Diffusely infiltrating astrocytomas: pathology, molecular mechanisms and markers

Diffusely infiltrating astrocytomas include diffuse astrocytomas WHO grade II and anaplastic astrocytomas WHO grade III and are classified under astrocytic tumours according to the current WHO Classification. Although the patients generally have longer survival as compared to those with glioblastoma, the timing of inevitable malignant progression ultimately determines the prognosis. Recent advances in molecular genetics have uncovered that histopathologically diagnosed astrocytomas may consist of two genetically different groups of tumours. The majority of diffusely infiltrating astrocytomas regardless of WHO grade have concurrent mutations of IDH1 or IDH2, TP53 and ATRX. Among these astrocytomas, no other genetic markers that may distinguish grade II and grade III tumours have been identified. Those astrocytomas without IDH mutation tend to have a distinct genotype and a poor prognosis comparable to that of glioblastomas. On the other hand, diffuse astrocytomas that arise in children do not harbour IDH/TP53 mutations, but instead display mutations of BRAF or structural alterations involving MYB/MYBL1 or FGFR1. A molecular classification may thus help delineate diffusely infiltrating astrocytomas into distinct pathogenic and prognostic groups, which could aid in determining individualised therapeutic strategies.

Molecular subgroups of atypical teratoid rhabdoid tumours in children: an integrated genomic and clinicopathological analysis

BACKGROUND

Rhabdoid brain tumours, also called atypical teratoid rhabdoid tumours, are lethal childhood cancers with characteristic genetic alterations of SMARCB1/hSNF5. Lack of biological understanding of the substantial clinical heterogeneity of these tumours restricts therapeutic advances. We integrated genomic and clinicopathological analyses of a cohort of patients with atypical teratoid rhabdoid tumours to find out the molecular basis for clinical heterogeneity in these tumours.

METHODS

We obtained 259 rhabdoid tumours from 37 international institutions and assessed transcriptional profiles in 43 primary tumours and copy number profiles in 38 primary tumours to discover molecular subgroups of atypical teratoid rhabdoid tumours. We used gene and pathway enrichment analyses to discover group-specific molecular markers and did immunohistochemical analyses on 125 primary tumours to evaluate clinicopathological significance of molecular subgroup and ASCL1-NOTCH signalling.

FINDINGS

Transcriptional analyses identified two atypical teratoid rhabdoid tumour subgroups with differential enrichment of genetic pathways, and distinct clinicopathological and survival features. Expression of ASCL1, a regulator of NOTCH signalling, correlated with supratentorial location (p=0·004) and superior 5-year overall survival (35%, 95% CI 13-57, and 20%, 6-34, for ASCL1-positive and ASCL1-negative tumours, respectively; p=0·033) in 70 patients who received multimodal treatment. ASCL1 expression also correlated with superior 5-year overall survival (34%, 7-61, and 9%, 0-21, for ASCL1-positive and ASCL1-negative tumours, respectively; p=0·001) in 39 patients who received only chemotherapy without radiation. Cox hazard ratios for overall survival in patients with differential ASCL1 enrichment treated with chemotherapy with or without radiation were 2·02 (95% CI 1·04-3·85; p=0·038) and 3·98 (1·71-9·26; p=0·001). Integrated analyses of molecular subgroupings with clinical prognostic factors showed three distinct clinical risk groups of tumours with different therapeutic outcomes.

INTERPRETATION

An integration of clinical risk factors and tumour molecular groups can be used to identify patients who are likely to have improved long-term radiation-free survival and might help therapeutic stratification of patients with atypical teratoid rhabdoid tumours.

FUNDING

C17 Research Network, Genome Canada, b.r.a.i.n.child, Mitchell Duckman, Tal Doron and Suri Boon foundations.

BRAF mutation and CDKN2A deletion define a clinically distinct subgroup of childhood secondary high-grade glioma

PURPOSE

To uncover the genetic events leading to transformation of pediatric low-grade glioma (PLGG) to secondary high-grade glioma (sHGG).

