Pain results from the complex processing of neural signals at different levels of the central nervous system, with each signal potentially offering multiple opportunities for pharmacological intervention. A logical strategy for developing novel analgesics is to target the beginning of the pain pathway, and aim potential treatments directly at the nociceptors — the high-threshold primary sensory neurons that detect noxious stimuli. The largest group of receptors that function as noxious stimuli detectors in nociceptors is the transient receptor potential (TRP) channel family. This Review highlights evidence supporting particular TRP channels as targets for analgesics, indicates the likely efficacy profiles of TRP-channel-acting drugs, and discusses the development pathways needed to test candidates as analgesics in humans.

We used a mouse with deletion of exons 4, 5, and 6 of the SCN11A (sodium channel, voltage-gated, type XI, ␣) gene that encodes the voltage-gated sodium channel Na v 1.9 to assess its contribution to pain. Na v 1.9 is present in nociceptor sensory neurons that express TRPV1, bradykinin B 2 , and purinergic P2X 3 receptors. In Na v 1.9 ؊/؊ mice, the non-inactivating persistent tetrodotoxin-resistant sodium TTXr-Per current is absent, whereas TTXr-Slow is unchanged. TTXs currents are unaffected by the mutation of Na v 1.9. Pain hypersensitivity elicited by intraplantar administration of prostaglandin E 2 , bradykinin, interleukin-1␤, capsaicin, and P2X 3 and P2Y receptor agonists, but not NGF, is either reduced or absent in Na v 1.9 ؊/؊ mice, whereas basal thermal and mechanical pain sensitivity is unchanged. Thermal, but not mechanical, hypersensitivity produced by peripheral inflammation (intraplanatar complete Freund's adjuvant) is substantially diminished in the null allele mutant mice, whereas hypersensitivity in two neuropathic pain models is unchanged in the Na v 1.9 ؊/؊ mice. Na v 1.9 is, we conclude, an effector of the hypersensitivity produced by multiple inflammatory mediators on nociceptor peripheral terminals and therefore plays a key role in mediating peripheral sensitization.

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Convergence Pharmaceuticals.