Metabolic targeting of EGFRvIII/PDK1 axis in temozolomide resistant glioblastoma.

Kiran K Velpula,Kamlesh Sahu,Sarah E Bach,Jack Tuszynski,Justin D Lathia,Swapna Asuthkar,Maheedhara R Guda,Andrew J Tsung

doi:10.18632/oncotarget.16767

Abstract

Glioblastomas are characterized by amplification of EGFR. Approximately half of tumors with EGFR over-expression also express a constitutively active ligand independent EGFR variant III (EGFRvIII). While current treatments emphasize surgery followed by radiation and chemotherapy with Temozolomide (TMZ), acquired chemoresistance is a universal feature of recurrent GBMs. To mimic the GBM resistant state, we generated an in vitro TMZ resistant model and demonstrated that dichloroacetate (DCA), a metabolic inhibitor of pyruvate dehydrogenase kinase 1 (PDK1), reverses the Warburg effect. Microarray analysis conducted on the TMZ resistant cells with their subsequent treatment with DCA revealed PDK1 as its sole target. DCA treatment also induced mitochondrial membrane potential change and apoptosis as evidenced by JC-1 staining and electron microscopic studies. Computational homology modeling and docking studies confirmed DCA binding to EGFR, EGFRvIII and PDK1 with high affinity. In addition, expression of EGFRvIII was comparable to PDK1 when compared to EGFR in GBM surgical specimens supporting our in silico prediction data. Collectively our current study provides the first in vitro proof of concept that DCA reverses the Warburg effect in the setting of EGFRvIII positivity and TMZ resistance leading to GBM cytotoxicity, implicating cellular tyrosine kinase signaling in cancer cell metabolism.

Highlights

Glioblastoma multiforme (GBM) is the most frequent and aggressive type of brain tumor
We further showed that DCA treatment altered glucose metabolism by inhibiting the pyruvate dehydrogenase kinase 1 (PDK1)/EGFR/EGFRvIII interaction leading to mitochondrial membrane depolarization forcing the cells to undergo apoptosis
To better understand how tyrosine kinase signaling in conjunction with PDK1 regulates the Warburg effect, we analyzed the expression of EGFR, PDK1 and EGFRvIII

Summary

Introduction

Glioblastoma multiforme (GBM) is the most frequent and aggressive type of brain tumor. GBM tumors are like most cancers in that they utilize aerobic glycolysis in the presence of adequate oxygen, which is referred to as the Warburg effect, the advantage it confers in GBM cells remain www.impactjournals.com/oncotarget unclear. The emergence of new potential targets for therapeutic intervention for molecularly targeted drugs has brought new promise that modulation of the Warburg metabolic phenotype could be targeted to further increase survival in GBMs. One intriguing candidate that has emerged is pyruvate dehydrogenase kinase 1(PDK1), reported to be important in promoting tumor metabolism and growth in variety of cancers including GBM [7,8,9]. We showed that PDK1 plays an important role in regulating GBM metabolism via simultaneous targeting of mitochondrial epidermal growth factor receptor (mtEGFR) protein levels and signaling activities with resultant tumor regression. We demonstrated that by targeting the ubiquitous EGFR found on GBM, DCA reversed this EGFR-mediated component of the Warburg effect by PDK1 binding reducing lactate production in GBM [9]

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Results

Conclusion