Medulloblastoma: Tumor Biology and Relevance to Treatment and Prognosis Paradigm

Effects of different molecular subtypes and tumor biology on the prognosis of medulloblastoma

PURPOSE

Medulloblastoma is one of the most common malignant brain tumors in the pediatric population. Recent studies identified four distinct medulloblastoma subgroups with different molecular alterations and pathways, and natural courses and outcomes. To evaluate the results of surgical and medical treatments of patients with medulloblastoma and compare them among the medulloblastoma subgroups.

METHODS

The clinical and radiological features, medical and surgical management and treatment outcomes and their correlation with molecular subgroups of 58 patients treated for medulloblastoma in the last 20 years were evaluated.

RESULTS

Fifty-eight patients, of whom 35 were male and 23 were female, were evaluated. The median age was 6 years (range, 1-19 years). The most common symptoms were nausea and vomiting (60%). Forty-three percent of the patients had headache and 40% had ataxia. Previous pathology reports revealed that 43 (74%), eight (14%), five (8%), and two (3%) had classic, desmoplastic, desmoplastic/nodular, and anaplastic morphologies, respectively. After the subgroup analyses, five patients (12%) were attributed to the wingless subgroup (WNT) group; 14 (32.5%), to the sonic hedgehog subgroup (SHH) group; and 24 (56%), to the non-WNT non-SHH group. On the basis of immunohistochemical analysis results, 15 patients could not be attributed to any subgroups. The clinical risk groups (average vs high-risk) and age at diagnosis (≥ 3 years vs < 3 years of age) were significant for 5-year event free survival (86% vs 43%, p:0.011 and 59% vs 36%, p:0.039). There was no significant difference in survival or event free survival according to molecular subtypes in this cohort.

CONCLUSION

In corporation of molecular features to the clinicopathologic classification leads to risk-adapted treatment. Although the molecular subgroups did not affect outcome significantly in this study, more studies with larger numbers of patients are needed to understand the tumor pathophysiology of medulloblastoma and design the future medical practice.

3D hydrogels reveal medulloblastoma subgroup differences and identify extracellular matrix subtypes that predict patient outcome

Medulloblastoma (MB) is the most common malignant brain tumour in children and is subdivided into four subgroups: WNT, SHH, Group 3, and Group 4. These molecular subgroups differ in their metastasis patterns and related prognosis rates. Conventional 2D cell culture methods fail to recapitulate these clinical differences. Realistic 3D models of the cerebellum are therefore necessary to investigate subgroup‐specific functional differences and their role in metastasis and chemoresistance. A major component of the brain extracellular matrix (ECM) is the glycosaminoglycan hyaluronan. MB cell lines encapsulated in hyaluronan hydrogels grew as tumour nodules, with Group 3 and Group 4 cell lines displaying clinically characteristic laminar metastatic patterns and levels of chemoresistance. The glycoproteins, laminin and vitronectin, were identified as subgroup‐specific, tumour‐secreted ECM factors. Gels of higher complexity, formed by incorporation of laminin or vitronectin, revealed subgroup‐specific adhesion and growth patterns closely mimicking clinical phenotypes. ECM subtypes, defined by relative levels of laminin and vitronectin expression in patient tissue microarrays and gene expression data sets, were able to identify novel high‐risk MB patient subgroups and predict overall survival. Our hyaluronan model system has therefore allowed us to functionally characterize the interaction between different MB subtypes and their environment. It highlights the prognostic and pathological role of specific ECM factors and enables preclinical development of subgroup‐specific therapies. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Effective Inhibition of MYC-Amplified Group 3 Medulloblastoma Through Targeting EIF4A1

Purpose

In medulloblastoma (MB), group 3 (G3) patients with MYC amplification tend to exhibit worse prognosis, thus creating a need for novel effective therapies. As the driver and crucial dependency for MYC-amplified G3-MB, MYC has been proven to be a prospective therapeutic target. Here, we aimed to identify novel effective therapeutic strategies against MYC-amplified G3-MB via targeting MYC translation.

Materials and Methods

Major components of translation initiation complex eIF4F were subjected to MB tumor dataset analysis, and EIF4A1 was identified to be a potential therapeutic target of MYC-amplified G3-MB. Validation was performed through genetic or pharmacological approaches with multiple patient-derived tumor models of MYC-amplified G3-MB in vitro and in vivo. Underlying mechanisms were further explored by Western blot, quantitative real-time PCR and mass spectrometry (MS) analyses.

Results

MB tumor datasets analyses showed that EIF4A1 was significantly up-regulated in G3-MB patients relative to normal cerebella, positively correlated with MYC in G3-MB at transcriptional level and a crucial cancer dependency in MYC-amplified G3-MB cells. Targeting EIF4A1 with a CRISPR/Cas9 approach or small-molecule inhibitor silvestrol effectively attenuated growth in multiple preclinical models of MYC-amplified G3-MB via blocking proliferation and inducing apoptosis. Mechanistically, EIF4A1 inhibition effectively impeded MYC expression at translational level, and its potency was positively associated with MYC level. Whole-proteome MS analysis of silvestrol-treated cells further unveiled other biological functions and pathways influenced by EIF4A1 inhibition.

