Dose-dependent efficacy and safety toxicology of hydroxypyridinonate actinide decorporation agents in rodents: towards a safe and effective human dosing regimen

Investigation of Chelating Agents for the Removal of Thorium from Human Teeth upon Nuclear Contamination

Thorium-232 (232Th) is a radioactive heavy metal that is of increasing interest as a source of nuclear energy. However, upon nuclear incidents, the ingestion or inhalation of Th in major quantities can contribute to chemical and radiological health problems, including accumulation in the bone tissue and an increased risk of developing pancreatic, lung, and hematopoietic cancers. The major mineral component of the bone is hydroxyapatite (HAP)─also the major mineral component of the teeth. As such, the teeth are the first site of exposure upon oral ingestion of Th-contaminated materials, and Th can pose a potential risk to teeth development. In essence, in the case of human contamination, it is critical to identify effective chelating agents capable of removing Th. Using a batch study methodology, this present work investigates the uptake and the removal of Th from synthetic HAP and from teeth samples by diethylenetriamine pentaacetate (DTPA), ethylenediaminetetraacetic acid (EDTA), and other promising chelating agents. Th uptake over synthetic HAP exceeds 98% at physiological pH with <1 min of contact time and uptake exceeds 90% across the entire pH range. Regarding teeth, over 1 mg Th uptaken per gram of tooth is observed after 24 h. The overall effectiveness of chelating agents for the removal of Th from is as follows: DTPA > EDTA > NaF/mouthwash/3,4,3-LI(1,2-HOPO); this trend was observed both in synthetic HAP and Th-impregnated teeth samples.

Chelation therapy with 3,4,3-Li(1,2-HOPO) after pulmonary exposure to plutonium in rats

Internal exposure to plutonium can occur through inhalation for the nuclear worker, but also for the public if the radionuclide was released into the atmosphere in the context of a nuclear accident or terrorist attack. DieThylenetriaminePentaAcetic acid (DTPA) is currently still the only authorized chelator that can be used to decorporate internalized plutonium. The Linear HydrOxyPyridinOne-based ligand named 3,4,3-Li(1,2-HOPO) remains the most promising drug candidate to replace it in the hopes of improving chelating treatment. This study aimed to assess the efficacy of 3,4,3-Li(1,2-HOPO) in removing plutonium from rats exposed to the lungs, depending on the timing and route of treatment, and almost always compared to DTPA at a ten-fold higher dose used as a reference chelator. First, early intravenous injection or inhalation of 3,4,3-Li(1,2-HOPO) demonstrated superior efficacy over DTPA in preventing plutonium accumulation in liver and bone in rats exposed by injection or lung intubation. However, this superiority of 3,4,3-Li(1,2-HOPO) was much less pronounced with delayed treatment. In rats given plutonium in the lungs, the experiments also showed that 3,4,3-Li-HOPO reduced pulmonary retention of plutonium more effectively than DTPA only when the chelators were injected early but not at delayed times, while it was always the better of the two chelators when they were inhaled. Under our experimental conditions, the rapid oral administration of 3,4,3-Li(1,2-HOPO) was successful in preventing systemic accumulation of plutonium, but not in decreasing lung retention. Thus, after exposure to plutonium by inhalation, the best emergency treatment would be the rapid inhalation of a 3,4,3-Li(1,2-HOPO) aerosol to limit pulmonary retention of plutonium and prevent extrapulmonary deposition of plutonium in target systemic tissues.

Hydration of divalent lanthanides, Sm2+ and Eu2+ : A molecular dynamics study with polarizable AMOEBA force field

The chemistry of divalent lanthanides, Ln2+ , is a growing sub-field of heavy element chemistry owing to new synthetic approaches. However, some theoretical aspects of these unusual cations are currently underdeveloped, especially as they relate to their dynamic properties in solution. In this work, we address the hydration of two of the classical Ln2+ cations, Sm2+ and Eu2+ , using atomic multipole optimized energetic for biomolecular applications (AMOEBA) force fields. These cations have not been parameterized to date with AMOEBA, and few studies are available because of their instability with respect to oxidation in aqueous media. Coordination numbers (CN's) of 8.2 and 8.1 respectively for Sm2+ and Eu2+ , and 8.8 for both Sm3+ and Eu3+ have been obtained and are in good agreement with the few available AIMD and X-ray absorption fine structures studies. The decreased CN of Ln2+ compared with Ln3+ arises from progressive water exchange events that indicates the gradual stabilization of 8-coordinate structures with respect to 9-coordinate geometries. Moreover, the effects of the chloride counter anions on the coordination of Ln2+ cations have been studied at different chloride concentrations in this work. Lastly, water exchange times of Ln2+ cations have been calculated to provide a comprehensive understanding of the behavior of Eu2+ and Sm2+ in aqueous chloride media.

