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Fu H, Rong J, Chen Z, Zhou J, Collier T, Liang SH. Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors. J Med Chem 2022; 65:10755-10808. [PMID: 35939391 DOI: 10.1021/acs.jmedchem.2c00633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.
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Affiliation(s)
- Hualong Fu
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Jian Rong
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.,Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Zhen Chen
- Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, International Innovation Center for Forest Chemicals and Materials, College of Chemical Engineering, Nanjing Forestry University, Nanjing, Jiangsu 210037, China
| | - Jingyin Zhou
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Thomas Collier
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.,Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Steven H Liang
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.,Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115, United States
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2
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Mangeant R, Dubost E, Cailly T, Collot V. Radiotracers for the Central Serotoninergic System. Pharmaceuticals (Basel) 2022; 15:ph15050571. [PMID: 35631397 PMCID: PMC9143978 DOI: 10.3390/ph15050571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Revised: 04/27/2022] [Accepted: 04/28/2022] [Indexed: 12/10/2022] Open
Abstract
This review lists the most important radiotracers described so far for imaging the central serotoninergic system. Single-photon emission computed tomography and positron emission tomography radiotracers are reviewed and critically discussed for each receptor.
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Affiliation(s)
- Reynald Mangeant
- Centre d’Etudes et de Recherche sur le Médicament de Normandie (CERMN), UNICAEN, Normandie Univ., 14000 Caen, France; (R.M.); (E.D.)
- Institut Blood and Brain @ Caen Normandie (BB@C), Boulevard Henri Becquerel, 14000 Caen, France
| | - Emmanuelle Dubost
- Centre d’Etudes et de Recherche sur le Médicament de Normandie (CERMN), UNICAEN, Normandie Univ., 14000 Caen, France; (R.M.); (E.D.)
- Institut Blood and Brain @ Caen Normandie (BB@C), Boulevard Henri Becquerel, 14000 Caen, France
| | - Thomas Cailly
- Centre d’Etudes et de Recherche sur le Médicament de Normandie (CERMN), UNICAEN, Normandie Univ., 14000 Caen, France; (R.M.); (E.D.)
- Institut Blood and Brain @ Caen Normandie (BB@C), Boulevard Henri Becquerel, 14000 Caen, France
- UNICAEN, IMOGERE, Normandie Univ., 14000 Caen, France
- CHU Côte de Nacre, Department of Nuclear Medicine, 14000 Caen, France
- Correspondence: (T.C.); (V.C.)
| | - Valérie Collot
- Centre d’Etudes et de Recherche sur le Médicament de Normandie (CERMN), UNICAEN, Normandie Univ., 14000 Caen, France; (R.M.); (E.D.)
- Institut Blood and Brain @ Caen Normandie (BB@C), Boulevard Henri Becquerel, 14000 Caen, France
- Correspondence: (T.C.); (V.C.)
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Hazari PP, Pandey A, Chaturvedi S, Mishra AK. New Trends and Current Status of Positron-Emission Tomography and Single-Photon-Emission Computerized Tomography Radioligands for Neuronal Serotonin Receptors and Serotonin Transporter. Bioconjug Chem 2017; 28:2647-2672. [PMID: 28767225 DOI: 10.1021/acs.bioconjchem.7b00243] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The critical role of serotonin (5-hydroxytryptamine; 5-HT) and its receptors (5-HTRs) in the pathophysiology of diverse neuropsychiatric and neurodegenerative disorders render them attractive diagnostic and therapeutic targets for brain disorders. Therefore, the in vivo assessment of binding of 5-HT receptor ligands under a multitude of physiologic and pathologic scenarios may support more-accurate identification of disease and its progression and the patient's response to therapy as well as the screening of novel therapeutic strategies. The present Review aims to focus on the current status of radioligands used for positron-emission tomography (PET) and single-photon-emission computerized tomography (SPECT) imaging of human brain serotonin receptors. We further elaborate upon and emphasize the attributes that qualify a radioligand for theranostics on the basis of its frequency of use in clinics, its benefit to risk assessment in humans, and its continuous evolution, along with the major limitations.
