ABSTRACT: Defining the formation and function of carcinoma-associated mesenchymal stem cells in the ovarian cancer microenvironment Ovarian cancer is the most deadly US gynecologic malignancy with a mortality rate that exceeds 50% at 5 years. Ovarian cancer is characterized by early intraperitoneal metastasis and the development of a complex microenvironment which supports tumor cell growth, survival and spread. Understanding and eventually targeting this cancer-promoting tumor microenvironment offers the potential for powerful new therapeutic approaches. My ultimate goal is to become a world-class independent physician scientist studying the ovarian cancer microenvironment in order to develop new treatments and improve outcomes for women with ovarian cancer. This proposal describes important and innovative research which will lay the foundation for my future career in addition to providing the necessary skills and mentorship vital for my success. The ovarian tumor microenvironment (TME) is a diverse system of cellular and chemical components. The cellular TME includes tumor cells and non-malignant stromal cells. The chemical TME is marked by acidosis and hypoxia. Carcinoma-associated mesenchymal stem cells (CA-MSCs) are multi-potent stromal cells within the cellular TME that can differentiate into multiple pro-tumorigenic stromal cell types including fibroblasts, myofibroblasts, and adipocytes. CA-MSCs are genotypically normal without malignant potential but are functionally different than normal tissue or bone marrow derived MSCs. Compared to normal MSCs, CA-MSCs demonstrate a unique molecular phenotype with very high expression of bone morphogenetic proteins (BMPs). Due to this unique phenotype, these CA-MSCs strongly promote ovarian cancer growth, enhance chemotherapy resistance and enrich the cancer stem cell-like population. How CA-MSCs develop their unique phenotype remains unclear. My preliminary data indicate that tumor secreted factors induce some of the molecular changes associated with CA-MSCs. Another potential mediator of the CA-MSC phenotype is hypoxia. Hypoxia is a hallmark of the chemical TME known to impact normal MSC function. In cancer, hypoxia influences tumor:stromal interactions and hypoxia is a key regulator of BMP expression—high levels of which characterize ovarian cancer CA-MSCs. Preliminary data indicates that hypoxia enhances the ability of tumor cells to induce a CA-MSC expression profile in normal MSCs. While the mechanism of this induction is unknown, given CA-MSCs are genetically normal yet maintain their unique phenotype across multiple passages, tumor-induced epigenetic regulation may be critical to the formation of the CA-MSC phenotype. Indeed, preliminary data indicates CA-MSCs exhibit significant hypomethylation compared to normal MSCs. In addition to influencing the formation of a CA-MSC, hypoxia may also critically regulate the function of CA- MSCs already established in the ovarian TME. My preliminary data...