Cancer stem-like cells of ovarian clear cell carcinoma are enriched in the ALDH-high population associated with an accelerated scavenging system in reactive oxygen species

• Published in: Gynecologic oncology 2015-05, Vol.137 (2), p.299-305
• Main Authors: Mizuno, T, Suzuki, N, Makino, H, Furui, T, Morii, E, Aoki, H, Kunisada, T, Yano, M, Kuji, S, Hirashima, Y, Arakawa, A, Nishio, S, Ushijima, K, Ito, K, Itani, Y, Morishige, K
• Format: Article
• Language: English
• Subjects: Adenocarcinoma, Clear Cell - metabolism; Adenocarcinoma, Clear Cell - pathology; Adult; Aged; Aged, 80 and over; Aldehyde dehydrogenase; Cancer stem-like cell; Carcinoma, Ovarian Epithelial; Cell Line, Tumor; Chemoresistance; Female; Hematology, Oncology and Palliative Medicine; Humans; Immunohistochemistry; Isoenzymes - metabolism; Middle Aged; Neoplasms, Glandular and Epithelial - metabolism; Neoplasms, Glandular and Epithelial - pathology; Neoplastic Stem Cells - enzymology; Neoplastic Stem Cells - metabolism; Neoplastic Stem Cells - pathology; Nrf2-antioxidant pathway; Obstetrics and Gynecology; Ovarian clear cell carcinoma; Ovarian Neoplasms - metabolism; Ovarian Neoplasms - pathology; Prognosis; Reactive oxygen species; Reactive Oxygen Species - metabolism; Retinal Dehydrogenase - metabolism
• ISSN: 0090-8258; 1095-6859
• DOI: 10.1016/j.ygyno.2014.12.005

Abstract Objective In ovarian cancer cases, recurrence after chemotherapy is frequently observed, suggesting the involvement of ovarian cancer stem-like cells (CSCs). The chemoresistance of ovarian clear cell carcinomas is particularly strong in comparison to other epithelial ovarian cancer subtypes. We investigated the relationship between a CSC marker, aldehyde dehydrogenase 1 (ALDH1), and clinical prognosis using ovarian clear cell carcinoma tissue samples. Furthermore, we investigated the antioxidant mechanism by which CSCs maintain a lower reactive oxygen species (ROS) level, which provides protection from chemotherapeutic agents. Methods Immunohistochemical staining was performed to examine the CSC markers (CD133, CD44, ALDH1) using ovarian clear cell carcinoma tissue samples (n = 81). Clear cell carcinoma cell lines (KOC-7C, OVTOKO) are separated into the ALDH-high and ALDH-low populations by ALDEFLUOR assay and fluorescence-activated cell sorting (FACS). We compared the intracellular ROS level, mRNA level of the antioxidant enzymes and Nrf2 expression of the two populations. Results High ALDH1 expression levels are related to advanced stage in clear cell carcinoma cases. ALDH1 expression significantly reduced progression free survival. Other markers are not related to clinical stage and prognosis. ALDH-high cells contained a lower ROS level than ALDH-low cells. Antioxidant enzymes were upregulated in ALDH-high cells. ALDH-high cells showed increased expression of Nrf2, a key transcriptional factor of the antioxidant system. Conclusions ALDH-positive CSCs might have increased Nrf2-induced antioxidant scavengers, which lower ROS level relevant to chemoresistance in ovarian clear cell carcinoma.