XPO1 R749Q Mutations Co-occur with POLE Mutations in Cancer and Can Be Targeted to Overcome Chemoresistance.

Exportin-1 (XPO1) is a nuclear export receptor that is essential for cell survival. Previous genomic analyses have identified recurrent XPO1 hotspot mutations in cancer. In this study, we conducted a large-scale genomic analysis of 217,570 patients with cancer to identify and characterize XPO1 variants from real-world patient tumors. XPO1 harbored an R749Q mutation in various solid tumors, with a clear enrichment in endometrial and colorectal cancers, and XPO1R749Q mutations significantly co-occurred with polymerase epsilon (POLE) mutations. Analysis of isogenic colon cancer cell lines revealed that XPO1R749Q localized more in the cytoplasm than wild-type XPO1, with enhanced export of a large number of proteins. Structural modeling of XPO1R749Q suggested an increase in RanGTP affinity, which is consistent with enhanced protein export. A compound library screen using more than 200 FDA-approved anticancer drugs indicated a general trend toward chemoresistance, specifically to topoisomerase I inhibition, in XPO1R749Q-mutant cells. Mechanistically, XPO1R749Q-mutant cells exhibited an enhanced DNA damage response via replication protein A phosphorylation in response to topoisomerase I inhibition. Combining XPO1 and topoisomerase I inhibitors reduced DNA damage-induced replication protein A phosphorylation and mediated synergistic antitumor effects in cells harboring the XPO1R749Q mutation. Finally, the combination of selinexor and irinotecan overcame chemotherapeutic resistance in xenograft mouse models, prolonging survival. These findings suggest that XPO1 alterations in cancer are selected in POLE-mutant tumors and may confer resistance to DNA-damaging chemotherapies, which have implications for patients with tumors bearing XPO1R749Q and for XPO1 inhibitor development in cancer. SIGNIFICANCE: XPO1 R749Q is a recurrent mutation in cancer that is associated with POLE mutations and corresponds to topoisomerase I inhibitor resistance, which can be overcome by addition of the XPO1 inhibitor selinexor.