Screen for IDH1, IDH2, IDH3, D2HGDH and L2HGDH mutations in glioblastoma

Isocitrate dehydrogenases (IDHs) catalyse oxidative decarboxylation of isocitrate to α-ketoglutarate (α-KG). IDH1 functions in the cytosol and peroxisomes, whereas IDH2 and IDH3 are both localized in the mitochondria. Heterozygous somatic mutations in IDH1 occur at codon 132 in 70% of grade II-III gliomas and secondary glioblastomas (GBMs), and in 5% of primary GBMs. Mutations in IDH2 at codon 172 are present in grade II-III gliomas at a low frequency. IDH1 and IDH2 mutations cause both loss of normal enzyme function and gain-of-function, causing reduction of α-KG to D-2-hydroxyglutarate (D-2HG) which accumulates. Excess hydroxyglutarate (2HG) can also be caused by germline mutations in D- and L-2-hydroxyglutarate dehydrogenases (D2HGDH and L2HGDH). If loss of IDH function is critical for tumourigenesis, we might expect some tumours to acquire somatic IDH3 mutations. Alternatively, if 2HG accumulation is critical, some tumours might acquire somatic D2HGDH or L2HGDH mutations. We therefore screened 47 glioblastoma samples looking for changes in these genes. Although IDH1 R132H was identified in 12% of samples, no mutations were identified in any of the other genes. This suggests that mutations in IDH3, D2HGDH and L2HGDH do not occur at an appreciable frequency in GBM. One explanation is simply that mono-allelic IDH1 and IDH2 mutations occur more frequently by chance than the bi-allelic mutations expected at IDH3, D2HGDH and L2HGDH. Alternatively, both loss of IDH function and 2HG accumulation might be required for tumourigenesis, and only IDH1 and IDH2 mutations have these dual effects.     

Reductive carboxylation and 2-hydroxyglutarate formation by wild-type IDH2 in breast carcinoma cells

Mitochondrial NADPH-dependent isocitrate dehydrogenase, IDH2, and cytosolic IDH1, catalyze reductive carboxylation of 2-oxoglutarate. Both idh2 and idh1 monoallelic mutations are harbored in grade 2/3 gliomas, secondary glioblastomas and acute myeloid leukemia. Mutant IDH1/IDH2 enzymes were reported to form an oncometabolite r-2-hydroxyglutarate (2HG), further strengthening malignancy. We quantified CO₂-dependent reductive carboxylation glutaminolysis (RCG) and CO₂-independent 2HG production in HTB-126 and MDA-MB-231 breast carcinoma cells by measuring ¹³C incorporation from 1-¹³C-glutamine into citrate, malate, and 2HG. For HTB-126 cells, ¹³C-citrate, ¹³C-malate, and ¹³C-2-hydroxyglutarate were enriched by 2-, 5-, and 15-fold at 5 mM glucose (2-, 2.5-, and 13-fold at 25 mM glucose), respectively, after 6 h. Such enrichment decreased by 6% with IDH1 silencing, but by 30–50% upon IDH2 silencing while cell respiration and ATP levels rose up to 150%. Unlike 2HG production RCG declined at decreasing CO₂. At hypoxia (5% O₂), IDH2-related and unrelated ¹³C-accumulation into citrate and malate increased 1.5–2.5-fold with unchanged IDH2 expression; whereas hypoxic 2HG formation did not. ¹³C–2HG originated by ∼50% from other than IDH2 or IDH1 reactions, substantiating remaining activity in IDH1&2-silenced cells. Relatively high basal ¹²C–2HG levels existed (5-fold higher vs. non-tumor HTB-125 cells) and ¹³C–2HG was formed despite the absence of any idh2 and idh1 mutations in HTB-126 cells. Since RCG is enhanced at hypoxia (frequent in solid tumors) and 2HG can be formed without idh1/2 mutations, we suggest 2HG as an analytic marker (in serum, urine, or biopsies) predicting malignancy of breast cancer in all patients.     

