The oncometabolite 2-hydroxyglutarate inhibits histone lysine demethylases

Advances in the Immunotherapeutic Potential of Isocitrate Dehydrogenase Mutations in Glioma

Isocitrate dehydrogenase (IDH) is an essential metabolic enzyme in the tricarboxylic acid cycle (TAC). The high mutation frequency of the IDH gene plays a complicated role in gliomas. In addition to affecting gliomas directly, mutations in IDH can also alter their immune microenvironment and can change immune-cell function in direct and indirect ways. IDH mutations mediate immune-cell infiltration and function by modulating immune-checkpoint gene expression and chemokine secretion. In addition, IDH mutation-derived D2-hydroxyglutarate can be absorbed by surrounding immune cells, also affecting their functioning. In this review, we summarize current knowledge about the effects of IDH mutations as well as other gene mutations on the immune microenvironment of gliomas. We also describe recent preclinical and clinical data related to IDH-mutant inhibitors for the treatment of gliomas. Finally, we discuss different types of immunotherapy and the immunotherapeutic potential of IDH mutations in gliomas.

Recent advances of IDH1 mutant inhibitor in cancer therapy

Isocitrate dehydrogenase (IDH) is the key metabolic enzyme that catalyzes the conversion of isocitrate to α-ketoglutarate (α-KG). Two main types of IDH1 and IDH2 are present in humans. In recent years, mutations in IDH have been observed in several tumors, including glioma, acute myeloid leukemia, and chondrosarcoma. Among them, the frequency of IDH1 mutations is higher than IDH2. IDH1 mutations have been shown to increase the conversion of α-KG to 2-hydroxyglutarate (2-HG). IDH1 mutation-mediated accumulation of 2-HG leads to epigenetic dysregulation, altering gene expression, and impairing cell differentiation. A rapidly emerging therapeutic approach is through the development of small molecule inhibitors targeting mutant IDH1 (mIDH1), as evidenced by the recently approved of the first selective IDH1 mutant inhibitor AG-120 (ivosidenib) for the treatment of IDH1-mutated AML. This review will focus on mIDH1 as a therapeutic target and provide an update on IDH1 mutant inhibitors in development and clinical trials.

Identifying α-KG-dependent prognostic signature for lower-grade glioma based on transcriptome profiles

The inhibition of alpha-ketoglutarate (α-KG)-dependent dioxygenases is thought to contribute to isocitrate dehydrogenase (IDH) mutation-derived malignancy. Herein, we aim to thoroughly investigate the expression pattern and prognostic significance of genes encoding α-KG-dependent enzymes for lower-grade glioma (LGG) patients. In this retrospective study, a total of 775 LGG patients were enrolled. The generalized linear model, least absolute shrinkage and selection operator Cox regression, and nomogram were applied to identify the enzyme-based signature. With the use of gene set enrichment analysis and Gene Ontology, the probable molecular abnormalities underlying high-risk patients were investigated. By comprehensively analyzing mRNA data, we observed that 41 genes were differentially expressed between IDHMUT and IDHWT LGG patients. A risk signature comprising 10 genes, which could divide samples into high- and low-risk groups of distinct prognoses, was developed and independently validated. This enzyme-based signature was indicative of a more malignant phenotype. The nomogram model incorporating the risk signature, molecular biomarkers, and clinicopathological parameters proved the incremental utility of the α-KG-dependent signature by achieving a more accurate prediction impact. Our study demonstrates that the α-KG-dependent enzyme-encoding genes were differentially expressed in relation to the IDH phenotype and may serve as a promising indicator for clinical outcomes of LGG patients.

The epigenetic dysfunction underlying malignant glioma pathogenesis

Comprehensive molecular profiling has dramatically transformed the diagnostic neuropathology of brain tumors. Diffuse gliomas, the most common and deadly brain tumor variants, are now classified by highly recurrent biomarkers instead of histomorphological characteristics. Several of the key molecular alterations driving glioma classification involve epigenetic dysregulation at a fundamental level, implicating fields of biology not previously thought to play major roles glioma pathogenesis. This article will review the major epigenetic alterations underlying malignant gliomas, their likely mechanisms of action, and potential strategies for their therapeutic targeting.

Obstacles to Glioblastoma Treatment Two Decades after Temozolomide

Simple Summary

Glioblastomas are the most common and aggressive brain tumors in adults, with a median survival of 15 months. Treatment is surgical removal, followed by chemotherapy and/or radiotherapy. Current chemotherapeutics do not kill all the tumor cells and some cells survive, leading to the appearance of a new tumor resistant to the treatment. These treatment-resistant cells are called tumor stem cells. In addition, glioblastoma cells have a high capacity for migration, forming new tumors in areas distant from the original tumor. Studies are now focused on understanding the molecular mechanisms of chemoresistance and controlling drug entry into the brain to improve drug performance. Another promising therapeutic approach is the use of viruses that specifically destroy glioblastoma cells, preserving the neural tissue around the tumor. In this review, we summarize the main biological features of glioblastoma and the therapeutic targets that are currently under study for new clinical trials.

Abstract

Glioblastomas are considered the most common and aggressive primary brain tumor in adults, with an average of 15 months’ survival rate. The treatment is surgery resection, followed by chemotherapy with temozolomide, and/or radiotherapy. Glioblastoma must have wild-type IDH gene and some characteristics, such as TERT promoter mutation, EGFR gene amplification, microvascular proliferation, among others. Glioblastomas have great heterogeneity at cellular and molecular levels, presenting distinct phenotypes and diversified molecular signatures in each tumor mass, making it difficult to define a specific therapeutic target. It is believed that the main responsibility for the emerge of these distinct patterns lies in subcellular populations of tumor stem cells, capable of tumor initiation and asymmetric division. Studies are now focused on understanding molecular mechanisms of chemoresistance, the tumor microenvironment, due to hypoxic and necrotic areas, cytoskeleton and extracellular matrix remodeling, and in controlling blood brain barrier permeabilization to improve drug delivery. Another promising therapeutic approach is the use of oncolytic viruses that are able to destroy specifically glioblastoma cells, preserving the neural tissue around the tumor. In this review, we summarize the main biological characteristics of glioblastoma and the cutting-edge therapeutic targets that are currently under study for promising new clinical trials.

The first-in-human phase I study of a brain-penetrant mutant IDH1 inhibitor DS-1001 in patients with recurrent or progressive IDH1-mutant gliomas

BACKGROUND

Approximately 70% of lower-grade gliomas harbor isocitrate dehydrogenase 1 (IDH1) mutations, resulting in the accumulation of oncometabolite D-2-hydroxyglutarate (D-2-HG); this leads to epigenetic dysregulation, oncogenesis, and subsequent clonal expansion. DS-1001 is an oral brain-penetrant mutant IDH1 selective inhibitor. This first-in-human study investigated the safety, pharmacokinetics, pharmacodynamics, and efficacy of DS-1001.

