Henrik Klitgaard

Evidence for a unique profile of levetiracetam in rodent models of seizures and epilepsy.

The protective and adverse effect potentials of levetiracetam ((S)-alpha-ethyl-2-oxo-pyrrolidine acetamide) in rodent models of seizures and epilepsy were compared with the profile of several currently prescribed and newly developed antiepileptic drugs. Levetiracetam was devoid of anticonvulsant activity in the acute maximal electroshock seizure test and in the maximal pentylenetetrazol seizure test in mice (up to 540 mg/kg, i.p.) but exhibited potent protection against generalised epileptic seizures in electrically and pentylenetetrazol-kindled mice (ED50 values = 7 and 36 mg/kg, respectively, i.p.). This differs markedly from established and most new antiepileptic drugs which induce significant protection in both the acute seizure tests and the kindling models. Furthermore, levetiracetam was devoid of anticonvulsant activity in several maximal chemoconvulsive seizure tests although an interesting exception was the potent protection observed against secondarily generalised activity from focal seizures induced by pilocarpine in mice (ED50 value = 7 mg/kg, i.p.), pilocarpine and kainic acid in rats (minimum active dose = 17 and 54 mg/kg, respectively, i.p.). The protection afforded by levetiracetam on the threshold for methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM)-induced seizures persisted after chronic administration (17-170 mg/kg, i.p., twice daily/14 days) and levetiracetam did not lower the seizure threshold for the proconvulsant action of the inverse benzodiazepine receptor agonist, N-methyl-beta-carboline-3-carboxamide (FG 7142). The main metabolite of levetiracetam (ucb L057; (S)-alpha-ethyl-2-oxo-1-pyrrolidine acetic acid) was found to be inactive in sound-sensitive mice after acute administration of doses up to 548 mg/kg, i.p. Levetiracetam induced only minor behavioural alterations in both normal and amygdala-kindled rats (54-1700 mg/kg, i.p.) resulting in an unusually high safety margin between rotarod impairment and seizure suppression of 148 in corneally kindled mice and 235 in Genetic Absence Epilepsy Rats from Strasbourg. In comparison, existing antiepileptic drugs have ratios between 2 and 17 in the corneally kindled mouse model. These studies reveal a unique profile of levetiracetam in rodent models. Characteristics are a general lack of anticonvulsant activity against maximal, acute seizures and selective protection with a very high safety margin in genetic and kindled animals and against chemoconvulsants producing partial epileptic seizures. This activity differs markedly from that of the established and newly introduced antiepileptic drugs and appears to derive from the parent compound since its major metabolite was inactive in all models studied. Together these results therefore suggest that levetiracetam may offer an effective, broad-spectrum treatment of epileptic seizures in patients, with a minimum of adverse effects.

The anti-epileptic drug levetiracetam reverses the inhibition by negative allosteric modulators of neuronal GABA- and glycine-gated currents

In this study in vitro and in vivo approaches were combined in order to investigate if the anti‐epileptic mechanism(s) of action of levetiracetam (LEV; Keppra®) may involve modulation of inhibitory neurotransmission. GABA‐ and glycine‐gated currents were studied in vitro using whole‐cell patch‐clamp techniques applied on cultured cerebellar granule, hippocampal and spinal neurons. Protection against clonic convulsions was assessed in vivo in sound‐susceptible mice. The effect of LEV was compared with reference anti‐epileptic drugs (AEDs): carbamazepine, phenytoin, valproate, clonazepam, phenobarbital and ethosuximide. LEV contrasted the reference AEDs by an absence of any direct effect on glycine‐gated currents. At high concentrations, beyond therapeutic relevance, it induced a small reduction in the peak amplitude and a prolongation of the decay phase of GABA‐gated currents. A similar action on GABA‐elicited currents was observed with the reference AEDs, except ethosuximide. These minor direct effects contrasted with a potent ability of LEV (EC50=1 – 10 μM) to reverse the inhibitory effects of the negative allosteric modulators zinc and β‐carbolines on both GABAA and glycine receptor‐mediated responses. Clonazepam, phenobarbital and valproate showed a similar ability to reverse the inhibition of β‐carbolines on GABA‐gated currents. Blockade of zinc inhibition of GABA responses was observed with clonazepam and ethosuximide. Phenytoin was the only AED together with LEV that inhibited the antagonism of zinc on glycine‐gated currents and only clonazepam and phenobarbital inhibited the action of DMCM. LEV (17 mg kg−1) produced a potent suppression of sound‐induced clonic convulsions in mice. This protective effect was significantly abolished by co‐administration of the β‐carboline FG 7142, from a dose of 5 mg kg−1. In contrast, the benzodiazepine receptor antagonist flumazenil (up to 10 mg kg−1) was without any effect on the protection afforded by LEV. The results of the present study suggest that a novel ability to oppose the action of negative modulators on the two main inhibitory ionotropic receptors may be of relevance for the anti‐epileptic mechanism(s) of action of LEV.

