Telomerase inhibition abolishes the tumorigenicity of pediatric ependymoma tumor-initiating cells

Pediatric ependymomas are highly recurrent tumors resistant to conventional chemotherapy. Telomerase, a ribonucleoprotein critical in permitting limitless replication, has been found to be critically important for the maintenance of tumor-initiating cells (TICs). These TICs are chemoresistant, repopulate the tumor from which they are identified, and are drivers of recurrence in numerous cancers. In this study, telomerase enzymatic activity was directly measured and inhibited to assess the therapeutic potential of targeting telomerase. Telomerase repeat amplification protocol (TRAP) (n = 36) and C-circle assay/telomere FISH/ATRX staining (n = 76) were performed on primary ependymomas to determine the prevalence and prognostic potential of telomerase activity or alternative lengthening of telomeres (ALT) as telomere maintenance mechanisms, respectively. Imetelstat, a phase 2 telomerase inhibitor, was used to elucidate the effect of telomerase inhibition on proliferation and tumorigenicity in established cell lines (BXD-1425EPN, R254), a primary TIC line (E520) and xenograft models of pediatric ependymoma. Over 60 % of pediatric ependymomas were found to rely on telomerase activity to maintain telomeres, while no ependymomas showed evidence of ALT. Children with telomerase-active tumors had reduced 5-year progression-free survival (29 +/- A 11 vs 64 +/- A 18 %; p = 0.03) and overall survival (58 +/- A 12 vs 83 +/- A 15 %; p = 0.05) rates compared to those with tumors lacking telomerase activity. Imetelstat inhibited proliferation and self-renewal by shortening telomeres and inducing senescence in vitro. In vivo, Imetelstat significantly reduced subcutaneous xenograft growth by 40 % (p = 0.03) and completely abolished the tumorigenicity of pediatric ependymoma TICs in an orthotopic xenograft model. Telomerase inhibition represents a promising therapeutic approach for telomerase-active pediatric ependymomas found to characterize high-risk ependymomas.Canadian Institutes of Health Research [MOP 82727]info:eu-repo/semantics/publishedVersio

Comprehensive Integrated Genomic and Histopathological Analysis of Paediatric Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is a devastating, inoperable paediatric brain neoplasm with no effective therapy and near 100% fatality. Diagnosis is based mainly on radiological findings and numerous clinical trials using adjuvant chemotherapy over the last four decades have not shown a survival benefit compared to radiation alone. Although the delicate location of these lesions is a contributing factor to the dismal outcomes seen in these children, most of these clinical trials were designed based on adult protocols, with assumptions that paediatric brainstem tumours, whose histology most often resembles high-grade supratentorial glioblastoma (GBM) of adults, would respond to similar therapies. By combining histological review, methylation profiling, whole-genome and whole-exome sequencing, gene expression profiling, and copy number analysis of a large cohort of DIPG, we describe differences to adult disease, uncover mutations in novel cancer drivers, histone H3 mutation in 78.5% and ACVR1 mutations in 21.25% of DIPG patients, respectively and discover that DIPGs are three molecularly distinct subgroups (H3-K27M, Silent and MYCN). The H3-K27M subgroup is highly p.Lys27Met histone H3 mutated and associated with additional hits including activating mutations in ACVR1, frequent RB1 and TP53 deletions, PVT-1/MYC or PDGFRA gains/amplifications, genomic instability and alternative lengthening of telomeres. Histone mutations confer a worse overall survival (p = 0.0026). The MYCN subgroup is not associated with histone mutations and is instead characterized by hypermethylation and chromothripsis of chromosome 2p with high-level amplifications of MYCN and ID2. The Silent subgroup affects younger children, has genomes with minimal genomic instability and fewer mutations. Histologically, DIPG represent a spectrum of grade II-IV disease with vast regional differences and frequent leptomeningeal dissemination.Our results show that this seemingly homogeneous entity in fact comprises three distinct subgroups with different genomic, molecular and histopathological features. This complexity needs to be considered when designing new therapeutic approaches in order to improve outcome for these children.Ph.D

Targeted detection of genetic alterations reveal the prognostic impact of H3K27M and MAPK pathway aberrations in paediatric thalamic glioma

