JS09.5.A SPATIAL TRANSCRIPTOMIC AND ELECTRODIAGNOSTIC PROFILING REVEALS SYNAPTIC CONNECTIVITY IS A HALLMARK OF OLIGODENDROGLIOMA RECURRENCE AND MALIGNANT TRANSFORMATION

Abstract BACKGROUND Oligodendrogliomas are prone to malignant transformation despite surgery and cytotoxic therapy. Mechanistic insight into this evolution has been encumbered by limited preclinical models and the scarcity of patient-matched newly diagnosed and recurrent samples. Here we integrate multiplatform molecular and functional profiling to reveal synaptic connectivity as a driver of oligodendroglioma evolution and identify new prognostic biomarkers and therapeutic targets. METHODS Thirty-three patient-matched newly diagnosed and recurrent oligodendroglioma samples were analyzed using spatial RNA sequencing (55,737 transcriptomes), targeted NGS, immunofluorescence, and single-cell ATAC sequencing. Cell states, copy number alterations (CNAs), and chromatin accessibility were integrated with clinical and transcriptomic data. A 28-gene synaptic connectivity score was developed and validated in non-overlapping oligodendroglioma (n=5), astrocytoma (n=16), and institutional and external (TCGA) IDH-mutant glioma cohorts. Functional analyses employed resting-state high-density subdural array local field potentials from oligodendroglioma-infiltrated cortex (n=10) and multielectrode array recordings of 3D co-cultures comprised of mouse cortical neurons and human patient-derived tumor organoids (n=17). RESULTS Oligodendroglioma spatial transcriptomes were enriched in gene expression programs related to synaptic transmission, trans-synaptic signaling, and axon development in recurrent compared to newly diagnosed tumors irrespective of cell state, WHO grade, or treatment history. A 28-gene connectivity score encompassing the most differentially expressed genes in recurrent versus newly diagnosed oligodendrogliomas was enriched in spatial transcriptomes from areas of cortical infiltration, including Tsp1 and Connexin 43. In recurrent oligodendrogliomas, genes in the connectivity score showed increased chromatin accessibility at transcriptional start sites that was independent of SNVs or CNAs. In TCGA IDH-mutant gliomas, the 28-gene connectivity score stratified progression-free and overall survival. Subdural arrays revealed increased high-gamma functional connectivity in recurrent versus newly diagnosed tumor-infiltrated cortex. 3D co-cultures exhibited neuronal hyperexcitability and increased synaptic density, which promoted oligodendroglioma cell proliferation. These effects were reversed by pharmacologic inhibition of Tsp1 (gabapentin) or Connexin 43 (meclofenamic acid). CONCLUSION Synaptic remodeling due to epigenetic dysregulation is a conserved, spatially-organized hallmark of oligodendroglioma evolution. These findings identify neuron-glioma interactions as a driver of malignant progression and a targetable vulnerability, with implications for new biomarkers and new treatments for patients.