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Xiao Z, Wei H, Xu Y, Haider A, Wei J, Yuan S, Rong J, Zhao C, Li G, Zhang W, Chen H, Li Y, Zhang L, Sun J, Zhang S, Luo HB, Yan S, Cai Q, Hou L, Che C, Liang SH, Wang L. Discovery of a highly specific 18F-labeled PET ligand for phosphodiesterase 10A enabled by novel spirocyclic iodonium ylide radiofluorination. Acta Pharm Sin B 2022; 12:1963-1975. [PMID: 35847497 PMCID: PMC9279629 DOI: 10.1016/j.apsb.2021.11.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 09/30/2021] [Accepted: 10/20/2021] [Indexed: 12/14/2022] Open
Abstract
As a member of cyclic nucleotide phosphodiesterase (PDE) enzyme family, PDE10A is in charge of the degradation of cyclic adenosine (cAMP) and guanosine monophosphates (cGMP). While PDE10A is primarily expressed in the medium spiny neurons of the striatum, it has been implicated in a variety of neurological disorders. Indeed, inhibition of PDE10A has proven to be of potential use for the treatment of central nervous system (CNS) pathologies caused by dysfunction of the basal ganglia–of which the striatum constitutes the largest component. A PDE10A-targeted positron emission tomography (PET) radioligand would enable a better assessment of the pathophysiologic role of PDE10A, as well as confirm the relationship between target occupancy and administrated dose of a given drug candidate, thus accelerating the development of effective PDE10A inhibitors. In this study, we designed and synthesized a novel 18F-aryl PDE10A PET radioligand, codenamed [18F]P10A-1910 ([18F]9), in high radiochemical yield and molar activity via spirocyclic iodonium ylide-mediated radiofluorination. [18F]9 possessed good in vitro binding affinity (IC50 = 2.1 nmol/L) and selectivity towards PDE10A. Further, [18F]9 exhibited reasonable lipophilicity (logD = 3.50) and brain permeability (Papp > 10 × 10−6 cm/s in MDCK-MDR1 cells). PET imaging studies of [18F]9 revealed high striatal uptake and excellent in vivo specificity with reversible tracer kinetics. Preclinical studies in rodents revealed an improved plasma and brain stability of [18F]9 when compared to the current reference standard for PDE10A-targeted PET, [18F]MNI659. Further, dose–response experiments with a series of escalating doses of PDE10A inhibitor 1 in rhesus monkey brains confirmed the utility of [18F]9 for evaluating target occupancy in vivo in higher species. In conclusion, our results indicated that [18F]9 is a promising PDE10A PET radioligand for clinical translation.
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Affiliation(s)
- Zhiwei Xiao
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
| | - Huiyi Wei
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Yi Xu
- Department of Cardiology, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Ahmed Haider
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
| | - Junjie Wei
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Shiyu Yuan
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Jian Rong
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
| | - Chunyu Zhao
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
| | - Guocong Li
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Weibin Zhang
- State Key Laboratory of Chemical Oncogenomics, Key Laboratory of Chemical Genomics, Peking University Shenzhen Graduate School, Shenzhen 518055, China
| | - Huangcan Chen
- State Key Laboratory of Chemical Oncogenomics, Key Laboratory of Chemical Genomics, Peking University Shenzhen Graduate School, Shenzhen 518055, China
| | - Yuefeng Li
- Guangdong Landau Biotechnology Co. Ltd., Guangzhou 510555, China
| | - Lingling Zhang
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Jiyun Sun
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
| | - Shaojuan Zhang
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Hai-Bin Luo
- Key Laboratory of Tropical Biological Resources of Ministry of Education, School of Pharmaceutical Sciences, Hainan University, Haikou 570228, China
| | - Sen Yan
- Guangdong-Hongkong-Macau Institute of CNS Regeneration, Ministry of Education CNS Regeneration Collaborative Joint Laboratory, Jinan University, Guangzhou 510632, China
| | - Qijun Cai
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Lu Hou
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
| | - Chao Che
- State Key Laboratory of Chemical Oncogenomics, Key Laboratory of Chemical Genomics, Peking University Shenzhen Graduate School, Shenzhen 518055, China
- Corresponding authors. Tel./fax: +86 755 26032530 (Chao Che), +1 617 7266165 (Steven H. Liang), +86 20 38688692 (Lu Wang).
| | - Steven H. Liang
- Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital & Department of Radiology, Harvard Medical School, Boston, MA 02114, USA
- Corresponding authors. Tel./fax: +86 755 26032530 (Chao Che), +1 617 7266165 (Steven H. Liang), +86 20 38688692 (Lu Wang).
| | - Lu Wang
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, the First Affiliated Hospital of Jinan University, Guangzhou 510630, China
- Corresponding authors. Tel./fax: +86 755 26032530 (Chao Che), +1 617 7266165 (Steven H. Liang), +86 20 38688692 (Lu Wang).
