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Biso L, Aringhieri S, Carli M, Scarselli M, Longoni B. Therapeutic Drug Monitoring in Psychiatry: Enhancing Treatment Precision and Patient Outcomes. Pharmaceuticals (Basel) 2024; 17:642. [PMID: 38794212 PMCID: PMC11124530 DOI: 10.3390/ph17050642] [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: 04/12/2024] [Revised: 05/09/2024] [Accepted: 05/14/2024] [Indexed: 05/26/2024] Open
Abstract
Psychiatric disorders often require pharmacological interventions to alleviate symptoms and improve quality of life. However, achieving an optimal therapeutic outcome is challenging due to several factors, including variability in the individual response, inter-individual differences in drug metabolism, and drug interactions in polytherapy. Therapeutic drug monitoring (TDM), by measuring drug concentrations in biological samples, represents a valuable tool to address these challenges, by tailoring medication regimens to each individual. This review analyzes the current landscape of TDM in psychiatric practice, highlighting its significance in optimizing drug dosages, minimizing adverse effects, and improving therapeutic efficacy. The metabolism of psychiatric medications (i.e., mood stabilizers, antipsychotics, antidepressants) often exhibits significant inter-patient variability. TDM can help address this variability by enhancing treatment personalization, facilitating early suboptimal- or toxic-level detection, and allowing for timely interventions to prevent treatment failure or adverse effects. Furthermore, this review briefly discusses technological advancements and analytical methods supporting the implementation of TDM in psychiatric settings. These innovations enable quick and cost-effective drug concentration measurements, fostering the widespread adoption of TDM as a routine practice in psychiatric care. In conclusion, the integration of TDM in psychiatry can improve treatment outcomes by individualizing medication regimens within the so-called precision medicine.
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Affiliation(s)
- Letizia Biso
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, 56126 Pisa, Italy; (L.B.); (M.C.); (M.S.)
| | - Stefano Aringhieri
- Mental Health and Pathological Addiction Department, AUSL Romagna Forlì-Cesena, 47121 Forlì, Italy;
| | - Marco Carli
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, 56126 Pisa, Italy; (L.B.); (M.C.); (M.S.)
| | - Marco Scarselli
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, 56126 Pisa, Italy; (L.B.); (M.C.); (M.S.)
| | - Biancamaria Longoni
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, 56126 Pisa, Italy; (L.B.); (M.C.); (M.S.)
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Fu H, Rong J, Chen Z, Zhou J, Collier T, Liang SH. Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors. J Med Chem 2022; 65:10755-10808. [PMID: 35939391 DOI: 10.1021/acs.jmedchem.2c00633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.
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Affiliation(s)
- Hualong Fu
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Jian Rong
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.,Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Zhen Chen
- Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, International Innovation Center for Forest Chemicals and Materials, College of Chemical Engineering, Nanjing Forestry University, Nanjing, Jiangsu 210037, China
| | - Jingyin Zhou
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Thomas Collier
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.,Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Steven H Liang
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114, United States.,Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115, United States
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3
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Casey AB, Cui M, Booth RG, Canal CE. "Selective" serotonin 5-HT 2A receptor antagonists. Biochem Pharmacol 2022; 200:115028. [PMID: 35381208 DOI: 10.1016/j.bcp.2022.115028] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 03/25/2022] [Accepted: 03/29/2022] [Indexed: 01/29/2023]
Abstract
Blockade of the serotonin 5-HT2A G protein-coupled receptor (5-HT2AR) is a fundamental pharmacological characteristic of numerous antipsychotic medications, which are FDA-approved to treat schizophrenia, bipolar disorder, and as adjunctive therapies in major depressive disorder. Meanwhile, activation of the 5-HT2AR by serotonergic psychedelics may be useful in treating neuropsychiatric indications, including major depressive and substance use disorders. Serotonergic psychedelics and other 5-HT2AR agonists, however, often bind other receptors, and standard 5-HT2AR antagonists lack sufficient selectivity to make well-founded mechanistic conclusions about the 5-HT2AR-dependent effects of these compounds and the general neurobiological function of 5-HT2ARs. This review discusses the limitations and strengths of currently available "selective" 5-HT2AR antagonists, the molecular determinants of antagonist selectivity at 5-HT2ARs, and the utility of molecular pharmacological and computational methods in guiding the discovery of novel unambiguously selective 5-HT2AR antagonists.
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Affiliation(s)
- Austen B Casey
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Meng Cui
- Department of Pharmaceutical Sciences, Boston, Massachusetts 02115, USA; Center for Drug Discovery, Northeastern University, Boston, Massachusetts 02115, USA
| | - Raymond G Booth
- Department of Pharmaceutical Sciences, Boston, Massachusetts 02115, USA; Department of Chemistry and Chemical Biology, Boston, Massachusetts 02115, USA; Center for Drug Discovery, Northeastern University, Boston, Massachusetts 02115, USA
| | - Clinton E Canal
- Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University Health Sciences Center, Mercer University, 3001 Mercer University Drive, Atlanta, Georgia 30341, USA
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Barrett FS, Zhou Y, Carbonaro TM, Roberts JM, Smith GS, Griffiths RR, Wong DF. Human Cortical Serotonin 2A Receptor Occupancy by Psilocybin Measured Using [ 11C]MDL 100,907 Dynamic PET and a Resting-State fMRI-Based Brain Parcellation. FRONTIERS IN NEUROERGONOMICS 2022; 2:784576. [PMID: 38235248 PMCID: PMC10790884 DOI: 10.3389/fnrgo.2021.784576] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/29/2021] [Indexed: 01/19/2024]
Abstract
Psilocybin (a serotonin 2A, or 5-HT2A, receptor agonist) has shown preliminary efficacy as a treatment for mood and substance use disorders. The current report utilized positron emission tomography (PET) with the selective 5-HT2A receptor inverse agonist radioligand [11C]MDL 100,907 (a.k.a. M100,907) and cortical regions of interest (ROIs) derived from resting-state functional connectivity-based brain parcellations in 4 healthy volunteers (2 females) to determine regional occupancy/target engagement of 5-HT2A receptors after oral administration of a psychoactive dose of psilocybin (10 mg/70 kg). Average 5-HT2A receptor occupancy across all ROIs was 39.5% (± 10.9% SD). Three of the ROIs with greatest occupancy (between 63.12 and 74.72% occupancy) were within the default mode network (subgenual anterior cingulate and bilateral angular gyri). However, marked individual variability in regional occupancy was observed across individuals. These data support further investigation of the relationship between individual differences in the acute and enduring effects of psilocybin and the degree of regional 5-HT2A receptor occupancy.
