Holtman_2011_Eur.J.Pharmacol_670_500

Chronic pain is inadequately managed with currently available classes of analgesic drugs. Recently, peptide antagonists of the alpha9alpha10 nicotinic acetylcholine receptor were shown to be analgesic. The present study was conducted to characterize a novel small molecule, non-peptide antagonist at nicotinic receptors. The tetrakis-quaternary ammonium compound ZZ-204G was evaluated for functional activity on cloned nicotinic receptors expressed in Xenopus oocytes. In-vivo efficacy was assessed in rat models of tonic inflammatory pain (formalin test), neuropathic pain (chronic constriction nerve injury), and thermal nociception (tail flick test). ZZ-204G was an antagonist at nicotinic receptors inhibiting the alpha9alpha10 subtype with an IC(5)(0) of 0.51 (0.35-0.72) nM. Antagonist activity at other nicotinic subtypes (alpha1beta1deltaepsilon, alpha2beta2, alpha2beta4, alpha3beta2, alpha3beta4, alpha4beta2, alpha4beta4, alpha6/alpha3beta2beta3, alpha6/alpha3beta4 and alpha7) was 10-1000-fold lower than at the alpha9alpha10 subtype. In competition binding assays, the k(i) of ZZ-204G at gamma-aminobutyric acid(A), serotonin(3), gamma-aminobutyric acid(B), kappa- and mu-opioid receptors was 1000- to >10,000-fold lower than at alpha9alpha10 nicotinic receptors. Parenteral administration of ZZ-204G dose-dependently decreased nociceptive behaviors (paw flinches) in the formalin test and mechanical hyperalgesia in the chronic constriction nerve injury model of neuropathic pain. ZZ-204G was not antinociceptive in the tail flick assay. Results from the rotarod assay indicated that lower doses of ZZ-204G that were analgesic did not alter motor function. In summary, ZZ-204G represents a prototype small molecule antagonist for alpha9alpha10 nicotinic receptors and provides a novel molecular scaffold for analgesic agents with the potential to treat chronic inflammatory or neuropathic pain.