Pediatric High-grade Gliomas Research Articles

TMIC-15. GENETIC AND SPATIAL HETEROGENEITY OF PEDIATRIC HIGH-GRADE GLIOMAS CONFER UNIQUE INFLAMMATORY MICROENVIRONMENTS

Abstract Significant progress has been made molecularly defining pediatric high-grade gliomas (pHGG), including diffuse midline gliomas (DMG), yet little progress has been made with respect to delineating the inflammatory microenvironment. We utilize molecularly defined human samples and immunocompetent genetic mouse models to study how tumor location and genetic driver mutations influence the tumor microenvironment (TME). We report human DMGs have a significant enrichment of Elane+ neutrophils compared to their hemispheric counterparts. We validate this utilizing the RCAS-Tva mouse model, which histologically and genetically recapitulates human pHGGs. Using this model we demonstrate each distinct pHGG/DMG entity confers unique transcriptional identities as made evident by NanoString RNA expression profiles and whole-tumor single-cell RNA sequencing. H3.3WT DMGs and H3.3K27M DMGs cluster together and have high expression of inflammatory genes such as Ptprc, Trem2, Lag3, and Cd274 while H3.3WT and H3.3G34R hemispheric tumors, and H3.1K27M DMGs cluster together with low expression of these genes. Several genes were found to significantly correlate with median survival in human bulk RNA sequencing data including IL13RA2. Flow cytometry and immunohistochemistry demonstrate H3WT DMGs are enriched for monocytes and lymphocytes while H3.3K27M DMGs are enriched for microglia. Genetic perturbations were made to prevent TAM or neutrophil infiltration, including targeting Ccl3, Cxcl1, and Ccl8/12. Only Ccl8/12 knockout resulted in significant extension of survival in H3K27M DMGs, which was met with an increase in CD4+ and CD8+ T-cells and decreased neutrophil infiltration. CD4+ T-cell depletion and anti-PD1 therapy was performed to further study the role of lymphocyte infiltration in DMGs. Lastly, CCR1/CCR5 inhibitors were utilized to abrogate TAM infiltration in DMGs, resulting in decreased microglia infiltration and significant survival extension comparable to radiation therapy. Together, this work provides the foundation for developing or improving immunotherapies designed at specific subgroups of pHGG and DMGs, such as CAR-T-cell, oncolytic viral therapy, and checkpoint blockade.

BIOM-61. EXPLORING HOMOLOGOUS RECOMBINATION DEFICIENCY IN PEDIATRIC HIGH-GRADE GLIOMAS

Abstract Homologous recombination deficiency (HRD) has been extensively studied in breast cancer and ovarian cancer given its correlation with sensitivity to Poly (ADP-ribose) polymerases (PARP) inhibitors. In these cancers, HRD is most frequently caused by biallelic inactivation of BRCA1/2 and tumors often exhibit ‘genomic scars’ such as elevated HRD.sum score and specific mutational signatures, including specific single nucleotide variant (SNV), small insertion/deletion (Indel), and structural variant (SV) signatures. Despite its clinical relevance, HRD has not been systematically studied in pediatric cancers and its therapeutic predictive value is unknown. Here, we evaluated HRD in 255 tumor-normal paired whole-genome-sequenced (WGS) samples of pediatric high-grade glioma (pHGG) and 23 tumor-normal paired WGS samples of breast cancer (BC) as comparison. We found that 9% of the pHGG samples have HRD.sum score greater than 40, an indicator of HRD in several adult cancers. However, while we identified HRD-related SNV signature SBS3 and SV signature RS5 in some of the pHGG samples, HRD-related Indel signature ID6 was not identified. We also evaluated two composite scores, namely, HRDetect and CHORD, on our samples. While virtually all BC samples with BRCA1/2 loss were predicted to be HRD by both scores, none of the pHGG samples was predicted to be HRD by either score. We profiled somatic and germline variants from over 500 DNA damage response genes in the pHGG samples and identified TP53 as the most frequently mutated genes with biallelic loss, whereas biallelic loss of BRCA1/2 was not found. Overall, our study suggests that HRD exists in a fraction of pHGG samples, but is driven by inactivation of genes other than BRCA1/2, resulting in a different set of genomic scars compared to those in BCs. Functional analysis of sensitivity to PARP inhibitor and related DNA damage inhibitors is ongoing to evaluate potential therapeutic relevance of these genomic scars.

