Medulloblastomics: the end of the beginning

HDAC and PI3K Antagonists Cooperate to Inhibit Growth of MYC-Driven Medulloblastoma

Medulloblastoma (MB) is a highly malignant pediatric brain tumor. Despite aggressive therapy, many patients succumb to the disease, and survivors experience severe side effects from treatment. MYC-driven MB has a particularly poor prognosis and would greatly benefit from more effective therapies. We used an animal model of MYC-driven MB to screen for drugs that decrease viability of tumor cells. Among the most effective compounds were histone deacetylase inhibitors (HDACIs). HDACIs potently inhibit survival of MYC-driven MB cells in vitro, in part by inducing expression of the FOXO1 tumor suppressor gene. HDACIs also synergize with phosphatidylinositol 3-kinase inhibitors to inhibit tumor growth in vivo. These studies identify an effective combination therapy for the most aggressive form of MB.

Prognostic value of medulloblastoma extent of resection after accounting for molecular subgroup: a retrospective integrated clinical and molecular analysis

Background

Incomplete surgical resection of medulloblastoma is controversially considered a marker of high-risk disease; driving aggressive surgical resections, “second-look” surgeries, and/or intensified chemoradiotherapy. All prior publications evaluating the clinical importance of extent of resection (EOR) failed to account for molecular subgroup. We analysed the prognostic value of EOR across 787 medulloblastoma samples in a subgroup-specific manner.

Methods

We retrospectively identified patients from Medulloblastoma Advanced Genomics International Consortium (MAGIC) centres with a histological diagnosis of medulloblastoma and complete extent of resection and survival data. Specimens were collected from 35 international institutions. Medulloblastoma subgroup affiliation was determined using nanoString gene expression profiling on frozen or formalin-fixed paraffin-embedded tissues. Extent of resection (EOR) based on post-operative imaging was classified as gross total (GTR), near total (NTR, <1·5cm²), or subtotal (STR, ≥ 1·5cm²). Overall survival (OS) and progression-free survival (PFS) multivariable analyses including subgroup, age, metastatic status, geographical location of therapy (North America/Australia vs world), and adjuvant therapy regimen were performed. The primary endpoint was the impact of surgical EOR by molecular subgroup and other clinical variables on OS and PFS.

Findings

787 medulloblastoma patients (86 WNT, 242 SHH, 163 Group 3, and 296 Group 4) were included in a multivariable Cox model of PFS and OS. The marked benefit of EOR in the overall cohort was greatly attenuated after including molecular subgroup in the multivariable analysis. There was an observed PFS benefit of GTR over STR (hazard ration [HR] 1·45, 95% CI; 1·07–1·96, p=0·02) but there was no observed PFS or OS benefit of GTR over NTR (HR 1·05, 0·71–1·53, p=0·82 and HR 1·14, 0·75–1·72, p=0.55). There was no statistically significant survival benefit to greater EOR for patients with WNT, SHH, or Group 3 patients (HR 1·03, 0·67–1·58, p=0·9 for STR vs. GTR). There was a PFS benefit for GTR over STR in patients with Group 4 medulloblastoma (HR1·97, 1·22–3·17, p=0·01), particularly those with metastatic disease (HR 2·22, 1–4·93, p=0·05). A nomogram based on this multivariable cox proportional hazards model shows the comparably smaller impact of EOR on relative risk for PFS and OS than subgroup affiliation, metastatic status, radiation dose, and adjuvant chemotherapy.

Interpretation

The prognostic benefit of EOR for patients with medulloblastoma is attenuated after accounting for molecular subgroup affiliation. Although maximal safe surgical resection should remain the standard of care, surgical removal of small residual portions of medulloblastoma is not recommended when the likelihood of neurological morbidity is high as there is no definitive benefit to GTR over NTR. Our results suggest a re-evaluation of the long-term implications of intensified craniospinal irradiation (36 Gy) in children with small residual portions of medulloblastoma.

Funding

Funding Canadian Cancer Society Research Institute, Terry Fox Research Institute, Canadian Institutes of Health Research, National Institutes of Health, Pediatric Brain Tumor Foundation, Garron Family Chair in Childhood Cancer Research.

Knockdown of EphB1 receptor decreases medulloblastoma cell growth and migration and increases cellular radiosensitization

The expression of members of the Eph family of receptor tyrosine kinases and their ephrin ligands is frequently dysregulated in medulloblastomas. We assessed the expression and functional role of EphB1 in medulloblastoma cell lines and engineered mouse models. mRNA and protein expression profiling showed expression of EphB1 receptor in the human medulloblastoma cell lines DAOY and UW228. EphB1 downregulation reduced cell growth and viability, decreased the expression of important cell cycle regulators, and increased the percentage of cells in G1 phase of the cell cycle. It also modulated the expression of proliferation, and cell survival markers. In addition, EphB1 knockdown in DAOY cells resulted in significant decrease in migration, which correlated with decreased β1-integrin expression and levels of phosphorylated Src. Furthermore, EphB1 knockdown enhanced cellular radiosensitization of medulloblastoma cells in culture and in a genetically engineered mouse medulloblastoma model. Using genetically engineered mouse models, we established that genetic loss of EphB1 resulted in a significant delay in tumor recurrence following irradiation compared to EphB1-expressing control tumors. Taken together, our findings establish that EphB1 plays a key role in medulloblastoma cell growth, viability, migration, and radiation sensitivity, making EphB1 a promising therapeutic target.

Somatic mutations of DICER1 and KMT2D are frequent in intraocular medulloepitheliomas

Intraocular medulloepithelioma (IO-MEPL) is an uncommon embryonal neuroepithelial neoplasm of the eye. Little is known about the cytogenetics, molecular biology, and pathogenesis of this tumor. In the present study we investigated the mutational landscape of 19 IO-MEPL using targeted next-generation sequencing. Routinely prepared paraffin-embedded samples were assessed with high-coverage genome sequencing on the Illumina NextSeq 500 platform using a customized gene panel set covering the coding region of 130 genes. This revealed several notable genomic alterations, including mutations of DICER1 (6 tumors) and KMT2D (also known as MLL2; 5 tumors)-which are frequently recurrent and mutually exclusive molecular events for IO-MEPL. Non-recurrent mutations in the cancer-associated genes BRCA2, BRCA1, NOTCH2, CDH1, and GSE1 were also identified. IO-MEPL samples harboring a DICER1 mutation disclosed few chromosomal alterations and formed a separate DNA methylation cluster, indicating potential differences in genetic and epigenetic events arising perhaps from the presence of this aberration in the tumor genome. The high proportion of recurrent somatic DICER1 and KMT2D mutations in this series of sporadic IO-MEPL points to their likely important roles in the molecular pathogenesis of these rare embryonal tumors, and perhaps suggests the existence of distinct molecular variants of IO-MEPL. Although the precise role of these recurrent mutations in the development of IO-MEPL, and their relationship to pro-oncogenic molecular mechanisms, have yet to be determined, unraveling their roles could eventually be exploited for nonsurgical therapies of these neoplasms.

