Characterization of the secondary neutron field inside a cyclotron for production of radiopharmaceuticals.

During production of radiopharmaceuticals, the radiation situation in cyclotron pit is an important parameter, which is being monitored to ensure fulfilment of the limits and conditions of safe operation. The neutron flux in the structural components of the accelerator is also an important parameter, because the secondary neutrons are responsible for activation of cyclotron structural components and may even affect structural changes in it. This paper aims to characterize the neutron field in inner positions of medical accelerator IBA 18/9 by activation detectors and by means of scintillation spectrometry. The backward angle measurement was realized also in special liquid water target (H218O) at U120M cyclotron to confirm the data obtained in IBA 18/9 cyclotron.

Radiolabelled Cyclic Bisarylmercury: High Chemical and in†vivo Stability for Theranostics.

We show the synthesis of an in vivo stable mercury compound with functionality suitable for radiopharmaceuticals. The designed cyclic bisarylmercury was based on the water tolerance of organomercurials, higher bond dissociation energy of Hg-Ph to Hg-S, and the experimental evidence that acyclic structures suffer significant cleavage of one of the Hg-R bonds. The bispidine motif was chosen for its in vivo stability, chemical accessibility, and functionalization properties. Radionuclide production results in 197(m) HgCl2 (aq), so the desired mercury compound was formed via a water-tolerant organotin transmetallation. The Hg-bispidine compound showed high chemical stability in tests with an excess of sulfur-containing competitors and high in vivo stability, without any observable protein interaction by human serum assay, and good organ clearance demonstrated by biodistribution and SPECT studies in rats. In particular, no retention in the kidneys was observed, typical of unstable mercury compounds. The nat Hg analogue allowed full characterization by NMR and HRMS.

Simple new method for labelling of PSMA-11 with 68Ga in NaHCO3.

BACKGROUND: Prostate specific membrane antigen (PSMA) is a type II membrane protein widely expressed on the surface of prostate cancer cells. One of its functions is to act as a receptor mediating the ligand internalization. This PSMA property is employed in the diagnostics and therapy of prostate cancer. Over the years, small molecules with high affinity for PSMA have been developed and labelled with positron emitters (e.g. 68Ga, 18F, 11C, 64Cu, or 86Y). One of these radiolabelled ligands, [68Ga] PSMA-11, is one of the most widespread tracers for PET imaging of the prostate cancer. Many techniques have been proposed and tested for the 68Ga labelling of PSMA-11. The aim of our work was to design a labelling method of PSMA-11 that minimizes number of the used chemicals and steps, providing quantitative labelling yield at laboratory temperature and may be easily automated. METHODOLOGY: A68Ge/68Ga generator eluate in 0.1 M HCl was loaded on an activated Oasis MCX cartridge, and the cartridge was then thoroughly washed with water. The radionuclide 68Ga was eluted from the cartridge with 0.1 M NaHCO3 (pH = 8.5, n = 36) or with the same solution with pH adjusted to 7.2-9.0 (n = 38). Precursor PSMA-11 was mixed directly with the cartridge eluate of 68Ga in 0.1 M NaHCO3 of given pH. For the stability test, samples of 68GaPSMA-11 in 0.1 M NaHCO3 (pH 8.5) were mixed in ratio 1 : 1 with the following solutions: 0.1 M NaHCO3 (pH 8.5), human serum, PBS and 0.9% NaCl. In order to estimate an effect of the time elapsed between 68Ga elution from the cartridge in 0.1 M NaHCO3 (pH 8.5) and the labelling onset of PSMA-11, the latter was initiated 0, 5, 10 and 20 min post elution and radiochemical yield was monitored. All the PSMA-11 labelled samples were subjected to radiochemical purity test using HPLC. The whole process starting from generator elution up to HPLC analysis commencement took 10-15 min. RESULTS: Recovery of 68Ga from cartridge Oasis MCX using 0.1 M NaHCO3 at pH 8.5 was 71.5 ± 1.4%. Thirty six PSMA-11 samples (10 µg in reaction mixture) were labelled at pH 8.5 with total average radiochemical yield of 98 ± 2%. Recovery of 68Ga from cartridge Oasis MCX using 0.1 M NaHCO3 at variable pH of 7.2-9.0 was 62.5 ± 1.8% showing certain decrease with decreasing pH. A total of 138 samples of PSMA-11 were labelled with 68 Ga at variable pH (7.2-9.0) and four different amounts of PSMA-11 (1, 2.5, 5 and 10 µg) resulting in the labelling yields of 54.0 ± 5.3%, 88.2 ± 3.2%, 99.4 ± 0.3% and 99.9 ± 0.1%, respectively. Irrespective of the pH, the radiolabelling yield was quantitative for the molar ratio PSMA-11: 68Ga > 5000 : 1 in the reaction mixture. Stability tests in 0.1 M NaHCO3 (pH 8.5), human serum, PBS and 0.9% NaCl revealed no observable release of 68Ga from the 68Ga-PSMA-11 complex within 3 h. Similarly, the delay between the 68Ga elution from the Oasis MCX cartridge in 0.1 M NaHCO3 (pH 8.5) and start of the labelling of PSMA-11 labelling has no effect on the radiochemical yield. CONCLUSION: A new method of labelling PSMA-11 ligand with 68Ga in 0.1 M NaHCO3 using Oasis MCX cartridges was proposed, developed and tested. The results demonstrated that it is rapid, simple, reproducible and easy to automate.