DDDR-30. IDENTIFICATION OF DRIVERS OF RESISTANCE IN BRAFV600E PEDIATRIC HIGH-GRADE GLIOMA AND NOVEL THERAPEUTIC TARGETS

Abstract The BRAFV600E mutation has recently been discovered as a driver mutation in a subset of pediatric high-grade gliomas (pHGG), with tumors driven by this mutation responding to targeted BRAF and MEK inhibitors. Unfortunately, resistance inevitability develops, resulting in disease progression. There is currently limited understanding of the mechanisms underlying drug resistance in BRAFV600E pHGG, and no effective counter-therapies exist. This study aimed to identify driver pathways of resistance in BRAFV600E pHGG and subsequently novel therapeutic targets. BRAF inhibitor-resistant, MEK inhibitor-resistant and BRAF+MEK inhibitor-resistant BRAFV600E pHGG cultures were derived through chronic exposure of a BRAFV600E patient-derived culture to vemurafenib (BRAF inhibitor), trametinib (MEK inhibitor) or a combination of both drugs, respectively. Cytotoxicity assays confirmed resistance. All resistant cell lines spontaneously changed from a spheroid phenotype to adherent growth, indicating changes in tumor characteristics. RNAseq identified > 1500 genes of interest, with subsequent Gene Set Enrichment Analysis identifying key pathways as novel drivers of resistance, the top-ranked gene sets being neural development and plasma membrane/cell adhesion. Approximately 45% of gene sets were enriched across all drug-resistant lines, indicating overlapping resistance mechanisms. Interrogation of the receptor tyrosine kinase (RTK) gene sets identified potent upregulation of several RTKs. Notably, overexpression of the RTK, EGFR, was confirmed through RNAseq and western blot as a potential key mediator of the acquired resistance. Combined treatment with vemurafenib and the EGFR inhibitor, dacomitinib, resulted in synergistic activity against both vemurafenib-resistant BRAFV600E pHGG cells and matched parental cells, providing a viable therapeutic option for drug-resistant BRAFV600E pHGG. Overall, novel drivers of resistance have been identified in BRAFV600E pHGG. EGFR overexpression was pinpointed as a key mediator and dual BRAF/EGFR inhibition displayed promising efficacy as a therapeutic option. Future studies will continue to elucidate the mechanisms of resistance using multi-omic approaches and the in vivo efficacy of dual BRAF/EGFR inhibition.

The impact of radiation therapy variables on pediatric high-grade glioma outcomes: A National Cancer Database analysis.

The purpose of this analysis is to report patterns of care for pediatric patients with high-grade glioma (pHGG) and evaluate the impact of radiotherapy (RT) variables on outcomes using the National Cancer Database (NCDB). Eligibility criteria included age<22 years, histologically diagnosed WHO grade III-IV gliomas treated with ≥50Gy and<76Gy RT between 2004 and 2013, and RT initiation within 90 days of diagnosis. RT variables including RT dose, RT timing, and RT modality were analyzed along with baseline demographic, tumor, and treatment variables to assess the impact on overall survival. A total of 498 pHGG patients were included. The median age was 15 years (range, 0-21), common diagnoses were astrocytoma (55%) and glioblastoma (30%), 73.5% underwent surgical resection and 90.2% received chemotherapy. The median RT dose was 59.4Gy (SD 2.9Gy) starting at a median of 4.4weeks from diagnosis (SD 2.5weeks). Fourteen patients were treated with proton therapy. Median follow-up was 19.6 months with 1- and 3-year overall survival of 78.4% and 40.4%, respectively. On multivariable analysis, female gender, older age, and RT delay of ≥6weeks were significantly associated with a lower rate of death; glioblastoma histology, no surgical resection/biopsy only, and earlier RT initiation<6weeks from diagnosis were associated with a higher rate of death. There was no relationship between RT dose or proton versus photon therapy and overall survival. Outcomes for pHGG are poor. There was no benefit to early RT timing when RT is initiated within 90 days of diagnosis or higher RT dose in this dataset.

Tumor and immune cell types interact to produce heterogeneous phenotypes of pediatric high-grade glioma.

