<p>Radioactive substances are used <i>in vivo</i> to localize and characterize malignant tumours, generally by scintigraphic methods. In this context positron emission tomography (PET) in combination with radiolabelled monoclonal antibodies (mAbs) may provide a sensitive and specific method for detection of cancer. Individual dose calculations, based on such PET measurements, may be carried out to predict the possible use of mAbs labelled with therapeutic nuclides. The positron emitter ⁷⁶Br, with a half-life of 16 h, is a well-suited candidate for radiolabelling and PET imaging. One drawback of radiobromine is that bromide, the ultimate catabolite after degradation of brominated mAb, is only tardily excreted from the body and is evenly distributed throughout the extracellular space, thereby increasing the background radioactivity. The aim of this work was to produce ⁷⁶Br-mAb preparations with high accumulation and retention in tumour tissue together with a quick clearance of ⁷⁶Br-labelled catabolites. Furthermore, the possibility to use brominated or iodinated mAbs in combination with PET to predict ²¹¹At-mAb dosimetry was evaluated.</p><p>Monoclonal Abs directed against colorectal cancer were labelled with ⁷⁶Br using the direct Chloramine-T-method or indirectly by labelling the precursor molecule N-succinimidyl para-(tri-methylstannyl) benzoate with ⁷⁶Br, which was subsequently conjugated to the mAbs. Monoclonal Ab A33 labelled with ⁷⁶Br using the two labelling protocols was characterized in vitro and in vivo in a rat tumour xenograft model. The mAb A33 was also labelled with ¹²⁵I for comparison. In addition, mAb A33 was labelled with ²¹¹At, ¹²⁵I and ⁷⁶Br using the indirect labelling protocol and the mAb pharmacokinetics was studied in normal rats in order to estimate if data from brominated or iodinated mAb could be used for dosimetry of ²¹¹At in healthy organs and tissue.</p><p>In conclusion, both direct and indirect labelling resulted in high yields and mAbs with preserved immunoreactivity. <i>In vivo</i> characterization of ⁷⁶Br-brominated mAb A33 showed that the indirect labelling method makes ⁷⁶Br-brominated mAb A33 a promising candidate for tumour imaging with PET due to the faster excretion of radiolabelled catabolites compared with direct bromination. Finally, mAb A33 labelled with ⁷⁶Br and ^124/125I can be used to predict the ²¹¹At dose of astatinated mAb A33 in most organs given that a correction factor is applied for organs with varying uptake.</p>

<p>In about half of all newly diagnosed cancer cases, conventional treatment is not adequately curative, mainly due to the failure of conventional techniques to find and kill residual cells and metastases, which might consist of only a few malignant cells, without causing unacceptable complications to healthy tissue. To solve the problem a more selective delivery of cytotoxic substances to tumour cells is needed. The approach applied here is called ‘tumour targeting’ and implies the use of biomolecules that recognise specific molecular structures on the malignant cell surface. Such molecules are then used for a selective transport of toxic agents to the cancer cells. </p><p>The use of radionuclides as cytotoxic substances has a number of advantages: 1) radiation does not cause severe resistance; 2) there is a cross-fire effect and 3) smaller amounts of nuclides are required than other cytotoxic substances to cause the same damage. Such an approach is called radionuclide tumour therapy. Several factors are important for the success of radionuclide therapy, such as the pharmacokinetics of the radiolabelled substance and its radiocatabolites, as well as the physical and chemical properties of the radiolabel used.</p><p>Nuclear properties of the label should be consistent with the problem to be solved: primary diagnostics; quantification of pharmacokinetics and dose planning; or therapy. From this point of view, radiohalogens are an attractive group of radiolabels. Halogens have nuclides with a variety of physical properties while the chemical and biological properties of halogens are very similar. The same labelling procedures can be used for all heavy halogens, i.e. bromine, iodine and astatine. It has been demonstrated that the biodistribution of proteins labelled with different heavy halogens is quite similar. </p><p>The main goal of the study was to develop protein radiohalogenation methods that provide a stable halogen-protein bond, convenient labelling chemistry that preserves the binding properties of proteins, long intracellular retention of radioactivity in targeted cells and quick release of radiohalogenated catabolites from the blood circulation. Radiohalogenation of proteins using indirect methods was studied, including optimisation of labelling chemistry and biological characterisation of some labelled conjugates. Two groups for indirect radiohalogenation were used, representing two different labelling principles: activated ester of benzoic acid (1) and the derivative of <i>closo</i>-dodecaborate anion (2). The non-phenolic linker (1) as well as the borate-halogen moiety (2) probably prevent dehalogenation. The negative charge of the potential catabolic products of (2) might trap radiohalogens intracellularly. </p>