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Affiliation(s)
- Frederick S. Barrett
- Center for Psychedelic and Consciousness Research, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Yun Zhou
- United Imaging Intelligence, Shanghai, China
| | - Theresa M. Carbonaro
- Center for Psychedelic and Consciousness Research, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Joshua M. Roberts
- Center for Psychedelic and Consciousness Research, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Gwenn S. Smith
- Division of Geriatric Psychiatry and Neuropsychiatry, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Division of Nuclear Medicine and Molecular Imaging, Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Roland R. Griffiths
- Center for Psychedelic and Consciousness Research, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Dean F. Wong
- Departments of Radiology, Psychiatry, Neurology, and Neuroscience, Mallinckrodt Institute of Radiology, Washington University in St Louis, St. Louis, MO, United States
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Characterization of the serotonin 2A receptor selective PET tracer (R)-[ 18F]MH.MZ in the human brain. Eur J Nucl Med Mol Imaging 2019; 47:355-365. [PMID: 31606832 DOI: 10.1007/s00259-019-04527-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 09/05/2019] [Indexed: 12/24/2022]
Abstract
PURPOSE The serotonin receptor subtype 2A antagonist (5-HT2AR) (R)-[18F]MH.MZ has in preclinical studies been identified as a promising PET imaging agent for quantification of cerebral 5-HT2ARs. It displays a very similar selectivity profile as [11C]MDL 100907, one of the most selective compounds identified thus far for the 5-HT2AR. As [11C]MDL 100907, (R)-[18F]MH.MZ also displays slow brain kinetics in various animal models; however, the half-life of fluorine-18 allows for long scan times and consequently, a more precise determination of 5-HT2AR binding could still be feasible. In this study, we aimed to evaluate the potential of (R)-[18F]MH.MZ PET to image and quantify the 5-HT2AR in the human brain in vivo. METHODS Nine healthy volunteers underwent (R)-[18F]MH.MZ PET at baseline and four out of these also received a second PET scan, after ketanserin pretreatment. Regional time-activity curves of 17 brain regions were analyzed before and after pretreatment. We also investigated radiometabolism, time-dependent stability of outcomes measures, specificity of (R)-[18F]MH.MZ 5-HT2AR binding, and performance of different kinetic modeling approaches. RESULTS Highest uptake was determined in 5-HT2AR rich regions with a BPND of approximately 1.5 in cortex regions. No radiometabolism was observed. 1TCM and 2TCM resulted in similar outcome measure, whereas reference tissue models resulted in a small, but predictable bias. (R)-[18F]MH.MZ binding conformed to the known distribution of 5-HT2AR and could be blocked by pretreatment with ketanserin. Moreover, outcomes measures were stable after 100-110 min. CONCLUSION (R)-[18F]MH.MZ is a suitable PET tracer to image and quantify the 5-HT2AR system in humans. In comparison with [11C]MDL 100907, faster and more precise outcome measure could be obtained using (R)-[18F]MH.MZ. We believe that (R)-[18F]MH.MZ has the potential to become the antagonist radiotracer of choice to investigate the human 5-HT2AR system.
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6
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Psychedelic effects of psilocybin correlate with serotonin 2A receptor occupancy and plasma psilocin levels. Neuropsychopharmacology 2019; 44:1328-1334. [PMID: 30685771 PMCID: PMC6785028 DOI: 10.1038/s41386-019-0324-9] [Citation(s) in RCA: 219] [Impact Index Per Article: 43.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 12/17/2018] [Accepted: 12/26/2018] [Indexed: 11/08/2022]
Abstract
The main psychedelic component of magic mushrooms is psilocybin, which shows promise as a treatment for depression and other mental disorders. Psychedelic effects are believed to emerge through stimulation of serotonin 2A receptors (5-HT2ARs) by psilocybin's active metabolite, psilocin. We here report for the first time the relationship between intensity of psychedelic effects, cerebral 5-HT2AR occupancy and plasma levels of psilocin in humans. Eight healthy volunteers underwent positron emission tomography (PET) scans with the 5-HT2AR agonist radioligand [11C]Cimbi-36: one at baseline and one or two additional scans on the same day after a single oral intake of psilocybin (3-30 mg). 5-HT2AR occupancy was calculated as the percent change in cerebral 5-HT2AR binding relative to baseline. Subjective psychedelic intensity and plasma psilocin levels were measured during the scans. Relations between subjective intensity, 5-HT2AR occupancy, and plasma psilocin levels were modeled using non-linear regression. Psilocybin intake resulted in dose-related 5-HT2AR occupancies up to 72%; plasma psilocin levels and 5-HT2AR occupancy conformed to a single-site binding model. Subjective intensity was correlated with both 5-HT2AR occupancy and psilocin levels as well as questionnaire scores. We report for the first time that intake of psilocybin leads to significant 5-HT2AR occupancy in the human brain, and that both psilocin plasma levels and 5-HT2AR occupancy are closely associated with subjective intensity ratings, strongly supporting that stimulation of 5-HT2AR is a key determinant for the psychedelic experience. Important for clinical studies, psilocin time-concentration curves varied but psilocin levels were closely associated with psychedelic experience.
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7
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Sander CY, Hooker JM, Catana C, Rosen BR, Mandeville JB. Imaging Agonist-Induced D2/D3 Receptor Desensitization and Internalization In Vivo with PET/fMRI. Neuropsychopharmacology 2016; 41:1427-36. [PMID: 26388148 PMCID: PMC4793127 DOI: 10.1038/npp.2015.296] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 09/14/2015] [Accepted: 09/14/2015] [Indexed: 12/23/2022]
Abstract
This study investigated the dynamics of dopamine receptor desensitization and internalization, thereby proposing a new technique for non-invasive, in vivo measurements of receptor adaptations. The D2/D3 agonist quinpirole, which induces receptor internalization in vitro, was administered at graded doses in non-human primates while imaging with simultaneous positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). A pronounced temporal divergence between receptor occupancy and fMRI signal was observed: occupancy remained elevated while fMRI responded transiently. Analogous experiments with an antagonist (prochlorperazine) and a lower-affinity agonist (ropinirole) exhibited reduced temporal dissociation between occupancy and function, consistent with a mechanism of desensitization and internalization that depends upon drug efficacy and affinity. We postulated a model that incorporates internalization into a neurovascular-coupling relationship. This model yielded in vivo desensitization/internalization rates (0.2/min for quinpirole) consistent with published in vitro measurements. Overall, these results suggest that simultaneous PET/fMRI enables characterization of dynamic neuroreceptor adaptations in vivo, and may offer a first non-invasive method for assessing receptor desensitization and internalization.