PATIENTS AND METHODS

We retrospectively identified patients with sHGG from a population-based cohort of 886 patients with PLGG with long clinical follow-up. Exome sequencing and array CGH were performed on available samples followed by detailed genetic analysis of the entire sHGG cohort. Clinical and outcome data of genetically distinct subgroups were obtained.

RESULTS

sHGG was observed in 2.9% of PLGGs (26 of 886 patients). Patients with sHGG had a high frequency of nonsilent somatic mutations compared with patients with primary pediatric high-grade glioma (HGG; median, 25 mutations per exome; P = .0042). Alterations in chromatin-modifying genes and telomere-maintenance pathways were commonly observed, whereas no sHGG harbored the BRAF-KIAA1549 fusion. The most recurrent alterations were BRAF V600E and CDKN2A deletion in 39% and 57% of sHGGs, respectively. Importantly, all BRAF V600E and 80% of CDKN2A alterations could be traced back to their PLGG counterparts. BRAF V600E distinguished sHGG from primary HGG (P = .0023), whereas BRAF and CDKN2A alterations were less commonly observed in PLGG that did not transform (P < .001 and P < .001 respectively). PLGGs with BRAF mutations had longer latency to transformation than wild-type PLGG (median, 6.65 years [range, 3.5 to 20.3 years] v 1.59 years [range, 0.32 to 15.9 years], respectively; P = .0389). Furthermore, 5-year overall survival was 75% ± 15% and 29% ± 12% for children with BRAF mutant and wild-type tumors, respectively (P = .024).

CONCLUSION

BRAF V600E mutations and CDKN2A deletions constitute a clinically distinct subtype of sHGG. The prolonged course to transformation for BRAF V600E PLGGs provides an opportunity for surgical interventions, surveillance, and targeted therapies to mitigate the outcome of sHGG.

WNT activation by lithium abrogates TP53 mutation associated radiation resistance in medulloblastoma

TP53 mutations confer subgroup specific poor survival for children with medulloblastoma. We hypothesized that WNT activation which is associated with improved survival for such children abrogates TP53 related radioresistance and can be used to sensitize TP53 mutant tumors for radiation. We examined the subgroup-specific role of TP53 mutations in a cohort of 314 patients treated with radiation. TP53 wild-type or mutant human medulloblastoma cell-lines and normal neural stem cells were used to test radioresistance of TP53 mutations and the radiosensitizing effect of WNT activation on tumors and the developing brain. Children with WNT/TP53 mutant medulloblastoma had higher 5-year survival than those with SHH/TP53 mutant tumours (100% and 36.6% ± 8.7%, respectively (p < 0.001)). Introduction of TP53 mutation into medulloblastoma cells induced radioresistance (survival fractions at 2Gy (SF2) of 89% ± 2% vs. 57.4% ± 1.8% (p < 0.01)). In contrast, β-catenin mutation sensitized TP53 mutant cells to radiation (p < 0.05). Lithium, an activator of the WNT pathway, sensitized TP53 mutant medulloblastoma to radiation (SF2 of 43.5% ± 1.5% in lithium treated cells vs. 56.6 ± 3% (p < 0.01)) accompanied by increased number of γH2AX foci. Normal neural stem cells were protected from lithium induced radiation damage (SF2 of 33% ± 8% for lithium treated cells vs. 27% ± 3% for untreated controls (p = 0.05). Poor survival of patients with TP53 mutant medulloblastoma may be related to radiation resistance. Since constitutive activation of the WNT pathway by lithium sensitizes TP53 mutant medulloblastoma cells and protect normal neural stem cells from radiation, this oral drug may represent an attractive novel therapy for high-risk medulloblastomas.

