XPO1R749Q Mutations Co-occur with POLE Mutations in Cancer and can be Targeted to Overcome Chemoresistance.

XPO1 is a nuclear export receptor that is essential for cell survival. Previous genomic analyses have identified recurrent XPO1 hotspot mutations in cancer. Here, we conducted a large-scale genomic analysis of 217,570 cancer patients to identify and characterize XPO1 variants from real-world patient tumors. XPO1 harbored a R749Q mutation in various solid tumors, with a clear enrichment in endometrial and colorectal cancers, and XPO1R749Q mutations significantly co-occurred with POLE mutations. Analysis of isogenic colon cancer cell lines revealed that XPO1R749Q localized more in the cytoplasm than wildtype 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 over 200 FDA-approved anticancer drugs indicated a general trend towards chemoresistance, specifically to topoisomerase I inhibition, in XPO1R749Q mutant cells. Mechanistically, XPO1R749Q mutant cells exhibited enhanced DNA damage response via RPA phosphorylation in response to topoisomerase I inhibition. Combining XPO1 and topoisomerase I inhibitors reduced DNA damage-induced RPA 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 for 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.