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Mattner F, Katsifis A, Bourdier T, Loc'h C, Berghofer P, Fookes C, Hung TT, Jackson T, Henderson D, Pham T, Lee BJ, Shepherd R, Greguric I, Wyatt N, Le T, Poon J, Power C, Fulham M. Synthesis and pharmacological evaluation of [ 18F]PBR316: a novel PET ligand targeting the translocator protein 18 kDa (TSPO) with low binding sensitivity to human single nucleotide polymorphism rs6971. RSC Med Chem 2021; 12:1207-1221. [PMID: 34355185 PMCID: PMC8292990 DOI: 10.1039/d1md00035g] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 03/15/2021] [Indexed: 02/04/2023] Open
Abstract
Radiopharmaceuticals that target the translocator protein 18 kDa (TSPO) have been investigated with positron emission tomography (PET) to study neuroinflammation, neurodegeneration and cancer. We have developed the novel, achiral, 2-phenylimidazo[1,2-a]pyridine, PBR316 that targets the translocator protein 18 kDa (TSPO) that addresses some of the limitations inherent in current TSPO ligands; namely specificity in binding, blood brain barrier permeability, metabolism and insensitivity to TSPO binding in subjects as a result of rs6971 polymorphism. PBR316 has high nanomolar affinity (4.7-6.0 nM) for the TSPO, >5000 nM for the central benzodiazepine receptor (CBR) and low sensitivity to rs6971 polymorphism with a low affinity binders (LABs) to high affinity binders (HABs) ratio of 1.5. [18F]PBR316 was prepared in 20 ± 5% radiochemical yield, >99% radiochemical purity and a molar activity of 160-400 GBq μmol-1. Biodistribution in rats showed high uptake of [18F]PBR316 in organs known to express TSPO such as heart (3.9%) and adrenal glands (7.5% ID per g) at 1 h. [18F]PBR316 entered the brain and accumulated in TSPO-expressing regions with an olfactory bulb to brain ratio of 3 at 15 min and 7 at 4 h. Radioactivity was blocked by PK11195 and Ro 5-4864 but not Flumazenil. Metabolite analysis showed that radioactivity in adrenal glands and the brain was predominantly due to the intact radiotracer. PET-CT studies in mouse-bearing prostate tumour xenografts indicated biodistribution similar to rats with radioactivity in the tumour increasing with time. [18F]PBR316 shows in vitro binding that is insensitive to human polymorphism and has specific and selective in vivo binding to the TSPO. [18F]PBR316 is suitable for further biological and clinical studies.
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Affiliation(s)
- Filomena Mattner
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
| | - Andrew Katsifis
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
- School of Pharmacy, University of Sydney Sydney NSW 2006 Australia
| | - Thomas Bourdier
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
| | - Christian Loc'h
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Paula Berghofer
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Christopher Fookes
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Tzong-Tyng Hung
- Biological Resources Imaging Laboratory, University of New South Wales Sydney NSW Australia
| | - Timothy Jackson
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - David Henderson
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
| | - Tien Pham
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Brendan J Lee
- Biological Resources Imaging Laboratory, University of New South Wales Sydney NSW Australia
| | - Rachael Shepherd
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Ivan Greguric
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Naomi Wyatt
- Australian Nuclear Science and Technology Organisation Lucas Heights NSW Australia
| | - Thanh Le
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
| | - Jackson Poon
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
| | - Carl Power
- Biological Resources Imaging Laboratory, University of New South Wales Sydney NSW Australia
| | - Michael Fulham
- Department of Molecular Imaging, Royal Prince Alfred Hospital Camperdown NSW 2050 Australia
- Faculty of Engineering and Information Technologies, University of Sydney Sydney NSW 2006 Australia
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Caymaz B, Yıldız U, Akkoç S, Gerçek Z, Şengül A, Coban B. Synthesis, Characterization, and Antiproliferative Activity Studies of Novel Benzimidazole‐Imidazopyridine Hybrids as DNA Groove Binders. ChemistrySelect 2020. [DOI: 10.1002/slct.202001580] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Bahar Caymaz
- Zonguldak Bülent Ecevit UniversityFaculty of Arts and SciencesDepartment of Chemistry 67100 Zonguldak Turkey
| | - Ufuk Yıldız
- Zonguldak Bülent Ecevit UniversityFaculty of Arts and SciencesDepartment of Chemistry 67100 Zonguldak Turkey
| | - Senem Akkoç
- Department of Basic Pharmaceutical SciencesFaculty of PharmacySüleyman Demirel University Isparta 32260 Turkey
| | - Zuhal Gerçek
- Zonguldak Bülent Ecevit UniversityFaculty of Arts and SciencesDepartment of Chemistry 67100 Zonguldak Turkey
| | - Abdurrahman Şengül
- Zonguldak Bülent Ecevit UniversityFaculty of Arts and SciencesDepartment of Chemistry 67100 Zonguldak Turkey
| | - Burak Coban
- Zonguldak Bülent Ecevit UniversityFaculty of Arts and SciencesDepartment of Chemistry 67100 Zonguldak Turkey
