Mechanism of Action and Structure–Activity Relationship of α‑Conotoxin Mr1.1 at the Human α9α10 Nicotinic Acetylcholine Receptor

α-Conotoxins (α-CTxs) can selectively target
nicotinic
acetylcholine receptors (nAChRs) and are important drug leads for
the treatment of cancer, chronic pain, and neuralgia. Here, we chemically
synthesized a formerly defined rat α7 nAChR targeting α-CTx
Mr1.1 and evaluated its activity at human nAChRs. Mr1.1 was most potent
at the human (h) α9α10 nAChR with a half-maximal inhibitory
concentration (IC50) of 92.0 nM. Molecular dynamic simulations
suggested that Mr1.1 favorably binds at the α10(+)α9(−)
and α9(+)α9(−) sites via hydrogen bonds and salt
bridges, stabilizing the channel in a closed conformation. Although
Mr1.1 and another antagonist, α-CTx Vc1.1 share high sequence
similarity and disulfide-bond framework, Mr1.1 has distinct orientations
at hα9α10. Based on the Mr1.1-hα9α10 model,
analogues were generated, and the more potent Mr1.1[S4Dap], antagonized
hα9α10 with an IC50 of 4.0 nM. Furthermore,
Mr1.1[S4Dap] displayed analgesic activity in the rat chronic constriction
injury (CCI) pain model and therefore presents a promising drug candidate.