Pediatric high-grade gliomas (PHGG) are aggressive brain tumors with 5-year survival rates ranging from <2% to 20% depending upon subtype. PHGG presents differently from patient to patient and is intratumorally heterogeneous, posing challenges in designing therapies. We hypothesized that heterogeneity occurs because PHGG comprises multiple distinct tumor and immune cell types in varying proportions, each of which may influence tumor characteristics. We obtained 19 PHGG samples from our institution's pediatric brain tumor bank. We constructed a comprehensive transcriptomic dataset at the single-cell level using single-cell RNA-Seq (scRNA-Seq), identified known glial and immune cell types, and performed differential gene expression and gene set enrichment analysis. We conducted multi-channel immunofluorescence (IF) staining to confirm the transcriptomic results. Our PHGG samples included 3 principal predicted tumor cell types: astrocytes, oligodendrocyte progenitors (OPCs), and mesenchymal-like cells (Mes). These cell types differed in their gene expression profiles, pathway enrichment, and mesenchymal character. We identified a macrophage population enriched in mesenchymal and inflammatory gene expression as a possible source of mesenchymal tumor characteristics. We found evidence of T-cell exhaustion and suppression. PHGG comprises multiple distinct proliferating tumor cell types. Microglia-derived macrophages may drive mesenchymal gene expression in PHGG. The predicted Mes tumor cell population likely derives from OPCs. The variable tumor cell populations rely on different oncogenic pathways and are thus likely to vary in their responses to therapy.

Review of imaging recommendations from Response Assessment in Pediatric Neuro-Oncology (RAPNO).

The Response Assessment in Pediatric Neuro-Oncology (RAPNO) working group includes neuroradiologists, neuro-oncologists, neurosurgeons, radiation oncologists, and clinicians in various additional specialties. This review paper will summarize the imaging recommendations from RAPNO for the six RAPNO publications to date covering pediatric low-grade glioma, pediatric high-grade glioma, medulloblastoma and other leptomeningeal seeding tumors, diffuse intrinsic pontine glioma, ependymoma, and craniopharyngioma.

Novel combination of GammaTile cesium-131 brachytherapy with 5-aminolevulinic acid fluorescence-guided resection in the re-irradiation of pediatric recurrent high-grade glioma: illustrative case.

Herein, the authors describe the successful utilization of 5-aminolevulinic acid (5-ALA) and the first case of GammaTile cesium-131 therapy in a pediatric patient with recurrent high-grade glioma. 5-ALA was utilized to optimize gross-total resection prior to GammaTile implantation. After conversion to an equivalent dose in 2-Gy fractions (EQD2), a composite was made of the GammaTile dose with the initial external beam radiotherapy. Two hypothetical plans consisting of a standard hypofractionated strategy for glioma reirradiation and a CyberKnife plan using GammaTile's planning target volume were developed and likewise underwent EQD2 conversion and composite plan generation with the initial radiotherapy. 5-ALA was useful in achieving gross-total resection with no acute toxicity from the surgery or GammaTile irradiation. When compared with the hypothetical composite doses, GammaTile's composite, axium point dose (D0.03cc) to the brainstem was 32.9 Gy less than the hypofractionated and the CyberKnife composite plans at 38.7 Gy and 40.2 Gy, respectively. The right hippocampus demonstrated a substantially reduced composite plan dose with GammaTile with a D0.03cc of 62.4 Gy versus 71.7 and 80.7 Gy for the hypofractionated and CyberKnife composite plans, respectively. Utilization of 5-ALA and GammaTile therapy yielded clinically superior tumor debulking and effective radiotherapy dose localization with sparing of organs at risk, respectively.

H3K27M mutant glioma: Disease definition and biological underpinnings.

High-grade glioma (HGG) is the most common cause of cancer death in children and the most common primary central nervous system tumor in adults. While pediatric HGG was once thought to be biologically similar to the adult form of disease, research has shown these malignancies to be significantly molecularly distinct, necessitating distinct approaches to their clinical management. However, emerging data have shown shared molecular events in pediatric and adult HGG including the histone H3K27M mutation. This somatic missense mutation occurs in genes encoding one of two isoforms of the Histone H3 protein, H3F3A (H3.3), or HIST1H3B (H3.1), and is detected in up to 80% of pediatric diffuse midline gliomas and in up to 60% of adult diffuse gliomas. Importantly, the H3K27M mutation is associated with poorer overall survival and response to therapy compared to patients with H3 wild-type tumors. Here, we review the clinical features and biological underpinnings of pediatric and adult H3K27M mutant glioma, offering a groundwork for understanding current research and clinical approaches for the care of patients suffering with this challenging disease.