METHODS

This was a multicenter, open-label, dose-escalation, phase I study of DS-1001 for recurrent/progressive IDH1-mutant (R132) glioma (N = 47) (NCT03030066). DS-1001 was administered orally at 125-1400 mg twice daily. Dose-escalation used a modified continual reassessment method.

RESULTS

The maximum tolerated dose was not reached. Eight patients were continuing treatment at the data cutoff. Most adverse events (AEs) were grade 1-2. Twenty patients (42.6%) experienced at least 1 grade 3 AE. No grade 4 or 5 AEs or serious drug-related AEs were reported. Common AEs (>20%) were skin hyperpigmentation, diarrhea, pruritus, alopecia, arthralgia, nausea, headache, rash, and dry skin. The objective response rates were 17.1% for enhancing tumors and 33.3% for non-enhancing tumors. Median progression-free survival was 10.4 months (95% confidence interval [CI], 6.1 to 17.7 months) and not reached (95% CI, 24.1 to not reached) for the enhancing and non-enhancing glioma cohorts, respectively. Seven on-treatment brain tumor samples showed a significantly lower amount of D-2-HG compared with pre-study archived samples.

CONCLUSIONS

DS-1001 was well tolerated with a favorable brain distribution. Recurrent/progressive IDH1-mutant glioma patients responded to treatment. A study of DS-1001 in patients with chemotherapy- and radiotherapy-naïve IDH1-mutated WHO grade 2 glioma is ongoing (NCT04458272).

2-Hydroxyglutarate in Acute Myeloid Leukemia: A Journey from Pathogenesis to Therapies

The oncometabolite 2-hydroxyglutarate (2-HG) plays a key role in differentiation blockade and metabolic reprogramming of cancer cells. Approximatively 20–30% of acute myeloid leukemia (AML) cases carry mutations in the isocitrate dehydrogenase (IDH) enzymes, leading to a reduction in the Krebs cycle intermediate α-ketoglutarate (α-KG) to 2-HG. Relapse and chemoresistance of AML blasts following initial good response to standard therapy account for the very poor outcome of this pathology, which represents a great challenge for hematologists. The decrease of 2-HG levels through pharmacological inhibition of mutated IDH enzymes induces the differentiation of AML blasts and sensitizes leukemic cells to several anticancer drugs. In this review, we provide an overview of the main genetic mutations in AML, with a focus on IDH mutants and the role of 2-HG in AML pathogenesis. Moreover, we discuss the impact of high levels of 2-HG on the response of AML cells to antileukemic therapies and recent evidence for highly efficient combinations of mutant IDH inhibitors with other drugs for the management of relapsed/refractory (R/R) AML.

Mitochondria-actin cytoskeleton crosstalk in cell migration

Mitochondria perform diverse functions in the cell and their roles during processes such as cell survival, differentiation, and migration are increasingly being appreciated. Mitochondrial and actin cytoskeletal networks not only interact with each other, but this multifaceted interaction shapes their functional dynamics. The interrelation between mitochondria and the actin cytoskeleton extends far beyond the requirement of mitochondrial ATP generation to power actin dynamics, and impinges upon several major aspects of cellular physiology. Being situated at the hub of cell signaling pathways, mitochondrial function can alter the activity of actin regulatory proteins and therefore modulate the processes downstream of actin dynamics such as cellular migration. As we will discuss, this regulation is highly nuanced and operates at multiple levels allowing mitochondria to occupy a strategic position in the regulation of migration, as well as pathological events that rely on aberrant cell motility such as cancer metastasis. In this review, we summarize the crosstalk that exists between mitochondria and actin regulatory proteins, and further emphasize on how this interaction holds importance in cell migration in normal as well as dysregulated scenarios as in cancer.

Distinct Roles of Glutamine Metabolism in Benign and Malignant Cartilage Tumors With IDH Mutations

Enchondromas and chondrosarcomas are common cartilage neoplasms that are either benign or malignant, respectively. The majority of these tumors harbor mutations in either IDH1 or IDH2. Glutamine metabolism has been implicated as a critical regulator of tumors with IDH mutations. Using genetic and pharmacological approaches, we demonstrated that glutaminase-mediated glutamine metabolism played distinct roles in enchondromas and chondrosarcomas with IDH1 or IDH2 mutations. Glutamine affected cell differentiation and viability in these tumors differently through different downstream metabolites. During murine enchondroma-like lesion development, glutamine-derived α-ketoglutarate promoted hypertrophic chondrocyte differentiation and regulated chondrocyte proliferation. Deletion of glutaminase in chondrocytes with Idh1 mutation increased the number and size of enchondroma-like lesions. In contrast, pharmacological inhibition of glutaminase in chondrosarcoma xenografts reduced overall tumor burden partially because glutamine-derived non-essential amino acids played an important role in preventing cell apoptosis. This study demonstrates that glutamine metabolism plays different roles in tumor initiation and cancer maintenance. Supplementation of α-ketoglutarate and inhibiting GLS may provide a therapeutic approach to suppress enchondroma and chondrosarcoma tumor growth, respectively. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Biology of IDH mutant cholangiocarcinoma

Isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are the most frequently mutated metabolic genes across human cancers. These hotspot gain-of-function mutations cause the IDH enzyme to aberrantly generate high levels of the oncometabolite, R-2-hydroxyglutarate, which competitively inhibits enzymes that regulate epigenetics, DNA repair, metabolism, and other processes. Among epithelial malignancies, IDH mutations are particularly common in intrahepatic cholangiocarcinoma (iCCA). Importantly, pharmacological inhibition of mutant IDH (mIDH) 1 delays progression of mIDH1 iCCA, indicating a role for this oncogene in tumor maintenance. However, not all patients receive clinical benefit, and those who do typically show stable disease rather than significant tumor regressions. The elucidation of the oncogenic functions of mIDH is needed to inform strategies that can more effectively harness mIDH as a therapeutic target. This review will discuss the biology of mIDH iCCA, including roles of mIDH in blocking cell differentiation programs and suppressing antitumor immunity, and the potential relevance of these effects to mIDH1-targeted therapy. We also cover opportunities for synthetic lethal therapeutic interactions that harness the altered cell state provoked by mIDH1 rather than inhibiting the mutant enzyme. Finally, we highlight key outstanding questions in the biology of this fascinating and incompletely understood oncogene.

