Optimization of radioiodination and biotinylation of monoclonal antibody chimeric BR96: an indirect labeling using N-succinimidyl-3-(tri-n-butylstannyl)benzoate conjugate.

Chimeric BR96 (chiBR96) is an oxidant sensitive, highly tumor-reactive and internalizing monoclonal antibody. Radioiodination of chiBR96 with direct labeling methods has a high risk of damaging the antibody's immunoreactivity. Combination of iodination and biotinylation of chiBR96 has been particularly difficult. In present studies, indirect radioiodine labeling by use of a conjugate of N-succinimidyl 3-(tri-n-butylstannyl)benzoate (ATE) was introduced for chiBR96 radioiodination and for combination of iodination and biotinylation of chiBR96. ATE was synthesised, radioiodinated with a modified and simplified method by omitting one step of separation. A same or slightly higher labeling efficiency was obtained comparing to earlier reports. Simultaneous biotinylation of the chiBR96 was performed by use of biotin reagent of N-hydroxysuccinimido-biotin. In a comparative study of biotinylated and unbiotinylated 125I-chiBR96 iodinated with ATE conjugate, it was found that 125I-chiBR96 with or without biotinylation had the same stability, immunoreactivity and biodistribution with a high tumor targeting capacity. Hence, the ATE conjugate radioiodination method enables the combination of iodination and simultaneous biotinylation of chiBR96.