Isocitrate dehydrogenase (IDH) is one of the key enzymes in the tricarboxylic acid cycle, catalyzing the conversion of isocitric acid to ?-ketoglutaric acid (?-KG) using NADP+. DNA sequencing of a large number of human gilomas has revealed that ~75% of low - medium grade gliomas and secondary glioblastoma multiforme (GBM, a highly lethal form of brain tumor) carry IDH mutations, with IDH1 R132H mutation being predominant (~90%). Genetic investigations have found that IDH mutations are always heterozygous, suggesting the wild-type enzyme is essential for both normal and tumor cells, and IDH mutation is an early and critical event in the glioma tumorigenesis. Biochemical characterization of the mutant proteins revealed that they are inactive in converting isocitrate to ?-KG. Rather, all of the mutant proteins, e.g., IDH1(R132H), possess a new enzymatic activity: they catalyze the reduction of ?-KG to D-2-hydroxyglutaric acid (2-HG) using NADPH. This neo-function is responsible for the greatly elevated (>100x) level of 2-HG in primary tumor cells bearing IDH mutations. Growing evidence strongly supports 2-HG is an onco-metabolite and mutant IDH a target for intervention. Although it is clear that a high level of 2-HG is very harmfu to human health (especially central nervous system), whether inhibition of mutant IDH blocks the growth or induces apoptosis of this type of tumor cells remains to be answered. This is because there have been no inhibitors of mutant IDH to date. In addition, RNA interference (RNAi) is not appropriate for this study, since it will also knock down the wild-type IDH enzyme, whose function is essential for both normal and tumor cells. The first Specific Aim is to use medicinal chemistry, protein X-ray crystallography and quantitative structure activity relationship (QSAR) to develop potent and selective inhibitors of IDH1(R132H). The second Specific Aim is to test in vitro biological activities of compounds synthesized in Aim 1 as well as pharmacokinetic and toxicological properties of selected compounds. The third Specific Aim is to determine the in vivo antitumor activity of our potent IDH1(R132H) inhibitors in intra-cerebral xenograft mouse models as well as to use molecular and cell biology methods to identify the mechanisms of action of these novel inhibitors.
Genetic investigations have found the majority (~75%) of human gliomas (a major form of brain cancer) carry mutations of a key enzyme called IDH, which play important roles for the initiation of the tumor. The research proposed is designed to lead to new potential therapeutics to treat this type of cancer.
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