MAL gene overexpression as a marker of high-grade serous ovarian carcinoma stem-like cells that predicts chemoresistance and poor prognosis

Laura Zanotti,Laura Tassone,Franco Odicino,Chiara Romani,Antonella Ravaggi,Francesca Ricci,Stefano Calza,Eliana Bignotti,Paola Todeschini,Maurizio D’Incalci,Giovanna Damia,Sergio Pecorelli,Laura Ardighieri,Luca Beltrame,Germana Tognon,Renata Alessandra Tassi,Enrico Sartori,Sergio Marchini,Elisabetta Bandiera

doi:10.1186/s12885-017-3334-1

Abstract

BackgroundThe existence of cancer stem cells (CSCs) within a tumor bulk has been demonstrated for many solid tumors including epithelial ovarian carcinoma (EOC). CSCs have been associated to tumor invasion, metastasis and development of chemoresistant recurrences. In this context, we aim to characterize EOC CSCs from the molecular point of view in order to identify potential biomarkers associated with chemoresistance.MethodsWe isolated a population of cells with stem-like characteristics (OVA-BS4 spheroids) from a primary human EOC cell line under selective conditions. OVA-BS4 spheroids were characterized for drug response by cytotoxicity assays and their molecular profile was investigated by microarray and RT-qPCR. Finally, we performed a gene expression study in a cohort of 74 high-grade serous EOC (HGSOC) patients by RT-qPCR.ResultsSpheroids exhibited properties of self-renewal and a pronounced expression of well-known stem cell genes. Moreover, they demonstrated greater resistance towards several anticancer drugs compared to parent cell line, consistent with their higher ABCG2 gene expression. From microarray studies MAL (T-cell differentiation protein) emerged as the most up-regulated gene in spheroids, compared to parent cell line. In HGSOC patients, MAL was significantly overexpressed in platinum-resistant compared to platinum-sensitive patients and resulted as an independent prognostic marker of survival.ConclusionsThis investigation provides an important contribution to the identification of molecular markers of ovarian CSCs and chemoresistance. Successful translation of molecular findings would lead to a better comprehension of the mechanisms triggering chemoresistant recurrences, to the individuation of novel therapeutic targets and to the personalization of treatment regimens.

Highlights

The existence of cancer stem cells (CSCs) within a tumor bulk has been demonstrated for many solid tumors including epithelial ovarian carcinoma (EOC)
Short tandem repeat (STR) analysis Comparison of DNA fingerprinting results in DSMZ database confirmed the unique identity of both OVABS4 cell lines
Self-renewing spheroids could be successfully isolated from a primary EOC cell line Under selective culture conditions OVA-BS4 primary cell line aggregated into floating spheroid clusters (Fig. 1)

Summary

Introduction

The existence of cancer stem cells (CSCs) within a tumor bulk has been demonstrated for many solid tumors including epithelial ovarian carcinoma (EOC). CSCs have been associated to tumor invasion, metastasis and development of chemoresistant recurrences. In this context, we aim to characterize EOC CSCs from the molecular point of view in order to identify potential biomarkers associated with chemoresistance. One emerging model for the development of drugresistant tumors invokes a pool of self-renewing malignant progenitors, known as cancer stem cells (CSCs) [4]. CSCs have been originally identified in leukemia [5] and more recently described in solid tumors, such as breast [6], colon [7] and ovarian carcinoma [8, 9]

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Results