Carbamazepine, but not valproate, displays pharmacoresistance in lamotrigine-resistant amygdala kindled rats

Innovative drug discovery strategies in epilepsy: integrating next-generation syndrome-specific mouse models to address pharmacoresistance and epileptogenesis

INTRODUCTION

Although there are numerous treatment options already available for epilepsy, over 30% of patients remain resistant to these antiseizure medications (ASMs). Historically, ASM discovery has relied on the demonstration of efficacy through the use of 'traditional' acute in vivo seizure models (e.g. maximal electroshock, subcutaneous pentylenetetrazol, and kindling). However, advances in genetic sequencing technologies and remaining medical needs for people with treatment-resistant epilepsy or special patient populations have encouraged recent efforts to identify novel compounds in syndrome-specific models of epilepsy. Syndrome-specific models, including Scn1a variant models of Dravet syndrome and APP/PS1 mice associated with familial early-onset Alzheimer's disease, have already led to the discovery of two mechanistically novel treatments for developmental and epileptic encephalopathies (DEEs), namely cannabidiol and soticlestat, respectively.

AREAS COVERED

In this review, the authors discuss how it is likely that next-generation drug discovery efforts for epilepsy will more comprehensively integrate syndrome-specific epilepsy models into early drug discovery providing the reader with their expert perspectives.

EXPERT OPINION

The percentage of patients with pharmacoresistant epilepsy has remained unchanged despite over 30 marketed ASMs. Consequently, there is a high unmet need to reinvent and revise discovery strategies to more effectively address the remaining needs of patients with specific epilepsy syndromes, including drug-resistant epilepsy and DEEs.

Identification of New Antiseizure Medication Candidates in Preclinical Animal Studies

Epilepsy is a multifactorial neurologic disease that often leads to many devastating disabilities and an enormous burden on the healthcare system. Until now, drug-resistant epilepsy has presented a major challenge for approximately 30% of the epileptic population. The present article summarizes the validated rodent models of seizures employed in pharmacological researches and comprehensively reviews updated advances of novel antiseizure candidates in the preclinical phase. Newly discovered compounds that demonstrate antiseizure efficacy in preclinical trials will be discussed in the review. It is inspiring that several candidates exert promising antiseizure activities in drug-resistant seizure models. The representative compounds consist of derivatives of hybrid compounds that integrate multiple approved antiseizure medications, novel positive allosteric modulators targeting subtype-selective γ-Aminobutyric acid type A receptors, and a derivative of cinnamamide. Although the precise molecular mechanism, pharmacokinetic properties, and safety are not yet fully clear in every novel antiseizure candidate, the adapted approaches to design novel antiseizure medications provide new insights to overcome drug-resistant epilepsy.

Animal Models of Drug-Resistant Epilepsy as Tools for Deciphering the Cellular and Molecular Mechanisms of Pharmacoresistance and Discovering More Effective Treatments

In the last 30 years, over 20 new anti-seizure medicines (ASMs) have been introduced into the market for the treatment of epilepsy using well-established preclinical seizure and epilepsy models. Despite this success, approximately 20-30% of patients with epilepsy have drug-resistant epilepsy (DRE). The current approach to ASM discovery for DRE relies largely on drug testing in various preclinical model systems that display varying degrees of ASM drug resistance. In recent years, attempts have been made to include more etiologically relevant models in the preclinical evaluation of a new investigational drug. Such models have played an important role in advancing a greater understanding of DRE at a mechanistic level and for hypothesis testing as new experimental evidence becomes available. This review provides a critical discussion of the pharmacology of models of adult focal epilepsy that allow for the selection of ASM responders and nonresponders and those models that display a pharmacoresistance per se to two or more ASMs. In addition, the pharmacology of animal models of major genetic epilepsies is discussed. Importantly, in addition to testing chemical compounds, several of the models discussed here can be used to evaluate other potential therapies for epilepsy such as neurostimulation, dietary treatments, gene therapy, or cell transplantation. This review also discusses the challenges associated with identifying novel therapies in the absence of a greater understanding of the mechanisms that contribute to DRE. Finally, this review discusses the lessons learned from the profile of the recently approved highly efficacious and broad-spectrum ASM cenobamate.

miR-9a-5p expression is decreased in the hippocampus of rats resistant to lamotrigine: A behavioural, molecular and bioinformatics assessment

The major obstacle in developing new treatment strategies for refractory epilepsy is the complexity and poor understanding of its mechanisms. Utilizing the model of lamotrigine-resistant seizures, we evaluated whether changes in the expression of sodium channel subunits are responsible for the diminished responsiveness to lamotrigine (LTG) and if miRNAs, may also be associated. Male rats were administered LTG (5 mg/kg) before each stimulation during kindling acquisition. Challenge stimulation following LTG exposure (30 mg/kg) was performed to confirm resistance in fully kindled rats. RT-PCR was used to measure the mRNA levels of sodium channel subunits (SCN1A, SCN2A, and SCN3A) and miRNAs (miR-155-5p, miR-30b-5p, miR-137-3p, miR-342-5p, miR-301a-3p, miR-212-3p, miR-9a-5p, and miR-133a-3p). Western blot analysis was utilized to measure Nav1.2 protein, and bioinformatics tools were used to perform target prediction and enrichment analysis for miR-9a-5p, the only affected miRNA according to the responsiveness to LTG. Amygdala kindling seizures downregulated Nav1.2, miR-137-3p, miR-342-5p, miR-155-5p, and miR-9a-5p as well as upregulated miR-212-3p. miR-9a-5p was the only molecule decreased in rats resistant to LTG. The bioinformatic assessment and disease enrichment analysis revealed that miR-9a-5p targets expressed with high confidence in the hippocampus are the most significantly associated with epilepsy. Due to the miR-9a-5p dysregulation, major pathways affected are neurotrophic processes, neurotransmission, inflammatory response, cell proliferation and apoptosis. Interaction network analysis identified LTG target SCN2A as interacting with highest number of genes regulated by miR-9-5p. Further studies are needed to propose specific genes and miRNAs responsible for diminished responsiveness to LTG. miR-9a-5p targets, like KCNA4, KCNA2, CACNB2, SCN4B, KCNC1, should receive special attention in them.

Frontline Sodium Channel-Blocking Antiseizure Medicine Use Promotes Future Onset of Drug-Resistant Chronic Seizures

The mechanisms of treatment-resistant epilepsy remain unclear. We have previously shown that frontline administration of therapeutic doses of lamotrigine (LTG), which preferentially inhibits the fast-inactivation state of sodium channels, during corneal kindling of mice promotes cross-resistance to several other antiseizure medicines (ASMs). However, whether this phenomenon extends to monotherapy with ASMs that stabilize the slow inactivation state of sodium channels is unknown. Therefore, this study assessed whether lacosamide (LCM) monotherapy during corneal kindling would promote future development of drug-resistant focal seizures in mice. Male CF-1 mice (n = 40/group; 18-25 g) were administered an anticonvulsant dose of LCM (4.5 mg/kg, i.p.), LTG (8.5 mg/kg, i.p.), or vehicle (0.5% methylcellulose) twice daily for two weeks during kindling. A subset of mice (n = 10/group) were euthanized one day after kindling for immunohistochemical assessment of astrogliosis, neurogenesis, and neuropathology. The dose-related antiseizure efficacy of distinct ASMs, including LTG, LCM, carbamazepine, levetiracetam, gabapentin, perampanel, valproic acid, phenobarbital, and topiramate, was then assessed in the remaining kindled mice. Neither LCM nor LTG administration prevented kindling: 29/39 vehicle-exposed mice were kindled; 33/40 LTG-exposed mice were kindled; and 31/40 LCM-exposed mice were kindled. Mice administered LCM or LTG during kindling became resistant to escalating doses of LCM, LTG, and carbamazepine. Perampanel, valproic acid, and phenobarbital were less potent in LTG- and LCM-kindled mice, whereas levetiracetam and gabapentin retained equivalent potency across groups. Notable differences in reactive gliosis and neurogenesis were also appreciated. This study indicates that early, repeated administration of sodium channel-blocking ASMs, regardless of inactivation state preference, promotes pharmacoresistant chronic seizures. Inappropriate ASM monotherapy in newly diagnosed epilepsy may thus be one driver of future drug resistance, with resistance being highly ASM class specific.

