Tissue metabolites in diffuse glioma and their modulations by IDH1 mutation, histology, and treatment.

The discovery of the oncometabolite 2-hydroxyglutarate in isocitrate dehydrogenase 1-mutated (IDH1-mutated) tumor entities affirmed the role of metabolism in cancer. However, large databases with tissue metabolites that are modulated by IDH1 mutation remain an area of development. Here, we present an unprecedented and valuable resource for tissue metabolites in diffuse glioma and their modulations by IDH1 mutation, histology, and tumor treatments in 101 tissue samples from 73 diffuse glioma patients (24 astrocytoma, 17 oligodendroglioma, 32 glioblastoma), investigated by NMR-based metabolomics and supported by RNA-Seq. We discovered comparison-specific metabolites and pathways modulated by IDH1 (IDH1 mutation status cohort) and tumor entity. The Longitudinal investigation cohort provides metabolic profiles of untreated and corresponding treated glioma samples at first progression. Most interestingly, univariate and multivariate cox regressions and Kaplan-Meier analyses revealed that tissue metabolites correlate with progression-free and overall survival. Thus, this study introduces potentially novel candidate prognostic and surrogate metabolite biomarkers for future prospective clinical studies, aiming at further refining patient stratification in diffuse glioma. Furthermore, our data will facilitate the generation of so-far-unanticipated hypotheses for experimental studies to advance our molecular understanding of glioma biology.

AHA1 upregulates IDH1 and metabolic activity to promote growth and metastasis and predicts prognosis in osteosarcoma.

Osteosarcoma (OS) is the most common primary malignant bone tumor in children and adolescents. Although activator of HSP90 ATPase activity 1 (AHA1) is reported to be a potential oncogene, its role in osteosarcoma progression remains largely unclear. Since metabolism reprogramming is involved in tumorigenesis and cancer metastasis, the relationship between AHA1 and cancer metabolism is unknown. In this study, we found that AHA1 is significantly overexpressed in osteosarcoma and related to the prognosis of osteosarcoma patients. AHA1 promotes the growth and metastasis of osteosarcoma both in vitro and in vivo. Mechanistically, AHA1 upregulates the metabolic activity to meet cellular bioenergetic needs in osteosarcoma. Notably, we identified that isocitrate dehydrogenase 1 (IDH1) is a novel client protein of Hsp90-AHA1. Furthermore, the IDH1 protein level was positively correlated with AHA1 in osteosarcoma. And IDH1 overexpression could partially reverse the effect of AHA1 knockdown on cell growth and migration of osteosarcoma. Moreover, high IDH1 level was also associated with poor prognosis of osteosarcoma patients. This study demonstrates that AHA1 positively regulates IDH1 and metabolic activity to promote osteosarcoma growth and metastasis, which provides novel prognostic biomarkers and promising therapeutic targets for osteosarcoma patients.

Does the expression of glial fibrillary acid protein (GFAP) stain in glioblastoma tissue have a prognostic impact on survival?

OBJECTIVE: Several parameters are known to predict the survival of glioblastoma (GB), including extent of resection and MGMT promotor methylation. Staining for glial fibrillary acidic protein (GFAP) is a common component of routine histological work-up, but its clinical utility in GB is unclear. The aim of the present study was to analyze the predictive value of quantitative GFAP measurements for survival of patients with GB. METHODS: All subjects in our institutional database of patients with primary GB who underwent surgery between 2011 and 2014 with examination of immunohistochemical staining of GFAP were included. Percentage GFAP staining was measured in 5% increments (5-100%). Univariate and multivariate analyses were performed between GFAP values and survival data. Clinically relevant cut-offs for GFAP staining were identified by receiver operating characteristic (ROC) curves. RESULTS: The final cohort consisted of 272GB patients with available quantitative GFAP measurements (mean age, 62 (±11.1) years, 117 females [43%]). Overall survival was 11.4 months (±8.6). Median GFAP value was 70% (range, 5-100%). The ROC curve showed the clinically relevant cut-off for GFAP at 75% (area under the curve: 0.691). Accordingly, GB patients with GFAP≥75% presented poorer survival on Kaplan-Meier survival estimation (P=0.021). Multivariate analysis adjusted for age, extent of resection, preoperative Karnofsky performance status scale, IDH1 mutation and MGMT methylation status confirmed the independent predictive value of GFAP≥75% for overall survival (P=0.032). Finally, patients with GFAP≥75% showed significantly poorer long-term survival than those with GFAP<75%: 5.8% vs. 15.2% (P=0.0183) and 0.8% vs. 8% (P=0.0076) for 2- and 3-year survival, respectively. CONCLUSION: Quantitative immunohistochemical assessment of GFAP staining could provide a novel biomarker for overall and especially long-term survival of patients with GB. Prospective multi-center validation of the prognostic value of GFAP for GB survival is needed.

