1
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Li D, Kirberger M, Qiao J, Gui Z, Xue S, Pu F, Jiang J, Xu Y, Tan S, Salarian M, Ibhagui O, Hekmatyar K, Yang JJ. Protein MRI Contrast Agents as an Effective Approach for Precision Molecular Imaging. Invest Radiol 2024; 59:170-186. [PMID: 38180819 DOI: 10.1097/rli.0000000000001057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2024]
Abstract
ABSTRACT Cancer and other acute and chronic diseases are results of perturbations of common molecular determinants in key biological and signaling processes. Imaging is critical for characterizing dynamic changes in tumors and metastases, the tumor microenvironment, tumor-stroma interactions, and drug targets, at multiscale levels. Magnetic resonance imaging (MRI) has emerged to be a primary imaging modality for both clinical and preclinical applications due to its advantages over other modalities, including sensitivity to soft tissues, nondepth limitations, and the use of nonionizing radiation. However, extending the application of MRI to achieve both qualitative and quantitative precise molecular imaging with the capability to quantify molecular biomarkers for early detection, staging, and monitoring therapeutic treatment requires the capacity to overcome several major challenges including the trade-off between metal-binding affinity and relaxivity, which is an issue frequently associated with small chelator contrast agents. In this review, we will introduce the criteria of ideal contrast agents for precision molecular imaging and discuss the relaxivity of current contrast agents with defined first shell coordination water molecules. We will then report our advances in creating a new class of protein-targeted MRI contrast agents (ProCAs) with contributions to relaxivity largely derived from the secondary sphere and correlation time. We will summarize our rationale, design strategy, and approaches to the development and optimization of our pioneering ProCAs with desired high relaxivity, metal stability, and molecular biomarker-targeting capability, for precision MRI. From first generation (ProCA1) to third generation (ProCA32), we have achieved dual high r1 and r2 values that are 6- to 10-fold higher than clinically approved contrast agents at magnetic fields of 1.5 T, and their relaxivity values at high field are also significantly higher, which enables high resolution during small animal imaging. Further engineering of multiple targeting moieties enables ProCA32 agents that have strong biomarker-binding affinity and specificity for an array of key molecular biomarkers associated with various chronic diseases, while maintaining relaxation and exceptional metal-binding and selectivity, serum stability, and resistance to transmetallation, which are critical in mitigating risks associated with metal toxicity. Our leading product ProCA32.collagen has enabled the first early detection of liver metastasis from multiple cancers at early stages by mapping the tumor environment and early stage of fibrosis from liver and lung in vivo, with strong translational potential to extend to precision MRI for preclinical and clinical applications for precision diagnosis and treatment.
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Affiliation(s)
- Dongjun Li
- From the Center for Diagnostics and Therapeutics, Advanced Translational Imaging Facility, Department of Chemistry, Georgia State University, Atlanta, GA (D.L., M.K., J.Q., Z.G., S.X., P.F., J.J., S.T., M.S., O.I., K.H., J.J.Y.); and InLighta BioSciences, LLC, Marietta, GA (Y.X., J.J.Y)
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2
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Mouchel Dit Leguerrier D, Barré R, Ruet Q, Imbert D, Philouze C, Fries PH, Martel-Frachet V, Molloy JK, Thomas F. Lanthanide complexes of DOTA-nitroxide conjugates for redox imaging: spectroelectrochemistry, CEST, relaxivity, and cytotoxicity. Dalton Trans 2021; 50:10826-10837. [PMID: 34291274 DOI: 10.1039/d1dt01628h] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The lanthanide(iii) complexes (Gd, Eu, Dy, and Yb) of DOTA tris(amide) and bis(amide) derivatives (L1 and L2) featuring one redox active TEMPO arm were prepared. Ligand L2 harbours an alkyne fragment for further functionalization. The X-ray crystal structure of ligand L2 in complexation with Na+ was solved. The complexes showed in their CV one oxidation wave (0.26-0. 34 V vs. Fc+/Fc) due to an oxoammonium/nitroxide redox couple and a broad reduction corresponding to the nitroxide/hydroxylamine system. The Eu complexes demonstrated the presence of one water molecule in their coordination sphere. The nitroxide complexes were characterized by EPR spectroscopy, showing the typical 3-line pattern in the high temperature regime, which is quenched upon the addition of ascorbate (reduction into hydroxylamine). In their nitroxide form, the complexes show essentially no CEST peak. Conversely, the reduced complexes demonstrate a 12% CEST peak at 51 ppm, corresponding to the metal bound water molecule. Fast exchange precluded the CEST activity for the amide protons. All the complexes proved to be essentially non-toxic for M21 cells at concentrations up to 50 μM.