Conclusion

Our investigation shows that interrupting MYC translation by EIF4A1 inhibition could be a potential effective therapeutic approach when treating patients with MYC-amplified G3-MB.

Aggressive Medulloblastoma-Derived Exosomal miRNAs Promote In Vitro Invasion and Migration of Tumor Cells Via Ras/MAPK Pathway

Medulloblastomas (MBs) are currently divided into 4 molecular subgroups: WNT, SHH, Group 3, and Group 4. Among them, Group 3 MB has the worst prognosis, and 40%-50% of Group 3 cases are already metastatic at the time of diagnosis. Emerging evidence indicates that exosomes drive tumor invasion, but very little is known about exosomes in MBs. In this study, we initially discovered that exosomes isolated from Group 3 MB cell lines altered in vitro behaviors of a less invasive SHH MB cell line and yielded a much more aggressive phenotype. RNA-sequencing analysis revealed 7 exosomal miRNAs with markedly different expression levels between the SHH and Group 3 MB cell lines. They were all predicted to be related to the Ras/MAPK pathway according to the Kyoto Encyclopedia of Genes and Genomes data analysis. Increased expression of miR-181a-5p, miR-125b-5p, and let-7b-5p was further confirmed in Group 3 MB cells with real-time PCR and was shown to increase in vitro invasion and migratory abilities of tumor cells through the activation of ERK in Ras/MAPK pathway. Collectively, our findings suggest that exosomal miRNAs have a critical role in MB progression in vitro and might serve as diagnostic biomarkers and therapeutic targets.

Understanding Abnormal SMO-SHH Signaling in Autism Spectrum Disorder: Potential Drug Target and Therapeutic Goals

Autism is a multifactorial neurodevelopmental condition; it demonstrates some main characteristics, such as impaired social relationships and increased repetitive behavior. The initiation of autism spectrum disorder is mostly triggered during brain development by the deregulation of signaling pathways. Sonic hedgehog (SHH) signaling is one such mechanism that influences neurogenesis and neural processes during the development of the central nervous system. SMO-SHH signaling is also an important part of a broad variety of neurological processes, including neuronal cell differentiation, proliferation, and survival. Dysregulation of SMO-SHH signaling leads to many physiological changes that lead to neurological disorders such as ASD and contribute to cognitive decline. The aberrant downregulation of SMO-SHH signals contributes to the proteolytic cleavage of GLI (glioma-associated homolog) into GLI3 (repressor), which increases oxidative stress, neuronal excitotoxicity, neuroinflammation, and apoptosis by suppressing target gene expression. We outlined in this review that SMO-SHH deregulation plays a crucial role in the pathogenesis of autism and addresses the current status of SMO-SHH pathway modulators. Additionally, a greater understanding of the SHH signaling pathway is an effort to improve successful treatment for autism and other neurological disorders.

Lipidome signatures of metastasis in a transgenic mouse model of sonic hedgehog medulloblastoma

Medulloblastoma (MB), the most common malignant pediatric brain tumor, has high propensity to metastasize. Currently, the standard treatment for MB patients includes radiation therapy administered to the entire brain and spine for the purpose of treating or preventing against metastasis. Due to this aggressive treatment, the majority of long-term survivors will be left with permanent and debilitating neurocognitive impairment, for the 30-40% patients that fail to respond to treatment, all will relapse with terminal metastatic disease. An understanding of the underlying biology that drives MB metastasis is lacking, and is critically needed in order to develop targeted therapeutics for its prevention. To examine the metastatic biology of sonic hedgehog (SHH) MB, the human MB subgroup with the worst clinical outcome in children, we first generated a robust SmoA1-Math-GFP mouse model that reliably reproduces human SHH MB whereby metastases can be visualized under fluorescence microscopy. Lipidome alterations associated with metastasis were then investigated by applying ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) under positive ionization mode to primary tumor samples collected from mice without (n = 18) and with (n = 7) metastasis. Thirty-four discriminant lipids associated with SHH MB metastasis were successfully annotated, including ceramides (Cers), sphingomyelins (SMs), triacylglycerols (TGs), diacylglycerols (DGs), phosphatidylcholines (PCs), and phosphatidic acids (PAs). This study provides deeper insights into dysregulations of lipid metabolism associated with SHH MB metastatic progression, and thus serves as a guide toward novel targeted therapies.

Updates in Pediatric Malignant Gliomas

Malignant gliomas constitute a smaller portion of brain tumors in children compared with adults. Nevertheless, they can be devastating tumors with poor prognosis. Recent advances and improved understanding of the genetic and molecular characterization of pediatric brain tumors, including those of malignant gliomas, have led to the reclassification of many pediatric brain tumors and new entities have been defined. In this paper, we will present some of the more recent characterization and pertinent changes in pediatric high-grade gliomas, along with the conventional and advanced imaging features associated with these entities. Implications of the recent changes in pediatric malignant glioma classifications will also be discussed.

