1
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Giladi M, Montgomery AP, Kassiou M, Danon JJ. Structure-based drug design for TSPO: Challenges and opportunities. Biochimie 2024:S0300-9084(24)00120-2. [PMID: 38782353 DOI: 10.1016/j.biochi.2024.05.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Revised: 04/27/2024] [Accepted: 05/21/2024] [Indexed: 05/25/2024]
Abstract
The translocator protein 18 kDa (TSPO) is an evolutionarily conserved mitochondrial transmembrane protein implicated in various neuropathologies and inflammatory conditions, making it a longstanding diagnostic and therapeutic target of interest. Despite the development of various classes of TSPO ligand chemotypes, and the elucidation of bacterial and non-human mammalian experimental structures, many unknowns exist surrounding its differential structural and functional features in health and disease. There are several limitations associated with currently used computational methodologies for modelling the native structure and ligand-binding behaviour of this enigmatic protein. In this perspective, we provide a critical analysis of the developments in the uses of these methods, outlining their uses, inherent limitations, and continuing challenges. We offer suggestions of unexplored opportunities that exist in the use of computational methodologies which offer promise for enhancing our understanding of the TSPO.
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Affiliation(s)
- Mia Giladi
- School of Chemistry, The University of Sydney, 2050, Sydney, NSW, Australia
| | | | - Michael Kassiou
- School of Chemistry, The University of Sydney, 2050, Sydney, NSW, Australia.
| | - Jonathan J Danon
- School of Chemistry, The University of Sydney, 2050, Sydney, NSW, Australia.
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2
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Chen H, Jiang Z, Cheng X, Zheng W, Sun Y, Yu Z, Yang T, Zhang L, Yan J, Liu Y, Ji X, Wu Z. [ 18F]BIBD-239: 18F-Labeled ER176, a Positron Emission Tomography Tracer Specific for the Translocator Protein. Mol Pharm 2022; 19:2351-2366. [PMID: 35671264 DOI: 10.1021/acs.molpharmaceut.2c00157] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
[11C]ER176 has adequate sensitivity to image the human brain translocator protein (TSPO) in all three genotypes by positron emission tomography (PET). However, its clinical application is limited by the short half-life of 11C (20.38 min). To overcome the deficiency of [11C]ER176 and keep the pharmacophore features of ER176 to the maximum extent, we designed four fluorine-labeled ER176 derivatives using the deuterium method. In vitro competition binding confirmed that the designed compounds had high affinity for TSPO. Biodistribution experiments showed that tissues with high expression of TSPO had high uptake of these compounds, as well as that the compound showed high brain penetration and mild defluorination in vivo. Therefore, [18F]BIBD-239 with simple synthesis conditions was selected for further biological evaluation. Theoretical simulations showed that BIBD-239 and ER176 have similar binding modes and sites to Ala147-TSPO and Thr147-TSPO, which indicated that the tracers may have consistent sensitivity to the three affinity genotypes. In vitro autoradiography and in vivo PET studies of the ischemic rat brain showed dramatically higher uptake of [18F]BIBD-239 on the lesion site compared to the contralateral side with good brain kinetics. Additionally, [18F]BIBD-239 provided clear tumor PET images in a GL261 glioma model. Importantly, PET imaging and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) results showed that in vivo defluorination and other metabolites of [18F]BIBD-239 did not interfere with brain imaging. Conclusively, [18F]BIBD-239, similar to ER176 with low polymorphism sensitivity, has simple labeling conditions, high labeling yield, high affinity, and high specificity for TSPO, and it is planned for further evaluation in higher species.
