EFEMP1 induces γ-secretase/Notch-mediated temozolomide resistance in glioblastoma

Lotte Hiddingh,Esther Hulleman,W Peter Vandertop,Thomas Wurdinger,Judith Jeuken,Bas Tops,Jian Teng,Pieter Wesseling,Sandra H Boots-Sprenger,Gertjan J.L Kaspers,David P Noske,Bakhos A Tannous

doi:10.18632/oncotarget.1620

Abstract

Glioblastoma is the most common malignant primary brain tumor. Temozolomide (TMZ) is the standard chemotherapeutic agent for this disease. However, intrinsic and acquired TMZ-resistance represents a major obstacle for this therapy. In order to identify factors involved in TMZ-resistance, we engineered different TMZ-resistant glioblastoma cell lines. Gene expression analysis demonstrated that EFEMP1, an extracellular matrix protein, is associated with TMZ-resistant phenotype. Silencing of EFEMP1 in glioblastoma cells resulted in decreased cell survival following TMZ treatment, whereas overexpression caused TMZ-resistance. EFEMP1 acts via multiple signaling pathways, including γ-secretase-mediated activation of the Notch pathway. We show that inhibition of γ-secretase by RO4929097 causes at least partial sensitization of glioblastoma cells to temozolomide in vitro and in vivo. In addition, we show that EFEMP1 expression levels correlate with survival in TMZ-treated glioblastoma patients. Altogether our results suggest EFEMP1 as a potential therapeutic target to overcome TMZ-resistance in glioblastoma.

Highlights

Glioblastoma is the most common malignant primary brain tumor in humans
EFEMP1 is overexpressed in TMZ-resistant glioblastoma cells
These cell lines were characterized for MGMT methylation and mismatch repair (MMR) status to assess canonical TMZ-resistance mechanisms, but no significant differences were observed between the parental cell line and the resistant subclones (Supplementary Table S1), suggesting that a non-canonical TMZresistance mechanism was acquired by these cells, and – - resulting in a useful tool to study noncanonical TMZ-resistance

Summary

Introduction

Glioblastoma is the most common malignant primary brain tumor in humans. Outcome for glioblastoma patients is dismal, and carries a median survival of only 14 months [1]. Standard treatment consists of surgery (if possible), followed by radiotherapy and adjuvant temozolomide (TMZ) chemotherapy [1, 2]. The addition of TMZ to radiotherapy has resulted in an overall increase in survival of glioblastoma patients, therapy still fails in almost all glioblastoma patients due to incomplete tumor resection, and/or the apparent resistance of tumor cells to irradiation and TMZ. Some tumors are insensitive to TMZ already at diagnosis, whereas others may develop acquired TMZ-resistance during treatment. TMZ-resistance represents a major obstacle in the treatment of this disease

Methods

Results

Conclusion