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Affiliation(s)
| | - R Barré
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France.
| | - Q Ruet
- Institute for Advanced Biosciences, INSERM U1209, UMR CNRS 5309, Grenoble Alpes University, 38700 La Tronche, France
| | - D Imbert
- Univ. Grenoble Alpes, CEA, CNRS, IRIG-LCBM, 38000 Grenoble, France
| | - C Philouze
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France.
| | - P H Fries
- Univ. Grenoble Alpes, CEA, CNRS, IRIG-LCBM, 38000 Grenoble, France
| | - V Martel-Frachet
- Institute for Advanced Biosciences, INSERM U1209, UMR CNRS 5309, Grenoble Alpes University, 38700 La Tronche, France and EPHE, PSL Research University, 75014 Paris, France
| | - J K Molloy
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France.
| | - F Thomas
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France.
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3
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Rodríguez-Rodríguez A, Zaiss M, Esteban-Gómez D, Angelovski G, Platas-Iglesias C. Paramagnetic chemical exchange saturation transfer agents and their perspectives for application in magnetic resonance imaging. INT REV PHYS CHEM 2020. [DOI: 10.1080/0144235x.2020.1823167] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Aurora Rodríguez-Rodríguez
- Departamento de Química, Facultade de Ciencias & Centro de Investigacións Científicas Avanzadas (CICA), Universidade da Coruña, 15071 A Coruña, Spain
| | - Moritz Zaiss
- Department of Neuroradiology, University Clinic Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - David Esteban-Gómez
- Departamento de Química, Facultade de Ciencias & Centro de Investigacións Científicas Avanzadas (CICA), Universidade da Coruña, 15071 A Coruña, Spain
| | - Goran Angelovski
- MR Neuroimaging Agents, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
- Lab of Molecular and Cellular Neuroimaging, International Center for Primate Brain Research (ICPBR), Center for Excellence in Brain Science and Intelligence Technology (CEBSIT), Chinese Academy of Science (CAS), Shanghai, P.R. China
| | - Carlos Platas-Iglesias
- Departamento de Química, Facultade de Ciencias & Centro de Investigacións Científicas Avanzadas (CICA), Universidade da Coruña, 15071 A Coruña, Spain
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Scepaniak JJ, Kang EB, John M, Kaminsky W, Dechert S, Meyer F. Non‐Macrocyclic Schiff Base Complexes of Iron(II) as ParaCEST Agents for MRI. Eur J Inorg Chem 2019. [DOI: 10.1002/ejic.201801565] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Jeremiah J. Scepaniak
- Institut für Anorganische Chemie Georg‐August‐Universität Göttingen Tammannstrasse 4 37077 Göttingen Germany
- Department of Chemistry Drexel University 32 S. 32nd St. Disque Hall 506 19104 Philadelphia PA USA
| | - Eun Byoung Kang
- Department of Chemistry Drexel University 32 S. 32nd St. Disque Hall 506 19104 Philadelphia PA USA
| | - Michael John
- Institut für Anorganische Chemie Georg‐August‐Universität Göttingen Tammannstrasse 4 37077 Göttingen Germany
| | - Werner Kaminsky
- Department of Chemistry University of Washington Box 351700 98195‐1700 Seattle WA USA
| | - Sebastian Dechert
- Institut für Anorganische Chemie Georg‐August‐Universität Göttingen Tammannstrasse 4 37077 Göttingen Germany
| | - Franc Meyer
- Institut für Anorganische Chemie Georg‐August‐Universität Göttingen Tammannstrasse 4 37077 Göttingen Germany
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5
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Electronic Effects of the Substituents on Relaxometric and CEST Behaviour of Ln(III)-DOTA-Tetraanilides. INORGANICS 2019. [DOI: 10.3390/inorganics7040043] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Three different 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide (DOTAM) derivatives bearing as amide N-substituents phenyl, p-methoxyphenyl and p-ethylbenzoate groups were synthesized and the 1H and 17O NMR relaxometric behaviour of the Gd(III)-chelates and chemical exchange saturation transfer (CEST) effect of the Eu(III) complexes were evaluated. The electronic properties of the substituents were shown to strongly influence the coordinated water exchange rate (kex), resulting in five times faster kex for the electron donating phenylmethoxy group compared to the electron withdrawing ethylbenzoate group.
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6
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Wahsner J, Gale EM, Rodríguez-Rodríguez A, Caravan P. Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers. Chem Rev 2019; 119:957-1057. [PMID: 30350585 PMCID: PMC6516866 DOI: 10.1021/acs.chemrev.8b00363] [Citation(s) in RCA: 849] [Impact Index Per Article: 169.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Tens of millions of contrast-enhanced magnetic resonance imaging (MRI) exams are performed annually around the world. The contrast agents, which improve diagnostic accuracy, are almost exclusively small, hydrophilic gadolinium(III) based chelates. In recent years concerns have arisen surrounding the long-term safety of these compounds, and this has spurred research into alternatives. There has also been a push to develop new molecularly targeted contrast agents or agents that can sense pathological changes in the local environment. This comprehensive review describes the state of the art of clinically approved contrast agents, their mechanism of action, and factors influencing their safety. From there we describe different mechanisms of generating MR image contrast such as relaxation, chemical exchange saturation transfer, and direct detection and the types of molecules that are effective for these purposes. Next we describe efforts to make safer contrast agents either by increasing relaxivity, increasing resistance to metal ion release, or by moving to gadolinium(III)-free alternatives. Finally we survey approaches to make contrast agents more specific for pathology either by direct biochemical targeting or by the design of responsive or activatable contrast agents.