Correlation of IDH1 and B7H3 expression with prognosis of CRC patients.

BACKGROUND: B7H3 is an immuno-stimulatory glycoprotein that is overexpressed in cancer. However, its functional contributions to cancer development and progression are not well understood. In several reports, it was demonstrated that B7H3 reprograms lipid metabolism and regulates glucose metabolism. Isocitrate dehydrogenase 1 (IDH1), a metabolic enzyme in the TCA cycle, its reaction product is involved in lipid synthesis. Thus, we aimed to identify a novel marker to predict the prognosis of CRC patients and to investigate the relationship between IDH1 and B7H3. METHODS: We analyzed IDH1 and B7H3 expression levels in 225 CRC specimens by immunochemistry. Moreover, in vitro studies were performed to demonstrate the correlation between IDH1 and B7H3. RESULTS: Among 225 tissues, the positive rates of IDH1 and B7H3 were 37.8% (85/225) and 87.6% (197/225), respectively. In CRC samples, IDH1 significantly correlated with B7H3 expression (P = 0.044). Moreover, multivariate analyses revealed that high expression of both B7H3 and IDH1 and a high tumor grade were related to the prognosis of CRC patients. Kaplan-Meier survival analysis revealed that patients with co-expression of IDH1 and B7H3 had a poor overall survival. In SW480B7H3-EGFP cells, which highly express B7H3, IDH1 was up-regulated. Similarly, knockdown of B7H3 expression in Caco-2-shB7-H3 contributed to reduced IDH1 levels. CONCLUSIONS: Although IDH1 and B7H3 cannot be used as independent prognostic factors, co-expression of IDH1 and B7H3 significantly correlated with the prognosis of CRC patients and may serve as a combined predictive marker. Thus, the correlation between IDH1 and B7H3 has been proven in vivo and in vitro.

Diffuse Astrocytoma, IDH-Wildtype: A Dissolving Diagnosis.

The histological and molecular features and even the mere existence of diffuse astrocytoma, IDH-wildtype, remain unclear. We therefore examined 212 diffuse astrocytomas (grade II WHO) in adults using IDH1(R132H) immunohistochemistry followed by IDH1/IDH2 sequencing and neuroimaging review. DNA methylation status and copy number profiles were assessed by Infinium HumanMethylation450k BeadChip. Only 25/212 patients harbored tumors without IDH1/IDH2 hotspot mutations and without contrast enhancement. By DNA methylation profiling, 10/25 tumors were classified as glioblastoma, IDH-wildtype, and an additional 7 cases could not be classified using methylome analysis, but showed genetic characteristics of glioblastoma. Histologically, all of these 17 tumors were low-grade diffuse astrocytomas. Nevertheless, 10/17 patients experienced early malignant progression. Other methylation classes included diffuse midline glioma, H3 K27M-mutant, diffuse astrocytoma, IDH-mutant, pilocytic astrocytoma, and normal or reactive brain tissue (total n = 8). In conclusion, no convincing diffuse astrocytoma, IDH-wildtype, was identified. Most IDH-wildtype tumors showing histopathological and radiological features of low-grade diffuse astrocytoma exhibit molecular and clinical features of high-grade glioma and may represent an early stage of primary glioblastoma. Our findings have implications for the biology, classification and neuropathological diagnosis of diffuse astrocytoma, IDH-wildtype in adults.

New Clues in the Malignant Progression of Glioblastoma: Can the Thioredoxin System Play a Role?