CNS-PNETs with C19MC amplification and/or LIN28 expression comprise a distinct histogenetic diagnostic and therapeutic entity

Amplification of the C19MC oncogenic miRNA cluster and high LIN28 expression has been linked to a distinctly aggressive group of cerebral CNS-PNETs (group 1 CNS-PNETs) arising in young children. In this study, we sought to evaluate the diagnostic specificity of C19MC and LIN28, and the clinical and biological spectra of C19MC amplified and/or LIN28+ CNS-PNETs. We interrogated 450 pediatric brain tumors using FISH and IHC analyses and demonstrate that C19MC alteration is restricted to a sub-group of CNS-PNETs with high LIN28 expression; however, LIN28 immunopositivity was not exclusive to CNS-PNETs but was also detected in a proportion of other malignant pediatric brain tumors including rhabdoid brain tumors and malignant gliomas. C19MC amplified/LIN28+ group 1 CNS-PNETs arose predominantly in children <4 years old; a majority arose in the cerebrum but 24 % (13/54) of tumors had extra-cerebral origins. Notably, group 1 CNS-PNETs encompassed several histologic classes including embryonal tumor with abundant neuropil and true rosettes (ETANTR), medulloepithelioma, ependymoblastoma and CNS-PNETs with variable differentiation. Strikingly, gene expression and methylation profiling analyses revealed a common molecular signature enriched for primitive neural features, high LIN28/LIN28B and DNMT3B expression for all group 1 CNS-PNETs regardless of location or tumor histology. Our collective findings suggest that current known histologic categories of CNS-PNETs which include ETANTRs, medulloepitheliomas, ependymoblastomas in various CNS locations, comprise a common molecular and diagnostic entity and identify inhibitors of the LIN28/let7/PI3K/mTOR axis and DNMT3B as promising therapeutics for this distinct histogenetic entity.

Cytogenetic prognostication within medulloblastoma subgroups

PURPOSE

Medulloblastoma comprises four distinct molecular subgroups: WNT, SHH, Group 3, and Group 4. Current medulloblastoma protocols stratify patients based on clinical features: patient age, metastatic stage, extent of resection, and histologic variant. Stark prognostic and genetic differences among the four subgroups suggest that subgroup-specific molecular biomarkers could improve patient prognostication.

PATIENTS AND METHODS

Molecular biomarkers were identified from a discovery set of 673 medulloblastomas from 43 cities around the world. Combined risk stratification models were designed based on clinical and cytogenetic biomarkers identified by multivariable Cox proportional hazards analyses. Identified biomarkers were tested using fluorescent in situ hybridization (FISH) on a nonoverlapping medulloblastoma tissue microarray (n = 453), with subsequent validation of the risk stratification models.

RESULTS

Subgroup information improves the predictive accuracy of a multivariable survival model compared with clinical biomarkers alone. Most previously published cytogenetic biomarkers are only prognostic within a single medulloblastoma subgroup. Profiling six FISH biomarkers (GLI2, MYC, chromosome 11 [chr11], chr14, 17p, and 17q) on formalin-fixed paraffin-embedded tissues, we can reliably and reproducibly identify very low-risk and very high-risk patients within SHH, Group 3, and Group 4 medulloblastomas.

CONCLUSION

Combining subgroup and cytogenetic biomarkers with established clinical biomarkers substantially improves patient prognostication, even in the context of heterogeneous clinical therapies. The prognostic significance of most molecular biomarkers is restricted to a specific subgroup. We have identified a small panel of cytogenetic biomarkers that reliably identifies very high-risk and very low-risk groups of patients, making it an excellent tool for selecting patients for therapy intensification and therapy de-escalation in future clinical trials.

Overcoming resistance to Sonic Hedgehog inhibition by targeting p90 ribosomal S6 kinase in pediatric medulloblastoma

BACKGROUND

Molecular subtyping has allowed for the beginning of personalized treatment in children suffering from medulloblastoma (MB). However, resistance inevitably emerges against these therapies, particularly in the Sonic Hedgehog (SHH) subtype. We found that children with SHH subtype have the worst outcome underscoring the need to identify new therapeutic targets.