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Affiliation(s)
- Jessica Wahsner
- Athinoula A. Martinos Center for Biomedical Imaging and the Institute for Innovation in Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
| | - Eric M. Gale
- Athinoula A. Martinos Center for Biomedical Imaging and the Institute for Innovation in Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
| | - Aurora Rodríguez-Rodríguez
- Athinoula A. Martinos Center for Biomedical Imaging and the Institute for Innovation in Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
| | - Peter Caravan
- Athinoula A. Martinos Center for Biomedical Imaging and the Institute for Innovation in Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA
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7
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Caravan P, Esteban-Gómez D, Rodríguez-Rodríguez A, Platas-Iglesias C. Water exchange in lanthanide complexes for MRI applications. Lessons learned over the last 25 years. Dalton Trans 2019; 48:11161-11180. [DOI: 10.1039/c9dt01948k] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Coordination chemistry offers convenient strategies to modulate the exchange of coordinated water molecules in lanthanide-based contrast agents.
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Affiliation(s)
- Peter Caravan
- The Institute for Innovation in Imaging and the A. A. Martinos Center for Biomedical Imaging
- Massachusetts General Hospital
- Harvard Medical School
- Charlestown
- USA
| | - David Esteban-Gómez
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química
- Universidade da Coruña
- 15008 A Coruña
- Spain
| | - Aurora Rodríguez-Rodríguez
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química
- Universidade da Coruña
- 15008 A Coruña
- Spain
| | - Carlos Platas-Iglesias
- Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química
- Universidade da Coruña
- 15008 A Coruña
- Spain
- The Institute for Innovation in Imaging and the A. A. Martinos Center for Biomedical Imaging
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8
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Dastrù W, Menchise V, Ferrauto G, Fabretto S, Carrera C, Terreno E, Aime S, Castelli DD. Modulation of the Prototropic Exchange Rate in pH-Responsive Yb-HPDO3A Derivatives as ParaCEST Agents. ChemistrySelect 2018. [DOI: 10.1002/slct.201800283] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Walter Dastrù
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
| | - Valeria Menchise
- Istituto di Biostrutture e Bioimmagini; Consiglio Nazionale delle Ricerche; via Mezzocannone 16 80134 Napoli Italy
| | - Giuseppe Ferrauto
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
| | - Serena Fabretto
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
| | - Carla Carrera
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
| | - Enzo Terreno
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
| | - Silvio Aime
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
| | - Daniela Delli Castelli
- Department of Molecular Biotechnology and Health Sciences; Molecular Imaging Center; University of Torino; Via Nizza 52 10126 Torino Italy
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9
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Mishra P, Barnes CA, Strickland M, Tjandra N. Solvent saturation transfer to proteins (SSTP) for structural and functional characterization of proteins. JOURNAL OF BIOMOLECULAR NMR 2018; 70:11-20. [PMID: 29189927 PMCID: PMC5820130 DOI: 10.1007/s10858-017-0151-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Accepted: 11/04/2017] [Indexed: 06/07/2023]
Abstract
Protein structure determination using NMR is dependent on experimentally acquired distance restraints. Often, however, an insufficient number of these restraints are available for determining a protein's correct fold, much less its detailed three-dimensional structure. In consideration of this problem, we propose a simple means to acquire supplemental structural restraints from protein surface accessibilities using solvent saturation transfer to proteins (SSTP), based on the principles of paramagnetic chemical-exchange saturation transfer. Here, we demonstrate the utility of SSTP in structure calculations of two proteins, TSG101 and ubiquitin. The observed SSTP was found to be directly proportional to solvent accessibility. Since SSTP does not involve the direct excitation of water, which compromises the analysis of protein protons entangled in the breadth of the water resonance, it has an advantage over conventional water-based magnetization transfers. Inclusion of structural restraints derived from SSTP improved both the precision and accuracy of the final protein structures in comparison to those determined by traditional approaches, when using minimal amounts of additional structural data. Furthermore, we show that SSTP can detect weak protein-protein interactions which are unobservable by chemical shift perturbations.
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Affiliation(s)
- Pushpa Mishra
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - C Ashley Barnes
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Madeleine Strickland
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Nico Tjandra
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
- National Heart, Lung, and Blood Institute, National Institutes of Health, Building 50, Room 3503, Bethesda, MD, 20892, USA.