Active medulloblastoma enhancers reveal subgroup-specific cellular origins

Medulloblastoma is a highly malignant paediatric brain tumour, often inflicting devastating consequences on the developing child. Genomic studies have revealed four distinct molecular subgroups with divergent biology and clinical behaviour. An understanding of the regulatory circuitry governing the transcriptional landscapes of medulloblastoma subgroups, and how this relates to their respective developmental origins, is lacking. Here, using H3K27ac and BRD4 chromatin immunoprecipitation followed by sequencing (ChIP-seq) coupled with tissue-matched DNA methylation and transcriptome data, we describe the active cis-regulatory landscape across 28 primary medulloblastoma specimens. Analysis of differentially regulated enhancers and super-enhancers reinforced inter-subgroup heterogeneity and revealed novel, clinically relevant insights into medulloblastoma biology. Computational reconstruction of core regulatory circuitry identified a master set of transcription factors, validated by ChIP-seq, that is responsible for subgroup divergence, and implicates candidate cells of origin for Group 4. Our integrated analysis of enhancer elements in a large series of primary tumour samples reveals insights into cis-regulatory architecture, unrecognized dependencies, and cellular origins.

Non-canonical Hedgehog/AMPK-Mediated Control of Polyamine Metabolism Supports Neuronal and Medulloblastoma Cell Growth

Developmental Hedgehog signaling controls proliferation of cerebellar granule cell precursors (GCPs), and its aberrant activation is a leading cause of medulloblastoma. We show here that Hedgehog promotes polyamine biosynthesis in GCPs by engaging a non-canonical axis leading to the translation of ornithine decarboxylase (ODC). This process is governed by AMPK, which phosphorylates threonine 173 of the zinc finger protein CNBP in response to Hedgehog activation. Phosphorylated CNBP increases its association with Sufu, followed by CNBP stabilization, ODC translation, and polyamine biosynthesis. Notably, CNBP, ODC, and polyamines are elevated in Hedgehog-dependent medulloblastoma, and genetic or pharmacological inhibition of this axis efficiently blocks Hedgehog-dependent proliferation of medulloblastoma cells in vitro and in vivo. Together, these data illustrate an auxiliary mechanism of metabolic control by a morphogenic pathway with relevant implications in development and cancer.

Divergent clonal selection dominates medulloblastoma at recurrence

The development of targeted anti-cancer therapies through the study of cancer genomes is intended to increase survival rates and decrease treatment-related toxicity. We treated a transposon-driven, functional genomic mouse model of medulloblastoma with 'humanized' in vivo therapy (microneurosurgical tumour resection followed by multi-fractionated, image-guided radiotherapy). Genetic events in recurrent murine medulloblastoma exhibit a very poor overlap with those in matched murine diagnostic samples (<5%). Whole-genome sequencing of 33 pairs of human diagnostic and post-therapy medulloblastomas demonstrated substantial genetic divergence of the dominant clone after therapy (<12% diagnostic events were retained at recurrence). In both mice and humans, the dominant clone at recurrence arose through clonal selection of a pre-existing minor clone present at diagnosis. Targeted therapy is unlikely to be effective in the absence of the target, therefore our results offer a simple, proximal, and remediable explanation for the failure of prior clinical trials of targeted therapy.

miR-106b is overexpressed in medulloblastomas and interacts directly with PTEN

AIMS

MicroRNAs (miRNAs) are an abundant group of small non-coding RNAs that have been implicated in tumorigenesis. They regulate expression of target genes by complementary base pairing. The purposes of this study were to delineate miR-106b expression in medulloblastoma (MB) and to explore its functional contributions to MB pathogenesis.

METHODS

We analysed expression of miR-106b in 32 MB samples by quantitative RT-PCR. We applied gain- and loss-of-function strategies to delineate the functional roles of miR-106b in MB. Luciferase reporter assay was conducted to confirm target gene of miR-106b.

RESULTS

Expression of miR-106b was overexpressed in MB, and was significantly associated with its host gene MCM7 (P = 0.020). Transfection of miR-106b inhibitor in MB cell lines markedly reduced cell proliferation, migration and invasion potential, and tumour sphere formation. Cell cycle analysis indicated that miR-106b inhibition induced G1 arrest and apoptosis. The cell cycle regulators, p21 and cyclin D1, and apoptotic marker cleaved PARP were differentially expressed in miR-106b inhibitor-transfected cells. PTEN was identified as a direct target gene of miR-106b. Luciferase reporter assay confirmed miR-106b directly interacted with the 3' UTR of PTEN. We found miR-106b directly targeted PTEN at transcriptional and translational levels. Immunohistochemistry revealed a trend between PTEN and miR-106b in MB tumours (P = 0.07).

CONCLUSIONS

These data suggested the upregulation of miR-106b in MB and the involvement of miR-106b in MB biology.

p53 and Meduloblastoma

Our understanding of medulloblastoma biology has increased dramatically over the past decade, in part a result of the recognition that there exists tremendous intertumoral heterogeneity not apparent by morphology alone. A particular area that significantly changed our approach to medulloblastoma has been an increased understanding of the role of p53. A role for p53 in medulloblastoma has been established over the past 20 years, however, not until recently has its significance been identified. Recent developments in the understanding of intertumor heterogeneity has clarified the role of TP53 mutations, as the importance of TP53 mutations is highly dependent on the molecular subgroup of medulloblastoma, with TP53 mutant Sonic Hedgehog medulloblastomas forming an extremely high-risk group of patients. As such, there is now a tremendous push to understand the role that p53 plays in treatment resistance of medulloblastoma. In this review, we will summarize the current understanding of p53 in medulloblastoma drawn primarily from recent advances in integrated genomics.

The Molecular Signatures Database (MSigDB) hallmark gene set collection

The Molecular Signatures Database (MSigDB) is one of the most widely used and comprehensive databases of gene sets for performing gene set enrichment analysis. Since its creation, MSigDB has grown beyond its roots in metabolic disease and cancer to include >10,000 gene sets. These better represent a wider range of biological processes and diseases, but the utility of the database is reduced by increased redundancy across, and heterogeneity within, gene sets. To address this challenge, here we use a combination of automated approaches and expert curation to develop a collection of "hallmark" gene sets as part of MSigDB. Each hallmark in this collection consists of a "refined" gene set, derived from multiple "founder" sets, that conveys a specific biological state or process and displays coherent expression. The hallmarks effectively summarize most of the relevant information of the original founder sets and, by reducing both variation and redundancy, provide more refined and concise inputs for gene set enrichment analysis.

MR Imaging Characteristics of Wingless-Type-Subgroup Pediatric Medulloblastoma

BACKGROUND AND PURPOSE

"Transcriptionally different" medulloblastoma groups are associated with specific signaling pathway abnormalities; hence, they may present with distinct imaging manifestations. In this study, we sought to describe the MR imaging features of wingless-type-subgroup medulloblastomas with embryologic correlations.

MATERIALS AND METHODS

Pre- and postoperative imaging studies of 16 patients with wingless-type-subgroup medulloblastoma were evaluated for tumor location, involvement of surrounding CSF spaces or parenchymal structures, conventional and DWI signal properties, and postsurgical damage patterns. Laterality scores were assigned to tumors at each step in the evaluation process. Continuous variables were summarized by using descriptive statistics. The Wilcoxon signed rank test was performed to compare laterality scores. To determine the interobserver variability, we computed the intraclass correlation and Cohen κ coefficients.