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Affiliation(s)
- Christin Y Sander
- A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA,Harvard Medical School, Boston, MA, USA,A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, 149 Thirteenth Street, Room 2301, Charlestown, MA 02129, USA, Tel: +617 724 1839, Fax: +617 726 7422, E-mail:
| | - Jacob M Hooker
- A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA,Harvard Medical School, Boston, MA, USA
| | - Ciprian Catana
- A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA,Harvard Medical School, Boston, MA, USA
| | - Bruce R Rosen
- A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA,Harvard Medical School, Boston, MA, USA,Health Sciences and Technology, Harvard-MIT, Cambridge, MA, USA
| | - Joseph B Mandeville
- A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA,Harvard Medical School, Boston, MA, USA
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8
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Piel M, Vernaleken I, Rösch F. Positron Emission Tomography in CNS Drug Discovery and Drug Monitoring. J Med Chem 2014; 57:9232-58. [DOI: 10.1021/jm5001858] [Citation(s) in RCA: 111] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Markus Piel
- Institute
of Nuclear Chemistry, Johannes Gutenberg-University, Fritz-Strassmann-Weg 2, D-55128 Mainz, Germany
| | - Ingo Vernaleken
- Department
of Psychiatry, Psychotherapy, and Psychosomatics, RWTH Aachen University, Pauwelsstraße 30, D-52074 Aachen, Germany
| | - Frank Rösch
- Institute
of Nuclear Chemistry, Johannes Gutenberg-University, Fritz-Strassmann-Weg 2, D-55128 Mainz, Germany
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Cole PE, Schwarz AJ, Schmidt ME. Applications of Imaging Biomarkers in the Early Clinical Development of Central Nervous System Therapeutic Agents. Clin Pharmacol Ther 2012; 91:315-20. [DOI: 10.1038/clpt.2011.286] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Paterson LM, Kornum BR, Nutt DJ, Pike VW, Knudsen GM. 5-HT radioligands for human brain imaging with PET and SPECT. Med Res Rev 2011; 33:54-111. [PMID: 21674551 DOI: 10.1002/med.20245] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.
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Affiliation(s)
- Louise M Paterson
- Neuropsychopharmacology Unit, Division of Experimental Medicine, Imperial College London, Burlington Danes Building, Du Cane Road, London, United Kingdom
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Multi-graphical analysis of dynamic PET. Neuroimage 2009; 49:2947-57. [PMID: 19931403 DOI: 10.1016/j.neuroimage.2009.11.028] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Revised: 11/01/2009] [Accepted: 11/11/2009] [Indexed: 11/22/2022] Open
Abstract
In quantitative dynamic PET studies, graphical analysis methods including the Gjedde-Patlak plot, the Logan plot, and the relative equilibrium-based graphical plot (RE plot) (Zhou Y., Ye W., Brasić J.R., Crabb A.H., Hilton J., Wong D.F. 2009b. A consistent and efficient graphical analysis method to improve the quantification of reversible tracer binding in radioligand receptor dynamic PET studies. Neuroimage 44(3):661-670) are based on the theory of a compartmental model with assumptions on tissue tracer kinetics. If those assumptions are violated, then the resulting estimates may be biased. In this study, a multi-graphical analysis method was developed to characterize the non-relative equilibrium effects on the estimates of total distribution volume (DV(T)) from the RE plot. A novel bi-graphical analysis method using the RE plot with the Gjedde-Patlak plot (RE-GP plots) was proposed to estimate DV(T) for the quantification of reversible tracer kinetics that may not be at relative equilibrium states during PET study period. The RE-GP plots and the Logan plot were evaluated by 19 [(11)C]WIN35,428 and 10 [(11)C]MDL100,907 normal human dynamic PET studies with brain tissue tracer kinetics measured at both region of interest (ROI) and pixel levels. A 2-tissue compartment model (2TCM) was used to fit ROI time activity curves (TACs). By applying multi-graphical plots to the 2TCM fitted ROI TACs which were considered as the noise-free tracer kinetics, the estimates of DV(T) from the RE-GP plots, the Logan plot, and the 2TCM fitting were equal to each other. For the measured ROI TACs, there was no significant difference between the estimates of the DV(T) from the RE-GP plots and those from 2TCM fitting (p=0.77), but the estimates of the DV(T) from the Logan plot were significantly (p<0.001) lower, 2.3% on average, than those from 2TCM fitting. There was a highly linear correlation between the ROI DV(T) from the parametric images (Y) and those from the ROI kinetics (X) by using the RE-GP plots (Y=1.01X+0.23, R(2)=0.99). For the Logan plot, the ROI estimates from the parametric images were 13% to 83% lower than those from ROI kinetics. The computational time for generating parametric images was reduced by 69% on average by the RE-GP plots in contrast to the Logan plot. In conclusion, the bi-graphical analysis method using the RE-GP plots was a reliable, robust and computationally efficient kinetic modeling approach to improve the quantification of dynamic PET.
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12
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Atack JR, Eng WS, Gibson RE, Ryan C, Francis B, Sohal B, Dawson GR, Hargreaves RJ, Burns HD. The plasma-occupancy relationship of the novel GABAA receptor benzodiazepine site ligand, alpha5IA, is similar in rats and primates. Br J Pharmacol 2009; 157:796-803. [PMID: 19422390 DOI: 10.1111/j.1476-5381.2009.00216.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE alpha5IA (3-(5-methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-yl)methyloxy]-1,2,4-triazolo[3,4-a]phthalazine) is a triazolophthalazine with subnanomolar affinity for alpha1-, alpha2-, alpha3- and alpha5-containing GABA(A) receptors. Here we have evaluated the relationship between plasma alpha5IA concentrations and benzodiazepine binding site occupancy in rodents and primates (rhesus monkey). EXPERIMENTAL APPROACH In awake rats, occupancy was measured at various times after oral dosing with alpha5IA (0.03-30 mgxkg(-1)) using an in vivo {[(3)H]flumazenil (8-fluoro 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester)} binding assay. In anaesthetized rhesus monkeys, occupancy was measured using {[(123)I]iomazenil (ethyl 5,6-dihydro-7-iodo-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester)} gamma-scintigraphy and a bolus/infusion paradigm. In both rat and rhesus monkey, the plasma drug concentration corresponding to 50% occupancy (EC(50)) was calculated. KEY RESULTS In rats, alpha5IA occupancy was dose- and time-dependent with maximum occupancy occurring within the first 2 h. However, rat plasma EC(50) was time-independent, ranging from 42 to 67 ngxmL(-1) over a 24 h time course with the average being 52 ngxmL(-1) (i.e. occupancy decreased as plasma drug concentrations fell). In rhesus monkeys, the EC(50) for alpha5IA displacing steady-state [(123)I]iomazenil binding was 57 ngxmL(-1). CONCLUSIONS AND IMPLICATIONS Rat plasma EC(50) values did not vary as a function of time indicating that alpha5IA dissociates readily for the GABA(A) receptor in vivo. These data also suggest that despite the different assays used (terminal assays of [(3)H]flumazenil in vivo binding in rats and [(123)I]iomazenil gamma-scintigraphy in anaesthetized rhesus monkeys), these techniques produced similar plasma alpha5IA EC(50) values (52 and 57 ngxmL(-1) respectively) and that the plasma-occupancy relationship for alpha5IA translates across these two species.
