The
vanilloid receptor 1 (VR1 or TRPV1) is a membrane-bound, nonselective
cation channel expressed by peripheral sensory neurons. TRPV1 antagonists produce antihyperalgesic effects in animal models of inflammatory and
neuropathic pain. Here, we describe the in vitro and in vivo pharmacology of a novel TRPV1 antagonist,
AMG 9810, (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4]
dioxin-6-yl)acrylamide.
AMG 9810 is a competitive antagonist of
capsaicin activation (IC50 value for human TRPV1, 24.5 +/- 15.7 nM; rat TRPV1, 85.6 +/- 39.4 nM) and blocks all known modes of TRPV1 activation, including
protons (IC50 value for rat TRPV1, 294 +/- 192 nM; human TRPV1, 92.7 +/- 72.8 nM), heat (IC50 value for rat TRPV1, 21 +/- 17 nM; human TRPV1, 15.8 +/- 10.8 nM), and endogenous
ligands, such as
anandamide, N-
arachidonyl dopamine, and oleoyldopamine.
AMG 9810 blocks
capsaicin-evoked depolarization and
calcitonin gene-related peptide release in cultures of rat dorsal root ganglion primary neurons. Screening of
AMG 9810 against a panel of
G protein-coupled receptors and
ion channels indicated selectivity toward TRPV1. In vivo,
AMG 9810 is effective at preventing
capsaicin-induced eye wiping in a dose-dependent manner, and it reverses thermal and
mechanical hyperalgesia in a model of inflammatory
pain induced by intraplantar injection of complete
Freund's adjuvant. At effective doses,
AMG 9810 did not show any significant effects on motor function, as measured by open field locomotor activity and motor coordination tests.
AMG 9810 is the first cinnamide TRPV1 antagonist reported to block
capsaicin-induced eye wiping behavior and reverse
hyperalgesia in an animal model of inflammatory
pain.