New avenues for anti-epileptic drug discovery and development

Despite the introduction of over 15 third-generation anti-epileptic drugs, current medications fail to control seizures in 20–30% of patients. However, our understanding of the mechanisms mediating the development of epilepsy and the causes of drug resistance has grown substantially over the past decade, providing opportunities for the discovery and development of more efficacious anti-epileptic and anti-epileptogenic drugs. In this Review we discuss how previous preclinical models and clinical trial designs may have hampered the discovery of better treatments. We propose that future anti-epileptic drug development may be improved through a new joint endeavour between academia and the industry, through the identification and application of tools for new target-driven approaches, and through comparative preclinical proof-of-concept studies and innovative clinical trials designs.

Anti‐convulsive and anti‐epileptic properties of brivaracetam (ucb 34714), a high‐affinity ligand for the synaptic vesicle protein, SV2A

Screening of 12 000 compounds for binding affinity to the synaptic vesicle protein 2A (SV2A), identified a high‐affinity pyrrolidone derivative, brivaracetam (ucb 34714). This study examined its pharmacological profile in various in vitro and in vivo models of seizures and epilepsy, to evaluate its potential as a new antiepileptic drug.

SV2A protein is a broad-spectrum anticonvulsant target: functional correlation between protein binding and seizure protection in models of both partial and generalized epilepsy.

SV2A, a synaptic vesicle protein, has been recently identified as a binding target for levetiracetam (Keppra). The specific mechanism by which SV2A binding leads to seizure protection has not yet been fully elucidated. However, a functional correlation between SV2A binding affinity and anticonvulsant potency has been observed in the mouse audiogenic seizure model. The present study was undertaken to test whether similar correlations exist in rodent models of partial and generalized epilepsies. As expected, there was a high degree of correlation between anticonvulsant potency and SV2A binding affinity in the mouse audiogenic seizure model (r(2)=0.77; p<0.001). A similar correlation was also observed in the mouse corneal kindling (r(2)=0.80; p<0.01) and in the rat model of generalized absence epilepsy (GAERS) (r(2)=0.72; p<0.01). Moreover, there were no significant differences between the slopes and intercepts of regression lines in these models. Interestingly, the protective potencies in these three epilepsy models were also well correlated with each other. As such, protective doses of a given SV2A ligand in one model could be easily predicted based on the data obtained in another model. Taken together, these results support the concept that SV2A protein is an important target for both partial and generalized epilepsies and thereby relevant for the generation of new antiepileptic drugs with potential broad-spectrum efficacy.

Levetiracetam: The Preclinical Profile of a New Class of Antiepileptic Drugs?

Summary: Levetiracetam is a new antiepileptic drug (AED) devoid of anticonvulsant activity in the two classic screening models for AEDs, the maximal electroshock and pentylenetetrazol seizure tests in both mice and rats. This contrasts a potent seizure suppression in genetic and kindled mice and rats and against chemoconvulsants inducing partial seizures in rats. The highly selective action in “epileptic” animals distinguishes levetiracetam from classic and other new AEDs that have nearly equipotent effects in normal and “epileptic” animals. Levetiracetam induces minor behavioral alterations in normal and in kindled mice and rats. This results in an unusually high safety margin in animal models reflecting both partial and primary generalized epilepsy. Furthermore, experiments in the kindling model suggest that levetiracetam may possess antiepileptogenic properties due to a potent ability to prevent the development of kindling in mice and rats at doses devoid of adverse effects. Electrophysiologic recordings from different experimental models suggest that levetiracetam exerts a selective action against abnormal patterns of neuronal activity, which probably explains its selective protection in epileptic animals and its unique tolerability. This effect appears to derive from one or more novel mechanisms of action that do not involve a conventional interaction with traditional drug targets implicated in the modulation of inhibitory and excitatory neurotransmission. Instead, ligand‐binding assays have disclosed a brain‐specific binding site for levetiracetam. These studies reveal a unique preclinical profile of levetiracetam, distinct from that of all known AEDs, suggesting that levetiracetam could represent the first agent in a new class of AEDs.

