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GEANT4 is a Monte Carlo code originally implemented for high-energy physics applications and is well known for particle transport at high energies. The capacity of GEANT4 to simulate neutron transport in the thermal energy region is not equally well known. The aim of this article is to compare MCNP, a code commonly used in low energy neutron transport calculations and GEANT4 with experimental results and select the suitable code for gadolinium neutron capture applications. To account for the thermal neutron scattering from chemically bound atoms [S(alpha,beta)] in biological materials a comparison of thermal neutron fluence in tissue-like poly(methylmethacrylate) phantom is made with MCNP4B, GEANT4 6.0 patch1, and measurements from the neutron capture therapy (NCT) facility at the Studsvik, Sweden. The fluence measurements agreed with MCNP calculated results considering S(alpha,beta). The location of the thermal neutron peak calculated with MCNP without S(alpha,beta) and GEANT4 is shifted by about 0.5 cm towards a shallower depth and is 25%-30% lower in amplitude. Dose distribution from the gadolinium neutron capture reaction is then simulated by MCNP and compared with measured data. The simulations made by MCNP agree well with experimental results. As long as thermal neutron scattering from chemically bound atoms are not included in GEANT4 it is not suitable for NCT applications.

Adult Atlantic salmon (55–116 cm total length) with PIT-tags (n= 318) and both PIT-tags and gastric radio-tags (n= 127) in a regulated river showed similar upstream migration success, yet radio-tagged fish migrated faster than fish with only PIT-tags. Regurgitation rate of radio-tags was 9%.

Radiolabelled DNA-binding compounds can be used to increase the efficiency of radionuclide cancer therapy of disseminated disease. In this work, the aminoacridine compound N-[3-(acridine-9-ylamino)-propyl]-3-iodobenzamide (A3) labelled with the Auger-emitting nuclide 125I using Chloramine-T was studied. Optimal labelling conditions of 125I-A3 were investigated and the interaction with DNA was studied using a novel cell-free in vitro assay with naked human genomic DNA in agarose plugs. This novel assay showed to be simple and reliable. The results verify that 125I-A3 specifically binds DNA with low dissociation and is potent in causing double-strand breaks, yielding 1.0-1.4 breaks per decay. In conclusion, 125I-A3 is a most suitable DNA-binding compound for future therapeutic studies of Auger-electron emitters like 125I.

PURPOSE: The purpose of this study was to analyse the properties of the astatinated chimeric MAb (cMAb) U36 as a conjugate to selectively target and eradicate head and neck squamous cell carcinoma (HNSCC). METHODS: cMAb U36 was labelled with 211At via the linker N-succinimidyl 4-(trimethylstannyl)benzoate (SPMB). The quality of the conjugate was extensively evaluated for binding and internalisation capacity, and compared with 125I-SPMB-cMAb U36. The cellular toxicity of the astatinated conjugate was assessed in two types of in vitro growth assay and compared with 131I-labelled cMAb U36 (directly labelled). RESULTS: Comparisons between 211At-cMAb U36 and 125I-cMAb U36 demonstrated an optimal functional capacity of the labelled products. Immunoreactivity and affinity assays showed high immunoreactive fractions (>93%), and an affinity in good agreement between the astatinated and iodinated antibodies. For both conjugates, specific binding to HNSCC cells could be demonstrated, as well as some internalisation. Retention of the astatinated conjugate was just slightly lower than for the iodinated conjugate and still reasonable for therapeutic use (31+/-2% vs 42.6+/-1.0% at 22 h), demonstrating no adverse effects from astatination of the antibody. Studies on cellular toxicity demonstrated a dose-dependent and antigen-specific cellular toxicity for 211At-cMAb U36, with about 10% cell survival at 50 decays per cell. The 131I-labelled conjugate was not as efficient, with a surviving cell fraction of about 50% at 55 decays per cell. CONCLUSION: These results indicate that 211At-cMAb U36 might be a promising future candidate for eradicating HNSCC micrometastases in vivo.