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Brumberg J, Varrone A. New PET radiopharmaceuticals for imaging CNS diseases. Nucl Med Mol Imaging 2022. [DOI: 10.1016/b978-0-12-822960-6.00002-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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3
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Sun J, Xiao Z, Haider A, Gebhard C, Xu H, Luo HB, Zhang HT, Josephson L, Wang L, Liang SH. Advances in Cyclic Nucleotide Phosphodiesterase-Targeted PET Imaging and Drug Discovery. J Med Chem 2021; 64:7083-7109. [PMID: 34042442 DOI: 10.1021/acs.jmedchem.1c00115] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.
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Affiliation(s)
- Jiyun Sun
- Department of Radiology, Division of Nuclear Medicine and Molecular Imaging Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States
| | - Zhiwei Xiao
- Department of Radiology, Division of Nuclear Medicine and Molecular Imaging Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States
| | - Ahmed Haider
- Department of Radiology, Division of Nuclear Medicine and Molecular Imaging Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States
| | - Catherine Gebhard
- Department of Nuclear Medicine, University Hospital Zurich, Raemistrasse 100, Zurich 8006, Switzerland.,Center for Molecular Cardiology, University of Zurich, Wagistrasse 12, Schlieren 8952, Switzerland
| | - Hao Xu
- Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, The First Affiliated Hospital of Jinan University, 613 West Huangpu Road, Tianhe District, Guangzhou 510630, China
| | - Hai-Bin Luo
- School of Pharmaceutical Sciences, Sun Yat-Sen University, Guangzhou 510006, China
| | - Han-Ting Zhang
- Departments of Neuroscience, Behavioral Medicine & Psychiatry, and Physiology & Pharmacology, the Rockefeller Neuroscience Institute, West Virginia University Health Sciences Center, Morgantown, West Virginia 26506, United States
| | - Lee Josephson
- Department of Radiology, Division of Nuclear Medicine and Molecular Imaging Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States
| | - Lu Wang
- Department of Radiology, Division of Nuclear Medicine and Molecular Imaging Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States.,Center of Cyclotron and PET Radiopharmaceuticals, Department of Nuclear Medicine and PET/CT-MRI Center, The First Affiliated Hospital of Jinan University, 613 West Huangpu Road, Tianhe District, Guangzhou 510630, China
| | - Steven H Liang
- Department of Radiology, Division of Nuclear Medicine and Molecular Imaging Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States
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Świerczek A, Jankowska A, Chłoń-Rzepa G, Pawłowski M, Wyska E. Advances in the Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 2: Focus on Schizophrenia. Curr Drug Targets 2020; 20:1652-1669. [PMID: 31368871 DOI: 10.2174/1389450120666190801114210] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Revised: 07/15/2019] [Accepted: 07/19/2019] [Indexed: 12/31/2022]
Abstract
Schizophrenia is a debilitating mental disorder with relatively high prevalence (~1%), during which positive manifestations (such as psychotic states) and negative symptoms (e.g., a withdrawal from social life) occur. Moreover, some researchers consider cognitive impairment as a distinct domain of schizophrenia symptoms. The imbalance in dopamine activity, namely an excessive release of this neurotransmitter in the striatum and insufficient amounts in the prefrontal cortex is believed to be partially responsible for the occurrence of these groups of manifestations. Second-generation antipsychotics are currently the standard treatment of schizophrenia. Nevertheless, the existent treatment is sometimes ineffective and burdened with severe adverse effects, such as extrapyramidal symptoms. Thus, there is an urgent need to search for alternative treatment options of this disease. This review summarizes the results of recent preclinical and clinical studies on phosphodiesterase 10A (PDE10A), which is highly expressed in the mammalian striatum, as a potential drug target for the treatment of schizophrenia. Based on the literature data, not only selective PDE10A inhibitors but also dual PDE2A/10A, and PDE4B/10A inhibitors, as well as multifunctional ligands with a PDE10A inhibitory potency are compounds that may combine antipsychotic, precognitive, and antidepressant functions. Thus, designing such compounds may constitute a new direction of research for new potential medications for schizophrenia. Despite failures of previous clinical trials of selective PDE10A inhibitors for the treatment of schizophrenia, new compounds with this mechanism of action are currently investigated clinically, thus, the search for new inhibitors of PDE10A, both selective and multitarget, is still warranted.
