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Németh E, Gyuricza B, Forgács V, Cumming P, Henriksen G, Marton J, Bauer B, Mikecz P, Fekete A. Optimization of a Nucleophilic Two-Step Radiosynthesis of 6- O-(2-[ 18F]fluoroethyl)-6- O-desmethyl-diprenorphine ([ 18F]FE-DPN) for PET Imaging of Brain Opioid Receptors. Int J Mol Sci 2023; 24:13152. [PMID: 37685958 PMCID: PMC10487412 DOI: 10.3390/ijms241713152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 08/15/2023] [Accepted: 08/17/2023] [Indexed: 09/10/2023] Open
Abstract
We have established a method for nucleophilic one-pot, two-step radiosynthesis of the popular opioid receptor radioligand 6-O-(2-[18F]fluoroethyl)-6-O-desmethyl-diprenorphine ([18F]FE-DPN) from the novel precursor 6-O-(2-tosyloxyethyl)-6-O-desmethyl- 3-O-trityl-diprenorphine (TE-TDDPN), which we designate as the Henriksen precursor. We undertook an optimization of the synthesis conditions, aiming to enhance the accessibility of [18F]FE-DPN for positron emission tomography (PET) studies of μ-opioid receptors. Herein, we report an optimized direct nucleophilic 18F-fluorination and the deprotection conditions for a fully automated radiosynthesis of [18F]FE-DPN on a modified GE Tracerlab FX FE synthesis panel. Starting from 1-1.5 GBq of [18F]fluoride and applying an Oasis Max 1cc cartridge for fluorine-18 trapping with a reduced amount of K2CO3 (5.06 μmol K+ ion), [18F]FE-DPN ([18F]11) was produced with 44.5 ± 10.6 RCY (decay-corrected), high radiochemical purity (>99%), and a molar activity of 32.2 ± 11.8 GBq/μmol in 60-65 min.
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Affiliation(s)
- Enikő Németh
- Division of Nuclear Medicine and Translational Imaging, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei Krt. 98, H-4032 Debrecen, Hungary; (E.N.); (B.G.); (V.F.)
| | - Barbara Gyuricza
- Division of Nuclear Medicine and Translational Imaging, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei Krt. 98, H-4032 Debrecen, Hungary; (E.N.); (B.G.); (V.F.)
| | - Viktória Forgács
- Division of Nuclear Medicine and Translational Imaging, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei Krt. 98, H-4032 Debrecen, Hungary; (E.N.); (B.G.); (V.F.)
| | - Paul Cumming
- Department of Nuclear Medicine, Bern University Hospital, Freiburgstraße 18, CH-3010 Bern, Switzerland;
- School of Psychology and Counselling, Queensland University of Technology, Brisbane QLD-4059, Australia
| | - Gjermund Henriksen
- Norwegian Medical Cyclotron Centre Ltd., Sognsvannsveien 20, N-0372 Oslo, Norway;
- Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway
- Institute of Physics, University of Oslo, Sem Sælands Vei 24, N-0371 Oslo, Norway
| | - János Marton
- ABX Advanced Biochemical Compounds Biomedizinische Forschungsreagenzien GmbH, Heinrich-Glaeser-Strasse 10-14, D-01454 Radeberg, Germany; (J.M.); (B.B.)
| | - Beate Bauer
- ABX Advanced Biochemical Compounds Biomedizinische Forschungsreagenzien GmbH, Heinrich-Glaeser-Strasse 10-14, D-01454 Radeberg, Germany; (J.M.); (B.B.)
| | - Pál Mikecz
- Division of Nuclear Medicine and Translational Imaging, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei Krt. 98, H-4032 Debrecen, Hungary; (E.N.); (B.G.); (V.F.)
| | - Anikó Fekete
- Division of Nuclear Medicine and Translational Imaging, Department of Medical Imaging, Faculty of Medicine, University of Debrecen, Nagyerdei Krt. 98, H-4032 Debrecen, Hungary; (E.N.); (B.G.); (V.F.)
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Wang X, Wang T, Fan X, Zhang Z, Wang Y, Li Z. A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research. J Med Chem 2023; 66:6463-6497. [PMID: 37145921 DOI: 10.1021/acs.jmedchem.2c01965] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) 11C/18F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.