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Aggarwal R, Singh G, Sanz D, Claramunt RM, Torralba MC, Torres MR. NBS mediated one-pot regioselective synthesis of 2,3-disubstituted imidazo[1,2- a ]pyridines and their unambiguous characterization through 2D NMR and X-ray crystallography. Tetrahedron 2016. [DOI: 10.1016/j.tet.2016.04.072] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Mattner F, Quinlivan M, Greguric I, Pham T, Liu X, Jackson T, Berghofer P, Fookes CJR, Dikic B, Gregoire MC, Dolle F, Katsifis A. Radiosynthesis, In Vivo Biological Evaluation, and Imaging of Brain Lesions with [123I]-CLINME, a New SPECT Tracer for the Translocator Protein. DISEASE MARKERS 2015; 2015:729698. [PMID: 26199457 PMCID: PMC4496498 DOI: 10.1155/2015/729698] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2015] [Accepted: 06/10/2015] [Indexed: 11/17/2022]
Abstract
The high affinity translocator protein (TSPO) ligand 6-chloro-2-(4'-iodophenyl)-3-(N,N-methylethyl)imidazo[1,2-a]pyridine-3-acetamide (CLINME) was radiolabelled with iodine-123 and assessed for its sensitivity for the TSPO in rodents. Moreover neuroinflammatory changes on a unilateral excitotoxic lesion rat model were detected using SPECT imaging. [(123)I]-CLINME was prepared in 70-80% radiochemical yield. The uptake of [(123)I]-CLINME was evaluated in rats by biodistribution, competition, and metabolite studies. The unilateral excitotoxic lesion was performed by injection of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid unilaterally into the striatum. The striatum lesion was confirmed and correlated with TSPO expression in astrocytes and activated microglia by immunohistochemistry and autoradiography. In vivo studies with [(123)I]-CLINME indicated a biodistribution pattern consistent with TPSO distribution and the competition studies with PK11195 and Ro 5-4864 showed that [(123)I]-CLINME is selective for this site. The metabolite study showed that the extractable radioactivity was unchanged [(123)I]-CLINME in organs which expresses TSPO. SPECT/CT imaging on the unilateral excitotoxic lesion indicated that the mean ratio uptake in striatum (lesion:nonlesion) was 2.2. Moreover, TSPO changes observed by SPECT imaging were confirmed by immunofluorescence, immunochemistry, and autoradiography. These results indicated that [(123)I]-CLINME is a promising candidate for the quantification and visualization of TPSO expression in activated astroglia using SPECT.
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Affiliation(s)
- F. Mattner
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
- Department of Molecular Imaging, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia
| | - M. Quinlivan
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - I. Greguric
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - T. Pham
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - X. Liu
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - T. Jackson
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - P. Berghofer
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - C. J. R. Fookes
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - B. Dikic
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - M.-C. Gregoire
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - F. Dolle
- CEA, DSV/I2BM, Service Hospitalier Frédéric Joliot, 4 Place du Général Leclerc, 91401 Orsay, France
| | - A. Katsifis
- Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
- Department of Molecular Imaging, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia
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Liu G, Middleton RJ, Hatty CR, Kam WW, Chan R, Pham T, Harrison‐Brown M, Dodson E, Veale K, Banati RB. The 18 kDa translocator protein, microglia and neuroinflammation. Brain Pathol 2014; 24:631-53. [PMID: 25345894 PMCID: PMC8029074 DOI: 10.1111/bpa.12196] [Citation(s) in RCA: 166] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 08/19/2014] [Indexed: 12/17/2022] Open
Abstract
The 18 kDa translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, is expressed in the injured brain. It has become known as an imaging marker of "neuroinflammation" indicating active disease, and is best interpreted as a nondiagnostic biomarker and disease staging tool that refers to histopathology rather than disease etiology. The therapeutic potential of TSPO as a drug target is mostly based on the understanding that it is an outer mitochondrial membrane protein required for the translocation of cholesterol, which thus regulates the rate of steroid synthesis. This pivotal role together with the evolutionary conservation of TSPO has underpinned the belief that any loss or mutation of TSPO should be associated with significant physiological deficits or be outright incompatible with life. However, against prediction, full Tspo knockout mice are viable and across their lifespan do not show the phenotype expected if cholesterol transport and steroid synthesis were significantly impaired. Thus, the "translocation" function of TSPO remains to be better substantiated. Here, we discuss the literature before and after the introduction of the new nomenclature for TSPO and review some of the newer findings. In light of the controversy surrounding the function of TSPO, we emphasize the continued importance of identifying compounds with confirmed selectivity and suggest that TSPO expression is analyzed within specific disease contexts rather than merely equated with the reified concept of "neuroinflammation."
