Targeting KNa1.1 channels in KCNT1-associated epilepsy

Structure-Activity Relationship Studies in a Series of 2-Aryloxy-N-(pyrimidin-5-yl)acetamide Inhibitors of SLACK Potassium Channels

Epilepsy of infancy with migrating focal seizures (EIMFS) is a rare, serious, and pharmacoresistant epileptic disorder often linked to gain-of-function mutations in the KCNT1 gene. KCNT1 encodes the sodium-activated potassium channel known as SLACK, making small molecule inhibitors of SLACK channels a compelling approach to the treatment of EIMFS and other epilepsies associated with KCNT1 mutations. In this manuscript, we describe a hit optimization effort executed within a series of 2-aryloxy-N-(pyrimidin-5-yl)acetamides that were identified via a high-throughput screen. We systematically prepared analogs in four distinct regions of the scaffold and evaluated their functional activity in a whole-cell, automated patch clamp (APC) assay to establish structure-activity relationships for wild-type (WT) SLACK inhibition. Two selected analogs were also profiled for selectivity versus other members of the Slo family of potassium channels, of which SLACK is a member, and versus a panel of structurally diverse ion channels. The same two analogs were evaluated for activity versus the WT mouse channel as well as two clinically relevant mutant human channels.

Discovery of Potent and Selective Blockers Targeting the Epilepsy-Associated KNa1.1 Channel

Gain-of-function (GOF) mutations of the sodium-activated potassium channel KNa1.1 (Slack, Slo2.2, or KCa4.1) induce severe, drug-resistant forms of epilepsy in infants and children. Although quinidine has shown promise in treating KCNT1-related epilepsies compared to other drugs, its limited efficacy and substantial side effects necessitate the development of new KNa1.1 channel inhibitors. In this study, we developed a novel class of KNa1.1 inhibitors using combined silico approaches and structural optimization. Among these inhibitors, compound Z05 was identified as a selective potential KNa1.1 inhibitor, especially against the hERG channel. Moreover, its binding site and potential counteraction to a GOF mutant Y796H were identified by the mutation studies. Our data also showed that Z05 had significant pharmacological profiles, including high brain penetration and moderate oral bioavailability, offering a valuable in vitro tool compound for further drug development in treating KCNT1-related epilepsies.

Molecular Profiling of Mouse Models of Loss or Gain of Function of the KCNT1 (Slack) Potassium Channel and Antisense Oligonucleotide Treatment

The potassium sodium-activated channel subtype T member 1 (KCNT1) gene encodes the Slack channel KNa1.1, which is expressed in neurons throughout the brain. Gain-of-function variants in KCNT1 are associated with a spectrum of epilepsy syndromes, and mice carrying those variants exhibit a robust phenotype similar to that observed in patients. Kcnt1 knockout (KO) mice, however, have a normal lifespan without any epileptic phenotype. To understand the molecular differences between these two models, we conducted a comprehensive proteomic analysis of the cerebral cortices of Kcnt1 KO and Kcnt1R455H/+ mice, an animal model bearing a cytoplasmic C-terminal mutation homologous to a human R474H variant that results in EIMFS. The greatest change observed in Kcnt1 KO mice compared to the wild-type mice was the increased expression of multiple proteins of the inner mitochondrial membrane. Electron microscopy studies of cortical mitochondria from Kcnt1 KO mice further confirmed a significant increase in the density of mitochondrial cristae compared to that in wild-type mice. Kcnt1 reduction by a murine-specific Kcnt1 antisense oligonucleotide (ASO) in Kcnt1R455H/+ mice partially corrected the proteomic dysregulations in the disease model. The results support the hypothesis that ASO-mediated KCNT1 reduction could be therapeutically useful in the treatment of KCNT1 epilepsies.