Mechanism of Ba Zhen Tang Delaying Skin Photoaging Based on Network Pharmacology and Molecular Docking

Purpose

To study the efficacy of Ba Zhen Tang in delaying skin photoaging and its potential mechanism based on network pharmacology and molecular docking.

Methods

First, we screened the active components and targets of Ba Zhen Tang by Traditional Chinese Medicine Database and Analysis Platform (TCMSP) and The Universal Protein Resource (UniProt). The target genes of skin photoaging were obtained from GeneCards and GeneMap database. Then, we analyzed the protein–protein interaction (PPI) by STRING database. The network map was constructed by Cytoscape. Finally, we performed Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis by Metascape database. The molecular docking via Autodock Vina and Pymol. Furthermore, skin photoaging cellular models were established, and the effects of Ba Zhen Tang on ameliorating skin photoaging were investigated.

Results

A total of 160 active ingredients in Ba Zhen Tang and 60 targets of Ba Zhen Tang for delaying skin photoaging were identified. By GO enrichment analysis, 1153 biological process entries, 45 cellular component entries and 89 molecular functional entries were obtained. A total of 155 signal pathways were obtained by KEGG analysis. Ba Zhen Tang is related to MAPK signaling pathway, TNF signaling pathway and AGE-RAGE signaling pathway in diabetic complications, etc., which directly affect the key nodes of photoaging. The molecular docking results showed that there was a certain affinity between the main compounds (kaempferol, quercetin, β-sitosterol, naringenin) and core target genes (PTGS2, CASP3, MAPK1, MAPK3, TP53). Ba Zhen Tang-treated mouse serum inhibited the senescence and p16^INK4a expression of human immortalized keratinocyte (HaCaT) cells irradiated by ultraviolet-B (UVB).

Conclusion

Our study elucidated the potential pharmacological mechanism of Ba Zhen Tang in the treatment of photoaging through multiple targets and pathways. The therapeutic effects of Ba Zhen Tang on skin photoaging were validated in cellular models.

A network pharmacology-based study of the potential targets and mechanisms of action of Qibao Meiran Dan in delaying skin aging

OBJECTIVE

The aim of this study was to use network pharmacology to explore the potential targets and mechanisms of action of Qibao Meiran Dan in relation to delaying skin aging.

METHODS

The traditional Chinese medicine systems pharmacology database and analysis platform, and the traditional Chinese medicine integrated database, were used to screen the active ingredients and targets of Qibao Meiran Dan. The human gene database GeneCards and the gene database of the National Center for Biotechnology Information were jointly adopted to obtain skin aging-related target genes. The search tool for the retrieval of interacting genes/proteins (STRING) database was used for core analysis of protein-protein interaction.

RESULTS

In total, 72 effective active ingredients, 273 action targets, 234 skin-aging target genes, and 64 intersecting core targets were identified. GO enrichment analysis provided 393 biological process entries, and the KEGG analysis was represented by the tumor necrosis factor (TNF) signaling pathway, where the core targets of TNF-α and matrix metalloproteinase-1 (MMP-1) were enriched. The experimental results showed that cell morphology was clearer and more refractive in the Qibao Meiran Dan group than in the model group.

CONCLUSION

Qibao Meiran Dan may regulate oxidative stress injury and collagen metabolism by down-regulating the expression of TNF-α and MMP-1, thus slowing skin aging.

The effect of Yang Yan Qing E Wan on senescent phenotypes and the expression of β-catenin and p16INK4a in human skin fibroblasts