Excitation functions of the 165Ho(3He,xn)166,165,163Tm and natTi(3He,x)48V,48Cr reactions.

The cross-sections of the natTi(3He,x)48V,48Cr and the 165Ho(3He,xn)166,165,163Tm reactions were measured from the threshold to 47 MeV using well-established method of stacked-foil activation and off-line γ-ray spectrometry. The 3He-ion induced nuclear reaction cross-sections on 165Ho were measured for the first time. Their comparison with the prediction adopted from the TENDL-2017 library revealed significant difference. Thick target yields deduced from the experimental data are provided.

Radiolabeling of the antibody IgG M75 for epitope of human carbonic anhydrase IX by 61Cu and 64Cu and its biological testing.

Human carbonic anhydrase IX is a membrane enzyme that is significantly expressed in some types of cancer cells, while copper radioisotopes offer wide range of diagnostic, therapeutic and theranostic properties. The work was focused on a new approach to the labelling of antibody IgG M75 for epitope human carbonic anhydrase IX with copper radioisotopes 61Cu and 64Cu and its in vivo testing in mice with inoculated colorectal cancer. Monoclonal antibody IgG M75 for epitope human carbonic anhydrase IX was successfully conjugated with copper-specific chelator "phosphinate" and labelled with 61Cu and 64Cu The obtained molecule has considerable potential as a radioimmuno pharmaceutical suitable for imaging of tumours expressing carbonic anhydrase IX by positron emission tomography (PET).

Evaluation of Brain Nuclear Medicine Imaging Tracers in a Murine Model of Sepsis-Associated Encephalopathy.

