Abstract 3068: Everolimus mediated Radioprotection on surrounding healthy tissue in glioblastoma microbrain models
Authors: Halder Tithi Ghosh , del Villar Ryan Rodriguez , Lacombe Jerome , Drenner Kevin , Ng Serina , Thode Trason , Weston Alexis , Kaadige Mohan , Soldi Raffaella , Sharma Sunil 
Published: July 2021

Abstract
Background: After surgical resection, ionizing radiation alone or in combination with chemotherapy is the main treatment modality for brain tumors including glioblastoma (GBM). Although the effect of radiation-induced (RI) damage improves the patient survival ratio, injury to the neural stem and progenitor cell (NSPC) compartments and damage to NSPC populations is hypothesized to be central to the pathogenesis of RI cognitive decline in the patients. Studies on sensitivity of neural cell populations to radiation have shown that mature neurons and astrocytes have substantial radio resistance; in contrast, NSPC are highly sensitive to radiation, as exposure induces DNA double-strand breaks that when unrepaired can lead to cell death. Therefore, protection of NPCs is an important countermeasure against radiotherapy in normal tissues. Rapamycin, a small molecule inhibitor of mammalian target of rapamycin (mTOR), has been shown to exert a profoundly protective effect on epithelial and hematopoietic stem cells upon exposure to radiation therapy. Recently, several pharmacokinetically improved rapamycin analogs have secured FDA approval. In this study we investigate the potential of Everolimus as radio-protector for NSPCs in a GBM environment.
Materials and Methods: NSPCs generated from healthy donors and GBM cells were treated with different doses of Everolimus 24 h before and after a single dose 4 Gy irradiation. Survival was monitored using Cell Titer Glo assay. Western Blots, qPCR and immunofluorescence were used to assess mTOR pathway activation and NPC differentiation in 2D and 3D culture. Co-culture of NSPCs and GFP-tagged GBM cells were treated with Everolimus and irradiated with subsequent followup by confocal imaging to check the relative survival of these cells.
Results: Low doses of Everolimus restored survival and proliferation of irradiated NSPCs, while GBM cells remained radiosensitive. qPCR analysis of Nestin, SOX2 and FOXG1 revealed that NSPCs maintained their stemness after treatment. MAP2 and βIII tubulin analysis demonstrated that irradiated NSPCs were able to differentiate to neurons upon treatment. Everolimus treatment also reduced γH2A and phospho-PP2A levels and promoted phosphorylation of Akt suggesting that mTOR inhibition with Everolimus could activate DNA repair in irradiated NPCs.
Conclusions: Our findings suggest that pretreatment with low-dose Everolimus may protect NSPCs from radiation induced injuries after radiation therapy, while maintaining radiation sensitivity to GBM cells. This study suggests low-dose Everolimus as a potential radio-protector for clinical treatment of glioblastoma and other brain malignancies.
Citation Format: Tithi Ghosh Halder, Ryan Rodriguez del Villar, Jerome Lacombe, Kevin Drenner, Serina Ng, Trason Thode, Alexis Weston, Mohan Kaadige, Raffaella Soldi, Sunil Sharma. Everolimus mediated Radioprotection on surrounding healthy tissue in glioblastoma microbrain models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3068.