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.
Department of Pharmaceutical Sciences, University of Ferrara, Italy.
S
S
Salvadori
M
M
Attila
G
G
Balboni
C
C
Bianchi
S D
SD
Bryant
O
O
Crescenzi
R
R
Guerrini
D
D
Picone
T
T
Tancredi
P A
PA
Temussi
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