Preparation of Re-labeled antibody (A7) by a simple method using rhenium(I) tricarbonyl complex

Ogawa, Kazuma*; Kawashima, Hidekazu*; Kinuya, Seigo*; Yoshimoto, Mitsuyoshi*; Shiba, Kazuhiro*; Kimura, Hiroyuki*; Hashimoto, Kazuyuki; Mori, Hirofumi*; Saji, Hideo*

Re is one of the most useful radionuclides for internal radiotherapy. However, there is a problem when protein such as antibody is used as a carrier of Re. The labeling method using bifunctional chelating agents require the conjugation of Re-complex to protein after radiolabeling with the bifunctional chelating agent. Then, we planned the preparation of a stable Re-labeled protein by a simple method. A7 monoclonal antibody was labeled by reacting Re(I) tricarbonyl precursor with A7 directly. Re labeled A7 was prepared with radiochemical yield of 23%. After purification, Re labeled A7 showed radiochemical purity over 98%. After 24 hours of incubation, about 93% of Re-A7 remained intact, which indicates Re-A7 is stable in vitro. In biodistribution experiment, 11.2% of the injected dose/g of Re-A7 accumulated in the tumor at 24 hours postinjection, and tumor to blood ratio was over 1.0 at the same time.