Metabolic abnormalities of cancers provide opportunities for novel tumor-specific therapies. Isocitrate dehydrogenases (IDHs) catalyze the oxidative decarboxylation of isocitrate to α-ketoglutarate (αKG) and the reduction of NAD(P)+ to NAD(P)H. Oncogenic mutations in two IDH-encoding genes (IDH1 and IDH2) have been identified in acute myelogenous leukemia, low-grade glioma, and secondary glioblastoma (GBM), however it has been demonstrated that primary GBM patients with wild-type IDH1 have a shorter overall survival compared to those patients with mutated IDH1. We therefore decided to determine if wild-type IDH1 might have a role in the pathogenesis of GBM. We employed in silico analysis of The Cancer Genome Atlas (TCGA) data with wet-bench analysis of tumor extracts and discovered that non-mutated IDH1 mRNA and protein are commonly overexpressed in primary GBM. We show that genetic inactivation of IDH1 decreases GBM cell growth and prolongs survival of animal subjects bearing patient-derived xenografts (PDXs). On molecular levels, diminished IDH1 activity results in reduced αKG and NADPH production, which is paralleled by deficient metabolic flux from glucose or acetate into lipids. Loss of IDH1 expression also promotes a more differentiated tumor cell state, as seen by enhanced histone methylation and differentiation marker expression, and leads to increased levels of Reactive Oxygen Species (ROS) and exhaustion of reduced glutathione. While targeted therapies, including receptor tyrosine kinase inhibitors (RTKi) have been developed for GBM, their potential has yet to be realized in the clinic. IDH1 protein and mRNA levels are increased in response to RTKi treatment through a FoxO6-mediated mechanism, and IDH1 loss increases apoptosis in response to these targeted therapies, pointing to IDH1 as a resistance mechanism for RTKi therapeutics. We furthermore use a pharmacologic inhibitor of IDH1, which reduces NADPH levels, increases RTKi-induced apoptosis, and prolongs the survival of GBM xenograft bearing mice. Our findings suggest that IDH1 upregulation represents a common mechanism of metabolic adaptation of GBM to support macromolecular synthesis, aggressive growth, and therapy resistance, and point to IDH1 inhibition as a promising therapeutic strategy, especially in combination with RTKi, for GBM.

Last modified

• 04/27/2018

Creator

• Andrea Calvert

DOI

• https://doi.org/10.21985/N26D8J

Subject

• Driskill Graduate Training Program in Life Sciences

Keyword

• lipids
• Glioblastoma (GBM)
• targeted therapy
• wild-type IDH1
• NADPH
• metabolism

Date created

• 2017-01-01

Resource type

• Dissertation

Rights statement

• In Copyright