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

Abstract

Purpose: KPT-8602 (Eltanexor) is a second generation exportin-1 (XPO1) inhibitor with potent activity against acute lymphoblastic leukemia (ALL) in pre-clinical models and with minimal effects on normal cells. In this study, we evaluated if 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 (PDX) 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 to 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. Conclusion: Our pre-clinical 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.