SLC1A1-mediated cellular and mitochondrial influx of R-2-hydroxyglutarate in vascular endothelial cells promotes tumor angiogenesis in IDH1-mutant solid tumors

Mutant isocitrate dehydrogenase 1 (mIDH1) drives tumorigenesis via producing oncometabolite R-2-hydroxyglutarate (R-2-HG) across various tumor types. However, mIDH1 inhibitors appear only effective in hematological tumors. The therapeutic benefit in solid tumors remains elusive, likely due to the complex tumor microenvironment. In this study, we discover that R-2-HG produced by IDH1-mutant tumor cells is preferentially imported into vascular endothelial cells and remodels mitochondrial respiration to promote tumor angiogenesis, conferring a therapeutic vulnerability in IDH1-mutant solid tumors. Mechanistically, SLC1A1, a Na⁺-dependent glutamate transporter that is preferentially expressed in endothelial cells, facilitates the influx of R-2-HG from the tumor microenvironment into the endothelial cells as well as the intracellular trafficking of R-2-HG from cytoplasm to mitochondria. R-2-HG hijacks SLC1A1 to promote mitochondrial Na⁺/Ca²⁺ exchange, which activates the mitochondrial respiratory chain and fuels vascular endothelial cell migration in tumor angiogenesis. SLC1A1 deficiency in mice abolishes mIDH1-promoted tumor angiogenesis as well as the therapeutic benefit of mIDH1 inhibitor in solid tumors. Moreover, we report that HH2301, a newly discovered mIDH1 inhibitor, shows promising efficacy in treating IDH1-mutant cholangiocarcinoma in preclinical models. Together, we identify a new role of SLC1A1 as a gatekeeper of R-2-HG-mediated crosstalk between IDH1-mutant tumor cells and vascular endothelial cells, and demonstrate the therapeutic potential of mIDH1 inhibitors in treating IDH1-mutant solid tumors via disrupting R-2-HG-promoted tumor angiogenesis.

The Role of Ten-Eleven Translocation Proteins in Inflammation

Ten-eleven translocation proteins (TET1-3) are dioxygenases that oxidize 5-methyldeoxycytosine, thus taking part in passive and active demethylation. TETs have shown to be involved in immune cell development, affecting from self-renewal of stem cells and lineage commitment to terminal differentiation. In fact, dysfunction of TET proteins have been vastly associated with both myeloid and lymphoid leukemias. Recently, there has been accumulating evidence suggesting that TETs regulate immune cell function during innate and adaptive immune responses, thereby modulating inflammation. In this work, we pursue to review the current and recent evidence on the mechanistic aspects by which TETs regulate immune cell maturation and function. We will also discuss the complex interplay of TET expression and activity by several factors to modulate a multitude of inflammatory processes. Thus, modulating TET enzymes could be a novel pharmacological approach to target inflammation-related diseases and myeloid and lymphoid leukemias, when their activity is dysregulated.

The epigenetic-metabolic interplay in gliomagenesis

Although tumourigenesis occurs due to genetic mutations, the role of epigenetic dysregulations in cancer is also well established. Epigenetic dysregulations in cancer may occur as a result of mutations in genes encoding histone/DNA-modifying enzymes and chromatin remodellers or mutations in histone protein itself. It is also true that misregulated gene expression without genetic mutations in these factors could also support tumour initiation and progression. Interestingly, metabolic rewiring has emerged as a hallmark of cancer due to gene mutations in specific metabolic enzymes or dietary/environmental factors. Recent studies report an intricate cross-talk between epigenetic and metabolic reprogramming in cancer. This review discusses the role of epigenetic and metabolic dysregulations and their cross-talk in tumourigenesis with a special focus on gliomagenesis. We also discuss the role of recently developed human embryonic stem cells/induced pluripotent stem cells-derived organoid models of gliomas and how these models are proving instrumental in uncovering human-specific cellular and molecular complexities of gliomagenesis.

Epigenetic Regulation in Uterine Fibroids-The Role of Ten-Eleven Translocation Enzymes and Their Potential Therapeutic Application

Uterine fibroids (UFs) are monoclonal, benign tumors that contain abnormal smooth muscle cells and the accumulation of extracellular matrix (ECM). Although benign, UFs are a major source of gynecologic and reproductive dysfunction, ranging from menorrhagia and pelvic pain to infertility, recurrent miscarriage, and preterm labor. Many risk factors are involved in the pathogenesis of UFs via genetic and epigenetic mechanisms. The latter involving DNA methylation and demethylation reactions provide specific DNA methylation patterns that regulate gene expression. Active DNA demethylation reactions mediated by ten-eleven translocation proteins (TETs) and elevated levels of 5-hydroxymethylcytosine have been suggested to be involved in UF formation. This review paper summarizes the main findings regarding the function of TET enzymes and their activity dysregulation that may trigger the development of UFs. Understanding the role that epigenetics plays in the pathogenesis of UFs may possibly lead to a new type of pharmacological fertility-sparing treatment method.

Cancer metabolism and tumor microenvironment: fostering each other?

The changes associated with malignancy are not only in cancer cells but also in environment in which cancer cells live. Metabolic reprogramming supports tumor cell high demand of biogenesis for their rapid proliferation, and helps tumor cell to survive under certain genetic or environmental stresses. Emerging evidence suggests that metabolic alteration is ultimately and tightly associated with genetic changes, in particular the dysregulation of key oncogenic and tumor suppressive signaling pathways. Cancer cells activate HIF signaling even in the presence of oxygen and in the absence of growth factor stimulation. This cancer metabolic phenotype, described firstly by German physiologist Otto Warburg, insures enhanced glycolytic metabolism for the biosynthesis of macromolecules. The conception of metabolite signaling, i.e., metabolites are regulators of cell signaling, provides novel insights into how reactive oxygen species (ROS) and other metabolites deregulation may regulate redox homeostasis, epigenetics, and proliferation of cancer cells. Moreover, the unveiling of noncanonical functions of metabolic enzymes, such as the moonlighting functions of phosphoglycerate kinase 1 (PGK1), reassures the importance of metabolism in cancer development. The metabolic, microRNAs, and ncRNAs alterations in cancer cells can be sorted and delivered either to intercellular matrix or to cancer adjacent cells to shape cancer microenvironment via media such as exosome. Among them, cancer microenvironmental cells are immune cells which exert profound effects on cancer cells. Understanding of all these processes is a prerequisite for the development of a more effective strategy to contain cancers.

Post-translational modifications on mitochondrial metabolic enzymes in cancer

Mitochondrion is the powerhouse of the cell. The research of nearly a century has expanded our understanding of mitochondrion, far beyond the view that mitochondrion is an important energy generator of cells. During the initiation, growth and survival of tumor cells, significant mitochondrial metabolic changes have taken place in the important enzymes of respiratory chain and tricarboxylic acid cycle, mitochondrial biogenesis and dynamics, oxidative stress regulation and molecular signaling. Therefore, mitochondrial metabolic proteins are the key mediators of tumorigenesis. Post-translational modification is the molecular switch that regulates protein function. Understanding how these mitochondria-related post-translational modification function during tumorigenesis will bring new ideas for the next generation of cancer treatment.