Translational Considerations in the Development of Intranasal Treatments for Epilepsy

Epilepsy is a common and serious neurological disorder, to which a high proportion of patients continue to be considered "drug-resistant", despite the availability of a host of anti-seizure drugs. Investigation into new treatment strategies is therefore of great importance. One such strategy is the use of the nose to deliver drugs directly to the brain with the help of pharmaceutical formulation to overcome the physical challenges presented by this route. The following review explores intranasal delivery of anti-seizure drugs, covering the link between the nose and seizures, pathways from the nose to the brain, current formulations in clinical use, animal seizure models and their proposed application in studying intranasal treatments, and a critical discussion of relevant pre-clinical studies in the literature.

Pentylenetetrazole kindling-induced epilepsy rat models: Insight on the severity state, a comparative study

This study aimed to carry out a comparative study of the main models of chronic epilepsy induced by pentylenetetrazole (PTZ)-kindling method and to assess the efficacy of sodium valproate, one of the main antiepileptics, on the best epilepsy-inducing kindling model. Two sets of 24 animals were divided into 4 groups of 6 animals and treated as follow: Set 1 included: group 1, control; group 2, the classic kindling PTZ group (UKEOD); group 3, PTZ kindling every other day group with challenge (CKEOD); group 4, PTZ kindling every day group, with challenge (CKED); Set 2 included: group 1, control; group 2, CKEOD group; group 3 and 4, receiving either valproate 200 mg/kg or valproate 300 mg/kg + CKEOD procedure. Results show that CKEOD group significantly reduced the number of injections necessary to reach the fully-kindled state, increased the severity of seizures and improved the stability of seizures. In addition, the CKEOD group significantly increased the level of malondialdehyde and GABA transaminase, reduced the level of reduced glutathione, catalase and GABA. Furthermore, it had no impact on plasma levels of alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT). Valproate 300 mg/kg significantly protected animals against kindling induced by CKEOD. The kindling model with a challenge dose administered on day 1 (CKEOD) thus allows to induce more severe, more stable chronic epilepsy and in a shorter period of time, and could thus contribute to a better understanding of epilepsy, as well as its uses in drug discovery.

Eslicarbazepine, but Not Lamotrigine or Ranolazine, Shows Anticonvulsant Efficacy in Carbamazepine-Resistant Rats Developed by Window-Pentylenetetrazole Kindling

Approximately 30% of epileptic patients develop Drug-Resistant Epilepsy. Based on evidence that shows a loss of efficacy in some sodium channel blocker antiseizure drugs in epilepsy, we focus our study on assessing the anticonvulsant efficacy of different sodium channel blockers on carbamazepine (CBZ)-resistant seizures generated using the window-pentylenetetrazole (PTZ) kindling model to verify whether one of these drugs presents some anticonvulsant effect that could have potential therapeutic use. Wistar rats were treated with a subthreshold dose of PTZ (35 mg/kg) three times/week. Fully kindled rats were then treated with a single dose of CBZ (40 mg/kg i.p.) at 2, 9 and 16 days after their last kindling stimulation to obtain CBZ-resistant rats. Right after, sodium channel blockers were tested for anticonvulsant action (lamotrigine, 30 mg/kg i.p.; eslicarbazepine, 150 or 300 mg/kg i.p.; ranolazine, 10, 20 or 40 mg/kg i.p.). Behavioral parameters included severity, latency or duration of convulsions. Our data showed for the first time directly that eslicarbazepine does have an anticonvulsant effect over CBZ-resistant seizures, while lamotrigine shows drug resistance and ranolazine demonstrates severe seizure worsening. It is of potential therapeutic relevance that eslicarbazepine could be useful to control seizures resistant to common sodium channel blockers such as CBZ.

Antiseizure medication discovery: Recent and future paradigm shifts

Despite the ever-increasing number of available options for the treatment of epilepsies and the remarkable advances on the understanding of their pathophysiology, the proportion of refractory patients has remained approximately unmodified during the last 100 years. How efficient are we translating positive outcomes from basic research to clinical trials and/or the clinical scenario? It is possible that fresh thinking and exploration of new paradigms is required to arrive at truly novel therapeutic solutions, as seemingly proven by recently approved first-in-class antiseizure medications and drug candidates undergoing late clinical trials. Here, the author discusses some approximations in line with the network pharmacology philosophy, which may result in highly innovative (and, hopefully, safer and/or more efficacious) medications for the control of seizures, as embodied with some recent examples in the field, namely tailored multi-target agents and low-affinity ligands.

New advances in pharmacoresistant epilepsy towards precise management-from prognosis to treatments

Epilepsy, one of the most severe neurological diseases, is characterized by abrupt recurrent seizures. Despite great progress in the development of antiseizure drugs (ASDs) based on diverse molecular targets, more than one third of epilepsy patients still show resistance to ASDs, a condition termed pharmacoresistant epilepsy. The management of pharmacoresistant epilepsy involves serious challenges. In the past decade, promising advances have been made in the use of interdisciplinary techniques involving biophysics, bioinformatics, biomaterials and biochemistry, which allow more precise prognosis and development of drug target for pharmacoresistant epilepsy. Notably, novel experimental tools such as viral vector gene delivery, optogenetics and chemogenetics have provided a framework for promising approaches to the precise treatment of pharmacoresistant epilepsy. In this review, historical achievements especially recent advances of the past decade in the prognosis and treatment of pharmacoresistant epilepsy from both clinical and laboratory settings are presented and summarized. We propose that the further development of novel experimental tools at cellular or molecular levels with both temporal and spatial precision are necessary to make improve the management and drug development for pharmacoresistant epilepsy in the clinical arena.

PTZ kindling model for epileptogenesis, refractory epilepsy, and associated comorbidities: relevance and reliability

Pentylenetetrazole (PTZ)-induced seizure is one of the gold standard mouse models for rapid evaluation of novel anticonvulsants. Synchronically, PTZ induced kindling in mice is also a simple and well accepted model of chronic epilepsy. PTZ kindling has been explored for studying epileptogenesis, epilepsy-associated comorbidities, and refractory epilepsy. This review summarizes the potential of PTZ kindling in mice and its modifications for its face, construct, and predictive validity to screen antiepileptogenic drugs, combined or add on novel and safe therapies for treatment of epilepsy-associated depression and cognitive impairment as well as effective interventions for pharmacoresistant epilepsy.

Long-term music adjuvant therapy enhances the efficacy of sub-dose antiepileptic drugs in temporal lobe epilepsy

Aims

Noninvasive music adjuvant therapy shows great potential in improving seizure control when combined with routine antiepileptic drugs. However, the diversity of previous music protocols has resulted in disparate outcomes. The optimized protocol and features for music adjuvant therapy are still not fully understood which limits its feasibility.

Methods

By applying different regimens of music therapy in various temporal lobe epilepsy models, we evaluated the effect of music in combination with sub‐dose drugs on epileptic seizures to determine the optimized protocol.

Results

A subgroup of kindled mice that were responsive to music adjuvant therapy was screened. In those mice, sub‐dose drugs which were noneffective on kindled seizures, alleviated seizure severity after 12 h/day Mozart K.448 for 14 days. Shorter durations of music therapy (2 and 6 h/day) were ineffective. Furthermore, only full‐length Mozart K.448, not its episodes or other music varieties, was capable of enhancing the efficacy of sub‐dose drugs. This music therapeutic effect was not due to increasing cerebral drug concentration, but instead was related with the modulation of seizure electroencephalogram (EEG) spectral powers in the hippocampus.

