Abstracts

Rationale: Despite advances in the treatment of epilepsy, a substantial patient population remains refractory to existing anti-seizure drugs (ASDs). The Anticonvulsant Drug Development (ADD) Program at the University of Utah, under the direction of the Epilepsy Therapy Screening Program (ETSP) at NINDS, aims to facilitate the discovery and development of novel ASDs that hold the promise of eliminating seizures in this pharacoresistant population. Thus, assays that model pharmacoresistant seizures are needed to identify promising new compounds. One approach is to evaluate compounds for their ability to eliminate the spontaneous electrographic bursting observed in the medial entorhinal cortex (mEC) of brain slices obtained from rats who have experienced kainic acid (KA)-induced status epilepticus. However, typical methods that record from single brain slices are time-consuming, and thus, a comprehensive evaluation of pharmacoresistance in this assay to ASDs from multiple classes is lacking. To remedy these deficits, this study evaluated a broad representation of ASDs for their abilities to eliminate spontaneous bursting in this model and improved throughput by recording from 8-10 brain slices simultaneously. Methods: Male Sprague Dawley rats were given multiple systemic injections of low-dose KA and allowed to develop stage 4-5 seizures. Fourteen to 21 days later, horizontal brain slices containing the mEC and the hippocampus were made. Slices were transferred to the recording chambers of the 8-channel Scientifica Slicemaster where they were perfused with artificial cerebral spinal fluid supplemented with 10M glycine, 6 mM KCl, and 0.1 mM MgSO4. Field excitatory postsynaptic potentials were recorded from layer II of the mEC. After 20 minutes of baseline recording of spontaneous seizure-like burst activity, compounds were applied via bath exchange for 20 minutes. Results: Although phenytoin, carbamazepine, lamotrigine, lacosamide, ezogabine, clobazam, midazolam, phenobarbital, tiagabine, vigabatrin, and topiramate significantly attenuated spontaneous electrographic bursts in this model, these compounds (with the exception of carbamazepine) did so only at concentrations between 2-200 times the effective plasma concentrations reported in rats and/or humans. Furthermore, ethosuximide, gabapentin, levetiracetam, valproic acid, and felbamate failed to affect spontaneous bursts at any concentration tested. Conclusions: Established ASDs tested in this model exhibited varying efficacies and potencies. Generally, ASDs that target voltage-gated ion channels had the greatest efficacy but only at concentrations well above their reported effective plasma concentrations. This model's profile is therefore consistent with accepted definitions of pharmacoresistance and may be useful for the early identification of compounds effective against pharmacoresistant seizures. Funding: NINDS, HHSN271201100029C