P03.08.A HIGH-DIMENSIONAL CHARACTERISATION OF THE CELLULAR AND MOLECULAR CHANGES IN THE HUMAN BRAIN AFTER RADIOTHERAPY

Abstract BACKGROUND In the UK ~40,000 intrinsic and metastatic brain tumours are diagnosed each year. Although targeted radiotherapy (RT) is integral to increasing survival of cancer patients, it has significant side-effects, the cellular and molecular mechanisms of which are not fully understood. During RT treatment epigenetic changes occur in the neoplastic tissue, but few studies have assessed these in non-neoplastic brain tissue and results are highly variable. MATERIAL AND METHODS To explore the effects of RT on patient-specific methylation, we retrospectively identified 19 samples, mainly metastatic tumours, that had undergone stereotactic-RT followed by resection, and contained peri-lesional brain tissue, as well as 14 controls. Peri-lesional brain was micro-dissected, followed by DNA methylation profiling and RNA-sequencing. RESULTS Clustering of DNA methylation data showed distinct patterns between the two groups, whilst RNA-seq revealed 1,887 differentially expressed genes. Pathway analysis with GSEA identified differentially represented pathways, including: innate immune system, trans-synaptic signalling, olfactory signalling, regulation of supramolecular fibre organisation, and pattern specification. Computational deconvolution of cellular composition showed increased activated dendritic cells and B-cells, and reduced smooth muscle cells and several sub-sets of astrocytes in the RT samples. CONCLUSION We are currently further investigating these findings using spatial transcriptomics and proteomics to produce the first high-dimensional characterisation of the irradiated human brain. This will also provide the first direct evidence of epigenetic dysregulation after targeted-RT, and assess novel epigenetically-regulated genes, which will be validated with single cell tissue-based imaging techniques. A range of epigenetic-based drugs are undergoing clinical trials and we aim to identify targets for radiomitigation in brain tumour patients.