Conclusion

These results indicate that long‐term full‐length Mozart K.448 could enhance the anti‐seizure efficacy of sub‐dose drugs and may be a promising noninvasive adjuvant therapy for temporal lobe epilepsy.

Developing precision treatments for epilepsy using patient and animal models

Introduction: Phenytoin was the first antiepileptic drug (AED) discovered in an animal model of seizures whose clinical efficacy was subsequently confirmed. This clearly indicated that a search for other AEDs had to consider animal studies.Areas covered: Main seizure tests used for the evaluation of possible anticonvulsive activity of potential anticonvulsants and their predictive values have been reviewed. Procedures used for the estimation of antiepileptogenic effects have been also included.Expert opinion: First-line seizure models comprise maximal electroshock (MES)-, pentylenetetrazol (PTZ)- and kindling-induced convulsions in rodents. The MES test may be considered as a convenient and easy model of generalized tonic-clonic seizures, PTZ test - as a model of generalized myoclonic seizures and to a certain degree - absence seizures. Kindled seizures (for example, from amygdala) may be regarded as a model of focal seizures. Some tests have been suggested for the search of AEDs effective in drug-resistant seizures - for instance, 6 Hz (44 mA) test or intrahippocampal kainate model of mesial temporal lobe epilepsy. There are also recommendations from experimental epileptology on synergistic AED combinations for patients with drug-resistant seizures. The clinical evidence on this issue is scarce and favors a combined treatment with valproate + lamotrigine.

Antiseizure drug efficacy and tolerability in established and novel drug discovery seizure models in outbred vs inbred mice

OBJECTIVE

Initial identification of new investigational drugs for the treatment of epilepsy is commonly conducted in well-established mouse acute and chronic seizure models: for example, maximal electroshock (MES), 6 Hz, and corneal kindling. Comparison of the median effective dose (ED50) of approved antiseizure drugs (ASDs) vs investigational agents in these models provides evidence of their potential for clinical efficacy. Inbred and outbred mouse strains exhibit differential seizure susceptibility. However, few comparisons exist of the ED50 or median behaviorally impairing dose (TD50) of prototype ASDs in these models in inbred C57Bl/6 vs outbred CF-1 mice, both of which are often used for ASD discovery.

METHODS

We defined the strain-related ED50s and TD50s of several mechanistically distinct ASDs across established acute seizure models (MES, 6 Hz, and corneal-kindled mouse). We further quantified the strain-related effect of the MES ED50 of each ASD on gross behavior in a locomotor activity assay. Finally, we describe a novel pharmacoresistant corneal-kindling protocol that is suitable for moderate-throughput ASD screening and demonstrates highly differentiated ASD sensitivity.

RESULTS

We report significant strain-related differences in the MES ED50 of valproic acid (CF-1 ED50: 90 mg/kg [95% confidence interval (CI) 165-214] vs C57Bl/6: 276 mg/kg [226-366]), as well as significant differences in the ED50 of levetiracetam in the pharmacoresistant 6 Hz test (CF-1: 22.5 mg/kg [14.7-30.2] vs C57Bl/6: >500 mg/kg [CI not defined]). There were no differences in the calculated TD50 of these ASDs between strains. Furthermore, the MES ED50 of phenobarbital significantly enhanced locomotor activity of outbred CF-1, but not C57Bl/6, mice.

SIGNIFICANCE

Altogether, this study provides strain-related information to differentiate investigational agents from ASD standards-of-care in commonly employed preclinical discovery models and describes a novel kindled seizure model to further explore the mechanisms of drug-resistant epilepsy.

Evaluation of subchronic administration of antiseizure drugs in spontaneously seizing rats

OBJECTIVE

Approximately 30% of patients with epilepsy do not experience full seizure control on their antiseizure drug (ASD) regimen. Historically, screening for novel ASDs has relied on evaluating efficacy following a single administration of a test compound in either acute electrical or chemical seizure induction. However, the use of animal models of spontaneous seizures and repeated administration of test compounds may better differentiate novel compounds. Therefore, this approach has been instituted as part of the National Institute of Neurological Disorders and Stroke Epilepsy Therapy Screening Program screening paradigm for pharmacoresistant epilepsy.

METHODS

Rats were treated with intraperitoneal kainic acid to induce status epilepticus and subsequent spontaneous recurrent seizures. After 12 weeks, rats were enrolled in drug screening studies. Using a 2-week crossover design, selected ASDs were evaluated for their ability to protect against spontaneous seizures, using a video-electroencephalographic monitoring system and automated seizure detection. Sixteen clinically available compounds were administered at maximally tolerated doses in this model. Dose intervals (1-3 treatments/d) were selected based on known half-lives for each compound.

RESULTS

Carbamazepine (90 mg/kg/d), phenobarbital (30 mg/kg/d), and ezogabine (15 mg/kg/d) significantly reduced seizure burden at the doses evaluated. In addition, a dose-response study of topiramate (20-600 mg/kg/d) demonstrated that this compound reduced seizure burden at both therapeutic and supratherapeutic doses. However, none of the 16 ASDs conferred complete seizure freedom during the testing period at the doses tested.

SIGNIFICANCE

Despite reductions in seizure burden, the lack of full seizure freedom for any ASD tested suggests that this screening paradigm may be useful for testing novel compounds with potential utility in pharmacoresistant epilepsy.

The current approach of the Epilepsy Therapy Screening Program contract site for identifying improved therapies for the treatment of pharmacoresistant seizures in epilepsy

The Epilepsy Therapy Screening Program (ETSP), formerly known as the Anticonvulsant Screening Program (ASP), has played an important role in the preclinical evaluation of many of the antiseizure drugs (ASDs) that have been approved by the FDA and thus made available for the treatment of seizures. Recent changes to the animal models used at the contract site of the ETSP at the University of Utah have been implemented in an attempt to better model the unmet clinical needs of people with pharmacoresistant epilepsy and thus identify improved therapies. In this review, we describe the changes that have occurred over the last several years in the screening approach used at the contract site and, in particular, detail the pharmacology associated with several of the animal models and assays that are either new to the program or have been recently characterized in more depth. There is optimism that the refined approach used by the ETSP contract site, wherein etiologically relevant models that include those with spontaneous seizures are used, will identify novel, potentially disease modifying therapies for people with pharmacoresistant epilepsy and those at risk for developing epilepsy. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Structure-activity relationship and cardiac safety of 2-aryl-2-(pyridin-2-yl)acetamides as a new class of broad-spectrum anticonvulsants derived from Disopyramide

A series of 2-aryl-2-(pyridin-2-yl)acetamides were synthesized and screened for their anticonvulsant activity in animal models of epilepsy. The compounds were broadly active in the 'classical' maximal electroshock seizure (MES) and subcutaneous Metrazol (scMET) tests as well as in the 6 Hz and kindling models of pharmacoresistant seizures. Furthermore, the compounds showed good therapeutic indices between anticonvulsant activity and motor impairment. Structure-activity relationship (SAR) trends clearly showed the highest activity resides in unsubstituted phenyl derivatives or compounds having ortho- and meta- substituents on the phenyl ring. The 2-aryl-2-(pyridin-2-yl)acetamides were derived by redesign of the cardiotoxic sodium channel blocker Disopyramide (DISO). Our results show that the compounds preserve the capability of the parent compound to inhibit voltage gated sodium currents in patch-clamp experiments; however, in contrast to DISO, a representative compound from the series 1 displays high levels of cardiac safety in a panel of in vitro and in vivo experiments.