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Affiliation(s)
- Guo‐Jun Liu
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Ryan J. Middleton
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
| | - Claire R. Hatty
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Winnie Wai‐Ying Kam
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Ronald Chan
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Tien Pham
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
| | - Meredith Harrison‐Brown
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Eoin Dodson
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
| | - Kelly Veale
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Richard B. Banati
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
- National Imaging Facility and Ramaciotti Brain Imaging CentreSydneyNSWAustralia
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Andersson JD, Halldin C. PET radioligands targeting the brain GABAA/benzodiazepine receptor complex. J Labelled Comp Radiopharm 2013; 56:196-206. [DOI: 10.1002/jlcr.3008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 11/15/2012] [Accepted: 11/16/2012] [Indexed: 11/09/2022]
Affiliation(s)
- Jan D. Andersson
- Department of Clinical Neuroscience; Center for Psychiatric Research and Education, Karolinska Institutet; Stockholm; Sweden
| | - Christer Halldin
- Department of Clinical Neuroscience; Center for Psychiatric Research and Education, Karolinska Institutet; Stockholm; Sweden
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Grimwood S, Hartig PR. Target site occupancy: Emerging generalizations from clinical and preclinical studies. Pharmacol Ther 2009; 122:281-301. [DOI: 10.1016/j.pharmthera.2009.03.002] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Accepted: 03/04/2009] [Indexed: 01/17/2023]
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Wegner F, Deuther-Conrad W, Scheunemann M, Brust P, Fischer S, Hiller A, Diekers M, Strecker K, Wohlfarth K, Allgaier C, Steinbach J, Hoepping A. GABAA receptor pharmacology of fluorinated derivatives of the novel sedative-hypnotic pyrazolopyrimidine indiplon. Eur J Pharmacol 2008; 580:1-11. [DOI: 10.1016/j.ejphar.2007.10.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 10/08/2007] [Accepted: 10/15/2007] [Indexed: 10/22/2022]
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Fischer S, Hiller A, Scheunemann M, Deuther-Conrad W, Hoepping A, Diekers M, Wegner F, Brust P, Steinbach J. Radiosynthesis of novel18F-labelled derivatives of indiplon as potential GABAA receptor imaging tracers for PET. J Labelled Comp Radiopharm 2008. [DOI: 10.1002/jlcr.1473] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Pharmacological evaluation of [123I]-CLINDE: a radioiodinated imidazopyridine-3-acetamide for the study of peripheral benzodiazepine binding sites (PBBS). Eur J Nucl Med Mol Imaging 2007; 35:779-89. [PMID: 18057934 DOI: 10.1007/s00259-007-0645-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Accepted: 10/23/2007] [Indexed: 10/22/2022]
Abstract
PURPOSE The study aims to evaluate the iodinated imidazopyridine, N',N'-diethyl-6-Chloro-(4'-[(123)I]iodophenyl)imidazo[1,2-a]pyridine-3-acetamide ([(123)I]-CLINDE) as a tracer for the study of peripheral benzodiazepine binding sites (PBBS). MATERIALS AND METHODS In vitro studies were performed using membrane homogenates and sections from kidney, adrenals, and brain cortex of Sprague-Dawley (SD) rats and incubated with [(123)I]-CLINDE. For in vivo studies, the rats were injected with [(123)I]-CLINDE. In competition studies, PBBS-specific drugs PK11195 and Ro 5-4864 and the CBR specific drug Flumazenil were injected before the radiotracer. RESULTS In vitro binding studies in adrenal, kidney, and cortex mitochondrial membranes indicated that [(123)I]-CLINDE binds with high affinity to PBBS, K(d) = 12.6, 0.20, and 3.84 nM, respectively. The density of binding sites was 163, 5.3, and 0.34 pmol/mg protein, respectively. In vivo biodistribution indicated high uptake in adrenals (5.4), heart (1.5), lungs (1.5), kidney (1.5) %ID/g at 6 h p.i. In the central nervous system (CNS), the olfactory bulbs displayed the highest uptake; up to six times the activity in blood. Pre-administration of unlabeled CLINDE, PK11195 and Ro 5-4864 (1 mg/kg) reduced the uptake of [(123)I]-CLINDE by 70-55% in olfactory bulbs. In the kidney and heart, a reduction of 60-80% ID/g was observed, while an increase was observed in the adrenals requiring 10 mg/kg for significant displacement. Flumazenil had no effect on uptake in peripheral organs and brain. Metabolite analysis indicated >90% of the radioactivity in the above tissues was intact [(123)I]-CLINDE. CONCLUSION [(123)I]-CLINDE displays high and selective uptake for the PBBS and warrants further development as a probe for imaging PBBS using single photon emission computed tomography (SPECT).
