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

Abstract

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 (Na_V1.8) 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 Na_V1.8, 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 Na_V1.8 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 Na_V 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 Na_V subtypes (≥ 31,000-fold) and 180 other molecular targets. Suzetrigine inhibits Na_V1.8 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 Na_V1.8 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 Na_V1.8 pain signal inhibitors acting in the peripheral nervous system to safely treat pain without addictive potential.

Keywords: Moderate to severe pain; NaV1.8; Non-opioid analgesic; Selective pain signal inhibitor; Suzetrigine; VX-548.

Fig. 1

Suzetrigine (SUZ) is a potent and selective inhibitor of human Na_V1.8 over other human Na_V subtypes and other Na_V1.8 orthologs. a Chemical structure of SUZ. b Inhibition of Na_V1.8 current by 10 nM SUZ in HEK cells expressing human Na_V1.8 and using automated electrophysiology techniques. Inset shows the voltage protocol used to generate the Na_V1.8 current trace shown (c). Inhibition of human Na_V subtypes 1.1–1.9 expressed in HEK or CHO cells and recorded using automated electrophysiology platforms. SUZ is ≥ 31,000-fold selective for Na_V1.8 over other human Na_V subtypes [48]. d Normalized inhibition of TTX-r Na_V1.8 current in DRG neurons using manual patch clamp electrophysiology. Average of data taken from n = 3 cells isolated from four (human) or one (monkey, rat, mouse, rabbit, and dog) tissue samples. Human IC₅₀ = 0.68 ± 0.16 nM across four biological replicates, monkey IC₅₀ = 0.75 nM (95% CI of IC₅₀ 0.44–1.4 nM), rat IC₅₀ = 56 nM (95% CI of IC₅₀ 36–93 nM), mouse IC₅₀ = 210 nM (95% CI of IC₅₀ 98–860 nM), rabbit IC₅₀ = 52 nM (95% CI of IC₅₀ 37–75 nM), dog IC₅₀ = 740 nM (95% CI of IC₅₀ 420–2100 nM)

Fig. 2

Suzetrigine (SUZ) inhibits Na_V1.8 through interactions with VSD2. a Schematic and sample electrophysiological traces showing effect of 11 nM SUZ on different Na_V1.8_Na_V1.2 chimeras and mutations. The domains in Na_V1.2 replaced with the corresponding Na_V1.8 region are shown in red in the schematic. b VSD2 sequence alignment highlighting unique motif (red) in S3–S4 loop in Na_V1.8. Conserved amino acids comprising the basic voltage sensing residues are in bold. c Representative SUZ concentration response curves in different Na_V1.8_Na_V1.2 chimeras. d SUZ binds directly to purified Na_V1.8 VSD2 chimera protein (K_d = 65 ± 10 nM) but not Na_V1.2 VSD2 protein. Representative curves from one experiment are shown in (c and d). Three independent experiments were conducted with a minimum of three technical replicates in each experiment

Fig. 3

Suzetrigine (SUZ) inhibits Na_V1.8 through stabilization of the closed state resulting in tonic inhibition. a Twenty-four membrane-spanning helices from four homologous domains of the Na_V1.8 protein are shown as cylinders (top). Na_V1.8 channels form around a central ion-conducting pore domain, which can adopt closed, open and inactivated conformations influenced by the position of peripheral voltage sensors shown in black (bottom). Adapted from [22]. SUZ binding to the closed state is represented by a blue oval (b and c) Pre-pulse voltages are applied to drive the Na_V1.8 channel to different states in the presence of SUZ. After a brief recovery pulse, inhibition of Na_V1.8 at different concentrations of SUZ is assessed and plotted against pre-pulse voltage. d Protocol to probe repetitive stimulation using a physiologically relevant voltage waveform. Inset shows expanded view of voltage protocol for each pulse in the 5 Hz train. e Representative current traces from 5 Hz repetitive stimulation experiment showing control and 10 nM SUZ. f Potency of SUZ is constant from first to last pulse measurements, consistent with a tonic mechanism of inhibition. Representative curves from one experimental replicate are shown in (c and f). Three independent experiments were conducted with a minimum of three technical replicates per experiment

Fig. 4

Suzetrigine (SUZ) inhibits pain signals in human DRG neurons. a Representative single AP from a human DRG neuron elicited by a 20 ms (from 10 to 30 ms), 1.1 × rheobase current injection before (black) and after (blue) application of 10 nM SUZ. b Raster plot of evoked action potentials fired in response to 100, 1 Hz current injections at 1.1 × rheobase in the absence (baseline) and presence of increasing concentrations of SUZ. c Concentration–response relationship showing APs remaining following application of increasing concentrations of SUZ in 10 cells that responded (greater than 5% reduction in APs) out of 17 total cells recorded from 3 human donors. *** Denotes p = 0.0001; **** denotes p < 0.0001 (repeated-measures one-way ANOVA with Dunnett’s multiple comparisons)

Fig. 5

Suzetrigine (SUZ) administration to female rats for 30 days followed by abrupt cessation did not produce signs of withdrawal. a Mean body weight (±SD). Rat body weight was measured on days 1, 15, and 30 during the treatment (Tx) period and daily during the withdrawal period. Body weight loss was observed in the morphine-positive control group beginning immediately during the withdrawal period but was not observed with SUZ. Significance was based on Kruskal–Wallis with post hoc Dunn’s significance testing. b Mean body temperature (±SD). Morphine treatment was associated with hyperthermia during treatment, and hypothermia in the period following withdrawal of treatment. SUZ did not display any effects on body temperature during the withdrawal period. Significance was evaluated with ANOVA using post hoc Dunnett’s test. c Least squares mean motor activity (±SE). In the 14 h following abrupt withdrawal of treatment, motor activity of the animals was monitored. Both basic and fine movements were decreased in the morphine-positive control group during the overnight hours (when rats are most active), while motor activity in the SUZ group was comparable to the vehicle control group