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

Abstract

Background: Glioblastoma 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. Methods: To 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. Results: Our 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. Conclusions: The 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.

Valproic Acid Enhanced Apoptosis by Promoting Autophagy Via Akt/mTOR Signaling in Glioma

“…Further in vivo experiments found that VPA prevented invasion in surrounding tissues and inhibited tumor angiogenesis 13,14 . While Chen et al reported that amphiregulin (AR) secretion induced by VPA conferred resistance to TMZ 35 . Clinically, only a few phase I trials have unfolded that VPA was probably correlated with improved survival, histological progression, and decrease in progression-free survival in glioma patients 38,55 .…”

“…Therefore, repurposing existing drugs has become a potential treatment option, which led to the application of VPA in our experiment. As the most frequently used antiepileptic drug (AED) in neurosurgery, VPA has been reported to have inhibitory effects on the progression, invasion, and apoptosis of glioma cells 26,35 . However, the underlying molecular mechanism has not yet been clarified, making it difficult to obtain satisfactory results in limited clinical trials 36,37 .…”

Elevated XRCC5 expression level can promote temozolomide resistance and predict poor prognosis in glioblastoma

“…Both the DBTRG-05MG and DBTRG-05MG-R cells had a significant increase in XRCC5 protein expression level following TMZ treatment. This could be the result of DBTRG-05MG itself being a relatively resistant cell line initially ( 37 ).…”

The Impact of Epigenetic Modifications on Adaptive Resistance Evolution in Glioblastoma

“…HDACs have been implicated in chemoradiation resistance through inhibition of DNA double-strand break repair [ 125 , 126 ]. Furthermore, HDAC-mediated resistance to TMZ is easily reversed with inhibitors of HDACs in GBM [ 127 , 128 , 129 , 130 , 131 ]. HDAC inhibitors target several processes that are integral to tumorigenesis including the induction of cell cycle arrest, differentiation, senescence, cell death, and inhibition of angiogenesis [ 132 , 133 ].…”