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Affiliation(s)
- Artur Świerczek
- Department of Pharmacokinetics and Physical Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Krakow, Poland
| | - Agnieszka Jankowska
- Department of Medicinal Chemistry, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Krakow, Poland
| | - Grażyna Chłoń-Rzepa
- Department of Medicinal Chemistry, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Krakow, Poland
| | - Maciej Pawłowski
- Department of Medicinal Chemistry, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Krakow, Poland
| | - Elżbieta Wyska
- Department of Pharmacokinetics and Physical Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Krakow, Poland
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The Potent PDE10A Inhibitor MP-10 (PF-2545920) Suppresses Microglial Activation in LPS-Induced Neuroinflammation and MPTP-Induced Parkinson’s Disease Mouse Models. J Neuroimmune Pharmacol 2020; 16:470-482. [DOI: 10.1007/s11481-020-09943-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Accepted: 07/08/2020] [Indexed: 12/12/2022]
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6
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Gallezot JD, Nabulsi N, Henry S, Pracitto R, Planeta B, Ropchan J, Lin SF, Labaree D, Kapinos M, Shirali A, Lara-Jaime T, Gao H, Matuskey D, Walzer M, Marek GJ, Bellaire S, Yuan N, Carson RE, Huang Y. Imaging the Enzyme 11β-Hydroxysteroid Dehydrogenase Type 1 with PET: Evaluation of the Novel Radiotracer 11C-AS2471907 in Human Brain. J Nucl Med 2019; 60:1140-1146. [DOI: 10.2967/jnumed.118.219766] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2018] [Accepted: 01/07/2019] [Indexed: 11/16/2022] Open
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7
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Moein MM, Nakao R, Amini N, Abdel-Rehim M, Schou M, Halldin C. Sample preparation techniques for radiometabolite analysis of positron emission tomography radioligands; trends, progress, limitations and future prospects. Trends Analyt Chem 2019. [DOI: 10.1016/j.trac.2018.10.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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8
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Liu H, Jin H, Luo Z, Yue X, Zhang X, Flores H, Su Y, Perlmutter JS, Tu Z. In Vivo Characterization of Two 18F-Labeled PDE10A PET Radioligands in Nonhuman Primate Brains. ACS Chem Neurosci 2018; 9:1066-1073. [PMID: 29400443 PMCID: PMC5955820 DOI: 10.1021/acschemneuro.7b00458] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Positron emission tomography (PET) with phosphodiesterase 10A (PDE10A) specific radioligands provides a noninvasive and quantitative imaging tool to access the expression of this enzyme in vivo under normal and diseased conditions. We recently reported two potent 18F-labeled PDE10A radioligands (18F-TZ19106B and 18F-TZ8110); initial evaluation in rats and nonhuman primates indicated stable metabolic profiles and excellent target-to-nontarget ratio (striatum/cerebellum) for both tracers. Herein, we focused on in vivo characterization of 18F-TZ19106B and 18F-TZ8110 to identify a suitable radioligand for imaging PDE10A in vivo. We directly compared microPET studies of these two radiotracers in adult male Macaca fascicularis nonhuman primates (NHPs). 18F-TZ19106B had higher striatal uptake and tracer retention in NHP brains than 18F-TZ8110, quantified by either standardized uptake values (SUVs) or nondisplaceable binding potential (BPND) estimated using reference-based modeling analysis. Blocking and displacement studies using the PDE10A inhibitor MP-10 indicated the binding of 18F-TZ19106B to PDE10A was specific and reversible. We also demonstrated sensitivity of 18F-TZ19106B binding to varying number of specific binding sites using escalating doses of MP-10 blockade (0.3, 0.5, 1.0, 1.5, and 2.0 mg/kg). Pretreatment with a dopamine D2-like receptor antagonist enhanced the striatal uptake of 18F-TZ19106B. Our results indicate that 18F-TZ19106B is a promising radioligand candidate for imaging PDE10A in vivo and it may be used to determine target engagement of PDE10A inhibitors and serve as a tool to evaluate the effect of novel antipsychotic therapies.
