Perampanel, an antagonist of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, for the treatment of epilepsy: studies in human epileptic brain and nonepileptic brain and in rodent models

AMPA receptors play an important role in the biological consequences of spinal cord injury: Implications for AMPA receptor modulators for therapeutic benefit

Spinal cord injury (SCI) afflicts millions of individuals globally. There are few therapies available to patients. Ascending and descending excitatory glutamatergic neural circuits in the central nervous system are disrupted by SCI, making α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) a potential therapeutic drug target. Emerging research in preclinical models highlights the involvement of AMPARs in vital processes following SCI including breathing, pain, inflammation, bladder control, and motor function. However, there are no clinical trial data reported in this patient population to date. No work on the role of AMPA receptors in sexual dysfunction after SCI has been disclosed. Compounds with selective antagonist and potentiating effects on AMPA receptors have benefit in animal models of SCI, with antagonists generally showing protective effects early after injury and potentiators (ampakines) producing improved breathing and bladder function. The role of AMPARs in pathophysiology and recovery after SCI depends upon the time post injury, and the timing of AMPAR augmentation or antagonism. The roles of inflammation, synaptic plasticity, sensitization, neurotrophic factors, and neuroprotection are considered in this context. The data summarized and discussed in this paper document proof of principle and strongly encourage additional studies on AMPARs as novel gateways to therapeutic benefit for patients suffering from SCI. The availability of both AMPAR antagonists such as perampanel and AMPAR allosteric modulators (i.e., ampakines) such as CX1739, that have been safely administered to humans, provides an expedited means of clinical inquiry for possible therapeutic advances.

Long-term treatment with Perampanel of Chinese patients with focal-onset seizures, especially in sleep-related epilepsy: a prospective real-world observational study

Background

There is currently a lack of studies examining the long-term therapeutic effectiveness of the third-generation anti-sezure medication, perampanel (PER), for focal-onset seizures (FOS), particularly in Chinese patients with sleep-related epilepsy (SRE). Additionally, the appropriate dosage, plasma concentration, and the relationship between dose and plasma concentration of PER in Chinese patients are still uncertain.

Methods

A prospective, single-center, 24-month observational study was conducted in patients diagnosed with FOS, with a focus on patients with SRE. Changes in seizure frequency from baseline, adverse events, and retention rates were analyzed at 12 and 24 months following the start of the treatment. Tolerability was evaluated based on adverse events and discontinuation profiles. PER plasma concentrations were used to assess dose-concentration-response relationships.

Results

A total of 175 patients were included (median age: 25 years; range: 4-72 years; 53. 1% males and 46.9% females), with the SRE population accounting for 49. 1% (n = 86). The patients diagnosed with SRE showed considerably higher response rates than those who did not have this diagnosis (p = 0.025, odds ratio = 3.8). Additionally, the SRE group adhered better to PER treatment (r = 0.0009). Patients with a shorter duration of epilepsy (median: 3 years; range:2-7 years) demonstrated a more favorable therapeutic response to PER (p = 0.032). Throughout the administration of maintenance doses, among the entire FOS population, the concentration of PER (C0) ranged between 101.5 and 917.4 ng/mL (median, 232.0 ng/mL), and the mean plasma concentration of PER in the responders was 292.8 ng/mL. We revealed a linear relationship between PER dose and plasma concentration, regardless of whether PER was used as monotherapy or add-on therapy. The retention rates were 77.7% and 65. 1% at 12 and 24 months, respectively. Drug-related adverse events occurred in 45.0% of the patients and were mostly manageable.

Conclusion

PER effectively reduced seizure frequency in Chinese patients with FOS, particularly in those with SRE, over a 24-month period. The treatment was well-tolerated and had a clear linear dose-plasma concentration relationship.

KRM-II-81 suppresses epileptifom activity across the neural network of cortical tissue from a patient with pharmacoresistant epilepsy

A clinical case of a 19-year-old male patient with pharmacoresistant seizures occurring following parieto-occipital tumor-resection at age 6 is described. Seizure surgery work-up included prolonged video EEG monitoring and head CT without contrast. Seizure focus was localized to the left temporal lobe, and we felt that the patient was an excellent candidate for seizure surgery. The patient underwent a left frontotemporal craniotomy for removal of the seizure focus with intraoperative electrocorticography (ECoG) conducted pre and post resection. ECoG recordings pre- and post-resection confirmed resolution of seizure generation. Imaging obtained immediately postoperatively showed complete resection of the residual tumor with no evidence of recurrence in follow-ups. A year after the surgery the patient is seizure-free but remains on seizure medication. With the patient's consent the excised epileptogenic tissue was used for ex-vivo research studies. The microelectrode recordings confirmed epileptiform activity in the excised tissue incubated in excitatory artificial cerebrospinal fluid. The epileptiform activity in the epileptogenic tissue was suppressed by addition of KRM-II-81, a novel α2/3 subtype preferring GABAA receptor (GABAAR) potentiator with previously demonstrated antiepileptic efficacy in multiple animal models of epilepsy and with reduced potential for CNS side-effects compared to classical benzodiazepine GABAAR potentiators. These findings support the proposition that KRM-II-81 might reduce seizure burden in pharmacoresistant patients.

Thiazole Derivatives as Modulators of GluA2 AMPA Receptors: Potent Allosteric Effects and Neuroprotective Potential

Thiazole carboxamide derivatives were synthesized in this investigation, with a subsequent examination of their impact on GluA2 AMPA receptors. The synthesized compounds, namely MMH-1-5, were subjected to characterization using high-resolution mass spectrometry (HRMS), proton nuclear magnetic resonance (1H-NMR), and carbon-13 nuclear magnetic resonance (13C-NMR). The present work thoroughly investigates the impact of five thiazole derivatives on GluA2 AMPA receptors. This investigation examined their effects on both whole-cell currents and receptor kinetics. In addition, the cytotoxicity of the samples was assessed using the MTS test. The compound MMH-5 had the highest effect level, resulting in a notable drop in current amplitude by a factor of six. Similarly, MMH-4 and MMH-3 also caused major reductions in the current amplitude. The compounds mentioned above also influenced the rates of deactivation and desensitization. MMH-5 and MMH-4 exhibited an increase in deactivation, while MMH-5 showed reduced desensitization. Our research findings highlight the efficacy of MMH-5 as a negative allosteric modulator of GluA2 AMPA receptors, exerting substantial effects on both the magnitude and time course of receptor activity. Significantly, the compound MMH-2 demonstrated noteworthy cytotoxic effects, as evidenced by cell viability rates dropping below 6.79% for all cancer cell lines and 17.52% for the normal cell line (LX-2). Of particular interest is the pronounced cytotoxicity observed in MMH-5, suggesting its potential as a safe neuroprotective agent targeting the AMPA receptor, as indicated by cell viability percentages exceeding 85.44% across all cancer and normal cell lines. Docking simulations were performed to determine possible modes of interaction between MMH5 and the GluA2-AMPA receptor (PDB:7RZ5). The abovementioned facts and the well-documented effects of further thiazole derivatives provide a strong foundation for future research endeavors to enhance tailored treatments for neurological disorders that rely heavily on GluA2 signaling. The present study elucidates the intricate association between thiazole derivatives and GluA2 receptors, providing valuable perspectives on the prospects of enhanced and specific therapeutic interventions for diverse neurological conditions.

