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Marques TR, Natesan S, Rabiner EA, Searle GE, Gunn R, Howes OD, Kapur S. Adenosine A 2A receptor in schizophrenia: an in vivo brain PET imaging study. Psychopharmacology (Berl) 2022; 239:3439-3445. [PMID: 34175983 PMCID: PMC9584985 DOI: 10.1007/s00213-021-05900-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 06/08/2021] [Indexed: 11/24/2022]
Abstract
Adenosine A2A receptors are highly enriched in the basal ganglia system, a region that is functionally implicated in schizophrenia. Preclinical evidence suggests a cross-regulation between adenosine A2A and dopamine D2 receptors in this region and that it is linked to the sensitization of the dopamine system. However, the relationship between A2A receptor availability and schizophrenia has not been directly examined in vivo in patients with this disorder. To investigate, using positron emission tomography (PET), the availability of A2A receptors in patients diagnosed with schizophrenia in comparison to matched healthy controls. A2A receptor availability was measured using the PET tracer [11C]SCH442416. Twelve male patients with chronic schizophrenia were compared to 13 matched healthy subjects. All patients were medicated with antipsychotics and none presented with any motor or extrapyramidal symptoms. Binding potential (BPND), a ratio measure between specific and non-specific tracer uptake, were compared between the groups for the caudate, putamen, accumbens and globus pallidum. There was no differences between A2A receptor binding potential (BPND) of schizophrenia patients in the caudate (p = 0.16), putamen (p = 0.86), accumbens (p = 0.44) and globus pallidum (p = 0.09) to that of matched healthy subjects. There was also no significant correlation between [11C]SCH442416 binding and severity of psychotic symptoms (p = 0.2 to 0.82) or antipsychotic dosage (p = 0.13 to 0.34). By showing that A2A receptor availability in medicated patients with chronic male schizophrenia is not different than in healthy controls, this study does not support the primary role of this receptor in the pathogenesis of schizophrenia.
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Affiliation(s)
- Tiago Reis Marques
- Psychiatric Imaging Group, MRC London Institute of Medical Sciences (LMS), Hammersmith Hospital, Imperial College London, London, UK. .,Psychiatric Imaging Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London, UK. .,Department of Psychosis Studies, Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK.
| | - Sridhar Natesan
- Psychiatric Imaging Group, MRC London Institute of Medical Sciences (LMS), Hammersmith Hospital, Imperial College London, London, UK.,Psychiatric Imaging Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London, UK.,Department of Psychosis Studies, Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK
| | - Eugenii A Rabiner
- Centre for Neuroimaging Sciences, Institute of Psychiatry, King's College London, London, UK.,Centre for Imaging Sciences, London, UK
| | | | | | - Oliver D Howes
- Psychiatric Imaging Group, MRC London Institute of Medical Sciences (LMS), Hammersmith Hospital, Imperial College London, London, UK.,Psychiatric Imaging Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London, UK.,Department of Psychosis Studies, Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK
| | - Shitij Kapur
- Department of Psychosis Studies, Institute of Psychiatry, Psychology and Neuroscience, Kings College London, London, UK
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Chen Y, Goorden MC, Beekman FJ. Convolutional neural network based attenuation correction for 123I-FP-CIT SPECT with focused striatum imaging. Phys Med Biol 2021; 66. [PMID: 34492646 DOI: 10.1088/1361-6560/ac2470] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Accepted: 09/07/2021] [Indexed: 11/12/2022]
Abstract
SPECT imaging with123I-FP-CIT is used for diagnosis of neurodegenerative disorders like Parkinson's disease. Attenuation correction (AC) can be useful for quantitative analysis of123I-FP-CIT SPECT. Ideally, AC would be performed based on attenuation maps (μ-maps) derived from perfectly registered CT scans. Suchμ-maps, however, are most times not available and possible errors in image registration can induce quantitative inaccuracies in AC corrected SPECT images. Earlier, we showed that a convolutional neural network (CNN) based approach allows to estimate SPECT-alignedμ-maps for full brain perfusion imaging using only emission data. Here we investigate the feasibility of similar CNN methods for axially focused123I-FP-CIT scans. We tested our approach on a high-resolution multi-pinhole prototype clinical SPECT system in a Monte Carlo simulation study. Three CNNs that estimateμ-maps in a voxel-wise, patch-wise and image-wise manner were investigated. As the added value of AC on clinical123I-FP-CIT scans is still debatable, the impact of AC was also reported to check in which cases CNN based AC could be beneficial. AC using the ground truthμ-maps (GT-AC) and CNN estimatedμ-maps (CNN-AC) were compared with the case when no AC was done (No-AC). Results show that the effect of using GT-AC versus CNN-AC or No-AC on striatal shape and symmetry is minimal. Specific binding ratios (SBRs) from localized regions show a deviation from GT-AC≤2.5% for all three CNN-ACs while No-AC systematically underestimates SBRs by 13.1%. A strong correlation (r≥0.99) was obtained between GT-AC based SBRs and SBRs from CNN-ACs and No-AC. Absolute quantification (in kBq ml-1) shows a deviation from GT-AC within 2.2% for all three CNN-ACs and of 71.7% for No-AC. To conclude, all three CNNs show comparable performance in accurateμ-map estimation and123I-FP-CIT quantification. CNN-estimatedμ-map can be a promising substitute for CT-basedμ-map.
