Cancer-associated IDH mutations: biomarker and therapeutic opportunities

The discovery of somatic mutations in the isocitrate dehydrogenase (IDH) enzymes through a genome-wide mutational analysis in glioblastoma represents a milestone event in cancer biology. The nature of the heterozygous, point mutations mapping to arginine residues involved in the substrate binding inspired several research teams to investigate their impact on the biochemical activity of these enzymes. Soon, it became clear that the mutations identified impaired the ability of IDH1 and IDH2 to catalyze the conversion of isocitrate to α-ketoglutarate (αKG), whereas conferring a gain of a novel enzymatic activity leading to the reduction of αKG to the metabolite D2-hydroxyglutarate (D-2HG). Across glioma as well as several hematologic malignancies, mutations in IDH1 and IDH2 have shown prognostic value. Several hypotheses implicating the elevated levels of D-2HG and tumorigenesis, and the therapeutic potential of targeting mutant IDH enzymes will be discussed.     

IDH mutations in cancer and progress toward development of targeted therapeutics

Isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are key metabolic enzymes, converting isocitrate to &agr;-ketoglutarate (&agr;KG). IDH1 and IDH2 mutations have been identified in multiple tumor types, including gliomas and myeloid malignancies such as acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). Here we provide an overview of the function of normal and mutated IDH, discuss the role of IDH mutations in tumorigenesis and progression and review the key clinical considerations when treating IDH-mutated tumors based on emerging clinical data from mutant IDH1/2 inhibitor trials. IDH1 and IDH2 mutations confer neomorphic activity in the mutant protein, resulting in the conversion of &agr;KG to the oncometabolite, D-2-hydroxyglutarate (2-HG). The subsequent accumulation of 2-HG results in epigenetic dysregulation via inhibition of &agr;KG-dependent histone and DNA demethylases, and a block in cellular differentiation. There is growing preclinical and clinical evidence suggesting that IDH mutations are involved in neoplasia. Furthermore, preclinical studies assessing small molecule inhibitors of mutant IDH1/2 enzymes have provided proof of concept that this approach decreases intracellular 2-HG levels, reverses epigenetic dysregulation and induces cellular differentiation. Phase I studies of mutant IDH inhibitors are currently ongoing in patients with IDH-mutant hematologic and solid tumors, with early data in hematologic tumors suggesting a manageable safety profile as well as clinical benefit, with a mechanism of action based on differentiation of malignant cells. Inhibition of mutant IDH shows promise as a treatment approach in hematologic malignancies, with further development ongoing in solid tumors and glioma. The mutant IDH inhibitors may have clinical utility both as single agents and in combination strategies that target additional oncogenic pathways.     

Lactate dehydrogenase A silencing in IDH mutant gliomas

Background

Mutations of the isocitrate dehydrogenase 1 and 2 gene (IDH1/2) were initially thought to enhance cancer cell survival and proliferation by promoting the Warburg effect. However, recent experimental data have shown that production of 2-hydroxyglutarate by IDH mutant cells promotes hypoxia-inducible factor (HIF)1α degradation and, by doing so, may have unexpected metabolic effects.

Methods

We used human glioma tissues and derived brain tumor stem cells (BTSCs) to study the expression of HIF1α target genes in IDH mutant (^mt) and IDH wild-type (^wt) tumors. Focusing thereafter on the major glycolytic enzyme, lactate dehydrogenase A (LDHA), we used standard molecular methods and pyrosequencing-based DNA methylation analysis to identify mechanisms by which LDHA expression was regulated in human gliomas.

Results

We found that HIF1α-responsive genes, including many essential for glycolysis (SLC2A1, PDK1, LDHA, SLC16A3), were underexpressed in IDH^mt gliomas and/or derived BTSCs. We then demonstrated that LDHA was silenced in IDH^mt derived BTSCs, including those that did not retain the mutant IDH1 allele (mIDH^wt), matched BTSC xenografts, and parental glioma tissues. Silencing of LDHA was associated with increased methylation of the LDHA promoter, as was ectopic expression of mutant IDH1 in immortalized human astrocytes. Furthermore, in a search of The Cancer Genome Atlas, we found low expression and high methylation of LDHA in IDH^mt glioblastomas.

