Abstract 4490: Selinexor (KPT-330) radio-sensitizes non-small cell lung cancer cells in vitro and in vivo

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA The primary nuclear export protein, Exportin 1 (XPO1/CRM1), is overexpressed in most cancers and this overexpression is frequently correlated with poor prognosis. Selective Inhibitors of Nuclear Export (SINE) compounds are a family of small-molecule bioavailable drugs that bind covalently to XPO1 to inhibit nuclear export. This results in nuclear retention of major tumor suppressor proteins, such as p53, pRB, FOXO3A and other critical proteins in cancer biology, which leads to selective cancer cell death. Selinexor is the most advanced SINE with >500 hematological and solid tumor cancer patients treated to date in a number of Phase I/II clinical trials. Blocking XPO1 function also blocks nuclear transport of key DNA damage repair (DDR) proteins and we therefore hypothesized that combination of selinexor with radiation therapy (RT) would lead to synergistic anti-tumor activity. Radiation-chemotherapy combination is an established therapeutic option for patients with medically inoperable non-small cell lung cancer (NSCLC), but its use is limited due to tolerability and adverse effects. Moreover, this treatment strategy typically has short-term benefits and the patients relapse with progressive disease. Here we report on studies designed to test whether selinexor could interfere with DDR and synergize with radiation to enhance anti-tumor potency relative to either treatment alone. Cell cycle analysis and clonogenic assays were conducted in the presence or absence of selinexor in combination with escalating doses of RT on the radiation-sensitive and radiation-insensitive H1299 and A549 cell lines, respectively. Interestingly, Selinexor-treatment induced G1 cell cycle arrest in the p53-deficient cell line H1299 and a prominent G2 cell cycle arrest in p53-wild type A549 cells 24 hrs post treatment. Furthermore, clonogenic assays revealed that selinexor + RT treatment act synergistically to produce a dose-dependent growth inhibition in both cell lines. In vivo combination treatment in the A549 NSCLC xenograft model with low doses of selinexor and RT displayed a strong synergistic effect for reduction of tumor volume. In addition, microscopic and immunohistochemical analysis of the resected tumors showed an overall reduction in tumor cell numbers, increased fibrosis and induction of apoptosis in the selinexor-RT treated tumors compared to controls. Finally, mechanistic studies revealed that selinexor does not induce DNA damage like RT, but downregulates CHK1, RAD51 and other DDR proteins. Together, our results suggest that selinexor treatment sensitizes cells to RT by preventing single-stranded DNA break repair via downregulation of DDR protein expression. In contrast, selinexor induces cell cycle arrest at G1 in p53 deficient H1299 cells, allowing DNA damage accumulation and induction of apoptosis. These results provide a rationale basis for combining selinexor with RT in clinical trials studies. Citation Format: Tami Rashal, Sivan Elloul, Marsha Crochiere, Trinayan Kashyap, William Senapedis, Ryan George, Sharon Friedlander, Maya Ilouze, Yosef Landesman, Robert Carlson, Nir Peled, Michael Kauffman, Sharon Shacham, Yaacov Lawrence. Selinexor (KPT-330) radio-sensitizes non-small cell lung cancer cells in vitro and in vivo . [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 4490. doi:10.1158/1538-7445.AM2015-4490