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Affiliation(s)
- Hui Liu
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Hongjun Jin
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Zonghua Luo
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Xuyi Yue
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Xiang Zhang
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Hubert Flores
- Department of Neurology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Yi Su
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Joel S. Perlmutter
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
- Department of Neurology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
- Department of Neuroscience, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
| | - Zhude Tu
- Department of Radiology, Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri 63110, United States
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Gallezot JD, Nabulsi NB, Holden D, Lin SF, Labaree D, Ropchan J, Najafzadeh S, Donnelly DJ, Cao K, Bonacorsi S, Seiders J, Roppe J, Hayes W, Huang Y, Du S, Carson RE. Evaluation of the Lysophosphatidic Acid Receptor Type 1 Radioligand 11C-BMT-136088 for Lung Imaging in Rhesus Monkeys. J Nucl Med 2017; 59:327-333. [PMID: 28864634 DOI: 10.2967/jnumed.117.195073] [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: 04/28/2017] [Accepted: 08/22/2017] [Indexed: 01/01/2023] Open
Abstract
The lysophosphatidic acid receptor type 1 (LPA1) is 1 of 6 known receptors of the extracellular signaling molecule lysophosphatidic acid. It mediates effects such as cell proliferation, migration, and differentiation. In the lung, LPA1 is involved in pathways leading, after lung tissue injury, to pulmonary fibrosis instead of normal healing, by mediating fibroblast recruitment and vascular leakage. Thus, a LPA1 PET radiotracer may be useful for studying lung fibrosis or for developing LPA1-targeting drugs. We developed and evaluated the radiotracer 11C-BMT-136088 (1-(4'-(3-methyl-4-(((1(R)-(3-11C-methylphenyl)ethoxy)carbonyl)amino)isoxazol-5-yl)-[1,1'-biphenyl]-4-yl)cyclopropane-1-carboxylic acid) in rhesus monkeys to image LPA1 in the lung in vivo with PET. Methods: The study consisted of 3 parts: test-retest scans; self-saturation to estimate the tracer's in vivo dissociation constant, nondisplaceable volume of distribution (VND), and nondisplaceable binding potential (BPND); and dosimetry. In the first 2 parts, the radiotracer was administered using a bolus-plus-infusion protocol, the arterial input function was measured, and the animals underwent 2 scans per day separated by about 4 h. Lung regions of interest were segmented, and the tissue density estimated, from CT images. A fixed blood volume correction was applied. The tracer volume of distribution (VT) was estimated using multilinear analysis 1 (MA1) or equilibrium analysis (EA). Results:11C-BMT-136088 baseline VT was 1.83 ± 0.16 (MA1, n = 5) or 2.1 ± 0.55 (EA, n = 7) mL of plasma per gram of tissue in the left and right lung regions of interest, with a test-retest variability of -6% (MA1, n = 1) or -1% ± 14% (EA, n = 2). For the self-saturation study, 11C-BMT-136088 VND and BPND were estimated to be 0.9 ± 0.08 mL of plasma per gram of tissue and 1.1 ± 0.14, respectively. The unlabeled drug dose and plasma concentration leading to a 50% reduction of 11C-BMT-136088 specific binding were 73 ± 30 nmol/kg and 28 ± 12 nM, respectively. The average plasma free fraction was 0.2%; thus, the tracer's in vivo dissociation constant was estimated to be 55 pM. For the dosimetry study, the highest organ dose was in the liver (43.1 ± 4.9 and 68.9 ± 9.4 μSv/MBq in reference human male and female phantoms, respectively), and the effective dose equivalent was 6.9 ± 0.6 and 8.7 ± 0.6 μSv/MBq, respectively. Conclusion: Specific binding of 11C-BMT-136088 can be reliably measured to quantify LPA1 in the lungs of rhesus monkeys in vivo.
