Targeting Glioblastoma Stem Cells with 2-Deoxy-D-Glucose (2-DG) Potentiates Radiation-Induced Unfolded Protein Response (UPR)

Sumedh Shah,Steven Vanni,Winston Walters,Jeffrey Prince,Gregor Rodriguez,Megan Marlow,Brian Marples,Nicolas De Cordoba,Regina Graham,Eric Barbarite,Alexis Musick,Ricardo Komotar

doi:10.3390/cancers11020159

Abstract

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, and despite optimized treatment options, median survival remains dismal. Contemporary evidence suggests disease recurrence results from expansion of a robustly radioresistant subset of GBM progenitor cells, termed GBM stem cells (GSCs). In this study, we utilized transmission electron microscopy to uncover ultrastructural effects on patient-derived GSC lines exposed to supratherapeutic radiotherapy levels. Elevated autophagosome formation and increased endoplasmic reticulum (ER) internal diameter, a surrogate for ER stress and activation of unfolded protein response (UPR), was uncovered. These observations were confirmed via protein expression through Western blot. Upon interrogating genomic data from an open-access GBM patient database, overexpression of UPR-related chaperone protein genes was inversely correlated with patient survival. This indicated controlled UPR may play a role in promoting radioresistance. To determine if potentiating UPR further can induce apoptosis, we exposed GSCs to radiation with an ER stress-inducing drug, 2-deoxy-D-glucose (2-DG), and found dose-dependent decreases in viability and increased apoptotic marker expression. Taken together, our results indicate GSC radioresistance is, in part, achieved by overexpression and overactivation of ER stress-related pathways, and this effect can be overcome via potentiation of UPR, leading to loss of GSC viability.

Highlights

Glioblastoma (GBM) is the most common and aggressive form of primary brain cancer, and despite optimized therapy consisting of surgery, chemotherapy, and radiation, its expected median survival remains under two years [1]
GBM stem cells (GSCs) grown in normal culture conditions maintain their phenotype as spheroid clusters of cells, termed neurospheres, and a morphology change towards a monolayer pattern indicates loss of stemness [2]
We see an additive effect of 2-DG on literature has focused on the role of GSCs in tumor formation, progression, and recurrence given their robust resistance to conventional chemotherapy and radiotherapy; understanding mechanisms of resistance and developing cell specific therapies against GSCs are crucial in eliminating GBM [37,38]

Summary

Introduction

Glioblastoma (GBM) is the most common and aggressive form of primary brain cancer, and despite optimized therapy consisting of surgery, chemotherapy, and radiation, its expected median survival remains under two years [1]. GSCs are implicated in tumor recurrence through mechanisms including expression of drug efflux pumps and ability to withstand radiotherapy, and characterizing resistance mechanisms may uncover potential therapeutic targets and augment current cancer therapy [6]. Activation of pro-survival pathways designed to mitigate the effect of these stressors can inadvertently impart a survival advantage to cells exposed to cytotoxic therapy. One such survival mechanism is stimulation of the endoplasmic reticulum (ER) stress pathway, commonly referred to as the unfolded protein response (UPR) [10,11,12,13]

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Conclusion