Paediatric brain tumours arising in the thalamus present significant diagnostic and therapeutic challenges to physicians due to their sensitive midline location. As such, genetic analysis for biomarkers to aid in the diagnosis, prognosis and treatment of these tumours is needed. Here, we identified 64 thalamic gliomas with clinical follow-up and characterized targeted genomic alterations using newly optimized droplet digital and NanoString-based assays. The median age at diagnosis was 9.25 years (range, 0.63–17.55) and median survival was 6.43 (range, 0.01–27.63) years. Our cohort contained 42 and 22 tumours reviewed as low and high grade gliomas, respectively. Five (12 %) low grade and 11 (50 %) high grade gliomas were positive for the H3F3A/HIST1H3B K27M (H3K27M) mutation. Kaplan-Meier survival analysis revealed significantly worse overall survival for patients harbouring the H3K27M mutation versus H3F3A/HIST1H3B wild type (H3WT) samples (log-rank p < 0.0001) with a median survival of 1.02 vs. 9.12 years. Mitogen-activated protein kinase (MAPK) pathway activation via BRAF or FGFR1 hotspot mutations or fusion events were detected in 44 % of patients, and was associated with long-term survival in the absence of H3K27M (log-rank p < 0.0001). Multivariate analysis demonstrated H3K27M status and high grade histology to be the most significant independent predictors of poor overall survival with hazard ratios of 6.945 and 7.721 (p < 0.0001), respectively. In contrast, MAPK pathway activation is a predictor of favourable patient outcome, although not independent of other clinical factors. Importantly, we show that low grade malignancies may harbour H3K27M mutations and that these tumours show a dismal survival compared to low grade H3WT cases. Our data strongly supports the inclusion of targeted genetic testing in childhood thalamic tumours to most accurately stratify patients into appropriate risk groups.Medicine, Faculty ofOther UBCNon UBCMedicine, Department ofNeurology, Division ofPediatrics, Department ofSurgery, Department ofReviewedFacult

Targeted detection of genetic alterations reveal the prognostic impact of H3K27M and MAPK pathway aberrations in paediatric thalamic glioma

Abstract Paediatric brain tumours arising in the thalamus present significant diagnostic and therapeutic challenges to physicians due to their sensitive midline location. As such, genetic analysis for biomarkers to aid in the diagnosis, prognosis and treatment of these tumours is needed. Here, we identified 64 thalamic gliomas with clinical follow-up and characterized targeted genomic alterations using newly optimized droplet digital and NanoString-based assays. The median age at diagnosis was 9.25 years (range, 0.63–17.55) and median survival was 6.43 (range, 0.01–27.63) years. Our cohort contained 42 and 22 tumours reviewed as low and high grade gliomas, respectively. Five (12 %) low grade and 11 (50 %) high grade gliomas were positive for the H3F3A/HIST1H3B K27M (H3K27M) mutation. Kaplan-Meier survival analysis revealed significantly worse overall survival for patients harbouring the H3K27M mutation versus H3F3A/HIST1H3B wild type (H3WT) samples (log-rank p < 0.0001) with a median survival of 1.02 vs. 9.12 years. Mitogen-activated protein kinase (MAPK) pathway activation via BRAF or FGFR1 hotspot mutations or fusion events were detected in 44 % of patients, and was associated with long-term survival in the absence of H3K27M (log-rank p < 0.0001). Multivariate analysis demonstrated H3K27M status and high grade histology to be the most significant independent predictors of poor overall survival with hazard ratios of 6.945 and 7.721 (p < 0.0001), respectively. In contrast, MAPK pathway activation is a predictor of favourable patient outcome, although not independent of other clinical factors. Importantly, we show that low grade malignancies may harbour H3K27M mutations and that these tumours show a dismal survival compared to low grade H3WT cases. Our data strongly supports the inclusion of targeted genetic testing in childhood thalamic tumours to most accurately stratify patients into appropriate risk groups

Additional file 11: Table S7. of Targeted detection of genetic alterations reveal the prognostic impact of H3K27M and MAPK pathway aberrations in paediatric thalamic glioma

Histology Kaplan-Meier survival analysis within the A) SickKids cohort and B) Canadian cohort. (DOCX 12 kb

Additional file 5: Figure S3. of Targeted detection of genetic alterations reveal the prognostic impact of H3K27M and MAPK pathway aberrations in paediatric thalamic glioma

Droplet digital PCR pre-PCR digestion versus no digestion comparison. (PPTX 102 kb