CPP-115, a vigabatrin analogue, decreases spasms in the multiple-hit rat model of infantile spasms

Revisiting the concept of drug-resistant epilepsy: A TASK1 report of the ILAE/AES Joint Translational Task Force

Despite progress in the development of anti-seizure medications (ASMs), one third of people with epilepsy have drug-resistant epilepsy (DRE). The working definition of DRE, proposed by the International League Against Epilepsy (ILAE) in 2010, helped identify individuals who might benefit from presurgical evaluation early on. As the incidence of DRE remains high, the TASK1 workgroup on DRE of the ILAE/American Epilepsy Society (AES) Joint Translational Task Force discussed the heterogeneity and complexity of its presentation and mechanisms, the confounders in drawing mechanistic insights when testing treatment responses, and barriers in modeling DRE across the lifespan and translating across species. We propose that it is necessary to revisit the current definition of DRE, in order to transform the preclinical and clinical research of mechanisms and biomarkers, to identify novel, effective, precise, pharmacologic treatments, allowing for earlier recognition of drug resistance and individualized therapies.

Cortical Parvalbumin-Positive Interneuron Development and Function Are Altered in the APC Conditional Knockout Mouse Model of Infantile and Epileptic Spasms Syndrome

Infantile and epileptic spasms syndrome (IESS) is a childhood epilepsy syndrome characterized by infantile or late-onset spasms, abnormal neonatal EEG, and epilepsy. Few treatments exist for IESS, clinical outcomes are poor, and the molecular and circuit-level etiologies of IESS are not well understood. Multiple human IESS risk genes are linked to Wnt/β-catenin signaling, a pathway that controls developmental transcriptional programs and promotes glutamatergic excitation via β-catenin's role as a synaptic scaffold. We previously showed that deleting adenomatous polyposis coli (APC), a component of the β-catenin destruction complex, in excitatory neurons (APC cKO mice, APCfl/fl x CaMKIIαCre) increased β-catenin levels in developing glutamatergic neurons and led to infantile behavioral spasms, abnormal neonatal EEG, and adult epilepsy. Here, we tested the hypothesis that the development of GABAergic interneurons (INs) is disrupted in APC cKO male and female mice. IN dysfunction is implicated in human IESS, is a feature of other rodent models of IESS, and may contribute to the manifestation of spasms and seizures. We found that parvalbumin-positive INs (PV+ INs), an important source of cortical inhibition, were decreased in number, underwent disproportionate developmental apoptosis, and had altered dendrite morphology at P9, the peak of behavioral spasms. PV+ INs received excessive excitatory input, and their intrinsic ability to fire action potentials was reduced at all time points examined (P9, P14, P60). Subsequently, GABAergic transmission onto pyramidal neurons was uniquely altered in the somatosensory cortex of APC cKO mice at all ages, with both decreased IPSC input at P14 and enhanced IPSC input at P9 and P60. These results indicate that inhibitory circuit dysfunction occurs in APC cKOs and, along with known changes in excitation, may contribute to IESS-related phenotypes.SIGNIFICANCE STATEMENT Infantile and epileptic spasms syndrome (IESS) is a devastating epilepsy with limited treatment options and poor clinical outcomes. The molecular, cellular, and circuit disruptions that cause infantile spasms and seizures are largely unknown, but inhibitory GABAergic interneuron dysfunction has been implicated in rodent models of IESS and may contribute to human IESS. Here, we use a rodent model of IESS, the APC cKO mouse, in which β-catenin signaling is increased in excitatory neurons. This results in altered parvalbumin-positive GABAergic interneuron development and GABAergic synaptic dysfunction throughout life, showing that pathology arising in excitatory neurons can initiate long-term interneuron dysfunction. Our findings further implicate GABAergic dysfunction in IESS, even when pathology is initiated in other neuronal types.

Animal Models in Epileptic Spasms and the Development of Novel Treatment Options

SUMMARY

The infantile spasms (IS) syndrome is a catastrophic developmental epileptic encephalopathy syndrome characterized by an age-specific expression of epileptic spasms that are associated with extremely abnormal, oftentimes described as chaotic, interictal EEG pattern known as hypsarrhythmia. Patients with IS generally have poor neurodevelopmental outcomes, in large part because of the frequent epileptic spasms and interictal EEG abnormalities. Current first-line treatments such as adrenocorticotropic hormone or vigabatrin are often ineffective and are associated with major toxic side effects. There is therefore a need for better and safer treatments for patients with IS, especially for the intractable population. Hope is on the horizon as, over the past 10 years, there has been robust progress in the development of etiology-specific animal models of IS. These models have been used to identify potential new treatments for IS and are beginning to provide some important insights into the pathophysiological substrates for this disease. In this review, we will highlight strengths and weaknesses of the currently available animal models of IS in addition to new insights into the pathophysiology and treatment options derived from these models.

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.

OV329, a novel highly potent γ-aminobutyric acid aminotransferase inactivator, induces pronounced anticonvulsant effects in the pentylenetetrazole seizure threshold test and in amygdala-kindled rats

OBJECTIVE

An attractive target to interfere with epileptic brain hyperexcitability is the enhancement of γ-aminobutyric acidergic (GABAergic) inhibition by inactivation of the GABA-metabolizing enzyme GABA aminotransferase (GABA-AT). GABA-AT inactivators were designed to control seizures by raising brain GABA levels. OV329, a novel drug candidate for the treatment of epilepsy and addiction, has been shown in vitro to be substantially more potent as a GABA-AT inactivator than vigabatrin, an antiseizure drug approved as an add-on therapy for adult patients with refractory complex partial seizures and monotherapy for pediatric patients with infantile spasms. Thus, we hypothesized that OV329 should produce pronounced anticonvulsant effects in two different rat seizure models.

METHODS

We therefore examined the effects of OV329 (5, 20, and 40 mg/kg ip) on the seizure threshold of female Wistar Unilever rats, using the timed intravenous pentylenetetrazole (ivPTZ) seizure threshold model as a seizure test particularly sensitive to GABA-potentiating manipulations, and amygdala-kindled rats as a model of difficult-to-treat temporal lobe epilepsy.