RESULTS

Wingless-type-subgroup medulloblastomas in our series were histopathologically "classic." Wingless-type-subgroup medulloblastomas occur in specific sites, with involvement of the foramen of Luschka (75%), the fourth ventricle (68.75%), the cisterna magna (31.25%), and the cerebellopontine angle cistern (18.75%). Laterality scores were low (<2) when preoperative primary and secondary anatomic features were evaluated separately, but they increased (>2) when all pre- and postoperative anatomic features were considered. Results were statistically shown to be reproducible (interclass correlation coefficient, 0.71-0.94; Cohen κ, 0.63-1.00). On the basis of anatomic lesion patterns, 4 location-based subtypes may be distinguished: 1) midline-intraventricular, 2) midline-extraventricular, 3) off-midline-intraventricular, and 4) off-midline-extraventricular, which represent a continuum.

CONCLUSIONS

Wingless-type-subgroup medulloblastomas are lateralized tumors arising from the brain stem and cerebellum around the foramen of Luschka. Our current understanding of their embryologic origins is in concordance with the spatial distribution of these tumors.

Medulloblastoma development: tumor biology informs treatment decisions

Medulloblastoma is the most common malignant pediatric brain tumor. Current treatments including surgery, craniospinal radiation and high-dose chemotherapy have led to improvement in survival. However, the risk for recurrence as well as significant long-term neurocognitive and endocrine sequelae associated with current treatment modalities underscore the urgent need for novel tumor-specific, normal brain-sparing therapies. It has also provided the impetus for research focused on providing a better understanding of medulloblastoma biology. The expectation is that such studies will lead to the identification of new therapeutic targets and eventually to an increase in personalized treatment approaches.

Evolving molecular era of childhood medulloblastoma: time to revisit therapy

Currently medulloblastoma is treated with a uniform therapeutic approach based on histopathology and clinico-radiological risk stratification, resulting in unpredictable treatment failure and relapses. Improved understanding of the biological, molecular and genetic make-up of these tumors now clearly identifies it as a compendium of four distinct subtypes (WNT, SHH, group 3 and 4). Advances in utilization of the genomic and epigenomic machinery have now delineated genetic aberrations and epigenetic perturbations in each subgroup as potential druggable targets. This has resulted in endeavors to profile targeted therapy. The challenge and future of medulloblastoma therapeutics will be to keep pace with the evolving novel biological insights and translating them into optimal targeted treatment regimens.

Pediatric Targeted Therapy: Clinical Feasibility of Personalized Diagnostics in Children with Relapsed and Progressive Tumors

The "pediatric targeted therapy" (PTT) program aims to identify the presence and activity of druggable targets and evaluate the clinical benefit of a personalized treatment approach in relapsed or progressive tumors on an individual basis. 10 markers (HDAC2, HR23B, p-AKT, p-ERK, p-S6, p-EGFR, PDGFR-alpha/beta, p53 and BRAFV600E) were analyzed by immunohistochemistry. Pediatric patients with tumors independent of the histological diagnosis, with relapse or progression after treatment according to standard protocols were included. N = 61/145 (42%) cases were eligible for analysis between 2009 and 2013, the most common entities being brain tumors. Immunohistochemical stainings were evaluated by the H-Score (0-300). In 93% of the cases potentially actionable targets were identified. The expressed or activated pathways were histone deacetylase (HDACs; 83.0% of cases positive), EGFR (87.2%), PDGFR (75.9%), p53 (50.0%), MAPK/ERK (43.3%) and PI3K/mTOR (36.1%). Follow-up revealed partial or full implementation of PTT results in treatment decision-making in 41% of the cases. Prolonged disease stabilization responses in single cases were noticed, however, response rates did not differ from cases treated with other modalities. Further studies evaluating the feasibility and clinical benefit of personalized diagnostic approaches using paraffin material are warranted.

Wnt/β-catenin pathway regulates MGMT gene expression in cancer and inhibition of Wnt signalling prevents chemoresistance

The DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) is commonly overexpressed in cancers and is implicated in the development of chemoresistance. The use of drugs inhibiting MGMT has been hindered by their haematologic toxicity and inefficiency. As a different strategy to inhibit MGMT we investigated cellular regulators of MGMT expression in multiple cancers. Here we show a significant correlation between Wnt signalling and MGMT expression in cancers with different origin and confirm the findings by bioinformatic analysis and immunofluorescence. We demonstrate Wnt-dependent MGMT gene expression and cellular co-localization between active β-catenin and MGMT. Pharmacological or genetic inhibition of Wnt activity downregulates MGMT expression and restores chemosensitivity of DNA-alkylating drugs in mouse models. These findings have potential therapeutic implications for chemoresistant cancers, especially of brain tumours where the use of temozolomide is frequently used in treatment.

The high expression of the DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT) often confers resistance to chemotherapy in several cancers. In this study, the authors propose the inhibition of the Wnt signalling pathway as an alternative strategy to modulate MGMT expression and sensitize tumours to chemotherapy.

Biomarker-driven stratification of disease-risk in non-metastatic medulloblastoma: Results from the multi-center HIT-SIOP-PNET4 clinical trial

PURPOSE

To improve stratification of risk-adapted treatment for non-metastatic (M0), standard-risk medulloblastoma patients by prospective evaluation of biomarkers of reported biological or prognostic significance, alongside clinico-pathological variables, within the multi-center HIT-SIOP-PNET4 trial.

METHODS

Formalin-fixed paraffin-embedded tumor tissues were collected from 338 M0 patients (>4.0 years at diagnosis) for pathology review and assessment of the WNT subgroup (MBWNT) and genomic copy-number defects (chromosome 17, MYC/MYCN, 9q22 (PTCH1) and DNA ploidy). Clinical characteristics were reviewed centrally.

RESULTS

The favorable prognosis of MBWNT was confirmed, however better outcomes were observed for non-MBWNT tumors in this clinical risk-defined cohort compared to previous disease-wide clinical trials. Chromosome 17p/q defects were heterogeneous when assessed at the cellular copy-number level, and predicted poor prognosis when they occurred against a diploid (ch17(im)/diploid(cen)), but not polyploid, genetic background. These factors, together with post-surgical tumor residuum (R+) and radiotherapy delay, were supported as independent prognostic markers in multivariate testing. Notably, MYC and MYCN amplification were not associated with adverse outcome. In cross-validated survival models derived for the clinical standard-risk (M0/R0) disease group, (ch17(im)/diploid(cen); 14% of patients) predicted high disease-risk, while the outcomes of patients without (ch17(im)/diploid(cen)) did not differ significantly from MBWNT, allowing re-classification of 86% as favorable-risk.

CONCLUSIONS

Biomarkers, established previously in disease-wide studies, behave differently in clinically-defined standard-risk disease. Distinct biomarkers are required to assess disease-risk in this group, and define improved risk-stratification models. Routine testing for specific patterns of chromosome 17 imbalance at the cellular level, and MBWNT, provides a strong basis for incorporation into future trials.