Dabrafenib-trametinib is effective in paediatric high-grade glioma.

Dabrafenib-trametinib is effective in paediatric high-grade glioma.

Sex-related incidence and survival differences in pediatric high-grade glioma subtypes: A population-based cohort study

Not much is known on sex differences in incidence, survival, and treatment characteristics for midline and hemispheric pHGGs. This population-based study confirms previously reported study results that found worse survival outcomes for malignant diffuse gliomas in girls in the age group 0-9 years. Additionally, in our study we pinpoint this difference to girls with midline pHGGs aged 0-4 years. We provide insight in the possible underlying mechanisms contributing to sex survival differences in pHGG patients. With first line treatment having no impact on the higher risk of dying for girls, but age and tumor characteristics having a neutralizing effect. The results of this population-based study serve as a basis for future pre-clinical and clinical studies to further unravel the underlying mechanisms responsible for the survival gap between sexes in midline pHGG.

ADULT HISTONE G34 MUTANT GLIOMAS - A SINGLE CENTRE EXPERIENCE OVER 10 YEARS

Abstract AIMS Histone G-34-mutant (H3 G34) gliomas are rare, aggressive infiltrating tumours of the cerebral hemispheres and are classified as WHO grade 4 paediatric type diffuse high-grade glioma. They most commonly affect children and adolescents. We describe the clinicopathological characteristics of adult H3 G34-mutant gliomas seen at the National Hospital for Neurology and Neurosurgery over the last 10 years. METHOD We retrospectively analyzed clinic radiological data on all cases identified from the neuropathology database. Data were extracted on patient demographics, clinical and radiological features and outcome. RESULTS Six patients (2 male, 4 female) were identified, The median age of onset was 26 years (range 17-38 years). One patient presented with a Motor Neurone Disease type syndrome (progressive asymmetric spastic tetraparesis and bulbar symptoms), two with cognitive decline and three with symptoms of raised intracranial pressure. All tumours were supratentorial - 2 patients had mass lesions typical of a high-grade glioma, 1 patient had imaging features consistent with an intraventricular ependymoma. 3 patients had imaging findings that suggested a non-tumour diagnosis with extensive white matter disease more in keeping with an inflammatory demyelinating process or a leucodystrophy. The median overall survival was 23 Months (range 10 - 68 months). CONCLUSIONS Adult Histone G34-mutant gliomas have a variable presentation and are associated with a prognosis similar to other high-grade gliomas. The diagnosis should be considered in the differential of patients presenting with a predominantly white matter disorder. Multi-centre studies are needed to better delineate the phenotype and prognostic features.

THE LINK BETWEEN M6A RNA METHYLATION AND R LOOPS IN PAEDIATRIC HIGH-GRADE GLIOMAS AND EPENDYMOMAS

Abstract AIMS Paediatric high-grade glioma (HGG) and ependymoma (EPN) are two devastating malignant tumours of the central nervous system that unfortunately carry a poor prognosis. As R loops are a known source of genomic instability in eukaryotic cells and have previously been revealed to undergo m6A RNA methylation, we sought to investigate the potential link between m6A methylation and R loops in relation to the pathogenesis of paediatric gliomas. METHOD Paediatric HGG cell lines including KNS42, GCE62 and SF188, and paediatric EPN cell lines including BXD- 1425EPN and EPN9, were utilised for experimental analysis, in addition to normal human astrocytes. Immuno- cytochemistry was performed to assess m6A and R loop levels in tumour cell lines compared to normal human astrocytes. Moreover, DNA damage levels and the effects of anti-cancer drugs on R loop levels were also examined. RESULTS Immunocytochemistry analysis revealed that overall m6A and R loop levels were higher in tumour cell lines compared to normal human astrocytes. Furthermore, differences in R loop levels were observed as a result of pharmacological and biological manipulation, including reduction in R loop abundance with PARP inhibitors. CONCLUSIONS The link between m6A methylation and R loops in relation to the pathogenesis of paediatric HGG and EPN is being investigated. The results of these experiments will be presented.