PROCEDURE

High content screening of a 129 compound library identified agents that inhibited SHH MB growth. Lead molecular target levels, p90 ribosomal S6 kinase (RSK) were characterized by immunoblotting and qRT-PCR. Comparisons were made to human neural stem cells (hNSC). Impact of inhibiting RSK with the small molecule BI-D1870 or siRNA was assessed in growth assays (monolayer, neurosphere, and soft agar). NanoString was used to detect RSK in a cohort of 66 patients with MB. To determine BI-D1870 pharmacokinetics/pharmacodynamics, 100 mg/kg was I.P. injected into mice and tissues were collected at various time points.

RESULTS

Daoy, ONS76, UW228, and UW426 MB cells were exquisitely sensitive to BI-D1870 but unresponsive to SHH inhibitors. Anti-tumor growth corresponded with inactivation of RSK in MB cells. BI-D1870 had no effect on hNSCs. Inhibiting RSK with siRNA or BI-D1870 suppressed growth, induced apoptosis, and sensitized cells to SHH agents. Notably, RSK expression is correlated with SHH patients. In mice, BI-D1870 was well-tolerated and crossed the blood-brain barrier (BBB).

CONCLUSIONS

RSK inhibitors are promising because they target RSK which is correlated with SHH patients as well as cause high levels of apoptosis to only MB cells. Importantly, BI-D1870 crosses the BBB, acting as a scaffold for development of more long-lived RSK inhibitors.

TERT promoter mutations are highly recurrent in SHH subgroup medulloblastoma

Telomerase reverse transcriptase (TERT) promoter mutations were recently shown to drive telomerase activity in various cancer types, including medulloblastoma. However, the clinical and biological implications of TERT mutations in medulloblastoma have not been described. Hence, we sought to describe these mutations and their impact in a subgroup-specific manner. We analyzed the TERT promoter by direct sequencing and genotyping in 466 medulloblastomas. The mutational distributions were determined according to subgroup affiliation, demographics, and clinical, prognostic, and molecular features. Integrated genomics approaches were used to identify specific somatic copy number alterations in TERT promoter-mutated and wild-type tumors. Overall, TERT promoter mutations were identified in 21 % of medulloblastomas. Strikingly, the highest frequencies of TERT mutations were observed in SHH (83 %; 55/66) and WNT (31 %; 4/13) medulloblastomas derived from adult patients. Group 3 and Group 4 harbored this alteration in <5 % of cases and showed no association with increased patient age. The prognostic implications of these mutations were highly subgroup-specific. TERT mutations identified a subset with good and poor prognosis in SHH and Group 4 tumors, respectively. Monosomy 6 was mostly restricted to WNT tumors without TERT mutations. Hallmark SHH focal copy number aberrations and chromosome 10q deletion were mutually exclusive with TERT mutations within SHH tumors. TERT promoter mutations are the most common recurrent somatic point mutation in medulloblastoma, and are very highly enriched in adult SHH and WNT tumors. TERT mutations define a subset of SHH medulloblastoma with distinct demographics, cytogenetics, and outcomes.

Subgroup-specific structural variation across 1,000 medulloblastoma genomes

Medulloblastoma, the most common malignant paediatric brain tumour, is currently treated with nonspecific cytotoxic therapies including surgery, whole-brain radiation, and aggressive chemotherapy. As medulloblastoma exhibits marked intertumoural heterogeneity, with at least four distinct molecular variants, previous attempts to identify targets for therapy have been underpowered because of small samples sizes. Here we report somatic copy number aberrations (SCNAs) in 1,087 unique medulloblastomas. SCNAs are common in medulloblastoma, and are predominantly subgroup-enriched. The most common region of focal copy number gain is a tandem duplication of SNCAIP, a gene associated with Parkinson's disease, which is exquisitely restricted to Group 4α. Recurrent translocations of PVT1, including PVT1-MYC and PVT1-NDRG1, that arise through chromothripsis are restricted to Group 3. Numerous targetable SCNAs, including recurrent events targeting TGF-β signalling in Group 3, and NF-κB signalling in Group 4, suggest future avenues for rational, targeted therapy.

