Abstract 3193: Combination treatment with selinexor and bortezomib for management of highly aggressive neuroblastoma
Authors: Galinski Basia , Luxemburg Marcus , Landesman Yosef , Weiser Daniel 
Published: August 2018

Abstract
Background: Neuroblastoma is an embryonic tumor of the peripheral nervous system. Comparative proteomics of high-risk neuroblastoma patients with poor prognosis outcomes demonstrated increased expression of Exportin-1 (XPO1), a nuclear transport protein with over 200 recognized cargo, in those who do not survive. Inhibition of nuclear export with the selective inhibitor of nuclear export, orally bioavailable drug molecule selinexor (Karyopharm Therapeutics) has shown anticancer activity. Treatment decreased tumor burden and increased survival in animal models. Advance-phase clinical trials using selinexor in hematologic and solid cancers are ongoing. In neuroblastoma cell lines, we have found correlation between decreased steady state protein levels of IkB, the inhibitor of NF-kB, and increased XPO1 protein expression. Likewise, proteasome inhibition with bortezomib leads to decreased NF-kB levels and decreased proliferation in neuroblastoma cells. We hypothesize that combination treatment of selinexor and bortezomib will have a greater than additive effect on the inhibition of neuroblastoma cellular proliferation. Such effect would be due in part to decreased NF-kB transcription activity through stabilization of IkB as a result of proteasome activity inhibition and forced localization of IkB into the nucleus where it may be protected from degradation.
Methods: Neuroblastoma cell lines were used for all experiments. MTT assays were used to generate dose-response curves for single-agent selinexor and bortezomib, as well as sequential treatment combination (bortezomib then selinexor six hours later). Apoptosis and cell cycle regulation were assessed for all treatment conditions. NF-kB activity was measured by ELISA in cell lysates with decreased XPO1 expression through siRNA knockdown of XPO1. Western analysis and immunofluorescence were used to quantify NF-kB and IkB protein expression in treated and knockdown conditions.
Results: Sequential combination treatment showed decreased cell viability compared to treatment with a single agent. Western analysis of NF-kB in treated single- and double-agent conditions saw decreased protein expression of NF-kB active and inactive forms. We expect flow cytometry experiments to demonstrate increased levels of apoptosis and cell cycle arrest. Future ELISA analysis of siRNA and combination treated cells will assess NF-kB transcription activity.
Conclusions: Regulation of IkB protein expression through nuclear localization as well as decreased proteasome degradation can halt NF-kB-driven cellular proliferation. Combination therapy with selinexor and bortezomib has potential to be effective against highly aggressive neuroblastoma that is, in part, driven by NF-kB. Future work will define additional pathways altered with combination treatment and guide in vivo testing and clinical development of this therapeutic strategy.
Citation Format: Basia Galinski, Marcus Luxemburg, Yosef Landesman, Daniel Weiser. Combination treatment with selinexor and bortezomib for management of highly aggressive neuroblastoma [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 3193.