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Affiliation(s)
- Puja Panwar Hazari
- Division of Cyclotron and Radiopharmaceutical Sciences, Institute of Nuclear Medicine and Allied Sciences , Brig S.K. Mazumdar Road, Delhi 110054, India
| | - Ankita Pandey
- Division of Cyclotron and Radiopharmaceutical Sciences, Institute of Nuclear Medicine and Allied Sciences , Brig S.K. Mazumdar Road, Delhi 110054, India
| | - Shubhra Chaturvedi
- Division of Cyclotron and Radiopharmaceutical Sciences, Institute of Nuclear Medicine and Allied Sciences , Brig S.K. Mazumdar Road, Delhi 110054, India
| | - Anil Kumar Mishra
- Division of Cyclotron and Radiopharmaceutical Sciences, Institute of Nuclear Medicine and Allied Sciences , Brig S.K. Mazumdar Road, Delhi 110054, India
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4
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Mu L, Müller Herde A, Rüefli PM, Sladojevich F, Milicevic Sephton S, Krämer SD, Thompson AJ, Schibli R, Ametamey SM, Lochner M. Synthesis and Pharmacological Evaluation of [ 11C]Granisetron and [ 18F]Fluoropalonosetron as PET Probes for 5-HT 3 Receptor Imaging. ACS Chem Neurosci 2016; 7:1552-1564. [PMID: 27571447 DOI: 10.1021/acschemneuro.6b00192] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Serotonin-gated ionotropic 5-HT3 receptors are the major pharmacological targets for antiemetic compounds. Furthermore, they have become a focus for the treatment of irritable bowel syndrome (IBS) and there is some evidence that pharmacological modulation of 5-HT3 receptors might alleviate symptoms of other neurological disorders. Highly selective, high-affinity antagonists, such as granisetron (Kytril) and palonosetron (Aloxi), belong to a family of drugs (the "setrons") that are well established for clinical use. To enable us to better understand the actions of these drugs in vivo, we report the synthesis of 8-fluoropalonosetron (15) that has a binding affinity (Ki = 0.26 ± 0.05 nM) similar to the parent drug (Ki = 0.21 ± 0.03 nM). We radiolabeled 15 by nucleophilic 18F-fluorination of an unsymmetrical diaryliodonium palonosetron precursor and achieved the radiosynthesis of 1-(methyl-11C)-N-granisetron ([11C]2) through N-alkylation with [11C]CH3I, respectively. Both compounds [18F]15 (chemical and radiochemical purity >95%, specific activity 41 GBq/μmol) and [11C]2 (chemical and radiochemical purity ≥99%, specific activity 170 GBq/μmol) were evaluated for their utility as positron emission tomography (PET) probes. Using mouse and rat brain slices, in vitro autoradiography with both [18F]15 and [11C]2 revealed a heterogeneous and displaceable binding in cortical and hippocampal regions that are known to express 5-HT3 receptors at significant levels. Subsequent PET experiments suggested that [18F]15 and [11C]2 are of limited utility for the PET imaging of brain 5-HT3 receptors in vivo.