This aim of this study was to observe the effect of Yang Yan Qing E Wan (YYQEW) on senescent phenotypes and the expression of β-catenin and p16^INK4a in the hydrogen peroxide (H₂O₂)-induced premature senescence of normal human skin fibroblasts (NHSFs). Primary normal human skin fibroblasts were randomly divided into a normal group, a blank group, a model group, and a YYQEW group. The cells of the model group and the YYQEW group were exposed to 150 μmol/L H₂O₂ for 2 h. The morphological changes of the cells were analyzed by microscopy and by kits used to estimate the activities of the senescence-associated β-galactosidase (SA-β-gal), reactive oxygen species (ROS), and superoxide dismutase (SOD). The outcomes revealed that dyeing rate proportion of SA-β-gal was 2.78% ± 0.22% in the normal group, 2.83% ± 0.29% in the blank group, 37.58% ± 2.56% in the model group, and 28.39% ± 0.93% in the YYQEW group. The number of SA-β-gal positive cells was thus significantly higher in the model group than in the normal or blank group. There were also fewer SA-β-gal positive cells in the YYQEW group compared with the model group. The expression of ROS and p16^INK4a in the model group increased significantly compared with that in the normal or blank groups, while the expression of ROS and p16^INK4a in the YYQEW group decreased significantly compared with that in the model group. The expression of SOD and β-catenin in the model group decreased significantly compared with that in the normal or blank group, and the expression of SOD and β-catenin in the YYQEW group increased significantly compared with that in the model group. Overall, it was found that YYQEW was able to delay the senescence of NHSFs induced by H₂O₂ treatment by alleviating oxidative stress and regulating a number of senescence-related molecules, such as β-catenin and p16^INK4a.

Developing scandium and yttrium coordination chemistry to advance theranostic radiopharmaceuticals

The octadentate siderophore analog 3,4,3-LI(1,2-HOPO), denoted 343-HOPO hereafter, is known to have high affinity for both trivalent and tetravalent lanthanide and actinide cations. Here we extend its coordination chemistry to the rare-earth cations Sc³⁺ and Y³⁺ and characterize fundamental metal-chelator binding interactions in solution via UV-Vis spectrophotometry, nuclear magnetic resonance spectroscopy, and spectrofluorimetric metal-competition titrations, as well as in the solid-state via single crystal X-ray diffraction. Sc³⁺ and Y³⁺ binding with 343-HOPO is found to be robust, with both high thermodynamic stability and fast room temperature radiolabeling, indicating that 343-HOPO is likely a promising chelator for in vivo applications with both metals. As a proof of concept, we prepared a ⁸⁶Y-343-HOPO complex for in vivo PET imaging, and the results presented herein highlight the potential of 343-HOPO chelated trivalent metal cations for therapeutic and theranostic applications.

Americium Systemic Biokinetic Model for Rats

In this work, a baseline compartmental model of the distribution and retention of americium in the rat for a systemic intake was derived. The model was derived from data obtained from a study designed to evaluate the behavior of americium in the first 28 days after incorporation. A pharmacokinetic (PK)-front-end modeling approach was used to specify transfer to and from the extracellular fluids (ECF) in the various tissues in terms of vascular flow and volumes of ECF. Back-end rates representing transport into and out of the cells were determined empirically. Uncertainties in transfer rates were investigated using Markov chain Monte Carlo (MCMC). The combination of PK-front-end model and the back-end model structure used allowed for extrapolation to the earliest times with small uncertainty. This approach clearly demonstrated the rapid transfer of material from ECF to liver and bone. This model provides a baseline for modeling the action of decorporation agents, such as DTPA.

AN ACCIDENT OF INTERNAL CONTAMINATION WITH PLUTONIUM AND AMERICIUM AT A NUCLEAR FACILITY IN JAPAN: A PRELIMINARY REPORT AND THE POSSIBILITY OF DTPA ADMINISTRATION ADDING TO THE DIAGNOSIS

This article introduces the first accident of internal contamination with plutonium (Pu) or americium (Am) in Japan for which treatment was carried out. An accident of internal contamination with Pu and Am occurred at a Pu research facility at Oarai-town of Ibaraki prefecture in Japan. A plastic bag containing these radionuclides ruptured when five workers were inspecting a storage container in a hood. As a consequence, these workers were internally contaminated with Pu and Am. Although contamination on the body surface was observed in all five workers, a positive nasal swab was detected in only three of them. A chelating agent, calcium diethylenetriaminepenta-acetate (CaDTPA), was administered to all of them including the two workers without a positive nasal swab. However, bioassay detected a significant amount of Pu and Am in urine after administration of DTPA in these two workers, whereas the levels of these nuclides were below minimum detectable levels in urine before the administration. Since the prevalence of adverse reactions in DTPAs is low, the present results suggest that administration of DTPA can be used for the diagnosis of internal contamination even when a nasal swab is negative or contamination around body orifices is not detected.