Role of kainate receptors in pruriceptive processing in the mouse spinal cord

Pruritus, including neuropathic and psychogenic pruritus, is an unpleasant feeling that causes a desire to scratch, which negatively impacts physical and psychological aspects of daily life. Nonetheless, little is known about the neural mechanisms involved in pruritus. Glutamate is a predominant excitatory neurotransmitter in the mammalian central nervous system and exerts its effects by binding to various glutamate receptors, including kainate (KA) receptors; however, the precise involvement of each glutamate receptor in pruriceptive processing remains unclear, particularly that of KA receptors. Therefore, the roles of KA receptors in histamine-dependent and -independent itch were investigated using CNQX, an AMPA/KA receptors antagonist, UBP310 and UBP302, antagonists of KA receptors, and small interfering (si)RNAs against KA receptor subunits in mice with acute and chronic pruritus. The effects of KA receptor antagonists on histamine-induced c-Fos expression in the spinal cord were also examined. The intrathecal administration of CNQX reduced the number of scratching events induced by histamine and chloroquine. On the other hand, UBP310 or UBP302 and the siRNAs of KA receptor subunits 1-3 significantly inhibited the induction of scratching events in mice treated with histamine, while no significant change was observed in the induction of spontaneous scratching events in mice with chronic pruritus. In addition, antagonists of KA receptors attenuated c-Fos expression in the superficial layers of the dorsal horn induced by histamine. These results indicate that KA receptors are involved in acute pruriceptive processing in the spinal cord induced by histamine, but not chloroquine or chronic itch.

The broad-spectrum activity of perampanel: state of the art and future perspective of AMPA antagonism beyond epilepsy

Glutamate is the brain's main excitatory neurotransmitter. Glutamatergic neurons primarily compose basic neuronal networks, especially in the cortex. An imbalance of excitatory and inhibitory activities may result in epilepsy or other neurological and psychiatric conditions. Among glutamate receptors, AMPA receptors are the predominant mediator of glutamate-induced excitatory neurotransmission and dictate synaptic efficiency and plasticity by their numbers and/or properties. Therefore, they appear to be a major drug target for modulating several brain functions. Perampanel (PER) is a highly selective, noncompetitive AMPA antagonist approved in several countries worldwide for treating different types of seizures in various epileptic conditions. However, recent data show that PER can potentially address many other conditions within epilepsy and beyond. From this perspective, this review aims to examine the new preclinical and clinical studies-especially those produced from 2017 onwards-on AMPA antagonism and PER in conditions such as mesial temporal lobe epilepsy, idiopathic and genetic generalized epilepsy, brain tumor-related epilepsy, status epilepticus, rare epileptic syndromes, stroke, sleep, epilepsy-related migraine, cognitive impairment, autism, dementia, and other neurodegenerative diseases, as well as provide suggestions on future research agenda aimed at probing the possibility of treating these conditions with PER and/or other AMPA receptor antagonists.

Efficacy and Safety of Perampanel in Children with Drug-Resistant Focal-Onset Seizures: A Retrospective Review

BACKGROUND

Epilepsy is one of the most common neurological disorders. Existing antiseizure medications (ASMs) are still unable to control seizures in one-third of these patients, making the discovery of antiseizure therapies with novel mechanisms of action a necessity.

AIM OF THE STUDY

This study aimed to determine the safety and efficacy of perampanel (PER) as an adjuvant treatment for children with drug-resistant focal-onset seizures with or without focal to bilateral tonic-clonic seizures.

PATIENTS AND METHODS

This is a single-center retrospective study of 38 epileptic pediatric patients, aged 2 to 14, at King Faisal Specialist Hospital and Research Center whose seizures were pharmaco-resistant to more than two antiseizure medications and followed for at least three months after PER adjuvant therapy initiation. Efficacy was assessed by the PER response rate at 3-, 6-, and 12-month follow-up evaluations, and side effects were also reported.

RESULTS

Multiple seizure types were reported. Myoclonic seizures were the predominant type of epilepsy in 17 children (44.7%). At 3 months, 6 months, and 12 months of follow-up, approximately 23.4%, 23.4%, and 18.4% of the patients were seizure-free at these time points, respectively. Adverse events were documented in 14 patients (35.7%) and led to the discontinuation of PER in 26.3%, 31.6%, and 36.8% of the studied group at the 3-, 6-, and 12-month follow-ups, respectively. The most common adverse events included dizziness or drowsiness, irritability, gait disturbance, and confusion; however, all were transient, and no serious adverse effects occurred.

CONCLUSION

Our findings confirm the therapeutic efficacy of adjunctive PER in the treatment of drug-resistant epilepsy in children. As an adjunctive treatment for epilepsy, perampanel demonstrated sufficient effectiveness and tolerability.

Modulatory mechanisms of TARP γ8-selective AMPA receptor therapeutics

AMPA glutamate receptors (AMPARs) mediate excitatory neurotransmission throughout the brain. Their signalling is uniquely diversified by brain region-specific auxiliary subunits, providing an opportunity for the development of selective therapeutics. AMPARs associated with TARP γ8 are enriched in the hippocampus, and are targets of emerging anti-epileptic drugs. To understand their therapeutic activity, we determined cryo-EM structures of the GluA1/2-γ8 receptor associated with three potent, chemically diverse ligands. We find that despite sharing a lipid-exposed and water-accessible binding pocket, drug action is differentially affected by binding-site mutants. Together with patch-clamp recordings and MD simulations we also demonstrate that ligand-triggered reorganisation of the AMPAR-TARP interface contributes to modulation. Unexpectedly, one ligand (JNJ-61432059) acts bifunctionally, negatively affecting GluA1 but exerting positive modulatory action on GluA2-containing AMPARs, in a TARP stoichiometry-dependent manner. These results further illuminate the action of TARPs, demonstrate the sensitive balance between positive and negative modulatory action, and provide a mechanistic platform for development of both positive and negative selective AMPAR modulators.

Metabolic modulation of synaptic failure and thalamocortical hypersynchronization with preserved consciousness in Glut1 deficiency

Individuals with glucose transporter type I deficiency (G1D) habitually experience nutrient-responsive epilepsy associated with decreased brain glucose. However, the mechanistic association between blood glucose concentration and brain excitability in the context of G1D remains to be elucidated. Electroencephalography (EEG) in G1D individuals revealed nutrition time-dependent seizure oscillations often associated with preserved volition despite electrographic generalization and uniform average oscillation duration and periodicity, suggesting increased facilitation of an underlying neural loop circuit. Nonlinear EEG ictal source localization analysis and simultaneous EEG/functional magnetic resonance imaging converged on the thalamus-sensorimotor cortex as one potential circuit, and ¹⁸F-deoxyglucose positron emission tomography (¹⁸F-DG-PET) illustrated decreased glucose accumulation in this circuit. This pattern, reflected in a decreased thalamic to striatal ¹⁸F signal ratio, can aid with the PET imaging diagnosis of the disorder, whereas the absence of noticeable ictal behavioral changes challenges the postulated requirement for normal thalamocortical activity during consciousness. In G1D mice, ¹⁸F-DG-PET and mass spectrometry also revealed decreased brain glucose and glycogen, but preserved tricarboxylic acid cycle intermediates, indicating no overall energy metabolism failure. In brain slices from these animals, synaptic inhibition of cortical pyramidal neurons and thalamic relay neurons was decreased, and neuronal disinhibition was mitigated by metabolic sources of carbon; tonic-clonic seizures were also suppressed by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor inhibition. These results pose G1D as a thalamocortical synaptic disinhibition disease associated with increased glucose-dependent neuronal excitability, possibly in relation to reduced glycogen. Together with findings in other metabolic defects, inhibitory neuron dysfunction is emerging as a modulable mechanism of hyperexcitability.

Affecting AMPA Receptor Biophysical Gating Properties with Negative Allosteric Modulators

Glutamatergic chemical synapses mediate excitatory neurotransmission by the ion flow through α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors in the central nervous system (CNS). AMPA receptor-mediated synaptic transmission abnormalities may play a role in neurologic and neurodegenerative diseases, and compounds that can modulate AMPA receptor (AMPAR) signaling have been studied for decades as possible therapies for Alzheimer's disease, Parkinson's disease, depression, and epilepsy. Here, we aimed to determine the modulating effect of allosteric regulators on AMPA receptors by comparing their actions on AMPA-evoked currents, desensitization, and deactivation rate in human embryonic kidney cells (HEK293T) recombinant AMPAR subunits. In this study, patch-clamp electrophysiology was performed to examine how the AMPA subunit responded to benzodioxole (BDZ) derivatives. Our results showed that the BDZ derivatives affected AMPARs as negative modulators, particularly BDZs (8, 9, and 15), where they increased the desensitization rate and delayed the deactivation process. The BDZ compounds were utilized in this study as AMPA modulators to investigate fundamental and clinical AMPA receptor processes. We test BDZs as negative allosteric AMPAR modulators to reestablish glutamatergic synaptic transmission. These efforts have resulted in important molecules with neuroprotective properties on AMPA receptors.