Markers of survival and metastatic potential in childhood CNS primitive neuro-ectodermal brain tumours: an integrative genomic analysis

BACKGROUND

Childhood CNS primitive neuro-ectodermal brain tumours (PNETs) are very aggressive brain tumours for which the molecular features and best treatment approaches are unknown. We assessed a large cohort of these rare tumours to identify molecular markers to enhance clinical management of this disease.

METHODS

We obtained 142 primary hemispheric CNS PNET samples from 20 institutions in nine countries and examined transcriptional profiles for a subset of 51 samples and copy number profiles for a subset of 77 samples. We used clustering, gene, and pathway enrichment analyses to identify tumour subgroups and group-specific molecular markers, and applied immunohistochemical and gene-expression analyses to validate and assess the clinical significance of the subgroup markers.

FINDINGS

We identified three molecular subgroups of CNS PNETs that were distinguished by primitive neural (group 1), oligoneural (group 2), and mesenchymal lineage (group 3) gene-expression signatures with differential expression of cell-lineage markers LIN28 and OLIG2. Patients with group 1 tumours were most often female (male:female ratio 0·61 for group 1 vs 1·25 for group 2 and 1·63 for group 3; p=0·043 [group 1 vs groups 2 and 3]), youngest (median age at diagnosis 2·9 years [95% CI 2·4-5·2] for group 1 vs 7·9 years [6·0-9·7] for group 2 and 5·9 years [4·9-7·8] for group 3; p=0·005), and had poorest survival (median survival 0·8 years [95% CI 0·5-1·2] in group 1, 1·8 years [1·4-2·3] in group 2 and 4·3 years [0·8-7·8] in group 3; p=0·019). Patients with group 3 tumours had the highest incidence of metastases at diagnosis (no distant metastasis:metastasis ratio 0·90 for group 3 vs 2·80 for group 1 and 5·67 for group 2; p=0·037).

INTERPRETATION

LIN28 and OLIG2 are promising diagnostic and prognostic molecular markers for CNS PNET that warrant further assessment in prospective clinical trials.

FUNDING

Canadian Institute of Health Research, Brainchild/SickKids Foundation, and the Samantha Dickson Brain Tumour Trust.

Abstract 1432: The heterogeneous genomic landscape of posterior fossa ependymoma

Brain tumors are the most common cause of cancer-related death in childhood. Ependymomas, are the third most common pediatric brain tumor. The disease remains incurable for about 45% of patients even after gross total resection and radiotherapy. Despite showing a very homogeneous histological picture, ependymomas display distinct molecular behavior, which supports the existence of several independent entities of the disease. We examined two non-overlapping cohorts of 102 and 75 ependymomas by mRNA expression profiling, on two different array platforms (Affymetrix, Agilent). When performing multiple statistical clustering methods (unsupervised consensus NMF and consensus HCL), we could consistently identify three major clusters, including two subgroups of posterior fossa (PF) ependymoma, a variant common in children and associated with heterogeneous clinical outcome. Subgroup-specific chromosome aberrations of PF tumors were detected by aCGH, and biological signaling pathways distinguishing PF subgroups were identified by gene set enrichment analysis and visualized in Cytoscape. We validated the most significantly classifying markers of each subgroup by immunohistochemistry on a tissue microarray containing an independent set of 265 PF ependymomas. Our findings delineate two subgroups of PF ependymoma (groups A and B) which are demographically, transcriptionally, genetically, and clinically distinct. Group A patients are younger, have laterally located tumors with a balanced genome, more frequently develop secondary metastases and are much more likely to have an extremely poor outcome as compared with group B patients. Based on a multi-variate Cox proportional-hazards model, our identified markers have the strongest independent prognostic value among demographic and molecular variables with Hazard ratios of 8.45 (PFS) and 10.55 (OS). Prognostic significance and predictive impact is being validated in the GPOH HIT2000 Ependymoma study. The identification of two distinct subgroups of PF ependymoma, and markers applicable for their clinical distinction, will allow for better prognostication of individual cases, independent of age, level of resection and WHO grade, and also for stratification in future ependymoma clinical trials.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1432. doi:1538-7445.AM2012-1432

