Unknown,Transcriptomics,Genomics,Proteomics

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Comprehensive Mapping of Paediatric High Grade Glioma

ABSTRACT: Overall paediatric high grade glioma (pHGG) has a poor prognosis, in part due to the lack of understanding of the underlying biology. We therefore used high resolution 244k oligo array comparative genomic hybridisation (oligo aCGH) (Agilent Technologies) to analyse DNA from 38 formalin-fixed paraffin embedded pHGG samples, including 13 DIPG (ten pre-treatment samples and three post-mortem). The pattern of gains and losses were distinct from those seen in HGG arising in adults. In particular we found 1q gain in 22% of our cohort compared to 9% in adults. Homozygous loss at 8p12 was seen in 6/38 (15%) of pHGG. This deletion has not been previously reported in adult or paediatric high grade gliomas. The minimal deleted region is of the gene ADAM3A and homozygous deletion of ADAM3A was confirmed by quantitative real time PCR (qPCR). This novel homozygous deletion of ADAM3A in pHGG merits further study. Loss of CDKN2A/CDKN2B was seen in 4/38 (10%) samples by oligo a CGH, confirmed by FISH on TMAs and was restricted to supratentorial tumours. Amplification of the 4q11-13 region was detected in 8% of cases and included PDGFRA and KIT, subsequent qPCR analysis was consistent with amplification of PDGFRA. MYCN amplification was seen in 2/38 samples (5%) and was shown to be significantly associated with anaplastic astrocytomas (p=0.03). Overall DIPG shared similar spectrum of changes to supratentorial HGG with some notable differences including high frequency of 17p loss and 14q loss and lack of CDKN2A/CDKN2B deletion. To our knowledge, this study examines the largest DIPG cohort to date using high-throughput genetic techniques. 38 high grade glioma samples including 13 DIPG (ten pre-treatment samples and three post-mortem) analysed by Agilent 244K array CGH. Samples BSG 1, 2, 3, 5, 6, 7, 8, 9, 10 and 11 are the ten pre-treatment DIPG samples. Samples BSG 4, 12 and 13 are the three post-treatment DIPG samples.

ORGANISM(S): Homo sapiens

SUBMITTER: Jennifer Barrow

PROVIDER: E-GEOD-21420 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Diffuse intrinsic pontine glioma (DIPG) is one of the most devastating of paediatric malignancies and one for which no effective therapy exists. A major contributor to the failure of therapeutic trials is the assumption that biologic properties of brainstem tumours in children are identical to cerebral high-grade gliomas of adults. A better understanding of the biology of DIPG itself is needed in order to develop agents targeted more specifically to these childrenâs disease. Here we address this lack of knowledge by performing the first high-resolution SNP-based DNA microarray analysis of a series of DIPGs. Eleven samples (nine post-mortem and two pre-treatment surgical samples), the largest series thus far examined, were hybridized to Affymetrix SNP arrays (250k or 6.0). The study was approved by the Research Ethics Board at our institution (Hospital for Sick Children, Toronto, Ontario, Canada). All Array findings were validated using quantitative-PCR, fluorescence in-situ hybridization, immunohistochemistry and/or microsatellite analysis. Analysis of DIPG copy number alterations showed recurrent changes distinct from those of paediatric supratentorial high-grade astrocytomas. 36% of DIPGs had gains in PDGFRA and all showed PDGF-R-Î± expression. Gains in PARP-1 were identified in 3 cases. Pathway analysis revealed genes with loss of heterozygosity were enriched for DNA repair pathways. Our data provides the first, comprehensive high-resolution genomic analysis of paediatric DIPG. Our findings of recurrent involvement of the PDGFR pathway as well as defects in DNA repair pathways coupled with gain of PARP-1 highlight two potential, biologically-based, therapeutic targets directed specifically at this devastating disease. Affymetrix SNP arrays were performed according to the manufacturer's directions on DNA extracted from snap frozen biopsy and autopsy brain tissue from DIPG patients. Copy number analysis of Affymetrix 250K and 6.0 SNP arrays was performed for 11 paediatric DIPG samples, 7 matched normal brain samples, and HapMap samples.

