Modeling the diffusion of D-2-hydroxyglutarate from IDH1 mutant gliomas in the central nervous system

IDH inhibition in gliomas: from preclinical models to clinical trials

Gliomas are the most common malignant primary brain tumours in adults and cannot usually be cured with standard cancer treatments. Gliomas show intratumoural and intertumoural heterogeneity at the histological and molecular levels, and they frequently contain mutations in the isocitrate dehydrogenase 1 (IDH1) or IDH2 gene. IDH-mutant adult-type diffuse gliomas are subdivided into grade 2, 3 or 4 IDH-mutant astrocytomas and grade 2 or 3 IDH-mutant, 1p19q-codeleted oligodendrogliomas. The product of the mutated IDH genes, D-2-hydroxyglutarate (D-2-HG), induces global DNA hypermethylation and interferes with immunity, leading to stimulation of tumour growth. Selective inhibitors of mutant IDH, such as ivosidenib and vorasidenib, have been shown to reduce D-2-HG levels and induce cellular differentiation in preclinical models and to induce MRI-detectable responses in early clinical trials. The phase III INDIGO trial has demonstrated superiority of vorasidenib, a brain-penetrant pan-mutant IDH inhibitor, over placebo in people with non-enhancing grade 2 IDH-mutant gliomas following surgery. In this Review, we describe the pathway of development of IDH inhibitors in IDH-mutant low-grade gliomas from preclinical models to clinical trials. We discuss the practice-changing implications of the INDIGO trial and consider new avenues of investigation in the field of IDH-mutant gliomas.

Epilepsy in gliomas: recent insights into risk factors and molecular pathways

PURPOSE OF REVIEW

The purpose of this review is to discuss the molecular pathways governing the development of seizures in glioma patients.

RECENT FINDINGS

The intrinsic epileptogenicity of the neuronal component of glioneuronal and neuronal tumors is the most relevant factor for seizure development. The two major molecular alterations behind epileptogenicity are the rat sarcoma virus (RAS)/mitogen-activated protein kinase / extracellular signal-regulated kinase (MAPK/ERK) and phosphatidylinositol-3-kinase / protein kinase B / mammalian target of rapamycin (P13K/AKT/mTOR) pathways. The BRAFv600E mutation has been shown in experimental models to contribute to epileptogenicity, and its inhibition is effective in controlling both seizures and tumor growth. Regarding circumscribed astrocytic gliomas, either BRAFv600E mutation or mTOR hyperactivation represent targets of treatment. The mechanisms of epileptogenicity of diffuse lower-grade gliomas are different: in addition to enhanced glutamatergic mechanisms, the isocitrate dehydrogenase (IDH) 1/2 mutations and their product D2-hydroxyglutarate (D2HG), which is structurally similar to glutamate, exerts excitatory effects on neurons also dependent on the presence of astrocytes. In preclinical models IDH1/2 inhibitors seem to impact both tumor growth and seizures. Conversely, the molecular factors behind the epileptogenicity of glioblastoma are unknown.

SUMMARY

This review summarizes the current state of molecular knowledge on epileptogenicity in gliomas and highlights the relationships between epileptogenicity and tumor growth.

Glioma Response to IDH Inhibition: Real-World Experience

Treatment of IDH-mutated non-enhancing grade 2 and 3 diffuse gliomas with ivosidenib leads to reduction of tumor size when assessed via volumetric MRI. Isocitrate dehydrogenase inhibition has a therapeutic benefit in patients with these tumors. See related article by Kamson et al., p. 4863.

D-2-hydroxyglutarate regulates human brain vascular endothelial cell proliferation and barrier function

