Efficient discrimination of transplutonium actinides by in vivo models.

Transplutonium actinides are among the heaviest elements whose macroscale chemical properties can be experimentally tested. Being scarce and hazardous, their chemistry is rather unexplored, and they have traditionally been considered a rather homogeneous group, with most of their characteristics extrapolated from lanthanide surrogates. Newly emerged applications for these elements, combined with their persistent presence in nuclear waste, however, call for a better understanding of their behavior in complex living systems. In this work, we explored the biodistribution and excretion profiles of four transplutonium actinides (248Cm, 249Bk, 249Cf and 253Es) in a small animal model, and evaluated their in vivo sequestration and decorporation by two therapeutic chelators, diethylenetriamine pentaacetic acid and 3,4,3-LI(1,2-HOPO). Notably, the organ deposition patterns of those transplutonium actinides were element-dependent, particularly in the liver and skeleton, where lower atomic number radionuclides showed up to 7-fold larger liver/skeleton accumulation ratios. Nevertheless, the metal content in multiple organs was significantly decreased for all tested actinides, particularly in the liver, after administering the therapeutic agent 3,4,3-LI(1,2-HOPO) post-contamination. Lastly, the systematic comparison of the radionuclide biodistributions showed discernibly element-dependent organ depositions, which may provide insights into design rules for new bio-inspired chelating systems with high sequestration and separation performance.

Developing the 134Ce and 134La pair as companion positron emission tomography diagnostic isotopes for 225Ac and 227Th radiotherapeutics.

Developing targeted α-therapies has the potential to transform how diseases are treated. In these interventions, targeting vectors are labelled with α-emitting radioisotopes that deliver destructive radiation discretely to diseased cells while simultaneously sparing the surrounding healthy tissue. Widespread implementation requires advances in non-invasive imaging technologies that rapidly assay therapeutics. Towards this end, positron emission tomography (PET) imaging has emerged as one of the most informative diagnostic techniques. Unfortunately, many promising α-emitting isotopes such as 225Ac and 227Th are incompatible with PET imaging. Here we overcame this obstacle by developing large-scale (Ci-scale) production and purification methods for 134Ce. Subsequent radiolabelling and in vivo PET imaging experiments in a small animal model demonstrated that 134Ce (and its 134La daughter) could be used as a PET imaging candidate for 225AcIII (with reduced 134CeIII) or 227ThIV (with oxidized 134CeIV). Evaluating these data alongside X-ray absorption spectroscopy results demonstrated how success relied on rigorously controlling the CeIII/CeIV redox couple.

Evaluating 225Ac and 177Lu Radioimmunoconjugates against Antibody-Drug Conjugates for Small-Cell Lung Cancer.

Interest in the use of 225Ac for targeted alpha therapies has increased dramatically over the past few years, resulting in a multitude of new isotope production and translational research efforts. However, 225Ac radioimmunoconjugate (RIC) research is still in its infancy, with most prior experience in hematologic malignancies and only one reported preclinical solid tumor study using 225Ac RICs. In an effort to compare 225Ac RICs to other current antibody conjugates, a variety of RICs are tested against intractable small-cell lung cancer (SCLC). We directly compare, in vitro and in vivo, two promising candidates of each α or ß- category, 225Ac and 177Lu, versus pyrrolobenzodiazepine (PBD) nonradioactive benchmarks. The monoclonal antibody constructs are targeted to either delta like 3 protein (DLL3), a recently discovered SCLC target, or CD46 as a positive control. An immunocompromised maximum tolerated dose assay is performed on NOD SCID mice, along with tumor efficacy proof-of-concept studies in vivo. We overview the conjugation techniques required to create serum-stable RICs and characterize and compare in vitro cell killing with RICs conjugated to nonspecific antibodies (huIgG1) with either native or site-specific thiol loci against tumor antigen DLL3-expressing and nonexpressing cell lines. Using patient-derived xenografts of SCLC onto NOD SCID mice, solid tumor growth was controlled throughout 3 weeks before growth appeared, in comparison to PBD conjugate controls. NOD SCID mice showed lengthened survival using 225Ac compared to 177Lu RICs, and PBD dimers showed full tumor suppression with nine out of ten mice. The exploration of RICs on a variety of antibody-antigen systems is necessary to direct efforts in cancer research toward promising candidates. However, the anti-DLL3-RIC system with 225Ac and 177Lu appears to be not as effective as the anti-DLL3-PBD counterpart in SCLC therapy with matched antibodies and portrays the challenges in both SCLC therapy as well as the specialized utility of RICs in cancer treatment.

