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Oviatt A, Gibson EG, Huang J, Mattern K, Neuman KC, Chan PF, Osheroff N. Interactions between Gepotidacin and Escherichia coli Gyrase and Topoisomerase IV: Genetic and Biochemical Evidence for Well-Balanced Dual-Targeting. ACS Infect Dis 2024; 10:1137-1151. [PMID: 38606465 PMCID: PMC11015057 DOI: 10.1021/acsinfecdis.3c00346] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 02/07/2024] [Accepted: 02/13/2024] [Indexed: 04/13/2024]
Abstract
Antimicrobial resistance is a global threat to human health. Therefore, efforts have been made to develop new antibacterial agents that address this critical medical issue. Gepotidacin is a novel, bactericidal, first-in-class triazaacenaphthylene antibacterial in clinical development. Recently, phase III clinical trials for gepotidacin treatment of uncomplicated urinary tract infections caused by uropathogens, including Escherichia coli, were stopped for demonstrated efficacy. Because of the clinical promise of gepotidacin, it is important to understand how the compound interacts with its cellular targets, gyrase and topoisomerase IV, from E. coli. Consequently, we determined how gyrase and topoisomerase IV mutations in amino acid residues that are involved in gepotidacin interactions affect the susceptibility of E. coli cells to the compound and characterized the effects of gepotidacin on the activities of purified wild-type and mutant gyrase and topoisomerase IV. Gepotidacin displayed well-balanced dual-targeting of gyrase and topoisomerase IV in E. coli cells, which was reflected in a similar inhibition of the catalytic activities of these enzymes by the compound. Gepotidacin induced gyrase/topoisomerase IV-mediated single-stranded, but not double-stranded, DNA breaks. Mutations in GyrA and ParC amino acid residues that interact with gepotidacin altered the activity of the compound against the enzymes and, when present in both gyrase and topoisomerase IV, reduced the antibacterial activity of gepotidacin against this mutant strain. Our studies provide insights regarding the well-balanced dual-targeting of gyrase and topoisomerase IV by gepotidacin in E. coli.
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Affiliation(s)
- Alexandria
A. Oviatt
- Department
of Biochemistry, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232, United States
| | - Elizabeth G. Gibson
- Department
of Biochemistry, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232, United States
- Department
of Pharmacology, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232, United States
| | - Jianzhong Huang
- Infectious
Diseases Research Unit, GlaxoSmithKline, Collegeville, Pennsylvania 19426, United States
| | - Karen Mattern
- Infectious
Diseases Research Unit, GlaxoSmithKline, Collegeville, Pennsylvania 19426, United States
| | - Keir C. Neuman
- Laboratory
of Single Molecule Biophysics, National
Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20982, United States
| | - Pan F. Chan
- Infectious
Diseases Research Unit, GlaxoSmithKline, Collegeville, Pennsylvania 19426, United States
| | - Neil Osheroff
- Department
of Biochemistry, Vanderbilt University School
of Medicine, Nashville, Tennessee 37232, United States
- Department
of Medicine (Hematology/Oncology), Vanderbilt
University School of Medicine, Nashville, Tennessee 37232, United States
- VA
Tennessee
Valley Healthcare System, Nashville, Tennessee 37212, United States
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Gibson EG, Campagne O, Selvo NS, Gajjar A, Stewart CF. Population pharmacokinetic analysis of crizotinib in children with progressive/recurrent high-grade and diffuse intrinsic pontine gliomas. Cancer Chemother Pharmacol 2021; 88:1009-1020. [PMID: 34586478 DOI: 10.1007/s00280-021-04357-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 09/19/2021] [Indexed: 10/20/2022]
Abstract
PURPOSE Crizotinib, a potent oral tyrosine kinase inhibitor, was evaluated in combination with dasatinib in a phase 1 trial (NCT01644773) in children with progressive or recurrent high-grade and diffuse intrinsic pontine gliomas (HGG and DIPG). This study aimed to characterize the pharmacokinetics of crizotinib in this population and identify significant covariates. METHODS Patients (N = 36, age range 2.9-21.3 years) were treated orally once or twice-daily with 100-215 mg/m2 crizotinib and 50-65 mg/m2 dasatinib. Pharmacokinetic studies were performed for crizotinib alone after the first dose and at steady state, and for the drug combination at steady state. Crizotinib plasma concentrations were measured using a validated LC-MS/MS method. Population modeling was performed (Monolix) and the impact of factors including patient demographics and co-medications were investigated on crizotinib pharmacokinetics. RESULTS Crizotinib concentrations were described with a linear two-compartment model and absorption lag time. Concomitant dasatinib and overweight/obese status significantly influenced crizotinib pharmacokinetics, resulting in clinically relevant impact (> 20%) on drug exposure. Crizotinib mean apparent clearance (CL/F) was 66.7 L/h/m2 after single-dose and decreased to 26.5 L/h/m2 at steady state when given alone, but not when combined with dasatinib (mean 60.8 L/h/m2). Overweight/obese patients exhibited lower crizotinib CL/F and apparent volume V1/F (mean 46.2 L/h/m2 and 73.3 L/m2) compared to other patients (mean 75.5 L/h/m2 and 119.3 L/m2, p < 0.001). CONCLUSION A potential pharmacokinetic interaction was observed between crizotinib and dasatinib in children with HGG and DIPG. Further, crizotinib exposure was significantly higher in overweight/obese patients, who may require a dosing adjustment.
