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Ion channels are targets of considerable therapeutic interest to address a wide variety of neurologic indications, including pain perception. Current pharmacological strategies have focused mostly on small molecule approaches that can be limited by selectivity requirements within members of a channel family or superfamily. Therapeutic antibodies have been proposed, designed, and characterized to alleviate this selectivity limitation; however, there are no Food and Drug Administration-approved therapeutic antibody-based drugs targeting ion channels on the market to date. Here, in an effort to identify novel classes of engineered ion channel modulators for potential neurologic therapeutic applications, we report the generation and characterization of six (EC

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The voltage-gated sodium channel NaV1.7 has received much attention from the scientific community due to compelling human genetic data linking gain- and loss-of-function mutations to pain phenotypes. Despite this genetic validation of NaV1.7 as a target for pain, high quality pharmacological tools facilitate further understanding of target biology, establishment of target coverage requirements and subsequent progression into the clinic. Within the sulfonamide class of inhibitors, reduced potency on rat NaV1.7 versus human NaV1.7 was observed, rendering in vivo rat pharmacology studies challenging. Herein, we report the discovery and optimization of novel benzoxazine sulfonamide inhibitors of human, rat and mouse NaV1.7 which enabled pharmacological assessment in traditional behavioral rodent models of pain and in turn, established a connection between formalin-induced pain and histamine-induced pruritus in mice. The latter represents a simple and efficient means of measuring target engagement.

Potent and selective antagonists of the voltage-gated sodium channel NaV1.7 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 NaV1.7 channels with an IC50 of 8.5 nM and endogenous tetrodotoxin (TTX)-sensitive sodium channels in dorsal root ganglion (DRG) neurons with an IC50 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 NaV family members, including NaV1.4 expressed in muscle and NaV1.5 expressed in the heart, as well as TTX-resistant NaV 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 NaV1.7-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 NaV1.7 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.

Several reports have recently emerged regarding the identification of heteroarylsulfonamides as NaV1.7 inhibitors that demonstrate high levels of selectivity over other NaV isoforms. The optimization of a series of internal NaV1.7 leads that address a number of metabolic liabilities including bioactivation, PXR activation, as well as CYP3A4 induction and inhibition led to the identification of potent and selective inhibitors that demonstrated favorable pharmacokinetic profiles and were devoid of the aforementioned liabilities. The key to achieving this within a series prone to transporter-mediated clearance was the identification of a small range of optimal cLogD values and the discovery of subtle PXR SAR that was not lipophilicity dependent. This enabled the identification of compound 20, which was advanced into a target engagement pharmacodynamic model where it exhibited robust reversal of histamine-induced scratching bouts in mice.

Because of its strong genetic validation, NaV1.7 has attracted significant interest as a target for the treatment of pain. We have previously reported on a number of structurally distinct bicyclic heteroarylsulfonamides as NaV1.7 inhibitors that demonstrate high levels of selectivity over other NaV isoforms. Herein, we report the discovery and optimization of a series of atropisomeric quinolinone sulfonamide inhibitors [Bicyclic sulfonamide compounds as sodium channel inhibitors and their preparation. WO 2014201206, 2014] of NaV1.7, which demonstrate nanomolar inhibition of NaV1.7 and exhibit high levels of selectivity over other sodium channel isoforms. After optimization of metabolic and pharmacokinetic properties, including PXR activation, CYP2C9 inhibition, and CYP3A4 TDI, several compounds were advanced into in vivo target engagement and efficacy models. When tested in mice, compound 39 (AM-0466) demonstrated robust pharmacodynamic activity in a NaV1.7-dependent model of histamine-induced pruritus (i...

The voltage-gated sodium channel Na

Because of its strong genetic validation, Na

Several reports have recently emerged regarding the identification of heteroarylsulfonamides as Na

The majority of potent and selective hNaV1.7 inhibitors possess common pharmacophoric features that include a heteroaryl sulfonamide headgroup and a lipophilic aromatic tail group. Recently, reports of similar aromatic tail groups in combination with an acyl sulfonamide headgroup have emerged, with the acyl sulfonamide bestowing levels of selectivity over hNaV1.5 comparable to the heteroaryl sulfonamide. Beginning with commercially available carboxylic acids that met selected pharmacophoric requirements in the lipophilic tail, a parallel synthetic approach was applied to rapidly generate the derived acyl sulfonamides. A biaryl acyl sulfonamide hit from this library was elaborated, optimizing for potency and selectivity with attention to physicochemical properties. The resulting novel leads are potent, ligand and lipophilic efficient, and selective over hNaV1.5. Representative lead 36 demonstrates selectivity over other human NaV isoforms and good pharmacokinetics in rodents. The biaryl acyl sulfonamides reported herein may also offer ADME advantages over known heteroaryl sulfonamide inhibitors.

Recapitulating human disease pathophysiology using genetic animal models is a powerful approach to enable mechanistic understanding of genotype–phenotype relationships for drug development. NaV1.7 ...