DDX3, a potential target for cancer treatment

RNA helicases are a large family of proteins with a distinct motif, referred to as the DEAD/H (Asp-Glu-Ala-Asp/His). The exact functions of all the human DEAD/H box proteins are unknown. However, it has been consistently demonstrated that these proteins are associated with several aspects of energy-dependent RNA metabolism, including translation, ribosome biogenesis, and pre-mRNA splicing. In addition, DEAD/H box proteins participate in nuclear-cytoplasmic transport and organellar gene expression.

A member of this RNA helicase family, DDX3, has been identified in a variety of cellular biogenesis processes, including cell-cycle regulation, cellular differentiation, cell survival, and apoptosis. In cancer, DDX3 expression has been evaluated in patient samples of breast, lung, colon, oral, and liver cancer. Both tumor suppressor and oncogenic functions have been attributed to DDX3 and are discussed in this review. In general, there is concordance with in vitro evidence to support the hypothesis that DDX3 is associated with an aggressive phenotype in human malignancies. Interestingly, very few cancer types harbor mutations in DDX3, which result in altered protein function rather than a loss of function.

Efficacy of drugs to curtail cancer growth is hindered by adaptive responses that promote drug resistance, eventually leading to treatment failure. One way to circumvent development of resistant disease is to develop novel drugs that target over-expressed proteins involved in this adaptive response. Moreover, if the target gene is developmentally regulated, there is less of a possibility to abruptly accumulate mutations leading to drug resistance. In this regard, DDX3 could be a druggable target for cancer treatment. We present an overview of DDX3 biology and the currently available DDX3 inhibitors for cancer treatment.

Somatic cell transfer of c-Myc and Bcl-2 induces large-cell anaplastic medulloblastomas in mice

A highly aggressive subgroup of the pediatric brain tumor medulloblastoma is characterized by overexpression of the proto-oncogene c-Myc, which encodes a transcription factor that normally maintains neural progenitor cells in an undifferentiated, proliferating state during embryonic development. Myc-driven medulloblastomas typically show a large-cell anaplastic (LCA) histological pattern, in which tumor cells display large, round nuclei with prominent nucleoli. This subgroup of medulloblastoma is therapeutically challenging because it is associated with a high rate of metastatic dissemination, which is a powerful predictor of short patient survival times. Genetically engineered mouse models have revealed important insights into the pathogenesis of medulloblastoma and served as preclinical testing platforms for new therapies. Here we report a new mouse model of Myc-driven medulloblastoma, in which tumors arise in situ after retroviral transfer and expression of Myc in Nestin-expressing neural progenitor cells in the cerebella of newborn mice. Tumor induction required concomitant loss of Tp53 or overexpression of the antiapoptotic protein Bcl-2. Like Myc-driven medulloblastomas in humans, the tumors induced in mice by Myc + Bcl-2 and Myc - Tp53 showed LCA cytoarchitecture and a high rate of metastatic dissemination to the spine. The fact that Myc - Tp53 tumors arose only in Tp53(-/-) mice, coupled with the inefficient germline transmission of the Tp53-null allele, made retroviral transfer of Myc + Bcl-2 a more practical method for generating LCA medulloblastomas. The high rate of spinal metastasis (87% of brain tumor-bearing mice) will be an asset for testing new therapies that target the most lethal aspect of medulloblastoma.

Exogenous HGF Bypasses the Effects of ErbB Inhibition on Tumor Cell Viability in Medulloblastoma Cell Lines

Recent clinical trials investigating receptor tyrosine kinase (RTK) inhibitors showed a limited clinical response in medulloblastoma. The present study investigated the role of micro-environmental growth factors expressed in the brain, such as HGF and EGF, in relation to the effects of hepatocyte growth factor receptor (MET) and epidermal growth factor receptor family (ErbB1-4) inhibition in medulloblastoma cell lines. Medulloblastoma cell lines were treated with tyrosine kinase inhibitors crizotinib or canertinib, targeting MET and ErbB1-4, respectively. Upon treatment, cells were stimulated with VEGF-A, PDGF-AB, HGF, FGF-2 or EGF. Subsequently, we measured cell viability and expression levels of growth factors and downstream signaling proteins. Addition of HGF or EGF phosphorylated MET or EGFR, respectively, and demonstrated phosphorylation of Akt and ERK1/2 as well as increased tumor cell viability. Crizotinib and canertinib both inhibited cell viability and phosphorylation of Akt and ERK1/2. Specifically targeting MET using shRNA’s resulted in decreased cell viability. Interestingly, addition of HGF to canertinib significantly enhanced cell viability as well as phosphorylation of Akt and ERK1/2. The HGF-induced bypass of canertinib was reversed by addition of crizotinib. HGF protein was hardly released by medulloblastoma cells itself. Addition of canertinib did not affect RTK cell surface or growth factor expression levels. This manuscript points to the bypassing capacity of exogenous HGF in medulloblastoma cell lines. It might be of great interest to anticipate on these results in developing novel clinical trials with a combination of MET and EGFR inhibitors in medulloblastoma.

ABCB1 in children's brain tumours

Tumours of the central nervous system are the most common solid tumour, accounting for a quarter of the 1500 cases of childhood cancer diagnosed each year in the U.K. They are the most common cause of cancer-related death in children. Treatment consists of surgery followed by adjuvant chemotherapy and/or radiotherapy. Survival rates have generally increased, but many survivors suffer from radiotherapy-related neurocognitive and endocrine side effects as well as an increased risk of secondary cancer. Adjuvant chemotherapy is normally given in combination to circumvent chemoresistance, but several studies have demonstrated it to be ineffective in the absence of radiotherapy. The identification of children with drug-resistant disease at the outset could allow stratification of those that are potentially curable by chemotherapy alone. Ultimately, however, what is required is a means to overcome this drug resistance and restore the effectiveness of chemotherapy. Medulloblastomas and ependymomas account for over 30% of paediatric brain tumours. Advances in neurosurgery, adjuvant radiotherapy and chemotherapy have led to improvements in 5-year overall survival rates. There remain, however, significant numbers of medulloblastoma patients that have intrinsically drug-resistant tumours and/or present with disseminated disease. Local relapse in ependymoma is also common and has an extremely poor prognosis with only 25% of children surviving first relapse. Each of these is consistent with the acquisition of drug and radiotherapy resistance. Since the majority of chemotherapy drugs currently used to treat these patients are transport substrates for ATP-binding cassette sub-family B member 1 (ABCB1) we will address the hypothesis that ABCB1 expression underlies this drug resistance.

Genetic and molecular alterations across medulloblastoma subgroups

Medulloblastoma is the most common malignant brain tumour diagnosed in children. Over the last few decades, advances in radiation and chemotherapy have significantly improved the odds of survival. Nevertheless, one third of all patients still succumb to their disease, and many long-term survivors are afflicted with neurocognitive sequelae. Large-scale multi-institutional efforts have provided insight into the transcriptional and genetic landscape of medulloblastoma. Four distinct subgroups of medulloblastoma have been identified, defined by distinct transcriptomes, genetics, demographics and outcomes. Integrated genomic profiling of each of these subgroups has revealed distinct genetic alterations, driving pathways and in some instances cells of origin. In this review, we highlight, in a subgroup-specific manner, our current knowledge of the genetic and molecular alterations in medulloblastoma and underscore the possible avenues for future therapeutic intervention.