Voltage-gated ion channels in epilepsies: circuit dysfunctions and treatments

Epileptic encephalopathies are generally considered to be functional disruptions in the balance between neural excitation and inhibition. Excitatory and inhibitory voltage-gated ion channels are key targets of antiepileptic drugs, playing a critical role in regulating neuronal excitation and synaptic transmission. Recent research has highlighted the significance of ion channels in various aspects of epilepsy, including presynaptic neurotransmitter release, intrinsic neuronal excitability, and neural synchrony. Genetic alterations in excitatory and inhibitory ion channels within principal neurons and in inhibitory interneurons have also been identified as key contributors to the development of epilepsies. We review these recent studies and shed light on the bidirectional relationship between epilepsy and neuronal excitability and the latest advancements in pharmacological therapeutics targeting ion channels for epilepsy treatment.

The expanding field of genetic developmental and epileptic encephalopathies: current understanding and future perspectives

Recent advances in genetic testing technologies have revolutionised the identification of genetic abnormalities in early onset developmental and epileptic encephalopathies (DEEs). In this Review, we provide an update on the expanding landscape of genetic factors contributing to DEEs, encompassing over 800 reported genes. We focus on the cellular and molecular mechanisms driving epileptogenesis, with an emphasis on emerging therapeutic strategies and effective treatment options. We explore noteworthy, novel genes linked to DEE phenotypes, such as gBRAT-1 and GNAO1, and gene families such as GRIN and HCN. Understanding the network-level effects of gene variants will pave the way for potential gene therapy applications. Given the diverse comorbidities associated with DEEs, a multidisciplinary team approach is essential. Despite ongoing efforts and improved genetic testing, DEEs lack a cure, and treatment complexities persist. This Review underscores the necessity for larger international prospective studies focusing on both seizure outcomes and developmental trajectories.

High-frequency terahertz stimulation alleviates neuropathic pain by inhibiting the pyramidal neuron activity in the anterior cingulate cortex of mice

Neuropathic pain (NP) is caused by a lesion or disease of the somatosensory system and is characterized by abnormal hypersensitivity to stimuli and nociceptive responses to non-noxious stimuli, affecting approximately 7-10% of the general population. However, current first-line drugs like non-steroidal anti-inflammatory agents and opioids have limitations, including dose-limiting side effects, dependence, and tolerability issues. Therefore, developing new interventions for the management of NP is urgent. In this study, we discovered that the high-frequency terahertz stimulation (HFTS) at approximately 36 THz effectively alleviates NP symptoms in mice with spared nerve injury. Computational simulation suggests that the frequency resonates with the carbonyl group in the filter region of Kv1.2 channels, facilitating the translocation of potassium ions. In vivo and in vitro results demonstrate that HFTS reduces the excitability of pyramidal neurons in the anterior cingulate cortex likely through enhancing the voltage-gated K+ and also the leak K+ conductance. This research presents a novel optical intervention strategy with terahertz waves for the treatment of NP and holds promising applications in other nervous system diseases.

In Silico Assisted Identification, Synthesis, and In Vitro Pharmacological Characterization of Potent and Selective Blockers of the Epilepsy-Associated KCNT1 Channel

Gain-of-function (GoF) variants in KCNT1 channels cause severe, drug-resistant forms of epilepsy. Quinidine is a known KCNT1 blocker, but its clinical use is limited due to severe drawbacks. To identify novel KCNT1 blockers, a homology model of human KCNT1 was built and used to screen an in-house library of compounds. Among the 20 molecules selected, five (CPK4, 13, 16, 18, and 20) showed strong KCNT1-blocking ability in an in vitro fluorescence-based assay. Patch-clamp experiments confirmed a higher KCNT1-blocking potency of these compounds when compared to quinidine, and their selectivity for KCNT1 over hERG and Kv7.2 channels. Among identified molecules, CPK20 displayed the highest metabolic stability; this compound also blocked KCNT2 currents, although with a lower potency, and counteracted GoF effects prompted by 2 recurrent epilepsy-causing KCNT1 variants (G288S and A934T). The present results provide solid rational basis for future design of novel compounds to counteract KCNT1-related neurological disorders.