Conclusion

To our knowledge, this is the first demonstration of downregulation of LDHA in cancer. Although unexpected findings, silencing of LDHA and downregulation of several other glycolysis essential genes raise the intriguing possibility that IDH^mt gliomas have limited glycolytic capacity, which may contribute to their slow growth and better prognosis.     

Diagnostic Value of Plasma and Urinary 2‐Hydroxyglutarate to Identify Patients With Isocitrate Dehydrogenase‐Mutated Glioma

Background.

Mutant isocitrate dehydrogenase (IDH) 1/2 enzymes can convert α-ketoglutarate into 2-hydroxyglutarate (2HG). The aim of the present study was to explore whether 2HG in plasma and urine could predict the presence of IDH1/2 mutations in patients with glioma.

Materials and Methods.

All patients had histological confirmation of glioma and a recent brain magnetic resonance imaging scan showing the neoplastic lesion. Plasma and urine samples were taken from all patients, and the 2HG concentrations were determined using liquid chromatography tandem mass spectrometry.

Results.

A total of 84 patients were enrolled: 38 with R132H-IDH1 mutated and 46 with wild type. Among the 38 patients with mutant IDH1, 21 had high-grade glioma and 17 had low-grade glioma. Among the 46 patients with IDH1 wild-type glioma, 35 and 11 had high- and low-grade glioma, respectively. In all patients, we analyzed the mean 2HG concentration in the plasma, urine, and plasma/urine ratio (Ratio_2HG). We found a significant difference in the Ratio_2HG between patients with and without an IDH1 mutation (22.2 ± 8.7 vs. 15.6 ± 6.8; p < .0001). The optimal cutoff value for Ratio_2HG to identify IDH1 mutation was 19 (sensitivity, 63%; specificity, 76%; accuracy, 70%). In the patients with high-grade glioma only, the optimal cutoff value was 20 (sensitivity, 76%; specificity, 89%; accuracy, 84%; positive predictive value, 80%; negative predictive value, 86%). In 7 of 7 patients with high-grade glioma, we found a correlation between the Ratio_2HG value and the response to treatment.

Conclusion.

Ratio_2HG might be a predictor of the presence of IDH1 mutation. The measurement of 2HG could be useful for disease monitoring and also to assess the treatment effects in these patients.     

D-2-hydroxyglutarate is essential for maintaining oncogenic property of mutant IDH-containing cancer cells but dispensable for cell growth

Cancer-associated isocitrate dehydrogenase (IDH) 1 and 2 mutations gain a new activity of reducing α-KG to produce D-2-hydroxyglutarate (D-2-HG), which is proposed to function as an oncometabolite by inhibiting α-KG dependent dioxygenases. We investigated the function of D-2-HG in tumorigenesis using IDH1 and IDH2 mutant cancer cell lines. Inhibition of D-2-HG production either by specific deletion of the mutant IDH1-R132C allele or overexpression of D-2-hydroxyglutarate dehydrogenase (D2HGDH) increases α-KG and related metabolites, restores the activity of some α-KG-dependent dioxygenases, and selectively alters gene expression. Ablation of D-2-HG production has no significant effect on cell proliferation and migration, but strongly inhibits anchorage independent growth in vitro and tumor growth in xenografted mouse models. Our study identifies a new activity of oncometabolite D-2-HG in promoting tumorigenesis.     

Detection of 2-hydroxyglutaric acid in vivo by proton magnetic resonance spectroscopy in U87 glioma cells overexpressing isocitrate dehydrogenase–1 mutation

