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Hong WC, Wasko MJ, Wilkinson DS, Hiranita T, Li L, Hayashi S, Snell DB, Madura JD, Surratt CK, Katz JL. Dopamine Transporter Dynamics of N-Substituted Benztropine Analogs with Atypical Behavioral Effects. J Pharmacol Exp Ther 2018; 366:527-540. [PMID: 29945932 DOI: 10.1124/jpet.118.250498] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 06/22/2018] [Indexed: 01/07/2023] Open
Abstract
Atypical dopamine transporter (DAT) inhibitors, despite high DAT affinity, do not produce the psychomotor stimulant and abuse profile of standard DAT inhibitors such as cocaine. Proposed contributing features for those differences include off-target actions, slow onsets of action, and ligand bias regarding DAT conformation. Several 3α-(4',4''-difluoro-diphenylmethoxy)tropanes were examined, including those with the following substitutions: N-(indole-3''-ethyl)- (GA1-69), N-(R)-2''-amino-3''-methyl-n-butyl- (GA2-50), N-2''aminoethyl- (GA2-99), and N-(cyclopropylmethyl)- (JHW013). These compounds were previously reported to have rapid onset of behavioral effects and were presently evaluated pharmacologically alone or in combination with cocaine. DAT conformational mode was assessed by substituted-cysteine accessibility and molecular dynamics (MD) simulations. As determined by substituted-cysteine alkylation, all BZT analogs except GA2-99 showed bias for a cytoplasmic-facing DAT conformation, whereas cocaine stabilized the extracellular-facing conformation. MD simulations suggested that several analog-DAT complexes formed stable R85-D476 "outer gate" bonds that close the DAT to extracellular space. GA2-99 diverged from this pattern, yet had effects similar to those of other atypical DAT inhibitors. Apparent DAT association rates of the BZT analogs in vivo were slower than that for cocaine. None of the compounds was self-administered or stimulated locomotion, and each blocked those effects of cocaine. The present findings provide more detail on ligand-induced DAT conformations and indicate that aspects of DAT conformation other than "open" versus "closed" may facilitate predictions of the actions of DAT inhibitors and may promote rational design of potential treatments for psychomotor-stimulant abuse.
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Affiliation(s)
- Weimin C Hong
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Michael J Wasko
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Derek S Wilkinson
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Takato Hiranita
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Libin Li
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Shuichiro Hayashi
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - David B Snell
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Jeffry D Madura
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Christopher K Surratt
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
| | - Jonathan L Katz
- Department of Pharmaceutical Sciences, Butler University, Indianapolis, Indiana (W.C.H.); Division of Pharmaceutical Sciences (M.J.W., C.K.S.) and Department of Chemistry and Biochemistry (J.D.M.), Duquesne University, Pittsburgh; and Molecular Neuropsychiatry Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland (D.S.W., T.H., L.L., S.H., D.B.S., J.L.K.)
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Lever SZ, Fan KH, Lever JR. Tactics for preclinical validation of receptor-binding radiotracers. Nucl Med Biol 2017; 44:4-30. [PMID: 27755986 PMCID: PMC5161541 DOI: 10.1016/j.nucmedbio.2016.08.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2016] [Revised: 08/24/2016] [Accepted: 08/24/2016] [Indexed: 12/20/2022]
Abstract
INTRODUCTION Aspects of radiopharmaceutical development are illustrated through preclinical studies of [125I]-(E)-1-(2-(2,3-dihydrobenzofuran-5-yl)ethyl)-4-(iodoallyl)piperazine ([125I]-E-IA-BF-PE-PIPZE), a radioligand for sigma-1 (σ1) receptors, coupled with examples from the recent literature. Findings are compared to those previously observed for [125I]-(E)-1-(2-(2,3-dimethoxy-5-yl)ethyl)-4-(iodoallyl)piperazine ([125I]-E-IA-DM-PE-PIPZE). METHODS Syntheses of E-IA-BF-PE-PIPZE and [125I]-E-IA-BF-PE-PIPZE were accomplished by standard methods. In vitro receptor binding studies and autoradiography were performed, and binding potential was predicted. Measurements of lipophilicity and protein binding were obtained. In vivo studies were conducted in mice to evaluate radioligand stability, as well as specific binding to σ1 sites in brain, brain regions and peripheral organs in the presence and absence of potential blockers. RESULTS E-IA-BF-PE-PIPZE exhibited high affinity and selectivity for σ1 receptors (Ki = 0.43 ± 0.03 nM, σ2/σ1 = 173). [125I]-E-IA-BF-PE-PIPZE was prepared in good yield and purity, with high specific activity. Radioligand binding provided dissociation (koff) and association (kon) rate constants, along with a measured Kd of 0.24 ± 0.01 nM and Bmax of 472 ± 13 fmol/mg protein. The radioligand proved suitable for quantitative autoradiography in vitro using brain sections. Moderate lipophilicity, Log D7.4 2.69 ± 0.28, was determined, and protein binding was 71 ± 0.3%. In vivo, high initial whole brain uptake, >6% injected dose/g, cleared slowly over 24 h. Specific binding represented 75% to 93% of total binding from 15 min to 24 h. Findings were confirmed and extended by regional brain biodistribution. Radiometabolites were not observed in brain (1%). CONCLUSIONS Substitution of dihydrobenzofuranylethyl for dimethoxyphenethyl increased radioligand affinity for σ1 receptors by 16-fold. While high specific binding to σ1 receptors was observed for both radioligands in vivo, [125I]-E-IA-BF-PE-PIPZE displayed much slower clearance kinetics than [125I]-E-IA-DM-PE-PIPZE. Thus, minor structural modifications of σ1 receptor radioligands lead to major differences in binding properties in vitro and in vivo.
