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Scott PJH, Shao X, Desmond TJ, Hockley BG, Sherman P, Quesada CA, Frey KA, Koeppe RA, Kilbourn MR, Bohnen NI. Investigation of Proposed Activity of Clarithromycin at GABAA Receptors Using [(11)C]Flumazenil PET. ACS Med Chem Lett 2016; 7:746-50. [PMID: 27563397 DOI: 10.1021/acsmedchemlett.5b00435] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 06/01/2016] [Indexed: 11/28/2022] Open
Abstract
Clarithromycin is a potential treatment for hypersomnia acting through proposed negative allosteric modulation of GABAA receptors. We were interested whether this therapeutic benefit might extend to Parkinson's disease (PD) patients because GABAergic neurotransmission is implicated in postural control. Prior to initiating clinical studies in PD patients, we wished to better understand clarithromycin's mechanism of action. In this work we investigated whether the proposed activity of clarithromycin at the GABAA receptor is associated with the benzodiazepine binding site using in vivo [(11)C]flumazenil positron emission tomography (PET) in primates and ex vivo [(3)H]flumazenil autoradiography in rat brain. While the studies demonstrate that clarithromycin does not change the K d of FMZ, nor does it competitively displace FMZ, there is preliminary evidence from the primate PET imaging studies that clarithromycin delays dissociation and washout of flumazenil from the primate brain in a dose-dependent fashion. These findings would be consistent with the proposed GABAA allosteric modulator function of clarithromycin. While the results are only preliminary, further investigation of the interaction of clarithromycin with GABA receptors and/or GABAergic medications is warranted, and therapeutic applications of clarithromycin alone or in combination with flumazenil, to treat hyper-GABAergic status in PD at minimally effective doses, should also be pursued.
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Affiliation(s)
- Peter J. H. Scott
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- The Interdepartmental Program in Medicinal Chemistry, The University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Xia Shao
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Timothy J. Desmond
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Brian G. Hockley
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Phillip Sherman
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Carole A. Quesada
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Kirk A. Frey
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Department
of Neurology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Robert A. Koeppe
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Michael R. Kilbourn
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
| | - Nicolaas I. Bohnen
- Division of Nuclear Medicine, Department of Radiology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Department
of Neurology, The University of Michigan Medical School, Ann Arbor, Michigan 48109, United States
- Neurology Service and Geriatrics Research,
Education, and Clinical Center, Veterans Affairs Ann Arbor Healthcare System, Ann Arbor, Michigan United States
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Rodnick ME, Hockley BG, Sherman P, Quesada C, Battle MR, Jackson A, Linder KE, Macholl S, Trigg WJ, Kilbourn MR, Scott PJH. Novel fluorine-18 PET radiotracers based on flumazenil for GABAA imaging in the brain. Nucl Med Biol 2013; 40:901-5. [PMID: 23890694 PMCID: PMC3769461 DOI: 10.1016/j.nucmedbio.2013.06.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2013] [Revised: 06/08/2013] [Accepted: 06/14/2013] [Indexed: 10/26/2022]
Abstract
INTRODUCTION Two 7-fluoroimidazobenzodiazepines (AH114726 and GEH120348), analogs of flumazenil, were labeled with fluorine-18 and evaluated as alternative radioligands for in vivo imaging of the GABAA/benzodiazepine receptor by comparing them to [(11)C]flumazenil in rhesus monkey. METHODS Radiotracers were prepared from the corresponding nitro-precursors in an automated synthesis module, and primate imaging studies were conducted on a Concorde MicroPET P4 scanner. The brain was imaged for 60 (12 × 5 min frames) or 90 min (18 × 5 min frames), and data was reconstructed using the 3D MAP algorithm. Specificity of [(18)F]AH114726 and [(18)F]GEH120348 was confirmed by displacement studies using unlabeled flumazenil. RESULTS [(18)F]GEH120348 and [(18)F]AH114726 were obtained in 13-24% yields (end of synthesis) with high chemical (>95%) and radiochemical (>99%) purities, and high specific activities (2061 ± 985 Ci/mmol). The in vivo pharmacokinetics of [(18)F]AH114726 and [(18)F]GEH120348 were determined in a non-human primate and directly compared with [(11)C]flumazenil. Both fluorine-18 radioligands showed time-dependent regional brain distributions that correlated with the distribution of [(11)C]flumazenil and the known concentrations of GABAA/benzodiazepine receptors in the monkey brain. [(18)F]AH114726 exhibited maximal brain uptake and tissue time-radioactivity curves that were most similar to [(11)C]flumazenil. In contrast, [(18)F]GEH120348 showed higher initial brain uptake but very different pharmacokinetics with continued accumulation of radioactivity into the cortical regions of high GABA/benzodiazepine receptor concentrations and very little clearance from the regions of low receptor densities. Rapid washout of both radiotracers occurred upon treatment with unlabeled flumazenil. CONCLUSION The ease of the radiochemical synthesis, together with in vivo brain pharmacokinetics most similar to [(11)C]flumazenil, support that [(18)F]AH114726 is a suitable option for imaging the GABAA receptor.