RESULTS

GABA-AT inactivation by OV329 clearly increased the threshold of both ivPTZ-induced and amygdala-kindled seizures. OV329 further showed a 30-fold greater anticonvulsant potency on ivPTZ-induced myoclonic jerks and clonic seizures compared to vigabatrin investigated previously. Notably, all rats were responsive to OV329 in both seizure models.

SIGNIFICANCE

These results reveal an anticonvulsant profile of OV329 that appears to be superior in both potency and efficacy to vigabatrin and highlight OV329 as a highly promising candidate for the treatment of seizures and pharmacoresistant epilepsies.

Antiepileptogenic effects of rapamycin in a model of infantile spasms due to structural lesions

OBJECTIVE

Infantile spasms may evolve into persistent epilepsies including Lennox-Gastaut syndrome. We compared adult epilepsy outcomes in models of infantile spasms due to structural etiology (multiple-hit model) or focal cortical inflammation and determined the anti-epileptogenic effects of pulse-rapamycin, previously shown to stop spasms in multiple-hit rats.

METHODS

Spasms were induced in 3-day-old male rats via right intracerebral doxorubicin/lipopolysaccharide (multiple-hit model) infusions. Controls and sham rats were used. Separate multiple-hit rats received pulse-rapamycin or vehicle intraperitoneally between postnatal days 4 and 6. In adult mice, video-EEG (electroencephalography) scoring for seizures and sleep and histology were done blinded to treatment.

RESULTS

Motor-type seizures developed in 66.7% of multiple-hit rats, usually from sleep, but were reduced in the pulse-rapamycin-treated group (20%, p = .043 vs multiple-hit) and rare in other groups (0-9.1%, p < .05 vs multiple-hit). Spike-and-wave bursts had a slower frequency in multiple-hit rats (5.4-5.8Hz) than in the other groups (7.6-8.3Hz) (p < .05); pulse rapamycin had no effect on the hourly spike-and-wave burst rates in adulthood. Rapamycin, however, reduced the time spent in slow-wave-sleep (17.2%), which was increased in multiple-hit rats (71.6%, p = .003). Sham rats spent more time in wakefulness (43.7%) compared to controls (30.6%, p = .043). Multiple-hit rats, with or without rapamycin treatment, had right more than left corticohippocampal, basal ganglia lesions. There was no macroscopic pathology in the other groups.

SIGNIFICANCE

Structural corticohippocampal/basal ganglia lesions increase the risk for post-infantile spasms epilepsy, Lennox-Gastaut syndrome features, and sleep dysregulation. Pulse rapamycin treatment for infantile spasms has anti-epileptogenic effects, despite the structural lesions, and decreases the time spent in slow wave sleep.

Remarkable and Unexpected Mechanism for (S)-3-Amino-4-(difluoromethylenyl)cyclohex-1-ene-1-carboxylic Acid as a Selective Inactivator of Human Ornithine Aminotransferase

Human ornithine aminotransferase (hOAT) is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that was recently found to play an important role in the metabolic reprogramming of hepatocellular carcinoma (HCC) via the proline and glutamine metabolic pathways. The selective inhibition of hOAT by compound 10 exhibited potent in vivo antitumor activity. Inspired by the discovery of the aminotransferase inactivator (1S,3S)-3-amino-4-(difluoromethylene)cyclopentane-1-carboxylic acid (5), we rationally designed, synthesized, and evaluated a series of six-membered-ring analogs. Among them, 14 was identified as a new selective hOAT inactivator, which demonstrated a potency 22× greater than that of 10. Three different types of protein mass spectrometry approaches and two crystallographic approaches were employed to identify the structure of hOAT-14 and the formation of a remarkable final adduct (32') in the active site. These spectral studies reveal an enzyme complex heretofore not observed in a PLP-dependent enzyme, which has covalent bonds to two nearby residues. Crystal soaking experiments and molecular dynamics simulations were carried out to identify the structure of the active-site intermediate 27' and elucidate the order of the two covalent bonds that formed, leading to 32'. The initial covalent reaction of the activated warhead occurs with *Thr322 from the second subunit, followed by a subsequent nucleophilic attack by the catalytic residue Lys292. The turnover mechanism of 14 by hOAT was supported by a mass spectrometric analysis of metabolites and fluoride ion release experiments. This novel mechanism for hOAT with 14 will contribute to the further rational design of selective inactivators and an understanding of potential inactivation mechanisms by aminotransferases.

Antiepileptogenesis and disease modification: Progress, challenges, and the path forward-Report of the Preclinical Working Group of the 2018 NINDS-sponsored antiepileptogenesis and disease modification workshop

Epilepsy is one of the most common chronic brain diseases and is often associated with cognitive, behavioral, or other medical conditions. The need for therapies that would prevent, ameliorate, or cure epilepsy and the attendant comorbidities is a priority for both epilepsy research and public health. In 2018, the National Institute of Neurological Disease and Stroke (NINDS) convened a workshop titled "Accelerating the Development of Therapies for Antiepileptogenesis and Disease Modification" that brought together preclinical and clinical investigators and industry and regulatory bodies' representatives to discuss and propose a roadmap to accelerate the development of antiepileptogenic (AEG) and disease-modifying (DM) new therapies. This report provides a summary of the discussions and proposals of the Preclinical Science working group. Highlights of the progress of collaborative preclinical research projects on AEG/DM of ongoing research initiatives aiming to improve infrastructure and translation to clinical trials are presented. Opportunities and challenges of preclinical epilepsy research, vis-à-vis clinical research, were extensively discussed, as they pertain to modeling of specific epilepsy types across etiologies and ages, the utilization of preclinical models in AG/DM studies, and the strategies and study designs, as well as on matters pertaining to transparency, data sharing, and reporting research findings. A set of suggestions on research initiatives, infrastructure, workshops, advocacy, and opportunities for expanding the borders of epilepsy research were discussed and proposed as useful initiatives that could help create a roadmap to accelerate and optimize preclinical translational AEG/DM epilepsy research.

