The Functional Topology of Phenylpiperazinium Agonists and Antagonists on the Nicotinic Acetylcholine Receptor Landscape: Pointing the Way for Future Therapeutic Management of Inflammation and Neuropathic Pain.

The ganglionic blocker 1,1-dimethyl-4-phenylpiperazinium (diMPP) has agonist activity on a variety of neuronal nicotinic acetylcholine receptors (nAChRs). Recently, the related compound 1,1-diethyl-4-phenylpiperazinium (diEPP) has been used as a scaffold for the development of compounds with selectivity for homomeric α7 and α9 nAChRs, with the specific activity profiles depending on the side groups present on the phenyl group. We surveyed the activity of a family of phenylpiperazinium compounds with systematically designed differences in the base nitrogen and/or the phenyl side groups, on different nAChR subtypes. We evaluated activity on adult muscle type (α1β1εδ), ganglionic-like (α3β4), high affinity brain type (α4β2), and homomeric α7 and α9 nAChRs. In general, compounds with the dimethyl base group had the best activity for heteromeric receptors and homomeric α7 receptors. This activity could be tuned by the specific phenyl side groups. In contrast to the other subtypes studied, α9 receptors were better activated by analogs with larger alkyl groups on the base nitrogen, especially when the groups were asymmetrical on the base nitrogen, such that ethylmethyl-phenylpiperaziniums and propylmethyl-phenylpiperaziniums were more active on α9 than diethyl-phenylpiperaziniums. Our results may prove especially useful for the development of new drugs to treat inflammation and pain by targeting α9 nAChRs.