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Affiliation(s)
- Elizabeth G Gibson
- Department of Pharmacy and Pharmaceutical Sciences, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN, 38105, USA.,Bristol Myers Squibb, Princeton, NJ, USA
| | - Olivia Campagne
- Department of Pharmacy and Pharmaceutical Sciences, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN, 38105, USA
| | - Nicholas S Selvo
- Department of Pharmacy and Pharmaceutical Sciences, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN, 38105, USA
| | - Amar Gajjar
- Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA
| | - Clinton F Stewart
- Department of Pharmacy and Pharmaceutical Sciences, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN, 38105, USA.
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Gibson EG, Davis A, Zhong B, Campagne O, Roussel MF, Stewart CF. Abstract 3031: Characterization of gemcitabine triphosphate formation in mice to aid in the development of a translational tumor model. Cancer Res 2020. [DOI: 10.1158/1538-7445.am2020-3031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Gemcitabine (dFdC), a cytosine analog, is currently being evaluated in combination with other chemotherapeutic agents as therapy to treat children and young adults with CNS tumors in institutional clinical trials (NCT01878617, NCT03434262, and NCT04023669). Once in cells, dFdC undergoes a complex transformation into its active metabolite, gemcitabine triphosphate (dFdCTP), which exerts cytotoxic effects by inhibiting DNA synthesis. Our overall goal is to develop a translational pharmacokinetic (PK) model to predict dFdCTP concentrations in brain tumor tissue from mice to humans. This model will provide insights to potentially adjust clinical dFdC dosages. The intracellular formation of dFdCTP is known to be limited in humans due to the saturation of deoxycytidine kinase (dCK), an enzyme involved in dFdC metabolism, which occurs at dFdC plasma concentrations ~20 µM. It is critical to include the saturation of dCK in the PK model to assure the translatability between species; however, it has not been well characterized in mice. Thus, the objective of this study was to determine the formation of dFdCTP in peripheral blood mononuclear cells (PBMCs) in mice at clinically relevant dosages to investigate the dCK saturation. CD-1 nude mice (N=4 per group) were dosed with 40, 60, and 120 mg/kg dFdC via IV bolus (<1 min infusion). dFdC and dFdCTP concentrations were measured in plasma and in PBMCs, respectively, for up to 4h post-single dose, using validated LC-MS/MS methods, and analyzed with a naïve-pooled modeling approach using ADAPT 5 (BSMR, Los Angeles, CA, USA). dFdC plasma PK data were adequately fitted with a two-compartment model, and dFdCTP PBMC data were captured with a one-compartment model linked to the dFdC model. The 40, 60, and 120 mg/kg dosages resulted in plasma dFdC exposures (area under the curve, AUC) of 20.9 ± 6.8 µM·h, 30.1 ± 8.1 µM·h, and 62.8 ± 17.0 µM·h, which were within the range of dFdC AUC values previously published for children with brain tumors (Campagne et al, J Clin Oncol, suppl.e13547). The dFdCTP formation rate decreased in a nonlinear manner as the dFdC dosage increased from 40 mg/kg (0.80 /h) to 60 mg/kg (0.21 /h) to 120 mg/kg (0.13 /h) leading to higher dFdCTP exposures after 40 mg/kg (76.1 ± 26 µM·h) compared with 60 mg/kg (31.1 ± 10.0 µM·h) or 120 mg/kg (35.2 ± 12.0 µM·h). These results suggest an inhibition of dFdCTP intracellular formation, more than a saturation, at high dFdC dosages in mice. The plasma and PBMC murine model are now being used along with the pediatric trial PK data to develop a translational model to predict dFdCTP exposure in PBMCs. This translational model will then be extended to include the murine brain tumor tissue compartment.
