BIODISTRIBUTION AND CATABOLISM OF GA-67-LABELED ANTI-TAC DSFV FRAGMENT

The disulfide-linked fragment (dsFv) of the antibody to the a subunit of the IL2 receptor has been radiolabelled with a [Ga-67] Ga-2-(p-SCN- Bz)-NOTA derivative linked through an isothiocyanato group to either t he E-amino group of lysine or the a-amino group of the N-terminal amin o acids. This low molecular weight protein (LMWP) has been proposed as a tumor diagnostic agent. However, >60% of the injected dose localize d in the mouse kidney. The major catabolites (>95%) in the kidney were identified as the Ga-2-(p-SCN-Bz)-NOTA conjugate with either lysine o r methionine, with no evidence of transchelation of Ga-67. Since diffe rent amino acids in the dsFv were radiolabelled according to this proc edure, it was possible to study the relative residence times of the va rious catabolites. The methionine conjugate had a significantly shorte r residence time than the lysine conjugate in the same kidney. Labelli ng the appropriate amino acid in a LMWP may lead to reduced residence times and increased diagnostic or therapeutic ratios.