A tale of two subunits: how the neomorphic R132H IDH1 mutation enhances production of αHG

Heterozygously expressed single-point mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2, respectively) render these dimeric enzymes capable of producing the novel metabolite α-hydroxyglutarate (αHG). Accumulation of αHG is used as a biomarker for a number of cancer types, helping to identify tumors with similar IDH mutations. With IDH1, it has been shown that one role of the mutation is to increase the rate of conversion from αKG to αHG. To improve our understanding of the function of this mutation, we have detailed the kinetics of the normal (isocitrate to αKG) and neomorphic (αKG to αHG) reactions, as well as the coupled conversion of isocitrate to αHG. We find that the mutant IDH1 is very efficient in this coupled reaction, with the ability to form αHG from isocitrate and NADP(+). The wild type/wild type IDH1 is also able to catalyze this conversion, though it is much more sensitive to concentrations of isocitrate. This difference in behavior can be attributed to the competitive binding between isocitrate and αKG, which is made more favorable for αKG by the neomorphic mutation at arginine 132. Thus, each partial reaction in the heterodimer is functionally isolated from the other. To test whether there is a cooperative effect resulting from the two subunits being in a dimer, we selectively inactivated each subunit with a secondary mutation in the NADP/H binding site. We observed that the remaining, active subunit was unaffected in its associated activity, reinforcing the notion of each subunit being functionally independent. This was further demonstrated using a monomeric form of IDH from Azotobacter vinelandii, which can be shown to gain the same neomorphic reaction when a homologous mutation is introduced into that protein.     

Glioma-derived mutations in IDH: From mechanism to potential therapy

Heterozygous mutations in either the R132 residue of isocitrate dehydrogenase I (IDH1) or the R172 residue of IDH2 in human gliomas were recently highlighted. Heterozygous mutations in the IDH1 occur in the majority of grade II and grade III gliomas and secondary glioblastomas and change the structure of the enzyme, which diminishes its ability to convert isocitrate (ICT) to α-ketoglutarate (α-KG) and provides it with a newly acquired ability to convert α-KG to R(-)-2-hydroxyglutarate [R(-)-2HG]. The IDH1 and IDH2 mutations are relevant to the progression of gliomas, the prognosis and treatment of the patients with gliomas harboring the mutation. In this paper, we reviewed these recent findings which were essential for the further exploration of human glioma cancer and might be responsible for developing a newer and more effective therapeutic approach in clinical treatment of this cancer.     

Treatment with a Small Molecule Mutant IDH1 Inhibitor Suppresses Tumorigenic Activity and Decreases Production of the Oncometabolite 2-Hydroxyglutarate in Human Chondrosarcoma Cells

Chondrosarcomas are malignant bone tumors that produce cartilaginous matrix. Mutations in isocitrate dehydrogenase enzymes (IDH1/2) were recently described in several cancers including chondrosarcomas. The IDH1 inhibitor AGI-5198 abrogates the ability of mutant IDH1 to produce the oncometabolite D-2 hydroxyglutarate (D-2HG) in gliomas. We sought to determine if treatment with AGI-5198 would similarly inhibit tumorigenic activity and D-2HG production in IDH1-mutant human chondrosarcoma cells. Two human chondrosarcoma cell lines, JJ012 and HT1080 with endogenous IDH1 mutations and a human chondrocyte cell line C28 with wild type IDH1 were employed in our study. Mutation analysis of IDH was performed by PCR-based DNA sequencing, and D-2HG was detected using tandem mass spectrometry. We confirmed that JJ012 and HT1080 harbor IDH1 R132G and R132C mutation, respectively, while C28 has no mutation. D-2HG was detectable in cell pellets and media of JJ012 and HT1080 cells, as well as plasma and urine from an IDH-mutant chondrosarcoma patient, which decreased after tumor resection. AGI-5198 treatment decreased D-2HG levels in JJ012 and HT1080 cells in a dose-dependent manner, and dramatically inhibited colony formation and migration, interrupted cell cycling, and induced apoptosis. In conclusion, our study demonstrates anti-tumor activity of a mutant IDH1 inhibitor in human chondrosarcoma cell lines, and suggests that D-2HG is a potential biomarker for IDH mutations in chondrosarcoma cells. Thus, clinical trials of mutant IDH inhibitors are warranted for patients with IDH-mutant chondrosarcomas.     