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Affiliation(s)
- Xiaoxiao Wang
- Center for Molecular Imaging and Translational Medicine, State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, Department of Laboratory Medicine, School of Public Health, Xiamen University, Xiamen, Fujian 361102, China
| | - Tao Wang
- Center for Molecular Imaging and Translational Medicine, State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, Department of Laboratory Medicine, School of Public Health, Xiamen University, Xiamen, Fujian 361102, China
| | - Xiaowei Fan
- Center for Molecular Imaging and Translational Medicine, State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, Department of Laboratory Medicine, School of Public Health, Xiamen University, Xiamen, Fujian 361102, China
| | - Zhao Zhang
- Department of Anesthesiology, Huashan Hospital, Fudan University, Shanghai 200040, China
| | - Yingwei Wang
- Department of Anesthesiology, Huashan Hospital, Fudan University, Shanghai 200040, China
| | - Zijing Li
- Center for Molecular Imaging and Translational Medicine, State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, Department of Laboratory Medicine, School of Public Health, Xiamen University, Xiamen, Fujian 361102, China
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Diels–Alder Adducts of Morphinan-6,8-Dienes and Their Transformations. Molecules 2022; 27:molecules27092863. [PMID: 35566212 PMCID: PMC9102320 DOI: 10.3390/molecules27092863] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 04/19/2022] [Accepted: 04/20/2022] [Indexed: 02/04/2023] Open
Abstract
6,14-ethenomorphinans are semisynthetic opiate derivatives containing an ethylene bridge between positions 6 and 14 in ring-C of the morphine skeleton that imparts a rigid molecular structure. These compounds represent an important family of opioid receptor ligands in which the 6,14-etheno bridged structural motif originates from a [4 + 2] cycloaddition of morphinan-6,8-dienes with dienophiles. Certain 6,14-ethenomorphinans having extremely high affinity for opioid receptors are often non-selective for opioid receptor subtypes, but this view is now undergoing some revision. The agonist 20R-etorphine and 20R-dihydroetorphine are several thousand times more potent analgesics than morphine, whereas diprenorphine is a high-affinity non-selective antagonist. The partial agonist buprenorphine is used as an analgesic in the management of post-operative pain or in substitution therapy for opiate addiction, sometimes in combination with the non-selective antagonist naloxone. In the context of the current opioid crisis, we communicated a summary of several decades of work toward generating opioid analgesics with lesser side effects or abuse potential. Our summary placed a focus on Diels–Alder reactions of morphinan-6,8-dienes and subsequent transformations of the cycloadducts. We also summarized the pharmacological aspects of radiolabeled 6,14-ethenomorphinans used in molecular imaging of opioid receptors.
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Kaur T, Brooks AF, Hockley BG, Torres J, Henderson BD, Scott PJH, Shao X. An updated synthesis of N 1 '-([ 11 C]methyl)naltrindole for positron emission tomography imaging of the delta opioid receptor. J Labelled Comp Radiopharm 2020; 64:187-193. [PMID: 33274468 DOI: 10.1002/jlcr.3898] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 11/30/2020] [Accepted: 11/30/2020] [Indexed: 11/08/2022]
Abstract
A new method for the synthesis of the highly selective delta opioid receptor (DOR) antagonist radiotracer N1 '-([11 C]methyl)naltrindole ([11 C]MeNTI) is described. The original synthesis required hydrogenation of a benzyl protecting group after 11 C-labeling, which is challenging in modern radiochemistry laboratories that tend to be heavily automated and operate according to current good manufacturing practice. To address this challenge, we describe development of a novel MeNTI precursor bearing a methoxymethyl acetal (MOM) protecting group, which is easily removed with HCl, and employ it in an updated synthesis of [11 C]MeNTI. The new synthesis is fully automated and validated for clinical use. The total synthesis time is 45 min and provides [11 C]MeNTI in good activity yield (49 ± 8 mCi), molar activity (3,926 ± 326 Ci/mmol) and radiochemical purity (97% ± 2%).
