IDH mutations in human glioma

IMPDH Inhibition Decreases TERT Expression and Synergizes the Cytotoxic Effect of Chemotherapeutic Agents in Glioblastoma Cells

IMP dehydrogenase (IMPDH) inhibition has emerged as a new target therapy for glioblastoma multiforme (GBM), which remains one of the most refractory tumors to date. TCGA analyses revealed distinct expression profiles of IMPDH isoenzymes in various subtypes of GBM and low-grade glioma (LGG). To dissect the mechanism(s) underlying the anti-tumor effect of IMPDH inhibition in adult GBM, we investigated how mycophenolic acid (MPA, an IMPDH inhibitor) treatment affected key oncogenic drivers in glioblastoma cells. Our results showed that MPA decreased the expression of telomerase reverse transcriptase (TERT) in both U87 and U251 cells, and the expression of O6-methylguanine-DNA methyltransferase (MGMT) in U251 cells. In support, MPA treatment reduced the amount of telomere repeats in U87 and U251 cells. TERT downregulation by MPA was associated with a significant decrease in c-Myc (a TERT transcription activator) in U87 but not U251 cells, and a dose-dependent increase in p53 and CCCTC-binding factor (CTCF) (TERT repressors) in both U87 and U251 cells. In U251 cells, MPA displayed strong cytotoxic synergy with BCNU and moderate synergy with irinotecan, oxaliplatin, paclitaxel, or temozolomide (TMZ). In U87 cells, MPA displayed strong cytotoxic synergy with all except TMZ, acting primarily through the apoptotic pathway. Our work expands the mechanistic potential of IMPDH inhibition to TERT/telomere regulation and reveals a synthetic lethality between MPA and anti-GBM drugs.

The role of immune subtyping in glioma mRNA vaccine development

Studies on the development of mRNA vaccines for central nervous system tumors have used gene expression profiles, clinical data and RNA sequencing from sources such as The Cancer Genome Atlas and Chinese Glioma Genome Atlas to identify effective antigens. These studies revealed several immune subtypes of glioma, each one linked to unique prognoses and genetic/immune-modulatory changes. Potential antigens include ARPC1B, BRCA2, COL6A1, ITGB3, IDH1, LILRB2, TP53 and KDR, among others. Patients with immune-active and immune-suppressive phenotypes were found to respond better to mRNA vaccines. While these findings indicate the potential of mRNA vaccines in cancer therapy, further research is required to optimize administration and adjuvant selection, and precisely identify target antigens.

A Comprehensive View(COUP D'OEIL) of Brain Tumors from Eastern India

BACKGROUND

Brain tumors have always fascinated and intrigued histopathologists due to their diverse morphology and rarity. Recent surge in the molecular developments has further posed a challenge in diagnosis especially in a resource limited setting. Therefore, comprehensive tumor registries have become quintessential to compare our existing database with new found knowledge.

METHODS

A descriptive retrospective study was carried out on archival data of 5 years in a neuroscience institute. All neurosurgical cases operated with complete clinical history and definitive histopathological diagnosis were included. The cases were analyzed with reference to age, sex, location of the lesion, grade of the tumor, and immunohistochemical profile as available and compared with existing registries and literature.

RESULTS

The primary brain tumors accounted for 38.29% of all pathologies. Majority of cases clustered around 40-70 years of age (65%). Pediatric (0-19 years) cases comprised 7%. Most common primary brain tumor found in the adult population was meningioma (28%) followed by Glioblastoma (25%). The most common neoplasm in pediatric age group were gliomas (46.29%) followed by embryonal neoplasms. Pituitary adenomas (PAs) constituted 16% of all intracranial neoplasm. Gonadotroph adenoma was the most common of the nonfunctional adenomas constituting one half of the PAs (51.72%). Somatotroph adenoma was most common in the functional group constituting 20% of all PAs.

CONCLUSIONS

The layout of cases when compared with available brain tumor registries showed nearly similar trends in distribution. Our study succored data from the population in eastern part of India of which our institute is a major referral centre for neurosurgical cases.

Based on clinical Ki-67 expression and serum infiltrating lymphocytes related nomogram for predicting the diagnosis of glioma-grading

Background

Compelling evidence indicates that elevated peripheral serum lymphocytes are associated with a favorable prognosis in various cancers. However, the association between serum lymphocytes and glioma is contradictory. In this study, a nomogram was established to predict the diagnosis of glioma-grading through Ki-67 expression and serum lymphocytes.

Methods

We performed a retrospective analysis of 239 patients diagnosed with LGG and 178 patients with HGG. Immunohistochemistry was used to determine the Ki-67 expression. Following multivariate logistic regression analysis, a nomogram was established and used to identify the most related factors associated with HGG. The consistency index (C-index), decision curve analysis (DCA), and a calibration curve were used to validate the model.

Results

The number of LGG patients with more IDH1/2 mutations and 1p19q co-deletion was greater than that of HGG patients. The multivariate logistic analysis identified Ki-67 expression, serum lymphocyte count, and serum albumin (ALU) as independent risk factors associated with HGG, and these factors were included in a nomogram in the training cohort. In the validation cohort, the nomogram demonstrated good calibration and high consistency (C-index = 0.794). The Spearman correlation analysis revealed a significant association between HGG and serum lymphocyte count (r = −0.238, P <0.001), ALU (r = −0.232, P <0.001), and Ki-67 expression (r = 0.457, P <0.001). Furthermore, the Ki-67 expression was negatively correlated with the serum lymphocyte count (r = −0.244, P <0.05). LGG patients had lower Ki-67 expression and higher serum lymphocytes compared with HGG patients, and a combination of these two variables was significantly higher in HGG patients.

Conclusion

The constructed nomogram is capable of predicting the diagnosis of glioma-grade. A decrease in the level of serum lymphocyte count and increased Ki-67 expression in HGG patients indicate that their immunological function is diminished and the tumor is more aggressive.

Early atypical malignant transformation of diffuse low-grade astrocytoma: The importance of genotyping

Diffuse astrocytoma (WHO grade II) has classically been considered a slow growing tumour, typically affecting young adults, with tendency for late malignant conversion. We describe a case of early atypical malignant transformation of diffuse astrocytoma seventeen months after complete surgical removal, as an intraventricular high-grade glioma (HGG). Retrospective laboratory findings for the presence of IDH 1/2 (isocitrate dehydrogenase) mutations were negative. There is growing evidence that IDH-wildtype (wt) astrocytomas behave more aggressively, therefore identifying IDH-mutation status should be mandatory in order to determine disease prognosis and guide treatment course.

