James P. Johnson

The assessment of the efficacy of antiseizure medications (ASMs) in animal models of acute seizures has played a critical role in these drugs’ success in clinical trials for human epilepsy. One of the most widely used animal models for this purpose is the maximal electroshock seizure (MES) model. While there are numerous published reports on the efficacy of conventional ASMs in MES models, there is a need to expand the understanding on the brain concentrations that are needed to achieve optimal levels of efficacy in this model. We assessed the pharmacokinetic/pharmacodynamic (PK/PD) profiles of six ASMs, namely carbamazepine (CBZ), phenytoin (PHT), valproic acid (VPA), lacosamide (LSM), cenobamate (CNB), and retigabine (RTG), using MES models in mice and rats. EC₅₀ values for plasma and the brain were generally higher in mice than rats, with fold differences ranging from 1.3- to 8.6-fold for plasma and from 1.2- to 11.5-fold for brain. Phenytoin showed the largest interspecies divergence. These results suggest that rats may exhibit greater sensitivity to seizure protection in the MES model, likely reflecting species differences in metabolism and brain penetration. These findings highlight the value of considering concentration–response variations and species-specific differences when assessing the efficacy of both conventional ASMs and novel compounds exhibiting anticonvulsant activity.

Background/Objective: The assessment of the efficacy of antiseizure medications (ASMs) in animal models of acute seizures has played a critical role in these drugs’ success in clinical trials for human epilepsy. One of the most widely used animal models for this purpose is the maximal electroshock seizure (MES) model. While there are numerous published reports on the efficacy of conventional ASMs in MES models, there is a need to expand the understanding on the brain concentrations that are needed to achieve optimal levels of efficacy in this model. Methods: We evaluated six clinically available ASMs in both a mouse and a rat MES model by analyzing dose-response and concentration-response for brain and plasma exposure levels: carbamazepine (CBZ), phenytoin (PHT), valproic acid (VPA), lacosa-mide (LSM), cenobamate (CNB), and retigabine (RTG). Results: Our data indicate that these ASMs tend to be more effective in reducing seizures in the rat MES, with notable differences in drug metabolism and brain penetrance be-tween mice and rats. Conclusion: These findings highlight the value of considering concentration-response variations and species-specific differences when assessing the efficacy of both conventional ASMs and novel compounds exhibiting anticonvulsant activity.

Background and Purpose: Inhibitors of voltage‐gated sodium channels (Na_Vs) are important anti‐epileptic drugs, but the contribution of specific channel isoforms is unknown since available inhibitors are non‐selective. We aimed to create novel, isoform selective inhibitors of Na_v channels as a means of informing the development of improved antiseizure drugs.Experimental Approach: We created a series of compounds with diverse selectivity profiles enabling block of Na_V1.6 alone or together with Na_V1.2. These novel Na_V inhibitors were evaluated for their ability to inhibit electrically evoked seizures in mice with a heterozygous gain‐of‐function mutation (N1768D/+) in Scn8a (encoding Na_V1.6) and in wild‐type mice.Key Results: Pharmacologic inhibition of Na_V1.6 in Scn8a^N1768D/+ mice prevented seizures evoked by a 6‐Hz shock. Inhibitors were also effective in a direct current maximal electroshock seizure assay in wild‐type mice. Na_V1.6 inhibition correlated with efficacy in both models, even without inhibition of other CNS Na_V isoforms.Conclusions and Implications: Our data suggest Na_V1.6 inhibition is a driver of efficacy for Na_V inhibitor anti‐seizure medicines. Sparing the Na_V1.1 channels of inhibitory interneurons did not compromise efficacy. Selective Na_V1.6 inhibitors may provide targeted therapies for human Scn8a developmental and epileptic encephalopathies and improved treatments for idiopathic epilepsies.