The humanized antibody A33 binds to the A33 antigen, expressed in 95% of primary and metastatic colorectal carcinomas. The restricted pattern of expression in normal tissue makes this antigen a possible target for radioimmunotherapy of colorectal micrometastases. In this study, the A33 antibody was labeled with the therapeutic nuclide 211At using N-succinimidyl para-(tri-methylstannyl)benzoate (SPMB). The in vitro characteristics of the 211At-benzoate-A33 conjugate (211At-A33) were investigated and found to be similar to those of 125I-benzoate-A33 (125I-A33) in different assays. Both conjugates bound with high affinity to SW1222 cells (Kd = 1.7 ± 0.2 nM, and 1.8 ± 0.1 nM for 211At-A33 and 125I-A33, respectively), and both showed good intracellular retention (70% of the radioactivity was still cell associated after 20 hours). The cytotoxic effect of 211At-A33 was also confirmed. After incubation with 211At-A33, SW1222 cells had a survival of approximately 0.3% when exposed to some 150 decays per cell (DPC). The cytotoxic effect was found to be dose-dependent, as cells exposed to only 56 DPC had a survival of approximately 5%. The 211At-A33 conjugate shows promise as a potential radioimmunotherapy agent for treatment of micrometastases originating from colorectal carcinoma.

About one third of all cancer develops into a spread disease that is difficult to treat. Radioimmunotherapy has during the last years proven to be of help when other therapy modalities fail in e.g. lymphomas. The development in this area is fast mainly due to substantial improvements in molecular biology and in our increasing understanding of specific receptor expressions in cancer cells. However, radionuclides used today, 131I and 90Y, are not optimal in that sense that they emit radiation mainly suitable to treat the bulk tumor and not the single cell and micrometastases present in spread disease. The article stresses the importance that radionuclides with more suitable emission of particles like 177Lu and 211At are made available for clinical research and routine.

The aim of this study was to evaluate whether the HER2 expression in breast cancer is retained in metastases. The HER2 expression in primary tumours and the corresponding lymph node metastases were evaluated in parallel samples from 47 patients. The HercepTest was used for immunohistochemical analyses of HER2 overexpression in all cases. CISH/FISH was used for analysis of gene amplification in some cases. HER2 overexpression (HER2-scores 2+ or 3+) was found in 55% of both the primary tumours and of the lymph node metastases. There were only small changes in the HER2-scores; six from 1+ to 0 and one from 3+ to 2+ when the metastases were compared to the corresponding primary tumours. However, there were no cases with drastic changes in HER2 expression between the primary tumours and the corresponding lymph node metastases. The literature was reviewed for similar investigations, and it is concluded that breast cancer lymph node metastases generally overexpress HER2 to the same extent as the corresponding primary tumours. This also seems to be the case when distant metastases are considered. It has been noted that not all patients with HER2 overexpression respond to HER2-targeted Trastuzumab treatment. The stability in HER2 expression is encouraging for efforts to develop complementary forms of therapy, for example, therapy with radionuclide-labelled Trastuzumab.

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.

An important application of quantitative imaging in nuclear medicine is the estimation of absorbed doses in radionuclide therapy. Depending on the radionuclide used for therapy, quantitative imaging of the kinetics of the therapeutic radiopharmaceutical could be done using planar imaging, SPECT or PET. Since many nuclear medicine departments have a gamma camera system that is also suitable for coincidence imaging, the performance of these systems with respect to quantitative imaging of PET isotopes that could be of use in radionuclide dosimetry is of interest. We investigated the performance of a gamma camera with coincidence imaging capabilities with 99mTc, 111In, 18F and 76Br and a dedicated PET system with 18F and 76Br, using a single standard set of phantom measurements. Here, 76Br was taken as a typical example of prompt gamma-emitting PET isotopes that are applicable in radionuclide therapy dosimetry such as 86Y and 124I. Image quality measurements show comparable image contrasts for 76Br coincidence imaging and 111In SPECT. Although the spatial resolution of coincidence imaging is better than single photon imaging, the contrast obtained with 76Br is not better than that with 99mTc or 111In because of the prompt gamma involved. Additional improvements are necessary to allow for quantitative coincidence imaging of long-lived, prompt gamma producing positron emitters.