Gain-of-function mutations in isocitrate dehydrogenase (IDH) genes result in excessive production of (D)-2-hydroxyglutarate (D-2HG) which intrinsically modifies tumor cell epigenetics and impacts surrounding noncancerous cells through nonepigenetic pathways. However, whether D-2HG has a paracrine effect on endothelial cells in the tumor microenvironment needs further clarification. We quantified microvessel density by immunohistochemistry using tissue sections from 60 high-grade astrocytic gliomas with or without IDH mutation. Microvessel density was found to be reduced in tumors carrying an IDH mutation. Ex vivo experiments showed that D-2HG inhibited endothelial cell migration, wound healing, and tube formation by suppressing cell proliferation but not viability, possibly through reduced activation of the mTOR/STAT3 pathway. Further, D-2HG reduced fluorescent dextran permeability and decreased paracellular T-cell transendothelial migration by augmenting expression of junctional proteins thereby collectively increasing endothelial barrier function. These results indicate that D-2HG may influence the tumor vascular microenvironment by reducing the intratumoral vasculature density and by inhibiting the transport of metabolites and extravasation of circulating cells into the astrocytoma microenvironment. These observations provide a rationale for combining IDH inhibition with antitumor immunological/angiogenic approaches and suggest a molecular basis for resistance to antiangiogenic drugs in patients whose tumors express a mutant IDH allele.

Postoperative risk of IDH-mutant glioma-associated seizures and their potential management with IDH-mutant inhibitors

Seizures are a frequent complication of adult-type diffuse gliomas, and are often difficult to control with medications. Gliomas with mutations in isocitrate dehydrogenase 1 or 2 (IDHmut) are more likely than IDH-wild type (IDHwt) gliomas to cause seizures as part of their initial clinical presentation. However, whether IDHmut is also associated with seizures during the remaining disease course, and whether IDHmut inhibitors can reduce seizure risk, are unclear. Clinical multivariable analyses showed that preoperative seizures, glioma location, extent of resection, and glioma molecular subtype (including IDHmut status) all contributed to postoperative seizure risk in adult-type diffuse glioma patients, and that postoperative seizures were often associated with tumor recurrence. Experimentally, the metabolic product of IDHmut, d-2-hydroxyglutarate, rapidly synchronized neuronal spike firing in a seizure-like manner, but only when non-neoplastic glial cells were present. In vitro and in vivo models recapitulated IDHmut glioma-associated seizures, and IDHmut inhibitors currently being evaluated in glioma clinical trials inhibited seizures in those models, independent of their effects on glioma growth. These data show that postoperative seizure risk in adult-type diffuse gliomas varies in large part by molecular subtype, and that IDHmut inhibitors could play a key role in mitigating such risk in IDHmut glioma patients.

Mutant IDH in Gliomas: Role in Cancer and Treatment Options

Altered metabolism is a common feature of many cancers and, in some cases, is a consequence of mutation in metabolic genes, such as the ones involved in the TCA cycle. Isocitrate dehydrogenase (IDH) is mutated in many gliomas and other cancers. Physiologically, IDH converts isocitrate to α-ketoglutarate (α-KG), but when mutated, IDH reduces α-KG to D2-hydroxyglutarate (D2-HG). D2-HG accumulates at elevated levels in IDH mutant tumours, and in the last decade, a massive effort has been made to develop small inhibitors targeting mutant IDH. In this review, we summarise the current knowledge about the cellular and molecular consequences of IDH mutations and the therapeutic approaches developed to target IDH mutant tumours, focusing on gliomas.

D-2-Hydroxyglutarate Inhibits Calcineurin Phosphatase Activity to Abolish NF-AT Activation and IL-2 Induction in Stimulated Lymphocytes

Gliomas expressing mutant isocitrate dehydrogenases excessively synthesize d-2-hydroxyglutarate (D2HG), suppressing immune surveillance. A portion of this D2HG is released from these tumor cells, but the way environmental D2HG inhibits lymphocyte function is undefined. We incubated human PBLs or Jurkat T cells with D2HG at concentrations present within and surrounding gliomas or its obverse l-2-hydroxyglutarate (L2HG) stereoisomer. We quantified each 2HG stereoisomer within washed cells by N-(p-toluenesulfonyl)-l-phenylalanyl chloride derivatization with stable isotope-labeled D2HG and L2HG internal standards, HPLC separation, and mass spectrometry. D2HG was present in quiescent cells and was twice as abundant as L2HG. Extracellular 2HG rapidly increased intracellular levels of the provided stereoisomer by a stereoselective, concentration-dependent process. IL-2 expression, even when elicited by A23187 and PMA, was abolished by D2HG in a concentration-dependent manner, with significant reduction at just twice its basal level. In contrast, L2HG was only moderately inhibitory. IL-2 expression is regulated by increased intracellular Ca2+ that stimulates calcineurin to dephosphorylate cytoplasmic phospho-NF-AT, enabling its nuclear translocation. D2HG abolished stimulated expression of a stably integrated NF-AT-driven luciferase reporter that precisely paralleled its concentration-dependent inhibition of IL-2. D2HG did not affect intracellular Ca2+. Rather, surface plasmon resonance showed D2HG, but not L2HG, bound calcineurin, and D2HG, but not L2HG, inhibited Ca2+-dependent calcineurin phosphatase activity in stimulated Jurkat extracts. Thus, D2HG is a stereoselective calcineurin phosphatase inhibitor that prevents NF-AT dephosphorylation and so abolishes IL-2 transcription in stimulated lymphocytes. This occurs at D2HG concentrations found within and adjacent to gliomas independent of its metabolic or epigenetic transcriptional regulation.