Citation Format: Elizabeth G. Gibson, Abi Davis, Bo Zhong, Olivia Campagne, Martine F. Roussel, Clinton F. Stewart. Characterization of gemcitabine triphosphate formation in mice to aid in the development of a translational tumor model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3031.
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Affiliation(s)
| | - Abi Davis
- St. Jude Children's Research Hospital, Memphis, TN
| | - Bo Zhong
- St. Jude Children's Research Hospital, Memphis, TN
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Abstract
Agarose gel electrophoresis is one of the most straightforward techniques that can be used to differentiate between topoisomers of closed circular DNA molecules. Generally, the products of reactions that monitor the interconversion of DNA between negatively supercoiled and relaxed DNA or positively supercoiled and relaxed DNA can be resolved by one-dimensional gel electrophoresis. However, in more complex reactions that contain both positively and negatively supercoiled DNA, one-dimensional resolution is insufficient. In these cases, a second dimension of gel electrophoresis is necessary. This chapter describes the technique of two-dimensional agarose gel electrophoresis and how it can be used to resolve a spectrum of DNA topoisomers.
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Affiliation(s)
- Elizabeth G. Gibson
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
| | - Alexandria A. Oviatt
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
| | - Neil Osheroff
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States,,Department of Medicine (Hematology/Oncology), Vanderbilt University School of Medicine, Nashville, TN 37232, United States,,VA Tennessee Valley Healthcare System, Nashville, TN 37212, United States
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Gibson EG, Oviatt AA, Cacho M, Neuman KC, Chan PF, Osheroff N. Bimodal Actions of a Naphthyridone/Aminopiperidine-Based Antibacterial That Targets Gyrase and Topoisomerase IV. Biochemistry 2019; 58:4447-4455. [PMID: 31617352 PMCID: PMC7450530 DOI: 10.1021/acs.biochem.9b00805] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Gyrase and topoisomerase IV are the targets of fluoroquinolone antibacterials. However, the rise in antimicrobial resistance has undermined the clinical use of this important drug class. Therefore, it is critical to identify new agents that maintain activity against fluoroquinolone-resistant strains. One approach is to develop non-fluoroquinolone drugs that also target gyrase and topoisomerase IV but interact differently with the enzymes. This has led to the development of the "novel bacterial topoisomerase inhibitor" (NBTI) class of antibacterials. Despite the clinical potential of NBTIs, there is a relative paucity of data describing their mechanism of action against bacterial type II topoisomerases. Consequently, we characterized the activity of GSK126, a naphthyridone/aminopiperidine-based NBTI, against a variety of Gram-positive and Gram-negative bacterial type II topoisomerases, including gyrase from Mycobacterium tuberculosis and gyrase and topoisomerase IV from Bacillus anthracis and Escherichia coli. GSK126 enhanced single-stranded DNA cleavage and suppressed double-stranded cleavage mediated by these enzymes. It was also a potent inhibitor of gyrase-catalyzed DNA supercoiling and topoisomerase IV-catalyzed decatenation. Thus, GSK126 displays a similar bimodal mechanism of action across a variety of species. In contrast, GSK126 displayed a variable ability to overcome fluoroquinolone resistance mutations across these same species. Our results suggest that NBTIs elicit their antibacterial effects by two different mechanisms: inhibition of gyrase/topoisomerase IV catalytic activity or enhancement of enzyme-mediated DNA cleavage. Furthermore, the relative importance of these two mechanisms appears to differ from species to species. Therefore, we propose that the mechanistic basis for the antibacterial properties of NBTIs is bimodal in nature.
