Preparation of 67Ga-labelled human IgG and its Fab fragments using desferoxamine as chelating agent

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Abstract
Human IgG and its Fab fragments were chosen as a model system for studying the desferoxamine (DF) coupling reaction using glutaraldelyde or carbodiimide at various concentrations. The labelling of the IgG-DF conjugates with 67Ga proved to be highly efficient and reproductible. The labelling efficiency in relation to storage time of the conjugate was analysed over a 1-month period by Sephadex-G-50 chromatography. Gel-filtration analysis on Sephacryl S-300 showed that, following the coupling procedure, a high proportion (more than 80%) of the conjugate remained monomeric. Immunoelectrophoresis on agar plates demonstrated that the antibody immunoreactivity was preserved. The biodistribution in mice of the 67Ga-DF-IgG conjugates was comparable to that of the conventional radiopharmaceutical, 125I-HSA. Conditions were established for the coupling of DF to two rat IgG2b monoclonal antibodies M10/76 and 11/160, that are specific for the Hooded rat sarcomata MC 24 and HSN respectively; the immunoreactivity of these conjugates was tested by a cellbinding assay. The data indicate that monoclonal-antibody/DF conjugates prepared with the bifunctional reagent glutaraldelyde maintain their capacity for binding to their tumour-associated antigens.