Investigations of avidin and biotin for imaging applications.

The attractive properties of avidin (streptavidin) and biotin, in particular their strong affinities (Kd = 10(-15)M), may be used to advantage in imaging applications. These molecules have been used in this preliminary investigation to improve the targeting of 111In in animals. Antibodies have been conjugated with biotin and administered unlabeled while, at a later time, the radiolabel was administered attached to DTPA-coupled avidin or streptavidin. An alternative procedure was also considered whereby the antibodies were conjugated with avidin and administered before the administration of radiolabeled biotin. Using a model in which the target consisted of conjugated agarose beads deposited in the peritoneum of mice, it has been shown that the target/nontarget radioactivity ratios may be significantly improved with respect to the conventional procedures through the use of this approach.