Faculty Bibliography

Low-grade astrocytomas (LGAs) carry neomorphic mutations in isocitrate dehydrogenase (IDH) concurrently with P53 and ATRX loss. To model LGA formation, we introduced R132H IDH1, P53 shRNA, and ATRX shRNA into human neural stem cells (NSCs). These oncogenic hits blocked NSC differentiation, increased invasiveness in vivo, and led to a DNA methylation and transcriptional profile resembling IDH1 mutant human LGAs. The differentiation block was caused by transcriptional silencing of the transcription factor SOX2 secondary to disassociation of its promoter from a putative enhancer. This occurred because of reduced binding of the chromatin organizer CTCF to its DNA motifs and disrupted chromatin looping. Our human model of IDH mutant LGA formation implicates impaired NSC differentiation because of repression of SOX2 as an early driver of gliomagenesis.

Resistance to antiangiogenic therapy glioblastoma (GBM) patients may involve hypoxia-induced expression of stromal cell-derived factor (SDF)-1alpha receptor C-X-C chemokine receptor 4 (CXCR4) on invading tumor, macrophage/microglial cells (MGCs), and glioma stem cells (GSCs). We determined whether antagonizing CXCR4 with peptide epitope mimetic POL5551 disrupts anti-vascular endothelial growth factor therapy-induced glioma growth and dissemination. Mice bearing orthotopic CT-2A or GL261 gliomas received POL5551 and/or anti-vascular endothelial growth factor antibody B20-4.1.1 for 2 weeks. Brain tissue was analyzed for tumor volume, invasiveness, hypoxia, vascular density, proliferation, apoptosis, GSCs, and MGCs. Glioma cells were evaluated for CXCR4 expression and polymorphism and POL5551's effect on CXCR4 ligand binding, cell viability, and migration. No CXCR4 mutations were identified. POL5551 inhibited SDF-1alpha CXCR4 binding and reduced hypoxia- and SDF-1alpha-mediated migration dose dependently but minimally affected cell viability. B20-4.1.1 increased hypoxic foci and invasiveness, as seen in GBM patients, but when administered with POL5551, reduced glioma invasiveness by 16% to 39%. B20-4.1.1 reduced vascular density by 16% to 28%, which was further reduced by addition of POL5551 in both glioma models. Immunopositive GSCs and MGCs were also reduced in CT-2A tumors. POL5551 concentrations, evaluated by mass spectrometry, were higher in tumors than in neighboring brain tissues, likely accounting for the results. Inhibiting CXCR4-regulated tumoral, stem cell, and immune mechanisms, adjunctive POL5551 CXCR4 antagonists may help overcome antiangiogenic therapy resistance, benefiting GBM patients.