A proteomic analysis of pediatric seizure cases associated with astrocytic inclusions

Cerebral hyaline astrocytic inclusions have been observed in a subset of patients with early onset epilepsy, brain structural anomalies, and developmental delay, which indicates that it may represent a unique clinicopathologic entity. To further characterize this condition we use proteomics to investigate differentially expressed proteins in epileptic brain tissue from three pediatric epileptic patients with cerebral hyaline astrocytic inclusions, ranging in age from 5-13 years, and compare to brain tissue from two normal controls. Catalase and carbonic anhydrase I both exhibited increased expression in epileptic brain tissue compared to controls. These findings were confirmed by Western blot analysis. Furthermore, both proteins were localized to astrocytes and in epileptic brain were located within the cerebral hyaline astrocytic inclusions, suggesting a potential role in the generation of this pathologic feature of early onset epilepsy with cerebral hyaline astrocytic inclusions.

Delineation of two clinically and molecularly distinct subgroups of posterior fossa ependymoma

Despite the histological similarity of ependymomas from throughout the neuroaxis, the disease likely comprises multiple independent entities, each with a distinct molecular pathogenesis. Transcriptional profiling of two large independent cohorts of ependymoma reveals the existence of two demographically, transcriptionally, genetically, and clinically distinct groups of posterior fossa (PF) ependymomas. Group A patients are younger, have laterally located tumors with a balanced genome, and are much more likely to exhibit recurrence, metastasis at recurrence, and death compared with Group B patients. Identification and optimization of immunohistochemical (IHC) markers for PF ependymoma subgroups allowed validation of our findings on a third independent cohort, using a human ependymoma tissue microarray, and provides a tool for prospective prognostication and stratification of PF ependymoma patients.

Medulloblastoma comprises four distinct molecular variants

PURPOSE

Recent genomic approaches have suggested the existence of multiple distinct subtypes of medulloblastoma. We studied a large cohort of medulloblastomas to determine how many subgroups of the disease exist, how they differ, and the extent of overlap between subgroups.

METHODS

We determined gene expression profiles and DNA copy number aberrations for 103 primary medulloblastomas. Bioinformatic tools were used for class discovery of medulloblastoma subgroups based on the most informative genes in the data set. Immunohistochemistry for subgroup-specific signature genes was used to determine subgroup affiliation for 294 nonoverlapping medulloblastomas on two independent tissue microarrays.

RESULTS

Multiple unsupervised analyses of transcriptional profiles identified the following four distinct, nonoverlapping molecular variants: WNT, SHH, group C, and group D. Supervised analysis of these four subgroups revealed significant subgroup-specific demographics, histology, metastatic status, and DNA copy number aberrations. Immunohistochemistry for DKK1 (WNT), SFRP1 (SHH), NPR3 (group C), and KCNA1 (group D) could reliably and uniquely classify formalin-fixed medulloblastomas in approximately 98% of patients. Group C patients (NPR3-positive tumors) exhibited a significantly diminished progression-free and overall survival irrespective of their metastatic status.

CONCLUSION

Our integrative genomics approach to a large cohort of medulloblastomas has identified four disparate subgroups with distinct demographics, clinical presentation, transcriptional profiles, genetic abnormalities, and clinical outcome. Medulloblastomas can be reliably assigned to subgroups through immunohistochemistry, thereby making medulloblastoma subclassification widely available. Future research on medulloblastoma and the development of clinical trials should take into consideration these four distinct types of medulloblastoma.