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Affiliation(s)
| | - Nabeel B Nabulsi
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Daniel Holden
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Shu-Fei Lin
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - David Labaree
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Jim Ropchan
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Soheila Najafzadeh
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - David J Donnelly
- Discovery Chemistry Platforms, Bristol-Myers Squibb, Princeton, New Jersey
| | - Kai Cao
- Discovery Chemistry Platforms, Bristol-Myers Squibb, Princeton, New Jersey
| | - Samuel Bonacorsi
- Discovery Chemistry Platforms, Bristol-Myers Squibb, Princeton, New Jersey
| | - Jon Seiders
- Amira Pharmaceuticals, San Diego, California; and
| | | | - Wendy Hayes
- Imaging, Bristol-Myers Squibb, Princeton, New Jersey
| | - Yiyun Huang
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Shuyan Du
- Imaging, Bristol-Myers Squibb, Princeton, New Jersey
| | - Richard E Carson
- Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
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Geerts H, Spiros A, Roberts P. Phosphodiesterase 10 inhibitors in clinical development for CNS disorders. Expert Rev Neurother 2016; 17:553-560. [DOI: 10.1080/14737175.2017.1268531] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Hugo Geerts
- In Silico Biosciences Perelman School of Medicine, University of Pennsylvania, Berwyn, PA, USA
| | - Athan Spiros
- In Silico Biosciences Perelman School of Medicine, University of Pennsylvania, Berwyn, PA, USA
| | - Patrick Roberts
- In Silico Biosciences Perelman School of Medicine, University of Pennsylvania, Berwyn, PA, USA
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Yang KC, Stepanov V, Amini N, Martinsson S, Takano A, Nielsen J, Bundgaard C, Bang-Andersen B, Grimwood S, Halldin C, Farde L, Finnema SJ. Characterization of [ 11C]Lu AE92686 as a PET radioligand for phosphodiesterase 10A in the nonhuman primate brain. Eur J Nucl Med Mol Imaging 2016; 44:308-320. [PMID: 27817159 PMCID: PMC5215309 DOI: 10.1007/s00259-016-3544-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 10/03/2016] [Indexed: 11/28/2022]
Abstract
Purpose [11C]Lu AE92686 is a positron emission tomography (PET) radioligand that has recently been validated for examining phosphodiesterase 10A (PDE10A) in the human striatum. [11C]Lu AE92686 has high affinity for PDE10A (IC50 = 0.39 nM) and may also be suitable for examination of the substantia nigra, a region with low density of PDE10A. Here, we report characterization of regional [11C]Lu AE92686 binding to PDE10A in the nonhuman primate (NHP) brain. Methods A total of 11 PET measurements, seven baseline and four following pretreatment with unlabeled Lu AE92686 or the structurally unrelated PDE10A inhibitor MP-10, were performed in five NHPs using a high resolution research tomograph (HRRT). [11C]Lu AE92686 binding was quantified using a radiometabolite-corrected arterial input function and compartmental and graphical modeling approaches. Results Regional time-activity curves were best described with the two-tissue compartment model (2TCM). However, the distribution volume (VT) values for all regions were obtained by the Logan plot analysis, as reliable cerebellar VT values could not be derived by the 2TCM. For cerebellum, a proposed reference region, VT values increased by ∼30 % with increasing PET measurement duration from 63 to 123 min, while VT values in target regions remained stable. Both pretreatment drugs significantly decreased [11C]Lu AE92686 binding in target regions, while no significant effect on cerebellum was observed. Binding potential (BPND) values, derived with the simplified reference tissue model (SRTM), were 13–17 in putamen and 3–5 in substantia nigra and correlated well to values from the Logan plot analysis. Conclusions The method proposed for quantification of [11C]Lu AE92686 binding in applied studies in NHP is based on 63 min PET data and SRTM with cerebellum as a reference region. The study supports that [11C]Lu AE92686 can be used for PET examinations of PDE10A binding also in substantia nigra. Electronic supplementary material The online version of this article (doi:10.1007/s00259-016-3544-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Kai-Chun Yang
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.
| | - Vladimir Stepanov
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Nahid Amini
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Stefan Martinsson
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Akihiro Takano
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Jacob Nielsen
- Synaptic Transmission, H. Lundbeck A/S, Valby, Denmark
| | | | | | - Sarah Grimwood
- Neuroscience and Pain Research Unit, Pfizer Inc., Cambridge, MA, USA
| | - Christer Halldin
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Lars Farde
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.,Personalized Health Care and Biomarkers, AstraZeneca PET Science Center at Karolinska Institutet, Stockholm, Sweden
| | - Sjoerd J Finnema
- Department of Clinical Neuroscience, Center for Psychiatric Research, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.,Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA
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Novel Radioligands for Cyclic Nucleotide Phosphodiesterase Imaging with Positron Emission Tomography: An Update on Developments Since 2012. Molecules 2016; 21:molecules21050650. [PMID: 27213312 PMCID: PMC6273803 DOI: 10.3390/molecules21050650] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Revised: 05/09/2016] [Accepted: 05/10/2016] [Indexed: 12/19/2022] Open
Abstract
Cyclic nucleotide phosphodiesterases (PDEs) are a class of intracellular enzymes that inactivate the secondary messenger molecules, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Thus, PDEs regulate the signaling cascades mediated by these cyclic nucleotides and affect fundamental intracellular processes. Pharmacological inhibition of PDE activity is a promising strategy for treatment of several diseases. However, the role of the different PDEs in related pathologies is not completely clarified yet. PDE-specific radioligands enable non-invasive visualization and quantification of these enzymes by positron emission tomography (PET) in vivo and provide an important translational tool for elucidation of the relationship between altered expression of PDEs and pathophysiological effects as well as (pre-)clinical evaluation of novel PDE inhibitors developed as therapeutics. Herein we present an overview of novel PDE radioligands for PET published since 2012.
