Preclinical Evaluation of a 64Cu-Based Theranostic Approach in a Murine Model of Multiple Myeloma.

Although the concept of theranostics is neither new nor exclusive to nuclear medicine, it is a particularly promising approach for the future of nuclear oncology. This approach is based on the use of molecules targeting specific biomarkers in the tumour or its microenvironment, associated with optimal radionuclides which, depending on their emission properties, allow the combination of diagnosis by molecular imaging and targeted radionuclide therapy (TRT). Copper-64 has suitable decay properties (both ß+ and ß- decays) for PET imaging and potentially for TRT, making it both an imaging and therapy agent. We developed and evaluated a theranostic approach using a copper-64 radiolabelled anti-CD138 antibody, [64Cu]Cu-TE1PA-9E7.4 in a MOPC315.BM mouse model of multiple myeloma. PET imaging using [64Cu]Cu-TE1PA-9E7.4 allows for high-resolution PET images. Dosimetric estimation from ex vivo biodistribution data revealed acceptable delivered doses to healthy organs and tissues, and a very encouraging tumour absorbed dose for TRT applications. Therapeutic efficacy resulting in delayed tumour growth and increased survival without inducing major or irreversible toxicity has been observed with 2 doses of 35 MBq administered at a 2-week interval. Repeated injections of [64Cu]Cu-TE1PA-9E7.4 are safe and can be effective for TRT application in this syngeneic preclinical model of MM.

Synthesis and In Vitro Comparison of DOTA, NODAGA and 15-5 Macrocycles as Chelators for the 64Cu-Labelling of Immunoconjugates.

The development of 64Cu-based immuno-PET radiotracers requires the use of copper-specific bifunctional chelators (BFCs) that contain functional groups allowing both convenient bioconjugation and stable copper complexes to limit in vivo bioreduction, transmetallation and/or transchelation. The excellent in vivo kinetic inertness of the pentaazamacrocyclic [64Cu]Cu-15-5 complex prompted us to investigate its potential for the 64Cu-labelling of monoclonal antibodies (mAbs), compared with the well-known NODAGA and DOTA chelators. To this end, three NODAGA, DOTA and 15-5-derived BFCs, containing a pendant azadibenzocyclooctyne moiety, were synthesised and a robust methodology was determined to form covalent bonds between them and azide-functionalised trastuzumab, an anti-HER2 mAb, using strain-promoted azide-alkyne cycloaddition. Unlike the DOTA derivative, the NODAGA- and 15-5-mAb conjugates were radiolabelled with 64Cu, obtaining excellent radiochemical yields, under mild conditions. Although all the radioimmunoconjugates showed excellent stability in PBS or mouse serum, [64Cu]Cu-15-5- and [64Cu]Cu-NODAGA-trastuzumab presented higher resistance to transchelation when challenged by EDTA. Finally, the immunoreactive fraction of the radioimmunoconjugates (88-94%) was determined in HER-2 positive BT474 human breast cancer cells, confirming that the bioconjugation and radiolabelling processes implemented had no significant impact on antigen recognition.

Complexation of europium(III) with exopolysaccharides from a marine bacterium envisaged as luminescent probe in a theranostic approach.

Exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium, showed anti-metastatic properties in osteosarcoma (bone tumor). These EPSs could be employed as new drug delivery systems for therapeutic uses. They may represent a new class of ligands to be combined in a theranostic approach with fluorescent metals, such as Eu(III), to serve as imaging probe. The goal of this work was to investigate the feasibility of such coupling by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Since these EPSs are polyelectrolytes their conformation could affect the complexation properties. Thus, viscosimetric measurements were performed as a function of their concentration as well as the background electrolyte concentration. Polysaccharides conformation exhibited a lower hydrodynamic volume for the highest ionic strengths. The resulting random-coiled conformation could affect the complexation with metal for high concentration but no change was evidenced when increasing europium concentration. Two sites of complexation of Eu(III) were evidenced by TRLFS in heparin, whereas only one site was evidenced in two modified EPSs produced from Alteromonas infernus.