Erbb4 Is Required for Cerebellar Developmentand Malignant Phenotype of Medulloblastoma

Medulloblastoma is the most common and malignant pediatric brain tumor in childhood. It originates from dysregulation of cerebellar development, due to an excessive proliferation of cerebellar granule neuron precursor cells (CGNPs). The underlying molecular mechanisms, except for the role of SHH and WNT pathways, remain largely unknown. ERBB4 is a tyrosine kinase receptor whose activity in cancer is tissue dependent. In this study, we characterized the role of ERBB4 during cerebellum development and medulloblastoma progression paying particular interests to its role in CGNPs and medulloblastoma stem cells (MBSCs). Our results show that ERBB4 is expressed in the CGNPs during cerebellum development where it plays a critical role in migration, apoptosis and differentiation. Similarly, it is enriched in the population of MBSCs, where also controls those critical processes, as well as self-renewal and tumor initiation for medulloblastoma progression. These results are translated to clinical samples where high levels of ERBB4 correlate with poor outcome in Group 4 and all medulloblastomas groups. Transcriptomic analysis identified critical processes and pathways altered in cells with knock-down of ERBB4. These results highlight the impact and underlying mechanisms of ERBB4 in critical processes during cerebellum development and medulloblastoma.

Predisposition of Wingless Subgroup Medulloblastoma for Primary Tumor Hemorrhage

BACKGROUND

Primary intratumoral hemorrhage as a presenting sign is rare in children with medulloblastomas but may result in severe complications. Given the distinct properties of molecular medulloblastoma subgroups, the impact on neurosurgical practice has still to be defined.

OBJECTIVE

To investigate both clinical and radiological presentation of intratumoral hemorrhage in medulloblastoma patients in the context of molecular subgroups.

METHODS

Data of all consecutive medulloblastoma patients treated at our institution between 1993 and 2018 (n = 104) were retrospectively reviewed in respect of clinical and radiological presentation as well as molecular subgroups. For cases with available tumor tissue (n = 86), subgroups were assigned by either 450 K methylation array or immunohistochemistry and CTNNB1 sequencing. Available imaging at diagnosis (n = 62) was reviewed by an experienced neuroradiologist.

RESULTS

Within the entire cohort, 4 patients (4%) presented with massive spontaneous hemorrhage. Although no patient died as a direct consequence of hemorrhage, all suffered from serious sequelae. Moreover, 3 additional patients displayed radiological evidence of significant hemorrhage. Interestingly, all 7 cases belonged to the wingless (WNT) subgroup (n = 13), resulting in intratumoral hemorrhage in 54% (7/13) of pediatric WNT medulloblastomas. In contrast, significant hemorrhage was absent in all other molecular subgroups.

CONCLUSION

Our results suggest that a substantial proportion of pediatric WNT medulloblastomas display significant intratumoral hemorrhage at the time of diagnosis. Consequently, the presence of significant hemorrhage in fourth ventricle childhood tumors is suggestive of WNT medulloblastoma and should lead to a less aggressive attempt for total resection in this prognostically favorable tumor type.

TSP2 acts as a suppresser of cell invasion, migration and angiogenesis in medulloblastoma by inhibiting the Notch signaling pathway

Medulloblastoma (MB) represents a fatal malignancy often occurring in children. Angiogenesis is a hallmark of the progression of MB. Over the past decade, investigators have attempted to develop more effective and less toxic anti-angiogenic strategies to treat MB. Thrombospondin (TSP) family is observed to be a key regulator of angiogenesis. Thus, the current study aimed to elucidate the function of TSP2 in patients with MB and the underlying mechanism. The expression of TSP2, Notch1 and VEGF in MB and adjacent tissues collected from clinical samples as well as a MB cell line (Daoy) was examined. The results demonstrated that in the MB tissues and Daoy cells, TSP2 was downregulated, while Notch1 and VEGF were upregulated. Then, after the Daoy cells were treated with TSP2 silencing, TSP2 overexpression, or Notch signaling pathway inhibition, a series of in vitro cell experiments were performed to verify the interaction between TSP2 and Notch signaling pathway, and to examine the abilities of cell proliferation, migration, invasion, and tube formation. Upregulation of TSP2 was observed to lead to the downregulation of the Notch signaling pathway. Moreover, cells overexpressing TSP2 exhibited diminished proliferation, invasion, migration, and tube formation. In addition, a significant attenuation of tumor growth and angiogenesis was identified in vivo in the Daoy cells overexpressing TSP2 inoculated in nude mice. Taken together, the key findings of this study revealed the inhibitory role of TSP2 in the development of MB via blockade of the Notch signaling pathway, highlighting its potential as a treatment target for MB treatment.