Polysaccharides are not degradable by proteolytic enzymes in lysosomes and do not diffuse through cellular membranes. Thus, attached to an internalizing, targeting protein, such polysaccharide linkers, will remain intracellularly after protein degradation. They can be labeled with halogens and provide then a so called residualizing label. Such an approach improves tumor-to-non-tumor radioactivity ratio and, consequently, the results of radionuclide diagnostics and therapy. In this study we present a new approach to obtain a stable halogenation of the polysaccharide dextran using 7-(3-amino-propyl)-7,8-dicarba-nido-undecaborate (-) (ANC). Dextran T10 was partially oxidized by metaperiodate, and ANC was coupled to dextran by reductive amination. The conjugate was then labeled with 125I using either Chloramine-T or IodoGen as oxidants. Labeling efficiency was 69-85%. Stability of the label was evaluated in rat liver homogenates. Under these conditions, the ANC-dextran conjugate was found to be more stable than labeled albumin, which was used as a control protein.

QC 20111213

The overexpression of epidermal growth factor receptors, EGFR, in glioblastomas is well documented. Hence, the EGFR can be used as target structure for a specific targeting of glioblastomas. Both radiolabeled anti-EGFR antibodies and the natural ligand EGF are candidate agents for targeting. However, EGF, which has a rather low molecular weight (6 kDa), might have better tissue penetration properties through both normal tissue and tumors in comparison with anti-EGF antibodies and their fragments. The aim of this study was to prepare and evaluate in vitro an EGF-based antiglioma conjugate with residualizing label. Human recombinant EGF (hEGF) was coupled to isothiocyanate-benzyl-DTPA. The conjugate was purified from unreacted chelator using solid-phase extraction and labeled with (111)In. The labeling yield was 87% +/- 7%. The label was reasonably stable; the transchelation of (111)In to serum proteins was about 5% after incubation at 37 degrees C during 24 hours. The obtained [(111)In]benzyl-DTPA-hEGF conjugate was characterized in vitro using the EGFR expressing glioma cell line U343MGaCl2:6. The binding affinity, internalization, and retention of the conjugate were studied. The conjugate had receptor specific binding and the radioactivity was quickly internalized. The intracellular retention of radioactivity after interrupted incubation with conjugate was 71% +/- 1% and 59% +/- 1.5% at 24 and 45 hours, respectively. The dissociation constant was estimated to 2.0 nM. The results indicate that [(111)In]benzyl-DTPA-hEGF is a potential candidate for targeting glioblastoma cells, possibly using locoregional injection.

We have investigated a method for direct astatine labeling of proteins. Binding sites for astatine were created by coupling of a nido-carborane derivative to a protein, the human epidermal growth factor (hEGF), using two different conjugation methods - by glutaraldehyde cross-linking or by introduction of sulfohydryl groups by Traut's reagent with subsequent linking of ANC-1 with m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester. The conjugates were astatinated using the Chloramine-T method in high yield. The best labeling was obtained by the glutaraldehyde conjugate with an average yield of 68±9%. In vitro stability tests indicated that the glutaraldehyde conjugated label was as stable as hEGF labeled with astatobenzoate.

Specific targeting of radionuclides is a promising approach to improve diagnosis and treatment of tumors. Targeting vectors may be monoclonal antibodies directed toward tumour-specific antigens or regulatory peptides binding to receptors overexpressed on or by malignant cells. Depending on the aim of the procedure and the biokinetics of the targeting vectors, radionuclides with different nuclear properties (decay scheme, half-life, etc.) must be applied. Halogen radioisotopes are attractive since they exhibit a variety of nuclear properties suitable for various applications. At the same time, their chemistry shows great similarities, which enables the use of similar labelling procedures for different nuclides. A problem in using radiohalogens for labelling of tumour-targeting proteins and peptides is that the commonly used radiohalogenation methods provide labels, which, after internalisation and lysosomal digestion, rapidly "leak" from malignant cells as radiohalogenated degradation products. The main reason for such leakage is free diffusion of the radiometabolites through lysosomal and cellular membranes. This review describes current approaches in molecular design to improve cellular retention of radiohalogen labels. These approaches include the use of prosthetic groups for the attachment of radiohalogens to targeting vectors of bulky hydrophilic non-charged molecules, molecules positively charged at lysosomal pH and negatively charged molecules. The emphasis in this paper is on labelling chemistry and the results of the biological testing of labelled compounds.

