Pediatric high-grade gliomas (pHGGs) are aggressive and incurable tumors, reasons why there is a pressing need for novel therapeutic approaches to treat them. Proactive translational studies wish to go further discovering new targetable proteins in these tumors, especially those participating to the modulation of microenvironmental extrinsic features. To do so, we were focusing on specific actors involved in hypoxic tumor environment. We looked, first, to Hypoxia-Inducible factors (HIFs) expression in a pHGG cohort to see their potential prognostic and outcome impacts. In a second step, we tested the anti-HIFs strategies.
We designed this work to determine in a collection of 45 diagnostic FFPE pHGGs (17 DIPGs, 4 gliomatosis cerebri and 24 thalamic/hemispheric tumors) and 7 relapsing samples the expression of HIF-1alpha and HIF-2alpha by immunohistochemistry and its correlation with cell metabolism (HRMAS technique). We also checked HIFs’ expression in 6 PDCLs (H3.3 mutated or wild-type). We focused on HIF-2alpha to study its role, its induction in normoxic and hypoxic microenvironments and its transcriptional targets using RNAseq, metabolomics and ChipSeq analyses. Complementary functional analyses were performed using inhibition strategies with commercialized and non-commercialized antagonists to evaluate antiproliferative and pro-apoptotic effects.
We confirmed hyperexpression of HIF-1alpha in 61% of diagnostic samples and HIF-2alpha in 40%. All relapses were acquiring a HIF-2alpha hyperexpression associated to metabolomic resistant features. Only HIF-2alpha was linked to a worst outcome, reason why we focused on it. HIF-2alpha is involved in pHGG stemness features in culture and has a direct link with cell metabolism adaptation and specific interactions with histones. The use of inhibitors in a single and combinatorial strategy targeting HIF-2alpha plus another hypoxic biomarkers was highly effective for cell arrest and apoptosis and stopped cell migration.
Our results confirmed the central role of HIF-2alpha, which seems to be a major biomarker to be targeted in pHGGs.