PDTM-09. DIFFUSE INTRINSIC PONTINE GLIOMA AND PEDIATRIC GLIOBLASTOMA DERIVED-EXOSOMES HAVE SPECIFIC ONCOGENIC SIGNATURES

Diffuse intrinsic pontine glioma (DIPG) and pediatric glioblastoma (pGBM) are heterogeneous brain tumors characterized by different anatomical and molecular subgroups and the presence of genetically and phenotypically distinct subclonal cell populations. It is recognized that exosomes mediate cross-talk among tumor cells. We hypothesize that there are different exosome-mediated paracrine signaling promoting tumour progression in DIPG and pGBM. Our aim was to determine the specific DIPG and pGBM-derived exosome oncogenic signatures. We used a panel of fifteen patient primary-derived cell lines, which included nine DIPG (seven H3.3 K27M, one H3.3 K27M/ACVR1 and one H3.1 K27M/ACVR1), one diffuse midline glioma H3.3 K27M and three GBM (one H3.3 G34R and two histone WT). Conditioned medium was collected from cells maintained under stem-cell culture condition, adherent on laminin and/or as neurospheres (NS), and exosomes harvested through serial centrifugations. Electron microscopy demonstrated that the isolated microvescicles are exosomes sized between 50–80 nm. DIPG derived-exosomes appeared to have a variable cargo of total protein (µg)/106 cells, which was higher than for pGBM-exosomes. Proteomic analysis revealed that proteins associated with vesicle docking, exocytosis and synaptic transmission were exclusively enriched in pontine-derived exosomes, while cell-cell and cell-matrix interaction proteinswere exclusive tohemispheric ones. Proteins in common to the two locations were involved in metabolism and energy pathways. Interestingly, principle component analysis on the different molecular subgroups suggests that ACVR1 may be not implicated in the exosomal proteomic signature. Exosomal miRNA profile appeared to be driven by the two main histone mutated subgroups H3.3 K27M and H3.1 K27M with the latter overexpressing hypoxia and angiogenic-associated miRNAs, leading to distinct oncogenic programs with different specific potential therapeutic targets. This study aimed to development new diagnostic/prognostic tools for DIPG and pGBM patients. Further investigations are aimed to identify new therapeutic strategies to inhibit the cross-talk among glioma subpopulations.