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Affiliation(s)
- John R Atack
- Merck Sharp and Dohme Research Laboratories, The Neuroscience Research Centre, Harlow, Essex, UK.
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13
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Landolt HP, Wehrle R. Antagonism of serotonergic 5-HT2A/2C receptors: mutual improvement of sleep, cognition and mood? Eur J Neurosci 2009; 29:1795-809. [PMID: 19473234 DOI: 10.1111/j.1460-9568.2009.06718.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Serotonin [5-hydroxytryptamine (5-HT)] and 5-HT receptors are involved in sleep and in waking functions such as cognition and mood. Animal and human studies support a particular role for the 5-HT(2A) receptor in sleep, which has led to renewed interest in this receptor subtype as a target for the development of novel pharmacological agents to treat insomnia. Focusing primarily on findings in healthy human volunteers, a review of the available data suggests that antagonistic interaction with 5-HT(2A) receptors (and possibly also 5-HT(2C) receptors) prolongs the duration of slow wave sleep and enhances low-frequency (< 7 Hz) activity in the sleep electroencephalogram (EEG), a widely accepted marker of sleep intensity. Despite certain differences, the changes in sleep and the sleep EEG appear to be remarkably similar to those of physiologically more intense sleep after sleep deprivation. It is currently unclear whether these changes in sleep are associated with improved vigilance, cognition and mood during wakefulness. While drug-induced interaction with sleep must be interpreted cautiously, too few studies are available to provide a clear answer to this question. Moreover, functional relationships between sleep and waking functions may differ between healthy controls and patients with sleep disorders. A multimodal approach investigating subjective and objective aspects of sleep and wakefulness provides a promising research avenue for shedding light on the complex relationships among 5-HT(2A/2C) receptor-mediated effects on sleep, the sleep EEG, cognition and mood in health and various diseases associated with disturbed sleep and waking functions.
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Affiliation(s)
- H-P Landolt
- Institute of Pharmacology and Toxicology, University of Zürich, Zürich, Switzerland.
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14
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Effect of menstrual cycle phase on dopamine D2 receptor availability in female cynomolgus monkeys. Neuropsychopharmacology 2009; 34:548-54. [PMID: 18256593 DOI: 10.1038/npp.2008.3] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Sex differences have been reported in a variety of affective and neurodegenerative disorders that involve dysfunctional dopamine (DA) neurotransmission. In addition, there is evidence for differences in sensitivity to the abuse-related effects of psychostimulants across the menstrual cycle which may result from effects of ovarian hormones on DA function. The goal of the present study was to extend previous work examining menstrual cycle-related changes in DA D2 receptor availability in humans to drug-naive female cynomolgus monkeys (n=7) using the selective D2-like receptor ligand [(18)F]fluoroclebopride (FCP) and a high-resolution microPET P4 scanner. Menstrual cycle phase was characterized by daily vaginal swabs and measurements of serum progesterone levels. PET studies were conducted once during the luteal phase and once during the follicular phase. Regions of interest in the caudate nucleus, putamen, and cerebellum were defined on coregistered MRIs. Distribution volumes were calculated for FCP in each structure and the distribution volume ratio (DVR) for both brain regions relative to the cerebellum was used as a measure of D2 receptor availability. FCP DVRs were significantly higher in the luteal phase compared to the follicular phase in both the caudate nucleus (11.7% difference, p=0.02) and putamen (11.6% difference, p=0.03). These findings extend earlier work in humans and suggest that changes in DA receptor availability may be involved in the variation in symptoms of various neuropsychiatric disorders across the menstrual cycle, including differences in sensitivity to the abuse-related effects of stimulants.
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15
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Abstract
Neuroimaging, particularly that of neuroreceptor radioisotope and functional magnetic resonance imaging (fMRI), has played a fundamental role in neuropharmacology and neurophysiology. Because of the unique and pioneering role, especially of the radiolabeling of central nervous system (CNS) drugs for receptor and neurotransmitter system imaging, there is an increasingly major role to aid in CNS drug development. One component is providing evidence for proof of concept of the target for which candidate drugs are being tested for receptor occupancy mechanism of action and ultimately rational drug dosing. There is also a role for other areas of neuroimaging, including fMRI and magnetic resonance spectroscopy in other magnetic resonance-based techniques that, together with radioisotope imaging, represent 'CNS molecular imaging.' The role of these approaches and a review of the recent advances in such neuroimaging for proof-of-concept studies is the subject for this paper. Moreover, hypothetical examples and possible algorithms for early discovery/phase I development using neuroimaging provide specific working approaches. In summary, this article reviews the vital biomarker approach of neuroimaging in proof of concept studies.
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Validation of a rat in vivo [3H]M100907 binding assay to determine a translatable measure of 5-HT2A receptor occupancy. Eur J Pharmacol 2008; 591:136-41. [DOI: 10.1016/j.ejphar.2008.06.063] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Revised: 06/04/2008] [Accepted: 06/12/2008] [Indexed: 11/24/2022]
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17
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Li JX, Rice KC, France CP. Discriminative stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane in rhesus monkeys. J Pharmacol Exp Ther 2008; 324:827-33. [PMID: 17993605 DOI: 10.1124/jpet.107.130625] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Discriminative stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) and related drugs have been studied extensively in rodents, although the generality of those findings across species is not known. The goals of this study were to see whether monkeys could discriminate DOM and to characterize the DOM discriminative stimulus by studying a variety of drugs, including those with hallucinogenic activity in humans. Four rhesus monkeys discriminated between 0.32 mg/kg s.c. DOM and vehicle after an average of 116 (range = 85-166) sessions while responding under a fixed ratio 5 schedule of stimulus shock termination. Increasing doses of DOM occasioned increased responding on the drug lever with the training dose occasioning DOM-lever responding for up to 2 h. The serotonin (5-HT)(2A/2C) receptor antagonists ritanserin and ketanserin, the 5-HT(2A) receptor antagonist (+)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol] (MDL100907), and its (-)stereoisomer MDL100009 [(-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol], but not haloperidol, completely blocked the discriminative stimulus effects of DOM. Quipazine as well as several drugs with hallucinogenic activity in humans, including (+)lysergic acid diethylamide, (-)DOM, and 2,5-dimethoxy-4-(n)-propylthiophenethylamine (2C-T-7), occasioned DOM-lever responding. The kappa-opioid receptor agonists U-50488 and salvinorin A (a hallucinogen) did not exert DOM-like effects and neither did ketamine, phencyclidine, amphetamine, methamphetamine, cocaine, morphine, yohimbine, fenfluramine, 8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT), or (+/-)-2-(N-phenethyl-N-1'-propyl)amino-5-hydroxytetralin hydrochloride (N-0434). These data confirm in nonhuman primates a prominent role for 5-HT(2A) receptors in the discriminative stimulus effects of some drugs with hallucinogenic activity in humans. The failure of another drug with hallucinogenic activity (salvinorin A) to substitute for DOM indicates that different classes of hallucinogens exert qualitatively different discriminative stimulus effects in nonhumans.
