Synthesis, Biological Activity and Molecular Docking of Chimeric Peptides Targeting Opioid and NOP Receptors

Abstract

Recently, mixed opioid/NOP agonists came to the spotlight for their favorable functional profiles and promising outcomes in clinical trials as novel analgesics. This study reports on two novel chimeric peptides incorporating the fragment Tyr-c[D-Lys-Phe-Phe]Asp-NH2 (RP-170), a cyclic peptide with high affinity for µ and κ opioid receptors (or MOP and KOP, respectively), conjugated with the peptide Ac-RYYRIK-NH2, a known ligand of the nociceptin/orphanin FQ receptor (NOP), yielding RP-170-RYYRIK-NH2 (KW-495) and RP-170-Gly3-RYYRIK-NH2 (KW-496). In vitro, the chimeric KW-496 gained affinity for KOP, hence becoming a dual KOP/MOP agonist, while KW-495 behaved as a mixed MOP/NOP agonist with low nM affinity. Hence, KW-495 was selected for further in vivo experiments. Intrathecal administration of this peptide in mice elicited antinociceptive effects in the hot-plate test; this action was sensitive to both the universal opioid receptor antagonist naloxone and the selective NOP antagonist SB-612111. The rotarod test revealed that KW-495 administration did not alter the mice motor coordination performance. Computational studies have been conducted on the two chimeras to investigate the structural determinants at the basis of the experimental activities, including any role of the Gly3 spacer.

Analgesic Peptides: From Natural Diversity to Rational Design

“…The NOP receptor plays important roles in various physiological functions, most importantly in learning and memory, locomotion, and anxiety. Antinociceptive effects mediated via the NOP receptor are complex; activation via N/OFQ was shown to produce either anti-or pro-nociceptive effects, depending on the animal species, dosage, route of administration, as well as the pain model [29,30].…”

“…This single-chain peptide contains 35 amino acid residues, including 8 cysteines involved in 4 intramolecular disulfide bridges (Table 4). Three disulfide bridges (Cys 3 -Cys 16 , Cys 10 -Cys 21 , and Cys 15 -Cys 32 ) form the cystine knot, although there is also a loop secured by the disulfide bridge Cys 23 -Cys 30 . PT1 selectively inhibits P2X3 receptors, which are known to be implicated in pain mechanisms.…”

“…Wtorek et al, reported two novel chimeric peptides composed of MOR/KOR cyclic ligand C36 and the NOP receptor-binding peptide Ac-Arg-Tyr-Tyr-Arg-Ile-Lys-NH 2 , linked either directly (KW-495) or through a three-glycine spacer KW-496 [30]. In vitro binding and functional assays showed that KW-496 was a mixed ligand with inverted KOR > MOR affinity without activity at the NOP receptor.…”