Plasmid-transformed Bifidobacterium longum 105A secreting β-glucuronidase for prodrug conversion of SN-38 glucuronide.

The development of tumor-selective prodrug activation strategies remains a major challenge in cancer pharmacotherapy. In this study, we focused on SN-38 glucuronide (SN-38G), a highly hydrophilic prodrug with low membrane permeability that remains pharmacologically inactive unless hydrolyzed by β-glucuronidase. To enable localized activation of SN-38G within tumors, we engineered a recombinant Bifidobacterium longum 105A strain capable of secreting β-glucuronidase. The enzyme was efficiently secreted under anaerobic conditions and retained stable catalytic activity in mildly acidic and hypoxic environments that resemble the tumor microenvironment. In an MTT assay using CT26 colon carcinoma cells, co-treatment with β-glucuronidase and SN-38G induced marked growth inhibition, whereas SN-38G alone showed no cytotoxic effect. Furthermore, HPLC analysis of culture supernatants confirmed enzymatic conversion of SN-38G into the active metabolite SN-38. Together, these results provide a proof-of-concept for a microbial-enhanced prodrug activation approach in which plasmid-driven expression in Bifidobacterium longum 105A enables targeted release of SN-38. This strategy may contribute to the development of tumor-localized drug production systems capable of selectively activating diverse anticancer prodrugs with distinct mechanisms of action.