A new technique developed in our laboratory to add phosphorylation sites into proteins by genetic engineering will be applied to monoclonal antibodies with the aim of producing a highly labeled and specific reagent for use in cancer diagnosis and therapy. This method, which is based on the introduction of amino acid recognition sites for the CAMP- dependent protein kinase into the polypeptide chain, allows radiophosphate groups (32P) to be introduced into antibodies which previously could not be labeled and allows the antibody to retain its immunoreactivity. Radiolabeled monoclonal antibodies have several advantages over toxin-conjugated monoclonal antibodies for the treatment of cancer. Because tumor cells express antigens in a heterogeneous manner with some cells not producing antigens, MAbs will not bind to every cell in a tumor. Radiolabeled Mabs have the advantage of killing cells within a radius of a few cell diameters from the cell to which the Mab is bound so that tumor cells not expressing antigen would also be lethally irradiated. Additionally, i the case of carcinomas in which the surface antigens are not internalized, radiolabeled Mabs will kill by binding to the cell and do not require uptake of the antibody by the cell. A third advantage is that radiolabeled Mabs can be used in the diagnosis of patients and can help determine how well a particular Mab will bind to an individual patient's tumor. This information provides insight into the therapeutic potential of a given Mab in a specific patient. The construction of cassettes of recognition sites within an antibody molecule could provide massive concentrated radioisotopic doses directed at specific tumors. The overall aims of this proposal are to develop Mabs with kinase recognition sites and utilize these in radioimmunodiagnostics and radioimmunotherapy of tumors.
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