Imaging of Transmembrane AMPA Receptor Regulatory Proteins by Positron Emission Tomography

The transmembrane α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) receptor regulatory protein γ-8 (TARP γ-8) constitutes an auxiliary subunit of AMPA receptors, which mediates various brain functions including learning and memory. TARP γ-8 has emerged as a promising therapeutic target for central nervous system disorders. Despite considerable efforts, previously reported TARP γ-8 PET radioligands, such as [11C]TARP-1903 and [11C]TARP-1811 series, were plagued by limited brain uptake and/or high nonspecific binding in vivo. Herein, we developed two novel 11C-labeled probes, [11C]8 and [11C]15 (also named as [11C]TARP-2105), of which the latter exhibited a reasonable brain uptake as well as specific binding toward TARP γ-8 both in vitro and in vivo, as confirmed by blocking experiments with the commercially available TARP γ-8 inhibitor, JNJ-55511118 in the TARP γ-8-rich hippocampus. Overall, [11C]15 exhibited promising tracer characteristics and proved to be a lead positron-emission tomography ligand for the non-invasive quantification of TARP γ-8 in the mammalian brain.

Influence of the TARP γ8-Selective Negative Allosteric Modulator JNJ-55511118 on AMPA Receptor Gating and Channel Conductance

AMPA-type gultamate receptors (AMPARs) mediate excitatory signaling in the brain and are therapeutic targets for the treatment of diverse neurological disorders. The receptors interact with a variety of auxiliary subunits, including the transmembrane AMPAR regulatory proteins (TARPs). The TARPs influence AMPAR biosynthesis and trafficking and enhance receptor responses by slowing desensitization and deactivation and increasing single-channel conductance. TARP γ8 has an expression pattern that is distinct from that of other TARPs, being enriched in the hippocampus. Recently, several compounds have been identified that selectivity inhibit γ8-containing AMPARs. One such inhibitor, JNJ-55511118, has shown considerable promise for the treatment of epilepsy. However, key details of its mechanism of action are still lacking. Here, using patch-clamp electrophysiological recording from heterologously expressed AMPARs, we show that JNJ-55511118 inhibits peak currents of γ8-containing AMPARs by decreasing their single-channel conductance. The drug also modifies hallmark features of AMPAR pharmacology, including the TARP-dependent actions of intracellular polyamines and the partial agonist kainate. Moreover, we find that JNJ-55511118 reduces the influence of γ8 on all biophysical measures, aside from its effect on the recovery from desensitization. The drug is also effective when applied intracellularly, suggesting it may access its binding site from within the membrane. Additionally, we find that AMPARs incorporating TARP γ2 mutated to contain the JNJ-55511118 binding site, exhibit greater block than seen with AMPARs containing γ8, potentially reflecting differences in TARP stoichiometry. Taken together, our data provide new insight into the mechanism by which γ8-selective drugs inhibit AMPARs. SIGNIFICANCE STATEMENT: Although modulation of AMPA-type glutamate receptors shows promise for the treatment various neurological conditions, the absence of subtype-selective drugs has hindered adoption of this therapeutic strategy. We made patch-clamp recordings to characterize the actions of the γ8-selective AMPAR inhibitor JNJ-55511118 on GluA2(Q) receptors expressed in HEK cells. We report that JNJ-55511118 inhibits AMPAR-mediated currents by reducing single-channel conductance, providing clear insight into the mechanism of action of this important class of AMPAR modulators.

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.

The AMPA receptor antagonist perampanel suppresses epileptic activity in human focal cortical dysplasia

Focal cortical dysplasia (FCD) is one of the most common malformations causing refractory epilepsy. Dysregulation of glutamatergic systems plays a critical role in the hyperexcitability of dysplastic neurons in FCD lesions. The pharmacoresistant nature of epilepsy associated with FCD may be due to a lack of well‐tolerated and precise antiepileptic drugs that can target glutamate receptors. Here, for the first time in human FCD brain slices, we show that the established, noncompetitive α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor antagonist, perampanel has potent antiepileptic action. Moreover, we demonstrate that this effect is due to a reduction in burst firing behavior in human FCD microcircuits. These data support a potential role for the treatment of refractory epilepsy associated with FCD in human patients.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

AMPA receptor trafficking and LTP: Carboxy-termini, amino-termini and TARPs

AMPA receptors (AMPARs) are fundamental elements in excitatory synaptic transmission and synaptic plasticity in the CNS. Long term potentiation (LTP), a form of synaptic plasticity which contributes to learning and memory formation, relies on the accumulation of AMPARs at the postsynapse. This phenomenon requires the coordinated recruitment of different elements in the AMPAR complex. Based on recent research reviewed herein, we propose an updated AMPAR trafficking and LTP model which incorporates both extracellular as well as intracellular mechanisms. This article is part of the special Issue on 'Glutamate Receptors - AMPA receptors'.

Role of glutamate excitotoxicity and glutamate transporter EAAT2 in epilepsy: Opportunities for novel therapeutics development

Epilepsy is a complex neurological syndrome characterized by seizures resulting from neuronal hyperexcitability and sudden and synchronized bursts of electrical discharges. Impaired astrocyte function that results in glutamate excitotoxicity has been recognized to play a key role in the pathogenesis of epilepsy. While there are 26 drugs marketed as anti-epileptic drugs no current treatments are disease modifying as they only suppress seizures rather than the development and progression of epilepsy. Excitatory amino acid transporters (EAATs) are critical for maintaining low extracellular glutamate concentrations and preventing excitotoxicity. When extracellular glutamate concentrations rise to abnormal levels, glutamate receptor overactivation and the subsequent excessive influx of calcium into the post-synaptic neuron can trigger cell death pathways. In this review we discuss targeting EAAT2, the predominant glutamate transporter in the CNS, as a promising approach for developing therapies for epilepsy. EAAT2 upregulation via transcriptional and translational regulation has proven successful in vivo in reducing spontaneous recurrent seizures and offering neuroprotective effects. Another approach to regulate EAAT2 activity is through positive allosteric modulation (PAM). Novel PAMs of EAAT2 have recently been identified and are under development, representing a promising approach for the advance of novel therapeutics for epilepsy.

Liquid chromatographic methods for determination of the new antiepileptic drugs stiripentol, retigabine, rufinamide and perampanel: A comprehensive and critical review

The new antiepileptic drugs perampanel, retigabine, rufinamide and stiripentol have been recently approved for different epilepsy types. Being them an innovation in the antiepileptics armamentarium, a lot of investigations regarding their pharmacological properties are yet to be performed. Besides, considering their broad anticonvulsant activities, an extension of their therapeutic indications may be worthy of investigation, especially regarding other seizure types as well as other central nervous system disorders. Although different liquid chromatographic (LC) methods coupled with ultraviolet, fluorescence, mass or tandem-mass spectrometry detection have already been developed for the determination of perampanel, retigabine, rufinamide and stiripentol, new and more cost-effective methods are yet required. Therefore, this review summarizes the main analytical aspects regarding the liquid chromatographic methods developed for the analysis of perampanel, retigabine (and its main active metabolite), rufinamide and stiripentol in biological samples and pharmaceutical dosage forms. Furthermore, the physicochemical and stability properties of the target compounds will also be addressed. Thus, this review gathers, for the first time, important background information on LC methods that have been developed and applied for the determination of perampanel, retigabine, rufinamide and stiripentol, which should be considered as a starting point if new (bio)analytical techniques are aimed to be implemented for these drugs.

