Preclinical characterization of a reversible XPO1 inhibitor for cancer therapy.

Exportin 1 (XPO1/CRM1) is a clinically validated anticancer target whose inhibition blocks nuclear export and promotes cancer cell apoptosis. Current XPO1 inhibitors rely on covalent Michael addition to Cys528 in the nuclear export signal binding groove of XPO1. Here, we describe a novel XPO1 inhibitor, FR-027, that targets Cys528 through nucleophilic aromatic substitution. In contrast to clinical-stage XPO1 inhibitors selinexor and eltanexor, FR-027 acts reversibly and does not promote XPO1 protein degradation. Structural analysis of the XPO1-FR-027 complex reveals covalent modification of Cys528 and a closed-groove conformation that prevents degradation. FR-027 demonstrates potent on-target activity across multiple cancer cell types and delays disease progression while extending overall survival in xenograft and syngeneic models, including intracranial tumors. Notably, FR-027 does not induce significant thrombocytopenia, lymphopenia, or neutropenia in heavily treated mice. These findings underscore the distinct molecular and pharmacological properties of FR-027 and support its further evaluation for clinical development in diseases with significant unmet medical needs.