Antiproliferative Properties of Scandium Exopolysaccharide Complexes on Several Cancer Cell Lines.

Antimetastatic properties on both murine and human osteosarcoma cell lines (POS-1 and KHOS) have been evidenced using exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium. These derivatives had no significant effect on the cell cycle neither a pro-apoptotic effect on osteosarcoma cells. Based on this observation, these EPSs could be employed as new drug delivery systems for therapeutic uses. A theranostic approach, i.e., combination of a predictive biomarker with a therapeutic agent, has been developed notably by combining with true pair of theranostic radionuclides, such as scandium 47Sc/44Sc. However, it is crucial to ensure that, once complexation is done, the biological properties of the vector remain intact, allowing the molecular tropism of the ligand to recognize its molecular target. It is important to assess if the biological properties of EPS evidenced on osteosarcoma cell lines remain when scandium is complexed to the polymers and can be extended to other cancer cell types. Scandium-EPS complexes were thus tested in vitro on human cell lines: MNNG/HOS osteosarcoma, A375 melanoma, A549 lung adenocarcinoma, U251 glioma, MDA231 breast cancer, and Caco2 colon cancer cells. An xCELLigence Real Cell Time Analysis (RTCA) technology assay was used to monitor for 160 h, the proliferation kinetics of the different cell lines. The tested complexes exhibited an anti-proliferative effect, this effect was more effective compared to EPS alone. This increase of the antiproliferative properties was explained by a change in conformation of EPS complexes due to their polyelectrolyte nature that was induced by complexation. Alterations of both growth factor-receptor signaling, and transmembrane protein interactions could be the principal cause of the antiproliferative effect. These results are very promising and reveal that EPS can be coupled to scandium for improving its biological effects and also suggesting that no major structural modification occurs on the ligand.

Marine Exopolysaccharide Complexed With Scandium Aimed as Theranostic Agents.

(1) Background: Exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium, showed anti-metastatic properties. They may represent a new class of ligands to be combined with theranostic radionuclides, such as 47Sc/44Sc. The goal of this work was to investigate the feasibility of such coupling. (2) Methods: EPSs, as well as heparin used as a drug reference, were characterized in terms of molar mass and dispersity using Asymmetrical Flow Field-Flow Fractionation coupled to Multi-Angle Light Scattering (AF4-MALS). The intrinsic viscosity of EPSs at different ionic strengths were measured in order to establish the conformation. To determine the stability constants of Sc with EPS and heparin, a Free-ion selective radiotracer extraction (FISRE) method has been used. (3) Results: AF4-MALS showed that radical depolymerization produces monodisperse EPSs, suitable for therapeutic use. EPS conformation exhibited a lower hydrodynamic volume for the highest ionic strengths. The resulting random-coiled conformation could affect the complexation with metal for high concentration. The LogK of Sc-EPS complexes have been determined and showing that they are comparable to the Sc-Hep. (4) Conclusions: EPSs are very promising to be coupled with the theranostic pair of scandium for Nuclear Medicine.

Uptake and Removal of Uranium by and from Human Teeth.

Uranium-238 (238U), a long-lived radiometal, is widespread in the environment because of both naturally occurring processes and anthropogenic processes. The ingestion or inhalation of large amounts of U is a major threat to humans, and its toxicity is considered mostly chemical rather than radiological. Therefore, a way to remove uranium ingested by humans from uranium-contaminated water or from the air is critically needed. This study investigated the uranium uptake by hydroxyapatite (HAP), a compound found in human bone and teeth. The uptake of U by teeth is a result of U transport as dissolved uranyl (UO22+) in contaminated water, and U adsorption has been linked to delays in both tooth eruption and development. In this present work, the influence of pH, contact time, initial U concentration, and buffer solution on the uptake and removal of U in synthetic HAP was investigated and modeled. The influence of pH (pH of human saliva, 6.7-7.4) on the uptake of uranyl was negligible. Furthermore, the kinetics were extremely fast; in one second of exposure, 98% of uranyl was uptaken by HAP. The uptake followed pseudo-second-order kinetics and a Freundlich isotherm model. A 0.2 M sodium carbonate solution removed all the uranyl from HAP after 1 h. Another series of in vitro tests were performed with real teeth as targets. We found that, for a 50 mg/L U in PBS solution adjusted to physiological pH, ∼35% of the uranyl was uptaken by the tooth after 1 h, following pseudo-first-order kinetics. Among several washing solutions tested, a commercially available carbonate, as well as a commercially available fluoride solution, enabled removal of all the uranyl taken up by the teeth.

