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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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Schröder S, Scheunemann M, Wenzel B, Brust P. Challenges on Cyclic Nucleotide Phosphodiesterases Imaging with Positron Emission Tomography: Novel Radioligands and (Pre-)Clinical Insights since 2016. Int J Mol Sci 2021; 22:ijms22083832. [PMID: 33917199 PMCID: PMC8068090 DOI: 10.3390/ijms22083832] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 03/29/2021] [Accepted: 03/31/2021] [Indexed: 12/21/2022] Open
Abstract
Cyclic nucleotide phosphodiesterases (PDEs) represent one of the key targets in the research field of intracellular signaling related to the second messenger molecules cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP). Hence, non-invasive imaging of this enzyme class by positron emission tomography (PET) using appropriate isoform-selective PDE radioligands is gaining importance. This methodology enables the in vivo diagnosis and staging of numerous diseases associated with altered PDE density or activity in the periphery and the central nervous system as well as the translational evaluation of novel PDE inhibitors as therapeutics. In this follow-up review, we summarize the efforts in the development of novel PDE radioligands and highlight (pre-)clinical insights from PET studies using already known PDE radioligands since 2016.
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Affiliation(s)
- Susann Schröder
- Department of Research and Development, ROTOP Pharmaka Ltd., 01328 Dresden, Germany
- Department of Neuroradiopharmaceuticals, Institute of Radiopharmaceutical Cancer Research, Research Site Leipzig, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 04318 Leipzig, Germany; (M.S.); (B.W.); (P.B.)
- Correspondence: ; Tel.: +49-341-234-179-4631
| | - Matthias Scheunemann
- Department of Neuroradiopharmaceuticals, Institute of Radiopharmaceutical Cancer Research, Research Site Leipzig, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 04318 Leipzig, Germany; (M.S.); (B.W.); (P.B.)
| | - Barbara Wenzel
- Department of Neuroradiopharmaceuticals, Institute of Radiopharmaceutical Cancer Research, Research Site Leipzig, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 04318 Leipzig, Germany; (M.S.); (B.W.); (P.B.)
| | - Peter Brust
- Department of Neuroradiopharmaceuticals, Institute of Radiopharmaceutical Cancer Research, Research Site Leipzig, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 04318 Leipzig, Germany; (M.S.); (B.W.); (P.B.)
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Makai S, Falk E, Morandi B. Direct Synthesis of Unprotected 2-Azidoamines from Alkenes via an Iron-Catalyzed Difunctionalization Reaction. J Am Chem Soc 2020; 142:21548-21555. [DOI: 10.1021/jacs.0c11025] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Szabolcs Makai
- ETH Zürich, Vladimir-Prelog-Weg 3, HCI, 8093 Zürich, Switzerland
| | - Eric Falk
- ETH Zürich, Vladimir-Prelog-Weg 3, HCI, 8093 Zürich, Switzerland
| | - Bill Morandi
- ETH Zürich, Vladimir-Prelog-Weg 3, HCI, 8093 Zürich, Switzerland
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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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Thomae D, Morley TJ, Lee HS, Barret O, Constantinescu C, Papin C, Baldwin RM, Tamagnan GD, Alagille D. Identification and in vivo evaluation of a fluorine-18 rolipram analogue, [(18) F]MNI-617, as a radioligand for PDE4 imaging in mammalian brain. J Labelled Comp Radiopharm 2016; 59:205-13. [PMID: 27006107 DOI: 10.1002/jlcr.3389] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Revised: 02/18/2016] [Accepted: 02/22/2016] [Indexed: 12/17/2022]
Abstract
Phosphodiesterase (PDE) 4 is the most prevalent PDE in the central nervous system (CNS) and catalyzes hydrolysis of intracellular cAMP, a secondary messenger. By therapeutic inhibition of PDE4, intracellular cAMP levels can be stabilized, and the symptoms of psychiatric and neurodegenerative disorders including depression, memory loss and Parkinson's disease can be ameliorated. Radiotracers targeting PDE4 can be used to study PDE4 density and function, and evaluate new PDE4 therapeutics, in vivo in a non-invasive way, as has been shown using the carbon-11 labeled PDE4 inhibitor R-(-)-rolipram. Herein we describe a small series of rolipram analogs that contain fluoro- or iodo-substituents that could be used as fluorine-18 PET or iodine-123 SPECT PDE4 radiotracers. This series was evaluated with an in vitro binding assay and a 4-(fluoromethyl) derivative of rolipram, MNI-617, was identified, with a five-fold increase in affinity for PDE4 (Kd = 0.26 nM) over R-(-)-rolipram (Kd = 1.6 nM). A deutero-analogue d2 -[(18) F]MNI-617 was radiolabeled and produced in 23% yield with high (>5 Ci/µmol) specific activity and evaluated in non-human primate, where it rapidly entered the brain, with SUVs between 4 and 5, and with a distribution pattern consistent with that of PDE4.