Mitochondrial superoxide targets energy metabolism to modulate epigenetic regulation of NRF2-mediated transcription

Mitochondria are central to the metabolic circuitry that generates superoxide radicals/anions (O2•-) as a by-product of oxygen metabolism. By regulating superoxide levels, manganese superoxide dismutase plays important roles in numerous biochemical and molecular events essential for the survival of aerobic life. In this study, we used MitoParaquat (mPQ) to generate mitochondria-specific O2•- and stable isotope-resolved metabolomics tracing in primary human epidermal keratinocytes to investigate how O2•- generated in mitochondria regulates gene expression. The results reveal that isocitrate is blocked from conversion to α-ketoglutarate and that acetyl-coenzyme A (CoA) accumulates, which is consistent with a reduction in oxygen consumption rate and inactivation of isocitrate dehydrogenase (IDH) activity. Since acetyl-CoA is linked to histone acetylation and gene regulation, we determined the effect of mPQ on histone acetylation. The results demonstrate an increase in histone H3 acetylation at lysines 9 and 14. Suppression of IDH increased histone acetylation, providing a direct link between metabolism and epigenetic alterations. The activity of histone acetyltransferase p300 increased after mPQ treatment, which is consistent with histone acetylation. Importantly, mPQ selectively increased the nuclear levels and activity of the oxidative stress-sensitive nuclear factor erythroid 2-related factor 2. Together, the results establish a new paradigm that recognizes O2•- as an initiator of metabolic reprogramming that activates epigenetic regulation of gene transcription in response to mitochondrial dysfunction.

Isocitrate Dehydrogenase IDH1 and IDH2 Mutations in Human Cancer: Prognostic Implications for Gliomas

Background: There are isolated reports of mutations in genes for isocitrate dehydrogenases (IDH1 and IDH2), but few have been examined in a large number of different malignancies. We aimed to analyze mutational prevalence of these genes in a large series of cancers and determine their significance in most mutated phenotype.

Methods: We analyzed the frequencies of IDH1 and IDH2 mutations in 14,726 malignancies of 37 cancers. Furthermore, we examined these mutations in the most frequent cancer (gliomas, 923 cases) from a single cohort, and determined their clinical significance.

Results:IDH1 mutations were present in 3% (473/14,726) of cancers. The highest frequencies were in oligodendrogliomas (91/102, 89%), anaplastic oligodendrogliomas (40/46, 87%), and diffuse astrocytomas (89/116, 77%). IDH2 mutation was detected in <1% (83/14,726) of cancers, but were present in 13% (6/46) of anaplastic oligodendrogliomas, 9% (9/102) of oligodendrogliomas, and in 5% (2/39) of cutaneous squamous cell carcinomas. Further analyses of 923 gliomas revealed 34 and 1% of IDH1 and IDH2 mutations, respectively. In up to 342 months of follow-up, IDH1 and IDH2 mutations were significantly linked with better overall (OS) (both p = 0.01) and progression-free survival (PFS) (p = 0.01; p = 0.004), respectively.

Conclusion:IDH1 and IDH2 are often mutated in a tissue-specific manner, most commonly in gliomas. Mutation in both genes is linked to OS and PFS. Our findings suggest that these genes are promising therapeutic targets and strong prognostic biomarkers in gliomas.

New Approaches with Precision Medicine in Adult Brain Tumors

Simple Summary

Primary brain tumors are rare neoplasms with limited effective systemic treatment options. Recent advances in new molecular techniques have brought about novel information about molecular markers and potential targetable molecular alterations in brain tumors. Targeted therapeutic approaches are already established in several extracranial malignancies and its application is increasingly used and studied in the management of primary brain tumors. The aim of this article is to summarize the latest progress in precision medicine approaches in primary brain tumors.

Abstract

Primary central nervous system (CNS) tumors represent a heterogenous group of tumors. The 2021 fifth edition of the WHO Classification of Tumors of the CNS emphasizes the advanced role of molecular diagnostics with routine implementation of molecular biomarkers in addition to histologic features in the classification of CNS tumors. Thus, novel diagnostic methods such as DNA methylome profiling are increasingly used to provide a more precise diagnostic work-up of CNS tumors. In addition to these diagnostic precision medicine advantages, molecular alterations are also addressed therapeutically with targeted therapies. Like in other tumor entities, precision medicine has therefore also arrived in the treatment of CNS malignancies as the application of targeted therapies has shown promising response rates. Nevertheless, large prospective studies are currently missing as most targeted therapies were evaluated in single arm, basket, or platform trials. In this review, we focus on the current evidence of precision medicine in the treatment of primary CNS tumors in adults. We outline the pathogenic background and prevalence of the most frequent targetable genetic alterations and summarize the existing evidence of precision medicine approaches for the treatment of primary CNS tumors.

Tumor suppressor CEBPA interacts with and inhibits DNMT3A activity

DNA methyltransferases (DNMTs) catalyze DNA methylation, and their functions in mammalian embryonic development and diseases including cancer have been extensively studied. However, regulation of DNMTs remains under study. Here, we show that CCAAT/enhancer binding protein α (CEBPA) interacts with the long splice isoform DNMT3A, but not the short isoform DNMT3A2. CEBPA, by interacting with DNMT3A N-terminus, blocks DNMT3A from accessing DNA substrate and thereby inhibits its activity. Recurrent tumor-associated CEBPA mutations, such as preleukemic CEBPA^N321D mutation, which is particularly potent in causing AML with high mortality, disrupt DNMT3A association and cause aberrant DNA methylation, notably hypermethylation of PRC2 target genes. Consequently, leukemia cells with the CEBPA^N321D mutation are hypersensitive to hypomethylation agents. Our results provide insights into the functional difference between DNMT3A isoforms and the regulation of de novo DNA methylation at specific loci in the genome. Our study also suggests a therapeutic strategy for the treatment of CEBPA-mutated leukemia with DNA-hypomethylating agents.

Cancer as a Metabolic Disorder

Cancer has long been considered a genetic disease characterized by a myriad of mutations that drive cancer progression. Recent accumulating evidence indicates that the dysregulated metabolism in cancer cells is more than a hallmark of cancer but may be the underlying cause of the tumor. Most of the well-characterized oncogenes or tumor suppressor genes function to sustain the altered metabolic state in cancer. Here, we review evidence supporting the altered metabolic state in cancer including key alterations in glucose, glutamine, and fatty acid metabolism. Unlike genetic alterations that do not occur in all cancer types, metabolic alterations are more common among cancer subtypes and across cancers. Recognizing cancer as a metabolic disorder could unravel key diagnostic and treatments markers that can impact approaches used in cancer management.