IDH1 gene mutation activates Smad signaling molecules to regulate the expression levels of cell cycle and biological rhythm genes in human glioma U87‑MG cells

Isocitrate dehydrogenase1 (IDH1) mutation is the most important genetic change in glioma. The most common IDH1 mutation results in the amino acid substitution of arginine 132 (Arg/R132), which is located at the active site of the enzyme. IDH1 Arg132His (R132H) mutation can reduce the proliferative rate of glioma cells. Numerous diseases follow circadian rhythms, and there is growing evidence that circadian disruption may be a risk factor for cancer in humans. Dysregulation of the circadian clock serves an important role in the development of malignant tumors, including glioma. Brain-Muscle Arnt-Like protein 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) are the main biological rhythm genes. The present study aimed to further study whether there is an association between IDH1 R132H mutation and biological rhythm in glioma, and whether this affects the occurrence of glioma. The Cancer Genome Atlas (TCGA) database was used to detect the expression levels of the biological rhythm genes BMAL1 and CLOCK in various types of tumor. Additionally, U87-MG cells were infected with wild-type and mutant IDH1 lentiviruses. Colony formation experiments were used to detect cell proliferation in each group, cell cycle distribution was detected by flow cytometry and western blotting was used to detect the expression levels of wild-type and mutant IDH1, cyclins, biological rhythm genes and Smad signaling pathway-associated genes in U87-MG cells. TCGA database results suggested that BMAL1 and CLOCK were abnormally expressed in glioma. Cells were successfully infected with wild-type and mutant IDH1 lentiviruses. Colony formation assay revealed decreased cell proliferation in the IDH1 R132H mutant group. The cell cycle distribution detected by flow cytometry indicated that IDH1 gene mutation increased the G₁ phase ratio and decreased the S phase ratio in U87-MG cells. The western blotting results demonstrated that IDH1 R132H mutation decreased the expression levels of the S phase-associated proteins Cyclin A and CDK2, and increased the expression levels of the G₁ phase-associated proteins Cyclin D3 and CDK4, but did not significantly change the expression levels of the G₂/M phase-associated protein Cyclin B1. The expression levels of the positive and negative rhythm regulation genes BMAL1, CLOCK, period (PER s (PER1, 2 and 3) and cryptochrom (CRY)s (CRY1 and 2) were significantly decreased, those of the Smad signaling pathway-associated genes Smad2, Smad3 and Smad2-3 were decreased, and those of phosphorylated (p)-Smad2, p-Smad3 and Smad4 were increased. Therefore, the present results suggested that the IDH1 R132H mutation may alter the cell cycle and biological rhythm genes in U87-MG cells through the TGF-β/Smad signaling pathway.

Integrated Proteogenomic Characterization across Major Histological Types of Pediatric Brain Cancer

We report a comprehensive proteogenomics analysis, including whole-genome sequencing, RNA sequencing, and proteomics and phosphoproteomics profiling, of 218 tumors across 7 histological types of childhood brain cancer: low-grade glioma (n = 93), ependymoma (32), high-grade glioma (25), medulloblastoma (22), ganglioglioma (18), craniopharyngioma (16), and atypical teratoid rhabdoid tumor (12). Proteomics data identify common biological themes that span histological boundaries, suggesting that treatments used for one histological type may be applied effectively to other tumors sharing similar proteomics features. Immune landscape characterization reveals diverse tumor microenvironments across and within diagnoses. Proteomics data further reveal functional effects of somatic mutations and copy number variations (CNVs) not evident in transcriptomics data. Kinase-substrate association and co-expression network analysis identify important biological mechanisms of tumorigenesis. This is the first large-scale proteogenomics analysis across traditional histological boundaries to uncover foundational pediatric brain tumor biology and inform rational treatment selection.

Early atypical malignant transformation of diffuse low-grade astrocytoma: The importance of genotyping

Diffuse astrocytoma (WHO grade II) has classically been considered a slow growing tumour, typically affecting young adults, with tendency for late malignant conversion. We describe a case of early atypical malignant transformation of diffuse astrocytoma seventeen months after complete surgical removal, as an intraventricular high-grade glioma (HGG). Retrospective laboratory findings for the presence of IDH 1/2 (isocitrate dehydrogenase) mutations were negative. There is growing evidence that IDH-wildtype (wt) astrocytomas behave more aggressively, therefore identifying IDH-mutation status should be mandatory in order to determine disease prognosis and guide treatment course.

Metabolic plasticity of IDH1-mutant glioma cell lines is responsible for low sensitivity to glutaminase inhibition

Background

Targeting glutamine metabolism in cancer has become an increasingly vibrant area of research. Mutant IDH1 (IDH1^mut) gliomas are considered good candidates for targeting this pathway because of the contribution of glutamine to their newly acquired function: synthesis of 2-hydroxyglutarate (2HG).

Methods

We have employed a combination of ¹³C tracers including glutamine and glucose for investigating the metabolism of patient-derived IDH1^mut glioma cell lines through NMR and LC/MS. Additionally, genetic loss-of-function (in vitro and in vivo) approaches were performed to unravel the adaptability of these cell lines to the inhibition of glutaminase activity.

Results

We report the adaptability of IDH1^mut cells’ metabolism to the inhibition of glutamine/glutamate pathway. The glutaminase inhibitor CB839 generated a decrease in the production of the downstream metabolites of glutamate, including those involved in the TCA cycle and 2HG. However, this effect on metabolism was not extended to viability; rather, our patient-derived IDH1^mut cell lines display a metabolic plasticity that allows them to overcome glutaminase inhibition.

Conclusions

Major metabolic adaptations involved pathways that can generate glutamate by using alternative substrates from glutamine, such as alanine or aspartate. Indeed, asparagine synthetase was upregulated both in vivo and in vitro revealing a new potential therapeutic target for a combinatory approach with CB839 against IDH1^mut gliomas.

Novel Treatment Strategies for Glioblastoma

Glioblastoma (GBM) is the most common primary central nervous system tumor in adults. It is a highly invasive disease, making it difficult to achieve a complete surgical resection, resulting in poor prognosis with a median survival of 12–15 months after diagnosis, and less than 5% of patients survive more than 5 years. Surgical, instrument technology, diagnostic and radio/chemotherapeutic strategies have slowly evolved over time, but this has not translated into significant increases in patient survival. The current standard of care for GBM patients involving surgery, radiotherapy, and concomitant chemotherapy temozolomide (known as the Stupp protocol), has only provided a modest increase of 2.5 months in median survival, since the landmark publication in 2005. There has been considerable effort in recent years to increase our knowledge of the molecular landscape of GBM through advances in technology such as next-generation sequencing, which has led to the stratification of the disease into several genetic subtypes. Current treatments are far from satisfactory, and studies investigating acquired/inherent resistance to current therapies, restricted drug delivery, inter/intra-tumoral heterogeneity, drug repurposing and a tumor immune-evasive environment have been the focus of intense research over recent years. While the clinical advancement of GBM therapeutics has seen limited progression compared to other cancers, developments in novel treatment strategies that are being investigated are displaying encouraging signs for combating this disease. This aim of this editorial is to provide a brief overview of a select number of these novel therapeutic approaches.

Clinicopathological Features and Prognosis of Indonesian Patients with Gliomas with IDH Mutation: Insights into Its Significance in a Southeast Asian Population

Background:

Gliomas remain one of the most common primary brain tumors. Mutations in the isocitrate dehydrogenase (IDH) gene are associated with a distinct set of clinicopathological profiles. However, the distribution and significance of these mutations have never been studied in the Indonesian population. This study aimed to elucidate the association between IDH mutations and clinicopathological as well as prognostic profiles of Indonesian patients with gliomas.