IDH1 and IDH2 have critical roles in 2-hydroxyglutarate production in D-2-hydroxyglutarate dehydrogenase depleted cells

D-2-hydroxyglutaric aciduria (D-2HGA) is a hereditary metabolic disorder characterized by the elevated levels of D-2-hydroxyglutaric acid (D-2HG) in urine, plasma and cerebrospinal fluid. About half of the patients have autosomal recessive mutations in D-2-hydroxyglutarate dehydrogenase (D2HGDH) gene. To analyze the origin of D-2HG in D2HGDH-depleted cells, we used small interfering RNA (siRNA) techniques. We found that knockdown of D2HGDH in MCF7 cells increased the levels of 2HG, mimicking D2HGDH mutant cells. Additional knockdown of isocitrate dehydrogenase 1 (IDH1) or isocitrate dehydrogenase 2 (IDH2) decreased the level of 2HG in D2HGDH knockdown MCF7 cells. Conversely, ectopic expression of IDH1 or IDH2 increased 2HG in MCF7 cells. These results suggest that IDH1 and IDH2 have roles in production of D-2HG in cells.     

2-hydroxyglutarate production, but not dominant negative function, is conferred by glioma-derived NADP-dependent isocitrate dehydrogenase mutations

Background

Gliomas frequently contain mutations in the cytoplasmic NADP⁺-dependent isocitrate dehydrogenase (IDH1) or the mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2). Several different amino acid substitutions recur at either IDH1 R132 or IDH2 R172 in glioma patients. Genetic evidence indicates that these mutations share a common gain of function, but it is unclear whether the shared function is dominant negative activity, neomorphic production of (R)-2-hydroxyglutarate (2HG), or both.

Methodology/Principal Findings

We show by coprecipitation that five cancer-derived IDH1 R132 mutants bind IDH1-WT but that three cancer-derived IDH2 R172 mutants exert minimal binding to IDH2-WT. None of the mutants dominant-negatively lower isocitrate dehydrogenase activity at physiological (40 µM) isocitrate concentrations in mammalian cell lysates. In contrast to this, all of these mutants confer 10- to 100-fold higher 2HG production to cells, and glioma tissues containing IDH1 R132 or IDH2 R172 mutations contain high levels of 2HG compared to glioma tissues without IDH mutations (54.4 vs. 0.1 mg 2HG/g protein).

Conclusions

Binding to, or dominant inhibition of, WT IDH1 or IDH2 is not a shared feature of the IDH1 and IDH2 mutations, and thus is not likely to be important in cancer. The fact that the gain of the enzymatic activity to produce 2HG is a shared feature of the IDH1 and IDH2 mutations suggests that this is an important function for these mutants in driving cancer pathogenesis.     

D-2-Hydroxyglutarate does not mimic all the IDH mutation effects,in particular the reduced etoposide-triggered apoptosis mediated by an alteration in mitochondrial NADH