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Affiliation(s)
- Susan Z Lever
- Department of Chemistry, University of Missouri, Columbia, MO, USA; University of Missouri Research Reactor Center, Columbia, MO, USA.
| | - Kuo-Hsien Fan
- Department of Chemistry, University of Missouri, Columbia, MO, USA
| | - John R Lever
- Department of Radiology, University of Missouri, Columbia, MO, USA; Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO, USA.
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N-phenylpropyl-N'-substituted piperazines occupy sigma receptors and alter methamphetamine-induced hyperactivity in mice. Pharmacol Biochem Behav 2016; 150-151:198-206. [PMID: 27851908 DOI: 10.1016/j.pbb.2016.11.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 11/10/2016] [Accepted: 11/12/2016] [Indexed: 11/21/2022]
Abstract
This study examined the effect of the N-phenylpropyl-N'-substituted piperazine ligands SA4503 (3.4-dimethoxyphenethyl), YZ-067 (4-methoxyphenethyl), YZ-185 (3-methoxyphenethyl) and Nahas-3h (4-methoxybenzyl) on methamphetamine-induced hyperactivity in mice. In a previous study in rats, SA4503 increased methamphetamine-induced hyperactivity at a lower ligand dose and enhanced it at a higher dose. The other ligands have not been investigated in this assay. Presently, mice were administered sigma ligands, and specific [125I]E-IA-DM-PE-PIPZE and [125I]RTI-121 binding was measured to determine σ1 sigma receptor and dopamine transporter occupancy, respectively. Mice were also administered sigma ligands followed by methamphetamine, and locomotor activity was measured. Each of the ligands occupied σ1 sigma receptors (ED50=0.2-0.6μmol/kg) with similar potency, but none occupied the transporter (ED50>10μmol/kg). At the highest dose tested (31.6μmol/kg) all four sigma ligands significantly attenuated methamphetamine-induced hyperactivity. Interestingly, SA4503, YZ-067 and Nahas-3h, but not YZ-185, enhanced methamphetamine-induced hyperactivity at lower ligand doses (1-3.16μmol/kg). These results suggest that these ligands function as stimulant agonists at lower doses and as antagonists at higher does, with subtle changes in the substitution pattern at the 3- and 4-positions of the phenethyl group contributing to the nature of the interactions. Overall, these data indicate a complex role for σ1 sigma receptor ligands in methamphetamine's behavioral effects.
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LEVER JOHNR, FERGASON-CANTRELL EMILYA, WATKINSON LISAD, CARMACK TERRYL, LORD SARAHA, XU RONG, MILLER DENNISK, LEVER SUSANZ. Cocaine occupancy of sigma1 receptors and dopamine transporters in mice. Synapse 2016; 70:98-111. [PMID: 26618331 PMCID: PMC4724290 DOI: 10.1002/syn.21877] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 11/11/2015] [Accepted: 11/23/2015] [Indexed: 01/12/2023]
Abstract
Activation of sigma1 (σ1) receptors contributes to the behavioral and toxic effects of (-)-cocaine. We studied a key step, the ability of (-)-cocaine to occupy σ1 receptors in vivo, using CD-1(®) mice and the novel radioligand [(125) I]E-N-1-(3'-iodoallyl)-N'-4-(3",4"-dimethoxyphenethyl)-piperazine ([(125) I]E-IA-DM-PE-PIPZE). (-)-Cocaine displayed an ED50 of 68 μmol/kg for inhibition of specific radioligand binding in whole brain, with values between 73 and 80 μmol/kg for heart, lung, and spleen. For comparison, an ED50 of 26 μmol/kg for (-)-cocaine occupancy of striatal dopamine transporters (DAT) was determined by inhibition of [(125) I]3β-(4-iodophenyl)tropan-2β-carboxylic acid isopropyl ester ([(125) I]RTI-121) binding. A chief finding is the relatively small potency difference between (-)-cocaine occupancy of σ1 receptors and the DAT, although the DAT occupancy is likely underestimated. Interactions of (-)-cocaine with σ1 receptors were assessed further using [(125) I]E-IA-DM-PE-PIPZE for regional cerebral biodistribution studies and quantitative ex vivo autoradiography of brain sections. (-)-Cocaine binding to cerebral σ1 receptors proved directly proportional to the relative site densities known for the brain regions. Nonradioactive E-IA-DM-PE-PIPZE gave an ED50 of 0.23 μmol/kg for occupancy of cerebral σ1 receptors, and a 3.16 μmol/kg (i.p.) dose attenuated (-)-cocaine-induced locomotor hyperactivity by 30%. This effect did not reach statistical significance, but suggests that E-IA-DM-PE-PIPZE is a probable σ1 receptor antagonist. As groundwork for the in vivo studies, we used standard techniques in vitro to determine ligand affinities, site densities, and pharmacological profiles for the σ1 and σ2 receptors expressed in CD-1(®) mouse brain.