The arginine 132 (R132) mutation of isocitrate dehydrogenase –1 (IDH1^R132) results in production of 2-hydroxyglutarate (2-HG) and is associated with a better prognosis compared with wild-type (WT) in glioma patients. The majority of lower-grade gliomas express IDH1^R132, whereas this mutation is rare in grade IV gliomas. The aim of this study was to noninvasively investigate metabolic and physiologic changes associated with the IDH1 mutation in a mouse glioma model. Using a 7T magnet, we compared MRI and proton magnetic resonance spectroscopy (MRS) in U87 glioma cells overexpressing either the mutated IDH1^R132 or IDH1 wild-type (IDH1^WT) gene in a mouse flank xenograft model. Flank tumors overexpressing IDH1^R132 showed a resonance at 2.25 ppm corresponding to the 2-HG peak described for human IDH1^R132 gliomas. WT tumors lacked this peak in all cases. IDH1 mutant tumors demonstrated significantly reduced glutamate by in vivo MRS. There were no significant differences in T₂, apparent diffusion coefficient (ADC), or perfusion values between the mutant and IDH1^WT tumors. The IDH1^R132 mutation results in 2-HG resonance at 2.25 ppm and a reduction of glutamate levels as determined by MRS. Our results establish a model system where 2-HG can be monitored noninvasively, which should be helpful in validating 2-HG levels as a prognostic and/or predictive biomarker in glioma.     

Activation of the NRF2 pathway and its impact on the prognosis of anaplastic glioma patients

Background

Nuclear factor erythroid 2–related factor 2 (NRF2) plays pivotal roles in cytoprotection. We aimed at clarifying the contribution of the NRF2 pathway to malignant glioma pathology.

Methods

NRF2 target gene expression and its association with prognosis were examined in 95 anaplastic gliomas with or without isocitrate dehydrogenase (IDH) 1/2 gene mutations and 52 glioblastomas. To explore mechanisms for the altered activity of the NRF2 pathway, we examined somatic mutations and expressions of the NRF2 gene and those encoding NRF2 regulators, Kelch-like ECH-associated protein 1 (KEAP1) and p62/SQSTSM. To clarify the functional interaction between IDH1 mutations and the NRF2 pathway, we introduced a mutant IDH1 to T98 glioblastoma-derived cells and examined the NRF2 activity in these cells.

Results

NRF2 target genes were elevated in 13.7% and 32.7% of anaplastic gliomas and glioblastomas, respectively. Upregulation of NRF2 target genes correlated with poor prognosis in anaplastic gliomas but not in glioblastomas. Neither somatic mutations of NRF2/KEAP1 nor dysregulated expression of KEAP1/p62 explained the increased expression of NRF2 target genes. In most cases of anaplastic glioma with mutated IDH1/2, NRF2 and its target genes were downregulated. This was reproducible in IDH1 R132H–expressing T98 cells. In minor cases of IDH1/2-mutant anaplastic gliomas with increased expression of NRF2 target genes, the clinical outcomes were significantly poor.

Conclusions

The NRF2 activity is increased in a significant proportion of malignant gliomas in general but decreased in the majority of IDH1/2-mutant anaplastic gliomas. It is plausible that the NRF2 pathway plays an important role in tumor progression of anaplastic gliomas with IDH1/2 mutations.     

Accumulation of 2-hydroxyglutarate is not a biomarker for malignant progression in IDH-mutated low-grade gliomas

Objectives

To determine whether accumulation of 2-hydroxyglutarate in IDH-mutated low-grade gliomas (LGG; WHO grade II) correlates with their malignant transformation and to evaluate changes in metabolite levels during malignant progression.

Methods

Samples from 54 patients were screened for IDH mutations: 17 patients with LGG without malignant transformation, 18 patients with both LGG and their consecutive secondary glioblastomas (sGBM; n = 36), 2 additional patients with sGBM, 10 patients with primary glioblastomas (pGBM), and 7 patients without gliomas. The cellular tricarboxylic acid cycle metabolites, citrate, isocitrate, 2-hydroxyglutarate, α-ketoglutarate, fumarate, and succinate were profiled by liquid chromatography–tandem mass spectrometry. Ratios of 2-hydroxyglutarate/isocitrate were used to evaluate differences in 2-hydroxyglutarate accumulation in tumors from LGG and sGBM groups, compared with pGBM and nonglioma groups.

