Isocitrate Dehydrogenase 1 Tumors Research Articles

Combination of isocitrate dehydrogenase 1 (IDH1) mutation and podoplanin expression in brain tumors identifies patients at high or low risk of venous thromboembolism

Essentials Risk stratification for venous thromboembolism (VTE) in patients with brain tumors is challenging.Patients with IDH1 wildtype and high podoplanin expression have a 6‐month VTE risk of 18.2%.Patients with IDH1 mutation and no podoplanin expression have a 6‐month VTE risk of 0%. IDH1 mutation and podoplanin overexpression in primary brain tumors appear to be exclusive. SummaryBackgroundVenous thromboembolism (VTE) is a frequent complication in primary brain tumor patients. Independent studies revealed that podoplanin expression in brain tumors is associated with increased VTE risk, whereas the isocitrate dehydrogenase 1 (IDH1) mutation is associated with very low VTE risk.ObjectivesTo investigate the interrelation between intratumoral podoplanin expression and IDH1 mutation, and their mutual impact on VTE development.Patients/MethodsIn a prospective cohort study, intratumoral IDH1 R132H mutation and podoplanin were determined in brain tumor specimens (mainly glioma) by immunohistochemistry. The primary endpoint of the study was symptomatic VTE during a 2‐year follow‐up.ResultsAll brain tumors that expressed podoplanin to a medium‐high extent showed also an IDH1 wild‐type status. A score based on IDH1 status and podoplanin expression levels allowed prediction of the risk of VTE. Patients with wild‐type IDH1 brain tumors and high podoplanin expression had a significantly increased VTE risk compared with those with mutant IDH1 tumors and no podoplanin expression (6‐month risk 18.2% vs. 0%).Conclusions IDH1 mutation and podoplanin overexpression seem to be exclusive. Although brain tumor patients with IDH1 mutation are at very low risk of VTE, the risk of VTE in patients with IDH1 wild‐type tumors is strongly linked to podoplanin expression levels.

Synthesis and evaluation of radiolabeled AGI-5198 analogues as candidate radiotracers for imaging mutant IDH1 expression in tumors

Mutations in the metabolic enzyme isocitrate dehydrogenase 1 (IDH1) are commonly found in gliomas. AGI-5198, a potent and selective inhibitor of the mutant IDH1 enzyme, was radiolabeled with radioiodine and fluorine-18. These radiotracers were evaluated as potential probes for imaging mutant IDH1 expression in tumors with positron emission tomography (PET). Radioiodination of AGI-5198 was achieved using a tin precursor in 79 ± 6% yield (n = 9), and 18F-labeling was accomplished by the Ugi reaction in a decay-corrected radiochemical yield of 2.6 ± 1.6% (n = 5). The inhibitory potency of the analogous nonradioactive compounds against mutant IDH1 (IDH1-R132H) was determined in enzymatic assays. Cell uptake studies using radiolabeled AGI-5198 analogues revealed somewhat higher uptake in IDH1-mutated cells than that in wild-type IDH1 cells. The radiolabeled compounds displayed favorable tissue distribution characteristics in vivo, and good initial uptake in IDH1-mutated tumor xenografts; however, tumor uptake decreased with time. Radioiodinated AGI-5198 exhibited higher tumor-to-background ratios compared with 18F-labeled AGI-5198; unfortunately, similar results were observed in wild-type IDH1 tumor xenografts as well, indicating lack of selectivity for mutant IDH1 for this tracer. These results suggest that AGI-5198 analogues are not a promising platform for radiotracer development. Nonetheless, insights gained from this study may help in design and optimization of novel chemical scaffolds for developing radiotracers for imaging the mutant IDH1 enzyme.

The role of FilGAP, a Rac-specific Rho-GTPase-activating protein, in tumor progression and behavior of astrocytomas.

FilGAP, a Rac‐specific Rho‐GTPase‐activating protein (GAP), acts as a mediator of Rho/ROCK‐dependent amoeboid movement, and its knockdown results in Rac‐driven mesenchymal morphology. Herein, we focused on the possible roles of FilGAP expression in astrocytomas. In clinical samples, FilGAP expression was significantly increased in grade (G) II astrocytomas as compared to normal astrocytes, but its expression strongly decreased in a grade‐dependent manner, and was positively associated with isocitrate dehydrogenase 1 (IDH1) mutations and inversely to cytoplasmic Rac1. Patients with astrocytoma showing a high FilGAP score had favorable overall survival as compared to the low score patients. Multivariate Cox regression analysis also showed that a high FilGAP score was a significant and independent favorable prognostic factor. Moreover, patients with high FilGAP score and IDH1 mutant‐type astrocytomas had significantly the best Overall survival (OS) and Progression‐free survival (PFS), in contrast to the patients with low FilGAP score and wild‐type IDH1 tumors who had the worst prognosis. In GIV tumors (GBM: glioblastomas), elongated tumor cells with low FilGAP expression were frequently observed in tumor core lesions, whereas the rounded cells with abundant expression were found in the peripheral areas adjacent to non‐neoplastic brain tissues. In an astrocytoma cell line, suppression of endogenous FilGAP expression by siRNAs caused an increased proportion of mesenchymal elongated cells, probably through increased Rac1 activity. These findings suggest that FilGAP, as well as IDH1 status, may be useful for predicting the behavior of astrocytomas. In addition, the FilGAP/Rac1 axis may serve as an important regulator of tumor progression in GBMs, probably through alteration of cell morphology.

