Pursuing Orally Bioavailable Hepcidin Analogues via Cyclic N-Methylated Mini-Hepcidins

The peptide hormone hepcidin is one of the key regulators of iron absorption, plasma iron levels, and tissue iron distribution. Hepcidin functions by binding to and inducing the internalisation and subsequent lysosomal degradation of ferroportin, which reduces both iron absorption in the gut and export of iron from storage to ultimately decrease systemic iron levels. The key interaction motif in hepcidin has been localised to the highly conserved N-terminal region, comprising the first nine amino acid residues, and has led to the development of mini-hepcidin analogs that induce ferroportin internalisation and have improved drug-like properties. In this work, we have investigated the use of head-to-tail cyclisation and N-methylation of mini-hepcidin as a strategy to increase oral bioavailability by reducing proteolytic degradation and enhancing membrane permeability. We found that backbone cyclisation and N-methylation was well-tolerated in the mini-hepcidin analogues, with the macrocylic analogues often surpassing their linear counterparts in potency. Both macrocyclisation and backbone N-methylation were found to improve the stability of the mini-hepcidins, however, there was no effect on membrane-permeabilizing activity.