Simplified method for conjugating macrocyclic bifunctional chelating agents to antibodies via 2-iminothiolane.

A one-step method for conjugating macrocyclic chelators to antibodies using the protein modification reagent 2-iminothiolane controls aggregation, maintains immunoreactivity, and produces consistent chelate/antibody ratios. Conjugation conditions have been investigated with the macrocyclic chelates 6-[p-(bromoacetamido)benzyl]-1,4,8,11-tetraazacyclotetradecane-N,N ',N",N"'-tetraacetic acid and 2-[p-(bromoacetamido)benzyl]-1,4,7,10-tetraazacyclododecane-N,N',N ",N"'-tetraacetic acid, with three different monoclonal antibodies. The bifunctional chelating agents are prepared by bromoacetylation of their amine precursors using a two-phase H2O/CHCl3 system, which improves product purity.