Stiripentol, a Putative Antiepileptic Drug, Enhances the Duration of Opening of GABAA-Receptor Channels

Use of Stiripentol in Dravet Syndrome: A Guide for Clinicians

Dravet syndrome is a developmental and epileptic encephalopathy characterized by frequent, prolonged convulsive seizures and status epilepticus. Symptoms usually appear in the first year of life, and in addition to ongoing severe and intractable epilepsy, children with Dravet syndrome experience neurodevelopmental, behavioral, and motor impairments, along with high rates of mortality, especially in the first 12 years of life. Prompt diagnosis and initiation of treatment with broad-spectrum antiseizure medications are recommended to reduce seizure frequency and status epilepticus, and to potentially minimize the comorbidities associated with the epileptic encephalopathy. Stiripentol is an antiseizure medication approved for adjunctive use in Dravet syndrome in patients aged as young as six months. Data from randomized clinical trials and real-world studies demonstrate that stiripentol added to first-line therapy with clobazam and/or valproate is associated with high rates of seizure control, including freedom from status epilepticus, for extended periods of time including into adulthood. Stiripentol has multiple mechanisms of action and also inhibits several metabolic drug-metabolizing enzymes that can enhance the efficacy of coadministered antiseizure medications. Stiripentol is well tolerated, and treatment-emergent adverse events can often be managed by dose adjustments of comedications. This review updates the use of stiripentol in the modern era.

Efficacy and safety of stiripentol in the prevention and cessation of status epilepticus: A systematic review

Status epilepticus (SE) is a life-threatening emergency with high morbidity and mortality. In people with epilepsy, the management of SE is focused on early medical treatment. Stiripentol is a third-generation antiseizure medication (ASM) approved for refractory generalized tonic-clonic seizures in Dravet syndrome. The aim of this systematic review was to evaluate the effectiveness and safety of stiripentol in reducing the incidence of SE in patients with Dravet syndrome or any epilepsy characterized by recurrent SE. The PubMed and Cochrane databases were systematically searched, and gray literature was hand-searched. Search results were screened by title and abstract; studies with data on the effect of stiripentol on SE outcomes, including the cessation of SE, reduction in number of SE episodes, or reduction in hospitalizations, were included. Of 66 records identified, 17 studies were eligible for inclusion, of which 15 were human studies (n = 474; aged 1.1-78 years), and two were animal experiments. Results of retrospective or prospective observational studies showed that stiripentol as add-on therapy to ASMs such as clobazam or valproate reduced the incidence of SE in patients with Dravet syndrome or other developmental and epileptic encephalopathies (DEEs). A mean of 68% of patients (range 41%-100%) had a ≥50% reduction in SE episodes from baseline, and 26%-100% of patients (mean 77%) became SE-free after stiripentol initiation. Moreover, this review found stiripentol, used as acute treatment, may also be effective for the cessation of super-refractory SE, but data are limited to three retrospective case series. Stiripentol was generally well-tolerated. In conclusion, stiripentol reduces the incidence of SE episodes in patients with Dravet syndrome and potentially other DEEs, and it promotes cessation of super-refractory SE in patients with and without a history of seizures. PLAIN LANGUAGE SUMMARY: Status epilepticus (SE) is a life-threatening, long-lasting seizure occurring in patients with/without epilepsy. This article analyzed 15 published studies that investigated the effects and safety of the anti-seizure medication stiripentol for preventing SE in epilepsy patients (prevention) or stopping an SE episode (cessation), and two animal studies that investigated how stiripentol works. In epilepsy patients, stiripentol halved the number of SE episodes in 41-100% of patients, 26-100% of patients became SE-free, and stiripentol was considered to be well tolerated. In patients with/without epilepsy, stiripentol may stop the SE episode after other drugs like anesthetics have not worked.

Stiripentol efficacy against status epilepticus and associated mortality in mice

Stiripentol (STP, Diacomit©) is an antiseizure medication indicated for Dravet syndrome, a rare developmental and epileptic encephalopathy characterized by drug-resistant seizures, including status epilepticus (SE). SE is a life-threatening event that may lead to increased risk of morbidity and mortality. Here, we evaluated the effect of STP on SE and SE-associated mortality using a CBA mouse model induced by systemic administration of methionine sulfoximine (MSO), an irreversible inhibitor of glutamine synthetase. MSO induces convulsions, prolonged seizure (SE) and death, with an increase of blood ammonia level. A single acute intraperitoneal pretreatment with 200-300-400 mg/kg of STP significantly inhibited the number of seizures, SE occurrence and death in MSO-treated animals in a dose-dependent manner. Regarding blood ammonia level, STP significantly reduced by 41 % the hyperammonemia induced by MSO. In conclusion, our results show protective effects of STP to reduce and or suppress the occurrence of SE as well as its associated mortality in mice.

Twenty-first century antiepileptic drugs. An overview of their targets and synthetic approaches

The therapeutic use of the traditional drugs against epilepsy has been hindered by their toxicity and low selectivity. These limitations have stimulated the design and development of new generations of antiepileptic drugs. This review explores the molecular targets and synthesis of the antiepileptic drugs that have entered the market in the 21st century, with a focus on manufacturer synthesis.

An Update on Stiripentol Mechanisms of Action: A Narrative Review

Stiripentol (Diacomit®) (STP) is an orally active antiseizure medication (ASM) indicated as adjunctive therapy, for the treatment of seizures associated with Dravet syndrome (DS), a severe form of childhood epilepsy, in conjunction with clobazam and, in some regions valproic acid. Since the discovery of STP, several mechanisms of action (MoA) have been described that may explain its specific effect on seizures associated with DS. STP is mainly considered as a potentiator of gamma-aminobutyric acid (GABA) neurotransmission: (i) via uptake blockade, (ii) inhibition of degradation, but also (iii) as a positive allosteric modulator of GABAA receptors, especially those containing α3 and δ subunits. Blockade of voltage-gated sodium and T-type calcium channels, which is classically associated with anticonvulsant and neuroprotective properties, has also been demonstrated for STP. Finally, several studies indicate that STP could regulate glucose energy metabolism and inhibit lactate dehydrogenase. STP is also an inhibitor of several cytochrome P450 enzymes involved in the metabolism of other ASMs, contributing to boost their anticonvulsant efficacy as add-on therapy. These different MoAs involved in treatment of DS and recent data suggest a potential for STP to treat other neurological or non-neurological diseases.

Established and emerging GABAA receptor pharmacotherapy for epilepsy

Drugs that modulate the GABAA receptor are widely used in clinical practice for both the long-term management of epilepsy and emergency seizure control. In addition to older medications that have well-defined roles for the treatment of epilepsy, recent discoveries into the structure and function of the GABAA receptor have led to the development of newer compounds designed to maximise therapeutic benefit whilst minimising adverse effects, and whose position within the epilepsy pharmacologic armamentarium is still emerging. Drugs that modulate the GABAA receptor will remain a cornerstone of epilepsy management for the foreseeable future and, in this article, we provide an overview of the mechanisms and clinical efficacy of both established and emerging pharmacotherapies.

