Metal Radionuclides Research Articles

Assessment of PSMA targeting ligands bearing novel chelates with application to theranostics: Stability and complexation kinetics of 68Ga3 +, 111In3 +, 177Lu3 + and 225Ac3 +

IntroductionRecent successes in the treatment of metastatic castration-resistant prostate cancer (mCRPCa) by systemic endoradiotherapy has sparked renewed interest in developing small molecule ligands targeting prostate-specific membrane antigen (PSMA) and chelators capable of stable complexation of metal radionuclides for imaging and therapy. As the size and coordination number of metals for imaging, such as 68Ga3+, and for targeted therapy, such as 177Lu3+ and 225Ac3+, are substantially different, they may show a preference for macrocycles of different denticity. We have prepared three simple conjugates that target PSMA and form radiometal complexes through coordination by either octa-, deca-, or dodecadentate tetraazacyclododecane chelators. The complex formation and metal ion selectivity of these constructs were determined at two relevant temperatures, complex stability was examined in vitro, and tumor targeting was demonstrated in preclinical PCa models with a view towards identifying a candidate with potential value as a theranostic agent for the imaging and therapy of mCRPCa. MethodsThree bifunctional chelates with high denticity, including the octadentate chelate DOTA, the decadentate 3p-C-DEPA and a novel dodecadentate analogue of DEPA, were synthesized and conjugated to a glutamate-urea-lysine (EuK) pharmacophore (EuK-DOTA, EuK-107 and EuK-106, respectively) to enable targeting of PSMA. The metal ion selectivity for each construct was determined by incubation at 25 °C and 95 °C with the trivalent radiometals 68Ga3+, 111In3+, 177Lu3+ and 225Ac3+. PSMA binding affinity was determined by competitive binding using LNCaP cells, while in vivo tumor targeting of the 68Ga-labeled constructs was examined by positron emission tomography (PET) in LNCaP xenograft tumor-bearing mice. ResultsPMSA affinities (IC50 values) were 13.3 ± 0.9 nM for EuK-DOTA, 18.0 ± 3.7 nM for EuK-107 and 42.6 ± 6.6 nM for EuK-106. EuK-107 and EuK-DOTA proved to rapidly and near quantitatively complex 68Ga3+, 111In3+, 177Lu3+ and 225Ac3+ at 95 °C, with EuK-107 also rapidly complexing 111In3+ and 177Lu3+ at 25 °C. The inability of EuK-106 to chelate 177Lu3+ and 225Ac3+ suggests that size of the cavity of the macrocylic ring may be more critical than the number of donor groups for the chelation of larger radiometals. In vivo, 68Ga-EuK-107 proved to have similar uptake to 68Ga-DKFZ-PSMA-617, a theranostic ligand currently in clinical evaluation, in a PSMA positive xenograft tumor model. ConclusionsThe broad metal ion selectivity, good in vitro affinity for PSMA and good in vivo tumor targeting suggest that EuK-107, with the 3p-C-DEPA chelator, merits further evaluation as a theranostics construct in prostate cancer.

Dual-Nuclide Radiopharmaceuticals for Positron Emission Tomography Based Dosimetry in Radiotherapy.

Improvement of the accuracy of dosimetry in radionuclide therapy has the potential to increase patient safety and therapeutic outcomes. Although positron emission tomography (PET) is ideally suited for acquisition of dosimetric data because PET is inherently quantitative and offers high sensitivity and spatial resolution, it is not directly applicable for this purpose because common therapeutic radionuclides lack the necessary positron emission. This work reports on the synthesis of dual‐nuclide labeled radiopharmaceuticals with therapeutic and PET functionality, which are based on common and widely available metal radionuclides. Dual‐chelator conjugates, featuring interlinked cyclen‐ and triazacyclononane‐based polyphosphinates DOTPI and TRAP, allow for strictly regioselective complexation of therapeutic (e.g., 177Lu, 90Y, or 213Bi) and PET (e.g., 68Ga) radiometals in the same molecular framework by exploiting the orthogonal metal ion selectivity of these chelators (DOTPI: large cations, such as lanthanide(III) ions; TRAP: small trivalent ions, such as GaIII). Such DOTPI–TRAP conjugates were decorated with 3 Gly‐urea‐Lys (KuE) motifs for targeting prostate‐specific membrane antigen (PSMA), employing Cu‐catalyzed (CuAAC) as well as strain‐promoted (SPAAC) click chemistry. These were labeled with 177Lu or 213Bi and 68Ga and used for in vivo imaging of LNCaP (human prostate carcinoma) tumor xenografts in SCID mice by PET, thus proving practical applicability of the concept.