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Affiliation(s)
- Melissa E. Rodnick
- Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Brian G. Hockley
- Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Phillip Sherman
- Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Carole Quesada
- Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Mark R. Battle
- GE Healthcare, Medical Diagnostics, The Grove Centre, White Lion Road, Amersham, Buckinghamshire, UK
| | - Alexander Jackson
- GE Healthcare, Medical Diagnostics, The Grove Centre, White Lion Road, Amersham, Buckinghamshire, UK
| | - Karen E. Linder
- GE Healthcare, Medical Diagnostics, 101 Carnegie Center, Princeton, NJ, USA
| | - Sven Macholl
- GE Healthcare, Medical Diagnostics, The Grove Centre, White Lion Road, Amersham, Buckinghamshire, UK
| | - William J. Trigg
- GE Healthcare, Medical Diagnostics, The Grove Centre, White Lion Road, Amersham, Buckinghamshire, UK
| | - Michael R. Kilbourn
- Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Peter J. H. Scott
- Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, MI, USA
- The Interdepartmental Program in Medicinal Chemistry, The University of Michigan, Ann Arbor, MI, USA
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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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Sakiyama Y, Saito M, Inoue O. Acute treatment with pentobarbital alters the kinetics of in vivo receptor binding in the mouse brain. Nucl Med Biol 2006; 33:535-41. [PMID: 16720246 DOI: 10.1016/j.nucmedbio.2006.02.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 02/03/2006] [Accepted: 02/08/2006] [Indexed: 11/15/2022]
Abstract
The effect of pentobarbital, a sedative-hypnotic barbiturate, on the in vivo binding of benzodiazepine receptors in the mouse brain was investigated. Dose-related changes in the apparent binding of [3H]Ro15-1788 ([3H]flumazenil) in the cerebral cortex, cerebellum and pons-medulla were observed by pretreatment with pentobarbital. For quantification of the kinetic properties of the in vivo binding of [3H]Ro15-1788, time courses of radioactivity following its injection were examined, and kinetic analysis was performed using the compartment model. The time courses of radioactivity following injection of [3H]Ro15-1788 with 3 mg/kg Ro15-1788 were used as input function. In all regions studied, rate constants between input compartment and specific binding compartment were significantly decreased by pentobarbital. However, no significant alterations in the binding potential (BP=K3/K4) of benzodiazepine receptors by pentobarbital were observed in any of the regions. A saturation experiment indicated that the decrease in the input rate constant (K3), which includes both the association rate constant (k(on)) and the number of binding sites available (B(max)), was mainly due to decrease in k(on). These results suggest that apparent increases in binding at 20 min after tracer injection were due to the decrease in the association and dissociation rates of binding in vivo.
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Affiliation(s)
- Yojiro Sakiyama
- Division of Clinical Research, National Institute of Radiological Sciences, Inage-ku, Chibashi 263-8555, Japan.
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Maeda J, Suhara T, Kawabe K, Okauchi T, Obayashi S, Hojo J, Suzuki K. Visualization of alpha5 subunit of GABAA/benzodiazepine receptor by 11C Ro15-4513 using positron emission tomography. Synapse 2003; 47:200-8. [PMID: 12494402 DOI: 10.1002/syn.10169] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Although [(11)C]Ro15-4513 and [(11)C]flumazenil both bind to the central benzodiazepine (BZ) receptors, the distributions of the two ligands are not identical in vivo. Moreover, the in vivo pharmacological properties of [(11)C]Ro15-4513 have not been thoroughly examined. In the present study, we examined the pharmacological profile of [(11)C]Ro15-4513 binding in the monkey brain using positron emission tomography (PET). [(11)C]Ro15-4513 showed relatively high accumulation in the anterior cingulate cortex, hippocampus, and insular cortex, with the lowest uptake being observed in the pons. Accumulation in the cerebral cortex was significantly diminished by the BZ antagonist flumazenil (0.1 mg/kg, i.v.), but not that in the pons. Using the pons as a reference region, the specific binding of [(11)C]Ro15-4513 in most of the cerebral cortex including the limbic regions clearly revealed two different affinity sites. On the other hand, specific binding in the occipital cortex and cerebellum showed only a low affinity site. Zolpidem with affinity for alpha1, alpha2, and alpha3 subunits of GABA(A)/BZ receptor fully inhibited [(11)C]Ro15-4513 binding in the occipital cortex and cerebellum, while only about 23% of the binding was blocked in the anterior cingulate cortex. Diazepam with affinity for alpha1, alpha2, alpha3, and alpha5 subunits inhibited the binding in all brain regions. Since Ro15-4513 has relatively high affinity for the alpha5 subunit in vitro, these in vivo bindings of [(11)C]Ro15-4513 can be interpreted as the relatively high accumulation in the fronto-temporal limbic regions representing binding to the GABA(A)/BZ receptor alpha5 subunit.
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Affiliation(s)
- Jun Maeda
- Brain Imaging Project, National Institute of Radiological Sciences, Chiba, Japan
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