Valproic Acid and Epilepsy: From Molecular Mechanisms to Clinical Evidences

After more than a century from its discovery, valproic acid (VPA) still represents one of the most efficient antiepi-leptic drugs (AEDs). Pre and post-synaptic effects of VPA depend on a very broad spectrum of actions, including the regu-lation of ionic currents and the facilitation of GABAergic over glutamatergic transmission. As a result, VPA indirectly mod-ulates neurotransmitter release and strengthens the threshold for seizure activity. However, even though participating to the anticonvulsant action, such mechanisms seem to have minor impact on epileptogenesis. Nonetheless, VPA has been reported to exert anti-epileptogenic effects. Epigenetic mechanisms, including histone deacetylases (HDACs), BDNF and GDNF modulation are pivotal to orientate neurons toward a neuroprotective status and promote dendritic spines organization. From such broad spectrum of actions comes constantly enlarging indications for VPA. It represents a drug of choice in child and adult with epilepsy, with either general or focal seizures, and is a consistent and safe IV option in generalized convulsive sta-tus epilepticus. Moreover, since VPA modulates DNA transcription through HDACs, recent evidences point to its use as an anti-nociceptive in migraine prophylaxis, and, even more interestingly, as a positive modulator of chemotherapy in cancer treatment. Furthermore, VPA-induced neuroprotection is under investigation for benefit in stroke and traumatic brain injury. Hence, VPA has still got its place in epilepsy, and yet deserves attention for its use far beyond neurological diseases. In this review, we aim to highlight, with a translational intent, the molecular basis and the clinical indications of VPA.

Activation of adenosine receptors modulates the efflux transporters in brain capillaries and restores the anticonvulsant effect of carbamazepine in carbamazepine resistant rats developed by window-pentylenetetrazole kindling

Up-regulation of efflux transporters in brain capillaries may lead to the decreased therapeutic efficacy of antiepileptic drugs in patients with Drug Resistant Epilepsy. Adenosine receptor activation in brain capillaries can modulate blood-brain barrier permeability by decreasing the protein levels and function of efflux transporters. Therefore, we aimed to investigate whether the activation of adenosine receptors improves convulsions outcome in carbamazepine (CBZ) resistant animals and modulates the protein levels of efflux transporters (P-GP, MRP1, MRP2) in brain capillaries. We employed the window-pentylenetetrazol (PTZ) kindling model to develop CBZ resistant rats by CBZ administration during the post-kindling phase, and tested if these animals displayed subsequent resistance to other antiepileptic drugs. Crucially, we investigated if the administration of a broad-spectrum adenosine agonist (NECA) improves convulsions control in CBZ resistant rats. Of potential therapeutic relevance, in CBZ resistant rats NECA restored the anticonvulsant effect of CBZ. We also evaluated how the resistance to CBZ and the activation of adenosine receptors with NECA affect protein levels of efflux transporters in brain capillaries, as quantified by western blot. While CBZ resistance was associated with the up-regulation of both P-GP/MRP2 in brain capillaries, with the administration of NECA in CBZ resistant rats, we observed a decrease of P-GP and an increase of MRP2 levels, in brain capillaries. Since the activation of adenosine receptors improves the outcome of convulsions probably through the modulation of the efflux transporters protein levels in brain capillaries, adenosine agonists could be useful as an adjunct therapy for the control of Drug Resistant Epilepsy.

Repeated Intraperitoneal Administration of Low-Concentration Methylcellulose Leads to Systemic Histologic Lesions Without Loss of Preclinical Phenotype

Methylcellulose (MC; 0.5% concentration) is commonly used when evaluating investigational agents for efficacy in preclinical models of disease. When administered by the oral (PO) route, MC is considered a Food and Drug Administration "generally recognized as safe" compound. Yet, there is limited data pertaining to the tolerability and impact on model fidelity of repeated intraperitoneal administration of 0.5% MC. Chronic administration of high-concentration MC (2%-2.5%) has been used to induce anemia, splenomegaly, and lesions in multiple organ systems in several preclinical species. Histopathological findings from a diagnostic pathologic analysis of a single mouse from our laboratory with experimentally induced chronic seizures that had received repeated intraperitoneal administration of antiseizure drugs delivered in MC revealed similar widespread lesions. This study thus tested the hypothesis that chronic administration of intraperitoneal, but not PO, MC incites histologic lesions without effects on preclinical phenotype. Male CF-1 mice (n = 2-14/group) were randomized to receive either 6 weeks of twice weekly 0.5% MC or saline (intraperitoneal or PO) following induction of chronic seizures. Histology of a subset of mice revealed lesions in kidney, liver, mediastinal lymph nodes, mesentery, aorta, and choroid plexus only in intraperitoneal MC-treated mice (n = 7/7). Kindled mice that received MC PO (n = 5) or saline (intraperitoneal n = 6, PO n = 3) had no lesions. There were no effects of intraperitoneal MC treatment on body weight, appearance, seizure stability, or behavior. Nonetheless, our findings suggest that repeated intraperitoneal, but not PO, MC elicits systemic organ damage without impacting the model phenotype, which may confound interpretation of investigational drug-induced histologic lesions. SIGNIFICANCE STATEMENT: Methylcellulose (0.5% concentration) is commonly used when evaluating investigational agents for efficacy in preclinical models of disease. Herein, we demonstrate that repeated administration of 0.5% methylcellulose by the intraperitoneal, but not oral, route results in systemic inflammation and presence of foam-laden macrophages but does not impact the behavioral phenotype of a rodent model of neurological disease.

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

OBJECTIVE

The lamotrigine-resistant amygdala kindling model uses repeated administration of a low dose of lamotrigine during the kindling process to produce resistance to lamotrigine, which also extends to some other antiseizure drugs (ASDs). This model of pharmacoresistant epilepsy has been incorporated into the testing scheme utilized by the Epilepsy Therapy Screening Program (ETSP). Although some ASDs have been evaluated in this model, a comprehensive evaluation of ASD prototypes has not been reported.

METHODS

Following depth electrode implantation and recovery, rats were exposed to lamotrigine (5 mg/kg, i.p.) prior to each stimulation during the kindling development process (~3 weeks). A test dose of lamotrigine was used to confirm that fully kindled rats were lamotrigine-resistant. Efficacy (unambiguous protection against electrically elicited convulsive seizures) was defined as a Racine score < 3 in the absence of overt compound-induced side effects. Various ASDs, comprising several mechanistic classes, were administered to fully kindled, lamotrigine-resistant rats. Where possible, multiple doses of each drug were administered in order to obtain median effective dose (ED50) values.

RESULTS

Five sodium channel blockers tested (eslicarbazepine, lacosamide, lamotrigine, phenytoin, and rufinamide) were either not efficacious or effective only at doses that were not well-tolerated in this model. In contrast, compounds targeting either GABA receptors (clobazam, clonazepam, phenobarbital) or GABA-uptake proteins (tiagabine) produced dose-dependent efficacy against convulsive seizures. Compounds acting to modulate Ca2+ channels show differential activity: Ethosuximide was not effective, whereas gabapentin was moderately efficacious. Ezogabine and valproate were also highly effective, whereas topiramate and levetiracetam were not effective at the doses tested.

SIGNIFICANCE

These results strengthen the conclusion that the lamotrigine-resistant amygdala kindling model demonstrates pharmacoresistance to certain ASDs, including, but not limited to, sodium channel blockers, and supports the utility of the model for helping to identify compounds with potential efficacy against pharmacoresistant seizures.