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Affiliation(s)
- Linjing Mu
- Department
of Nuclear Medicine, University Hospital Zürich, Rämistrasse
100, 8091 Zürich, Switzerland
| | - Adrienne Müller Herde
- Center for Radiopharmaceutical
Sciences of ETH, PSI and USZ, Vladimir-Prelog-Weg
4, 8093 Zürich, Switzerland
| | - Pascal M. Rüefli
- Department
of Chemistry and Biochemistry, University of Bern, Freiestrasse
3, 3012 Bern, Switzerland
| | - Filippo Sladojevich
- Center for Radiopharmaceutical
Sciences of ETH, PSI and USZ, Vladimir-Prelog-Weg
4, 8093 Zürich, Switzerland
| | - Selena Milicevic Sephton
- Center for Radiopharmaceutical
Sciences of ETH, PSI and USZ, Vladimir-Prelog-Weg
4, 8093 Zürich, Switzerland
| | - Stefanie D. Krämer
- Center for Radiopharmaceutical
Sciences of ETH, PSI and USZ, Vladimir-Prelog-Weg
4, 8093 Zürich, Switzerland
| | - Andrew J. Thompson
- Department
of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | - Roger Schibli
- Center for Radiopharmaceutical
Sciences of ETH, PSI and USZ, Vladimir-Prelog-Weg
4, 8093 Zürich, Switzerland
| | - Simon M. Ametamey
- Center for Radiopharmaceutical
Sciences of ETH, PSI and USZ, Vladimir-Prelog-Weg
4, 8093 Zürich, Switzerland
| | - Martin Lochner
- Department
of Chemistry and Biochemistry, University of Bern, Freiestrasse
3, 3012 Bern, Switzerland
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5
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Kumar JSD, Mann JJ. PET tracers for serotonin receptors and their applications. Cent Nerv Syst Agents Med Chem 2015; 14:96-112. [PMID: 25360773 DOI: 10.2174/1871524914666141030124316] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Revised: 10/26/2014] [Accepted: 10/28/2014] [Indexed: 11/22/2022]
Abstract
Serotonin receptors (5-HTRs) are implicated in the pathophysiology of a variety of neuropsychiatric and neurodegenerative disorders and are also targets for drug therapy. In the CNS, most of these receptors are expressed in high abundance in specific brain regions reflecting their role in brain functions. Quantifying binding to 5-HTRs in vivo may permit assessment of physiologic and pathologic conditions, and monitoring disease progression, evaluating treatment response, and for investigating new treatment modalities. Positron emission tomography (PET) molecular imaging has the sensitivity to quantify binding of 5-HTRs in CNS disorders and to measure drug occupancy as part of a process of new drug development. Although research on PET imaging of 5-HTRs have been performed more than two decades, the successful radiotracers so far developed for human studies are limited to 5-HT₁AR, 5-HT₁BR, 5-HT₂AR, 5-HT₄R and 5-HT₆R. Herein we review the development and application of radioligands for PET imaging of 5-HTRs in living brain.
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Affiliation(s)
| | - J John Mann
- Division of Molecular Imaging and Neuropathology, New York State Psychiatric institute, 1051 Riverside Drive, Box: 42, New York, NY, 10032, USA.
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6
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Eleventh international symposium on radiopharmaceutical chemistry: Abstracts. J Labelled Comp Radiopharm 2012. [DOI: 10.1002/jlcr.2580370301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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7
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Paterson LM, Kornum BR, Nutt DJ, Pike VW, Knudsen GM. 5-HT radioligands for human brain imaging with PET and SPECT. Med Res Rev 2011; 33:54-111. [PMID: 21674551 DOI: 10.1002/med.20245] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.