Radioactive substances are used in vivo to localize and characterize malignant tumours, generally by scintigraphic methods. In this context positron emission tomography (PET) in combination with radiolabelled monoclonal antibodies (mAbs) may provide a sensitive and specific method for detection of cancer. Individual dose calculations, based on such PET measurements, may be carried out to predict the possible use of mAbs labelled with therapeutic nuclides. The positron emitter 76Br, with a half-life of 16 h, is a well-suited candidate for radiolabelling and PET imaging. One drawback of radiobromine is that bromide, the ultimate catabolite after degradation of brominated mAb, is only tardily excreted from the body and is evenly distributed throughout the extracellular space, thereby increasing the background radioactivity. The aim of this work was to produce 76Br-mAb preparations with high accumulation and retention in tumour tissue together with a quick clearance of 76Br-labelled catabolites. Furthermore, the possibility to use brominated or iodinated mAbs in combination with PET to predict 211At-mAb dosimetry was evaluated. Monoclonal Abs directed against colorectal cancer were labelled with 76Br using the direct Chloramine-T-method or indirectly by labelling the precursor molecule N-succinimidyl para-(tri-methylstannyl) benzoate with 76Br, which was subsequently conjugated to the mAbs. Monoclonal Ab A33 labelled with 76Br using the two labelling protocols was characterized in vitro and in vivo in a rat tumour xenograft model. The mAb A33 was also labelled with 125I for comparison. In addition, mAb A33 was labelled with 211At, 125I and 76Br using the indirect labelling protocol and the mAb pharmacokinetics was studied in normal rats in order to estimate if data from brominated or iodinated mAb could be used for dosimetry of 211At in healthy organs and tissue. In conclusion, both direct and indirect labelling resulted in high yields and mAbs with preserved immunoreactivity. In vivo characterization of 76Br-brominated mAb A33 showed that the indirect labelling method makes 76Br-brominated mAb A33 a promising candidate for tumour imaging with PET due to the faster excretion of radiolabelled catabolites compared with direct bromination. Finally, mAb A33 labelled with 76Br and 124/125I can be used to predict the 211At dose of astatinated mAb A33 in most organs given that a correction factor is applied for organs with varying uptake.

In about half of all newly diagnosed cancer cases, conventional treatment is not adequately curative, mainly due to the failure of conventional techniques to find and kill residual cells and metastases, which might consist of only a few malignant cells, without causing unacceptable complications to healthy tissue. To solve the problem a more selective delivery of cytotoxic substances to tumour cells is needed. The approach applied here is called ‘tumour targeting’ and implies the use of biomolecules that recognise specific molecular structures on the malignant cell surface. Such molecules are then used for a selective transport of toxic agents to the cancer cells. The use of radionuclides as cytotoxic substances has a number of advantages: 1) radiation does not cause severe resistance; 2) there is a cross-fire effect and 3) smaller amounts of nuclides are required than other cytotoxic substances to cause the same damage. Such an approach is called radionuclide tumour therapy. Several factors are important for the success of radionuclide therapy, such as the pharmacokinetics of the radiolabelled substance and its radiocatabolites, as well as the physical and chemical properties of the radiolabel used. Nuclear properties of the label should be consistent with the problem to be solved: primary diagnostics; quantification of pharmacokinetics and dose planning; or therapy. From this point of view, radiohalogens are an attractive group of radiolabels. Halogens have nuclides with a variety of physical properties while the chemical and biological properties of halogens are very similar. The same labelling procedures can be used for all heavy halogens, i.e. bromine, iodine and astatine. It has been demonstrated that the biodistribution of proteins labelled with different heavy halogens is quite similar. The main goal of the study was to develop protein radiohalogenation methods that provide a stable halogen-protein bond, convenient labelling chemistry that preserves the binding properties of proteins, long intracellular retention of radioactivity in targeted cells and quick release of radiohalogenated catabolites from the blood circulation. Radiohalogenation of proteins using indirect methods was studied, including optimisation of labelling chemistry and biological characterisation of some labelled conjugates. Two groups for indirect radiohalogenation were used, representing two different labelling principles: activated ester of benzoic acid (1) and the derivative of closo-dodecaborate anion (2). The non-phenolic linker (1) as well as the borate-halogen moiety (2) probably prevent dehalogenation. The negative charge of the potential catabolic products of (2) might trap radiohalogens intracellularly.

No description available.