Evaluating the potential of chelation therapy to prevent and treat gadolinium deposition from MRI contrast agents

Several MRI contrast agent clinical formulations are now known to leave deposits of the heavy metal gadolinium in the brain, bones, and other organs of patients. This persistent biological accumulation of gadolinium has been recently recognized as a deleterious outcome in patients administered Gd-based contrast agents (GBCAs) for MRI, prompting the European Medicines Agency to recommend discontinuing the use of over half of the GBCAs currently approved for clinical applications. To address this problem, we find that the orally-available metal decorporation agent 3,4,3-LI(1,2-HOPO) demonstrates superior efficacy at chelating and removing Gd from the body compared to diethylenetriaminepentaacetic acid, a ligand commonly used in the United States in the GBCA Gadopentetate (Magnevist). Using the radiotracer ¹⁵³Gd to obtain precise biodistribution data, the results herein, supported by speciation simulations, suggest that the prophylactic or post-hoc therapeutic use of 3,4,3-LI(1,2-HOPO) may provide a means to mitigate Gd retention in patients requiring contrast-enhanced MRI.

Intramolecular sensitization of americium luminescence in solution: shining light on short-lived forbidden 5f transitions

The photophysical properties and solution thermodynamics of water soluble trivalent americium (Am(III)) complexes formed with multidentate chromophore-bearing ligands, 3,4,3-LI(1,2-HOPO), Enterobactin, and 5-LIO(Me-3,2-HOPO), were investigated. The three chelators were shown to act as antenna chromophores for Am(III), generating sensitized luminescence emission from the metal upon complexation, with very short lifetimes ranging from 33 to 42 ns and low luminescence quantum yields (10(-3) to 10(-2)%), characteristic of Near Infra-Red emitters in similar systems. The specific emission peak of Am(III) assigned to the (5)D1 → (7)F1 f-f transition was exploited to characterize the high proton-independent stability of the complex formed with the most efficient sensitizer 3,4,3-LI(1,2-HOPO), with a log β110 = 20.4 ± 0.2 value. In addition, the optical and solution thermodynamic features of these Am(III) complexes, combined with density functional theory calculations, were used to probe the influence of electronic structure on coordination properties across the f-element series and to gain insight into ligand field effects.

Chelation and stabilization of berkelium in oxidation state +IV

Berkelium (Bk) has been predicted to be the only transplutonium element able to exhibit both +III and +IV oxidation states in solution, but evidence of a stable oxidized Bk chelate has so far remained elusive. Here we describe the stabilization of the heaviest 4+ ion of the periodic table, under mild aqueous conditions, using a siderophore derivative. The resulting Bk(IV) complex exhibits luminescence via sensitization through an intramolecular antenna effect. This neutral Bk(IV) coordination compound is not sequestered by the protein siderocalin-a mammalian metal transporter-in contrast to the negatively charged species obtained with neighbouring trivalent actinides americium, curium and californium (Cf). The corresponding Cf(III)-ligand-protein ternary adduct was characterized by X-ray diffraction analysis. Combined with theoretical predictions, these data add significant insight to the field of transplutonium chemistry, and may lead to innovative Bk separation and purification processes.

From early prophylaxis to delayed treatment: Establishing the plutonium decorporation activity window of hydroxypyridinonate chelating agents

The potential consequences of a major radiological event are not only large-scale external radiation exposure of the population, but also uncontrolled dissemination of, and internal contamination with, radionuclides. When planning an emergency response to radiological and nuclear incidents, one must consider the need for not only post-exposure treatment for contaminated individuals, but also prophylactic measures to protect the workforce facing contaminated areas and patients in the aftermath of such events. In addition to meeting the desired criteria for post-exposure treatments such as safety, ease of administration, and broad-spectrum efficacy against multiple radionuclides and levels of challenge, ideal prophylactic countermeasures must include rapid onset; induce minimal to no performance-decrementing side effects; be compatible with current military Chemical, Biological, Radiological, Nuclear, and Explosive countermeasures; and require minimal logistical burdens. Hydroxypyridinone-based actinide decorporation agents have shown the most promise as decorporation strategies for various radionuclides of concern, including the actinides plutonium and americium. The studies presented here probe the extent of plutonium decorporation efficacy for two chelating agents, 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), from early pre-exposure time points to a delay of up to 7 days in parenteral or oral treatment administration, i.e., well beyond the initial hours of emergency response. Despite delayed treatment after a contamination event, both ligands clearly enhanced plutonium elimination through the investigated 7-day post-treatment period. In addition, a remarkable prophylactic efficacy was revealed for 3,4,3-LI(1,2-HOPO) with treatment as early as 48 h before the plutonium challenge. This work provides new perspectives in the indication and use of experimental actinide decorporation treatments.

