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Knippenberg N, Bauwens M, Schijns O, Hoogland G, Florea A, Rijkers K, Cleij TJ, Eersels K, van Grinsven B, Diliën H. Visualizing GABA transporters in vivo: an overview of reported radioligands and future directions. EJNMMI Res 2023; 13:42. [PMID: 37171631 PMCID: PMC10182260 DOI: 10.1186/s13550-023-00992-5] [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: 03/23/2023] [Accepted: 05/02/2023] [Indexed: 05/13/2023] Open
Abstract
By clearing GABA from the synaptic cleft, GABA transporters (GATs) play an essential role in inhibitory neurotransmission. Consequently, in vivo visualization of GATs can be a valuable diagnostic tool and biomarker for various psychiatric and neurological disorders. Not surprisingly, in recent years several research attempts to develop a radioligand have been conducted, but so far none have led to suitable radioligands that allow imaging of GATs. Here, we provide an overview of the radioligands that were developed with a focus on GAT1, since this is the most abundant transporter and most of the research concerns this GAT subtype. Initially, we focus on the field of GAT1 inhibitors, after which we discuss the development of GAT1 radioligands based on these inhibitors. We hypothesize that the radioligands developed so far have been unsuccessful due to the zwitterionic nature of their nipecotic acid moiety. To overcome this problem, the use of non-classical GAT inhibitors as basis for GAT1 radioligands or the use of carboxylic acid bioisosteres may be considered. As the latter structural modification has already been used in the field of GAT1 inhibitors, this option seems particularly viable and could lead to the development of more successful GAT1 radioligands in the future.
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Affiliation(s)
- Niels Knippenberg
- Sensor Engineering Department, Faculty of Science and Engineering, Maastricht University, 6200 MD, Maastricht, The Netherlands.
| | - Matthias Bauwens
- Department of Nuclear Medicine, University Hospital Aachen, RWTH Aachen University, 52074, Aachen, Germany
- Department of Radiology and Nuclear Medicine, Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
| | - Olaf Schijns
- Department of Neurosurgery, Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
- School for Mental Health and Neuroscience (MHeNS), Maastricht University, 6200 MD, Maastricht, The Netherlands
- Academic Center for Epileptology (ACE), Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
| | - Govert Hoogland
- Department of Neurosurgery, Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
- School for Mental Health and Neuroscience (MHeNS), Maastricht University, 6200 MD, Maastricht, The Netherlands
| | - Alexandru Florea
- Department of Nuclear Medicine, University Hospital Aachen, RWTH Aachen University, 52074, Aachen, Germany
- Department of Radiology and Nuclear Medicine, Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
- School for Cardiovascular Diseases (CARIM), Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
| | - Kim Rijkers
- Department of Neurosurgery, Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
- School for Mental Health and Neuroscience (MHeNS), Maastricht University, 6200 MD, Maastricht, The Netherlands
- Academic Center for Epileptology (ACE), Maastricht University Medical Centre+ (MUMC+), 6229 HX, Maastricht, The Netherlands
| | - Thomas J Cleij
- Sensor Engineering Department, Faculty of Science and Engineering, Maastricht University, 6200 MD, Maastricht, The Netherlands
| | - Kasper Eersels
- Sensor Engineering Department, Faculty of Science and Engineering, Maastricht University, 6200 MD, Maastricht, The Netherlands
| | - Bart van Grinsven
- Sensor Engineering Department, Faculty of Science and Engineering, Maastricht University, 6200 MD, Maastricht, The Netherlands
| | - Hanne Diliën
- Sensor Engineering Department, Faculty of Science and Engineering, Maastricht University, 6200 MD, Maastricht, The Netherlands
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Sowa AR, Brooks AF, Shao X, Henderson BD, Sherman P, Arteaga J, Stauff J, Lee AC, Koeppe RA, Scott PJH, Kilbourn MR. Development of Positron Emission Tomography Radiotracers for the GABA Transporter 1. ACS Chem Neurosci 2018; 9:2767-2773. [PMID: 29763549 DOI: 10.1021/acschemneuro.8b00183] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In vivo positron emission tomography (PET) imaging of the γ-aminobutyric acid (GABA) receptor complex has been accomplished using radiolabeled benzodiazepine derivatives, but development of specific presynaptic radioligands targeting the neuronal membrane GABA transporter type 1 (GAT-1) has been less successful. The availability