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Affiliation(s)
- Tanpreet Kaur
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Allen F Brooks
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Brian G Hockley
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Jovany Torres
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Bradford D Henderson
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Peter J H Scott
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Xia Shao
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
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A Survey of Molecular Imaging of Opioid Receptors. Molecules 2019; 24:molecules24224190. [PMID: 31752279 PMCID: PMC6891617 DOI: 10.3390/molecules24224190] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 11/11/2019] [Accepted: 11/13/2019] [Indexed: 01/09/2023] Open
Abstract
The discovery of endogenous peptide ligands for morphine binding sites occurred in parallel with the identification of three subclasses of opioid receptor (OR), traditionally designated as μ, δ, and κ, along with the more recently defined opioid-receptor-like (ORL1) receptor. Early efforts in opioid receptor radiochemistry focused on the structure of the prototype agonist ligand, morphine, although N-[methyl-11C]morphine, -codeine and -heroin did not show significant binding in vivo. [11C]Diprenorphine ([11C]DPN), an orvinol type, non-selective OR antagonist ligand, was among the first successful PET tracers for molecular brain imaging, but has been largely supplanted in research studies by the μ-preferring agonist [11C]carfentanil ([11C]Caf). These two tracers have the property of being displaceable by endogenous opioid peptides in living brain, thus potentially serving in a competition-binding model. Indeed, many clinical PET studies with [11C]DPN or [11C]Caf affirm the release of endogenous opioids in response to painful stimuli. Numerous other PET studies implicate μ-OR signaling in aspects of human personality and vulnerability to drug dependence, but there have been very few clinical PET studies of μORs in neurological disorders. Tracers based on naltrindole, a non-peptide antagonist of the δ-preferring endogenous opioid enkephalin, have been used in PET studies of δORs, and [11C]GR103545 is validated for studies of κORs. Structures such as [11C]NOP-1A show selective binding at ORL-1 receptors in living brain. However, there is scant documentation of δ-, κ-, or ORL1 receptors in healthy human brain or in neurological and psychiatric disorders; here, clinical PET research must catch up with recent progress in radiopharmaceutical chemistry.
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Liang SH, Collier TL, Rotstein BH, Lewis R, Steck M, Vasdev N. Rapid microfluidic flow hydrogenation for reduction or deprotection of 18F-labeled compounds. Chem Commun (Camb) 2014; 49:8755-7. [PMID: 23948863 DOI: 10.1039/c3cc45166f] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We have combined the benefits of both microfluidics and flow hydrogenation to provide facile access to previously underutilized reduction and protecting group chemistries for PET imaging applications. The rapid removal of an O-benzyl protecting group to prepare 2-[(18)F]fluoroquinolin-8-ol and the reduction of a nitro group in the synthesis of 4-[(18)F]fluoroaniline were achieved within 3 minutes.
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Affiliation(s)
- Steven H Liang
- Department of Radiology, Harvard Medical School, 55 Fruit Street, Boston, MA, USA 02114.
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Dannals RF. Positron emission tomography radioligands for the opioid system. J Labelled Comp Radiopharm 2013; 56:187-95. [DOI: 10.1002/jlcr.3005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Revised: 11/08/2012] [Accepted: 11/09/2012] [Indexed: 11/06/2022]
Affiliation(s)
- Robert F. Dannals
- Division of Nuclear Medicine, Department of Radiology; The Johns Hopkins University School of Medicine; Baltimore; Maryland; USA; 21287
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Vasdev N, Cao P, van Oosten EM, Wilson AA, Houle S, Hao G, Sun X, Slavine N, Alhasan M, Antich PP, Bonte FJ, Kulkarni P. Synthesis and PET imaging studies of [18F]2-fluoroquinolin-8-ol ([18F]CABS13) in transgenic mouse models of Alzheimer's disease. MEDCHEMCOMM 2012. [DOI: 10.1039/c2md20075a] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Duval RA, Allmon RL, Lever JR. Indium-Labeled Macrocyclic Conjugates of Naltrindole: High-Affinity Radioligands for In Vivo Studies of Peripheral δ Opioid Receptors. J Med Chem 2007; 50:2144-56. [PMID: 17402725 DOI: 10.1021/jm0700013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have identified a series of hydrophilic indium-labeled DOTA and DO3A conjugates of naltrindole (NTI) that are suited to in vivo studies of peripheral delta opioid receptors. Indium(III) complexes, linked to the indole nitrogen of NTI by six- to nine-atom spacers, display high affinities (0.1-0.2 nM) and excellent selectivities for binding to delta sites in vitro. The [111In]-labeled complexes can be prepared in good isolated yields ( approximately 65%) with high specific radioactivities (>3300 mCi/mumol). The spacers serve as pharmacokinetic modifiers, and log D7.4 values range from -2.74 to -1.79. These radioligands exhibit a high level of specific binding (75-94%) to delta opioid receptors in mouse gut, heart, spleen, and pancreas in vivo. Uptakes of radioactivity are saturable by the non-radioactive complexes, inhibited by naltrexone, and blocked by NTI. Thus, these radiometal-labeled NTI analogues warrant further study by single-photon emission computed tomography.