Pan-cancer atlas of somatic core and linker histone mutations

Recent genomic data points to a growing role for somatic mutations altering core histone and linker histone-encoding genes in cancer. However, the prevalence and the clinical and biological implications of histone gene mutations in malignant tumors remain incompletely defined. To address these knowledge gaps, we analyzed somatic mutations in 88 linker and core histone genes across 12,743 tumors from pediatric, adolescent and young adult (AYA), and adult cancer patients. We established a pan-cancer histone mutation atlas contextualized by patient age, survival outcome, and tumor location. Overall, 11% of tumors harbored somatic histone mutations, with the highest rates observed among chondrosarcoma (67%), pediatric high-grade glioma (pHGG, >60%), and lymphoma (>30%). Previously unreported histone mutations were discovered in pHGG and other pediatric brain tumors, extending the spectrum of histone gene alterations associated with these cancers. Histone mutation status predicted patient survival outcome in tumor entities including adrenocortical carcinoma. Recurrent pan-cancer histone mutation hotspots were defined and shown to converge on evolutionarily conserved and functional residues. Moreover, we studied histone gene mutations in 1700 pan-cancer cell lines to validate the prevalence and spectrum of histone mutations seen in primary tumors and derived histone-associated drug response profiles, revealing candidate drugs targeting histone mutant cancer cells. This study presents the first-of-its-kind atlas of both core and linker histone mutations across pediatric, AYA, and adult cancers, providing a framework by which specific cancers may be redefined in the context of histone and chromatin alterations.

Therapeutic HDAC inhibition in hypermutant diffuse intrinsic pontine glioma

Constitutional mismatch repair deficiency (CMMRD) is a cancer predisposition syndrome associated with the development of hypermutant pediatric high-grade glioma, and confers a poor prognosis. While therapeutic histone deacetylase (HDAC) inhibition of diffuse intrinsic pontine glioma (DIPG) has been reported; here, we use a clinically relevant biopsy-derived hypermutant DIPG model (PBT-24FH) and a CRISPR-Cas9 induced genetic model to evaluate the efficacy of HDAC inhibition against hypermutant DIPG. We screened PBT-24FH cells for sensitivity to a panel of HDAC inhibitors (HDACis) in vitro, identifying two HDACis associated with low nanomolar IC50s, quisinostat (27 nM) and romidepsin (2 nM). In vivo, quisinostat proved more efficacious, inducing near-complete tumor regression in a PBT-24FH flank model. RNA sequencing revealed significant quisinostat-driven changes in gene expression, including upregulation of neural and pro-inflammatory genes. To validate the observed potency of quisinostat in vivo against additional hypermutant DIPG models, we tested quisinostat in genetically-induced mismatch repair (MMR)-deficient DIPG flank tumors, demonstrating that loss of MMR function increases sensitivity to quisinostat in vivo. Here, we establish the preclinical efficacy of quisinostat against hypermutant DIPG, supporting further investigation of epigenetic targeting of hypermutant pediatric cancers with the potential for clinical translation. These findings support further investigation of HDAC inhibitors against pontine high-grade gliomas, beyond only those with histone mutations, as well as against other hypermutant central nervous system tumors.

A comprehensive genomic study of 390 H3F3A-mutant pediatric and adult diffuse high-grade gliomas, CNS WHO grade 4.

