Multifunctional opioid receptor agonism and antagonism by a novel macrocyclic tetrapeptide prevents reinstatement of morphine-seeking behaviour

Background and Purpose The macrocyclic tetrapeptide natural product CJ-15,208 (cyclo[Phe-d-Pro-Phe-Trp]) is a multifunctional mu-opioid receptor and kappa-opioid receptor agonist and kappa-opioid receptor antagonist that produces antinociception and prevents stress-induced reinstatement of extinguished cocaine-conditioned place preference (CPP). We hypothesized that an analogue of CJ-15,208,cyclo[Pro-Sar-Phe-d-Phe], would demonstrate multifunctional mu-opioid receptor and kappa-opioid receptor ligand activity, producing potent antinociception with fewer liabilities than selective mu-opioid receptor agonists, while preventing both drug- and stress-induced reinstatement of morphine-induced CPP. Experimental Approach The opioid receptor agonist and antagonist activity ofcyclo[Pro-Sar-Phe-d-Phe] was characterized after i.c.v. and i.p. administration to C57BL/6J or transgenic opioid receptor knockout mice using the 55 degrees C warm-water tail-withdrawal assay. Liabilities of locomotor coordination, respiration and spontaneous ambulation, and direct rewarding or aversive properties were assessed. Finally, the ability ofcyclo[Pro-Sar-Phe-d-Phe] to block morphine- and stress-induced reinstatement of extinguished CPP was determined. Key Results cyclo[Pro-Sar-Phe-d-Phe] demonstrated dose-dependent, short-lasting antinociception, with an ED50(and 95% confidence interval) of 0.15 (0.05-0.21) nmol i.c.v. and 1.91 (0.40-3.54) mg center dot kg(-1)i.p., mediated by mu- and kappa-opioid receptors. The macrocyclic tetrapeptide also demonstrated potent dose-dependent kappa-opioid receptor antagonist-like activity at 2.5, but not at 4.5, h after administration.cyclo[Pro-Sar-Phe-d-Phe] displayed reduced liabiities compared with morphine, attributed to its additional activity at kappa-receptors. Pretreatment withcyclo[Pro-Sar-Phe-d-Phe] prevented stress- and drug-induced reinstatement of extinguished morphine-place preference responses in a time-dependent manner. Conclusions and Implications These data suggest thatcyclo[Pro-Sar-Phe-d-Phe] is a promising lead compound for both the treatment of pain with reduced sideeffects and preventing both drug- and stress-induced relapse in morphine-abstinent subjects.