Abstract 3810: Leptomycin B sensitizes ovarian and endometrial cancer cells to TRAIL-induced apoptosis
Authors: Fabi François , Joncas France-Hélène , Parent Sophie , Leblanc Valérie , Asselin Eric 
Published: August 2015

Abstract
One of our most important line of defense against cancer is the use of chemotherapy. Resistance to these drugs represents, however, a fundamental limitation in our ability to treat tumors, especially in ovarian cancer (OC) as well as in endometrial cancer (EC). Both of these cancers display high mortality rate due to the establishment of chemoresistance. It is thus of utmost importance that we develop new approaches to overcome this problem and restore chemosensitivity in cancer cells. Nuclear transport has been shown to be exceedingly important in cell fate dynamics. CRM1, also known as XPO1, is a nuclear export receptor that recognize leucine-rich domain known as “Nuclear Export Signal”. Indeed, substantial CRM1 enrichment is indicative of highly invasive and resistant tumors and is generally suggestive of lower chance of survival. On the other hand, Par-4, an exceptionally rarely mutated protein capable of inducing cell death only in transformed cells while sparing normal cells, is suggested to be activated upon nuclear localization; it is thus considered a powerful, cancer-specific, inducer of cell death. Recent findings suggest that reinstating the ability of Par-4 to accumulate in the nucleus could re-establish its capacity to induce apoptosis. Our hypothesis was that CRM1 nuclear exclusion of Par-4 could be an acquired resistance mechanism in cancer cells.
To explore this hypothesis, we first treated various OC and EC cell types with Leptomycin B to observe whether Par-4 would accumulate to the nucleus; to this end, we performed immunofluorescence as well as subcellular protein fractionations. The obtained results suggested that Par-4 was enriched in the nucleus of cells following Leptomycin B treatments. We then treated multiple OC and EC cell lines with a combination of Leptomycin B, cisplatin and TRAIL recombinant protein to determine if Par-4 enrichment through CRM-1 inhibition could sensitizes tumor cells through either extrinsic or intrinsic death pathways. We then assessed cell death and Par-4 cleavage, an important event in Par-4 induced cell death, using western blot and confirmed the results pertaining to cell death by flow cytometry (Annexin V/PI). The obtained results suggested that the combination of Leptomycin B and TRAIL largely increased cell death and apoptosis when compared to their treatment alone.
Taken together, these results suggest that CRM1 control export of various tumor suppressors including Par-4, and this could be a putative mechanism responsible for the establishment of chemoresistance in OC as well as EC. The use of CRM1 inhibitors in combination to chemotherapeutic drug treatments could be an attractive strategy to reverse chemoresistance in the context of gynecological cancer therapy.
Citation Format: François Fabi, France-Hélène Joncas, Sophie Parent, Valérie Leblanc, Eric Asselin. Leptomycin B sensitizes ovarian and endometrial cancer cells to TRAIL-induced apoptosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3810. doi:10.1158/1538-7445.AM2015-3810