AIM: To evaluate and compare the expression of thioredoxin reductase 1 (TrxR1) in primary and secondary glioblastoma samples. MATERIAL AND METHODS: Surgically resected human glioblastoma samples from 40 patients who underwent surgery at our institution were extracted from their histopathological specimens and divided into three groups. Ten histopathologically regular cerebral tissue samples, acquired from the non-neoplastic portion of the specimens, were assigned as the control group. Twenty specimens that included tumoral tissue from each type of glioblastoma (WHO grade IV, primary and secondary) were assigned as the primary and secondary glioblastoma groups. TrxR1 expression was analyzed by using both quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry. Isocitrate dehydrogenase 1 (IDH1) mutation was analyzed by immunohistochemistry. Ki-67 proliferative index and apoptosis were also analyzed by immunohistochemistry. The differences between the groups were statistically compared and the correlation between these parameters was analyzed. RESULTS: The expressions of TrxR1 and Ki-67 values were significantly higher in primary glioblastoma. IDH1 mutation was significantly higher in secondary glioblastoma. TrxR1 expression was found to be highly correlated with the Ki-67 index. The apoptotic index was similar between primary and secondary glioblastoma. CONCLUSION: This study showed a high TrxR1 expression in primary glioblastoma which could indicate a role of the Trx system in promoting the malignant progression by some complex processes.

A simple algorithmic approach using histology and immunohistochemistry for the current classification of adult diffuse glioma in a resource-limited set-up.

AIMS: The WHO 2016 classification of diffuse gliomas combines histological and molecular parameters for diagnosis. However, in view of cost constraints for molecular testing, an economical working formula is essential to reach a meaningful diagnosis in a resource-limited setting. The aim of this study was to establish a practical algorithmic approach using histology and immunohistochemistry (IHC) in the classification of diffuse gliomas in such a set-up. METHODS: Diffuse gliomas of WHO grade II and III diagnosed in our institute in the year 2016 were analysed for histological and IHC features, using the markers isocitrate dehydrogenase 1 (IDH1R132H) and α thalassemia/mental retardation syndrome X-linked gene (ATRX). Fluorescence in situ hybridisation (FISH) for 1p/19q co-deletion was performed when requested. RESULTS: 449 diffuse gliomas (grades II/III) were included in the study. Integrating histology and IHC features, as per the WHO 2016 guidelines, we derived the following groups: Astrocytoma, IDH-mutant (A,IDH-mt, 37.2%); astrocytoma, not otherwise specified (A,NOS, 12.7%); oligoastrocytoma, NOS (OA,NOS, 4.5%); and oligodendroglioma, NOS (ODG,NOS, 45.6%). FISH was performed in a subset of ODG,NOS, OA,NOS and A,NOS gliomas. This revealed 1p/19q co-deletion in all cases of ODG,NOS, 15.8% of OA,NOS and 37.5% of A,NOS. Sequencing for rare IDH 1/2 mutations was not carried out in this study. CONCLUSION: In a resource-limited set-up, histology with IHC (IDH1(R132H) and ATRX) form the baseline to reasonably derive four histomolecular subgroups of diffuse glioma. Of these, we recommend, OA,NOS and IDH1(R132H)-non-mt ODG,NOS to be our priority for performing 1p/19q co-deletion studies in comparison to IDH-mt ODG,NOS, and it would not be mandatory for astrocytoma. Sequencing for rare IDH mutations is advised for A,NOS and OA,NOS groups, but not for the IDH1(R132H)-non-mutant diffuse gliomas with 1p/19q co-deletion.

Expression of Idh1R132H in the Murine Subventricular Zone Stem Cell Niche Recapitulates Features of Early Gliomagenesis.

Isocitrate dehydrogenase 1 mutations drive human gliomagenesis, probably through neomorphic enzyme activity that produces D-2-hydroxyglutarate. To model this disease, we conditionally expressed Idh1R132H in the subventricular zone (SVZ) of the adult mouse brain. The mice developed hydrocephalus and grossly dilated lateral ventricles, with accumulation of 2-hydroxyglutarate and reduced α-ketoglutarate. Stem and transit amplifying/progenitor cell populations were expanded, and proliferation increased. Cells expressing SVZ markers infiltrated surrounding brain regions. SVZ cells also gave rise to proliferative subventricular nodules. DNA methylation was globally increased, while hydroxymethylation was decreased. Mutant SVZ cells overexpressed Wnt, cell-cycle and stem cell genes, and shared an expression signature with human gliomas. Idh1R132H mutation in the major adult neurogenic stem cell niche causes a phenotype resembling gliomagenesis.