Abstract 1847: The mRNA-binding protein HuR, regulates mutant and wild type IDH1 expression in IDH1-mutated cancer

Abstract Introduction: Isocitrate dehydrogenase 1 (IDH1) is mutated in various types of human cancers, predominantly an arginine to histidine amino acid change at codon 132. This structural alteration drives the catalysis of α-ketoglutarate to the oncometabolite D-2-hydroxyglutarate (2HG), which enhances DNA and protein hypermethylation and cellular dedifferentiation. Pharmacologic inhibitors of the mutant IDH1 protein show promise in clinical trials, yet the regulation of IDH1 has not been fully elucidated. We recently discovered in wild type IDH1 tumors that the regulatory RNA-binding and stress response protein, HuR (ELAVL1), protects cancer cells under nutrient deprivation by regulating the expression of core metabolic enzymes, including IDH1. We mapped the regulatory HuR binding site on the IDH1 transcript to the 3’-untranslated region. Since wild type and mutant IDH1 alleles both contain this binding sequence, we hypothesize that HuR is an important regulator of both isozymes and is biologically important in mutant IDH1 tumors. Methods: HuR expression was suppressed by siRNA in a fibrosarcoma cell line (HT-1080) harboring a natural heterozygous IDH1 mutation and cell viability was determined by PicoGreen and Trypan blue exclusion assays. Sensitivity to pharmacologic inhibition of the mutant IDH1 protein was assessed. Sanger sequencing and mRNP-IP were performed to determine HuR's impact on the expression of each IDH1 allele. To further characterize the post-transcriptional regulation of IDH1 by HuR, CRISPR/CAS 9 editing of the HuR gene was performed. Results: Sanger sequencing of IDH1 after depletion of HuR in HT1080 cells, as well as after HuR mRNP-IP, revealed that HuR regulates both the mutant and wild type IDH1. Drug sensitivity assays to a mutant IDH1 inhibitor (AGI-5198) under varying glucose concentrations revealed glucose deprivation to be a novel driver of chemo-resistance. However, HuR silencing abrogated HT1080 resistance to AGI-5198 under these conditions. Targeted knockout of HuR using the CRISPR/CAS9 system resulted in potent suppression of mutant and wild type IDH1, at both the mRNA and protein levels when compared to CRISPR/Cas9 control. Conclusions: These findings reveal that harsh metabolic conditions present in the tumor microenvironment induce chemo-resistance in an IDH1 mutant cell line to a mutant IDH1 inhibitor, in an HuR dependent manner. Moreover, both mutant and wild type IDH1 alleles are potently regulated by HuR. Therapeutic strategies that target the HuR-IDH1 axis and block this resistance mechanism may enhance the efficacy of mutant IDH1 inhibitors for relevant tumors. Citation Format: Mahsa Zarei, Shruti Lal, Nicole C. Mambelli-Lisboa, Edwin Cheung, Saswati N. Chand, Charles J. Yeo, Jonathan R. Brody, Jordan M. Winter. The mRNA-binding protein HuR, regulates mutant and wild type IDH1 expression in IDH1-mutated cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1847.

Mutant IDH1 expression is associated with down-regulation of monocarboxylate transporters.

Mutations in isocitrate dehydrogenase 1 (IDH1) are characteristic of low-grade gliomas. We recently showed that mutant IDH1 cells reprogram cellular metabolism by down-regulating pyruvate dehydrogenase (PDH) activity. Reduced pyruvate metabolism via PDH could lead to increased pyruvate conversion to lactate. The goal of this study was therefore to investigate the impact of the IDH1 mutation on the pyruvate-to-lactate flux. We used 13C magnetic resonance spectroscopy and compared the conversion of hyperpolarized [1-13C]-pyruvate to [1-13C]-lactate in immortalized normal human astrocytes expressing mutant or wild-type IDH1 (NHAIDHmut and NHAIDHwt). Our results indicate that hyperpolarized lactate production is reduced in NHAIDHmut cells compared to NHAIDHwt. This reduction was associated with lower expression of the monocarboxylate transporters MCT1 and MCT4 in NHAIDHmut cells. Furthermore, hyperpolarized lactate production was comparable in lysates of NHAIDHmut and NHAIDHwt cells, wherein MCTs do not impact hyperpolarized pyruvate delivery and lactate production. Collectively, our findings indicated that lower MCT expression was a key contributor to lower hyperpolarized lactate production in NHAIDHmut cells. The SLC16A3 (MCT4) promoter but not SLC16A1 (MCT1) promoter was hypermethylated in NHAIDHmut cells, pointing to possibly different mechanisms mediating reduced MCT expression. Finally analysis of low-grade glioma patient biopsy data from The Cancer Genome Atlas revealed that MCT1 and MCT4 expression was significantly reduced in mutant IDH1 tumors compared to wild-type. Taken together, our study shows that reduced MCT expression is part of the metabolic reprogramming of mutant IDH1 gliomas. This finding could impact treatment and has important implications for metabolic imaging of mutant IDH1 gliomas.