PURPOSE: The purpose of this study was to evaluate a set of widely used nuclear medicine imaging agents as possible methods to study the early effects of systemic inflammation on the living brain in a mouse model of sepsis-associated encephalopathy (SAE). The lipopolysaccharide (LPS)-induced murine systemic inflammation model was selected as a model of SAE. PROCEDURES: C57BL/6 mice were used. A multimodal imaging protocol was carried out on each animal 4 h following the intravenous administration of LPS using the following tracers: [99mTc][2,2-dimethyl-3-[(3E)-3-oxidoiminobutan-2-yl]azanidylpropyl]-[(3E)-3-hydroxyiminobutan-2-yl]azanide ([99mTc]HMPAO) and ethyl-7-[125I]iodo-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate ([125I]iomazenil) to measure brain perfusion and neuronal damage, respectively; 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) to measure cerebral glucose uptake. We assessed microglia activity on another group of mice using 2-[6-chloro-2-(4-[125I]iodophenyl)-imidazo[1,2-a]pyridin-3-yl]-N-ethyl-N-methyl-acetamide ([125I]CLINME). Radiotracer uptakes were measured in different brain regions and correlated. Microglia activity was also assessed using immunohistochemistry. Brain glutathione levels were measured to investigate oxidative stress. RESULTS: Significantly reduced perfusion values and significantly enhanced [18F]FDG and [125I]CLINME uptake was measured in the LPS-treated group. Following perfusion compensation, enhanced [125I]iomazenil uptake was measured in the LPS-treated group's hippocampus and cerebellum. In this group, both [18F]FDG and [125I]iomazenil uptake showed highly negative correlation to perfusion measured with ([99mTc]HMPAO uptake in all brain regions. No significant differences were detected in brain glutathione levels between the groups. The CD45 and P2Y12 double-labeling immunohistochemistry showed widespread microglia activation in the LPS-treated group. CONCLUSIONS: Our results suggest that [125I]CLINME and [99mTc]HMPAO SPECT can be used to detect microglia activation and brain hypoperfusion, respectively, in the early phase (4 h post injection) of systemic inflammation. We suspect that the enhancement of [18F]FDG and [125I]iomazenil uptake in the LPS-treated group does not necessarily reflect neural hypermetabolism and the lack of neuronal damage. They are most likely caused by processes emerging during neuroinflammation, e.g., microglia activation and/or immune cell infiltration.

In vitro evaluation of the monoclonal antibody 64Cu-IgG M75 against human carbonic anhydrase IX and its in vivo imaging.

Specific oncology diagnostics requires new types of the selective radiopharmaceuticals, particularly those suitable for the molecular PET imaging. The aim of this work is to present a new, specific PET-immunodiagnostic radiopharmaceutical based on the monoclonal antibody IgG M75 targeting human carbonic anhydrase IX labelled with 64Cu (T½ = 12.70h) and its in vitro and in vivo evaluation. The antibody IgG M75 was conjugated with a non-commercial copper-specific chelator "phosphinate" and then labelled with the positron emitter 64Cu. Stability of the labelled conjugated was tested in human serum. The immunoreactivity of the labelled conjugate was evaluated in vitro on a suitable cell cultures of the colorectal carcinoma (HT-29) and its imaging properties were estimated in vivo on a mouse model with inoculated colorectal carcinoma HT-29 imaged on a µPET/CT. The tested radioimmunoconjugate was obtained in a specific activity of 0.25-0.5 MBq/µg. In vitro uptake experiments revealed specific binding to the HT-29 cells (45 ± 2.8% of the total added activity) and the measured KD value was found to be 9.2nM. Imaging clearly demonstrated significant uptake of the labelled monoclonal antibody in the tumour at 18h post administration. The radioimmunoconjugate 64Cu-PS-IgG M75 seems to be a suitable candidate for PET diagnostics of hypoxic tumours expressing human carbonic anhydrase IX.

Imaging of protein synthesis: in vitro and in vivo evaluation of (44)Sc-DOTA-puromycin.

PURPOSE: The purpose of this study was to investigate whether (44)Sc-labeled puromycin can be utilized for imaging of protein synthesis in vivo. METHODS: For micro-positron emission tomographic (µPET) studies, 20-25 MBq of [(44)Sc]-DOTA-puromycin was administered to tumor-bearing rats, and animals were scanned for 1 h dynamically. Results were further validated by dissecting organs and tissues of the animals after the measurement and in vitro blocking experiments using puromycin or cycloheximide to block protein synthesis. RESULTS: µPET images of tumor-bearing rats showed significant tumor uptake of [(44)Sc]-DOTA-puromycin and a clear-cut tumor visualization. In both blocking experiments, cellular uptake of [(44)Sc]-DOTA-puromycin ([(44)Sc]-DOTA-Pur) could be suppressed by blocking protein synthesis. CONCLUSIONS: We report for the first time successful µPET imaging with (44)Sc obtained from a (44)Ti/(44)Sc generator, as well as noninvasive µPET imaging of ribosomal activity, respectively protein synthesis, with a puromycin-based radiopharmaceutical and the direct correlation between cellular uptake of [(44)Sc]-DOTA-Pur and protein synthesis.

