Abstract 4444: The XPO1 inhibitor Selinexor attenuates global translation and enhances the radiosensitivity of glioblastoma cells grown in vitro and in vivo

Radiation therapy remains a primary treatment modality for glioblastoma (GBM). To identify novel targets for GBM radiosensitization, the radiation-induced translatome was defined for a series of glioblastoma stem-like cells (GSCs). Analysis of the radiation-induced translatome of GSCs identified an interacting network in which Exportin 1 (XPO1) serves as a major hub protein. XPO1 transports a variety of proteins and RNAs from the nucleus to the cytoplasm via the nuclear pore complex and is dysregulated in multiple types of cancers, including GBM. To determine whether XPO1 provides a target for GBM radiosensitization, we defined the effects of the clinically relevant XPO1-inhibitor Selinexor (KPT-330) on the radiosensitivity of GSC lines. Using clonogenic survival analysis, Selinexor was shown to enhance the in vitro radiosensitivity of GSCs but not normal fibroblast cell lines. Because XPO1 mediates the nuclear export of ribosomal subunits, we tested the effect of Selinexor on gene translation using polysomes profiles to calculate translational efficiency and O-propargyl-puromycin (OPP) incorporation to measure de novo protein synthesis. Selinexor significantly reduced translational efficiency in GSCs beginning at 1-6h after treatment, which was accompanied by a decrease in protein synthesis. Moreover, Selinexor exposure increased in 18S and 5S rRNA accumulation in the nucleus with corresponding decreases in the cytoplasm suggesting that the inhibition of rRNA export plays a role in the Selinexor-mediated decrease in protein synthesis. In contrast to the tumor cells, Selinexor had no effect on protein synthesis in normal fibroblast cell lines and astrocytes. To determine the effect of XPO1 inhibition on GBM cells in vivo, mice bearing orthotopic xenografts initiated from a GSC line (NSC11) were treated with Selinexor (20 mg/kg) and tumors were collected over 48 hours. Polysome profiles generated from these orthotopic xenografts indicated that Selinexor treatment resulted in a decrease in translational efficiency with the greatest effect at 24 hours after treatment. These results suggest that consistent with in vitro data, Selinexor inhibits global translation in GBM cells grown under orthotopic, in vivo conditions. To determine the effect of XPO1 inhibition on radioresponse in vivo, mice bearing orthotopic xenografts were treated with Selinexor in combination with fractionated radiation. Whereas Selinexor alone had no effect on survival, the XPO1 inhibitor enhanced radiation-induced prolongation of animal survival with an apparent dose enhancement factor of 2. These results suggest that Selinexor delivered in combination with radiotherapy may improve the effectiveness of GBM treatment. Citation Format: Amy Wahba, John W. O9Neill, Barbara H. Rath, Kevin Camphausen, Philip J. Tofilon. The XPO1 inhibitor Selinexor attenuates global translation and enhances the radiosensitivity of glioblastoma cells grown in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4444.