Radiolabeled antibodies as in-vivo cancer probes (review)

Cancer imaging with radiolabeled antibodies, or radioimmunodetection (RAID), has undergone a gradual multidisciplinary development over a period of at least 2 decades, resulting in rapid, simple, and accurate targeting agents that are now in final stage evaluation as a new class of cancer imaging and detection reagents. In its development, RAID has focused on different antigen targets, antibodies and antibody forms, radiolabels, and scanning instruments and procedures. Antibodies and imaging agents for a large variety of cancer types have been investigated clinically, and require well controlled, prospective trials to determine clinical applications, utility and safety. At the present time, truly cancer-specific antibodies are not required for successful RAID; many different patients with a similar tumor type can be imaged with a single pancarcinoma antibody; shed tumor antigens do not appear to prevent antibody targeting because of complexation with the administered antibodies; very small doses of antibody, even below 1 mg, can succeed in RAID; few adverse reactions have resulted from RAID, even with the development of human anti-mouse antibodies (HAMA) in patients given high doses of intact immunoglobulin; HAMA can affect monoclonal antibody-based immunoassay results; antibody fragments are less immunogenic and result in a lower incidence of HAMA than intact immunoglobulins; single-photon emission computed tomography (SPECT) usually improves image resolution in RAID, as compared to planar imaging; and RAID can complement conventional imaging agents and can often disclose tumors missed by, conventional scanning methods. A recent advance has been the development of Tc-99m-labeled Fab' fragments by simple and rapid conjugation kits, which enable detection of small lesions, including those in the liver, within a few hours after injection, especially with SPECT scanning.