This Article demonstrates that tumour-associated IDH1 somatic mutations result in a gain of enzyme function that causes the accumulation of R(-)-2-hydroxyglutarate (2HG). We proposed that accumulation of 2HG might drive oncogenesis, and referenced work demonstrating 2HG accumulation in patients with 2-hydroxyglutaric aciduria 1 . As a plausible mechanism of oncogenesis, we proposed that R(-)-2HG induces redox stress owing to impairment of the respiratory chain. This hypothesis suggests that R(-)-2HG may promote cancer mutations, and is consistent with the latency observed in glioma development and the fact that gliomas increase in incidence with age. Nonetheless, we do appreciate that there are other possible mechanisms by which R(-)-2HG may promote tumour formation. Further work has identified that the abnormal production of 2HG is associated with tumours bearing a mutation in either IDH1 or IDH2 and supports a link between 2HG accumulation and cancer. So far, we have not found any tumour samples containing IDH1 or IDH2 mutations that do not have increased 2HG levels. Determining the mechanistic link between 2HG accumulation and cancer formation, and how each stereoisomer of 2HG may drive malignancy by the same or distinct mechanism is the subject of continuing investigation by our group and others. Hum Genet. 2005; 76:358-360. [PubMed: 15609246] NIH Public Access

Cancer cells engage in a metabolic program to enhance biosynthesis and support cell proliferation. The regulatory properties of pyruvate kinase M2 (PKM2) influence altered glucose metabolism in cancer. PKM2 interaction with phosphotyrosine-containing proteins inhibits enzyme activity and increases availability of glycolytic metabolites to support cell proliferation. This suggests that high pyruvate kinase activity may suppress tumor growth. We show that expression of PKM1, the pyruvate kinase isoform with high constitutive activity, or exposure to published small molecule PKM2 activators inhibit growth of xenograft tumors. Structural studies reveal that small molecule activators bind PKM2 at the subunit interaction interface, a site distinct from that of the endogenous activator fructose-1,6-bisphosphate (FBP). However, unlike FBP, binding of activators to PKM2 promotes a constitutively active enzyme state that is resistant to inhibition by tyrosine-phosphorylated proteins. These data support the notion that small molecule activation of PKM2 can interfere with anabolic metabolism.

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2), are present in most gliomas and secondary glioblastomas, but are rare in other neoplasms. IDH1/2 mutations are heterozygous, and affect a single arginine residue. Recently, IDH1 mutations were identified in 8% of acute myelogenous leukemia (AML) patients. A glioma study revealed that IDH1 mutations cause a gain-of-function, resulting in the production and accumulation of 2-hydroxyglutarate (2-HG). Genotyping of 145 AML biopsies identified 11 IDH1 R132 mutant samples. Liquid chromatography-mass spectrometry metabolite screening revealed increased 2-HG levels in IDH1 R132 mutant cells and sera, and uncovered two IDH2 R172K mutations. IDH1/2 mutations were associated with normal karyotypes. Recombinant IDH1 R132C and IDH2 R172K proteins catalyze the novel nicotinamide adenine dinucleotide phosphate (NADPH)–dependent reduction of α-ketoglutarate (α-KG) to 2-HG. The IDH1 R132C mutation commonly found in AML reduces the affinity for isocitrate, and increases the affinity for NADPH and α-KG. This prevents the oxidative decarboxylation of isocitrate to α-KG, and facilitates the conversion of α-KG to 2-HG. IDH1/2 mutations confer an enzymatic gain of function that dramatically increases 2-HG in AML. This provides an explanation for the heterozygous acquisition of these mutations during tumorigenesis. 2-HG is a tractable metabolic biomarker of mutant IDH1/2 enzyme activity.

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Somatic gain-of-function mutations in isocitrate dehydrogenases (IDH) 1 and 2 are found in multiple hematologic and solid tumors, leading to accumulation of the oncometabolite (R)-2-hydroxyglutarate (2HG). 2HG competitively inhibits α-ketoglutarate-dependent dioxygenases, including histone demethylases and methylcytosine dioxygenases of the TET family, causing epigenetic dysregulation and a block in cellular differentiation. In vitro studies have provided proof of concept for mutant IDH inhibition as a therapeutic approach. We report the discovery and characterization of AG-221, an orally available, selective, potent inhibitor of the mutant IDH2 enzyme. AG-221 suppressed 2HG production and induced cellular differentiation in primary human IDH2 mutation-positive acute myeloid leukemia (AML) cells ex vivo and in xenograft mouse models. AG-221 also provided a statistically significant survival benefit in an aggressive IDH2 R140Q -mutant AML xenograft mouse model. These findings supported initiation of the ongoing clinical trials of AG-221 in patients with IDH2 mutation-positive advanced hematologic malignancies. SIGNIFICANCE:Mutations in IDH1/2 are identified in approximately 20% of patients with AML and contribute to leukemia via a block in hematopoietic cell differentiation. We have shown that the targeted inhibitor AG-221 suppresses the mutant IDH2 enzyme in multiple preclinical models and induces differentiation of malignant blasts, supporting its clinical development. Cancer Discov; 7(5); 478-93.