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Affiliation(s)
- Yuan Chen
- Section Biomedical Imaging, Department of Radiation, Science and Technology, Delft University of Technology, Delft, The Netherlands
| | - Marlies C Goorden
- Section Biomedical Imaging, Department of Radiation, Science and Technology, Delft University of Technology, Delft, The Netherlands
| | - Freek J Beekman
- Section Biomedical Imaging, Department of Radiation, Science and Technology, Delft University of Technology, Delft, The Netherlands.,MILabs B.V., Utrecht, The Netherlands.,Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, The Netherlands
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Zou R, Wang X, Li S, Chan HCS, Vogel H, Yuan S. The role of metal ions in G protein‐coupled receptor signalling and drug discovery. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2021. [DOI: 10.1002/wcms.1565] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Rongfeng Zou
- Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen China
- AlphaMol Science Ltd Shenzhen China
| | - Xueying Wang
- Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen China
| | - Shu Li
- Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen China
| | - H. C. Stephen Chan
- Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen China
| | - Horst Vogel
- Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen China
- AlphaMol Science Ltd Shenzhen China
- Ecole Polytechnique Fédérale de Lausanne (EPFL) Lausanne Switzerland
| | - Shuguang Yuan
- Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen China
- AlphaMol Science Ltd Shenzhen China
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Chu Y, Muller S, Tavares A, Barret O, Alagille D, Seibyl J, Tamagnan G, Marek K, Luk KC, Trojanowski JQ, Lee VMY, Kordower JH. Intrastriatal alpha-synuclein fibrils in monkeys: spreading, imaging and neuropathological changes. Brain 2019; 142:3565-3579. [PMID: 31580415 PMCID: PMC7962904 DOI: 10.1093/brain/awz296] [Citation(s) in RCA: 68] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 07/17/2019] [Accepted: 08/01/2019] [Indexed: 12/29/2022] Open
Abstract
Several studies have demonstrated that intrastriatal injections of fibrillar α-synuclein in rodent brain induced a Parkinson's disease-like propagation of Lewy body pathology with significant nigrostriatal neurodegeneration. This study evaluated the pathological features when exogenous α-synuclein preformed fibrils were injected into the putamen of non-human primates. Eight cynomolgus monkeys received unilateral intraputamen injections of α-synuclein preformed fibrils and four monkeys received sham surgery. Monkeys were assessed with 123I-PE2I single-photon emission computerized tomography scans targeting the dopamine transprter at baseline, 3, 6, 9, 12, and 15 months. Imaging revealed a robust increase in dopamine transporter binding, an effect confirmed by port-mortem immunohistochemical analyses, suggesting that upregulation of dopamine transporter occurs as part of an early pathological process. Histochemistry and immunohistochemistry revealed that α-synuclein preformed fibrils injections into the putamen induced intraneuronal inclusions positive for phosphorylated α-synuclein in ipsilateral substantia nigra and adjacent to the injection site. α-Synuclein inclusions were thioflavin-S-positive suggesting that the inclusions induced by α-synuclein preformed fibrils exhibited pathological properties similar to amyloid-like Lewy body pathology in Parkinson's disease brains. The α-synuclein preformed fibrils resulted in Lewy pathology in the ipsilateral substantia nigra with significant reduction (-29.30%) of dopaminergic neurons as compared with controls. Nigral neurons with α-synuclein inclusions exhibited a phenotypic downregulation of the dopamine markers tyrosine hydroxylase and Nurr1. Taken together, our findings demonstrate that α-synuclein preformed fibrils induce a synucleinopathy in non-human primates with authentic Lewy pathology and nigrostriatal changes indicative of early Parkinson's disease.