Research Status, Synthesis and Clinical Application of Antiepileptic Drugs

According to the 2017 ILAE's official definition, epilepsy is a slow brain disease state characterized by recurrent episodes. Due to information released by ILAE in 2017, it can be divided into four types, including focal epilepsy, generalized epilepsy, combined generalized, and focal epilepsy, and unknown epilepsy. Since 1989, 24 new antiepileptic drugs have been approved to treat different types of epilepsy. Besides, there are a variety of antiepileptic medications under clinical monitoring. These novel antiepileptic drugs have plenty of advantages. Over the past 33 years, there have been many antiepileptic drugs on the mearket, but no one has been found that can completely cure epilepsy. In this paper, the mentioned drugs were classified according to their targets, and the essential information, and clinical studies of each drug were described. The structure-activity relationship of different chemical structures was summarized. This paper provides help for the follow-up research on epilepsy drugs.

Anticonvulsant effect of equilibrative nucleoside transporters 1 inhibitor in a mouse model of Dravet syndrome

There are limited therapeutic options for patients with Dravet syndrome (DS). The equilibrative nucleoside transporters 1 (ENT1) mediate both the influx and efflux of adenosine across the cell membrane exerted beneficial effects in the treatment of epilepsy. This study aimed to evaluate the anticonvulsant effect of the ENT1 inhibitor in an animal model of DS (Scn1aE1099X/+ mice). J7 (5 mg/kg) treatment was efficacious in elevating seizure threshold in Scn1aE1099X/+ mice after hyperthermia exposure. Moreover, the J7 treatment significantly reduced the frequency of spontaneous excitatory post-synaptic currents (sEPSCs, ~35% reduction) without affecting the amplitude in dentate gyrus (DG) granule cells. Pretreatment with the adenosine A1 receptor (A1R) antagonist, DPCPX, abolished the J7 effects on sEPSCs. These observations suggest that the J7 shows an anticonvulsant effect in hyperthermia-induced seizures in Scn1aE1099X/+ mice. This effect possibly acts on presynaptic A1R-mediated signaling modulation in granule cells.

Pharmacological diversity amongst approved and emerging antiseizure medications for the treatment of developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies (DEEs) are rare neurodevelopmental disorders characterised by early-onset and often intractable seizures and developmental delay/regression, and include Dravet syndrome and Lennox-Gastaut syndrome (LGS). Rufinamide, fenfluramine, stiripentol, cannabidiol and ganaxolone are antiseizure medications (ASMs) with diverse mechanisms of action that have been approved for treating specific DEEs. Rufinamide is thought to suppress neuronal hyperexcitability by preventing the functional recycling of voltage-gated sodium channels from the inactivated to resting state. It is licensed for adjunctive treatment of seizures associated with LGS. Fenfluramine increases extracellular serotonin levels and may reduce seizures via activation of specific serotonin receptors and positive modulation of the sigma-1 receptor. Fenfluramine is licensed for adjunctive treatment of seizures associated with Dravet syndrome and LGS. Stiripentol is a positive allosteric modulator of type-A gamma-aminobutyric acid (GABAA) receptors. As a broad-spectrum inhibitor of cytochrome P450 enzymes, its antiseizure effects may additionally arise through pharmacokinetic interactions with co-administered ASMs. Stiripentol is licensed for treating seizures associated with Dravet syndrome in patients taking clobazam and/or valproate. The mechanism(s) of action of cannabidiol remains largely unclear although multiple targets have been proposed, including transient receptor potential vanilloid 1, G protein-coupled receptor 55 and equilibrative nucleoside transporter 1. Cannabidiol is licensed as adjunctive treatment in conjunction with clobazam for seizures associated with Dravet syndrome and LGS, and as adjunctive treatment of seizures associated with tuberous sclerosis complex. Like stiripentol, ganaxolone is a positive allosteric modulator at GABAA receptors. It has recently been licensed in the USA for the treatment of seizures associated with cyclin-dependent kinase-like 5 deficiency disorder. Greater understanding of the causes of DEEs has driven research into the potential use of other novel and repurposed agents. Putative ASMs currently in clinical development for use in DEEs include soticlestat, carisbamate, verapamil, radiprodil, clemizole and lorcaserin.

SCN1A and Its Related Epileptic Phenotypes

Epilepsy is one of the most common neurological disorders, with a lifetime incidence of 1 in 26. Approximately two-thirds of epilepsy has a substantial genetic component in its etiology. As a result, simultaneous screening for mutations in multiple genes and performing whole exome sequencing (WES) are becoming very frequent in the clinical evaluation of children with epilepsy. In this setting, mutations in voltage-gated sodium channel (SCN) α-subunit genes are the most commonly identified cause of epilepsy, with sodium channel genes (i.e., SCN1A, SCN2A, SCN8A) being the most frequently identified causative genes. SCN1A mutations result in a wide spectrum of epilepsy phenotypes ranging from simple febrile seizures to Dravet syndrome, a severe epileptic encephalopathy. In case of mutation of SCN1A, it is also possible to observe behavioral alterations, such as impulsivity, inattentiveness, and distractibility, which can be framed in an attention deficit hyperactivity disorder (ADHD) like phenotype. Despite more than 1,200 SCN1A mutations being reported, it is not possible to assess a clear phenotype–genotype correlations. Treatment remains a challenge and seizure control is often partial and transitory.

The Antiepileptic Drug Oxcarbazepine Inhibits the Growth of Patient-Derived Isocitrate Dehydrogenase Mutant Glioma Stem-like Cells

Patients diagnosed with isocitrate dehydrogenase mutant (IDH^mut) gliomas suffer frequently from seizures. Although the clinical course is less aggressive than that of its IDH wildtype counterpart, recent discoveries have shown that epileptic activity can promote tumor proliferation. However, it is not known if antiepileptic drugs confer additional value by inhibiting tumor growth. In this study, the antineoplastic properties of 20 FDA-approved antiepileptic drugs (AEDs) were tested in six patient-derived IDH^mut glioma stem-like cells (GSCs). Cell proliferation was assessed using the CellTiterGlo-3D assay. Two of the screened drugs (oxcarbazepine and perampanel) demonstrated an antiproliferative effect. A subsequent eight-point dose-response curve proved the dose-dependent growth inhibition for both drugs, but only oxcarbazepine reached an IC₅₀ value below 100 µM in 5/6 GSCs (mean 44.7 µM; range 17.4-98.0 µM), approximating the possible c_max for oxcarbazepine in patient serums. Furthermore, the treated GSC spheroids were 82% smaller (mean volume 1.6 nL vs. 8.7 nL; p = 0.01 (live/dead^TM fluorescence staining)), and the apoptotic events increased by more than 50% (caspase-3/7 activity; p = 0.006). Taken together, this drug screen of a large series of antiepileptic drugs identified oxcarbazepine as a potent proapoptotic drug in IDH^mut GSCs, which combines antiepileptic and antineoplastic properties to treat this seizure-prone patient population.