Somatic mutations in isocitrate dehydrogenase (IDH)-1 and -2 have recently been described in glioma. This mutation leads to a neomorphic enzymatic activity as the conversion of isocitrate to alpha ketoglutarate (αKG) is replaced by the conversion of αKG to D-2-hydroxyglutarate (D-2HG) with NADPH oxidation. It has been suggested that this oncometabolite D-2HG via inhibition of αKG-dioxygenases is involved in multiple functions such as epigenetic modifications or hypoxia responses. The present study is aimed at deciphering how the mutant IDH can affect cancer pathogenesis, in particular with respect to its associated oncometabolite D-2HG. We show that the overexpression of mutant IDH in glioma cells or treatment with D-2HG triggered an increase in cell proliferation. However, although mutant IDH reduced cell sensitivity to the apoptotic inducer etoposide, D-2HG exhibited no effect on apoptosis. Instead, we found that the apoptotic effect was mediated through the mitochondrial NADH pool reduction and could be inhibited by oxamate. These data show that besides D-2HG production, mutant IDH affects other crucial metabolite pools. These observations lead to a better understanding of the biology of IDH mutations in gliomas and their response to therapy.Gliomas are the most common type of human brain tumors and can be classified based on clinical and pathological criteria in four grades. The grade IV glioma, commonly known as glioblastoma multiforme (GBM), is the most invasive form and has a dismal prognosis with <5% patient survival at 5 years. These GBM can develop de novo (primary GBM) or through the progression from low-grade tumors (secondary GBM). Although these two types of GBM are histologically similar, primary and secondary GBM exhibit distinct genetic patterns. A recent integrated genome analysis of human GBM shows that 12% of these tumors have a mutation in the gene encoding isocitrate dehydrogenase 1 (IDH1) and to a lesser extent in IDH2 gene.¹ This mutation is present in >90% secondary GBMs, whereas it is present in <5% primary GBMs.² Mutations in IDH1 and IDH2 have also been identified in acute myeloid leukemia (AML)³ and chondrosarcomas.⁴ The occurrence of IDH mutations predicts a significantly longer survival for patients affected by GBM or grade III gliomas.^{1, 2} Whether this difference is driven by IDH mutations or reflects other fundamental biological differences between primary and secondary GBM is, as yet, unclear. For example, the prognostic significance of IDH mutations may be secondary to their prevalence among younger patients, as age is a well-known prognostic factor in gliomas.⁵ In AML, the prognostic significance of IDH mutations is more ambiguous. Several studies have reported that IDH mutations do not affect the prognosis in AML, whereas other studies have found that IDH mutations are associated with an increased or decreased risk of relapse when compared with IDH wild-type patients.^{6, 7}The human genome has five IDH genes coding for three different IDH isoforms, the activities of which depend on either nicotinamide adenine dinucleotide (NAD+) for IDH3 or nicotinamide adenine dinucleotide phosphate (NADP+) for IDH1 and IDH2. Both IDH2 and IDH3 are located in the mitochondria where they participate in the TCA cycle, whereas IDH1 is mostly cytosolic.⁸ To date, all reported mutations are located in the IDH1 and IDH2 genes and result in an amino-acid substitution at residues located in the enzymatic active site, respectively, R132 for IDH1 and R140 or R172 for IDH2. This mutation disrupts the normal enzymatic function of IDH, that is, the conversion of isocitrate to alpha ketoglutarate (αKG) with the concomitant production of NADPH. Instead, mutant IDH displays a neomorphic activity converting αKG into D-2-hydroxyglutarate (D-2HG), although reducing NADPH.⁹ As a result, mutant IDH may alter the redox state of cells, modulate the activity of metabolic and epigenetic tumor suppressor enzymes that use αKG as a co-substrate.¹⁰ Loss of IDH function may also alter normal mitochondrial function and promote a metabolic switch in cancer cells to glycolysis.^{11, 12}Mutant IDH is widely believed to have the ability to transform cells by modulating αKG-dependent enzymes. D-2HG and αKG are structurally similar suggesting that D-2HG may act as a competitive inhibitor of αKG-dioxygenases including prolyl hydroxylase involved in HIF-1α stability, histone demethylases and the Ten-Eleven Translocation (TET) family of 5-methylcytosine hydroxylases involved in epigenetic modifications of DNA.^{13, 14} In fact, IDH mutations lead to numerous metabolic abnormalities besides D-2HG production. Deciphering the relative importance of either D-2HG production, αKG or NADPH reduction in cancer pathogenesis remains to be determined. In this paper, we show that mutant IDH increases cell proliferation and reduces etoposide (ETO)-induced cell death through different metabolic pathways. Although cell proliferation changes are mediated through D-2HG, alteration in the mitochondrial NADH pool is involved in the response to apoptosis.     

Glioma-derived mutations in isocitrate dehydrogenase 2 beneficial to traditional chemotherapy

Heterozygous mutations in either the R132 residue of isocitrate dehydrogenase I (IDH1) or the R172 residue of IDH2 in human gliomas were recently highlighted. In the present study, we report that mutations of IDH1 and IDH2 are not detected in the rat C6 glioma cell line model, which suggests that these mutations are not required for the development of glioblastoma induced by N,N′-nitroso-methylurea. The effects of IDH2 and IDH2^R172G on C6 cells proliferation and sensitivity to chemotherapy and the possible mechanism are analyzed at the cellular level. IDH1 and IDH2 mutations lead to simultaneous loss and gain of activities in the production of α-ketoglutarate (α-KG) and 2-hydroxyglutarate (2HG), respectively, and result in lowering NADPH levels even further. The low NADPH levels can sensitize tumors to chemotherapy, and account for the prolonged survival of patients harboring the mutations. Our data extrapolate potential importance of the in vitro rat C6 glioma cell model, show that the IDH2^R172G mutation in gliomas may give a benefit to traditional chemotherapy of this cancer and serve as an important complement to existing research on this topic.     