Malignant brain tumors, known as H3K27-altered diffuse midline glioma (DMG) and H3G34-mutant diffuse hemispheric glioma (DHG), can affect individuals of all ages and are classified as CNS WHO grade 4. We comprehensively characterized 390 H3F3A-mutant diffuse gliomas (201 females, 189 males) arising in pediatric patients (under 20years old) and adults (20years and older) evaluated by the CGP program at Foundation Medicine between 2013 and 2020. We assessed information from pathology reports, histopathology review, and clinical data. The cohort included 304 H3K27M-mutant DMG (156 females, 148 males) and 86 H3G34-mutant DHG (45 females, 41 males). Median patient age was 20years (1-74years). The frequency of H3K27M-mutant DMG was similar in both pediatric and adult patients in our cohort-48.6% of the patients were over 20years old, 31.5% over 30, and 18% over 40 at initial diagnosis. FGFR1 hotspot point mutations (N546K and K656E) were exclusively identified in H3K27M-mutant DMG tumors (64/304, 21%; p = 0.0001); these tend tooccur in older patients (median age: 32.5years) and mainly arose in the diencephalon. H3K27M-mutant DMG had higher rates of mutations in NF1 (31.0 vs 8.1%; p = 0.0001) and PIK3CA/PIK3R1 (27.9% vs 15.1%; p = 0.016) compared to H3G34-mutant DHG. However, H3G34-mutant DHG had higher rates of targetable alterations in cell-cycle pathway genes (CDK4 and CDK6 amplification; CDKN2A/B deletion) (27.0 vs 9.0%). Potentially targetable PDGFRA alterations were identified in ~ 20% of both H3G34-mutant DHG and H3K27M-mutant DMG. Overall, in the present study H3K27M-mutant DMG occurred at similar rates in both adult and patient patients. Through our analysis, we were able to identify molecular features characteristic of DMG and DHG. By identifying the recurrent co-mutations including actionable FGFR1 point mutations found in nearly one-third of H3K27M-mutant DMG in young adults, our findings can inform clinical translational studies, patient diagnosis, and clinical trial design.

Boswellic acid formulations are not suitable for treatment of pediatric high-grade glioma due to tumor promoting potential

Background and aimPediatric high-grade gliomas (pedHGG) comprise a very poor prognosis. Thus, parents of affected children are increasingly resorting to complementary and alternative medicine (CAM), among those Boswellia extracts. However, nothing is known about the therapeutic effectiveness of their active substances, Boswellic acids (BA) in pedHGG. Thus, we aimed to investigate if the three main Boswellic acids (BA) present in Boswellia plants, alpha-boswellic acid (α-BA), beta-boswellic acid (β-BA) and 3-acetyl-11-keto-beta-boswellic acid (AKBA) hold any promising potential for treatment of affected pedHGG patients. Experimental procedureHistone 3 (H3)-wildtype and H3.3K27M-mutant pedHGG cell lines were treated with BA, either alone or in combination with radio-chemotherapy with temozolomide. Cell viability, stemness properties, apoptosis, in ovo tumor growth and the transcriptome was investigated upon BA treatment. Results and conclusionInterestingly, α-BA and β-BA treatment promoted certain tumor properties in both pedHGG cells. AKBA treatment reduced cell viability and colony growth accompanied by induction of slight anti-inflammatory effects especially in H3.3K27M-mutant pedHGG cells. However, no effects on apoptosis and in ovo tumor growth were found. In conclusion, besides positive anti-tumor effects of AKBA, tumor promoting effects were observed upon treatment with α-BA and β-BA. Thus, only pure AKBA formulations may be used to exploit any potential positive effects in pedHGG patients. In conclusion, the use of commercially available supplements with a mixture of different BA cannot be recommended due to detrimental effects of certain BA whereas pure AKBA formulations might hold some potential as therapeutic supplement for treatment of pedHGG patients.

Pakistan National Guidelines for Pediatric High-Grade Gliomas.

Pediatric high-grade glioma (pHGG) is highly malignant central nervous system tumor and constitute 10% of the pediatric gliomas. Effective treatment needs a functioning multi-disciplinary team including pediatric neuro oncologist, neurosurgeon, neuroradiologist, neuropathologist and radiation oncologist. Despite surgical resection, radiotherapy and chemotherapy, most HGG will recur resulting in early death. A significant proportion of HGG occurs in context of cancer predisposition syndromes like Constitutional Mismatch Repair Deficiency (CMMRD) also known as Biallelic Mismatch Repair Deficiency (bMMRD) characterized by high mutational burden. The incidence of HGG with CMMRD is one per million patients. bMMRD is caused by homozygous germline mutations in one of the four Mis Match Repair (MMR) genes (PMS2, MLH1, MSH2, and MSH6). The use of TMZ is now avoided in CMMRD related HGG due to its limited response and known ability to increase the accumulation of somatic mutations in these patients, increasing the risk of secondary tumors. HGG should be managed under the care of multidisciplinary team to receive optimum treatment. This is particularly important for low middle-income countries (LMIC) with limited resources like Pakistan.

