Valproic acid-induced amphiregulin secretion confers resistance to temozolomide treatment in human glioma cells

Jui-Chieh Chen,Yu-Ping Wu,Martin Hsiu-Chu Lin,Cheng Huang,Ming-Hsueh Lee,Jen-Tsung Yang,I-Neng Lee,Chiu-Yen Chung

doi:10.1186/s12885-019-5843-6

Abstract

BackgroundGlioblastoma multiforme (GBM) is the most severe type of primary brain tumor with a high mortality rate. Although extensive treatments for GBM, including resection, irradiation, chemotherapy and immunotherapy, have been tried, the prognosis is still poor. Temozolomide (TMZ), an alkylating agent, is a front-line chemotherapeutic drug for the clinical treatment of GBM; however, its effects are very limited because of the chemoresistance. Valproic acid (VPA), an antiepileptic agent with histone deacetylase inhibitor activity, has been shown to have synergistic effects with TMZ against GBM. The mechanism of action of VPA on TMZ combination therapy is still unclear. Accumulating evidence has shown that secreted proteins are responsible for the cross talking among cells in the tumor microenvironment, which may play a critical role in the regulation of drug responses.MethodsTo understand the effect of VPA on secreted proteins in GBM cells, we first used the antibody array to analyze the cell culture supernatant from VPA-treated and untreated GBM cells. The results were further confirmed by lentivirus-mediated knockdown and exogenous recombinant administration.ResultsOur results showed that amphiregulin (AR) was highly secreted in VPA-treated cells. Knockdown of AR can sensitize GBM cells to TMZ. Furthermore, pretreatment of exogenous recombinant AR significantly increased EGFR activation and conferred resistance to TMZ. To further verify the effect of AR on TMZ resistance, cells pre-treated with AR neutralizing antibody markedly increased sensitivity to TMZ. In addition, we also observed that the expression of AR was positively correlated with the resistance of TMZ in different GBM cell lines.ConclusionsThe present study aimed to identify the secreted proteins that contribute to the modulation of drug response. Understanding the full set of secreted proteins present in glial cells might help reveal potential therapeutic opportunities. The results indicated that AR may potentially serve as biomarker and therapeutic approach for chemotherapy regimens in GBM.

Highlights

Glioblastoma multiforme (GBM) is the most severe type of primary brain tumor with a high mortality rate
To understand the mechanisms by which Valproic acid (VPA), TMZ, or TMZ/VPA combined treatment is related to the induction of apoptosis, cleaved PARP and cleaved caspase-3 were evaluated by Western blot analysis
These results indicate that the addition of VPA results in an increase in the cytotoxic effect of TMZ against glioblastoma cells

Summary

Introduction

Glioblastoma multiforme (GBM) is the most severe type of primary brain tumor with a high mortality rate. Extensive treatments for GBM, including resection, irradiation, chemotherapy and immunotherapy, have been tried, the prognosis is still poor. Temozolomide (TMZ), an alkylating agent, is a front-line chemotherapeutic drug for the clinical treatment of GBM; its effects are very limited because of the chemoresistance. Valproic acid (VPA), an antiepileptic agent with histone deacetylase inhibitor activity, has been shown to have synergistic effects with TMZ against GBM. A type of tumor that originates from glial cells, is usually found in the brain and occasionally in the spinal cord. Glioblastoma, known as glioblastoma multiforme (GBM), is the most aggressive and frequently diagnosed primary brain neoplasm. Surgical resection and radiotherapy, combined with adjuvant chemotherapy, are standard strategies for treatment of glioblastoma. The median survival of glioblastoma patients is only 12– 15 months from diagnosis [4,5,6]

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