DIPG-61. ARGININE DEPRIVATION USING ADI-PEG20 IMPROVES SURVIVAL IN A SYNGENEIC DIFFUSE MIDLINE GLIOMA MOUSE MODEL

Abstract

Abstract BACKGROUND Diffuse midline glioma (DMG-H3K27) presents a significant challenge in paediatric oncology, with a <10% two-year survival rate despite standard palliative radiotherapy. Tumour infiltration behind the blood-brain barrier hampers drug delivery, contributing to clinical trial failures. ADI-PEG20 exploits tumour metabolic vulnerabilities: lack of argininosuccinate synthetase and reliability on extracellular arginine for proliferation. This study investigates ADI-PEG20’s efficacy in a syngeneic DMG mouse model. METHODS Twenty C57BL/6J mice were intracranially injected with a DMG cell line (H1H3BK27M, DNp53, PDGFRAD642V, Acvr1G328V) and monitored via bioluminescence imaging from day 7. Weekly treatments began on day 10, comprising ADI-PEG20 (5 I.U.) alone, ADI-PEG20 with concurrent radiation (2 Gy), radiation alone, or saline (0.9%), with each group comprising n=5. Radiation was administered 24 hours post-drug treatment. Bioluminescence imaging was conducted twice weekly, with mice culled upon symptom onset. Immunohistochemistry was performed on brain tissue. RESULTS The combination and ADI-PEG20 monotherapy cohorts exhibited comparable median survival rates, both surpassing those of the radiation-only and saline groups, with the latter exhibiting the lowest median survival. A significant disparity in survival curves was observed overall (p<0.0001), confirmed by log-rank (Mantel-Cox) test. Pairwise comparisons revealed significant differences in survival curves between the combination and radiation-only (p=0.0066), ADI-PEG20 monotherapy and radiation-only (p=0.0018), and ADI-PEG20 monotherapy and saline (p=0.0062) groups. Minimal divergence in IVIS signal intensity was noted across groups. Histological examination via H&E staining demonstrated marked tumour regression in mice treated with ADI-PEG20 ± radiation, contrasting with the persistent tumour mass evident in the radiation-only and saline cohorts, alongside discernible heterogeneity in cellular phenotypes within the ADI-PEG20 ± groups. CONCLUSIONS In conclusion, ADI-PEG20 shows promise as a therapeutic strategy for DMG, offering a significant survival advantage over radiation and saline. Ongoing efforts will elucidate its mechanistic underpinnings, explore its efficacy across diverse DMG models, and assess synergistic interactions with immune-based therapies.