Discovery of a recurrent hotspot IDH1 mutation in the vast majority of low-grade gliomas and secondary glioblastomas has revolutionized our understanding of the molecular pathogenesis of these malignancies. The canonical glioma-associated IDH1 mutation encodes a mutant isocitrate dehydrogenase enzyme, IDH1 R132H, that gains the neomorphic ability to convert 2-oxoglutarate (2-OG) to the ?oncometabolite? R-2-hydroxyglutarate (2-HG). Consequently, 2-HG accumulates to millimolar levels in IDH1 mutant gliomas, representing a 100- to 1000-fold increase relative to normal brain tissue. The structural similarity between 2-HG and 2-OG enables 2-HG to competitively modulate the activity of many 2-OGdependent dioxygenases, including JmjC family histone demethylases, TET family DNA hydroxylases, and the hypoxia-responsive prolyl hydroxylase EglN1. Studies from our group and others demonstrate fundamental roles for epigenetic rewiring and HIF1alpha suppression in the oncogenic program induced by IDH1 mutations in glioma. Although our understanding of the function of the IDH1 R132H oncoprotein has expanded tremendously, successful exploitation of the inherent difference in 2-HG content between normal and malignant brain tissue to improve clinical outcomes has not yet been realized. Our proposal seeks to address this impediment to progress in two ways. First, we aim to use 2-HG as a biomarker of IDH mutational status and optimize methodology to quantify this metabolite non-invasively through magnetic resonance spectroscopy (MRS) imaging. We hypothesize that MRS-generated 3D maps of 2HG concentration could be used as a complement to traditional T2/FLAIR imaging to enable more precise delineation of tumor boundaries and yield improvements in the efficiency of surgical resection and the quantification of therapeutic responses in glioma patients. Furthermore, 2HG 3D MRS imaging represents an ideal approach to assess pharmacodynamic responses in patients enrolled in ongoing clinical trials of IDH targeting therapeutics. Second, we aim to develop novel therapeutic strategies designed to preferentially eradicate IDH1 mutant glioma cells by targeting vulnerabilities engendered by high 2-HG accumulation. Pharmacological inhibitors of mutant IDH enzymes have shown remarkable activity in IDH mutant leukemia but early clinical data suggest that such inhibitors will be considerably less active in IDH mutant gliomas. An alternative approach to directly targeting mutant IDH enzymes entails the exploitation of synthetic lethality with the IDH1- R132H oncogene. We have undertaken orthogonal hypothesis-driven and screening-based approaches to identify NAD+ metabolism and de novo pyrimidine synthesis as targetable vulnerabilities in IDH1 mutant glioma cells. We propose to evaluate the safety and efficacy of targeting these metabolic pathways in preclinical models of IDH1 mutant glioma to establish rationale for clinical studies of these novel therapeutic strategies.
Genomic sequencing studies carried out over the past decade have revealed that the vast majority of lowgrade glioma and secondary glioblastoma brain tumors share a single, common mutation in the metabolic enzyme IDH1 that causes aberrant accumulation of a small molecule metabolite termed 2HG. We seek to leverage this new insight by developing imaging technology to directly measure 2HG content in brain tissue and identifying new, effective therapeutic strategies that exploit vulnerabilities unique to IDH1 mutant gliomas. These tumors are more common in patients younger than age 45, and therefore the work is highly relevant to the NCI mission and public health.
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