of new structure-activity studies of GAT-1 inhibitors and the introduction of a GAT-1 inhibitor (tiagabine, Gabatril) into clinical use prompted us to reinvestigate the syntheses of PET ligands for this transporter. Initial synthesis and rodent PET studies of N-[11C]methylnipecotic acid confirmed the low brain uptake of that small and polar molecule. The common design approach to improve blood-brain barrier permeability of GAT-1 inhibitors is the attachment of a large lipophilic substituent. We selected an unsymmetrical bis-aromatic residue attached to the ring nitrogen by a vinyl ether spacer from a series recently reported by Wanner and coworkers. Nucleophilic aromatic substitution of an aryl chloride precursor with [18F]fluoride was used to prepare the desired candidate radiotracer ( R, E/ Z)-1-(2-((4-fluoro-2-(4-[18F]fluorobenzoyl)styryl)oxy)ethyl)piperidine-3-carboxylic acid (( R, E/ Z)-[18F]10). PET studies in rats showed no brain uptake, which was not altered by pretreatment of animals with the P-glycoprotein inhibitor cyclosporine A, indicating efflux by Pgp was not responsible. Subsequent PET imaging studies of ( R, E/ Z)-[18F]10 in rhesus monkey brain showed very low brain uptake. Finally, to test if the free carboxylic acid group was the likely cause of poor brain uptake, PET studies were done using the ethyl ester derivative of ( R, E/ Z)-[18F]10. Rapid and significant monkey brain uptake of the ester was observed, followed by a slow washout over 90 min. The blood-brain barrier permeability of the ester supports a hypothesis that the free acid function limits brain uptake of nipecotic acid-based GAT-1 radioligands, and future radiotracer efforts should investigate the use of carboxylic acid bioisosteres.
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Affiliation(s)
- Alexandra R. Sowa
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48105, United States
| | - Allen F. Brooks
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Xia Shao
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Bradford D. Henderson
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Philip Sherman
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Janna Arteaga
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Jenelle Stauff
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Adam C. Lee
- E.I. du Pont de Nemours and Company, DuPont Haskell Global Center for Health Sciences, P.O. Box 30, Newark, Delaware 19714, United States
| | - Robert A. Koeppe
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Peter J. H. Scott
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48105, United States
| | - Michael R. Kilbourn
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
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Van Horn JD, Bhattrai A, Irimia A. Multimodal Imaging of Neurometabolic Pathology due to Traumatic Brain Injury. Trends Neurosci 2016; 40:39-59. [PMID: 27939821 DOI: 10.1016/j.tins.2016.10.007] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2016] [Revised: 10/21/2016] [Accepted: 10/25/2016] [Indexed: 12/28/2022]
Abstract
The impact of traumatic brain injury (TBI) involves a combination of complex biochemical processes beginning with the initial insult and lasting for days, months and even years post-trauma. These changes range from neuronal integrity losses to neurotransmitter imbalance and metabolite dysregulation, leading to the release of pro- or anti-apoptotic factors which mediate cell survival or death. Such dynamic processes affecting the brain's neurochemistry can be monitored using a variety of neuroimaging techniques, whose combined use can be particularly useful for understanding patient-specific clinical trajectories. Here, we describe how TBI changes the metabolism of essential neurochemical compounds, summarize how neuroimaging approaches facilitate the study of such alterations, and highlight promising ways in which neuroimaging can be used to investigate post-TBI changes in neurometabolism.
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Affiliation(s)
- John Darrell Van Horn
- USC Mark and Mary Stevens Neuroimaging and Informatics Institute, 2025 Zonal Avenue, Keck School of Medicine of USC, University of Southern California, Los Angeles, California 90033, USA.
| | - Avnish Bhattrai
- USC Mark and Mary Stevens Neuroimaging and Informatics Institute, 2025 Zonal Avenue, Keck School of Medicine of USC, University of Southern California, Los Angeles, California 90033, USA
| | - Andrei Irimia
- USC Mark and Mary Stevens Neuroimaging and Informatics Institute, 2025 Zonal Avenue, Keck School of Medicine of USC, University of Southern California, Los Angeles, California 90033, USA
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