Abstracts

Rationale: Uncontrolled seizures in patients with low grade gliomas have a significant impact on quality of life and morbidity, yet the mechanisms through which these tumors cause seizures remain unknown. Albeit there are multiple features that contribute to tumor related epileptogenesis, IDH mutations are determined to be an independent factor, although the pathogenesis remains poorly understood. Here, we hypothesize that the active metabolite D-2-hydroxyglutarate (D-2-HG) produced by the IDH-mutant enzyme leads to metabolic disruptions in surrounding cortical neurons that consequently promote seizures.

Methods: We use a complementary study of in vitro cortical cultures and electrographically sorted human cortical tissue from patients (n=5) with IDH-mutant gliomas to test this hypothesis. We developed an in vitro model consisting of a microelectrode array (MEA) plated with rat cortical neurons, which allowed us to record their electrical activity. Using transwell inserts, we created a brain-tumor microenvironment that allowed communication between neurons and wild-type (IDH^wt) or IDH^R132H murine glioma cells. Finally, we treated the neurons with D-2-HG directly in addition to mTOR inhibitors to further elucidate the epileptogenic mechanism. Electrographically sorted human brain tissue from five patients with WHO grade II-III IDH mutant gliomas with seizures underwent subdural electrode placement were analyzed with immunofluorescence and metabolomic analyses.

Results: We demonstrate that IDH^R132H glioma cells and D-2-HG leads to increased neuronal spiking activity (p < 0.0001) relative to IDH^WT and control, respectively. Furthermore, D-2-HG promotes a distinct metabolic profile in surrounding neurons and upregulation of mTOR signaling (p < 0.0001), which is consistent in human epileptic cortex compared to peritumoral nonepileptic cortex. Furthermore, increases in neuronal activity are induced by mTOR activation and reversed with mTOR inhibition.