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Tosato M, Franchi S, Isse AA, Del Vecchio A, Zanoni G, Alker A, Asti M, Gyr T, Di Marco V, Mäcke H. Is Smaller Better? Cu 2+/Cu + Coordination Chemistry and Copper-64 Radiochemical Investigation of a 1,4,7-Triazacyclononane-Based Sulfur-Rich Chelator. Inorg Chem 2023; 62:20621-20633. [PMID: 37115633 PMCID: PMC10731632 DOI: 10.1021/acs.inorgchem.3c00621] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Indexed: 04/29/2023]
Abstract
The biologically triggered reduction of Cu2+ to Cu+ has been postulated as a possible in vivo decomplexation pathway in 64/67Cu-based radiopharmaceuticals. In an attempt to hinder this phenomenon, we have previously developed a family of S-containing polyazamacrocycles based on 12-, 13-, or 14-membered tetraaza rings able to stabilize both oxidation states. However, despite the high thermodynamic stability of the resulting Cu2+/+ complexes, a marked [64Cu]Cu2+ release was detected in human serum, likely as a result of the partially saturated coordination sphere around the copper center. In the present work, a new hexadentate macrocyclic ligand, 1,4,7-tris[2-(methylsulfanyl)ethyl)]-1,4,7-triazacyclononane (NO3S), was synthesized by hypothesizing that a smaller macrocyclic backbone could thwart the observed demetalation by fully encapsulating the copper ion. To unveil the role of the S donors in the metal binding, the corresponding alkyl analogue 1,4,7-tris-n-butyl-1,4,7-triazacyclononane (TACN-n-Bu) was considered as comparison. The acid-base properties of the free ligands and the kinetic, thermodynamic, and structural properties of their Cu2+ and Cu+ complexes were investigated in solution and solid (crystal) states through a combination of spectroscopic and electrochemical techniques. The formation of two stable mononuclear species was detected in aqueous solution for both ligands. The pCu2+ value for NO3S at physiological pH was 6 orders of magnitude higher than that computed for TACN-n-Bu, pointing out the significant stabilizing contribution arising from the Cu2+-S interactions. In both the solid state and solution, Cu2+ was fully embedded in the ligand cleft in a hexacoordinated N3S3 environment. Furthermore, NO3S exhibited a remarkable ability to form a stable complex with Cu+ through the involvement of all of the donors in the coordination sphere. Radiolabeling studies evidenced an excellent affinity of NO3S toward [64Cu]Cu2+, as quantitative incorporation was achieved at high apparent molar activity (∼10 MBq/nmol) and under mild conditions (ambient temperature, neutral pH, 10 min reaction time). Human serum stability assays revealed an increased stability of [64Cu][Cu(NO3S)]2+ when compared to the corresponding complexes formed by 12-, 13-, or 14-membered tetraaza rings.
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Affiliation(s)
- Marianna Tosato
- Department
of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Sara Franchi
- Department
of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | | | | | - Giordano Zanoni
- Department
of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - André Alker
- Roche
Pharmaceutical Research and Early Development, Roche Innovation Center Basel F. Hoffmann-La Roche, 4058 Basel, Switzerland
| | - Mattia Asti
- Radiopharmaceutical
Chemistry Section, Nuclear Medicine Unit, AUSL-IRCCS Reggio Emilia, 42122 Reggio Emilia, Italy
| | - Thomas Gyr
- Division
of Radiopharmaceutical Chemistry, Clinic of Radiology and Nuclear
Medicine, University Hospital Basel, 4031 Basel, Switzerland
| | - Valerio Di Marco
- Department
of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Helmut Mäcke
- Department
of Nuclear Medicine, University Hospital
Freiburg, D-79106 Freiburg, Germany
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Chelation of Theranostic Copper Radioisotopes with S-Rich Macrocycles: From Radiolabelling of Copper-64 to In Vivo Investigation. Molecules 2022; 27:molecules27134158. [PMID: 35807404 PMCID: PMC9268100 DOI: 10.3390/molecules27134158] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 06/21/2022] [Accepted: 06/22/2022] [Indexed: 12/10/2022] Open
Abstract
Copper radioisotopes are generally employed for cancer imaging and therapy when firmly coordinated via a chelating agent coupled to a tumor-seeking vector. However, the biologically triggered Cu2+-Cu+ redox switching may constrain the in vivo integrity of the resulting complex, leading to demetallation processes. This unsought pathway is expected to be hindered by chelators bearing N, O, and S donors which appropriately complements the borderline-hard and soft nature of Cu2+ and Cu+. In this work, the labelling performances of a series of S-rich polyazamacrocyclic chelators with [64Cu]Cu2+ and the stability of the [64Cu]Cu-complexes thereof were evaluated. Among the chelators considered, the best results were obtained with 1,7-bis [2-(methylsulfanyl)ethyl]-4,10,diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). DO2A2S was labelled at high molar activities in mild reaction conditions, and its [64Cu]Cu2+ complex showed excellent integrity in human serum over 24 h. Biodistribution studies in BALB/c nude mice performed with [64Cu][Cu(DO2A2S)] revealed a behavior similar to other [64Cu]Cu-labelled cyclen derivatives characterized by high liver and kidney uptake, which could either be ascribed to transchelation phenomena or metabolic processing of the intact complex.