Project description:The outcome for children with high-grade gliomas (HGG) remains dismal, with a two-year survival rate of only 10-30%. Approximately half of pediatric HGGs are diffuse intrinsic pontine glioma (DIPG), a brainstem tumor that arises almost exclusively in children. Genome-wide analyses of copy number imbalances previously showed that platelet derived growth factor receptor alpha (PDGFRA) is the most frequent target of focal amplification in pediatric HGGs. To determine whether the PDGFRA is also targeted by more subtle mutations not detected by copy number analysis, we sequenced all PDGFRA coding exons from a cohort of pediatric HGGs. Somatic activating mutations were identified in 14.4% (13/90) of non-brainstem pediatric HGGs and 4.7% (2/43) of DIPGs, including missense mutations and in-frame deletions and insertions not previously described. 40% of tumors with mutation showed concurrent amplification, while 60% carried heterozygous mutations. Six different mutations impacting different domains all resulted in ligand-independent receptor activation that was blocked by small molecule inhibitors of PDGFR. Expression of mutants in p53-null primary mouse astrocytes conferred a proliferative advantage in vitro, and generated HGGs in vivo with complete penetrance when implanted into brain. The gene expression signatures reflected the spectrum of human diffuse HGGs. PDGFRA intragenic deletion of exons 8 and 9 were previously shown in adult HGG, but were not detected in 83 non-brainstem pediatric HGG and 57 DIPGs. Thus, a distinct spectrum of mutations confers constitutive receptor activation and oncogenic activity to PDGFR in childhood HGG. To better understand the consequence of PDGFRα mutation in pediatric gliomagenesis, retroviral constructs expressing wild-type PDGFRα or six selected PDGFRα mutants that affect different regions of the receptor were generated for functional studies. p53-null primary mouse astrocyte (PMA) cultures were chosen as a relevant cellular background to assess PDGFRα function.

Project description:Purpose: To define copy number alterations and gene expression signatures underlying pediatric high-grade glioma (HGG). Patients and Methods: We conducted a high-resolution analysis of genomic imbalances in 78 de novo pediatric HGG, including 7 diffuse intrinsic pontine gliomas, and 10 HGG cases arising in children who received cranial irradiation for a previous cancer, using Affymetrix 500K GeneChips. Gene expression signatures for 53 tumors were analyzed with Affymetrix U133v2 arrays. Results were compared with publicly available data from adult tumors. Results: Pediatric and adult glioblastoma were clearly distinguished by frequent gain of chromosome 1q (30% vs 9%) and lower frequency of chromosome 7 gain (13% vs 74%), respectively. The most common focal amplifications also differed, with PDGFRA and EGFR predominant in childhood and adult populations respectively. These common alterations in pediatric HGG were detected at higher frequency in irradiation-induced tumors, suggesting that these are initiating events in childhood gliomagenesis. CDKN2A was the most common tumor suppressor gene targeted by homozygous deletion in pediatric HGG. No IDH1 hotspot mutations were found in pediatric tumors, highlighting molecular differences in pathogenesis between childhood HGG and adult secondary glioblastoma. Integrated copy number and gene expression data indicated that deregulated PDGFRA signaling plays a major role in pediatric HGG. Conclusions: Integrated molecular profiling showed substantial differences in the molecular features underlying pediatric and adult HGG, indicating that findings in adult tumors cannot be simply extrapolated to younger patients. PDGFRA may be a useful target for pediatric HGG including diffuse pontine gliomas. Keywords: disease state analysis 78 samples for SNP analysis, including 10 samples arising in children who received cranial irradiation for a previous cancer and 7 diffuse pontine gliomas; 53 of them with gene expression analysis; 2 tumor grades To have access to SNP CEL files, please contact Dr. Suzanne Baker (suzzane.baker@stjude.org).

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Comprehensive Mapping of Paediatric High Grade Glioma

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