Eleanor G. Rogan

Estrogen mediation of breast tumor formation involves estrogen receptor-dependent, as well as independent, genotoxic effects.

Long‐term exposure to estrogens influences the development of breast cancer in women, but the precise mechanisms involved are not clearly defined. Our working hypothesis is that estrogen modulates this process by two separate processes. One involves the binding of estradiol to estrogen receptor (ER) alpha with stimulation of cell proliferation. Errors in DNA occurring during replication result in fixed mutations when not repaired. The other process results from the formation of genotoxic metabolites of estradiol, which can bind to DNA, cause depurination, and result in mutations. Our collaborative group, funded by a Department of Defense Center of Excellence grant, has examined this hypothesis using a variety of experimental methods. Estradiol and its catechol‐estrogen metabolite 4‐OH‐estradiol causes mutations in cell culture systems and can transform benign MCF‐10F cells, allowing them to cause tumors in SCID mice. We have demonstrated loss of heterozygosity and gains and losses of DNA segments by comparative genomic hybridization methodology. The depurinated estradiol‐guanine and ‐adenine adducts are measurable in MCF‐7 breast cancer cells in culture and in mouse mammary tissue. The double transgenic, alpha estrogen receptor knockout/Wnt‐1 knockin mouse model allows us to dissect out the separate effects of ER‐mediated and ER‐independent actions of estradiol. Knock out of the ER alpha delays the onset of breast tumors in this model, demonstrating a role of receptor‐mediated actions. Oophorectomy delays the onset of tumors and reduces overall incidence, providing evidence for an ER‐independent effect. Taken together, these data suggest that both ER‐dependent and genotoxic ER‐independent effects of estradiol mediate breast cancer development.

Modulation of Cellular Response to Arsenic Trioxide Toxicity by Resveratrol

Arsenic trioxide (As2O3) is an environmental carcinogen and a putative endocrine disruptor. Resveratrol has been shown to reverse As2O3-induced oxidative damage. In immortalized but nontransformed estrogen receptor α-negative human breast cells (MCF10A), we observed that 25 μM resveratrol ameliorated As2O3-induced cytotoxicity. As2O3, in the presence or absence of 25 μM resveratrol, induced quinone reductase (NAD(P)H quinone dehydrogenase 1), via the induction of NFE2-related factor 2. As2O3 caused a repression of cytochrome P450 (CYP)1B1, but the addition of 25 μM resveratrol rescued the expression of cytochrome P450 1B1 and kept it at a constant level. Therefore, 25 μM resveratrol can modulate the effects of As2O3 on enzymes involved in estrogen metabolism.