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Tosato M, Pelosato M, Franchi S, Isse AA, May NV, Zanoni G, Mancin F, Pastore P, Badocco D, Asti M, Di Marco V. When ring makes the difference: coordination properties of Cu 2+/Cu + complexes with sulfur-pendant polyazamacrocycles for radiopharmaceutical applications. NEW J CHEM 2022. [DOI: 10.1039/d2nj01032a] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The Cu2+/+ complexes formed by sulfur-containing polyazamacrocycles were studied in aqueous solution using potentiometry, UV-Vis, NMR, EPR, and cyclic voltammetry.
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Affiliation(s)
- Marianna Tosato
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Matteo Pelosato
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Sara Franchi
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | | | - Nóra Veronica May
- Centre for Structural Science, Research Centre for Natural Sciences, 1117 Budapest, Hungary
| | - Giordano Zanoni
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Fabrizio Mancin
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Paolo Pastore
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Denis Badocco
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
| | - Mattia Asti
- Radiopharmaceutical Chemistry Section, Nuclear Medicine Unit, AUSL-IRCCS di Reggio Emilia, 42122 Reggio Emilia, Italy
| | - Valerio Di Marco
- Department of Chemical Sciences, University of Padova, 35131 Padova, Italy
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Tosato M, Dalla Tiezza M, May NV, Isse AA, Nardella S, Orian L, Verona M, Vaccarin C, Alker A, Mäcke H, Pastore P, Di Marco V. Copper Coordination Chemistry of Sulfur Pendant Cyclen Derivatives: An Attempt to Hinder the Reductive-Induced Demetalation in 64/67Cu Radiopharmaceuticals. Inorg Chem 2021; 60:11530-11547. [PMID: 34279088 PMCID: PMC8389837 DOI: 10.1021/acs.inorgchem.1c01550] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The Cu2+ complexes formed by a series of cyclen derivatives bearing sulfur pendant arms, 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis[2-(methylsulfanyl)ethyl]-4,10-diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S), were studied in aqueous solution at 25 °C from thermodynamic and structural points of view to evaluate their potential as chelators for copper radioisotopes. UV-vis spectrophotometric out-of-cell titrations under strongly acidic conditions, direct in-cell UV-vis titrations, potentiometric measurements at pH >4, and spectrophotometric Ag+-Cu2+ competition experiments were performed to evaluate the stoichiometry and stability constants of the Cu2+ complexes. A highly stable 1:1 metal-to-ligand complex (CuL) was found in solution at all pH values for all chelators, and for DO2A2S, protonated species were also detected under acidic conditions. The structures of the Cu2+ complexes in aqueous solution were investigated by UV-vis and electron paramagnetic resonance (EPR), and the results were supported by relativistic density functional theory (DFT) calculations. Isomers were detected that differed from their coordination modes. Crystals of [Cu(DO4S)(NO3)]·NO3 and [Cu(DO2A2S)] suitable for X-ray diffraction were obtained. Cyclic voltammetry (CV) experiments highlighted the remarkable stability of the copper complexes with reference to dissociation upon reduction from Cu2+ to Cu+ on the CV time scale. The Cu+ complexes were generated in situ by electrolysis and examined by NMR spectroscopy. DFT calculations gave further structural insights. These results demonstrate that the investigated sulfur-containing chelators are promising candidates for application in copper-based radiopharmaceuticals. In this connection, the high stability of both Cu2+ and Cu+ complexes can represent a key parameter for avoiding in vivo demetalation after bioinduced reduction to Cu+, often observed for other well-known chelators that can stabilize only Cu2+.
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Affiliation(s)
- Marianna Tosato
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy
| | - Marco Dalla Tiezza
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy
| | - Nóra V May
- Centre for Structural Science, Research Centre for Natural Sciences, Magyar tudósok Körútja 2, 1117 Budapest, Hungary
| | - Abdirisak Ahmed Isse
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy
| | - Sonia Nardella
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy.,Department of Pharmaceutical Sciences, University of Padova, via Marzolo 8, 35131 Padova, Italy
| | - Laura Orian
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy
| | - Marco Verona
- Department of Pharmaceutical Sciences, University of Padova, via Marzolo 8, 35131 Padova, Italy
| | - Christian Vaccarin
- Department of Pharmaceutical Sciences, University of Padova, via Marzolo 8, 35131 Padova, Italy
| | - André Alker
- Roche Pharmaceutical Research and Early Development, Roche Innovation Center Basel F. Hoffmann-La Roche, Grenzacherstrasse 124, 4058 Basel, Switzerland
| | - Helmut Mäcke
- Department of Nuclear Medicine, University Hospital Freiburg, Hugstetterstrasse 55, D-79106 Freiburg, Germany
| | - Paolo Pastore
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy
| | - Valerio Di Marco
- Department of Chemical Sciences, University of Padova, via Marzolo 1, 35131 Padova, Italy
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