Targeting Exportin 1 as treatment for cutaneous squamous cell carcinoma

e21564 Background: Cutaneous squamous cell carcinomas (cSCC) are among the most frequent solid cancers in humans and in the U.S., cSCC cases are increasing. Molecular mechanisms transitioning premalignant lesions to cancer are not well characterized. As a result, targeted therapies need to be identified to treat these lesions. Preliminary data shows that Exportin 1 (XPO1) is one of the major proteins regulating nuclear export of proteins, helping to maintain cellular homeostasis. Previous work showed that Exportin 1 modulates the nuclear:cytoplasmic ratio of signaling proteins in skin cancer; resulting in an anti-apoptotic effect by adjusting the nuclear-cytoplasmic balance of pro-survival proteins such as CDC25A and Survivin. XPO1 expression is upregulated in many cancers, thereby affecting the nuclear:cytoplasmic ratio of many pro-survival proteins and enhancing tumorigenesis. This research project was designed to investigate the effects of XPO1 inhibition on cSCC survival. Selinexor is FDA cleared for treatment of multiple myeloma patients. Selinexor is a selective inhibitor of XPO1 regulated nuclear transport causing target molecules to remain within the cell leading to decreased cancer cell growth and decreased cancer cell survival. We hypothesize that inhibiting XPO1 with Selinexor or by CRISPRi genetic knockdown of XPO1 in cSCC cells will reduce proliferation and increase apoptosis in cSCC cells. Methods: Human cSCC cell lines SCC13 and SRB12 were seeded in 96-well plates at 8,000 cells/well density and 3,000 cells/well, respectively. Cells were treated with varying concentrations of Selinexor (0.005mM – 5mM) or DMSO as vehicle control. At 24-hour intervals, cell imaging and Neutral red staining assays were conducted to determine the IC 50 concentration for Selinexor in cSCC cell lines. SCC13 cells stably expressing dCas9-KRAB and a doxycycline-inducible XPO1 guide RNA were used for CRISPRi experiments. Cells were treated with doxycycline daily and apoptosis was assayed by Caspase Glo 3/7 daily for four days. CRIPSRi enabled a doxycycline inducible XPO1 knock down on SCC13 cells allowing us to disrupt the cellular transporter protein XPO1. Results: Selinexor treatment of SRB12 cells resulted in an IC 50 of 1.174 μM and 0.071 μM for SCC13. In contrast, normal human keratinocyte cell lines had higher IC 50 values of 2.18 μM for HaCaT and 5.29 μM for KerCT cells. Apoptosis significantly increased after 72 and 96 hours of XPO1 knock down in SCC13 cells measured by Caspase Glo. Conclusions: These results document how XPO1 inhibition reduces proliferation and is toxic to both normal keratinocytes and cSCC cells. Additionally, cSCC cells had lower IC 50 values for Selinexor, suggesting cSCC may be more sensitive to XPO1 inhibition compared to normal keratinocytes. Further, targeting XPO1 also increases apoptosis in these cells. This data supports the hypothesis that targeting XPO1 may be effective in treating cSCC.