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

doi:10.1016/j.ygyno.2014.12.005

Gynecologic Oncology

Volume 137, Issue 2, May 2015, Pages 299-305

https://doi.org/10.1016/j.ygyno.2014.12.005 Get rights and content

Highlights

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Aldehyde dehydrogenase (ALDH)1 expression is related to poor prognosis in ovarian clear cell carcinoma.
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Antioxidant enzymes are upregulated in ALDH-high cells, associated with Nrf2 induction.
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The Nrf2-antioxidant pathway might be relevant to inducing chemoresistance of CSCs in ovarian clear cell carcinoma.

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.

Introduction

Globally, epithelial ovarian cancer is the most lethal gynecological cancer. Ovarian cancer is relatively sensitive to first-line chemotherapy based on platinum/taxane [1]. It has been implied that ovarian clear cell carcinoma has shown resistance to conventional platinum-based chemotherapy. Recent studies have shown that objective response was observed in 11–27% of patients treated with a conventional platinum-based regimen, whereas patients with the serous adenocarcinoma (SAC) subtype showed a significantly higher response rate of 73–81% [2], [3], [4]. The majority of patients will have a relapse of disease within 5 years. Recurrent disease is typically less responsive to current chemotherapeutic strategies.

The cancer stem cell model has been understood in recent cancer research. Cancer stem-like cells (CSCs) are defined as having high tumorigenicity, multiple differentiation ability and self-renewal capacity [5]. In addition, these characteristics are related to chemoresistance.

Among several markers that have been used to identify CSCs, aldehyde dehydrogenase-1A1 (ALDH1A1)-active populations have been identified as tumor-initiating cells in multiple malignancies including those of the breast [6], colon [7], pancreas [8], and liver [9]. Landen et al. were the first to isolate putative CSCs in ovarian cancer by high ALDH activity and showed that high ALDH expression predicts poor outcome in ovarian cancer patients [10]. Furthermore, Liu et al. demonstrated that elevated ALDH expression was associated with poor prognosis using meta-analysis [11].

Recently, reactive oxygen species (ROS) have been associated with multiple cellular functions such as cell proliferation, differentiation and apoptosis.

Though little is known about the ROS levels of CSCs, recent studies indicate that CSCs show lower intracellular ROS content than non-CSCs, which may be due to the increased expression of free radical scavenging systems [12], [13]. Regarding CSC molecules, Kim et al. showed that CD13 negatively regulates ROS with a resultant increase of stemness in liver CSCs. CD13 is also associated with increased ROS scavenger capacity in human liver CSCs [14].

We investigated the relationship between ALDH1 expression as a CSC marker and clinical prognosis using ovarian clear cell carcinoma tissue samples. Furthermore, we analyzed the relationship between ovarian CSC and oxidative stress, by examining the involvement of the antioxidant pathway in ALDH high activity cells.

Section snippets

Patients and clinical data

We analyzed ovarian clear cell carcinoma samples from 81 patients who were diagnosed with clear cell carcinoma and undergone initial surgery at 7 hospitals in Japan (Nagoya City University Hospital, Nara Prefecture General Medical Center, Kansai Rosai Hospital, Shizuoka Cancer Center Hospital, Kurume University Hospital, Oita University Hospital, and Gifu University Hospital). These sample and patient's information were kindly provided from Kansai Clinical Oncology Group/ intergroup study in

ALDH1 expression and patients' prognosis

Eighty-one subjects were included in this study, and divided into an ALDH1-high group (positive cells were > 10% of cancer cells) and an ALDH1-low group (positive cells were < 10% of cancer cells). Their clinical characteristics are summarized in Table 1. Though age and median follow-up time were not related to ALDH1 expression, FIGO stage was strongly related to ALDH1 expression. Comparison of ALDH1 expression between early stage (stages I and II) and advanced stage (stages III and IV) is shown

Discussion

A previous study demonstrated that ALDH1-positive cells exhibit cancer stem cell properties such as self-renewal, and tumorigenicity and poor prognosis [17]. However, the prognostic significance of ALDH in ovarian cancer is controversial. Although some studies have reported that ALDH1 expression was associated with poor prognosis in ovarian cancer [17], [18], [19], Chang et al. showed that ALDH1 was a favorable predictor in ovarian cancer [20]. In addition, Ricci et al. showed that ALDH1 is not

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Citation Excerpt :
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¹: 1-1 Yanagido, Gifu City, Gifu Prefecture 501-1194, Japan. Tel.: + 81 58 230 6349; fax: + 81 58 230 6348.

View full text

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

Highlights

Abstract

Objective

Methods

Results

Conclusions

Introduction

Section snippets

Patients and clinical data

ALDH1 expression and patients' prognosis

Discussion

Gynecol Oncol

Cell Stem Cell

Gastroenterology

Am J Pathol

Mod Pathol

Trends Mol Med

Crit Rev Oncol Hematol

The biology of ovarian cancer: new opportunities for translation

Nat Rev Cancer

Clinical characteristics of clear cell carcinoma of the ovary: a distinct histologic type with poor prognosis and resistance to platinum-based chemotherapy

Cancer

Paclitaxel–platinum combination chemotherapy for advanced or recurrent ovarian clear cell adenocarcinoma: a multicenter trial

Int J Gynecol Cancer

Identification and characterization of ovarian cancer-initiating cells from primary human tumors

Cancer Res

Aldehyde dehydrogenase 1 is a marker for normal and malignant human colonic stem cell (SC) and tracks SC overexpression during colon tumorigenesis

Cancer Res

Characterization and functional analysis of a slow cycling stem cell-like subpopulation in pancreas adenocarcinoma

Clin Exp Metastasis

Targeting aldehyde dehydrogenase cancer stem cells in ovarian cancer

Mol Cancer Ther

Prognostic value of cancer stem cell marker aldehyde dehydrogenase in ovarian cancer: a meta-analysis

PLoS One

Association of reactive oxygen species levels and radioresistance in cancer stem cell

Nature