Adolescent Clinical Development of Ezogabine/Retigabine as Adjunctive Therapy for Partial-Onset Seizures: Pharmacokinetics and Tolerability

Behavior of KCNQ Channels in Neural Plasticity and Motor Disorders

The broad distribution of voltage-gated potassium channels (VGKCs) in the human body makes them a critical component for the study of physiological and pathological function. Within the KCNQ family of VGKCs, these aqueous conduits serve an array of critical roles in homeostasis, especially in neural tissue. Moreover, the greater emphasis on genomic identification in the past century has led to a growth in literature on the role of the ion channels in pathological disease as well. Despite this, there is a need to consolidate the updated findings regarding both the pharmacotherapeutic and pathological roles of KCNQ channels, especially regarding neural plasticity and motor disorders which have the largest body of literature on this channel. Specifically, KCNQ channels serve a remarkable role in modulating the synaptic efficiency required to create appropriate plasticity in the brain. This role can serve as a foundation for clinical approaches to chronic pain. Additionally, KCNQ channels in motor disorders have been utilized as a direction for contemporary pharmacotherapeutic developments due to the muscarinic properties of this channel. The aim of this study is to provide a contemporary review of the behavior of these channels in neural plasticity and motor disorders. Upon review, the behavior of these channels is largely dependent on the physiological role that KCNQ modulatory factors (i.e., pharmacotherapeutic options) serve in pathological diseases.

Pharmacokinetics of XEN496, a Novel Pediatric Formulation of Ezogabine, Under Fed and Fasted Conditions: A Phase 1 Trial

INTRODUCTION

XEN496 is a novel, granular, immediate-release formulation of ezogabine intended for pediatric use. The objective of this study was to assess the effect of food on the pharmacokinetics (PK) of XEN496 and its N-acetyl metabolite (NAMR) in healthy volunteers.

METHODS

Twenty-four adult subjects were enrolled in this phase 1, single center, open-label, randomized, single-dose, two-way crossover study. Subjects received 400 mg XEN496 as an oral suspension in both fed and fasted states separated by a 6-day washout period. Serial blood samples were collected up to 48 h post-administration. PK parameters evaluated included maximum observed plasma concentration (C_max), time of maximum observed plasma concentration (T_max), and area under the concentration-time curve (AUC_(0-t) and AUC_inf). Safety was assessed by laboratory evaluations, physical exam, and adverse event monitoring.

RESULTS

For XEN496, median T_max was 3 and 2 h in the fed and fasted states, respectively. AUC parameters in the fed and fasted states were equivalent, whereas food decreased C_max of XEN496 by 32% compared to the fasted state. The ratio of geometric means [90% CI] for C_max was 72% [64-82%]. For NAMR, food delayed T_max by 1 h, while C_max and AUC parameters were equivalent in the fed and fasted states. The safety profile of XEN496 in this study appeared comparable to that previously reported for ezogabine tablets.

CONCLUSION

The biopharmaceutical performance of XEN496 in this study was as expected for an immediate-release, granular dosage formulation, and generally comparable to that reported for ezogabine tablets. Future studies are needed to characterize the efficacy, safety, and PK of XEN496 in a pediatric population.

The Role of Kv7.2 in Neurodevelopment: Insights and Gaps in Our Understanding

Kv7.2 subunits encoded by the KCNQ2 gene constitute a critical molecular component of the M-current, a subthreshold voltage-gated potassium current controlling neuronal excitability by dampening repetitive action potential firing. Pathogenic loss-of-function variants in KCNQ2 have been linked to epilepsy since 1998, and there is ample functional evidence showing that dysfunction of the channel indeed results in neuronal hyperexcitability. The recent description of individuals with severe developmental delay with or without seizures due to pathogenic variants in KCNQ2 (KCNQ2-encephalopathy) reveals that Kv7.2 channels also have an important role in neurodevelopment. Kv7.2 channels are expressed already very early in the developing brain when key developmental processes such as proliferation, differentiation, and synaptogenesis play a crucial role in brain morphogenesis and maturation. In this review, we will discuss the available evidence for a role of Kv7.2 channels in these neurodevelopmental processes, focusing in particular on insights derived from KCNQ2-related human phenotypes, from the spatio-temporal expression of Kv7.2 and other Kv7 family member, and from cellular and rodent models, highlighting critical gaps and research strategies to be implemented in the future. Lastly, we propose a model which divides the M-current activity in three different developmental stages, correlating with the cell characteristics during these particular periods in neuronal development, and how this can be linked with KCNQ2-related disorders. Understanding these mechanisms can create opportunities for new targeted therapies for KCNQ2-encephalopathy.

Ion Channels in Genetic Epilepsy: From Genes and Mechanisms to Disease-Targeted Therapies

Epilepsy is a common and serious neurologic disease with a strong genetic component. Genetic studies have identified an increasing collection of disease-causing genes. The impact of these genetic discoveries is wide reaching-from precise diagnosis and classification of syndromes to the discovery and validation of new drug targets and the development of disease-targeted therapeutic strategies. About 25% of genes identified in epilepsy encode ion channels. Much of our understanding of disease mechanisms comes from work focused on this class of protein. In this study, we review the genetic, molecular, and physiologic evidence supporting the pathogenic role of a number of different voltage- and ligand-activated ion channels in genetic epilepsy. We also review proposed disease mechanisms for each ion channel and highlight targeted therapeutic strategies.