Methods:

In total, 106 patients with gliomas were recruited from a tertiary academic medical center in Yogyakarta, Indonesia. Formalin-fixed paraffin-embedded and fresh tissue specimens were obtained and sectioned for hematoxylin-eosin staining and immunohistochemical examinations. Genomic DNA was isolated and analyzed for the presence of IDH mutations using standard polymerase chain reaction and nucleotide sequencing methods. Clinicopathological data were collected from medical records.

Results:

Although no IDH2 mutation was identified, IDH1 mutations were found in 23 (21.7%) of the patients. Patients with IDH1 mutations tended to have a history of smoking and a shorter interval between onset of symptoms and initial surgical interventions. Frontal lobe involvement, oligodendroglial histology, lower Ki67 expression, WHO grades II and III gliomas, and methylated O6-methylguanine-DNA methyltransferase (MGMT) promoters were significantly associated with the presence of IDH1 mutations. Compared with patients with IDH1-wild-type, patients with IDH1 mutation were observed to have a longer overall survival.

Conclusions:

IDH1 mutations are associated with certain clinicopathological and prognostic profiles in Indonesian patients with gliomas. This finding demonstrates the importance of identifying IDH mutations as part of the management of patients with glioma in Indonesia.

Molecular Classification of Diffuse Gliomas

Technological advances in the field of molecular genetics have improved the ability to classify brain tumors into subgroups with distinct clinical features and important therapeutic implications. The World Health Organization’s newest update on classification of gliomas (2016) incorporated isocitrate dehydrogenase 1 and 2 mutations, ATRX loss, 1p/19q codeletion status, and TP53 mutations to allow for improved classification of glioblastomas, low-grade and anaplastic gliomas. This paper reviews current advances in the understanding of diffuse glioma classification and the impact of molecular markers and DNA methylation studies on survival of patients with these tumors. We also discuss whether the classification and grading of diffuse gliomas should be based on histological findings, molecular markers, or DNA methylation subgroups in future iterations of the classification system.

Wild-Type IDH1 and Mutant IDH1 Opposingly Regulate Podoplanin Expression in Glioma

Isocitrate dehydrogenase (IDH) mutations occur frequently in lower-grade gliomas, which result in genome-wide epigenetic alterations. The wild-type IDH1 is reported to participate in lipid biosynthesis and amino acid metabolism, but its role in tumorigenesis is still unclear. In this study, the expressions of IDH1 and podoplanin (Pdpn) were determined in IDH-mutated and IDH-wild-type gliomas, and their relationships in glioma were further analyzed. In addition, the regulation of wild-type IDH1 and mutant IDH1 on Pdpn expression was investigated by luciferase assays and promoter methylation analysis. Our study showed that Pdpn was almost undetectable in IDH-mutated glioma but strongly expressed in higher-grade IDH-wild-type glioma. Pdpn overexpression promoted the migration of glioma cells but had little effect on cell growth. Moreover, Pdpn expression was positively correlated with the increased wild-type IDH1 levels in IDH-wild-type glioma. Consistently, the wild-type IDH1 greatly promoted the transcription and expression of Pdpn, but the mutant IDH1 and D-2-hydroxyglutarate significantly suppressed Pdpn expression in glioma cells. Besides, our results revealed that the methylation of CpG islands in the Pdpn promoter was opposingly regulated by wild-type and mutant IDH1 in glioma. Collectively, our results indicated that wild-type and mutant IDH1 opposingly controlled the Pdpn expression in glioma by regulating its promoter methylation, which provides a basis for understanding the relationship between wild-type and mutant IDH1 in epigenetic regulation and tumorigenesis.

Comparison Between 18F-Dopa and 18F-Fet PET/CT in Patients with Suspicious Recurrent High Grade Glioma: A Literature Review and Our Experience

PURPOSES

The aims of the present study were to: 1- critically assess the utility of L-3,4- dihydroxy-6-18Ffluoro-phenyl-alanine (18F-DOPA) and O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET) Positron Emission Tomography (PET)/Computed Tomography (CT) in patients with high grade glioma (HGG) and 2- describe the results of 18F-DOPA and 18F-FET PET/CT in a case series of patients with recurrent HGG.

METHODS

We searched for studies using the following databases: PubMed, Web of Science and Scopus. The search terms were: glioma OR brain neoplasm and DOPA OR DOPA PET OR DOPA PET/CT and FET OR FET PET OR FET PET/CT. From a mono-institutional database, we retrospectively analyzed the 18F-DOPA and 18F-FET PET/CT of 29 patients (age: 56 ± 12 years) with suspicious for recurrent HGG. All patients underwent 18F-DOPA or 18F-FET PET/CT for a multidisciplinary decision. The final definition of recurrence was made by magnetic resonance imaging (MRI) and/or multidisciplinary decision, mainly based on the clinical data.

RESULTS

Fifty-one articles were found, of which 49 were discarded, therefore 2 studies were finally selected. In both the studies, 18F-DOPA and 18F-FET as exchangeable in clinical practice particularly for HGG patients. From our institutional experience, in 29 patients, we found that sensitivity, specificity and accuracy of 18F-DOPA PET/CT in HGG were 100% (95% confidence interval- 95%CI - 81-100%), 63% (95%CI: 39-82%) and 62% (95%CI: 39-81%), respectively. 18F-FET PET/CT was true positive in 4 and true negative in 4 patients. Sensitivity, specificity and accuracy for 18F-FET PET/CT in HGG were 100%.

CONCLUSION

18F-DOPA and 18F-FET PET/CT have a similar diagnostic accuracy in patients with recurrent HGG. However, 18F-DOPA PET/CT could be affected by inflammation conditions (false positive) that can alter the final results. Large comparative trials are warranted in order to better understand the utility of 18F-DOPA or 18F-FET PET/CT in patients with HGG.

Twenty Metabolic Genes Based Signature Predicts Survival of Glioma Patients

Background: Glioma, caused by carcinogenesis of brain and spinal glial cells, is the most common primary malignant brain tumor. To find the important indicator for glioma prognosis is still a challenge and the metabolic alteration of glioma has been frequently reported recently.

Methods: In our current work, a risk score model based on the expression of twenty metabolic genes was developed using the metabolic gene expressions in The Cancer Genome Atlas (TCGA) dataset, the methods of which included the cox multivariate regression and the random forest variable hunting, a kind of machine learning algorithm, and the risk score generated from this model is used to make predictions in the survival of glioma patients in the training dataset. Subsequently, the result was further verified in other three verification sets (GSE4271, GSE4412 and GSE16011). Risk score related pathways collected in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were identified using Gene Set Enrichment Analysis (GSEA).

Results: The risk score generated from our model makes good predictions in the survival of glioma patients in the training dataset and other three verification sets. By assessing the relationships between clinical indicators and the risk score, we found that the risk score was an independent and significant indicator for the prognosis of glioma patients. Simultaneously, we conducted a survival analysis of the patients who received chemotherapy and who did not, finding that the risk score was equally valid in both cases. And signaling pathways related to the genesis and development of multiple cancers were also identified.

Conclusions: In summary, our risk score model is predictive for 967 glioma patients' survival from four independent datasets, and the risk score is a meaningful and independent parameter of the clinicopathological information.