Voltage-gated sodium ion channels allow for the initiation and transmission of action potentials. There is a high interest in research and drug development to selectively target these ion channels to treat epilepsy and other disorders such as pain. Scientific literature and presentations often incorporate maps of these integral membrane proteins with markers indicating gene mutations to highlight genotype/phenotype correlations. There is a need for automated tools to create high quality figures with mutation (variant) locations displayed on these channel maps. This manuscript introduces a simple application to create visualization for mutations on alpha voltage-gated sodium channels, created using the D3.js library. The application allows for mapping of variant sequences, as well as important properties like the type of variant and the phenotypes linked to the variant. It also allows for customizability and the production of high-quality images for publication. This application and code base can further be extrapolated to other ion channels as well.

Inhibitors of voltage-gated sodium channels (Na _V s) are important anti-epileptic drugs, but the contribution of specific channel isoforms is unknown since available inhibitors are nonselective. We created a series of compounds with diverse selectivity profiles enabling block of Na _V 1.6 alone or together with Na _V 1.2. Mice with a heterozygous gain-of-function mutation (N1768D/+) in Scn8a (encoding Na _V 1.6) responded with a tonic-clonic seizure to a mild 6 Hz stimulus that was innocuous to wild-type mice. Pharmacologic inhibition of Na _V 1.6 in Scn8a ^N1768D/+ mice prevented seizures. Inhibitors were also effective in a direct current maximal electroshock seizure assay in wild-type mice. Na _V 1.6 inhibition correlated with efficacy in both models, even without inhibition of other CNS Na _V isoforms. Our data suggest Na _V 1.6 inhibition is a driver of efficacy for Na _V inhibitor anti-seizure medicines. Selective Na _V 1.6 inhibitors may provide targeted therapies for human Scn8a developmental and epileptic encephalopathies and better tolerated treatments for idiopathic epilepsies. Graphical

Sodium channel inhibitors are used to treat neurological disorders of hyperexcitability. However, all currently available sodium channel targeting anti-seizure medications are non-selective among the Na _V isoforms which potentially limits efficacy and therapeutic safety margins. XPC-7724 and XPC-5462 represent a new class of small molecule compounds. These compounds target inhibition of the Na _V 1.6 and Na _V 1.2 channels in excitatory pyramidal neurons and possess a molecular selectivity of >100 fold against Na _V 1.1 channels that are dominant in inhibitory cells. This profile will enable pharmacological dissection of the physiological roles of Na _V 1.2 and Na _V 1.6 and help to define the role of each channel in disease states. These compounds bind to and stabilize the inactivated-state of the channels, demonstrate higher potency with longer residency times, and slower off-rates than carbamazepine and phenytoin. These compounds possess cellular selectivity ex vivo in inhibiting action potential firing in cortical excitatory pyramidal neurons, whilst sparing fast spiking inhibitory interneurons. XPC-5462 also suppresses epileptiform activity in an ex vivo brain slice seizure model. This class of compounds provides a unique approach for treating neuronal excitability disorders by selectively down-regulating excitatory circuits. Graphical

NBI-921352 (formerly XEN901) is a novel sodium channel inhibitor designed to specifically target Na_V1.6 channels. Such a molecule provides a precision-medicine approach to targetSCN8A-related epilepsy syndromes (SCN8A-RES), where gain-of-function (GoF) mutations lead to excess Na_V1.6 sodium current, or other indications where Na_V1.6 mediated hyper-excitability contributes to disease (Gardella and Møller, 2019; Johannesen et al., 2019; Veeramah et al., 2012). NBI-921352 is a potent inhibitor of Na_V1.6 (IC₅₀0.051 µM), with exquisite selectivity over other sodium channel isoforms (selectivity ratios of 756 X for Na_V1.1, 134 X for Na_V1.2, 276 X for Na_V1.7, and >583 Xfor Na_V1.3, Na_V1.4, and Na_V1.5). NBI-921352is a state-dependent inhibitor, preferentially inhibiting inactivatedchannels. The state dependence leads to potent stabilization of inactivation, inhibiting Na_V1.6 currents, including resurgent and persistent Na_V1.6 currents, while sparing the closed/rested channels. The isoform-selective profile of NBI-921352 led to a robust inhibition of action-potential firing in glutamatergic excitatory pyramidal neurons, while sparing fast-spiking inhibitory interneurons, where Na_V1.1 predominates. Oral administration of NBI-921352 prevented electrically induced seizures in aScn8aGoF mouse,as well as in wild-type mouse and ratseizure models. NBI-921352 was effective in preventing seizures at lower brain and plasma concentrations than commonly prescribed sodium channel inhibitor anti-seizure medicines (ASMs) carbamazepine, phenytoin, and lacosamide. NBI-921352 waswell tolerated at higher multiples of the effective plasma and brain concentrations than those ASMs. NBI-921352 is entering phase II proof-of-concept trials for the treatment ofSCN8A-developmental epileptic encephalopathy (SCN8A-DEE) and adult focal-onset seizures.

