TMIC-48. Hypoxia-driven reprogramming of tumour-microglia interactions in paediatric high-grade gliomas

Abstract Paediatric high-grade gliomas (pHGGs) are aggressive brain tumours and the leading cause of cancer-related deaths in children. Treatment typically involves surgery and radiotherapy, but their diffuse, invasive nature and unfavourable location often make them inoperable. Additionally, the histone H3 mutation causing the H3K27M substitution, is associated with poor patient’s prognosis. At the time of diagnosis, pHGGs are in advanced stages with developed regions of hypoxia (low oxygen), which may impair the effectiveness of radiotherapy. Recent findings indicate that microglia play a key role in the tumour microenvironment of pHGGs and may contribute to therapy resistance. The roles of hypoxia and tumour-host interactions in pHGGs are not well understood. This study aims to uncover the molecular mechanisms driving microglia-glioma crosstalk and the role of hypoxia in these interactions in different subgroups of pHGGs. Co-detection by indexing (CODEX) staining for hypoxia markers was used to assess hypoxia in patient samples from various subtypes of pHGGs and localization of microglia cells to these regions. To investigate tumour-microglia interactions, we are utilising in vitro pHGG-microglia co-cultures. CODEX staining for the HIF-1α downstream target, GLUT-1, revealed a higher prevalence of hypoxic regions in the hemispheric H3-wildtype pHGGs compared to diffuse midline gliomas (DMG) with the H3K27M mutation. Therefore, we examined the hypoxic response in glioma cells with and without the H3K27M mutation, revealing mutation-specific differences in HIF-1α pathway regulation. Microglia promoted cell invasiveness in co-cultures and this influence was higher in a case of DMG with the H3K27M mutation, hypoxic stress did not affect the invasion. Transcriptomic and functional analyses were performed to clarify the role of altered HIF-1α pathway in pHGGs on the function of microglia in hypoxic conditions. The study is funded by the European Health and Digital Executive Agency under the EU Cancer Mission Horizon Europe HIT-GLIO project (no 101136835).