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Affiliation(s)
- Hualong Chen
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Zeng Jiang
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Xuebo Cheng
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Wei Zheng
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Yuli Sun
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Ziyue Yu
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Tingyu Yang
- School of Pharmaceutical Science, Capital Medical University, Beijing 100069, China
| | - Lu Zhang
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Jun Yan
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
| | - Yajing Liu
- School of Pharmaceutical Science, Capital Medical University, Beijing 100069, China
| | - Xunming Ji
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China.,Institute of Hypoxia Medicine, Xuanwu Hospital, Capital Medical University, Beijing 100053, China
| | - Zehui Wu
- Beijing Institute of Brain Disorders, Laboratory of Brain Disorders, Ministry of Science and Technology, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing 100069, China
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3
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Adhikari A, Pandey A, Kumar D, Tiwari AK. Determination of Hybrid TSPO Ligands with Minimal Impact of SNP
(rs6971) through Molecular Docking and MD Simulation Study. LETT DRUG DES DISCOV 2022. [DOI: 10.2174/1570180818666210413130326] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Background:
In an endeavor to ascertain high-affinity TSPO ligands with minimal single
nucleotide polymorphism (SNP), six hybrid molecules have been identified as new leads for future
inflammation PET imaging.
Objective:
Genesis for chemical design was encouraged from structural families of well-known ligands
FEBMP and PBR28/ DAA1106 that have demonstrated remarkable TSPO binding characteristics.
Methods:
All proposed hybrid ligands 1-6 are subjected to molecular docking and simulation studies
with wild and mutant protein to study their interactions, binding, consistency of active conformations
and are correlated with well-established TSPO ligands.
Results:
Each hybrid ligand demonstrate better docking score > -11.00 kcal/mol with TSPO with
respect to gold standard PK11195, i.e., -11.00 kcal/mol for 4UC3 and -12.94 kcal/mol for 4UC1. On
comparison with FEBMP and GE-180 (-12.57, -7.24 kcal/mol for 4UC3 and -14.10, -11.32
kcal/mol for 4UC1), ligand 3 demonstrates maximum docking energy (> -15.50 kcal/mol) with
minimum SNP (0.26 kcal/mol).
Discussion:
Presence of strong hydrogen bond Arg148-3.27Å (4UC1) and Trp50-2.43Å, Asp28-
2.57Å (4UC3) apart from short-range interactions, including π–π interactions with the aromatic residues,
such as (Trp39, Phe46, Trp135) and (Trp39, Trp108), attributes towards its strong binding.
Conclusion:
Utilizing the results of binding energy, we concluded stable complex formation of these
hybrid ligands that could bind to TSPO with the least effect of SNP with similar interactions to
known ligands. Overall, ligand 3 stands out as the best ligand having insignificant deviations per
residue of protein that can be further explored and assessed in detail for future inflammation PET
application after subsequent detailed biological evaluation.
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Affiliation(s)
- Anupriya Adhikari
- Department of Chemistry, Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh, India
| | - Anwesh Pandey
- Department of
Physics, Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh, India
| | - Devesh Kumar
- Department of
Physics, Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh, India
| | - Anjani K. Tiwari
- Department of Chemistry, Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh, India
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Lee SH, Denora N, Laquintana V, Mangiatordi GF, Lopedota A, Lopalco A, Cutrignelli A, Franco M, Delre P, Song IH, Kim HW, Kim SB, Park HS, Kim K, Lee SY, Youn H, Lee BC, Kim SE. Radiosynthesis and characterization of [ 18F]BS224: a next-generation TSPO PET ligand insensitive to the rs6971 polymorphism. Eur J Nucl Med Mol Imaging 2021; 49:110-124. [PMID: 34783879 PMCID: PMC8712300 DOI: 10.1007/s00259-021-05617-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 11/03/2021] [Indexed: 01/03/2023]
Abstract
