AN IMPROVED METHOD OF DIRECT LABELING MONOCLONAL-ANTIBODIES WITH TC-99M

An improved method of direct labeling MAbs with Tc-99m is described. Two murine monoclonal antibodies, designated Lym-1 and B72.3, have been successfully labeled with Tc-99m in 0.1 M borate buffer at pH 9.3. The choice of buffer and pH was essential for obtaining a radiolabeling yield greater-than-or-equal-to 98%. In vitro studies demonstrated that the radiolabeled antibodies were stable and retained their immunoreactivity. Imaging and biodistribution studies using Raji and LS174T human tumor-bearing nude mice demonstrated a significant tumor uptake at 24-h post-injection of Tc-99m-labeled MAbs. This improved labeling method showed better stability than those of previously published methods and resulted in significant improvement in the uptake of antibody in tumor. External images at 24 h post-injection revealed clearly visible tumors demonstrating the benefit of this method for tumor immunoscintigraphy.