NBI-921352 (formerly XEN901) is a novel sodium channel inhibitor designed to specifically target Na _V 1.6 channels. Such a molecule provides a precision-medicine approach to target SCN8A -related epilepsy syndromes ( SCN8A -RES), where gain-of-function (GoF) mutations lead to excess Na _V 1.6 sodium current, or other indications where Na _V 1.6 mediated hyper-excitability contributes to disease (Gardella and Moller, 2019; Johannesen et al., 2019; Veeramah et al., 2012). NBI-921352 is a potent inhibitor of Na _V 1.6 (IC ₅₀ 0.051 µM), with exquisite selectivity over other sodium channel isoforms (selectivity ratios of 756X for Na _V 1.1, 134X for Na _V 1.2, 276X for Na _V 1.7, and >583X for Na _V 1.3, Na _V 1.4, and Na _V 1.5). NBI-921352 is a state-dependent inhibitor, preferentially inhibiting activated (inactivated or open) channels. The state dependence leads to potent stabilization of inactivation, inhibiting Na _V 1.6 currents, including resurgent and persistent Na _V 1.6 currents, while sparing the closed/rested channels. The isoform-selective profile of NBI-921352 led to a robust inhibition of action-potential firing in glutamatergic excitatory pyramidal neurons, while sparing fast-spiking inhibitory interneurons, where Na _V 1.1 predominates. Oral administration of NBI-921352 prevented electrically induced seizures in a Scn8a GoF mouse, as well as in wild-type mouse and rat seizure models. NBI-921352 was effective in preventing seizures at lower brain and plasma concentrations than commonly prescribed sodium channel inhibitor antiseizure medicines (ASMs) carbamazepine, phenytoin, and lacosamide. NBI-921352 was well tolerated at higher multiples of the effective plasma and brain concentrations than those ASMs. NBI-921352 is entering phase II proof-of-concept trials for the treatment of SCN8A- developmental epileptic encephalopathy ( SCN8A -DEE) and adult focal-onset seizures.

Nonselective antagonists of voltage-gated sodium (NaV) channels have been long used for the treatment of epilepsies. The efficacy of these drugs is thought to be due to the block of sodium channels on excitatory neurons, primarily NaV1.6 and NaV1.2. However, these currently marketed drugs require high drug exposure and suffer from narrow therapeutic indices. Selective inhibition of NaV1.6, while sparing NaV1.1, is anticipated to provide a more effective and better tolerated treatment for epilepsies. In addition, block of NaV1.2 may complement the anticonvulsant activity of NaV1.6 inhibition. We discovered a novel series of aryl sulfonamides as CNS penetrant, isoform-selective NaV1.6 inhibitors, which also displayed potent block of NaV1.2. Optimization focused on increasing selectivity over NaV1.1, improving metabolic stability, reducing active efflux, and addressing a PXR (pregnane X-receptor) liability. We obtained compounds 30-32, which produced potent anticonvulsant activity in mouse seizure models, including a direct current maximal electroshock (DC-MES) seizure assay.