title: Novel opioid cyclic tetrapeptides: Trp isomers of CJ-15,208 exhibit distinct opioid receptor agonism and short-acting κ opioid receptor antagonism.
abstract: OBJECTIVE
  The κ opioid receptor antagonists demonstrate potential for maintaining abstinence from psychostimulant abuse, but existing non-peptide κ-receptor selective antagonists show exceptionally long activity. We hypothesized that the L- and D-Trp isomers of CJ-15,208, a natural cyclic tetrapeptide reported to be a κ-receptor antagonist in vitro, would demonstrate short-acting, dose-dependent antagonism in vivo, preventing reinstatement of cocaine-seeking behaviour.
  
  
  METHODS
  Affinity, selectivity and efficacy of the L-Trp and D-Trp isomers for opioid receptors were assessed in vitro in radioligand and GTPγS binding assays. Opioid receptor agonist and antagonist activities were characterized in vivo following i.c.v. administration with the 55°C warm water tail-withdrawal assay. The D-Trp isomer, which demonstrated primarily κ-receptor selective antagonist activity, was further evaluated for its prevention of stress- and drug-induced reinstatement of extinguished cocaine conditioned place preference (CPP).
  
  
  RESULTS
  The two isomers showed similar affinity and selectivity for κ receptors (K(i)  30-35 nM) as well as κ receptor antagonism in vitro. As expected, the D-Trp cyclic tetrapeptide exhibited minimal agonist activity and induced dose-dependent κ-receptor selective antagonism lasting less than 18 h in vivo. Pretreatment with this peptide prevented stress-, but not cocaine-induced, reinstatement of extinguished cocaine CPP. In contrast, the L-Trp cyclic tetrapeptide unexpectedly demonstrated mixed opioid agonist/antagonist activity.
  
  
  CONCLUSIONS
  The L-Trp and the D-Trp isomers of CJ-15,208 demonstrate stereospecific opioid activity in vivo. The relatively brief κ opioid receptor antagonism, coupled with the prevention of stress-induced reinstatement of extinguished cocaine-seeking behaviour, suggests the D-Trp isomer could be used therapeutically to maintain abstinence from psychostimulant abuse.
authors.affiliation: Torrey Pines Institute for Molecular Studies, Port St Lucie, FL 34987, USA.
authors.forename: Nicolette C
authors.initials: NC
authors.lastname: Ross
authors.forename: Kate J
authors.initials: KJ
authors.lastname: Reilley
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Murray
authors.forename: Jane V
authors.initials: JV
authors.lastname: Aldrich
authors.forename: Jay P
authors.initials: JP
authors.lastname: McLaughlin
mesh_terms: D000701:Analgesics, Opioid / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D016466:CHO Cells; D019970:Cocaine-Related Disorders / Q000188:drug therapy / Q000503:physiopathology; D003213:Conditioning, Psychological / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D058999:Drug-Seeking Behavior / Q000187:drug effects; D005108:Extinction, Psychological / Q000187:drug effects; D007536:Isomerism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009292:Narcotic Antagonists / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D010146:Pain / Q000188:drug therapy / Q000503:physiopathology; D010456:Peptides, Cyclic / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use; D017473:Receptors, Opioid, kappa / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000502:physiology; D014364:Tryptophan / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D000701:Analgesics, Opioid; C540936:CJ 15,208; D009292:Narcotic Antagonists; D010456:Peptides, Cyclic; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D014364:Tryptophan