State-Dependent Inhibition of Nav1.8 Sodium Channels by VX-150 and VX-548

Differential state-dependent Nav1.8 inhibition by suzetrigine, LTGO-33, and A-887826

Nav1.8 sodium channels are expressed in pain-sensing neurons, and some Nav1.8 inhibitors significantly reduce pain in clinical trials. Several Nav1.8 inhibitors have an unusual state dependence whereby inhibition is relieved by depolarization. We compared the state-dependent action of several Nav1.8 channel inhibitors to test whether inhibition is relieved during action potential (AP) firing under physiological conditions to produce "reverse use dependence." A-887826 inhibition was substantially relieved by AP waveforms applied at 20 Hz at 37°C. In contrast, there was no relief during AP trains with suzetrigine (VX-548) or LTGO-33, even though inhibition could be effectively removed by long, strong depolarizations. These differences were explained by differences in the voltage dependence and kinetics with which the compounds dissociate from depolarized channels and rebind to resting state channels. Suzetrigine required the strongest depolarizations for relief (midpoint +33 mV) and relief was slow (tau >300 ms at +20 mV), so almost no relief occurred during an AP waveform. Relief from A-887826 required weaker depolarizations (midpoint +13 mV) and was much faster, so some relief occurred during each AP waveform and accumulated during 20-Hz trains. LTGO-33 required the weakest depolarizations for relief (midpoint -11 mV) and relief was even faster than for A-887826, but reinhibition between AP waveforms was far faster than for A-887826, so that relief did not accumulate during AP trains at 20 Hz. The results show that, unlike A-887826, there is no use-dependent relief of inhibition by suzetrigine or LTGO-33 with physiological voltage waveforms at physiological temperatures, but each for different reasons.

Sensory neuron sodium channels as pain targets; from cocaine to Journavx (VX-548, suzetrigine)

Voltage-gated sodium channels underpin electrical signaling in sensory neurons. Their activity is an essential element in the vast majority of pain conditions, making them significant drug targets. Sensory neuron sodium channels play roles not only in afferent signaling but also in a range of efferent regulatory mechanisms. Side effects through actions on other cell types and efferent signaling are thus important issues to address during analgesic drug development. As an example, the human genetic evidence for NaV1.7 as an ideal pain target contrasts with the side effects of NaV1.7 antagonists. In this review, we describe the history and progress toward the development of useful analgesic drugs and the renewed focus on NaV1.8 as a key target in pain treatment. NaV1.8 antagonists alone or in combination with other analgesics are likely to provide new opportunities for pain relief for the vast number of people (about 33% of the population) impacted by chronic pain, particularly present in aging populations.

Pharmacology and Mechanism of Action of Suzetrigine, a Potent and Selective NaV1.8 Pain Signal Inhibitor for the Treatment of Moderate to Severe Pain

INTRODUCTION

There is a high unmet need for safe and effective non-opioid medicines to treat moderate to severe pain without risk of addiction. Voltage-gated sodium channel 1.8 (NaV1.8) is a genetically and pharmacologically validated pain target that is selectively expressed in peripheral pain-sensing neurons and not in the central nervous system (CNS). Suzetrigine (VX-548) is a potent and selective inhibitor of NaV1.8, which has demonstrated clinical efficacy and safety in multiple acute pain studies. Our study was designed to characterize the mechanism of action of suzetrigine and assess both nonclinical and clinical data to test the hypothesis that selective NaV1.8 inhibition translates into clinical efficacy and safety, including lack of addictive potential.

METHODS

Preclinical pharmacology and mechanism of action studies were performed in vitro using electrophysiology and radiolabeled binding methods in cells recombinantly expressing human NaV channels, human proteins, and primary human dorsal root ganglion (DRG) sensory neurons. Safety and addictive potential assessments included in vitro secondary pharmacology studies, nonclinical repeat-dose toxicity and dependence studies in rats and/or monkeys, and a systematic analysis of adverse event data generated from 2447 participants from phase 3 acute pain studies of suzetrigine.

RESULTS

Suzetrigine is selective against all other NaV subtypes (≥ 31,000-fold) and 180 other molecular targets. Suzetrigine inhibits NaV1.8 by binding to the protein's second voltage sensing domain (VSD2) to stabilize the closed state of the channel. This novel allosteric mechanism results in tonic inhibition of NaV1.8 and reduces pain signals in primary human DRG sensory neurons. Nonclinical and clinical safety assessments with suzetrigine demonstrate no adverse CNS, cardiovascular or behavioral effects and no evidence of addictive potential or dependence.

CONCLUSIONS

The comprehensive pharmacology assessment presented here indicates that suzetrigine represents the first in a new class of non-opioid analgesics that are selective NaV1.8 pain signal inhibitors acting in the peripheral nervous system to safely treat pain without addictive potential.

In vitro inhibition of voltage-dependent sodium currents by the antifungal drug amorolfine

Voltage-gated sodium (Nav) channels are critical for electrical signaling, and their pharmacological modulation can be leveraged for the development of therapeutic agents targeting various disorders. The local anesthetic (LA) site on Nav channels is particularly important, as it is a common target for many clinically used inhibitors, including anticonvulsants and antiarrhythmics. Our goal was to identify novel Nav channel inhibitors by leveraging physicochemical criteria, focusing on potential LA site binding candidates. We identified amorolfine (AMF), a phenyl-propyl morpholine derivative, as a putative modulator. Our results demonstrate that AMF acts as a state-dependent inhibitor of Nav channels, with a ∼30-fold preference for inactivated states. It stabilizes channel inactivation and prevents channel from conducting, driven through its stabilization of inactivation. These findings suggest that AMF represents a new compound that inhibits Nav channels, offering insights into the development of future therapeutic agents targeting Nav and potentially other ion channels.

Novel non-opioid analgesics in pain management

Effective pain management has long been hindered by the limitations and risks associated with opioid analgesics, necessitating the exploration of novel, non-opioid alternatives. A comprehensive literature search was conducted using PubMed and Google Scholar during October and November 2024 to identify studies on emerging non-opioid pain management therapeutics. This review evaluates three promising classes of mechanism-specific therapeutics: nerve growth factor (NGF) monoclonal antibodies, transient receptor potential vanilloid 1 (TRPV1) antagonists, and selective sodium channel blockers. By targeting distinct pathways involved in pain sensation, these therapies aim to provide relief for various pain types, including chronic, inflammatory, and neuropathic pain, with potentially fewer side effects. Through a detailed analysis of their mechanisms of action and current evidence, this review highlights the clinical potential of each class, addressing both their efficacy and safety challenges. Ultimately, these emerging therapies represent significant advancements in non-opioid pain management, with the potential to reshape standard approaches to patient care.