Validated animal models for antiseizure drug (ASD) discovery: Advantages and potential pitfalls in ASD screening

Since 1993, over 20 new anti-seizure drugs (ASDs) have been identified in well-established animal seizure and epilepsy models and subsequently demonstrated to be clinically effective in double-blinded, placebo-controlled clinical trials in patients with focal onset seizures. All clinically-available ASDs on the market today are effective in at least one of only three preclinical seizure and epilepsy models: the acute maximal electroshock (MES), the acute subcutaneous pentylenetetrazol (scPTZ) test, or the kindled rodent with chronic evoked seizures. Thus, it reasons that preclinical ASD discovery does not need significant revision to successfully identify ASDs for the symptomatic treatment of epilepsy. Unfortunately, a significant need still persists for more efficacious and better tolerated ASDs. This is particularly true for those patients whose seizures remain drug resistant. This review will focus on the continued utility of the acute MES and scPTZ tests, as well as the kindled rodent for current and future ASD discovery. These are the only "clinically validated" rodent models to date and been heavily used in the search for novel and more efficacious ASDs. This is to say that promising ASDs have been brought to the clinic on the basis of efficacy in these particular seizure and epilepsy models alone. This review also discusses some of the inherent advantages and limitations of these models relative to existing and emerging preclinical models. It then offers insight into future efforts to develop a preclinical model that will advance a truly transformative therapy for the symptomatic treatment of difficult to treat focal onset epilepsy. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Serotonergic mechanisms in the 6-Hz psychomotor seizures in mice

Serotonin (5-hydroxytrytamine (5-HT)) plays an important role in experimental seizures. Recently, we reported the depletion of 5-HT by parachlorophynylalanine (PCPA) in whole brain to enhance 6-Hz psychomotor seizures in mice. In the present work, we investigated the effect of 5-HT depletion in cortex and hippocampus, brain regions relevant for epilepsy, on behavioral and ultra-structural changes following 6-Hz psychomotor seizures in mice. In addition, we studied the effect of sodium valproate (SVP) on behavioral, biochemical, and ultra-structural effects induced by 6 Hz. Behavioral changes induced by 6 Hz stimulation were characterized as the increased duration of Straub's tail, stun position, twitching of vibrissae, forelimb clonus, and increased rearing and grooming. PCPA administration further enhanced while SVP reduced these behaviors in mice. The 6-Hz psychomotor seizure induced ultra-structural changes in both cortex and hippocampus in mice treated with PCPA. Furthermore, PCPA administrations followed by 6Hz-induced seizures were accompanied by reduced hippocampal and cortical 5-HT. SVP attenuated the PCPA-induced ultra-structural changes and alterations of 5-HT content in the mouse brain. The study suggests the involvement of 5-HT in the 6 Hz psychomotor seizures and in the mechanisms of action of SVP against such seizures in mice.

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

Preclinical pharmacology studies in animal models of seizures and epilepsy have provided a platform to identify more than 20 antiseizure drugs in recent decades. To minimize variability in lab‐to‐lab studies and to harmonize approaches to data collection and reporting methodology in pharmacologic evaluations of the next generation of therapies, we present common data elements (CDEs), case report forms (CRFs), and this companion manuscript to help with the implementation of methods for studies in established preclinical seizure and epilepsy models in adult rodents. The development of and advocacy for CDEs in preclinical research has been encouraged previously by both clinical and preclinical groups. It is anticipated that adoption and implementation of these CDEs in preclinical studies may help standardize approaches to minimize variability and increase the reproducibility of preclinical studies. Moreover, they may provide a methodologic framework for pharmacology studies in atypical animal models or models in development, which may ultimately promote novel therapy development. In the present document, we refer selectively to animal models that have a long history of preclinical use, and in some cases, are clinically validated.

DSP-4 induced depletion of brain noradrenaline and increased 6-hertz psychomotor seizure susceptibility in mice is prevented by sodium valproate

The central neurotransmitters assume a noteworthy part in the pathophysiology of epilepsy, noradrenaline is one of them. However, its role in 6 Hz induced psychomotor seizures is not known. The present study was, therefore, designed to investigate the role of noradrenaline (NA) in 6 Hz-induced psychomotor seizures in Swiss albino mice using N-2-Chloroethyl-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4), a well-known depletor of NA. The vehicle and DSP-4 treated mice were given 6 Hz stimulation. A sham treatment was utilized as a comparator and sodium valproate (SVP) was utilized as a reference anti-epileptic medication. Behavioral changes instigated by 6 Hz stimulation were described as the increased duration of Straub's tail, stun position, twitching of vibrissae, forelimb clonus and increased rearing and grooming. DSP-4 administration further amplified the seizures and behavioral changes while pretreatment with SVP reduced the same in mice. Further, SVP pre-treatment also attenuated the ultra-structural changes observed in cortex and hippocampus of mice treated with DSP-4 and 6 Hz. Finally, the neurochemical estimation of NA in cortex and hippocampus confirmed the depletion of NA following DSP-4 and 6 Hz seizures. SVP pretreatment (but not post-treatment) protected the mice from 6 Hz seizures and attenuated the DSP-4 induced alterations of nor-adrenaline content in the mouse brain. The study indicates low brain NA content to enhance pharmacoresistant seizures in mice and demonstrates that SVP mediated protection against 6 Hz results possibly via modulation of NA content.

In vitro and in vivo experimental models employed in the discovery and development of antiepileptic drugs for pharmacoresistant epilepsy

Epilepsy is one of the most common chronic, recurrent and progressive neurological diseases. In spite of the large number of antiepileptic drugs currently available for the suppression of seizures, about one-third of patients develop drug-resistant epilepsy, even when they are administered the most appropriate treatment available. Thus, nonclinical models can be valuable tools for the elucidation of the mechanisms underlying the development of pharmacoresistance and also for the development of new therapeutic agents that may be promising therapeutic approaches for this unmet medical need. Up today, several epilepsy and seizure models have been developed, exhibiting similar physiopathological features of human drug-resistant epilepsy; moreover, pharmacological response to antiepileptic drugs clinically available tends to be similar in animal models and humans. Therefore, they should be more intensively used in the preclinical discovery and development of new candidates to antiepileptic drugs. Although useful, in vitro models cannot completely replicate the complexity of a living being and their potential for a systematic use in antiepileptic drug screening is limited. The whole-animal models are the most commonly employed and they can be classified as per se drug-resistant due to an inherent poor drug response or be based on the selection of subgroups of epileptic animals that respond or not to a specific antiepileptic drug. Although more expensive and time-consuming, the latter are chronic models of epilepsy that better exhibit the disease-associated alterations found in human epilepsy. Several antiepileptic drugs in development or already marketed have been already tested and shown to be effective in these models of drug-resistant epilepsy, constituting a new hope for the treatment of drug-resistant epilepsy. This review will provide epilepsy researchers with detailed information on the in vitro and in vivo nonclinical models of interest in drug-resistant epilepsy, which may enable a refined selection of most relevant models for understanding the mechanisms of the disease and developing novel antiepileptic drugs.

Lamotrigine-resistant corneal-kindled mice: A model of pharmacoresistant partial epilepsy for moderate-throughput drug discovery

OBJECTIVE

Despite numerous treatments for epilepsy, over 30% of patients remain resistant to available antiseizure drugs (ASDs). Thus, there is a strong need for more effective ASDs for these individuals. Early ASD discovery has historically relied on acute in vivo seizure models (maximal electroshock, subcutaneous pentylenetetrazol, 6 Hz), which lack the pathophysiology that defines chronic epilepsy. Etiologically relevant rodent models of pharmacoresistant epilepsy exist (eg, phenytoin (PHT)- and lamotrigine (LTG)-resistant amygdala-kindled rat and focal kainic acid mouse), but these models are resource- and labor-intensive and thus unsuitable for frontline ASD discovery.

METHODS

We adapted the LTG-resistant amygdala-kindled rat protocol to the 60 Hz corneal-kindled mouse (CKM) to develop a medium-throughput model of pharmacoresistant chronic seizures. Male CF-1 mice were administered either vehicle (VEH; 0.5% methylcellulose) or LTG (8.5 mg/kg, ip) 30 minutes prior to each twice-daily corneal stimulation until mice achieved kindling criterion. Prototype ASDs were then evaluated in fully kindled mice. Compounds with specific mechanisms of action of interest to epilepsy (fluoxetine, minocycline, and celecoxib) were also evaluated.