GLUT5 increases fructose utilization and promotes tumor progression in glioma

Fructose is now such an important component of human diets, and several studies have found that some cancer cells could utilize fructose to overcome low glucose micro-environment, but the study on the role of fructose in glioma is rare. To explore the role of fructose in glioma, we detected the proliferation and colony formation ability of glioma cells in fructose medium, and found that the abilities of proliferation and colony formation of glioma cells in fructose medium were similar with abilities in glucose medium, however, fructose just partly restored proliferation ability of normal glial cells. To explore the mechanism, we compared the expression level of GLUT5 (Glucose transporter type 5) in these cell lines, and the results showed that glioma cell lines had higher GLUT5 expression than normal glial cell lines. And knockdown of GLUT5 could significantly inhabit cell proliferation of glioma cells in fructose medium. Furthermore, we found that GLUT5 was also higher expressed in glioma tissues, and GLUT5 expression correlated significantly with glioma malignancy and poor survival of glioma patients (p < 0.01). In addition, we also demonstrated that knockdown of GLUT5 could significantly inhabit tumor proliferation in vivo, and intake fructose could increase tumor volume prominently. Taken together, our data show that fructose can be used by glioma cells, and restrict the fructose intake or targeting GLUT5 could be efficacious strategies in glioma.

The diagnostic accuracy of detecting malignant transformation of low-grade glioma using O-(2-[18F]fluoroethyl)-l-tyrosine positron emission tomography: a retrospective study

OBJECTIVE

The diagnostic accuracy of O-(2-[18F]fluoroethyl)-l-tyrosine (FET) PET scanning in detecting the malignant transformation of low-grade gliomas (LGGs) is controversial. In this study, the authors retrospectively assessed the diagnostic potential of FET PET in patients with MRI-suspected malignant progression of LGGs that had previously been treated and the relationship between FET uptake and MRI and molecular biomarkers.

METHODS

Forty-two patients who had previously undergone surgical or multimodal treatment for a histologically verified LGG were referred for FET PET assessment because of clinical signs and/or MRI findings suggestive of tumor progression. Maximal and mean tumor-to-brain ratios (TBRmax and TBRmean, respectively) on FET PET as well as kinetic FET PET parameters (time to peak [TTP] and time-activity curve [TAC]) were determined. Final diagnoses were confirmed histologically. The diagnostic accuracy of FET parameters, separately and combined, for the detection of malignant progression was evaluated using receiver operating characteristic (ROC) curve analysis. Possible predictors that might influence the diagnostic accuracy of FET PET were assessed using multiple linear regression analysis. Spearman’s rank correlation r method was applied to determine the correlation between TBRmax and TAC, and molecular biomarkers from tumor tissues.

RESULTS

A total of 47 FET PET scans were obtained and showed no significant association between FET parameters and contrast enhancement on MRI. ROC curve analyses overall were unable to demonstrate any significant differentiation between nontransformed LGGs and LGGs that had transformed to high-grade gliomas when evaluating FET parameters separately or combined. After excluding the oligodendroglial subgroup, a significant difference was observed between nontransformed and transformed LGGs when combining FET parameters (i.e., TBRmax > 1.6, TAC describing a plateau or decreasing pattern, and TTP < 25 minutes), with the best result yielded by a combined analysis of TBRmax > 1.6 and TAC with a plateau or decreasing pattern (sensitivity 75% and specificity 83%, p = 0.003). The difference was even greater when patients who had previously undergone oncological treatment were also excluded (sensitivity 93% and specificity 100%, p = 0.001). Multiple linear regression analysis revealed that the presence of an oligodendroglial component (p = 0.029), previous oncological treatment (p = 0.039), and the combined FET parameters (p = 0.027) were significant confounding factors in the detection of malignant progression. TBRmax was positively correlated with increasing cell density (p = 0.040) and inversely correlated with IDH1 mutation (p = 0.006).

CONCLUSIONS

A single FET PET scan obtained at the time of radiological and/or clinical progression seems to be of limited value in distinguishing transformed from nontransformed LGGs, especially if knowledge of the primary tumor histopathology is not known. Therefore, FET PET imaging alone is not adequate to replace histological confirmation, but it may provide valuable information on the location and delineation of active tumor tissue, as well as an assessment of tumor biology in a subgroup of LGGs.

Interaction Between the Contributions of Tumor Location, Tumor Grade, and Patient Age to the Survival Benefit Associated with Gross Total Resection

BACKGROUND

Gross total resection (GTR) in patients with glioblastoma (GB) and anaplastic astrocytoma (AA) is associated with improved survival. We examined how tumor location, tumor grade, and age affected this benefit.

METHODS

We selected patients with lobar AA or GB in the Surveillance, Epidemiology, and End Results database from 1999 to 2010. Survival analyses were performed using Kaplan-Meier curves and Cox proportional hazards models.

RESULTS

We identified and studied 1429 patients with lobar AA and 12,537 patients with lobar GB in the Surveillance, Epidemiology, and End Results database. In multivariate Cox proportional hazards analysis, GTR of frontal lobe AA was associated with approximately 50% reduction in risk of death compared with subtotal resection (STR) (hazard ratio 0.51; 95% confidence interval, 0.36-0.73; P < 0.001). This hazard ratio corresponds to a median increase in overall survival of >8 years with GTR compared with STR. In nonfrontal AAs, there was no survival difference between GTR and STR (hazard ratio 0.79; 95% confidence interval, 0.58-1.08; P = 0.143). Location-specific survival benefit from GTR in AAs was significant in patients ≤50 years old but was not evident in patients >50 years old. In patients with GB, no location-dependent survival benefit with GTR was observed.

CONCLUSIONS

Our results demonstrate complex interaction between tumor grade, frontal lobe location, and age in their various contributions to survival benefit gained from GTR. The greatest survival benefit of GTR relative to STR was observed in patients ≤50 years old with frontal AAs.

Non-canonical IDH1 and IDH2 mutations: a clonal and relevant event in an Italian cohort of gliomas classified according to the 2016 World Health Organization (WHO) criteria

According to the 2016 World Health Organization (WHO) classification of tumors of the central nervous system, assessment of exon 4 mutations in isocitrate dehydrogenase 1 or 2 genes (IDH1 or IDH2) is an essential step in the characterization of gliomas. The p.R132H mutation is the most frequent alteration in IDH genes, however other non-canonical IDH mutations can be identified. The aim of this study is to investigate in depth the prevalence of non-R132H IDH ("non-canonical") mutations in brain tumors classified according to the 2016 WHO scheme and their clonal distribution in neoplastic cells. A total of 288 consecutive cases of brain gliomas (grade II-IV) were analyzed for exon 4 IDH1 and IDH2 mutations. IDH1 and IDH2 analysis was performed using next generation sequencing. Non-canonical IDH mutations were identified in 13/52 (25.0%) grade II gliomas (astrocytomas: 8/31, 25.8%; oligodendrogliomas: 5/21, 23.8%) and in 5/40 (12.5%) grade III gliomas (astrocytomas: 3/25, 12.0%; oligodendrogliomas: 2/15, 13.3%). They were not identified in 196 grade IV gliomas (192 glioblastomas, 4 gliosarcomas). In the large majority (>80%) of tumors IDH mutations, both IDH1-R132H and the non-canonical ones, were present in the large majority (>80%) of neoplastic cells. Our data highlight the importance of investigating not only the IDH1-R132H mutation but also the non-canonical ones. These mutations are clonally distributed, with proportions of mutated neoplastic cells overlapping with those of p.R132H, a finding consistent with their driver role in gliomagenesis.