Neuroprotective properties of the novel antiepileptic drug levetiracetam in the rat middle cerebral artery occlusion model of focal cerebral ischemia

Levetiracetam (LEV) is a new antiepileptic drug with a promising preclinical profile involving both anticonvulsant and antiepileptogenic effects in kindling models. The latter stimulated the present study to compare its neuroprotective properties with the potent and selective, non-competitive NMDA antagonist, MK-801, in the rat middle cerebral artery occlusion model. Twenty-four hours after a transient occlusion of 90 minutes the animals were sacrificed and infarct volume and lesion distribution were determined from stained coronal sections. LEV was administered by intraperitoneal (i.p.) bolus injections of 5.5, 11, 22 and 44 mg x kg(-1), 30 minutes before occlusion followed by a continuous 24 hour i.p. infusion of 1.25, 2.6, 5.1 and 10.2 mg x kg(-1) per hour, respectively. LEV administration did not alter body temperature but reduced the infarct volume by 33% (P< 0.05) at the highest dose tested. An i.p. bolus injection of 0.04, 0.12 and 0.4 mg x kg(-1) of MK-801 followed by continuous i.p. infusion of 0.036, 0.108 and 0.36 mg x kg(-1) per hour, reduced the infarct volume by 49, 51 and 74% (P< 0.05), respectively. However, only the highest dose of MK-801 induced a significant reduction in the infarct volume (P< 0.05) and this was associated with hypothermia. These results suggest that LEV possesses neuroprotective properties which may be relevant for its antiepileptogenic action.

Proepileptic phenotype of SV2A-deficient mice is associated with reduced anticonvulsant efficacy of levetiracetam

Purpose:  Synaptic vesicle protein 2A (SV2A) constitutes a distinct binding site for an antiepileptic drug levetiracetam (Keppra). In the present study we characterized SV2A (+/−) heterozygous mice in several seizure models and tested if the anticonvulsant efficacy of levetiracetam is reduced in these mice.

Issues related to development of antiepileptogenic therapies.

Several preclinical proof‐of‐concept studies have provided evidence for positive treatment effects on epileptogenesis. However, none of these hypothetical treatments has advanced to the clinic. The experience in other fields of neurology such as stroke, Alzheimers disease, or amyotrophic lateral sclerosis has indicated several problems in the design of preclinical studies, which likely contribute to failures in translating the positive preclinical data to the clinic. The Working Group on “Issues related to development of antiepileptogenic therapies” of the International League Against Epilepsy (ILAE) and the American Epilepsy Society (AES) has considered the possible problems that arise when moving from proof‐of‐concept antiepileptogenesis (AEG) studies to preclinical AEG trials, and eventually to clinical AEG trials. This article summarizes the discussions and provides recommendations on how to design a preclinical AEG monotherapy trial in adult animals. We specifically address study design, animal and model selection, number of studies needed, issues related to administration of the treatment, outcome measures, statistics, and reporting. In addition, we give recommendations for future actions to advance the preclinical AEG testing.

Finding a better drug for epilepsy: Preclinical screening strategies and experimental trial design

The antiepileptic drugs (AEDs) introduced during the past two decades have provided several benefits: they offered new treatment options for symptomatic treatment of seizures, improved ease of use and tolerability, and lowered risk for hypersensitivity reactions and detrimental drug–drug interactions. These drugs, however, neither attenuated the problem of drug‐refractory epilepsy nor proved capable of preventing or curing the disease. Therefore, new preclinical screening strategies are needed to identify AEDs that target these unmet medical needs. New therapies may derive from novel targets identified on the basis of existing hypotheses for drug‐refractory epilepsy and the biology of epileptogenesis; from research on genetics, transcriptomics, and epigenetics; and from mechanisms relevant for other therapy areas. Novel targets should be explored using new preclinical screening strategies, and new technologies should be used to develop medium‐ to high‐throughput screening models. In vivo testing of novel drugs should be performed in models mimicking relevant aspects of drug refractory epilepsy and/or epileptogenesis. To minimize the high attrition rate associated with drug development, which arises mainly from a failure to demonstrate sufficient clinical efficacy of new treatments, it is important to define integrated strategies for preclinical screening and experimental trial design. An important tool will be the discovery and implementation of relevant biomarkers that will facilitate a continuum of proof‐of‐concept approaches during early clinical testing to rapidly confirm or reject preclinical findings, and thereby lower the risk of the overall development effort. In this review, we overview some of the issues related to these topics and provide examples of new approaches that we hope will be more successful than those used in the past.