Fig. 1.

Figure adapted with permission from “Impact of Antibody Modifications on Tumor Targeting” by Stephen I. Rudnick, Ph.D. (AAPS-NBC 2009 Meeting). Differential cellular catabolite retention of non-residualizing (radiohalogen) or residualizing (radiometal–chelate) probes. For antibodies labeled with radiohalogens, following receptor-mediated internalization and lysosomal degradation, the resultant catabolic products are cleared from the cell. For antibodies labeled with radiometal–chelates, the resultant catabolized radiometal–chelate (usually present as an amino acid adduct) is trapped in the cell due to the highly polar nature of the chelate. The different cellular retention of their respective catabolic products can be used to understand antibody tissue kinetics (radiohalogen) or cumulative tissue exposure (radiometal–chelate)