Chlorogenic Acid Prevents Osteoporosis by Shp2/PI3K/Akt Pathway in Ovariectomized Rats

Cortex Eucommiae is used worldwide in traditional medicine, various constituents of Cortex Eucommiae, such as chlorogenic acid (CGA), has been reported to exert anti-osteoporosis activity in China, but the mechanism about their contribution to the overall activity is limited. The aims of this study were to determine whether chlorogenic acid can prevent estrogen deficiency-induced osteoporosis and to analyze the mechanism of CGA bioactivity. The effect of CGA on estrogen deficiency-induced osteoporosis was performed in vivo. Sixty female Sprague-Dawley rats were divided randomly among a sham-operated group and five ovariectomy (OVX) plus treatment subgroups: saline vehicle, 17α-ethinylestradiol (E2), or CGA at 9, 27, or 45 mg/kg/d. The rats’ femoral metaphyses were evaluated by micro-computed tomography (μCT). The mechanism of CGA bioactivity was investigated in vitro. Bone mesenchymal stem cells (BMSCs) were treated with CGA, with or without phosphoinositide 3-kinase (PI3K) inhibitor LY294002. BMSCs proliferation and osteoblast differentiation were assessed with 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and alkaline phosphatase, with or without Shp2 interfering RNA (RNAi). The results display that CGA at 27 and 45 mg/kg/day inhibited the decrease of bone mineral density (BMD) that induced by OVX in femur (p< 0.01), significantly promoted the levels of bone turnover markers, and prevented bone volume fraction (BV/TV), connectivity density (CoonD), trabecular number (Tb.N), trabecular thickness (Tb.Th) (all p< 0.01) to decrease and prevented the trabecular separation (Tb.Sp), structure model index (SMI)(both p< 0.01) to increase. CGA at 1 or 10 μM enhanced BMSC proliferation in a dose-dependent manner. CGA at 0.1 to 10 μM increased phosphorylated Akt (p-Akt) and cyclin D1. These effects were reversed by LY294002. CGA at 1 or 10 μM increased BMSC differentiation to osteoblasts (p< 0.01), Shp2 RNAi suppressed CGA-induced osteoblast differentiation by decreasing Shp2, p-Akt, and cyclin D1. This study found that CGA improved the BMD and trabecular micro-architecture for the OVX-induced osteoporosis. Therefore, CGA might be an effective alternative treatment for postmenopausal osteoporosis. CGA promoted proliferation of osteoblast precursors and osteoblastic differentiation of BMSCs via the Shp2/PI3K/Akt/cyclin D1 pathway.

Engineered Recognition of Tetravalent Zirconium and Thorium by Chelator-Protein Systems: Toward Flexible Radiotherapy and Imaging Platforms

Targeted α therapy holds tremendous potential as a cancer treatment: it offers the possibility of delivering a highly cytotoxic dose to targeted cells while minimizing damage to surrounding healthy tissue. The metallic α-generating radioisotopes ²²⁵Ac and ²²⁷Th are promising radionuclides for therapeutic use, provided adequate chelation and targeting. Here we demonstrate a new chelating platform composed of a multidentate high-affinity oxygen-donating ligand 3,4,3-LI(CAM) bound to the mammalian protein siderocalin. Respective stability constants log β₁₁₀ = 29.65 ± 0.65, 57.26 ± 0.20, and 47.71 ± 0.08, determined for the Eu^III (a lanthanide surrogate for Ac^III), Zr^IV, and Th^IV complexes of 3,4,3-LI(CAM) through spectrophotometric titrations, reveal this ligand to be one of the most powerful chelators for both trivalent and tetravalent metal ions at physiological pH. The resulting metal-ligand complexes are also recognized with extremely high affinity by the siderophore-binding protein siderocalin, with dissociation constants below 40 nM and tight electrostatic interactions, as evidenced by X-ray structures of the protein:ligand:metal adducts with Zr^IV and Th^IV. Finally, differences in biodistribution profiles between free and siderocalin-bound ²³⁸Pu^IV-3,4,3-LI(CAM) complexes confirm in vivo stability of the protein construct. The siderocalin:3,4,3-LI(CAM) assembly can therefore serve as a "lock" to consolidate binding to the therapeutic ²²⁵Ac and ²²⁷Th isotopes or to the positron emission tomography emitter ⁸⁹Zr, independent of metal valence state.