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Affiliation(s)
- David Thomae
- Molecular NeuroImaging LLC, New Haven, CT, 06510, USA
| | | | - Hsiaoju S Lee
- Molecular NeuroImaging LLC, New Haven, CT, 06510, USA
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Amini N, Nakao R, Schou M, Halldin C. Determination of plasma protein binding of positron emission tomography radioligands by high-performance frontal analysis. J Pharm Biomed Anal 2014; 98:140-3. [DOI: 10.1016/j.jpba.2014.05.024] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 05/14/2014] [Accepted: 05/16/2014] [Indexed: 10/25/2022]
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Analysis of (R)- and (S)-[(11)C]rolipram kinetics in canine myocardium for the evaluation of phosphodiesterase-4 with PET. Mol Imaging Biol 2012; 14:225-36. [PMID: 21424298 DOI: 10.1007/s11307-011-0482-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
PURPOSE (R)-[(11)C]rolipram and (S)-[(11)C]rolipram have been proposed to investigate phosphodiesterase-4 and, indirectly, cAMP-mediated signaling with PET. This study assessed binding of these tracers to phosphodiesterase-4 in canine myocardium. PROCEDURES Seven dogs underwent (R)-[(11)C]rolipram and (S)-[(11)C]rolipram dynamic PET imaging at baseline and with co-injection of saturating doses of (R)-rolipram. Dual-input compartment models were applied to estimate the volumes of distribution (V(T)). RESULTS The model comprising one compartment for unmetabolized tracer and one compartment for labeled metabolites provided excellent fits to data acquired with (S)-[(11)C]rolipram at baseline and with both enantiomers during co-injection scans. Use of two compartments for unmetabolized (R)-[(11)C]rolipram at baseline was warranted according to Akaike and Schwarz criteria. V(T) estimates obtained with these models were robust (CV ≤ 8.2%) and reproducible (CV ≤ 15%). CONCLUSION An important fraction (~65%) of the V (T) of (R)-[(11)C]rolipram at baseline reflects specific binding. Thus, the latter may be a useful index of phosphodiesterase-4 levels in canine myocardium.
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Thomas AJ, DaSilva JN, Lortie M, Renaud JM, Kenk M, Beanlands RS, deKemp RA. PET of (R)-11C-Rolipram Binding to Phosphodiesterase-4 Is Reproducible and Sensitive to Increased Norepinephrine in the Rat Heart. J Nucl Med 2011; 52:263-9. [DOI: 10.2967/jnumed.110.082701] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Kenk M, Thackeray JT, Thorn SL, Dhami K, Chow BJ, Ascah KJ, DaSilva JN, Beanlands RS. Alterations of pre- and postsynaptic noradrenergic signaling in a rat model of adriamycin-induced cardiotoxicity. J Nucl Cardiol 2010; 17:254-63. [PMID: 20182926 DOI: 10.1007/s12350-009-9190-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2009] [Accepted: 12/19/2009] [Indexed: 01/08/2023]
Abstract
BACKGROUND Altered sympathetic nervous system signaling is known to play a role in the cardiotoxicity of the anthracycline chemotherapeutic agents, but the interaction of pre- and postsynaptic function is not well understood. METHODS AND RESULTS Our aim was to study the noradrenergic signaling in an established rat model of adriamycin cardiotoxicity (15 mg/kg administered i.p. over 2 weeks) using radiotracers having potential applicability for imaging with positron emission tomography (PET). Ex vivo biodistribution was performed 1 and 3 weeks post-adriamycin treatment with the noradrenaline analogue [(11)C]meta-hydroxyephedrine ([(11)C]HED), beta-adrenergic receptor antagonist [(3)H]CGP12177, and phosphodiesterase-4 inhibitor (R)-[(11)C]rolipram. Cardiac function (echocardiographic parameters) and heart/body weight ratio were not affected. Myocardial retention of [(11)C]HED, [(3)H]CGP12177, and (R)-[(11)C]rolipram were unchanged 1 week post-adriamycin. Compared to controls, 3 weeks post-treatment [(3)H]CGP12177 uptake decreased (left ventricle free wall and septum; P < 0.05), while [(11)C]HED and (R)-[(11)C]rolipram uptake were unaffected. Following acute increase in myocardial noradrenaline levels with desipramine treatment, (R)-[(11)C]rolipram retention increased in the left atrium, right ventricle, left ventricle free wall and septum (P < 0.05) in vehicle-, but not adriamycin-treated animals. CONCLUSION Our results suggest that adriamycin-induced toxicity exhibits no change in presynaptic noradrenaline uptake, but decreased beta-adrenergic receptors in cardiac tissues, supporting a role for PET imaging of noradrenaline signaling in the study of anthracycline cardiotoxicity.