New insights into the Immune TME of adult-type diffuse gliomas

PURPOSE OF REVIEW

Adult-type diffuse gliomas are highly heterogeneous tumors. Bulk transcriptome analyses suggested that the composition of the tumor microenvironment (TME) corresponds to genetic and clinical features. In this review, we highlight novel findings on the intratumoral heterogeneity of IDH-wildtype and IDH-mutant gliomas characterized at single-cell resolution, and emphasize the mechanisms shaping the immune TME and therapeutic implications.

RECENT FINDINGS

Emergent evidence indicates that in addition to genetic drivers, epigenetic mechanisms and microenvironmental factors influence the glioma subtypes. Interactions between glioma and immune cells contribute to immune evasion, particularly in aggressive tumors. Spatial and temporal heterogeneity of malignant and immune cell subpopulations is high in recurrent gliomas. IDH-wildtype and IDH-mutant tumors display distinctive changes in their myeloid and lymphoid compartments, and D-2HG produced by IDH-mutant cells impacts the immune TME.

SUMMARY

The comprehensive dissection of the intratumoral ecosystem of human gliomas using single-cell and spatial transcriptomic approaches advances our understanding of the mechanisms underlying the immunosuppressed state of the TME, supports the prognostic value of tumor-associated macrophages and microglial cells, and sheds light on novel therapeutic options.

The Oncogenesis of Glial Cells in Diffuse Gliomas and Clinical Opportunities

Glioma is the most common and lethal intrinsic primary tumor of the brain. Its controversial origins may contribute to its heterogeneity, creating challenges and difficulties in the development of therapies. Among the components constituting tumors, glioma stem cells are highly plastic subpopulations that are thought to be the site of tumor initiation. Neural stem cells/progenitor cells and oligodendrocyte progenitor cells are possible lineage groups populating the bulk of the tumor, in which gene mutations related to cell-cycle or metabolic enzymes dramatically affect this transformation. Novel approaches have revealed the tumor-promoting properties of distinct tumor cell states, glial, neural, and immune cell populations in the tumor microenvironment. Communication between tumor cells and other normal cells manipulate tumor progression and influence sensitivity to therapy. Here, we discuss the heterogeneity and relevant functions of tumor cell state, microglia, monocyte-derived macrophages, and neurons in glioma, highlighting their bilateral effects on tumors. Finally, we describe potential therapeutic approaches and targets beyond standard treatments.

Oncometabolite d-2HG alters T cell metabolism to impair CD8+ T cell function

Gain-of-function mutations in isocitrate dehydrogenase (IDH) in human cancers result in the production of d-2-hydroxyglutarate (d-2HG), an oncometabolite that promotes tumorigenesis through epigenetic alterations. The cancer cell-intrinsic effects of d-2HG are well understood, but its tumor cell-nonautonomous roles remain poorly explored. We compared the oncometabolite d-2HG with its enantiomer, l-2HG, and found that tumor-derived d-2HG was taken up by CD8⁺ T cells and altered their metabolism and antitumor functions in an acute and reversible fashion. We identified the glycolytic enzyme lactate dehydrogenase (LDH) as a molecular target of d-2HG. d-2HG and inhibition of LDH drive a metabolic program and immune CD8⁺ T cell signature marked by decreased cytotoxicity and impaired interferon-γ signaling that was recapitulated in clinical samples from human patients with IDH1 mutant gliomas.