Differential acute impact of therapeutically effective and overdose concentrations of lithium on human neuronal single cell and network function

Lithium salts are used as mood-balancing medication prescribed to patients suffering from neuropsychiatric disorders, such as bipolar disorder and major depressive disorder. Lithium salts cross the blood-brain barrier and reach the brain parenchyma within few hours after oral application, however, how lithium influences directly human neuronal function is unknown. We applied patch-clamp and microelectrode array technology on human induced pluripotent stem cell (iPSC)-derived cortical neurons acutely exposed to therapeutic (<1 mM) and overdose concentrations (>1 mM) of lithium chloride (LiCl) to assess how therapeutically effective and overdose concentrations of LiCl directly influence human neuronal electrophysiological function at the synapse, single-cell, and neuronal network level. We describe that human iPSC-cortical neurons exposed to lithium showed an increased neuronal activity under all tested concentrations. Furthermore, we reveal a lithium-induced, concentration-dependent, transition of regular synchronous neuronal network activity using therapeutically effective concentration (<1 mM LiCl) to epileptiform-like neuronal discharges using overdose concentration (>1 mM LiCl). The overdose concentration lithium-induced epileptiform-like activity was similar to the epileptiform-like activity caused by the GABA_A-receptor antagonist. Patch-clamp recordings reveal that lithium reduces action potential threshold at all concentrations, however, only overdose concentration causes increased frequency of spontaneous AMPA-receptor mediated transmission. By applying the AMPA-receptor antagonist and anti-epileptic drug Perampanel, we demonstrate that Perampanel suppresses lithium-induced epileptiform-like activity in human cortical neurons. We provide insights in how therapeutically effective and overdose concentration of lithium directly influences human neuronal function at synapse, a single neuron, and neuronal network levels. Furthermore, we provide evidence that Perampanel suppresses pathological neuronal discharges caused by overdose concentrations of lithium in human neurons.

Perampanel, a potent AMPA receptor antagonist, protects against tetramethylenedisulfotetramine-induced seizures and lethality in mice: comparison with diazepam

Tetramethylenedisulfotetramine (TETS), a noncompetitive GABA_A receptor antagonist, is a potent, highly lethal convulsant that is considered to be a chemical threat agent. Here, we assessed the ability of the AMPA receptor antagonist perampanel to protect against TETS-induced seizures and lethality in mice when administered before or after treatment with the toxicant. For comparison, we conducted parallel testing with diazepam, which is a first-line treatment for chemically induced seizures in humans. Pre-treatment of mice with either perampanel (1–4 mg/kg, i.p.) or diazepam (1–5 mg/kg, i.p.) conferred protection in a dose-dependent fashion against tonic seizures and lethality following a dose of TETS (0.2 mg/kg, i.p.) that rapidly induces seizures and death. The ED₅₀ values for protection against mortality were 1.6 mg/kg for perampanel and 2.1 mg/kg for diazepam. Clonic seizures were unaffected by perampanel and only prevented in a minority of animals by high-dose diazepam. Neither treatment prevented myoclonic body twitches. Perampanel and diazepam also conferred protection against tonic seizures and lethality when administered 15 min following a 0.14 mg/kg, i.p., dose of TETS and 5 min following a 0.2 mg/kg, i.p., dose of TETS. Both posttreatments were highly potent at reducing tonic seizures and lethality in animals exposed to the lower dose of TETS whereas greater doses of both treatments were required in animals exposed to the larger dose of TETS. Neither treatment was as effective suppressing clonic seizures. In an experiment where 0.4 mg/kg TETS was administered by oral gavage and the treatment drugs were administered 5 min later, perampanel only partially protected against lethality whereas diazepam produced nearly complete protection. We conclude that perampanel and diazepam protect against TETS-induced tonic seizures and lethality but have less impact on clonic seizures. Both drugs could have utility in the treatment of TETS intoxication but neither eliminates all seizure activity.

Transcriptomic expression of AMPA receptor subunits and their auxiliary proteins in the human brain

Receptors to glutamate of the AMPA type (AMPARs) serve as the major gates of excitation in the human brain, where they participate in fundamental processes underlying perception, cognition and movement. Due to their central role in brain function, dysregulation of these receptors has been implicated in neuropathological states associated with a large variety of diseases that manifest with abnormal behaviors. The participation of functional abnormalities of AMPARs in brain disorders is strongly supported by genomic, transcriptomic and proteomic studies. Most of these studies have focused on the expression and function of the subunits that make up the channel and define AMPARs (GRIA1-GRIA4), as well of some accessory proteins. However, it is increasingly evident that native AMPARs are composed of a complex array of accessory proteins that regulate their trafficking, localization, kinetics and pharmacology, and a better understanding of the diversity and regional expression of these accessory proteins is largely needed. In this review we will provide an update on the state of current knowledge of AMPA receptors subunits in the context of their accessory proteins at the transcriptome level. We also summarize the regional expression in the human brain and its correlation with the channel forming subunits. Finally, we discuss some of the current limitations of transcriptomic analysis and propose potential ways to overcome them.

Rapid effects of neurosteroids on neuronal plasticity and their physiological and pathological implications

Current neuroscience research on neurosteroids and their synthetic analogues - neuroactive steroids - clearly demonstrate their drug likeness in a variety of neurological and psychiatric conditions. Moreover, research on neurosteroids continues to provide novel mechanistic insights into receptor activation or inhibition of various receptors. This mini-review will provide a high-level overview of the research area and discuss the various classes of potential physiological and pathological implications discovered so far.

Perampanel attenuates scratching behavior induced by acute or chronic pruritus in mice

An itch is defined as an unpleasant sensation that evokes a desire to scratch. Glutamate is a major excitatory neurotransmitter in the mammalian central nervous system and has a crucial role in pruriceptive processing in the spinal dorsal horn. It is well known that glutamate exerts its effects by binding to various glutamate receptors including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and that AMPA/kainate receptors play a crucial role in pruriceptive processing; however, the precise role of AMPA receptors remains uncertain. Perampanel, an antiepileptic drug, is an antagonist of AMPA receptors. Pretreatment with perampanel dose-dependently attenuated the induction of scratching, a behavior typically associated with pruritus, by intradermal administration of the pruritogen chloroquine. In addition, the induction of scratching in mice painted with diphenylcyclopropenone and NC/Nga mice treated with Biostir AD, animal models of contact dermatitis and atopic dermatitis, respectively, was dose-dependently alleviated by administration of perampanel. These findings indicate that AMPA receptors play a crucial role in pruriceptive processing in mice with acute or chronic pruritus.

Targeting receptor complexes: a new dimension in drug discovery

Targeting receptor proteins, such as ligand-gated ion channels and G protein-coupled receptors, has directly enabled the discovery of most drugs developed to modulate receptor signalling. However, as the search for novel and improved drugs continues, an innovative approach - targeting receptor complexes - is emerging. Receptor complexes are composed of core receptor proteins and receptor-associated proteins, which have profound effects on the overall receptor structure, function and localization. Hence, targeting key protein-protein interactions within receptor complexes provides an opportunity to develop more selective drugs with fewer side effects. In this Review, we discuss our current understanding of ligand-gated ion channel and G protein-coupled receptor complexes and discuss strategies for their pharmacological modulation. Although such strategies are still in preclinical development for most receptor complexes, they exemplify how receptor complexes can be drugged, and lay the groundwork for this nascent area of research.