Somatic point mutations at a key arginine residue (R132) within the active site of the metabolic enzyme isocitrate dehydrogenase 1 (IDH1) confer a novel gain of function in cancer cells, resulting in the production of d-2-hydroxyglutarate (2-HG), an oncometabolite. Elevated 2-HG levels are implicated in epigenetic alterations and impaired cellular differentiation. IDH1 mutations have been described in an array of hematologic malignancies and solid tumors. Here, we report the discovery of AG-120 (ivosidenib), an inhibitor of the IDH1 mutant enzyme that exhibits profound 2-HG lowering in tumor models and the ability to effect differentiation of primary patient AML samples ex vivo. Preliminary data from phase 1 clinical trials enrolling patients with cancers harboring an IDH1 mutation indicate that AG-120 has an acceptable safety profile and clinical activity.

V(D)J recombination requires both lymphoid-specific and generally expressed enzymatic activities. All three known generally expressed activities involved in V(D)J recombination are also involved in DNA double-strand break repair (DSBR). Two of these are components of the DNA-dependent protein kinase (DNA-PK) and include Ku80 and DNA-PK catalytic subunit (DNA-PKcs); the third, XRCC4, is a protein of unknown function. The Ku70 protein is an additional component of DNA-PK; Ku70 forms a heterodimer with Ku80 to generate the DNA end-binding component of the enzyme. To test putative functions for Ku70, we have used gene-targeted mutation to generate a murine embryonic stem cell line which lacks Ku70 expression. We find that the Ku70 ؊/؊ cells produce no detectable Ku70 and very little Ku80, suggesting a direct interrelationship between their levels. Correspondingly, these cells lack the nonspecific DNA end-binding activity associated with Ku. Significantly, the Ku70 ؊/؊ embryonic stem cells have markedly increased sensitivity to ␥-irradiation relative to Ku70 ؉/؊ or wild-type embryonic stem cells. Furthermore, the Ku70 ؊/؊ cells lack the ability to effectively rejoin signal and coding ends liberated in transiently introduced V(D)J recombination substrates by enforced RAG-1 and RAG-2 expression. We conclude that the Ku70 gene product is involved in DSBR and V(D)J recombination and confirm that the Ku70 gene can be classified as a member of the x-ray cross-complementation group 6 (XRCC6). Potential differences between the Ku70 ؊/؊ and Ku80 ؊/؊ V(D)J recombination defects are discussed.Immunoglobulin ( In this regard, the completion of the V(D)J recombination reaction can also be viewed as a DSBR process in which generally expressed factors are recruited to repair the specifically broken ends generated by RAG-1 and RAG-2 activity. The three known gene products that are required for the DSBR portion of the V(D)J recombination reaction were identified through studies of ionizing-radiation-sensitive Chinese hamster cell lines and cells from severe combined immunedeficient (Scid) mice (10). There are at least eight x-ray crosscomplementation (XRCC) groups, based on somatic cell hybrid studies (12, 13). Of these, groups XRCC4, XRCC5, and XRCC7, which have specific defects in DSBR (14-17), were also found to have defects in their ability to support V(D)J recombination (18)(19)(20). In this regard, following introduction of RAG-1 and RAG-2 gene expression, cell lines from each complementation group were capable of initiating V(D)J recombination on transiently introduced V(D)J recombination substrates. However, XR-1 and xrs-6 cells (representing the XRCC4 and -5 groups, respectively) were defective in their ability to form both coding and RS joins (18,19), whereas V3 cells (from the XRCC7 group) had impaired ability to form coding joins but were relatively normal in ability to form RS joins (18, 21). V3 cells were further shown to represent the same genetic complementation group as the murine Scid mutation (20).xrs-6 cel...

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