Introduction: Bevacizumab is a standard treatment for glioblastomas (GBM), which targets VEGF-A and has been shown to increase angiogenic Epithelial Membrane Protein 2 (EMP2). Hypoxia-inducible factors (HIFs) 1α and 2α and the EMP2 axis are implicated in tumor-mediated invasion, DNA repair, and apoptosis. Current literature regarding HIF1α and HIF2α response to chemotherapy is limited and lacks consensus. We evaluated the changes in HIF1α and HIF2α expression in matched pre- and post-bevacizumab GBM patient samples as potential biomarkers related to chemoresistance.
Methods: Nine newly diagnosed GBM patient samples were collected at initial surgery and recurrence post-bevacizumab. Immunohistochemistry (IHC) of HIF1α and HIF2α was conducted on the pre- and post-bevacizumab samples and scored by two independent pathologists. Furthermore, HIF1α and HIF2α expressions in 270 GBM samples were analyzed via the IVY Glioblastoma Atlas Project (IVY GAP) and survival probability was assessed using The Cancer Genome Atlas (TCGA).
Results: HIF2α expression increased in post-bevacizumab samples (p=0.08), trending towards significance, and non-significantly in HIF1α (p=0.33). Cox regression analysis reveals adjuvant treatments (DCVax, Ponatinib, VB 111, VEGF-Trap) showed no significant improvement in OS, progression-free survival (PFS), or symptom-free survival post-bevacizumab. Log-rank Mentel Cox test demonstrated a significant difference in OS of the upregulated HIF2a cohort (p=0.02). Upregulation of HIF1a was associated with a trend towards significance for PFS (p=0.10). In validating this, Kaplan-Meier analysis of TCGA data (n=157) presented a significantly lower OS for the upregulated HIF1α expression cohort versus the downregulated cohort (p=0.03). RNA expression with normalized Z-scores from IVY GAP revealed the highest expression of HIF1α in the cellular tumor region and for HIF2α in the microvascular proliferation histological zone.
Conclusion : We present the first characterization of hypoxia-inducible factor expressions in matched pre- and post-bevacizumab-treated GBM samples. Bevacizumab treatment increased HIF2α expression, potentially implicated in chemoresistance.
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