Ataxia-telangiectasia mutated (Atm) disruption sensitizes spatially-directed H3.3K27M/TP53 diffuse midline gliomas to radiation therapy

Diffuse midline gliomas (DMGs) are lethal brain tumors characterized by inactivating p53 mutations and oncohistone H3.3K27M mutations that rewire the cellular response to genotoxic stress, presenting therapeutic opportunities. We used RCAS/tv-a retroviruses and Cre recombinase to inactivate p53 and induce K27M in the native H3f3a allele in a lineage- and spatially-directed manner, yielding primary mouse DMGs. Disruption of the DNA damage response kinase Ataxia-telangiectasia mutated (Atm) enhanced the efficacy of focal brain irradiation, extending mouse survival. This finding suggests that targeting ATM will enhance the efficacy of radiation therapy for p53-mutant DMG but not p53-wildtype DMG. We used spatial in situ transcriptomics and an allelic series of primary murine DMG models to identify transactivation-independent p53 activity as the key mediator of such radiosensitivity. Primary mouse models of diffuse midline glioma were treated with tumoral Atm loss and/or focal brain irradiation.