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Affiliation(s)
- Miran Kenk
- National Cardiac PET Centre, Division of Cardiology (Department of Medicine), University of Ottawa Heart Institute, 40 Ruskin St., Ottawa, ON, K1Y 4W7, Canada
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Greene M, Thackeray JT, Kenk M, Thorn SL, Bevilacqua L, Harper ME, Beanlands RS, Dasilva JN. Reduced in vivo phosphodiesterase-4 response to acute noradrenaline challenge in diet-induced obese rats. Can J Physiol Pharmacol 2009; 87:196-202. [PMID: 19295660 DOI: 10.1139/y09-001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Altered sympathetic nervous activity has been linked to the development and persistence of obesity, partly relating to overfeeding. Binding of the selective, positron-emitting phosphodiesterase-4 (PDE4) inhibitor (R)-[11C]rolipram provides a direct index of the cAMP-hydrolyzing enzyme PDE4. This study examines progressive alterations in PDE4 in a high-fat-fed obese animal model. (R)-[11C]Rolipram was injected into diet-induced obese (DIO) and diet-resistant (DR) rats; the animals were killed after 45 min, tissues were extracted, and radioactivity was quantified. Responsiveness of PDE4 to acute noradrenaline (NA) stimulation was determined by 3 h pretreatment with the NA reuptake inhibitor desipramine. There was minimal variance in caloric intake, weight gain, fasting glucose, insulin, and energy expenditure (indirect calorimetry) measures. Basal (R)-[11C]rolipram binding was comparable between DIO and DR rats at 2 or 8 weeks of feeding. The normal increase of PDE4 levels in response to elevated NA by desipramine pretreatment was ablated in PDE4-rich tissues, including brain, heart, and skeletal muscle, of DIO animals after 8 weeks of high-fat diet. Lean DR rats maintained PDE4 responsiveness indicative of a normal NA signal transduction.
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Affiliation(s)
- Michael Greene
- National Cardiac PET Centre, Division of Cardiology, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, ON K1Y4W7, Canada; and Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
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Kenk M, Greene M, Lortie M, deKemp RA, Beanlands RS, DaSilva JN. Use of a column-switching high-performance liquid chromatography method to assess the presence of specific binding of (R)- and (S)-[11C]rolipram and their labeled metabolites to the phosphodiesterase-4 enzyme in rat plasma and tissues. Nucl Med Biol 2008; 35:515-21. [DOI: 10.1016/j.nucmedbio.2008.01.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Revised: 12/20/2007] [Accepted: 01/22/2008] [Indexed: 10/22/2022]
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Kenk M, Greene M, Thackeray J, deKemp RA, Lortie M, Thorn S, Beanlands RS, DaSilva JN. In vivo selective binding of (R)-[11C]rolipram to phosphodiesterase-4 provides the basis for studying intracellular cAMP signaling in the myocardium and other peripheral tissues. Nucl Med Biol 2006; 34:71-7. [PMID: 17210463 DOI: 10.1016/j.nucmedbio.2006.10.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2006] [Revised: 09/25/2006] [Accepted: 10/07/2006] [Indexed: 11/19/2022]
Abstract
INTRODUCTION Phosphodiesterase-4 (PDE4) enzymes specifically break down the second messenger cAMP, thereby terminating the intracellular signaling cascade that plays an essential role in neurohormonal modulation of many physiological systems. PDE4 activity and expression are regulated by cAMP levels, suggesting that measurement of PDE4 provides an index of intracellular cAMP signaling. METHODS Male Sprague-Dawley rats were administered (R)- or the less active enantiomer (S)-[11C]rolipram and sacrificed 30 min later with tracer retention measured in various tissues. Co-injections