Hyperpolarized (13)C MR imaging detects no lactate production in mutant IDH1 gliomas: Implications for diagnosis and response monitoring.

Metabolic imaging of brain tumors using 13C Magnetic Resonance Spectroscopy (MRS) of hyperpolarized [1-13C] pyruvate is a promising neuroimaging strategy which, after a decade of preclinical success in glioblastoma (GBM) models, is now entering clinical trials in multiple centers. Typically, the presence of GBM has been associated with elevated hyperpolarized [1-13C] lactate produced from [1-13C] pyruvate, and response to therapy has been associated with a drop in hyperpolarized [1-13C] lactate. However, to date, lower grade gliomas had not been investigated using this approach. The most prevalent mutation in lower grade gliomas is the isocitrate dehydrogenase 1 (IDH1) mutation, which, in addition to initiating tumor development, also induces metabolic reprogramming. In particular, mutant IDH1 gliomas are associated with low levels of lactate dehydrogenase A (LDHA) and monocarboxylate transporters 1 and 4 (MCT1, MCT4), three proteins involved in pyruvate metabolism to lactate. We therefore investigated the potential of 13C MRS of hyperpolarized [1-13C] pyruvate for detection of mutant IDH1 gliomas and for monitoring of their therapeutic response. We studied patient-derived mutant IDH1 glioma cells that underexpress LDHA, MCT1 and MCT4, and wild-type IDH1 GBM cells that express high levels of these proteins. Mutant IDH1 cells and tumors produced significantly less hyperpolarized [1-13C] lactate compared to GBM, consistent with their metabolic reprogramming. Furthermore, hyperpolarized [1-13C] lactate production was not affected by chemotherapeutic treatment with temozolomide (TMZ) in mutant IDH1 tumors, in contrast to previous reports in GBM. Our results demonstrate the unusual metabolic imaging profile of mutant IDH1 gliomas, which, when combined with other clinically available imaging methods, could be used to detect the presence of the IDH1 mutation in vivo.

Genome-wide transcriptional analyses of Chinese patients reveal cell migration is attenuated in IDH1-mutant glioblastomas

Patients with isocitrate dehydrogenase 1 (IDH1)-mutant glioblastoma exhibit increased survival compared with those with wild-type IDH1 tumors. The magnitude of this finding has led to the use of IDH1 mutations as diagnostic and prognostic biomarkers. However, the mechanisms underlying the reported correlation between the IDH1 mutation and increased survival have not been fully revealed. In this work, based on genome-wide transcriptional analyses of 69 Chinese patients with glioblastoma, we have found that the focal adhesion pathway is significantly downregulated in IDH1-mutant glioblastomas. The impaired focal adhesion leads to compromised cell migration and tumor invasion, contributing to the optimistic prognosis of these patients. Moreover, the signature genes of HIF-1α, the downstream factor of mutated IDH1, are found to be suppressed in IDH1-mutant gliomas. Given the role of HIF-1α in cell migration, we conclude that the attenuation of HIF-1α-dependent glioblastoma cell infiltration contributes to the better outcomes of patients with IDH1-mutant gliomas.

Hyperpolarized [1-13C] Glutamate: A Metabolic Imaging Biomarker of IDH1 Mutational Status in Glioma