Epilepsy in Dravet Syndrome—Current and Future Therapeutic Opportunities

Dravet Syndrome (DS) is a developmental epileptic encephalopathy characterized by drug-resistant seizures and other clinical features, including intellectual disability and behavioral, sleep, and gait problems. The pathogenesis is strongly connected to voltage-gated sodium channel dysfunction. The current consensus of seizure management in DS consists of a combination of conventional and recently approved drugs such as stiripentol, cannabidiol, and fenfluramine. Despite promising results in randomized clinical trials and extension studies, the prognosis of the developmental outcomes of patients with DS remains unfavorable. The article summarizes recent changes in the therapeutic approach to DS and discusses ongoing clinical research directions. Serotonergic agents under investigation show promising results and may replace less DS-specific medicines. The use of antisense nucleotides and gene therapy is focused not only on symptom relief but primarily addresses the underlying cause of the syndrome. Novel compounds, after expected safe and successful implementation in clinical practice, will open a new era for patients with DS. The main goal of causative treatment is to modify the natural course of the disease and provide the best neurodevelopmental outcome with minimum neurological deficit.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Scavengome of an antioxidant

The term "scavengome" refers to the chemical space of all the metabolites that may be formed from an antioxidant upon scavenging reactive oxygen or nitrogen species (ROS/RNS). This chemical space covers a wide variety of free radical metabolites with drug discovery potential. It is very rich in structures representing an increased chemical complexity as compared to the parent antioxidant: a wide range of unusual heterocyclic structures, new CC bonds, etc. may be formed. Further, in a biological environment, this increased chemical complexity is directly translated from the localized conditions of oxidative stress that determines the amounts and types of ROS/RNS present. Biomimetic oxidative chemistry provides an excellent tool to model chemical reactions between antioxidants and ROS/RNS. In this chapter, we provide an overview on the known metabolites obtained by biomimetic oxidation of a few selected natural antioxidants, i.e., a stilbene (resveratrol), a pair of hydroxycinnamates (caffeic acid and methyl caffeate), and a flavonol (quercetin), and discuss the drug discovery perspectives of the related chemical space.

Stiripentol add-on therapy for drug-resistant focal epilepsy

BACKGROUND

This is an updated version of the Cochrane Review first published in 2014 and last updated in 2020. For nearly 30% of people with epilepsy, current treatments do not control seizures. Stiripentol is an antiepileptic drug (AED) that was developed in France and was approved by the European Medicines Agency (EMA) in 2007 as an adjunctive therapy with valproate and clobazam for the treatment of Dravet syndrome.

OBJECTIVES

To evaluate the efficacy and tolerability of stiripentol as add-on treatment for people with drug-resistant focal epilepsy who are taking AEDs.

SEARCH METHODS

For the latest update, we searched the Cochrane Register of Studies (CRS Web) and MEDLINE on 28 March 2022. We contacted the manufacturer of stiripentol and epilepsy experts to identify published, unpublished and ongoing trials.

SELECTION CRITERIA

Randomised controlled trials of add-on stiripentol in people with drug-resistant focal epilepsy.

DATA COLLECTION AND ANALYSIS

Review authors independently selected trials for inclusion and extracted data. We investigated outcomes including 50% or greater reduction in seizure frequency, seizure freedom, adverse effects, treatment withdrawal and changes in quality of life.

MAIN RESULTS

On the basis of our selection criteria, we included no new studies in the present review update. We included only one study from the original review (32 children with focal epilepsy). This study adopted a responder-enriched design and found no clear evidence of a reduction of 50% or more in seizure frequency (risk ratio (RR) 1.51, 95% confidence interval (CI) 0.81 to 2.82; low-certainty evidence) and no clear evidence of seizure freedom (RR 1.18, 95% CI 0.31 to 4.43; low-certainty evidence) when comparing add-on stiripentol with placebo. Stiripentol led to a greater risk of adverse effects considered as a whole (RR 2.65, 95% CI 1.08 to 6.47; low-certainty evidence). When we considered specific adverse effects, CIs were very wide and showed the possibility of substantial increases and small reductions in risks of neurological adverse effects (RR 2.65, 95% CI 0.88 to 8.01; low-certainty evidence). Researchers noted no clear reduction in the risk of study withdrawal (RR 0.66, 95% CI 0.30 to 1.47; low-certainty evidence), which was high in both groups (53.3% in placebo group and 35.3% in stiripentol group; low-certainty evidence). The external validity of this study was limited because only responders to stiripentol (i.e. participants experiencing a decrease in seizure frequency of 50% or greater during an open prerandomisation phase compared with baseline) were included in the randomised, add-on, placebo-controlled, double-blind phase. Furthermore, carry-over and withdrawal effects probably influenced outcomes related to seizure frequency. Very limited information derived from the only included study shows that adverse effects considered as a whole may occur more often with add-on stiripentol than with add-on placebo.

AUTHORS' CONCLUSIONS

We have found no new studies since the last version of this review was published. Hence, we have made no changes to the conclusions as presented in previous versions. We can draw no conclusions to support the use of stiripentol as add-on treatment for drug-resistant focal epilepsy. Additional large, randomised, well-conducted trials are needed.

Efficacy and Safety of Long-Term Treatment with Stiripentol in Children and Adults with Drug-Resistant Epilepsies: A Retrospective Cohort Study of 196 Patients

BACKGROUND

Stiripentol is an antiseizure medication with multiple potential mechanisms of action, indicated as adjunctive therapy in people with Dravet syndrome, whose seizures are not adequately controlled with clobazam and valproate. However, there are scattered data on its efficacy in other epilepsy aetiologies and types. We previously reported our single-centre experience on the efficacy of adjunctive stiripentol treatment in a cohort of 132 patients with different types of refractory epilepsies.

OBJECTIVE

We aimed to expand our analysis to a larger cohort of 196 patients with a long-term follow-up.

METHODS

We retrospectively evaluated long-term efficacy, tolerability and predictors of treatment response in 196 patients with a long-term follow-up (range 0.5-232.8 months).

RESULTS

After an initial median follow-up of 3 months after stiripentol introduction, we observed a responder rate of 53% including seizure freedom in 9%. At subsequent follow-ups at 12 and 24 months, responder rates were 29% and 22%, respectively. Aetiology was associated with sustained response over time, with Dravet syndrome being the aetiology with the highest responder rate (64%) at 48 months compared with syndromes with other genetic causes (13%) or unknown aetiology (38%). A higher responder rate over time was also observed in patients with generalised (44%) and combined focal and generalised epilepsies (28%) than in patients with focal epilepsies (20%). The highest relapse free-survival was observed when stiripentol was initiated at the youngest age (0-4 years) or in adulthood. The retention rate (i.e. proportion of patients who continued stiripentol with no change in either pharmacological or non-pharmacological therapy) was 53% at 12 months and 33% at 24 months.

CONCLUSIONS

Based on our findings, we suggest that stiripentol is an effective and well-tolerated therapeutic option not only in Dravet syndrome but also in other epilepsy syndromes with or without an established genetic aetiology. Response duration was influenced by age at stiripentol initiation across different aetiologies.

Classification of antiseizure drugs in cultured neuronal networks using multielectrode arrays and unsupervised learning

OBJECTIVE

Antiseizure drugs (ASDs) modulate synaptic and ion channel function to prevent abnormal hypersynchronous or excitatory activity arising in neuronal networks, but the relationship between ASDs with respect to their impact on network activity is poorly defined. In this study, we first investigated whether different ASD classes exert differential impact upon network activity, and we then sought to classify ASDs according to their impact on network activity.

