Synthesis and Pharmacological Characterization of Nociceptin/Orphanin FQ Dimeric Ligands

The neuropeptide nociceptin/orphanin FQ (N/OFQ) plays a key role in regulating several physiological functions and pathological states, which makes its receptor (NOP) a promising target for therapeutic interventions. In this study, we synthesized homodimeric N/OFQ-NH2 derivatives linked by disulfide bonds between cysteines appropriately introduced in the addressing region of the native peptide in place of the original amino acids. The in vitro activity of the compounds was evaluated using both an NOP-G protein interaction BRET assay and a calcium mobilization assay. The most potent compound, 1h (pEC50 >9), was obtained by coupling two monomeric precursors via a Leu14-to-Cys substitution. In vivo, 1h demonstrated 3-fold greater potency than N/OFQ in eliciting loss of the righting reflex in mice and produced a long-lasting effect monitored for up to 7 h, supporting multimerization as a viable approach to developing long-acting peptide-based NOP ligands.