Abstract
Vanilloid receptor-1 (TRPV1) is a nonselective cation channel, predominantly expressed by sensory neurons, which plays a key role in the detection of noxious painful stimuli such as capsaicin, acid, and heat. TRPV1 antagonists may represent novel therapeutic agents for the treatment of a range of conditions including chronic pain, migraine, and gastrointestinal disorders. Here we describe the in vitro pharmacology of N-(2-bromophenyl)-N′-[((R)-1-(5-trifluoromethyl-2-pyridyl)pyrrolidin-3-yl)]urea (SB-705498), a novel TRPV1 antagonist identified by lead optimization of N-(2-bromophenyl)-N′-{2-[ethyl(3-methylphenyl)amino]ethyl}urea (SB-452533), which has now entered clinical trials. Using a Ca2+-based fluorometric imaging plate reader (FLIPR) assay, SB-705498 was shown to be a potent competitive antagonist of the capsaicin-mediated activation of the human TRPV1 receptor (pKi = 7.6) with activity at rat (pKi = 7.5) and guinea pig (pKi = 7.3) orthologs. Whole-cell patch-clamp electrophysiology was used to confirm and extend these findings, demonstrating that SB-705498 can potently inhibit the multiple modes of receptor activation that may be relevant to the pathophysiological role of TRPV1 in vivo: SB-705498 caused rapid and reversible inhibition of the capsaicin (IC50 = 3 nM)-, acid (pH 5.3)-, or heat (50°C; IC50 = 6 nM)-mediated activation of human TRPV1 (at -70 mV). Interestingly, SB-705498 also showed a degree of voltage dependence, suggesting an effective enhancement of antagonist action at negative potentials such as those that might be encountered in neurons in vivo. The selectivity of SB-705498 was defined by broad receptor profiling and other cellular assays in which it showed little or no activity versus a wide range of ion channels, receptors, and enzymes. SB-705498 therefore represents a potent and selective multimodal TRPV1 antagonist, a pharmacological profile that has contributed to its definition as a suitable drug candidate for clinical development.
Footnotes
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.116657.
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ABBREVIATIONS: TRPV1, transient receptor potential vanilloid 1; TRP, transient receptor potential; BCTC, N-(4-tertiarybutyl-phenyl)-4-(3-chloropyridin-2-yl) tetrahydropyrazine-1(2H)-carboxamide; AMG 9810, [(E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)acrylamide]; A-425619, [1-isoquinolin-5-yl-3-(4-trifluoromethyl-benzyl)-urea]; SB-366791, (N-(3-methoxyphenyl)-4-chlorocinnamide); SB-452533, N-(2-bromophenyl)-N′-{2-[ethyl(3-methylphenyl)amino]ethyl}urea; SB-705498, N-(2-bromophenyl)-N′-[((R)-1-(5-trifluoromethyl-2-pyridyl)pyrrolidin-3-yl)]urea; TRPV4, transient receptor potential vanilloid 4; TRPM8, melastatin 8; HEK293, human embryonic kidney 293 (cells); DMEM, Dulbecco's modified Eagle's medium; FLIPR, fluorometric imaging plate reader; DRG, dorsal root ganglion; h, human.
- Received November 7, 2006.
- Accepted March 26, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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