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Affiliation(s)
- Jun-Xu Li
- Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
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18
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Abstract
Brain imaging represents a potent tool to characterize biomarkers, biological traits that are pathognomonic for specific neurological and neuropsychiatric disorders. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are imaging techniques used to identify alterations in the density and distribution of neurotransmitters, neuroreceptors, and transporters in specific regions of the brains of people with these disorders. Brain imaging research currently facilitates the elucidation of dysfunction of dopamine, serotonin, acetylcholine, and other substances in people with Alzheimer's and Parkinson's diseases, schizophrenia, alcoholism and other substance abuse disorders, attention deficit/hyperactivity disorder, and the syndromes of restless legs, Lesch-Nyhan, Rett, and Tourette. Thus, brain imaging research offers great potential for the diagnosis, treatment, prevention, and cure of neurological and neuropsychiatric disorders. Brain imaging research also facilitates new drug development and helps establish therapeutic doses of novel drugs. In particular, studies of specific receptors, such as the dopamine D2 receptor, before and after the administration of doses of drugs that occupy these D2 receptors, provide the means to determine receptor occupancy. For example, an optimal dose of D2 antagonist antipsychotics produces occupancy of 65% to 80% of D2 receptors, while a greater dose carries a risk of extrapyramidal side effects.
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Affiliation(s)
- Dean F Wong
- The Russell H. Morgan Department of Radiology and Radiological Science, Division of Nuclear Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-0807, USA.
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19
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Kumar JSD, Prabhakaran J, Erlandsson K, Majo VJ, Simpson NR, Pratap M, Van Heertum RL, Mann JJ, Parsey RV. Synthesis and in vivo evaluation of [O-methyl-11C](2R,4R)-4-hydroxy-2-[2-[2-[2-(3-methoxy)phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine as a 5-HT2A receptor PET ligand. Nucl Med Biol 2006; 33:565-74. [PMID: 16720250 DOI: 10.1016/j.nucmedbio.2006.02.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Revised: 01/23/2006] [Accepted: 02/08/2006] [Indexed: 11/29/2022]
Abstract
The serotonin2A (5-HT2A) receptor is implicated in the pathophysiology of schizophrenia and mood disorders, and in vivo studies of this receptor would be of value in studying the pathophysiology of these disorders and in measuring the relationship of clinical response to receptor occupancy for 5-HT2A antagonists such as atypical antipsychotics. Therefore, (2R,4R)-4-hydroxy-2-[2-[2-[2-(3-methoxy)-phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine (MPM) (13), a selective and high-affinity (K(i)=0.79 nM) 5HT2A antagonist, has been radiolabeled with carbon-11 by O-methylation of the corresponding desmethyl analogue (2R,4R)-4-hydroxy-2-[2-[2-[2-(3-hydroxy)phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine (12) with [11C]methyltriflate in order to determine the suitability of [11C]MPM to quantify 5-HT2A in living brain using PET. Desmethyl-MPM 12 and standard MPM were prepared, starting from 3-hydroxymethylphenol (2), in excellent yield. The yield obtained for radiolabeling was 40+/-5% (EOB), and the total synthesis time was 30 min at EOS. PET studies with [11C]MPM in baboon showed a distribution in the brain consistent with the known distribution of 5-HT2A receptors. The time-activity curves for the high-binding regions peaked at approximately 45 min after injection. Blocking studies with M100907 demonstrated not only 38-57% blocking of tracer binding in brain regions known to have 5-HT2A receptors but also 38% blocking in cerebellum, which has a low 5-HT2A receptor concentration. Although [11C]MPM exhibits appropriate kinetics in baboon for imaging 5-HT2A receptors, its specific binding in cerebellum and higher proportion of nonspecific binding limit its usefulness for the in vivo quantification of 5-HT2A receptors with PET.
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Affiliation(s)
- J S Dileep Kumar
- Department of Psychiatry, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.
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20
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Abstract
Although the second-generation or atypical antipsychotic drugs have been breakthrough medicines for the treatment of schizophrenia and other psychotic conditions, cognitive dysfunction and to some extent negative symptoms of the disease continue to be the main cause of poor vocational status of the patients. Thus, the majority of investigational drug development efforts today target these unmet medical needs. This review postulates that the field of schizophrenia research has advanced sufficiently to develop biochemical hypotheses of the etiopathology of the disease and target the same for revolutionary disease modifying therapy. This postulate is based on recent studies that have begun to provide a testable etiopathology model that integrates interactions between genetic vulnerability factors, neurodevelopmental anomalies, and neurotransmitter systems. This review begins with a brief overview of the nosology and etiopathology of schizophrenia and related psychotic disorders to establish a context for subsequent detailed discussions on drug discovery and development for psychotic disorders. Particular emphasis is placed on recent advances in genetic association studies of schizophrenia and how this can be integrated with evidence supporting neurodevelopmental abnormalities associated with the disease to generate a testable model of the disease etiopathology. An in-depth review of the plethora of new targets and approaches targeting the unmet medical need in the treatment of schizophrenia exemplify the challenges and opportunities in this area. We end the review by offering an approach based on emerging genetic, clinical, and neurobiological studies to discover and validate novel drug targets that could be classified as disease modifying approaches.