Structure-Activity Relationship Studies in a Series of Xanthine Inhibitors of SLACK Potassium Channels

Gain-of-function mutations in the KCNT1 gene, which encodes the sodium-activated potassium channel known as SLACK, are associated with the rare but devastating developmental and epileptic encephalopathy known as epilepsy of infancy with migrating focal seizures (EIMFS). The design of small molecule inhibitors of SLACK channels represents a potential therapeutic approach to the treatment of EIMFS, other childhood epilepsies, and developmental disorders. Herein, we describe a hit optimization effort centered on a xanthine SLACK inhibitor (8) discovered via a high-throughput screen. Across three distinct regions of the chemotype, we synthesized 58 new analogs and tested each one in a whole-cell automated patch-clamp assay to develop structure-activity relationships for inhibition of SLACK channels. We further evaluated selected analogs for their selectivity versus a variety of other ion channels and for their activity versus clinically relevant SLACK mutants. Selectivity within the series was quite good, including versus hERG. Analog 80 (VU0948578) was a potent inhibitor of WT, A934T, and G288S SLACK, with IC50 values between 0.59 and 0.71 µM across these variants. VU0948578 represents a useful in vitro tool compound from a chemotype that is distinct from previously reported small molecule inhibitors of SLACK channels.

Discovery of a Small Molecule Activator of Slack (Kcnt1) Potassium Channels That Significantly Reduces Scratching in Mouse Models of Histamine-Independent and Chronic Itch

Various disorders are accompanied by histamine-independent itching, which is often resistant to the currently available therapies. Here, it is reported that the pharmacological activation of Slack (Kcnt1, KNa1.1), a potassium channel highly expressed in itch-sensitive sensory neurons, has therapeutic potential for the treatment of itching. Based on the Slack-activating antipsychotic drug, loxapine, a series of new derivatives with improved pharmacodynamic and pharmacokinetic profiles is designed that enables to validate Slack as a pharmacological target in vivo. One of these new Slack activators, compound 6, exhibits negligible dopamine D2 and D3 receptor binding, unlike loxapine. Notably, compound 6 displays potent on-target antipruritic activity in multiple mouse models of acute histamine-independent and chronic itch without motor side effects. These properties make compound 6 a lead molecule for the development of new antipruritic therapies targeting Slack.

Coupling of Slack and NaV1.6 sensitizes Slack to quinidine blockade and guides anti-seizure strategy development

Quinidine has been used as an anticonvulsant to treat patients with KCNT1-related epilepsy by targeting gain-of-function KCNT1 pathogenic mutant variants. However, the detailed mechanism underlying quinidine's blockade against KCNT1 (Slack) remains elusive. Here, we report a functional and physical coupling of the voltage-gated sodium channel NaV1.6 and Slack. NaV1.6 binds to and highly sensitizes Slack to quinidine blockade. Homozygous knockout of NaV1.6 reduces the sensitivity of native sodium-activated potassium currents to quinidine blockade. NaV1.6-mediated sensitization requires the involvement of NaV1.6's N- and C-termini binding to Slack's C-terminus and is enhanced by transient sodium influx through NaV1.6. Moreover, disrupting the Slack-NaV1.6 interaction by viral expression of Slack's C-terminus can protect against SlackG269S-induced seizures in mice. These insights about a Slack-NaV1.6 complex challenge the traditional view of 'Slack as an isolated target' for anti-epileptic drug discovery efforts and can guide the development of innovative therapeutic strategies for KCNT1-related epilepsy.

