Direct labeling of monoclonal antibodies with technetium-99m by photoactivation

Direct radiolabeling methods currently rely on the addition of exogenous chemical reagents to create the necessary binding sites for 99mTc binding to monoclonal antibodies (MAbs). This work describes the use of ultraviolet (UV) light to facilitate photoactivation of MAbs for 99mTc radiolabeling.

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 chimeric MAb were photoactivated using a 300-nm (nominal) wavelength, eight-lamp (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 photoactivated preparation was compared to a stannous ion reduced preparation by radiochemical (radiolabeling yield, serum stability cysteine challenge), biochemical (SDS-PAGE, IEF, SE-HPLC) and immunochemical (immunoreactivity) assays and biodistribution studies in mice.

Photoactivation produced high radiolabeling yields for all the MAbs studied and MAb-170 produced comparable in vitro quality control profiles and in vivo biodistribution data.

The use of this relatively simple, short and easily controlled photoactivation process for MAbs facilitates facile radiolabeling with 99mTc and provides an alternative to the direct chemical radiolabeling procedures.