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Affiliation(s)
- JOHN R. LEVER
- Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, Missouri 65211
- Research Service, Harry S. Truman Memorial Veterans’ Hospital, Columbia, Missouri 65201
| | - EMILY A. FERGASON-CANTRELL
- Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, Missouri 65211
- Research Service, Harry S. Truman Memorial Veterans’ Hospital, Columbia, Missouri 65201
| | - LISA D. WATKINSON
- Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, Missouri 65211
- Research Service, Harry S. Truman Memorial Veterans’ Hospital, Columbia, Missouri 65201
| | - TERRY L. CARMACK
- Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, Missouri 65211
- Research Service, Harry S. Truman Memorial Veterans’ Hospital, Columbia, Missouri 65201
| | - SARAH A. LORD
- Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, Missouri 65211
- Research Service, Harry S. Truman Memorial Veterans’ Hospital, Columbia, Missouri 65201
| | - RONG XU
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211
| | - DENNIS K. MILLER
- Department of Psychological Sciences, University of Missouri, Columbia, Missouri 65211
- Center for Translational Neuroscience, University of Missouri, Columbia, Missouri 65211
| | - SUSAN Z. LEVER
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211
- MU Research Reactor Center, University of Missouri, Columbia, Missouri 65212
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Kumar V, Yarravarapu N, Lapinsky DJ, Perley D, Felts B, Tomlinson MJ, Vaughan RA, Henry LK, Lever JR, Newman AH. Novel Azido-Iodo Photoaffinity Ligands for the Human Serotonin Transporter Based on the Selective Serotonin Reuptake Inhibitor (S)-Citalopram. J Med Chem 2015; 58:5609-19. [PMID: 26153715 PMCID: PMC4515784 DOI: 10.1021/acs.jmedchem.5b00682] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Three photoaffinity ligands (PALs)
for the human serotonin transporter
(hSERT) were synthesized based on the selective serotonin reuptake
inhibitor (SSRI), (S)-citalopram (1).
The classic 4-azido-3-iodo-phenyl group was appended to either the
C-1 or C-5 position of the parent molecule, with variable-length linkers,
to generate ligands 15, 22, and 26. These ligands retained high to moderate affinity binding (Ki = 24–227 nM) for hSERT, as assessed
by [3H]5-HT transport inhibition. When tested against Ser438Thr
hSERT, all three PALs showed dramatic rightward shifts in inhibitory
potency, with Ki values ranging from 3.8
to 9.9 μM, consistent with the role of Ser438 as a key residue
for high-affinity binding of many SSRIs, including (S)-citalopram. Photoactivation studies demonstrated irreversible adduction
to hSERT by all ligands, but the reduced (S)-citalopram
inhibition of labeling by [125I]15 compared
to that by [125I]22 and [125I]26 suggests differences in binding mode(s). These radioligands
will be useful for characterizing the drug–protein binding
interactions for (S)-citalopram at hSERT.
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Affiliation(s)
- Vivek Kumar
- †Medicinal Chemistry Section, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, 333 Cassell Drive, Baltimore, Maryland 21224, United States
| | - Nageswari Yarravarapu
- ‡Division of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States
| | - David J Lapinsky
- ‡Division of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States
| | - Danielle Perley
- §Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202, United States
| | - Bruce Felts
- §Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202, United States
| | - Michael J Tomlinson
- §Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202, United States
| | - Roxanne A Vaughan
- §Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202, United States
| | - L Keith Henry
- §Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202, United States
| | - John R Lever
- ∥Department of Radiology, University of Missouri, One Hospital Drive, Columbia, Missouri 65212, United States.,⊥Harry S. Truman Memorial Veterans' Hospital, 800 Hospital Drive, Columbia, Missouri 65201, United States
| | - Amy Hauck Newman
- †Medicinal Chemistry Section, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, 333 Cassell Drive, Baltimore, Maryland 21224, United States
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Xu R, Lord SA, Peterson RM, Fergason-Cantrell EA, Lever JR, Lever SZ. Ether modifications to 1-[2-(3,4-dimethoxyphenyl)ethyl]-4-(3-phenylpropyl)piperazine (SA4503): effects on binding affinity and selectivity for sigma receptors and monoamine transporters. Bioorg Med Chem 2015; 23:222-30. [PMID: 25468036 PMCID: PMC4274187 DOI: 10.1016/j.bmc.2014.11.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 10/25/2014] [Accepted: 11/04/2014] [Indexed: 11/22/2022]
Abstract
