Abstract 828: Radiosensitization of glioblastoma stem-like cells by Selinexor, a selective inhibitor of nuclear export (SINE) compound
Authors: Wahba Amy , O'Neill John W. , Camphausen Kevin , Tofilon Philip J. 
Published: July 2017

Radiation therapy remains a primary treatment modality for glioblastoma (GBM). Recently, radiation-induced translational control has been implicated in regulating processes involved in the cellular radioresponse of GSCs. Reactome analysis disclosed that one major pathway under translational control after irradiation in GSCs is the nuclear export pathway, specifically by the nuclear export receptor Exportin 1 (XPO1, also referred to as CRM1). XPO1 transports over 200 cargo proteins from the nucleus to the cytoplasm via the nuclear pore complex, including several tumor suppressor proteins and it is dysregulated in multiple types of cancers. Selinexor (KPT-330), a SINE compound, is an XPO1 inhibitor that has shown antineoplastic activity in preclinical and clinical models, both alone and in combination with other treatments. In this study, we investigated the effect of XPO1 inhibition by Selinexor in combination with radiation on GSCs. To determine whether XPO1 could serve as a target for GSC radiosensitization we focused on the GSC cell line NSC11. Based on clonogenic survival assay, addition of Selinexor 1h before irradiation significantly enhanced the radiosensitivity of NSC11 cell as compared to controls. To begin to investigate the mechanism behind Selinexor-mediated radiosensitivity, γH2AX foci dispersal, a surrogate marker for DNA double strand breaks (DSB) was evaluated. NSC11 cells treated with Selinexor 1h before irradiation (2Gy) and collected 1-24h later for analysis of γH2AX demonstrated a significant delay in DNA DSB repair 24h after irradiation. Because XPO1 is responsible for export of various cargo proteins out of the nucleus, including several ribosomal subunits, it is predicted to play a role in global translation. To evaluate the effects of XPO1 inhibition on GSCs, the polysome profiles of NSC11 treated with Selinexor were evaluated. Polysome profiles of NSC11 cells demonstrated significant attenuation of the polysome portion of the profile as early as 1h after treatment with Selinexor. After 24h of Selinexor treatment, polysomes were almost undetectable with a decrease in translational efficiency (TE) by more than half. This attenuation is not accompanied by a change in the monosomal peaks, suggesting that poly-ribosome binding to mRNA is specifically affected by radiation. Taken together, these data suggest that XPO1 plays a role in translation as well as in cellular radioresponse, and inhibition of XPO1 by Selinexor enhances GSC radiosensitivity, possibly by inhibiting global translation.

Citation Format: Amy Wahba, John W. O'Neill, Kevin Camphausen, Philip J. Tofilon. Radiosensitization of glioblastoma stem-like cells by Selinexor, a selective inhibitor of nuclear export (SINE) compound [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 828. doi:10.1158/1538-7445.AM2017-828