³²P-Postlabeling analysis of DNA adducts in human and rat mammary epithelial cells

Abstract

The etiology of human breast cancer is currently undefined. However, it has been hypothesized that exposure to chemical carcinogens may be an important factor. Extrapolation from rodent models for chemically-induced mammary cancer suggests the possibility that human mammary epithelial cells in situ might contain DNA adducts due to exposure to environmental chemicals. We have therefore screened breast epithelial cells from 10 donors for the existence of DNA adducts using the 32P-postlabeling assay. In order to validate this analysis technique, we also examined the DNA adducts formed in human mammary cells exposed to benzo[a]pyrene (B[a]P) in vitro, and adducts formed in rat mammary epithelial cells exposed to B[a]P in vitro and in vivo. Confirming previous results using HPLC analysis of [3H]B[a]P-DNA adducts, the major B[a]P-DNA adduct formed by human mammary epithelial cells in vitro was (+)-anti-B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE):deoxyguanosine. This adduct did not appear to be formed by rat mammary cells exposed to B[a]P in vitro. However, 32P-postlabeling analysis of mammary epithelial cell DNA from rats exposed to B[a]P in vivo indicated that (+)-anti-BPDE-deoxyguanosine was a major B[a]P-DNA adduct under these exposure conditions. When the mammary epithelial cells from 10 human donors were screened for DNA adducts formed in situ, cells from three donors exhibited distinct adduct patterns. None of these adducts appeared to be (+)-anti-BPDE-deoxyguanosine. The existence of DNA adducts in human mammary epithelial cells in situ, coupled with the data indicating that rat mammary cells form different B[a]P adducts in vitro and in situ, suggests the need for further study of human breast cell adducts.

Interindividual variation in the metabolic activation of heterocyclic amines and their N-hydroxy derivatives in primary cultures of human mammary epithelial cells

“…Li et al reported higher adduct levels in tumour-adjacent breast tissue from cancer patients compared with the levels observed in reduction mammoplasty (control) patients (43). In another study DNA adducts were detected in three out of ten untreated reduction mammoplasty samples (44). However the identity of these adducts remains to be determined.…”

“…A larger study will be required to determine whether this observation can be reproduced and achieve statistical significance. Several studies have demonstrated that pre-existing DNA adducts are present in human breast tissue (43)(44)(45). Li et al reported higher adduct levels in tumour-adjacent breast tissue from cancer patients compared with the levels observed in reduction mammoplasty (control) patients (43).…”

Review of the Etiology of Breast Cancer with Special Attention to Organochlorines as Potential Endocrine Disruptors

“…A study of premenopausal breast cancer reported a trend of increasing risk associated with the probability of PAH exposure, particularly evident for ER-positive tumors (Petralia et al, 1999). Several other epidemiologic studies have either been ecologic or too small to draw conclusions (Dusich et al, 1980;Gupta, 1984;Li et al, 1996;Routledge et al, 1992;Seidman et al, 1988). Given ubiquitous exposure and biologic plausibility, PAHs should continue to be studied as potential contributors to breast cancer.…”

Tumorigenicity of Polycyclic Aromatic Hydrocarbons: "On the Possible Contribution of PAHs and their Nitro-Derivatives to the Development of Human Breast Cancer"

“…As described, putative PAH-DNA adducts have been detected in both human blood and breast tissue. [38][39][40][41][42][43][44][45] For a better understanding of the etiology of breast cancer, it is essential to develop and/or improve sensitivity and selectivity of existing methods. Such improved methods are needed to assess the extent of human exposure, determine the ability of breast tissue to metabolically activate PAHs to DNA-damaging intermediates, and define the carcinogenic potential at doses that mimic human exposure to individual PAHs and combinations thereof.…”