METHODS

We used multielectrode arrays (MEAs) to record the network activity of cultured cortical neurons after applying ASDs from two classes: sodium channel blockers (SCBs) and γ-aminobutyric acid type A receptor-positive allosteric modulators (GABA PAMs). A two-dimensional representation of changes in network features was then derived, and the ability of this low-dimensional representation to classify ASDs with different molecular targets was assessed.

RESULTS

A two-dimensional representation of network features revealed a separation between the SCB and GABA PAM drug classes, and could classify several test compounds known to act through these molecular targets. Interestingly, several ASDs with novel targets, such as cannabidiol and retigabine, had closer similarity to the SCB class with respect to their impact upon network activity.

SIGNIFICANCE

These results demonstrate that the molecular target of two common classes of ASDs is reflected through characteristic changes in network activity of cultured neurons. Furthermore, a low-dimensional representation of network features can be used to infer an ASDs molecular target. This approach may allow for drug screening to be performed based on features extracted from MEA recordings.

Stiripentol inhibits spike‐and‐waves discharges in animal models of absence seizures, a new mechanism of action involving T‐type calcium channels?

Objective

Stiripentol (STP; Diacomit®) is an antiepileptic drug indicated for Dravet syndrome that has been identified as a γ‐aminobutyric acid (GABAergic) positive allosteric modulator. Dravet syndrome is characterized by multiple seizure types: generalized tonic–clonic, focal, myoclonic, and absence seizures. In addition to its antiepileptic effects on tonic–clonic seizures, STP has also been reported to reduce the frequency of atypical absence seizures in patients. Our study focused on STP potential effects on absence seizures, to better characterize its full spectrum of mechanisms of action.

Methods

STP effects on absence seizures were quantified by electroencephalographic recording in two animal models: rats treated with a low dose of pentylenetetrazol (20 mg/kg ip) and rats from the WAG/Rij strain. In addition, we characterized STP effects on T‐type calcium channel activity. Peak currents were recorded with manual patch clamp on cells transfected with cDNA encoding for the human isoform for Ca_v3.1, Ca_v3.2, and Ca_v3.3.

Results

STP administered before pentylenetetrazol almost completely abolished the generation of spike‐and‐wave discharges (SWDs) at the dose of 300 mg/kg. At this dose, STP also statistically significantly decreased SWD cumulated duration and number in WAG/Rij rats. Its antiepileptic effect was maintained in WAG/Rij rats, whose seizures were aggravated by the GABA agonist THIP (gaboxadol hydrochloride). Furthermore, electrophysiological recordings showed that STP inhibits T‐type calcium channel peak activity, with a higher specificity for the Ca_v3.3 subtype.

Significance

In addition to its previously characterized anticonvulsive properties, these data highlight a new mechanism of action of STP on abnormal thalamocortical activity. This strong antiabsence effect on seizures is correlated with an inhibition of T‐type calcium channels. This new mechanism of action could be implicated in the specificity of STP therapeutic effects in Dravet syndrome.

Discovery of 7-alkyloxy- [1,2,4] triazolo[1,5-a] pyrimidine derivatives as selective positive modulators of GABAA1 and GABAA4 receptors with potent antiepileptic activity

A series of 7-alkoxy - [1,2,4] triazolo [1, 5-a] pyrimidine derivatives were designed and synthesized. Maximal electroshock (MES) and pentylenetetrazole (PTZ) tests were utilized to access their anticonvulsant activity. Most of the series of compounds exhibited significant anti-seizure effects. Further studies demonstrated that the anticonvulsant activity of these compounds mainly depended on their allosteric potentiation of GABA_A receptors. Among them, compound 10c was picked for the mechanism study due to its potent activity. The compound is more sensitive to subunit configurations of synaptic α1β2γ2 and extrasynaptic α4β3δ GABA_A receptors, but there were no effects on NMDA receptors and Nav1.2 sodium channels. Meanwhile, 10c acted on the sites of GABA_A receptors distinct from commonly used anticonvulsants benzodiazepines and barbiturates. Furthermore, studies from native neurons demonstrated that compound 10c also potentiated the activity of native GABA_A receptors and reduced action potential firings in cultured cortical neurons. Such structural compounds may lay a foundation for further designing novel antiepileptic molecules.

Novel and emerging therapeutics for genetic epilepsies

INTRODUCTION

Disease-specific treatments are available only for a minority of patients with genetic epilepsies, while the rest are treated with anticonvulsants, which are ineffective in almost one-third of patients.

AREAS COVERED

Recently approved and the most effective emerging therapeutics under development for the treatment of genetic epilepsies are overviewed after systematic search and analysis of relevant literature.

EXPERT OPINION

New and emerging drugs for genetic epilepsies exploit one of the two approaches: inhibiting hyperactive brain foci through blocking excitatory or augmenting inhibitory neurotransmission, or correcting the underlying genetic defect. The first is limited by insufficient selectivity of available compounds, and the second by imperfection of currently used vectors of genetic material, unselective and transient transgene expression. Besides, the treatment may come too late, after structural abnormalities and epilepsy deterioration takes place. However, with recent improvements, we can expect to see soon gradual decline in the number of patients with therapy-resistant genetic epilepsies.

Precision Medicine Approaches for Infantile-Onset Developmental and Epileptic Encephalopathies

Epilepsy is an etiologically heterogeneous condition; however, genetic factors are thought to play a role in most patients. For those with infantile-onset developmental and epileptic encephalopathy (DEE), a genetic diagnosis is now obtained in more than 50% of patients. There is considerable motivation to utilize these molecular diagnostic data to help guide treatment, as children with DEEs often have drug-resistant seizures as well as developmental impairment related to cerebral epileptiform activity. Precision medicine approaches have the potential to dramatically improve the quality of life for these children and their families. At present, treatment can be targeted for patients with diagnoses in many genetic causes of infantile-onset DEE, including genes encoding sodium or potassium channel subunits, tuberous sclerosis, and congenital metabolic diseases. Precision medicine may refer to more intelligent choices of conventional antiseizure medications, repurposed agents previously used for other indications, novel compounds, enzyme replacement, or gene therapy approaches. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Drug treatment of epilepsy: From serendipitous discovery to evolutionary mechanisms

Epilepsy is a chronic brain disorder caused by abnormal firing of neurons. Up to now, using antiepileptic drugs is the main method of epilepsy treatment. The development of antiepileptic drugs lasted for centuries. In general, most agents entering clinical practice act on the balance mechanisms of brain "excitability-inhibition". More specifically, they target voltage-gated ion channels, GABAergic transmission and glutamatergic transmission. In recent years, some novel drugs representing new mechanisms of action have been discovered. Although there are about 30 available drugs in the market, it is still in urgent need of discovering more effective and safer drugs. The development of new antiepileptic drugs is into a new era: from serendipitous discovery to evolutionary mechanism-based design. This article presents an overview of drug treatment of epilepsy, including a series of traditional and novel drugs.

Is the mechanism of action of antiseizure drugs a key element in the choice of treatment?

