Abstract
BACKGROUND: Diffuse midline glioma (DMG) is the most aggressive primary brain tumor in children. The only approved standard of care is radiation therapy (RT). Studies examining the role of other systemic agents have failed to demonstrate a survival benefit, partially due to tumor extension to areas of the brain where the blood-brain barrier (BBB) remains intact. As our laboratory has recently determined active NAD(P)H Quinone Dehydrogenase 1 (NQO1) expression in patient-derived DMG tumor samples, we sought to investigate NQO1 bioactivatable agent Napabucasin to augment reactive oxygen species (ROS) production and overcome radioresistance in DMG. Furthermore, we explore the safety and feasibility of convection-enhanced deliver (CED) to overcome limitations of the BBB. METHODS: Using two DMG cell lines, we performed clonogenic survival assays with increasing doses of RT with and without Napabucasin. We then created subcutaneous xenograft mouse models, treating with (1) vehicle control, (2) Napabucasin, (3) 2 Gy of RT daily, or (4) combination treatment with RT and Napabucasin. Using a syngeneic orthotopic DMG mouse model, we implanted 7-day osmotic infusion pumps containing either vehicle control or 80uM Napabucasin. Mice then underwent a second randomization with or without daily RT for 5 days. RESULTS: We identified a robust radiosensitizing effect with Napabucasin using in vitro clonogenic survival assays. In subcutaneous flank models, combination treatment led to a statistically significant smaller tumor volume post-treatment completion when compared to any monotherapy. In our syngeneic orthotopic DMG mouse model, RT after CED pump implantation in the brainstem did not lead to significant morbidity or mortality. Combination RT and CED of Napabucasin led to a significant survival benefit when compared to monotherapy. CONCLUSIONS: In this study, we show Napabucasin as a promising radiosensitizer in DMG. Furthermore, this is the first preclinical study showing safety/efficacy of CED with concurrent RT in DMG.