Proposed Bioactive Conformations of Opiorphin, an Endogenous Dual APN/NEP Inhibitor

The conformational profiles for the endogenous peptide Opiorphin and a set of seven analogues exhibiting different inhibitory activities toward human aminopeptidase N (hAPN) and human neprilysin (hNEP) were independently computed to deduce a bioactive conformation that Opiorphin may adopt when binding these two enzymes. The conformational space was thoroughly sampled using an iterative simulated annealing protocol, and a library of low-energy conformers was generated for each peptide. Bioactive Opiorphin conformations fitting our experimental structure–activity relationship data were identified for hAPN and hNEP using computational pairwise comparisons between each of the unique low-energy conformations of Opiorphin and its analogues. The obtained results provide a structural explanation for the dual hAPN and hNEP inhibitory activity of Opiorphin and show that the inborn flexibility of Opiorphin is essential for its analgesic activity

Structure–Activity Relationship Study of Opiorphin, a Human Dual Ectopeptidase Inhibitor with Antinociceptive Properties

Toward developing new potential analgesics, this first structure–activity relationship study of opiorphin (H-Gln-Arg-Phe-Ser-Arg-OH), a human peptide inhibiting enkephalin degradation, was performed. A systematic Ala scanning proved that Phe³ is a key residue for neprilysin and aminopeptidase N (AP-N) ectoenkephalinase inhibition. A series of Phe³-halogenated analogues revealed that halogen bonding based optimization strategies are not applicable to this residue. Additional substituted Phe³ derivatives showed that replacing l-Phe³ for d-Phe³ increased the AP-N inhibition potency by 1 order of magnitude. NMR studies and molecular mechanics calculations indicated that the improved potency may be due to CH−π stacking interactions between the aromatic ring of d-Phe³ and the Hγ protons of Arg². This structural motif is not possible for the native opiorphin and may be useful for the design of further potent and metabolically stable analogues

Proteolytically Stable Foldamer Mimics of Host-Defense Peptides with Protective Activities in a Murine Model of Bacterial Infection

The synthesis of bioinspired unnatural backbones leading to foldamers can provide effective peptide mimics with improved properties in a physiological environment. This approach has been applied to the design of structural mimics of membrane active antimicrobial peptides (AMPs) for which activities <i>in vitro</i> have been reported. Yet activities and pharmacokinetic properties <i>in vivo</i> in animal models have remained largely unexplored. Here, we report helical oligourea AMP mimics that are active <i>in vitro</i> against bacterial forms of <i>Bacillus anthracis</i> encountered <i>in vivo</i>, as well as <i>in vivo</i> in inhalational and cutaneous mouse models of <i>B. anthracis</i> infection. The pharmacokinetic profile and the tissue distribution were investigated by β-radio imager whole-body mapping in mice. Low excretion and recovery of the native oligourea in the kidney following intravenous injection is consistent with high stability <i>in vivo</i>. Overall these results provide useful information that support future biomedical development of urea-based foldamer peptide mimics