A Practical Route for the Preparation of 1,4,7-Triazacyclononanyl Diacetates with a Hydroxypyridinonate Pendant Arm

The preparation of triazamacrocyclic hydroxypyridinonate (HOPO-TACN) derivatives as potential chelators for metals in biomedical applications was reported. The synthesis is based on a convergent synthetic approach, in which the key intermediate di-tert-butyl-2,2′-(1,4,7-triazonane-1,4-diyl) diacetate was coupled with a hydroxypyridinonate pendant arm. The method is suitable for rapid syntheses of metal chelator HOPO-TACNs of biomedical interest.

Chelation therapy for treatment of systemic intoxication with uranium: A review

Elevated levels of naturally occurring uranium have been found in small geographic areas throughout the world. Exposure of the general public to uranium is most often by the ingestion of food and water containing natural uranium from the hydrogeological environment, but this likelihood is remote. However, the risk is increased in regions where uranium is mined, milled, processed and/or fabricated as well as in the vicinity of former battlefields where depleted uranium munitions were deployed. Exposure in such cases is by the inhalation route. Internalized uranium is a long-term hazard the toxicity of which depends upon the dose and the dose rate as well as other parameters such as the chemical form and site of deposition of the uranium and the physiology of the host. The radiological toxicity and the chemical toxicity of uranium and its compounds are responsible for kidney damage and lung cancer. The vulnerable groups are the very young and the very old, individuals predisposed to hypertension or osteoporosis and individuals with chronic kidney disease. Those subject to long-term exposure from internalized uranium are a greater risk for the long-term implications. The accumulation of uranium may be mitigated by decreasing its absorption, distribution and deposition and increasing its elimination with chelating agents. The formation of soluble chelates may enhance the mobilization of uranium deposited in tissue and expedite its transport to and elimination from the renal system. The focus of this review is on the use of chelating agents to enhance decorporation of uranium thereby reducing the risk of intoxication.

Novel drug delivery systems for actinides (uranium and plutonium) decontamination agents

The possibility of accidents in the nuclear industry or of nuclear terrorist attacks makes the development of new decontamination strategies crucial. Among radionuclides, actinides such as uranium and plutonium and their different isotopes are considered as the most dangerous contaminants, plutonium displaying mostly a radiological toxicity whereas uranium exhibits mainly a chemical toxicity. Contamination occurs through ingestion, skin or lung exposure with subsequent absorption and distribution of the radionuclides to different tissues where they induce damaging effects. Different chelating agents have been synthesized but their efficacy is limited by their low tissue specificity and high toxicity. For these reasons, several groups have developed smart delivery systems to increase the local concentration of the chelating agent or to improve its biodistribution. The aim of this review is to highlight these strategies.

Hydroxypyridinonate complex stability of group (IV) metals and tetravalent f-block elements: the key to the next generation of chelating agents for radiopharmaceuticals

The solution thermodynamics of the water-soluble complexes formed between 3,4,3-LI(1,2-HOPO) and Zr(IV) or Pu(IV) were investigated to establish the metal coordination properties of this octadentate chelating agent. Stability constants log β110 = 43.1 ± 0.6 and 43.5 ± 0.7 were determined for [Zr(IV)(3,4,3-LI(1,2-HOPO))] and [Pu(IV)(3,4,3-LI(1,2-HOPO))], respectively, by spectrophotometric competition titrations against Ce(IV). Such high thermodynamic stabilities not only confirm the unparalleled Pu(IV) affinity of 3,4,3-LI(1,2-HOPO) as a decorporation agent but also corroborate the great potential of hydroxypyridinonate ligands as new (89)Zr-chelating platforms for immuno-PET applications. These experimental values are in excellent agreement with previous estimates and are discussed with respect to ionic radius and electronic configuration, in comparison with those of Ce(IV) and Th(IV). Furthermore, a liquid chromatography assay combined with mass spectrometric detection was developed to probe the separation of the neutral [M(IV)(3,4,3-LI(1,2-HOPO))] complex species (M = Zr, Ce, Th, and Pu), providing additional insight into the coordination differences between group IV and tetravalent f-block metals and on the role of d and f orbitals in bonding interactions.

