Expression of biomarkers for transformation in 7,12-dimethylbenz[a]anthracene-treated mammary epithelial-cells.

The ability of the mammary procarcinogen 7,12-dimethylbenz(a)anthracene (DMBA) to induce the expression of selected molecular and cellular biomarkers for preneoplastic transformation is examined in a newly developed, immortalized but nontumorigenic mammary epithelial cell line C57/MG. This cell line is established from the mammary tissues of virgin female C57BL/6J strain of mouse. The biomarkers examined included: DMBA-DNA adduct formation and DNA repair (molecular markers), and anchorage-dependent and anchorage-independent growth (cellular markers). Log phase cultures of C57/MG cells were treated for 24 h with 2, 20, and 200 ng/ml of DMBA, and were assayed for DNA adduct formation by the P-32-postlabeling, for DNA repair by the hydroxyurea (HU)-insensitive H-3-thymidine uptake, and for anchorage-dependent and anchorage-independent growth by colony forming efficiency in adherent and non-adherent conditions, respectively. A DMBA dose-dependent increase was detected in DNA adduct formation ranging from 6 adducts/10(9) nucleotides at 2 ng/ml to >1600 adducts/10(9) nucleotides at 200 ng/ml DMBA concentration and in induction of DNA repair synthesis ranging from 10 to 251%. The colony forming efficiency in adherent and non-adherent conditions, exhibited progressive increase up to the dose of 200 ng/ml of DMBA. These results indicate that C57/MG cells are capable of metabolizing the procarcinogen DMBA to generate DNA adducts which may, in part, be responsible for the aberrant proliferation. These molecular and cellular biomarkers that are expressed prior to tumorigenesis may thus constitute useful endpoints for preneoplastic transformation.