S. Salvadori, M. Attila, Giofranco Balboni
Sep 1, 1995
Citations
1
Influential Citations
104
Citations
Quality indicators
Journal
Molecular Medicine
Abstract
BackgroundTyr-Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) and Tyr-Tic-Ala were the first peptides with δ 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).Materials and MethodsTyr 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.ResultsH-Dmt-Tic-OH had high affinity (Kiδ = 0.022 nM) and extraordinary selectivity (Kiμ/Kiδ = 150,000); H-Dmt-Tic-Ala-OH had a Kiδ = 0.29 nM and δ 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 (η = 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 (η = 0.708−0.801, F 18.9−26.0, p < 0.0001). Amidation increased μ affinity by 10- to 100-fold and acted synergistically with d-Tic2 to reverse selectivity (δ→μ). Dmt-Tic di- and tripeptides exhibited δ antagonist bioactivity (Ke = 4−66 nM) with mouse vas deferens and lacked agonist μ activity (> 10 µM) in guinea-pig ileum preparations. Dmt-Tic analogs weakly interacted with κ receptors in the 1 to >20 µM range.ConclusionsDmt-Tic opioidmimetic peptides represent a highly potent class of opioid peptide antagonists with greater potency than the nonopioid δ antagonist naltrindole and have potential application as clinical and therapeutic compounds.