High-throughput in vitro drug screening and in vivo studies identify fenretinide as a brain-penetrant DMG therapeutic.

Background: Diffuse midline glioma, characterised by H3K27 alteration (DMG), is the predominant high-grade glioma in children. It commonly originates in the brainstem, yet effective treatments for these patients remain elusive.

Methods: To identify novel therapies for DMG, we conducted high-throughput drug screens (HTS) using biologically active, clinically approved compounds against DMG neurospheres. Multiple primary DMG cultures were utilised in conjunction with in vitro cytotoxicity and clonogenic assays to validate the efficacy of top compounds. Molecularly diverse patient-derived and transgenic DMG orthotopic models were employed to assess therapeutic efficacy alongside pharmacokinetic and immunohistochemical analyses. Mechanistic studies, including RNA sequencing, western blotting, and flow cytometry, were conducted to elucidate the antitumour efficacy of the most promising compound, fenretinide, in DMG cells.

Results: Through HTS, six compounds were identified and validated for their potent cytotoxic activity. However, most of these compounds failed to improve survival in an orthotopic Diffuse Midline Glioma (DMG) model due to limited blood-brain barrier (BBB) penetration. In contrast, fenretinide exhibited effective BBB penetration, significantly enhancing the survival of tumour-bearing animals. Mechanistic studies revealed that fenretinide increased reactive oxygen species (ROS) generation and induced apoptosis by inhibiting PDGFRα. RNA-sequencing further elucidated that fenretinide upregulates the Unfolded Protein Response (UPR) and endoplasmic reticulum (ER) stress pathways while downregulating neurogenesis. The in vivo antitumour efficacy of two fenretinide formulations was demonstrated in PDGFRα-amplified and transgenic DMG models.

Conclusion: This comprehensive study has identified new DMG therapeutic vulnerabilities and highlights fenretinide as a brain-penetrant, anti-DMG agent.