1
|
López-Picón FR, Kirjavainen AK, Forsback S, Takkinen JS, Peters D, Haaparanta-Solin M, Solin O. In vivo characterization of a novel norepinephrine transporter PET tracer [ 18F]NS12137 in adult and immature Sprague-Dawley rats. Am J Cancer Res 2019; 9:11-19. [PMID: 30662550 PMCID: PMC6332804 DOI: 10.7150/thno.29740] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 11/16/2018] [Indexed: 12/31/2022] Open
Abstract
Norepinephrine modulates cognitive processes such as working and episodic memory. Pathological changes in norepinephrine and norepinephrine transporter (NET) function and degeneration of the locus coeruleus produce irreversible impairments within the whole norepinephrine system, disrupting cognitive processes. Monitoring these changes could enhance diagnostic accuracy and support development of novel therapeutic components for several neurodegenerative diseases. Thus, we aimed to develop a straightforward nucleophilic fluorination method with high molar activity for the novel NET radiotracer [18F]NS12137 and to demonstrate the ability of [18F]NS12137 to quantify changes in NET expression. Methods: We applied an 18F-radiolabeling method in which a brominated precursor was debrominated by nucleophilic 18F-fluorination in dimethyl sulfoxide. Radiolabeling was followed by a deprotection step, purification, and formulation of the radiotracer. The [18F]NS12137 brain uptake and distribution were studied with in vivo PET/CT and ex vivo autoradiography using both adult and immature Sprague-Dawley rats because postnatal NET expression peaks at 10-20 days post birth. The NET specificity for the tracer was demonstrated by pretreatment of the animals with nisoxetine, which is well-known to have a high affinity for NET. Results: [18F]NS12137 was successfully synthesized with radiochemical yields of 18.6±5.6%, radiochemical purity of >99%, and molar activity of >500 GBq/μmol at the end of synthesis. The in vivo [18F]NS12137 uptake showed peak standard uptake values (SUV) of over 1.5 (adult) and 2.2 (immature) in the different brain regions. Peak SUV/30 min and peak SUV/60 min ratios were calculated for the different brain regions of the adult and immature rats, with a peak SUV/60 min ratio of more than 4.5 in the striatum of adult rats. As expected, in vivo studies demonstrated uptake of the tracer in brain areas rich in NET, particularly thalamus, neocortex, and striatum, and remarkably also in the locus coeruleus, a quite small volume for imaging with PET. The uptake was significantly higher in immature rats compared to the adult animals. Ex vivo studies using autoradiography showed very strong specific binding in NET-rich areas such as the locus coeruleus and the bed nucleus of the stria terminalis, and high binding in larger grey matter areas such as the neocortex and striatum. The uptake of [18F]NS12137 was dramatically reduced both in vivo and ex vivo by pretreatment with nisoxetine, demonstrating the specificity of binding. Conclusions: [18F]NS12137 was synthesized in good yield and high molar activity and demonstrated the characteristics of a good radiotracer, such as good brain penetration, fast washout, and high specific binding to NET.
Collapse
|
2
|
Kirjavainen AK, Forsback S, López-Picón FR, Marjamäki P, Takkinen J, Haaparanta-Solin M, Peters D, Solin O. 18F-labeled norepinephrine transporter tracer [ 18F]NS12137: radiosynthesis and preclinical evaluation. Nucl Med Biol 2017; 56:39-46. [PMID: 29172120 DOI: 10.1016/j.nucmedbio.2017.10.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 10/11/2017] [Accepted: 10/16/2017] [Indexed: 01/16/2023]
Abstract
INTRODUCTION Several psychiatric and neurodegenerative diseases are associated with malfunction of brain norepinephrine transporter (NET). However, current clinical evaluations of NET function are limited by the lack of sufficiently sensitive methods of detection. To this end, we have synthesized exo-3-[(6-[18F]fluoro-2-pyridyl)oxy]-8-azabicyclo[3.2.1]-octane ([18F]NS12137) as a radiotracer for positron emission tomography (PET) and have demonstrated that it is highly specific for in vivo detection of NET-rich regions of rat brain tissue. METHODS We applied two methods of electrophilic, aromatic radiofluorination of the precursor molecule, exo-3-[(6-trimethylstannyl-2-pyridyl)oxy]-8-azabicyclo-[3.2.1]octane-8-carboxylate: (1) direct labeling with [18F]F2, and (2) labeling with [18F]Selectfluor, a derivative of [18F]F2, using post-target produced [18F]F2. The time-dependent distribution of [18F]NS12137 in brain tissue of healthy, adult Sprague-Dawley rats was determined by ex vivo autoradiography. The specificity of [18F]NS12137 binding was demonstrated on the basis of competitive binding by nisoxetine, a known NET antagonist of high specificity. RESULTS [18F]NS12137 was successfully synthesized with radiochemical yields of 3.9% ± 0.3% when labeled with [18F]F2 and 10.2% ± 2.7% when labeled with [18F]Selectfluor. The