PURPOSE Translocator protein 18-kDa (TSPO) positron emission tomography (PET) is a valuable tool to detect neuroinflammed areas in a broad spectrum of neurodegenerative diseases. However, the clinical application of second-generation TSPO ligands as biomarkers is limited because of the presence of human rs6971 polymorphism that affects their binding. Here, we describe the ability of a new TSPO ligand, [18F]BS224, to identify abnormal TSPO expression in neuroinflammation independent of the rs6971 polymorphism. METHODS An in vitro competitive inhibition assay of BS224 was conducted with [3H]PK 11195 using membrane proteins isolated from 293FT cells expressing TSPO-wild type (WT) or TSPO-mutant A147T (Mut), corresponding to a high-affinity binder (HAB) and low-affinity binder (LAB), respectively. Molecular docking was performed to investigate the interaction of BS224 with the binding sites of rat TSPO-WT and TSPO-Mut. We synthesized a new 18F-labeled imidazopyridine acetamide ([18F]BS224) using boronic acid pinacol ester 6 or iodotoluene tosylate precursor 7, respectively, via aromatic 18F-fluorination. Dynamic PET scanning was performed up to 90 min after the injection of [18F]BS224 to healthy mice, and PET imaging data were obtained to estimate its absorbed doses in organs. To evaluate in vivo TSPO-specific uptake of [18F]BS224, lipopolysaccharide (LPS)-induced inflammatory and ischemic stroke rat models were used. RESULTS BS224 exhibited a high affinity (Ki = 0.51 nM) and selectivity for TSPO. The ratio of IC50 values of BS224 for LAB to that for HAB indicated that the TSPO binding affinity of BS224 has low binding sensitivity to the rs6971 polymorphism and it was comparable to that of PK 11195, which is not sensitive to the polymorphism. Docking simulations showed that the binding mode of BS224 is not affected by the A147T mutation and consequently supported the observed in vitro selectivity of [18F]BS224 regardless of polymorphisms. With optimal radiochemical yield (39 ± 6.8%, decay-corrected) and purity (> 99%), [18F]BS224 provided a clear visible image of the inflammatory lesion with a high signal-to-background ratio in both animal models (BPND = 1.43 ± 0.17 and 1.57 ± 0.37 in the LPS-induced inflammatory and ischemic stroke rat models, respectively) without skull uptake. CONCLUSION Our results suggest that [18F]BS224 may be a promising TSPO ligand to gauge neuroinflammatory disease-related areas in a broad range of patients irrespective of the common rs6971 polymorphism.
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Affiliation(s)
- Sang Hee Lee
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
- Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826 Republic of Korea
| | - Nunzio Denora
- Department of Pharmacy – Drug Sciences, University of Bari “A. Moro”, 70121 Bari, Italy
| | - Valentino Laquintana
- Department of Pharmacy – Drug Sciences, University of Bari “A. Moro”, 70121 Bari, Italy
| | | | - Angela Lopedota
- Department of Pharmacy – Drug Sciences, University of Bari “A. Moro”, 70121 Bari, Italy
| | - Antonio Lopalco
- Department of Pharmacy – Drug Sciences, University of Bari “A. Moro”, 70121 Bari, Italy
| | - Annalisa Cutrignelli
- Department of Pharmacy – Drug Sciences, University of Bari “A. Moro”, 70121 Bari, Italy
| | - Massimo Franco
- Department of Pharmacy – Drug Sciences, University of Bari “A. Moro”, 70121 Bari, Italy
| | - Pietro Delre
- Institute of Crystallography, National Research Council, Via G. Amendola 122/O, 70126 Bari, Italy
- Department of Chemistry, University of Bari “A. Moro”, Via E. Orabona, 4, 70125 Bari, Italy
| | - In Ho Song
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
| | - Hye Won Kim
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
- Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826 Republic of Korea
| | - Su Bin Kim
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
- Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826 Republic of Korea
| | - Hyun Soo Park
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
| | - Kyungmin Kim
- Department of Nuclear Medicine, Seoul National University Hospital, Seoul, 03080 Republic of Korea
- Department of Biomedical Sciences, Seoul National University Graduate School, Seoul, 03080 Republic of Korea
- Laboratory of Molecular Imaging and Therapy, Cancer Research Institute, Seoul National University College of Medicine, Seoul, 03080 Republic of Korea
| | - Seok-Yong Lee
- Department of Nuclear Medicine, Seoul National University Hospital, Seoul, 03080 Republic of Korea
- Department of Biomedical Sciences, Seoul National University Graduate School, Seoul, 03080 Republic of Korea
- Laboratory of Molecular Imaging and Therapy, Cancer Research Institute, Seoul National University College of Medicine, Seoul, 03080 Republic of Korea
