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Beaurain M, Talmont F, Pierre D, Péran P, Boucher S, Hitzel A, Rols MP, Cuvillier O, Payoux P, Salabert AS. Pharmacological Characterization of [ 18F]-FNM and Evaluation of NMDA Receptors Activation in a Rat Brain Injury Model. Mol Imaging Biol 2023:10.1007/s11307-023-01811-y. [PMID: 36944798 DOI: 10.1007/s11307-023-01811-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 02/27/2023] [Accepted: 03/01/2023] [Indexed: 03/23/2023]
Abstract
PURPOSE NMDA receptors (NMDARs) dysfunction plays a central role in the physiopathology of psychiatric and neurodegenerative disorders whose mechanisms are still poorly understood. The development of a PET (positron emission tomography) tracer able to selectively bind to the NMDARs intra-channel PCP site may make it possible to visualize NMDARs in an open and active state. We describe the in vitro pharmacological characterization of [18F]-fluoroethylnormemantine ([18F]-FNM) and evaluate its ability to localize activated NMDA receptors in a rat preclinical model of excitotoxicity. PROCEDURES The affinity of the non-radioactive analog for the intra-channel PCP site was determined in a radioligand competition assay using [3H]TCP ([3H]N-(1-[thienyl]cyclohexyl)piperidine) on rat brain homogenates. Selectivity was also investigated by the displacement of specific radioligands targeting various cerebral receptors. In vivo brain lesions were performed using stereotaxic quinolinic acid (QA) injections in the left motor area (M1) of seven Sprague Dawley rats. Each rat was imaged with a microPET/CT camera, 40 min after receiving a dose of 30 MBq + / - 20 of [18F]-FNM, 24 and 72 h after injury. Nine non-injured rats were also imaged using the same protocol. RESULTS FNM displayed IC50 value of 13.0 ± 8.9 µM in rat forebrain homogenates but also showed significant bindings on opioid receptors. In the frontal and left somatosensory areas, [18F]FNM PET detected a mean of 37% and 41% increase in [18F]FNM uptake (p < 0,0001) 24 and 72 h after QA stereotaxic injection, respectively, compared to the control group. CONCLUSIONS In spite of FNM's poor affinity for NMDAR PCP site, this study supports the ability of this tracer to track massive activation of NMDARs in neurological diseases.
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Affiliation(s)
- Marie Beaurain
- Toulouse NeuroImaging Center, ToNIC, UMR1214 Inserm, Toulouse, France.
- Nuclear Medicine Department, Toulouse Purpan University Hospital, Toulouse, France.
| | - Franck Talmont
- Institut de Pharmacologie Et de Biologie Structurale, Université de Toulouse, CNRS, UPS, 31059, Toulouse, France
| | - Damien Pierre
- Toulouse NeuroImaging Center, ToNIC, UMR1214 Inserm, Toulouse, France
| | - Patrice Péran
- Toulouse NeuroImaging Center, ToNIC, UMR1214 Inserm, Toulouse, France
| | - Samuel Boucher
- Toulouse NeuroImaging Center, ToNIC, UMR1214 Inserm, Toulouse, France
| | - Anne Hitzel
- Nuclear Medicine Department, Toulouse Purpan University Hospital, Toulouse, France
| | - Marie-Pierre Rols
- Institut de Pharmacologie Et de Biologie Structurale, Université de Toulouse, CNRS, UPS, 31059, Toulouse, France
| | - Olivier Cuvillier
- Institut de Pharmacologie Et de Biologie Structurale, Université de Toulouse, CNRS, UPS, 31059, Toulouse, France
| | - Pierre Payoux
- Toulouse NeuroImaging Center, ToNIC, UMR1214 Inserm, Toulouse, France
- Nuclear Medicine Department, Toulouse Purpan University Hospital, Toulouse, France
| | - Anne-Sophie Salabert
- Toulouse NeuroImaging Center, ToNIC, UMR1214 Inserm, Toulouse, France
- Nuclear Medicine Department, Toulouse Purpan University Hospital, Toulouse, France