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Wu J, Lin SF, Gallezot JD, Chan C, Prasad R, Thorn SL, Stacy MR, Huang Y, Zonouz TH, Liu YH, Lampert RJ, Carson RE, Sinusas AJ, Liu C. Quantitative Analysis of Dynamic 123I-mIBG SPECT Imaging Data in Healthy Humans with a Population-Based Metabolite Correction Method. J Nucl Med 2016; 57:1226-32. [PMID: 27081169 DOI: 10.2967/jnumed.115.171710] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 03/11/2016] [Indexed: 01/08/2023] Open
Abstract
UNLABELLED Conventional 2-dimensional planar imaging of (123)I-metaiodobenzylguanidine ((123)I-mIBG) is not fully quantitative. To develop a more accurate quantitative imaging approach, we investigated dynamic SPECT imaging with kinetic modeling in healthy humans to obtain the myocardial volume of distribution (VT) for (123)I-mIBG. METHODS Twelve healthy humans underwent 5 serial 15-min SPECT scans at 0, 15, 90, 120, and 180 min after bolus injection of (123)I-mIBG on a hybrid cadmium zinc telluride SPECT/CT system. Serial venous blood samples were obtained for radioactivity measurement and radiometabolite analysis. List-mode data of all the scans were binned into frames and reconstructed with attenuation and scatter corrections. Myocardial and blood-pool volumes of interest were drawn on the reconstructed images to derive the myocardial time-activity curve and input function. A population-based blood-to-plasma ratio (BPR) curve was generated. Both the population-based metabolite correction (PBMC) and the individual metabolite correction (IMC) curves were generated for comparison. VT values were obtained from different compartment models, using different input functions with and without metabolite and BPR corrections. RESULTS The BPR curve reached the peak value of 2.1 at 13 min after injection. Parent fraction was approximately 58% ± 13% at 15 min and stabilized at approximately 40% ± 5% by 180 min after injection. Two radiometabolite species were observed. When the reversible 2-tissue-compartment fit was used, the mean VT value was 29.0 ± 12.4 mL/cm(3) with BPR correction and PBMC, a 188% ± 32% increase compared with that without corrections. There was significant difference in VT with BPR correction (P = 2.3e-04) as well as with PBMC (P = 1.6e-05). The mean difference in VT between PBMC and IMC was -3% ± 8%, which was insignificant (P = 0.39). The intersubject coefficients of variation after PBMC (43%) and IMC (42%) were similar. CONCLUSION The myocardial VT of (123)I-mIBG was established in healthy humans for the first time. Accurate kinetic modeling of (123)I-mIBG requires both BPR and metabolite corrections. Population-based BPR correction and metabolite correction curves were developed, allowing more convenient absolute quantification of dynamic (123)I-mIBG SPECT images.
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Affiliation(s)
- Jing Wu
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Shu-Fei Lin
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | | | - Chung Chan
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Rameshwar Prasad
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Stephanie L Thorn
- Department of Internal Medicine (Cardiology), Yale University, New Haven, Connecticut
| | - Mitchel R Stacy
- Department of Internal Medicine (Cardiology), Yale University, New Haven, Connecticut
| | - Yiyun Huang
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | | | - Yi-Hwa Liu
- Department of Internal Medicine (Cardiology), Yale University, New Haven, Connecticut Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan; and Department of Biomedical Engineering, Chung Yuan Christian University, Taoyuan, Taiwan
| | - Rachel J Lampert
- Department of Internal Medicine (Cardiology), Yale University, New Haven, Connecticut
| | - Richard E Carson
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
| | - Albert J Sinusas
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut Department of Internal Medicine (Cardiology), Yale University, New Haven, Connecticut
| | - Chi Liu
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut
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Li J, Zhang X, Jin H, Fan J, Flores H, Perlmutter JS, Tu Z. Synthesis of Fluorine-Containing Phosphodiesterase 10A (PDE10A) Inhibitors and the In Vivo Evaluation of F-18 Labeled PDE10A PET Tracers in Rodent and Nonhuman Primate. J Med Chem 2015; 58:8584-600. [PMID: 26430878 DOI: 10.1021/acs.jmedchem.5b01205] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
A series of fluorine-containing PDE10A inhibitors were designed and synthesized to improve the metabolic stability of [(11)C]MP-10. Twenty of the 22 new analogues had high potency and selectivity for PDE10A: 18a-j, 19d-j, 20a-b, and 21b had IC50 values <5 nM for PDE10A. Seven F-18 labeled compounds [(18)F]18a-e, [(18)F]18g, and [(18)F]20a were radiosynthesized by (18)F-introduction onto the quinoline rather than the pyrazole moiety of the MP-10 pharmacophore and performed in vivo evaluation. Biodistribution studies in rats showed ~2-fold higher activity in the PDE10A-enriched striatum than nontarget brain regions; this ratio increased from 5 to 30 min postinjection, particularly for [(18)F]18a-d and [(18)F]20a. MicroPET studies of [(18)F]18d and [(18)F]20a in nonhuman primates provided clear visualization of striatum with suitable equilibrium kinetics and favorable metabolic stability. These results suggest this strategy may identify a (18)F-labeled PET tracer for quantifying the levels of PDE10A in patients with CNS disorders including Huntington's disease and schizophrenia.