Role of Potassium Ion Channels in Epilepsy: Focus on Current Therapeutic Strategies

BACKGROUND

Epilepsy is one of the prevalent neurological disorders characterized by disrupted synchronization between inhibitory and excitatory neurons. Disturbed membrane potential due to abnormal regulation of neurotransmitters and ion transport across the neural cell membrane significantly contributes to the pathophysiology of epilepsy. Potassium ion channels (KCN) regulate the resting membrane potential and are involved in neuronal excitability. Genetic alterations in the potassium ion channels (KCN) have been reported to result in the enhancement of the release of neurotransmitters, the excitability of neurons, and abnormal rapid firing rate, which lead to epileptic phenotypes, making these ion channels a potential therapeutic target for epilepsy. The aim of this study is to explore the variations reported in different classes of potassium ion channels (KCN) in epilepsy patients, their functional evaluation, and therapeutic strategies to treat epilepsy targeting KCN.

METHODOLOGY

A review of all the relevant literature was carried out to compile this article.

RESULTS

A large number of variations have been reported in different genes encoding various classes of KCN. These genetic alterations in KCN have been shown to be responsible for disrupted firing properties of neurons. Antiepileptic drugs (AEDs) are the main therapeutic strategy to treat epilepsy. Some patients do not respond favorably to the AEDs treatment, resulting in pharmacoresistant epilepsy.

CONCLUSION

Further to address the challenges faced in treating epilepsy, recent approaches like optogenetics, chemogenetics, and genome editing, such as clustered regularly interspaced short palindromic repeats (CRISPR), are emerging as target-specific therapeutic strategies.

Design, synthesis, and biological evaluation of a novel series of 1,2,4-oxadiazole inhibitors of SLACK potassium channels: Identification of in vitro tool VU0935685

Malignant migrating partial seizure of infancy (MMPSI) is a devastating and pharmacoresistant form of infantile epilepsy. MMPSI has been linked to multiple gain-of-function (GOF) mutations in the KCNT1 gene, which encodes for a potassium channel often referred to as SLACK. SLACK channels are sodium-activated potassium channels distributed throughout the central nervous system (CNS) and the periphery. The investigation described here aims to discover SLACK channel inhibitor tool compounds and profile their pharmacokinetic and pharmacodynamic properties. A SLACK channel inhibitor VU0531245 (VU245) was identified via a high-throughput screen (HTS) campaign. Structure-activity relationship (SAR) studies were conducted in five distinct regions of the hit VU245. VU245 analogs were evaluated for their ability to affect SLACK channel activity using a thallium flux assay in HEK-293 cells stably expressing wild-type (WT) human SLACK. Selected analogs were tested for metabolic stability in mouse liver microsomes and plasma-protein binding in mouse plasma. The same set of analogs was tested via thallium flux for activity versus human A934T SLACK and other structurally related potassium channels, including SLICK and Maxi-K. In addition, potencies for selected VU245 analogs were obtained using whole-cell electrophysiology (EP) assays in CHO cells stably expressing WT human SLACK through an automated patch clamp system. Results revealed that this scaffold tolerates structural changes in some regions, with some analogs demonstrating improved SLACK inhibitory activity, good selectivity against the other channels tested, and modest improvements in metabolic clearance. Analog VU0935685 represents a new, structurally distinct small-molecule inhibitor of SLACK channels that can serve as an in vitro tool for studying this target.

Reduction of Kcnt1 is therapeutic in mouse models of SCN1A and SCN8A epilepsy

Developmental and epileptic encephalopathies (DEEs) are severe seizure disorders with inadequate treatment options. Gain- or loss-of-function mutations of neuronal ion channel genes, including potassium channels and voltage-gated sodium channels, are common causes of DEE. We previously demonstrated that reduced expression of the sodium channel gene Scn8a is therapeutic in mouse models of sodium and potassium channel mutations. In the current study, we tested whether reducing expression of the potassium channel gene Kcnt1 would be therapeutic in mice with mutation of the sodium channel genes Scn1a or Scn8a. A Kcnt1 antisense oligonucleotide (ASO) prolonged survival of both Scn1a and Scn8a mutant mice, suggesting a modulatory effect for KCNT1 on the balance between excitation and inhibition. The cation channel blocker quinidine was not effective in prolonging survival of the Scn8a mutant. Our results implicate KCNT1 as a therapeutic target for treatment of SCN1A and SCN8A epilepsy.