RESULTS

LTG did not modify kindling acquisition. A challenge dose of 17 mg/kg (ip) LTG did not block the secondarily generalized kindled seizure in LTG-kindled mice (mean seizure score [MSS] ± standard error of the mean: 5.67 ± 0.14), whereas VEH-treated mice were sensitive (MSS: 2.25 ± 0.30); confirming LTG-resistance. LTG-resistant CKM were also resistant to carbamazepine, retigabine, and valproic acid at doses that significantly reduced MSS in VEH-treated kindled mice. Fluoxetine, minocycline, and celecoxib were ineffective at the doses tested in either kindled cohort. Finally, the behavioral phenotype of LTG-resistant CKM was also characterized. CKM demonstrated exacerbated hyperexcitability and increased anxiety-like behavior in an open field relative to sham-kindled mice regardless of LTG sensitivity.

SIGNIFICANCE

The pharmacoresistant LTG-resistant CKM provides an etiologically relevant moderate-throughput platform that is suitable for early compound discovery before advancing to more resource-intensive models of epilepsy.

Taurine supplementation to anti-seizure drugs as the promising approach to treat pharmacoresistant epilepsy: A pre-clinical study

Background Pharmacoresistance leads to severe, irreversible disabilities and premature death in ∼30% cases of epilepsy despite adequate and appropriate treatment with available anti-seizure drugs (ASDs) without any underlying cause. In light of the large body of evidence which suggests the anti-seizure action of taurine in experimental animals and its wide safety margins in human, supplementation of this inhibitory amino-sulfonic acid to available ASDs seems promising to treat pharmacoresistant epilepsy.

Methods We examined the anti-seizure effect of lamotrigine (15 mg/kg), levetiracetam (40 mg/kg), carbamazepine (40 mg/kg), phenytoin (35 mg/kg) & taurine (50, 100 & 200 mg/kg) in lamotrigine pre-treated pentylenetetrazole-kindled mice (LPK) which mimic core features of pharmacoresistant epilepsy, either alone ASDs or in combinations whereby three different doses of taurine were supplemented with tested ASDs.

Results Both, the ASDs and the taurine were failed to suppress generalized tonic-clonic seizures in LPK mice. However, taurine supplementation clearly restored the anti-seizure effect of tested ASDs. Further neurochemical studies revealed that higher levels of taurine in the hippocampus and cerebral cortex restored the imbalance between major excitatory neurotransmitters glutamate & its inhibitory counterpart GABA.

Conclusions These findings emphasize that supplementation of taurine with ASDs may be useful to treat pharmacoresistant epilepsy. Thus, further clinical validation is encouraged.

Effect of zonisamide on refractory epilepsy during pregnancy in lamotrigine resistant kindled rats

Drug-resistant epilepsy with uncontrolled severe seizures despite state-of-the-art medical treatment continues to be a major clinical problem. Pregnancy is a state where drug pharmacokinetic changes are more pronounced and more rapid than any other period of life. The current study investigated the effect of zonisamide (ZNS) on refractory epilepsy during pregnancy in lamotrigine-resistant kindled rats. Fifty-six lamotrigine (LTG)-resistant kindled Wistar rats were divided into five experimental (four pregnant and one non-pregnant) and 2 positive controls (pregnant and non-pregnant) groups and eight intact Wistar rats were put in the negative pregnant control group. Experimental groups received daily ZNS 50mg/kg by oral gavage and 30min later, pentylenetetrazol (PTZ) (30mg/kg) was injected intraperitoneal (i.p) on Gestational Days 10-15 (in rats with or without ZNS or methanol and ethyl acetate as a ZNS solvent challenge in days -5 to 0) or Days 15-20 and for six days in the non-pregnant group. The positive control groups received the ZNS solvent for the same number of days, but the negative pregnant control group did not receive any treatment. Epilepsy was significantly controlled by ZNS in the experimental groups compared to the positive control groups. It was concluded that ZNS can control refractory epilepsy during pregnancy and increase pregnancy survival in refractory epileptic rats.

The National Institute of Neurological Disorders and Stroke (NINDS) Epilepsy Therapy Screening Program (ETSP)

For over 40 years, the National Institute of Neurological Disorders and Stroke/National Institutes of Health-funded Anticonvulsant Screening Program has provided a preclinical screening service for participants world-wide that helped identify/characterize new antiseizure compounds, a number of which advanced to the market for the treatment of epilepsy. The newly-renamed Epilepsy Therapy Screening Program (ETSP) has a refocused mission to identify novel agents which will help address the considerable remaining unmet medical needs in epilepsy. These include identifying antiseizure agents for treatment-resistant epilepsy, as well as anti-epileptogenic agents that will prevent the development of epilepsy or disease-modifying agents that will ameliorate or even cure established epilepsy and its comorbidities. This manuscript provides an overview of the ETSP's efforts aimed at identifying the next generation of therapeutic agents to further reduce the suffering from and burden of epilepsy.

Evaluation of Cannabidiol in Animal Seizure Models by the Epilepsy Therapy Screening Program (ETSP)

Cannabidiol (CBD) is a cannabinoid component of marijuana that has no significant activity at cannabinoid receptors or psychoactive effects. There is considerable interest in CBD as a therapy for epilepsy. Almost a third of epilepsy patients are not adequately controlled by clinically available anti-seizure drugs (ASDs). Initial studies appear to demonstrate that CBD preparations may be a useful treatment for pharmacoresistant epilepsy. The National Institute of Neurological Disorders and Stroke (NINDS) funded Epilepsy Therapy Screening Program (ETSP) investigated CBD in a battery of seizure models using a refocused screening protocol aimed at identifying pharmacotherapies to address the unmet need in pharmacoresistant epilepsy. Applying this new screening workflow, CBD was investigated in mouse 6 Hz 44 mA, maximal electroshock (MES), corneal kindling models and rat MES and lamotrigine-resistant amygdala kindling models. Following intraperitoneal (i.p.) pretreatment, CBD produced dose-dependent protection in the acute seizure models; mouse 6 Hz 44 mA (ED₅₀ 164 mg/kg), mouse MES (ED₅₀ 83.5 mg/kg) and rat MES (ED₅₀ 88.9 mg/kg). In chronic models, CBD produced dose-dependent protection in the corneal kindled mouse (ED₅₀ 119 mg/kg) but CBD (up to 300 mg/kg) was not protective in the lamotrigine-resistant amygdala kindled rat. Motor impairment assessed in conjunction with the acute seizure models showed that CBD exerted seizure protection at non-impairing doses. The ETSP investigation demonstrates that CBD exhibits anti-seizure properties in acute seizure models and the corneal kindled mouse. However, further preclinical and clinical studies are needed to determine the potential for CBD to address the unmet needs in pharmacoresistant epilepsy.

Development and pharmacologic characterization of the rat 6 Hz model of partial seizures

OBJECTIVE

The mouse 6 Hz model of psychomotor seizures is a well-established and commonly used preclinical model for antiseizure drug (ASD) discovery. Despite its widespread use both in the identification and differentiation of novel ASDs in mice, a corresponding assay in rats has not been developed. We established a method for 6 Hz seizure induction in rats, with seizure behaviors similar to those observed in mice including head nod, jaw clonus, and forelimb clonus.

METHODS

A convulsive current that elicits these seizure behaviors in 97% of rats (CC₉₇ ) was determined using a Probit analysis. Numerous prototype ASDs were evaluated in this model using stimulus intensities of 1.5× and 2× the CC₉₇ , which is comparable to the approach used in the mouse 6 Hz seizure model (e.g., 32 and 44 mA stimulus intensities). The ASDs evaluated include carbamazepine, clobazam, clonazepam, eslicarbazepine, ethosuximide, ezogabine, gabapentin, lacosamide, lamotrigine, levetiracetam, phenobarbital, phenytoin, rufinamide, tiagabine, topiramate, and sodium valproate. Median effective dose (ED₅₀ ) and median toxic (motor impairment) dose (TD₅₀ ) values were obtained for each compound.

