Comparison of two methods of labeling proteins with 111In

DTPA N-hydroxysuccinimide pentaester (DHSE) can be used as an alternative to bicyclic anhydride for coupling proteins with DTPA. However, in-vitro analysis of labeled proteins coupled with DHSE compared to bicyclic anhydride showed more high molecular weight product and less serum stability. We studied the magnitude of these differences in vivo by coupling HSA and IgG with DTPA using both methods, labeling with 111In, and analyzing the biodistribution in mice. The results of this analysis showed comparable activity in the liver, kidneys and blood.