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10
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Zhang L, Martins AF, Zhao P, Wu Y, Tircsó G, Sherry AD. Lanthanide-Based T 2ex and CEST Complexes Provide Insights into the Design of pH Sensitive MRI Agents. Angew Chem Int Ed Engl 2017; 56:16626-16630. [PMID: 29024242 PMCID: PMC5879776 DOI: 10.1002/anie.201707959] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Indexed: 02/02/2023]
Abstract
The CEST and T1 /T2 relaxation properties of a series of Eu3+ and Dy3+ DOTA-tetraamide complexes with four appended primary amine groups are measured as a function of pH. The CEST signals in the Eu3+ complexes show a strong CEST signal after the pH was reduced from 8 to 5. The opposite trend was observed for the Dy3+ complexes where the r2ex of bulk water protons increased dramatically from ca. 1.5 mm-1 s-1 to 13 mm-1 s-1 between pH 5 and 9 while r1 remained unchanged. A fit of the CEST data (Eu3+ complexes) to Bloch theory and the T2ex data (Dy3+ complexes) to Swift-Connick theory provided the proton-exchange rates as a function of pH. These data showed that the four amine groups contribute significantly to proton-catalyzed exchange of the Ln3+ -bound water protons even though their pKa 's are much higher than the observed CEST or T2ex effects. This demonstrated the utility of using appended acidic/basic groups to catalyze prototropic exchange for imaging tissue pH by MRI.
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Affiliation(s)
- Lei Zhang
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
| | - André F Martins
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX, 75390, USA
| | - Piyu Zhao
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
| | - Yunkou Wu
- Advanced Imaging Research Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX, 75390, USA
| | - Gyula Tircsó
- Department of Inorganic and Analytical Chemistry, University of Debrecen, Egyetemtér 1, 4010, Debrecen, Hungary
| | - A Dean Sherry
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX, 75390, USA
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11
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Zhang L, Martins AF, Zhao P, Wu Y, Tircsó G, Sherry AD. Lanthanide-Based T2ex
and CEST Complexes Provide Insights into the Design of pH Sensitive MRI Agents. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201707959] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Lei Zhang
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
| | - André F. Martins
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
- Advanced Imaging Research Center; UT Southwestern Medical Center; 5323 Harry Hines Blvd. Dallas TX 75390 USA
| | - Piyu Zhao
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
| | - Yunkou Wu
- Advanced Imaging Research Center; UT Southwestern Medical Center; 5323 Harry Hines Blvd. Dallas TX 75390 USA
| | - Gyula Tircsó
- Department of Inorganic and Analytical Chemistry; University of Debrecen; Egyetemtér 1 4010 Debrecen Hungary
| | - A. Dean Sherry
- Department of Chemistry and Biochemistry; The University of Texas at Dallas; 800 West Campbell Road Richardson TX 75080 USA
- Advanced Imaging Research Center; UT Southwestern Medical Center; 5323 Harry Hines Blvd. Dallas TX 75390 USA
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12
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Zhang L, Evbuomwan OM, Tieu M, Zhao P, Martins AF, Sherry AD. Protonation of carboxyl groups in EuDOTA-tetraamide complexes results in catalytic prototropic exchange and quenching of the CEST signal. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2017; 375:20170113. [PMID: 29038382 PMCID: PMC5647270 DOI: 10.1098/rsta.2017.0113] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/23/2017] [Indexed: 05/29/2023]
Abstract
The CEST properties of EuDOTA-tetraamide complexes bearing pendant carboxylate and carboxyl ethyl esters were measured as a function of pH. The CEST signal from the Eu3+-bound water molecule decreased in intensity between pH 8.5 and 4.5 while the proton exchange rates (kex) increased over this same pH range. In comparison, the CEST signal in the corresponding carboxyl ester derivatives was nearly constant. Both observations are consistent with stepwise protonation of the four carboxylic acid groups over this same pH range. This indicates that negative charges on the carboxyl groups above pH 6 facilitate the formation of a strong hydrogen-bonding network in the coordination second sphere above the single Eu3+-bound water molecule, thereby decreasing prototropic exchange of protons on the bound water molecule with bulk water protons. The percentage of square antiprismatic versus twisted square antiprism coordination isomers also decreased as the appended carboxylic acid groups were positioned further away from the amide. The net effect of lowering the pH was an overall increase in kex and a quenching of the CEST signal.This article is part of the themed issue 'Challenges for chemistry in molecular imaging'.