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Affiliation(s)
- Yaping Chu
- Department of Neurological Sciences, Rush University Medical Center, Chicago, IL, USA
| | - Scott Muller
- Department of Neurological Sciences, Rush University Medical Center, Chicago, IL, USA
| | | | | | | | - John Seibyl
- Molecular NeuroImaging, LLC New Haven, CT, USA
| | | | - Ken Marek
- Molecular NeuroImaging, LLC New Haven, CT, USA
| | - Kelvin C Luk
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
- Center for Neurodegenerative Disease Research, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
| | - John Q Trojanowski
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
| | - Virginia M Y Lee
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
| | - Jeffrey H Kordower
- Department of Neurological Sciences, Rush University Medical Center, Chicago, IL, USA
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Chen Y, Vastenhouw B, Wu C, Goorden MC, Beekman FJ. Optimized image acquisition for dopamine transporter imaging with ultra-high resolution clinical pinhole SPECT. ACTA ACUST UNITED AC 2018; 63:225002. [DOI: 10.1088/1361-6560/aae76c] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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Vala C, Morley TJ, Zhang X, Papin C, Tavares AAS, Lee HS, Constantinescu C, Barret O, Carroll VM, Baldwin RM, Tamagnan GD, Alagille D. Synthesis and in vivo Evaluation of Fluorine-18 and Iodine-123 Pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine Derivatives as PET and SPECT Radiotracers for Mapping A2A Receptors. ChemMedChem 2016; 11:1936-43. [PMID: 27407017 DOI: 10.1002/cmdc.201600219] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 06/15/2016] [Indexed: 11/06/2022]
Abstract
Imaging agents that target adenosine type 2A (A2A ) receptors play an important role in evaluating new pharmaceuticals targeting these receptors, such as those currently being developed for the treatment of movement disorders like Parkinson's disease. They are also useful for monitoring progression and treatment efficacy by providing a noninvasive tool to map changes in A2A receptor density and function in neurodegenerative diseases. We previously described the successful evaluation of two A2A -specific radiotracers in both nonhuman primates and in subsequent human clinical trials: [(123) I]MNI-420 and [(18) F]MNI-444. Herein we describe the development of both of these radiotracers by selection from a series of A2A ligands, based on the pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine core of preladenant. Each of this series of 16 ligands was found to bind to recombinant human A2A receptor in the low nanomolar range, and of these 16, six were radiolabeled with either fluorine-18 or iodine-123 and evaluated in nonhuman primates. These initial in vivo results resulted in the identification of 7-(2-(4-(4-(2-[(18) F]fluoroethoxy)phenyl)piperazin-1-yl)ethyl)-2-(furan-2-yl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine ([(18) F]MNI-444) and 7-(2-(4-(2-fluoro-4-[(123) I]iodophenyl)piperazin-1-yl)ethyl)-2-(furan-2-yl)-7H-imidazo[1,2-c]pyrazolo[4,3-e]pyrimidin-5-amine ([(123) I]MNI-420) as PET and SPECT radiopharmaceuticals for mapping A2A receptors in brain.
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Affiliation(s)
- Christine Vala
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Thomas J Morley
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA.