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Hoepping A, Scheunemann M, Fischer S, Deuther-Conrad W, Hiller A, Wegner F, Diekers M, Steinbach J, Brust P. Radiosynthesis and biological evaluation of an 18F-labeled derivative of the novel pyrazolopyrimidine sedative-hypnotic agent indiplon. Nucl Med Biol 2007; 34:559-70. [PMID: 17591556 DOI: 10.1016/j.nucmedbio.2007.03.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2007] [Revised: 03/19/2007] [Accepted: 03/27/2007] [Indexed: 11/17/2022]
Abstract
INTRODUCTION Gamma amino butyric acid type A (GABA(A)) receptors are involved in a variety of neurological and psychiatric diseases, which have promoted the development and use of radiotracers for positron emission tomography imaging. Radiolabeled benzodiazepine antagonists such as flumazenil have most extensively been used for this purpose so far. Recently, the non-benzodiazepine pyrazolopyrimidine derivative indiplon with higher specificity for the alpha(1) subtype of the GABA(A) receptor has been introduced for treatment of insomnia. The aim of this study was the development and biological evaluation of an (18)F-labeled derivative of indiplon. METHODS Both [(18)F]fluoro-indiplon and its labeling precursor were synthesized by two-step procedures starting from indiplon. The radiosynthesis of [(18)F]fluoro-indiplon was performed using the bromoacetyl precursor followed by multiple-stage purification using semipreparative HPLC and solid phase extraction. Stability, partition coefficients, binding affinities and regional brain binding were determined in vitro. Biodistribution and radiotracer metabolism were studied in vivo. RESULTS [(18)F]Fluoro-indiplon was readily accessible in good yields (38-43%), with high purity and high specific radioactivity (>150 GBq/micromol). It displays high in vitro stability and moderate lipophilicity. [(18)F]Fluoro-indiplon has an affinity to GABA(A) receptors comparable to indiplon (K(i)=8.0 nM vs. 3.4 nM). In vitro autoradiography indicates high [(18)F]fluoro-indiplon binding in regions with high densities of GABA(A) receptors. However, ex vivo autoradiography and organ distribution studies show no evidence of specific binding of [(18)F]fluoro-indiplon. Furthermore, the radiotracer is rapidly metabolized with high accumulation of labeled metabolites in the brain. CONCLUSIONS Although [(18)F]fluoro-indiplon shows good in vitro features, it is not suitable for in vivo imaging studies because of its metabolism. Structural modifications are needed to develop derivatives with higher in vivo stability.
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Homes TP, Mattner F, Keller PA, Katsifis A. Synthesis and in vitro binding of N,N-dialkyl-2-phenylindol-3-yl-glyoxylamides for the peripheral benzodiazepine binding sites. Bioorg Med Chem 2006; 14:3938-46. [PMID: 16480880 DOI: 10.1016/j.bmc.2006.01.039] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2005] [Revised: 01/16/2006] [Accepted: 01/20/2006] [Indexed: 11/16/2022]
Abstract
A series of N,N-dialkyl-2-phenylindol-3-ylglyoxylamides bearing the halogens iodine and bromine were synthesised and their binding affinity for the peripheral benzodiazepine binding sites (PBBS) in rat kidney mitochondrial membranes was evaluated using [(3)H]PK11195. Central benzodiazepine receptor (CBR) affinities were also evaluated in rat cortices using [(3)H]flumazenil to determine their selectivity for PBBS over CBR. The tested compounds had PBBS binding affinities (IC(50)) ranging from 7.86 to 618 nM, with all compounds showing high selectivity over the CBR (CBR IC(50) > 5000 nM). Among the 12 compounds tested, those with a diethylamide group were the most potent. The highest affinity iodinated PBBS ligand, N,N-diethyl-[5-chloro-2-(4-iodophenyl)indol-3-yl]glyoxylamide, was radiolabelled with iodine-123. This high affinity and selective radioligand may be useful for imaging neurodegeneration, inflammation and tumours using single photon emission computed tomography.
