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    Awarded Grants
    Identification and Characterization of Breast Cancer Stem Cells

    Scientific Abstract:
    Background: A subpopulation of highly tumorigenic human breast cancer cells has been reported to initiate new tumors after transplantation into etoposide-treated NOD/SCID mice. Can a similar population of cancer stem cells be identified by syngeneic transplantation studies using well defined mouse models of breast cancer in which the microenvironment should not provide a confounding factor? Do breast cancer and mammary gland stem cells utilize the same self-renewal pathways? Are there any differences in these pathways, which might provide unique therapeutic targets? A novel p53 null mouse model that mimics a subset of human breast cancer progression will be employed to elucidate the properties of breast cancer stem cells and to identify differences between cancer and normal stem cells. Objective /Hypothesis: The activation of oncogenes and/or loss of tumor suppressor genes in specific mammary stem/progenitor cells may contribute to the heterogeneity of breast cancer, as well as the generation of breast cancer stem cells. If unique signal transduction pathways are required for breast cancer stem cell self-renewal, it may be possible to develop treatments to eliminate residual disease. Specific Aims: 1) To identify and characterize a tumorigenic breast cancer stem cell subpopulation using a mouse mammary tumor model. 2) To perform gene profiling to identify any differences between the cancer and normal stem cells, and any unique pathways or molecular targets, which may exist in the breast cancer stem cells. 3) To test the functional importance of these molecular targets by selective activation or knockdown of the gene activity involved in these pathways, which are critical for stem cells self-renewal. Study Design: Techniques previously well established will be utilized to identify and characterize functional cancer stem cells from a p53 null Balb/c mouse mammary tumor model. These include Hoechst dye efflux, FACS analysis using cell surface markers Sca-1 and c-Kit, alpha 6- and/or beta 1-integrins, and CD44+/CD24- followed by functional transplantation into the cleared mammary fat pad of syngeneic mice. The gene expression profiles of tumor stem cells will be studied using microarrays and SAGE. Potential Outcomes and Benefits of the Research: Breast cancer recurs, possibly resulting from the existence of cancer stem cells, which are thought to be resistant to conventional therapies. This study is of critical importance in understanding both the etiology of breast cancer, and for the development of new therapeutic strategies to eliminate residual disease.

    Lay Abstract:
    Background: The identification of tumorigenic breast cancer cells with stem cell characteristics has created substantial excitement. However, the initial groundbreaking studies identifying breast cancer stem cells were performed with only a few human breast cancers, and further proof of the existence of these cells and detailed characterization especially with respect to their ability to give rise to the diverse subtypes of breast cancer is required. This is especially important in breast cancer because it is a heterogeneous disease with diverse clinical outcomes. In addition, it will be critical to identify any unique survival and self-renewal mechanisms of breast cancer stem cell, which may be targeted with new drugs without harming the normal stem cells. Objective/Hypothesis: To validate the existence of breast cancer stem cells using a novel mouse model, which gives rise to breast cancers similar to human breast cancer. The use of a mouse model will allow functional transplantation studies without concerns about the microenvironment, and detailed genetic studies not feasible in patients. The identification of any unique pathways in these cells may provide new targets for the treatment of residual disease in breast cancer. Specific Aims: The specific questions are: 1) Is there a highly tumorigenic cancer stem cell subpopulation, which contributes to the heterogeneity of breast cancer? 2) Are there unique pathways in breast cancer stem cells as compared to normal stem cells, which can be discovered using powerful gene profiling technology? 3) Can selective activation or knockdown of essential genes in these breast cancer stem cells provide us useful information on eradicating residual disease in breast cancer? Study Design: Flow cytometry will be employed to separate stem cells isolated from mammary tumors which develop in the mouse model lacking the p53 tumor suppressor gene, using techniques and antibodies to available cell surface markers, which have already been shown to identify stem cells in both normal human and mouse breast. Gene expression profiling technologies will be used to pick up specific tags either of breast cancer stem cells or of mammary gland stem cells. Potential Outcomes and Benefits of the Research: This study is focused on the identification and characterization of functional breast cancer stem cells, which are thought to be resistant to current therapies. Such studies have the potential to identify new gene targets and pathways not currently being used to treat breast cancer in order to eradicate residual disease in breast cancer.