Abstract 1126: Extracellular vesicle mediated radioresistance in H3K27M-diffuse midline glioma
Authors: Oza Viral , Sampathi Shilpa , Chernyavskava Yelena , Flores Kenan , Blackburn Jessica 
Published: March 2024

Abstract
H3K27M-Diffuse Midline Gliomas (DMGs) are a subset of uncurable malignant pediatric gliomas and the deadliest form of brain tumors in children worldwide. Radiation therapy, the current standard of care, is initially effective but all tumors become resistant within 4-6 months. H3K27M-DMGs are heterogenous, comprised of an average of 6 genetically distinct subclones. Some subclones harbor mutations in genes previously linked to radiation resistance, such as TP53. We have found subclones are also functionally distinct, with some clones harboring intrinsic radiation resistance. Extracellular signaling between clones is linked with therapy resistance and tumor progression in other tumors, and we hypothesized that radioresistant H3K27M-DMG release small extracellular vesicles (sEVs) that impact the radiosensitivity of neighboring tumor cells. We found that all patient-derived H3K27M-DMG samples examined (n=6) produced sEVs (&lt; 220nm), indicating this is a common feature in this tumor type. We isolated sEVs from a radioresistant (RR) patient-derived H3K27M-DMG cell line and used them to treat radiosensitive (RS) DMG cells. Using flow cytometry to profile sEV uptake dynamics, we found that RR-sEVs are internalized by RS cells within 2 hours of exposure and are retained at 18 hours (p&lt;0.001, compared to control). This uptake can be significantly abrogated by proteinase K treatment of the sEVs, (p&lt;0.001), indicating that uptake involves sEV surface proteins. We then applied a biosensor approach to assess single-cell phenotypic changes in RS DMG after RR-sEV treatment on radiation-induced cell death, DNA damage, and cell senescence, three dynamic processes. Using a genetically encoded death indicator (GEDI), we found that RR-sEVs significantly enhanced the survival of RS cells after acute radiation exposure (p&lt;0.001). This was due to enhanced DNA damage repair as measured by 53BP1 foci (p&lt;0.01). Small RNA sequencing of sEV cargo demonstrated that RR-sEVs express multiple miRNAs that are involved in oncogenic signaling such as the miR-7 family, miR-1246, and miR-1290 at several log fold higher than RS-sEVs. Overall, this data reveals the first functional role for sEVs in the context of radiation induced tumor transformation in DMG. We plan to further investigate the primary route of sEV uptake and define the mechanism through which sEV cargo alters radiosensitivity. This study provides new insight into the impact of heterogeneity and sEVs in mediating radioresistance in H3K27M-DMG and may lead to the development of novel radiosensitizers, which are critically needed for all patients.
Citation Format: Viral Oza, Shilpa Sampathi, Yelena Chernyavskava, Kenan Flores, Jessica Blackburn. Extracellular vesicle mediated radioresistance in H3K27M-diffuse midline glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1126.