Influence of neutrophil-lymphocyte ratio in prognosis of glioblastoma multiforme

Neutrophil-lymphocyte ratio (NLR) is a hematological marker of systemic inflammation and several studies demonstrate an association between a higher NLR and a worse prognosis in many malignancies. However, literature analyzing its prognostic value in glioblastoma multiforme (GBM) is still scarce. We intended to analyze the correlation of NLR with overall survival and progression-free survival in patients with GBM performing a retrospective review of the patients with diagnosis of GBM submitted to a resection surgery in the department of neurosurgery of a tertiary care hospital, between January/2005 and January/2013. 140 patients were included. Mean age at surgery was 62.9 ± 10.0 years and mean age at death was 64.4 ± 9.8 years. Mean overall survival was 19.4 ± 14.3 months and mean progression-free survival was 9.4 ± 8.7 months. There was no correlation of NLR, platelets-lymphocyte ratio (PLR) or absolute counts of neutrophils, lymphocytes and platelets with overall survival in multivariate analysis. However, a preoperative NLR ≤ 5 correlated with a shorter progression-free survival [HR 1.56 (SD 95% 1.04-2.34); p = 0.032]. We performed a subgroup analysis of patients who completed Stupp protocol. In this subgroup of 117 patients, a preoperative NLR > 7 correlated with a shorter overall survival [HR 1.65 (SD 95% 1.07-2.53); p = 0.023]. The results from our total cohort didn't confirm the correlation between a higher NRL and worse survival in GBM. However, in the subgroup analysis of patients who completed Stupp protocol, a higher NLR was an independent prognostic factor to a shorter overall survival, similar to existent literature data about GBM.

Threshold of the extent of resection for WHO Grade III gliomas: retrospective volumetric analysis of 122 cases using intraoperative MRI

OBJECTIVE WHO Grade III gliomas are relatively rare and treated with multiple modalities such as surgery, chemotherapy, and radiotherapy. The impact of the extent of resection (EOR) on improving survival in patients with this tumor type is unclear. Moreover, because of the heterogeneous radiological appearance of Grade III gliomas, the MRI sequence that best correlates with tumor volume is unknown. In the present retrospective study, the authors evaluated the prognostic significance of EOR. METHODS Clinical and radiological data from 122 patients with newly diagnosed WHO Grade III gliomas who had undergone intraoperative MRI-guided resection at a single institution between March 2000 and December 2011 were analyzed retrospectively. Patients were divided into 2 groups by histological subtype: 81 patients had anaplastic astrocytoma (AA) or anaplastic oligoastrocytoma (AOA), and 41 patients had anaplastic oligodendroglioma (AO). EOR was calculated using pre- and postoperative T2-weighted and contrast-enhanced T1-weighted MR images. Univariate and multivariate analyses were performed to evaluate the prognostic significance of EOR on overall survival (OS). RESULTS The 5-, 8-, and 10-year OS rates for all patients were 74.28%, 70.59%, and 65.88%, respectively. The 5- and 8-year OS rates for patients with AA and AOA were 72.2% and 67.2%, respectively, and the 10-year OS rate was 62.0%. On the other hand, the 5- and 8-year OS rates for patients with AO were 79.0% and 79.0%; the 10-year OS rate is not yet available. The median pre- and postoperative T2-weighted high-signal intensity volumes were 56.1 cm³ (range 1.3-268 cm³) and 5.9 cm³ (range 0-180 cm³), respectively. The median EOR of T2-weighted high-signal intensity lesions (T2-EOR) and contrast-enhanced T1-weighted lesions were 88.8% (range 0.3%-100%) and 100% (range 34.0%-100%), respectively. A significant survival advantage was associated with resection of 53% or more of the preoperative T2-weighted high-signal intensity volume in patients with AA and AOA, but not in patients with AO. Univariate analysis showed that preoperative Karnofsky Performance Scale score (p = 0.0019), isocitrate dehydrogenase 1 ( IDH1) mutation (p = 0.0008), and T2-EOR (p = 0.0208) were significant prognostic factors for survival in patients with AA and AOA. Multivariate analysis demonstrated that T2-EOR (HR 3.28; 95% CI 1.22-8.81; p = 0.0192) and IDH1 mutation (HR 3.90; 95% CI 1.53-10.75; p = 0.0044) were predictive of survival in patients with AA and AOA. CONCLUSIONS T2-EOR was one of the most important prognostic factors for patients with AA and AOA. A significant survival advantage was associated with resection of 53% or more of the preoperative T2-weighted high-signal intensity volume in patients with AA and AOA.

New Molecular Considerations for Glioma: IDH, ATRX, BRAF, TERT, H3 K27M

PURPOSE OF REVIEW

This review will discuss the role of several key players in glioma classification and biology, namely isocitrate dehydrogenase 1 and 2 (IDH1/2), alpha thalassemia/mental retardation syndrome X-linked (ATRX), B-Raf (BRAF), telomerase reverse transcriptase (TERT), and H3K27M.

RECENT FINDINGS

IDH1/2 mutation delineates oligoden-droglioma, astrocytoma, and secondary glioblastoma (GBM) from primary GBM and lower-grade gliomas with biology similar to GBM. Additional mutations including TERT, 1p/19q, and ATRX further guide glioma classification and diagnosis, as well as pointing directions toward individualized treatments for these distinct molecular subtypes. ATRX and TERT mutations suggest the importance of telomere maintenance in gliomagenesis. BRAF alterations are key in certain low-grade gliomas and pediatric gliomas but rarely in high-grade gliomas in adults. Histone mutations (e.g., H3K27M) and their effect on chromatin modulation are novel mechanisms of cancer generation and uniquely seen in midline gliomas in children and young adults. Over the past decade, a remarkable accumulation of knowledge from the genomic study of gliomas has led to reclassification of tumors, new understanding of oncogenic mechanisms, and novel treatment strategies.

An analysis of 170 glioma patients and systematic review to investigate the association between IDH-1 mutations and preoperative glioma-related epilepsy

Seizure is a common presenting symptom of glioma, and many biomarkers have been suggested to be associated with preoperative seizure; however, the relationships between IDH (isocitrate dehydrogenase) mutations and glioma-related epilepsy only recently been studied. The authors aimed to examine the correlations between IDH mutations in glioma patients with preoperative seizures and tumor location. A series of 170 glioma samples were analyzed for IDH1 R132H mutations (amino acid change from arginine to histidine at codon 132) with immunohistochemistry (IHC) staining and for IDH mutations with direct DNA sequencing when the IHC results were negative. If either the IHC or direct DNA sequencing result was positive, the IDH status was defined as mutated. The results of the IDH mutation examinations were used to analyze the relationship between mutations and glioma-related epilepsy. The study population consisted of 64 (37.6%) World Health Organization (WHO) grade II gliomas, 58 (34.1%) grade III, and 48 (28.3%) grade IV gliomas. A total of 84 samples with IDH1 mutations were observed in our study, and 54 of these presented with seizures as the initial symptoms, whereas 28 of the patients with wild-type IDH status presented with seizures (p=0.043 for the WHO grade II gliomas, p=0.002 for the grade III gliomas and p=0.942 for the grade IV gliomas, chi-squared tests). Among the WHO grade II and III gliomas, IDH1 mutations were significantly associated with preoperative seizures, but no significant relationship between IDH mutations and preoperative seizures was found with glioblastoma multiforme.