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Affiliation(s)
- Lei Zhang
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080, USA
| | - Osasere M Evbuomwan
- Department of chemistry and biochemistry, Gonzaga University, Spokane, WA 99258, USA
| | - Michael Tieu
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080, USA
| | - Piyu Zhao
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080, USA
| | - Andre F Martins
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080, USA
- Advanced Imaging Research Center, University of Texas Southwestern Medcial Center, Dallas, TX, USA
| | - A Dean Sherry
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080, USA
- Advanced Imaging Research Center, University of Texas Southwestern Medcial Center, Dallas, TX, USA
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13
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Singh J, Rustagi V, Zhang S, Sherry AD, Udugamasooriya DG. On-bead combinatorial synthesis and imaging of europium(III)-based paraCEST agents aids in identification of chemical features that enhance CEST sensitivity. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2017; 55:747-753. [PMID: 28220538 PMCID: PMC5501467 DOI: 10.1002/mrc.4588] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 02/15/2017] [Accepted: 02/16/2017] [Indexed: 05/08/2023]
Abstract
The rate of water exchange between the inner sphere of a paramagnetic ion and bulk water is an important parameter in determining the magnitude of the chemical exchange saturation transfer signal from paramagnetic CEST agents (paraCEST). This is governed by various geometric, steric and ligand field factors created by macrocyclic ligands surrounding the paramagnetic metal ion. Our previous on-bead combinatorial studies of di-peptoid-europium(III)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-tetraamide complexes revealed that negatively charged groups in the immediate vicinity of the metal center strongly enhances the CEST signal. Here, we report a solid phase synthesis and on-bead imaging of 76 new DOTA derivatives that are developed by coupling with a single residue onto each of the three arms of a DOTA-tetraamide scaffold attached to resin beads. This single residue predominantly carries negatively charged groups blended with various physico-chemical characteristics. We found that non-bulky negatively charged groups are best suited at the immediate vicinity of the metal ion, while positive, bulky and halogen containing moieties suppress the CEST signal. Copyright © 2017 John Wiley & Sons, Ltd.
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Affiliation(s)
- Jaspal Singh
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 3455 Cullen Blvd, Houston, TX, 77204-5037, USA
| | - Vineeta Rustagi
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 3455 Cullen Blvd, Houston, TX, 77204-5037, USA
| | - Shanrong Zhang
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-8568, USA
| | - A Dean Sherry
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-8568, USA
- Department of Chemistry, University of Texas at Dallas, 800 West Campbell Rd, Richardson, TX, 75083-3021, USA
| | - D Gomika Udugamasooriya
- Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 3455 Cullen Blvd, Houston, TX, 77204-5037, USA
- Department of Cancer Systems Imaging, MD Anderson Cancer Center, 1881 East Road, Houston, TX, 77030-4009, USA
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14
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Strickland M, Schwieters CD, Göbl C, Opina ACL, Strub MP, Swenson RE, Vasalatiy O, Tjandra N. Characterizing the magnetic susceptibility tensor of lanthanide-containing polymethylated-DOTA complexes. JOURNAL OF BIOMOLECULAR NMR 2016; 66:125-139. [PMID: 27659040 PMCID: PMC6628275 DOI: 10.1007/s10858-016-0061-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 09/13/2016] [Indexed: 05/16/2023]
Abstract
Lanthanide complexes based on the DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) cage are commonly used as phase contrast agents in magnetic resonance imaging, but can also be utilized in structural NMR applications due to their ability to induce either paramagnetic relaxation enhancement or a pseudocontact shift (PCS) depending on the choice of the lanthanide. The size and sign of the PCS for any given atom is determined by its coordinates relative to the metal center, and the characteristics of the lanthanide's magnetic susceptibility tensor. Using a polymethylated DOTA tag (Ln-M8-SPy) conjugated to ubiquitin, we calculated the position of the metal center and characterized the susceptibility tensor for a number of lanthanides (dysprosium, thulium, and ytterbium) under a range of pH and temperature conditions. We found that there was a difference in temperature sensitivity for each of the complexes studied, which depended on the size of the lanthanide ion as well as the isomeric state of the cage. Using 17O-NMR, we confirmed that the temperature sensitivity of the compounds was enhanced by the presence of an apically bound water molecule. Since amide-containing lanthanide complexes are known to be pH sensitive and can be used as probes of physiological pH, we also investigated the effect of pH on the Ln-M8-SPy susceptibility tensor, but we found that the changes in this pH range (5.0-7.4) were not significant.