The Extension of the LeiCNS-PK3.0 Model in Combination with the "Handshake" Approach to Understand Brain Tumor Pathophysiology

Micrometastatic brain tumor cells, which cause recurrence of malignant brain tumors, are often protected by the intact blood–brain barrier (BBB). Therefore, it is essential to deliver effective drugs across not only the disrupted blood-tumor barrier (BTB) but also the intact BBB to effectively treat malignant brain tumors. Our aim is to predict pharmacokinetic (PK) profiles in brain tumor regions with the disrupted BTB and the intact BBB to support the successful drug development for malignant brain tumors. LeiCNS-PK3.0, a comprehensive central nervous system (CNS) physiologically based pharmacokinetic (PBPK) model, was extended to incorporate brain tumor compartments. Most pathophysiological parameters of brain tumors were obtained from literature and two missing parameters of the BTB, paracellular pore size and expression level of active transporters, were estimated by fitting existing data, like a “handshake”. Simultaneous predictions were made for PK profiles in extracellular fluids (ECF) of brain tumors and normal-appearing brain and validated on existing data for six small molecule anticancer drugs. The LeiCNS-tumor model predicted ECF PK profiles in brain tumor as well as normal-appearing brain in rat brain tumor models and high-grade glioma patients within twofold error for most data points, in combination with estimated paracellular pore size of the BTB and active efflux clearance at the BTB. Our model demonstrated a potential to predict PK profiles of small molecule drugs in brain tumors, for which quantitative information on pathophysiological alterations is available, and contribute to the efficient and successful drug development for malignant brain tumors.

Tissue 2-Hydroxyglutarate and Preoperative Seizures in Patients With Diffuse Gliomas

BACKGROUND AND OBJECTIVES

Mutant isocitrate dehydrogenase (IDH) 1/2 gene products gain a new ability to produce D-2-hydroxyglutarate (D2HG). IDH1/2 mutations are thought to be associated with seizures owing to the structural similarity between D2HG and glutamate. However, the effects of D2HG on seizures in clinical settings are not fully understood. We sought to investigate the relationship between tissue 2-hydroxyglutarate (2HG) concentration and preoperative seizures using clinical samples.

METHODS

We included 104 consecutive patients with diffuse glioma who underwent surgery from August 2008 to May 2016 and whose clinical presentation and IDH1/2 status were identified. The presence of preoperative seizures, tumor location, histopathologic diagnosis, IDH1/2 status, and 1p/19q codeletion were assessed from the patient charts. Tissue 2HG concentration was measured using liquid chromatography-tandem mass spectrometry. To evaluate 2HG distribution without artefactual tissue disruption, we applied matrix-assisted laser desorption/ionization high-resolution mass spectrometry imaging (MALDI-MSI) in 12 patients' surgically resected samples. We assessed the correlation of preoperative seizures with tissue 2HG concentration, IDH1/2 status, WHO grade, and 1p/19q codeletion.

RESULTS

Tissue 2HG concentration was higher in IDH1/2 mutant tumors (IDH-Mut, n = 42) than in IDH1/2 wild-type tumors (IDH-WT, n = 62) (median 4,860 ng/mg vs 75 ng/mg) (p < 0.0001). MALDI-MSI could detect 2HG signals in IDH-Mut, but not in IDH-WT. Preoperative seizures were observed in 64.3% of patients with IDH-Mut and 21.0% patients with IDH-WT (p < 0.0001). The optimal cutoff value of tissue 2HG concentration for predicting preoperative seizures was 1,190 ng/mg, as calculated by the receiver operating characteristic curve. Increased preoperative seizure risk was only observed in tumors with 2HG concentration above the cutoff value among IDH-Mut (IDH-Mut with above the cutoff value: 71.4% vs IDH-Mut with below the cutoff value: 28.6%; p = 0.031). Multivariate analysis, including IDH1/2 mutation status, tissue 2HG concentration, WHO grade, and 1p/19q codeletion, revealed that only increased tissue 2HG concentration was associated with preoperative seizures (odds ratio 5.86, 95% confidence interval 1.02-48.5; p = 0.048).