Two series of novel ether analogs of the sigma (σ) receptor ligand 1-[2-(3,4-dimethoxyphenyl)ethyl]-4-(3-phenylpropyl)piperazine (SA4503) have been prepared. In one series, the alkyl portion of the 4-methoxy group was replaced with allyl, propyl, bromoethyl, benzyl, phenethyl, and phenylpropyl moieties. In the second series, the 3,4-dimethoxy was replaced with cyclic methylenedioxy, ethylenedioxy and propylenedioxy groups. These ligands, along with 4-O-des-methyl SA4503, were evaluated for σ1 and σ2 receptor affinity, and compared to SA4503 and several known ether analogs. SA4503 and a subset of ether analogs were also evaluated for dopamine transporter (DAT) and serotonin transporter (SERT) affinity. The highest σ1 receptor affinities, Ki values of 1.75-4.63 nM, were observed for 4-O-des-methyl SA4503, SA4503 and the methylenedioxy analog. As steric bulk increased, σ1 receptor affinity decreased, but only to a point. Allyl, propyl and bromoethyl substitutions gave σ1 receptor Ki values in the 20-30 nM range, while bulkier analogs having phenylalkyl, and Z- and E-iodoallyl, ether substitutions showed higher σ1 affinities, with Ki values in the 13-21 nM range. Most ligands studied exhibited comparable σ1 and σ2 affinities, resulting in little to no subtype selectivity. SA4503, the fluoroethyl analog and the methylenedioxy congener showed modest six- to fourteen-fold selectivity for σ1 sites. DAT and SERT interactions proved much more sensitive than σ receptor interactions to these structural modifications. For example, the benzyl congener (σ1Ki=20.8 nM; σ2Ki=16.4 nM) showed over 100-fold higher DAT affinity (Ki=121 nM) and 6-fold higher SERT affinity (Ki=128nM) than the parent SA4503 (DAT Ki=12650 nM; SERT Ki=760 nM). Thus, ether modifications to the SA4503 scaffold can provide polyfunctional ligands having a broader spectrum of possible pharmacological actions.
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Affiliation(s)
- Rong Xu
- Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
| | - Sarah A Lord
- Department of Radiology, University of Missouri, Columbia, MO 65212, USA; Harry S. Truman Memorial Veterans' Hospital, Columbia, MO, USA
| | - Ryan M Peterson
- Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
| | - Emily A Fergason-Cantrell
- Department of Radiology, University of Missouri, Columbia, MO 65212, USA; Harry S. Truman Memorial Veterans' Hospital, Columbia, MO, USA
| | - John R Lever
- Department of Radiology, University of Missouri, Columbia, MO 65212, USA; Harry S. Truman Memorial Veterans' Hospital, Columbia, MO, USA.
| | - Susan Z Lever
- Department of Chemistry, University of Missouri, Columbia, MO 65211, USA; Department of MU Research Reactor Center, University of Missouri, Columbia, MO 65211, USA.
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Lever JR, Miller DK, Fergason-Cantrell EA, Green CL, Watkinson LD, Carmack TL, Lever SZ. Relationship between cerebral sigma-1 receptor occupancy and attenuation of cocaine's motor stimulatory effects in mice by PD144418. J Pharmacol Exp Ther 2014; 351:153-63. [PMID: 25100754 PMCID: PMC4165029 DOI: 10.1124/jpet.114.216671] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Accepted: 08/05/2014] [Indexed: 01/28/2023] Open
Abstract
Psychostimulant effects of cocaine are mediated partly by agonist actions at sigma-1 (σ1) receptors. Selective σ1 receptor antagonists attenuate these effects and provide a potential avenue for pharmacotherapy. However, the selective and high affinity σ1 antagonist PD144418 (1,2,3,6-tetrahydro-5-[3-(4-methylphenyl)-5-isoxazolyl]-1-propylpyridine) has been reported not to inhibit cocaine-induced hyperactivity. To address this apparent paradox, we evaluated aspects of PD144418 binding in vitro, investigated σ1 receptor and dopamine transporter (DAT) occupancy in vivo, and re-examined effects on locomotor activity. PD144418 displayed high affinity for σ1 sites (Ki 0.46 nM) and 3596-fold selectivity over σ2 sites (Ki 1654 nM) in guinea pig brain membranes. No appreciable affinity was noted for serotonin and norepinephrine transporters (Ki >100 μM), and the DAT interaction was weak (Ki 9.0 μM). In vivo, PD144418 bound to central and peripheral σ1 sites in mouse, with an ED50 of 0.22 μmol/kg in whole brain. No DAT occupancy by PD144418 (10.0 μmol/kg) or possible metabolites were observed. At doses that did not affect basal locomotor activity, PD144418 (1, 3.16, and 10 μmol/kg) attenuated cocaine-induced hyperactivity in a dose-dependent manner in mice. There was good correlation (r(2) = 0.88) of hyperactivity reduction with increasing cerebral σ1 receptor occupancy. The behavioral ED50 of 0.79 μmol/kg corresponded to 80% occupancy. Significant σ1 receptor occupancy and the ability to mitigate cocaine's motor stimulatory effects were observed for 16 hours after a single 10.0 μmol/kg dose of PD144418.