| | - Hyewon Youn
- Department of Nuclear Medicine, Seoul National University Hospital, Seoul, 03080 Republic of Korea
- Laboratory of Molecular Imaging and Therapy, Cancer Research Institute, Seoul National University College of Medicine, Seoul, 03080 Republic of Korea
| | - Byung Chul Lee
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
- Center for Nanomolecular Imaging and Innovative Drug Development, Advanced Institutes of Convergence Technology, Suwon, 16229 Republic of Korea
| | - Sang Eun Kim
- Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, 13620 Republic of Korea
- Center for Nanomolecular Imaging and Innovative Drug Development, Advanced Institutes of Convergence Technology, Suwon, 16229 Republic of Korea
- Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826 Republic of Korea
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5
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Danon JJ, Tregeagle DFL, Kassiou M. Adventures in Translocation: Studies of the Translocator Protein (TSPO) 18 kDa. Aust J Chem 2021. [DOI: 10.1071/ch21176] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The 18 kDa translocator protein (TSPO) is an evolutionarily conserved transmembrane protein found embedded in the outer mitochondrial membrane. A secondary target for the benzodiazepine diazepam, TSPO has been a protein of interest for researchers for decades, particularly owing to its well-established links to inflammatory conditions in the central and peripheral nervous systems. It has become a key biomarker for assessing microglial activation using positron emission tomography (PET) imaging in patients with diseases ranging from atherosclerosis to Alzheimer’s disease. This Account describes research published by our group over the past 15 years surrounding the development of TSPO ligands and their use in probing the function of this high-value target.
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6
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Sokias R, Werry EL, Alison Cheng HW, Lloyd JH, Sohler G, Danon JJ, Montgomery AP, Du JJ, Gao Q, Hibbs DE, Ittner LM, Reekie TA, Kassiou M. Tricyclic heterocycles display diverse sensitivity to the A147T TSPO polymorphism. Eur J Med Chem 2020; 207:112725. [DOI: 10.1016/j.ejmech.2020.112725] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 08/02/2020] [Accepted: 08/03/2020] [Indexed: 12/11/2022]
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7
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An update into the medicinal chemistry of translocator protein (TSPO) ligands. Eur J Med Chem 2020; 209:112924. [PMID: 33081988 DOI: 10.1016/j.ejmech.2020.112924] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 10/06/2020] [Accepted: 10/06/2020] [Indexed: 01/16/2023]
Abstract
The Translocator Protein 18 kDa (TSPO) has been discovered in 1977 as an alternative binding site for the benzodiazepine diazepam. It is an evolutionary well-conserved and tryptophan-rich 169-amino acids protein with five alpha helical transmembrane domains stretching the outer mitochondrial membrane, with the carboxyl-terminus in the cytosol and a short amino-terminus in the intermembrane space of mitochondrion. At this level, together with the voltage-dependent anion channel (VDAC) and the adenine nucleotide translocase (ANT), it forms the mitochondrial permeability transition pore (MPTP). TSPO expression is ubiquitary, with higher levels in steroid producing tissues; in the central nervous system, it is mainly expressed in glial cells and in neurons. TSPO is implicated in a variety of fundamental cellular processes including steroidogenesis, heme biosynthesis, mitochondrial respiration, mitochondrial membrane potential, cell proliferation and differentiation, cell life/death balance, oxidative stress. Altered TSPO expression has been found in some pathological conditions. In particular, high TSPO expression levels have been documented in cancer, neuroinflammation, and brain injury. Conversely, low TSPO expression levels have been evidenced in anxiety disorders. Therefore, TSPO is not only an interesting drug target for therapeutic purpose (anticonvulsant, anxiolytic, etc.), but also a valid diagnostic marker of related-diseases detectable by fluorescent or radiolabeled ligands. The aim of this report is to present an update of previous reviews dealing with the medicinal chemistry of TSPO and to highlight the most outstanding advances in the development of TSPO ligands as potential therapeutic or diagnostic tools, especially referring to the last five years.