About 25 antiseizure drugs are available for the treatment of patients with epilepsy. The choice of the most suited drug for a specific patient is primarily based on the results of the pivotal randomized clinical trials and on the patient's characteristics and comorbidities. Whether or not the mechanism of action of the antiseizure drugs should be also taken into account to better predict the patient's response to the treatment remains a matter of debate. Despite the apparent complexity and diversity of antiseizure drug mechanisms of action, the reality unfortunately remains that they are very close, in particular with regard to their relationship with the pathophysiology of epilepsy. With the only exception of the association between lamotrigine and sodium valproate, there are no clinical data that formally support a synergistic association between certain antiseizure drugs in terms of efficacy. However, anticipating risk of adverse events by limiting as far as possible the combination of drugs, which share the same mechanisms of action, is undoubtedly an important driver of daily therapeutic decisions.

Current Pharmacologic Strategies for Treatment of Intractable Epilepsy in Children

Epileptic encephalopathy (EE) is a devastating pediatric disease that features medically resistant seizures, which can contribute to global developmental delays. Despite technological advancements in genetics, the neurobiological mechanisms of EEs are not fully understood, leaving few therapeutic options for affected patients. In this review, we introduce the most common EEs in pediatrics (i.e., Ohtahara syndrome, Dravet syndrome, and Lennox-Gastaut syndrome) and their molecular mechanisms that cause excitation/inhibition imbalances. We then discuss some of the essential molecules that are frequently dysregulated in EEs. Specifically, we explore voltage-gated ion channels, synaptic transmission-related proteins, and ligand-gated ion channels in association with the pathophysiology of Ohtahara syndrome, Dravet syndrome, and Lennox-Gastaut syndrome. Finally, we review currently available antiepileptic drugs used to treat seizures in patients with EEs. Since these patients often fail to achieve seizure relief even with the combination therapy, further extensive research efforts to explore the involved molecular mechanisms will be required to develop new drugs for patients with intractable epilepsy.

Neurocognitive Effects of Antiseizure Medications in Children and Adolescents with Epilepsy

Impairments in cognition are common in epilepsy and may be caused or exacerbated by antiseizure medications (ASMs). Positive effects on cognition may also be seen with some ASMs. Cognitive outcomes are of particular concern in children who may be at an increased risk of cognitive adverse effects of treatment. A comprehensive literature search was conducted in PubMed in order to evaluate the evidence for cognitive changes associated with treatment with ASMs in paediatric epilepsy patients. The ASMs considered were those in the current edition of the British National Formulary (BNF). For most ASMs, remarkably few studies providing robust data on cognitive effects in paediatric patients were identified. The available evidence suggests cognitive impairments may be associated with treatment with phenobarbital. Topiramate and phenytoin are also associated with negative effects on cognition, in particular word-finding difficulties and other language deficits with topiramate, but there are few data available specifically on children. Lamotrigine, levetiracetam and fenfluramine are associated with improvements in some cognitive domains, although it is unclear whether these effects are directly attributable to the medications or are a result of improvements in seizures. Neutral effects on cognition (no substantial evidence of worsening) were suggested for carbamazepine, everolimus, lacosamide, oxcarbazepine, perampanel and valproate. There is limited data for cannabidiol, clobazam, eslicarbazepine acetate, ethosuximide, rufinamide, vigabatrin and zonisamide, although the available evidence suggests these drugs are not associated with severe cognitive impairment. There was too little information to reach conclusions about the effects of brivaracetam, felbamate, gabapentin, pregabalin, retigabine, stiripentol or tiagabine.

Using Self-Nanoemulsifying System to Improve Oral Bioavailability of a Pediatric Antiepileptic Agent Stiripentol: Formulation and Pharmacokinetics Studies

This study aimed to develop a self-nanoemulsifying drug delivery system (SNEDDS) for poorly water-soluble drug stiripentol (STP) with enhanced oral bioavailability. Optimal excipients were selected by constructing pseudo-ternary phase diagrams using determined solubilities of STP, and then the proper composition of SNEDDS was investigated by employing a central composite design method. The optimized SNEDDS was composed of oil (ethyl oleate 39.61%), surfactant (Cremophor® RH 40 43.18%), co-surfactant (1,2-propanediol 17.21%), and STP of 50 mg/mL. The hydrodynamic size, zeta potential, and polydispersity index (PDI) were found to be 45.52 ± 1.99 nm, - 21.67 ± 0.24 mV, and 0.076 ± 0.011, respectively. The optimized STP-SNEDDS showed good stability in accelerated and dilution stability studies. It was also helpful to suppress STP degradation in acidic solution. Compared with STP suspension, STP-SNEDDS presented much faster dissolution rate. STP-SNEDDS successfully resulted in superior levels of C_max and AUC_{0 → 6 h} (4048.38 ± 704.54 μg/L and 7754.58 ± 1489.37 h μg/L, respectively) to STP suspension (1894.09 ± 1077.64 μg/L and 3556.93 ± 2470.01 h μg/L, respectively). The relative oral bioavailability of STP was 218.01%. The brain biodistribution studies showed that STP-SNEDDS presented significantly higher STP concentrations in the brain at 0.5 h and 1 h than that of STP suspension after administration. These findings indicated that a SNEDDS-based oral formulation of STP would be helpful for increasing its therapeutic potential.

Stiripentol add-on therapy for drug-resistant focal epilepsy

BACKGROUND

This is an updated version of the Cochrane Review first published in 2014, and last updated in 2018. For nearly 30% of people with epilepsy, seizures are not controlled by current treatments. Stiripentol is an antiepileptic drug (AED) that was developed in France and was approved by the European Medicines Agency (EMA) in 2007 for the treatment of Dravet syndrome as an adjunctive therapy with valproate and clobazam.

OBJECTIVES

To evaluate the efficacy and tolerability of stiripentol as add-on treatment for people with drug-resistant focal epilepsy who are taking AEDs.

SEARCH METHODS

For the latest update, we searched the following databases on 27 February 2020: Cochrane Register of Studies (CRS Web); and MEDLINE (Ovid, 1946 to 26 February 2020). CRS Web includes randomised or quasi-randomised controlled trials from the Specialized Registers of Cochrane Review Groups including Epilepsy, Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, Embase, ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform (ICTRP). We contacted Biocodex (the manufacturer of stiripentol) and epilepsy experts to identify published, unpublished and ongoing trials.

SELECTION CRITERIA

Randomised, controlled, add-on trials of stiripentol in people with drug-resistant focal epilepsy.

DATA COLLECTION AND ANALYSIS

Review authors independently selected trials for inclusion and extracted data. We investigated outcomes including 50% or greater reduction in seizure frequency, seizure freedom, adverse effects, treatment withdrawal and changes in quality of life.

MAIN RESULTS

On the basis of our selection criteria, we included no new studies in the present review update. We included only one study from the earlier review (32 children with focal epilepsy). This study adopted a responder-enriched design and found no clear evidence of a reduction in seizure frequency (≥ 50% seizure reduction) (risk ratio (RR) 1.51, 95% confidence interval (CI) 0.81 to 2.82; low-certainty evidence) or evidence of seizure freedom (RR 1.18, 95% CI 0.31 to 4.43; low-certainty evidence) when add-on stiripentol was compared with placebo. Stiripentol led to a greater risk of adverse effects considered as a whole (RR 2.65, 95% CI 1.08 to 6.47; low-certainty evidence). When we considered specific adverse events, confidence intervals were very wide and showed the possibility of substantial increases and small reductions in risks of neurological adverse effects (RR 2.65, 95% CI 0.88 to 8.01; low-certainty evidence) and gastrointestinal adverse effects (RR 11.56, 95% CI 0.71 to 189.36; low-certainty evidence). Researchers noted no clear reduction in the risk of study withdrawal (RR 0.66, 95% CI 0.30 to 1.47; low-certainty evidence), which was high in both groups (35.0% in add-on placebo and 53.3% in stiripentol group; low-certainty evidence). The external validity of this study was limited because only responders to stiripentol (i.e. patients experiencing a ≥ 50% decrease in seizure frequency compared with baseline) were included in the randomised, add-on, placebo-controlled, double-blind phase. Furthermore, carry-over and withdrawal effects probably influenced outcomes related to seizure frequency. Very limited information derived from the only included study shows that adverse effects considered as a whole seemed to occur significantly more often with add-on stiripentol than with add-on placebo.