人脑胶质瘤中的IDH1/2突变

胶质母细胞瘤的基因组突变分析中发现的异柠檬酸脱氢酶(isocitrate dehydrogenase,IDH1)突变对胶质瘤的认识具有突破性意义。随后,在胶质瘤中发现了IDH1的R132碱基和IDH2的R172碱基突变。IDH1突变较多的发生在WHOII-III级胶质瘤和继发胶质母细胞瘤中。这种突变改变了异柠檬酸脱氢酶的结构,从而使将异柠檬酸转化为a-酮戊二酸的能力丧失,而获得将a-酮戊二酸转化为2-羟基戊二酸这一新的酶活性。在临床中,IDH1和IDH2突变已经显示对胶质瘤患者有诊断和预后意义。同时,现今也发展了一些检测方法。     

The driver and passenger effects of isocitrate dehydrogenase 1 and 2 mutations in oncogenesis and survival prolongation

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are key events in the development of glioma, acute myeloid leukemia (AML), chondrosarcoma, intrahepatic cholangiocarcinoma (ICC), and angioimmunoblastic T-cell lymphoma. They also cause D-2-hydroxyglutaric aciduria and Ollier and Maffucci syndromes. IDH1/2 mutations are associated with prolonged survival in glioma and in ICC, but not in AML. The reason for this is unknown. In their wild-type forms, IDH1 and IDH2 convert isocitrate and NADP⁺ to α-ketoglutarate (αKG) and NADPH. Missense mutations in the active sites of these enzymes induce a neo-enzymatic reaction wherein NADPH reduces αKG to D-2-hydroxyglutarate (D-2HG). The resulting D-2HG accumulation leads to hypoxia-inducible factor 1α degradation, and changes in epigenetics and extracellular matrix homeostasis. Such mutations also imply less NADPH production capacity. Each of these effects could play a role in cancer formation. Here, we provide an overview of the literature and discuss which downstream molecular effects are likely to be the drivers of the oncogenic and survival-prolonging properties of IDH1/2 mutations. We discuss interactions between mutant IDH1/2 inhibitors and conventional therapies. Understanding of the biochemical consequences of IDH1/2 mutations in oncogenesis and survival prolongation will yield valuable information for rational therapy design: it will tell us which oncogenic processes should be blocked and which “survivalogenic” effects should be retained.     

Isocitrate dehydrogenase variants in cancer — Cellular consequences and therapeutic opportunities

Abnormal metabolism is common in cancer cells and often correlates with mutations in genes encoding for enzymes involved in small-molecule metabolism. Isocitrate dehydrogenase 1 (IDH1) is the most frequently mutated metabolic gene in cancer. Cancer-associated substitutions in IDH1 and IDH2 impair wild-type production of 2-oxoglutarate and reduced nicotinamide adenine dinucleotide phosphate (NADPH) from isocitrate and oxidised nicotinamide adenine dinucleotide phosphate (NADP⁺ ), and substantially promote the IDH variant catalysed conversion of 2-oxoglutarate to d-2-hydroxyglutarate (d-2HG). Elevated d-2HG is a biomarker for some cancers, and inhibition of IDH1 and IDH2 variants is being pursued as a medicinal chemistry target. We provide an overview of the types of cancer-associated IDH variants, discuss some of the proposed consequences of altered metabolism as a result of elevated d-2HG, summarise therapeutic efforts targeting IDH variants and identify areas for future research.     

Metabolomic comparison between cells over‐expressing isocitrate dehydrogenase 1 and 2 mutants and the effects of an inhibitor on the metabolism

The R132H and R172K mutations of isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) have neomorphic activity of generating 2‐hydroxyglutarate (2‐HG) which has been implicated in the oncogenesis. Although similarities in structure and enzyme activity for the two isotypic mutations have been suggested, the difference in their cellular localization and biochemical properties suggests differential effects on the metabolic oncogenesis. Using U87 cells transfected with either wild‐type (WT) and mutant (MT) IDH genes, the MT‐IDH1 and MT‐IDH2 cells were compared with NMR‐based metabolomics. When normalized with the respective WT‐IDH cells, the general metabolic shifts of MT‐IDH1 and IDH2 were almost opposite. Subsequent analysis with LC‐MS and metabolic pathway mapping showed that key metabolites in pentose phosphate pathway and tricarboxylic acid cycle are disproportionately altered in the two mutants, suggesting different activities in the key metabolic pathways. Notably, lactate level was lower in MT‐IDH2 cells which produced more 2‐HG than MT‐IDH1 cells, indicating that the Warburg effects can be overridden by the production of 2‐HG. We also found that the effect of a mutant enzyme inhibitor is mainly reduction of the 2‐HG level rather than general metabolic normalization. Overall, the metabolic alterations in the MT‐IDH1 and 2 can be different and seem to be commensurate with the degree of 2‐HG production.