Measurement of protein synthesis: in vitro comparison of (68)Ga-DOTA-puromycin, [ (3)H]tyrosine, and 2-fluoro-[ (3)H]tyrosine.

AIM: Puromycin has played an important role in our understanding of the eukaryotic ribosome and protein synthesis. It has been known for more than 40 years that this antibiotic is a universal protein synthesis inhibitor that acts as a structural analog of an aminoacyl-transfer RNA (aa-tRNA) in eukaryotic ribosomes. Due to the role of enzymes and their synthesis in situations of need (DNA damage, e.g., after chemo- or radiation therapy), determination of protein synthesis is important for control of antitumor therapy, to enhance long-term survival of tumor patients, and to minimize side-effects of therapy. Multiple attempts to reach this goal have been made through the last decades, mostly using radiolabeled amino acids, with limited or unsatisfactory success. The aim of this study is to estimate the possibility of determining protein synthesis ratios by using (68)Ga-DOTA-puromycin ((68)Ga-DOTA-Pur), [(3)H]tyrosine, and 2-fluoro-[(3)H]tyrosine and to estimate the possibility of different pathways due to the fluorination of tyrosine. METHODS: DOTA-puromycin was synthesized using a puromycin-tethered controlled-pore glass (CPG) support by the usual protocol for automated DNA and RNA synthesis following our design. (68)Ga was obtained from a (68)Ge/(68)Ga generator as described previously by Zhernosekov et al. (J Nucl Med 48:1741-1748, 2007). The purified eluate was used for labeling of DOTA-puromycin at 95°C for 20 min. [(3)H]Tyrosine and 2-fluoro-[(3)H]tyrosine of the highest purity available were purchased from Moravek (Bera, USA) or Amersham Biosciences (Hammersmith, UK). In vitro uptake and protein incorporation as well as in vitro inhibition experiments using cycloheximide to inhibit protein synthesis were carried out for all three substances in DU145 prostate carcinoma cells (ATCC, USA). (68)Ga-DOTA-Pur was additionally used for µPET imaging of Walker carcinomas and AT1 tumors in rats. Dynamic scans were performed for 45 min after IV application (tail vein) of 20-25 MBq (68)Ga-DOTA-Pur. RESULTS: No significant differences in the behavior of [(3)H]tyrosine and 2-fluoro-[(3)H]tyrosine were observed. Uptake of both tyrosine derivatives was decreased by inhibition of protein synthesis, but only to a level of 45-55% of initial uptake, indicating no direct link between tyrosine uptake and protein synthesis. In contrast, (68)Ga-DOTA-Pur uptake was directly linked to ribosomal activity and, therefore, to protein synthesis. (68)Ga-DOTA-Pur µPET imaging in rats revealed high tumor-to-background ratios and clearly defined regions of interest in the investigated tumors. SUMMARY: Whereas the metabolic pathway of (68)Ga-DOTA-Pur is directly connected with the process of protein synthesis and shows high tumor uptake during µPET imaging, neither [(3)H]tyrosine nor 2-fluoro-[(3)H]tyrosine can be considered useful for determination of protein synthesis.

Assessment of radionuclidic impurities in cyclotron produced (99m)Tc.