IAEA Activities on 67Cu, 186Re, 47Sc Theranostic Radionuclides and Radiopharmaceuticals.

Despite interesting properties, the use of 67Cu, 186Re and 47Sc theranostic radionuclides in preclinical studies and clinical trials is curtailed by their limited availability due to a lack of widely established production methods. An IAEA Coordinated Research Project (CRP) was initiated to identify important technical issues related to the production and quality control of these emerging radionuclides and related radiopharmaceuticals, based on the request from IAEA Member States. The international team worked on targetry, separation, quality control and radiopharmaceutical aspects of the radionuclides obtained from research reactors and cyclotrons leading to preparation of a standard recommendations for all Member States. The CRP was initiated in 2016 with fourteen participants from thirteen Member States from four continents. Extraordinary results on the production, quality control and preclinical evaluation of selected radionuclides were reported in this project that was finalized in 2020. The outcomes, outputs and results of this project achieved by participating Member States are described in this minireview.

Promising Scandium Radionuclides for Nuclear Medicine: A Review on the Production and Chemistry up to In Vivo Proofs of Concept.

Scandium radionuclides have been identified in the late 1990s as promising for nuclear medicine applications, but have been set aside for about 20 years. Among the different isotopes of scandium, 43Sc and 44Sc are interesting for positron emission tomography imaging, whereas 47Sc is interesting for therapy. The 44Sc/47Sc or 43Sc/47Sc pairs could be thus envisaged as true theranostic pairs. Another interesting aspect of scandium is that its chemistry is governed by the trivalent ion, Sc3+. When combined with its hardness and its size, it gives this element a lanthanide-like behavior. It is then also possible to use it in a theranostic approach in combination with 177Lu or other lanthanides. This article aims to review the progresses that have been made over the last decade on scandium isotope production and coordination chemistry. It also reviews the radiolabeling aspects and the first (pre) clinical studies performed.

Is Polonium-210 a Good Indicator for Anthropogenic Radioactivity?

Anthropogenic radioactivity generated by nuclear or chemical events results in the liberation of quadrillions of Becquerel and tons of materials to the environment. These events include nuclear accidents, nuclear weapon experiments, and high levels of generated radioactive and chemical waste. 210Po is a high-energy α emitter that presents in the environment at extremely low concentration. It is considered as one of the highly toxic elements and is estimated to contribute about 7% of the total effective dose equivalent to humans from ingested natural internal radiation. The assessment of 210Po activity/concentration in the environment could be used as an indicator of the level of anthropogenic radioactivity. The 210Po concentration present in the most frequently sold cigarette produced in Lebanon was assayed using α spectrometry after a radiochemical separation and spontaneous deposition of Po on a copper disk. Although the geographical nature of Lebanese land is an extension of Syrian territory, the polonium activity concentration obtained is 8.8 times higher and attributable to the excessive use of phosphate fertilizers in agriculture. The individual committed effective dose was estimated to be equal to 219 ± 17 µSv/year of cigarette smoking.

Evidence for the Heaviest Expected Halide Species in Aqueous Solution, At-, by Electromobility Measurements.