Updates on Management of Adult Medulloblastoma

OPINION STATEMENT

Medulloblastoma (MB) is a malignant embryonal tumor of the posterior fossa and is the most common type of brain cancer in pediatric patients. In contrast, adult MB is very rare with an incidence of 0.6 per million per year and mostly affects young adults below the age of 40. Recent molecular analyses of pediatric and adult MB have classified these tumors into at least four individual molecular subgroups (SHH, WNT, group 3, and group 4) with distinct demographics, histology, and prognosis. The discrete biological composition of these tumors likely explains the marked heterogeneity in responses seen to conventional therapies such as radiation and cytotoxic chemotherapies. Given the low incidence of adult MB, prospective studies are challenging and scarce, and management guidelines are largely derived from the pediatric MB patient population and retrospective data. However, adult MB is clinically and molecularly distinct from pediatric MB and a comprehensive review of published literature on adult MB highlighting their differences is warranted. Here, we review the management of adult MB focusing on recent studies exploring the effectiveness of upfront chemotherapy, clinical trials in the context of molecular subgroup-specific therapies, and the potential role of immunotherapy in treating this disease.

Host Genome Variation is Associated with Neurocognitive Outcome in Survivors of Pediatric Medulloblastoma

Host genome analysis is a promising source of predictive information for long-term morbidity in cancer survivors. However, studies on genetic predictors of long-term outcome, particularly neurocognitive function following chemoradiation in pediatric oncology, are limited. Here, we evaluated variation in host genome of long-term survivors of medulloblastoma and its association with neurocognitive outcome. Whole-genome sequencing was conducted on peripheral blood of long-term survivors of pediatric medulloblastoma who also completed neuropsychological testing. Cognitively impaired and less impaired survivors did not differ in exposure to chemoradiation therapy or age at treatment. Unsupervised consensus clustering yielded two distinct variant clusters that were significantly associated with neurocognitive outcome. Interestingly, 34 of the 36 significant variants were found in noncoding DNA regions with unknown regulatory function. A separate unsupervised cluster analysis of variants within DNA repair genes identified discrete variant groups that were not associated with neurocognitive outcome, suggesting that variations in genes corresponding to a single functional group may be insufficient to predict long-term outcome alone. These findings are supportive of the presence of a genetic diathesis for treatment-related neurocognitive morbidity in medulloblastoma that may be driven by variation in noncoding regulatory elements.

Medulloblastoma: optimizing care with a multidisciplinary approach

Medulloblastoma is a malignant tumor of the cerebellum and the most frequent malignant brain tumor in children. The standard of care consists of maximal resection surgery, followed by craniospinal irradiation and chemotherapy. Such treatment allows long-term survival rates of nearly 70%; however, there are wide disparities among patient outcomes, and in any case, major long-term morbidity is observed with conventional treatment. In the last two decades, the molecular understanding of medulloblastoma has improved drastically, allowing us to revolutionize our understanding of medulloblastoma pathophysiological mechanisms. These advances led to an international consensus in 2010 that defined four prognostic molecular subgroups named after their affected signaling pathways, that is, WNT, SHH, Group 3 and Group 4. The molecular understanding of medulloblastoma is starting to translate through to clinical settings due to the development of targeted therapies. Moreover, recent improvements in radiotherapy modalities and the reconsideration of craniospinal irradiation according to the molecular status hold promise for survival preservation and the reduction of radiation-induced morbidity. This review is an overview of the current knowledge of medulloblastoma through a molecular approach, and therapeutic prospects currently being developed in surgery, radiotherapy and targeted therapies to optimize the treatment of medulloblastoma with a multidisciplinary approach will also be discussed.

Childhood Medulloblastoma Revisited

Medulloblastoma is the most common malignant solid tumor in childhood and the most common embryonal neuroepithelial tumor of the central nervous system. Several morphological variants are recognized: classic medulloblastoma, large cell/anaplastic medulloblastoma, desmoplastic/nodular medulloblastoma, and medulloblastoma with extensive nodularity. Recent advances in transcriptome and methylome profiling of these tumors led to a molecular classification that includes 4 major genetically defined groups. Accordingly, the 2016 revision of the World Health Organization's Classification of Tumors of the Central Nervous System recognizes the following medulloblastoma entities: Wingless (WNT)-activated, Sonic hedgehog (SHH)-activated, Group 3, and Group 4. This transcriptionally driven classification constitutes the basis of new risk stratification schemes applied to current therapeutic clinical trials. Because additional layers of molecular tumor heterogeneities are being progressively unveiled, several clinically relevant subgroups within the 4 major groups have already been identified. The purpose of this article is to review the recent basic science and clinical advances in the understanding of "medulloblastomas," and their diagnostic imaging correlates and the implications of those on current neuroimaging practice.

Transcriptional repressor REST drives lineage stage-specific chromatin compaction at Ptch1 and increases AKT activation in a mouse model of medulloblastoma

