L1 Cell Adhesion Molecule Confers Radioresistance to Ovarian Cancer and Defines a New Cancer Stem Cell Population

Nastassja Terraneo,Roger Schibli,Anna Dubrovska,Christiane Krudewig,Francis Jacob,Claudia Peitzsch,Jürgen Grünberg,Viola Heinzelmann-Schwarz,Yen-Lin Huang,Martin Béhé

doi:10.3390/cancers12010217

Abstract

Many solid tumors, including ovarian cancer, contain small populations of cancer stem cells (CSCs). These cells are usually resistant against conventional cancer therapies and play a role in disease recurrence. We demonstrated that the L1 cell adhesion molecule (L1CAM) is a new CSC target in ovarian cancer, triggering radioresistance. Using fluorescence-activated cell sorting, specific cell populations expressing L1CAM alone or in combination with the established CSC marker CD133 were isolated from three ovarian cancer cell lines. Double-positive L1CAM+/CD133+ cells displayed higher spherogenic and clonogenic properties in comparison to L1CAM−/CD133− cells. Furthermore, L1CAM+/CD133+ cells retained highest clonogenic capacity after irradiation and exhibited up-regulation of some CSC-specific genes, enhanced tumor-initiating capacity, self-renewal and higher tumor take rate in nude mice when compared with other cell populations. Superior radioresistance by L1CAM expression was confirmed by deletion of L1CAM using CRISPR-Cas9 technology. Moreover, we found expression signatures associated with epithelial-to-mesenchymal transition phenotype in L1CAM deleted cells. These results indicate that L1CAM in combination with CD133 defines a new cancer cell population of ovarian tumor-initiating cells with the implication of targeting L1CAM as a novel therapeutic approach for ovarian CSCs.

Highlights

Ovarian cancer (OC) is the fifth most common type of cancer in females and one of the most lethal gynecologic tumors [1,2]
We investigated the clonogenic capacity, the clonogenic survival upon irradiation together with the sphere-forming capacity of different OC cell populations defined by the expression of L1 cell adhesion molecule (L1CAM) and CD133
IGROV1 (p53wt) and SKOV3ip (p53del) cells were stained with fluorescent-labeled antibodies and three different cancer cell populations were isolated by fluorescence-activated cell sorting (FACS) (Figure 1A)

Summary

Introduction

Ovarian cancer (OC) is the fifth most common type of cancer in females and one of the most lethal gynecologic tumors [1,2]. Standard treatment for advanced OC includes cytoreductive surgery combined with platinum- and taxane-based chemotherapy. Despite a good response rate towards first-line chemotherapy (50–80%), most patients relapse within 5 years, developing therapy-resistant tumors with a median progression-free survival of 18 months [4,5]. In recent years, targeted therapies including both antibodies and specific tyrosine kinase inhibitors have been employed to treat OC; the clinical benefits have been limited so far [6]. There is persuading evidence that OC contains distinct subpopulations of cells with stem cell-like properties, termed cancer stem cells (CSCs), which are the cause of tumor development, therapy resistance, tumor recurrence and metastasis [7]. Apart from self-renewal and generation of well-differentiated progeny, these cells are highly tumorigenic and resistant toward conventional cancer treatment regimens [8]. Radio- and chemoresistance is due to intrinsic or acquired mechanisms, such as senescence, increased DNA repair capacity, overexpression of ATP-binding cassette (ABC) drug efflux transporters, activation of survival pathways and intracellular scavenging of reactive oxygen species (ROS) [9]

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