Isocitrate Dehydrogenase 2 Dysfunction Contributes to 5-hydroxymethylcytosine Depletion in Gastric Cancer Cells.

The isocitrate dehydrogenase (IDH) family of enzymes comprises of the key functional metabolic enzymes in the Krebs cycle that catalyze the conversion of isocitrate to α-ketoglutarate (α-KG). α-KG acts as a cofactor in the conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). However, the relationship between 5hmC and IDH in gastric cancer remains unclear. Our study revealed that the 5hmC level was substantially lower and 5mC level was slightly higher in gastric cancer tissues; however, 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) levels did not change significantly in these tissues. We further examined the expression levels of IDH1 and IDH2 in gastric cancer tissues and observed that IDH2 levels were significantly lower in gastric cancer tissues than in the adjacent normal tissues. The ectopic expression of IDH2 can increase 5hmC levels in gastric cancer cells. In conclusion, our results suggested that IDH2 dysfunction is involved in 5hmC depletion during gastric cancer progression.

[The expression of IDH1 (R132H) is positively correlated with cell proliferation and angiogenesis in glioma samples].

OBJECTIVE: To explore the correlations of the expression of mutant isocitrate dehydrogenase (IDH1) (R132H) protein with angiogenesis and cell proliferation in glioma. METHODS: We performed polymerase chain reaction-based IDH gene mutation screening in 385 glioma samples, and the subcellular localization and expression levels of IDH1 (R132H) was examined by immunohistochemistry (IHC). Ki-67 labeling index was introduced to determine the proliferation of glioma cells, and the microvessel density was measured through CD34 staining. Statistical analyses were performed to show the correlations of IDH1 mutation with cell proliferation and microvessel density. RESULTS: The mutant rates of IDH1 were about 50%-60% in grade II-III gliomas and secondary glioblastomas, which were significantly higher than those in pilocytic astrocytoma (grade I) and primary glioblastoma (grade IV). Moreover, the level of IDH1 (R132H) protein was positively correlated with Ki-67 labeling index and microvessel density. CONCLUSION: IDH mutation was common in grade II-III glioma and secondary glioblastoma, and the mutant IDH1 (R132H) might play a critical role in the cell proliferation and angiogenesis of glioma.

Isocitrate dehydrogenase 2 inhibits gastric cancer cell invasion via matrix metalloproteinase 7.

Isocitrate dehydrogenase 2 (IDH2) is a mitochondrial NADP-dependent isocitrate dehydrogenase and has been found to be a tumor suppressor in several types of tumors. However, the roles of IDH2 in hepatocellular carcinoma (GC) as well as underlying mechanisms remain unknown. Here, the IDH2 and matrix metalloproteinase 7 (MMP7) levels in the specimens from 30 GC patients were investigated by Western blot and ELISA, respectively. Their relationship was examined by correlation analyses. Patient survival with high IDH2 levels and low IDH2 levels was compared. IDH2 levels, and MMP7 levels were modified in a human GC cell line. The effects of IDH2 or MMP7 modulation on the expression of each other were analyzed. The dependence of nuclear factor κB (NF-κB) signaling was examined using a specific inhibitor. We found that the IDH2 levels significantly decreased in GC, and were even lower in GC with metastases, compared to those without metastases. IDH2 levels inversely correlated with MMP7 levels in GC. GC patients with low IDH2 had lower 5-year survival. MMP7 levels did not regulate IDH2 levels, while IDH2 inhibited MMP7 levels in GC cells, in a NF-κB signaling dependent manner. Together, these data suggest that IDH2 may be a tumor suppressor in that its loss may promote malignant progression of GC via NF-κB-dependent increases in MMP7 activity.

IDH1, a CHOP and C/EBPß-responsive gene under ER stress, sensitizes human melanoma cells to hypoxia-induced apoptosis.