molar activity of radiotracer was 8.8 ± 0.7 GBq/μmol with [18F]F2 labeling and 6.9 ± 0.4 GBq/μmol with [18F]Selectfluor labeling at the end of synthesis of [18F]NS12137. Uptake of [18F]NS12137 in NET-rich areas in rat brain was demonstrated with the locus coeruleus (LCoe) having the highest regional uptake. Prior treatment of rats with nisoxetine showed no detectable [18F]NS12137 in the LCoe. Analyses of whole brain samples for radiometabolites showed only the parent compound [18F]NS12137. Uptake of 18F-radioactivity in bone increased with time. CONCLUSIONS The two electrophilic 18F-labeling methods proved to be suitable for synthesis of [18F]NS12137 with the [18F]Selectfluor method providing an approximate three-fold higher yield than the [18F]F2 method. As an electrostatically neutral radiotracer [18F]NS12137 crosses the blood-brain barrier and enabled specific labeling of NET-rich regions of rat brain tissue with the highest concentration in the LCoe.
Collapse
Affiliation(s)
- Anna K Kirjavainen
- Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland.
| | - Sarita Forsback
- Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland; Department of Chemistry, University of Turku, Turku, Finland
| | - Francisco R López-Picón
- Preclinical Imaging, Turku PET Centre, University of Turku, Turku, Finland; Medicity Research Laboratory, University of Turku, Turku, Finland
| | | | - Jatta Takkinen
- Preclinical Imaging, Turku PET Centre, University of Turku, Turku, Finland; Medicity Research Laboratory, University of Turku, Turku, Finland
| | - Merja Haaparanta-Solin
- Preclinical Imaging, Turku PET Centre, University of Turku, Turku, Finland; Medicity Research Laboratory, University of Turku, Turku, Finland
| | - Dan Peters
- DanPET AB, Malmö, Sweden; Neurobiology Research Unit, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Olof Solin
- Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland; Department of Chemistry, University of Turku, Turku, Finland; Accelerator Laboratory, Åbo Akademi University, Turku, Finland
| |
Collapse
|
3
|
Buiter HJ, Windhorst AD, Huisman MC, De Maeyer JH, Schuurkes JA, Lammertsma AA, Leysen JE. Radiosynthesis and preclinical evaluation of [11C]prucalopride as a potential agonist PET ligand for the 5-HT4 receptor. EJNMMI Res 2013; 3:24. [PMID: 23557209 PMCID: PMC3623622 DOI: 10.1186/2191-219x-3-24] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 03/22/2013] [Indexed: 01/05/2023] Open
Abstract
Background Serotonin 5-HT4 receptor (5-HT4-R) agonists are potential therapeutic agents for enterokinetic and cognitive disorders and are marketed for treatment of constipation. The aim of this study was to develop an agonist positron emission tomography (PET) ligand in order to label the active G-protein coupled 5-HT4-R in peripheral and central tissues. For this purpose prucalopride, a high-affinity selective 5-HT4-R agonist, was selected. Methods [11C]Prucalopride was synthesized from [11C]methyl triflate and desmethyl prucalopride, and its LogDoct,pH7.4 was determined. Three distinct studies were performed with administration of IV [11C]prucalopride in male rats: (1) The biodistribution of radioactivity was measured ex vivo; (2) the kinetics of radioactivity levels in brain regions and peripheral organs was assessed in vivo under baseline conditions and following pre-treatment with tariquidar, a P-glycoprotein efflux pump inhibitor; and (3) in vivo stability of [11C]prucalopride was checked ex vivo in plasma and brain extracts using high-performance liquid chromatography. Results [11C]Prucalopride was synthesized in optimised conditions with a yield of 21% ± 4% (decay corrected) and a radiochemical purity (>99%), its LogDoct,pH7.4 was 0.87. Ex vivo biodistribution studies with [11C]prucalopride in rats showed very low levels of radioactivity in brain (maximal 0.13% ID·g−1) and ten times higher levels in certain peripheral tissues. The PET studies confirmed very low brain levels of radioactivity under baseline conditions; however, it was increased three times after pre-treatment with tariquidar. [11C]Prucalopride was found to be very rapidly metabolised in rats, with no parent compound detectable in plasma and brain extracts at 5 and 30 min following IV administration. Analysis of levels of radioactivity in peripheral tissues revealed a distinct PET signal in the caecum, which was reduced following tariquidar pre-treatment. The latter is in line with the role of the P-glycoprotein pump in the gut. Conclusion [11C]Prucalopride demonstrated low radioactivity levels in rat brain; a combination of reasons may include rapid metabolism in the rat in particular, low passive diffusion and potential P-glycoprotein substrate. In humans, further investigation of [11C]prucalopride for imaging the active state of 5-HT4-R is worthwhile, in view of the therapeutic applications of 5-HT4 agonists for treatment of gastrointestinal motility disorders.
