Enzyme immunoconjugates utilizing glucose oxidase and myeloperoxidase are cytotoxic to Candida tropicalis

A dual-enzyme immunoconjugate system was evaluated for its cytotoxic effect on Candida tropicalis. Glucose oxidase, which generates hydrogen peroxide in the presence of glucose and oxygen and myeloperoxidase, which catalyzes the oxidation of halides in the presence of hydrogen peroxide, were each conjugated to a C. tropicalis-specific monoclonal antibody. Neither the glucose oxidase nor the myeloperoxidase conjugates exhibited any significant cytotoxic effect by themselves. A combination of glucose oxidase conjugate (3.2 ng/ml) and myeloperoxidase conjugate (12.8 ng/ml) in the presence of 5 mg of glucose per ml, 150 mM chloride, and 50 microM iodide was cytotoxic to C. tropicalis, killing 99.9% of the treated sample. Flow cytometry was used to characterize the binding of the conjugates to yeast cells and demonstrated that the binding of both conjugates to the yeast cell surface is required for cytotoxicity. In addition, the concentrations of conjugates required for a cytotoxic effect were below the concentrations required to saturate all of the yeast cell surface antibody-binding sites.