Properties of technetium-99m labeled monoclonal antibodies

This study was designed to determine the chemical and immunochemical properties of monoclonal antibodies or fragments which have been labeled with Tc-99m using the pretinning method. The labeled proteins were evaluated using: Sephadex G-25 gel column scanning to determine percentage radiolabeled protein; HPLC to determine the molecular weight and purity of the proteins; reactivity with solid phase antigens to determine immunoreactivity under a variety of storage conditions; and the Tc-99m transchelation method of a previous study to determine the strength of the bonding. Percentage labeled protein ranges from 65 to 95%. Under certain labeling conditions small fractions of the F(ab')2 protein can be converted to aggregates of Fab fragments. Immunoreactivity depends on the purity and immunoreactivity of the original protein and is not changed by the labeling procedure. Transchelation is minimal (less than 5% at 4000 molar excess of EDTA). It is concluded that the pretinning method can be used to produce an extremely stable, immunoreactive, Tc-99m labeled antibody or antibody fragments. The labeled proteins retain their biologic activity during storage or during incubation with human plasma