A monoclonal antibody against human β-glucuronidase for application in antibody-directed enzyme prodrug therapy

The selectivity of anticancer agents may be improved by antibody-directed enzyme prodrug therapy (ADEPT). The immunogenicity of antibody-enzyme conjugates and the low tumor to normal tissue ratio calls for the use of a human enzyme and the development of a monoclonal antibody (MAb) against that enzyme for rapid clearance of the conjugate from the circulation. We isolated β-glucuronidase from human liver. BALB/c mice were immunized with the roughly purified human liver β-glucuronidase and we obtained an MAb designated 105. Immunoblotting showed reactivity with native tetrameric human β-glucuronidase. MAb 105 neither bound to enzyme from bovine liver, rat liver, or mouse liver nor reacted with other human lysosomal enzymes. The antibody appeared to be useful to further purify human β-glucuronidase from human liver or human placenta to homogeneity by affinity chromatography. MAb 105 did not inhibit the activity of human β-glucuronidase. When human β- glucuronidase was injected iv into BALB/c mice, the newly generated MAb 105 could indeed accelerate the clearance of the enzyme with a 50% drop in its activity within 5 min.