Functional activation of antibodies on modification with Pd(II) coproporphyrin I N-Hydroxysuccinimide ester

Metalloporphyrin-antibody conjugates provide a significant advantage over other types of conjugates in biomedical use for phosphorescence immunoassay, targeted immunotherapy, and internal imaging of malignant tumors. Monoclonal HSF102 antibody of mouse IgG2a subclass and monospecific rabbit IgG, both antibodies directed to human spleen ferritin, were modified with the new reagent Pd(II) coproporphyrin I tetra-N-hydroxysuccinimide ester. Functional study of the conjugates obtained revealed a 7- and 1.4-fold increase in the antigen binding activity for monoclonal HSF102 and monospecific IgG antibodies, respectively. For rabbit monospecific IgG, a concomitant increase in binding to anti-rabbit IgG antibodies directed to the epitopes of the CH2 domain in the Fc fragment was observed. In all cases, the maximum functional activation was found after conjugating one mole porphyrin per mole antibody. These results suggest that functional activation of the conjugates might be due to an increase in conformational flexibility of an antibody molecule after the modification. This increase in flexibility involves the Fab fragments and a pair of the CH2 domains in the Fc fragment and might be due to a significant charge shift (minus 5 charge units per modified amino group) that occurs after conjugation of an antibody with tetracarboxylic porphyrin.