     

胶质瘤中的异柠檬酸脱氢酶突变

胶质母细胞瘤的基因组突变分析中发现的异柠檬酸脱氢酶（isocitrate dehydrogenase,IDH）突变对胶质瘤的认识具有突破性意义.随后,在胶质瘤中发现了IDH1的R132碱基和IDH2的R172碱基突变.IDH1突变较多的发生在WHOⅡ～Ⅲ级胶质瘤和继发胶质母细胞瘤中.这种突变改变了异柠檬酸脱氢酶的结构,从而使将异柠檬酸转化为α-酮戊二酸的能力丧失,而获得将α-酮戊二酸转化为D-2-羟基戊二酸这一新的酶活性.在临床中,IDH1和IDH2突变已经显示对胶质瘤患者有诊断和预后意义.同时,现今也发展了一些检测方法.     

On the Utility of Short Echo Time (TE) Single Voxel 1H–MRS in Non–Invasive Detection of 2–Hydroxyglutarate (2HG); Challenges and Potential Improvement Illustrated with Animal Models Using MRUI and LCModel

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) are frequently found in brain tumors, and the resulting onco–metabolite, 2–hydroxyglutarate (2HG), has been suggested to be a potential diagnostic and prognostic biomarker of the diseases. Indeed, recent studies have demonstrated the feasibility of non–invasively detecting 2HG by using proton magnetic resonance spectroscopy (1H–MRS). Due to severe spectral overlaps of 2HG with its background metabolites and spectral baselines, however, the majority of those previous studies employed spectral editing methods with long echo times (TEs) instead of the most commonly used short TE approach with spectral fitting. Consequently, the results obtained with spectral editing methods may potentially be prone to errors resulting from substantial signal loss due to relaxation. Given that the spectral region where the main signal of 2HG resides is particularly sensitive to spectral baseline in metabolite quantification, we have investigated the impact of incorporating voxel–specifically measured baselines into the spectral basis set on the performance of the conventional short TE approach in 2HG detection in rodent models (Fisher 344 rats; n = 19) of IDH1/2 mutant–overexpressing F98 glioma at 9.4T. Metabolite spectra were acquired (SPECIAL sequence) for a tumor region and the contralateral normal region of the brain for each animal. For the estimation of spectral baselines metabolite–nulled spectra were obtained (double–inversion–recovery SPECIAL sequence) for each individual voxels. Data were post–processed with and without the measured baselines using MRUI and LCModel—the two most widely used data post–processing packages. Our results demonstrate that in–vivo detection of 2HG using the conventional short TE approach is challenging even at 9.4T. However, incorporation of voxel–specifically measured spectral baselines may potentially improve its performance. Upon more thorough validation in a larger number of animals and more importantly in human patients, the potential utility of the proposed short TE acquisition with voxel–specific baseline measurement approach in 2HG detection may need to be considered in the study design.     

IDH1 mutation identified in one human melanoma metastasis, but not correlated with metastases to the brain

Isocitrate dehydrogenase 1 (IDH1) and isocitrate dehydrogenase 2 (IDH2) are enzymes which convert isocitrate to α-ketoglutarate while reducing nicotinamide adenine dinucleotide phosphate (NADP + to NADPH). IDH1/2 were recently identified as mutated in a large percentage of progressive gliomas. These mutations occur at IDH1^R132 or the homologous IDH2^R172. Melanomas share some genetic features with IDH1/2-mutated gliomas, such as frequent TP53 mutation. We sought to test whether melanoma is associated with IDH1/2 mutations. Seventy-eight human melanoma samples were analyzed for IDH1^R132 and IDH2^R172 mutation status. A somatic, heterozygous IDH1 c.C394T (p.R132C) mutation was identified in one human melanoma metastasis to the lung. Having identified this mutation in one metastasis, we sought to test the hypothesis that certain selective pressures in the brain environment may specifically favor the cell growth or survival of tumor cells with mutations in IDH1/2, regardless of primary tumor site. To address this, we analyzed IDH1^R132 and IDH2^R172 mutation status 53 metastatic brain tumors, including nine melanoma metastases. Results revealed no mutations in any samples. This lack of mutations would suggest that mutations in IDH1^R132 or IDH2^R172 may be necessary for the formation of tumors in a cell-lineage dependent manner, with a particularly strong selective pressure for mutations in progressive gliomas; this also suggests the lack of a particular selective pressure for growth in brain tissue in general. Studies on the cell-lineages of tumors with IDH1/2 mutations may help clarify the role of these mutations in the development of brain tumors.     