AUTHORS' CONCLUSIONS

We have found no new studies since the last version of this review was published. Hence, we have made no changes to the conclusions of this update as presented in the initial review. We can draw no conclusions to support the use of stiripentol as add-on treatment for drug-resistant focal epilepsy. Additional large, randomised, well-conducted trials are needed.

Stiripentol: A Review in Dravet Syndrome

Stiripentol (Diacomit^®) is an orally-active, structurally unique anti-epileptic drug (AED) with multiple potential mechanisms of action, including enhancement of central γ-aminobutyric acid transmission. In the EU, stiripentol is indicated for use in conjunction with clobazam and valproate as adjunctive therapy of refractory generalized tonic-clonic seizures in patients with Dravet syndrome (DS; previously known as severe myoclonic epilepsy of infancy), whose seizures are not adequately controlled with clobazam and valproate. This approval (and similar DS indications in the USA, Canada and Japan), reflect the results of the STICLO studies, two small, randomized controlled trials in which stiripentol as adjunctive therapy was associated with a markedly superior response rate after 2 months compared with placebo in patients aged between 3 and ≈ 21 years with DS that was inadequately controlled with clobazam and valproate. These short-term results have subsequently been supported and extended by findings from longer-term, open-label, observational studies, including a retrospective longitudinal cohort study, which showed that the efficacy of combining stiripentol with clobazam and valproate when started at paediatric age was maintained in mid-adulthood with up to 24 years of exposure, and up to 40 years of age. Drowsiness, appetite loss, weight loss, ataxia and tremor are the most common adverse events associated with the addition of stiripentol to clobazam and valproate. Based on the available evidence, stiripentol, as an adjunct to clobazam and valproate, is a demonstrably beneficial and generally well-tolerated second-line treatment for patients with DS.

Mechanisms of action of currently used antiseizure drugs

Antiseizure drugs (ASDs) prevent the occurrence of seizures; there is no evidence that they have disease-modifying properties. In the more than 160 years that orally administered ASDs have been available for epilepsy therapy, most agents entering clinical practice were either discovered serendipitously or with the use of animal seizure models. The ASDs originating from these approaches act on brain excitability mechanisms to interfere with the generation and spread of epileptic hyperexcitability, but they do not address the specific defects that are pathogenic in the epilepsies for which they are prescribed, which in most cases are not well understood. There are four broad classes of such ASD mechanisms: (1) modulation of voltage-gated sodium channels (e.g. phenytoin, carbamazepine, lamotrigine), voltage-gated calcium channels (e.g. ethosuximide), and voltage-gated potassium channels [e.g. retigabine (ezogabine)]; (2) enhancement of GABA-mediated inhibitory neurotransmission (e.g. benzodiazepines, tiagabine, vigabatrin); (3) attenuation of glutamate-mediated excitatory neurotransmission (e.g. perampanel); and (4) modulation of neurotransmitter release via a presynaptic action (e.g. levetiracetam, brivaracetam, gabapentin, pregabalin). In the past two decades there has been great progress in identifying the pathophysiological mechanisms of many genetic epilepsies. Given this new understanding, attempts are being made to engineer specific small molecule, antisense and gene therapies that functionally reverse or structurally correct pathogenic defects in epilepsy syndromes. In the near future, these new therapies will begin a paradigm shift in the treatment of some rare genetic epilepsy syndromes, but targeted therapies will remain elusive for the vast majority of epilepsies until their causes are identified. 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'.

Recent Advances in the Drug Treatment of Dravet Syndrome

Dravet syndrome is a rare but severe epilepsy syndrome that begins in the first year of life with recurrent seizures triggered by fever that are typically prolonged and hemiclonic. The epilepsy is highly drug resistant. Although development is normal at onset, over time, most patients develop moderate-to-severe intellectual disability, behavior disorders, and a characteristic crouch gait. There is a significant mortality, predominantly owing to sudden unexpected death in epilepsy. Complete seizure control is rarely attainable. Initial therapy includes valproic acid and clobazam, but response is typically inadequate. The results of new drugs for Dravet syndrome, including stiripentol, cannabidiol, and fenfluramine, are very promising. Stiripentol was associated with a greater than 50% reduction in convulsive seizure frequency in 71% of cases, when added to valproic acid and clobazam, and also markedly reduced status epilepticus. Pharmaceutical-grade cannabidiol resulted in a median change in monthly motor seizures from baseline of - 36.5%. Fenfluramine was associated with a greater than 50% reduction in seizures of 70%, with one quarter of cases achieving near seizure freedom over the duration of the trial. These agents are generally well tolerated, with few patients discontinuing for adverse effects. There is limited evidence to date regarding improvement in cognition with these newer agents; however, a meaningful change is challenging to assess over short trial periods and requires longer follow-up studies. While current treatments focus predominantly on seizure control, newer therapies including genetic treatments and antisense oligonucleotides can target the SCN1A channelopathy, and thus, may also significantly impact the important co-morbidities associated with this syndrome.

Diagnostic Yield and Treatment Impact of Targeted Exome Sequencing in Early-Onset Epilepsy

Targeted whole-exome sequencing (WES) is a powerful diagnostic tool for a broad spectrum of heterogeneous neurological disorders. Here, we aim to examine the impact on diagnosis, treatment and cost with early use of targeted WES in early-onset epilepsy. WES was performed on 180 patients with early-onset epilepsy (≤5 years) of unknown cause. Patients were classified as Retrospective (epilepsy diagnosis >6 months) or Prospective (epilepsy diagnosis <6 months). WES was performed on an Ion Proton™ and variant reporting was restricted to the sequences of 620 known epilepsy genes. Diagnostic yield and time to diagnosis were calculated. An analysis of cost and impact on treatment was also performed. A molecular diagnoses (pathogenic/likely pathogenic variants) was achieved in 59/180 patients (33%). Clinical management changed following WES findings in 23 of 59 diagnosed patients (39%) or 13% of all patients. A possible diagnosis was identified in 21 additional patients (12%) for whom supporting evidence is pending. Time from epilepsy onset to a genetic diagnosis was faster when WES was performed early in the diagnostic process (mean: 145 days Prospective vs. 2,882 days Retrospective). Costs of prior negative tests averaged $8,344 per patient in the Retrospective group, suggesting savings of $5,110 per patient using WES. These results highlight the diagnostic yield, clinical utility and potential cost-effectiveness of using targeted WES early in the diagnostic workup of patients with unexplained early-onset epilepsy. The costs and clinical benefits are likely to continue to improve. Advances in precision medicine and further studies regarding impact on long-term clinical outcome will be important.

