Abstract 4378: Defining the role of mammary stem cells and progenitor cells in the development of estrogen-induced mammary cancer in the rat

Abstract

Abstract Substantial data implicate both estrogens and progestins in the etiology of breast cancer. However, the mechanisms through which these steroid hormones elicit their effects on breast cancer risk have not been elucidated. The ACI rat serves as a unique model for investigating the mechanisms through which estrogens and progestins contribute to breast cancer development and for defining the genetic bases of inherited risk of breast cancer. When treated with physiologic levels of 17β-estradiol (E2), female ACI rats develop mammary cancer at an incidence that approaches 100%. Interestingly, rapid development of mammary cancer in E2 treated ACI rats is dependent upon progesterone. The mammary cancers that develop in E2 treated ACI rats are estrogen dependent, frequently exhibit non-random patterns of genome instability, and are invasive. Because each of these phenotypes is also commonly exhibited by breast cancers in humans, the ACI rat appears to be highly relevant to the study of breast cancer etiology. Whereas female ACI rats are highly susceptible to E2-induced mammary cancer, female Brown Norway (BN) rats are resistant. Genetic studies performed by our laboratory localized a total of six quantitative trait loci (QTL), designated Emca3 through Emca9, that account for a large fraction of inherited susceptibility in F2 progeny generated in intercrosses between ACI and BN rats. The purpose of this study is to test the hypothesis that ACI and BN rats exhibit differences in the responsiveness of their mammary stem cell (MaSCs) and/or progenitor cell (MaPCs) populations to E2 and/or progesterone. By using a combination of markers CD31, CD45, CD24, CD29 and fluorescence-activated cell sorting, we have identified four distinct populations of mammary cells. To quantify the numbers of MaSC and MaPC in these populations, we are evaluating the ability of the basal (Lin-CD24+CD29high) and luminal (Lin-CD24+CD29low) cell populations to form colonies when cultured in vitro and to generate mamamry gland outgrowths when transplanted into the interscapular fat pad of recipient syngenaic or (ACIxBN)F1 rats. Any observed differeces in MaSC and/or MaPC number or function will be evaluated further using a set of congenic rat strains that harbor BN alleles across an individual Emca locus on the ACI genetic background. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4378. doi:10.1158/1538-7445.AM2011-4378