Correction to Purification-Free Method for Preparing Technetium-99m-Labeled Multivalent Probes for Enhanced in Vivo Imaging of Saturable Systems.

Metallic radionuclides provide target-specific radiolabeled probes for molecular imaging in radiochemical yields sufficient for administration to subjects without purification. However, unlabeled ligands in the injectate can compete for targeted molecules with radiolabeled probes, which eventually necessitates postlabeling purification. Herein we describe a “1 to 3” design to circumvent the issue by taking advantage of inherent coordination properties of technetium-99m (99mTc). A monovalent RGD ligand possessing an isonitrile as a coordinating moiety (CN-RGD) was reacted with [99mTc(CO)3(OH2)3]+ to prepare [99mTc(CO)3(CN-RGD)3]+ in over 95% radiochemical yields. This complex exhibited higher integrin αvβ3 binding affinity than its unlabeled monovalent ligand, primarily due to its multivalency. This compound visualized a murine tumor without removing unlabeled ligands, while a 99mTc-labeled monovalent probe derived from a monovalent ligand could not. The metal coordination-mediated synthesis of radiolabele...

Radiation carcinogenesis: Mechanisms and experimental models - A meeting report

The first International School on Radiation Research (2017) of Society for Radiation Research on the theme of “Radiation Carcinogenesis: Mechanisms and Experimental Models” was held in the Department of Biochemistry and Biotechnology, Annamalai University, Chidambaram, Tamil Nadu, India, during February 2–4, 2017. The school gathered basic/translational scientists and young researchers interested in recent developments in molecular and clinical aspects of cancer and radiation carcinogenesis. The objective of the School was to educate and train the young researchers about the theoretical and practical aspects of radiation carcinogenesis. The renowned faculties from India and aboard delivered expert lectures and conducted practical sessions during the school. The topics ranged from the basics of cancer and carcinogenesis; role of DNA damage and genomic instability in the mechanism of carcinogenesis; heavy metal radionuclides induced carcinogenesis; low-dose radiobiology and risk of cancer; ultraviolet (UV)-induced carcinogenesis; experimental models for carcinogenesis studies, and cancer incidence during cancer radiotherapy. During the practical session, demonstrations were arranged of techniques such as DNA damage, apoptosis, measurement of reactive oxygen species, mitochondrial membrane potential, fluorescence in situ hybridization, animal model of UV carcinogenesis, and histopathological observations of various stages of oral cancer. This report presents a brief overview of the scientific and practical sessions of the school.

Effect of carbon impurity in irradiated mixed uranium–plutonium nitride on the phase composition upon β−-decay of fission products

As shown by thermodynamic modeling, accumulation of fission products in the course of irradiation of mixed uranium–plutonium nitride containing 0.25 wt % C impurity leads to the formation of a multicomponent carbonitride solid solution containing U, Pu, Am, Np, Zr, Y, lanthanides, and also separate carbide (UMoC2, U2RuC2, URu3C0,7, BaC2, SrC2) and nitride (U2N3) phases and intermetallic compounds U(Ru, Rh, Pd)3. The β−-decay of metallic radionuclides in separate carbide phases of spent nuclear fuel leads to changes in their chemical compositions. The transformation kinetics of separate dicarbide (89SrC2 → 89YC2, 90SrC2 → 90YC2 → 90ZrC + C, 140BaC2 → 140LaC2 → 140CeC2) and complex carbide (U99MoC2 → UC2 + 99Tc) phases was calculated.