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8
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Vo SV, Banister SD, Freelander I, Werry EL, Reekie TA, Ittner LM, Kassiou M. Reversing binding sensitivity to A147T translocator protein. RSC Med Chem 2020; 11:511-517. [PMID: 33479652 PMCID: PMC7489257 DOI: 10.1039/c9md00580c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Accepted: 02/22/2020] [Indexed: 11/21/2022] Open
Abstract
The translocator protein (TSPO) is a target for the development of neuroinflammation imaging agents. Clinical translation of TSPO PET ligands, such as [11C]DPA-713, has been hampered by the presence of a common polymorphism (A147T TSPO), at which all second-generation TSPO ligands lose affinity. Little is known about what drives binding at A147T compared to WT TSPO. This study aimed to identify moieties in DPA-713, and related derivatives, that influence binding at A147T compared to WT TSPO. We found changes to the nitrogen position and number in the heterocyclic core influences affinity to WT and A147T to a similar degree. Hydrogen bonding groups in molecules with an indole core improve binding at A147T compared to WT, a strategy that generated compounds that possess up to ten-times greater affinity for A147T. These results should inform the future design of compounds that bind both A147T and WT TSPO for use in neuroinflammation imaging.
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Affiliation(s)
- Sophie V Vo
- Faculty of Medicine and Health , The University of Sydney , Sydney , New South Wales 2006 , Australia
| | - Samuel D Banister
- The Lambert Initiative for Cannabinoid Therapeutics , Brain and Mind Centre , The University of Sydney , Camperdown , NSW 2050 , Australia
- School of Chemistry , The University of Sydney , Sydney , New South Wales 2006 , Australia .
| | - Isaac Freelander
- School of Chemistry , The University of Sydney , Sydney , New South Wales 2006 , Australia .
| | - Eryn L Werry
- School of Chemistry , The University of Sydney , Sydney , New South Wales 2006 , Australia .
| | - Tristan A Reekie
- Research School of Chemistry , The Australian National University , Canberra , Australian Capital Territory 2600 , Australia
| | - Lars M Ittner
- Department of Biomedical Sciences , Faculty of Medicine and Health Sciences , Macquarie University , 2 Technology Place , North Ryde , New South Wales 2109 , Australia
| | - Michael Kassiou
- School of Chemistry , The University of Sydney , Sydney , New South Wales 2006 , Australia .
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10
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Cheng HWA, Sokias R, Werry EL, Ittner LM, Reekie TA, Du J, Gao Q, Hibbs DE, Kassiou M. First Nondiscriminating Translocator Protein Ligands Produced from a Carbazole Scaffold. J Med Chem 2019; 62:8235-8248. [DOI: 10.1021/acs.jmedchem.9b00980] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
| | | | | | - Lars M. Ittner
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, 2 Technology Place, North Ryde, New South Wales 2109, Australia
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11
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Recent Developments in TSPO PET Imaging as A Biomarker of Neuroinflammation in Neurodegenerative Disorders. Int J Mol Sci 2019; 20:ijms20133161. [PMID: 31261683 PMCID: PMC6650818 DOI: 10.3390/ijms20133161] [Citation(s) in RCA: 144] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 05/20/2019] [Accepted: 05/20/2019] [Indexed: 12/12/2022] Open
Abstract
Neuroinflammation is an inflammatory response in the brain and spinal cord, which can involve the activation of microglia and astrocytes. It is a common feature of many central nervous system disorders, including a range of neurodegenerative disorders. An overlap between activated microglia, pro-inflammatory cytokines and translocator protein (TSPO) ligand binding was shown in early animal studies of neurodegeneration. These findings have been translated in clinical studies, where increases in TSPO positron emission tomography (PET) signal occur in disease-relevant areas across a broad spectrum of neurodegenerative diseases. While this supports the use of TSPO PET as a biomarker to monitor response in clinical trials of novel neurodegenerative therapeutics, the clinical utility of current TSPO PET radioligands has been hampered by the lack of high affinity binding to a prevalent form of polymorphic TSPO (A147T) compared to wild type TSPO. This review details recent developments in exploration of ligand-sensitivity to A147T TSPO that have yielded ligands with improved clinical utility. In addition to developing a non-discriminating TSPO ligand, the final frontier of TSPO biomarker research requires developing an understanding of the cellular and functional interpretation of the TSPO PET signal. Recent insights resulting from single cell analysis of microglial phenotypes are reviewed.
