In vitro and in vivo activity of cyclopeptide Dmt-c[d-Lys-Phe-Asp]NH2, a mu opioid receptor agonist biased toward β-arrestin

Morphine and related drugs, which are the most effective analgesics for the relief of severe pain, act through activating opioid receptors. The endogenous ligands of these receptors are opioid peptides which cannot be used as antinociceptive agents due to their low bioactivity and stability in biological fluids. The major goal of opioid research is to understand the mechanism of action of opioid receptor agonists in order to improve therapeutic utility of opioids. Analgesic effects of morphine are mediated mostly through activation of the mu opioid receptor. However, in the search for safer and more effective drug candidates, analogs with mixed opioid receptor profile gained a lot of interest. Recently, the concept of biased agonists able to differentially activate GPCR downstream pathways, became a new approach in the design of novel drug candidates. It is hypothesized that compounds promoting G-protein signaling may produce analgesia while β-arrestin recruitment may be responsible for opioid side effects. In this report we showed that replacement of the tyrosine residue in the mu-selective ligand Tyr-c[d-Lys-Phe-Asp]NH₂ with 2',6'-dimethyltyrosine (Dmt) produced a cyclopeptide Dmt-c[d-Lys-Phe-Asp]NH₂ with mu/delta opioid receptor agonist profile. This analog showed improved antinociception in the hot-plate test, probably due to the simultaneous activation of mu and delta receptors but also significantly inhibited the gastrointestinal transit. Using the bioluminescence resonance energy transfer (BRET) assay it was shown that this analog was a mu receptor agonist biased toward β-arrestin. β-Arrestin-dependent signaling is most likely responsible for the observed inhibition of gastrointestinal motility exerted by the novel cyclopeptide.

Anti-inflammatory action of a novel orally available peptide 317 in mouse models of inflammatory bowel diseases

BACKGROUND

The endogenous opioid system constitutes an attractive target in the treatment of GI disorders, including inflammatory bowel diseases (IBD). The aim of our study was to characterize the anti-inflammatory and antinociceptive effect of P-317, a novel cyclic analog of opioid peptide morphiceptin, in animal models of IBD.

METHODS

The anti-inflammatory effect of P-317 after intraperitoneal (ip) and oral (po) administration was assessed in two mouse models of IBD - Crohn's disease, induced by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS) and ulcerative colitis, induced by addition of dextran sodium sulfate (DSS) into drinking water. The antinociceptive action of P-317 was characterized in mice with acute colitis using mustard oil-induced pain test. Real time RT PCR was used to assess semiquantitatively the expression of IL-1β and TNF-α mRNA in mouse colonic samples. To translate our results to clinical conditions, MOP and KOP mRNA were quantified in human colonic biopsies from IBD patients.

RESULTS

P-317 (0.1mg/kg, ip and 1mg/kg, po) alleviated colonic inflammation in TNBS- and DSS-treated mice in the opioid receptor-dependent manner. The anti-inflammatory effect of P-317 was associated with the decrease in mRNA expression of proinflammatory cytokines. The antinociceptive effect of P-317 was observed after ip and po administration in mice with acute colitis.

CONCLUSION

Our results show a potent anti-inflammatory and antinociceptive effect of P-317 in mouse models of colitis upon activation of opioid receptors. The unique bioavailability of P-317 after oral administration suggests that it is a promising drug candidate for future treatment of IBD.