Modeling epileptic spasms during infancy: Are we heading for the treatment yet?

Infantile spasms (IS or epileptic spasms during infancy) were first described by Dr. William James West (aka West syndrome) in his own son in 1841. While rare by definition (occurring in 1 per 3200-3400 live births), IS represent a major social and treatment burden. The etiology of IS varies - there are many (>200) different known pathologies resulting in IS and still in about one third of cases there is no obvious reason. With the advancement of genetic analysis, role of certain genes (such as ARX or CDKL5 and others) in IS appears to be important. Current treatment strategies with incomplete efficacy and serious potential adverse effects include adrenocorticotropin (ACTH), corticosteroids (prednisone, prednisolone) and vigabatrin, more recently also a combination of hormones and vigabatrin. Second line treatments include pyridoxine (vitamin B6) and ketogenic diet. Additional treatment approaches use rapamycin, cannabidiol, valproic acid and other anti-seizure medications. Efficacy of these second line medications is variable but usually inferior to hormonal treatments and vigabatrin. Thus, new and effective models of this devastating condition are required for the search of additional treatment options as well as for better understanding the mechanisms of IS. Currently, eight models of IS are reviewed along with the ideas and mechanisms behind these models, drugs tested using the models and their efficacy and usefulness. Etiological variety of IS is somewhat reflected in the variety of the models. However, it seems that for finding precise personalized approaches, this variety is necessary as there is no "one-size-fits-all" approach possible for both IS in particular and epilepsy in general.

Treatment of infantile spasms: why do we know so little?

INTRODUCTION

Infantile spasm (IS) is an epileptic syndrome with typical onset within the first 2 years of life. This condition might be caused by several etiologies. IS is associated with pathological neuronal networks; however, definite hypotheses on neurobiological processes are awaited.

AREAS COVERED

Changes in NMDA and GABA_B receptors and increase of Ca²⁺ conductance are some of the possible pathophysiological mechanisms. Animal models can help, but most have only some features of IS. Outcome is strongly affected by etiology and the timing of treatment, which relies still on ACTH, oral steroids, and vigabatrin. No significant differences in terms of efficacy have been documented, though a combination of ACTH and vigabatrin seems to be associated with better long-term outcomes. Despite the increasing knowledge about the etiology and pathophysiology of IS, in the last years, no new treatment approaches have been recognized to be able to modify the neurobiological process underlying IS. Precision medicine has far to come in IS.

EXPERT OPINION

Recently, no new therapeutic options for IS have emerged, probably due to the lack of reliable animal models and to the extreme variability in etiologies. Consequently, the outlook for patients and families is poor and early recognition and intervention remain research priorities.

Infantile Spasms: An Update on Pre-Clinical Models and EEG Mechanisms

Infantile spasms (IS) is an epileptic encephalopathy with unique clinical and electrographic features, which affects children in the middle of the first year of life. The pathophysiology of IS remains incompletely understood, despite the heterogeneity of IS etiologies, more than 200 of which are known. In particular, the neurobiological basis of why multiple etiologies converge to a relatively similar clinical presentation has defied explanation. Treatment options for this form of epilepsy, which has been described as “catastrophic” because of the poor cognitive, developmental, and epileptic prognosis, are limited and not fully effective. Until the pathophysiology of IS is better clarified, novel treatments will not be forthcoming, and preclinical (animal) models are essential for advancing this knowledge. Here, we review preclinical IS models, update information regarding already existing models, describe some novel models, and discuss exciting new data that promises to advance understanding of the cellular mechanisms underlying the specific EEG changes seen in IS—interictal hypsarrhythmia and ictal electrodecrement.

Applications of fluorine-containing amino acids for drug design

Fluorine-containing amino acids are becoming increasingly prominent in new drugs due to two general trends in the modern pharmaceutical industry. Firstly, the growing acceptance of peptides and modified peptides as drugs; and secondly, fluorine editing has become a prevalent protocol in drug-candidate optimization. Accordingly, fluorine-containing amino acids represent one of the more promising and rapidly developing areas of research in organic, bio-organic and medicinal chemistry. The goal of this Review article is to highlight the current state-of-the-art in this area by profiling 42 selected compounds that combine fluorine and amino acid structural elements. The compounds under discussion represent pharmaceutical drugs currently on the market, or in clinical trials as well as examples of drug-candidates that although withdrawn from development had a significant impact on the progress of medicinal chemistry and/or provided a deeper understanding of the nature and mechanism of biological action. For each compound, we present features of biological activity, a brief history of the design principles and the development of the synthetic approach, focusing on the source of tailor-made amino acid structures and fluorination methods. General aspects of the medicinal chemistry of fluorine-containing amino acids and synthetic methodology are briefly discussed.

AQB-565 shows promise in preclinical testing in the model of epileptic spasms during infancy: Head-to-head comparison with ACTH

Epileptic spasms during infancy (infantile spasms) represent a serious treatment and social problem despite their rare occurrence. Current treatments include hormonal therapy (adrenocorticotropin-ACTH or corticosteroids) or vigabatrin (per se or in the combination). These treatments are partially effective and with potentially significant adverse effects. Thus, the search for new effective drugs is warranted. We tested efficacy of a novel fusion peptide AQB-565 developed by Aequus Biopharma in a model of infantile spasms consisting of prenatal exposure to betamethasone and repeated postnatal trigger of spasms with N-methyl-d-aspartic acid (NMDA). AQB-565 molecule includes the first 24 amino acids of ACTH, a ten amino acid linker and a modified melanocyte-stimulating hormone molecule. In contrast to ACTH with almost uniform activity over all peripheral and central melanocortin receptor isoforms, AQB is preferentially active on central melanocortin receptors MC3 and MC4. Here, we used equivalent doses of rat ACTH (full molecule) and AQB-565 and compared their efficacy in a prospective randomized test against of repeated bouts of spasms on postnatal days (P)12, P13 and P15 in the rat model. All doses of ACTH (range 0.02-1.0 mg/kg s.c.) and all doses but one of AQB-565 in the same range suppressed spasms in P15 rats (treatment stopped on P14). There was no dose-dependent effect and both compounds had all-or-none effect that is similar to clinical outcome of hormonal treatment of infantile spasms in children. Thus, AQB-565 may represent a novel treatment of infantile spasms similarly effective as ACTH but with potentially limited side effects.