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Affiliation(s)
- John R Lever
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
| | - Dennis K Miller
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
| | - Emily A Fergason-Cantrell
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
| | - Caroline L Green
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
| | - Lisa D Watkinson
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
| | - Terry L Carmack
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
| | - Susan Z Lever
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri (J.R.L., E.A.F.-C., L.D.W., T.L.C.); and Department of Radiology and Radiopharmaceutical Sciences Institute (J.R.L., E.A.F.-C., L.D.W., T.L.C.), Department of Medical Pharmacology and Physiology (J.R.L.), Department of Psychological Sciences (D.K.M., C.L.G.), Center for Translational Neuroscience (D.K.M.), Department of Chemistry (S.Z.L.), and MU Research Reactor Center (S.Z.L.), University of Missouri, Columbia, Missouri
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8
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Lever JR, Miller DK, Green CL, Fergason-Cantrell EA, Watkinson LD, Carmack TL, Fan KH, Lever SZ. A selective sigma-2 receptor ligand antagonizes cocaine-induced hyperlocomotion in mice. Synapse 2014; 68:73-84. [PMID: 24123353 DOI: 10.1002/syn.21717] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 09/07/2013] [Indexed: 11/06/2022]
Abstract
Cocaine functions, in part, through agonist actions at sigma-1 (σ1 ) receptors, while roles played by sigma-2 (σ2 ) receptors are less established. Attempts to discriminate σ2 receptor-mediated effects of cocaine in locomotor hyperactivity assays have been hampered by the lack of potent and selective antagonists. Certain tetrahydroisoquinolinyl benzamides display high σ2 receptor affinity, and excellent selectivity for binding to σ2 over σ1 receptors. The behavioral properties of this structural class of σ ligands have not yet been investigated. The present study evaluated 5-bromo-N-[4-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-butyl)]-2,3-dimethoxy-benzamide, 1, a ligand shown by others to bind preferentially to σ2 over σ1 receptors, as well as dopamine D2 and D3 sites. First, we determined binding to monoamine transporters and opioid receptors, and noted 57-fold selectivity for σ2 receptors over the serotonin transporter, and >800-fold selectivity for σ2 receptors over the other sites tested. We then examined 1 in locomotor activity studies using male CD-1® mice, and saw no alteration of basal activity at doses up to 31.6 µmol/kg. Cocaine produced a fivefold increase in locomotor activity, which was attenuated by 66% upon pretreatment of mice with 1 at 31.6 µmol/kg. In vivo radioligand binding studies also were performed, and showed no occupancy of σ1 receptors or the dopamine transporter by 1, or its possible metabolites, at the 31.6 µmol/kg dose. Thus, ligand 1 profiles behaviorally as a σ2 receptor-selective antagonist that is able to counteract cocaine's motor stimulatory effects.
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Affiliation(s)
- John R Lever
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, 65201; Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, Missouri, 65211; Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, 65211
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9
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Desai RI, Grandy DK, Lupica CR, Katz JL. Pharmacological characterization of a dopamine transporter ligand that functions as a cocaine antagonist. J Pharmacol Exp Ther 2013; 348:106-15. [PMID: 24194528 DOI: 10.1124/jpet.113.208538] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
An N-butyl analog of benztropine, JHW007 [N-(n-butyl)-3α-[bis(4'-fluorophenyl)methoxy]-tropane], binds to dopamine transporters (DAT) but has reduced cocaine-like behavioral effects and antagonizes various effects of cocaine. The present study further examined mechanisms underlying these effects. Cocaine dose-dependently increased locomotion, whereas JHW007 was minimally effective but increased activity 24 hours after injection. JHW007 (3-10 mg/kg) dose-dependently and fully antagonized the locomotor-stimulant effects of cocaine (5-60 mg/kg), whereas N-methyl and N-allyl analogs and the dopamine (DA) uptake inhibitor GBR12909 [1-(2-[bis(4-fluorophenyl)methoxy]ethyl)-4-(3-phenylpropyl)piperazine dihydrochloride] stimulated activity and failed to antagonize effects of cocaine. JHW007 also blocked the locomotor-stimulant effects of the DAT inhibitor GBR12909 but not stimulation produced by the δ-opioid agonist SNC 80 [4-[(R)-[(2S,5R)-4-allyl-2,5-dimethylpiperazin-1-yl](3-methoxyphenyl)methyl]-N,N-diethylbenzamide], which increases activity through nondopaminergic mechanisms. JHW007 blocked locomotor-stimulant effects of cocaine in both DA D2- and CB1-receptor knockout and wild-type mice, indicating a lack of involvement of these targets. Furthermore, JHW007 blocked effects of cocaine on stereotyped rearing but enhanced stereotyped sniffing, suggesting that interference with locomotion by enhanced stereotypies is not responsible for the cocaine-antagonist effects of JHW007. Time-course data indicate that administration of JHW007 antagonized the locomotor-stimulant effects of cocaine within 10 minutes of injection, whereas occupancy at the DAT, as determined in vivo, did not reach a maximum until 4.5 hours after injection. The σ1-receptor antagonist BD 1008 [N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine dihydrobromide] blocked the locomotor-stimulant effects of cocaine. Overall, these findings suggest that JHW007 has cocaine-antagonist effects that are deviate from its DAT occupancy and that some other mechanism, possibly σ-receptor antagonist activity, may contribute to the cocaine-antagonist effect of JHW007 and like drugs.