At- (astatide) is commonly expected to be the heaviest halide in the halogen group. However, there is no proof for the existence of this -1 charged species. Furthermore, investigations with astatine are restricted by its specific radioactive properties, which entail working at ultratrace concentrations (typically less than 10-10 M). In this work, an especially built electromigration device is applied to obtain information about the charge/size ratio characterizing an ion in aqueous solution. An anionic At species is observed in reducing conditions. Moreover, we propose the first absolute mobility value for the astatine species in acidic reducing condition: (-8.26 ± 0.59) × 10-4 cm2·V-1·s-1. This value appears close to that of I- ((-8.30 ± 0.33) × 10-4 cm2·V-1·s-1), which is obtained by the same method. The similar absolute mobilities obtained for both ions are coherent with theoretical calculations indicating similar diffusion behaviors for At- and I-. This good agreement confirms the existence of the At- species.

Investigation of a new "N2S2O2" chelating agent with high Po(iv) affinity.

A water-soluble "N2S2O2" complexing agent was designed for polonium(iv) decorporation. The bifunctional ligand showed outstanding Po(iv) complexing abilities, with a conditional stability constant three orders of magnitude higher than the reference ligand BAL.

Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)2 (-) over At(-) in Basic Conditions.

It is generally assumed that astatide (At(-) ) is the predominant astatine species in basic aqueous media. This assumption is questioned in non-complexing and non-reductive aqueous solutions by means of high-pressure anion-exchange chromatography. Contrary to what is usually believed, astatide is found to be a minor species at pH=11. A different species, which also bears a single negative charge, becomes predominant when the pH is increased beyond 7. Using competition experiments, an equilibrium constant value of 10(-6.9) has been determined for the formation of this species from AtO(OH) with the exchange of one proton. The identification of this species, AtO(OH)2 (-) , is achieved through relativistic quantum mechanical calculations, which rule out the significant formation of the AtO2 (-) species, while leading to a hydrolysis constant of AtO(OH) in excellent agreement with experiment when the AtO(OH)2 (-) species is considered. Beyond the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of (211) At radiolabeling protocols.

Is there an interest to use deuteron beams to produce non-conventional radionuclides?

With the recent interest on the theranostic approach, there has been a renewed interest for alternative radionuclides in nuclear medicine. They can be produced using common production routes, i.e., using protons accelerated by biomedical cyclotrons or neutrons produced in research reactors. However, in some cases, it can be more valuable to use deuterons as projectiles. In the case of Cu-64, smaller quantities of the expensive target material, Ni-64, are used with deuterons as compared with protons for the same produced activity. For the Sc-44m/Sc-44g generator, deuterons afford a higher Sc-44m production yield than with protons. Finally, in the case of Re-186g, deuterons lead to a production yield five times higher than protons. These three examples show that it is of interest to consider not only protons or neutrons but also deuterons to produce alternative radionuclides.

Radiolabeling of HTE1PA: A new monopicolinate cyclam derivative for Cu-64 phenotypic imaging. In vitro and in vivo stability studies in mice.

INTRODUCTION: HTE1PA, a monopicolinate-N-alkylated cyclam-based ligand has previously demonstrated fast complexation process, high kinetic inertness and important thermodynamic and electrochemical stability with respect to natural copper. In this work we first developed a new synthetic route to obtain HTE1PA in good yields. Then, we investigated HTE1PA chelation properties towards copper-64 and assessed in vitro and in vivo stability of the resulting compound. METHODS: Radiolabeling of HTE1PA with copper-64 was tested at different ligand concentrations in ammonium acetate medium. In vitro stability study was carried out by incubating [(64)Cu]TE1PA complex in human serum at both 37°C and 4°C; chromatographic controls were performed over 24h. Biodistribution, pharmacokinetic and hepatic metabolism of [(64)Cu]TE1PA were conducted in BALC/c mice in comparison with [(64)Cu]acetate and [(64)Cu]DOTA, used as a reference ligand. RESULTS: The promising results obtained for natural copper complexation were confirmed. HTE1PA was quantitatively radiolabeled in 15 min at room temperature. The resulting complex showed high serum stability. [(64)Cu]TE1PA induced a significant uptake in the liver and kidneys at early biodistribution time point. Nevertheless, a high speed wash out was observed at 24h leading to significantly lower uptake into the liver compared to [(64)Cu]DOTA. The metabolism study was consistent with a high resistance to transchelation as the initial uptake into liver matches with the intact form of [(64)Cu]TE1PA. CONCLUSION: Despite the partial elimination of HTE1PA - as copper-64 complex - through the hepatic route, its high selectivity for copper and its resistance to transchelation make it a promising ligand for antibody radiolabeling with either copper-64 or copper-67.