DISCUSSION

We showed that high tissue 2HG concentration was associated with preoperative seizures, suggesting that excess 2HG increases risk of preoperative seizures in IDH1/2 mutant tumors.

Methods for intratumoral microdialysis probe targeting and validation in murine brain tumor models

BACKGROUND

Microdialysis is a well validated sampling technique that can be used for pharmacokinetic studies of oncological drugs targeting the central nervous system. This technique has also been applied to evaluate tumor metabolism and identify pharmacodynamic biomarkers of drug activity. Despite the potential utility of microdialysis for therapeutic discovery, variability in tumor size and location hamper routine use of microdialysis as a preclinical tool. Quantitative validation of microdialysis membrane location relative to radiographically evident tumor regions could facilitate rigorous preclinical studies. However, a widely accessible standardized workflow for preclinical catheter placement and validation is needed.

NEW METHOD

We provide methods for a workflow to yield tailored placement of microdialysis probes within a murine intracranial tumor and illustrate in an IDH1-mutant patient-derived xenograft (PDX) model. This detailed workflow uses a freely available on-line tool built within 3D-slicer freeware to target microdialysis probe placement within the tumor core and validate probe placement fully within the tumor.

RESULTS

We illustrate use of this workflow to validate microdialysis probe location relative to implanted IDH1-mutant PDXs, using the microdialysis probes to quantify levels of extracellular onco-metabolite D-2 hydroxyglutarate.

COMPARISON WITH EXISTING METHODS

Previous methods have used 3D slicer to reliably measure tumor volumes. Prior microdialysis studies have targeted expected tumor locations without validation.

CONCLUSIONS

The new method offers a streamlined and freely available workflow in 3D slicer to optimize and validate microdialysis probe placement within a murine brain tumor.

Contemporary Mouse Models in Glioma Research

Despite advances in understanding of the molecular pathogenesis of glioma, outcomes remain dismal. Developing successful treatments for glioma requires faithful in vivo disease modeling and rigorous preclinical testing. Murine models, including xenograft, syngeneic, and genetically engineered models, are used to study glioma-genesis, identify methods of tumor progression, and test novel treatment strategies. Since the discovery of highly recurrent isocitrate dehydrogenase (IDH) mutations in lower-grade gliomas, there is increasing emphasis on effective modeling of IDH mutant brain tumors. Improvements in preclinical models that capture the phenotypic and molecular heterogeneity of gliomas are critical for the development of effective new therapies. Herein, we explore the current status, advancements, and challenges with contemporary murine glioma models.

The diagnostic value of lower glucose consumption for IDH1 mutated gliomas on FDG-PET

Background

Non-invasive diagnosis of IDH1 mutation for gliomas has great clinical significance, and PET has natural advantage to detect metabolism, as IDH mutated gliomas share lower glucose consumption.

Methods

Clinical data of patients with gliomas and ¹⁸F-FDG PET were retrospectively reviewed. Receiver operating characteristic curve (ROC) analysis was conducted, and standard uptake value (SUV) was estimated in combination with grades or IDH1 mutation. The glucose consumption was investigated with U251 cells expressing wild-type or mutated IDH1 by glucose assay. Quantification of glucose was determined by HPLC in clinical tissues. Meanwhile, bioinformatics and western blot were applied to analyze the expression level of metabolic enzymes (e.g. HK1, PKM2, PC) in gliomas.

Results

Seventy-one glioma cases were enrolled, including 30 carrying IDH1 mutation. The sensitivity and specificity dependent on SUV_max (3.85) predicting IDH1 mutation reached 73.2 and 86.7%, respectively. The sensitivity and specificity of differentiating grades by SUVmax (3.1) were 92.3 and 64.4%, respectively. Glucose consumption of U251 IDH1 mutant cells (0.209 ± 0.0472 mg/ml) was obviously lower than IDH1wild-type cells (0.978 ± 0.0773 mg/ml, P = 0.0001) and astrocyte controls (0.335 ± 0.0592 mg/ml, P = 0.0451). Meanwhile, the glucose quantity in IDH1mutant glioma samples were significantly lower than those in IDH1 wild-type tissues (1.033 ± 1.19608 vs 6.361 ± 4.3909 mg/g, P = 0.0051). Silico analysis and western blot confirmed that HK1 and PKM2 in IDH1 wild-type gliomas were significantly higher than in IDH1 mutant group, while PC was significantly higher in IDH1 mutant gliomas.