Identification of alsterpaullone as a novel small molecule inhibitor to target group 3 medulloblastoma

Advances in the molecular biology of medulloblastoma revealed four genetically and clinically distinct subgroups. Group 3 medulloblastomas are characterized by frequent amplifications of the oncogene MYC, a high incidence of metastasis, and poor prognosis despite aggressive therapy. We investigated several potential small molecule inhibitors to target Group 3 medulloblastomas based on gene expression data using an in silico drug screen. The Connectivity Map (C-MAP) analysis identified piperlongumine as the top candidate drug for non-WNT medulloblastomas and the cyclin-dependent kinase (CDK) inhibitor alsterpaullone as the compound predicted to have specific antitumor activity against Group 3 medulloblastomas. To validate our findings we used these inhibitors against established Group 3 medulloblastoma cell lines. The C-MAP predicted drugs reduced cell proliferation in vitro and increased survival in Group 3 medulloblastoma xenografts. Alsterpaullone had the highest efficacy in Group 3 medulloblastoma cells. Genomic profiling of Group 3 medulloblastoma cells treated with alsterpaullone confirmed inhibition of cell cycle-related genes, and down-regulation of MYC. Our results demonstrate the preclinical efficacy of using a targeted therapy approach for Group 3 medulloblastomas. Specifically, we provide rationale for advancing alsterpaullone as a targeted therapy in Group 3 medulloblastoma.

Disseminated Medulloblastoma in a Child with Germline BRCA2 6174delT Mutation and without Fanconi Anemia

Medulloblastoma, the most common malignant brain tumor in children, occurs with increased frequency in individuals with Fanconi anemia who have biallelic germline mutations in BRCA2. We describe an 8-year-old child who had disseminated anaplastic medulloblastoma and a deleterious heterozygous BRCA2 6174delT germline mutation. Molecular profiling was consistent with Group 4 medulloblastoma. The posterior fossa mass was resected and the patient received intensive chemotherapy and craniospinal irradiation. Despite this, the patient succumbed to a second recurrence of his medulloblastoma, which presented 8 months after diagnosis as malignant pleural and peritoneal effusions. Continuous medulloblastoma cell lines were isolated from the original tumor (CHLA-01-MED) and the malignant pleural effusion (CHLA-01R-MED). Here, we provide their analyses, including in vitro and in vivo growth, drug sensitivity, comparative genomic hybridization, and next generation sequencing analysis. In addition to the BRCA2 6174delT, the medulloblastoma cells had amplification of MYC, deletion at Xp11.2, and isochromosome 17, but no structural variations or overexpression of GFI1 or GFI1B. To our knowledge, this is the first pair of diagnosis/recurrence medulloblastoma cell lines, the only medulloblastoma cell lines with BRCA2 6174delT described to date, and the first reported case of a child with medulloblastoma associated with a germline BRCA2 6174delT who did not also have Fanconi anemia.

Pediatric Brain Tumors: Innovative Genomic Information Is Transforming the Diagnostic and Clinical Landscape

Pediatric neuro-oncology has undergone an exciting and dramatic transformation during the past 5 years. This article summarizes data from collaborative group and institutional trials that have advanced the science of pediatric brain tumors and survival of patients with these tumors. Advanced genomic analysis of the entire spectrum of pediatric brain tumors has heralded an era in which stakeholders in the pediatric neuro-oncology community are being challenged to reconsider their current research and diagnostic and treatment strategies. The incorporation of this new information into the next-generation treatment protocols will unleash new challenges. This review succinctly summarizes the key advances in our understanding of the common pediatric brain tumors (ie, medulloblastoma, low- and high-grade gliomas, diffuse intrinsic pontine glioma, and ependymoma) and some selected rare tumors (ie, atypical teratoid/rhabdoid tumor and CNS primitive neuroectodermal tumor). The potential impact of this new information on future clinical protocols also is discussed. Cutting-edge genomics technologies and the information gained from such studies are facilitating the identification of molecularly defined subgroups within patients with particular pediatric brain tumors. The number of evaluable patients in each subgroup is small, particularly in the subgroups of rare diseases. Therefore, international collaboration will be crucial to draw meaningful conclusions about novel approaches to treating pediatric brain tumors.

In vivo Mn-enhanced MRI for early tumor detection and growth rate analysis in a mouse medulloblastoma model

Mouse models have increased our understanding of the pathogenesis of medulloblastoma (MB), the most common malignant pediatric brain tumor that often forms in the cerebellum. A major goal of ongoing research is to better understand the early stages of tumorigenesis and to establish the genetic and environmental changes that underlie MB initiation and growth. However, studies of MB progression in mouse models are difficult due to the heterogeneity of tumor onset times and growth patterns and the lack of clinical symptoms at early stages. Magnetic resonance imaging (MRI) is critical for noninvasive, longitudinal, three-dimensional (3D) brain tumor imaging in the clinic but is limited in resolution and sensitivity for imaging early MBs in mice. In this study, high-resolution (100 μm in 2 hours) and high-throughput (150 μm in 15 minutes) manganese-enhanced MRI (MEMRI) protocols were optimized for early detection and monitoring of MBs in a Patched-1 (Ptch1) conditional knockout (CKO) model. The high tissue contrast obtained with MEMRI revealed detailed cerebellar morphology and enabled detection of MBs over a wide range of stages including pretumoral lesions as early as 2 to 3 weeks postnatal with volumes close to 0.1 mm³. Furthermore, longitudinal MEMRI allowed noninvasive monitoring of tumors and demonstrated that lesions within and between individuals have different tumorigenic potentials. 3D volumetric studies allowed quantitative analysis of MB tumor morphology and growth rates in individual Ptch1-CKO mice. These results show that MEMRI provides a powerful method for early in vivo detection and longitudinal imaging of MB progression in the mouse brain.