A two-step strategy to radiolabel choline phospholipids with 99mTc in S180 cell membranes via strain-promoted cyclooctyne–azide cycloaddition reaction

As tumor markers, the radiolabeling of choline (Cho)-containing phospholipids in cellular membranes with 99mTc is a challenge. The conventional strategy to combine the metallic radionuclide with Cho by large ligand damages the bioactivity of Cho, resulting in low tumor-to-nontumor ratios. Pretargeting strategy based on strain-promoted cyclooctyne–azide cycloaddition (SPAAC) reaction was applied to solve this general problem. Functional click synthons were synthesized as pretargeting components: azidoethyl-choline (AECho) serves as tumor marker and azadibenzocyclooctyne (ADIBO) conjugated to bis(2-pieolyl) amine (BPA) ligand (ADIBO-BPA) as 99mTc(CO)3-labeling and azido-binding group. Both in vitro cell experiment and in vivo biodistribution experiment indicate that it is versatile to radiolabel Cho in cellular membranes via this two-step pretargeting strategy. We believe that this pretargeting strategy can indeed enhance the target-specificity and also reduce background signals to optimize imaging quality.

ChemInform Abstract: A Practical Guide on the Synthesis of Metal Chelates for Molecular Imaging and Therapy by Means of Click Chemistry

AbstractReview: [67 refs.

Application of new bifunctional chelator DOTA and its derivatives in the metal radionuclide labeled compounds

DOTA and its derivatives are most widely used novel bifunctional chelators. They have not only mature synthesis route, but also good coordination and chelating ability. Therefore, DOTA metal complexes of DOTA-peptide conjugates are increasingly used as MRI contrast agents, radionuclide targeted imaging agents and therapeutic radiopharmaceuticals in the biomedical field. This review covers the bifunctional derivatives of DOTA, the synthesis of DOTA-peptide conjugates, and the applications of DOTA-peptide conjugate metal complexes. Key words: DOTA; Analogs & derivatives; Isotope labeling; Metals; Trends

A Practical Guide on the Synthesis of Metal Chelates for Molecular Imaging and Therapy by Means of Click Chemistry.

The copper-catalyzed cycloaddition of organic azides and alkynes (CuAAC) is one of the most popular reactions for rapid assembly of multifunctional molecular frameworks from commercially available building blocks. It is also attractive for synthesis of conjugates of multidentate chelate ligands (chelators) with molecular targeting vectors, such as peptides or proteins, which serve as precursors for labeling with metal radionuclides or are useful as MRI contrast agents after Gd(III) complexation. However, applicability of CuAAC for such purposes is complicated by formation of unwanted copper chelates. The alternative use of copper-free click chemistry, for example, the strain-promoted alkyne-azide cycloaddition (SPAAC) or the Diels-Alder reaction of tetrazines and strained alkenes, entails other specific challenges: Introduction of large, isomerically non-homogeneous and hydrophobic linker groups affects product homogeneity and can severely change pharmacokinetic profiles. Against this background, this review elucidates scope and applicability of both Cu-catalyzed and Cu-free alkyne-azide cycloadditions pertinent to the elaboration of radiometal chelates and MRI contrast agents, with an emphasis on strategies to tackle the problem of copper complexation during CuAAC.

Efficient Extraction of Radioactive Isotopes of Cobalt, Europium, Cerium, Strontium, and Copper From Aqueous Solutions

One of the most effective and simple methods of natural and wastewaters from heavy metals and radionuclides is a sorption extraction. Assorbents proposed the use of polymers, natural materials, and other oxides. Theparticles of iron oxide Fe2O3 and Fe3O4 are among the most promising materialsfor inorganic heavy metal ions and radionuclides from water bodies. Theiradvantage over other compounds is the lack of toxic effects on the human body,low cost, and ease of obtaining precursors.

Purification-Free Method for Preparing Technetium-99m-Labeled Multivalent Probes for Enhanced in Vivo Imaging of Saturable Systems.