In medulloblastomas (MBs), the expression and activity of RE1-silencing transcription factor (REST) is increased in tumors driven by the sonic hedgehog (SHH) pathway, specifically the SHH-α (children 3 to 16 years) and SHH-β (infants) subgroups. Neuronal maturation is greater in SHH-β than SHH-α tumors, but both correlate with poor overall patient survival. We studied the contribution of REST to MB using a transgenic mouse model (RESTTG ) wherein conditional NeuroD2-controlled REST transgene expression in lineage-committed Ptch1 ^+/- cerebellar granule neuron progenitors (CGNPs) accelerated tumorigenesis and increased penetrance and infiltrative disease. This model revealed a neuronal maturation context-specific antagonistic interplay between the transcriptional repressor REST and the activator GLI1 at Ptch1 Expression of Arrb1, which encodes β-arrestin1 (a GLI1 inhibitor), was substantially reduced in proliferating and, to a lesser extent, lineage-committed RESTTG cells compared with wild-type proliferating CGNPs. Lineage-committed REST^TG cells also had decreased GLI1 activity and increased histone H3K9 methylation at the Ptch1 locus, which correlated with premature silencing of Ptch1 These cells also had decreased expression of Pten, which encodes a negative regulator of the kinase AKT. Expression of PTCH1 and GLI1 were less, and ARRB1 was somewhat greater, in patient SHH-β than SHH-α MBs, whereas that of PTEN was similarly lower in both subtypes than in others. Inhibition of histone modifiers or AKT reduced proliferation and induced apoptosis, respectively, in cultured REST-high MB cells. Our findings linking REST to differentiation-specific chromatin remodeling, PTCH1 silencing, and AKT activation in MB tissues reveal potential subgroup-specific therapeutic targets for MB patients.

Lsd1 as a therapeutic target in Gfi1-activated medulloblastoma

Drugs that modify the epigenome are powerful tools for treating cancer, but these drugs often have pleiotropic effects, and identifying patients who will benefit from them remains a major clinical challenge. Here we show that medulloblastomas driven by the transcription factor Gfi1 are exquisitely dependent on the enzyme lysine demethylase 1 (Kdm1a/Lsd1). We demonstrate that Lsd1 physically associates with Gfi1, and that these proteins cooperate to inhibit genes involved in neuronal commitment and differentiation. We also show that Lsd1 is essential for Gfi1-mediated transformation: Gfi1 proteins that cannot recruit Lsd1 are unable to drive tumorigenesis, and genetic ablation of Lsd1 markedly impairs tumor growth in vivo. Finally, pharmacological inhibitors of Lsd1 potently inhibit growth of Gfi1-driven tumors. These studies provide important insight into the mechanisms by which Gfi1 contributes to tumorigenesis, and identify Lsd1 inhibitors as promising therapeutic agents for Gfi1-driven medulloblastoma.

Medulloblastoma is one of the most prevalent malignant brain tumors in children and has very poor prognosis. In this study, the authors show, using a mouse model of medulloblastoma, that Gfi1 promotes tumor growth by recruiting Lsd1, that this interaction inhibits genes involved in neuronal differentiation, and that Lsd1 may be a therapeutic target in Gfi1-activated tumors.

Clinical Characteristics and Outcome of Children With Relapsed Medulloblastoma: A Retrospective Study at a Single Center in China

Relapsed medulloblastoma (MB) has a dire prognosis, and chemotherapy remains the main therapeutic option. We retrospectively analyzed the clinical characteristics and survival rates of 60 Chinese children with relapsed MB. The patients received 11 cycles of chemotherapy in sequence, followed by 12 cycles of oral temozolomide and etoposide. Thirty patients were simultaneously administered intrathecal methotrexate (IT-MTX). The Kaplan-Meier method was used to determine survival rates; the patients' median survival time after relapse was 2.8 years, 5-year progression-free survival (PFS) and overall survival (OS) rates were 26.7%±5.7% and 31.6%±6.9%, respectively. There was no significant difference between these rates according to histology or molecular subgroup. Tumor cells were detected in the cerebrospinal fluid of over 40% of patients; such patients had significantly shorter OS and PFS rates. Patients who received IT-MTX showed significantly longer survival than those who did not (3.73 vs. 2.06 y, respectively, P=0.000); the corresponding 5-year PFS and OS rates were 43.3%±9.0% versus 10.0%±5.5% and 49.5%±11.1% versus 14.6%±6.9%, respectively (P=0.000). In addition, tumor cell-positive cerebrospinal fluid and IT-MTX use significantly influenced PFS and OS in relapsed patients. Taken together, our data show that IT-MTX improves the survival of patients with relapsed MB.

Targeting mTOR as a Therapeutic Approach in Medulloblastoma

Mechanistic target of rapamycin (mTOR) is a master signaling pathway that regulates organismal growth and homeostasis, because of its implication in protein and lipid synthesis, and in the control of the cell cycle and the cellular metabolism. Moreover, it is necessary in cerebellar development and stem cell pluripotency maintenance. Its deregulation has been implicated in the medulloblastoma and in medulloblastoma stem cells (MBSCs). Medulloblastoma is the most common malignant solid tumor in childhood. The current therapies have improved the overall survival but they carry serious side effects, such as permanent neurological sequelae and disability. Recent studies have given rise to a new molecular classification of the subgroups of medulloblastoma, specifying 12 different subtypes containing novel potential therapeutic targets. In this review we propose the targeting of mTOR, in combination with current therapies, as a promising novel therapeutic approach.

New Onset Persistent Refractory Hypertension after Medulloblastoma Excision in Children-An Indicator of Poor Prognosis: A Case Series

Hypertension in the clinical setting of posterior fossa tumors is a known entity and occurs due to medullary compression by the tumor. Such hypertension usually responds to tumor excision. Postoperative hypertension occurring after posterior fossa tumor excision has been attributed to brain stem edema in a single report earlier, which resolved without any intervention. Here, we report two pediatric patients who developed new onset refractory, persistent postoperative hypertension after medulloblastoma excision, and discuss possible causes and the prognostic significance of this condition.