Whole Exome- and mRNA-Sequencing of an AT/RT Case Reveals Few Somatic Mutations and Several Deregulated Signalling Pathways in the Context of SMARCB1 Deficiency

Background. AT/RTs are rare aggressive brain tumours, mainly affecting young children. Most cases present with genetic inactivation of SMARCB1, a core member of the SWI/SNF chromatin-remodeling complex. We have performed whole exome- and mRNA-sequencing on an early onset AT/RT case for detection of genetic events potentially contributing to the disease. Results. A de novo germline variant in SMARCB1, c.601C>T p.Arg201^∗, in combination with somatic deletion of the healthy allele is likely the major tumour causing event. Only seven somatic small scale mutations were discovered (hitting SEPT03, H2BFM, ZIC4, HIST2H2AB, ZIK1, KRTAP6-3, and IFNA8). All were found with subclonal allele frequencies (range 5.7–17%) and none were expressed. However, besides SMARCB1, candidate genes affected by predicted damaging germline variants that were expressed were detected (KDM5C, NUMA1, and PCM1). Analysis of differently expressed genes revealed many dysregulated pathways in the tumour, such as cell cycle, CXCR4 pathway, GPCR-signalling, and neuronal system. FGFR1, CXCR4, and MDK were upregulated and may represent possible drug targets. Conclusion. The loss of SMARCB1 function leads to AT/RT development and deregulated genes and pathways. Additional predisposing events may however contribute. Studies utilizing NGS technologies in larger cohorts will probably identify recurrent genetic and epigenetic alterations and molecular subgroups with implications for clinical practice and development of targeted therapies.

miR-367 promotes proliferation and stem-like traits in medulloblastoma cells

In medulloblastoma, abnormal expression of pluripotency factors such as LIN28 and OCT4 has been correlated with poor patient survival. The miR-302/367 cluster has also been shown to control self-renewal and pluripotency in human embryonic stem cells and induced pluripotent stem cells, but there is limited, mostly correlational, information about these pluripotency-related miRNA in cancer. We evaluated whether aberrant expression of such miRNA could affect tumor cell behavior and stem-like traits, thereby contributing to the aggressiveness of medulloblastoma cells. Basal expression of primary and mature forms of miR-367 were detected in four human medulloblastoma cell lines and expression of the latter was found to be upregulated upon enforced expression of OCT4A. Transient overexpression of miR-367 significantly enhanced tumor features typically correlated with poor prognosis; namely, cell proliferation, 3-D tumor spheroid cell invasion and the ability to generate neurosphere-like structures enriched in CD133 expressing cells. A concurrent downregulation of the miR-367 cancer-related targets RYR3, ITGAV and RAB23, was also detected in miR-367-overexpressing cells. Overall, these findings support the pro-oncogenic activity of miR-367 in medulloblastoma and reveal a possible mechanism contributing to tumor aggressiveness, which could be further explored to improve patient stratification and treatment of this important type of pediatric brain cancer.

Molecular and cellular heterogeneity: the hallmark of glioblastoma

There has been increasing awareness that glioblastoma, which may seem histopathologically similar across many tumors, actually represents a group of molecularly distinct tumors. Emerging evidence suggests that cells even within the same tumor exhibit wide-ranging molecular diversity. Parallel to the discoveries of molecular heterogeneity among tumors and their individual cells, intense investigation of the cellular biology of glioblastoma has revealed that not all cancer cells within a given tumor behave the same. The identification of a subpopulation of brain tumor cells termed "glioblastoma cancer stem cells" or "tumor-initiating cells" has implications for the management of glioblastoma. This focused review will therefore summarize emerging concepts on the molecular and cellular heterogeneity of glioblastoma and emphasize that we should begin to consider each individual glioblastoma to be an ensemble of molecularly distinct subclones that reflect a spectrum of dynamic cell states.

Molecular insights into pediatric brain tumors have the potential to transform therapy

High-throughput genomic technologies have shed light on the biologic heterogeneity of several pediatric brain tumors. The biology of the four common pediatric brain tumors-namely medulloblastoma; ependymoma; high-grade glioma (HGG), including diffuse intrinsic pontine glioma; and low-grade glioma-is highlighted in this CCR Focus article. The discovery that medulloblastoma consists of four different subgroups, namely WNT, SHH, Group 3, and Group 4, each with distinct clinical and molecular features, has affected the treatment of children with medulloblastoma. Prospective studies have documented the efficacy of SMO inhibitors in a subgroup of patients with SHH medulloblastoma. Efforts are ongoing to develop specific therapies for each of the subgroups of medulloblastoma. Similar efforts are being pursued for ependymoma, HGG, and diffuse intrinsic pontine glioma where the disease outcome for the latter two tumors has not changed over the past three decades despite several prospective clinical trials. Developing and testing targeted therapies based on this new understanding remains a major challenge to the pediatric neuro-oncology community. The focus of this review is to summarize the rapidly evolving understanding of the common pediatric brain tumors based on genome-wide analysis. These novel insights will add impetus to translating these laboratory-based discoveries to newer therapies for children diagnosed with these tumors.

[Evolution of the management of pediatric and adult medulloblastoma]

Medulloblastoma are cerebellar tumours belonging to the group of primitive neuroectodermal tumours (PNET) and are the most common malignant brain tumours of childhood. These tumours are rare and heterogeneous, requiring some multicentric prospective studies and multidisciplinary care. The classical therapeutic approaches are based on clinical, radiological and surgical data. They involve surgery, radiation therapy and chemotherapy. Some histological features were added to characterize risk. More recently, molecular knowledge has allowed to devise risk-adapted strategies and helped to define groups with good outcome and reduce long-term sequelae, improve the prognostic of high-risk medulloblastoma and develop new therapeutic tools.

Regulatory effects of a Mnk2-eIF4E feedback loop during mTORC1 targeting of human medulloblastoma cells

The mTOR pathway controls mRNA translation of mitogenic proteins and is a central regulator of metabolism in malignant cells. Development of malignant cell resistance is a limiting factor to the effects of mTOR inhibitors, but the mechanisms accounting for such resistance are not well understood. We provide evidence that mTORC1 inhibition by rapamycin results in engagement of a negative feedback regulatory loop in malignant medulloblastoma cells, involving phosphorylation of the eukaryotic translation-initiation factor eIF4E. This eIF4E phosphorylation is Mnk2- mediated, but Mnk1-independent, and acts as a survival mechanism for medulloblastoma cells. Pharmacological targeting of Mnk1/2 or siRNA-mediated knockdown of Mnk2 sensitizes medulloblastoma cells to mTOR inhibition and promotes suppression of malignant cell proliferation and anchorage-independent growth. Altogether, these findings provide evidence for the existence of a Mnk2-controlled feedback loop in medulloblastoma cells that accounts for resistance to mTOR inhibitors, and raise the potential for combination treatments of mTOR and Mnk inhibitors for the treatment of medulloblastoma.

Somatic CRISPR/Cas9-mediated tumour suppressor disruption enables versatile brain tumour modelling

In vivo functional investigation of oncogenes using somatic gene transfer has been successfully exploited to validate their role in tumorigenesis. For tumour suppressor genes this has proven more challenging due to technical aspects. To provide a flexible and effective method for investigating somatic loss-of-function alterations and their influence on tumorigenesis, we have established CRISPR/Cas9-mediated somatic gene disruption, allowing for in vivo targeting of TSGs. Here we demonstrate the utility of this approach by deleting single (Ptch1) or multiple genes (Trp53, Pten, Nf1) in the mouse brain, resulting in the development of medulloblastoma and glioblastoma, respectively. Using whole-genome sequencing (WGS) we characterized the medulloblastoma-driving Ptch1 deletions in detail and show that no off-targets were detected in these tumours. This method provides a fast and convenient system for validating the emerging wealth of novel candidate tumour suppressor genes and the generation of faithful animal models of human cancer.

Gene transfer is a powerful technique to investigate the mechanistic basis of tumorigenesis. Here Zuckermann et al. adapt CRISPR/Cas9 genome editing to target potential oncogenes somatically in vivo, establishing a fast and convenient system for validating novel genetic candidates.