Negative geotaxis: An early age behavioral hallmark to VPA rat model of autism

Background

Negative geotaxis (NG) is an important parameter, commonly used in study of different CNS diseases and neurodevelopmental disorders. Neurobehavioural change following brain injury was easily identified by negative geotaxis.

Purpose

Although NG is evaluated in the settings of ASD, most of the studies are conducted for short duration (1-3 day) and the overall trend of acquisition of NG is not evaluated. In this context, we wanted to evaluate the trend of acquisition of negative geotaxis as a behavioural marker of autism in Valproic acid (VPA) model of ASD.

Methods

Dams in the VPA group were treated with intraperitoneal injections of VPA 600 mg/kg single dose on gestational day 12.5, while the control animals received normal saline of similar volume. Developmental parameters {body weight (PND 8, 10 & 12), body length (PND 4, 5, 6 8, 10), eye opening (PND 10, 12, 14, 15 and 16) and motor development (grid walking test on PND 20)} were monitored. Negative geotaxis test was performed at PND 6, 10, 15 and 17.

Results

The results of the present experiments demonstrate that VPA exposed rats exhibited delayed developmental parameters, aberration of the pattern of acquisition of negative geotaxis, enhanced negative geotaxis in early postnatal period (PND 6) and enhanced negative geotaxis in absence of visual clues (PND 17).

Conclusion

NG can be a valuable biomarker in early detection of autistic behavior and in absence of visual clues. The abberant negative geotaxis developmental pattern can serve as a marker to detect ASD. Thus NG can serve as an important early age biomarker of ASD. Further studies are required to validate this finding.

Treatment of infantile spasms

The treatment of infantile spasms is challenging, especially in the context of the following: (1) a severe phenotype with high morbidity and mortality; (2) the urgency of diagnosis and successful early response to therapy; and (3) the paucity of effective, safe, and well-tolerated therapies. Even after initially successful treatment, relapse risk is substantial and the most effective therapies pose considerable risk with long-term administration. In evaluating any treatment for infantile spasms, the key short-term outcome measure is freedom from both epileptic spasms and hypsarrhythmia. In contrast, the most important long-term outcomes are enduring seizure-freedom and measures of intellectual performance in later childhood and adulthood. First-line treatment options-namely hormonal therapy and vigabatrin-display moderate to high efficacy but also exhibit substantial side-effect burdens. Data on efficacy and safety of each class of therapy, as well as the combination of these therapies, are reviewed in detail. Specific hormonal therapies (adrenocorticotropic hormone and various corticosteroids) are contrasted. Those etiologies that prompt specific therapies are reviewed briefly, as are an array of second-line therapies supported by less-compelling data. The ketogenic diet is discussed in greater detail, with a focus on the limitations of numerous available studies that generally suggest that it is efficacious. Special discussion is allocated to cannabidiol-the investigational therapy that has received the most attention, and which is already in use in the form of various artisanal cannabis extracts. Finally, a treatment algorithm reflecting the concepts and controversies discussed in this review is presented.

Acquired parvalbumin-selective interneuronopathy in the multiple-hit model of infantile spasms: A putative basis for the partial responsiveness to vigabatrin analogs?

West syndrome, an age-specific epileptic encephalopathy, manifests with infantile spasms (IS) and impaired neurodevelopmental outcomes and epilepsy. The multiple-hit rat model of IS is a chronic model of IS due to structural etiology, in which spasms respond partially to vigabatrin analogs. Using this model, we investigated whether IS due to structural etiology may have deficits in parvalbumin (PRV) and somatostatin (SST) immunoreactive (-ir) interneurons, and calretinin-ir (CR-ir) neurons of the primary somatosensory cortex of postnatal day (PN) 20-24 rats, using specific immunohistochemical assays. PN3 Sprague-Dawley male rats underwent the multiple-hit induction protocol, were monitored until PN20-24, and were transcardially perfused to collect brains for histology. Age-matched sham and naive control male rats were also used. Coronal brain cryosections were stained with anti-PRV, anti-CR, and anti-SST antibodies, and regions of interest (ROIs) from the primary somatosensory cortices were selected to determine PRV-, CR-, and SST-ir cell counts and cortical ROI volumes, with blinding to experimental group. Statistical analyses were done using a linear mixed model accounting for repeated measures. We found PRV-ir interneuronal selective reduction, sparing of the CR-ir and SST-ir neurons, and bilateral cortical atrophy. Our findings provide evidence for acquired PRV-selective interneuronopathy, possibly underlying the pathogenesis of IS, neurodevelopmental deficits, and epilepsy, and potentially contributing to the partial response to vigabatrin analogs in this model.

A companion to the preclinical common data elements on neurobehavioral comorbidities of epilepsy: a report of the TASK3 behavior working group of the ILAE/AES Joint Translational Task Force

The provided companion has been developed by the Behavioral Working Group of the Joint Translational Task Force of the International League Against Epilepsy (ILAE) and the American Epilepsy Society (AES) with the purpose of assisting the implementation of Preclinical Common Data Elements (CDE) for studying and for reporting neurobehavioral comorbidities in rodent models of epilepsy. Case Report Forms (CRFs) are provided, which should be completed on a per animal/per test basis, whereas the CDEs are a compiled list of the elements that should be reported. This companion is not designed as a list of recommendations, or guidelines for how the tests should be run-rather, it describes the different types of assessments, and highlights the importance of rigorous data collection and transparency in this regard. The tests are divided into 7 categories for examining behavioral dysfunction on the syndrome level: deficits in learning and memory; depression; anxiety; autism; attention deficit/hyperactivity disorder; psychosis; and aggression. Correspondence and integration of these categories into the National Institute of Mental Health (NIMH) Research Domain Criteria (RDoC) is introduced. Developmental aspects are addressed through the introduction of developmental milestones. Discussion includes complexities, limitations, and biases associated with neurobehavioral testing, especially when performed in animals with epilepsy, as well as the importance of rigorous data collection and of transparent reporting. This represents, to our knowledge, the first such resource dedicated to preclinical CDEs for behavioral testing of rodents.