Abstract 4355: The C19MC miRNA polycistron are frequent targets of gene amplification in aggressive primitive neuroectodermal brain tumors and encode oncogenic miRNAs that inhibit normal neural stem cell differentiation

Embryonal brain tumors which include medulloblastoma and primitive neuroectodermal brain tumors (CNS-PNET) comprise the largest group of malignant pediatric brain tumors and account for substantial cancer related morbidity and mortality in childhood. Unlike medulloblastoma, a common, cerebellar PNET, few CNS-PNET arising in extracerebellar locations have been characterized. Lack of insight into the molecular pathogenesis of CNS-PNET is a major obstacle towards development of much-needed disease-specific models and treatments for these devastating tumors. In this study, we performed high-resolution DNA copy number analysis on a substantial collection of primary CNS-PNET obtained through an international collaborative group, and discovered a frequent amplicon in 25% (11/46) of CNS-PNET which span 34 protein coding genes and two miRNA clusters, C19MC and miR-371-373, on chr19q13.41. Detailed mapping studies revealed C19MC, which encode 54 primate-specific miRNAs, as the specific target of gene amplification resulting in striking tumor-specific overexpression of a sub-set of miRNAs, including miR-520 g and miR- 517c. Stable expression of miR-520 g and miR-517c promoted in vitro and in vivo oncogenicity and conferred cell survival in tumor cell lines. Strikingly expression of both miR-520g and 517c promoted growth and inhibited differentiation of untransformed normal human neural stem cells. Notably, clinicopathologic analyses revealed that C19MC amplification identifies a distinct group of CNS-PNET with similar gene expression profiles, characteristic histology, and much poorer survival. Our aggregate findings which point to C19MC as an important, new oncogenic locus in a human cancer, have significant implications for the diagnosis and clinical management of embryonal brain tumors in children.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4355.

Abstract 3109: Myc confers aggressive medulloblastoma phenotypes by regulating cell migration and adhesion genes

Mechanisms by which Myc confers aggressive phenotypes and adverse outcomes in medulloblastoma remain largely unknown. In this study, we demonstrate using 2 medulloblastoma cell line models that high Myc expression increases cell migration/invasion and induces metastatic orthotopic tumors which recapitulate the aggressive histology of primary anaplastic medulloblastoma. Using ChIP-chip and expression analysis on Myc transformed medulloblastoma cell lines, we identified a subset of cell migration and adhesion genes as direct Myc repressed transcriptional targets. These include ING4, PVRL3, PPAP2B and Tsp-1/THBS1, a potent tumor suppressor not previously implicated in medulloblastoma. Tsp-1 expression in medulloblastoma cell lines and primary tumors were consistently and significantly diminished in the presence of high Myc (n=101, p=0.032). Using ChIP and reporter assays we confirmed Myc and Max co-localization to a basal Tsp-1 promoter and decreased Tsp-1 transcription in the presence of Myc. Our analyses also revealed that JPO2, a Myc interacting protein linked to metastatic medulloblastoma, directly binds the Tsp-1 promoter and augments Myc-mediated Tsp-1 repression. Interestingly, we observed that stable Tsp-1 expression significantly diminished soft agar growth and drastically decreased cell invasion/migration in high-Myc expressing medulloblastoma cell lines without effects on cellular proliferation. Our collective findings highlight a novel and important role for Tsp-1 in Myc- induced metastatic medulloblastoma phenotypes and suggest Tsp-1 agonists may represent attractive, therapeutics for primary metastatic medulloblastoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3109.

Cap myopathy caused by a mutation of the skeletal alpha-actin gene ACTA1

Cap myopathy is a congenital myopathy with cap-like structures under the sarcolemma. Mutations in TPM2 and TPM3 genes have been reported in cap myopathy so far. We report a newborn boy with persistent profound weakness who required gastro-jejunal tube feeding, tracheostomy and life-long ventilation until he died at 5 years of age. Muscle biopsy at 5 weeks of age was uninformative. Repeat biopsy at 4.5 years revealed subsarcolemmally located caps that were immunopositive for alpha-actinin, actin and to some extent, desmin. EM confirmed loosely arranged thin filaments and paucity of thick filaments. Molecular analysis of ACTA1 gene identified a novel de novo Met49Val [corrected] mutation. In addition to a new ACTA1 gene mutation, our case emphasizes the genetic heterogeneity of cap myopathy and its association with ACTA1 gene as well as the importance of repeat muscle biopsy in patients with undiagnosed muscle weakness.

