Metal Coordination Properties of a Chromophoric Desferrioxamine (DFO) Derivative: Insight on the Coordination Stoichiometry and Thermodynamic Stability of Zr4+ Complexes

Combining Desferriferrioxamine B and 1-Hydroxy-2-Piperidone ((PIPO)H) to Chelate Zirconium. Solution Structure of a Model Complex of the [89Zr]Zr-DFOcyclo*-mAb Radioimmunoconjugate

89Zr-immunoPET is a hot topic as 89Zr cumulates the advantages of 64Cu and 124I without their drawbacks. We report the synthesis of a model ligand of a chiral bioconjugable tetrahydroxamic chelator combining the desferriferrioxamine B siderophore and 1-hydroxy-2-piperidone ((PIPO)H), a chiral cyclic hydroxamic acid derivative, and the study by NMR spectroscopy of its zirconium complex. Nuclear Overhauser effect measurements (ROESY) indicated that the complex exists in the form of two diastereomers, in 77 : 23 ratio, resulting from the combination of the central chiralities at the 3-C of the (PIPO)H component and at the Zr4+ cation. The 44 lowest energy structures out of more than 1000 configurations/conformations returned by calculations based on density functional theory were examined. Comparison of the ROESY data and the calculated interatomic H⋅⋅⋅H distances allowed us to select the most probable configuration and conformations of the major complex.

Zirconium Coordination Chemistry and Its Role in Optimizing Hydroxymate Chelation: Insights from Molecular Dynamics

In the past decade, there has been a growth in using Zirconium-89 (89Zr) as a radionuclide in nuclear medicine for cancer diagnostic imaging and drug discovery processes. Although one of the most popular chelators for 89Zr, desferrioxamine (DFO) is typically presented as a hexadentate ligand, our work suggests a different scenario. The coordination structure of the Zr4+-DFO complex has primarily been informed by DFT-based calculations, which typically ignore temperature and therefore entropic and dynamic solvent effects. In this work, free energy calculations using molecular dynamics simulations, where the conformational fluctuations of both the ligand and the solvent are explicitly included, are used to compare the binding of Zr4+ cations with two different chelators, DFO and 4HMS, the latter of which is an octadentate ligand that has been recently proposed as a better chelator due to the presence of four hydroxymate groups. We find that thermally induced disorder leads to an open hexadentate chelate structure of the Zr4+-DFO complex, leaving the Zr4+ metal exposed to the solvent. A stable coordination of Zr4+ with 4HMS, however, is formed by involving both hydroxamate groups and water molecules in a more closely packed structure.

Evaluation of coumarin-tagged deferoxamine as a Zr(IV)-based PET/fluorescence dual imaging probe

Desferoxamine (DFO) is currently the golden standard chelator for 89Zr4+, a promising nuclide for positron emission tomography imaging (PET). The natural siderophore DFO had previously been conjugated with fluorophores to obtain Fe(III) sensing molecules. In this study, a fluorescent coumarin derivative of DFO (DFOC) has been prepared and characterized (potentiometry, UV-Vis spectroscopy) for what concerns its protonation and metal coordination properties towards PET-relevant ions (Cu(II), Zr(IV)), evidencing strong similarity with pristine DFO. Retention of DFOC fluorescence emission upon metal binding has been checked (fluorescence spectrophotometry), as it would - and does - allow for optical (fluorescent) imaging, thus unlocking bimodal (PET/fluorescence) imaging for 89Zr(IV) tracers. Crystal violet and MTT assays on NIH-3 T3 fibroblasts and MDA-MB 231 mammary adenocarcinoma cell lines demonstrated, respectively, no cytotoxicity nor metabolic impairment at usual radiodiagnostic concentrations of ZrDFOC. Clonogenic colony-forming assay performed on X-irradiated MDA-MB 231 cells showed no interference of ZrDFOC with radiosensitivity. Morphological biodistribution (confocal fluorescence, transmission electron microscopy) assays on the same cells suggested internalization of the complex through endocytosis. Overall, these results support fluorophore-tagged DFO as a suitable option to achieve dual imaging (PET/fluorescence) probes based on 89Zr.

Deferoxamine Supplementation Abolished Iron-Related Toxicity of Ilex paraguariensis Extract: Behavioral and Biochemical Evaluation in Adult Zebrafish (Danio rerio)

Ilex paraguariensis (Herb mate) is a native plant from South America, widely consumed through the infusion of dried leaves. The presence of antioxidant properties in herb mate may be relevant and contribute to evaluating the effect of its compounds against oxidative stress, which could cause neurodegenerative diseases. Despite having health benefits, there are reports of the presence of heavy metals in extracts obtained from the infusion. One of these metals is iron (Fe), found in large amounts in herb mate. To reverse the cumulative effects of metals and Fe in the body, the use of Deferoxamine (Dfx) is indicated, being a potent chelator of Fe. In this work, we aimed to evaluate the antioxidant potential of the micro-encapsulated extract of I. paraguariensis (MEIP) supplemented with Dfx on zebrafish behavior and biochemical biomarkers. To evaluate the effect per se and the supplementation, four groups were established: the first group was the control (water); the second, fish treated with MEIP; the third group was formed of fish treated with Dfx; while the fourth group was treated with both MEIP and Dfx. When applied alone, Dfx presents an anxiogenic-like pattern on zebrafish (Danio rerio), while the MEIP shows an anxiolytic-like behavior. The antioxidant enzymes are re-modulated close to control when the MEIP + Dfx is applied. The cholinergic system shows an activation of the signaling, as well as the heme radical group formation, which is not affected by the Dfx-chelating effect. Thus, the supplementation of MEIP with Dfx is important to transform this extract into one that is safer and healthier for human consumption.

Heptadentate chelates for 89Zr-radiolabelling of monoclonal antibodies

Zirconium complexation chemistry is an important area of research in the context of developing radiolabelled proteins for applications in diagnostic positron emission tomography (PET) imaging. Herein, we report the synthesis...