Investigation of astatine(III) hydrolyzed species: experiments and relativistic calculations.

This work aims to resolve some controversies about astatine(III) hydroxide species present in oxidant aqueous solution. AtO(+) is the dominant species existing under oxidizing and acidic pH conditions. This is consistent with high-performance ion-exchange chromatography data showing the existence of one species holding one positive charge. A change in speciation occurs as the pH changes from 1 to 4, while remaining under oxidizing conditions. Dynamic experiments with ion-exchange resins evidence the existence of a neutral species witnessed by its elution in the void volume. Batch-experiments using a competition method show the exchange of one proton indicating the formation of the AtO(OH) species. The hydrolysis thermodynamic constant, extrapolated to zero ionic strength, was determined to be 10(-1.9). This value is supported by two-component relativistic quantum calculations and therefore allows disclosing unambiguously the structure of the formed species.

Alpha-emitters for immuno-therapy: a review of recent developments from chemistry to clinics.

Alpha-particles are of considerable growing interest for Targeted Alpha Therapy (TAT). TAT gains more attention as new targets, chemical labeling techniques and α-particle emitters are developed but translation of TAT into the clinic has been slow, in part because of the limited availability and the short physical half-lives of some of the available α-particle emitters. This article is an up-to-date overview of the literature concerning α-emitters used for TAT of cancer. It briefly describes the nuclear characteristics, the production parameters (targets, extraction and purification), the complexation properties of these radionuclides to chelates and biological vectors and finally draws-upon the preclinical and clinical studies that have been performed over the past two decades. Radiobiology and dosimetry aspects are also presented in this paper.

Speciation of technetium(IV) in bicarbonate media.

The technetium isotope (99)Tc is a major fission product from nuclear reactors. Ultimately it is disposed of as radioactive waste since it has few applications outside of scientific research. Geochemical modeling of the dissolution of nuclear waste and of the solubility and speciation of the dissolved radionuclides in groundwater is an important part of the Performance Assessment for the safety of nuclear waste repositories. It relies on the availability of a critically assessed thermodynamic database. The potential of the Tc(VII)/Tc(IV) redox couple is measured here under various chemical conditions to verify the stoichiometries of Tc complexes and determine their stabilities: (i) -log(10)[H(+)] in the range 7.0-10.0, for 0.3, 0.6, and 0.7 M [CO(3)](total); (ii) [CO(3)](total) in the range 0.01-0.6 M at -log(10)[H(+)] approximately 8.6; and (iii) [Tc(VII)]/[Tc(IV] ratios of (6.02 10(-5) M)/(10(-6) M) and (6.02 10(-5) M)/(6.02 10(-5) M) at -log(10)[H(+)] = -9.1 and [CO(3)](total) = 1 M. Assuming that Tc(VII), TcO(4)(-) is the only species which exists under all the above chemical conditions, the potentiometric results can be interpreted by considering the presence of two hydroxide-carbonate monomeric complexes. The hydrolysis equilibrium between these two complexes is Tc(CO(3))(OH)(2) + H(2)O <--> Tc(CO(3))(OH)(3)(-) + H(+) with -log(10)[H(+)](1/2) = 8.69 +/- 0.20, which is consistent with the -8.3 +/- 0.6 corresponding hydrolysis constant of the NEA TDB review. 733 +/- 44 mV/SHE and 575 +/- 60 mV/SHE are measured for the standard potentials of the TcO(4)(-)/Tc(CO(3))(OH)(2), and for the TcO(4)(-)/Tc(CO(3))(OH)(3)(-) redox couples respectively. The corresponding formation constants from TcO(OH)(2) are log(10)K(1,2) = 19.8 +/- 0.5 and log(10)K(1,3) = 10.5 +/- 0.5, to be compared with the 19.3 +/- 0.3 and 11.0 +/- 0.6 values proposed by the NEA TDB review. Note that these values have been converted for the formation reactions described here, thus the given values are not those of the NEA TDB review. However, Tc(CO(3))(OH)(2) is predicted to dominate over a surprisingly large range of chemical conditions. The monomeric character of the Tc(IV) complexes is verified in this study.