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.

Closo-dodecaborate dianion is a three-dimensional aromatic inorganic molecule, which can be easily halogenated forming a stable halogen-boron bond. Derivatives of closo-dodecaborate were considered as a convenient chemical form of delivery of enriched 10B to malignant tumors for boron neutron capture therapy (BNCT). Some properties of closo-dodecaborate (hydrophilicity, strength of halogen-boron bond, charge at lysosomal pH) make it attractive as a potential prosthetic group for attachment of radioactive halogens to tumor-targeting proteins. Bromine radioisotopes possess a variety of useful nuclear characteristics, and can be used in different areas of clinical diagnostics and therapy. In this work, a basic chemistry of closo-dodecaborate radiobromination was studied. It was found, that di(triethylamonium) dodecahydro-closo-dodecaborate can be labelled in high yield, more then 90%, in a wide pH range. By decreasing the pH, the bromination can be directed to closo-dodecaborate in the presence of phenolic compounds. The results of the study indicate a possibility of using the radioactive bromine label for investigation of pharmacokinetics of boronated compounds for BNCT.

Ingår i avhandling: urn:nbn:se:uu:diva-1908

Several positron emitting nuclides with applications in PET, such as 76Br, 124I, 110In and 86Y, also emit gamma radiation in their decays. Measured coincidences between annihilation photons and this cascade gamma radiation are essentially true coincidences and the standard PET corrections do not account for them. We investigated the performance of 76Br in 2D and 3D PET, the effect of the gamma radiation emitted by 76Br on quantitative accuracy and the distribution of cascade gamma radiation coincidences in 2D and 3D PET sinograms. A correction method for cascade gamma radiation coincidences was implemented and evaluated. Count rate linearity was affected by the gamma radiation from the 76Br decay. Spatial resolution and sphere recovery were slightly worse for 76Br compared to 18F. Correction for cascade gamma radiation coincidences by subtraction of a linear projection tail fit improved total correction accuracy to similar values as for positron-only emitters such as 18F, and improved image contrast significantly.

We propose the use of the Auger electron and positron-emitting generator 134Ce/134La (half-lives 3.16 d and 6.45 min) for radionuclide therapy. It combines emission of high-energy beta particles with Auger electrons. The high-energy beta particles have similar energies as those emitted by 90Y. Many cancer patients receiving radionuclide therapy have both bulk tumours, which are best treated with high-energy beta particles, and single spread cells or micrometastasis, which are preferably treated with low-energy electrons such as Auger and conversion electrons. Furthermore, the positron-emitting 134La can be used to study kinetics and dosimetry using PET. Production and PET performance were investigated and theoretical dosimetry calculations were made. PET resolution, recovery and quantitative accuracy were slightly degraded for 134La compared to 18F. 134Ce/134La absorbed doses to single cells were higher than absorbed doses from 90Y and 111In. Absorbed doses to spheres representing bulk tumours were almost as high as for 90Y, and a factor 10 higher than for 111In. Whole-body absorbed doses, based on kinetics of the somatostatin analogue octreotide, were higher for 134Ce/134La than for 90Y because of the 134La annihilation photons. This initial study of the therapeutic possibilities of 134Ce/134La is encouraging and justifies further investigations.