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Affiliation(s)
- Madeleine Strickland
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Charles D Schwieters
- Office of Intramural Research, Center for Information Technology, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Christoph Göbl
- Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, 85748, Garching, Germany
| | - Ana C L Opina
- Imaging Probe Development Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, MD, 20850, USA
| | - Marie-Paule Strub
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Rolf E Swenson
- Imaging Probe Development Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, MD, 20850, USA
| | - Olga Vasalatiy
- Imaging Probe Development Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, MD, 20850, USA
| | - Nico Tjandra
- Laboratory of Molecular Biophysics, Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
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15
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Sun Y, Wang W, Cheng H, Jiang X, Wu J. Study of the binding and energy transfer of erbium ion with rhaponticin and its pharmacokinetics application. LUMINESCENCE 2016. [DOI: 10.1002/bio.3098] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Yang Sun
- School of Chemical Engineering and Food science; Hubei University of Arts and Science; 296 Longzhong Road Xiangyang Hubei 441053 China
| | - Wanqiang Wang
- School of Chemical Engineering and Food science; Hubei University of Arts and Science; 296 Longzhong Road Xiangyang Hubei 441053 China
| | - Hua Cheng
- School of Chemical Engineering and Food science; Hubei University of Arts and Science; 296 Longzhong Road Xiangyang Hubei 441053 China
| | - Xiangsheng Jiang
- School of Chemical Engineering and Food science; Hubei University of Arts and Science; 296 Longzhong Road Xiangyang Hubei 441053 China
| | - Junjun Wu
- School of Chemical Engineering and Food science; Hubei University of Arts and Science; 296 Longzhong Road Xiangyang Hubei 441053 China
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16
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Krchová T, Gálisová A, Jirák D, Hermann P, Kotek J. Ln(iii)-complexes of a DOTA analogue with an ethylenediamine pendant arm as pH-responsive PARACEST contrast agents. Dalton Trans 2016; 45:3486-96. [DOI: 10.1039/c5dt04443j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
New contrast agents useful for pH determination (in the biologically relevant pH range) by Magnetic Resonance Imaging (MRI) using magnetization transfer ratio approach are presented.
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Affiliation(s)
- T. Krchová
- Department of Inorganic Chemistry
- Faculty of Science
- Universita Karlova (Charles University)
- 128 43 Prague 2
- Czech Republic
| | - A. Gálisová
- Department of Radiodiagnostic and Interventional Radiology
- Magnetic Resonance Unit
- Institute for Clinical and Experimental Medicine
- Prague 4
- Czech Republic
| | - D. Jirák
- Department of Radiodiagnostic and Interventional Radiology
- Magnetic Resonance Unit
- Institute for Clinical and Experimental Medicine
- Prague 4
- Czech Republic
| | - P. Hermann
- Department of Inorganic Chemistry
- Faculty of Science
- Universita Karlova (Charles University)
- 128 43 Prague 2
- Czech Republic
| | - J. Kotek
- Department of Inorganic Chemistry
- Faculty of Science
- Universita Karlova (Charles University)
- 128 43 Prague 2
- Czech Republic
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17
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Krchová T, Kotek J, Jirák D, Havlíčková J, Císařová I, Hermann P. Lanthanide(III) complexes of aminoethyl-DO3A as PARACEST contrast agents based on decoordination of the weakly bound amino group. Dalton Trans 2014; 42:15735-47. [PMID: 24051547 DOI: 10.1039/c3dt52031e] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
2-Aminoethyl DOTA analogues with unsubstituted (H3L1), monomethylated (H3L2) and dimethylated (H3L3) amino groups were prepared by improved synthetic procedures. Their solid-state structures exhibit an extensive system of intramolecular hydrogen bonds, which is probably present in solution and leads to the rather high value of the last dissociation constant. The protonation sequence of H3L1 in solution corresponds to that found in the solid state. The stability constants of the H3L1 complexes with La(3+) and Gd(3+) (20.02 and 22.23, respectively) are similar to those of DO3A and the reduction of the pK(A) value of the pendant amino group from 10.51 in the free ligand to 6.06 and 5.83 in the La(3+) and Gd(3+) complexes, respectively, points to coordination of the amino group. It was confirmed in the solid state structure of the [Yb(L1)] complex, where disorder between the SA' and TSA' isomers was found. A similar situation is expected in solution, where a fast equilibration among the isomers hampers the unambiguous determination of the isomer ratio in solution. The PARACEST effect was observed in Eu(III)-H3L1/H3L2 and Yb(III)-H3L1/H3L2 complexes, being dependent on pH in the region of 4.5-7.5 and pH-independent in more alkaline solutions. The decrease of the PARACEST effect parallels with the increasing abundance of the complex protonated species, where the pendant amino group is not coordinating. Surprisingly, a small PARACEST effect was also observed in solutions of Eu(III)/Yb(III)-H3L3 complexes, where the pendant amino group is dimethylated. The effect is detectable in a narrow pH region, where both protonated and deprotonated complex species are present in equilibrium. The data points to the new mechanism of the PARACEST effect, where the slow coordination-decoordination of the pendant amine is coupled with the fast proton exchange between the free amino group and bulk water mediates the magnetization transfer. The pH-dependence of the effect was proved to be measurable by MRI and, thus, the complexes extend the family of pH-sensitive probes.
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Affiliation(s)
- Tereza Krchová
- Department of Inorganic Chemistry, Universita Karlova (Charles University), Hlavova 2030, 128 40 Prague 2, Czech Republic.
