Structure- Activity Relationship Study and Function-Based Petidomimetic Design of Human Opiorphin with Improved Bioavailability Property and Unaltered Analgesic Activity

Alexandra Bogeas ,Evelyne Dufour ,Jean-François Bisson ,Michaël Messaoudi ,Catherine Rougeot

doi:10.4172/2167-0501.1000122

Abstract

Human opiorphin inhibits enkephalin-inactivating ectopeptidases to produce analgesic and antidepressant-like effects in standard murine models via activation of μ and/or δ opioid pathways. It is an endogenous peptide regulator of enkephalin bioavailability. Opiorphin molecule, a QRFSR-peptide, is thus a promising prototype for the design of an improved class of analgesics. The major limitation on the clinical use of peptide drugs is their rapid degradation by circulating peptidases. Our goal was, therefore, to search for functional derivatives of opiorphin with improved metabolic stability. In order to identify the functional amino acid groups required for opiorphin inhibitory potency toward both AP-N and NEP human ectopeptidases, we used the Structure-Activity Relationship (SAR) method. From this data, a series of opiorphin derivatives was designed and selected. The best performing compound then underwent a complete metabolic profile using in vitro kinetic models. Finally, its safety profile relative to the native peptide as well as its efficacy in an in vivo rat model was evaluated. We demonstrated a tight structural selectivity in the functional interaction of opiorphin with both human NEP and AP-N targets by SAR studies. Nevertheless, we found that the addition of an N-terminal Zn-chelating group, a Cys-thiol group and the replacement of the first labile peptide bond by a polyethylene surrogate, a [CH2]6 linker,and, finally, the substitution of Ser4 by Ser-O-[CH2]8, results in a high performing C-[(CH2)6]-QRF[S-O-[CH2]8]-R peptidomimetic product. This designed opiorphin analog shows reinforced inhibitory potency toward human AP-N activity (more than 10-fold increase) and NEP activities (more than 40-fold increase) relative to the QRFSR native peptide. It also has increased metabolic stability in human plasma and yet retains full analgesic activity in the behavioral formalin-induced rat pain model. C-[(CH2)6]-QRF[S-O-[CH2]8]-R thus represents a very attractive and promising analgesic drug-candidate.

Highlights

Opiorphin QRFSR-peptide is an endogenous human regulator that was discovered using a functional biochemical approach [1,2]
All opiorphin-induced effects are mediated via endogenous enkephalin-related activation of μ and/or δ opioid pathways
In order to identify the amino acid residues or functional groups required for opiorphin inhibitory potency toward both AP-N and NEP human ectopeptidases, the molecular relationship of structure to activity, namely Structure-Activity Relationship (SAR), of opiorphin native peptide was first investigated

Summary

Introduction

Opiorphin QRFSR-peptide is an endogenous human regulator that was discovered using a functional biochemical approach [1,2]. Its characterization demonstrated that it is an authentic physiological dual inhibitor of Zn-dependent metallo-ectopeptidases, neutral endopeptidase (NEP EC3.4.21.11) and aminopeptidase N (AP-N EC3.4.11.2). These enzymes are implicated in the rapid inactivation of endogenous circulating opioid agonists, namely the enkephalins. Opiorphin improves the specific binding and affinity of enkephalin-related peptides to membrane opioid receptors [3]. By increasing the half-life of circulating enkephalins, opiorphin, at systemically or centrally active doses (1-2 mg/kg I.V. or 5-10 μg/kg I.C.V.), produces analgesia in various murine models of pain [1,9,10]. All opiorphin-induced effects are mediated via endogenous enkephalin-related activation of μ and/or δ opioid pathways

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