Identification of epilepsy-associated neuronal subtypes and gene expression underlying epileptogenesis

Epilepsy is one of the most common neurological disorders, yet its pathophysiology is poorly understood due to the high complexity of affected neuronal circuits. To identify dysfunctional neuronal subtypes underlying seizure activity in the human brain, we have performed single-nucleus transcriptomics analysis of >110,000 neuronal transcriptomes derived from temporal cortex samples of multiple temporal lobe epilepsy and non-epileptic subjects. We found that the largest transcriptomic changes occur in distinct neuronal subtypes from several families of principal neurons (L5-6_Fezf2 and L2-3_Cux2) and GABAergic interneurons (Sst and Pvalb), whereas other subtypes in the same families were less affected. Furthermore, the subtypes with the largest epilepsy-related transcriptomic changes may belong to the same circuit, since we observed coordinated transcriptomic shifts across these subtypes. Glutamate signaling exhibited one of the strongest dysregulations in epilepsy, highlighted by layer-wise transcriptional changes in multiple glutamate receptor genes and strong upregulation of genes coding for AMPA receptor auxiliary subunits. Overall, our data reveal a neuronal subtype-specific molecular phenotype of epilepsy.

The pathophysiology of epilepsy is unclear. Here, the authors present single-nuclei transcriptomic profiling of human temporal lobe epilepsy from patients. They identified epilepsy-associated neuronal subtypes, and a panel of dysregulated genes, predicting neuronal circuits contributing to epilepsy.

Perampanel reduces paroxysmal depolarizing shift and inhibitory synaptic input in excitatory neurons to inhibit epileptic network oscillations

BACKGROUND AND PURPOSE

Perampanel is a newly approved anticonvulsant uniquely targeting AMPA receptors, which mediate the most abundant form of excitatory synaptic transmission in the brain. However, the network mechanism underlying the anti-epileptic effect of the AMPAergic inhibition remains to be explored.

EXPERIMENTAL APPROACH

The mechanism of perampanel action was studied with the basolateral amygdala network containing pyramidal-inhibitory neuronal resonators in seizure models of 4-aminopyridine (4-AP) and electrical kindling.

KEY RESULTS

Application of either 4-AP or electrical kindling to the basolateral amygdala readily induces AMPAergic transmission-dependent reverberating activities between pyramidal-inhibitory neuronal resonators, which are chiefly characterized by burst discharges in inhibitory neurons and corresponding recurrent inhibitory postsynaptic potentials in pyramidal neurons. Perampanel reduces post-kindling "paroxysmal depolarizing shift" especially in pyramidal neurons and, counterintuitively, eliminates burst activities in inhibitory neurons and inhibitory synaptic inputs onto excitatory pyramidal neurons to result in prevention of epileptiform discharges and seizure behaviours. Intriguingly, similar effects can be obtained with not only the AMPA receptor antagonist CNQX but also the GABA_A receptor antagonist bicuculline, which is usually considered as a proconvulsant.

CONCLUSION AND IMPLICATIONS

Ictogenesis depends on the AMPA receptor-dependent recruitment of pyramidal-inhibitory neuronal network oscillations tuned by dynamic glutamatergic and GABAergic transmission. The anticonvulsant effect of perampanel then stems from disruption of the coordinated network activities rather than simply decreased neuronal excitability or excitatory transmission. Positive or negative modulation of epileptic network reverberations may be pro-ictogenic or anti-ictogenic, respectively, constituting a more applicable rationale for the therapy against seizures.

Abolishing spontaneous epileptiform activity in human brain tissue through AMPA receptor inhibition

Objective

The amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor (AMPAR) is increasingly recognized as a therapeutic target in drug‐refractory pediatric epilepsy. Perampanel (PER) is a non‐competitive AMPAR antagonist, and pre‐clinical studies have shown the AMPAR‐mediated anticonvulsant effects of decanoic acid (DEC), a major medium‐chain fatty acid provided in the medium‐chain triglyceride ketogenic diet.

Methods

Using brain tissue resected from children with intractable epilepsy, we recorded the effects of PER and DEC in vitro.

Results

We found resected pediatric epilepsy tissue exhibits spontaneous epileptic activity in vitro, and showed that DEC and PER inhibit this epileptiform activity in local field potential recordings as well as excitatory synaptic transmission.

Interpretation

This study confirms AMPAR antagonists inhibit epileptiform discharges in brain tissue resected in a wide range of pediatric epilepsies.

Post-translational palmitoylation of ionotropic glutamate receptors in excitatory synaptic functions

In the mammalian CNS, glutamate is the major excitatory neurotransmitter. Ionotropic glutamate receptors (iGluRs) are responsible for the glutamate-mediated postsynaptic excitation of neurons. Regulation of glutamatergic synapses is critical for higher brain functions including neural communication, memory formation, learning, emotion, and behaviour. Many previous studies have shown that post-translational protein S-palmitoylation, the only reversible covalent attachment of lipid to protein, regulates synaptic expression, intracellular localization, and membrane trafficking of iGluRs and their scaffolding proteins in neurons. This modification mechanism is extremely conserved in the vertebrate lineages. The failure of appropriate palmitoylation-dependent regulation of iGluRs leads to hyperexcitability that reduces the maintenance of network stability, resulting in brain disorders, such as epileptic seizures. This review summarizes advances in the study of palmitoylation of iGluRs, especially AMPA receptors and NMDA receptors, and describes the current understanding of palmitoylation-dependent regulation of excitatory glutamatergic synapses. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.4/issuetoc.

Intrathecally administered perampanel alleviates neuropathic and inflammatory pain in rats

Chronic pain conditions such as neuropathic pain and persistent inflammatory pain are difficult to manage. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors modulate nociceptive processing at the spinal dorsal horn. Previous studies have shown that intrathecal AMPA receptor antagonists exert antinociception in various pain states. Perampanel is a selective, noncompetitive inhibitor of the AMPA receptor and used clinically as an antiepileptic drug. Little is known about antinociceptive action of perampanel in the spinal cord. Here, we explored whether intrathecal perampanel attenuates neuropathic and inflammatory pain. A chronic constriction injury (CCI) to the sciatic nerve was induced in male Sprague-Dawley rats. We evaluated the effects of intrathecal perampanel (10, 30, or 100 μg) on mechanical and cold hyperalgesia using the electronic von Frey and cold plate tests, respectively. Normal rats were assessed in terms of inflammatory nociception using the formalin test, and motor function employing the rotarod test. In the CCI rats, spinally applied perampanel inhibited mechanical and cold hyperalgesia dose-dependently. In normal rats, perampanel remarkably suppressed the early- and late-phase responses in the formalin test, and it weakly affected motor performance for a short period at the highest dose. These results suggest that perampanel exerts antinociceptive actions on neuropathic and persistent inflammatory pain in the spinal cord. Perampanel may be safe and beneficial remedy for patients with such pain conditions. In addition, AMPA receptor can be a promising target for treatment of chronic pain.

Radiosynthesis and preliminary evaluation of 11C-labeled 4-cyclopropyl-7-(3-methoxyphenoxy)-3,4-dihydro-2H-benzo[e] [1,2,4] thiadiazine 1,1-dioxide for PET imaging AMPA receptors

The α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) belong to the family of ionotropic transmembrane receptors for glutamate (iGluRs) that are implicated in the pathology of neurological disorders and neurodegenerative diseases. Inspired by a recently developed positive allosteric modulator of AMPARs, 4-cyclopropyl-7-(3-methoxyphenoxy)-3,4-dihydro-2H-benzo[ e ][1,2,4]thiadiazine 1,1-dioxide (16; EC₅₀ = 2.0 nM), we designed a new synthetic route for N-protected phenolic precursor 13 and efficiently radiolabeled a PET ligand [¹¹C]AMPA-1905 ([¹¹C]16) using a modified one-pot two-step strategy in high radiochemical yield and high molar activity. Preliminary in vivo evaluation was carried out to investigate the suitability of [¹¹C]16 as a potential PET probe for AMPAR imaging.