RESULTS

Compounds that were effective at the 1.5 × CC₉₇ stimulus intensity at protective index (PI) values >1 included clobazam, ethosuximide, ezogabine, levetiracetam, phenobarbital, and sodium valproate. Compounds that were effective at the 2 × CC₉₇ stimulus intensity at PI values >1 included ezogabine, phenobarbital, and sodium valproate.

SIGNIFICANCE

In a manner similar to the use of the mouse 6 Hz model, development of a rat 6 Hz test will aid in the differentiation of ASDs, as well as in study design and dose selection for chronic rat models of pharmacoresistant epilepsy. The limited number of established ASDs with demonstrable efficacy at the higher stimulus intensity suggests that, like the mouse 6 Hz 44 mA model, the rat 6 Hz seizure model may be a useful screening tool for pharmacoresistant seizures.

The impact of nonadherence to antiseizure drugs on seizure outcomes in an animal model of epilepsy

OBJECTIVE

Nonadherence to prescribed dosing regimens is a significant problem in the treatment of pediatric and adult chronic epilepsy, and can result in severe consequences to patient outcomes. In this first-of-kind preclinical study, the impact of nonadherence on seizure control was studied by simulating human patterns of nonadherence in an animal epilepsy model.

METHODS

In study 1, three different patterns of nonadherence were modeled in newly diagnosed epileptic rats treated with carbamazepine: perfect adherence (100% of pellets contained carbamazepine), variable nonadherence (50% of pellets contained carbamazepine with different dosing patterns between animals), and complete nonadherence (0% of pellets contained carbamazepine). In study 2, a cohort of newly diagnosed epileptic rats were subjected to a "drug holiday" nonadherence paradigm, that is, a 2-week on (100%), 2-week off (0%), and 2-week on (100%) carbamazepine paradigm.

RESULTS

In the first experiment, the 100% (0.3 ± 0.2 SD convulsive seizures per day) adherent cohort demonstrated better seizure control than either the 0% (1.1 ± 0.8 SD) or 50% (0.8 ± 0.6 SD) adherent cohorts, which had similar levels of seizure control. In the second study, poor seizure control was exhibited during the second 2 weeks; that is, the drug holiday epoch; however, this did not negatively affect restoration of seizure control upon reinstatement of CBZ.

SIGNIFICANCE

The results from this pilot investigation suggest that nonadherence to carbamazepine is associated with significant negative but reversible effects on seizure control in an animal model of epilepsy. Furthermore, these results demonstrate that animal studies of nonadherence can yield potentially important and translatable insights into the consequences of nonadherence on seizure control.

Validation of a Preclinical Drug Screening Platform for Pharmacoresistant Epilepsy

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.

Animal Models of Seizures and Epilepsy: Past, Present, and Future Role for the Discovery of Antiseizure Drugs

The identification of potential therapeutic agents for the treatment of epilepsy requires the use of seizure models. Except for some early treatments, including bromides and phenobarbital, the antiseizure activity of all clinically used drugs was, for the most part, defined by acute seizure models in rodents using the maximal electroshock and subcutaneous pentylenetetrazole seizure tests and the electrically kindled rat. Unfortunately, the clinical evidence to date would suggest that none of these models, albeit useful, are likely to identify those therapeutics that will effectively manage patients with drug resistant seizures. Over the last 30 years, a number of animal models have been developed that display varying degrees of pharmacoresistance, such as the phenytoin- or lamotrigine-resistant kindled rat, the 6-Hz mouse model of partial seizures, the intrahippocampal kainate model in mice, or rats in which spontaneous recurrent seizures develops after inducing status epilepticus by chemical or electrical stimulation. As such, these models can be used to study mechanisms of drug resistance and may provide a unique opportunity for identifying a truly novel antiseizure drug (ASD), but thus far clinical evidence for this hope is lacking. Although animal models of drug resistant seizures are now included in ASD discovery approaches such as the ETSP (epilepsy therapy screening program), it is important to note that no single model has been validated for use to identify potential compounds for as yet drug resistant seizures, but rather a battery of such models should be employed, thus enhancing the sensitivity to discover novel, highly effective ASDs. The present review describes the previous and current approaches used in the search for new ASDs and offers some insight into future directions incorporating new and emerging animal models of therapy resistance.

Physicochemical and biological evaluation of a cinnamamide derivative R,S-(2E)-1-(3-hydroxypiperidin-1-yl)-3-phenylprop-2-en-1-one (KM-608) for nervous system disorders

A cinnamamide scaffold has been successfully incorporated in several compounds possessing desirable pharmacological activities in central and peripheral nervous system such as anticonvulsant, antidepressant, neuroprotective, analgesic, anti-inflammatory, muscle relaxant, and sedative/hypnotic properties. R,S-(2E)-1-(3-hydroxypiperidin-1-yl)-3-phenylprop-2-en-1-one (KM-608), a cinnamamide derivative, was synthesized, its chemical structure was confirmed by means of spectroscopy and crystallography, and additionally, thermal analysis showed that it exists in one crystalline form. The compound was evaluated in vivo in rodents as anticonvulsant, antiepileptogenic, analgesic, and neuroprotective agent. The beneficial properties of the compound were found in animal models of seizures evoked electrically (maximal electroshock test, 6-Hz) and chemically (subcutaneous pentylenetetrazole seizure test) as well as in three animal models of epileptogenesis: corneal-kindled mice, hippocampal-kindled rats, and lamotrigine-resistant amygdala-kindled rats. Quantitative pharmacological parameters calculated for the tested compound were comparable to those of currently used antiepileptic drugs. In vivo pharmacological profile of KM-608 corresponds with the activity of valproic acid.

Trimetazidine potentiates the antiepileptic activity and ameliorates the metabolic changes associated with pentylenetetrazole kindling in rats treated with valproic acid

Oxidative stress is implicated in epileptogenesis as well as in the metabolic changes associated with increased risk of atherosclerotic vascular disease in epilepsy. The present work investigated the impact of the antioxidant trimetazidine (TMZ) on the antiepileptic activity of valproic acid (VPA) and on the metabolic and histological changes in hippocampal, aortic, and hepatic tissues associated with epilepsy and (or) VPA. Rats were divided into non-pentylenetetrazole (non-PTZ) group subdivided into control and VPA-treated groups, and PTZ-treated group subdivided into PTZ, PTZ/VPA, PTZ/TMZ, and PTZ/VPA + TMZ groups. VPA treatment in PTZ rats resulted in an antioxidant effect with improvement in oxidative stress, metabolic and histopathological changes induced by PTZ in hippocampus, aortic, and hepatic tissues. TMZ exhibited anticonvulsant activity and potentiated the anticonvulsant effect of VPA. Combination of TMZ with VPA induced a greater reduction in oxidative stress, improvement in the metabolic and histopathological changes compared to VPA treatment. In contrast, VPA administration in non-PTZ-treated rats induced a pro-oxidative effect, associated with metabolic and histopathological changes in aortic and hepatic tissues. These findings suggest that co-administration of TMZ with VPA in epilepsy might antagonize not only the oxidative stress associated with epilepsy but might also counteract a potential pro-oxidative effect of VPA.

