Abstracts

This is a Late Breaking abstract

Rationale: Seizures, neural hyperexcitability and other comorbidities, such as cognitive impairment, are frequent presenting symptoms of glioma. They can persist even after successful tumor resection, herald tumor recurrence, and show high rates of pharmacoresistance. Recently, different types and combinations of AEDs have increasingly been studied. However, the timing and individual response characteristics to AEDs is highly heterogeneous in the patient population. Glioma exploits the complex interplay between neurons and glia to create a microenvironment favorable for its own expansion, and several lines of evidence have implicated mechanisms linking neuronal signaling and glioma proliferation, such as neosynaptogenesis, reduced GABAergic inhibition, and excess peritumoral glutamate. Most reported studies have used in vitro preparations or tumor cell xenografts in immunocompromised animals. Therefore, more comprehensive, longitudinal in vivo models are needed to understand the progression of the reciprocal feedback between hyperexcitability and tumor growth.

Methods: We established a novel CRISPR-Cas9 in-utero electroporation system to induce two distinct GBM tumor models in immunocompetent mice in combination with prolonged EEG recording and widefield and 2-photon imaging of calcium and glutamate reporters to analyze dynamic changes in peritumoral cortical network activity at different spatial and temporal scales. We imaged bilateral cortical windows over 6-18 weeks per animal and analyzed changes in calcium and glutamate dynamics as well as tumor growth on various spatial and temporal scales (Figure 1).

Results: We find a biphasic elevation in neuronal calcium activity followed by a partially overlapping accumulation of peritumoral glutamate during tumor growth, indicating these processes are not entirely coordinated (Figure 2A-E). The patterns are strongly influenced by tumor genetics. Tumor growth rates were highly nonlinear over time, and when they exceeded 10e5 µm2/day, the amplitude of calcium events extracted from widefield recordings was significantly higher near the tumor core than >1 mm from the tumor margin (Figure 2F). These changes were accompanied by increased EEG spiking and gradual emergence of seizures. Furthermore, the global changes in excitability homeostasis alter the higher order modularity and connectivity patterns of local and remote neuronal populations and can transform inter-areal brain information processing over time.

Conclusions: Despite considerable efforts, advances in both survival rates and seizure control have been poor for several decades. We found a nonlinear relationship between hyperexcitability, glutamate accumulation and tumor growth, indicating that high-precision therapeutic approaches, engineered for the specific genetic makeup of the tumor, are needed. The ability to analyze chronic, nonlinear changes in multiple aspects of cortical activity at different temporal and spatial scales, while monitoring tumor progression, underscores the power of this novel technique that is expected to be of significant value in studying a variety of rodent models of neurological disorders.

Funding: Supported by NCI R01CA223388 (JLN, BD) and Blue Bird Circle Foundation (JLN)