Results

IDH1 mutations were detected in 27 (77.1%) of 37 patients with LGG. In addition, in patients with LGG with malignant progression (n = 18), 17 patients were IDH1 mutated with a stable mutation status during their malignant progression. None of the patients with pGBM or nonglioma tumors had an IDH mutation. Increased 2-hydroxyglutarate/isocitrate ratios were seen in patients with IDH1-mutated LGG and sGBM, in comparison with those with IDH1-nonmutated LGG, pGBM, and nonglioma groups. However, no differences in intratumoral 2-hydroxyglutarate/isocitrate ratios were found between patients with LGG with and without malignant transformation. Furthermore, in patients with paired samples of LGG and their consecutive sGBM, the 2-hydroxyglutarate/isocitrate ratios did not differ between both tumor stages.

Conclusion

Although intratumoral 2-hydroxyglutarate accumulation provides a marker for the presence of IDH mutations, the metabolite is not a useful biomarker for identifying malignant transformation or evaluating malignant progression.     

IDH1 mutations inhibit multiple α-ketoglutarate-dependent dioxygenase activities in astroglioma

The mechanism of tumorigenesis associated with nicotinamide adenine dinucleotide phosphate (NADP(+))-dependent isocitrate dehydrogenase?1 (IDH1) mutations in gliomas is not fully understood. Loss of catalytic activity leading to a decrease in α-ketoglutarate (αKG) and gain of novel catalytic activity leading to production of D: -2-hydroxylglutarate (D: -2-HG) are both found in IDH1-mutated glioma cells. Both the decrease of αKG and accumulation of D: -2-HG inhibit the activity of multiple dioxygenases including prolyl hydroxylase domain-2 (PHD2), collagen prolyl-4-hydroxylase, histone demethylases, and the ten-eleven translocation (TET) family of 5-methylcytosine hydroxylases. Here we correlated the products of these dioxygenases after IDH1 gene mutations with tumorigenesis in human astroglioma samples. DNA sequencing was carried out for 253 astroglioma samples to identify IDH1 mutations. Immunohistochemistry analysis was employed to verify the levels of endostatin, dimethylated H3k79 (H3k79me2), and 5-hydroxymethylcytosine (5hmC) in these astroglioma samples. IDH1 mutations occurred frequently in low grades of astrocytoma. One case bearing both IDH1 and IDH2 mutations was identified. IDH1-mutated cases displayed more frontal lobe location and p53-positive immunostaining than wild-type cases. IDH1 mutations were associated with increased histone methylation and decreased 5hmC. By inhibiting endostatin expression, IDH1 mutations indirectly promoted angiogenesis in gliomas. All these changes were same in astroglioma at different malignancy grade. IDH1 mutations showed wide regulation of angiogenesis and genome-wide change of histone and DNA methylation, which were not suppressed as the malignancy level progressed, suggesting an early role of IDH1 mutations in astrocytoma tumorigenesis.     

5-azacytidine reduces methylation,promotes differentiation and induces tumor regression in a patient-derived IDH1 mutant glioma xenograft

Somatic mutations in Isocitrate Dehydrogenase 1 (IDH1) are frequent in low grade and progressive gliomas and are characterized by the production of 2-hydroxyglutarate (2-HG) from α-ketoglutarate by the mutant enzyme. 2-HG is an “oncometabolite” that competitively inhibits α-KG dependent dioxygenases resulting in various widespread cellular changes including abnormal hypermethylation of genomic DNA and suppression of cellular differentiation. Despite the growing understanding of IDH mutant gliomas, the development of effective therapies has proved challenging in part due to the scarcity of endogenous mutant in vivo models. Here we report the generation of an endogenous IDH1 anaplastic astrocytoma model which rapidly grows in vivo, produces 2-HG and exhibits DNA hypermethylation. Using this model, we have demonstrated the preclinical efficacy and mechanism of action of the FDA approved demethylating drug 5-azacytidine in vivo. Long term administration of 5-azacytidine resulted in reduction of DNA methylation of promoter loci, induction of glial differentiation, reduction of cell proliferation and a significant reduction in tumor growth. Tumor regression was observed at 14 weeks and subsequently showed no signs of re-growth at 7 weeks despite discontinuation of therapy. These results have implications for clinical trials of demethylating agents for patients with IDH mutated gliomas.     

