Abstract
Voltage-gated calcium channel (Cav)2.2 (N-type calcium channels) are key components in nociceptive transmission pathways. Ziconotide, a state-independent peptide inhibitor of Cav2.2 channels, is efficacious in treating refractory pain but exhibits a narrow therapeutic window and must be administered intrathecally. We have discovered an N-triazole oxindole, (3R)-5-(3-chloro-4-fluorophenyl)-3-methyl-3-(pyrimidin-5-ylmethyl)-1-(1H-1,2,4-triazol-3-yl)-1,3-dihydro-2H-indol-2-one (TROX-1), as a small-molecule, state-dependent blocker of Cav2 channels, and we investigated the therapeutic advantages of this compound for analgesia. TROX-1 preferentially inhibited potassium-triggered calcium influx through recombinant Cav2.2 channels under depolarized conditions (IC50 = 0.27 μM) compared with hyperpolarized conditions (IC50 > 20 μM). In rat dorsal root ganglion (DRG) neurons, TROX-1 inhibited ω-conotoxin GVIA-sensitive calcium currents (Cav2.2 channel currents), with greater potency under depolarized conditions (IC50 = 0.4 μM) than under hyperpolarized conditions (IC50 = 2.6 μM), indicating state-dependent Cav2.2 channel block of native as well as recombinant channels. TROX-1 fully blocked calcium influx mediated by a mixture of Cav2 channels in calcium imaging experiments in rat DRG neurons, indicating additional block of all Cav2 family channels. TROX-1 reversed inflammatory-induced hyperalgesia with maximal effects equivalent to nonsteroidal anti-inflammatory drugs, and it reversed nerve injury-induced allodynia to the same extent as pregabalin and duloxetine. In contrast, no significant reversal of hyperalgesia was observed in Cav2.2 gene-deleted mice. Mild impairment of motor function in the Rotarod test and cardiovascular functions were observed at 20- to 40-fold higher plasma concentrations than required for analgesic activities. TROX-1 demonstrates that an orally available state-dependent Cav2 channel blocker may achieve a therapeutic window suitable for the treatment of chronic pain.
Footnotes
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.166363.
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ABBREVIATIONS:
- MVIIA
- ω-conotoxin MVIIA
- Cav
- voltage-gated calcium channel
- CNS
- central nervous system
- TROX-1
- (3R)-5-(3-chloro-4-fluorophenyl)-3-methyl-3-(pyrimidin-5-ylmethyl)-1-(1H-1,2,4-triazol-3-yl)-1,3-dihydro-2H-indol-2-one
- DMA
- N,N-dimethylacetamide
- PEG
- polyethylene glycol
- CBK
- Cav2.2 HEK cell line
- DRG
- dorsal root ganglia
- R
- fluorescence intensity ratio
- CFA
- complete Freund's adjuvant
- CgTX
- ω-conotoxin
- SNL
- spinal nerve ligation
- IOA
- iodoacetate
- MAP
- mean arterial pressure
- HR
- heart rate
- Nav
- voltage-gated sodium channel
- SNP
- sodium nitroprusside
- PE
- phenylephrine
- BP50
- median blood pressure.
- Received January 23, 2010.
- Accepted April 30, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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