Extracellular beta-glucuronidase for gene-directed enzyme-prodrug therapy.

Abstract

AbstractMost enzymes used for antibody-directed enzyme-prodrug therapy (ADEPT) and gene-directed enzyme-prodrug therapy (GDEPT) are of bacterial, yeast, or viral origin. These xenogeneic proteins can induce an immune response, which might be a hindrance to their application of these enzymes in humans (1). On the other hand, when choosing a human enzyme for prodrug conversion cleavage by the respective endogenuous enzyme obviously needs to be avoided. Lysosomal enzymes seem to be particularly suitable candidates, because under normal circumstances, the endogenous enzymes are restricted to intracellular vesicles and therefore not available for premature prodrug conversion. In addition, lysosomal enzymes leaking out of cells are rapidly internalized via the mannose-6-phosphate (M6P) receptor expressed on the surface of most cells and at particulary high levels on reticuloendothelial cells (2,3). The human lysosomal enzyme β-glucuronidase has been used for ADEPT (4–8) and GDEPT (9,10). This exoglycosidase removes terminal β-glucuronic acids from glycosami-noglycans and other glycoconjugates. The enzyme is highly specific for the glucuronyl residue but has little specificity for the conjugated aglycone. Therefore, different drugs could be developed as prodrugs (see Table 1). Elevated β-glucuronidase levels in tumor tissue have been reported, released from dying tumor cells and invading macrophages and neutrophils (18,19,36,37). β-Glucuronides of different drugs might be exploited for tumor-specific conversion by released endogenous enzymes (“monotherapy”) as well as for ADEPT and GDEPT approaches. Table 1 Glucuronidated Prodrugs Developed for Monotherapy, ADEPT, and GDEPT Full size table KeywordsSodium Acetate BufferLysosomal Storage DiseaseFreeze Tissue SectionGene Therapeutic ApproachSaponin ExtractionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.