(2S,3R)β-Methyl-2′,6′-dimethyltyrosine-l-tetrahydroisoquinoline-3-carboxylic acid [(2S,3R)TMT-l-Tic-OH] Is a Potent, Selective δ-Opioid Receptor Antagonist in Mouse Brain

  1. Keiko Hosohata,
  2. Eva V. Varga,
  3. Josue Alfaro-Lopez,
  4. Xuejun Tang,
  5. Todd W. Vanderah,
  6. Frank Porreca,
  7. Victor J. Hruby,
  8. William R. Roeske and
  9. Henry I. Yamamura
  1. Departments of Pharmacology, Chemistry, Biochemistry, Psychiatry, and Medicine and the Sarver Heart Center, University of Arizona, Tucson, Arizona
  1. Dr. Henry I. Yamamura, Department of Pharmacology, College of Medicine, University of Arizona Health Sciences Center, Tucson, AZ 85724. E-mail: hiy{at}u.arizona.edu

Abstract

The constrained opioid peptide (2S,3R)β-methyl-2′,6′-dimethyltyrosine-l-tetrahydroisoquinoline-3-carboxylic acid [(2S,3R)TMT-l-Tic-OH] exhibits high affinity and selectivity for the δ-opioid receptors (Liao et al., 1997). In the present study, we examined the pharmacological properties of (2S,3R)TMT-l-Tic-OH in mouse brain. A 5′-O-(3-[35S]thiotriphosphate) ([35S]GTPγS) binding assay was used to determine the effect of (2S,3R)TMT-l-Tic-OH on G protein activity in vitro, in mouse brain membranes. δ- (SNC80; (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxy-benzyl]-N,N-diethyl-benzamide) or μ- (DAMGO; [d-Ala2, Me-Phe4,Gly(ol)5]enkephalin) selective opioid full agonists stimulated [35S]GTPγS binding in mouse brain membranes 150 ± 4.5% and 152 ± 5.7% over the basal level, respectively. (2S,3R)TMT-l-Tic-OH did not influence basal [35S]GTPγS binding in mouse brain membranes but dose dependently shifted the dose-response curve of SNC80 to the right, with a Ke value of 3.6 ± 0.7 nM. In contrast, (2S,3R)TMT-l-Tic-OH had no effect on the dose-response curve of the μ-selective opioid agonist, DAMGO. Warm water (55°C) tail-flick and radiant heat paw-withdrawal tests were used to determine the in vivo nociceptive properties of (2S,3R)TMT-l-Tic-OH in the mouse. Intracerebroventricular injection of (2S,3R)TMT-l-Tic-OH had no significant effect on withdrawal latencies in either nociceptive tests. (2S,3R)TMT-l-Tic-OH (30 nmol/mouse) attenuated deltorphin II- but not DAMGO-mediated antinociception (40 ± 13 and 100% of maximal possible effect, respectively) when administered intracerebroventricularly 10 min before the agonist. Taken together these results suggest that (2S,3R)TMT-l-Tic-OH is a potent highly selective neutral δ-opioid antagonist in mouse brain.

Footnotes

  • This work was supported in part by grants from the U.S. Public Health Service and from the National Institute of Drug Abuse (DA06284 and DA13449).

  • DOI: 10.1124/jpet.102.042929

  • Abbreviations:
    (2S,3R)TMT-l-Tic-OH
    (2S,3R)β-methyl-2′,6′-dimethyltyrosine-l-tetrahydroisoquinoline-3-carboxylic acid
    hDOR
    human δ-opioid receptor
    CHO
    Chinese hamster ovary
    [35S]GTPγS
    guanosine-5′-O-(3-[-[35S]thio)triphosphate
    SNC80
    (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxy-benzyl]-N,N-diethylbenzamide
    DAMGO
    [d-Ala2,Me-Phe4,Gly(ol)5]enkephalin
    Ke
    dissociation constant from Schild analysis
    MPE
    maximal possible effect
    DPDPE
    [d-Pen2,d-Pen5]-enkephalin
    ICI 174,864
    N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH
    SR 141,716
    N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride
    • Received August 13, 2002.
    • Accepted October 8, 2002.
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  1. doi: 10.1124/jpet.102.042929 JPET February 1, 2003 vol. 304 no. 2 683-688
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