Abstracts

Rationale: E2730, a novel un-competitive inhibitor of GABA transporter-1 (GAT-1), strongly suppresses spontaneous epileptic seizures with 2/3 animals becoming seizure free in a rat model of chronic drug resistant mesial temporal lobe epilepsy (MTLE), i.e. in the post-kainic acid status epilepticus (KASE) model (Ali et al., AES 2021, abstract#V.063). In this study, we tested the effects of E2730 on a variety of in-vivo measures of GABA function to establish their relationship to seizure suppression by E2730._x000D_
Methods: Nine weeks after KASE, rats (n=11) were randomly assigned to E2730 (100 mg/kg/day) or vehicle treatment for one week each (first treatment), and the treatment was then repeated during the second treatment (Figure 1). Treatment 1 examined the effect of E2730 (vs. vehicle) on in-vivo imaging biomarkers with [18F]Flumazenil positron emission tomography (PET) for GABA_A receptor, and 9.4T magnetic resonance spectroscopy (MRS) for measuring GABA and other brain metabolites. Treatment 2 examined the effects of E2730 on functional biomarkers, i.e., power of gamma frequency in EEG, transmagnetic stimulation (TMS) mediated motor activity, and continuous video-EEG to assess epileptic seizures.

Results: E2730 significantly reduced epileptic seizures (p< 0.001) with 8 of 11 animals becoming seizure free during E2730 vs 0 of 11 during the vehicle treatment (p=0.0004). GABA measured by MRS was significantly elevated (p=0.03) in the prefrontal cortex (PFC), with reduced (p< 0.001) taurine levels in hippocampus, striatum, and PFC during E2730 (vs. vehicle) treatment. In animals in which E2730 resulted in seizure freedom, [18F]flumazenil binding was significantly reduced (p< 0.05) and corresponded with reduced receptor affinity (KD) (p< 0.05), but an increase in receptor number (B_max) during E2730 (vs. vehicle) treatment. Following TMS of the cortex, a significant facilitation of short intracortical inhibition of motor responses were observed during E2730 (vs. vehicle) treatment, which is consistent with other anti-seizure medications (ASMs) in epilepsy patients. Lastly, the power of the gamma frequency in EEG was significantly reduced (p=0.001) in the hippocampus during E2730 (vs. vehicle) treatment. The ROC analysis of taurine levels in striatum (AUC=0.9, p=0.05) and B_max in hippocampus (AUC=0.90, p=0.052) during the vehicle treatment was predictive of the seizure freedom on E2730 treatment. The percent change in the power of gamma frequency band was also predictive of seizure freedom after E2730 (AUC=0.91, p=0.04).

Conclusions: Continuous infusion of E2730 by osmotic pump resulted in a marked, suppression of epileptic seizures in post-KASE rats, indicating strong promise that this will be an effective ASM for patients with chronic MTLE. Clinically translatable multimodality imaging and functional biomarkers of GABAergic activity show relevant changes with E2730 treatment that could represent predictive biomarkers for E2730 treatment responses._x000D_
Funding: This work was a research collaboration between Eisai and Monash University.