HG-122: EFFECTS OF THE XPO1 INHIBITOR SELINEXOR ON THE NF-κB PATHWAY IN HIGH-GRADE GLIOMA AND DIFFUSE INTRINSIC PONTINE GLIOMA

BACKGROUND: Selinexor, a small molecule inhibitor of the nuclear exporter XPO1, induces apoptosis in patient-derived high-grade glioma (HGG) and diffuse intrinsic pontine glioma (DIPG) cells in neurosphere culture and suppresses the growth of orthotopic patient-derived xenograft (PDX) HGG. Selinexor is now the subject of a national clinical trial focused on pediatric HGG. Its specific mechanism of action remains unclear. METHODS: A proteomics study using tandem mass spectrometry of HGG cells treated with selinexor identified differential protein expression levels versus control. Using functional genomics techniques, we knocked down expression of the proteins of interest, studied the effects using qPCR and immunofluorescence, and quantified the impact of knockdown on selinexor's effectiveness. RESULTS: Selinexor treatment of HGG cells induced the overexpression of nerve growth factor receptor Trk⁷⁵ (NGFR) in proteomic analyses, neurosphere culture (p < 0.01) and PDX models (p < 0.0005) versus vehicle. Selinexor treatment significantly increased levels of nuclear IκBα (p < 0.0005), an NF-κB inhibitor and XPO1 client protein. Stable shRNA knockdown of NGFR in HGG/DIPG cells increased proliferation rate (p < 0.05), as well as colony (p < 0.03) and neurosphere formation (p < 0.0005) versus non-targeted shRNA. NGFR knockdown increased the nuclear expression of NF-κB member RelA (p < 0.0005) and induced significant resistance to selinexor (p < 0.05), while NF-κB knockdown increased sensitivity to selinexor (p < 0.05). DISCUSSION: Selinexor appears to induce overexpression of NGFR and nuclear sequestration of IκBα in pediatric HGG/DIPG, inhibiting NF-κB-driven proliferation and leading to cell death. These proteins can now serve as biomarkers for the pharmacodynamic effect of Selinexor on pediatric HGG tissue in the current clinical trial.