-edited) The search for etiologic factors that contribute to the development of breast cancer has focused on environmental chemical carcinogens, environmental xenobiotics with estrogenic activity such as various organochlorines, as well as increased and/or inappropriate exposure to endogenous estrogens or their metabolites. Several recent reports have demonstrated increased catechol metabolites of estrogens in urine of women at increased risk for developing breast cancer, increased oxidative DNA damage in breast tumor tissue and increased oxidative DNA damage during estrogen carcinogenesis in animal model systems. In addition, catechol estrogens can be oxidized by copper leading to increased oxidative DNA damage and the key catechol estrogen inactivating enzyme, catechol O-methyltransferase (COMT) has been shown to be polymorphic with a fraction of women possessing low COMT activity. In light of these observations, the overall objective of this project is to begin to investigate the following two interrelated hypotheses: 1) Exposure of normal and tumorigenic breast epithelial tissue/cells to environmental chemicals at low doses can induce cytochrome P450 activities which metabolize estrogens to catechol metabolites resulting in increased oxidative stress and damage, particularly in tissue/cells with low COMT activity; 2) Oxidation of catechol estrogens, through a DNA-bound CuII/CuI-dependent redox cycling process, causes increased site-specific oxidative DNA damage (strand breaks and increased levels of 8-hydroxy-2'-deoxyguanosine (8-OH-dG)). Furthermore, since catechol estrogens are estrogenic the applicant hypothesizes that the estrogen receptor-estrogen-catechol complex can cause, upon binding to the estrogen response element of estrogen responsive genes, gene promoter-specific oxidative damage through a DNA-bound CuII-dependent mechanism.
The Specific Aims are: 1) to determine whether induction of P450 activity and/or decreased catechol O-methyltransferase activity in human breast epithelial cells leads to increased oxidative stress as indicated by activation of NF-kb and c-fos expression and damage in nuclear DNA as indicated by the appearance of strand breaks and increased 8-OH-dG levels; 2) to determine if catechol estrogens, through a DNA-bound CuII/Cul- dependent redox cycling process, can cause increased site-specific oxidative DNA damage (strand breaks) and whether the estrogen receptor-estrogen-catechol complex can, upon binding to the estrogen response element of estrogen responsive genes, cause gene promoter- specific oxidative damage through a DNA-bound CuII-dependent mechanism. If this investigation supports the hypotheses, it would become important to develop methods to determine catechol metabolite levels and/or potential for their formation in breast tissue as an indicator of increased risk for oxidative stress/damage and would suggest that interventions aimed at redirecting metabolism and/or inactivating the reactive oxygen species formed would decrease the risk for tumor development and/or progression.
| Yager, James D (2015) Mechanisms of estrogen carcinogenesis: The role of E2/E1-quinone metabolites suggests new approaches to preventive intervention--A review. Steroids 99:56-60 |
| Lavigne, J A; Helzlsouer, K J; Huang, H Y et al. (1997) An association between the allele coding for a low activity variant of catechol-O-methyltransferase and the risk for breast cancer. Cancer Res 57:5493-7 |
