Abstract
Nav1.8 sodium channels (Nav1.8) are an attractive therapeutic target for pain because they are prominent in primary pain-sensing neurons with little expression in most other kinds of neurons. Recently, two Nav1.8-targeted compounds, VX-150 and VX-548, have shown efficacy in clinical trials for reducing pain. We examined the characteristics of Nav1.8 inhibition by these compounds. The active metabolite form of VX-150 (VX-150m) inhibited human Nav1.8 channels with an IC(50) of 15 nM. VX-548 (suzetrigine) was even more potent (IC(50) 0.27 nM). Both VX-150m and VX-548 had the unusual property of "reverse use-dependence," whereby inhibition could be relieved by repetitive depolarizations, a property seen before with another Nav1.8 inhibitor, A-887826. The relief of VX-548 inhibition by large depolarizations occurred with a time constant of ∼40 milliseconds that was not concentration-dependent. Reinhibition at negative voltages occurred with a rate that was nearly proportional to drug concentration, consistent with the idea that relief of inhibition reflects dissociation of drug from the channel and reinhibition reflects rebinding. The relief of inhibition by depolarization suggests a remarkably strong and unusual state-dependence for both VX-150m and VX-548, with very weak binding to channels with fully activated voltage sensors despite very tight binding to channels with voltage sensors in the resting state. SIGNIFICANCE STATEMENT: The Nav1.8 sodium channel (Nav1.8) is a current target for new drugs for pain. This work describes the potency, selectivity, and state-dependent characteristics of inhibition of Nav1.8 channels by VX-150 and VX-548, compounds that have recently shown efficacy for relief of pain in clinical trials but whose mechanism of interaction with channels has not been described. The results show that the compounds share an unusual property whereby inhibition is relieved by depolarization, demonstrating a state-dependence different from most sodium channel inhibitors.