Feasibility of the radioastatination of a monoclonal antibody with astatine-211 purified by wet extraction

Astatine-211, a most promising alpha-particle emitter for targeted radiotherapy, is generally obtained by high-temperature distillation. However, a liquid-liquid extraction procedure (wet extraction) has also been described. The purpose of this study was to develop and optimize the labelling of the stannylated-activated ester N-hydroxysuccinimidyl-meta-trimethylstannylbenzoate ester (MeSTB) with astatine-211 extracted in di-isopropylether (DIPE) in the presence of the oxidant N-chlorosuccinimide (NCS). The effect of final volume, incubation duration and NCS amounts on radiolabelling yield was studied. The best yields (85-90%) of N-hydroxysuccinimidyl-meta-[At-211]astatobenzoate ester (SAB) were obtained with 20 nmol of MeSTB, 100 nmol of NCS in 120 mu L of DIPE after 15 min. The astatine-211-labelled-activated ester was then used to radiolabel a monoclonal antibody (mAb). The labelling yield was 20-25% and the radiochemical purity was 97-99%. These results show that mAbs may be efficiently labelled with astatine-211 obtained by wet extraction, a fully automatable technique that may prove to be a useful alternative to dry distillation for high activity labelling of radiopharmaceuticals.