Design and Mechanism of GABA Aminotransferase Inactivators. Treatments for Epilepsies and Addictions

When the brain concentration of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) diminishes below a threshold level, the excess neuronal excitation can lead to convulsions. This imbalance in neurotransmission can be corrected by inhibition of the enzyme γ-aminobutyric acid aminotransferase (GABA-AT), which catalyzes the conversion of GABA to the excitatory neurotransmitter l-glutamic acid. It also has been found that raising GABA levels can antagonize the rapid elevation and release of dopamine in the nucleus accumbens, which is responsible for the reward response in addiction. Therefore, the design of new inhibitors of GABA-AT, which increases brain GABA levels, is an important approach to new treatments for epilepsy and addiction. This review summarizes findings over the last 40 or so years of mechanism-based inactivators (unreactive compounds that require the target enzyme to catalyze their conversion to the inactivating species, which inactivate the enzyme prior to their release) of GABA-AT with emphasis on their catalytic mechanisms of inactivation, presented according to organic chemical mechanism, with minimal pharmacology, except where important for activity in epilepsy and addiction. Patents, abstracts, and conference proceedings are not covered in this review. The inactivation mechanisms described here can be applied to the inactivations of a wide variety of unrelated enzymes.

In Vivo Detection of CPP-115 Target Engagement in Human Brain

CPP-115, a next-generation γ-amino butyric acid (GABA)-aminotransferase (AT) inhibitor, shows comparable pharmacokinetics, improved safety and tolerability, and a more favorable toxicity profile when compared with vigabatrin. The pharmacodynamic characteristics of CPP-115 remain to be evaluated. The present study employed state-of-the-art proton magnetic resonance spectroscopy techniques to measure changes in brain GABA+ (the composite resonance of GABA, homocarnosine, and macromolecules) concentrations in healthy subjects receiving oral daily doses of CPP-115 or placebo. Six healthy adult males were randomized to receive either single daily 80 mg doses of CPP-115 (n=4) or placebo (n=2) for 6, 10, or 14 days. Metabolite-edited spectra and two-dimensional J-resolved spectroscopy data were acquired from the parietal-occipital cortex and supplementary motor area in all subjects. Four scans were performed in each subject that included a predrug baseline measure, two scans during the dosing timeframe, and a final scan that occurred 1 week after drug cessation. CPP-115 induced robust and significant increases in brain GABA+ concentrations that ranged between 52 and 141% higher than baseline values. Elevated GABA+ concentrations returned to baseline values following drug clearance. Subjects receiving placebo showed no significant changes in GABA+ concentration. CPP-115-induced changes were exclusive to GABA and homocarnosine, and CPP-115 afforded brain GABA+ concentration changes comparable to or greater than previous vigabatrin spectroscopy studies in healthy epilepsy-naive subjects. The return to baseline GABA+ concentration indicates the reversible GABA-AT resynthesis following drug washout. These preliminary data warrant further spectroscopy studies that characterize the acute pharmacodynamic effects of CPP-115 with additional dose-descending measures.

A resurging boom in new drugs for epilepsy and brain disorders

INTRODUCTION

Epilepsy is one of the most common neurological diseases affecting approximately 50 million people worldwide. Despite many advances in epilepsy research, nearly a third of patients with epilepsy have refractory or pharmacoresistant epilepsy. Despite the approval of a dozen antiepileptic drugs (AEDs) over the past decade, there are no agents that halt the development of epilepsy. Thus, newer and better AEDs that can prevent refractory seizures and modify the disease are needed for curing epilepsy. Areas covered: In this article, we highlight the recent advances and emerging trends in new and innovative drugs for epilepsy and seizure disorders. We review in detail top new drugs that are currently in clinical trials or agents that are under development and have novel mechanisms of action. Expert commentary: Among the new agents under clinical investigation, the majority were originally developed for treating other neurological diseases (everolimus, fenfluramine, nalutozan, bumetanide, and valnoctamide); several have mechanisms of action similar to those of conventional AEDs (AP, ganaxolone, and YKP3089); and some new agents represent novel mechanisms of actions (huperzine-A, cannabidiol, tonabersat, and VX-765).

INTERNEURONOPATHIES AND THEIR ROLE IN EARLY LIFE EPILEPSIES AND NEURODEVELOPMENTAL DISORDERS

GABAergic interneurons control the neural circuitry and network activity in the brain. The advances in genetics have identified genes that control the development, maturation and integration of GABAergic interneurons and implicated them in the pathogenesis of epileptic encephalopathies or neurodevelopmental disorders. For example, mutations of the Aristaless-Related homeobox X-linked gene (ARX) may result in defective GABAergic interneuronal migration in infants with epileptic encephalopathies like West syndrome (WS), Ohtahara syndrome or X-linked lissencephaly with abnormal genitalia (XLAG). The concept of "interneuronopathy", i.e. impaired development, migration or function of interneurons, has emerged as a possible etiopathogenic mechanism for epileptic encephalopathies. Treatments that enhance GABA levels, may help seizure control but do not necessarily show disease modifying effect. On the other hand, interneuronopathies can be seen in other conditions in which epilepsy may not be the primary manifestation, such as autism. In this review, we plan to outline briefly the current state of knowledge on the origin, development, and migration and integration of GABAergic interneurons, present neurodevelopmental conditions, with or without epilepsy, that have been associated with interneuronopathies and discuss the evidence linking certain types of interneuronal dysfunction with epilepsy and/or cognitive or behavioral deficits.