INTRODUCTION: The commercial viability of cyclotron-produced (99m)Tc as an alternative to generator-produced (99m)Tc depends on several factors. These include: production yield, ease of target processing and recycling of (100)Mo, radiochemical purity, specific activity as well as the presence of other radionuclides, particularly various Tc radioisotopes that cannot be separated chemically and will remain in the final clinical preparation. These Tc radionuclidic impurities are derived from nuclear interactions of the accelerated protons with other stable Mo isotopes present in the enriched (100)Mo target. The aim of our study was to determine experimentally the yields of Tc radioisotopes produced from these stable Mo isotopes as a function of incident beam energy in order to predict radionuclidic purity of (99m)Tc produced in highly enriched (100)Mo targets of known isotopic composition. METHODS: Enriched molybdenum targets of (95)Mo, (96)Mo, (97)Mo, (98)Mo and (100)Mo were prepared by pressing powdered metal into an aluminum target support. The thick targets were bombarded with 10 to 24MeV protons using the external beam line of the U-120M cyclotron of the Nuclear Physics Institute, Rez. The thick target yields of (94)Tc, (94m)Tc, (95)Tc, (95m)Tc, (96m+g)Tc and (97m)Tc were derived from their activities measured by γ spectrometry using a high purity Ge detector. These data were then used to assess the effect of isotopic composition of highly enriched (100)Mo targets on the radionuclidic purity of (99m)Tc as a function of proton beam energy. Estimates were validated by comparison to measured activities of Tc radioisotopes in proton irradiated, highly enriched (100)Mo targets of known isotopic composition. RESULTS: The measured thick target yields of (94)Tc, (94m)Tc, (95)Tc, (95m)Tc, (96m+g)Tc and (97m)Tc correspond well with recently published values calculated via the EMPIRE-3 code. However, the measured yields are more favourable with regard to achievable radionuclidic purity of (99m)Tc. Reliability of the measured thick target yields was demonstrated by comparison of the estimated and measured activities of (94)Tc, (95)Tc, (95m)Tc, and (96m+g)Tc in highly enriched (100)Mo (99%) targets that showed good agreement, with maximum differences within estimated uncertainties. Radioisotopes (94m)Tc and (97m)Tc were not detected in the irradiated (100)Mo targets due to their low activities and measurement conditions; on the other hand we detected small amounts of the short-lived positron emitter (93)Tc (T(½)=2.75h). In addition to (99m)Tc and trace amounts of the various Tc isotopes, significant activities of (96)Nb, (97)Nb and (99)Mo were detected in the irradiated (100)Mo targets. CONCLUSIONS: Radioisotope formation during the proton irradiation of Mo targets prepared from different, enriched stable Mo isotopes provides a useful data base to predict the presence of Tc radionuclidic impurities in (99m)Tc derived from proton irradiated (100)Mo targets of known isotopic composition. The longer-lived Tc isotopes including (94)Tc (T(½)=4.883h), (95)Tc (T(½)=20.0h), (95m)Tc (T(½)=61 d), (96m+g)Tc (T(½)=4.24 d) and (97m)Tc (T(½)=90 d) are of particular concern since they may affect the dosimetry in clinical applications. Our data demonstrate that cyclotron production of (99m)Tc, using highly enriched (100)Mo targets and 19-24MeV incident proton energy, will result in a product of acceptable radionuclidic purity for applications in nuclear medicine.

Preparation and preclinical evaluation of 177Lu-nimotuzumab targeting epidermal growth factor receptor overexpressing tumors.

