The Design of Stable Aryl Sulfonyl Fluoride Prosthetic Groups and Site Specific Radioimmunoconjugates

<p dir="ltr">Radiopharmaceuticals that use peptides and antibodies are valuable tools for diagnostic and therapeutic applications in nuclear medicine, however, they suffer limitations including in some cases poor metabolic stability and in other cases insufficient selectivity in production of radioimmunoconjugates. Two separate projects were conducted as part of this PhD study. The aim of the 1st project (Chapters 2-5) was to increase understanding of what features contribute to the metabolic instability of the S−F bond in aryl sulfonyl fluorides and identify approaches to increasing sulfonyl fluoride stability. Molecules that feature a sulfonyl fluoride (SO2F) moiety have been gaining increasing interest due to their unique reactivity and potential applications in synthetic chemistry, medicinal chemistry, and other biological uses. A particular interest is towards 18F-radiochemistry, where sulfonyl fluorides can be used to indirectly radiolabel biomolecules or can be used as radiofluoride relay reagents that facilitate radiolabelling of other molecules. Although sulfonyl fluoride prosthetic groups have been identified in the literature, the low metabolic stability of the sulfonyl fluoride S−F bond presents an issue and limits the applicability of sulfonyl fluoride prosthetic groups. The overall goal of the 1st project was to guide the development of stable aryl sulfonyl [18F]fluoride prosthetic groups that may provide a new method of indirectly radiolabelling biomolecules such as peptides and antibodies. To undertake this, 14 model aryl sulfonyl fluoride compounds with varying functional groups and substitution patterns were investigated. Synthesis of the 14 model aryl sulfonyl fluorides were attempted <i>via </i>three different synthetic routes including a palladium-catalysed route, a diazonium route and a halide exchange route. Due to the inability to synthesise the aryl sulfonyl fluorides <i>via </i>the palladium-catalysed route, synthesis of the 14 model aryl sulfonyl fluorides was primarily achieved <i>via </i>both the diazonium route and a halide exchange route. Each of the 14 model aryl sulfonyl fluorides stabilities were then examined in various media, including phosphate-buffered saline and rat serum as a model for biological conditions. The results indicated that both electronic and steric factors affect the stability of the S−F bond, with the 2,4,6-trisubstituted model aryl sulfonyl fluorides examined displaying the highest in vitro metabolic stability. The aim of the 2nd project (Chapters 6-8) was to investigate, optimise and characterise the functionalisation of the antibody trastuzumab with DOTA using both site-specific and non-site-specific methods. Monoclonal antibodies have emerged as a next generation of diagnostic and therapeutic drugs, particularly towards the diagnosis and treatment of cancer. A particular application of these is towards the use of radioimmunoconjugates for both diagnostics and therapy, which requires the attachment of chelator to the antibody to allow for radiolabelling. Conventional bioconjugation methods to install a chelator use nucleophilic processes to attach the chelator to the antibody. However, while these processes are simple the reactions are not site-specific and lack stoichiometric control, thus the resulting chelator antibody conjugates often demonstrate reduced affinity for target receptors. To overcome this issue, site-specific strategies have been proposed, including using dibromomaleimide rebridging technology that targets native interstrand disulfide regions of antibodies. In this project, a DOTA chelator was synthesised with a dibromomaleimide functional group before it was conjugated to trastuzumab using rebridging technology. As a comparison, a DOTA chelator was also conjugated to trastuzumab <i>via </i>a non-site-specific approach using an isothiocyanate functionality. Investigations of both site-specific and non-site-specific radioimmunoconjugates also involved optimisation of the radiolabelling procedures and assessing the physiochemical and biological properties of the radioimmunoconjugates.</p>