Neuroinflammation in epileptogenesis: Insights and translational perspectives from new models of epilepsy

Animal models have provided a wealth of information on mechanisms of epileptogenesis and comorbidogenesis, and have significantly advanced our ability to investigate the potential of new therapies. Processes implicating brain inflammation have been increasingly observed in epilepsy research. Herein we discuss the progress on animal models of epilepsy and comorbidities that inform us on the potential role of inflammation in epileptogenesis and comorbidity pathogenesis in rodent models of West syndrome and the Theiler's murine encephalomyelitis virus (TMEV) mouse model of viral encephalitis-induced epilepsy. Rat models of infantile spasms were generated in rat pups after right intracerebral injections of proinflammatory compounds (lipopolysaccharides with or without doxorubicin, or cytokines) and were longitudinally monitored for epileptic spasms and neurodevelopmental and cognitive deficits. Anti-inflammatory treatments were tested after the onset of spasms. The TMEV mouse model was induced with intracerebral administration of TMEV and prospective monitoring for handling-induced seizures or seizure susceptibility, as well as long-term evaluations of behavioral comorbidities of epilepsy. Inflammatory processes are evident in both models and are implicated in the pathogenesis of the observed seizures and comorbidities. A common feature of these models, based on the data so far available, is their pharmacoresistant profile. The presented data support the role of inflammatory pathways in epileptogenesis and comorbidities in two distinct epilepsy models. Pharmacoresistance is a common feature of both inflammation-based models. Utilization of these models may facilitate the identification of age-specific, syndrome- or etiology-specific therapies for the epilepsies and attendant comorbidities, including the drug-resistant forms.

Rational Optimization of Mechanism-Based Inhibitors through Determination of the Microscopic Rate Constants of Inactivation

Mechanism-based inhibitors (MBIs) are widely employed in chemistry, biology, and medicine because of their exquisite specificity and sustained duration of inhibition. Optimization of MBIs is complicated because of time-dependent inhibition resulting from multistep inactivation mechanisms. The global kinetic parameters k_inact and K_I have been used to characterize MBIs, but they provide far less information than is commonly assumed, as shown by derivation and simulation of these parameters. We illustrate an alternative and more rigorous approach for MBI characterization through determination of the individual microscopic rate constants. Kinetic analysis revealed the rate-limiting step of inactivation of the PLP-dependent enzyme BioA by dihydro-(1,4)-pyridone 1. This knowledge was subsequently applied to rationally design a second-generation inhibitor scaffold with a nearly optimal maximum inactivation rate (0.48 min^-1).

Preclinical Screening for Treatments for Infantile Spasms in the Multiple Hit Rat Model of Infantile Spasms: An Update

Infantile spasms are the typical seizures of West syndrome, an infantile epileptic encephalopathy with poor outcomes. There is an increasing need to identify more effective and better tolerated treatments for infantile spasms. We have optimized the rat model of infantile spasms due to structural etiology, the multiple-hit rat model, for therapy discovery. Here, we test three compounds administered after spasms induction in the multiple hit model for efficacy and tolerability. Specifically, postnatal day 3 (PN3) male Sprague-Dawley rats were induced by right intracerebral injections of doxorubicin and lipopolysaccharide. On PN5 p-chlorophenylalanine was given intraperitoneally (i.p.). Daily monitoring of weights and developmental milestones was done and rats were intermittently video monitored. A blinded, randomized, vehicle-controlled study design was followed. The caspase 1 inhibitor VX-765 (50-200 mg/kg i.p.) and the GABA_B receptor inhibitor CGP35348 (12.5-100 mg/kg i.p.) each was administered in different cohorts as single intraperitoneal injections on PN4, using a dose- and time-response design with intermittent monitoring till PN5. 17β-estradiol (40 ng/g/day subcutaneously) was given daily between PN3-10 and intermittent monitoring was done till PN12. None of the treatments demonstrated acute or delayed effects on spasms, yet all were well tolerated. We discuss the implications for therapy discovery and challenges of replication trials.

Inflammation in Epileptic Encephalopathies

West syndrome (WS) is an infantile epileptic encephalopathy that manifests with infantile spasms (IS), hypsarrhythmia (in ~60% of infants), and poor neurodevelopmental outcomes. The etiologies of WS can be structural-metabolic pathologies (~60%), genetic (12%-15%), or of unknown origin. The current treatment options include hormonal treatment (adrenocorticotropic hormone and high-dose steroids) and the GABA aminotransferase inhibitor vigabatrin, while ketogenic diet can be given as add-on treatment in refractory IS. There is a need to identify new therapeutic targets and more effective treatments for WS. Theories about the role of inflammatory pathways in the pathogenesis and treatment of WS have emerged, being supported by both clinical and preclinical data from animal models of WS. Ongoing advances in genetics have revealed numerous genes involved in the pathogenesis of WS, including genes directly or indirectly involved in inflammation. Inflammatory pathways also interact with other signaling pathways implicated in WS, such as the neuroendocrine pathway. Furthermore, seizures may also activate proinflammatory pathways raising the possibility that inflammation can be a consequence of seizures and epileptogenic processes. With this targeted review, we plan to discuss the evidence pro and against the following key questions. Does activation of inflammatory pathways in the brain cause epilepsy in WS and does it contribute to the associated comorbidities and progression? Can activation of certain inflammatory pathways be a compensatory or protective event? Are there interactions between inflammation and the neuroendocrine system that contribute to the pathogenesis of WS? Does activation of brain inflammatory signaling pathways contribute to the transition of WS to Lennox-Gastaut syndrome? Are there any lead candidates or unexplored targets for future therapy development for WS targeting inflammation?