| | - Xuechun Zhang
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Caroline Papin
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | | | - H Sharon Lee
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Cristian Constantinescu
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Olivier Barret
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Vincent M Carroll
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Ronald M Baldwin
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - Gilles D Tamagnan
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
| | - David Alagille
- Molecular NeuroImaging, a division of inviCRO, 60 Temple Street, Suite 8B, New Haven, CT, 06510, USA
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Barret O, Hannestad J, Vala C, Alagille D, Tavares A, Laruelle M, Jennings D, Marek K, Russell D, Seibyl J, Tamagnan G. Characterization in humans of 18F-MNI-444, a PET radiotracer for brain adenosine 2A receptors. J Nucl Med 2015; 56:586-91. [PMID: 25698783 DOI: 10.2967/jnumed.114.152546] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 01/26/2015] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED PET with selective adenosine 2A receptor (A2A) radiotracers can be used to study a variety of neurodegenerative and neuropsychiatric disorders in vivo and to support drug-discovery studies targeting A2A. The aim of this study was to describe the first in vivo evaluation of (18)F-MNI-444, a novel PET radiotracer for imaging A2A, in healthy human subjects. METHODS Ten healthy human volunteers were enrolled in this study; 6 completed the brain PET studies and 4 participated in the whole-body PET studies. Arterial blood was collected for invasive kinetic modeling of the brain PET data. Noninvasive methods of data quantification were also explored. Test-retest reproducibility was evaluated in 5 subjects. Radiotracer distribution and dosimetry was determined using serial whole-body PET images acquired over 6 h post-radiotracer injection. Urine samples were collected to calculate urinary excretion. RESULTS After intravenous bolus injection, (18)F-MNI-444 rapidly entered the brain and displayed a distribution consistent with known A2A densities in the brain. Binding potentials ranging from 2.6 to 4.9 were measured in A2A-rich regions, with an average test-retest variability of less than 10%. The estimated whole-body radiation effective dose was approximately 0.023 mSv/MBq. CONCLUSION (18)F-MNI-444 is a useful PET radiotracer for imaging A2A in the human brain. The superior in vivo brain kinetic properties of (18)F-MNI-444, compared with previously developed A2A radiotracers, provide the opportunity to foster global use of in vivo A2A PET imaging in neuroscience research.
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Affiliation(s)
- Olivier Barret
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
| | | | - Christine Vala
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
| | - David Alagille
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
| | | | | | - Danna Jennings
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
| | - Ken Marek
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
| | - David Russell
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
| | - John Seibyl
- Molecular NeuroImaging, LLC, New Haven, Connecticut; and
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Liu CH, Sastre A, Conroy R, Seto B, Pettigrew RI. NIH workshop on clinical translation of molecular imaging probes and technology--meeting report. Mol Imaging Biol 2014; 16:595-604. [PMID: 24833042 PMCID: PMC4161932 DOI: 10.1007/s11307-014-0746-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
A workshop on "Clinical Translation of Molecular Imaging Probes and Technology" was held August 2, 2013 in Bethesda, Maryland, organized and supported by the National Institute of Biomedical Imaging and Bioengineering (NIBIB). This workshop brought together researchers, clinicians, representatives from pharmaceutical companies, molecular probe developers, and regulatory science experts. Attendees met to talk over current challenges in the discovery, validation, and translation of molecular imaging (MI) probes for key clinical applications. Participants also discussed potential strategies to address these challenges. The workshop consisted of 4 sessions, with 14 presentations and 2 panel discussions. Topics of discussion included (1) challenges and opportunities for clinical research and patient care, (2) advances in molecular probe design, (3) current approaches used by industry and pharmaceutical companies, and (4) clinical translation of MI probes. In the presentations and discussions, there were general agreement that while the barriers for validation and translation of MI probes remain high, there are pressing clinical needs and development opportunities for targets in cardiovascular, cancer, endocrine, neurological, and inflammatory diseases. The strengths of different imaging modalities, and the synergy of multimodality imaging, were highlighted. Participants also underscored the continuing need for close interactions and collaborations between academic and industrial partners, and federal agencies in the imaging probe development process.
