Design, synthesis, and characterization of cyclic analogues of the iron regulatory peptide hormone hepcidin

The peptide hormone hepcidin is a key regulator of iron homeostasis in vertebrates. Hepcidin acts by binding to ferroportin, the sole known iron exporter, causing it to be internalized and thus trapping iron within the cell. Dysregulation of hepcidin concentrations is associated with a range of iron-related diseases and hepcidin-based therapeutics could be developed as candidate treatments for these diseases. However peptide-based drugs, despite their many advantages, are often limited by their susceptibility to degradation within the body. Here we describe the design, synthesis and characterization of a series of backbone cyclized hepcidin analogues as an approach to produce stable hepcidin-based leads. The cyclic peptides were shown by NMR to be structurally analogous to native hepcidin. Comparison of the stability of hepcidin with one of the cyclic analogues in human serum revealed that 77% of the cyclic peptide but only 18% of linear hepcidin remained after 24 h. The cyclic peptides were tested for their ability to induce internalization of GFP-ferroportin in vitro but were all found to be inactive. This study demonstrates that backbone cyclization of disulfide-rich peptides is a suitable approach for increasing stability. However, careful consideration of a number of factors, including location of important residues and their bioactive conformation, is required to generate biologically active lead molecules.