that AF is uniquely able to induce its own metabolic activation via CYP1A1/1A2 in duction to cytotoxic DNA-damaging species directly in tumor cells. AF, and possibly other agents, may offer a treatment strategy for tumors responsive to CYP1A1/1A2 induction, such as breast, ovarian, and renal cancers.

The organochlorine pesticide residues and antioxidant enzyme activities in human breast tumors: is there any association?

The levels of some organochlorine pesticides (OCP)s (hexachlorobenzene, HCB, alpha-hexachlorocyclohexane, alpha-HCH, beta-HCH, gamma-HCH, heptachlorepoxide, HE, bis (4-chlorophenyl)-1,1-dichloroethene, p.p'DDE, bis (4-chlorophenyl)-1,1,1-trichloroethane, p.p' DDT and total DDT (E-DDT) and antioxidant enzyme activities namely Cu, Zn superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathione peroxidase (Se-GSH-Px), total glutathione peroxidase (T-GSH-Px), selenium independent glutathione peroxidase (GSH-Px II), glutathione reductase (GRd), level of reduced glutathione (GSH) and lipid peroxidation (LP), glutathione S-transferase (GST) activity toward several substrates including 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), ethacrynic acid (EAA), 1,2-epoxy-3-(p-nitrophenoxy)-propane (ENPP) were measured in tumor and surrounding tumor free tissues of 24 female breast cancer patients and was evaluated whether there exist any association between the levels of OCPs and antioxidants. The mean levels of GSH, alpha-BHC, gamma-BHC and HE, and activities of SOD, Se-GSH-Px, T-GSH-Px, GSH-Px II,GRd, GST CDNB, and GST DCNB were significantly higher in tumors than in controls. In tumors, significant correlations were noted between: SOD and y-BHC; Se-GSH-Px and gamma-BHC; T-GSH-Px and gamma-BHC; GSH-Px II and alpha-BHC, gamma-BHC; GSH and alpha-BHC, gamma-BHC, HE; GRd and alpha-BHC; CDNB GST and alpha-BHC, gamma-BHC. These results show that free-radical mediated oxidative stress is, at least partly, associated with some of these OCP residues in human breast tumors.