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Affiliation(s)
- Gerard Marek
- Neuroscience Division, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana 46285, USA
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21
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Gomez-Mancilla B, Marrer E, Kehren J, Kinnunen A, Imbert G, Hillebrand R, Bergström M, Schmidt ME. Central nervous system drug development: an integrative biomarker approach toward individualized medicine. NeuroRx 2006; 2:683-95. [PMID: 16489375 PMCID: PMC1201325 DOI: 10.1602/neurorx.2.4.683] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Drug development for CNS disorders faces the same formidable hurdles as other therapeutic areas: escalating development costs; novel drug targets with unproven therapeutic potential; and health care systems and regulatory agencies demanding more compelling demonstrations of the value of new drug products. Extensive clinical testing remains the core of registration of new compounds; however, traditional clinical trial methods are falling short in overcoming these development hurdles. The most common CNS disorders targeted for drug treatment are chronic, slowly vitiating processes manifested by highly subjective and context dependent signs and symptoms. With the exception of a few rare familial degenerative disorders, they have ill-defined or undefined pathophysiology. Samples selected for treatment trials using clinical criteria are inevitably heterogeneous, and dependence on traditional endpoints results in early proof-of-concept trials being long and large, with very poor signal to noise. It is no wonder that pharmaceutical and biotechnology companies are looking to biomarkers as an integral part of decision-making process supported by new technologies such as genetics, genomics, proteomics, and imaging as a mean of rationalizing CNS drug development. The present review represent an effort to illustrate the integration of such technologies in drug development supporting the path of individualized medicine.
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Affiliation(s)
- B Gomez-Mancilla
- Neuroscience-Biomarker Development, Novartis Pharma, CH-4002 Basel, Switzerland.
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22
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Prabhakaran J, Parsey RV, Majo VJ, Van Heertum RL, John Mann J, Dileep Kumar JS. Synthesis andin vivo evaluation of [O-methyl-11C] 2-(4-methoxyphenyl)-N-(4-methylbenzyl)-N-(1-methyl- piperidin-4-yl)acetamide as an imaging probe for 5-HT2A receptors. J Labelled Comp Radiopharm 2006. [DOI: 10.1002/jlcr.1124] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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23
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Chernet E, Martin LJ, Li D, Need AB, Barth VN, Rash KS, Phebus LA. Use of LC/MS to assess brain tracer distribution in preclinical, in vivo receptor occupancy studies: Dopamine D2, serotonin 2A and NK-1 receptors as examples. Life Sci 2005; 78:340-6. [PMID: 16139310 DOI: 10.1016/j.lfs.2005.04.075] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2005] [Accepted: 04/22/2005] [Indexed: 11/19/2022]
Abstract
High performance liquid chromatography combined with either single quad or triple quad mass spectral detectors (LC/MS) was used to measure the brain distribution of receptor occupancy tracers targeting dopamine D2, serotonin 5-HT2A and neurokinin NK-1 receptors using the ligands raclopride, MDL-100907 and GR205171, respectively. All three non-radiolabeled tracer molecules were easily detectable in discrete rat brain areas after intravenous doses of 3, 3 and 30 microg/kg, respectively. These levels showed a differential brain distribution caused by differences in receptor density, as demonstrated by the observation that pretreatment with compounds that occupy these receptors reduced this differential distribution in a dose-dependent manner. Intravenous, subcutaneous and oral dose-occupancy curves were generated for haloperidol at the dopamine D2 receptor as were oral curves for the antipsychotic drugs olanzapine and clozapine. In vivo dose-occupancy curves were also generated for orally administered clozapine, olanzapine and haloperidol at the cortical 5-HT2A binding site. In vivo occupancy at the striatal neurokinin NK-1 binding site by various doses of orally administered MK-869 was also measured. Our results demonstrate the utility of LC/MS to quantify tracer distribution in preclinical brain receptor occupancy studies.
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Affiliation(s)
- Eyassu Chernet
- Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, Indiana 46285, USA
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24
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Mamo D, Sedman E, Tillner J, Sellers EM, Romach MK, Kapur S. EMD 281014, a specific and potent 5HT2 antagonist in humans: a dose-finding PET study. Psychopharmacology (Berl) 2004; 175:382-8. [PMID: 15007535 DOI: 10.1007/s00213-004-1817-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
While serotonin 5HT2-receptors have been implicated in the etiology and pharmacological treatment of a number of neuropsychiatric conditions, there are few potent and specific agents available for use in human clinical studies. EMD 281014 is a highly specific 5HT2-receptor antagonist that is currently under development. To find optimal doses for early clinical studies, we conducted a PET study using [18F]setoperone in nine healthy subjects scanned at baseline and following the administration of 1, 3, and 7 mg EMD 281014. The study drug was well tolerated by all study participants, and all doses resulted in > or =70% occupancy at frontal 5HT2-receptors 3 h after drug administration. The data suggest that daily dosing of > or =3 mg EMD 281014 should be sufficient to provide sustained high levels of 5HT2-receptor occupancy in future clinical trials.
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Affiliation(s)
- David Mamo
- Department of Psychiatry, University of Toronto, Toronto, Canada
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25
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Abstract
Factors that place constraints on radio-chemists who are seeking to design and develop radiopharmaceuticals for PET imaging studies include the short half-lives of 11C and 18F, minimum radiochemical yield and specific activity requirements, and high radiation fields that are associated with multi-Curie quantities of PET radionuclides. Nevertheless, during the past 20 years, considerable progress has been made in the development and application of a variety of PET radiotracers for a range of imaging studies in human subjects. We have highlighted a few areas of radiochemistry that focused on PET radiotracers that are described in this issue. Although the number of PET radiotracers synthesized is in the hundreds [6], much work remains to develop specific and useful PET radiotracers for a host of new and exciting noninvasive imaging applications.
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Affiliation(s)
- N Scott Mason
- Positron Emission Tomography Facility, Department of Radiology, University of Pittsburgh, B-938, UPMC Presbyterian, 200 Lothrop Street, Pittsburgh, PA 15213-2582, USA.
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26
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Abstract
Better mechanistic understanding of disease through mapping of the human and mouse genomes enables rethinking of human infirmity. In the case of cancer, for example, we may begin to associate disease states with their underlying genetic defects rather than with the organ system involved. That will enable more selective, nontoxic therapies in patients who are genetically predisposed to respond to them. Because one of the major goals of molecular imaging research is to interrogate gene expression noninvasively, it can impact greatly on that process. Most of molecular imaging research is undertaken in small animals, which provide a conduit between in vitro studies and human clinical imaging. We are fortunate to be able to manipulate small animals genetically, and to have increasingly better models of human disease. The ability to study those animals noninvasively and quantitatively with new, high-resolution imaging devices provides the most relevant milieu in which to find and examine new therapies.
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Affiliation(s)
- Martin G Pomper
- Johns Hopkins University School of Medicine, Department of Radiology, Baltimore, Maryland 21287-2182, USA.