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Affiliation(s)
- Junfeng Li
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
| | - Xiang Zhang
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
| | - Hongjun Jin
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
| | - Jinda Fan
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
| | - Hubert Flores
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
| | - Joel S Perlmutter
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
| | - Zhude Tu
- Department of Radiology and ‡Department of Neurology, Washington University School of Medicine , St. Louis, Missouri 63110, United States
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PET imaging evaluation of [(18)F]DBT-10, a novel radioligand specific to α7 nicotinic acetylcholine receptors, in nonhuman primates. Eur J Nucl Med Mol Imaging 2015; 43:537-47. [PMID: 26455500 DOI: 10.1007/s00259-015-3209-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Accepted: 09/28/2015] [Indexed: 12/17/2022]
Abstract
PURPOSE Positron emission tomography (PET) radioligands specific to α7 nicotinic acetylcholine receptors (nAChRs) afford in vivo imaging of this receptor for neuropathologies such as Alzheimer's disease, schizophrenia, and substance abuse. This work aims to characterize the kinetic properties of an α7-nAChR-specific radioligand, 7-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-2-[(18)F]-fluorodibenzo[b,d]thiophene 5,5-dioxide ([(18)F]DBT-10), in nonhuman primates. METHODS [(18)F]DBT-10 was produced via nucleophilic substitution of the nitro-precursor. Four Macaca mulatta subjects were imaged with [(18)F]DBT-10 PET, with measurement of [(18)F]DBT-10 parent concentrations and metabolism in arterial plasma. Baseline PET scans were acquired for all subjects. Following one scan, ex vivo analysis of brain tissue was performed to inspect for radiolabeled metabolites in brain. Three blocking scans with 0.69 and 1.24 mg/kg of the α7-nAChR-specific ligand ASEM were also acquired to assess dose-dependent blockade of [(18)F]DBT-10 binding. Kinetic analysis of PET data was performed using the metabolite-corrected input function to calculate the parent fraction corrected total distribution volume (V T/f P). RESULTS [(18)F]DBT-10 was produced within 90 min at high specific activities of 428 ± 436 GBq/μmol at end of synthesis. Metabolism of [(18)F]DBT-10 varied across subjects, stabilizing by 120 min post-injection at parent fractions of 15-55%. Uptake of [(18)F]DBT-10 in brain occurred rapidly, reaching peak standardized uptake values (SUVs) of 2.9-3.7 within 30 min. The plasma-free fraction was 18.8 ± 3.4%. No evidence for radiolabeled [(18)F]DBT-10 metabolites was found in ex vivo brain tissue samples. Kinetic analysis of PET data was best described by the two-tissue compartment model. Estimated V T/f P values were 193-376 ml/cm(3) across regions, with regional rank order of thalamus > frontal cortex > striatum > hippocampus > occipital cortex > cerebellum > pons. Dose-dependent blockade of [(18)F]DBT-10 binding by structural analog ASEM was observed throughout the brain, and occupancy plots yielded a V ND/f P estimate of 20 ± 16 ml/cm(3). CONCLUSION These results demonstrate suitable kinetic properties of [(18)F]DBT-10 for in vivo quantification of α7-nAChR binding in nonhuman primates.