In vitro metabolism and stability of the actinide chelating agent 3,4,3-LI(1,2-HOPO)

The hydroxypyridinonate ligand 3,4,3-LI(1,2-HOPO) is currently under development for radionuclide chelation therapy. The preclinical characterization of this highly promising ligand comprised the evaluation of its in vitro properties, including microsomal, plasma, and gastrointestinal fluid stability, cytochrome P450 inhibition, plasma protein binding, and intestinal absorption using the Caco-2 cell line. When mixed with active human liver microsomes, no loss of parent compound was observed after 60 min, indicating compound stability in the presence of liver microsomal P450. At the tested concentrations, 3,4,3-LI(1,2-HOPO) did not significantly influence the activities of any of the cytochromal isoforms screened. Thus, 3,4,3-LI(1,2-HOPO) is unlikely to cause drug-drug interactions by inhibiting the metabolic clearance of coadministered drugs metabolized by these enzymes. Plasma protein-binding assays revealed that the compound is protein-bound in dogs and less extensively in rats and humans. In the plasma stability study, the compound was stable after 1 h at 37°C in mouse, rat, dog, and human plasma samples. Finally, a bidirectional permeability assay demonstrated that 3,4,3-LI(1,2-HOPO) is not permeable across the Caco-2 monolayer, highlighting the need to further evaluate the effects of various compounds with known permeability enhancement properties on the permeability of the ligand in future studies.

Identification of process related trace level impurities in the actinide decorporation agent 3,4,3-LI(1,2-HOPO): Nozzle-skimmer fragmentation via ESI LC-QTOFMS

3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of liquid chromatography coupled with photo-diode array UV detection and electrospray ionization-quadrupole time of flight mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (nozzle-skimmer fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Time of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling.

Characterization, HPLC method development and impurity identification for 3,4,3-LI(1,2-HOPO), a potent actinide chelator for radionuclide decorporation

3,4,3-LI(1,2-HOPO), 1,5,10,14-tetra(1-hydroxy-2-pyridon-6-oyl)-1,5,10,14-tetraazatetradecane), is a potent octadentate chelator of actinides. It is being developed as a decorporation treatment for internal contamination with radionuclides. Conventional HPLC methods exhibited speciation peaks and bridging, likely attributable to the agent's complexation with residual metallic ions in the HPLC system. Derivatization of the target ligand in situ with Fe(III) chloride, however, provided a single homogeneous iron-complex that can readily be detected and analyzed by HPLC. The HPLC method used an Agilent Eclipse XDB-C18 column (150 mm × 4.6mm, 5 μm) at 25°C with UV detection at 280 nm. A gradient elution, with acetonitrile (11% to 100%)/buffer mobile phase, was developed for impurity profiling. The buffer consisted of 0.02% formic acid and 10mM ammonium formate at pH 4.6. An Agilent 1200 LC-6530 Q-TOF/MS system was employed to characterize the [Fe(III)-3,4,3-LI(1,2-HOPO)] derivative and impurities. The proposed HPLC method was validated for specificity, linearity (concentration range 0.13-0.35 mg/mL, r = 0.9999), accuracy (recovery 98.3-103.3%), precision (RSD ≤ 1.6%) and sensitivity (LOD 0.08 μg/mL). The LC/HRMS revealed that the derivative was a complex consisting of one 3,4,3-LI(1,2-HOPO) molecule, one hydroxide ligand, and two iron atoms. Impurities were also identified with LC/HRMS. The validated HPLC method was used in shelf-life evaluation studies which showed that the API remained unchanged for one year at 25°C/60% RH.

(238)Pu elimination profiles after delayed treatment with 3,4,3LI(1,2HOPO) in female and male Swiss-Webster mice

PURPOSE

To characterize the dose-dependent and sex-related efficacy of the hydroxypyridinonate decorporation agent 3,4,3-LI(1,2-HOPO) at enhancing plutonium elimination when post-exposure treatment is delayed.

MATERIALS AND METHODS

Six parenteral dose levels of 3,4,3-LI(1,2-HOPO) from 1-300 μmol/kg were evaluated for decorporating plutonium in female and male Swiss-Webster mice administered a soluble citrate complex of (238)Pu and treated 24 hours later. Necropsies were scheduled at four time-points (2, 4, 8, and 15 days post-contamination) for the female groups and at three time-points (2, 4, and 8 days post-contamination) for the male groups.