Prognostic Value of O-(2-[18F]-Fluoroethyl)-L-Tyrosine-Positron Emission Tomography Imaging for Histopathologic Characteristics and Progression-Free Survival in Patients with Low-Grade Glioma

OBJECTIVE

O-(2-[18F]-fluoroethyl)-L-tyrosine positron emission tomography ((18)F-FET-PET) imaging is applied for tumor grading, prognostic stratification, and diagnosis of tumor recurrence, especially in high-grade gliomas. Experience with (18)F-FET-PET imaging in low-grade gliomas is limited. Therefore, the objective of the present study was to assess (18)F-FET-PET tracer uptake in low-grade gliomas and to investigate possible correlations with contrast enhancement in magnetic resonance imaging (MRI) and histopathology.

METHODS

A total of 65 patients (29 female, 36 male, median age 38 years) with newly diagnosed or recurrent low-grade gliomas for whom preoperative MRI and (18)F-FET-PET imaging were available were included. Tumor entity, tumor location, as well as histopathology (isocitrate dehydrogenase [IDH] 1/2 mutation, Ki67, p53, oligodendroglial differentiation, 1p19q codeletion), and progression-free survival were assessed. (18)F-FET-PET images were acquired and fused to MRI (T2-weighted fluid-attenuated inversion recovery) and tumor volume was measured in areas with a tumor-to-background ratio >1.3, >1.6, and >2.0 and in MRI.

RESULTS

PET tracer uptake was observed in 78.5% of all World Health Organization Grade I and II tumors. (18)F-FET uptake showed a high negative predictive value for oligodendroglial components and for 1p19q codeletion. No further significant correlation between histologic features, progression-free survival, or IDH1/2 mutation status and tracer uptake was observed.

CONCLUSIONS

We found that 78.5% of low-grade gliomas do show elevated tracer uptake in (18)F-FET-PET imaging. Low-grade glioma without tracer uptake exclude oligodendroglial differentiation and 1p19q codeletion. Further differentiation between molecular subtypes is not possible with static (18)F-FET-PET. No correlation of progression-free survival to tracer uptake and IDH1/2-mutation status was observed.

The challenges and the promise of molecular targeted therapy in malignant gliomas

Malignant gliomas are the most common malignant primary brain tumors and one of the most challenging forms of cancers to treat. Despite advances in conventional treatment, the outcome for patients remains almost universally fatal. This poor prognosis is due to therapeutic resistance and tumor recurrence after surgical removal. However, over the past decade, molecular targeted therapy has held the promise of transforming the care of malignant glioma patients. Significant progress in understanding the molecular pathology of gliomagenesis and maintenance of the malignant phenotypes will open opportunities to rationally develop new molecular targeted therapy options. Recently, therapeutic strategies have focused on targeting pro-growth signaling mediated by receptor tyrosine kinase/RAS/phosphatidylinositol 3-kinase pathway, proangiogenic pathways, and several other vital intracellular signaling networks, such as proteasome and histone deacetylase. However, several factors such as cross-talk between the altered pathways, intratumoral molecular heterogeneity, and therapeutic resistance of glioma stem cells (GSCs) have limited the activity of single agents. Efforts are ongoing to study in depth the complex molecular biology of glioma, develop novel regimens targeting GSCs, and identify biomarkers to stratify patients with the individualized molecular targeted therapy. Here, we review the molecular alterations relevant to the pathology of malignant glioma, review current advances in clinical targeted trials, and discuss the challenges, controversies, and future directions of molecular targeted therapy.

Altered Expression of Oxidative Metabolism Related Genes in Cholangiocarcinomas

Cholangiocarcinoma (CCA) is a rare but highly fatal cancer for which the molecular mechanisms and diagnostic markers are obscure. We therefore investigated the kinetic expression of isocitrate dehydrogenase-1 (IDH1), isocitrate dehydrogenase-2 (IDH2) and homogentisate 1,2-dioxygenase (HGD) during the tumorigenesis of O. viverrini infection-associated CCA in an animal model, and confirmed down-regulation of expression in human cases of opisthorchiasis-associated CCA through real time PCR. Kinetic expression of HGD, IDH1 and IDH2 in the animal model of O. viverrini infection-induced CCA was correlated with human CCA cases. In the animal model, expression of HGD was decreased at all time points (p<0.01) and expression of both IDH1 and IDH2 was decreased in the CCA group. In human cases, expression of HGD, IDH1 and IDH2 was decreased more than 2 fold in 55 cases (70.5%), 25 cases (32.1%) and 24 cases (30.8%) respectively. The present study suggests that reduction of HGD, IDH1 and IDH2 may be involve in cholangiocarcinoma genesis and may be useful for molecular diagnosis.

Proteomic analysis of a nasopharyngeal carcinoma cell line and a nasopharyngeal epithelial cell line

BACKGROUND

Nasopharyngeal carcinoma (NPC) is an epithelial malignancy exhibiting a strong geographic preference and a close association with Epstein-Barr virus (EBV). The aim of this study was to investigate the precise mechanism of nasopharyngeal epithelial-to-NPC tumorigenesis and to identify possible biomarkers and targets for therapy.

METHODS

Proteomic analysis was performed on the immortalized nasopharyngeal epithelial cell line NP69 and the NPC cell line C666.

RESULTS

A comparative analysis of total lysates from the cell lines using 2-D gel electrophoresis-mass spectrometry resulted in the identification of 87 different protein spots. The different proteins were grouped into 5 main categories: (i) energy production and general metabolism, (ii) adaptation/stress tolerance, (iii) cell proliferation, (iv) cell structure and (v) epithelial-mesenchymal transition. The detection of metabolism-related proteins indicated that the NPC cells relied on aerobic glycolysis, with reduced use of the citric acid cycle. Glucose uptake and lactate secretion increased in the medium of C666 compared with NP69.

CONCLUSIONS

The present study revealed that glycolysis was up-regulated in the NPC cell lines compared with nasopharyngeal epithelial cells. A number of molecules involved in metabolism were identified, and further investigations will be needed to validate these potential biomarkers or targets.