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Affiliation(s)
- Louise M Paterson
- Neuropsychopharmacology Unit, Division of Experimental Medicine, Imperial College London, Burlington Danes Building, Du Cane Road, London, United Kingdom
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8
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XIIth international symposium on radiopharmaceutical chemistry: Abstracts and programme. J Labelled Comp Radiopharm 2010. [DOI: 10.1002/jlcr.2580400801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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9
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Kopczyńska B, Szereda-Przestaszewska M. 5HT2 and 5HT3 receptors' contribution to modeling of post-serotonin respiratory pattern in cats. Life Sci 2004; 75:2281-90. [PMID: 15350826 DOI: 10.1016/j.lfs.2004.03.029] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Accepted: 03/18/2004] [Indexed: 11/18/2022]
Abstract
Cardio-respiratory reflex effects of an exogenous serotonin challenge are suggested to be modulated by activation of the peripheral 5HT2 and 5HT3 receptors. In the present experiments the blocking effects of serotoninergic active drugs: ketanserin and tropanserin (MDL 72222) were studied in six pentobarbitone-chloralose anaesthetized cats. Bolus injection of serotonin (0.05 mg.kg(-1)) into the right femoral vein evoked prompt apnea, hypotension followed by tachypnoeic breathing. Pre-treatment with ketanserin (0.1 mg.kg(-1)), 5HT2 receptor antagonist, shortened the duration of post-serotonin apnea (P < 0.05), but had no effect on the pattern of post-apnoeic breathing. 5HT3 receptor blockade with the selective antagonist MDL 72222 (0.2 mg.kg(-1)) totally eliminated respiratory response to serotonin. In breaths that followed post-serotonin apnea, peak amplitude of the integrated phrenic signal was reduced (P < 0.001), unbiased by ketanserin blockade, and remained at the baseline level in MDL treated rats. Serotonin-induced hypotension was unaffected by the blockade of 5HT2 receptors. Inactivation of 5HT3 receptors with MDL attenuated the fall in blood pressure (P < 0.05). This data suggests that the squeal of serotonin-induced pulmonary chemoreflex, i.e. respiratory arrest, post-apnoeic pattern of breathing, bradycardia, and partially hypotension are mediated by 5HT3 receptors.
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MESH Headings
- Animals
- Apnea/physiopathology
- Blood Pressure/drug effects
- Blood Pressure/physiology
- Bradycardia/physiopathology
- Cats
- Dose-Response Relationship, Drug
- Injections, Intraperitoneal
- Ketanserin/pharmacology
- Larynx/physiopathology
- Male
- Phrenic Nerve/physiology
- Receptors, Serotonin, 5-HT2/drug effects
- Receptors, Serotonin, 5-HT2/physiology
- Receptors, Serotonin, 5-HT3/drug effects
- Receptors, Serotonin, 5-HT3/physiology
- Respiratory Mechanics/physiology
- Serotonin/physiology
- Serotonin Antagonists/pharmacology
- Tidal Volume/drug effects
- Tropanes/pharmacology
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Affiliation(s)
- Beata Kopczyńska
- Laboratory of Respiration Physiology, PAS Medical Research Center, 5 Pawiñskiego St., 02-106 Warsaw, Poland.
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10
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Guillouet S, Barre L, Gourand F, Lasne MC, Rault S. Synthesis of [11C]-S21007 a novel 5HT3 partial agonist as a potential tracer for PET studies. J Labelled Comp Radiopharm 1998. [DOI: 10.1002/(sici)1099-1344(199604)38:4<367::aid-jlcr846>3.0.co;2-n] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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11
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Vandersteene I, Audenaert K, Slegers G, Dierckx R. Synthesis of [11C]granisetron, a possible positron emission tomography ligand for 5-HT3 receptor studies. J Labelled Comp Radiopharm 1998. [DOI: 10.1002/(sici)1099-1344(199803)41:3<171::aid-jlcr66>3.0.co;2-f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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12
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Katounina T, Besret L, Dhilly M, Petit-Taboué MC, Barbelivien A, Baron JC, Dauphin F, Barré L. Synthesis and biological investigations of [18F]MR18445, a 5-HT3 receptor partial agonist. Bioorg Med Chem 1998; 6:789-95. [PMID: 9681144 DOI: 10.1016/s0968-0896(98)00035-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
18F Labelled MR18445 (4-[4-(4-[18F]fluorobenzyl)piperazino]-7-methoxypyrrolo++ +[1,2-alpha] quinoxaline), a selective 5-HT3 receptor partial agonist with nanomolar affinity, was synthesized and examined as a potential radioligand for PET imaging of brain 5HT3 receptors. Radiotracer was prepared by N-alkylation of the MR18491 precursor with 4-[18F]fluorobenzyl iodide. This latter was synthesized in a three-step procedure from 4-[18F]fluorobenzaldehyde obtained by 18F-nucleophilic displacement of 4-nitrobenzaldehyde, subsequently reduced to 4-[18F]fluorobenzyl alcohol and converted into reactive 4-[18F]fluorobenzyl iodide. The reduction step was performed on a column filled with NaBH4/Al2O3 and 4-[18F]fluorobenzyl alcohol was obtained with high reproducible yield (82-93% from 4-[18F]fluorobenzaldehyde) if there were traces of water in the system. The radiosynthesis of [18F]MR18445 required approximately 120 min. Semi-preparative HPLC purification followed by formulation gave injectable solutions of [18F]MR18445 with a radiochemical purity > 99%. The overall yield of the synthesis was mainly dependent upon the first step efficiency of aromatic incorporation of 18F- and varied from 12% to 29%. All the synthetic procedure was realized on a ZYMARK robotic system. Biological in vivo studies in rats showed that uptake of [18F]MR18445 in brain was rapid and high. No evidence of radiolabeled metabolites could be observed in the brain as late as 40 min after injection, despite the rapid appearance of metabolites in the plasma. However, neither phosphorimaging autoradiographic studies in rats nor PET experiments in baboons revealed specific binding of the radiotracer in brain, suggesting [18F]MR18445 is not suitable for 5-HT3 receptors PET studies.
