Abstract
The delta opioid receptor modulates nociceptive and emotional behaviors. This receptor has been shown to exhibit measurable spontaneous activity. Progress in understanding the biological relevance of this activity has been slow, partly due to limited characterization of compounds with intrinsic negative activity. Here, we have used constitutively active mutant (CAM) delta receptors in two different functional assays, guanosine 5′-O-(3-thio)triphosphate binding and a reporter gene assay, to test potential inverse agonism of 15 delta opioid compounds, originally described as antagonists. These include the classical antagonists naloxone, naltrindole, 7-benzylidene-naltrexone, and naltriben, a new set of naltrindole derivatives, H-Tyr-Tic-Phe-Phe-OH (TIPP) and H-Tyr-TicΨ[CH2N]Cha-Phe-OH [TICP(Ψ)], as well as three 2′,6′-dimethyltyrosine-1,2,3,4-tetrahydroquinoline-3-carboxylate (Dmt-Tic) peptides. A reference agonist, SNC 80 [(+)-4-[(αR)-α-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide], and inverse agonist, ICI 174864 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu), were also included. In a screen using wild-type and CAM M262T delta receptors, naltrindole (NTI) and close derivatives were mostly inactive, and TIPP behaved as an agonist, whereas Dmt-Tic-OH and N,N(CH3)2-Dmt-Tic-NH2 showed inverse agonism. The two latter compounds showed negative activity across 27 CAM receptors, suggesting that this activity was independent from the activation mechanism. These two compounds also exhibited nanomolar potencies in dose-response experiments performed on wild-type, M262T, Y308H, and C328R CAM receptors. TICP(Ψ) exhibited strong inverse agonism at the Y308H receptor. We conclude that the stable N,N(CH3)2-Dmt-Tic-NH2 compound represents a useful tool to explore the spontaneous activity of delta receptors, and NTI and novel derivatives behave as neutral antagonists.
Footnotes
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This work was supported by the Human Frontier Science Program, by the Institut National de la Santé et de la Recherche Médicale, by the Université Louis Pasteur, by the Association de la Recherche pour le Cancer, by the Institut UPSA de la Douleur, by the Mission Interministérielle de Lutte contre la Drogue et la Toxicomanie, and by National Institute on Drug Abuse (National Institutes of Health-National Institute on Drug Abuse Grant DA05010). Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.104.077321.
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ABBREVIATIONS: GPCR, G protein-coupled receptor; ICI 174864, N,N-diallyl-Tyr-Aib-Aib-Phe-Leu; CAM, constitutively active mutant; NLX, naloxone; NTI, naltrindole; NTB, naltriben; BNTX, 7-benzylidene-naltrexone; HS-378, 17-cyclopropylmethyl-4,5α-epoxy-14β-methylindolo[2′,3′:6,7]morhinan-3-ol hydrochloride; HS-414, 17-allyl-4,5α-epoxy-14β-ethoxyindolo[2′,3′:6,7]morphinan-3-ol methanesulfonate; HS-464, 17-cyclopropylmethyl-4,5α-epoxy-14β-ethoxyindolo[2′,3′:6,7]morphinan-3-ol hydrochloride; HS-510A, 17-cycloproplymethyl-4,5α-epoxy-14β-ethoxybenzofuro[2′,3′:6,7]morphinan-3-ol salicylate; HS-531, 17-allyl-4,5α-epoxy-14β-methoxy-1′-methylindolo[2′,3′:6,7]morphinan-3-ol hydrochloride; HS-595, 17-cyclopropylmethyl-4-methoxybenzofuro[2′,3′:6,7]morphinan-3,14β-diol; TIPP, H-Tyr-Tic-Phe-Phe-OH; TICP(Ψ), H-Tyr-TicΨ[CH2N]Cha-Phe-OH; Dmt-Tic, 2′,6′-dimethyltyrosine-1,2,3,4-tetrahydroquinoline-3-carboxylate; SNC 80, [(+)-4-[(αR)-α-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide]; GTPγS, guanosine 5′-O-(3-thio)triphosphate; WT, wild type; FCS, fetal calf serum; SEAP, secreted alkaline phosphatase; FK, forskolin.
- Received September 9, 2004.
- Accepted December 3, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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