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27
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Martinez D, Broft A, Laruelle M. Imaging neurochemical endophenotypes: promises and pitfalls. Pharmacogenomics 2001; 2:223-37. [PMID: 11535111 DOI: 10.1517/14622416.2.3.223] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
A large number of polymorphisms in genes coding for neurotransmitter receptors and transporters have been associated with neuropsychiatric conditions, although few of these associations have been consistently replicated. These proteins are critical targets of psychoactive drugs and the clarification of the functional significance of these polymorphisms might offer important leads for drug development and therapeutic applications. Brain imaging techniques such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) provide the means to monitor the expression and function of many of these proteins in the living human brain. This paper reviews brain imaging studies designed to evaluate the significance of polymorphisms in genes coding for important drug targets (e.g., the serotonin transporter [SERT], the dopamine transporter [DAT] and the dopamine D(2) receptor) in terms of expression or function. These studies illustrate the unique opportunities, as well as the pitfalls, generated by combining genetic analysis with brain imaging studies.
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Affiliation(s)
- D Martinez
- New York State Psychiatric Institute, 1051 Riverside Drive, Box #31, New York, NY 10032, USA.
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28
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Soares JC, van Dyck CH, Tan P, Zoghbi SS, Garg P, Soufer R, Baldwin RM, Fujita M, Staley JK, Fu X, Amici L, Seibyl J, Innis RB. Reproducibility of in vivo brain measures of 5-HT2A receptors with PET and. Psychiatry Res 2001; 106:81-93. [PMID: 11306248 DOI: 10.1016/s0925-4927(01)00071-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The test/retest reproducibility of brain measures of 5-HT2A receptors with positron emission tomography (PET) and [18F]deuteroaltanserin was examined in a group of eight healthy human subjects. PET measures of 5-HT2A receptors were obtained under an equilibrium paradigm, with a 40-min PET acquisition starting approximately at 300 min (308+/-11 min) after bolus plus constant infusion of the radiotracer. Three brain outcome measures were obtained at equilibrium, V(3) (ratio of specific brain uptake to free parent plasma concentration of radiotracer), V(3)' (ratio of specific brain uptake to total parent plasma concentration) and RT (ratio of specific to non-displaceable brain uptakes). V(3)' and RT had high test/retest reproducibility, as measured by mean intra-subject% change for cortical brain areas of 14.1 and 11.0%, respectively. They also had high reliability, as measured by mean intra-class correlation coefficients (ICC) for cortical brain areas of 0.86 and 0.88, respectively. V(3) had low test/retest reproducibility, due to high variability in the measures of free parent tracer in plasma. This study supports the feasibility of equilibrium imaging of 5-HT2A receptors with PET and [18F]deuteroaltanserin. The equilibrium imaging method with [18F]deuteroaltanserin allows a single acquisition and blood measurement to provide an image whose pixel values equal a receptor volume of distribution. Since the single image pixel values are proportional to receptor densities, the images can be used in pixel-by-pixel statistical methods, such as SPM, to assess the distribution and density of 5-HT2A receptors in neuropsychiatric disorders.
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Affiliation(s)
- J C Soares
- Department of Psychiatry, Yale University School of Medicine, VA Connecticut Healthcare System, West Haven, CT 06516, USA
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29
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Rowley M, Bristow LJ, Hutson PH. Current and novel approaches to the drug treatment of schizophrenia. J Med Chem 2001; 44:477-501. [PMID: 11170639 DOI: 10.1021/jm0002432] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
MESH Headings
- Animals
- Antipsychotic Agents/adverse effects
- Antipsychotic Agents/pharmacology
- Antipsychotic Agents/therapeutic use
- Cholinergic Agonists/adverse effects
- Cholinergic Agonists/pharmacology
- Cholinergic Agonists/therapeutic use
- Disease Models, Animal
- Dopamine Antagonists/adverse effects
- Dopamine Antagonists/pharmacology
- Dopamine Antagonists/therapeutic use
- Enzyme Inhibitors/adverse effects
- Enzyme Inhibitors/pharmacology
- Enzyme Inhibitors/therapeutic use
- Excitatory Amino Acid Antagonists/adverse effects
- Excitatory Amino Acid Antagonists/pharmacology
- Excitatory Amino Acid Antagonists/therapeutic use
- Humans
- Mice
- Mice, Transgenic
- Nitric Oxide Synthase/antagonists & inhibitors
- Receptor, Serotonin, 5-HT2A
- Receptors, AMPA/antagonists & inhibitors
- Receptors, Dopamine D2/drug effects
- Receptors, Dopamine D4
- Receptors, Metabotropic Glutamate/antagonists & inhibitors
- Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors
- Receptors, Neurotensin/agonists
- Receptors, Serotonin/drug effects
- Schizophrenia/drug therapy
- Schizophrenia/etiology
- Schizophrenia/metabolism
- Serotonin Antagonists/adverse effects
- Serotonin Antagonists/pharmacology
- Serotonin Antagonists/therapeutic use
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Affiliation(s)
- M Rowley
- Merck Sharp and Dohme, The Neuroscience Research Centre, Terlings Park, Eastwick Road, Harlow, Essex CM20 2QR, UK.
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30
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Abstract
Positron emission tomography (PET) is a quantitative imaging method that can be used to characterize binding properties of specific target molecules such as various receptors, transporter molecules and enzymes in vivo. Although already applied successfully, one of the greatest challenges for the technique is to understand better the in vivo complexities of ligand-receptor (target) interaction. The PET technique can be used efficiently in animal studies but, most importantly, also in human studies. PET imaging of patients and healthy volunteers can generate information on human pathophysiology at a molecular level currently unobtainable with other methods. Modern imaging techniques are increasingly applied to drug discovery and development. There are many ways of utilizing PET in pharmacodynamic studies, one interesting approach being the indirect exploration of synaptic neurotransmission with receptor ligands. The receptor occupancy-type studies with PET are rapidly becoming a state-of-the-art method for verifying the mechanism of action of a given drug in man and especially for facilitating the dose-finding procedures in early drug development. Thus far, PET has been mainly applied to pharmacodynamic studies in the central nervous system but will be used also in other areas of drug development such as cardiovascular diseases and oncology.
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Affiliation(s)
- J Hietala
- Department of Psychiatry, and the Turku PET Centre, Turku University Central Hospital, Finland.