Metallic radionuclides provide target-specific radiolabeled probes for molecular imaging in radiochemical yields sufficient for administration to subjects without purification. However, unlabeled ligands in the injectate can compete for targeted molecules with radiolabeled probes, which eventually necessitates postlabeling purification. Herein we describe a "1 to 3" design to circumvent the issue by taking advantage of inherent coordination properties of technetium-99m ((99m)Tc). A monovalent RGD ligand possessing an isonitrile as a coordinating moiety (CN-RGD) was reacted with [(99m)Tc(CO)3(OH2)3](+) to prepare [(99m)Tc(CO)3(CN-RGD)3](+) in over 95% radiochemical yields. This complex exhibited higher integrin αvβ3 binding affinity than its unlabeled monovalent ligand, primarily due to its multivalency. This compound visualized a murine tumor without removing unlabeled ligands, while a (99m)Tc-labeled monovalent probe derived from a monovalent ligand could not. The metal coordination-mediated synthesis of radiolabeled multivalent probes thereby can be a useful approach for preparing ready-to-use target-specific probes labeled with (99m)Tc and other metallic radionuclides of interest.

Biomineralization, Bioremediation and Biorecovery of Toxic Metals and Radionuclides

ABSTRACTMetal and mineral transformations are a cornerstone of geomicrobiological processes. Of central importance are the mechanisms by which microorganisms alter the speciation and mobility of metals, including their properties of mineral dissolution or mineral formation. Such processes underpin natural biogeochemical cycles for metals, and related elements such as metalloids, and metal radionuclides, as well as those elements that may be commonly associated with metal compounds and minerals, e.g., P and S. They may also determine the fate of contaminant toxic metals and radionuclides when introduced or redistributed in the environment as a result of natural or anthropogenic activities. Such contamination is an increasing problem, and microbe-based systems are increasingly viewed as potentially useful approaches for bioremediation, as well as for element biorecovery. Biomineralization is a general term for the processes by which living organisms form minerals, and this can result in metal removal from solution providing a means of detoxification as well as biorecovery. Dead biota and derived products may also provide a template for mineral deposition, the reversibility, or otherwise, of the reaction depending on physico-chemical conditions. The most common biominerals precipitated by microbes include oxides, phosphates, sulfides and oxalates, and these can have special chemical properties such as high metal sorption capacities and redox catalysis. Furthermore, some biominerals may be deposited in nanoscale dimensions, providing further significant physical, chemical and biological properties of applied significance. The purpose of this Special Issue of the Geomicrobiology Journal on Biomineralization, Bioremediation and Biorecovery is to bring together and highlight some specific examples of metal and radionuclide biomineralization by microorganisms from the different major microbial groups such as cyanobacteria, bacteria, microalgae and fungi. A range of elements and organisms are covered together with a variety of environmental and industrial contexts where a biomineralization approach may assist bioremediation, metal biorecovery or substrate stability.

金属放射性核種で標識した蛋白質プローブを用いたHaloTag技術のインビボ分子イメージングへの応用

金属放射性核種で標識した蛋白質プローブを用いたHaloTag技術のインビボ分子イメージングへの応用

In vivo click reaction between Tc-99m-labeled azadibenzocyclooctyne-MAMA and 2-nitroimidazole-azide for tumor hypoxia targeting.

The bioactivity of nitroimidazole in Tc-99m-labeled 2-nitroimidazole, a traditional solid tumor hypoxia-imaging agent for single photon emission computed tomography (SPECT), is reduced by the presence of large ligand and metallic radionuclide, exhibiting lower tumor-to-nontumor ratios. In an effort to solve this general problem, a pretargeting strategy based on click chemistry (strain-promoted cyclooctyne-azide cycloaddition) was applied. The functional click synthons were synthesized as pretargeting components: an azide group linked to 2-nitroimidazole (2NIM-Az) serves for tumor hypoxia-targeting and azadibenzocyclooctyne conjugated with monoamine monoamide dithiol ligand (AM) functions as radiolabeling and binding group to azides in vivo. 2NIM-triazole-MAMA was obtained from in vitro click reaction with a reaction rate constant of 0.98M(-1)s(-1). AM and 2NIM-triazole-MAMA were radiolabeled with Tc-99m. The hypoxia-pretargeting biodistribution was studied in Kunming mice bearing S180 tumor; (99m)Tc-AM and (99m)Tc-triazole-2NIM were used as blank control and conventional control. Compared to the control groups, the pretargeting experiment exhibits the best radio-uptake and retention in tumor, with higher tumor-to-muscle and tumor-to-blood ratios (up to 8.55 and 1.44 at 8h post-(99m)Tc-complex-injection, respectively). To some extent, the pretargeting strategy protects the bioactivity of nitroimidazole and therefore provides an innovative approach for the development of tumor hypoxia-SPECT imaging agents.

