Structure- and conformation-activity studies of nociceptin/orphanin FQ receptor dimeric ligands

Salvatore Pacifico,Erika Marzola,Girolamo Calò,Ettore Novellino,Claudio Trapella,Diego Brancaccio,Severo Salvadori,Remo Guerrini,Maria Camilla Cerlesi,Alfonso Carotenuto,Federica Ferrari,Delia Preti

doi:10.1038/srep45817

Abstract

The peptide nociceptin/orphanin FQ (N/OFQ) and the N/OFQ receptor (NOP) constitute a neuropeptidergic system that modulates various biological functions and is currently targeted for the generation of innovative drugs. In the present study dimeric NOP receptor ligands with spacers of different lengths were generated using both peptide and non-peptide pharmacophores. The novel compounds (12 peptide and 7 nonpeptide ligands) were pharmacologically investigated in a calcium mobilization assay and in the mouse vas deferens bioassay. Both structure- and conformation-activity studies were performed. Results demonstrated that dimerization did not modify the pharmacological activity of both peptide and non-peptide pharmacophores. Moreover, when dimeric compounds were obtained with low potency peptide pharmacophores, dimerization recovered ligand potency. This effect depends on the doubling of the C-terminal address sequence rather than the presence of an additional N-terminal message sequence or modifications of peptide conformation.

Highlights

The peptide nociceptin/orphanin FQ (N/OFQ) and the N/OFQ receptor (NOP) are the last discovered member of the opioidergic system
This study reports on the design, synthesis, pharmacological activity, and conformation/activity relationship of dimeric ligands of the NOP receptor
The dimeric ligands were generated using as pharmacophores both the peptide sequence of N/OFQ and the non-peptide NOP ligand Ro 65-6570

Summary

Introduction

The peptide nociceptin/orphanin FQ (N/OFQ) and the N/OFQ receptor (NOP) are the last discovered member of the opioidergic system. The 17-amino acid N/OFQ neuropeptide was purified from rat[3] or porcine[4] brain extracts and identified as the natural ligand of the NOP receptor. This was the first successful example of reverse pharmacology[5]. Despite high primary sequence homology (about 60%) between classical opioid and NOP receptors, N/OFQ activates with high affinity and selectivity the NOP receptor and opioid ligands do not interact with NOP6. Portoghese and co-workers identified dimeric ligands for opioid receptor heterodimers delta-kappa[19] (KDN series) and delta-mu[20] (MDAN series) that were of great value for studying the biological effects associated with opioid receptor oligomerization. Using NOP and mu receptor co-transfected cells[23,24,25] and rat dorsal root ganglia lysate[24] the existence of mu-NOP heteromers have been postulated. mu-NOP heterodimers might be implicated in NOP and mu receptor trafficking[24] and can be considered as a novel pharmacological target for the development of analgesics without the classical side effects of opioid drugs[25]

Methods

Results

Conclusion