Effect of chemical modification strategy on the characteristics of copper-67-Labeled immunoconjugates, Part I: Immunoreactivity

Abstract

The synthetic porphyrins N-benzyl-5,10,15,20-tetrakis(4-car-boxypheny1)porphine (N-bzHTCPP) and N-4-nitrobenzyl-5-(4carboxyphenyl)-l0,15,20-tris(4-sulfophenyl)porphine (NbzHCS3P) represent excellent radiocopper chelating agents that may find utility in antibody-mediated diagnosis and/or therapy. Detailed analyses were performed to explore the effect of the chemical modification strategy on the characteristics of immunoconjugates prepared from the anti-renal cell carcinoma monoclonal antibody A6H and N-bzHCS3P. The parameters included in the study were antibody type [intact A6H and two of its fragments, half A6H and A6H-F(ab')2], chemical linkage type and site, the presence or absence of intermediate linker molecules, and the nature of the chemical modification steps employed. The immunoconjugate synthesized by directly coupling N-bzHCS3P to whole antibody retained 7545% of the immunoreactivity of the unmodified antibody. In general, however, immunoconjugates prepared using the fragments or the intermediate linkers lacked immunoreactivity. This deficiency appeared to be a function of the multistep processes employed and not a function of the linker molecule. The