DIRECT LABELING OF MONOCLONAL-ANTIBODIES WITH TC-99M BY PHOTOACTIVATION

Direct radiolabeling methods currently rely on the addition of exogeno us chemical reagents to create the necessary binding sites for Tc-99m binding to monoclonal antibodies (MAbs). This work describes the use o f ultraviolet (UV) light to facilitate photoactivation of MAbs for Tc- 99m radiolabeling. Methods: The parameters of exposure wavelength and solution composition were investigated to provide a basis for further development. Based on these results, various murine MAbs and a chimeri c MAb were photoactivated using a 300-nm (nominal) wavelength, eight-l amp (3.9 W each) photochemical reactor providing exposure for defined time periods. The MAb preparations were stored frozen and subsequently labeled by the addition of pertechnetate. For MAb-170, the photoactiv ated preparation was compared to a stannous ion reduced preparation by radiochemical (radiolabeling yield, serum stability cysteine challeng e), biochemical (SDS-PAGE, IEF, SE-HPLC) and immunochemical (immunorea ctivity) assays and biodistribution studies in mice. Results: Photoact ivation produced high radiolabeling yields for all the MAbs studied an d MAb-170 produced comparable in vitro quality control profiles and in vivo biodistribution data. Conclusion: The use of this relatively sim ple, short and easily controlled photoactivation process for MAbs faci litates facile radiolabeling with Tc-99m and provides an alternative t o the direct chemical radiolabeling procedures.