Synthesis and Biological Characterization of Cyclic Disulfide-Containing Peptide Analogs of the Multifunctional Opioid/Neuropeptide FF Receptor Agonists That Produce Long-Lasting and Nontolerant Antinociception

Abstract

In a previously described chimeric peptide, we reported that the multifunctional opioid/neuropeptide FF (NPFF) receptor agonist 0 (BN-9) produced antinociception for 1.5 h after supraspinal administration. Herein, four cyclic disulfide analogs containing l- and/or d-type cysteine at positions 2 and 5 were synthesized. The cyclized analogs and their linear counterparts behaved as multifunctional agonists at both opioid and NPFF receptors in vitro and produced potent analgesia without tolerance development. In comparison to 0, cyclized peptide 6 exhibited sevenfold more potent μ-opioid receptor agonistic activity in vitro. Interestingly, the cyclized analog 6 possessed an improved stability in the brain and an increased blood–brain barrier permeability compared to the parent peptide 0 and produced more potent analgesia after supraspinal or subcutaneous administration with improved duration of action of 4 h. In addition, antinociceptive tolerance of analog 6 was greatly reduced after subcutaneous injection compared to fentanyl, as was the rewarding effect, withdrawal reaction, and gastrointestinal inhibition.

Development of Multifunctional and Orally Active Cyclic Peptide Agonists of Opioid/Neuropeptide FF Receptors that Produce Potent, Long-Lasting, and Peripherally Restricted Antinociception with Diminished Side Effects

“…The present work suggests that d -type basic amino acids at position 2 of lactam bridge cyclic DN-9 analogues are more stable against enzymatic degradation in plasma. The present results are consistent with our recent study that the cyclization at positions 2 and 5 of BN-9 via disulfide linkages had no significant effects on plasma stability …”

“…In theory, supraspinal RF9 administration may prevent the anti-opioid action of the NPFF moiety of analogue 1 then exhibiting increased analgesic activity, which supports the NPFF agonism of analogue 1 . Consistent with this hypothesis, a recent study suggested that NPFF 2 R in the brain was primarily involved in antinociceptive augmentation after the co-injection of RF9 and the opioid/NPFF receptor multifunctional peptides in NPFF 2 –/– transgenic mice . However, peripheral administration of RF9 did not alter the antinociception induced by s.c. or p.o.…”

“…Figure D shows that the mice did not exhibit significant abstinence syndrome compared with those with saline ( P > 0.05). In contrast, our previous studies demonstrated that the classical MOR agonists, including morphine and fentanyl, significantly induced psychological and physical addiction. , …”

“…was injected at 5 min prior to analogues. The doses and pretreatment times were determined according to previous reports. ,,− …”

“…The pharmacokinetic study was evaluated following our previous reports . Male Kunming mice were intravenously or orally injected with analogue 1 (868.1 nmol/kg).…”