Conclusion

SUV_max on PET can predict IDH1 mutation with adequate sensitivity and specificity, as is supported by reduced glucose consumption in IDH1 mutant gliomas.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07797-6.

Current biomarker-associated procedures of cancer modeling-a reference in the context of IDH1 mutant glioma

Isocitrate dehydrogenases (IDH1/2) are central molecular markers for glioblastoma. Providing in vitro or in vivo models with mutated IDH1/2 can help prepare facilities to understand the biology of these mutated genes as glioma markers, as well as help, improve therapeutic strategies. In this review, we first summarize the biology principles of IDH and its mutations and outline the core primary findings in the clinical context of neuro-oncology. Given the extensive research interest and exciting developments in current stem cell biology and genome editing, the central part of the manuscript is dedicated to introducing various routes of disease modeling strategies of IDH mutation (IDHMut) glioma and comparing the scientific-technological findings from the field using different engineering methods. Lastly, by giving our perspective on the benefits and limitations of patient-derived and donor-derived disease modeling respectively, we aim to propose leading research questions to be answered in the context of IDH1 and glioma.

Metabolic Landscape of a Genetically Engineered Mouse Model of IDH1 Mutant Glioma

Understanding the metabolic reprogramming of aggressive brain tumors has potential applications for therapeutics as well as imaging biomarkers. However, little is known about the nutrient requirements of isocitrate dehydrogenase 1 (IDH1) mutant gliomas. The IDH1 mutation involves the acquisition of a neomorphic enzymatic activity which generates D-2-hydroxyglutarate from α-ketoglutarate. In order to gain insight into the metabolism of these malignant brain tumors, we conducted metabolic profiling of the orthotopic tumor and the contralateral regions for the mouse model of IDH1 mutant glioma; as well as to examine the utilization of glucose and glutamine in supplying major metabolic pathways such as glycolysis and tricarboxylic acid (TCA). We also revealed that the main substrate of 2-hydroxyglutarate is glutamine in this model, and how this re-routing impairs its utilization in the TCA. Our 13C tracing analysis, along with hyperpolarized magnetic resonance experiments, revealed an active glycolytic pathway similar in both regions (tumor and contralateral) of the brain. Therefore, we describe the reprogramming of the central carbon metabolism associated with the IDH1 mutation in a genetically engineered mouse model which reflects the tumor biology encountered in glioma patients.

Intratumoral Susceptibility Signals Reflect Biomarker Status in Gliomas

Susceptibility-weighted imaging (SWI) can be a useful tool to depict vascular structures in brain tumors as well as micro-bleedings, which represent tumor invasion to blood vessels and could also be representative of tumoral angiogenesis. In this study, we investigated the relationship between SWI features and glioma grades, and the expression of key molecular markers isocitrate dehydrogenase 1 (IDH1), O-6-methylguanine-DNA methyltransferase (MGMT), and 1p19q. The gliomas were graded according to the intratumoral susceptibility signals (ITSS). We used the Mann-Whitney test to analyze the relationship between ITSS grades and the pathological level and status of these markers. Additionally, the area under the curve (AUC) was used to determine the predictive value of glioma SWI characteristics for the molecular marker status. In these cases, the ITSS grades of low-grade gliomas (LGG) were significantly lower than those of high-grade gliomas (HGG). Similarly, the ITSS grades of gliomas with IDH1 mutations and MGMT methylation were significantly lower than those of gliomas with Wild-type IDH1 and unmethylated MGMT. However, ITSS grades showed no relationship with 1p19q deletion status, while they did show significant predictive ability for glioma grade, IDH1 mutation, and MGMT methylation. These findings indicate an association between some molecular markers and cerebral microbleeds in gliomas, providing a new avenue for non-invasive prediction of molecular genetics in gliomas and an important basis for preoperative personalized surgical treatment based on molecular pathology.