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Liu H, Jin H, Yue X, Zhang X, Yang H, Li J, Flores H, Su Y, Perlmutter JS, Tu Z. Preclinical evaluation of a promising C-11 labeled PET tracer for imaging phosphodiesterase 10A in the brain of living subject. Neuroimage 2015. [PMID: 26216275 DOI: 10.1016/j.neuroimage.2015.07.049] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Phosphodiesterase 10A (PDE10A) plays a key role in the regulation of brain striatal signaling. A PET tracer for PDE10A may serve as a tool to evaluate PDE10A expression in vivo in central nervous system disorders with striatal pathology. Here, we further characterized the binding properties of a previously reported radioligand we developed for PDE10A, [(11)C]TZ1964B, in rodents and nonhuman primates (NHPs). The tritiated counterpart [(3)H]TZ1964B was used for in vitro binding characterizations in rat striatum homogenates and in vitro autoradiographic studies in rat brain slices. The carbon-11 labeled [(11)C]TZ1964B was utilized in the ex vivo autoradiography studies for the brain of rats and microPET imaging studies for the brain of NHPs. MicroPET scans of [(11)C]TZ1964B in NHPs were conducted at baseline, as well as with using a selective PDE10A inhibitor MP-10 for either pretreatment or displacement. The in vivo regional target occupancy (Occ) was obtained by pretreating with different doses of MP-10 (0.05-2.00 mg/kg). Both in vitro binding assays and in vitro autoradiographic studies revealed a nanomolar binding affinity of [(3)H]TZ1964B to the rat striatum. The striatal binding of [(3)H]TZ1964B and [(11)C]TZ1964B was either displaced or blocked by MP-10 in rats and NHPs. Autoradiography and microPET imaging confirmed that the specific binding of the radioligand was found in the striatum but not in the cerebellum. Blocking studies also confirmed the suitability of the cerebellum as an appropriate reference region. The binding potentials (BPND) of [(11)C]TZ1964B in the NHP striatum that were calculated using either the Logan reference model (LoganREF, 3.96 ± 0.17) or the simplified reference tissue model (SRTM, 4.64 ± 0.47), with the cerebellum as the reference region, was high and had good reproducibility. The occupancy studies indicated a MP-10 dose of 0.31 ± 0.09 mg/kg (LoganREF)/0.45 ± 0.17mg/kg (SRTM) occupies 50% striatal PDE10A binding sites. Studies in rats and NHPs demonstrated radiolabeled TZ1964B has a high binding affinity and good specificity for PDE10A, as well as favorable in vivo pharmacokinetic properties and binding profiles. Our data suggests that [(11)C]TZ1964B is a promising radioligand for in vivo imaging PDE10A in the brain of living subject.
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Affiliation(s)
- Hui Liu
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Hongjun Jin
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Xuyi Yue
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Xiang Zhang
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Hao Yang
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Junfeng Li
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Hubert Flores
- Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Yi Su
- Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Joel S Perlmutter
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Physical Therapy and Occupational Therapy, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Zhude Tu
- Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
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Cox CD, Hostetler ED, Flores BA, Evelhoch JL, Fan H, Gantert L, Holahan M, Eng W, Joshi A, McGaughey G, Meng X, Purcell M, Raheem IT, Riffel K, Yan Y, Renger JJ, Smith SM, Coleman PJ. Discovery of [¹¹C]MK-8193 as a PET tracer to measure target engagement of phosphodiesterase 10A (PDE10A) inhibitors. Bioorg Med Chem Lett 2015; 25:4893-4898. [PMID: 26077491 DOI: 10.1016/j.bmcl.2015.05.080] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2015] [Revised: 05/22/2015] [Accepted: 05/26/2015] [Indexed: 01/30/2023]
Abstract
Phosphodiesterase 10A (PDE10A) inhibition has recently been identified as a potential mechanism to treat multiple symptoms that manifest in schizophrenia. In order to facilitate preclinical development and support key proof-of-concept clinical trials of novel PDE10A inhibitors, it is critical to discover positron emission tomography (PET) tracers that enable plasma concentration/PDE10A occupancy relationships to be established across species with structurally diverse PDE10A inhibitors. In this Letter, we describe how a high-throughput screening hit was optimized to provide [(11)C]MK-8193 (8j), a PET tracer that supports the determination of plasma concentration/PDE10A occupancy relationships for structurally diverse series of PDE10A inhibitors in both rat and rhesus monkey.
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Affiliation(s)
- Christopher D Cox
- Discovery Chemistry, Merck Research Laboratories, West Point, PA 19486, USA.
| | | | - Broc A Flores
- Discovery Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
| | | | - Hong Fan
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Liza Gantert
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Marie Holahan
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Waisi Eng
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Aniket Joshi
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Georgia McGaughey
- Chemical Modeling & Informatics, Merck Research Laboratories, West Point, PA 19486, USA
| | - Xiangjun Meng
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Mona Purcell
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Izzat T Raheem
- Discovery Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
| | - Kerry Riffel
- Imaging, Merck Research Laboratories, West Point, PA 19486, USA
| | - Youwei Yan
- Structural Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
| | - John J Renger
- Neuroscience, Merck Research Laboratories, West Point, PA 19486, USA
| | - Sean M Smith
- Neuroscience, Merck Research Laboratories, West Point, PA 19486, USA
| | - Paul J Coleman
- Discovery Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
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