Telomerase inhibition as a novel therapy for pediatric ependymoma

Ependymomas are the third most common pediatric brain tumor with an overall survival of approximately 50%. Recently, we showed that telomerase [human telomerase reverse transcriptase (hTERT)] expression is a predictor of poor outcome in pediatric ependymoma. Thus, we hypothesized that ependymomas with functional telomerase may behave more aggressively and that these patients may benefit from anti-telomerase therapy. To address our hypothesis, we investigated the effect of telomerase inhibition on primary ependymoma cells harvested at the time of surgery, as no animal models or established cell lines are readily available for this tumor. The cells were characterized for glial fibrillary acidic protein (GFAP) and hTERT expression, initial telomere length and telomerase activity. They were then subjected to telomerase inhibition (MST-312, 1 microM) and tested for effects on cell viability (MTT assay), proliferation (MIB-1), apoptosis (cleaved caspase 3) and DNA damage (gammaH2AX). After 72 h of telomerase inhibition, primary ependymoma cells showed a significant decrease in cell number (P < 0.001), accompanied by increased DNA damage (gammaH2AX expression) (P < 0.01) and decreased proliferative index (MIB-1) (P < 0.01). Half showed an increase in apoptosis (cleaved caspase 3). These data suggest that telomerase inhibition may be an effective adjuvant therapy in pediatric ependymoma, potentially inducing tumor growth arrest in the short term, independent of telomere shortening.

Frequent amplification of a chr19q13.41 microRNA polycistron in aggressive primitive neuroectodermal brain tumors

We discovered a high-level amplicon involving the chr19q13.41 microRNA (miRNA) cluster (C19MC) in 11/45 ( approximately 25%) primary CNS-PNET, which results in striking overexpression of miR-517c and 520g. Constitutive expression of miR-517c or 520g promotes in vitro and in vivo oncogenicity, modulates cell survival, and robustly enhances growth of untransformed human neural stem cells (hNSCs) in part by upregulating WNT pathway signaling and restricting differentiation of hNSCs. Remarkably, the C19MC amplicon, which is very rare in other brain tumors (1/263), identifies an aggressive subgroup of CNS-PNET with distinct gene-expression profiles, characteristic histology, and dismal survival. Our data implicate miR-517c and 520g as oncogenes and promising biological markers for CNS-PNET and provide important insights into oncogenic properties of the C19MC locus.

Telomerase inhibition induces acute ATM-dependent growth arrest in human astrocytomas

The purpose of the study was to examine the degree of hTERT, the catalytic subunit of telomerase, expression in paediatric high-grade astrocytoma and to explore the potential of telomerase inhibition as a therapy for these tumours. hTERT was expressed at high levels in 36 of 44 paediatric astrocytomas. Telomerase inhibition induced acute DNA damage and ATM-pathway-dependent G2/M cell cycle arrest in astrocytomas in vitro, both occurring prior to telomere shortening itself. Our data suggest that telomerase inhibition could be a useful adjuvant therapy for high-grade astrocytomas, potentially inducing tumour growth arrest following short-term treatment.

Diffuse intrinsic brainstem tumors in neonates. Report of two cases

The authors report on 2 newborn infants with the unusual presentation of intrinsic brainstem tumors. Both nondysmorphic, full-term neonates had cranial nerve palsies and hypotonia. Diagnoses of diffuse intrinsic brainstem gliomas were made on the basis of magnetic resonance imaging, which showed large expansive, nonenhancing intrinsic pontine masses. Intrinsic pontine tumors, characteristically seen in school-age children, are most often high-grade gliomas that are almost invariably fatal. However, the microanatomy and natural history of pontine tumors in neonates are unknown. With parental consent, both newborns were treated expectantly with supportive care but died of progressive disease by 2 weeks of age. In one child, postmortem examination revealed a primary brainstem primitive neuroectodermal tumor. The authors conclude that, as in older children, neonatal intrinsic brainstem tumors may be of a highly malignant nature. The rapid tumor progression in both cases indicates that where a diagnostic procedure may pose significant risks, supportive observation can aid in distinguishing malignant from benign tumor growth.