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12
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Qiao L, Fisher E, McMurray L, Milicevic Sephton S, Hird M, Kuzhuppilly-Ramakrishnan N, Williamson DJ, Zhou X, Werry E, Kassiou M, Luthra S, Trigg W, Aigbirhio FI. Radiosynthesis of (R,S)-[ 18 F]GE387: A Potential PET Radiotracer for Imaging Translocator Protein 18 kDa (TSPO) with Low Binding Sensitivity to the Human Gene Polymorphism rs6971. ChemMedChem 2019; 14:982-993. [PMID: 30900397 PMCID: PMC6563049 DOI: 10.1002/cmdc.201900023] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 02/26/2019] [Indexed: 12/14/2022]
Abstract
Translocator protein (TSPO) is a biomarker of neuroinflammation, which is a hallmark of many neurodegenerative diseases and has been exploited as a positron emission tomography (PET) target. Carbon-11-labelled PK11195 remains the most applied agent for imaging TSPO, despite its short-lived isotope and low brain permeability. Second-generation radiotracers show variance in affinity amongst subjects (low-, mixed-, and high-affinity binders) caused by the genetic polymorphism (rs6971) of the TSPO gene. To overcome these limitations, a new structural scaffold was explored based on the TSPO pharmacophore, and the analogue with a low-affinity binder/high-affinity binder (LAB/HAB) ratio similar (1.2 vs. 1.3) to that of (R)-[11 C]PK11195 was investigated. The synthesis of the reference compound was accomplished in six steps and 9 % overall yield, and the precursor was prepared in eight steps and 8 % overall yield. The chiral separation of the reference and precursor compounds was performed using supercritical fluid chromatography with >95 % ee. The absolute configuration was determined by circular dichroism. Optimisation of reaction conditions for manual radiolabelling revealed acetonitrile as a preferred solvent at 100 °C. Automation of this radiolabelling method provided R and S enantiomers in respective 21.3±16.7 and 25.6±7.1 % decay-corrected yields and molar activities of 55.8±35.6 and 63.5±39.5 GBq μmol-1 (n=3). Injection of the racemic analogue into a healthy rat confirmed passage through the blood-brain barrier.
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Affiliation(s)
- Luxi Qiao
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Emily Fisher
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Lindsay McMurray
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Selena Milicevic Sephton
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Matthew Hird
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Nisha Kuzhuppilly-Ramakrishnan
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - David J Williamson
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Xiouyun Zhou
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
| | - Eryn Werry
- School of Chemistry, The University of Sydney, Building F11, Eastern Avenue, Sydney, NSW, 2006, Australia
| | - Michael Kassiou
- School of Chemistry, The University of Sydney, Building F11, Eastern Avenue, Sydney, NSW, 2006, Australia
| | | | | | - Franklin I Aigbirhio
- Molecular Imaging Chemical Laboratory, Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Biomedical Campus, Cambridge, CB2 0SZ, UK
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