OBJECTIVES: Nimotuzumab (h-R3) is a humanized monoclonal antibody (mAb) which recognizes the external domain of the epidermal growth factor receptor (EGFR) with high specificity. It was demonstrated that h-R3 has a unique clinical profile for immunotherapy of adult gliomas and pediatric pontine gliomas. The aim of this work was to evaluate the conjugate (177)Lu-h-R3 as a potential radioimmunoconjugate for radioimmunotherapy (RIT) of tumors overexpressing EGFR. METHODS: h-R3 was modified with the macrocylcic ligand S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (p-SCN-Bn-DOTA) and the acyclic ligand S-2-(4-Isothiocyanatobenzyl)-diethylenetriamine pentaacetic acid (p-SCN-Bn-DTPA); the immunoconjugates were labeled with no-carried added (177)Lu. Specificity and affinity were tested using radioimmunoassays in a cell line overexpressing EGFR. Biodistribution in mice, healthy or bearing A431 epithelial carcinoma xenografts, was performed for 11 days. Tumor uptake, the influence of the nature of the chelate and the way of administration were studied. Absorbed dose in tumor and selected organs was calculated using the OLINDA/EXM software; the data from the animals was extrapolated to humans. RESULTS: (177)Lu-h-R3 conjugates were obtained with specific activity up to 915 MBq/mg without significant loss of immunoreactivity. The binding of (177)Lu-h-R3 conjugates to A431 cells showed to be EGFR specific, and the affinity was similar to native h-R3. Tumor uptake reached a maximum value of 22.4±3.1 %ID/g at 72 h and remained ~20% ID/g over 1 week. Locoregional application showed better tumor/nontumor ratios than intravenous application. CONCLUSIONS: (177)Lu-h-R3 should be considered for further evaluations as a potential radiopharmaceutical for RIT of tumors overexpressing EGFR.

Thermoresponsive polymeric radionuclide delivery system--an injectable brachytherapy.

Brachytherapy is of increasing popularity in clinical oncology for the local therapy of solid tumors due to high radiation doses delivered to malignant tissue while keeping the whole-body radiation burden low. Pronounced dose-dependent tumor growth reduction was achieved by single dose of injectable intratumoral brachytherapy with iodine-131-labeled thermoresponsive polymer [poly(N-isopropyl acrylamide)] in murine xenograft model (PC3 human prostate adenocarcinoma). The two doses of radionuclide were used, 2 MBq/mouse and 25 MBq/mouse. The higher dose caused gradual tumor volume reduction and 2 of 6 mice from this group were cured. The lower dose caused tumor growth retardation only. In both cases there were no signs of inflammation. The effects of both doses were statistically significant compared to untreated controls. Such injectable system should keep advantages of brachytherapy while making system administration easier and less invasive (injection instead of implantation), patient-tailored (splitting of doses into several depoes) and bioerodable.

New measurement of excitation functions for (d,x) reactions on (nat)Mo with special regard to the formation of (95m)Tc, (96m+g)Tc, (99m)Tc and (99)Mo.

Cross-sections for the deuteron-induced reactions on natural molybdenum leading to (93m)Tc, (93m+g)Tc, (94)Tc, (94m)Tc, (95)Tc, (95m)Tc, (96m+g)Tc, (99m)Tc, (99)Mo, (101)Mo, (90m+g)Nb, (92m)Nb, (95)Nb and (89m+g)Zr were measured in the energy range 3.0-19.6 MeV on the cyclotron U-120 M in the Institute of Nuclear Physics AS CR. Special attention was paid to excitation functions and thick target yields for the formation of (95m)Tc, a suitable tracer for (99)Tc, of (96m+g)Tc, which might be used as a beam monitor, and of (99m)Tc and (99)Mo, the most widespread radionuclide generator pair in nuclear medicine. If appropriate, obtained data are compared with the heretofore published cross-sections.

New measurement of excitation functions for (p,x) reactions on (nat)Mo with special regard to the formation of (95m)Tc, (96m+g)Tc, (99m)Tc and (99)Mo.