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Salabert AS, Fonta C, Fontan C, Adel D, Alonso M, Pestourie C, Belhadj-Tahar H, Tafani M, Payoux P. Radiolabeling of [18F]-fluoroethylnormemantine and initial in vivo evaluation of this innovative PET tracer for imaging the PCP sites of NMDA receptors. Nucl Med Biol 2015; 42:643-53. [PMID: 25963911 DOI: 10.1016/j.nucmedbio.2015.04.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Revised: 03/19/2015] [Accepted: 04/01/2015] [Indexed: 01/01/2023]
Abstract
INTRODUCTION The N-methyl-D-aspartate receptor (NMDAr) is an ionotropic receptor that mediates excitatory transmission. NMDAr overexcitation is thought to be involved in neurological and neuropsychiatric disorders such as Alzheimer disease and schizophrenia. We synthesized [(18)F]-fluoroethylnormemantine ([(18)F]-FNM), a memantine derivative that binds to phencyclidine (PCP) sites within the NMDA channel pore. These sites are primarily accessible when the channel is in the active and open state. METHODS Radiosynthesis was carried out using the Raytest® SynChrom R&D fluorination module. Affinity of this new compound was determined by competition assay. We ran a kinetic study in rats and computed a time-activity curve based on a volume-of-interest analysis, using CARIMAS® software. We performed an ex vivo autoradiography, exposing frozen rat brain sections to a phosphorscreen. Adjacent sections were used to detect NMDAr by immunohistochemistry with an anti-NR1 antibody. As a control of the specificity of our compound for NMDAr, we used a rat anesthetized with ketamine. Correlation analysis was performed with ImageJ software between signal of autoradiography and immunostaining. RESULTS Fluorination yield was 10.5% (end of synthesis), with a mean activity of 3145 MBq and a specific activity above 355 GBq/μmol. Affinity assessment allowed us to determine [(19)F]-FNM IC50 at 6.1 10(-6)M. [(18)F]-FMN concentration gradually increased in the brain, stabilizing at 40 minutes post injection. The brain-to-blood ratio was 6, and 0.4% of the injected dose was found in the brain. Combined ex vivo autoradiography and immunohistochemical staining demonstrated colocalization of NMDAr and [(18)F]-FNM (r=0.622, p<0.0001). The highest intensity was found in the cortex and cerebellum, and the lowest in white matter. A low and homogeneous signal corresponding to unspecific binding was observed when PCP sites were blocked with ketamine. CONCLUSIONS [(18)F]-FNM appears to be a promising tracer for imaging NMDAr activity for undertaking preclinical studies in perspective of clinical detection of neurological or neuropsychological disorders.
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Affiliation(s)
- Anne-Sophie Salabert
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Radiopharmacy Department, University Hospital, Toulouse, France.
| | - Caroline Fonta
- Research Center for Brain and Cognition, University of Toulouse UPS, Toulouse, France; CerCo, CNRS, Toulouse, France
| | - Charlotte Fontan
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Radiopharmacy Department, University Hospital, Toulouse, France
| | - Djilali Adel
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France
| | - Mathieu Alonso
- Radiopharmacy Department, University Hospital, Toulouse, France
| | | | - Hafid Belhadj-Tahar
- Research and Expertise Group, French Association for the Promotion of Medical Research (AFPREMED), Toulouse, France
| | - Mathieu Tafani
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Radiopharmacy Department, University Hospital, Toulouse, France
| | - Pierre Payoux
- Brain Imaging and Neurological Disability UMR 825, INSERM, F-31059 Toulouse, France; Brain imaging and neurological disability UMR 825, University of Toulouse, UPS, CHU Purpan, Place du Dr Baylac, F-31059 Toulouse Cedex 9, France; Nuclear Medicine Department, University Hospital, Toulouse, France
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