A-803467, a potent and selective Na v 1.8 sodium channel blocker, attenuates neuropathic and inflammatory pain in the rat

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Abstract
Activation of tetrodotoxin-resistant sodium channels contributes to action potential electrogenesis in neurons. Antisense oligonucleotide studies directed against Na v 1.8 have shown that this channel contributes to experimental inflammatory and neuropathic pain. We report here the discovery of A-803467, a sodium channel blocker that potently blocks tetrodotoxin-resistant currents (IC 50 = 140 nM) and the generation of spontaneous and electrically evoked action potentials in vitro in rat dorsal root ganglion neurons. In recombinant cell lines, A-803467 potently blocked human Na v 1.8 (IC 50 = 8 nM) and was >100-fold selective vs. human Na v 1.2, Na v 1.3, Na v 1.5, and Na v 1.7 (IC 50 values ≥1 μM). A-803467 (20 mg/kg, i.v.) blocked mechanically evoked firing of wide dynamic range neurons in the rat spinal dorsal horn. A-803467 also dose-dependently reduced mechanical allodynia in a variety of rat pain models including: spinal nerve ligation (ED 50 = 47 mg/kg, i.p.), sciatic nerve injury (ED 50 = 85 mg/kg, i.p.), capsaicin-induced secondary mechanical allodynia (ED 50 ≈ 100 mg/kg, i.p.), and thermal hyperalgesia after intraplantar complete Freund's adjuvant injection (ED 50 = 41 mg/kg, i.p.). A-803467 was inactive against formalin-induced nociception and acute thermal and postoperative pain. These data demonstrate that acute and selective pharmacological blockade of Na v 1.8 sodium channels in vivo produces significant antinociception in animal models of neuropathic and inflammatory pain.