Feasibility of the radioastatination of a monoclonal antibody with astatine-211 purified by wet extraction.

Astatine-211, a most promising α-particle emitter for targeted radiotherapy, is generally obtained by high-temperature distillation. However, a liquid-liquid extraction procedure (wet extraction) has also been described. The purpose of this study was to develop and optimize the labelling of the stannylated-activated ester N-hydroxysuccinimidyl-meta-trimethylstannylbenzoate ester (MeSTB) with astatine-211 extracted in di-isopropylether (DIPE) in the presence of the oxidant N-chlorosuccinimide (NCS). The effect of final volume, incubation duration and NCS amounts on radiolabelling yield was studied. The best yields (85-90%) of N-hydroxysuccinimidyl-meta-[(211)At]astatobenzoate ester (SAB) were obtained with 20 nmol of MeSTB, 100 nmol of NCS in 120 µL of DIPE after 15 min. The astatine-211-labelled-activated ester was then used to radiolabel a monoclonal antibody (mAb). The labelling yield was 20-25% and the radiochemical purity was 97-99%. These results show that mAbs may be efficiently labelled with astatine-211 obtained by wet extraction, a fully automatable technique that may prove to be a useful alternative to dry distillation for high activity labelling of radiopharmaceuticals. Copyright © 2008 John Wiley & Sons, Ltd.

Effect of aqueous acetic, oxalic, and carbonic acids on the adsorption of europium(III) onto alpha-alumina.

Chemical retention, i.e., partition of the element between aqueous solution and mineral surface, is a key phenomenon for assessing the safety of possible nuclear waste disposal. For this purpose, the sorption of Eu(III) onto a model mineral-alpha-alumina-is studied here, including the effects of groundwater chemistry: pH and concentrations of small organic and inorganic ligands (acetate, oxalate, and carbonate anions). This work presents some experimental evidence for a synergic mechanism of sorption of europium-ligand complexes onto the alumina. Only cationic complexes were necessary to consider to model experimental results. Using the ion-exchange theory (IET) and a corresponding restricted set of parameters-exchange capacities and thermodynamic equilibrium constants-the whole set of sorption experiments of Eu(III) cationic species onto the alpha-alumina was modeled under various chemical conditions.

Sorption of aqueous carbonic, acetic, and oxalic acids onto alpha-alumina.

The presence of organic complexing agents can modify the behavior of a surface. This study aims to better understand the impact of carboxylic acids (acetic, oxalic, and carbonic acids) issued from cellulose degradation and equally naturally present in soils. First, evidence of two different kinds of sites for chloride adsorption onto alpha-alumina and another for sodium sorption was provided. Consequently, no competition between these cation and anion sorptions occurs on alpha-alumina. The associated exchange capacities and ionic exchange constants were measured. Second, the adsorption behavior of the carboxylic acids was studied as a function of aqueous -log[H(+)] and 0.01 to 0.1 M ionic strength (NaCl), and modeled by using mass action law for ideal biphasic systems. The carboxylic acids were found to be adsorbed on the same sites as chloride ions. The competition between organic ligands and chloride ions was satisfactorily accounted for by the model assuming the deprotonated form of the ligands was sorbed on alpha-alumina. The model also allowed us to interpret the adsorption of all species under various conditions without any extra fitting parameters.