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18
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Dorazio SJ, Olatunde AO, Tsitovich PB, Morrow JR. Comparison of divalent transition metal ion paraCEST MRI contrast agents. J Biol Inorg Chem 2014; 19:191-205. [PMID: 24253281 PMCID: PMC3946895 DOI: 10.1007/s00775-013-1059-4] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 10/28/2013] [Indexed: 01/06/2023]
Abstract
Transition-metal-ion-based paramagnetic chemical exchange saturation transfer (paraCEST) agents are a promising new class of compounds for magnetic resonance imaging (MRI) contrast. Members in this class of compounds include paramagnetic complexes of Fe(II), Co(II), and Ni(II). The development of the coordination chemistry for these paraCEST agents is presented with an emphasis on the choice of the azamacrocycle backbone and pendent groups with the goals of controlling the oxidation state, spin state, and stability of the complexes. Chemical exchange saturation transfer spectra and images are compared for different macrocyclic complexes containing amide or heterocyclic pendent groups. The potential of paraCEST agents that function as pH- and redox-activated MRI probes is discussed.
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Affiliation(s)
- Sarina J. Dorazio
- Department of Chemistry, University at Buffalo, Amherst, New York, 14260 USA
| | - Abiola O. Olatunde
- Department of Chemistry, University at Buffalo, Amherst, New York, 14260 USA
| | - Pavel B. Tsitovich
- Department of Chemistry, University at Buffalo, Amherst, New York, 14260 USA
| | - Janet R. Morrow
- Department of Chemistry, University at Buffalo, Amherst, New York, 14260 USA
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19
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Slack JR, Woods M. The effect of regioisomerism on the coordination chemistry and CEST properties of lanthanide(III) NB-DOTA-tetraamide chelates. J Biol Inorg Chem 2013; 19:173-89. [PMID: 24287873 DOI: 10.1007/s00775-013-1060-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Accepted: 10/24/2013] [Indexed: 01/31/2023]
Abstract
Chemical exchange saturation transfer (CEST) offers many advantages as a method of generating contrast in magnetic resonance images. However, many of the exogenous agents currently under investigation suffer from detection limits that are still somewhat short of what can be achieved with more traditional Gd(3+) agents. To remedy this limitation we have undertaken an investigation of Ln(3+) DOTA-tetraamide chelates (where DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) that have unusually rigid ligand structures: the nitrobenzyl derivatives of DOTA-tetraamides with (2-phenylethyl)amide substituents. In this report we examine the effect of incorporating hydrophobic amide substituents on water exchange and CEST. The ligand systems chosen afforded a total of three CEST-active isomeric square antiprismatic chelates; each of these chelates was found to have different water exchange and CEST characteristics. The position of a nitrobenzyl substituent on the macrocyclic ring strongly influenced the way in which the chelate and Ln(3+) coordination cage distorted. These differential distortions were found to affect the rate of water proton exchange in the chelates. But, by far the greatest effect arose from altering the position of the hydrophobic amide substituent, which, when forced upwards around the water binding site, caused a substantial reduction in the rate of water proton exchange. Such slow water proton exchange afforded a chelate that was 4.5 times more effective as a CEST agent than its isomeric counterparts in dry acetonitrile and at low temperatures and very low presaturation powers.
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Affiliation(s)
- Jacqueline R Slack
- Department of Chemistry, Portland State University, 1719 SW 10th Avenue, Portland, OR, 97201, USA
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20
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Elmehriki AA, Milne M, Suchý M, Bartha R, Hudson RH. Complexes of selected late period lanthanide(III) cations with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid amide (DOTAM)-alkyl ligands — A new platform for the development of paramagnetic chemical exchange saturation transfer (PARACEST) magnetic resonance imaging (MRI) contrast agents. CAN J CHEM 2013. [DOI: 10.1139/cjc-2012-0358] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A series of 18 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid amide (DOTAM)-alkyl derived complexes with selected late lanthanide(III) cations (Dy3+, Tb3+, and Tm3+) has been synthesized; their magnetic properties have been evaluated and compared to those derived from DOTAM. Peralkylation of cyclen with corresponding N-iodoacetyl amines was utilized as the key step in the synthesis. Chemical exchange saturation transfer (CEST) spectra of the complexes have been acquired at 37 °C, revealing that Tm3+-derived DOTAM-alkyl complexes possess the most favorable properties as potential paramagnetic chemical exchange saturation transfer (PARACEST) magnetic resonance imaging (MRI) contrast agents.
