Role of CD10 expression in endometriosis-associated mesenchymal stem cells on the progression of endometriosis-associated carcinoma.

5561 Background: Endometriosis-associated carcinomas (EACs) such as ovarian clear cell cancer (OCCC) are rare, aggressive, chemo-resistant malignancies. While endometriosis is a known chronic inflammatory condition, the molecular mechanisms for the malignant transformation of endometriosis is unknown. Mesenchymal stem cells (MSC) are a critical component of the ovarian cancer microenvironment. Cancer cells reprogram MSCs to form carcinoma-associated MSCs (CAMSCs), which promote cancer growth, chemotherapy resistance, and metastases. MSCs are also found within the endometriotic microenvironment. CD10, a surface protein expressed by endometrial stromal cells, is also expressed on endometriosis-associated MSCs (enMSCs). Preliminary data demonstrate CD10 expression is lost in a subset of enMSCs and this loss is correlated with the acquisition of tumor-promoting properties. We hypothesized that the CD10 negative subset of enMSCs behave similarly to CAMSCs and support the growth of OCCC. Methods: EnMSCs were isolated from primary human benign endometriosis deposits involving the ovary or fallopian tubes. Flow cytometry was used to measure surface CD10 expression. We investigated the role of low CD10 enMSCs versus high CD10 enMSCs on OCCC tumor cell growth, chemotherapy resistance and stem-like cell properties in vitro and tumor cell engraftment, growth, and metastases in vivo. Luciferase-expressing OCCC cells were (1) used alone, (2) mixed with low CD10 enMSCs, or (3) mixed with high CD10 enMSCs and injected orthotopically into the ovarian bursa of NSG mice. In vivo imaging system was used to follow tumor progression and metastasis. Results: Our results demonstrated that enMSCs have variable CD10 expression. EnMSCs with low CD10 expression significantly enhanced OCCC proliferation, resistance to cisplatin, and sphere formation compared to OCCC alone. In contrast, high CD10 expressing enMSCs significantly reduce OCCC proliferation and sphere formation. Interestingly, low CD10 enMSCs selectively enhanced OCCC cell growth and had no effect on high grade serious ovarian cancer cell growth. Moreover, a reduction of CD10 expression was observed over time when high CD10 enMSCs were co-cultured with OCCC cells. Our results also showed enhanced tumor engraftment when OCCC cells were co-injected with low CD10 enMSCs to 100% one week post-injection, compared to 40% with OCCC and high CD10 enMSCs and 60% with OCCC alone. Further, mice co-injected with low CD10 enMSCs demonstrated increased metastasis and decreased survival compared to mice co-injected with high CD10 enMSCs. Conclusions: Our results indicate there is a sub population of enMSCs, marked by decreased CD10 expression, which selectively enhances OCCC growth. This highlights the existence of a tumor-promoting stromal cell within endometriosis which may be critical to the formation and propagation of EACs.