title: The inhibitory effect of hypoxic cytotoxin on the expansion of cancer stem cells in ovarian cancer.
abstract: While an increase in progression free survival time is seen when an angiogenesis inhibitor is used in the treatment of high-relapse rate ovarian cancer, it has little effect on overall survival. A possible cause of treatment-resistance to angiogenesis inhibitors is the growth of stem cells in a hypoxic microenvironment built inside the tumor tissue by angiogenesis inhibition. In this study, we examined the possible suppression of stem cell and cancer stem cell (CSC) expansion by hypoxic cytotoxin, TX-402. TX-402, an analogue of tirapazamine, has been developed as a hypoxia selective prodrug with inhibitory effects of HIF-1 and angiogenesis. We considered TX-402 as a possible molecular-target drug candidate for ovarian cancer due to its inhibition of CSC expansion. In this study, we found that the expressions of HIF-1α and HIF-2α were increased under hypoxia in serous ovarian cancer cell lines. The expressions of HIF-1α and HIF-2α induced under hypoxia were repressed by TX-402 in a dose-dependent manner. Next, we investigated the effects of hypoxia on the expression levels of stem cell factors, Oct4, Nanog, Sox2 and Lin28, and showed that their expressions were induced by hypoxia. It was also observed that the expressions of putative ovarian cancer stem cell markers, CD133 and CD44 were induced under hypoxia. Furthermore, TX-402 was found to dose-dependently inhibit the expressions of CSC markers and stem cell factors. Oct4 expression was repressed by HIF-2α silencing, but not by HIF-1α silencing, indicating that TX-402 may repress the expression of Oct4 by inhibiting HIF-2α. We constructed CaOV3 spheroids as a 3-dimensional hypoxia model, in which the internal hypoxic region contained CSC-like cells expressing Oct4. The internal hypoxic region, which contained Oct4 expressing cells, disappeared following TX-402 treatment. In conclusion, hypoxia promoted the expansion of CSCs expressing CD133 and CD44 accompanied by an increase of stem cell factors. Its inhibition of hypoxia-induced CSC expansion makes TX-402 promising agent usable in combination for ovarian cancer therapy.
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University School of Medicine, 1-1 Yanagido, Gifu 501-1194, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Nozawa-Suzuki
authors.affiliation: Laboratory of Pharmaceutical and Medical Chemistry, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu 501-1195, Japan.
authors.forename: Hideko
authors.initials: H
authors.lastname: Nagasawa
authors.affiliation: Department of Biology, Center for Humanity and Sciences, Ibaraki Prefectural University of Health Sciences, Inashiki-gun, Ibaraki 300-0394, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Ohnishi
authors.affiliation: Department of Obstetrics and Gynecology, Gifu University School of Medicine, 1-1 Yanagido, Gifu 501-1194, Japan. Electronic address: mken@gifu-u.ac.jp.
authors.forename: Ken-Ichirou
authors.initials: K
authors.lastname: Morishige
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D015687:Cell Hypoxia / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003497:Cyclic N-Oxides / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D050814:Octamer Transcription Factor-3 / Q000235:genetics; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D010053:Ovary / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D011810:Quinoxalines / Q000494:pharmacology*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D000970:Antineoplastic Agents; D051792:Basic Helix-Loop-Helix Proteins; D003497:Cyclic N-Oxides; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D050814:Octamer Transcription Factor-3; D011810:Quinoxalines; D000099162:Endothelial PAS Domain-Containing Protein 1; C503709:3-amino-2-quinoxalinecarbonitrile; C494173:POU5F1 protein, human
keywords: Cancer stem cell; HIF (hypoxia inducible factor); Hypoxia; Stem cell factors