Autophagy Modulates Glioblastoma Cell Sensitivity to Selinexor-mediated XPO1 inhibition

Abstract Background Selinexor is a selective inhibitor of exportin-1 (XPO1), a key mediator of the nucleocytoplasmic transport for molecules critical to tumor cell survival. Selinexor’s lethality is generally associated with the induction of apoptosis, and in some cases, with autophagy-induced apoptosis. We performed this study to determine Selinexor’s action in glioblastoma (GBM) cells, which are notoriously resistant to apoptosis. Methods Patient-derived GBM cells were treated with Selinexor, and drug response and autophagy levels were monitored. Homozygous C528S XPO1 mutant GBM43 cells were generated by CRISPR/Cas9 editing. Single Selinexor or combination treatment with autophagy inhibitors was evaluated. In addition, bulk-tissue, single-cell, and spatial transcriptome were analyzed, and molecular docking was performed. Results Although all cell lines exhibited a dose- and time-dependent reduction of cell viability, the most profound molecular response to Selinexor was induction of autophagy instead of apoptosis. Selinexor-induced autophagy was an on-target consequence of XPO1 inhibition, and could be mitigated by expression of a mutant, Selinexor-resistant form of XPO1, and Selinexor-induced autophagy was related at least in part to nuclear trapping of the transcription factor TFEB. Furthermore, genetic or pharmacologic suppression of autophagy sensitized the cells to Selinexor-induced toxicity in association with the induction of apoptosis. Finally, in intracranial PDX studies, the combination of Selinexor with the autophagy inhibitor chloroquine significantly impeded tumor growth and extended mouse survival relative to single-agent treatment. Conclusion These results suggest that activation of autophagy confers a protective mechanism against Selinexor in GBM cells, and that the combination of Selinexor with autophagy inhibitors may serve as a viable means to enhance Selinexor-induced cell death.