Preparation and characterization of copper-67 porphyrin-antibody conjugates

Methods were developed to label antibodies with copper-67, a potentially useful medical radioisotope, using the porphyrin chelating agent N-benzyl-5,10,15,20-tetrakis(4-carboxyphenyl) porphine. The porphyrin was activated for coupling using either (1) 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide HCl and N-hydroxysuccinimide or (2) 1,1'-carbonyldiimidazole. The coupling reactions were optimized as a function of activation time, coupling time, coupling pH, and reagent concentrations to achieve maximum coupling to IgG monomer. Sodium dodecylsulfate polyacrylamide gel electrophoresis was used to determine coupling yields. After purification by gel filtration, the antibody-porphyrin conjugates were labeled with copper-67 in aqueous solution. The coupling protocols were used to label antibodies from several species, demonstrating the general utility of these methods. Characterization of the conjugates indicated that the porphyrin label was attached randomly to the IgG molecule. Antigen binding capacities after conjugation were unaltered or slightly lowered as determined by a competitive ELISA.