CNSC-57. HUMAN AND MOUSE PERITUMORAL SLICES DEMONSTRATE MTOR-DEPENDENT GABAERGIC NEURONAL DYSFUNCTION IN GLIOMA

Abstract Approximately 60-80% of all glioma patients experience seizures, and a significant number of these patients are unable to achieve seizure freedom with conventional anti-epileptic treatment alone. One suggested mechanism for these tumor-associated seizures (TAS) is through disrupted presynaptic and postsynaptic GABAergic signaling. Postsynaptic GABA response is determined by neuronal intracellular chloride state, largely regulated by the KCC2 chloride transporter, which is significantly downregulated in the peritumoral region. Recent studies in our group using our diffusely infiltrating glioma mouse model have implicated glioma-induced mTOR activation as a mechanism underlying local neuronal hyperexcitability and GABAergic dysfunction. Using this model, we hypothesize that neuronal chloride regulation in the tumor region is mTOR-dependent. We show via gene set enrichment that KCC2 is downregulated in excitatory neurons in the peritumoral region, and is recovered by mTOR inhibition, supporting this mechanistic link. We subsequently performed whole-cell patch-clamp electrophysiology on peritumoral excitatory neurons, demonstrating these neurons exhibit a depolarized resting membrane potential (RMP) and GABA reversal potential. Importantly, inhibiting mTOR signaling restores a hyperpolarized RMP and GABA reversal potential, normalizing these glioma-induced effects. We are translating these findings to surgically excised human peritumoral cortical tissue from patients undergoing resection for high grade glioma. Acute slices are treated ex vivo, and electrophysiologic recordings are performed via microelectrode array. Immunohistochemical (IHC) analysis after 6 hours of treatment with an mTOR inhibitor shows a significant reduction in neuronal mTOR activation and an increase in KCC2 expression. We then correlate these IHC findings to local field potential, multi-unit activity, and single unit neuronal activity isolated from electrophysiologic multi-electrode array recordings of tissue under different treatment conditions. Our findings reveal a mechanistic link between glioma-induced alterations in neuronal mTOR signaling and neuronal inhibitory dysfunction in both mouse and human glioma and point the way toward therapeutic strategies for treating pharmacoresistant glioma-associated epilepsy.