The oncometabolite 2-hydroxyglutarate inhibits microglial activation via the AMPK/mTOR/NF-κB pathway

Microglia, the brain-resident macrophage, is known as the innate immune cell type in the central nervous system. Microglia is also the major cellular component of tumor mass of gliomas that plays a key role in glioma development. Mutations of isocitrate dehydrogenases 1 and 2 (IDH1/2) frequently occur in gliomas, which leads to accumulation of oncometabolic product 2-hydroxyglutarate (2HG). Moreover, IDH1/2 mutations were found to correlate with better prognosis in glioma patients. In the present study, we investigated the effects of the 2HG on microglial inflammatory activation. We showed that the conditioned media (CM) from GL261 glioma cells stimulated the activation of BV-2 microglia cells, evidenced by markedly increased expression of interleukin-6 (IL-6), IL-1β, tumor necrosis factor-α (TNF-α), CCL2 (C-C motif chemokine ligand 2) and CXCL10 (C-X-C motif chemokine 10). CM-induced expression of proinflammatory genes was significantly suppressed by pretreatment with a synthetic cell-permeable 2HG (1 mM) or a nuclear factor-κB (NF-κB) inhibitor BAY11-7082 (10 μM). In lipopolysaccharide (LPS)- or TNF-α-stimulated BV-2 microglia cells and primary microglia, pretreatment with 2HG (0.25-1 mM) dose-dependently suppressed the expression of proinflammatory genes. We further demonstrated that 2HG significantly suppressed LPS-induced phosphorylation of IκB kinase α/β (IKKα/β), IκBα and p65, IκB degradation, and nuclear translocation of p65 subunit of NF-κB, as well as NF-κB transcriptional activity. Similarly, ectopic expression of mutant isocitrate dehydrogenase 1 (IDH1) (R132H) significantly decreased TNF-α-induced activation of NF-κB signaling pathway. Finally, we revealed that activation of adenosine 5'-monophosphate-activated protein kinase (AMPK) and subsequent inhibition of mammalian target of rapamycin (mTOR) signaling contributed to the inhibitory effect of 2HG on NF-κB signaling pathway in BV-2 cells. Taken together, these results, for the first time, show that oncometabolite 2HG inhibits microglial activation through affecting AMPK/mTOR/NF-κB signaling pathway and provide evidence that oncometabolite 2HG may regulate glioma development via modulating microglial activation in tumor microenvironment.

The need for mathematical modelling of spatial drug distribution within the brain

The blood brain barrier (BBB) is the main barrier that separates the blood from the brain. Because of the BBB, the drug concentration-time profile in the brain may be substantially different from that in the blood. Within the brain, the drug is subject to distributional and elimination processes: diffusion, bulk flow of the brain extracellular fluid (ECF), extra-intracellular exchange, bulk flow of the cerebrospinal fluid (CSF), binding and metabolism. Drug effects are driven by the concentration of a drug at the site of its target and by drug-target interactions. Therefore, a quantitative understanding is needed of the distribution of a drug within the brain in order to predict its effect. Mathematical models can help in the understanding of drug distribution within the brain. The aim of this review is to provide a comprehensive overview of system-specific and drug-specific properties that affect the local distribution of drugs in the brain and of currently existing mathematical models that describe local drug distribution within the brain. Furthermore, we provide an overview on which processes have been addressed in these models and which have not. Altogether, we conclude that there is a need for a more comprehensive and integrated model that fills the current gaps in predicting the local drug distribution within the brain.

Cancer-associated mutation and beyond: The emerging biology of isocitrate dehydrogenases in human disease

Isocitrate dehydrogenases (IDHs) are critical metabolic enzymes that catalyze the oxidative decarboxylation of isocitrate to α-ketoglutarate (αKG), NAD(P)H, and CO₂. IDHs epigenetically control gene expression through effects on αKG-dependent dioxygenases, maintain redox balance and promote anaplerosis by providing cells with NADPH and precursor substrates for macromolecular synthesis, and regulate respiration and energy production through generation of NADH. Cancer-associated mutations in IDH1 and IDH2 represent one of the most comprehensively studied mechanisms of IDH pathogenic effect. Mutant enzymes produce (R)-2-hydroxyglutarate, which in turn inhibits αKG-dependent dioxygenase function, resulting in a global hypermethylation phenotype, increased tumor cell multipotency, and malignancy. Recent studies identified wild-type IDHs as critical regulators of normal organ physiology and, when transcriptionally induced or down-regulated, as contributing to cancer and neurodegeneration, respectively. We describe how mutant and wild-type enzymes contribute on molecular levels to disease pathogenesis, and discuss efforts to pharmacologically target IDH-controlled metabolic rewiring.