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Affiliation(s)
- Rajeev I Desai
- Psychobiology Section (R.I.D., J.L.K.) and Electrophysiology Research Section (C.R.L.), National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland; and Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon (D.K.G.)
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10
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Lever SZ, Xu R, Fan KH, Fergason-Cantrell EA, Carmack TL, Watkinson LD, Lever JR. Synthesis, radioiodination and in vitro and in vivo sigma receptor studies of N-1-allyl-N´-4-phenethylpiperazine analogs. Nucl Med Biol 2012; 39:401-14. [PMID: 22172395 DOI: 10.1016/j.nucmedbio.2011.10.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Revised: 08/25/2011] [Accepted: 10/05/2011] [Indexed: 10/14/2022]
Abstract
INTRODUCTION Sigma-1 (σ(1)) receptor radioligands are useful for basic pharmacology studies and for imaging studies in neurology, psychiatry and oncology. We derived a hybrid structure, N-1-allyl-N´-4-phenethylpiperazine, from known ligands TPCNE and SA4503 for use as a scaffold for development of radioiodinated σ(1) receptor ligands. METHODS E-and Z-N-1-(3'-iodoallyl)-N´-4-(3″,4″-dimethoxyphenethyl)-piperazine (E-1 and Z-1), N-1-allyl-N´-4-(3',4'-dimethoxyphenethyl)-piperazine (2) and E-N-1-(3'-iodoallyl)-N´-4-(3″-methoxy-4'´-hydroxyphenethyl)-piperazine (3) were synthesized. Affinities for σ(1) and σ(2) receptors were determined. [(125)I]E-1 and [(125)I]Z-1 were prepared and evaluated in vivo in mice. [(125)I]E-1 was further evaluated in σ(1) receptor binding assays in vitro. RESULTS E-1 displayed moderately high apparent affinity (15 nM) for σ(1) sites and 84-fold selectivity against σ(2) sites. Z-1 showed similar σ(1) affinity, but only 23-fold selectivity. In contrast, 2 exhibited poor binding to both subtypes, while 3 had good affinities but poor selectivity. E-1 profiled as a probable antagonist in the phenytoin shift assay. [(125)I]E-1 and [(125)I]Z-1 were prepared in good yields and with high specific radioactivities. Log D(7.4) values (2.25 and 2.27) fall within the optimal range for in vivo studies. Both radioligands selectively labeled σ(1) receptors in mouse brain and peripheral organs in vivo. [(125)I]E-1 showed a higher level of specific binding than [(125)I]Z-1 and displayed good metabolic stability. Further, [(125)I]E-1 selectively labeled σ(1) receptors in mouse brain homogenates (K(d) 3.79 nM; B(max)=599 fmol/mg protein). CONCLUSIONS [(125)I]E-1 is a selective σ(1) receptor radioligand that exhibits properties amenable to in vitro and in vivo studies, with possible extension to single photon emission computed tomography using iodine-123.
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Affiliation(s)
- Susan Z Lever
- Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.
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11
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Parnas ML, Gaffaney JD, Zou MF, Lever JR, Newman AH, Vaughan RA. Labeling of dopamine transporter transmembrane domain 1 with the tropane ligand N-[4-(4-azido-3-[125I]iodophenyl)butyl]-2beta-carbomethoxy-3beta-(4-chlorophenyl)tropane implicates proximity of cocaine and substrate active sites. Mol Pharmacol 2008; 73:1141-50. [PMID: 18216182 DOI: 10.1124/mol.107.043679] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The novel photoaffinity ligand N-[4-(4-azido-3-(125)I-iodophenyl)-butyl]-2-beta-carbomethoxy-3beta-(4-chlorophenyl) tropane ([(125)I]MFZ 2-24) was used to investigate the site for cocaine binding on the dopamine transporter (DAT). [(125)I]MFZ 2-24 irreversibly labeled both rat striatal and expressed human DAT with high affinity and appropriate pharmacological specificity. Tryptic proteolysis of [(125)I]MFZ 2-24 labeled DAT followed by epitope-specific immunoprecipitation demonstrated that the ligand becomes adducted almost exclusively to transmembrane domains (TMs) 1-2. Further localization of [(125)I]MFZ 2-24 incorporation achieved by proteolyzing labeled wild-type and methionine mutant DATs with cyanogen bromide identified the sequence between residues 68 and 80 in TM1 as the ligand adduction site. This is in marked contrast to the previously identified attachment of the photoaffinity label [(125)I]RTI 82 in TM6. Because [(125)I]MFZ 2-24 and [(125)I]RTI 82 possess identical tropane pharmacophores and differ only in the placement of the reactive azido moieties, their distinct incorporation profiles identify the regions of the protein adjacent to different aspects of the cocaine molecule. These findings thus strongly support the direct interaction of cocaine on DAT with TM1 and TM6, both of which have been implicated by mutagenesis and homology to a bacterial leucine transporter as active sites for substrates. These results directly establish the proximity of TMs 1 and 6 in DAT and suggest that the mechanism of transport inhibition by cocaine involves close interactions with multiple regions of the substrate permeation pathway.