Isocitrate dehydrogenase mutations: new opportunities for translational research

Over the last decade, comprehensive genome-wide sequencing studies have enabled us to find out unexpected genetic alterations of metabolism in cancer. An example is the identification of arginine missense mutations of isocitrate dehydrogenases-1 and -2 (IDH1/2) in glioma, acute myeloid leukemia (AML), chondrosarcomas, and cholangiocarcinoma. These alterations are closely associated with the production of a new stereospecific metabolite, (R)-2-hydroxyglutarate (R-2HG). A large number of follow-up studies have been performed to address the molecular mechanisms of IDH1/2 mutations underlying how these events contribute to malignant transformation. In the meanwhile, the development of selective mutant IDH1/2 chemical inhibitors is being actively pursued in the scientific community and pharmaceutical industry. The present review article briefly discusses the important findings that highlight the molecular mechanisms of IDH1/2 mutations in cancer and provides a current status for development of selective mutant IDH1/2 chemical inhibitors. [BMB Reports 2015; 48(5): 266-270]     

Correlation of IDH1 mutation with clinicopathologic factors and prognosis in primary glioblastoma: a report of 118 patients from China

It has been reported that IDH1 (IDH1R132) mutation was a frequent genomic alteration in grade II and grade III glial tumors but rare in primary glioblastoma (pGBM). To elucidate the frequency of IDH1 mutation and its clinical significance in Chinese patients with pGBM, one hundred eighteen pGBMs were assessed by pyro-sequencing for IDH1 mutation status, and the results were correlated with clinical characteristics and molecular pathological factors. IDH1 mutations were detected in 19/118 pGBM cases (16.1%). Younger age, methylated MGMT promoter, high expression of mutant P53 protein, low expression of Ki-67 or EGFR protein were significantly correlated with IDH1 mutation status. Most notably, we identified pGBM cases with IDH1 mutation were mainly involved in the frontal lobe when compared with those with wild-type IDH1. In addition, Kaplan-Meier survival analysis revealed a highly significant association between IDH1 mutation and a better clinical outcome (p = 0.026 for progression-free survival; p = 0.029 for overall survival). However, in our further multivariable regression analysis, the independent prognostic effect of IDH1 mutation is limited when considering age, preoperative KPS score, extent of resection, TMZ chemotherapy, and Ki-67 protein expression levels, which might narrow its prognostic power in Chinese population in the future.     

IDH1/IDH2 Mutations Define the Prognosis and Molecular Profiles of Patients with Gliomas: A Meta-Analysis

Background

Isocitrate dehydrogenase isoforms 1 and 2 (IDH1 and IDH2) mutations have received considerable attention since the discovery of their relation with human gliomas. The predictive value of IDH1 and IDH2 mutations in gliomas remains controversial. Here, we present the results of a meta-analysis of the associations between IDH mutations and both progression-free survival (PFS) and overall survival (OS) in gliomas. The interrelationship between the IDH mutations and MGMT promoter hypermethylation, EGFR amplification, codeletion of chromosomes 1p/19q and TP53 gene mutation were also revealed.

Methodology and Principal Findings

An electronic literature search of public databases (PubMed, Embase databases) was performed. In total, 10 articles, including 12 studies in English, with 2,190 total cases were included in the meta-analysis. The IDH mutations were frequent in WHO grade II and III glioma (59.5%) and secondary glioblastomas (63.4%) and were less frequent in primary glioblastomas (7.13%). Our study provides evidence that IDH mutations are tightly associated with MGMT promoter hypermethylation (P<0.001), 1p/19q codeletion (P<0.001) and TP53 gene mutation (P<0.001) but are mutually exclusive with EGFR amplification (P<0.001). This meta-analysis showed that the combined hazard ratio (HR) estimate for overall survival and progression-free survival in patients with IDH mutations was 0.33 (95% CI: 0.25–0.42) and 0.38 (95% CI: 0.21–0.68), compared with glioma patients whose tumours harboured the wild-type IDH. Subgroup analyses based on tumour grade also revealed that the presence of IDH mutations was associated with a better outcome.

Conclusion

Our study suggests that IDH mutations, which are closely linked to the genomic profile of gliomas, are potential prognostic biomarkers for gliomas.