IDH mutations but not TERTp mutations are associated with seizures in lower-grade gliomas

Glioma is the most common malignant tumor in the central nervous system (CNS). Lower-grade gliomas (LGG) refer to Grade II and III gliomas. In LGG patients, seizure often appears as an initial symptom and play an important role in clinical performance and quality of life of the patients. To date, the relationship between the onset of seizures and the molecular pathology in gliomas is still poorly investigated. In this study, we investigate the potential relationship between isocitrate dehydrogenase (IDH)/telomerase reverse transcriptase promoter (TERTp) mutations and preoperative seizures in patients with LGG. 289 adult LGG patients were enrolled in this study. Data of clinical characteristics and molecular pathology were acquired. Sanger sequencing was used to detect IDH/TERTp mutations. Chi-square test was performed to determine if the IDH/TERTp mutations were associated with seizures and seizure types. In 289 LGG patients, preoperative seizures accounted for 25.3% (73/289), IDH mutations accounted for 34.3%(99/289), and TERTp mutations accounted for 44.3% (128/289). The correlation analysis demonstrated that IDH mutation is a significant factor influencing the occurrence of tumor-related epilepsy (P <.001, chi-square test). On the other hand, the statistical analysis revealed no significant correlation between TERTp mutations and seizure in LGG patients (P = .102, chi-square test). The tumor-related epilepsy rates vary among different subgroups according to IDH/TERTp mutations. However, there is no definite correlation between the IDH (P = 1.000, chi-square test)/TERTp (P = .613, chi-square test) mutations and the types of epileptic seizure. IDH mutations are more common in preoperative LGG patients with epileptic symptoms, suggesting that this mutation is positively correlated with seizures. However, there was no significant correlation between TERTp mutations and seizures. Different molecular pathologic types based on IDH/TERTp have different incidences of tumor-associated epilepsy in LGGs.

D-2-Hydroxyglutarate Is an Intercellular Mediator in IDH-Mutant Gliomas Inhibiting Complement and T Cells

Purpose: Somatic mutations in the isocitrate dehydrogenase (IDH)-1 and -2 genes are remarkably penetrant in diffuse gliomas. These highly effective gain-of-function mutations enable mutant IDH to efficiently metabolize isocitrate to D-2-hydroxyglutarate (D 2-HG) that accumulates to high concentrations within the tumor microenvironment. D 2-HG is an intracellular effector that promotes tumor growth through widespread epigenetic changes in IDH-mutant tumor cells, but its potential role as an intercellular immune regulator remains understudied.Experimental Design: Complement activation and CD4⁺, CD8⁺, or FOXP3⁺ T-cell infiltration into primary tumor tissue were determined by immunohistochemistry using sections from 72 gliomas of World Health Organization (WHO) grade III and IV with or without IDH mutations. Ex vivo experiments with D 2-HG identified immune inhibitory mechanisms.Results: IDH mutation associated with significantly reduced complement activation and decreased numbers of tumor-infiltrating CD4⁺ and CD8⁺ T cells with comparable FOXP3⁺/CD4⁺ ratios. D 2-HG potently inhibited activation of complement by the classical and alternative pathways, attenuated complement-mediated glioma cell damage, decreased cellular C3b(iC3b) opsonization, and impaired complement-mediated phagocytosis. Although D 2-HG did not affect dendritic cell differentiation or function, it significantly inhibited activated T-cell migration, proliferation, and cytokine secretion.Conclusions: D 2-HG suppresses the host immune system, potentially promoting immune escape of IDH-mutant tumors. Clin Cancer Res; 24(21); 5381-91. ©2018 AACR.