Conotoxins are disulfide-rich peptides isolated from the venoms of marine cone snails. They target a diverse range of membrane receptors and ion channels and have attracted considerable interest as potential therapeutic agents. Conotoxin MVIIA (PrialtÒ), for example, is marketed as a potent analgesic for the treatment of severe chronic pain, including cancer- and AIDS-related pain. Many other conotoxins specifically target nicotinic acetylcholine receptors (nAChRs), which are implicated in a range of neurological and other diseases, including Parkinson’s disease, Alzheimer’s disease, depression and small-cell lung carcinoma. However, like many peptides, conotoxins can have limited bioavailability and be susceptible to proteolytic degradation, which can restrict their therapeutic potential. This presentation describes strategies for improving the stability and therapeutic properties of diverse conotoxins through residue mutagenesis, thioamide substitution and peptide cyclisation. In particular, thioamidation provides a versatile strategy for enhancing peptide stability while retaining, and in some cases increasing, biological potency. The activity of a-conotoxin Vc1.1 and its thioamide analogues was examined at human a3b2 and a9a10 nAChRs. Concentration-response analyses showed that selected thioamide analogues were 2.5- to 3.5-fold more potent than Vc1.1 at these receptors. We also describe enzyme- and plant-based production systems for the efficient generation of cyclic conotoxin analogues, addressing the need for more sustainable approaches to the manufacture of peptide-based pharmaceutical leads. Together, these approaches demonstrate how chemical and biological engineering of conotoxins can generate more stable and therapeutically relevant peptide drug leads.
Keywords: conotoxins, peptide engineering, thioamidation, peptide stability, drug design
Acknowledgement: This work was supported by a grant from the Australian NHMRC (GNT2009546) and by access to the facilities of the Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science (CE200100012)