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13
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Besret L, Dauphin F, Guillouet S, Dhilly M, Gourand F, Blaizot X, Young AR, Petit-Taboué MC, Mickala P, Barbelivien A, Rault S, Barré L, Baron JC. [11C]S21007, a putative partial agonist for 5-HT3 receptors PET studies. Rat and primate in vivo biological evaluation. Life Sci 1998; 62:115-29. [PMID: 9488110 DOI: 10.1016/s0024-3205(97)01058-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We recently labeled with carbon-11, a high affinity, selective, 5-HT3 receptor (5-HT3R) ligand, S21007, for potential positron emission tomography (PET) applications. To evaluate the in vivo binding properties of [11C]S21007, its brain regional distribution, tissue and plasma pharmacokinetics and plasma metabolisation were characterized. To circumvent the problem of highly discrete brain localization of the 5-HT3R (area postrema, hippocampus), we designed an original approach combining high-resolution imaging techniques (ex vivo phosphor plate autoradiography and MRI-guided coronal PET in the rat and baboon, respectively). After i.v. injection of trace amounts of [11C]S21007 to rats, phosphorimager autoradiography failed to reveal in vivo specific binding to, nor selectivity for 5-HT3R-rich areas. PET studies in the baboon showed consistent results, i.e., there was no selective accumulation of [11C]S21007 in the area postrema or hippocampus, and neither displacement nor presaturation with cold S21007 resulted in significant changes in tissue distribution or kinetics of [11C]S21007.
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Affiliation(s)
- L Besret
- CEA/DSV/DRM GDM-TEP, INSERM U320, Université de Cean, Centre CYCERON, France.
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14
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Hewlett WA, Schmidt DE, Mason NS, Trivedi BL, Ebert MH, de Paulis T. Synthesis and 5-HT-3 receptor binding of 2- and 3-(halo)alkoxyl substituted (S)-N-(1-azabicyclo[2.2.2]oct-3-yl)-5-chlorobenzamides as potential radioligands. Nucl Med Biol 1998; 25:141-53. [PMID: 9468029 DOI: 10.1016/s0969-8051(97)00161-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In an effort to develop selective, high-affinity radioligands for the 5-HT-3 receptor, a series of homologues of 5-chloro-2,3-dimethoxy-N-(1-azabicyclo[2.2.2]oct-3-yl)benzamide (2b) was prepared in which individual methoxy groups were replaced by ethoxyl, (2-fluoroethoxyl), allyloxyl, propargyloxyl, or (3-iodoallyl)oxyl groups. Affinities for the 5-HT-3 receptor were determined by displacement of the binding of [125I]MIZAC (2a), a selective 5-HT-3 receptor antagonist radioligand, in rat brain homogenates. The 3-substituted homologues were more potent than the lead compound, 2b. The homologue having the largest 3-substituent, i.e., E-(S)-N-(1-azabicyclo[2.2.2]oct-3-yl)-5-chloro-3-(3-iodo-2-propenyl)oxy- 2-methoxybenzamide (3b, THIZAC), had one of the highest affinities, Ki 0.08 nM. The 2-substituted homologues were equipotent with 2b, having Ki 0.2-0.3 nM, regardless of the size of the substituent. The corresponding iodoallyl derivative, E-(S)-N-(1-azabicyclo[2.2.2]oct-3-yl)-5-chloro-2-(3-iodo-2-propenyl)oxy- 3-methoxybenzamide (4, LIZAC), displayed a Ki of 0.29 nM. Saturation binding of [125I]-4 gave a KD of 0.31 +/- 0.04 nM and a Bmax of 2.36 +/- 0.10 fmol/mg of entorhinal cortex. In vivo biodistribution of [125I]-4 in the rat brain showed increased accumulation in hippocampus relative to that in cerebellum. Both the high-affinity ligands [125I]-3b and [125I]-4 are potentially useful radioligands for studying the 5-HT-3 receptor.