Estimation of specific activity of 177Lu by 'saturation assay' principle using DOTA as ligand.

Lutetium-177 is a widely used therapeutic radionuclide in targeted therapy and it is important to know its specific activity at the time of radiopharmaceutical preparation, especially for radiolabeling peptides. However, there are no direct methods for the experimental determination of the specific activity which can be readily applied in a hospital radiopharmacy. A new technique based on the 'saturation assay' principle using DOTA as the binding agent for the estimation of specific activity of (177)Lu is reported. The studies demonstrate the proof of principle of this new assay technique. The method is general and can be modified and applied for the estimation of specific activity of other metallic radionuclides by using DOTA or other suitable chelating agents.

Preparation and evaluation of a mesoporous calcium-silicate material (MCSM) from coal fly ash for removal of Co(II) from wastewater

The widespread industrial use of cobalt and its salts has raised concerns associated with its efficient removal from wastewater. In this study, a mesoporous calcium-silicate material (MCSM, 733m2g−1) was prepared from desilication liquor of coal fly ash and examined for use in adsorbing Co(II) from aqueous solutions. At 2gL−1 dosage, 109.6–154.8mg of Co(II) could be removed by 1g of MCSM in the pH 2–7 within 4h. The effective component for sorption was found to be a layered single-chain calcium-silicate-hydrate(I), and its negatively charged surface was helpful for Co(II) sorption (pHPZC=1.6). Before precipitation, 76.7% of Co(II) was efficiently removed via ion exchange with Ca(II) in MCSM, while the rest of Co(II) was probably adsorbed by surface complexation. The sorption followed Langmuir one-site isotherms and the kinetics was controlled by surface and intra-particle diffusion processes. Unlike conventional sorbents or ion exchangers, increasing the MCSM dosage represents a viable and economic option for improving adverse effects from practical wastewater (strong acidity, high Co(II) concentration, and high salinity). More than 98.7% of the Co(II) and metal radionuclides could be removed from the wastewater samples using 15.4gL−1 of MCSM. The results suggest that MCSM has the potential for use as an effective and low-cost sorbent for removing Co(II), as well as related hazardous metal ions from wastewater. After being used as an sorbent, MCSM is suitable for use as a substitute of cement and disposed by inexpensive solidification/stabilization technique.

⁸⁹Zr-Labeled Versus ¹²⁴I-Labeled αHER2 Fab with Optimized Plasma Half-Life for High-Contrast Tumor Imaging In Vivo.

Immuno-PET imaging of the tumor antigen HER2/neu allows for the noninvasive detection and monitoring of oncogene expression; such detection and monitoring are of prognostic value in patients with breast cancer. Compared with the full-size antibody trastuzumab, smaller protein tracers with more rapid blood clearance permit higher imaging contrast at earlier time points. Antigen-binding fragments (Fabs) of antibodies with moderately prolonged circulation achieved through the genetic fusion with a long, conformationally disordered chain of the natural amino acids Pro, Ala, and Ser (PASylation)-a biologic alternative to chemical conjugation with polyethylene glycol, PEG-offer a promising tracer format with improved pharmacokinetics for in vivo imaging. Recently, the transition metal radionuclide (89)Zr has attracted increasing interest for immuno-PET studies, complementing the conventional halogen radionuclide (124)I. To allow direct comparison of these 2 radioactive labels for the same protein tracer, the recombinant αHER2 Fab fused with 200 Pro, Ala, and Ser (PAS200) residues was either conjugated with (124)I via an iodination reagent or coupled with deferoxamine (Df) and complexed with (89)Zr. After confirmation of the stability of both radioconjugates and quality control in vitro, immuno-PET and biodistribution studies were performed with CD1-Foxn1(nu) mice bearing HER2-positive human tumor xenografts. (89)Zr⋅Df-Fab-PAS200 and (124)I-Fab-PAS200 showed specific tumor uptake of 11 and 2.3 percentage injected dose per gram 24 h after injection, respectively; both led to high tumor-to-blood (3.6 and 4.4, respectively) and tumor-to-muscle (20 and 43, respectively) ratios. With regard to off-target accumulation, overt (124)I activity was seen in the thyroid, as expected, whereas high kidney uptake was evident for (89)Zr; the latter was probably due to glomerular filtration and reabsorption of the protein tracer in proximal tubular cells. Both (89)Zr- and (124)I-labeled versions of αHER2 Fab-PAS200 allowed PET tumor imaging with high contrast. With its residualizing radiometal, the tracer (89)Zr⋅Df-Fab-PAS200 showed better in vivo stability and higher tumor uptake.