Not all that glitters is gold: A guide to critical appraisal of animal drug trials in epilepsy

Preclinical studies have produced numerous drugs with antiseizure properties that currently are the standard of care. One third of the human population with epilepsy still continues to have seizures despite the ongoing discoveries. The recognized clinical gaps of care that need to be addressed are the identification of antiepileptogenic and disease‐modifying treatments, and treatments for refractory seizures or for seizures and epilepsies with limited or unsatisfactory treatments, such as early life epileptic encephalopathies. In this invited review, we provide a historical summary of the international efforts to reevaluate the strategies adopted in preclinical epilepsy therapy discovery studies. We discuss issues that may affect the quality, interpretation, and validation of preclinical studies and their translation to successful therapies for humans affected with epilepsy. These include the selection of animal models and the study design; research practices that affect rigor (such as appropriate use of statistics and reporting of study methods and results, their validation across models, labs, and preclinical‐clinical studies); the need to harmonize research methods and outcome assessment; and the importance of improving translation to clinically appropriate situations. The epilepsy research community is incrementally adopting collaborative research, including consortia or multicenter studies to meet these needs. Improving the infrastructure that can support these efforts will be instrumental in future success.

A case report on the efficacy of vigabatrin analogue (1S, 3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (CPP-115) in a patient with infantile spasms

West Syndrome is characterized by infantile spasms, a hypsarrhythmic electroencephalogram (EEG) pattern, and a poor neurodevelopmental prognosis. First-line treatments include adrenocorticotrophic hormone (ACTH) and vigabatrin, but adverse effects often limit their use. CPP-115 is a high-affinity vigabatrin analogue developed to increase therapeutic potency and to limit retinal toxicity. Here, we present a child treated with CPP-115 through an investigational new drug protocol who experienced a marked reduction of seizures with no evidence of retinal dysfunction. Given the potential consequences of ongoing infantile spasms and the limitations of available treatments, further assessment of CPP-115 is warranted.

Pediatric Epileptic Encephalopathies: Pathophysiology and Animal Models

Epileptic encephalopathies are syndromes in which seizures or interictal epileptiform activity contribute to or exacerbate brain function, beyond that caused by the underlying pathology. These severe epilepsies begin early in life, are associated with poor lifelong outcome, and are resistant to most treatments. Therefore, they represent an immense challenge for families and the medical care system. Furthermore, the pathogenic mechanisms underlying the epileptic encephalopathies are poorly understood, hampering attempts to devise novel treatments. This article reviews animal models of the three classic epileptic encephalopathies-West syndrome (infantile spasms), Lennox-Gastaut syndrome, and continuous spike waves during sleep or Landau-Kleffner syndrome-with discussion of how animal models are revealing underlying pathophysiological mechanisms that might be amenable to targeted therapy.

Stiripentol and vigabatrin current roles in the treatment of epilepsy

INTRODUCTION

Stiripentol and vigabatrin are the two anticonvulsant drugs currently approved in severe infantile-onset epilepsies, respectively Dravet syndrome and infantile spasms.

AREAS COVERED

For both, the indication was discovered by chance thanks to an exploratory study. Both demonstrated indisputable efficacy through randomized-controlled trials. Stiripentol as adjunctive therapy to clobazam and valproate performed better than placebo, and vigabatrin as first-line monotherapy better than the reference steroid therapy in spasms due to tuberous sclerosis. At one-year treatment vigabatrin and steroids were equally efficient in the other etiologies of spasms. However, it took more than 20 years for both drugs to be approved world-wide.

EXPERT OPINION

Stiripentol suffered from pharmacokinetic potentiation of clobazam, thus raising the question whether it was efficient per se. Finally, animal models and pharmacogenetic data on CYP2C19 confirmed its specific anticonvulsant effect. Stiripentol (in comedication with clobazam and valproate) is therefore to be recommended for Dravet patients. Vigabatrin was found to have a frequent and irreversible retinal toxicity, which required an alternative visual testing to be detected in young children. Today the benefit/risk ratio of vigabatrin as first-line is considered to be positive in infantile spasms, given the severity of this epilepsy and the lack of a safer alternative therapy.

Phenotypic abnormalities in a chorea-acanthocytosis mouse model are modulated by strain background

Chorea-acanthocytosis (ChAc) is an autosomal recessive hereditary disease characterized by neurodegeneration in the striatum and acanthocytosis that is caused by mutations in the VPS13A gene. We previously produced a ChAc model mice encoding a human disease mutation with deletion of exons 60-61 in the VPS13A gene. The behavioral and pathological phenotypes of the model mice varied a good deal from individual to individual, indicating that differences between individuals may be caused by the content of a genetic hybrid 129/Sv and C57BL/6J strain background. To establish the effect of the genetic background on phenotype, we backcrossed the ChAc-model mice to different inbred strains: C57BL/6J and 129S6/Sv. Although no significant difference between ChAc-mutant mice and wild-type mice on the C57BL/6J background was observed, the ChAc-mutant mice on the 129S6/Sv showed abnormal motor function and behavior. Furthermore, we produced ChAc-mutant mice on two different inbred strains: BALB/c and FVB. Significant reduction in weight was observed in ChAc mutant mice on the FVB and 129S6 backgrounds. We found a marked increase in the osmotic fragility of red blood cells in the ChAc mutant mice backcrossed to 129S6/Sv and FVB. The phenotypes varied according to strain, with ChAc mutant mice on the FVB and 129S6 backgrounds showing remarkably abnormal motor function and behavior. These results indicate that there are modifying genetic factors of ChAc symptoms.

Neonatal and Infantile Epilepsy: Acquired and Genetic Models

The incidence of seizures and epilepsies is particularly high during the neonatal and infantile periods. We will review selected animal models of early-life epileptic encephalopathies that have addressed the dyscognitive features of frequent interictal spikes, the pathogenesis and treatments of infantile spasms (IS) or Dravet syndrome, disorders with mammalian target of rapamycin (mTOR) dysregulation, and selected early-life epilepsies with genetic defects. Potentially pathogenic mechanisms in these conditions include interneuronopathies in IS or Dravet syndrome and mTOR dysregulation in brain malformations, tuberous sclerosis, and related genetic disorders, or IS of acquired etiology. These models start to generate the first therapeutic drugs, which have been specifically developed in immature animals. However, there are challenges in translating preclinical discoveries into clinically relevant findings. The advances made so far hold promise that the new insights may potentially have curative or disease-modifying potential for many of these devastating conditions.

