The XPO1 Inhibitor KPT-8602 Synergizes with Dexamethasone in Acute Lymphoblastic Leukemia

Purpose: KPT-8602 (Eltanexor) is a second-generation exportin-1 (XPO1) inhibitor with potent activity against acute lymphoblastic leukemia (ALL) in preclinical models and with minimal effects on normal cells. In this study, we evaluated whether KPT-8602 would synergize with dexamethasone, vincristine, or doxorubicin, three drugs currently used for the treatment of ALL. Experimental Design: First, we searched for the most synergistic combination of KPT-8602 with dexamethasone, vincristine, or doxorubicin in vitro in both B-ALL and T-ALL cell lines using proliferation and apoptosis as a readout. Next, we validated this synergistic effect by treatment of clinically relevant B- and T-ALL patient-derived xenograft models in vivo. Finally, we performed RNA-sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) to determine the mechanism of synergy. Results: KPT-8602 showed strong synergism with dexamethasone on human B-ALL and T-ALL cell lines as well as in vivo in three patient-derived ALL xenografts. Compared with single-drug treatment, the drug combination caused increased apoptosis and led to histone depletion. Mechanistically, integration of ChIP-seq and RNA-seq data revealed that addition of KPT-8602 to dexamethasone enhanced the activity of the glucocorticoid receptor (NR3C1) and led to increased inhibition of E2F-mediated transcription. We observed strong inhibition of E2F target genes related to cell cycle, DNA replication, and transcriptional regulation. Conclusions: Our preclinical study demonstrates that KPT-8602 enhances the effects of dexamethasone to inhibit B-ALL and T-ALL cells via NR3C1- and E2F-mediated transcriptional complexes, allowing to achieve increased dexamethasone effects for patients.