Collapse
Affiliation(s)
- Hans Jc Buiter
- Department of Radiology and Nuclear Medicine, VU University Medical Center, PO Box 7057, Amsterdam, MB, 1007, The Netherlands.
| | | | | | | | | | | | | |
Collapse
|
4
|
Buiter HJ, Leysen JE, Schuit RC, Fisher A, Lammertsma AA, Windhorst AD. Radiosynthesis and biological evaluation of the M1 muscarinic acetylcholine receptor agonist ligand [11C]AF150(S). J Labelled Comp Radiopharm 2012. [DOI: 10.1002/jlcr.2932] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Hans J.C. Buiter
- Department of Nuclear Medicine & PET Research; VU University Medical Center; PO Box 7057; 1007 MB; Amsterdam; The Netherlands
| | - Josée E. Leysen
- Department of Nuclear Medicine & PET Research; VU University Medical Center; PO Box 7057; 1007 MB; Amsterdam; The Netherlands
| | - Robert C. Schuit
- Department of Nuclear Medicine & PET Research; VU University Medical Center; PO Box 7057; 1007 MB; Amsterdam; The Netherlands
| | - Abraham Fisher
- Israel Institute for Biological Research; Ness-Ziona; Israel
| | - Adriaan A. Lammertsma
- Department of Nuclear Medicine & PET Research; VU University Medical Center; PO Box 7057; 1007 MB; Amsterdam; The Netherlands
| | - Albert D. Windhorst
- Department of Nuclear Medicine & PET Research; VU University Medical Center; PO Box 7057; 1007 MB; Amsterdam; The Netherlands
| |
Collapse
|
5
|
Zeng F, Mun J, Jarkas N, Stehouwer JS, Voll RJ, Tamagnan GD, Howell L, Votaw JR, Kilts CD, Nemeroff CB, Goodman MM. Synthesis, radiosynthesis, and biological evaluation of carbon-11 and fluorine-18 labeled reboxetine analogues: potential positron emission tomography radioligands for in vivo imaging of the norepinephrine transporter. J Med Chem 2009; 52:62-73. [PMID: 19067522 DOI: 10.1021/jm800817h] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Reboxetine analogues with methyl and fluoroalkyl substituents at position 2 of the phenoxy ring 1-4 were synthesized. In vitro competition binding with [(3)H]nisoxetine demonstrated that 1-4 have a high affinity for the norepinephrine transporter (NET) with K(i)'s = 1.02, 3.14, 3.68, and 0.30 nM, respectively. MicroPET imaging in rhesus monkeys showed that the relative regional distribution of [(11)C]1 and [(11)C]4 is consistent with distribution of the NET in the brain, while [(18)F]2 and [(18)F]3 showed only slight regional differentiation in brain uptake. Especially, the highest ratios of uptake of [(11)C]1 in NET-rich regions to that in caudate were obtained at 1.30-1.45 at 45 min and remained relatively constant over 85 min. Pretreatment of the monkey with the selective NET inhibitor, desipramine, decreased the specific binding for both [(11)C]1 and [(11)C]4. PET imaging in awake monkeys suggested that anesthesia influenced the binding potential of [(11)C]1 and [(11)C]4 at the NET.