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Affiliation(s)
- W A Hewlett
- Department of Psychiatry, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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15
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N-methylquipazine: Carbon-11 labelling of the 5-HT3 agonist and in vivo evaluation of its biodistribution using PET. Nucl Med Biol 1997. [DOI: 10.1016/s0969-8051(97)80007-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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Ishiwata K, Saito N, Yanagawa K, Furuta R, Ishii S, Kiyosawa M, Homma Y, Ishii K, Suzuki F, Senda M. Synthesis and evaluation of 5-HT3 receptor antagonist [11C]KF17643. Nucl Med Biol 1996; 23:285-90. [PMID: 8782238 DOI: 10.1016/0969-8051(95)02079-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
For imaging CNS 5-HT3 receptors by PET, a high affinity 5-HT3 receptor ligand, endo-8-methyl-8-azabicyclo[3.2.1]oct-3-yl 2-(n-propyloxy)-4-quinolinecarboxylate (KF17643), have been labeled with 11C. N-Methylation of the desmethyl compound with [11C]methyl iodide followed by HPLC separation produced [11C]KF17643 with the decay-corrected radiochemical yield of 19-28%, the specific activity of 7.5-49 GBq/mumol and the radiochemical purity of > 99% at 35-40 min from EOB. After i.v. injection of [11C]KF17643 into mice, it was taken by the brain at a high level and was stable for metabolism, but no sign for the 5-HT3 receptor selectivity was found in the brain tissues by the tissue sampling and autoradiography, probably because of large non-specific binding. The [11C]KF17643 was not suitable as a PET ligand for mapping the CNS 5-HT3 receptors.
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Affiliation(s)
- K Ishiwata
- Positron Medical Center, Tokyo Metropolitan Institute of Gerontology, Japan
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17
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Ishiwata K, Ishii K, Ishii S, Senda M. Synthesis of 5-HT3 receptor antagonists, [11C]Y-25130 and [11C]YM060. Appl Radiat Isot 1995; 46:907-10. [PMID: 7581293 DOI: 10.1016/0969-8043(95)00147-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Two high-affinity 5-HT3 receptor ligands, Y-25130 and YM 060, have been labeled with 11C for use in PET studies to measure 5-HT3 receptors. The [11C]Y-25130 was prepared by N-methylation of nor-Y-25130-BH3 complex with [11C]CH3I in the presence of K2CO3 followed by HCl hydrolysis. Likewise, N-methylation of nor-YM060 gave [11C]YM060. After HPLC separation, the decay-corrected radiochemical yield of the two 11C-labeled ligands was 34-40% based on [11C]CH3I, the specific activity was 10-12 GBq/mumol at 35-40 min from EOB, and the radiochemical and chemical purities were > 99%. In mice, the brain uptake of the two compounds was the lowest among the tissues investigated, but the level of the brain radioactivity increased with time.
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Affiliation(s)
- K Ishiwata
- Positron Medical Center, Tokyo Metropolitan Institute of Gerontology, Japan
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