Validation of a Preclinical Drug Screening Platform for Pharmacoresistant Epilepsy

Abstract

The successful identification of promising investigational therapies for the treatment of epilepsy can be credited to the use of numerous animal models of seizure and epilepsy for over 80 years. In this time, the maximal electroshock test in mice and rats, the subcutaneous pentylenetetrazol test in mice and rats, and more recently the 6 Hz assay in mice, have been utilized as primary models of electrically or chemically-evoked seizures in neurologically intact rodents. In addition, rodent kindling models, in which chronic network hyperexcitability has developed, have been used to identify new agents. It is clear that this traditional screening approach has greatly expanded the number of marketed drugs available to manage the symptomatic seizures associated with epilepsy. In spite of the numerous antiseizure drugs (ASDs) on the market today, the fact remains that nearly 30% of patients are resistant to these currently available medications. To address this unmet medical need, the National Institute of Neurological Disorders and Stroke (NINDS) Epilepsy Therapy Screening Program (ETSP) revised its approach to the early evaluation of investigational agents for the treatment of epilepsy in 2015 to include a focus on preclinical approaches to model pharmacoresistant seizures. This present report highlights the in vivo and in vitro findings associated with the initial pharmacological validation of this testing approach using a number of mechanistically diverse, commercially available antiseizure drugs, as well as several probe compounds that are of potential mechanistic interest to the clinical management of epilepsy.

A companion to the preclinical common data elements for pharmacologic studies in animal models of seizures and epilepsy. A Report of the TASK3 Pharmacology Working Group of the ILAE/AES Joint Translational Task Force

“…Group sizes should be appropriately powered, that is, 8 animals per group gives 80% power at 95% significance to detect a difference between the groups that is 1.5‐fold greater than the determined standard deviation. In our experience, 5–6 groups (n = 8/group) is sufficient to accurately calculate an ED 50 (or TD 50 /LD 50 ) with 95% confidence intervals within the dose range tested. Wherever possible, pharmacokinetic information (e.g., plasma concentrations of API) should be correlated to pharmacodynamic endpoints (e.g., protection from seizures) as well.…”

“…In designing the CDEs and CRFs for pharmacologic studies for epilepsy, this Task Force focused on minimizing the overall burden on researchers who want to use CDEs while still promoting rigor and reproducibility. Herein, we outline the characteristics and components of sound pharmacologic research that are based, in a large part, on the success of the NINDS‐sponsored ETSP . For investigators wishing to evaluate investigational agents or pursue pharmacologic studies for specific patient populations, we encourage the implementation of these CRFs and CDEs with adjustments for the specific model at hand.…”

“…Conversely, sodium channel blockers, such as phenytoin, are ineffective in the 6 Hz assay at doses that do not produce overt motor impairments (e.g., protective index [PI; the ratio of TD 50 /ED 50 ] is less than 1.5), thereby suggesting that the 6 Hz assay may be a pharmacoresistant model for some categories of ASDs, such as sodium channel modulators . The 6 Hz test thus now serves as a primary screening platform in the NINDS ETSP and is frequently used in the discovery of ASDs . Moreover, the 6 Hz assay may identify compounds with potentially novel mechanisms of action for the treatment of focal seizures in humans, including anti‐inflammatory agents like minocycline, serotonin receptor agonists, and adenosine receptor agonists .…”

“…The 6 Hz test thus now serves as a primary screening platform in the NINDS ETSP and is frequently used in the discovery of ASDs . Moreover, the 6 Hz assay may identify compounds with potentially novel mechanisms of action for the treatment of focal seizures in humans, including anti‐inflammatory agents like minocycline, serotonin receptor agonists, and adenosine receptor agonists . Variations on the protocol of Barton and colleagues certainly exist; for example, Walrave and colleagues report seizure duration as a reliable outcome measure in the 6 Hz assay and provide an approach for target validation using intracerebroventricular (i.c.v.)…”

Evaluation of antiseizure drug efficacy and tolerability in the rat lamotrigine‐resistant amygdala kindling model

“…12,13 One of the major goals for the development of novel ASDs is to minimize or eliminate side effects at therapeutic doses. Moreover, initial tolerability data obtained in seizure-and drug-naïve young adult rats 18,19 may not be replicated in seizure-experienced (eg, fully kindled) rats. 16 Further, despite the availability of a variety of animal models to aid in predictions of efficacy, initial tolerability estimates are typically performed in drug-and seizure-naïve young adult animals.…”