Neurodevelopmental outcomes in paediatric immune-mediated and autoimmune epileptic encephalopathy

Recognition of paediatric autoimmune/immune-mediated encephalitis and epileptic encephalopathy (e.g. NMDAR-Ab encephalitis) has rapidly increased over the last ten years. While we are succeeding in the diagnosis and identification and even early treatment of these encephalitidies, with studies describing >80% are making a "good" recovery, we are now recognising that a "good" medical outcome does not cover the cognitive, social and behavioural sequelae that can occur, particularly in paediatric patients. Basic measures of medical outcome, for example the modified Rankin Scale (MRS) or the Paediatric Cerebral Performance Category (PCPC), offer the advantage of being quick to use, but do not reveal the more complex difficulties that can impact the future of affected children. This article reviews the current literature on neurodevelopmental outcomes in children affected with autoimmune and immune-mediated encephalitis/epileptic encephalopathy and provides guidance on post-onset surveillance aimed at identifying those most likely to experience ongoing long-term difficulties.

AMPA Receptor Noncompetitive Inhibitors Occupy a Promiscuous Binding Site

Noncompetitive inhibitors of AMPA receptors have attracted interest in recent years as antiepileptic drugs. However, their development is hindered by a lack of detailed understanding of the protein-inhibitor interaction mechanisms. Recently, structures of AMPA receptor complexes with the structurally dissimilar, noncompetitive, small-molecule inhibitors pyridone perampanel (PMP), GYKI 53655 (GYKI), and CP 465022 (CP) were resolved, revealing that all three share a common binding site. However, due to the low resolution of the ligands, their exact binding modes and protein-ligand interactions remain ambiguous and insufficiently detailed. We carried out molecular dynamics (MD) simulations on X-ray-resolved and docked AMPA receptor complexes, including thermodynamic integration (TI) to compute ligand binding constants, in order to investigate the inhibitor binding modes in detail and identify key protein-ligand interaction mechanisms. Our analysis and simulations show that the ligand binding pocket at the interface of the receptor's transmembrane domain exhibits features also found in the binding pockets of the multidrug-resistance proteins. The inhibitors bind to such promiscuous pockets by forming multiple weak contacts, while the large, flexible pocket undergoes adjustments to accommodate structurally different ligands in different orientations. TI was able to identify a specific more favorable binding mode for GYKI, while PMP, which has a symmetric ring structure, produced several comparable poses indicating that it may bind in several orientations.

Mutational Analysis and Modeling of Negative Allosteric Modulator Binding Sites in AMPA Receptors

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) constitute a subclass of the ionotropic glutamate receptor superfamily, which functions as glutamate-gated cation channels to mediate the majority of excitatory neurotransmission in the central nervous system. AMPARs are therapeutic targets in a range of brain disorders associated with abnormal glutamate hyperactivity. Multiple classes of AMPAR inhibitors have been developed during the past decades, including competitive antagonists, ion channel blockers, and negative allosteric modulators (NAMs). At present, the NAM is the only class of AMPAR ligands that have been developed into safe and useful drugs in humans in the form of perampanel (Fycompa), which was recently approved for treatment of epilepsy. Compared with the detailed understanding of other AMPAR ligand classes, surprisingly little information has been available regarding the molecular mechanism of perampanel and other classes of NAMs at AMPARs; including the location and structure of NAM binding pockets in the receptor complex. However, structures of the AMPAR GluA2 in complex with NAMs were recently reported that unambiguously identified the NAM binding sites. In parallel with this work, our aim with the present study was to identify specific residues involved in the formation of the NAM binding site for three prototypical AMPAR NAMs. Hence, we have performed a mutational analysis of the AMPAR region that links the four extracellular ligand-binding domains to the central ion channel in the transmembrane domain region. Furthermore, we perform computational ligand docking of the NAMs into structural models of the homomeric GluA2 receptor and optimize side chain conformations around the NAMs to model how NAMs bind in this specific site. The new insights provide potentially valuable input for structure-based drug design of new NAMs. SIGNIFICANCE STATEMENT: The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are glutamate-gated ion channels that mediate the majority of excitatory neurotransmission in the brain. Negative allosteric modulators of AMPA receptors are considered to have significant therapeutic potential in diseases linked to glutamate hyperactivity. The present work employs mutational analysis and molecular modeling of the binding site for prototypical NAMs to provide new molecular insight into how NAMs interact with the AMPA receptor, which is of potential use for future design of new types of NAMs.

The value of human epileptic tissue in the characterization and development of novel antiepileptic drugs: The example of CERC-611 and KRM-II-81

The need for improved antiepileptics is clearly mandated despite the existence of multiple existing medicines from different chemical and mechanistic classes. Standard of care agents do not fully control epilepsies and have a variety of side-effect and safety issues. Patients typically take multiple antiepileptic drugs and yet many continue to have seizures. Antiepileptic-unresponsive seizures are life-disrupting and life-threatening. One approach to seizure control is surgical resection of affected brain tissue and associated neural circuits. Although non-human brain studies can provide insight into novel antiepileptic mechanisms, human epileptic brain is the bottom-line biological substrate. Human epileptic brain can provide definitive information on the presence or absence of the putative protein targets of interest in the patient population, the potential changes in these proteins in the epileptic state, and the engagement of novel molecules and their functional impact in target tissue. In this review, we discuss data on two novel potential antiepileptic drugs. CERC-611 (LY3130481) is an AMPA receptor antagonist that selectively blocks AMPA receptors associated with the auxiliary protein TARP γ-8 and is in clinical development. KRM-II-81 is a positive allosteric modulator of GABA_A receptors selectively associated with protein subunits α2 and α 3. Preclinical data on these compounds argue that patient-based biological data increase the probability that a newly discovered molecule will translate its antiepileptic potential to patients.

Synthesis and Pharmacological Evaluation of 3-[(4-Oxo-4H-pyrido[3,2-e][1,3]thiazin-2-yl)(phenyl)amino]propanenitrile Derivatives as Orally Active AMPA Receptor Antagonists

In our search for novel orally active α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, we found that conversion of an allyl group in the lead compound 2-[allyl(4-methylphenyl)amino]-4H-pyrido[3,2-e][1,3]thiazin-4-one (4) to a 2-cyanoethyl group significantly increased inhibitory activity against AMPA receptor-mediated kainate-induced toxicity in rat hippocampal cultures. Here, we synthesized 10 analogs bearing a 2-cyanoethyl group and administered them to mice to evaluate their anticonvulsant activity in maximal electroshock (MES)- and pentylenetetrazol (PTZ)-induced seizure tests, and their effects on motor coordination in a rotarod test. 3-{(4-Oxo-4H-pyrido[3,2-e][1,3]thiazin-2-yl)[4-(trifluoromethoxy)phenyl]amino}propanenitrile (25) and 3-[(2,2-difluoro-2H-1,3-benzodioxol-5-yl)(4-oxo-4H-pyrido[3,2-e][1,3]thiazin-2-yl)amino]propanenitrile (27) exhibited potent anticonvulsant activity in both seizure tests and induced minor motor disturbances as indicated in the rotarod test. The protective index values of 25 and 27 for MES-induced seizures (10.7 and 12.0, respectively) and PTZ-induced seizures (6.0 and 5.6, respectively) were considerably higher compared with those of YM928 (5) and talampanel (1).

Positron Emission Tomography (PET) Ligand Development for Ionotropic Glutamate Receptors: Challenges and Opportunities for Radiotracer Targeting N-Methyl-d-aspartate (NMDA), α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA), and Kainate Receptors

Ionotropic glutamate receptors (iGluRs) mediate excitatory neurotransmission within the mammalian central nervous system. iGluRs exist as three main groups: N-methyl-d-aspartate receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), and kainate receptors. The past decades have witnessed a remarkable development of PET tracers targeting different iGluRs including NMDARs and AMPARs, and several of the tracers have advanced to clinical imaging studies. Here, we assess the recent development of iGluR PET probes, focusing on tracer design, brain kinetics, and performance in PET imaging studies. Furthermore, this review will not only present challenges in the tracer development but also provide novel approaches in conjunction with most recent drug discovery efforts on these iGluRs, including subtype-selective NMDAR and transmembrane AMPAR regulatory protein modulators and positive allosteric modulators (PAMs) of AMPARs. These approaches, if successful as PET tracers, may provide fundamental knowledge to understand the roles of iGluR receptors under physiological and pathological conditions.