Lactate dehydrogenase 5: identification of a druggable target to reduce oxaluria

Excessive excretion of oxalate in the urine results in the formation of calcium oxalate crystals and subsequent kidney stone formation. Severe forms of hyperoxaluria, including genetic forms and those that result from ethylene glycol poisoning, can result in end-stage renal disease. Therapeutic interventions are limited and often rely on dietary intervention. In this issue of the JCI, Le Dudal and colleagues demonstrate that the lactate dehydrogenase 5 inhibitor (LDH5) stiripentol reduces urinary oxalate excretion. Importantly, stiripentol treatment of a single individual with primary hyperoxaluria reduced the urinary oxalate excretion. Together, these results support further evaluation of LDH5 as a therapeutic target for hyperoxaluria.

Potentiating α2 subunit containing perisomatic GABAA receptors protects against seizures in a mouse model of Dravet syndrome

KEY POINTS

Dravet syndrome mice (Scn1a^+/- ) demonstrate a marked strain dependence for the severity of seizures which is correlated with GABA_A receptor α₂ subunit expression. The α₂ /α₃ subunit selective positive allosteric modulator (PAM) AZD7325 potentiates inhibitory postsynaptic currents (IPSCs) specifically in perisomatic synapses. AZD7325 demonstrates stronger effects on IPSCs in the seizure resistant mouse strain, consistent with higher α₂ subunit expression. AZD7325 demonstrates seizure protective effects in Scn1a^+/- mice without apparent sedative effects in vivo.

ABSTRACT

GABA_A receptor potentiators are commonly used for the treatment of epilepsy, but it is not clear whether targeting distinct GABA_A receptor subtypes will have disproportionate benefits over adverse effects. Here we demonstrate that the α₂ /α₃ selective positive allosteric modulator (PAM) AZD7325 preferentially potentiates hippocampal inhibitory responses at synapses proximal to the soma of CA1 neurons. The effect of AZD7325 on synaptic responses was more prominent in mice on the 129S6/SvEvTac background strain, which have been demonstrated to be seizure resistant in the model of Dravet syndrome (Scn1a^+/- ), and in which the α₂ GABA_A receptor subunits are expressed at higher levels relative to in the seizure prone C57BL/6J background strain. Consistent with this, treatment of Scn1a^+/- mice with AZD7325 elevated the temperature threshold for hyperthermia-induced seizures without apparent sedative effects. Our results in a model system indicate that selectively targeting α₂ is a potential therapeutic option for Dravet syndrome.

The therapeutic effect of stiripentol in Gabrg2+/Q390X mice associated with epileptic encephalopathy

Anti-seizure drugs (ASDs) are widely used and known to increase inhibitory tone on neuro-circuits and reduce aberrant synchronous firing in epilepsy. Some ASDs act as agonist at the GABA_A receptor. Stiripentol, known to increase GABA_A receptor activity as well as the metabolites of GABA_A receptor agonists, is often used in the treatment of an epileptic encephalopathy, Dravet syndrome (DS), which is caused by mutations mainly in SCN1A and in other genes such as GABRG2. We have recently generated a Gabrg2^+/Q390X knockin mouse model associated with DS in humans. The objective of the study was to explore the effects of stiripentol in DS with GABA_A receptor functional deficiency because of the etiology heterogeneity in DS. Monotherapy (stiripentol or Diazepam) and polytherapy (stiripentol and diazepam) treatments were tested in Gabrg2^+/Q390X mice challenged with pentylenetetrazol (PTZ) seizure induction in conjunction with video-monitoring synchronized electroencephalogram (EEG) recordings. A combination of stiripentol and diazepam greatly reduced seizure-related events in Gabrg2^+/Q390X mice following PTZ administration and increased survival. However, the treatment of stiripentol alone was mostly ineffective in alleviating seizure-related events except that it reduced mortality in PTZ challenged Gabrg2^+/Q390X mice. The study suggests that stiripentol could be only used as add-on therapy for DS with GABA_A receptor functional deficiency, which is consistent with the most established clinical application of stiripentol. The study highlights the importance of mechanism-based precision treatment for DS considering the highly heterogeneous nature of etiology in DS and the fact that mutations in different genes give rise to the same clinical phenotype.

Efficacy of Stiripentol and the Clinical Outcome in Dravet Syndrome

Dravet syndrome is a rare and progressive epileptic encephalopathy of infancy. Stiripentol reduces the seizure frequency in patients with Dravet syndrome. We evaluated the clinical characteristics of patients with Dravet syndrome and their response to stiripentol. We retrospectively collected the data of 21 patients (11 females; mean age, 8.2 years, range: 5.4-15 years) with Dravet syndrome who were treated with stiripentol in our outpatient clinic between June 2016 and June 2017. Patients with seizure reduction ≥50% were considered responders. Most of our patients had severe (47%) or moderate (33%) cognitive disabilities, although 14% had mild cognitive disability. There was a significant difference in both status epilepticus and age between the groups with normal/mild versus severe/moderate neurocognitive prognoses. Of the patients, 85.7% were using stiripentol. The mean duration of stiripentol use was 41.2 months (range: 24-64 months). In 12 patients (57%), the seizure frequency decreased by more than 50%, and 2 of them were seizure-free. Status epilepticus was not recorded after stiripentol treatment in 8 of 11 patients with status epilepticus. Despite the small sample size, our results suggest that stiripentol has a favorable efficacy. In addition, considering the absence of status epilepticus after treatment and the negative effects of status epilepticus on cognitive development, early treatment should be initiated in SD patients, for whom disease control is difficult.

Electrical Control in Neurons by the Ketogenic Diet

The ketogenic diet is used as a diet treatment for drug-resistant epilepsy, but there are no antiepileptic drugs based on the ketogenic diet. The ketogenic diet changes energy metabolites (ketone bodies, glucose and lactate) in the brain, which consequently changes electrical activities in neurons and ultimately suppresses seizures in epileptic patients. In order to elucidate the antiseizure effects of the ketogenic diet, it is important to clarify the mechanism by which these metabolic changes are converted to electrical changes in neurons. In this review, we summarize electrophysiological studies focusing on electrical control in neurons by the ketogenic diet. Recent studies have identified electrical regulators driven by the ketogenic diet: ion channels (ATP-sensitive K+ channels and voltage-dependent Ca2+ channels), synaptic receptors (AMPA-type glutamate receptors and adenosine A1 receptors), neurotransmitter transporters (vesicular glutamate transporters), and others (BCL-2-associated agonist of cell death and lactate dehydrogenase). Thus, the ketogenic diet presumably elicits neuronal inhibition via the combined actions of these molecules. From the viewpoint of drug development, these molecules are valuable as targets for the development of new antiepileptic drugs. Drug therapy to mimic the ketogenic diet may be feasible in the future, through the combination of multiple antiepileptic drugs targeting these molecules.

Stiripentol efficacy and safety in Dravet syndrome: a 12-year observational study

AIM

To assess long-term safety and efficacy of stiripentol as an antiepileptic medication for people with Dravet syndrome.

