Our transgenic (Tg) strain carrying copies of the human c-Ha-ras proto-oncogene is highly susceptible to 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis, possibly due to activation of the transgene, and can be used in medium-term bioassay models to test for modifying effects of estrogenic environmental compounds on tumor development. The present study was conducted to assess the influence of dietary feeding of the endocrine disruptors atrazine and nonylphenol on DMBA-induced carcinogenesis in c-Ha-ras Tg rats. Animals of both sexes were given a single oral dose of DMBA (25 mg/kg body weight) at 50 days of age and thereafter received soybean-free diet containing 5, 50 or 500 ppm atrazine, or 10, 25, 100 or 250 ppm nonylphenol. In female Tg rats, atrazine at a dose of 5 ppm increased the incidences of mammary adenomas and adenocarcinomas (P < < < <0.01 and P < < < <0.05), while 50 ppm increased the adenocarcinoma incidence (P < < < <0.05). In males, skin tumor development, in contrast, was significantly decreased at the highest dose. Nonylphenol at 10 ppm increased adenocarcinoma and total mammary tumor multiplicity in female Tg rats (P < < < <0.05), but there was no dose dependence, a significant quadratic dose-response trend rather being observed (P < < < <0.05). In vitro, atrazine did not cause proliferation of MCF-7 cells at any of a range of doses tested. These results suggest that endocrine disruptors may enhance mammary carcinogenesis, but only in a certain limited dose range under the present experimental conditions. The doses applied, moreover, were all extremely high compared to the possible environmental human exposure levels. (Cancer Sci 2004; 95: 404-410) t is well documented that estrogen is an obligatory factor for development of the mammary gland.1, 2) The hormone also plays an important role in both the etiology and treatment of mammary cancer and accumulating evidence indicates that slightly elevated levels of circulating estrogens may predispose to tumorigenesis.3, 4) Exogenous estrogens may similarly increase mammary cancer risk.5-7) This may be of considerable importance, since recently, a number of environmental chemicals impacting on the endocrine system (endocrine disruptors) have been shown to exhibit estrogenic activity, these including triazine derivatives and alkylphenolic compounds.Among the symmetrical triazine-type herbicides, atrazine (6-chloro-N 2 -ethyl-N 4 -isopropyl-1,3,5-triazine-2,4-diamine) is one of the most widely and heavily used herbicides all over the world. It is employed in agriculture as a selective pre-and postemergence agent for annual control of grass and broad-leaved weeds. A number of studies have suggested that atrazine is an endocrine disruptor [8][9][10][11][12][13][14][15] and in female Sprague-Dawley, but not other strains of rats, high doses (50-1000 ppm) in the diet have been found to be associated with an increased incidence and/or an earlier onset of mammary gland tumors. [16][17][18][19][20] Alkylphenol polyethoxylates are the se...

We have established a transgenic rat line carrying 3 copies of the human c-Ha-ras proto-oncogene with its own promoter region (Jcl/SD-TgN(HrasGen)128Ncc) (Hras128 rat), expression being detectable in almost all organs. We have already demonstrated that the rat is highly sensitive to mammary, esophagus and bladder carcinogenesis. In the present study, male and female transgenic and wild-type littermates were topically treated with 2.5 mg of 7,12-dimethylbenz[a]anthracene (DMBA) dissolved in 1.0 ml of acetone on the back skin at 50 days after birth. Starting 1 week thereafter, they were again topically treated with 100 nmol of 12-O-tetradecanoylphorbol 13-acetate (TPA) dissolved in 0.5 ml of acetone 3 times weekly for the following 31 weeks. In males treated with DMBA and/or TPA, skin tumors, including both squamous cell papillomas (SCP) and carcinomas (SCC), were preferentially induced at the DMBA-TPA painting sites: DMBA-TPA, 15/15 (100%); DMBA, 6/8 (75%); TPA, 1/6 (16.7%). They were also, unexpectedly, induced on remote scrotal skin: DMBA-TPA, 13/15 (86.7%); DMBA, 5/8 (62.5%); TPA, 0/6 (0%). Lesions were thus more frequent in the DMBA-TPA group than with DMBA or TPA alone. In females, adenomas and adenocarcinomas of the mammary glands were preferentially induced: DMBA-TPA, 12/14 (85.7%); DMBA, 6/8 (75%); TPA, 3/6 (50%), with only a few small skin papillomas at painting sites. Incidences and numbers of the mammary and skin tumors were much greater in Hras128 rats than in their wild-type counterparts. PCR-RFLP analysis of the transgene indicated that the percentage of the cell populations harboring a mutation in codons 12 and/or 61 ranged from 2% to 60% in individual tumors; skin tumors showed more mutations in codon 61 in the DMBA-treated groups. In contrast, no mutations were detected in the endogenous rat c-Ha-ras gene. These results indicate that the Hras128 rat is highly susceptible to DMBA-TPA skin and mammary carcinogenesis, thus providing a unique painting model for skin as well as mammary gland carcinogenesis, that would be suitable for investigating the role of transgene mutations. (Cancer Sci 2004; 95: 205-210) arious transgenic and knockout mice have proven to be good animal models for analysis of gene functions. In the chemical carcinogenesis field, transgenic mice carrying human c-Ha-ras proto-oncogenes (rasH2 mice) have been shown to be highly susceptible to induction of skin, lung and lymphatic cell tumors by various carcinogens.1-6) However, rats are more frequently used for analysis of events occurring during tumor development. There are thus many more basic experimental data available for rats than mice regarding chemical carcinogenesis, and a variety of preneoplastic lesions, including hepatocellular enzyme-altered foci, for example, are available in rats as surrogate markers for cancer development. 7,8) Furthermore, mammary cancers in rats can be induced without the complication of a viral etiology irrelevant to the disease in man. So far, only limited types of transgenic rats have been de...

Although a great deal of concern has been raised about the hazard potential of endocrine disruptors present in the environment, the in vivo data available from both experimental and epidemiological studies suggest that the majority of those agents do not pose a risk with regard to cancer development. Indeed, naturally occurring examples such as isoflavonoids even appear to exert protective effects. Only for xenobiotics such as 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), polychlorinated biphenyls (PCBs) and tetrachloro-p-dioxin (TCDD) and special cases of phenols and phthalates is there unequivocal evidence of carcinogenicity and this appears to be directly linked to their toxicity. Thus, careful in vivo assessment is required before drawing any conclusions regarding agents capable of affecting the mammalian endocrine system.