Prognostic role of IDH mutations in gliomas: a meta-analysis of 55 observational studies

Background

IDH (Isocitrate dehydrogenase) mutations occur frequently in gliomas, but their prognostic impact has not been fully assessed. We performed a meta-analysis of the association between IDH mutations and survival in gliomas.

Methods

Pubmed and EMBASE databases were searched for studies reporting IDH mutations (IHD1/2 and IDH1) and survival in gliomas. The primary outcome was overall survival (OS); the secondary outcome was progression-free survival (PFS). Hazard ratios (HR) with 95% confidence interval (CI) were determined using the Mantel-Haenszel random-effect modeling. Funnel plot and Egger''s test were conducted to examine the risk of publication bias.

Results

Fifty-five studies (9487 patients) were included in the analysis. Fifty-four and twenty-seven studies investigated the association between IDH1/2 mutations and OS/PFS respectively in patients with glioma. The results showed that patients possessing an IDH1/2 mutation had significant advantages in OS (HR = 0.39, 95%CI: 0.34–0.45; P < 0.001) and PFS (HR = 0.42, 95% CI: 0.35–0.51; P < 0.001). Subgroup analysis showed a consistent result with pooled analysis, and patients with glioma of WHO grade III or II-III had better outcomes.

Conclusions

These findings provide further indication that patients with glioma harboring IDH mutations have improved OS and PFS, especially for patients with WHO grade III and grade II-III.     

Editor's choice: Integration of 2-hydroxyglutarate-proton magnetic resonance spectroscopy into clinical practice for disease monitoring in isocitrate dehydrogenase-mutant glioma

Background

The majority of WHO grades II and III gliomas harbor a missense mutation in the metabolic gene isocitrate dehydrogenase (IDH) and accumulate the metabolite R-2-hydroxyglutarate (R-2HG). Prior studies showed that this metabolite can be detected in vivo using proton magnetic-resonance spectroscopy (MRS), but the sensitivity of this methodology and its clinical implications are unknown.

Methods

We developed an MR imaging protocol to integrate 2HG-MRS into routine clinical glioma imaging and examined its performance in 89 consecutive glioma patients.

Results

Detection of 2-hydroxyglutarate (2HG) in IDH-mutant gliomas was closely linked to tumor volume, with sensitivity ranging from 8% for small tumors (<3.4 mL) to 91% for larger tumors (>8 mL). In patients undergoing 2HG-MRS prior to surgery, tumor levels of 2HG corresponded with tumor cellularity but not with tumor grade or mitotic index. Cytoreductive therapy resulted in a gradual decrease in 2HG levels with kinetics that closely mirrored changes in tumor volume.

Conclusions

Our study demonstrates that 2HG-MRS can be linked with routine MR imaging to provide quantitative measurements of 2HG in glioma and may be useful as an imaging biomarker to monitor the abundance of IDH-mutant tumor cells noninvasively during glioma therapy and disease monitoring.     

Efficient induction of differentiation and growth inhibition in IDH1 mutant glioma cells by the DNMT Inhibitor Decitabine

Mutation in the IDH1 or IDH2 genes occurs frequently in gliomas and other human malignancies. In intermediate grade gliomas, IDH1 mutation is found in over 70% of tumors. These mutations impart the mutant IDH enzyme with a neomorphic activity – the ability to synthesize 2-hydroxyglutarate (2-HG). This ability leads to a reprogramming of chromatin state, a block in differentiation, and the establishment of the glioma hypermethylator phenotype (G-CIMP). It has been hypothesized but not proven that the extensive DNA methylation that occurs in G-CIMP tumors helps maintain and “lock in” glioma cancer cells in a dedifferentiated state. Here, we tested this hypothesis by treating patient derived IDH1 mutant glioma initiating cells (GIC) with non-cytotoxic, epigenetically targeted doses of the DNMT inhibitor decitabine. Global methylome analysis of treated IDH1 mutant GICs showed that DAC treatment resulted in reversal of DNA methylation marks induced by IDH and the re-expression of genes associated with differentiation. Accordingly, treatment of IDH1 mutant glioma cells resulted in a dramatic loss of stem-like properties and efficient adoption of markers of differentiation, effects not seen in decitabine treated IDH wild-type GICs. Induction of differentiation was much more efficient than that seen following treatment with a specific inhibitor of mutant IDH enzyme (Agios). Decitabine also decreased replicative potential and tumor growth in vivo. Reexpression of polycomb regulated genes accompanied these DAC-induced phenotypes. In total, our data indicates that targeting the pathologic DNA methylation in IDH mutant cells can reverse mutant IDH induced hypermethylation and block in differentiation and promote tumor control. These findings have substantial impact for exploring new treatment strategies for patients with IDH mutant gliomas.     

