title: Possible enhancing effects of atrazine and nonylphenol on 7,12-dimethylbenz[a]anthracene-induced mammary tumor development in human c-Ha-ras proto-oncogene transgenic rats.
abstract: 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.
authors.affiliation: Experimental Pathology and Chemotherapy Division, National Cancer Center Research Institute, Chuo-ku, Tokyo 104-0045, Japan.
authors.forename: Katsumi
authors.initials: K
authors.lastname: Fukamachi
authors.forename: Beom Seok
authors.initials: BS
authors.lastname: Han
authors.forename: Chuel Kyu
authors.initials: CK
authors.lastname: Kim
authors.forename: Nobuo
authors.initials: N
authors.lastname: Takasuka
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Matsuoka
authors.forename: Eiji
authors.initials: E
authors.lastname: Matsuda
authors.forename: Tomomi
authors.initials: T
authors.lastname: Yamasaki
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tsuda
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity*; D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D030801:Animals, Genetically Modified; D001280:Atrazine / Q000008:administration & dosage / Q000494:pharmacology*; D001681:Biological Assay; D002273:Carcinogens / Q000633:toxicity*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004703:Endocrine System / Q000187:drug effects; D005260:Female; D011905:Genes, ras / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006540:Herbicides / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D008297:Male; D015674:Mammary Neoplasms, Animal / Q000139:chemically induced* / Q000235:genetics; D010636:Phenols / Q000008:administration & dosage / Q000494:pharmacology*; D000090063:Proto-Oncogene Mas; D051381:Rats; D018570:Risk Assessment
chemical_list: D002273:Carcinogens; D006540:Herbicides; C000715470:MAS1 protein, human; D010636:Phenols; D000090063:Proto-Oncogene Mas; D015127:9,10-Dimethyl-1,2-benzanthracene; C025256:nonylphenol; D001280:Atrazine