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Affiliation(s)
- Taryn P Homes
- Department of Chemistry, University of Wollongong, NSW 2500, Wollongong, Australia
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Mattner F, Mardon K, Loc'h C, Katsifis A. Pharmacological evaluation of an [(123)I] labelled imidazopyridine-3-acetamide for the study of benzodiazepine receptors. Life Sci 2006; 79:287-94. [PMID: 16464478 DOI: 10.1016/j.lfs.2006.01.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Revised: 11/30/2005] [Accepted: 01/05/2006] [Indexed: 10/25/2022]
Abstract
In vitro binding of the iodinated imidazopyridine, N',N'-dimethyl-6-methyl-(4'-[(123)I]iodophenyl)imidazo[1,2-a]pyridine-3-acetamide [(123)I]IZOL to benzodiazepine binding sites on brain cortex, adrenal and kidney membranes is reported. Saturation experiments showed that [(123)I]IZOL, bound to a single class of binding site (n(H)=0.99) on adrenal and kidney mitochondrial membranes with a moderate affinity (K(d)=30 nM). The density of binding sites was 22+/-6 and 1.2+/-0.4 pmol/mg protein on adrenal and kidney membranes, respectively. No specific binding was observed in mitochondrial-synaptosomal membranes of brain cortex. In biodistribution studies in rats, the highest uptake of [(123)I]IZOL was found 30 min post injection in adrenals (7.5% ID/g), followed by heart, kidney, lung (1% ID/g) and brain (0.12% ID/g), consistent with the distribution of peripheral benzodiazepine binding sites. Pre-administration of unlabelled IZOL and the specific PBBS drugs, PK 11195 and Ro 5-4864 significantly reduced the uptake of [(123)I]IZOL by 30% (p<0.05) in olfactory bulbs and by 51-86% (p<0.01) in kidney, lungs, heart and adrenals, while it increased by 30% to 50% (p<0.01) in the rest of the brain and the blood. Diazepam, a mixed CBR-PBBS drug, inhibited the uptake in kidney, lungs, heart, adrenals and olfactory bulbs by 32% to 44% (p<0.01) but with no effect on brain uptake and in blood concentration. Flumazenil, a central benzodiazepine drug and haloperidol (dopamine antagonist/sigma receptor drug) displayed no effect in [(123)I]IZOL in peripheral organs and in the brain. [(123)I]IZOL may deserve further development for imaging selectively peripheral benzodiazepine binding sites.
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Affiliation(s)
- Filomena Mattner
- Radiopharmaceuticals Research Institute, Australian Nuclear Science and Technology Organisation, PMB 1 Menai N.S.W. 2234, Sydney, Australia.
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Rowlett JK, Cook JM, Duke AN, Platt DM. Selective antagonism of GABAA receptor subtypes: an in vivo approach to exploring the therapeutic and side effects of benzodiazepine-type drugs. CNS Spectr 2005; 10:40-8. [PMID: 15618946 DOI: 10.1017/s1092852900009895] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Benzodiazepines (BZs) are clinically used as anxiolytic, hypnotic, anticonvulsant, and antispasmodic drugs. Research using transgenic mouse models has suggested that the effects of BZs involve multiple subtypes of the gamma-aminobutyric acid type A (GABAA) receptor, identified by specific a subunits (alpha1, alpha2, alpha3, alpha5). This review discusses the experimental uses of b-carboline-3-carboxylate-t-butyl ester (betaCCT), a drug that binds preferentially to the GABAA alpha1 subtype but exerts no action (ie, is a pharmacologic antagonist at the GABAA alpha1 subtype receptor). betaCCT blocks the anxiolytic-like effects of BZs, although studies in primates suggests this antagonism may reflect multiple receptor populations. betaCCT antagonized the ataxic but not muscle relaxant effects of BZs, a finding that implicates the GABAA alpha1 subtype receptor in ataxia but not muscle relaxation. The potential clinical utility of betaCCT is discussed, both in terms of treatment (ie, hepatic encephalopathy) and as a diagnostic imaging agent. Altogether, these results indicate that subtype-selective antagonists represent a useful approach to studying receptor mechanisms underlying the behavioral effects of BZ-type drugs.
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Affiliation(s)
- James K Rowlett
- Department of Psychiatry and Division of Behavioral Biology, Harvard Medical School, New England Primate Research Center, One Pine Hill Drive, Southborough, MA 01772, USA.
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