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Affiliation(s)
- Romain A Duval
- Departments of Radiology and the Radiopharmaceutical Sciences Institute, and Medical Pharmacology and Physiology, University of Missouri-Columbia, Columbia, Missouri 65212, USA
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Akgün E, Portoghese PS, Sajjad M, Nabi HA. Synthesis and124I-labeling ofm-iodophenylpyrrolomorphinan as a potential PET imaging agent for delta opioid (DOP) receptors. J Labelled Comp Radiopharm 2007. [DOI: 10.1002/jlcr.1216] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Akgün E, Sajjad M, Portoghese PS. N1'-(p-[18F]Fluorobenzyl)naltrindole (p-[18F]BNTI) as a potential PET imaging agent for DOP receptors. J Labelled Comp Radiopharm 2006. [DOI: 10.1002/jlcr.1095] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Clayson J, Jales A, Tyacke RJ, Hudson AL, Nutt DJ, Lewis JW, Husbands SM. Selective delta-opioid receptor ligands: potential PET ligands based on naltrindole. Bioorg Med Chem Lett 2001; 11:939-43. [PMID: 11294396 DOI: 10.1016/s0960-894x(01)00112-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Two series of delta-selective ligands related to the prototypic delta-antagonist naltrindole have been prepared and evaluated in opioid binding assays with the aim of developing new PET ligands for the delta-opioid receptor. One compound (5d) had significantly higher selectivity than naltrindole, but with substantially reduced binding affinity. For those compounds retaining similar affinity to naltrindole, those having ethyl and fluoroethyl substituents afforded the highest levels of selectivity. However, none of the compounds combined the high level of affinity and selectivity ideally suited to the development of an imaging agent.
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Affiliation(s)
- J Clayson
- School of Chemistry, University of Bristol, UK
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Ravert HT, Mathews WB, Musachio JL, Scheffel U, Finley P, Dannals RF. [11C]-methyl 4-[(3,4-dichlorophenyl)acetyl]-3-[(1-pyrrolidinyl)-methyl]-1- piperazinecarboxylate ([11C]GR89696): synthesis and in vivo binding to kappa opiate receptors. Nucl Med Biol 1999; 26:737-41. [PMID: 10628552 DOI: 10.1016/s0969-8051(99)00043-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GR89696, racemic methyl 4-[(3,4-dichlorophenyl)acetyl]-3-[(1-pyrrolidinyl) methyl]-1-piperazinecarboxylate, a kappa opioid receptor ligand, was labeled with [11C]methyl chloroformate. The radiochemical yield was 20% with an observed specific radioactivity of 75.5 GBq/micromol at end of synthesis (2,040 mCi/micromol). Five minutes after intravenous administration, 5.4% of the injected dose accumulated in mouse whole brain. Brain region to cerebellar ratios increased over time with ratios at 90 min of 7.8, 5.6, and 4.5 for the hypothalamus, olfactory tubercle, and striatum, respectively. The uptake of [11C]GR89696 correlated with known kappa opioid receptor densities and was inhibited by kappa opioid selective drugs.
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Affiliation(s)
- H T Ravert
- Department of Radiology, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21287-0750, USA.
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Smith JS, Zubieta JK, Price JC, Flesher JE, Madar I, Lever JR, Kinter CM, Dannals RF, Frost JJ. Quantification of delta-opioid receptors in human brain with N1'-([11C]methyl) naltrindole and positron emission tomography. J Cereb Blood Flow Metab 1999; 19:956-66. [PMID: 10478647 DOI: 10.1097/00004647-199909000-00003] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The regional binding of N1'-([11C]methyl)naltrindole (MeNTI), a selective delta-opioid antagonist, was studied in healthy human subjects with positron emission tomography (PET). After the bolus intravenous administration of high specific activity [11C]MeNTI, PET was performed over 90 minutes. Arterial plasma samples were obtained during the scanning period and assayed for the presence of radiolabeled metabolites. The data were analyzed with various kinetic (two- and three-compartment models, Patlak graphical analysis) and nonkinetic (apparent volume of distribution and activity at a late scanning time) approaches. This tracer showed irreversible binding characteristics during the scanning period used. The results of the analyses also were compared with the density and distribution of delta-opioid receptors in the human brain in vitro. Additionally, computer simulations were performed to assess the effects of changes in receptor binding and tracer transport changes on the perceived binding parameters obtained with the models. A constrained three-compartment kinetic model was demonstrated to be superior to other quantification models for the description of MeNTI kinetics and quantification of delta receptor binding in the human brain with 11C-labeled MeNTI.