Cross-sections for the proton induced reactions on natural molybdenum leading to (93m)Tc, (93m+g)Tc, (94)Tc, (94m)Tc, (95)Tc, (95m)Tc, (96m+g)Tc, (99m)Tc, (90)Mo, (93m)Mo, (99)Mo, (90m+g)Nb, (92m)Nb, (95)Nb and (89m+g)Zr were measured in the proton energy range 8.4-37.1MeV on the cyclotron U-120M at the Institute of Nuclear Physics AS CR. Special attention was paid to excitation functions and thick target yields for the formation of (95m)Tc, a suitable tracer for (99)Tc, of (96m+g)Tc, which was proposed as a proton beam monitor, and of (99m)Tc and (99)Mo, the most widespread radionuclide generator pair in nuclear medicine. If appropriate, obtained data are compared with the heretofore published cross-sections.

Biodistribution of a radiolabelled thermoresponsive polymer in mice.

Drug delivery systems based on thermoresponsive polymers might serve as suitable carriers for local radiotherapy. We have, therefore, designed and synthesized a radioiodine-labellable thermoresponsive polymer. The polymer was synthesized by copolymerization of N-isopropylacrylamide with N-methacryloyl tyrosinamide in tetrahydrofuran, and then labelled by (131)I. The solution of this labelled polymer in dimethylsulfoxide (4.4 MBq/ml; 1.8 wt% polymer) was applied to femoral muscle of male Balb/C mice (50 microl per animal). The biodistribution and excretion of radioactivity was followed in 2h and 1, 7, 14, 28 and 42 d post injection (n=6 per time point). As expected, the labelled polymer was left on the application site (ca 90% 2h post injection), decreasing slowly to ca 80% within 14 d. At 28 d post injection, ca 70% of the injected activity was still found on the application site, decreasing to ca 60% at 42 d. No organ-specific accumulation of the radioactivity released from the application site, including thyroid, was observed. Majority of the released radioactivity was excreted via urine and faeces. This preliminary study suggests that thermoresponsive polymers could be used as an effective delivery system for localized radiotherapy.

Production of 230U/226Th for targeted alpha therapy via proton irradiation of 231Pa.

(230)U and its daughter nuclide (226)Th are novel therapeutic nuclides for application in targeted alpha-therapy of cancer. We have investigated the feasibility of producing (230)U/(226)Th via proton irradiation of (231)Pa according to the reaction (231)Pa(p,2n)(230)U. The experimental excitation function for this reaction is reported for the first time. Cross sections were measured using thin targets of (231)Pa prepared by electrodeposition and (230)U yields were analyzed using alpha-spectrometry. Beam parameters (energy and intensity) were determined both by calculation using a mathematical model based on measured beam orbits and beam current integrator and by parallel monitor reactions on copper foils using high-resolution gamma-spectrometry and IAEA recommended cross-section data. The measured cross sections are in good agreement with model calculations using the EMPIRE-II code and are sufficiently high for the production of (230)U/(226)Th in clinically relevant amounts. A highly effective separation process was developed to isolate clinical grade (230)U from irradiated protactinium oxide targets. Product purity was assessed using alpha- and gamma-spectrometry as well as ICPMS.

New bioerodable thermoresponsive polymers for possible radiotherapeutic applications.

A new thermoresponsive system designed for local radiotherapy has been developed. In this system a radionuclide complex is entrapped in a thermoresponsive polymer locally precipitated at body temperature after injection of a polymer-complex solution into the tissue where a therapeutic effect is required. The lifetime of the system is controlled by the rate of polymer hydrolysis, its dissolution and elimination from the body. The thermoresponsive polymer with the cloud temperature (CT) below body temperature is based on copolymers of N-isopropylmethacrylamide with a methacrylamide-type comonomer containing hydrophobic n-alkyls of three different sizes (C(3), C(6) and C(12)) bonded by a hydrolytically labile hydrazone bond. Hydrolysis of hydrazone bond results in a copolymer soluble at body temperature. The copolymer containing 27.5 mole% of the comonomer with the C(6) moiety, which was chosen for further study, has the CT 22 degrees C and its phase separation is complete at 34 degrees C. Polymer dissolution is complete within 48 h at both pH 5.0 or 7.4. The model therapeutic radionuclide, (64)Cu, in the form of its hydrophobic chelate bis(quinolin-8-olato-N,O) [(64)Cu]copper, is efficiently kept hydrophobically entrapped in the phase-separated polymer until the dissolution by hydrolytic degradation is completed.