Engineering Mesoporous Silica Nanoparticles for Targeted Alpha Therapy against Breast Cancer.

Targeted alpha therapy, where highly cytotoxic doses are delivered to tumor cells while sparing surrounding healthy tissue, has emerged as a promising treatment against cancer. Radionuclide conjugation with targeting vectors and dose confinement, however, are still limiting factors for the widespread application of this therapy. In the current study, we developed multifunctional silica nanoconstructs for targeted alpha therapy that show targeting capabilities against breast cancer cells, cytotoxic responses at therapeutic dosages, and enhanced clearance. The silica nanoparticles were conjugated to transferrin, which promoted particle accumulation in cancerous cells, and 3,4,3-LI(1,2-HOPO), a chelator with high selectivity and binding affinity for f-block elements. High cytotoxic effects were observed when the nanoparticles were loaded with 225Ac, a clinically relevant radioisotope. Lastly, in vivo studies in mice showed that the administration of radionuclides with nanoparticles enhanced their excretion and minimized their deposition in bones. These results highlight the potential of multifunctional silica nanoparticles as delivery systems for targeted alpha therapy and offer insight into design rules for the development of new nanotherapeutic agents.

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.

Boron Difluoride Curcuminoid Fluorophores with Enhanced Two-Photon Excited Fluorescence Emission and Versatile Living-Cell Imaging Properties.

The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time-dependent (TD)-DFT calculations confirm the charge-transfer character of the second lowest-energy transition band and ascribe the lowest energy band to a "cyanine-like" transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV-visible absorption and fluorescence spectra. Two-photon-excited fluorescence and Z-scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two-photon cross section, reaching 5000 GM, with predominant two-photon absorption from the S0-S2 charge-transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two-photon active band for the curcuminoid derivatives has the same intramolecular charge-transfer character and therefore arises from a dipolar structure. Overall, this structure-relationship study allows the optimization of the two-photon brightness (i.e., 400-900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission.

Siderocalin-mediated recognition, sensitization, and cellular uptake of actinides.

Synthetic radionuclides, such as the transuranic actinides plutonium, americium, and curium, present severe health threats as contaminants, and understanding the scope of the biochemical interactions involved in actinide transport is instrumental in managing human contamination. Here we show that siderocalin, a mammalian siderophore-binding protein from the lipocalin family, specifically binds lanthanide and actinide complexes through molecular recognition of the ligands chelating the metal ions. Using crystallography, we structurally characterized the resulting siderocalin-transuranic actinide complexes, providing unprecedented insights into the biological coordination of heavy radioelements. In controlled in vitro assays, we found that intracellular plutonium uptake can occur through siderocalin-mediated endocytosis. We also demonstrated that siderocalin can act as a synergistic antenna to sensitize the luminescence of trivalent lanthanide and actinide ions in ternary protein-ligand complexes, dramatically increasing the brightness and efficiency of intramolecular energy transfer processes that give rise to metal luminescence. Our results identify siderocalin as a potential player in the biological trafficking of f elements, but through a secondary ligand-based metal sequestration mechanism. Beyond elucidating contamination pathways, this work is a starting point for the design of two-stage biomimetic platforms for photoluminescence, separation, and transport applications.

(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.

Gene conversion is strongly induced in human cells by double-strand breaks and is modulated by the expression of BCL-x(L).

Homology-directed repair (HDR) of DNA double-strand breaks (DSBs) contributes to the maintenance of genomic stability in rodent cells, and it has been assumed that HDR is of similar importance in DSB repair in human cells. However, some outcomes of homologous recombination can be deleterious, suggesting that factors exist to regulate HDR. We demonstrated previously that overexpression of BCL-2 or BCL-x(L) enhanced the frequency of X-ray-induced TK1 mutations, including loss of heterozygosity events presumed to arise by mitotic recombination. The present study was designed to test whether HDR is a prominent DSB repair pathway in human cells and to determine whether ectopic expression of BCL-x(L) affects HDR. Using TK6-neo cells, we find that a single DSB in an integrated HDR reporter stimulates gene conversion 40-50-fold, demonstrating efficient DSB repair by gene conversion in human cells. Significantly, DSB-induced gene conversion events are 3-4-fold more frequent in TK6 cells that stably overexpress the antiapoptotic protein BCL-X(L). Thus, HDR plays an important role in maintaining genomic integrity in human cells, and ectopic expression of BCL-x(L) enhances HDR of DSBs. This is the first study to highlight a function for BCL-x(L) in modulating DSB repair in human cells.