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

Astatine‐211, a most promising α ‐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 ‐[ 211 At]astatobenzoate ester (SAB) were obtained with 20 nmol of MeSTB, 100 nmol of NCS in 120 µL 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. Copyright © 2008 John Wiley & Sons, Ltd.