Abstract 2481: Targeting XPO1 overexpression with selinexor disrupts the survivin pathway in neuroblastoma
Authors: Castellanos Raquel , Galinski Basia , Tauber David , Landesman Yosef , Attiyeh Edward , Weiser Daniel 
Published: July 2016

Abstract
Background: Neuroblastoma (NB) is the most common extracranial solid tumor of childhood and accounts for a disproportionately high fraction (12%) of childhood cancer deaths. More than half of patients with high-risk NB will not survive their disease despite intensive treatment. Therefore new therapies that rationally target unique vulnerabilities in NB are urgently needed. The nuclear export protein Exportin-1 (XPO1) is more abundant in primary refractory NB (PRN), the most aggressive form of disease, making it an attractive therapeutic target. Overexpression of XPO1 has been implicated in tumor development and progression of multiple cancers. Selinexor (KPT-330, Karyopharm Therapeutics) targets XPO1 and inhibits its normal function of translocating tumor suppressor and growth regulatory proteins out of the nucleus. Inhibition of XPO1 results in forced nuclear retention of such proteins, which decreases cellular proliferation. Selinexor has demonstrated efficacy across a range of adult malignancies and is being developed for childhood cancer clinical studies. In this study we look at the effects of selinexor treatment in NB, specifically looking at proteins involved in apoptosis.
Methods: Whole protein cell lysates were extracted from NB cell lines IMR5 and NB-EBC1 after treatment with selinexor. Cells were treated across a range of concentrations (100nM-1000nM) and evaluated at three time points (24, 48, and 72 hours). Cytotoxic effects were measured by MTT proliferation assays.. Expression of XPO1, nuclear exported proteins, and downstream targets of the Survivin pathway were evaluated by immunoblots.
Results: Proliferation defects were observed in all NB cell lines treated with selinexor as compared to vehicle (DMSO) control. Expression of XPO1 was decreased in treated cells after 24, 48, and 72 hours of drug exposure. Expression of the anti-apoptotic protein Survivin was also decreased, as were STAT3 and acetylated STAT3. Cleaved Caspase-3 levels were increased and associated with apoptosis and decreased cellular proliferation.
Conclusions: This study provides a mechanism for XPO1 overexpression contributing to tumor progression in highly aggressive NB and explores its potential as a prognostic biological marker and therapeutic target in PRN. Treatment of NB cell lines with selinexor leads to apoptosis and associated decreased cellular proliferation. Inhibition of XPO1 function may have implications aside from nuclear export. Survivin, a pro-apoptotic protein, is decreased in the presence of selinexor, and downstream targets in the Survivin pathway are also disrupted. These data provide additional rationale for clinical development of selinexor for pediatric solid tumors, and particularly for diseases such as PRN where XPO1 is known to be overabundant. This work also suggests rational strategies for the optimal combinatorial approaches using selinexor for refractory neuroblastoma.
Citation Format: Raquel Castellanos, Basia Galinski, David Tauber, Yosef Landesman, Edward Attiyeh, Daniel Weiser. Targeting XPO1 overexpression with selinexor disrupts the survivin pathway in neuroblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2481.