Collapse
Affiliation(s)
- Fanxing Zeng
- Department of Radiology, Yerkes Regional Primate Research Center, Emory University, Atlanta, Georgia 30322, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
6
|
|
7
|
Jørgensen AM, Tagmose L, Jørgensen AMM, Bøgesø KP, Peters GH. Molecular dynamics simulations of Na+/Cl(-)-dependent neurotransmitter transporters in a membrane-aqueous system. ChemMedChem 2008; 2:827-40. [PMID: 17436258 DOI: 10.1002/cmdc.200600243] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We have performed molecular dynamics simulations of a homology model of the human serotonin transporter (hSERT) in a membrane environment and in complex with either the natural substrate 5-HT or the selective serotonin reuptake inhibitor escitalopram. We have also included a transporter homologue, the Aquifex aeolicus leucine transporter (LeuT), in our study to evaluate the applicability of a simple and computationally attractive membrane system. Fluctuations in LeuT extracted from simulations are in good agreement with crystallographic B factors. Furthermore, key interactions identified in the X-ray structure of LeuT are maintained throughout the simulations indicating that our simple membrane system is suitable for studying the transmembrane protein hSERT in complex with 5-HT or escitalopram. For these transporter complexes, only relatively small fluctuations are observed in the ligand-binding cleft. Specific interactions responsible for ligand recognition, are identified in the hSERT-5HT and hSERT-escitalopram complexes. Our findings are in good agreement with predictions from mutagenesis studies.
Collapse
Affiliation(s)
- Anne Marie Jørgensen
- MEMPHYS-Center for Biomembrane Physics, Department of Chemistry, Technical University of Denmark, Building 206, 2800 Kgs. Lyngby, Denmark
| | | | | | | | | |
Collapse
|
8
|
Seibyl JP. Single-photon emission computed tomography and positron emission tomography evaluations of patients with central motor disorders. Semin Nucl Med 2008; 38:274-86. [PMID: 18514083 DOI: 10.1053/j.semnuclmed.2008.03.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Neuroimaging biomarkers in movement disorders during the past decade have served as diagnostic agents (Europe), tools for evaluation of novel therapeutics, and a powerful means for describing pathophysiology by revealing in vivo changes at different stages of disease and within the course of an individual patient's illness. As imaging with agents tracking dopaminergic function become more available, the next decade promises to enhance our clinical sophistication in the optimal use of dopaminergic imaging biomarkers for differential diagnosis, characterization of at-risk populations, guiding selection and management of appropriate treatments. The clinical role of these agents as clinical tools goes hand in hand with the development and availability of disease-modifying drugs, which carry the additional requirement for early and accurate diagnosis and improved clinical monitoring once treatment is initiated. Challenges remain in the ideal application of neuroimaging in the clinical algorithms for patient assessment and management. Further, the application of imaging to other targets, both monamineric and nonmonoaminergic, could serve a function beyond the important delineation of pathologic change occurring in patients with Parkinson's disease to suggest some role in improved phenotyping and classification of patients with Parkinson's disease presenting with different symptom clusters. New areas of focus based on the elucidation of mechanisms at the cellular and molecular level, including intense interest in alpha-synuclein and other protein inclusions in neurons and glia, have piqued interest in their in vivo assessment using scinitigraphic methods. Perhaps ultimately, treatment that is targeted to a better delineated pathophysiology-based characterization of movement disorder patients will emerge. The application of neuroimaging biomarkers to multiple ends in movement disorders provides an important model for the multiple roles diagnostic imaging agents can serve in neurodegenerative disorders; for diagnosis, for elaborating pathophysiology in patient populations, for developing new drugs, ultimately for improving clinical management.
Collapse
Affiliation(s)
- John P Seibyl
- Institute for Neurodegenerative Disorders, Molecular Neuroimaging, LLC, Yale University School of Medicine, New Haven, CT, USA.
| |
Collapse
|
9
|
Jørgensen AM, Tagmose L, Jørgensen AMM, Topiol S, Sabio M, Gundertofte K, Bøgesø KP, Peters GH. Homology Modeling of the Serotonin Transporter: Insights into the Primary Escitalopram-binding Site. ChemMedChem 2007; 2:815-26. [PMID: 17405130 DOI: 10.1002/cmdc.200600242] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The serotonin transporter (SERT) is one of the neurotransmitter transporters that plays a critical role in the regulation of endogenous amine concentrations and therefore is an important target for therapeutic agents affecting the central nervous system. The recently published, high resolution X-ray structure of the closely related amino acid transporter, Aquifex aeolicus leucine transporter (LeuT), provides an opportunity to develop a three-dimensional model of the structure of SERT. We present herein a homology model of SERT using LeuT as the template and containing escitalopram as a bound ligand. Our model explains selectivities known from mutational studies and varying ligand data, which are discussed and illustrated in the paper.