Expression Levels and Localizations of DVL3 and sFRP3 in Glioblastoma

The expression patterns of critical molecular components of Wnt signaling, sFRP3 and DVL3, were investigated in glioblastoma, the most aggressive form of primary brain tumors, with the aim to offer potential biomarkers. The protein expression levels and localizations in tumor tissue were revealed by immunohistochemistry and evaluated by the semiquantitative method and immunoreactivity score. Majority of glioblastomas had moderate expression levels for both DVL3 (52.4%) and sFRP3 (52.3%). Strong expression levels were observed in 23.1% and 36.0% of samples, respectively. DVL3 was localized in cytoplasm in 97% of glioblastomas, of which 44% coexpressed the protein in the nucleus. sFRP3 subcellular distribution showed that it was localized in the cytoplasm in 94% of cases. Colocalization in the cytoplasm and nucleus was observed in 50% of samples. Wilcox test indicated that the domination of the strong signal is in connection with simultaneous localization of DVL3 protein in the cytoplasm and the nucleus. Patients with strong expression of DVL3 will significantly more often have the protein in the nucleus (P = 6.33 × 10⁻⁵). No significant correlation between the two proteins was established, nor were their signal strengths correlated with epidemiological parameters. Our study contributes to better understanding of glioblastoma molecular profile.

Functional analysis of HOXA10 and HOXB4 in human medulloblastoma cell lines

Medulloblastoma (MB) is a malignant childhood brain tumor which at molecular level is classified into at least four major subtypes: WNT, SHH, group C and group D differing in response to treatment. Previous studies have associated changes in expression levels and activation of certain HOX genes with MB development. In the present study, we investigate the role of HOX genes in two attributes acquired by tumor cells: migration and proliferation potential, as well as, in vivo tumorigenic potential. We analyzed UW402, UW473, DAOY and ONS-76 human pediatric MB cell lines and cerebellum primary cultures. Two-color microarray-based gene expression analysis was used to identify differentially expressed HOX genes. Among the various HOX genes significantly overexpressed in DAOY and ONS-76 cell lines compared to UW402 and UW473 cell lines, HOXA10 and HOXB4 were selected for further analysis. The expression levels of these HOX genes were validated by real-time PCR. A mouse model was used to study the effect of the HOXA10 and HOXB4 genes on the in vivo tumorigenic potential and the in vitro proliferative and migration potential of MB cell lines. Our results show that the inhibition of HOXA10 in DAOY cell line led to increased in vitro cell migration while in vitro cell proliferation or in vivo tumorigenic potential were unaffected. We also observed that induced expression of HOXB4 in the UW473 cell line significantly reduced in vitro cell proliferation and migration capability of UW473 cells with no effect on the in vivo tumorigenicity. This suggests that HOXA10 plays a role in migration events and the HOXB4 gene is involved in proliferation and migration processes of medulloblastoma cells, however, it appears that these genes are not essential for the tumorigenic process of these cells.

Extracellular Vesicles in Brain Tumors and Neurodegenerative Diseases

Extracellular vesicles (EVs) can be classified into apoptotic bodies, microvesicles (MVs), and exosomes, based on their origin or size. Exosomes are the smallest and best characterized vesicles which derived from the endosomal system. These vesicles are released from many different cell types including neuronal cells and their functions in the nervous system are investigated. They have been proposed as novel means for intercellular communication, which takes part not only to the normal neuronal physiology but also to the transmission of pathogenic proteins. Indeed, exosomes are fundamental to assemble and transport proteins during development, but they can also transfer neurotoxic misfolded proteins in pathogenesis. The present review will focus on their roles in neurological diseases, specifically brain tumors, such as glioblastoma (GBM), neuroblastoma (NB), medulloblastoma (MB), and metastatic brain tumors and chronic neurodegenerative diseases, such as Alzheimer, Parkinson, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington, and Prion diseseases highlighting their involvement in spreading neurotoxicity, in therapeutics, and in pathogenesis.

Functional expression of calcium-permeable canonical transient receptor potential 4-containing channels promotes migration of medulloblastoma cells

KEY POINTS

The proton sensing ovarian cancer G protein coupled receptor 1 (OGR1, aka GPR68) promotes expression of the canonical transient receptor potential channel subunit TRPC4 in normal and transformed cerebellar granule precursor (DAOY) cells. OGR1 and TRPC4 are prominently expressed in healthy cerebellar tissue throughout postnatal development and in primary cerebellar medulloblastoma tissues. Activation of TRPC4-containing channels in DAOY cells, but not non-transformed granule precursor cells, results in prominent increases in [Ca2+ ]i and promotes cell motility in wound healing and transwell migration assays. Medulloblastoma cells not arising from granule precursor cells show neither prominent rises in [Ca2+ ]i nor enhanced motility in response to TRPC4 activation unless they overexpressTRPC4. Our results suggest that OGR1 enhances expression of TRPC4-containing channels that contribute to enhanced invasion and metastasis of granule precursor-derived human medulloblastoma.

