Abstract 4960: Sox2, Oct4, and Nanog expression for identification of ovarian cancer tumor initiating cells

High Grade Serous Ovarian Cancer (HGSOC) is the most lethal gynecological disease in women, with over 70% of advanced stage disease relapsing within 18 months. Recent studies suggest that tumor-initiating cells (TICs) support tumor heterogeneity, chemoresistance, and relapse in HGSOC. Identification of TICs has traditionally relied on expression of surface markers such as CD133, CD44, and CD117 and/or enzymes such as aldehyde dehydrogenase (ALDH). Unfortunately, these markers are often cell type specific and not reproducible across patient samples. More reliable markers of TICs may include stem cell transcription factors such as Sox2, Oct4, and Nanog that function to support long-term self-renewal, multipotency, and quiescence, although these factors have not been comprehensively evaluated in ovarian cancer. We have previously shown that ovarian cancer cells cultured in 3D spheroid-supporting conditions have enhanced expression of Sox2, Oct4, and Nanog and are more tumorigenic than cells cultured in 2D as a monolayer. We hypothesize that Sox2, Oct4, and Nanog support spheroid formation, chemotherapy resistance, and tumorigenicity more reliably than traditional TIC markers. To investigate this hypothesis we evaluated five HGSOC cell lines (CAOV3/CAOV4/OV90/OVCAR4/OVCAR8), two undefined serous lines (ACI23, OVCAR5) and one non-serous line (SKOV3) in 2D vs 3D conditions and quantitated Sox2, Oct4, and Nanog expression, spheroid formation, chemotherapy resistance and tumorigenicity. Our data show that OVCAR4, OVCAR5, and OVCAR8 had the highest expression of Sox2, Oct4, and Nanog in 3D conditions and at least half of the cell lines had enriched expression of all three factors after chemotherapy treatment. A correlation analysis of the traditional TIC markers shows that the surface marker CD133 positively correlated with expression of Sox2, Oct4, and Nanog. Analysis of TCGA data shows that Sox2, Oct4, and Nanog are prone to amplification or gain of function events in 21%, 4%, and 7% of patients, respectively, and these patients are significantly more likely to have recurrent disease. Overall our findings suggest that Sox2, Oct4, and Nanog correlate with TIC features and may be more reliable markers for the identification of cells with enhanced tumor-initiation capacity and drug resistance. Our data further clarify specific ovarian cancer cell lines that have greater dependence on these factors. More reliable and consistent identification of ovarian TICs will improve our understanding of TIC biology and enable the design of therapies to overcome chemotherapy resistance and disease relapse. Citation Format: Mikella Robinson, Samuel F. Gilbert, Logan J. Alexander, Samuel E. Green, Omar Lujano-Olazaba, Omid Patrus, Jennifer A. Waters, Jacqueline M. Lara, Carrie D. House. Sox2, Oct4, and Nanog expression for identification of ovarian cancer tumor initiating cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4960.