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Affiliation(s)
- M Laura Parnas
- Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202, USA
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12
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Filer CN. The synthesis of dopaminergic radioligands labelled with tritium and iodine-125. J Labelled Comp Radiopharm 2007. [DOI: 10.1002/jlcr.1399] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Marazziti D, Baroni S, Fabbrini L, Italiani P, Catena M, Dell'Osso B, Betti L, Giannaccini G, Lucacchini A, Cassano GB. Binding of 3H-WIN-35,428 and 125I-RTI-121 to Human Platelet Membranes. Neurochem Res 2006; 31:361-5. [PMID: 16733812 DOI: 10.1007/s11064-005-9028-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/16/2005] [Indexed: 11/29/2022]
Abstract
The dopamine transporter (DAT) is a protein regulating dopamine concentration in the synaptic cleft through the re-uptake mechanism. The DAT is the main target of psychostimulants and seems to play a pivotal role in neuronal degeneration and different neuropsychiatric disorders involving the dopamine system. Exhaustive research, however, regarding the presence of this protein in human platelets is still inconclusive, although it is thought that it might provide a peripheral tool to serve as a mean of exploring the same structure present in the brain. Therefore, we assessed some binding assays in platelets derived from healthy human subjects by means of 3H-WIN 35,428, a compound which is considered a selective ligand for the labelling of this protein, and by means of 125I-RTI-121, another compound with high specificity for DAT. The results showed that the binding of 3H-WIN-35,428 was too low to enable the detection of any structure; the binding of 125I-RTI-121, on the other hand, revealed the presence of two binding sites with pharmacological profiles similar to that of the serotonin transporter (SERT). In conclusions, therefore, platelets would not seem to be a useful model for exploring the DAT, given the prevalence therein of the SERT and the difficulty of labelling the DAT with the currently available ligands.
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Affiliation(s)
- Donatella Marazziti
- Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, University of Pisa, Pisa, Italy.
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14
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Katsifis A, Papazian V, Jackson T, Loc'h C. A rapid and efficient preparation of [123I]radiopharmaceuticals using a small HPLC (Rocket®) column. Appl Radiat Isot 2006; 64:27-31. [PMID: 16129607 DOI: 10.1016/j.apradiso.2005.06.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Revised: 05/31/2005] [Accepted: 06/06/2005] [Indexed: 10/25/2022]
Abstract
A simplified method for the rapid and efficient preparation of [(123)I]radiopharmaceuticals is described. Three radiopharmaceuticals, [(123)I]beta-CIT, [(123)I]MIBG and [(123)I]clioquinol, were synthesised and purified as model compounds. The radiotracers were labelled with iodine-123 using electrophilic oxidative conditions and purified by a compact semi-preparative reverse phase column (C-18, 3 microm, 7 x 53 mm, Alltima Rocket, Alltech) using aqueous-ethanol as HPLC solvents that were directly used for radiopharmaceutical formulation. The radiochemical purity of the radioiodinated tracers as assessed by analytical HPLC was higher than 99% with specific activity higher than 3 GBq/nmol. The total preparation time of a radiotracer ranged from 40 to 60 min and, starting from 3.7 GBq of iodine-123, more than 2.5 GBq of formulated radiopharmaceuticals were available for clinical investigations.
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Affiliation(s)
- Andrew Katsifis
- Radiopharmaceuticals Division R&D, Australian Nuclear Science & Technology, Organisation, Menai, NSW 2234, Sydney, Australia.
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15
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Desai RI, Kopajtic TA, French D, Newman AH, Katz JL. Relationship between in Vivo Occupancy at the Dopamine Transporter and Behavioral Effects of Cocaine, GBR 12909 [1-{2-[Bis-(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)piperazine], and Benztropine Analogs. J Pharmacol Exp Ther 2005; 315:397-404. [PMID: 16014753 DOI: 10.1124/jpet.105.091231] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Analogs of benztropine (BZT) bind to the dopamine (DA) transporter and inhibit DA uptake but often have behavioral effects that differ from those of cocaine and other DA-uptake inhibitors. To better understand these differences, we examined the relationship between locomotor-stimulant effects of cocaine, 1-{2-[bis-(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)-piperazine (GBR 12909), and BZT analogs [(3alpha-[bis(4'-fluorophenyl)methoxy]-tropane) (AHN 1-055) and (N-allyl-3alpha-[bis(4'-fluorophenyl)methoxy]-tropane) (AHN 2-005)] and their in vivo displacement of the DA transporter ligand [125I]3beta-(4-iodophenyl)-tropan-2beta-carboxylic acid isopropyl ester hydrochloride (RTI-121) in striatum. Cocaine, GBR 12909, and BZT analogs each displaced [125I]RTI-121 and stimulated locomotor activity in a dose- and time-dependent manner. The time course revealed a slower onset of both effects for AHN 1-055 and AHN 2-005 compared with cocaine and GBR 12909. The BZT analogs were less effective than cocaine and GBR 12909 in stimulating locomotor activity. Locomotor stimulant effects of cocaine were generally greater than predicted by the regression of displacement of [125I]RTI-121 and effect at short times after injection and less than predicted at longer times after injection. This result suggests that the apparent rate of occupancy of the DA transporter, in addition to percentage of sites occupied, contributes to the behavioral effects of cocaine. The present results suggest that among drugs that act at the DA transporter, the slower apparent rates of occupancy with the DA transporter by the BZT analogs may contribute in an important way to differences in their effectiveness.
