Capsazepine is a competitive antagonist of vanilloid (capsaicin) receptor with IC50 value of 562 nM.[1]

Capsazepine is a synthetic analogue of capsaicin, which activates the TRPV1 ion channel, thereby, blocks the painful sensation of heat caused by capsaicin. Capsazepine blocked voltage-activated calcium currents in adult rat dorsal root ganglion neurons with EC50 value of 7.7±1.4 μM.[2] Capsazepine was also able to block the response of TRPM8 to menthol (IC50=18±1.1 μM).[3] Capsazepine also inhibited nicotinic acetylcholine receptors in rat trigeminal ganglia at 10μM.[4] In human colon cancer cells, capsazepine treatment activated caspase -8, –9, and -3, induced death receptors (DRs) DR5 and DR4, then sensitized the cells to TRAIL-induced apoptosis.[5] Capsazepine is thought to be a tool to study the TRPV1 ion channel.

References:
1. C. S. Walpole, S. Bevan, G. Bovermann, J. J. Boelsterli, R. Breckenridge, J. W. Davies, G. A. Hughes, I. James, L. Oberer, J. Winter and et al., J Med Chem 1994, 37, 1942-1954.
2. R. J. Docherty, J. C. Yeats and A. S. Piper, Br J Pharmacol 1997, 121, 1461-1467.
3. H. J. Behrendt, T. Germann, C. Gillen, H. Hatt and R. Jostock, Br J Pharmacol 2004, 141, 737-745.
4. L. Liu and S. A. Simon, Neurosci Lett 1997, 228, 29-32.
5. B. Sung, S. Prasad, J. Ravindran, V. R. Yadav and B. B. Aggarwal, Free Radic Biol Med 2012, 53, 1977-1987.