Backbone Cyclization Turns A Venom Peptide Into A Stable And Equipotent Ligand At Both Muscle And Neuronal Nicotinic Receptors

Venom peptides are promising drug leads, but their therapeutic use is often limited by stability and bioavailability issues. In this study, we designed cyclic analogues of alpha-conotoxin CIA, a potent muscle nicotinic acetylcholine receptor (nAChR) blocker with a significantly lower affinity at the neuronal alpha 3 beta 2 subtype. Remarkably, all analogues retained the low nanomolar activity of native CIA toward muscle-type nAChRs but showed greatly improved resistance to degradation in human serum and, surprisingly, displayed up to 52-fold higher potency for the alpha 3 beta 2 neuronal nAChR subtype (IC50 1.3 nM). Comparison of nuclear magnetic resonance-derived structures revealed some differences that might explain the gain of potency at alpha 3 beta 2 nAChRs. All peptides were highly paralytic when injected into adult zebrafish and bath-applied to zebrafish larvae, suggesting barrier-crossing capabilities and efficient uptake. Finally, these cyclic CIA analogues were shown to be unique pharmacological tools to investigate the contribution of the presynaptic alpha 3 beta 2 nAChR subtype to the train-of-four fade.