Beyond Isocitrate Dehydrogenase Mutations: Emerging Mechanisms for the Accumulation of the Oncometabolite 2-Hydroxyglutarate

2-Hydroxyglutarate (2-HG) is an unconventional oncometabolite of α-ketoglutarate. Isocitrate dehydrogenase mutation is generally acknowledged to be the main cause of 2-HG accumulation. In isocitrate dehydrogenase mutant tumors, 2-HG accumulation inhibits α-ketoglutarate/Fe(II)-dependent dioxygenases, resulting in epigenetic alterations. Recently, the increase of 2-HG has also been observed in the cases of mitochondrial dysfunction and hypoxia. In these cases, 2-HG not only inhibits α-ketoglutarate/Fe(II)-dependent dioxygenases to regulate epigenetics but also affects other cellular pathways, such as regulating hypoxia-inducible transcription factors and glycolysis. These provide a new perspective for the study of 2-HG.

Metabolomic Phenotyping of Gliomas: What Can We Get with Simplified Protocol for Intact Tissue Analysis?

Glioblastoma multiforme is one of the most malignant neoplasms among humans in their third and fourth decades of life, which is evidenced by short patient survival times and rapid tumor-cell proliferation after radiation and chemotherapy. At present, the diagnosis of gliomas and decisions related to therapeutic strategies are based on genetic testing and histological analysis of the tumor, with molecular biomarkers still being sought to complement the diagnostic panel. This work aims to enable the metabolomic characterization of cancer tissue and the discovery of potential biomarkers via high-resolution mass spectrometry coupled to liquid chromatography and a solvent-free sampling protocol that uses a microprobe to extract metabolites directly from intact tumors. The metabolomic analyses were performed independently from genetic and histological testing and at a later time. Despite the small cohort analyzed in this study, the results indicated that the proposed method is able to identify metabolites associated with different malignancy grades of glioma, as well as IDH and 1p19q codeletion mutations. A comparison of the constellation of identified metabolites and the results of standard tests indicated the validity of using the characterization of one comprehensive tumor phenotype as a reflection of all diagnostically meaningful information. Due to its simplicity, the proposed analytical approach was verified as being compatible with a surgical environment and applicable for large-scale studies.

Understanding the Crosstalk Between Epigenetics and Immunometabolism to Combat Cancer

The interaction between metabolic and epigenetic events shapes metabolic adaptations of cancer cells and also helps rewire the proliferation and activity of surrounding immune cells in the tumor microenvironment (TME). Recent studies indicate that the TME imposes metabolic constraints on immune cells, inducing them to attain a tolerogenic state, incompetent of mounting effective tumor eradication. Owing to extensive mutations acquired over repeated cell divisions, tumor cells selectively accumulate metabolites that regulate the activity of key epigenetic enzymes to mediate activation/suppression of genes associated with T-cell function and macrophage polarization. Further, multiple modulators connecting epigenetic and metabolic pathways help dictate the preferential induction of cytokines and expression of lineage-specifying genes associated with immunosuppressive T-cell differentiation.In this chapter, we attempt to discuss the mechanisms underpinning the metabolic and epigenetic interplay in immune cells of the TME and how modulating these events can boost the application of existing anticancer immunotherapy.

Diagnostic, therapeutic, and prognostic implications of the 2021 World Health Organization classification of tumors of the central nervous system

The 2016 revised fourth edition of the World Health Organization (WHO) classification of central nervous system (CNS) tumors incorporated molecular features with histologic grading, revolutionizing how oncologists conceptualize primary brain and spinal cord tumors as well as providing new insights into their management and prognosis. The 2021 revised fifth edition of the WHO classification further integrates molecular alterations for CNS tumor categorization, updating current understanding of the pathophysiology of many of these disease entities. Here, the authors review changes in the new classification for the most common primary adult tumors-gliomas (including astrocytomas, oligodendrogliomas, and ependymomas) and meningiomas-highlighting the key genomic alterations for each group classification to help clinicians interpret them as they consider therapeutic options-including clinical trials and targeted therapies-and discuss the prognosis of these tumors with their patients. The revised, updated 2021 WHO classification also further integrates molecular alterations in the classification of pediatric CNS tumors, but those are not covered in the current review.

IDH1/2 Mutations in Cancer Stem Cells and Their Implications for Differentiation Therapy

Isocitrate dehydrogenase 1 and 2 (IDH1/2) are enzymes recurrently mutated in various types of cancer, including glioma, cholangiocarcinoma, chondrosarcoma, and acute myeloid leukemia. Mutant IDH1/2 induce a block in differentiation and thereby contribute to the stemness and oncogenesis of their cells of origin. Recently, small-molecule inhibitors of mutant IDH1/2 have been Food and Drug Administration-approved for the treatment of IDH1/2-mutated acute myeloid leukemia. These inhibitors decrease the stemness of the targeted IDH1/2-mutated cancer cells and induce their differentiation to more mature cells. In this review, we elucidate the mechanisms by which mutant IDH1/2 induce a block in differentiation and the biological and clinical effects of the release into differentiation by mutant-IDH1/2 inhibitors. (J Histochem Cytochem 70:83-97, 2022).

Metabolic adaptations in cancers expressing isocitrate dehydrogenase mutations

The most frequently mutated metabolic genes in human cancer are those encoding the enzymes isocitrate dehydrogenase 1 (IDH1) and IDH2; these mutations have so far been identified in more than 20 tumor types. Since IDH mutations were first reported in glioma over a decade ago, extensive research has revealed their association with altered cellular processes. Mutations in IDH lead to a change in enzyme function, enabling efficient conversion of 2-oxoglutarate to R-2-hydroxyglutarate (R-2-HG). It is proposed that elevated cellular R-2-HG inhibits enzymes that regulate transcription and metabolism, subsequently affecting nuclear, cytoplasmic, and mitochondrial biochemistry. The significance of these biochemical changes for tumorigenesis and potential for therapeutic exploitation remains unclear. Here we comprehensively review reported direct and indirect metabolic changes linked to IDH mutations and discuss their clinical significance. We also review the metabolic effects of first-generation mutant IDH inhibitors and highlight the potential for combination treatment strategies and new metabolic targets.

Discovery of linear unnatural peptides as potent mutant isocitrate dehydrogenase 1 inhibitors by Ugi reaction

Isocitrate dehydrogenases 1 (IDH1) catalyzes the oxidative decarboxylation of isocitrate to ɑ-ketoglutaric acid (α-KG). It is the most frequently mutated metabolic gene in human cancer and its mutations interfere with cell metabolism and epigenetic regulation, thus promoting tumorigenesis. In order to discover potent new mutant IDH1 inhibitors, based on the structure of marketed inhibitor AG-120 (Ivosidenib), we designed, synthesized and evaluated a series of linear unnatural peptide analogues via Ugi reaction, as potential mutant IDH1 inhibitors. All these compounds were evaluated for their inhibition on mutant IDH1 enzyme activity. The structure-activity relationship was discussed on the basis of experimental data, with an attempt to pave the way for future studies. Among them, 43 exhibited potent and selective enzyme inhibitory activity, and showed strong binding affinity with mutant IDH1. It can decrease the cellular concentration of 2-HG, and suppress the proliferation of HT1080 and IDH1 mutant-U-87 cells by selectively inhibiting the activity of mutant IDH1.

