Abstract 3306: A novel reconstructed metastasis (rMet) model to understand the role of breast cancer stem cells in metastasis

Breast cancer is the most common malignancy in women, with 80% of patients suffering from invasive tumors and metastatic disease. Metastasis is a process where breast cancer cells disseminate from the mammary gland, invade through the extracellular matrix (ECM), intravasate, colonize a distant site such as the bone marrow (BM), and establish growing metastases. Further complicating the metastatic process is the requirement for permissive microenvironment at the secondary site to allow its colonization by the metastatic cells. It has been proposed that ‘cancer stem cells’ (CSCs) with the ability to self-renew, can drive the growth and spread of the tumor. However, the contribution of the breast CSCs (B-CSCs) to metastatic disease is not completely understood. The purpose of this study is to develop a novel 3-dimensional (3-D) tissue culture model to delineate the molecular events responsible for tumor metastasis and to determine whether B-CSCs are responsible for metastatic spread. We developed a ‘reconstructed metastasis’ (rMet) model that mimics the process of breast cancer metastasis to the bone. Using the MCF10A series of isogenic breast cancer progression cell lines, we evaluated the phenotype of metastatic MCF10CA1a cells based on the pattern of expression of epithelial, mesenchymal and B-CSC markers. We used zymography, electron microscopy, and non-linear optical imaging to evaluate ECM remodeling within the rMet system. We observed 3 distinct cell populations emerging in the rMet system: (1) a non-migratory, (2) an invasive, and (3) BM-colonizing, all with distinct phenotypes and genetic signature. A sub-population of non-malignant (MCF10A), pre-malignant (MCF10AneoT), malignant, but not metastatic (MCF10CA1h), and metastatic (MCF10CA1a) cell lines had the capacity to invade BM matrix. However, only a rare population of MCF10CA1a cells, morphologically distinct from their non-migratory counterparts, had the ability to survive and colonize the BM ECM. We found that the BM-colonizing cells display the B-CSC phenotype (CD44+CD24−ESA+ and ALDH+) suggesting their importance in the metastatic spread of breast cancer. The BM colonizing cells expressed a mixture of epithelial and mesenchymal markers, N-cadherin, keratin 18, fibronectin and vimentin, but not E-cadherin or keratin 17. Matrix degradation was observed in the ‘mammary gland’ matrix, but not the BM matrix indicating the possible role of matrix metalloproteases in ECM invasion by the primary tumor, but not in the colonization of a distant site. The rMet model recapitulates the complexity of metastatic disease and hence is a robust system to study bone matrix colonization by breast cancer cells. Identification of B-CSCs in the BM colonizing population signifies their role as a specific population mediating spread and hence emphasizes the requirement of new preventive strategies to target B-CSCs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3306. doi:1538-7445.AM2012-3306