Corresponding author: Philip J. Tofilon, PhD, National Cancer Institute, 10 Center Drive-MSC 1002, Building 10, B3B69B, Bethesda, MD 20892.
Neuro Oncol. 2014 Jan;16(1):29-37. doi: 10.1093/neuonc/not139. Epub 2013 Dec 4.
The mammalian target of rapamycin (mTOR) has been suggested as a target for radiosensitization. Given that radiotherapy is a primary treatment modality for glioblastoma (GBM) and that mTOR is often dysregulated in GBM, the goal of this study was to determine the effects of AZD2014, a dual mTORC1/2 inhibitor, on the radiosensitivity of GBM stem-like cells (GSCs).
mTORC1 and mTORC2 activities were defined by immunoblot analysis. The effects of this mTOR inhibitor on the in vitro radiosensitivity of GSCs were determined using a clonogenic assay. DNA double strand breaks were evaluated according to γH2AX foci. Orthotopic xenografts initiated from GSCs were used to define the in vivo response to AZD2014 and radiation.
Exposure of GSCs to AZD2014 resulted in the inhibition of mTORC1 and 2 activities. Based on clonogenic survival analysis, addition of AZD2014 to culture media 1 hour before irradiation enhanced the radiosensitivity of CD133+ and CD15+ GSC cell lines. Whereas AZD2014 treatment had no effect on the initial level of γH2AX foci, the dispersal of radiation-induced γH2AX foci was significantly delayed. Finally, the combination of AZD2014 and radiation delivered to mice bearing GSC-initiated orthotopic xenografts significantly prolonged survival as compared with the individual treatments.
These data indicate that AZD2014 enhances the radiosensitivity of GSCs both in vitro and under orthotopic in vivo conditions and suggest that this effect involves an inhibition of DNA repair. Moreover, these results suggest that this dual mTORC1/2 inhibitor may be a radiosensitizer applicable to GBM therapy.
哺乳动物雷帕霉素靶蛋白（mTOR）已被认为是放射增敏的靶点。鉴于放疗是胶质母细胞瘤（GBM）的主要治疗方式，并且 mTOR 在 GBM 中经常失调，本研究的目的是确定双重 mTORC1/2 抑制剂 AZD2014 对 GBM 干细胞样细胞（GSCs）放射敏感性的影响。
通过免疫印迹分析定义 mTORC1 和 mTORC2 的活性。使用集落形成测定法确定这种 mTOR 抑制剂对 GSCs 体外放射敏感性的影响。根据 γH2AX 焦点评估 DNA 双链断裂。使用源自 GSCs 的原位异种移植来定义对 AZD2014 和辐射的体内反应。
AZD2014 暴露导致 mTORC1 和 2 活性的抑制。基于集落形成存活分析，在照射前 1 小时将 AZD2014 添加到培养基中增强了 CD133+和 CD15+GSC 细胞系的放射敏感性。虽然 AZD2014 处理对初始 γH2AX 焦点水平没有影响，但辐射诱导的 γH2AX 焦点的分散明显延迟。最后，与单独治疗相比，将 AZD2014 和辐射联合用于携带 GSC 起始的原位异种移植的小鼠显著延长了生存期。
这些数据表明，AZD2014 增强了 GSCs 在体外和原位体内条件下的放射敏感性，并表明这种作用涉及 DNA 修复的抑制。此外，这些结果表明，这种双重 mTORC1/2 抑制剂可能是一种适用于 GBM 治疗的放射增敏剂。
