title: Lymphocyte mutant frequency in relation to DNA adduct formation in rats treated with tumorigenic doses of the mammary gland carcinogen 7,12-dimethylbenz[a]anthracene.
abstract: The ability of the rat lymphocyte hprt assay to detect tissue-specific carcinogens was evaluated using 7,12-dimethylbenz[a]anthracene (DMBA) administered under conditions that result in mammary gland tumors. Fifty-day-old female Sprague-Dawley rats were given single doses of 5 and 20 mg/kg DMBA by gavage, and the frequency of 6-thioguanine-resistant (TGr) T-lymphocytes was measured over a period of 21 weeks. A time- and dose-dependent increase in mutant frequency was found, with a maximum frequency found 9-15 weeks after treatment with 20 mg/kg of DMBA. Rats were also dosed with 1, 2.5, 5, 10, 15 and 20 mg/kg of DMBA and assayed for TGr mutant frequency 10 weeks after treatment. A significant linear dose-response was found, with all the DMBA doses resulting in significant increases in mutant frequency. To determine whether or not DMBA-induced mutants in rat lymphocytes reflected the DNA damage in the target tissue, rats were treated with 5 and 20 mg/kg of DMBA and spleen lymphocytes and mammary gland tissue were assayed for DNA adduct formation 1, 3 and 7 days later. A similar pattern of 32P- postlabeled adducts, involving both dG and dA nucleotides, was found in DNA from both the target tissue and the surrogate lymphocytes. Adduct formation was dose responsive in both tissues, with a 2.3- to 4-fold higher concentration in mammary gland as compared with lymphocytes. These results indicate that the rat lymphocyte hprt assay is sensitive to a mammary gland carcinogen and that similar types of DNA adducts are associated with both the lymphocyte mutants and the mammary gland tumors induced by DMBA.
authors.affiliation: Department of Health and Human Services, Food and Drug Administration, Jefferson, AR 72079, USA. mmanjanatha@nctr.fda.gov
authors.forename: M G
authors.initials: MG
authors.lastname: Manjanatha
authors.forename: L E
authors.initials: LE
authors.lastname: Lyn-Cook
authors.forename: S J
authors.initials: SJ
authors.lastname: Culp
authors.forename: F A
authors.initials: FA
authors.lastname: Beland
authors.forename: R H
authors.initials: RH
authors.lastname: Heflich
authors.forename: A
authors.initials: A
authors.lastname: Aidoo
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity*; D000818:Animals; D015197:Carcinogenicity Tests / Q000379:methods; D018736:DNA Adducts / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D005260:Female; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D008214:Lymphocytes / Q000187:drug effects*; D008321:Mammary Glands, Animal / Q000187:drug effects; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced; D051381:Rats; D017207:Rats, Sprague-Dawley; D013154:Spleen / Q000166:cytology; D013997:Time Factors
chemical_list: D018736:DNA Adducts; D015127:9,10-Dimethyl-1,2-benzanthracene; D007041:Hypoxanthine Phosphoribosyltransferase