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Affiliation(s)
- Elizabeth G. Gibson
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
| | - Alexandria A. Oviatt
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
| | - Monica Cacho
- Department of Diseases of the Developing World, GlaxoSmithKline, Parque Tecnológico de Madrid, Calle de Severo Ochoa, 2, 28760 Tres Cantos, Madrid, Spain
| | - Keir C. Neuman
- Laboratory of Single Molecule Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20982, United States
| | - Pan F. Chan
- Infectious Diseases Discovery, Medicines Opportunities Research Unit, GlaxoSmithKline, Collegeville, PA 19426, United States
| | - Neil Osheroff
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
- Department of Medicine (Hematology/Oncology), Vanderbilt University School of Medicine, Nashville, TN 37232, United States
- VA Tennessee Valley Healthcare System, Nashville, TN 37212, United States
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Gibson EG, Bax B, Chan PF, Osheroff N. Mechanistic and Structural Basis for the Actions of the Antibacterial Gepotidacin against Staphylococcus aureus Gyrase. ACS Infect Dis 2019; 5:570-581. [PMID: 30757898 DOI: 10.1021/acsinfecdis.8b00315] [Citation(s) in RCA: 84] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Gepotidacin is a first-in-class triazaacenaphthylene novel bacterial topoisomerase inhibitor (NBTI). The compound has successfully completed phase II trials for the treatment of acute bacterial skin/skin structure infections and for the treatment of uncomplicated urogenital gonorrhea. It also displays robust in vitro activity against a range of wild-type and fluoroquinolone-resistant bacteria. Due to the clinical promise of gepotidacin, a detailed understanding of its interactions with its antibacterial targets is essential. Thus, we characterized the mechanism of action of gepotidacin against Staphylococcus aureus gyrase. Gepotidacin was a potent inhibitor of gyrase-catalyzed DNA supercoiling (IC50 ≈ 0.047 μM) and relaxation of positively supercoiled substrates (IC50 ≈ 0.6 μM). Unlike fluoroquinolones, which induce primarily double-stranded DNA breaks, gepotidacin induced high levels of gyrase-mediated single-stranded breaks. No double-stranded breaks were observed even at high gepotidacin concentration, long cleavage times, or in the presence of ATP. Moreover, gepotidacin suppressed the formation of double-stranded breaks. Gepotidacin formed gyrase-DNA cleavage complexes that were stable for >4 h. In vitro competition suggests that gyrase binding by gepotidacin and fluoroquinolones are mutually exclusive. Finally, we determined crystal structures of gepotidacin with the S. aureus gyrase core fusion truncate with nicked (2.31 Å resolution) or intact (uncleaved) DNA (2.37 Å resolution). In both cases, a single gepotidacin molecule was bound midway between the two scissile DNA bonds and in a pocket between the two GyrA subunits. A comparison of the two structures demonstrates conformational flexibility within the central linker of gepotidacin, which may contribute to the activity of the compound.
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Affiliation(s)
| | - Ben Bax
- Medicines Discovery Institute, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
| | - Pan F. Chan
- Infectious Diseases Discovery, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Neil Osheroff
- VA Tennessee Valley Healthcare System, 1310 24th Avenue S., Nashville, Tennessee 37212, United States
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Gibson EG, Blower TR, Cacho M, Bax B, Berger JM, Osheroff N. Mechanism of Action of Mycobacterium tuberculosis Gyrase Inhibitors: A Novel Class of Gyrase Poisons. ACS Infect Dis 2018; 4:1211-1222. [PMID: 29746087 DOI: 10.1021/acsinfecdis.8b00035] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Tuberculosis is one of the leading causes of morbidity worldwide, and the incidences of drug resistance and intolerance are prevalent. Thus, there is a desperate need for the development of new antitubercular drugs. Mycobacterium tuberculosis gyrase inhibitors (MGIs) are napthyridone/aminopiperidine-based drugs that display activity against M. tuberculosis cells and tuberculosis in mouse models [Blanco, D., et al. (2015) Antimicrob. Agents Chemother. 59, 1868-1875]. Genetic and mutagenesis studies suggest that gyrase, which is the target for fluoroquinolone antibacterials, is also the target for MGIs. However, little is known regarding the interaction of these drugs with the bacterial type II enzyme. Therefore, we examined the effects of two MGIs, GSK000 and GSK325, on M. tuberculosis gyrase. MGIs greatly enhanced DNA cleavage mediated by the bacterial enzyme. In contrast to fluoroquinolones (which induce primarily double-stranded breaks), MGIs induced only single-stranded DNA breaks under a variety of conditions. MGIs work by stabilizing covalent gyrase-cleaved DNA complexes and appear to suppress the ability of the enzyme to induce double-stranded breaks. The drugs displayed little activity against type II topoisomerases from several other bacterial species, suggesting that these drugs display specificity for M. tuberculosis gyrase. Furthermore, MGIs maintained activity against M. tuberuclosis gyrase enzymes that contained the three most common fluoroquinolone resistance mutations seen in the clinic and displayed no activity against human topoisomerase IIα. These findings suggest that MGIs have potential as antitubercular drugs, especially in the case of fluoroquinolone-resistant disease.