ABSTRACT

Aberrant intracellular Ca2+ signalling contributes to the formation and progression of a range of distinct pathologies including cancers. Rises in intracellular Ca2+ concentration occur in response to Ca2+ influx through plasma membrane channels and Ca2+ release from intracellular Ca2+ stores, which can be mobilized in response to activation of cell surface receptors. Ovarian cancer G protein coupled receptor 1 (OGR1, aka GPR68) is a proton-sensing Gq -coupled receptor that is most highly expressed in cerebellum. Medulloblastoma (MB) is the most common paediatric brain tumour that arises from cerebellar precursor cells. We found that nine distinct human MB samples all expressed OGR1. In both normal granule cells and the transformed human cerebellar granule cell line DAOY, OGR1 promoted expression of the proton-potentiated member of the canonical transient receptor potential (TRPC) channel family, TRPC4. Consistent with a role for TRPC4 in MB, we found that all MB samples also expressed TRPC4. In DAOY cells, activation of TRPC4-containing channels resulted in large Ca2+ influx and enhanced migration, while in normal cerebellar granule (precursor) cells and MB cells not derived from granule precursors, only small levels of Ca2+ influx and no enhanced migration were observed. Our results suggest that OGR1-dependent increases in TRPC4 expression may favour formation of highly Ca2+ -permeable TRPC4-containing channels that promote transformed granule cell migration. Increased motility of cancer cells is a prerequisite for cancer invasion and metastasis, and our findings may point towards a key role for TRPC4 in progression of certain types of MB.

Overexpression of TEAD4 in atypical teratoid/rhabdoid tumor: New insight to the pathophysiology of an aggressive brain tumor

BACKGROUND

Atypical teratoid/rhabdoid tumor (AT/RT) is a highly malignant embryonal brain tumor that occurs mainly in early childhood. Although most of the tumors are characterized by inactivating mutations of the tumor suppressor gene, SMARCB1, the biological basis of its tumorigenesis and aggressiveness is still unknown.

PROCEDURE

We performed high-throughput copy number variation analysis of primary cell lines generated from primary and relapsed tumors from one of our patients to identify new genes involved in AT/RT biology. The expression of the identified gene was validated in 29 AT/RT samples by gene expression profiling, quantitative real-time polymerase chain reaction, and immunohistochemistry (IHC). Furthermore, we investigated the function of this gene by mutating it in rhabdoid tumor cells.

RESULTS

TEAD4 amplification was detected in the primary cell lines and its overexpression was confirmed at mRNA and protein levels in an independent cohort of AT/RT samples. TEAD4's co-activator, YAP1, and the downstream targets, MYC and CCND1, were also found to be upregulated in AT/RT when compared to medulloblastoma. IHC showed TEAD4 and YAP1 overexpression in all samples. Cell proliferation and migration were significantly reduced in TEAD4-mutated cells.

CONCLUSIONS

We report the overexpression of TEAD4 in AT/RT, which is a key component of Hippo pathway. Recent reports revealed that dysregulation of the Hippo pathway is implicated in tumorigenesis and poor prognosis of several human cancers. Our results suggest that TEAD4 plays a role in the pathophysiology of AT/RT, which represents a new insight into the biology of this aggressive tumor.

Regulation of USP37 Expression by REST-Associated G9a-Dependent Histone Methylation

The deubiquitylase (DUB) USP37 is a component of the ubiquitin system and controls cell proliferation by regulating the stability of the cyclin-dependent kinase inhibitor 1B, (CDKN1B/p27Kip1). The expression of USP37 is downregulated in human medulloblastoma tumor specimens. In the current study, we show that USP37 prevents medulloblastoma growth in mouse orthotopic models, suggesting that it has tumor-suppressive properties in this neural cancer. Here, we also report on the mechanism underlying USP37 loss in medulloblastoma. Previously, we observed that the expression of USP37 is transcriptionally repressed by the RE1 silencing transcription factor (REST), which requires chromatin remodeling factors for its activity. Genetic and pharmacologic approaches were employed to identify a specific role for G9a, a histone methyltransferase (HMT), in promoting methylation of histone H3 lysine-9 (H3K9) mono- and dimethylation, and surprisingly trimethylation, at the USP37 promoter to repress its gene expression. G9a inhibition also blocked the tumorigenic potential of medulloblastoma cells in vivo Using isogenic low- and high-REST medulloblastoma cells, we further showed a REST-dependent elevation in G9a activity, which further increased mono- and trimethylation of histone H3K9, accompanied by downregulation of USP37 expression. Together, these findings reveal a role for REST-associated G9a and histone H3K9 methylation in the repression of USP37 expression in medulloblastoma.Implications: Reactivation of USP37 by G9a inhibition has the potential for therapeutic applications in REST-expressing medulloblastomas. Mol Cancer Res; 15(8); 1073-84. ©2017 AACR.