Pathogenesis and new candidate treatments for infantile spasms and early life epileptic encephalopathies: A view from preclinical studies

Early onset and infantile epileptic encephalopathies (EIEEs) are usually associated with medically intractable or difficult to treat epileptic seizures and prominent cognitive, neurodevelopmental and behavioral consequences. EIEEs have numerous etiologies that contribute to the inter- and intra-syndromic phenotypic variability. Etiologies include structural and metabolic or genetic etiologies although a significant percentage is of unknown cause. The need to better understand their pathogenic mechanisms and identify better therapies has driven the development of animal models of EIEEs. Several rodent models of infantile spasms have emerged that recapitulate various aspects of the disease. The acute models manifest epileptic spasms after induction and include the NMDA rat model, the NMDA model with prior prenatal betamethasone or perinatal stress exposure, and the γ-butyrolactone induced spasms in a mouse model of Down syndrome. The chronic models include the tetrodotoxin rat model, the aristaless related homeobox X-linked (Arx) mouse models and the multiple-hit rat model of infantile spasms. We will discuss the main features and findings from these models on target mechanisms and emerging therapies. Genetic models have also provided interesting data on the pathogenesis of Dravet syndrome and proposed new therapies for testing. The genetic associations of many of the EIEEs have also been tested in rodent models as to their pathogenicity. Finally, several models have tested the impact of subclinical epileptiform discharges on brain function. The impact of these advances in animal modeling for therapy development will be discussed.

Early life status epilepticus and stress have distinct and sex-specific effects on learning, subsequent seizure outcomes, including anticonvulsant response to phenobarbital

AIMS

Neonatal status epilepticus (SE) is often associated with adverse cognitive and epilepsy outcomes. We investigate the effects of three episodes of kainic acid-induced SE (3KA-SE) and maternal separation in immature rats on subsequent learning, seizure susceptibility, and consequences, and the anticonvulsant effects of phenobarbital, according to sex, type, and age at early life (EL) event.

METHODS

3KA-SE or maternal separation was induced on postnatal days (PN) 4-6 or 14-16. Rats were tested on Barnes maze (PN16-19), or lithium-pilocarpine SE (PN19) or flurothyl seizures (PN32). The anticonvulsant effects of phenobarbital (20 or 40 mg/kg/rat, intraperitoneally) pretreatment were tested on flurothyl seizures. FluoroJadeB staining assessed hippocampal injury.

RESULTS

3KA-SE or separation on PN4-6 caused more transient learning delays in males and did not alter lithium-pilocarpine SE latencies, but aggravated its outcomes in females. Anticonvulsant effects of phenobarbital were preserved and potentiated in specific groups depending on sex, type, and age at EL event.

CONCLUSIONS

Early life 3KA-SE and maternal separation cause more but transient cognitive deficits in males but aggravate the consequences of subsequent lithium-pilocarpine SE in females. In contrast, on flurothyl seizures, EL events showed either beneficial or no effect, depending on gender, type, and age at EL events.

Mechanisms of epileptogenesis in pediatric epileptic syndromes: Rasmussen encephalitis, infantile spasms, and febrile infection-related epilepsy syndrome (FIRES)

The mechanisms of epileptogenesis in pediatric epileptic syndromes are diverse, and may involve disturbances of neurodevelopmental trajectories, synaptic homeostasis, and cortical connectivity, which may occur during brain development, early infancy, or childhood. Although genetic or structural/metabolic factors are frequently associated with age-specific epileptic syndromes, such as infantile spasms and West syndrome, other syndromes may be determined by the effect of immunopathogenic mechanisms or energy-dependent processes in response to environmental challenges, such as infections or fever in normally-developed children during early or late childhood. Immune-mediated mechanisms have been suggested in selected pediatric epileptic syndromes in which acute and rapidly progressive encephalopathies preceded by fever and/or infections, such as febrile infection-related epilepsy syndrome, or in chronic progressive encephalopathies, such as Rasmussen encephalitis. A definite involvement of adaptive and innate immune mechanisms driven by cytotoxic CD8(+) T lymphocytes and neuroglial responses has been demonstrated in Rasmussen encephalitis, although the triggering factor of these responses remains unknown. Although the beneficial response to steroids and adrenocorticotropic hormone of infantile spasms, or preceding fever or infection in FIRES, may support a potential role of neuroinflammation as pathogenic factor, no definite demonstration of such involvement has been achieved, and genetic or metabolic factors are suspected. A major challenge for the future is discovering pathogenic mechanisms and etiological factors that facilitate the introduction of novel targets for drug intervention aimed at interfering with the disease mechanisms, therefore providing putative disease-modifying treatments in these pediatric epileptic syndromes.

Recent advances in the pharmacotherapy of infantile spasms

Adrenocorticotrophic hormone (ACTH), oral corticosteroids and vigabatrin are now first-line treatments for infantile spasms in the US and Europe. There is now increased knowledge regarding the role of ACTH, corticosteroids and vigabatrin (e.g. efficacy, doses, side effects, treatment in specific aetiological subtypes of infantile spasms), and other antiepileptic drugs (i.e. topiramate, valproate, zonisamide, sulthiame, levetiracetam, lamotrigine, pyridoxine, ganaxolone), as well as adjunctive flunarizine and novel drugs not yet in clinical use for infantile spasms (i.e. pulse rapamycin and melanocortin receptor agonists). The existence of a latent period, weeks to months following a precipitating brain insult, raises the possibility of preventive interventions. Recent experimental data emerging from animal models of infantile spasms have provided optimism that new and innovative treatments can be developed, and knowledge that drug treatment can affect long-term cognitive outcome is increasing. The aim of this article is to review recent developments in the pharmacotherapy of infantile spasms and to highlight the practical implications of the latest research.