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Affiliation(s)
- Christina H Liu
- National Institute of Biomedical Imaging and Bioengineering, 6707 Democracy Blvd., Suite 200, Bethesda, MD, 20892, USA,
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Barret O, Hannestad J, Alagille D, Vala C, Tavares A, Papin C, Morley T, Fowles K, Lee H, Seibyl J, Tytgat D, Laruelle M, Tamagnan G. Adenosine 2A receptor occupancy by tozadenant and preladenant in rhesus monkeys. J Nucl Med 2014; 55:1712-8. [PMID: 25082853 DOI: 10.2967/jnumed.114.142067] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED Motor symptoms in Parkinson disease (PD) are caused by a loss of dopamine input from the substantia nigra to the striatum. Blockade of adenosine 2A (A(2A)) receptors facilitates dopamine D(2) receptor function. In phase 2 clinical trials, A(2A) antagonists (istradefylline, preladenant, and tozadenant) improved motor function in PD. We developed a new A(2A) PET radiotracer, (18)F-MNI-444, and used it to investigate the relationship between plasma levels and A(2A) occupancy by preladenant and tozadenant in nonhuman primates (NHP). METHODS A series of 20 PET experiments was conducted in 5 adult rhesus macaques. PET data were analyzed with both plasma-input (Logan graphical analysis) and reference-region-based (simplified reference tissue model and noninvasive Logan graphical analysis) methods. Whole-body PET images were acquired for radiation dosimetry estimates. Human pharmacokinetic parameters for tozadenant and preladenant were used to predict A(2A) occupancy in humans, based on median effective concentration (EC(50)) values estimated from the NHP PET measurements. RESULTS (18)F-MNI-444 regional uptake was consistent with A(2A) receptor distribution in the brain. Selectivity was demonstrated by dose-dependent blocking by tozadenant and preladenant. The specific-to-nonspecific ratio was superior to that of other A(2A) PET radiotracers. Pharmacokinetic modeling predicted that tozadenant and preladenant may have different profiles of A(2A) receptor occupancy in humans. CONCLUSION (18)F-MNI-444 appears to be a better PET radiotracer for A(2A) imaging than currently available radiotracers. Assuming that EC(50) in humans is similar to that in NHP, it appears that tozadenant will provide a more sustained A(2A) receptor occupancy than preladenant in humans at clinically tested doses.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Hsiaoju Lee
- Molecular NeuroImaging, LLC, New Haven, Connecticut
| | - John Seibyl
- Molecular NeuroImaging, LLC, New Haven, Connecticut
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Mishina M, Ishiwata K. Adenosine Receptor PET Imaging in Human Brain. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2014; 119:51-69. [DOI: 10.1016/b978-0-12-801022-8.00002-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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Tavares AAS, Batis JC, Papin C, Jennings D, Alagille D, Russell DS, Vala C, Lee H, Baldwin RM, Zubal IG, Marek KL, Seibyl JP, Barret O, Tamagnan GD. Kinetic modeling, test-retest, and dosimetry of 123I-MNI-420 in humans. J Nucl Med 2013; 54:1760-7. [PMID: 23970369 DOI: 10.2967/jnumed.113.119933] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED In vivo imaging of adenosine 2A receptors (A2A) in the brain has attracted significant interest from the scientific community, because studies have shown that dysregulation of these receptors is implicated in a variety of neurodegenerative and psychiatric disorders, including Parkinson and Huntington diseases. This work aimed to describe the kinetic properties, test-retest results, and dosimetry estimates of (123)I-MNI-420, a SPECT radiotracer for the in vivo imaging of A2A in the brain. METHODS Nine healthy human subjects were enrolled in this study; 7 completed (123)I-MNI-420 brain SPECT studies, and 2 participated in whole-body planar imaging evaluating (123)I-MNI-420 biodistribution and dosimetry. For 3 of the brain SPECT studies, arterial blood was collected for invasive modeling. Noninvasive models were also explored, including Logan graphical analysis and simplified reference tissue models. Test-retest reliability was assessed in 4 subjects. To evaluate radiotracer biodistribution and dosimetry, serial whole-body images were acquired immediately after injection and at selected time points after injection. Urine samples were collected over a period of 21 h to calculate urinary excretion. RESULTS (123)I-MNI-420 rapidly entered the human brain and displayed uptake consistent with known A2A densities. At pseudoequilibrium (reached at 90 min after radiotracer injection), stable target-to-cerebellum ratios of around 1.4-2.0 were determined. Binding potentials around 0.8-1.2 were estimated using different kinetic models and the cerebellum as the reference region. Average test-retest variability in the striatum was 4.8%, 3.5%, and 6.5% for the simplified reference tissue model, Logan graphical analysis, and standardized uptake value ratio methods, respectively. The estimated radiation effective dose determined from whole-body studies was 0.036 mSv/MBq. CONCLUSION The data indicate that (123)I-MNI-420 is a useful SPECT radiotracer for imaging A2A in the brain and has radiation doses that would allow for multiple scans in the same research subject each year. The availability of (123)I-MNI-420 offers the possibility of investigating A2A activity in specific conditions and evaluating drug occupancy for A2A candidate therapeutics.
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