Immunological low-dose radiation modulates the pediatric medulloblastoma antigens and enhances antibody-dependent cellular cytotoxicity

BACKGROUND

Immunotherapy can be an effective treatment for pediatric medulloblastoma (MB) patients. However, major subpopulations do not respond to immunotherapy, due to the lack of antigenic mutations or the immune-evasive properties of MB cells. Clinical observations suggest that radiation therapy (RT) may expand the therapeutic reach of immunotherapy. The aim of the present investigation is to study the effect of low-dose X-ray radiation (LDXR, 1 Gy) on the functional immunological responses of MB cells (DAOY, D283, and D341).

METHODS

Induction of MB cell death was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Production of reactive oxygen species (ROS) was measured by fluorescent probes. Changes in the expression of  human leukocyte antigen (HLA) molecules and caspase-3 activities during treatment were analyzed using Western blotting and caspase-3 assay.

RESULTS

Western blot analysis demonstrated that LDXR upregulated the expression of HLA class I and HLA II molecules by more than 20% compared with control and high-dose (12 Gy) groups in vitro. Several of these HLA subtypes, such as MAGE C1, CD137, and ICAM-1, have demonstrated upregulation. In addition, LDXR increases ROS production in association with phosphorylation of NF-κB and cell surface expression of mAb target molecules (HER2 and VEGF). These data suggest that a combined LDXR and mAb therapy can create a synergistic effect in vitro.

CONCLUSION

These results suggest that LDXR modulates HLA molecules, leading to alterations in T-cell/tumor-cell interaction and enhancement of T-cell-mediated MB cell death. Also, low-dose radiotherapy combined with monoclonal antibody therapy may one day augment the standard treatment for MB, but more investigation is needed to prove its utility as a new therapeutic combination for MB patients.

The ubiquitin-proteasome system and chromosome 17 in cerebellar granule cells and medulloblastoma subgroups

Chromosome 17 abnormalities are often observed in medulloblastomas (MBs), particularly those classified in the consensus Groups 3 and 4. Herein we review MB signature genes associated with chromosome 17 and the relationship of these signature genes to the ubiquitin-proteasome system. While clinical investigators have not focused on the ubiquitin-proteasome system in relation to MB, a substantial amount of data on the topic has been hidden in the form of supplemental datasets of gene expression. A supplemental dataset associated with the Thompson classification of MBs shows that a subgroup of MB with 17p deletions is characterized by reduced expression of genes for several core particle subunits of the beta ring of the proteasome (β1, β4, β5, β7). One of these genes (PSMB6, the gene for the β1 subunit) is located on chromosome 17, near the telomeric end of 17p. By comparison, in the WNT group of MBs only one core proteasome subunit, β6, associated with loss of a gene (PSMB1) on chromosome 6, was down-regulated in this dataset. The MB subgroups with the worst prognosis have a significant association with chromosome 17 abnormalities and irregularities of APC/C cyclosome genes. We conclude that the expression of proteasome subunit genes and genes for ubiquitin ligases can contribute to prognostic classification of MBs. The therapeutic value of targeting proteasome subunits and ubiquitin ligases in the various subgroups of MB remains to be determined separately for each classification of MB.

Targeting sonic hedgehog signaling in neurological disorders

Sonic hedgehog (Shh) signaling influences neurogenesis and neural patterning during the development of central nervous system. Dysregulation of Shh signaling in brain leads to neurological disorders like autism spectrum disorder, depression, dementia, stroke, Parkinson's diseases, Huntington's disease, locomotor deficit, epilepsy, demyelinating disease, neuropathies as well as brain tumors. The synthesis, processing and transport of Shh ligand as well as the localization of its receptors and signal transduction in the central nervous system has been carefully reviewed. Further, we summarize the regulation of small molecule modulators of Shh pathway with potential in neurological disorders. In conclusion, further studies are warranted to demonstrate the potential of positive and negative regulators of the Shh pathway in neurological disorders.

Albumin nanoparticles for glutathione-responsive release of cisplatin: New opportunities for medulloblastoma

Redox-responsive nanoparticles were synthesized by desolvation of bovine serum albumin followed by disulfide-bond crosslinking with N, N'-Bis (acryloyl) cystamine. Dynamic light scattering and transmission electron microscopy studies revealed spherical nanoparticles (mean diameter: 83nm, polydispersity index: 0.3) that were glutathione-responsive. Confocal microscopy revealed rapid, efficient internalization of the nanoparticles by Daoy medulloblastoma cells and healthy controls (HaCaT keratinocytes). Cisplatin-loaded nanoparticles with drug:carrier ratios of 5%, 10%, and 20% were tested in both cell lines. The formulation with the highest drug:carrier ratio reduced Daoy and HaCaT cell viability with IC₅₀ values of 6.19 and 11.17μgmL^-1, respectively. The differential cytotoxicity reflects the cancer cells' higher glutathione content, which triggers more extensive disruption of the disulfide bond-mediated intra-particle cross-links, decreasing particle stability and increasing their cisplatin release. These findings support continuing efforts to improve the safety and efficacy of antineoplastic drug therapy for pediatric brain tumors using selective nanoparticle-based drug delivery systems.