Signalling metabolite L-2-hydroxyglutarate activates the transcription factor HIF-1α in lipopolysaccharide-activated macrophages

Activated macrophages undergo metabolic reprogramming, which not only supports their energetic demands but also allows for the production of specific metabolites that function as signaling molecules. Several Krebs cycles, or Krebs-cycle-derived metabolites, including succinate, α-ketoglutarate, and itaconate, have recently been shown to modulate macrophage function. The accumulation of 2-hydroxyglutarate (2HG) has also been well documented in transformed cells and more recently shown to play a role in T cell and dendritic cell function. Here we have found that the abundance of both enantiomers of 2HG is increased in LPS-activated macrophages. We show that L-2HG, but not D-2HG, can promote the expression of the proinflammatory cytokine IL-1β and the adoption of an inflammatory, highly glycolytic metabolic state. These changes are likely mediated through activation of the transcription factor hypoxia-inducible factor-1α (HIF-1α) by L-2HG, a known inhibitor of the HIF prolyl hydroxylases. Expression of the enzyme responsible for L-2HG degradation, L-2HG dehydrogenase (L-2HGDH), was also found to be decreased in LPS-stimulated macrophages and may therefore also contribute to L-2HG accumulation. Finally, overexpression of L-2HGDH in HEK293 TLR4/MD2/CD14 cells inhibited HIF-1α activation by LPS, while knockdown of L-2HGDH in macrophages boosted the induction of HIF-1α-dependent genes, as well as increasing LPS-induced HIF-1α activity. Taken together, this study therefore identifies L-2HG as a metabolite that can regulate HIF-1α in macrophages.

Isocitrate dehydrogenase gene variants in cancer and their clinical significance

Human isocitrate dehydrogenase (IDH) genes encode for the IDH1, 2 & 3 isoenzymes which catalyse the formation of 2-oxoglutarate from isocitrate and are essential for normal mammalian metabolism. Although mutations in these genes in cancer were long thought to lead to a 'loss of function', combined genomic and metabolomic studies led to the discovery that a common IDH 1 mutation, present in low-grade glioma and acute myeloid leukaemia (AML), yields a variant (R132H) with a striking change of function leading to the production of (2R)-hydroxyglutarate (2HG) which consequently accumulates in large quantities both within and outside cells. Elevated 2HG is proposed to promote tumorigenesis, although the precise mechanism by which it does this remains uncertain. Inhibitors of R132H IDH1, and other subsequently identified cancer-linked 2HG producing IDH variants, are approved for clinical use in the treatment of chemotherapy-resistant AML, though resistance enabled by additional substitutions has emerged. In this review, we provide a current overview of cancer linked IDH mutations focussing on their distribution in different cancer types, the effects of substitution mutations on enzyme activity, the mode of action of recently developed inhibitors, and their relationship with emerging resistance-mediating double mutations.

Potential of IDH mutations as immunotherapeutic targets in gliomas: a review and meta-analysis

INTRODUCTION

Gliomas are stratified by the presence of a hotspot mutation in the enzyme isocitrate dehydrogenase genes (IDH1/2). While mutated IDH (mIDH) correlates with better prognosis, the role of this mutation in antitumor immunity and the response to immunotherapy is not completely understood. Understanding the relationship between the genetic features of these tumors and the tumor immune microenvironment (TIME) may help to develop appropriate therapeutic strategies.

AREAS COVERED

In this review we discussed the available literature related to the potential role of IDH mutations as an immunotherapeutic target in gliomas and profiled the immune transcriptome of glioma biopsies. We aimed to shed light on the role of mIDH on the immunological landscape of the different subtypes of gliomas, taking into account the most recent WHO classification of tumors of the central nervous system (CNS). We also discussed different immunotherapeutic approaches to target mIDH tumors and to overcome their immunosuppressive microenvironment.

EXPERT OPINION

Data presented here indicates that the TIME not only differs in association with IDH mutation status, but also within glioma subtypes, suggesting that the cellular context affects the overall effect of this genetic lesion. Thus, specific therapeutic combinations may help patients diagnosed with different glioma subtypes.

Oncometabolites as Regulators of DNA Damage Response and Repair

Dysregulation of DNA damage response and repair (DDR) contributes to oncogenesis, yet also generates the potential for targeted cancer therapies by exploiting synthetic lethal interactions. Oncometabolites, small intermediates of metabolism overproduced in certain cancers, have emerged as a new mechanism of DDR modulation through their effects on multiple DNA repair pathways. Increasing evidence suggests that oncometabolite-induced DDR defects may offer the opportunity for tumor-selective chemo- and radio-sensitization. Here we review the biology of oncometabolites and diverse mechanisms by which they impact DDR, with a focus on emerging therapeutic strategies and ongoing clinical trials targeting oncometabolite-induced DDR defects in cancer.

Mutant-IDH inhibits Interferon-TET2 signaling to promote immunoevasion and tumor maintenance in cholangiocarcinoma

Isocitrate dehydrogenase 1 mutations (mIDH1) are common in cholangiocarcinoma. (R)-2-hydroxyglutarate generated by the mIDH1 enzyme inhibits multiple a-ketoglutarate-dependent enzymes, altering epigenetics and metabolism. Here, by developing mIDH1-driven genetically engineered mouse models, we show that mIDH1 supports cholangiocarcinoma tumor maintenance through an immunoevasion program centered on dual (R)-2-hydroxyglutarate-mediated mechanisms - suppression of CD8+ T cell activity and tumor cell-autonomous inactivation of TET2 DNA demethylase. Pharmacological mIDH1 inhibition stimulates CD8+ T cell recruitment and IFN-y expression and promotes TET2-dependent induction of IFN-y response genes in tumor cells. CD8+ T cell depletion or tumor cell-specific ablation of TET2 or Interferon-gamma receptor 1 causes treatment resistance. Whereas immune checkpoint activation limits mIDH1 inhibitor efficacy, CTLA4 blockade overcomes immunosuppression, providing therapeutic synergy. The findings in this mouse model of cholangiocarcinoma demonstrate that immune function and the IFN-y-TET2 axis are essential for response to mIDH1 inhibition and suggest a novel strategy for harnessing these inhibitors therapeutically.