Microtransplantation of human brain receptors into oocytes to tackle key questions in drug discovery

It is important in drug discovery to demonstrate that activity of novel drugs found by screening on recombinant receptors translates to activity on native human receptors in brain areas affected by disease. In this review, we summarise the development and use of the microtransplantation technique. Native receptors are reconstituted from human brain tissues into oocytes from the frog Xenopus laevis where they can be functionally assessed. Oocytes microtransplanted with hippocampal tissue from an epileptic patient were used to demonstrate that new antiepileptic agents act on receptors in diseased tissue. Furthermore, frozen post-mortem human tissues were used to show that drugs are active on receptors in brain areas associated with a disease; but not in areas associated with side effects.

Deficiency of AMPAR-Palmitoylation Aggravates Seizure Susceptibility

Synaptic AMPAR expression controls the strength of excitatory synaptic transmission and plasticity. An excess of synaptic AMPARs leads to epilepsy in response to seizure-inducible stimulation. The appropriate regulation of AMPARs plays a crucial role in the maintenance of the excitatory/inhibitory synaptic balance; however, the detailed mechanisms underlying epilepsy remain unclear. Our previous studies have revealed that a key modification of AMPAR trafficking to and from postsynaptic membranes is the reversible, posttranslational S-palmitoylation at the C-termini of receptors. To clarify the role of palmitoylation-dependent regulation of AMPARs in vivo, we generated GluA1 palmitoylation-deficient (Cys811 to Ser substitution) knock-in mice. These mutant male mice showed elevated seizure susceptibility and seizure-induced neuronal activity without impairments in synaptic transmission, gross brain structure, or behavior at the basal level. Disruption of the palmitoylation site was accompanied by upregulated GluA1 phosphorylation at Ser831, but not at Ser845, in the hippocampus and increased GluA1 protein expression in the cortex. Furthermore, GluA1 palmitoylation suppressed excessive spine enlargement above a certain size after LTP. Our findings indicate that an abnormality in GluA1 palmitoylation can lead to hyperexcitability in the cerebrum, which negatively affects the maintenance of network stability, resulting in epileptic seizures.SIGNIFICANCE STATEMENT AMPARs predominantly mediate excitatory synaptic transmission. AMPARs are regulated in a posttranslational, palmitoylation-dependent manner in excitatory synapses of the mammalian brain. Reversible palmitoylation dynamically controls synaptic expression and intracellular trafficking of the receptors. Here, we generated GluA1 palmitoylation-deficient knock-in mice to clarify the role of AMPAR palmitoylation in vivo We showed that an abnormality in GluA1 palmitoylation led to hyperexcitability, resulting in epileptic seizure. This is the first identification of a specific palmitoylated protein critical for the seizure-suppressing process. Our data also provide insight into how predicted receptors such as AMPARs can effectively preserve network stability in the brain. Furthermore, these findings help to define novel key targets for developing anti-epileptic drugs.

Perampanel and decanoic acid show synergistic action against AMPA receptors and seizures

Perampanel is an adjunctive treatment for epilepsy that works through the direct inhibition of AMPA receptors. The same molecular mechanism has recently been shown for a fatty acid, decanoic acid, prescribed in the medium chain triglyceride ketogenic diet for the treatment of patients with drug-resistant epilepsy. Because each compound has been proposed to act through a distinct AMPA receptor binding site, we predicted that perampanel and decanoic acid would act synergistically against AMPA receptors and, consequently, seizures. Here, we show a synergistic interaction between perampanel and decanoic acid in direct AMPA receptor inhibition, in an ex vivo model of seizure activity, and against seizure-induced activity in human brain slices. These data support a potential role for combination treatment using perampanel and dietary decanoic acid to provide enhanced seizure control.

Synthesis, pharmacology and preclinical evaluation of 11C-labeled 1,3-dihydro-2H-benzo[d]imidazole-2-ones for imaging γ8-dependent transmembrane AMPA receptor regulatory protein

a-Amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are implicated in the pathology of neurological diseases such as epilepsy and schizophrenia. As pan antagonists for this target are often accompanied with undesired effects at high doses, one of the recent drug discovery approaches has shifted to subtype-selective AMPA receptor (AMPAR) antagonists, specifically, via modulating transmembrane AMPAR regulatory proteins (TARPs). The quantification of AMPARs by positron emission tomography (PET) would help obtain insights into disease conditions in the living brain and advance the translational development of AMPAR antagonists. Herein we report the design, synthesis and preclinical evaluation of a series of TARP γ-8 antagonists, amenable for radiolabeling, for the development of subtype-selective AMPAR PET imaging agents. Based on the pharmacology evaluation, molecular docking studies and physiochemical properties, we have identified several promising lead compounds 3, 17-19 and 21 for in vivo PET studies. All candidate compounds were labeled with [¹¹C]COCl₂ in high radiochemical yields (13-31% RCY) and high molar activities (35-196 GBq/μmol). While tracers 30 ([¹¹C]17) &32 ([¹¹C]21) crossed the blood-brain barrier and showed heterogeneous distribution in PET studies, consistent with TARP γ-8 expression, high nonspecific binding prevented further evaluation. To our delight, tracer 31 ([¹¹C]3) showed good in vitro specific binding and characteristic high uptake in the hippocampus in rat brain tissues, which provides the guideline for further development of a new generation subtype selective TARP γ-8 dependent AMPAR tracers.

Structural Determinants of the γ-8 TARP Dependent AMPA Receptor Antagonist

The forebrain specific AMPA receptor antagonist, LY3130481/CERC-611, which selectively antagonizes the AMPA receptors associated with TARP γ-8, an auxiliary subunit enriched in the forebrain, has potent antiepileptic activities without motor side effects. We designated the compounds with such activities as γ-8 TARP dependent AMPA receptor antagonists (γ-8 TDAAs). In this work, we further investigated the mechanisms of action using a radiolabeled γ-8 TDAA and ternary structural modeling with mutational validations to characterize the LY3130481 binding to γ-8. The radioligand binding to the cells heterologously expressing GluA1 and/or γ-8 revealed that γ-8 TDAAs binds to γ-8 alone without AMPA receptors. Homology modeling of γ-8, based on the crystal structures of a distant TARP homologue, murine claudin 19, in conjunction with knowledge of two γ-8 residues previously identified as critical for the LY3130481 TARP-dependent selectivity provided the basis for a binding mode prediction. This allowed further rational mutational studies for characterization of the structural determinants in TARP γ-8 for LY3130481 activities, both thermodynamically as well as kinetically.

[Perampanel in the treatment of patients with epilepsy]

Development of new antiepileptic drugs (AED) does not stop due to the fact that the number of patients with pharmacoresistant epilepsy remains at about 30%. One of the newest AEDs is perampanel (PER), a selective, non-competitive AMPA receptor antagonist to target post-synaptic glutamate transmission. PER is approved in the Russian Federation as adjunctive treatment for focal seizures with or without secondarily generalized seizures and for primary generalized tonic-clonic (PGTC) seizures in idiopathic generalized epilepsy (IGE) in patients with epilepsy aged ≥12 years. The drug is effective and well-tolerated in the dose of 4-8 mg/day, and most side effects are dose-dependent. The high efficacy of PER combined with the good tolerability, absence of life-threatening adverse reactions and convenient intake allow us to recommend PER as the first choice additional drug in treatment of patients with epilepsy.