Simultaneous Nbs1 and p53 inactivation in neural progenitors triggers high-grade gliomas.

Nijmegen breakage syndrome (NBS) is a rare autosomal recessive disorder caused by hypomorphic mutations of NBS1. NBS1 is a member of the MRE11-RAD50-NBS1 (MRN) complex that binds to DNA double-strand breaks and activates the DNA damage response (DDR). Nbs1 inactivation in neural progenitor cells leads to microcephaly and premature death. Interestingly, p53 homozygous deletion rescues the NBS1-deficient phenotype allowing long-term survival. The objective of this work was to determine whether simultaneous inactivation of Nbs1 and p53 in neural progenitors triggered brain tumorigenesis and if so in which category this tumour could be classified. We generated a mouse model with simultaneous genetic inactivation of Nbs1 and p53 in embryonic neural stem cells and analysed the arising tumours with in-depth molecular analyses including immunohistochemistry, array comparative genomic hybridisation (aCGH), whole exome-sequencing and RNA-sequencing. NBS1/P53-deficient mice develop high-grade gliomas (HGG) arising in the olfactory bulbs and in the cortex along the rostral migratory stream. In-depth molecular analyses using immunohistochemistry, aCGH, whole exome-sequencing and RNA-sequencing revealed striking similarities to paediatric human HGG with shared features with radiation-induced gliomas (RIGs). Our findings show that concomitant inactivation of Nbs1 and p53 in mice promotes HGG with RIG features. This model could be useful for preclinical studies to improve the prognosis of these deadly tumours, but it also highlights the singularity of NBS1 among the other DNA damage response proteins in the aetiology of brain tumours.

WDR82-Mediated H3K4me3 Is Associated with Tumor Proliferation and Therapeutic Efficacy in Pediatric High-Grade Gliomas.

Pediatric high-grade gliomas (pHGGs) are common malignant brain tumors without effective treatment and poor patient survival. Abnormal posttranslational modification at the histone H3 tail plays critical roles in tumor cell malignancy. We have previously shown that the trimethylation of lysine 4 at histone H3 (H3K4me3) plays a significant role in pediatric ependymoma malignancy and is associated with tumor therapeutic sensitivity. Here, we show that H3K4me3 and its methyltransferase WDR82 are elevated in pHGGs. A reduction in H3K4me3 by downregulating WDR82 decreases H3K4me3 promoter occupancy and the expression of genes associated with stem cell features, cell proliferation, the cell cycle, and DNA damage repair. A reduction in WDR82-mediated H3K4me3 increases the response of pediatric glioma cells to chemotherapy. These findings suggest that WDR82-mediated H3K4me3 is an important determinant of pediatric glioma malignancy and therapeutic response. This highlights the need for a more thorough understanding of the potential of WDR82 as an epigenetic target to increase therapeutic efficacy and improve the prognosis for children with malignant gliomas.

Oncolytic Virotherapy for High-Grade Glioma and Current Evidence and Factors to Consider for Incorporation into Clinical Practice.

Brain tumor incidence is on the rise, and glioblastoma comprises the majority of primary tumors. Despite maximal safe resection and adjuvant chemoradiation, median survival for high-grade glioma remains poor. For this reason, it is important to develop and incorporate new treatment strategies. Oncolytic virotherapy has emerged as a viable new therapeutic entity to fill this gap. Preclinical research has shown oncolytic virotherapy to be a robust and effective treatment option for brain tumors, and clinical trials for both adult and pediatric high-grade glioma are underway. The unique and protected environment of the nervous system, in part due to the blood-brain barrier, prevents traditional systemic therapies from achieving adequate penetration. Brain tumors are also heterogenous in nature due to their diverse molecular profiles, further complicating systemic treatment efforts. Oncolytic viruses may serve to fill this gap in brain tumor treatment given their amenability to genetic modification and ability to target unique tumor epitopes. In addition, direct inoculation of the oncolytic virus agent to the tumor bed following surgical resection absolves risk of systemic side effects and ensures adequate delivery. As virotherapy transitions from bench to bedside, it is important to discuss factors to make this transition more seamless. In this article, we describe the current clinical evidence as it pertains to oncolytic virotherapy and the treatment of brain tumors as well as factors to consider for its incorporation into neurosurgical workflow.