P02.15.b Glioblastoma in the Connectome: Neural Phenotypes Predict Tumor Integration and Connectivity

BACKGROUND Glioblastoma (GB) is a particularly aggressive brain tumor which is characterized by a low overall survival due to rapid formation of neuron-tumor-networks. The neural epigenetic subtype was linked to increased tumor-neural connectivity but the mechanisms underlying this integration remain poorly understood. Here, we aim to investigate the impact of the microenvironmental ecosystem on neuron-tumor synaptogenesis leveraging a human cortical slice model and single cell spatially resolved transcriptomic analysis. MATERIAL AND METHODS A human cortical slice model was employed to visualize and assess tumor-neuronal interactions using advanced retrograde tracing techniques in human derived cell lines (n = 12). This system was based on an EnvA-pseudotyped G-protein-deleted rabies virus. Spatial transcriptomics was conducted using multiplexed error-robust fluorescence in situ hybridization analysis (MERFISH). Additionally, we conducted immunohistochemical staining and confocal microscopy. RESULTS Spatial transcriptomic evaluation of neural high and low tumors revealed distinct microenvironmental ecosystems within the infiltrating rim of the tumors. Neural-high tumors exhibited a higher presence of synaptogenesis-inducing inflammatory myeloid cells driving neuronal synaptogenesis. Retrograde tracing of neural high vs low cell lines confirmed increased synaptic density and neuronal coupling in the neural high phenotype, which were associated with higher invasiveness, supported by stRNA-seq, which identified genes linked to synaptogenesis and connectivity. CONCLUSION Neural-high GB shows enhanced neuronal connectivity and invasiveness, contributing to accelerated tumor progression, which underlines the prognostic value of epigenetic tumor profiling and opens ways for novel therapeutic approaches.