Characterization of medulloblastoma in Fanconi Anemia: a novel mutation in the BRCA2 gene and SHH molecular subgroup

Fanconi Anemia (FA) is an inherited disorder characterized by the variable presence of multiple congenital somatic abnormalities, bone marrow failure and cancer susceptibility. Medulloblastoma (MB) has been described only in few cases of FA with biallelic inactivation in the tumor suppressor gene BRCA2/FANCD1 or its associated gene PALB2/FANCN.

We report the case of a patient affected by Fanconi Anemia with Wilms tumor and unusual presentation of two medulloblastomas (MB1 and MB2). We identified a new pathogenetic germline BRCA2 mutation: c.2944_2944delA. Molecular analysis of MBs allowed us to define new features of MB in FA. MBs were found to belong to the Sonic Hedgehog (SHH) molecular subgroup with some differences between MB1 and MB2. We highlighted that MB in FA could share molecular aspects and hemispheric localization with sporadic adult SHH-MB. Our report provides new findings that shed new light on the genetic and molecular pathogenesis of MB in FA patients with implications in the disease management.

The genetic signatures of pediatric high-grade glioma: no longer a one-act play

Advances in understanding pediatric high-grade glioma (pHGG) genetics have revealed key differences between pHGG and adult HGG and have uncovered unique molecular drivers among subgroups within pHGG. The 3 core adult HGG pathways, the receptor tyrosine kinase-Ras-phosphatidylinositide 3-kinase, p53, and retinoblastoma networks, are also disrupted in pHGG, but they exhibit a different spectrum of effectors targeted by mutation. There are also similarities and differences in the genomic landscape of diffuse intrinsic pontine glioma (DIPG) and pediatric nonbrainstem (pNBS)-HGG. In 2012, histone H3 mutations were identified in nearly 80% of DIPGs and ~35% of pNBS-HGG. These were the first reports of histone mutations in human cancer, implicating novel biology in pediatric gliomagenesis. Additionally, DIPG and midline pNBS-HGG vary in the frequency and specific histone H3 amino acid substitution compared with pNBS-HGGs arising in the cerebral hemispheres, demonstrating a molecular difference among pHGG subgroups. The gene expression signatures as well as DNA methylation signatures of these tumors are also distinctive, reflecting a combination of the driving mutations and the developmental context from which they arise. These data collectively highlight unique selective pressures within the developing brainstem and solidify DIPG as a specific molecular and biological entity among pHGGs. Emerging studies continue to identify novel mutations that distinguish subgroups of pHGG. The molecular heterogeneity among pHGGs will undoubtedly have clinical implications moving forward. The discovery of unique oncogenic drivers is a critical first step in providing patients with appropriate, targeted therapies. Despite these insights, our vantage point has been largely limited to an in-depth analysis of protein coding sequences. Given the clear importance of histone mutations in pHGG, it will be interesting to see how aberrant epigenetic regulation contributes to tumorigenesis in the pediatric context. New mechanistic insights may allow for the identification of distinct vulnerabilities in this devastating spectrum of childhood tumors.

New perspectives in the treatment of adult medulloblastoma in the era of molecular oncology

Medulloblastoma is the most common central nervous system tumor in children, while it is extremely rare in adults. Multimodal treatment involving surgery, radiotherapy and chemotherapy can improve the prognosis of this disease, and recent advances in molecular biology have allowed the identification of molecular subgroups (WNT, SHH, Groups 3 and 4), each of which have different cytogenetic, mutational and gene expression signatures, demographics, histology and prognosis. The present review focuses on the state of the art for adult medulloblastoma treatment and on novel molecular advances and their future implications in the treatment of this disease.

SHH inhibitors for the treatment of medulloblastoma

Medulloblastoma is the most common malignant brain tumor of childhood. It is currently stratified into four molecular variants through the advances in transcriptional profiling. They include: wingless, sonic hedgehog (SHH), Group III, and Group IV. The SHH group is characterized by constitutive activation of the SHH signaling pathway, and genetically characterized by mutations in patched homolog 1 (PTCH1) or other downstream pathway mutations. SHH inhibitors have become of great clinical interest in treating SHH-driven medulloblastoma. Many inhibitors are currently in different stages of development, some already approved for other SHH-driven cancers, such as basal cell carcinoma. In vitro and in vivo medulloblastoma studies have shown efficacy and these findings have been translated into Phase I and II clinical trials. In this review, we present an overview of SHH medulloblastoma, as well as a discussion of currently available SHH inhibitors, and the challenges associated with their use.

Next-generation (epi)genetic drivers of childhood brain tumours and the outlook for targeted therapies

Arguably, nowhere has there been a greater advance in our understanding of biological mechanisms and potential translational targets during the next-generation sequencing era than in paediatric brain tumours. The so-called omics revolution, enabled by high-throughput sequencing, has empowered large consortia and independent groups alike to make major genetic discoveries, from dominant-negative histone mutations and hijacking of distal enhancer elements, to new oncogenic gene fusions and aberrantly active gene expression. Epigenetic deregulation has also been revealed as a common theme across several tumour subtypes. This Review focuses on key findings that have been transforming the landscape of paediatric neuro-oncology research and how these results are opening new avenues towards potential therapeutic translation.

Molecular Classification of Ependymal Tumors across All CNS Compartments, Histopathological Grades, and Age Groups

Ependymal tumors across age groups are currently classified and graded solely by histopathology. It is, however, commonly accepted that this classification scheme has limited clinical utility based on its lack of reproducibility in predicting patients' outcome. We aimed at establishing a uniform molecular classification using DNA methylation profiling. Nine molecular subgroups were identified in a large cohort of 500 tumors, 3 in each anatomical compartment of the CNS, spine, posterior fossa, supratentorial. Two supratentorial subgroups are characterized by prototypic fusion genes involving RELA and YAP1, respectively. Regarding clinical associations, the molecular classification proposed herein outperforms the current histopathological classification and thus might serve as a basis for the next World Health Organization classification of CNS tumors.

Merkel Cell Carcinoma with a Suppressor of Fused (SUFU) Mutation: Case Report and Potential Therapeutic Implications

Introduction

Merkel cell carcinoma is a neuroendocrine malignancy. Suppressor of fused (SUFU) is a tumor suppressor oncogene that participates in the Hedgehog (Hh) signaling pathway. The aim of the study was to describe a patient whose Merkel cell carcinoma demonstrated a SUFU genomic alteration.

Case Study

The Hh signaling pathway is involved in the pathogenesis of several tumors, including nevoid basal cell carcinoma syndrome that is associated with an alteration of the patched-1 (PTCH1) gene. Targeted molecular therapy against smoothened (SMO) with vismodegib has been shown to be an effective therapeutic intervention for patients with PTCH-1 mutation. The reported patient was presented with metastatic Merkel cell carcinoma. Analysis of his tumor, using a next-generation sequencing-based assay, demonstrated a genomic aberration of SUFU protein, a component of the Hh signaling pathway that acts downstream to SMO and, therefore, is unlikely to be responsive to vismodegib. Of interest, arsenic trioxide or bromo and extra C-terminal inhibitors impact signals downstream to SUFU, making this aberration conceivably druggable. His tumor has initially been managed with chemotherapy (carboplatin and etoposide) and subsequent radiation therapy is planned.