with saturating doses of unlabeled (R)-rolipram, (S)-rolipram and Ro 20-1724, as well as subtype-selective PDE inhibitors vinpocetine, Bay 60-7550, cilostazol and zaprinast were used to establish binding selectivity for PDE4 over PDE1, PDE2, PDE3 and PDE5 subtypes, respectively. Autoradiography was performed to substantiate results of biodistribution studies in the myocardium. RESULTS In vivo (R)-[11C]rolipram retention was dose-dependently reduced by co-injections of (R)-rolipram and (S)-rolipram (ED50 values of 0.03 mg/kg and 0.2 mg/kg, respectively). Vinpocetine, Bay 60-7550, cilostazol and zaprinast had no effect on (R)-[11C]rolipram binding, while (R)-rolipram and Ro 20-1724 reduced the tracer uptake to nonspecific levels in PDE4-rich tissues. CONCLUSIONS In addition to the brain, (R)-[11C]rolipram binds selectively to PDE4 across all cardiac regions, skeletal muscle, lungs and pancreas, but not in the adipose tissues. In vivo findings were confirmed by in vitro autoradiography studies, suggesting that (R)-[11C]rolipram can be applied to evaluate alterations in central and peripheral PDE4 levels and cAMP-mediated signaling.
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Affiliation(s)
- Miran Kenk
- Cardiac PET Centre, Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada K1Y 4W7
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Lourenco CM, Kenk M, Beanlands RS, DaSilva JN. Increasing synaptic noradrenaline, serotonin and histamine enhances in vivo binding of phosphodiesterase-4 inhibitor (R)-[11C]rolipram in rat brain, lung and heart. Life Sci 2006; 79:356-64. [PMID: 16499932 DOI: 10.1016/j.lfs.2006.01.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2005] [Revised: 12/22/2005] [Accepted: 01/11/2006] [Indexed: 10/25/2022]
Abstract
Phosphodiesterase-4 (PDE4) is one of the main enzymes that specifically terminate the action of cAMP, thereby contributing to intracellular signaling following stimulation of various G protein-coupled receptors. PDE4 expression and activity are modulated by agents affecting cAMP levels. The selective PDE4 inhibitor (R)-rolipram labeled with C-11 was tested in vivo in rats to analyze changes in PDE4 levels following drug treatments that increase synaptic noradrenaline (NA), serotonin (5HT), histamine (HA) and dopamine (DA) levels. We hypothesized that increasing synaptic neurotransmitter levels and subsequent cAMP-mediated signaling would significantly enhance (R)-[(11)C]rolipram retention and specific binding to PDE4 in vivo. Pre-treatments were performed 3 h prior to tracer injection, and rats were sacrificed 45 min later. Biodistribution studies revealed a dose-dependent increase in (R)-[(11)C]rolipram uptake following administration of the monoamine oxidase (MAO) inhibitor tranylcypromine, NA and 5HT reuptake inhibitors (desipramine [DMI], maprotiline; and fluoxetine, sertraline, respectively), and the HA H(3) receptor antagonist (thioperamide), but not with DA transporter blockers GBR 12909, cocaine or DA D(1) agonist SKF81297. Significant increases in rat brain and heart reflect changes in PDE4 specific binding (total-non-specific binding [coinjection with saturating dose of (R)-rolipram]). These results demonstrate that acute treatments elevating synaptic NA, 5HT and HA, but not DA levels, significantly enhance (R)-[(11)C]rolipram binding. Use of (R)-[(11)C]rolipram and positron emission tomography as an index of PDE4 activity could provide insight into understanding disease states with altered NA, 5HT and HA concentrations.
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Affiliation(s)
- Celia M Lourenco
- PET Centre, Centre for Addiction and Mental Health, 250 College St., Toronto, Ontario, Canada M5T 1R8
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