New insights into glioma classification based on isocitrate dehydrogenase 1 and 2 gene status

In glioma, mutations in the isocitrate dehydrogenase 1 and 2 (IDH1/2) genes have been receiving attention. IDH1/2 mutations are frequently found in grade II and III gliomas. These genetic alterations occur very early in gliomagenesis and strongly predict favorable outcome in patients with high-grade gliomas. Despite the evolution of studies on this topic, the underlying mechanism of the IDH1/2 mutations remains unknown. Here, we briefly review the current knowledge of IDH1/2 and discuss molecular diagnostics based on IDH1/2 gene status.     

IDH1/2 mutation status combined with Ki-67 labeling index defines distinct prognostic groups in glioma

The current World Health Organization (WHO) classification of human gliomas is mainly based on morphology. However, it has limitations in prognostic prediction. We examined whether combining isocitrate dehydrogenase (IDH) 1/2 mutation status with the Ki-67 labeling index would improve the definition of prognostically distinct entities. We investigated the correlation of Ki-67 expression with IDH1/2 mutation status and their impact on clinical outcome in 703 gliomas. Low Ki-67 expression closely overlapped with IDH1/2 mutation in our cohort (P < 0.0001). Patients with IDH1/2 mutation survived significantly longer than patients with wild-type IDH1/2 did (P < 0.0001); higher Ki-67 expression was associated with shorter progression-free survival and overall survival (OS) (P < 0.0001). IDH1/2 combined with Ki-67 was used to re-classify glioma patients into five groups. IDH1/2 mutant patients with low and moderate Ki-67 expression (Group1) had the best prognosis, whereas patients with wild-type IDH1/2 and high Ki-67 expression (Group5) had the worst prognosis (Median OS = 1527 vs. 355 days, P < 0.0001). To summarize, our new classification model distinguishes biologically distinct subgroups and provides prognostic information regardless of the conventional WHO grade. Classification based on IDH1/2 mutation status and Ki-67 expression level could be more convenient for clinical application and guide personalized treatment in malignant gliomas.     

Overexpression of isocitrate dehydrogenase mutant proteins renders glioma cells more sensitive to radiation

Mutations in isocitrate dehydrogenase 1 (IDH1) or 2 (IDH2) are found in a subset of gliomas. Among the many phenotypic differences between mutant and wild-type IDH1/2 gliomas, the most salient is that IDH1/2 mutant glioma patients demonstrate markedly improved survival compared with IDH1/2 wild-type glioma patients. To address the mechanism underlying the superior clinical outcome of IDH1/2 mutant glioma patients, we investigated whether overexpression of the IDH1^R132H protein could affect response to therapy in the context of an isogenic glioma cell background. Stable clonal U87MG and U373MG cell lines overexpressing IDH1^WT and IDH1^R132H were generated, as well as U87MG cell lines overexpressing IDH2^WT and IDH2^R172K. In vitro experiments were conducted to characterize baseline growth and migration and response to radiation and temozolomide. In addition, reactive oxygen species (ROS) levels were measured under various conditions. U87MG-IDH1^R132H cells, U373MG-IDH1^R132H cells, and U87MG-IDH2^R172K cells demonstrated increased sensitivity to radiation but not to temozolomide. Radiosensitization of U87MG-IDH1^R132H cells was accompanied by increased apoptosis and accentuated ROS generation, and this effect was abrogated by the presence of the ROS scavenger N-acetyl-cysteine. Interestingly, U87MG-IDH1^R132H cells also displayed decreased growth at higher cell density and in soft agar, as well as decreased migration. Overexpression of IDH1^R132H and IDH2^R172K mutant protein in glioblastoma cells resulted in increased radiation sensitivity and altered ROS metabolism and suppression of growth and migration in vitro. These findings provide insight into possible mechanisms contributing to the improved outcomes observed in patients with IDH1/2 mutant gliomas.     