Mutations of the isocitrate dehydrogenase 1 (IDH1) gene are among the most prevalent in low-grade glioma and secondary glioblastoma, represent an early pathogenic event, and are associated with epigenetically driven modulations of metabolism. Of particular interest is the recently uncovered relationship between the IDH1 mutation and decreased activity of the branched-chain amino acid transaminase 1 (BCAT1) enzyme. Noninvasive imaging methods that can assess BCAT1 activity could therefore improve detection of mutant IDH1 tumors and aid in developing and monitoring new targeted therapies. BCAT1 catalyzes the transamination of branched-chain amino acids while converting α-ketoglutarate (α-KG) to glutamate. Our goal was to use (13)C magnetic resonance spectroscopy to probe the conversion of hyperpolarized [1-(13)C] α-KG to hyperpolarized [1-(13)C] glutamate as a readout of BCAT1 activity. We investigated two isogenic glioblastoma lines that differed only in their IDH1 status and performed experiments in live cells and in vivo in rat orthotopic tumors. Following injection of hyperpolarized [1-(13)C] α-KG, hyperpolarized [1-(13)C] glutamate production was detected both in cells and in vivo, and the level of hyperpolarized [1-(13)C] glutamate was significantly lower in mutant IDH1 cells and tumors compared with their IDH1-wild-type counterparts. Importantly however, in our cells the observed drop in hyperpolarized [1-(13)C] glutamate was likely mediated not only by a drop in BCAT1 activity, but also by reductions in aspartate transaminase and glutamate dehydrogenase activities, suggesting additional metabolic reprogramming at least in our model. Hyperpolarized [1-(13)C] glutamate could thus inform on multiple mutant IDH1-associated metabolic events that mediate reduced glutamate production.

Using Mutant IDH1 to Arm the Immune System in Cancer

A new antitumor vaccine targets mutant IDH1.

Editorial: Glioblastoma subtype

In this paper, the authors present a retrospective series of 302 consecutively treated patients with “primary” glioblastomas (GBMs).2 They parse the patients into 2 groups, those with labeling for neurofilament protein (NFP) of 1% or greater of tumor cells, and those with less than 1% labeling, based on immunohistochemistry. Using routine (but rigorous) statistical analysis on the 266 patients with adequate follow-up, they found that younger age at presentation, higher Karnofsky Performance Scale score, tumor not crossing the midline on imaging studies, degree of resection, use of adjuvant therapy, and positive staining for NFP were all associated with improved patient survival. Although the patients with positive NFP expression were younger and had more favorable tumor location, the presence of labeling for NFP remained a statistically significant positive prognostic variable on multivariate analysis, with those patients having positive tumor labeling surviving 13 months, compared with 7 months for those with negative tumor labeling. The authors eliminated “secondary” GBM from their analysis, suggesting that these tumors represent a different disease than “primary” tumors. They used clinical history, histopathology, and the presence of isocitrate dehydrogenase 1 (IDH1) mutations to classify and eliminate tumors as secondary. While the IDH1 mutation has been suggested as a marker of secondary GBM, the exact significance of IDH1 mutations is not clear.1,3 In a paper analyzing The Cancer Genome Atlas (TCGA) database for glioblastoma, Verhaak and coworkers4 reported that of 202 tumors, only 4 were secondary, but 12 had IDH1 mutations. Of note, the IDH1 mutations were classified almost exclusively into the proneural GBM subtype, a subtype with a better prognosis than that of the group as a whole. Were the results presented in the current paper biased by removing the IDH1 tumors (representing the good prognosis proneural group) from the NFP-negative tumors? In TCGA analysis, the GBMs were parsed into 4 tumor types based on 1740 genes consistently but variably expressed by the tumors.4 One group of these tumors, the neural subtype, was characterized by NFP expression, but only represented 16% (33/202) of the tumors investigated. Of note, the authors of the current study found that more than half of the patients (177/302, 58.6%) had positive immunohistochemical labeling for NFP, as defined by labeling of at least 1% of tumor cells. The reason for this discrepancy is not clear. Are the tumors identified in this study overlapping into subtypes of GBM other than the neural subtype, as defined by TCGA analysis? Are the 2 study populations simply very different in subgroup makeup, with the NFP-positive tumors truly representing the neural subgroup of GBMs? If the tumors identified as NFP-positive in the current study do represent the neural subgroup of GBMs, then the authors have provided evidence for the better prognosis of this group and have provided an easier way to identify the subgroup than that of gene expression. This situation would be analogous to that of IDH1 mutations; these mutations identify a group of tumors with an improved prognosis, but also label tumors as members of the proneural subgroup, which has been demonstrated to have a better prognosis than that of GBM as a whole.4 Regardless of the answers to questions raised by the data presented here, the authors have provided data that NFP labeling—defined as 1% or more of the tumor cells showing immunohistochemical labeling—is a positive prog nostic variable in the treatment of GBM. The exact meaning of this data will await further studies of patients with GBM that include both immunohistochemical labeling of the tumors for NFP and subtyping of the tumors by expression analysis, allowing for comparison and correlation between the immunohistochemical data and gene expression data. (http://thejns.org/doi/abs/10.3171/2012.1.JNS112254)

R132H-mutation of isocitrate dehydrogenase-1 is not sufficient for HIF-1α upregulation in adult glioma

R132H-mutation of isocitrate dehydrogenase-1 is not sufficient for HIF-1α upregulation in adult glioma