title: 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.
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.
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University Graduate School of Medicine, Japan. Electronic address: mizutomo@gifu-u.ac.jp.
authors.forename: T
authors.initials: T
authors.lastname: Mizuno
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University Graduate School of Medicine, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Suzuki
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University Graduate School of Medicine, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Makino
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University Graduate School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Furui
authors.affiliation: Department of Pathology, Osaka University Graduate School of Medicine, Japan.
authors.forename: E
authors.initials: E
authors.lastname: Morii
authors.affiliation: Department of Tissue and Organ Development, Gifu University Graduate School of Medicine, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Aoki
authors.affiliation: Department of Tissue and Organ Development, Gifu University Graduate School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kunisada
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Oita University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yano
authors.affiliation: Division of Gynecology, Shizuoka Cancer Center, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kuji
authors.affiliation: Division of Gynecology, Shizuoka Cancer Center, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Hirashima
authors.affiliation: Department of Obstetrics and Gynecology, Nagoya City University, Graduate School of Medicine, Aichi, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Arakawa
authors.affiliation: Department of Obstetrics and Gynecology, Kurume University School of Medicine, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nishio
authors.affiliation: Department of Obstetrics and Gynecology, Kurume University School of Medicine, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ushijima
authors.affiliation: Department of Obstetrics and Gynecology, Kansai Rosai Hospital, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ito
authors.affiliation: Department of Obstetrics and Gynecology,Nara Prefecture General Medical Center,Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Itani
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University Graduate School of Medicine, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Morishige
mesh_terms: D018262:Adenocarcinoma, Clear Cell / Q000378:metabolism* / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000080924:Aldehyde Dehydrogenase 1 Family; D000077216:Carcinoma, Ovarian Epithelial; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000378:metabolism*; D008875:Middle Aged; D009375:Neoplasms, Glandular and Epithelial / Q000378:metabolism* / Q000473:pathology; D014411:Neoplastic Stem Cells / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D010051:Ovarian Neoplasms / Q000378:metabolism* / Q000473:pathology; D011379:Prognosis; D017382:Reactive Oxygen Species / Q000378:metabolism*; D050697:Retinal Dehydrogenase / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D017382:Reactive Oxygen Species; D000080924:Aldehyde Dehydrogenase 1 Family; C510223:ALDH1A1 protein, human; D050697:Retinal Dehydrogenase
keywords: Aldehyde dehydrogenase; Cancer stem-like cell; Chemoresistance; Nrf2-antioxidant pathway; Ovarian clear cell carcinoma; Reactive oxygen species