Astatine-211 labeling of protein using TCP as a bi-functional linker: synthesis and preliminary evaluation in vivo and in vitro

With 2,3,5,6-tetrafluorophenyl 3-(nodo-carboranyl) propionate (TCP) as a new potential bi-functional linker, bovine serum albumin (BSA) was conjugated with 211At, and the conjugated model protein (211At-TCP-BSA) was preliminarily evaluated in vitro and in vivo by comparison with 211At-SAB-BSA and 211At-SAPC-BSA, which conjugated with 211At via aryl derivatives ATE (N-succinimidyl-3-(tri-n-butylstannyl) benzoate) or SPC (N-succinimidyl 5-(tributylstannyl)-3-pyridinecarboxylate). The radiolabeled intermediate 211At-TCP was coupled to BSA in yields ranging from 35 to 45% with radiochemical purity of more than 98%. The conjugated 211At-TCP-BSA exhibited considerable stability in vitro in 0.1 mol/L PBS (pH 7.6) at room temperature (RT), similar to 211At-SAPC-BSA and 211At-SAB-BSA. Biodistribution of the 211At conjugated protein was investigated in NIH strain mice by I.V injection. The results showed that 211At-TCP-BSA was constantly stable in vivo as well as in vitro, but more stable than 211At-SAPC-BSA and 211At-SAB-BSA. These results implied that radioastatinated carboranes based on B–At bonds are higher stability than radioastatinated aryl derivatives based on C–At to in vivo deastatination. In other word, TCP should be a promising bi-functional linker for 211At conjugation of proteins or antibodies.