Fit for purpose application of currently existing animal models in the discovery of novel epilepsy therapies

Animal seizure and epilepsy models continue to play an important role in the early discovery of new therapies for the symptomatic treatment of epilepsy. Since 1937, with the discovery of phenytoin, almost all anti-seizure drugs (ASDs) have been identified by their effects in animal models, and millions of patients world-wide have benefited from the successful translation of animal data into the clinic. However, several unmet clinical needs remain, including resistance to ASDs in about 30% of patients with epilepsy, adverse effects of ASDs that can reduce quality of life, and the lack of treatments that can prevent development of epilepsy in patients at risk following brain injury. The aim of this review is to critically discuss the translational value of currently used animal models of seizures and epilepsy, particularly what animal models can tell us about epilepsy therapies in patients and which limitations exist. Principles of translational medicine will be used for this discussion. An essential requirement for translational medicine to improve success in drug development is the availability of animal models with high predictive validity for a therapeutic drug response. For this requirement, the model, by definition, does not need to be a perfect replication of the clinical condition, but it is important that the validation provided for a given model is fit for purpose. The present review should guide researchers in both academia and industry what can and cannot be expected from animal models in preclinical development of epilepsy therapies, which models are best suited for which purpose, and for which aspects suitable models are as yet not available. Overall further development is needed to improve and validate animal models for the diverse areas in epilepsy research where suitable fit for purpose models are urgently needed in the search for more effective treatments.

Cross-species pharmacological characterization of the allylglycine seizure model in mice and larval zebrafish

Treatment-resistant seizures affect about a third of patients suffering from epilepsy. To fulfill the need for new medications targeting treatment-resistant seizures, a number of rodent models offer the opportunity to assess a variety of potential treatment approaches. The use of such models, however, has proven to be time-consuming and labor-intensive. In this study, we performed pharmacological characterization of the allylglycine (AG) seizure model, a simple in vivo model for which we demonstrated a high level of treatment resistance. (d,l)-Allylglycine inhibits glutamic acid decarboxylase (GAD) - the key enzyme in γ-aminobutyric acid (GABA) biosynthesis - leading to GABA depletion, seizures, and neuronal damage. We performed a side-by-side comparison of mouse and zebrafish acute AG treatments including biochemical, electrographic, and behavioral assessments. Interestingly, seizure progression rate and GABA depletion kinetics were comparable in both species. Five mechanistically diverse antiepileptic drugs (AEDs) were used. Three out of the five AEDs (levetiracetam, phenytoin, and topiramate) showed only a limited protective effect (mainly mortality delay) at doses close to the TD50 (dose inducing motor impairment in 50% of animals) in mice. The two remaining AEDs (diazepam and sodium valproate) displayed protective activity against AG-induced seizures. Experiments performed in zebrafish larvae revealed behavioral AED activity profiles highly analogous to those obtained in mice. Having demonstrated cross-species similarities and limited efficacy of tested AEDs, we propose the use of AG in zebrafish as a convenient and high-throughput model of treatment-resistant seizures.

On-demand pulsatile intracerebral delivery of carisbamate with closed-loop direct neurostimulation therapy in an electrically induced self-sustained focal-onset epilepsy rat model

OBJECT

The authors evaluated the preclinical feasibility of acutely stabilizing an active bihemispheric limbic epileptic circuit using closed-loop direct neurostimulation therapy in tandem with "on-demand'" convection-enhanced intracerebral delivery of the antiepileptic drug (AED) carisbamate. A rat model of electrically induced self-sustained focal-onset epilepsy was employed.

METHODS

A 16-contact depth-recording microelectrode was implanted bilaterally in the dentate gyrus (DG) of the hippocampus of Fischer 344 rats. The right microelectrode array included an integrated microcatheter for drug delivery at the distal tip. Bihemispheric spontaneous self-sustained limbic status epilepticus (SSLSE) was induced in freely moving rats using a 90-minute stimulation paradigm delivered to the right medial perforant white matter pathway. Immediately following SSLSE induction, closed-loop right PP stimulation therapy concurrent with on-demand nanoboluses of the AED [(14)C]-carisbamate (n = 4), or on-demand [(14)C]-carisbamate alone (n = 4), was introduced for a mean of 10 hours. In addition, 2 reference groups received either closed-loop stimulation therapy alone (n = 4) or stimulation therapy with saline vehicle only (n = 4). All animals were sacrificed after completing the specified therapy regimen. In situ [(14)C]-autoradiography was used to determine AED distribution.

RESULTS

Closed-loop direct stimulation therapy delivered unilaterally in the right PP aborted ictal runs detected in either ipsi- or contralateral hippocampi. Freely moving rats receiving closed-loop direct stimulation therapy with ondemand intracerebral carisbamate delivery experienced a significant reduction in seizure frequency (p < 0.001) and minimized seizure frequency variability during the final 50% of the therapy/recording session compared with closed-loop stimulation therapy alone.

CONCLUSIONS

Unilateral closed-loop direct stimulation therapy delivered to afferent hippocampal white matter pathways concurrent with on-demand ipsilateral intracerebral delivery of nano-bolused carisbamate can rapidly decrease the frequency of electrographic seizures in an active bihemispheric epileptic network. Additionally, direct pulsatile delivery of carisbamate can stabilize seizure frequency variability compared with direct stimulation therapy alone.

Advances on genetic rat models of epilepsy

Considering the suitability of laboratory rats in epilepsy research, we and other groups have been developing genetic models of epilepsy in this species. After epileptic rats or seizure-susceptible rats were sporadically found in outbred stocks, the epileptic traits were usually genetically-fixed by selective breeding. So far, the absence seizure models GAERS and WAG/Rij, audiogenic seizure models GEPR-3 and GEPR-9, generalized tonic-clonic seizure models IER, NER and WER, and Canavan-disease related epileptic models TRM and SER have been established. Dissection of the genetic bases including causative genes in these epileptic rat models would be a significant step toward understanding epileptogenesis. N-ethyl-N-nitrosourea (ENU) mutagenesis provides a systematic approach which allowed us to develop two novel epileptic rat models: heat-induced seizure susceptible (Hiss) rats with an Scn1a missense mutation and autosomal dominant lateral temporal epilepsy (ADLTE) model rats with an Lgi1 missense mutation. In addition, we have established episodic ataxia type 1 (EA1) model rats with a Kcna1 missense mutation derived from the ENU-induced rat mutant stock, and identified a Cacna1a missense mutation in a N-Methyl-N-nitrosourea (MNU)-induced mutant rat strain GRY, resulting in the discovery of episodic ataxia type 2 (EA2) model rats. Thus, epileptic rat models have been established on the two paths: ‘phenotype to gene’ and ‘gene to phenotype’. In the near future, development of novel epileptic rat models will be extensively promoted by the use of sophisticated genome editing technologies.

What new modeling approaches will help us identify promising drug treatments?

Despite the development of numerous novel antiepileptic drugs (AEDs) in recent years, several unmet clinical needs remain, including resistance to AEDs in about 30 % of patients with epilepsy, adverse effects of AEDs that can reduce quality of life, and the lack of treatments that can prevent development of epilepsy in patients at risk. Animal models of seizures and epilepsy have been instrumental in the discovery and preclinical development of novel AEDs, but obviously the previously used models have failed to identify drugs that address unmet medical needs. Thus, we urgently need fresh ideas for improving preclinical AED development. In this review, a number of promising models will be described, including the use of simple vertebrates such as zebrafish (Danio rerio), large animal models such as the dog and newly characterized rodent models of pharmacoresistant epilepsy. While these strategies, like any animal model approach also have their limitations, they offer hope that new more effective AEDs will be identified in the coming years.

Issues related to development of new antiseizure treatments

This report represents a summary of the discussions led by the antiseizure treatment working group of the International League Against Epilepsy (ILAE)/American Epilepsy Society (AES) Working Groups joint meeting in London (London Meeting). We review here what is currently known about the pharmacologic characteristics of current models of refractory seizures, both for adult and pediatric epilepsy. In addition, we address how the National Institute of Neurological Disorders and Stroke (NINDS)-funded Anticonvulsant Screening Program (ASP) is evolving to incorporate appropriate animal models in the search for molecules that might be sufficiently novel to warrant further pharmacologic development. We also briefly address what we believe is necessary, going forward, to achieve the goal of stopping seizures in all patients, with a call to arms for funding agencies, the pharmaceutical industry, and basic researchers.