Morin inhibits the transformation of fibroblasts towards myofibroblasts through regulating "PPAR-γ-glutaminolysis-DEPTOR" pathway in pulmonary fibrosis

Morin, a natural flavonoid exists in many foods and dietary plants, owns good bioactivities. Herein, we investigated its effect on pulmonary fibrosis (PF), and further explored the mechanisms. Results showed that morin remarkably improved the pathologic alterations, and inhibited the transformation of fibroblasts towards myofibroblasts in lungs of mice with bleomycin-induced PF as well as TGF-β1 or hypoxia-stimulated NIH-3T3 cells. Mechanistic studies revealed that morin activated peroxisome proliferator activated receptor-gamma (PPAR-γ), and GW9662 or siPPAR-γ significantly weakened the inhibition of morin on the transformation of NIH-3T3 cells. Furthermore, morin restricted glutaminolysis by down-regulating the level of glutaminase 1 (GLS1), which was confirmed by glutamine deprivation, and GLS1 overexpression. Replenishment of metabolite α-ketoglutarate (α-KG) and 2-hydroxyglutarate (2-HG) inhibited morin-prevented transformation of fibroblasts, but neither TGF-β1 nor hypoxia could induce the transformation of IDH2-knockdown fibroblasts, suggesting 2-HG was directly involved in the action of morin. Then, ubiquitination of DEPTOR was demonstrated to be prevented by morin, which was attributed to KDM4A, an enzyme inactivated by 2-HG, and leucine as well as KDM4A inhibitor obstructed the effect of morin. Finally, the mechanisms of morin were further confirmed in vivo. Collectively, morin inhibited PF through intervening in "PPAR-γ-glutaminolysis-DEPTOR" signals, and subsequent restriction on the transformation of fibroblasts towards myofibroblasts.

Inhibition of AlkB Nucleic Acid Demethylases: Promising New Epigenetic Targets

The AlkB family of nucleic acid demethylases is currently of intense chemical, biological, and medical interest because of its critical roles in several key cellular processes, including epigenetic gene regulation, RNA metabolism, and DNA repair. Emerging evidence suggests that dysregulation of AlkB demethylases may underlie the pathogenesis of several human diseases, particularly obesity, diabetes, and cancer. Hence there is strong interest in developing selective inhibitors for these enzymes to facilitate their mechanistic and functional studies and to validate their therapeutic potential. Herein we review the remarkable advances made over the past 20 years in AlkB demethylase inhibition research. We discuss the rational design of reported inhibitors, their mode-of-binding, selectivity, cellular activity, and therapeutic opportunities. We further discuss unexplored structural elements of the AlkB subfamilies and propose potential strategies to enable subfamily selectivity. It is hoped that this perspective will inspire novel inhibitor design and advance drug discovery research in this field.

2-Oxoglutarate derivatives can selectively enhance or inhibit the activity of human oxygenases

2-Oxoglutarate (2OG) oxygenases are validated agrochemical and human drug targets. The potential for modulating their activity with 2OG derivatives has not been explored, possibly due to concerns regarding selectivity. We report proof-of-principle studies demonstrating selective enhancement or inhibition of 2OG oxygenase activity by 2-oxo acids. The human 2OG oxygenases studied, factor inhibiting hypoxia-inducible transcription factor HIF-α (FIH) and aspartate/asparagine-β-hydroxylase (AspH), catalyze C3 hydroxylations of Asp/Asn-residues. Of 35 tested 2OG derivatives, 10 enhance and 17 inhibit FIH activity. Comparison with results for AspH reveals that 2OG derivatives selectively enhance or inhibit FIH or AspH. Comparison of FIH structures complexed with 2OG derivatives to those for AspH provides insight into the basis of the observed selectivity. 2-Oxo acid derivatives have potential as drugs, for use in biomimetic catalysis, and in functional studies. The results suggest that the in vivo activity of 2OG oxygenases may be regulated by natural 2-oxo acids other than 2OG.

The Interplay Between Prostate Cancer Genomics, Metabolism, and the Epigenome: Perspectives and Future Prospects

Prostate cancer is a high-incidence cancer, often detected late in life. The prostate gland is an accessory gland that secretes citrate; an impaired citrate secretion reflects imbalances in the activity of enzymes in the TCA Cycle in mitochondria. Profiling studies on prostate tumours have identified significant metabolite, proteomic, and transcriptional modulations with an increased mitochondrial metabolic activity associated with localised prostate cancer. Here, we focus on the androgen receptor, c-Myc, phosphatase and tensin Homolog deleted on chromosome 10 (PTEN), and p53 as amongst the best-characterised genomic drivers of prostate cancer implicated in metabolic dysregulation and prostate cancer progression. We outline their impact on metabolic function before discussing how this may affect metabolite pools and in turn chromatin structure and the epigenome. We reflect on some recent literature indicating that mitochondrial mutations and OGlcNAcylation may also contribute to this crosstalk. Finally, we discuss the technological challenges of assessing crosstalk given the significant differences in the spatial sensitivity and throughput of genomic and metabolomic profiling approaches.

Integration of Epigenetic Mechanisms into Non-Genotoxic Carcinogenicity Hazard Assessment: Focus on DNA Methylation and Histone Modifications

Epigenetics involves a series of mechanisms that entail histone and DNA covalent modifications and non-coding RNAs, and that collectively contribute to programing cell functions and differentiation. Epigenetic anomalies and DNA mutations are co-drivers of cellular dysfunctions, including carcinogenesis. Alterations of the epigenetic system occur in cancers whether the initial carcinogenic events are from genotoxic (GTxC) or non-genotoxic (NGTxC) carcinogens. NGTxC are not inherently DNA reactive, they do not have a unifying mode of action and as yet there are no regulatory test guidelines addressing mechanisms of NGTxC. To fil this gap, the Test Guideline Programme of the Organisation for Economic Cooperation and Development is developing a framework for an integrated approach for the testing and assessment (IATA) of NGTxC and is considering assays that address key events of cancer hallmarks. Here, with the intent of better understanding the applicability of epigenetic assays in chemical carcinogenicity assessment, we focus on DNA methylation and histone modifications and review: (1) epigenetic mechanisms contributing to carcinogenesis, (2) epigenetic mechanisms altered following exposure to arsenic, nickel, or phenobarbital in order to identify common carcinogen-specific mechanisms, (3) characteristics of a series of epigenetic assay types, and (4) epigenetic assay validation needs in the context of chemical hazard assessment. As a key component of numerous NGTxC mechanisms of action, epigenetic assays included in IATA assay combinations can contribute to improved chemical carcinogen identification for the better protection of public health.