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31
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Offord SJ, Wong DF, Nyberg S. The role of positron emission tomography in the drug development of M100907, a putative antipsychotic with a novel mechanism of action. J Clin Pharmacol 1999; 39:17S-24S. [PMID: 10434243 DOI: 10.1002/j.1552-4604.1999.tb05933.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Antipsychotic drug development has been a slow process since the discovery of chlorpromazine more than 45 years ago. Researchers identify a large number of potential compounds; screen them for antipsychotic activity in in vitro and animal test models; devise appropriate formulations; perform preclinical pharmacology, pharmacokinetic, and toxicology studies; perform healthy volunteer and then patient clinical studies; and finally negotiate with regulatory agencies for drug approval. In the United States, this process takes an average of 10 to 12 years and costs more than $500 million per approved drug. More recently, the pharmaceutical industry is benefiting from a new wave of technologic innovations that have advanced our understanding of the biology of disease processes and increased the efficiency of the research and development process. However, while these new technologies may appear to be expensive, by providing the basis for early go/no-go decisions, technologies such as PET can actually be cost-effective. To ensure that innovative drug research continues, a practical strategy (rational drug design) to evaluate drugs more efficiently in terms of both time and cost (fewer studies with fewer patients) must be developed for each new drug candidate. One of the most important and difficult steps in the drug development process is defining the dose-response relationship. Using M100907 as an example, we demonstrated that mechanism-based research promotes cost-effective drug development. The therapeutic index of M100907 was defined in phase I single- and multiple-dose tolerability studies. Nuclear imaging using PET technology was then used to confirm the mechanism of action of M100907 in the target organ (living human brain) and to target an appropriate dose range and regimen. With these data, clear go/no-go decision points could be established early within the clinical drug development process, and the selection of M100907 doses to carry forward into large-scale clinical trials in patients with schizophrenia could be narrowed.
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Affiliation(s)
- S J Offord
- Hoechst Marion Roussel, Inc., Bridgewater, New Jersey 08807-0800, USA
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32
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Burns HD, Hamill TG, Eng WS, Francis B, Fioravanti C, Gibson RE. Positron emission tomography neuroreceptor imaging as a tool in drug discovery, research and development. Curr Opin Chem Biol 1999; 3:388-94. [PMID: 10419855 DOI: 10.1016/s1367-5931(99)80059-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Improved communication and cooperation between research-driven drug companies and academic positron emission tomography (PET) centers, coupled with improvements in PET camera resolution, the availability of small animal PET cameras and a growing list of neuroreceptor-specific PET tracers, have all contributed to a substantial increase in the use and value of PET as a tool in central nervous system drug discovery and development.
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Affiliation(s)
- H D Burns
- Department of Pharmacology, Merck Research Laboratories, WP44C-2, Sumneytown Pike, West Point, PA 19438, USA.
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33
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Affiliation(s)
- R Frank
- Sanofi Research Division, Malvern, PA, USA
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Villemagne VL, Rothman RB, Yokoi F, Rice KC, Matecka D, Dannals RF, Wong DF. Doses of GBR12909 that suppress cocaine self-administration in non-human primates substantially occupy dopamine transporters as measured by [11C] WIN35,428 PET scans. Synapse 1999; 32:44-50. [PMID: 10188637 DOI: 10.1002/(sici)1098-2396(199904)32:1<44::aid-syn6>3.0.co;2-9] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
GBR12909 (GBR) is a high-affinity, selective, and long-acting inhibitor of dopamine (DA) uptake that produces a persistent and noncompetitive blockade of DA transporters and substantially reduces cocaine-induced increases in extracellular DA in the nucleus accumbens of rats. Prior studies showed that intravenous infusion of GBR to Rhesus monkeys selectively reduced (1 mg/kg) and eliminated (3 mg/kg) cocaine self-administration. This study tested the hypothesis that doses of GBR that reduce cocaine self-administration in nonhuman primates produce significant occupation of DA transporters. DA transporters were quantitated in two baboons using [11C]WIN35,428 and positron emission tomography (PET). Each baboon underwent paired control/blocked PET scans (performed on three separate study days, 3-4 weeks apart). On the first scan the baboon received saline (3 ml/kg) 90 minutes before the injection of the radiotracer. GBR (1 mg/kg i.v.) was infused 90 minutes before the second [11C]WIN 35,428 study. The same experimental design was repeated with GBR doses of 3 and 10 mg/kg, respectively. Doses of 1 (n = 2), 3 mg/kg (n = 2), and 10 mg/kg (n = 2) reduced binding potential by 26, 53, and 72%, respectively. GBR was well tolerated in all baboons. These results demonstrate that doses of GBR that suppress cocaine self-administration in nonhuman primates also produce high occupancy of the DA transporter. These data strongly suggest that occupancy for the DA transporter by GBR explains its ability to attenuate cocaine-induced increases in extracellular DA and to suppress cocaine self-administration. Moreover, these data suggest that experimental human studies of orally administered GBR to test the DA hypothesis of cocaine addiction should use doses that produce at least 70% occupancy of the DA transporter.
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Affiliation(s)
- V L Villemagne
- Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287-0807, USA
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Andrée B, Nyberg S, Ito H, Ginovart N, Brunner F, Jaquet F, Halldin C, Farde L. Positron emission tomographic analysis of dose-dependent MDL 100,907 binding to 5-hydroxytryptamine-2A receptors in the human brain. J Clin Psychopharmacol 1998; 18:317-23. [PMID: 9690698 DOI: 10.1097/00004714-199808000-00012] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Selective 5-hydroxytryptamine-2A (5-HT2A) antagonism has been proposed as a mechanism of atypical antipsychotic drug action. MDL 100,907, a new selective 5-HT2A receptor antagonist, has high affinity in vitro for 5-HT2A receptors and is being developed as a potential antipsychotic drug. In this study, neocortical 5-HT2A receptor occupancy was measured in six healthy male volunteers after placebo and escalating single doses (1-72 mg) of MDL 100,907 using positron emission tomography and the nonspecific radioligand [11C]N-methylspiperone ([11C]NMSP). Receptor occupancy was calculated using a ratio-equilibrium analysis, assuming that maximal radioligand binding inhibition represents 100% 5-HT2A receptor occupancy. Plasma concentrations of MDL 100,907 were measured with high-pressure liquid chromatography. The pharmacokinetic parameters area under the curve and peak plasma concentration increased linearly with dose, with rapid absorption and a 6- to 9-hour elimination half-life. The neocortical binding of [11C]NMSP was inhibited dose-dependently. After administration of 6 mg of MDL 100,907 the inhibition was 70%, corresponding to a 5-HT2A receptor occupancy of 90%. The calculated maximal inhibition was 77%. These observations indicate that MDL 100,907 passes the blood-brain barrier and binds to 5-HT2A receptors in a saturable manner in the living human brain. Repeated doses of MDL 100,907, 10 mg/day or more, should induce a sustained 5-HT2A receptor occupancy in most patients. Thus, MDL 100,907 provides a suitable tool to evaluate the potential of selective 5-HT2A receptor antagonism in the treatment of schizophrenia.
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Affiliation(s)
- B Andrée
- Karolinska Institutet, Department of Clinical Neuroscience, Karolinska Hospital, Stockholm, Sweden.
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