METHOD

A prospective, observational open-label study (2003-2015) of the efficacy and long-term safety of stiripentol in patients with Dravet syndrome and ongoing seizures. Frequency of generalized tonic-clonic seizures, focal seizures, status epilepticus, and adverse events were recorded.

RESULTS

Forty-one patients started stiripentol, with median age at enrolment 5 years 7 months (range 11mo-22y) and median duration of treatment 37 months (range 2-141mo). Twenty out of 41 patients had greater than or equal to 50% long-term reduction in frequency of generalized tonic-clonic seizures. Frequency of focal seizures was decreased by greater than or equal to 50% in 11 out of 23 patients over the long-term. Frequency of status epilepticus was decreased by 50% or more in 11 out of 26 patients. The most common adverse events were anorexia, weight loss, sedation, and behavioural changes. One patient had worsening of absence and myoclonic seizures. Another developed recurrent pancreatitis on concurrent valproate.

INTERPRETATION

Stiripentol improves long-term seizure frequency in approximately 50% of patients with Dravet syndrome, when used as part of unrestricted polytherapy. Long-term use appears safe. In more than 40% of patients, episodes of status epilepticus markedly decrease after stiripentol initiation. What this paper adds Frequency of status epilepticus is reduced in 40% of patients with Dravet syndrome after stiripentol initiation. Stiripentol is effective for generalized tonic-clonic and focal seizures. Stiripentol can be safely used with a range of antiepileptic drugs.

Stiripentol add-on therapy for focal refractory epilepsy

BACKGROUND

This is an updated version of the Cochrane review last published in 2015 (Issue 10). For nearly 30% of people with epilepsy, seizures are not controlled by current treatments. Stiripentol is a new antiepileptic drug (AED) that was developed in France and was approved by the European Medicines Agency (EMA) in 2007 for the treatment of Dravet syndrome as an adjunctive therapy with valproate and clobazam, with promising effects.

OBJECTIVES

To evaluate the efficacy and tolerability of stiripentol as add-on treatment for people with focal refractory epilepsy who are taking AEDs.

SEARCH METHODS

For the latest update, we searched the following databases on 21 August 2017: Cochrane Epilepsy Specialized Register, CENTRAL , MEDLINE, ClinicalTrials.gov, and the WHO International Clinical Trials Registry Platform (ICTRP). We contacted Biocodex (the manufacturer of stiripentol) and epilepsy experts to identify published, unpublished and ongoing trials.

SELECTION CRITERIA

Randomised, controlled, add-on trials of stiripentol in people with focal refractory epilepsy.

DATA COLLECTION AND ANALYSIS

Review authors independently selected trials for inclusion and extracted data. Outcomes investigated included 50% or greater reduction in seizure frequency, seizure freedom, adverse effects, treatment withdrawal and changes in quality of life.

MAIN RESULTS

On the basis of our selection criteria, we included no new studies in the present review. Only one study was included from the earlier review (32 children with focal epilepsy). This study adopted a 'responder enriched' design and found no clear evidence of a reduction in seizure frequency (≥ 50% seizure reduction) (risk ratio (RR) 1.51, 95% confidence interval (CI) 0.81 to 2.82, low-quality evidence) nor evidence of seizure freedom (RR 1.18, 95% CI 0.31 to 4.43, low-quality evidence) when add-on stiripentol was compared with placebo. Stiripentol led to a greater risk of adverse effects considered as a whole (RR 2.65, 95% CI 1.08 to 6.47, low-quality evidence). When specific adverse events were considered, confidence intervals were very wide and showed the possibility of substantial increases and small reductions in risks of neurological (RR 2.65, 95% CI 0.88 to 8.01, low-quality evidence) or gastrointestinal adverse effects (RR 11.56, 95% CI 0.71 to 189.36, low-quality evidence). Researchers noted no clear reduction in the risk of study withdrawal (RR 0.66, 95% CI 0.30 to 1.47, low-quality evidence), which was high in both groups (35.0% in add-on placebo and 53.3% in stiripentol group, low-quality evidence). The external validity of this study was limited because only responders to stiripentol (i.e. patients experiencing a ≥ 50% decrease in seizure frequency compared with baseline) were included in the randomised, add-on, placebo-controlled, double-blind phase. Furthermore, carry-over and withdrawal effects probably influenced outcomes related to seizure frequency. Very limited information derived from the only included study shows that adverse effects considered as a whole seemed to occur significantly more often with add-on stiripentol than with add-on placebo.

AUTHORS' CONCLUSIONS

Since the last version of this review was published, we have found no new studies. Hence, we have made no changes to the conclusions of this update as presented in the initial review. We can draw no conclusions to support the use of stiripentol as add-on treatment for focal refractory epilepsy. Additional large, randomised, well-conducted trials are needed.

Treatment Strategies for Dravet Syndrome

Dravet syndrome (DS) is a medically refractory epilepsy that onsets in the first year of life with prolonged seizures, often triggered by fever. Over time, patients develop other seizure types (myoclonic, atypical absences, drops), intellectual disability, crouch gait and other co-morbidities (sleep problems, autonomic dysfunction). Complete seizure control is generally not achievable with current therapies, and the goals of treatment are to balance reduction of seizure burden with adverse effects of therapies. Treatment of co-morbidities must also be addressed, as they have a significant impact on the quality of life of patients with DS. Seizures are typically worsened with sodium-channel agents. Accepted first-line agents include clobazam and valproic acid, although these rarely provide adequate seizure control. Benefit has also been noted with stiripentol, topiramate, levetiracetam, the ketogenic diet and vagal nerve stimulation. Several agents presently in development, specifically fenfluramine and cannabidiol, have shown efficacy in clinical trials. Status epilepticus is a recurring problem for patients with DS, particularly in their early childhood years. All patients should be prescribed a home rescue therapy (usually a benzodiazepine) but should also have a written seizure action plan that outlines when rescue should be given and further steps to take in the local hospital if the seizure persists despite home rescue therapy.

Efficacy of Stiripentol in Dravet Syndrome with or without SCN1A Mutations

Background and Purpose

The aim of this study was to determine the effectiveness of stiripentol (STP) add-on therapy to valproate and clobazam in patients with Dravet syndrome (DS) according to the presence of mutations in the sodium channel alpha-1 subunit gene (SCN1A).

Methods

We performed direct sequencing to analyze SCN1A mutations in 32 patients with clinically confirmed with DS, and classified them into mutation (pathogenic or likely pathogenic) and nonmutation groups based on American College of Medical Genetics and Genomics guidelines. We compared the efficacy of STP in reducing the seizure frequency between the two groups.

Results

The 32 patients comprised 15 patients in the mutation group (with definite SCN1A mutations) and 17 patients in the nonmutation group with variants of unknown significance or benign variants. The clinical profile did not differ significantly between the mutation and nonmutation groups. The seizure frequency relative to baseline reduced by 72.53±23.00% (mean±SD) in the mutation group versus 50.58±40.14% in the nonmutation group (p=0.004). The efficacy of STP was better in DS patients with missense mutations that in those with truncation mutations, and was not favorable in patients with mutations at linkers between domains (DII–DIII), linkers between segments of domain I (DI S1–S2), or splice sites, although the small number of patients prevented statistical analyses.

Conclusions

The efficacy of STP was significantly better in DS patients with definite SCN1A mutations than in those without mutations.