Investigating Novel Treatments to Improve Radiation Response in Diffuse Intrinsic Pontine Glioma

Abstract

Diffuse intrinsic pontine glioma (DIPG), now categorised under Diffuse Midline Glioma (DMG) is a fatal paediatric brainstem tumour. Radiotherapy (RT) remains the only effective treatment, however most DIPGs recur due to radioresistance. The hypoxic tumour microenvironment contributes to radioresistance, therefore alleviating hypoxia may improve RT efficacy and patient survival.

We found evidence suggesting increased oxidative phosphorylation (OXPHOS) in DIPG/DMG patient samples suggesting increased oxygen consumption and localised hypoxia. Hypoxia was also validated in DIPG xenografts by positive HIF-1α, VEGFA, and EF5 staining within tumour regions. Hence, we aimed to inhibit OXPHOS to reduce oxygen consumption rate (OCR), alleviate hypoxia and enhance radiosensitivity of DIPG. An anti-parasitic drug screening was performed and atovaquone was identified as the most potent OCR inhibitor. Atovaquone suppressed OCR across multiple DIPG models by targeting complex III, increasing oxidative stress, reducing hypoxia and sensitising DIPG cells to RT. Similar efficacy was observed between commercial and the higher blood-brain barrier (BBB)-penetrant version, amorphous solid dispersion (ASD) atovaquone formulation, supporting evaluation of ASD atovaquone in orthotopic DIPG models. ASD atovaquone demonstrated promising radiosensitising efficacy as it improved survival in orthotopic DIPG model in combination with RT. Mefloquine, another top candidate, inhibited both mitochondrial and glycolytic metabolism, reduced hypoxia and similarly improved radiosensitivity of DIPG cells.

Overall, this thesis provides evidence to support upregulated OXPHOS and the presence of hypoxia in DIPG. Inhibition of OXPHOS with atovaquone and mefloquine alleviated hypoxia and radiosensitised DIPG cells in vitro, with ASD atovaquone showing efficacy in vivo. These findings highlight OXPHOS inhibition as a promising radiosensitising strategy for DIPG and potentially other hypoxic brain tumours.