Valeria Molinari

Integrated Molecular Meta-Analysis of 1,000 Pediatric High-Grade and Diffuse Intrinsic Pontine Glioma

Summary We collated data from 157 unpublished cases of pediatric high-grade glioma and diffuse intrinsic pontine glioma and 20 publicly available datasets in an integrated analysis of >1,000 cases. We identified co-segregating mutations in histone-mutant subgroups including loss of FBXW7 in H3.3G34R/V, TOP3A rearrangements in H3.3K27M, and BCOR mutations in H3.1K27M. Histone wild-type subgroups are refined by the presence of key oncogenic events or methylation profiles more closely resembling lower-grade tumors. Genomic aberrations increase with age, highlighting the infant population as biologically and clinically distinct. Uncommon pathway dysregulation is seen in small subsets of tumors, further defining the molecular diversity of the disease, opening up avenues for biological study and providing a basis for functionally defined future treatment stratification.

Molecular, Pathological, Radiological, and Immune Profiling of Non-brainstem Pediatric High-Grade Glioma from the HERBY Phase II Randomized Trial

Summary The HERBY trial was a phase II open-label, randomized, multicenter trial evaluating bevacizumab (BEV) in addition to temozolomide/radiotherapy in patients with newly diagnosed non-brainstem high-grade glioma (HGG) between the ages of 3 and 18 years. We carried out comprehensive molecular analysis integrated with pathology, radiology, and immune profiling. In post-hoc subgroup analysis, hypermutator tumors (mismatch repair deficiency and somatic POLE/POLD1 mutations) and those biologically resembling pleomorphic xanthoastrocytoma ([PXA]-like, driven by BRAF_V600E or NF1 mutation) had significantly more CD8+ tumor-infiltrating lymphocytes, and longer survival with the addition of BEV. Histone H3 subgroups (hemispheric G34R/V and midline K27M) had a worse outcome and were immune cold. Future clinical trials will need to take into account the diversity represented by the term “HGG” in the pediatric population.

Abstract 3271: Novel orthotopic pediatric high grade glioma xenografts evaluated with magnetic resonance imaging mimic human disease

Pediatric high grade gliomas (pHGG) may arise supratentorially in the cerebral hemispheres, or in midline structures such as the thalamus or the pons (diffuse intrinsic pontine glioma, DIPG). Tumors have distinct underlying biology compared with adult disease, with genetic subtypes corresponding to anatomical location. Differential mutations in genes encoding histone H3.3/H3.1 variants occur in supratentorial and midline tumors, while mutations in the gene encoding the BMP type I receptor ACVR1 are restricted to the pons and occur in a quarter of DIPGs. Co-option of existing brain vasculature in areas of infiltrative tumor growth leaves the blood brain barrier (BBB) intact. It is imperative to accurately model these tumors in vivo for the evaluation of emerging targeted therapeutics. Assessment of such models in situ is vital and requires sensitive functional imaging. T2-weighted (T2-w) MRI of orthotopically implanted PBT7 cells (supratentorial glioblastoma (GBM), 9yr old, H3F3A wt) showed heterogeneous tumors with relatively well defined borders. Hypointensity on T2-w and fluid-attenuated inversion recovery (FLAIR) images suggests the presence of necrosis and edema. Minimal heterogenous enhancement following Gd-DTPA administration demonstrated some loss of BBB integrity. FLAIR hyperintensity is used clinically to identify infiltrative tumor. Serially xenografted D-212 MG cells (supratentorial giant-cell GBM, 11yr old, H3F3A wt) formed tumors with FLAIR hyperintensity principally at the rim and Gd-DTPA enhancement prevalent at the tumor core. Histopathological assessment of HE 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3271. doi:10.1158/1538-7445.AM2015-3271

Functional diversity and cooperativity between subclonal populations of pediatric glioblastoma and diffuse intrinsic pontine glioma cells

The failure to develop effective therapies for pediatric glioblastoma (pGBM) and diffuse intrinsic pontine glioma (DIPG) is in part due to their intrinsic heterogeneity. We aimed to quantitatively assess the extent to which this was present in these tumors through subclonal genomic analyses and to determine whether distinct tumor subpopulations may interact to promote tumorigenesis by generating subclonal patient-derived models in vitro and in vivo. Analysis of 142 sequenced tumors revealed multiple tumor subclones, spatially and temporally coexisting in a stable manner as observed by multiple sampling strategies. We isolated genotypically and phenotypically distinct subpopulations that we propose cooperate to enhance tumorigenicity and resistance to therapy. Inactivating mutations in the H4K20 histone methyltransferase KMT5B (SUV420H1), present in <1% of cells, abrogate DNA repair and confer increased invasion and migration on neighboring cells, in vitro and in vivo, through chemokine signaling and modulation of integrins. These data indicate that even rare tumor subpopulations may exert profound effects on tumorigenesis as a whole and may represent a new avenue for therapeutic development. Unraveling the mechanisms of subclonal diversity and communication in pGBM and DIPG will be an important step toward overcoming barriers to effective treatments.Genomic and functional analysis of intratumor heterogeneity in pediatric glioma uncovers early clonal divergence and stable spontaneous cooperation between subclonal populations throughout tumor evolution.