Metformin and temozolomide, a synergic option to overcome resistance in glioblastoma multiforme models.

Silvia Valtorta,Luisa Ottobrini,Alessia Lo Dico,Isabella Raccagni,Giulia Ercoli,Letterio S Politi,Cecilia Diceglie,Sara Belloli,Rosa Maria Moresco,Cristina Martelli,Marcella Bonanomi,Valentina Vaira,Daniela Gaglio

doi:10.18632/oncotarget.23028

Abstract

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor with poor survival. Cytoreduction in association with radiotherapy and temozolomide (TMZ) is the standard therapy, but response is heterogeneous and life expectancy is limited. The combined use of chemotherapeutic agents with drugs targeting cell metabolism is becoming an interesting therapeutic option for cancer treatment. Here, we found that metformin (MET) enhances TMZ effect on TMZ-sensitive cell line (U251) and overcomes TMZ-resistance in T98G GBM cell line. In particular, combined-treatment modulated apoptosis by increasing Bax/Bcl-2 ratio, and reduced Reactive Oxygen Species (ROS) production. We also observed that MET associated with TMZ was able to reduce the expression of glioma stem cells (GSC) marker CD90 particularly in T98G cells but not that of CD133. In vivo experiments showed that combined treatment with TMZ and MET significantly slowed down growth of TMZ-resistant tumors but did not affect overall survival of TMZ-sensitive tumor bearing mice. In conclusion, our results showed that metformin is able to enhance TMZ effect in TMZ-resistant cell line suggesting its potential use in TMZ refractory GBM patients. However, the lack of effect on a GBM malignancy marker like CD133 requires further evaluation since it might influence response duration.

Highlights

Temozolomide (TMZ), used as standard therapy for glioblastoma multiforme (GBM) [1], is an alkylating agent that exerts its antitumor action through the methylation of DNA
In order to determine the dose of TMZ able to discriminate U251 and T98G responsiveness, both cell lines were firstly exposed to different doses of TMZ for 48 h(Supplementary Figure 1). and cell viability was determined by Trypan blue exclusion test
While in U251 cells, the addition of MET to TMZ determined only an additive effect, in T98G cells MET synergistically acted with TMZ, triggering inhibition levels ranging from 34% (MET only) to 69% (Combo) at 48 h (Supplementary Figure 1)

Summary

Introduction

Temozolomide (TMZ), used as standard therapy for glioblastoma multiforme (GBM) [1], is an alkylating agent that exerts its antitumor action through the methylation of DNA. TMZ is effective against GBM tumors lacking the expression of DNA repair enzyme, O6-methylguanine-DNA methyltransferase (MGMT), which antagonizes the effect of alkylating agents. A number of targeted therapies administered alone or in combination is under evaluation Most of these drugs act on pathways that are heterogeneously expressed in tumors and this limits their efficacy [5]. Enhanced glycolysis and over expression of glucose transporters, GLUT3 and hexokinase II represent negative prognostic factors for patients with GBM [7, 8]. For this reason, targeting of cell metabolism represents an attractive therapeutic strategy for GBM [9]

Methods

Results

Conclusion