Preneoplastic transformation in mouse mammary tissue: identification and validation of intermediate biomarkers for chemoprevention

Abstract

Specific and sensitive markers capable of determining the extent of tumorigenesis are important end points not only for evaluating the carcinogenic potency, but also for assessment of chemopreventive efficacy of modulators. Prototypic mammary carcinogens induce a high frequency of mammary adenocarcinomas. The appearance of tumors, however, is a culmination of initiational and promotional events whose modulation may constitute an effective means for chemopreventive interventions. The purpose of this study was i) to identify intermediate biomarkers for mammary cell transformation and ii) to apply these biomarkers and validate the ability of selected fatty acids to modulate chemical carcinogen-induced tumorigenic transformation. An in vitro model derived from mouse mammary explant cultures was utilized to examine the effects of 7,12 dimethylbenz (a) anthracene (DMBA), a prototype chemical carcinogen for rodent mammary gland. The effects of DMBA exposure were quantified at the molecular level by determining induction of oncogene expression, at metabolic level by determining the extent of estradiol metabolism, and at cellular level by determining the emergence of hormone-independent mammary alveolar lesions (MAL) and their tumorigenic potential. DMBA treatment induced binding of ras oncogene product ras p21 to [alpha 32P] GTP, altered estradiol metabolism by increasing the ratio of C16 alpha/C2 hydroxylation in favor of 16 alpha-OHE1 formation, and exhibited high frequency of MAL. Transplantation of cells from these MAL produced rapidly growing tumors. Treatment of DMBA-exposed cultures with polyunsaturated n-6 fatty acids enhanced, and treatment with polyunsaturated n-3 fatty acid suppressed the molecular, metabolic and cellular intermediate biomarkers for tumorigenic transformation. Thus, oncogene expression, estradiol metabolism and formation of MAL may constitute useful molecular, metabolic and cellular intermediate biomarkers. Alteration of these biomarkers by selected fatty acids is suggestive of their utility as end points for the chemopreventive efficacy of dietary agents.