A better surgical resectability of WHO grade II gliomas is independent of favorable molecular markers

A higher extent of resection (EOR) in WHO grade II gliomas (GIIG) is correlated with longer survival. However, the molecular markers also feature prognostic relevance. Here, we examined whether maximal EOR was related to the genetic profile. We retrospectively investigated the predictive value of 1p19q, IDH1, 53 expression and Ki67 index for the EOR in 200 consecutive GIIGs (2007-2013). Data were modeled in a linear model. The analysis was performed with two statistical methods (arcsin-sqrt and Beta-regression model with logit link). There was no deletion 1p19q in 118 cases, codeletion 1p19q (57 cases), single deletion 1p (4 cases) or19q (16 cases). 155 patients had a mutation of IDH1. p53 was graded in 4 degrees (0:92 cases, 1:52 cases, 2:31 cases, 3:8 cases). Mean Ki67 index was 5.2 % (range 1-20 %). Mean preoperative tumor volume was 60.8 cm(3) (range 3.3-250 cm(3)) and mean EOR was 0.917 (range 0.574-1). The statistical analysis was significant for a lower EOR in patients with codeletion 1p19q (OR 0.738, p = 0.0463) and with a single deletion 19q (OR 0.641, p = 0.0168). There was no significant correlation between IDH1 or p53 and the EOR. Higher Ki67 was marginally associated with higher EOR (p = 0.0603). The study demonstrates in a large cohort of GIIG that a higher EOR is not attributable to favorable genetic markers. This original result supports maximal surgical resection as an important therapeutic factor per se to optimize prognosis, independently of the molecular pattern.

Management of high-grade gliomas in the pediatric patient: Past, present, and future

High-grade gliomas (HGGs) constitute ∼15% of all primary brain tumors in children and adolescents. Routine histopathological diagnosis is based on tissue obtained from biopsy or, preferably, from the resected tumor itself. The majority of pediatric HGGs are clinically and biologically distinct from histologically similar adult malignant gliomas; these differences may explain the disparate responses to therapy and clinical outcomes when comparing children and adults with HGG. The recently proposed integrated genomic classification identifies 6 distinct biological subgroups of glioblastoma (GBM) throughout the age spectrum. Driver mutations in genes affecting histone H3.3 (K27M and G34R/V) coupled with mutations involving specific proteins (TP53, ATRX, DAXX, SETD2, ACVR1, FGFR1, NTRK) induce defects in chromatin remodeling and may play a central role in the genesis of many pediatric HGGs. Current clinical practice in pediatric HGGs includes surgical resection followed by radiation therapy (in children aged > 3 years) with concurrent and adjuvant chemotherapy with temozolomide. However, these multimodality treatment strategies have had a minimal impact on improving survival. Ongoing clinical trials are investigating new molecular targets, chemoradiation sensitization strategies, and immunotherapy. Future clinical trials of pediatric HGG will incorporate the distinction between GBM molecular subgroups and stratify patients using group-specific biomarkers.

The role of mutation of metabolism-related genes in genomic hypermethylation

Genetic mutations, metabolic dysfunction, and epigenetic misregulation are commonly considered to play distinct roles in tumor development and maintenance. However, intimate relationships between these mechanisms are now emerging. In particular, mutations in genes for the core metabolic enzymes IDH, SDH, and FH are significant drivers of diverse tumor types. In each case, the resultant accumulation of particular metabolites inhibits TET enzymes responsible for oxidizing 5-methylcytosine, leading to pervasive DNA hypermethylation.

Genetically modeled mice with mutations in mitochondrial metabolic enzymes for the study of cancer

Mitochondrial dysfunction has long been implicated in progression of cancer. As a paradigm, the “Warburg effect,” which by means of a switch toward anaerobic metabolism enables cancer cells to proliferate in oxygen limiting conditions, is well established. Besides this metabolic transformation of tumors, it has been discovered that mutations in genes encoding mitochondrial proteins are the etiological factors in different types of cancer. This confers to mitochondrial dysfunction a causative role, rather than resultant, in tumor genesis beyond its role in tumor progression and development. Mitochondrial proteins encoded by tumor-suppressor genes are part of the succinate-dehydrogenase, the fumarate-hydratase, and the mitochondrial isocitrate-dehydrogenase enzymes, all of them participating in the Krebs cycle. The spectrum of tumors associated with mutations in these genes is becoming larger and varies between each enzyme. Several mechanisms of tumorigenesis have been proposed for the different enzymatic defects, most of them based on studies using cellular and animal models. Regarding the molecular pathways implicated in the oncogenic transformation, one of the first accepted theories was based on the constitutive expression of the hypoxia-inducible factor 1α (Hif1α) at normal oxygen tension, a theory referred to as “pseudo-hypoxic drive.” This mechanism has been linked to the three types of mutations, thus suggesting a central role in cancer. However, other alternative molecular processes, such as oxidative stress or altered chromatin remodeling, have been also proposed to play an onco-pathogenic role. In the recent years, the role of oncometabolites, a new concept emerged from biochemical studies upon these tumors, has acquired relevance as responsible for tumor formation. Nevertheless, the actual contribution of each of these mechanisms has not been definitively established. In this review, we summarize the results obtained from mouse strains genetically modified in the three different enzymes.

Paediatric and adult glioblastoma: multiform (epi)genomic culprits emerge

We have extended our understanding of the molecular biology that underlies adult glioblastoma over many years. By contrast, high-grade gliomas in children and adolescents have remained a relatively under-investigated disease. The latest large-scale genomic and epigenomic profiling studies have yielded an unprecedented abundance of novel data and provided deeper insights into gliomagenesis across all age groups, which has highlighted key distinctions but also some commonalities. As we are on the verge of dissecting glioblastomas into meaningful biological subgroups, this Review summarizes the hallmark genetic alterations that are associated with distinct epigenetic features and patient characteristics in both paediatric and adult disease, and examines the complex interplay between the glioblastoma genome and epigenome.

C-terminally truncated form of αB-crystallin is associated with IDH1 R132H mutation in anaplastic astrocytoma

Malignant gliomas are the most common human primary brain tumors. Point mutation of amino acid arginine 132 to histidine (R132H) in the IDH1 protein leads to an enzymatic gain-of-function and is thought to promote gliomagenesis. Little is known about the downstream effects of the IDH1 mutation on protein expression and how and whether changes in protein expression are involved in tumor formation or propagation. In the current study, we used 2D DIGE (difference gel electrophoresis) and mass spectrometry to analyze differences in protein expression between IDH1(R132H) mutant and wild type anaplastic (grade III) astrocytoma from human brain cancer tissues. We show that expression levels of many proteins are altered in IDH1(R132H) mutant anaplastic astrocytoma. Some of the most over-expressed proteins in the mutants include several forms of αB-crystallin, a small heat-shock and anti-apoptotic protein. αB-crystallin proteins are elevated up to 22-fold in IDH1(R132H) mutant tumors, and αB-crystallin expression appears to be controlled at the post-translational level. We identified the most abundant form of αB-crystallin as a low molecular weight species that is C-terminally truncated. We also found that overexpression of αB-crystallin can be induced by transfecting U251 human glioblastoma cell lines with the IDH1(R132H) mutation. In conclusion, the association of a C-terminally truncated form of αB-crystallin protein with the IDH1(R132H) mutation is a novel finding that could impact apoptosis and stress response in IDH1 mutant glioma.

