Differential stereochemical requirements of mu vs. delta opioid receptors for ligand binding and signal transduction: development of a class of potent and highly delta-selective peptide antagonists.
Opioid peptide analogs consisting entirely of aromatic amino acid residues and containing conformationally restricted phenylalanine derivatives in position 2 of the peptide sequence were synthesized and pharmacologically characterized in vitro. Both diastereoisomers of H-Tyr-(D or L)-NMePhe-Phe-Phe-NH2 (NMePhe is N alpha-methylphenylalanine) were mu-receptor-selective, were full agonists in the mu-receptor-representative guinea pig ileum assay, and were partial agonists in the mouse vas deferens assay, with the L-NMePhe2 analog displaying somewhat higher intrinsic activity than the D-NMePhe2 analog. Further conformational restriction at position 2 in the sequence, as achieved through substitution of D- or L-tetrahydro-3-isoquinoline carboxylic acid (Tic), produced a configuration-dependent differential effect on receptor selectivity and intrinsic activity, leading to a potent mu-selective mu agonist (the D-Tic2 analog) with increased intrinsic activity in the mouse vas deferens assay and to a potent delta-selective delta antagonist (the L-Tic2 analog). These results demonstrate that imposition of conformational constraints in a peptide not only may alter receptor selectivity but also may decrease, totally abolish, or even enhance intrinsic activity. The tetrapeptide H-Tyr-Tic-Phe-Phe-NH2 was a moderately potent full agonist in the guinea pig ileum assay and, thus, represents a compound with mixed mu-agonist/delta-antagonist properties. The corresponding peptide with a free C-terminal carboxyl group H-Tyr-Tic-Phe-Phe-OH showed high delta-receptor affinity (Ki delta = 1.2 nM), unprecedented delta selectivity (Ki mu/Ki delta = 1410), high potency as delta antagonist (Ke = 3-8 nM against various delta agonists in the mouse vas deferens assay) and, unlike other delta antagonists, had no mu-antagonist properties. The tripeptides H-Tyr-Tic-Phe-OH and H-Tyr-Tic-Phe-NH2 were also delta antagonists.
Schiller
P W
PW
Laboratory of Chemical Biology and Peptide Research, Clinical Research Institute of Montreal, PQ, Canada.
Nguyen
T M
TM
Weltrowska
G
G
Wilkes
B C
BC
Marsden
B J
BJ
Lemieux
C
C
Chung
N N
NN
D000595:Amino Acid Sequence; D000818:Animals; D001681:Biological Assay; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008024:Ligands; D008297:Male; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D013329:Structure-Activity Relationship
D008024:Ligands; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu