Radioiodination of protein using 2,3,5,6-tetrafluorophenyl 3-(nido-carboranyl) propionate (TCP) as a potential bi-functional linker: Synthesis and biodistribution in mice

2,3,5,6-Tetrafluorophenyl 3-(nido-carboranyl) propionate (TCP), as a new potential bi-functional linker for radiohalogenation of proteins or peptides, was synthesized. With this bi-functional linker, the first attempt to conjugate bovine serum albumin (BSA) with 125I was made and the biodistribution of the conjugated BSA (125I-TCP–BSA) was investigated in NIH strain mice. By the use of TCP as the linker, BSA was conjugated with 125I in a labeling yield of 58–75% and with radiochemical purity of 99.8% after purification by SephadexTM G-50. Even after being kept at room temperature for 72 h, the radiochemical purity of 125I-TCP–BSA was still more than 98%, much higher than that of the directly 125I-labeled BSA (125I-BSA). Meanwhile, biodistribution experiments in mice indicated that the uptake of 125I with 125I-TCP–BSA into thyroid was obviously less than that with 125I-BSA post-injection. All the results implied that the 125I-conjugated BSA (125I-TCP–BSA) was considerably stable in vivo as well as in vitro, and TCP was regarded as a promising bi-functional linker for radiohalogenation of proteins.