Modification of physico-chemical and biopharmaceutical properties of superoxide dismutase by conjugation to the copolymer of divinyl ether and maleic anhydride

The co-polymer of divinyl ether and maleic anhydride (MW 30 000) was covalently conjugated to superoxide dismutase in the presence of the protecting agent 2,3-dimethylmaleic anhydride as previously reported in this journal (T. Hirano et al., Synthesis of the conjugate of superoxide dismutase with the copolymer of divinyl ether and maleic anhydride retaining enzymatic activity, J. Control. Release 28 (1994) 203-209). The polymer-enzyme conjugate obtained has been now characterised with respect to its physico-chemical, structural, pharmacokinetic and biological properties. Polymer conjugation was found not to modify the protein structure as revealed by circular dichroism measurements but did enhance the thermal stability of the enzyme. On the other hand, covalent coupling of the polymer on the protein surface was found to decrease the reversible capability of exchanging the metal co-factor Cu2+ of superoxide dismutase. The pharmacokinetic profile of the conjugate after intravenous administration in rats indicated that the conjugate presented a rapid distribution phase, while the elimination rate was significantly delayed with respect to the native form. Immunoprecipitation studies were performed by using anti-superoxide dismutase serum, which was enriched with polyclonal antibodies. Decreased antigenicity of the polymer conjugate with respect to the native form was observed.