New use for an old drug: quinidine in KCNT1-related epilepsy therapy

KCNT1 has been known to encode a subunit of the tetrameric sodium activated potassium channel (K_Na1.1). Pathogenic variants of KCNT1, especially gain-of-function (GOF) variants, are associated with multiple epileptic disorders which are often refractory to conventional anti-seizure medications and summarized as KCNT1-related epilepsy. Although the detailed pathogenic mechanisms of KCNT1-related epilepsy remain unknown, increasing studies attempt to find effective medications for those patients by utilizing quinidine to inhibit hyperexcitable K_Na1.1. However, it has been shown that controversial outcomes among studies and partial success in some individuals may be due to multiple factors, such as poor blood-brain barrier (BBB) penetration, mutation-dependent manner, phenotype-genotype associations, and rational therapeutic schedule. In recent years, with higher resolution of K_Na1.1 structure in different activation states and advanced synthetic techniques, it improves the process performance of therapy targeting at K_Na1.1 channel to achieve more effective outcomes. Here, we systematically reviewed the study history of quinidine on KCNT1-related epilepsy and its corresponding therapeutic effects. Then, we analyzed and summarized the possible causes behind the different outcomes of the application of quinidine. Finally, we outlooked the recent advances in precision medicine treatment for KCNT1-related epilepsy.

Approaches for the discovery of drugs that target K Na 1.1 channels in KCNT1-associated epilepsy

INTRODUCTION

There are approximately 70 million people with epilepsy and about 30% of patients are not satisfactorily treated. A link between gene mutations and epilepsy is well documented. A number of pathological variants of KCNT1 gene (encoding the weakly voltage-dependent sodium-activated potassium channel - KNa 1.1) mutations has been found. For instance, epilepsy of infancy with migrating focal seizures, autosomal sleep-related hypermotor epilepsy or Ohtahara syndrome have been associated with KCNT1 gene mutations.

AREAS COVERED

Several methods for studies on KNa 1.1 channels have been reviewed - patch clamp analysis, Förster resonance energy transfer spectroscopy and whole-exome sequencing. The authors also review available drugs for the management of KCNT1 epilepsies.

EXPERT OPINION

The current methods enable deeper insights into electrophysiology of KNa 1.1 channels or its functioning in different activation states. It is also possible to identify a given KCNT1 mutation. Quinidine and cannabidiol show variable efficacy as add-on to baseline antiepileptic drugs so more effective treatments are required. A combined approach with the methods shown above, in silico methods and the animal model of KCNT1 epilepsies seems likely to create personalized treatment of patients with KCNT1 gene mutations.

Long-term follow-up of vagus nerve stimulation in drug-resistant KCNT1-related epilepsy: a case presentation

Background

The KCNT1 gene encodes a Na+-activated K+ channel. Gain-of-function mutations of KCNT1 lead to autosomal dominant sleep-related hypermotor epilepsy, early-onset epileptic encephalopathy, focal epilepsy and other epileptic encephalopathies. In this paper, we report a boy carrying a KCNT1 gene mutation, who presented with drug-resistant focal-onset seizures. He had decreased seizure frequency and improvement of background changes in electroencephalography (EEG) after vagus nerve stimulation (VNS).

Case presentation

The case was a nonverbal 9-year-old male who presented with drug-resistant focal-onset seizures since age 3 and had underwent VNS therapy for 2 years. He had hypermotor symptoms, automatism and bilateral asymmetric tonic seizures with cognitive decline and aphasis from age 3. The patient had a variety of seizure types that only occurred at night. The most common seizure type was automatisms, and ictal video EEG showed high-amplitude delta waves, followed by a fast rhythmic sharp activity in the mesial frontal and bitemporal regions. The patient was diagnosed with KCNT1-related epilepsy, epileptic encephalopathy and cognitive disorder. He was refractory to multiple anti-seizure medicines (ASM) and ketogenic diet. After VNS treatment at age 7, the frequency of seizures was reduced significantly and EEG was improved in background slowing.