Collapse
Affiliation(s)
- Anne Marie Jørgensen
- MEMPHYS-Center for Biomembrane Physics, Department of Chemistry, Technical University of Denmark, Building 206, 2800 Kgs. Lyngby, Denmark
| | | | | | | | | | | | | | | |
Collapse
|
10
|
Logan J, Wang GJ, Telang F, Fowler JS, Alexoff D, Zabroski J, Jayne M, Hubbard B, King P, Carter P, Shea C, Xu Y, Muench L, Schlyer D, Learned-Coughlin S, Cosson V, Volkow ND, Ding YS. Imaging the norepinephrine transporter in humans with (S,S)-[11C]O-methyl reboxetine and PET: problems and progress. Nucl Med Biol 2007; 34:667-79. [PMID: 17707807 DOI: 10.1016/j.nucmedbio.2007.03.013] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 03/03/2007] [Accepted: 03/27/2007] [Indexed: 11/22/2022]
Abstract
UNLABELLED Results from human studies with the PET radiotracer (S,S)-[(11)C]O-methyl reboxetine ([(11)C](S,S)-MRB), a ligand targeting the norepinephrine transporter (NET), are reported. Quantification methods were determined from test/retest studies, and sensitivity to pharmacological blockade was tested with different doses of atomoxetine (ATX), a drug that binds to the NET with high affinity (K(i)=2-5 nM). METHODS Twenty-four male subjects were divided into different groups for serial 90-min PET studies with [(11)C](S,S)-MRB to assess reproducibility and the effect of blocking with different doses of ATX (25, 50 and 100 mg, po). Region-of-interest uptake data and arterial plasma input were analyzed for the distribution volume (DV). Images were normalized to a template, and average parametric images for each group were formed. RESULTS [(11)C](S,S)-MRB uptake was highest in the thalamus (THL) and the midbrain (MBR) [containing the locus coeruleus (LC)] and lowest for the caudate nucleus (CDT). The CDT, a region with low NET, showed the smallest change on ATX treatment and was used as a reference region for the DV ratio (DVR). The baseline average DVR was 1.48 for both the THL and MBR with lower values for other regions [cerebellum (CB), 1.09; cingulate gyrus (CNG) 1.07]. However, more accurate information about relative densities came from the blocking studies. MBR exhibited greater blocking than THL, indicating a transporter density approximately 40% greater than THL. No relationship was found between DVR change and plasma ATX level. Although the higher dose tended to induce a greater decrease than the lower dose for MBR (average decrease for 25 mg=24+/-7%; 100 mg=31+/-11%), these differences were not significant. The different blocking between MBR (average decrease=28+/-10%) and THL (average decrease=17+/-10%) given the same baseline DVR indicates that the CDT is not a good measure for non-NET binding in both regions. Threshold analysis of the difference between the average baseline DV image and the average blocked image showed the expected NET distribution with the MBR (LC) and hypothalamus>THL>CNG and CB, as well as a significant change in the supplementary motor area. DVR reproducibility for the different brain regions was approximately 10%, but intersubject variability was large. CONCLUSIONS The highest density of NETs was found in the MBR where the LC is located, followed by THL, whereas the lowest density was found in basal ganglia (lowest in CDT), consistent with the regional localization of NETs in the nonhuman primate brain. While all three doses of ATX were found to block most regions, no significant differences between doses were found for any region, although the average percent change across subjects of the MBR did correlate with ATX dose. The lack of a dose effect could reflect a low signal-to-noise ratio coupled with the possibility that a sufficient number of transporters were blocked at the lowest dose and further differences could not be detected. However, since the lowest (25 mg) dose is less than the therapeutic doses used in children for the treatment of attention-deficit/hyperactivity disorder ( approximately 1.0 mg/kg/day), this would suggest that there may be additional targets for ATX's therapeutic actions.
Collapse
Affiliation(s)
- Jean Logan
- Medical Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|