RADIOLABELING OF FABS BY PHOTOCHEMICAL CONJUGATION

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DESCRIPTION: The proposed research is to prepare and evaluate bifunctional chelating agents designed for the purpose of photolabeling antibodies and antibody fragments with radionuclei (Tc-99m and Re-186/Re-188). These studies are based on the significant discovery that the photolabeling of proteins and antibodies with a perfluoroaryl azide photoprobe could be achieved with high efficiency (75-80%) in a 1:1 ratio of photoprobe: antibody, and with nearly complete retention of immunoreactivity of the antibody. These properties are ideal for radionuclear labeling and suggest that photolabeling has real potential for labeling of antibodies with therapeutic and diagnostic radionuclei. The proposed research has several objectives: synthesis of the radiolabeled photoprobe; attachment to antibodies and antibody fragments; and in vitro and in vivo testing of stability, immunoreactivity, biolocalization, and clearance. The initial effort will be the attachment of the photolabile moiety to nuclei-specific chelating agents, which are known to have good stability. Attachment will be achieved using linkers between the photoprobe an the chelating agents to insure electronic and spatial isolation. The linkers will also be designed to promote radioisotope clearance following catabolism b the organism. These synthesized bifunctional chelating agents will be labeled with the desired radiometal for testing of stability and photolabeling efficiency. The viability of these bifunctional radiolabels for antibody labeling will be tested with the B72.3 antibody and antibody fragments produce by limited proteolysis or recombinant expression in bacteria. Labeling efficiency will be determined by size exclusion HPLC using UV and/or radiation monitors using methods developed earlier. Those labels showing high attachment efficiency will be further evaluated using in vitro studies of stability and immunoreactivity. Finally, the labeled materials, which show the greatest promise, will be subjected to in vivo testing for biodistributon and clearance