School of Medicine and Health Sciences Poster Presentations

Title

Identification of Driver Mutations in Diffuse Intrinsic Pontine Glioma Using Comprehensive Spatial & Temporal Molecular Studies

Poster Number

19

Document Type

Poster

Publication Date

3-2016

Abstract

Diffuse intrinsic pontine glioma (DIPG) is a pediatric brainstem tumor with almost 100% rate of mortality. One of the major factors contributing to the poor prognosis is our limited understanding of DIPG biology, and thus the lack of effective therapy. Up to 80% of DIPG patients harbor a de novo mutation in genes (H3F3A, HIST13B/C) encoding histone variants (H3.1/3 K27M). However, the identity of potential partner mutations and the hetero/homogeneity of such mutations across tumor/brain are not known. To address tumor spatial heterogeneity, we obtained nine DIPG whole brains at autopsy. A total of 158 samples from formalin fixed and frozen tissue were produced for in depth analyses. Immunohistochemical staining was generated for all tumor and normal locations within each DIPG whole brain specimen (n=64) representing 11 neuroanatomical locations. Comprehensive molecular characterization (whole exome sequencing, MiSeq deep amplicon, RNA sequencing, digital droplet PCR, and methylation profiling) of 134 samples across nine whole brains were generated to assess tumor signature and hetero/homogeneity status. Histological and molecular data were merged and subjected to detailed bioinformatics screening to identify: i) novel driver and partner mutations, ii) accessory mutations, iii) spatial distribution of these mutations, iv) fidelity of mutation clusters in extended/metastatic tumor mass, and v) identification of clonal and subclonal tumor populations in primary and extended tumors. Our study identified H3K27M associated partner mutations, which include alterations in cell-cycle (TP53/PPM1D) or specific growth factor pathways (ACVR1/PIK3R1). Mutation based-evolutionary reconstruction indicated H3K27M mutations potentially arise first and are associated with obligate partner mutations throughout the tumor and its spread, from diagnosis to end-stage disease. This data supports the necessity of partner mutations for development of DIPG. Later oncogenic alterations arise in sub-clones and often affect the PI3K pathway. Our findings are consistent with early tumor spread outside the brainstem. Importantly, we show that needle biopsies are representative of the major H3K27M associated partner mutations in primary and extended tumors in DIPGs. Our identification of spatial and temporal homogeneity of driver mutations indicates that efforts to cure DIPG should be directed at specifically targeting obligate oncohistone partnerships.

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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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Presented at: GW Research Days 2016

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Identification of Driver Mutations in Diffuse Intrinsic Pontine Glioma Using Comprehensive Spatial & Temporal Molecular Studies

Diffuse intrinsic pontine glioma (DIPG) is a pediatric brainstem tumor with almost 100% rate of mortality. One of the major factors contributing to the poor prognosis is our limited understanding of DIPG biology, and thus the lack of effective therapy. Up to 80% of DIPG patients harbor a de novo mutation in genes (H3F3A, HIST13B/C) encoding histone variants (H3.1/3 K27M). However, the identity of potential partner mutations and the hetero/homogeneity of such mutations across tumor/brain are not known. To address tumor spatial heterogeneity, we obtained nine DIPG whole brains at autopsy. A total of 158 samples from formalin fixed and frozen tissue were produced for in depth analyses. Immunohistochemical staining was generated for all tumor and normal locations within each DIPG whole brain specimen (n=64) representing 11 neuroanatomical locations. Comprehensive molecular characterization (whole exome sequencing, MiSeq deep amplicon, RNA sequencing, digital droplet PCR, and methylation profiling) of 134 samples across nine whole brains were generated to assess tumor signature and hetero/homogeneity status. Histological and molecular data were merged and subjected to detailed bioinformatics screening to identify: i) novel driver and partner mutations, ii) accessory mutations, iii) spatial distribution of these mutations, iv) fidelity of mutation clusters in extended/metastatic tumor mass, and v) identification of clonal and subclonal tumor populations in primary and extended tumors. Our study identified H3K27M associated partner mutations, which include alterations in cell-cycle (TP53/PPM1D) or specific growth factor pathways (ACVR1/PIK3R1). Mutation based-evolutionary reconstruction indicated H3K27M mutations potentially arise first and are associated with obligate partner mutations throughout the tumor and its spread, from diagnosis to end-stage disease. This data supports the necessity of partner mutations for development of DIPG. Later oncogenic alterations arise in sub-clones and often affect the PI3K pathway. Our findings are consistent with early tumor spread outside the brainstem. Importantly, we show that needle biopsies are representative of the major H3K27M associated partner mutations in primary and extended tumors in DIPGs. Our identification of spatial and temporal homogeneity of driver mutations indicates that efforts to cure DIPG should be directed at specifically targeting obligate oncohistone partnerships.