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Affiliation(s)
- J S Smith
- Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
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Lever JR, Johnson SM. Synthesis of tritiated N1′-alkyl derivatives of the delta opioid receptor ligand naltrindole. J Labelled Comp Radiopharm 1998. [DOI: 10.1002/(sici)1099-1344(199702)39:2<115::aid-jlcr947>3.0.co;2-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Lever JR, Stathis M, Kinter CM, Scheffel U. In vivo labeling of delta opioid receptors in mouse brain by [3H]benzylidenenaltrexone, a ligand selective for the delta 1 subtype. Life Sci 1996; 58:PL331-6. [PMID: 8637403 DOI: 10.1016/0024-3205(96)00175-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
(E)-7-Benzylidenenaltrexone (BNTX) is a selective ligand for the putative delta 1 (delta 1) opioid receptor. To explore the feasibility of labeling delta 1 sites in vivo; we determined the cerebral distribution of radioactivity after systemic administration of [3H]BNTX to CD1 mice. Uptake was highest in striatum and lowest in cerebellum throughout the 4 hr time course. Specific radioligand binding, approximated as the difference in radioactivity concentrations between striatum and cerebellum, peaked at 0.32 percent injected dose/g at 30 min and comprised a modest 23% of total striatal radioactivity. For seven brain regions, radioactivity concentrations correlated with delta site densities known from prior in vitro studies (rS = 0.79, p = 0.03), and also with the uptake of N1'-([11C]methyl)naltrindole in vivo (rS = 0.78, p = 0.04) in mice. Specific binding in striatum, olfactory tubercles and cortical regions was saturable by BNTX, and was inhibited stereoselectively by the optical isomers of naloxone. Naltrindole and naltriben (NTB), delta antagonists, blocked 65-99% of [3H]BNTX specific binding at a dosage of 5.0 mumol/kg. Similar doses of the mu antagonist cyprodime, or the kappa agonist U50,488H, did not inhibit binding. Adjusted for the four-fold greater brain penetration of NTB relative to BNTX, dose-response studies suggested that delta 1 selective BNTX (ED50 = 1.51 mumol/kg) was 50% more potent than delta 2 selective NTB (ED50 = 0.56 mumol/kg) in blocking specific [3H]BNTX binding in striatum. In CXBK mice, a strain with functional delta 1 but not delta 2 receptors in antinociceptive assays, radioligand uptake and distribution proved similar to that in CD1 mice. In sum, [3H]BNTX labels murine delta opioid receptors in vivo with a low extent of specific binding. The data is consistent with, but not conclusive for, selective labeling of the delta 1 subtype.
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Affiliation(s)
- J R Lever
- Department of Environmental Health Sciences, Johns Hopkins University, Baltimore, Maryland 21205, USA
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Kinter CM, Lever JR. Synthesis of radioiodinated naltrindole analogues: ligands for studies of delta opioid receptors. Nucl Med Biol 1995; 22:599-606. [PMID: 7581169 DOI: 10.1016/0969-8051(94)00149-e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Analogues of naltrindole and N1'-methylnaltrindole having radioiodine in the 7'-position of the indole ring have been prepared for evaluation as delta opioid receptor ligands. The no-carrier-added radiosyntheses were conducted by Cu(I) assisted nucleophilic exchange of radioiodide for bromide under reducing conditions at 190 degrees C. A combination of HPLC and solid-phase extraction gave the 125I- or 123I-labeled products in satisfactory yields (47%) with high radiochemical purities (> 98%) and high specific activities (125I: 43-68 GBq/mumol, 1155-1833 mCi/mumol; 123I: > 92 GBq/mumol, 2500 mCi/mumol).
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Affiliation(s)
- C M Kinter
- Department of Environmental Health Sciences, Johns Hopkins University School of Hygiene and Public Health, Baltimore, MD 21205-2179, USA
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Eleventh international symposium on radiopharmaceutical chemistry: Abstracts. J Labelled Comp Radiopharm 1995. [DOI: 10.1002/jlcr.2580370401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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