Conclusion

The pathogenesis of Merkel cell carcinoma is multifactorial, and related to ultraviolet radiation exposure, immunosuppression, and Merkel cell polyomavirus. We report a patient with a mutation in SUFU, a potentially actionable component of the Hh signaling pathway.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-015-0074-5) contains supplementary material, which is available to authorized users.

Targeting class I histone deacetylase 2 in MYC amplified group 3 medulloblastoma

Introduction

Medulloblastoma (MB) is the most frequent malignant brain tumor in children. Four subgroups with distinct genetic, epigenetic and clinical characteristics have been identified. Survival remains particularly poor in patients with Group 3 tumors harbouring a MYC amplification. We herein explore the molecular mechanisms and translational implications of class I histone deacetylase (HDAC) inhibition in MYC driven MBs.

Material and Methods

Expression of HDACs in primary MB subgroups was compared to normal brain tissue. A panel of MB cell lines, including Group 3 MYC amplified cell lines, were used as model systems. Cells were treated with HDAC inhibitors (HDACi) selectively targeting class I or IIa HDACs. Depletion of HDAC2 was performed. Intracellular HDAC activity, cellular viability, metabolic activity, caspase activity, cell cycle progression, RNA and protein expression were analyzed.

Results

HDAC2 was found to be overexpressed in MB subgroups with poor prognosis (SHH, Group 3 and Group 4) compared to normal brain and the WNT subgroup. Inhibition of the enzymatic activity of the class I HDACs reduced metabolic activity, cell number, and viability in contrast to inhibition of class IIa HDACs. Increased sensitivity to HDACi was specifically observed in MYC amplified cells. Depletion of HDAC2 increased H4 acetylation and induced cell death. Simulation of clinical pharmacokinetics showed time-dependent on target activity that correlated with binding kinetics of HDACi compounds.

Conclusions

We conclude that HDAC2 is a valid drug target in patients with MYC amplified MB. HDACi should cover HDAC2 in their inhibitory profile and timing and dosing regimen in clinical trials should take binding kinetics of compounds into consideration.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0201-7) contains supplementary material, which is available to authorized users.

Measuring the optical characteristics of medulloblastoma with optical coherence tomography

Medulloblastoma is the most common malignant pediatric brain tumor. Standard treatment consists of surgical resection, followed by radiation and high-dose chemotherapy. Despite these efforts, recurrence is common, leading to reduced patient survival. Even with successful treatment, there are often severe long-term neurologic impacts on the developing nervous system. We present two quantitative techniques that use a high-resolution optical imaging modality: optical coherence tomography (OCT) to measure refractive index, and the optical attenuation coefficient. To the best of our knowledge, this study is the first to demonstrate OCT analysis of medulloblastoma. Refractive index and optical attenuation coefficient were able to differentiate between normal brain tissue and medulloblastoma in mouse models. More specifically, optical attenuation coefficient imaging of normal cerebellum displayed layers of grey matter and white matter, which were indistinguishable in the structural OCT image. The morphology of the tumor was distinct in the optical attenuation coefficient imaging. These inherent properties may be useful during neurosurgical intervention to better delineate tumor boundaries and minimize resection of normal tissue.

Pancreatic endoplasmic reticulum kinase activation promotes medulloblastoma cell migration and invasion through induction of vascular endothelial growth factor A

Evidence is accumulating that activation of the pancreatic endoplasmic reticulum kinase (PERK) in response to endoplasmic reticulum (ER) stress adapts tumor cells to the tumor microenvironment and enhances tumor angiogenesis by inducing vascular endothelial growth factor A (VEGF-A). Recent studies suggest that VEGF-A can act directly on certain tumor cell types in an autocrine manner, via binding to VEGF receptor 2 (VEGFR2), to promote tumor cell migration and invasion. Although several reports show that PERK activation increases VEGF-A expression in medulloblastoma, the most common solid malignancy of childhood, the role that either PERK or VEGF-A plays in medulloblastoma remains elusive. In this study, we mimicked the moderate enhancement of PERK activity observed in tumor patients using a genetic approach and a pharmacologic approach, and found that moderate activation of PERK signaling facilitated medulloblastoma cell migration and invasion and increased the production of VEGF-A. Moreover, using the VEGFR2 inhibitor SU5416 and the VEGF-A neutralizing antibody to block VEGF-A/VEGFR2 signaling, our results suggested that tumor cell-derived VEGF-A promoted medulloblastoma cell migration and invasion through VEGFR2 signaling, and that both VEGF-A and VEGFR2 were required for the promoting effects of PERK activation on medulloblastoma cell migration and invasion. Thus, these findings suggest that moderate PERK activation promotes medulloblastoma cell migration and invasion through enhancement of VEGF-A/VEGFR2 signaling.

MiR-148a, a microRNA upregulated in the WNT subgroup tumors, inhibits invasion and tumorigenic potential of medulloblastoma cells by targeting Neuropilin 1

Medulloblastoma, a common pediatric malignant brain tumor consists of four molecular subgroups viz. WNT, SHH, Group 3 and Group 4. MiR-148a is over-expressed in the WNT subgroup tumors, which have the lowest incidence of metastasis and excellent survival among all medulloblastomas. MiR-148a was expressed either in a transient manner using a synthetic mimic or in a stable doxycycline inducible manner using a lentiviral vector in non-WNT medulloblastoma cell lines. Expression of miR-148a to levels comparable to that in the WNT subgroup tumors was found to inhibit proliferation, clonogenic potential, invasion potential and tumorigenicity of medulloblastoma cells. MiR-148a expression in medulloblastoma cells brought about reduction in the expression of NRP1, a novel miR-148a target. Restoration of NRP1 expression in medulloblastoma cells was found to rescue the reduction in the invasion potential and tumorigenicity brought about by miR-148a expression. NRP1 is known to play role in multiple signaling pathways that promote tumor growth, invasion and metastasis. NRP1 expression in medulloblastomas was found to be associated with poor survival, with little or no expression in majority of the WNT tumors. The tumor suppressive effect of miR-148a expression accompanied by the down-regulation of NRP1 makes miR-148a an attractive therapeutic agent for the treatment of medulloblastomas.

The molecular landscape of pediatric brain tumors in the next-generation sequencing era

Pediatric brain tumors are a leading cause of cancer-related death in children. In recent years, the application of next-generation sequencing and other high-throughput technologies to analysis of pediatric brain tumors has generated an abundance of molecular information. This has provided an unprecedented understanding of their biology and is refining tumor classification into clinically relevant subgroups. In this review, we provide an overview of our evolving molecular knowledge of the commonest pediatric brain tumors, pilocytic astrocytomas, ependymomas, medulloblastomas, and pediatric glioblastomas, as well as the biological and potential clinical implications of this new knowledge. Studies aimed at investigating intratumoral heterogeneity are also discussed.