Phenylalanine Stereoisomers of CJ-15,208 and [d-Trp]CJ-15,208 Exhibit Distinctly Different Opioid Activity Profiles

Abstract

The macrocyclic tetrapeptide cyclo[Phe-d-Pro-Phe-Trp] (CJ-15,208) and its stereoisomer cyclo[Phe-d-Pro-Phe-d-Trp] exhibit different opioid activity profiles in vivo. The present study evaluated the influence of the Phe residues’ stereochemistry on the peptides’ opioid activity. Five stereoisomers were synthesized by a combination of solid-phase peptide synthesis and cyclization in solution. The analogs were evaluated in vitro for opioid receptor affinity in radioligand competition binding assays, and for opioid activity and selectivity in vivo in the mouse 55 °C warm-water tail-withdrawal assay. Potential liabilities of locomotor impairment, respiratory depression, acute tolerance development, and place conditioning were also assessed in vivo. All of the stereoisomers exhibited antinociception following either intracerebroventricular or oral administration differentially mediated by multiple opioid receptors, with kappa opioid receptor (KOR) activity contributing for all of the peptides. However, unlike the parent peptides, KOR antagonism was exhibited by only one stereoisomer, while another isomer produced DOR antagonism. The stereoisomers of CJ-15,208 lacked significant respiratory effects, while the [d-Trp]CJ-15,208 stereoisomers did not elicit antinociceptive tolerance. Two isomers, cyclo[d-Phe-d-Pro-d-Phe-Trp] (3) and cyclo[Phe-d-Pro-d-Phe-d-Trp] (5), did not elicit either preference or aversion in a conditioned place preference assay. Collectively, these stereoisomers represent new lead compounds for further investigation in the development of safer opioid analgesics.

Novel Approaches, Drug Candidates, and Targets in Pain Drug Discovery

“…Strategies such as glycosylation, cyclization, and orally delivering peptides via lipid-based delivery systems have been employed to overcome the pitfalls of opioid peptides . The multifunctional opioid receptor ligand and macrocyclic peptide CJ-15,208 ( 12 ) (Figure ) and its analogues produced antinociception and prevented stress-induced reinstatement of extinguished cocaine-conditioned place preference . Other opioid peptides like cyclic peptide 13 and H-Dmt- d -Arg-Phe-Lys-NH2 also produced potent analgesia with reduced abuse liability, tolerance, and respiratory depression (Figure ).…”

Bis-Cyclic Guanidine Heterocyclic Peptidomimetics as Opioid Ligands with Mixed μ-, κ- and δ-Opioid Receptor Interactions: A Potential Approach to Novel Analgesics

“…1968-22 was tested in a model of acute antinociceptive tolerance with repeated dosing (at 0 and 8 h, 0.001–100 nmol, i.c.v.) of morphine or 1968-22 [ 62 , 63 ]. The development of acute antinociceptive tolerance was assessed by pretreating with the ED 50 i.c.v.…”

“…Alternatively, the contrasting side effects of MOR and KOR agonism identified in 1968-22 may further counteract one another’s undesired effects, improving the therapeutic index. For instance, while MOR-selective agonists induce hyperlocomotion and are reinforcing, and KOR-selective agonists such as U50,488 both suppress coordinated locomotor activity [ 78 ] and cause conditioned place aversion [ 79 , 80 ], multifunctional opioids such as cyclo [Pro-Sar-Phe-D-Phe] demonstrate no such effects; behaviors attributed to the offsetting contributions of MOR and KOR agonism [ 62 , 65 ]. Notably, a handful of reports have shown KOR agonists to increase respiration, reversing MOR agonist-mediated respiratory depression [ 81 , 82 ].…”

Opioids and Their Receptors: Present and Emerging Concepts in Opioid Drug Discovery

“…Endogenous and naturally occurring opioid peptides have continuously served as important leads for the design of peptide analogues, with a repertoire of structural modifications that can be targeted when exploring SARs or focusing on the improvement of their pharmacodynamics and the pharmacokinetics of peptide active compounds. Four research articles [5][6][7][8] focused on this subject.…”

“…The SAR study by Brice-Tutt et al [8] studied the influence of the Phe residues' stereochemistry in the macrocyclic tetrapeptide CJ- 15 Unlike the parent peptides, KOR antagonism was exhibited by only one stereoisomer, while another isomer produced DOR antagonism. They identified the stereoisomer [D-Phe 1,3 ]CJ-15,208 as a potent antinociceptive after oral administration lacking respiratory depression and locomotor impairment and without preference or aversion in mice.…”