On Rhythms in Neuronal Networks with Recurrent Excitation

We investigate rhythms in networks of neurons with recurrent excitation, that is, with excitatory cells exciting each other. Recurrent excitation can sustain activity even when the cells in the network are driven below threshold, too weak to fire on their own. This sort of "reverberating" activity is often thought to be the basis of working memory. Recurrent excitation can also lead to "runaway" transitions, sudden transitions to high-frequency firing; this may be related to epileptic seizures. Not all fundamental questions about these phenomena have been answered with clarity in the literature. We focus on three questions here: (1) How much recurrent excitation is needed to sustain reverberating activity? How does the answer depend on parameters? (2) Is there a positive minimum frequency of reverberating activity, a positive "onset frequency"? How does it depend on parameters? (3) When do runaway transitions occur? For reduced models, we give mathematical answers to these questions. We also examine computationally to which extent our findings are reflected in the behavior of biophysically more realistic model networks. Our main results can be summarized as follows. (1) Reverberating activity can be fueled by extremely weak slow recurrent excitation, but only by sufficiently strong fast recurrent excitation. (2) The onset of reverberating activity, as recurrent excitation is strengthened or external drive is raised, occurs at a positive frequency. It is faster when the external drive is weaker (and the recurrent excitation stronger). It is slower when the recurrent excitation has a longer decay time constant. (3) Runaway transitions occur only with fast, not with slow, recurrent excitation. We also demonstrate that the relation between reverberating activity fueled by recurrent excitation and runaway transitions can be visualized in an instructive way by a (generalized) cusp catastrophe surface.

AMPA receptors and perampanel behind selected epilepsies: current evidence and future perspectives

INTRODUCTION

The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are the major mediators of glutamate-mediated excitatory neurotransmission, and are critical for synchronization and spread of epileptic activity. Areas covered: AMPA receptor antagonists have been also developed as antiepileptic drugs and perampanel (PER) is the first highly selective, non-competitive AMPA-type glutamate receptor antagonist that is available on the market. It is approved as adjunctive therapy for the treatment of partial-onset seizures with or without secondary generalization, and for primary generalized tonic-clonic seizures in idiopathic generalized epilepsy, in patients aged ≥ 12 years. This article reviews the role of AMPA receptors in the neuronal hyperexcitability underlying epilepsy, the mechanism of action and clinical experience on the anti-seizure activity of PER. Moreover, the rationale for targeting AMPA receptor in specific epileptic disorders, including brain tumor-related epilepsy, mesial temporal lobe epilepsy with/without hippocampal sclerosis, and status epilepticus is evaluated. Finally, the pharmacological rationale for the development of AMPA receptor antagonists in other neurological disorders beyond epilepsy is considered. Expert opinion: Further research aimed at better understanding the pharmacology and blocking mechanism of PER and other AMPA receptor antagonists will drive future development of therapeutic agents that target epilepsy and other neurological diseases.

Auxiliary subunits of AMPA receptors: The discovery of a forebrain-selective antagonist, LY3130481/CERC-611

Drugs originate from the discovery of compounds, natural or synthetic, that bind to proteins (receptors, enzymes, transporters, etc.), the interaction of which modulates biological cascades that have potential therapeutic benefit. Rational strategies for identifying novel drug therapies are typically based on knowledge of the structure of the target proteins and the design of new chemical entities that modulate these proteins in a beneficial manner. The present review discusses a novel approach to drug discovery based on the identification and characterization of auxiliary proteins, the transmembrane AMPA receptor regulatory proteins (TARPs) that are associated with AMPA receptors. Utilizing these auxiliary proteins in compound screening led to the discovery of the TARP-dependent-AMPA forebrain selective receptor antagonist (TDAA), LY3130481/CERC-611 that is currently in clinical development for epilepsy.

Electroencephalographic, cognitive, and neurochemical effects of LY3130481 (CERC-611), a selective antagonist of TARP-γ8-associated AMPA receptors

6-[(1S)-1-[1-[5-(2-hydroxyethoxy)-2-pyridyl]pyrazol-3-yl]ethyl]-3H-1,3-benzothiazol-2-one (LY3130481 or CERC-611) is a selective antagonist of AMPA receptors containing transmembrane AMPA receptor regulatory protein (TARP) γ-8. This molecule has been characterized as a potent and efficacious anticonvulsant in an array of acute and chronic epilepsy models in rodents. The present set of experiments was designed to assess the effects of LY3130481 on the electroencephelogram (EEG), cognitive function, and neurochemical outflow. LY3130481 disrupted food-maintained responding in rats and spontaneous alternation in a Y-maze in mice. In rat fear conditioning, LY3130481 caused a deficit in trace (hippocampal-dependent), but not in delay fear conditioning. Although these effects on cognitive performances were observed, the known cognitive-impairing anticonvulsant, topiramate, did not always produce deficits under these assay conditions. LY3130481 produced modest increases in wake times in rats. In addition, LY3130481 was able to attenuate some impairing effects of standard antiepileptic drugs. The motor-impairing effects of the lacosamide were attenuated by LY3130481 as was the decrease in non-rapid-eye movement sleep induced by carbamazepine. Evaluation of the effect of LY3130481 on neurotransmitter and metabolite efflux in the rat medial prefrontal cortex, using in vivo microdialysis, revealed significant increases in the pro-cognitive and wake-promoting neurotransmitters, histamine and acetylcholine, as well as in serotonin, telemethylhistamine, 5-HIAA, HVA and MHPG. LY3130481 thus presents a novel behavioral profile that will have to be evaluated in patients to fully appreciate its implications for therapeutics. LY3130481 is currently under clinical development as CERC-611 as an antiepileptic.

Screening for AMPA receptor auxiliary subunit specific modulators

AMPA receptors (AMPAR) are ligand gated ion channels critical for synaptic transmission and plasticity. Their dysfunction is implicated in a variety of psychiatric and neurological diseases ranging from major depressive disorder to amyotrophic lateral sclerosis. Attempting to potentiate or depress AMPAR activity is an inherently difficult balancing act between effective treatments and debilitating side effects. A newly explored strategy to target subsets of AMPARs in the central nervous system is to identify compounds that affect specific AMPAR-auxiliary subunit complexes. This exploits diverse spatio-temporal expression patterns of known AMPAR auxiliary subunits, providing means for designing brain region-selective compounds. Here we report a high-throughput screening-based pipeline that can identify compounds that are selective for GluA2-CNIH3 and GluA2-stargazin complexes. These compounds will help us build upon the growing library of AMPAR-auxiliary subunit specific inhibitors, which have thus far all been targeted to TARP γ-8. We used a cell-based assay combined with a voltage-sensitive dye (VSD) to identify changes in glutamate-gated cation flow across the membranes of HEK cells co-expressing GluA2 and an auxiliary subunit. We then used a calcium flux assay to further validate hits picked from the VSD assay. VU0612951 and VU0627849 are candidate compounds from the initial screen that were identified as negative and positive allosteric modulators (NAM and PAM), respectively. They both have lower IC₅₀/EC₅₀s on complexes containing stargazin and CNIH3 than GSG1L or the AMPAR alone. We have also identified a candidate compound, VU0539491, that has NAM activity in GluA2(R)-CNIH3 and GluA2(Q) complexes and PAM activity in GluA2(Q)-GSG1L complexes.

Precision therapy for a new disorder of AMPA receptor recycling due to mutations in ATAD1

OBJECTIVE

ATAD1 encodes Thorase, a mediator of α-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptor recycling; in this work, we characterized the phenotype resulting from ATAD1 mutations and developed a targeted therapy in both mice and humans.

METHODS

Using exome sequencing, we identified a novel ATAD1 mutation (p.E276X) as the etiology of a devastating neurologic disorder characterized by hypertonia, seizures, and death in a consanguineous family. We postulated that pathogenesis was a result of excessive AMPA receptor activity and designed a targeted therapeutic approach using perampanel, an AMPA-receptor antagonist.

RESULTS

Perampanel therapy in ATAD1 knockout mice reversed behavioral defects, normalized brain MRI abnormalities, prevented seizures, and prolonged survival. The ATAD1 patients treated with perampanel showed improvement in hypertonicity and resolution of seizures.

CONCLUSIONS

This work demonstrates that identification of novel monogenic neurologic disorders and observation of response to targeted therapeutics can provide important insights into human nervous system functioning.