Effect of chemical modification strategy on the characteristics of copper-67-labeled immunoconjugates .1. Immunoreactivity

The synthetic porphyrins N-benzyl-5,10,15,20-tetrakis(4-carboxyphenyl)porphine (N-bzHTCPP) and N-4-nitrobenzyl-5-(4-carboxyphenyl)-10,15,20-tris(4-sulfophenyl)porphine (NbzHCS(3)P) 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-bzHCS(3)P. 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-bzHCS(3)P to whole antibody retained 75-85% 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 tinker molecule. The results emphasize the critical importance of the type and number of antibody modification steps and the caution that must be exercised in the design of immunoconjugates for drug delivery purposes.