211 At‐labelling of polymer particles for radiotherapy: Synthesis, purification and stability

Cyclotron‐produced 211 At was distilled from a Bi metal target and coupled to N‐succinimidyl‐3‐(trimethylstannyl)benzoate. The resulting N‐succinimidyl‐3‐( 211 At)astatobenzoate was thereafter coupled to aminated monosized polymer particles with a diameter of 1.8 μm. The total time elapsed from the end of the cyclotron irradiation until the final product was prepared was about 2.5 hours. From 23 to 51% of the target activity at the end of bombardment was measured in the final conjugate. Solid‐liquid extraction purification of the astatinated intermediate, using Sep‐pak columns (Waters), gave more reproducible yields in the final conjugation step. The 211 At‐labelled particles were incubated with fetal calf serum, human serum and human full blood at room temperature. The 211 At activity on the particles was measured before and after three times washing at 4, 24 and 48 hours. The stability was not significantly different from 100% for all media and for all time points. This indicates that 211At‐labelled particles can be stable under in vivo conditions, and may thereby be a promising agent for intracavitary radiotherapy on freefloating cancer cells or surface fixed cells.