Conclusions

Children with KCNT1-related epilepsy usually have early onset of disease, are nonverbal, and are refractory to ASM. This boy with drug-resistant KCNT1-related epilepsy showed significantly reduced seizure frequency after VNS. This report may provide reference for management of cases of KCNT1-related epilepsy.

Neuroblastoma SH-SY5Y Cell Differentiation to Mature Neuron by AM580 Treatment

Neuroblastoma is a type of developmental childhood cancer that arises from the neural crest. It is the most common pediatric solid tumor in the world. AM580 is a powerful cyto-differentiating molecule on acute promyelocytic leukemia cells and induced pluripotent stem cells, but its effect on neuroblastoma is still unknown. In this study, the neuronal differentiation impact of AM580 was investigated using the human neuroblastoma cell line SH-SY5Y as a model. AM580 successfully stimulated the SH-SY5Y cells to develop into neuron-like cells. Functional enrichment analysis of RNAseq data revealed that differentially expressed genes (DEGs) were substantially enriched for GO keywords and KEGG pathways linked to neuron development. Some potassium ion channel genes associated with neuronal excitation, such as KCNT1, were shown to be upregulated. Through the MEA tests, we found the AM580-induced neurons possessed electrical spikes as mature neurons. AM580 also induced the neuronal marker β-tubulin III and mature neurons marker Neurofilament H. Our study proved that AM580 can promote the differentiation of neurons and has the potential to treat neuroblastoma, neurodevelopmental and neurodegenerative diseases.

Double-edged Role of KNa Channels in Brain Tuning: Identifying Epileptogenic Network Micro-Macro Disconnection

Epilepsy is commonly recognized as a disease driven by generalized hyperexcited and hypersynchronous neural activity. Sodium-activated potassium channels (K_Na channels), which are encoded by the Slo 2.2 and Slo 2.1 genes, are widely expressed in the central nervous system and considered as "brakes" to adjust neuronal adaptation through regulating action potential threshold or after-hyperpolarization under physiological condition. However, the variants in K_Na channels, especially gain-of-function variants, have been found in several childhood epileptic conditions. Most previous studies focused on mapping the epileptic network on the macroscopic scale while ignoring the value of microscopic changes. Notably, paradoxical role of K_Na channels working on individual neuron/microcircuit and the macroscopic epileptic expression highlights the importance of understanding epileptogenic network through combining microscopic and macroscopic methods. Here, we first illustrated the molecular and physiological function of K_Na channels on preclinical seizure models and patients with epilepsy. Next, we summarized current hypothesis on the potential role of K_Na channels during seizures to provide essential insight into what emerged as a micro-macro disconnection at different levels. Additionally, we highlighted the potential utility of K_Na channels as therapeutic targets for developing innovative anti-seizure medications.

Small-molecule inhibitors of Slack potassium channels as potential therapeutics for childhood epilepsies

Slack channels are sodium-activated potassium channels that are encoded by the KCNT1 gene. Several KCNT1 gain of function mutations have been linked to malignant migrating partial seizures of infancy. Quinidine is an anti-arrhythmic drug that functions as a moderately potent inhibitor of Slack channels; however, quinidine use is limited by its poor selectivity, safety and pharmacokinetic profile. Slack channels represent an interesting target for developing novel therapeutics for the treatment of malignant migrating partial seizures of infancy and other childhood epilepsies; thus, ongoing efforts are directed toward the discovery of small-molecules that inhibit Slack currents. This review summarizes patent applications published in 2020-2021 that describe the discovery of novel small-molecule Slack inhibitors.