Abstract 4223: Role of Breast Cancer Stem Cells in Bone Marrow Metastasis

Abstract Cancer stem cells have been increasingly indicated in disease progression. These cells have been shown to be capable of self-renewal and differentiation, and are commonly described by a CD44+/CD24-/low profile for breast cancer. Even in early stage breast cancer patients, CD44+/CD24-/low breast cancer cells were found in bone marrow, a primary site of breast cancer metastasis. Further, it is believed that certain molecules present in the bone marrow microenvironment contribute to the attraction, adhesion, and infiltration of circulating breast cancer cells. However, the influence of the cancer stem cell phenotype on metastatic capability is unknown. This study aims to determine the role of breast cancer stem cells and microenvironmental factors in bone marrow metastasis. Specifically, E-selectin, CXCR4, and CXCR4 ligand SDF-1α are the focus, as they play integral roles in cell adhesion and the migration of other cell types to bone. Seven breast cancer cell lines from the American Type Culture Collection (ATCC) were analyzed via flow cytometry for CD44 and CD24 expression to determine which cell lines expressed breast cancer stem cell markers. Subsequent analysis of these cells aimed to uncover the significance of the cancer stem cell phenotype in metastasis. E-selectin is an adhesion molecule that is constitutively expressed on bone marrow endothelium. The role of E-selectin in breast cancer cell adhesion to human umbilical vein endothelial cells and human bone marrow endothelial cells was analyzed using flow chamber adhesion assays. The adhesion relationship between MCF-7 breast cancer cells and both endothelial cell types relied on E-selectin. Mounting evidence alludes to the importance of CXCR4 and SDF-1α interaction in metastasis for breast cancer as well as many other cancer types. CXCR4 surface expression of the same ATCC cell lines was determined using flow cytometry. Also, addition of SDF-1α to flow chamber adhesion analyses aided in determining if the presence of this chemokine affects the adhesion capacity of migrating breast cancer cells. A current theory in cancer research is that tumor cells can undergo epithelial to mesenchymal transitions (EMT) to become more tumorigenic. In vitro, TGF-β can be used to induce EMT for further study of the role of cancer stem cells in metastasis. EMT was induced on a CD44+/CD24+ breast cancer line via TGF-β treatment. The transition was determined by a decrease in E-cadherin expression. These cells were then subjected to flow cytometry and flow adhesion assays. The results of these studies indicate that the breast cancer stem cell phenotype may not be necessary for cancer homing to the metastatic site, but may play a role in the formation of a new tumor upon bone marrow infiltration. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4223.