One Omics Approach Does Not Rule Them All: The Metabolome and the Epigenome Join Forces in Haematological Malignancies

Aberrant DNA methylation, dysregulation of chromatin-modifying enzymes, and microRNAs (miRNAs) play a crucial role in haematological malignancies. These epimutations, with an impact on chromatin accessibility and transcriptional output, are often associated with genomic instability and the emergence of drug resistance, disease progression, and poor survival. In order to exert their functions, epigenetic enzymes utilize cellular metabolites as co-factors and are highly dependent on their availability. By affecting the expression of metabolic enzymes, epigenetic modifiers may aid the generation of metabolite signatures that could be utilized as targets and biomarkers in cancer. This interdependency remains often neglected and poorly represented in studies, despite well-established methods to study the cellular metabolome. This review critically summarizes the current knowledge in the field to provide an integral picture of the interplay between epigenomic alterations and the cellular metabolome in haematological malignancies. Our recent findings defining a distinct metabolic signature upon response to enhancer of zeste homolog 2 (EZH2) inhibition in multiple myeloma (MM) highlight how a shift of preferred metabolic pathways may potentiate novel treatments. The suggested link between the epigenome and the metabolome in haematopoietic tumours holds promise for the use of metabolic signatures as possible biomarkers of response to treatment.

Inhibition of JMJD6 by 2-Oxoglutarate Mimics

Studies on the inhibition of the human 2-oxoglutarate dependent oxygenase JMJD6, which is a cancer target, by 2-oxoglutarate mimics / competitors, including human drugs, drug candidates, and metabolites relevant to cancer are described. JMJD6 assays employed NMR to monitor inhibitor binding and use of mass spectrometry to monitor JMJD6-catalysed lysine hydroxylation. Notably, some clinically applied prolyl hydroxylase inhibitors also inhibit JMJD6. The results will help enable the development of inhibitors selective for human oxygenases, including JMJD6.

Atomic Force Microscope Nanoindentation Analysis of Diffuse Astrocytic Tumor Elasticity: Relation with Tumor Histopathology

This study aims to investigate the influence of isocitrate dehydrogenase gene family (IDH) mutations, World Health Organization (WHO) grade, and mechanical preconditioning on glioma and adjacent brain elasticity through standard monotonic and repetitive atomic force microscope (AFM) nanoindentation. The elastic modulus was measured ex vivo on fresh tissue specimens acquired during craniotomy from the tumor and the peritumoral white matter of 16 diffuse glioma patients. Linear mixed-effects models examined the impact of tumor traits and preconditioning on tissue elasticity. Tissues from IDH-mutant cases were stiffer than those from IDH-wildtype ones among anaplastic astrocytoma patients (p = 0.0496) but of similar elasticity to IDH-wildtype cases for diffuse astrocytoma patients (p = 0.480). The tumor was found to be non-significantly softer than white matter in anaplastic astrocytomas (p = 0.070), but of similar elasticity to adjacent brain in diffuse astrocytomas (p = 0.492) and glioblastomas (p = 0.593). During repetitive indentation, both tumor (p = 0.002) and white matter (p = 0.003) showed initial stiffening followed by softening. Stiffening was fully reversed in white matter (p = 0.942) and partially reversed in tumor (p = 0.015). Tissue elasticity comprises a phenotypic characteristic closely related to glioma histopathology. Heterogeneity between patients should be further explored.

HIF-1-Independent Mechanisms Regulating Metabolic Adaptation in Hypoxic Cancer Cells

In solid tumours, cancer cells exist within hypoxic microenvironments, and their metabolic adaptation to this hypoxia is driven by HIF-1 transcription factor, which is overexpressed in a broad range of human cancers. HIF inhibitors are under pre-clinical investigation and clinical trials, but there is evidence that hypoxic cancer cells can adapt metabolically to HIF-1 inhibition, which would provide a potential route for drug resistance. Here, we review accumulating evidence of such adaptions in carbohydrate and creatine metabolism and other HIF-1-independent mechanisms that might allow cancers to survive hypoxia despite anti-HIF-1 therapy. These include pathways in glucose, glutamine, and lipid metabolism; epigenetic mechanisms; post-translational protein modifications; spatial reorganization of enzymes; signalling pathways such as Myc, PI3K-Akt, 2-hyxdroxyglutarate and AMP-activated protein kinase (AMPK); and activation of the HIF-2 pathway. All of these should be investigated in future work on hypoxia bypass mechanisms in anti-HIF-1 cancer therapy. In principle, agents targeted toward HIF-1β rather than HIF-1α might be advantageous, as both HIF-1 and HIF-2 require HIF-1β for activation. However, HIF-1β is also the aryl hydrocarbon nuclear transporter (ARNT), which has functions in many tissues, so off-target effects should be expected. In general, cancer therapy by HIF inhibition will need careful attention to potential resistance mechanisms.

D-2-Hydroxyglutarate in Glioma Biology

Isocitrate dehydrogenase (IDH) mutations are common genetic abnormalities in glioma, which result in the accumulation of an "oncometabolite", D-2-hydroxyglutarate (D-2-HG). Abnormally elevated D-2-HG levels result in a distinctive pattern in cancer biology, through competitively inhibiting α-ketoglutarate (α-KG)/Fe(II)-dependent dioxgenases (α-KGDDs). Recent studies have revealed that D-2-HG affects DNA/histone methylation, hypoxia signaling, DNA repair, and redox homeostasis, which impacts the oncogenesis of IDH-mutated cancers. In this review, we will discuss the current understanding of D-2-HG in cancer biology, as well as the emerging opportunities in therapeutics in IDH-mutated glioma.

IDH2 contributes to tumorigenesis and poor prognosis by regulating m6A RNA methylation in multiple myeloma

Epigenetic alterations have been previously shown to contribute to multiple myeloma (MM) pathogenesis via DNA methylations and histone modifications. RNA methylation, a novel epigenetic modification, is required for cancer cell survival, and targeting this pathway has been proposed as a new therapeutic strategy. The extent to the N6-methyladenosine (m6A)-regulatory pathway functions in MM remains unknown. Here, we show that an imbalance of RNA methylation may underlies the tumorigenesis of MM. Mechanistically, isocitrate dehydrogenase 2 (IDH2) is highly expressed in CD138+ cells from MM and its levels appear a progressive increase in the progression of plasma cell dyscrasias. Downregulation of IDH2 increases global m6A RNA levels and reduces myeloma cell growth in vitro, decreases the burden of disease and prolongs overall survival in vivo. IDH2 regulates RNA methylation by activating the RNA demethylase FTO, which is an α-KG-dependent dioxygenase. Furthermore, IDH2-mediated FTO activation decreases the m6A level on WNT7B transcripts, then increases WNT7B expression and thus activated Wnt signaling pathway. Moreover, survival analysis indicates that the elevated expression of IDH2 predicts a poor prognosis. Higher expression of FTO is related to higher International Staging System (ISS) stage and higher Revised-ISS (R-ISS) stage of MM. Collectively, our studies reveal that IDH2 regulates global m6A RNA modification in MM via targeting RNA demethylases FTO. The imbalance of m6A methylation activates the Wnt signaling pathway by enhancing the WNT7B expression, and thus promoting tumorigenesis and progression of MM. IDH2 might be used as a therapeutic target and a possible prognostic factor for MM.