ID #1061 Radiation induces DNA damage and immune microenvironment remodelling in a transgenic model of SHH-like medulloblastoma
Jorren Kuster, Sally Larder, Chloe Buckingham, Piyusha Johnson, Joshua Ninan, Alexandra Monson, Hilary Hii, Omar Elaskalani, Joost Lesterhuis, Nick Gottardo, Jessica Buck, Raelene EndersbyAbstract
Background
Multimodal therapy is required for effective treatment of medulloblastoma, with radiotherapy playing an essential role. DNA damage and associated immunological changes after radiotherapy in a preclinical setting must be studied to understand how treatment reshapes the brain tumour-immune microenvironment and drives tumour cell killing in SHH medulloblastoma.
Methods
We utilised a preclinical paediatric model of SHH-like medulloblastoma. Using MRI, flow cytometry and immunohistochemistry we characterised the local and systemic effects following fractionated radiotherapy initiated on postnatal day 15.
Results
Medulloblastomas in Atoh1-cre;Ptch1loxP/loxP mice are exquisitely sensitive to whole brain irradiation (WBIR). Multiple fractionation schedules were evaluated. Six or 10Gy WBIR (3 × 2Gy or 5 × 2Gy) resulted in no detectable disease up to 250 days post-treatment by MRI and histology. Lower doses of 3Gy (3 × 1Gy), 2.5Gy (5 × 0.5Gy) or 1.5Gy (3 × 0.5Gy) extended survival in a dose dependent manner. Irradiation significantly reduced cerebellar volume measured via MRI, and in lower-dose groups, volume increases 50-100 days post-treatment indicated disease relapse. Immunohistochemistry confirmed DNA damage induction, reduced proliferation, and increased apoptosis. Spectral flow cytometry using a custom-made antibody panel characterised irradiation-induced immunological changes in the cerebellum, meninges, skull bone marrow, femoral bone marrow and deep cervical lymph nodes. Tumour-bearing mice showed increased CD45high immune cells in the cerebellum post-irradiation, and no change in CD45intermediate cells. Notably, T cells and dendritic cells were increased, with treatment-associated changes in activation, differentiation and immune-suppressive markers across numerous myeloid and lymphoid subsets.
Conclusion
Ptch cKO mice represent a clinically-relevant model that recapitulates the developmental context of paediatric SHH medulloblastoma, enabling precise evaluation of radiotherapy responses with a developing immune system. Here, we defined fractionated WBIR doses that irradicate tumours or reliably model relapse, providing a foundation for future preclinical studies. Radiotherapy-induced remodelling of the medulloblastoma-immune microenvironment supports use of this model to investigate immunomodulatory strategies that may enhance radiotherapy efficacy.