Biologically active peptides have during the last decades made their way into conventional nuclear medicine diagnosis using single photon emission computed tomography (SPECT) and gamma-camera. Several clinical trails are also investigating the role of radiolabeled peptides for targeting radionuclide therapy. This has raised the question as to whether positron emission tomography (PET) can be used in order to obtain better quantitative information of the peptide distribution in tumor and healthy organs, i.e., to get a better dosimetry. Positron emitting analogs of the therapeutic radionuclides used have been produced and successfully applied in peptide pharmacokinetic measurements with PET. But the recent boom in (18)FDG-PET ((18)FDG = [(18)F]2-deoxy-2-fluoro-D-glucose), and with this a worldwide increasing number of PET systems, has also inspired several research groups to hunt for alternative labels to be used for peptide diagnostics and PET. The rapid kinetic of short peptides agrees well with the short half-lives of standard PET nuclides like (11)C and (18)F. Especially, (18)F appears to be excellent for labeling bioactive peptides due to its favorable physical and nuclear characteristics. However, with present techniques labeling peptides with (18)F is laborious and time-consuming, and is not yet a clinical alternative. Other halogens like (75, 76)Br and (124)I are, from the chemical point of view, easier to apply. But an even better labeling alternative may be positron emitting metal ions like (55)Co, (68)Ga, and (110m)In since they tend to give better intracellular retention and thus a better signal-to-background ratio than the halogen labels. The main drawback with these radionuclides is that they are not readily available. Some of these radionuclides also emit gamma in their decay that may affect the measuring properties of the PET equipment. This article reviews mainly the present situation of production and use of nonconventional positron emitters for pept

The somatostatin analog diethylenetriaminepentaacetic acid (DTPA)-D-Phe1-octreotide labeled with 111In has been applied extensively for diagnosis of neuroendocrine tumors using SPECT or planar scintigraphy. However, the spatial resolution of planar scintigraphy and SPECT prohibits imaging of small tumors, and the quantification accuracy of both methods is limited. METHODS: We developed a method to prepare the positron-emitting radiopharmaceutical 110mIn-DTPA-D-Phe1-octreotide based on a commercially available kit. Phantom studies were done to investigate and compare the performance of 110mIn PET and 111In SPECT. A clinical imaging study using 110mIn-DTPA-D-Phe1-octreotide and PET was done to investigate the application of this radiopharmaceutical. RESULTS: An almost 3-fold better resolution and much better quantitative capabilities were found for 110mIn PET than for 111In SPECT. The clinical imaging study demonstrated the potential use of 110mIn-octreotide in PET to image tumors and quantify radioactivity uptake in humans using (110m)In-DTPA-D-Phe1-octreotide. CONCLUSION: PET with 110mIn-DTPA-D-Phe1-octreotide greatly improved detection of small tumors and offers a possibility of more accurate quantification of tumor uptake than can be obtained with 111In-DTPA-D-Phe1-octreotide and SPECT.

Positron-emitting isotopes of arsenic, 70As (T 1/2 = 53 min), 71As (T 1/2 = 64 h), 72As (T 1/2 = 26 h), and 73As (T 1/2 = 17.8 d) are of interest in biomedical investigations using PET. A fast and simple method for their production using low-energy proton and deuteron reactions on enriched Ge-targets is presented. Dry distillation of GeO2 at 1105 °C during 2 hours provides a separation efficiency of more than 60%. The loss of target material is less than one per cent and the irradiated targets can be used several times. The method allows production of diagnostically useful amounts of positron-emitting arsenic isotopes using accelerators commonly available at PET-centres.

[111In]-DTPA-D-Phe1-octreotide (OctreoScan®, Mallinkrodt) is widely used for detection of neuroendocrine tumors and has lately been proposed for radionuclide therapy. We found, using HPLC and a GF-250 column (Zorbax®, Hewlett Packard), that OctreoScan® can be separated in two radiolabeled components of about equal amount. The analytical conditions for a quantitative isolation indicate that the two-peptide components of OctreoScan®have different lipophilicity. The isolated components are stable and do not transform into each other at room temperature during 6 hours (shelf-life of OctreoScan®).

In principle, alpha-emitting radionuclides, such as 211At, are more efficient than beta-emitters to inactive single disseminated cancer cells. However, cellular processing of astatinated proteins has not yet been studied in detail. In this study an anti-colorectal cancer monoclonal antibody (mAb) A33 was indirectly labeled with 211At and for comparison with 125I. Binding and retention of radioactivity was studied in the colorectal cancer cell-line SW1222. A similar pattern of binding and retention of the two radiohalogens was seen. The main difference found, that the retention time of astatinated mAb in SW1222 was almost two times longer, might be of advantage in radionuclide therapy.