Pharmacologic Characterization of AMG8379, a Potent and Selective Small Molecule Sulfonamide Antagonist of the Voltage-Gated Sodium Channel Na_V1.7

Abstract

Potent and selective antagonists of the voltage-gated sodium channel Na1.7 represent a promising avenue for the development of new chronic pain therapies. We generated a small molecule atropisomer quinolone sulfonamide antagonist AMG8379 and a less active enantiomer AMG8380. Here we show that AMG8379 potently blocks human Na1.7 channels with an IC of 8.5 nM and endogenous tetrodotoxin (TTX)-sensitive sodium channels in dorsal root ganglion (DRG) neurons with an IC of 3.1 nM in whole-cell patch clamp electrophysiology assays using a voltage protocol that interrogates channels in a partially inactivated state. AMG8379 was 100- to 1000-fold selective over other Na family members, including Na1.4 expressed in muscle and Na1.5 expressed in the heart, as well as TTX-resistant Na channels in DRG neurons. Using an ex vivo mouse skin-nerve preparation, AMG8379 blocked mechanically induced action potential firing in C-fibers in both a time-dependent and dose-dependent manner. AMG8379 similarly reduced the frequency of thermally induced C-fiber spiking, whereas AMG8380 affected neither mechanical nor thermal responses. In vivo target engagement of AMG8379 in mice was evaluated in multiple Na1.7-dependent behavioral endpoints. AMG8379 dose-dependently inhibited intradermal histamine-induced scratching and intraplantar capsaicin-induced licking, and reversed UVB radiation skin burn-induced thermal hyperalgesia; notably, behavioral effects were not observed with AMG8380 at similar plasma exposure levels. AMG8379 is a potent and selective Na1.7 inhibitor that blocks sodium current in heterologous cells as well as DRG neurons, inhibits action potential firing in peripheral nerve fibers, and exhibits pharmacodynamic effects in translatable models of both itch and pain.

Complementary roles of murine NaV1.7, NaV1.8 and NaV1.9 in acute itch signalling

“…In agreement with previous studies, we show that a deletion or inhibition of one Na V channel is not sufficient to fully abolish scratching in mice 28,[30][31][32][33] . The contribution of several Na V channels to acute itch signalling of different stimuli, shown here, supports the suggestion that a simultaneous inhibition of different Na V channels is required to reach full abolishment.…”

“…Corresponding inhibitory studies analysed the role of Na V subtypes in itch signalling. Inhibition of Na V 1.7 reduced acute scratch behaviour in mice upon histamine and selected non-histaminergic stimuli 19,[30][31][32][33] . Moreover, Na V 1.9 knockout mice showed reduced scratch behaviour upon treatment with histamine, chloroquine and BAM8-22 28 .…”

Discovery of a Selective, State-Independent Inhibitor of NaV1.7 by Modification of Guanidinium Toxins

“…(8) Examples include a cystine knot toxin that binds to VSD II and select sulfonamide inhibitors that bind to VSD IV. (44,(51)(52)(53). For this latter class of inhibitors, determining the level 40 of NaV1.7 target occupancy reached at these exposures is difficult given the variation in potency (i.e., IC50 values determined by electrophysiology) against resting and inactivated conformational states of the channel.…”

The influence of voltage‐gated sodium channels on human gastrointestinal nociception

“…Several pharmaceutical companies have also developed agents with increased selectivity for Na V 1.7 that have demonstrated potential efficacy in humans for management of pain associated with conditions including inherited erythromelalgia (XEN402), trigeminal neuralgia (BIIB074), diabetic neuralgia (PF‐05089771), and postherpetic neuralgia (TV‐45070) . Other Na V 1.7‐selective agents, such as AMG8379, have demonstrated the ability to block sodium currents in DRG neurons and diminish pain in animal models . Ambroxol, a secretolytic medication that has demonstrated preferential binding for the Na V 1.8 channel, has been tested for management of neuropathic pain and demonstrated efficacy as a topical application in humans in at least one study .…”

“…111 Other Na V 1.7-selective agents, such as AMG8379, have demonstrated the ability to block sodium currents in DRG neurons and diminish pain in animal models. 112 Ambroxol, a secretolytic medication that has demonstrated preferential binding for the Na V 1.8 channel, has been tested for management of neuropathic pain 113,114 and demonstrated efficacy as a topical application in humans in at least one study. 114 Other compounds have been developed that are at least partially selective for Na V 1.8 (eg, A-803467) 115,116 and have shown promise for management of neuropathic and inflammatory pain conditions in animal models 116,117 but have not, as of yet, been formally evaluated in human studies.…”