Astatination of nanoparticles containing silver as possible carriers of 211At.

The alpha emitter 211At is a prospective radionuclide for the therapy of smaller tumours and metastases. However, the chemical properties of 211At together with the fact that it is available only in trace amounts, makes the labelling of prospective astatine carriers rather complicated. In this context we have studied a new class of possible astatine carriers--nanoparticle systems, which tend to concentrate themselves in some types of tumours by means of the EPR effect. Additionally, such nanoparticles have the advantage that they may be chemically modified by the attachment of a tumour-seeking agent, and also directly applied to the target site. In order to reach high labelling yields, and in order to protect the nanoparticles from rapid degradation by the immune system, silver-containing particles covalently coated by poly(ethylene oxide) were developed and tested. The effect of the different reducing and oxidizing agents on the labelling yield was also determined. It was found that labelling yields were almost quantitative and well reproducible under reducing conditions, while under oxidizing conditions they dropped to ca. 50%. In the absence of any reducing or oxidizing agent, the labelling yields were randomly distributed between a range of 50% and 97%. The labelled nanoparticles were stable even in a large surplus of competing chloride ions.

Targeting against epidermal growth factor receptors. Cellular processing of astatinated EGF after binding to cultured carcinoma cells.

BACKGROUND: The alpha-emitting nuclide 211At is of great interest for radionuclide therapy when coupled to a tumor-targeting biomolecule, e.g. epidermal growth factor (EGF) the receptors of which are overexpressed in many malignancies. However, almost no information concerning the cellular processing of astatinated targeting agents is available. MATERIALS AND METHODS: We indirectly astatinated EGF ([211At]-benzoate-EGF) and studied its cellular processing in A-431 carcinoma cells in comparison with data concerning [125I]-benzoate-EGF. RESULTS: The biological half-life of astatine (3.5 h) was longer than the half-life of the iodine label (1.5 h). The increase of the half-life was due to longer retention of the internalised astatine radioactivity. The maximum accumulation for the astatine label occurred later (4-6h) than that for the iodine label (2-4h), indicating a slower excretion of astatine that was confirmed in experiment with 211At/1251-benzoate-EGF. CONCLUSION: The long retention of astatine might be advantageous for radionuclide therapy.

Comparative biodistribution of the radiohalogenated (Br, I and At) antibody A33. Implications for in vivo dosimetry.

The alpha-emitter astatine-211 (T(1/2) = 7.2 h) has great potential for use in targeted radionuclide therapy. Its potent alpha-radiation makes (211)At unsuitable for dose planning. Its x-rays can be used for gamma-camera monitoring of the radioactivity distribution during therapy but not for accurate estimation of absorbed dose in critical organs. This study was intended to establish whether the absorbed dose delivered by astatinated antibody could be accurately determined by analogue labeling with radiohalogens, better suited for quantitative measurements in vivo. PET facilitates quantitative pharmacokinetics; possible halogen labels are, e.g., (76)Br (T(1/2) = 16.2 h) and (124)I (T(1/2) = 4.18 d). Antibody A33 was labeled with (76)Br, (125)I and (211)At using N-succinimidyl-p-halobenzoates. The conjugates were co-injected into Sprague-Dawley rats. Radioactivity concentrations in different organs and tissues were measured at three time points. Pharmacokinetic data were used to calculate absorbed doses. (125)I and (76)Br reflected the biokinetics of astatine reasonably well. The absorbed doses in bladder, kidney, pancreas, liver, bone and brain were determined with 10% accuracy. The absorbed doses in stomach, spleen and thyroid were underestimated by a factor 2-3. Positron-emitting analogues can be used to predict the astatine-derived dose in critical organs. Correction factors should be used for stomach, spleen and thyroid.