Background/Aims: In this study, a subpopulation of stem-like cells in human high grade serous ovarian carcinomas (ovarian cancer stem cells; OCSCs) were isolated and characterized. Methods: Primary high-grade serous ovarian carcinoma (HGSC) fresh biopsies were cultured under serum-free conditions to produce floating spheres. Sphere formation assay, including self-renewal, differentiation potential, chemo-resistance, and tumorigenicity were determined in vitro or in vivo. Results: OCSCs overexpressed stem cell genes (Oct-4, Nanog, Sox-2, Bmi-1, Nestin, CD133, CD44, CD24, ALDH1, CD117, and ABCG2). Immunostaining of spheres showed overexpressed Oct-4, Nanog, and Sox-2. These isolated tumor cells expanded as spheroid colonies for more than 30 passages. In contrast, adherent cells expressed high levels of CA125 and CK7. Flow cytometry analysis showed increased CSC markers (CD44, CD24, CD117, CD133, ABCG2, and ALDH1) in the spheroid cell population. OCSCs displayed higher chemoresistance to cisplatin or paclitaxel compared to adherent cells. Moreover, subcutaneous injection of 1 × 104 sphere-forming cells into NOD/SCID mice gave rise to new tumors similar to the original human tumors and could be passaged in mice. Conclusion: These results revealed that HGSCs are created and propagated by a small number of undifferentiated tumorigenic cells, and therapeutic targeting of these cells could be beneficial for treatment of HGSCs.