Photoassisted Biodegradation of Irradiated Organics in Simulated Nuclear Wastewater.

The extent of dehalogenation and degradation of toxic aromatic compounds in a nuclear wastewater was evaluated using a two-stage system consisting of a photolytic reactor followed by a biological reactor. Experiments were performed by varying the initial 4-chlorophenol (4-CP) concentration from 50 to 1000 mg/L. The UV pretreatment stage improved the overall efficiency of biodegradation of the recalcitrant compound by facilitating degradability in the biological stage. Removal efficiencies greater than 98% were achieved at 4-CP feed concentrations < 50 mg/L. Adding an H2O2 dose of 0.1 mg/L as an oxidant further improved biodegradation under optimum operating conditions for the entire system. Some known aromatic compound degraders such as Pseudomonas aeruginosa and Pseudomonas mendocina were detected in the consortium using the 16S rRNA genetic fingerprint technique. To the authors' knowledge, this is the first study on biodegradation of halogenated aromatic compounds that are copollutants of metallic radionuclides in radioactive wastewater.

Global transcriptional analysis of short-term hepatic stress responses in Atlantic salmon (Salmo salar) exposed to depleted uranium.

Potential environmental hazards of radionuclides are often studied at the individual level. Sufficient toxicogenomics data at the molecular/cellular level for understanding the effects and modes of toxic action (MoAs) of radionuclide is still lacking. The current article introduces transcriptomic data generated from a recent ecotoxicological study, with the aims to characterize the MoAs of a metallic radionuclide, deplete uranium (DU) in an ecologically and commercially important fish species, Atlantic salmon (Salmo salar). Salmon were exposed to three concentrations (0.25, 0.5 and 1.0 mg/L) of DU for 48 h. Short-term global transcriptional responses were studied using Agilent custom-designed high density 60,000-feature (60 k) salmonid oligonucleotide microarrays (oligoarray). The microarray datasets deposited at Gene Expression Omnibus (GEO ID: GSE58824) were associated with a recently published study by Song et al. (2014) in BMC Genomics. The authors describe the experimental data herein to build a platform for better understanding the toxic mechanisms and ecological hazard of radionuclides such as DU in fish.

Development of new peptide-based chelating agents for site-specific radiolabeling with 64Cu

Radiolabeled monoclonal antibodies (mAbs) are very useful molecular probes for nuclear imaging technique due to their high-target specificity and high-stability in the bloodstream. MAbs are generally labeled by indirect method using the combination of relatively long-lived metallic radionuclides (including (64)Cu, (89)Zr, and (111)In) and bifunctional chelating agents which are capable of binding both antibodies and radio metals. The indirect radiolabeling method has some advantages such as high labeling efficiency and long-term retention ability within their target cells. However, this conventional labeling method can potentially lead to low-target affinity of the mAb probes, because of the non-site-specific introduction of the bifunctional chelators into the active site of the mAbs. To overcome the shortcoming, we proposed a new direct labeling method utilizing fusion proteins comprising mAbs linked to metal binding peptides at the N- or C-terminus. In this study, we synthesized new peptide derivatives possessing an N-terminal tripeptide sequence (Xaa-Yaa-His) called the amino terminal Cu(2+)- and Ni(2+)-binding (ATCUN) motif as (64)Cu binding peptides for the proposed labeling method. Moreover, we studied the stability constants of Cu(2+)-ATCUN peptide complexes by pH titration. From these studies, we found that a low basicity of the N-terminal amine in the peptide resulted in a high stability constant of the complex. This finding may provide valuable guidelines in designing the ATCUN peptide with high-binding affinity toward (64)Cu.