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Affiliation(s)
- Adam A.H. Elmehriki
- Department of Chemistry, The University of Western Ontario, London ON N6A5B7, Canada
| | - Mark Milne
- Department of Chemistry, The University of Western Ontario, London ON N6A5B7, Canada
| | - Mojmír Suchý
- Department of Chemistry, The University of Western Ontario, London ON N6A5B7, Canada
- Imaging Research Laboratories, Robarts Research Institute, The University of Western Ontario, London ON N6A 5K8, Canada
| | - Robert Bartha
- Imaging Research Laboratories, Robarts Research Institute, The University of Western Ontario, London ON N6A 5K8, Canada
| | - Robert H.E. Hudson
- Department of Chemistry, The University of Western Ontario, London ON N6A5B7, Canada
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21
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Suchý M, Li AX, Milne M, Bartha R, Hudson RHE. DOTAM-type ligands possessing arginine pendant groups for use in PARACEST MRI. CONTRAST MEDIA & MOLECULAR IMAGING 2013; 7:441-9. [PMID: 22821878 DOI: 10.1002/cmmi.1461] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A synthetic methodology was developed for the preparation of metal-chelating ligands that possess arginine pendant groups relying on the alkylation of 1,4,7,10-tetraazacyclododecane (cyclen) with arginine-containing electrophiles. Conditions for the selective trialkylation or peralkylation of cyclen are described, the outcome being dependent on the nature of the arginine-derived electrophile and the solvent used for the reaction. Lanthanide metal complexes of the ligands prepared by the described route were evaluated for their suitability as PARACEST contrast agents for use in magnetic resonance imaging. The Dy(3+) and Tm(3+) complexes display CEST effects that are associated with the amide protons proximate to the metal center. These signals exhibit pH dependence in the range of 6.0-8.0 and thus may have the potential for pH measurement in physiological range.
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Affiliation(s)
- Mojmír Suchý
- Department of Chemistry, The University of Western Ontario, London, ON, Canada, N6A 5B7
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22
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Shinoda S. Dynamic cyclen-metal complexes for molecular sensing and chirality signaling. Chem Soc Rev 2012; 42:1825-35. [PMID: 23034678 DOI: 10.1039/c2cs35295h] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Structural dynamism plays important roles in artificial and biological systems, because it controls structures and functions of various molecules and assemblies. In this review, molecular recognition and self-assembling behavior of dynamic armed cyclen-metal complexes are discussed at the molecular and supramolecular levels. These metal complexes provide useful platforms for molecular receptors, supramolecules, and molecular assemblies that can respond rapidly to guest molecules and environments. Since armed cyclens have many structural and geometrical variations, they form a wide variety of metal complexes having specific sensing and signaling functions. The Lewis acidity of the metal cations plays an essential role in anion binding and in hydrolytic catalysis of phosphate esters. Characteristic luminescence and magnetic properties of lanthanides also enable techniques for effective bio-imaging. They also serve as chiral building blocks for self-assembled architectures, which offer chirality integration effective for chirality sensing and signaling at the supramolecular level.
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Affiliation(s)
- Satoshi Shinoda
- Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
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23
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Webber BC, Carney CE, Woods M. Chemical Exchange Saturation Transfer is Unaffected by Modest Changes in Pressure. Eur J Inorg Chem 2012; 2012:2040-2043. [PMID: 23526478 DOI: 10.1002/ejic.201101291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
ParaCEST (paramagnetic Chemical Exchange Saturation Transfer) agents offer an unparalleled opportunity to perform quantitative molecular imaging by MRI. Agents that can alter the image contrast they generate in response to changes in local environmental parameters such as pH, glucose concentration or lactate concentration can be used ratiometrically to quantitatively describe the local tissue environment. However, when performing such quantitative measurements it is important that the results are not confounded by changes in a second environmental parameter. In vivo pressure varies quite considerably, both through the respiratory cycle and from tissue to tissue (tumors in particular have high interstitial pressures). Since paraCEST agents have positive activation volumes, their exchange kinetics and therefore the CEST effect that they generate are necessarily related to pressure. The purpose of this investigation was to examine whether the relatively small changes in pressure exhibited in vivo could affect CEST sufficiently to confound attempts to quantify other local environmental parameters. The CEST properties of a rigid EuDOTA-tetraamide was examined at temperatures ranging from 288 to 319 K, at applied pressures ranging from 0 to 414 kPa and pre-saturation (B1) powers ranging from 524 to 935 Hz. At no point was pressure found to affect the CEST generated by this chelate, indicating that changes in in vivo pressure is unlikely to confound the quantitative measurement of physiologically relevant parameters by paraCEST MRI.
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Affiliation(s)
- Benjamin C Webber
- Department of Chemistry, Portland State University, 1719 SW 10th, Ave, Portland, OR 97201, USA
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24
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Milne M, Chicas K, Li A, Bartha R, Hudson RHE. ParaCEST MRI contrast agents capable of derivatizationvia “click” chemistry. Org Biomol Chem 2012; 10:287-92. [DOI: 10.1039/c1ob06162c] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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25
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Platas-Iglesias C. The Solution Structure and Dynamics of MRI Probes Based on Lanthanide(III) DOTA as Investigated by DFT and NMR Spectroscopy. Eur J Inorg Chem 2011. [DOI: 10.1002/ejic.201101164] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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