2-Hydroxyglutarate concentration in serum from patients with gliomas does not correlate with IDH1/2 mutation status or tumor size

IDH1/2 mutations occur at high frequency in diffusely infiltrating gliomas of the WHO grades II and III and were identified as a strong prognostic marker in all WHO grades of gliomas. Mutated IDH1 or IDH2 protein leads to the generation of excessive amounts of the metabolite 2-hydroxyglutarate (2HG) in tumor cells. Here, we evaluated whether 2HG levels in preoperative serum samples from patients with gliomas correlate with the IDH1/2 mutation status and whether there is an association between 2HG levels and glioma size. In contrast to the strong accumulation of 2HG in the serum of patients with IDH1/2 mutated acute myeloid leukaemia, no accumulation was observed in this series of IDH1/2 mutated gliomas. Furthermore, we found no association between glioma size measured by magnetic resonance imaging and 2HG levels. We conclude that 2HG levels in preoperative sera from patients with diffusely infiltrating gliomas of the WHO grades II and III cannot be used as a marker to differentiate between tumors with versus without IDH1/2 mutation. Furthermore, the observation that there is no correlation between 2HG levels and tumor volume may indicate that 2HG cannot be utilized as marker to monitor tumor growth in gliomas.     

IDH1/2 mutations target a key hallmark of cancer by deregulating cellular metabolism in glioma

Isocitrate dehydrogenase (IDH) enzymes have recently become a focal point for research aimed at understanding the biology of glioma. IDH1 and IDH2 are mutated in 50%–80% of astrocytomas, oligodendrogliomas, oligoastrocytomas, and secondary glioblastomas but are seldom mutated in primary glioblastomas. Gliomas with IDH1/2 mutations always harbor other molecular aberrations, such as TP53 mutation or 1p/19q loss. IDH1 and IDH2 mutations may serve as prognostic factors because patients with an IDH-mutated glioma survive significantly longer than those with an IDH–wild-type tumor. However, the molecular pathogenic role of IDH1/2 mutations in the development of gliomas is unclear. The production of 2-hydroxyglutarate and enhanced NADP+ levels in tumor cells with mutant IDH1/2 suggest mechanisms through which these mutations contribute to tumorigenesis. Elucidating the pathogenesis of IDH mutations will improve understanding of the molecular mechanisms of gliomagenesis and may lead to development of a new molecular classification system and novel therapies.     

IDH mutations occur frequently in Chinese glioma patients and predict longer survival but not response to concomitant chemoradiotherapy in anaplastic gliomas

Mutations in the isocitrate dehydrogenase 1 and 2 genes (IDH1 and IDH2) appear to occur frequently and selectively in gliomas. Our aim was to assess whether IDH mutations are common in Chinese glioma patients and whether the mutations predict good response to concomitant chemoradiotherapy. In this study IDH1 and IDH2 mutations were detected in a series of 203 gliomas. IDH1 mutations were present in 75 of the 203 cases (36.9%) while IDH2 mutations in 5 of the 203 cases (2.5%). No tumor was mutated in both IDH1 and IDH2. IDH1/2 mutations were associated with prolonged overall survival in the whole series of patients exclusive of pilocytic astrocytoma (P<0.001), WHO grade Ⅱ patients who received no adjuvant therapy after surgery (P=0.014) and WHO grade Ⅲ patients who received concomitant chemoradiotherapy (standard schedule) after surgery (P=0.033). Furthermore, there was no correlation between IDH1/2 mutations and reponse to concomitant chemoradiotherapy in anaplastic gliomas. Our results suggest that IDH1 mutations also occur freuqently in Chinese glioma patients but the frequency of IDH1 mutations is below the findings reported by North American and European groups. Furthermore, we confirm the prognostic significance of IDH1/2 mutations in gliomas, but the mutations cannot predict a favorable response to concomitant chemoradiotherapy in anaplastic gliomas.