The influence of free DTPA on the dose distribution of yttrium-90 radiolabelled antibodies

Yttrium-90 (90Y) bound to antibody via a DTPA group, was stable in-vitro until exposed to buffers below pH 5.4. It also exhibited minimal transchelation to transferrin during serum incubation. In-vivo, two 90Y labelled antibodies of the same isotype but different specificities, showed similar distributions in tumour-bearing animals. Subsequent administration of a DTPA solution removed activity from liver and bone. This suggests that these tissues contain an environment in which a proportion of yttrium is released from the antibody, in a form suitable for removal with DTPA.