Molecular imaging is intended to localize disease based on distinct molecular/functional characteristics. Much of today's interest in molecular imaging is attributed to the increased acceptance and role of 18F-flurodeoxyglucose (18F-FDG) imaging in a variety of
tumors. The clinical acceptance of
18F-FDG has stimulated research for other positron emission tomography (PET) agents with improved specificity to aid in
tumor detection and assessment. In this regard, a number of highly specific
antibodies have been described for different
cancers. Although scintigraphic imaging with
antibodies in the past was helpful in patient management, most antibody-based imaging products have not been able to compete successfully with the sensitivity afforded by 18F-FDG-PET, especially when used in combination with computed tomography. Recently, however, significant advances have been made in reengineering
antibodies to improve their targeting properties. Herein, we describe progress being made in using a bispecific antibody pretargeting method for immuno-single-photon emission computed tomography and immunoPET applications, as contrasted to directly radiolabeled
antibodies. This approach not only significantly enhances
tumor/nontumor ratios but also provides high signal intensity in the
tumor, making it possible to visualize
micrometastases of
colonic cancer as small as 0.1 to 0.2 mm in diameter using an anti-
carcinoembryonic antigen bispecific antibody, whereas FDG failed to localize these lesions in a nude mouse model. Early detection of micrometastatic
non-Hodgkin's lymphoma is also possible using an anti-CD20-based bispecific antibody pretargeting procedure. Thus, this bispecific antibody pretargeting procedure may contribute to
tumor detection and could also contribute to the detection of other diseases having distinct
antigen targets and suitably specific
antibodies.