Delta opioidmimetic antagonists: prototypes for designing a new generation of ultraselective opioid peptides.
BACKGROUND
Tyr-Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) and Tyr-Tic-Ala were the first peptides with delta opioid antagonist activity lacking Phe, considered essential for opioid activity based on the N-terminal tripeptide sequence (Tyr-D-Xaa-Phe) of amphibian skin opioids. Analogs were then designed to restrain the rotational flexibility of Tyr by the substitution of 2,6-dimethyl-L-tyrosine (Dmt).


METHODS
Tyr and Dmt peptides were synthesized by solid phase and solution methods using Fmoc technology or condensing Boc-Dmt-OH or Boc-Tyr(But)-OH with H-L-Tic-OBut or H-D-Tic-OBut, respectively. Peptides were purified (> 99%) by HPLC and characteristics determined by 1H-NMR, FAB-MS, melting point, TLC, and amino acid analyses.


RESULTS
H-Dmt-Tic-OH had high affinity (Ki delta = 0.022 nM) and extraordinary selectivity (Ki mu/Ki delta = 150,000); H-Dmt-Tic-Ala-OH had a Ki delta = 0.29 nM and delta selectivity = 20,000. Affinity and selectivity increased 8700- and 1000-fold relative to H-Tyr-Tic-OH, respectively. H-Dmt-Tic-OH and H-Dmt-Tic-NH2 fitted one-site receptor binding models (eta = 0.939-0.987), while H-Dmt-Tic-ol, H-Dmt-Tic-Ala-OH and H-Dmt-Tic-Ala-NH2 best fitted two-site models (eta = 0.708-0.801, F 18.9-26.0, p < 0.0001). Amidation increased mu affinity by 10- to 100-fold and acted synergistically with D-Tic2 to reverse selectivity (delta-->mu). Dmt-Tic di- and tripeptides exhibited delta antagonist bioactivity (Ke = 4-66 nM) with mouse vas deferens and lacked agonist mu activity (> 10 microM) in guinea-pig ileum preparations. Dmt-Tic analogs weakly interacted with kappa receptors in the 1 to > 20 microM range.


CONCLUSIONS
Dmt-Tic opioidmimetic peptides represent a highly potent class of opioid peptide antagonists with greater potency than the nonopioid delta antagonist naltrindole and have potential application as clinical and therapeutic compounds.
Salvadori
S
S
Department of Pharmaceutical Sciences, University of Ferrara, Italy.
Attila
M
M
Balboni
G
G
Bianchi
C
C
Bryant
S D
SD
Crescenzi
O
O
Guerrini
R
R
Picone
D
D
Tancredi
T
T
Temussi
P A
PA
D000595:Amino Acid Sequence; D000663:Amphibians; D000818:Animals; D004151:Dipeptides / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D015195:Drug Design; D006168:Guinea Pigs; D007082:Ileum; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009292:Narcotic Antagonists / Q000138:chemical synthesis* / Q000494:pharmacology; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology*; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017473:Receptors, Opioid, kappa / Q000378:metabolism; D012867:Skin; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D044005:Tetrahydroisoquinolines; D014443:Tyrosine / Q000031:analogs & derivatives / Q000494:pharmacology
C097291:2-tyrosyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid; D004151:Dipeptides; D007202:Indicators and Reagents; D007546:Isoquinolines; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D044005:Tetrahydroisoquinolines; D014443:Tyrosine