Isocitrate dehydrogenase1 (IDH1) is of great importance in cell metabolism and energy conversion. However, alterations in IDH1 in response to stress and excise-regulated mechanisms are not well described. Here we investigated gene expression profiles under ER stress in melanoma cells and found that IDH1 was dramatically increased with ER stress induced by tunicamycin. Elevated IDH1 subsequently sensitized human melanoma cells to hypoxia-induced apoptosis and promoted HIF-1α degradation. In addition, we revealed that CHOP and C/EBPß were involved in hypoxia-induced apoptosis via transcriptional regulation of IDH1 expression. Our data indicate that IDH1, regulated by CHOP and C/EBPß in response to ER stress treatment, inhibits survival of melanoma cells under hypoxia and promotes HIF-1α degradation. Therefore, we propose that IDH1 may serve as a valuable target for melanoma therapy.

Prognostic significance of the markers IDH1 and YKL40 related to the subventricular zone.

Glioblastoma multiforme (GBM), a highly aggressive brain cancer characterized by uncontrolled proliferation, resistance to cell death, angiogenesis, and vascular edema, remains one of the deadliest types of cancer. The subventricular zone (SVZ) harbors cells with great proliferative potential, and the microenvironment within the SVZ is permissive to growth and proliferation. This neurogenic niche is suspected to be a vulnerable site for the origin of subtypes of GBM. The aim of our study was to determine the immunohistochemical expression of mIDH1 and YKL40 in relationship to the SVZ of GBMs. YKL40, also known as chitinase-like protein 1, is included as a mesenchymal marker and associated with a poor prognosis. The protein is a secreted inflammatory molecule with no chitinolytic activity. However, the mutation of IDH1 (mIDH1) has been found in the cytoplasm and peroxisomes of 70-80% of secondary GBMs. In our study we found that YKL40-positive GBM is significantly linked to SVZ types IV and V (p < 0.0001). Our results show the diversity among GBMs related to the SVZ, which should be considered in the design of future targeted therapies. There was a significant impact of patient age, mIDH1 positivity, SVZ type III, and chemoradiotherapy on overall survival.

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 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.

Identification of proteins responsible for adriamycin resistance in breast cancer cells using proteomics analysis.

Chemoresistance is a poor prognostic factor in breast cancer and is a major obstacle to the successful treatment of patients receiving chemotherapy. However, the precise mechanism of resistance remains unclear. In this study, a pair of breast cancer cell lines, MCF-7 and its adriamycin-resistant counterpart MCF-7/ADR was used to examine resistance-dependent cellular responses and to identify potential therapeutic targets. We applied nanoflow liquid chromatography (nLC) and tandem mass tags (TmT) quantitative mass spectrometry to distinguish the differentially expressed proteins (DEPs) between the two cell lines. Bioinformatics analyses were used to identify functionally active proteins and networks. 80 DEPs were identified with either up- or down-regulation. Basing on the human protein-protein interactions (PPI), we have retrieved the associated functional interaction networks for the DEPs and analyzed the biological functions. Six different signaling pathways and most of the DEPs strongly linked to chemoresistance, invasion, metastasis development, proliferation, and apoptosis. The identified proteins in biological networks served to resistant drug and to select critical candidates for validation analyses by western blot. The glucose-6-phosphate dehydrogenase (G6PD), gamma-glutamyl cyclotransferase (GGCT), isocitrate dehydrogenase 1 (NADP+,soluble)(IDH1), isocitrate dehydrogenase 2 (NADP+,mitochondrial) (IDH2) and glutathione S-transferase pi 1(GSTP1), five of the critical components of GSH pathway, contribute to chemoresistance.

Mutant IDH is sufficient to initiate enchondromatosis in mice.

Enchondromas are benign cartilage tumors and precursors to malignant chondrosarcomas. Somatic mutations in the isocitrate dehydrogenase genes (IDH1 and IDH2) are present in the majority of these tumor types. How these mutations cause enchondromas is unclear. Here, we identified the spectrum of IDH mutations in human enchondromas and chondrosarcomas and studied their effects in mice. A broad range of mutations was identified, including the previously unreported IDH1-R132Q mutation. These mutations harbored enzymatic activity to catalyze α-ketoglutarate to d-2-hydroxyglutarate (d-2HG). Mice expressing Idh1-R132Q in one allele in cells expressing type 2 collagen showed a disordered growth plate, with persistence of type X-expressing chondrocytes. Chondrocyte cell cultures from these animals or controls showed that there was an increase in proliferation and expression of genes characteristic of hypertrophic chondrocytes with expression of Idh1-R132Q or 2HG treatment. Col2a1-Cre;Idh1-R132Q mutant knock-in mice (mutant allele expressed in chondrocytes) did not survive after the neonatal stage. Col2a1-Cre/ERT2;Idh1-R132 mutant conditional knock-in mice, in which Cre was induced by tamoxifen after weaning, developed multiple enchondroma-like lesions. Taken together, these data show that mutant IDH or d-2HG causes persistence of chondrocytes, giving rise to rests of growth-plate cells that persist in the bone as enchondromas.

Selective inhibition of mutant isocitrate dehydrogenase 1 (IDH1) via disruption of a metal binding network by an allosteric small molecule.

Cancer-associated point mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) confer a neomorphic enzymatic activity: the reduction of α-ketoglutarate to d-2-hydroxyglutaric acid, which is proposed to act as an oncogenic metabolite by inducing hypermethylation of histones and DNA. Although selective inhibitors of mutant IDH1 and IDH2 have been identified and are currently under investigation as potential cancer therapeutics, the mechanistic basis for their selectivity is not yet well understood. A high throughput screen for selective inhibitors of IDH1 bearing the oncogenic mutation R132H identified compound 1, a bis-imidazole phenol that inhibits d-2-hydroxyglutaric acid production in cells. We investigated the mode of inhibition of compound 1 and a previously published IDH1 mutant inhibitor with a different chemical scaffold. Steady-state kinetics and biophysical studies show that both of these compounds selectively inhibit mutant IDH1 by binding to an allosteric site and that inhibition is competitive with respect to Mg(2+). A crystal structure of compound 1 complexed with R132H IDH1 indicates that the inhibitor binds at the dimer interface and makes direct contact with a residue involved in binding of the catalytically essential divalent cation. These results show that targeting a divalent cation binding residue can enable selective inhibition of mutant IDH1 and suggest that differences in magnesium binding between wild-type and mutant enzymes may contribute to the inhibitors' selectivity for the mutant enzyme.

Aberrant IDH3α expression promotes malignant tumor growth by inducing HIF-1-mediated metabolic reprogramming and angiogenesis.

Cancer cells gain a growth advantage through the so-called Warburg effect by shifting glucose metabolism from oxidative phosphorylation to aerobic glycolysis. Hypoxia-inducible factor 1 (HIF-1) has been suggested to function in metabolic reprogramming; however, the underlying mechanism has not been fully elucidated. We found that the aberrant expression of wild-type isocitrate dehydrogenase 3α (IDH3α), a subunit of the IDH3 heterotetramer, decreased α-ketoglutarate levels and increased the stability and transactivation activity of HIF-1α in cancer cells. The silencing of IDH3α significantly delayed tumor growth by suppressing the HIF-1-mediated Warburg effect and angiogenesis. IDH3α expression was associated with the poor postoperative overall survival of lung and breast cancer patients. These results justify the exploitation of IDH3 as a novel target for the diagnosis and treatment of cancers.

Decreasing GSH and increasing ROS in chemosensitivity gliomas with IDH1 mutation.

Gliomas are the most malignant and aggressive primary brain tumor in adults. Despite concerted efforts to improve therapies, their prognosis remains very poor. Isocitrate dehydrogenase 1 (IDH1) mutations have been discovered frequently in glioma patients and are strongly correlated with improved survival. However, the effect of IDH1 mutations on the chemosensitivity of gliomas remains unclear. In this study, we generated clonal U87 and U251 glioma cell lines overexpressing the R132H mutant protein (IDH1-R132H). Compared with control cells and cells overexpressing IDH wild type (IDH1-WT), both types of IDH1-R132H cells were more sensitive to temozolomide (TMZ) and cis-diamminedichloroplatinum (CDDP) in a time- and dose-dependent manner. The IDH1-R132H-induced higher chemosensitivity was associated with nicotine adenine disphosphonucleotide (NADPH), glutathione (GSH) depletion, and reactive oxygen species (ROS) generation. Accordingly, this IDH1-R132H-induced growth inhibition was effectively abrogated by GSH in vitro and in vivo. Our study provides direct evidence that the improved survival in patients with IDH1-R132H tumors may partly result from the effects of the IDH1-R132H protein on chemosensitivity. The primary cellular events associated with improved survival are the GSH depletion and increased ROS generation.