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Affiliation(s)
| | - Tim R. Blower
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, United States
| | - Monica Cacho
- Department of Diseases of the Developing World, GlaxoSmithKline, Parque Tecnológico de Madrid, Calle de Severo Ochoa, 2, 28760 Tres Cantos, Madrid, Spain
| | - Ben Bax
- Medicines Discovery Institute, Cardiff University, Cardiff CF10 3AT, United Kingdom
| | - James M. Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, United States
| | - Neil Osheroff
- VA Tennessee Valley Healthcare System, Nashville, Tennessee 37212, United States
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Affiliation(s)
- Elizabeth G. Gibson
- Department
of Pharmaceutical Sciences, Lipscomb University College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - McKenzie M. King
- Department
of Pharmaceutical Sciences, Lipscomb University College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Susan L. Mercer
- Department
of Pharmaceutical Sciences, Lipscomb University College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Joseph E. Deweese
- Department
of Pharmaceutical Sciences, Lipscomb University College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
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9
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Abstract
Topoisomerase II regulates DNA topology by generating transient double-stranded breaks. The anticancer drug etoposide targets topoisomerase II and is associated with the formation of secondary leukemias in patients. The quinone and catechol metabolites of etoposide may contribute to strand breaks that trigger leukemic translocations. To further analyze the characteristics of etoposide metabolites, we extend our previous analysis of etoposide quinone to the catechol. We demonstrate that the catechol is ∼2-3-fold more potent than etoposide and under oxidative reaction conditions induces high levels of double-stranded DNA cleavage. These results support a role for etoposide catechol in contributing to therapy-induced DNA damage.
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Affiliation(s)
- David A Jacob
- Department of Pharmaceutical Sciences, Lipscomb University College of Pharmacy and Health Sciences, Nashville, Tennessee 37204-3951, USA
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Deweese JE, Jacob DA, Gibson EG, Mercer SL. Etoposide Catechol Is an Oxidizable Topoisomerase II Poison. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.lb75] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Joseph E. Deweese
- Pharmaceutical SciencesLipscomb University College of PharmacyNashvilleTN
- BiochemistryVanderbilt University School of MedicineNashvilleTN
| | - David A. Jacob
- Pharmaceutical SciencesLipscomb University College of PharmacyNashvilleTN
| | | | - Susan L. Mercer
- Pharmaceutical SciencesLipscomb University College of PharmacyNashvilleTN
- PharmacologyVanderbilt University School of MedicineNashvilleTN
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Gibson EG, Burns HD, Thorpe HH, Eng WS, Ransom R, Solomon H. In vivo binding and autoradiographic imaging of (+)-3-[125I]Iodo-MK-801 to the NMDA receptor-channel complex in rat brain. Int J Rad Appl Instrum B 1992; 19:319-26. [PMID: 1378426 DOI: 10.1016/0883-2897(92)90117-h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Radioiodinated (+)-3-Iodo-MK-801 is a high affinity radioligand for the N-methyl-D-aspartate (NMDA) receptor-channel complex. We have demonstrated in vivo localization in the CNS of rat which is stereoselective and blocked by coinjection of unlabeled MK-801. Autoradiography indicates localization in vivo which is in concordance with in vitro autoradiographic studies. These results indicate that radioiodinated (+)-3-Iodo-MK-801 is a useful probe for in vitro and in vivo autoradiographic studies and suggest that radioligands for the NMDA receptor may be developed which will provide in vivo images of receptor distribution in man.
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Affiliation(s)
- E G Gibson
- Department of Radiopharmacology, Merck Sharp & Dohme Research Laboratories, West Point, PA 19486
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Bobko KJ, Gibson EG, Maroney SA, Muccio JD. Space Station Freedom crew training. Acta Astronaut 1990; 22:65-70. [PMID: 11542826 DOI: 10.1016/0094-5765(90)90008-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The nature of the Space Station Freedom Program presents an array of new and enhanced challenges which need to be addressed en route to developing an effective and affordable infrastructure for crew training. Such an infrastructure is essential for the safety and success of the program. The three major challenges that affect crew training are the long lifetime of the program (thirty years), the interdependence of successive increments, and the participation of the three International Partners (Canada, European Space Agency, and Japan) and a myriad of experimenters. This paper addresses these major challenges as they drive the development of a crew training capability and the actual conduct of crew training.
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Affiliation(s)
- K J Bobko
- Booz Allen & Hamilton, Inc., Reston, VA, USA
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