Genotoxic effects induced by equine estrogen metabolites in breast cancer cells.

摘要

Excessive exposure to synthetic and endogenous estrogens has been associated with the development of cancer in several tissues. One potential mechanism of estrogen carcinogenesis involves metabolism of estrogens to 2- and 4-hydroxylated catechols and these catechols are further oxidized to electrophilic/redox active o-quinones, which have the potential to both initiate and promote the carcinogenic process. Previously we showed that the major catechol metabolite of both equilin and equilenin, 4hydroxyequilenin (4-OHEN), could autoxidize to potent cytotoxic quinoids and cause a variety of DNA lesions in vitro.; In the present study, we found that 4-OHEN caused DNA damage in breast cancer cells and cells that contain estrogen receptor α (S30) were more sensitive to 4-OHEN-mediated DNA damage as compared to estrogen receptor negative cells (MDA-MB-231). Our data suggest that the mechanism of DNA damage induced by equine estrogens and their metabolites could involve oxidative stress and that the estrogen receptor may play a role in this process. Since these deleterious effects could contribute to estrogen-induced gene mutations, we studied the Chinese hamster V79 cells to ascertain the relative ability of 4-OHE ₂, 4,17β-OHEN, 4-OHE, 4-OHEN, to induce the mutation of the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene. The data showed that at 100 nM, 4-OHEN and 4,17β-OHEN formed significantly (p 0.005) more colonies than those of endogenous catechol estrogens, 4-OHE and 4-OHE ₂, which is probably due to the fact that oxidative enzymatic catalysis is required to form the o-quinones from the endogenous catechol estrogens. In contrast, 4-OHEN and 4,17β-OHEN can autoxidize to quinoids which can consume reducing equivalents and molecular oxygen and cause a variety of damage to DNA. In order to block catechol formation from equilenin, 4-halogenated equilenin derivatives were synthesized and the 4-fluoro derivatives were found to be more estrogenic than the 4-chloro and 4-bromo derivatives in vitro. In addition, we studied the relative ability of 4-halogenated equilenin derivatives to induce estrogenic effects in the ovariectomized rat model and the in vivo data showed a similar trend as found in vitro.; In summary, our data suggest that equine estrogen metabolites could play a major role in induction of DNA damage leading to the initiation/promotion of the carcinogenic process in hormone sensitive tissue.