RESULTS

Elimination enhancement was dose-dependent in the 1-100 μmol/kg dose range at all necropsy time-points, with some significant reductions in full body and tissue content for both female and male animals. The highest dose level resulted in slight toxicity, with a short recovery period, which delayed excretion of the radionuclide.

CONCLUSIONS

While differences were noted between the female and male cohorts in efficacy range and recovery times, all groups displayed sustained dose-dependent (238)Pu elimination enhancement after delayed parenteral treatment with 3,4,3-LI(1,2-HOPO), the actinide decorporation agent under development.

Highly luminescent and stable hydroxypyridinonate complexes: a step towards new curium decontamination strategies

The photophysical properties, solution thermodynamics, and in vivo complex stabilities of Cm(III) complexes formed with multidentate hydroxypyridinonate ligands, 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), are reported. Both chelators were investigated for their ability to act as antenna chromophores for Cm(III), leading to highly sensitized luminescence emission of the metal upon complexation, with long lifetimes (383 and 196 μs for 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO), respectively) and remarkable quantum yields (45 % and 16 %, respectively) in aqueous solution. The bright emission peaks were used to probe the electronic structure of the 5f complexes and gain insight into ligand field effects; they were also exploited to determine the high (and proton-independent) stabilities of the corresponding Cm(III) complexes (log β110 = 21.8(4) for 3,4,3-LI(1,2-HOPO) and log β120 = 24.5(5) for 5-LIO(Me-3,2-HOPO)). The in vivo complex stability for both ligands was assessed by using (248) Cm as a tracer in a rodent model, which provided a direct comparison with the in vitro thermodynamic results and demonstrated the great potential of 3,4,3-LI(1,2-HOPO) as a therapeutic Cm(III) decontamination agent.

Comparison of plutonium systemic distribution in rats and dogs with published data in humans

PURPOSE

This manuscript compares the behavior of monomeric (239)Pu(4+)-citrate injected intravenously in rats and dogs with a comparison of available humans' data.

MATERIAL AND METHODS

The experimental design for these two studies consisted of eight groups sacrificed at predetermined time-points post exposure. All organs and tissues as well as daily urinary and fecal excretion were analyzed.

RESULTS

Liver and skeleton were the organs with the highest (239)Pu uptake in both species; 76% in dogs and 70% in rats at 24 hours (h) post IV administration. By the end of the study (28 days, d), the activity in skeleton and liver was 85% in dogs and 65% in rats. The urinary excretion function seems to be similar for rats, dogs and humans but the daily fecal to urinary excretion ratio differs between species.

CONCLUSION

A rapid clearance from the liver of rats was observed compared to dogs. Skeleton-to-liver ratios are variable between species. Urinary and fecal excretion patterns for dogs are consistent with human data, indicating that dogs seem to represent better the (239)Pu behavior in humans. The data confirm that the better animal model to evaluate the efficacy of (239)Pu chelating compounds is the canine model.

Radionuclide decorporation: matching the biokinetics of actinides by transdermal delivery of pro-chelators

The threat of nuclear terrorism by the deliberate detonation of a nuclear weapon or radiological dispersion device ("dirty bomb") has made emergency response planning a priority. The only FDA-approved treatments for contamination with isotopes of the transuranic elements Am, Pu, and Cm are the Ca and Zn salts of diethylenetriaminepentaacetic acid (DTPA). These injectable products are not well suited for use in a mass contamination scenario as they require skilled professionals for their administration and are rapidly cleared from the circulation. To overcome the mismatch in the pharmacokinetics of the DTPA and the biokinetics of these transuranic elements, which are slowly released from contamination sites, the penta-ethyl ester of DTPA (C2E5) was prepared and formulated in a nonaqueous gel for transdermal administration. When gels comprised of 40% C2E5, 40-45% Miglyol® 840, and 15-20% ethyl cellulose were spiked with [(14)C]-C2E5 and applied to rat skin; over 60% of the applied dose was absorbed within a 24-h period. Radioactivity was observed in urinary and fecal excretions for over 3 days after removal of the gel. Using an (241)Am wound contamination model, transdermal C2E5 gels were able to enhance total body elimination and reduce the liver and skeletal burden of (241)Am in a dose-dependent manner. The efficacy achieved by a single 1,000 mg/kg dose to contaminated rats was statistically comparable to intravenous Ca-DTPA at 14 mg/kg. The effectiveness of this treatment, favorable sustained release profile of pro-chelators, and ease of administration support its use following radiological emergencies and for its inclusion in the Strategic National Stockpile.