Multifunctional porous microspheres encapsulating oncolytic bacterial spores and their potential for cancer immunotherapy.

Clostridium novyi -NT ( C. novyi -NT) is an anaerobic bacterium that can be used for targeted cancer therapy because it germinates selectively in the hypoxic regions of tumor tissues. However, systemic administration of C. novyi -NT spores cannot effectively treat tumors because of the limited intratumoral delivery of active spores. In this study, we demonstrated that multifunctional porous microspheres (MPMs) containing C. novyi -NT spores have the potential for image-guided local tumor therapy. The MPMs can be repositioned under an external magnetic field, enabling precise tumor targeting and retention. Polylactic acid-based MPMs were prepared using the oil-in-water emulsion technique and then coated with a cationic polyethyleneimine polymer prior to loading with negatively charged C. novyi -NT spores. The C. novyi -NT spores delivered by MPMs were released and germinated in a simulated tumor microenvironment, effectively secreting proteins cytotoxic to tumor cells. In addition, the germinated C. novyi -NT induced immunogenic death of the tumor cells and M1 polarization of macrophages. These results indicate that MPMs encapsulated with C. novyi -NT spores have great potential for image-guided cancer immunotherapy.