Indium binding to monoclonal antibodies: A study of bi-functional chelates using perturbed angular correlations

Time differential perturbed angular correlation measurements have been used to study the binding of 111In to DTPA and to the monoclonal antibody HMFG2 at room temperature and at 78 K. At the latter temperature, the quadrupole frequencies are similar (9.8±0.5 MHz in 111In-DTPA and 8.8±0.5 MHz in 111In-DTPA-HMFG) showing that the antibody labelling has not had any appreciable effect on the electric field gradient at the 111In binding site. The sequestration of 111In from the labelled antibody using increasing amounts of the plasma protein transferrin was investigated using time-integral PAC. At normal plasma concentrations, 20% of all 111In was found to have been sequestered by the transferrin. (orig.)