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Affiliation(s)
- Rajeev I Desai
- Medication Discovery Research Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD 21224, USA
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Madras BK, Gracz LM, Meltzer PC, Liang AY, Elmaleh DR, Kaufman MJ, Fischman AJ. Altropane, a SPECT or PET imaging probe for dopamine neurons: II. Distribution to dopamine-rich regions of primate brain. Synapse 1998; 29:105-15. [PMID: 9593101 DOI: 10.1002/(sici)1098-2396(199806)29:2<105::aid-syn2>3.0.co;2-b] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The dopamine transporter in brain, localized almost exclusively on dopamine neurons, is an effective window on dopamine neurons. SPECT or PET imaging of the transporter in brain requires selective imaging agents that display appropriate pharmacokinetic properties. We previously reported that [125I]altropane ([125I]IACFT,2beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1- iodoprop-1-en-3-yl)nortropane) bound with high affinity (Kd: 5.33 nM) to a single site on the dopamine transporter and was selective for dopamine over the serotonin transporter in homogenates of monkey striatum. To determine whether the selective binding of [125I]altropane is reflected in its brain distribution, the in vitro and ex vivo distribution of [125I]altropane in squirrel monkey (Saimiri sciureus) brain was determined by quantitative autoradiography of coronal brain sections. In vitro, [125I]altropane (2 nM) distribution was discrete and was detectable primarily in the dopamine-rich putamen, caudate nucleus, and nucleus accumbens. The resulting putamen:cerebellum ratio exceeded 120:1 (n = 3). The selective in vitro binding of [125I]altropane to the dopamine transporter, at concentrations approaching its Kd value (Kd: 5.33 nM, a single high affinity site), highlight its suitability for investigating the density of the dopamine transporter in various brain regions in vitro. Ex vivo autoradiography was conducted in monkeys to determine whether the brain distribution of [125I]altropane in vitro was predictive of its brain distribution pattern after intravenous administration. Thirty minutes after intravenous injection, highest levels of [125I]altropane (0.3 nmol/kg) were detected in the caudate-putamen and nucleus accumbens and lowest levels in the cerebellum and cortex. The putamen or caudate:cerebellum ratio was 7. SPECT imaging of the brain within 30 min of i.v. injection confirmed the rapid and selective accumulation of [123I]altropane to the striatum. The selective binding of altropane to the dopamine-rich striatum within 30 min of i.v. administration indicates that it is uniquely suited for SPECT or PET imaging of the dopamine transporter and associated dopamine neurons.
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Affiliation(s)
- B K Madras
- Dept. of Psychiatry, Harvard Medical School, New England Regional Primate Research Center, Southborough, Massachusetts 01772-9102, USA.
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Scheffel U, Lever JR, Abraham P, Parham KR, Mathews WB, Kopajtic T, Carroll FI, Kuhar MJ. N-substituted phenyltropanes as in vivo binding ligands for rapid imaging studies of the dopamine transporter. Synapse 1997; 25:345-9. [PMID: 9097393 DOI: 10.1002/(sici)1098-2396(199704)25:4<345::aid-syn5>3.0.co;2-a] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Variously substituted phenyltropanes are proven as superb binding ligands for the dopamine transporter (DAT). In this study, we examine four N-substituted phenyltropanes which are derivatives of RTI-55 as in vivo binding ligands in mice. In this series, the methyl group on the nitrogen was replaced by a propyl (RTI-310), an allyl (RTI-311), a butyl (RTI-312), or a fluoropropyl (RTI-313) group. The in vitro binding potencies of these compounds at rat striatal DAT varied somewhat but were about 1 nM. While these compounds did not display marked selectivity for the dopamine transporter, they were more selective than RTI-55. Injection of the radiolabeled compound into mice resulted in striatal-to-cerebellar ratios that varied from about 4.5-6.5. The ratios peaked most rapidly for RTI-311 and RTI-313, at about 20 min. Pharmacological inhibition studies indicated that these compounds were binding to DATs in the striatum, as expected. These findings suggest that some compounds of this type may be excellent in vivo binding ligands for rapid imaging studies of the DAT.
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Affiliation(s)
- U Scheffel
- Division of Nuclear Medicine and Radiation Health Sciences, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205-2179, USA
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