Hypoxia and metabolism in cancer

Interest in targeting metabolism has been renewed in recent years as research increases understanding of the altered metabolic profile of tumor cells compared with that of normal cells. Metabolic reprogramming allows cancer cells to survive and proliferate in the hostile tumor microenvironment. These metabolic changes support energy generation, anabolic processes, and the maintenance of redox potential, mechanisms that are all essential for the proliferation and survival of tumor cells. The metabolic switch in a number of key metabolic pathways is mainly regulated by genetic events, rendering cancer cells addicted to certain nutrients, such as glutamine. In addition, hypoxia is induced when highly proliferative tumor cells distance themselves from an oxygen supply. Hypoxia-inducible factor 1α is largely responsible for alterations in metabolism that support the survival of hypoxic tumor cells. Metabolic alterations and dependencies of cancer cells may be exploited to improve anticancer therapy. This chapter reviews the main aspects of altered metabolism in cancer cells, emphasizing recent advances in glucose, glutamine, and lipid metabolism.

Tumor metabolism of malignant gliomas

Constitutively activated oncogenic signaling via genetic mutations such as in the EGFR/PI3K/Akt and Ras/RAF/MEK pathways has been recognized as a major driver for tumorigenesis in most cancers. Recent insights into tumor metabolism have further revealed that oncogenic signaling pathways directly promote metabolic reprogramming to upregulate biosynthesis of lipids, carbohydrates, protein, DNA and RNA, leading to enhanced growth of human tumors. Therefore, targeting cell metabolism has become a novel direction for drug development in oncology. In malignant gliomas, metabolism pathways of glucose, glutamine and lipid are significantly reprogrammed. Moreover, molecular mechanisms causing these metabolic changes are just starting to be unraveled. In this review, we will summarize recent studies revealing critical gene alterations that lead to metabolic changes in malignant gliomas, and also discuss promising therapeutic strategies via targeting the key players in metabolic regulation.

Transcriptional analysis of aggressiveness and heterogeneity across grades of astrocytomas

Astrocytoma is the most common glioma, accounting for half of all primary brain and spinal cord tumors. Late detection and the aggressive nature of high-grade astrocytomas contribute to high mortality rates. Though many studies identify candidate biomarkers using high-throughput transcriptomic profiling to stratify grades and subtypes, few have resulted in clinically actionable results. This shortcoming can be attributed, in part, to pronounced lab effects that reduce signature robustness and varied individual gene expression among patients with the same tumor. We addressed these issues by uniformly preprocessing publicly available transcriptomic data, comprising 306 tumor samples from three astrocytoma grades (Grade 2, 3, and 4) and 30 non-tumor samples (normal brain as control tissues). Utilizing Differential Rank Conservation (DIRAC), a network-based classification approach, we examined the global and individual patterns of network regulation across tumor grades. Additionally, we applied gene-based approaches to identify genes whose expression changed consistently with increasing tumor grade and evaluated their robustness across multiple studies using statistical sampling. Applying DIRAC, we observed a global trend of greater network dysregulation with increasing tumor aggressiveness. Individual networks displaying greater differences in regulation between adjacent grades play well-known roles in calcium/PKC, EGF, and transcription signaling. Interestingly, many of the 90 individual genes found to monotonically increase or decrease with astrocytoma grade are implicated in cancer-affected processes such as calcium signaling, mitochondrial metabolism, and apoptosis. The fact that specific genes monotonically increase or decrease with increasing astrocytoma grade may reflect shared oncogenic mechanisms among phenotypically similar tumors. This work presents statistically significant results that enable better characterization of different human astrocytoma grades and hopefully can contribute towards improvements in diagnosis and therapy choices. Our results also identify a number of testable hypotheses relating to astrocytoma etiology that may prove helpful in developing much-needed biomarkers for earlier disease detection.

Codeletion of 1p and 19q determines distinct gene methylation and expression profiles in IDH-mutated oligodendroglial tumors

Oligodendroglial tumors (OTs) are primary brain tumors that show variable clinical and biological behavior. The 1p/19q codeletion is frequent in these tumors, indicating a better prognosis and/or treatment response. Recently, the prognostically favorable CpG island methylator phenotype (CIMP) in gliomas (G-CIMP+) was associated with mutations in the isocitrate dehydrogenase 1 and isocitrate dehydrogenase 2 (IDH) genes, as opposed to G-CIMP- tumors, highlighting the relevance of epigenetic mechanisms. We performed a whole-genome methylation study in 46 OTs, and a gene expression study of 25 tumors, correlating the methylation and transcriptomic profiles with molecular and clinical variables. Here, we identified two different epigenetic patterns within the previously described main G-CIMP+ profile. Both IDH mutation-associated methylation profiles featured one group of OTs with 1p/19q loss (CD-CIMP+), most of which were pure oligodendrogliomas, and a second group with intact 1p/19q and frequent TP53 mutation (CIMP+), most of which exhibited a mixed histopathology. A third group of OTs lacking the CIMP profile (CIMP-), and with a wild-type IDH and an intact 1p/19q, similar to the G-CIMP- subgroup, was also observed. The three CIMP groups presented a significantly better (CD-CIMP+), intermediate (CIMP+) or worse (CIMP-) prognosis. Furthermore, transcriptomic analyses revealed CIMP-specific gene expression signatures, indicating the impact of genetic status (IDH mutation, 1p/19q codeletion, TP53 mutation) on gene expression, and pointing to candidate biomarkers. Therefore, the CIMP profiles contributed to the identification of subgroups of OTs characterized by different prognoses, histopathologies, molecular features and gene expression signatures, which may help in the classification of OTs.

Oncogenic isocitrate dehydrogenase mutations: mechanisms, models, and clinical opportunities

Heterozygous mutations in catalytic arginine residues of isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) are common in glioma, acute myeloid leukemia, chondrosarcoma, cholangiocarcinoma, and angioimmunoblastic T-cell lymphoma. The mutant enzymes acquire a neomorphic activity that converts α-ketoglutarate (α-KG) to D-2-hydroxyglutarate (D2HG), a rare metabolite. In cells and tissues expressing mutant IDH, D2HG concentrations are highly elevated. D2HG may act as an "oncometabolite" by inhibiting a class of α-KG-dependent enzymes involved in epigenetic regulation, collagen synthesis, and cell signaling. Knock-in mouse models of IDH1 mutations have shed light on these mechanisms and will provide valuable animal models for further investigation.

Comparison of glioma stem cells to neural stem cells from the adult human brain identifies dysregulated Wnt- signaling and a fingerprint associated with clinical outcome

Glioblastoma is the most common brain tumor. Median survival in unselected patients is <10 months. The tumor harbors stem-like cells that self-renew and propagate upon serial transplantation in mice, although the clinical relevance of these cells has not been well documented. We have performed the first genome-wide analysis that directly relates the gene expression profile of nine enriched populations of glioblastoma stem cells (GSCs) to five identically isolated and cultivated populations of stem cells from the normal adult human brain. Although the two cell types share common stem- and lineage-related markers, GSCs show a more heterogeneous gene expression. We identified a number of pathways that are dysregulated in GSCs. A subset of these pathways has previously been identified in leukemic stem cells, suggesting that cancer stem cells of different origin may have common features. Genes upregulated in GSCs were also highly expressed in embryonic and induced pluripotent stem cells. We found that canonical Wnt-signaling plays an important role in GSCs, but not in adult human neural stem cells. As well we identified a 30-gene signature highly overexpressed in GSCs. The expression of these signature genes correlates with clinical outcome and demonstrates the clinical relevance of GSCs.