Application of genetically engineered Salmonella typhimurium for interferon-gamma–induced therapy against melanoma

Salmonella have been experimentally used as anti-cancer agents, because they show selective growth in tumours. In this study, we genetically modified attenuated Salmonella typhimurium to express and secrete interferon-gamma (IFN-γ) as a tumouricidal agent to enhance the therapeutic efficacy of Salmonella. IFN-γ was fused to the N-terminal region (residues 1–160) of SipB (SipB160) for secretion from bacterial cells. Attenuated S. typhimurium expressing recombinant IFN-γ (S. typhimurium (IFN-γ)) invaded the melanoma cells and induced cytotoxicity. Subcutaneous administration of S. typhimurium (IFN-γ) also efficiently inhibited tumour growth and prolonged the survival of C57BL/6 mice bearing B16F10 melanoma compared with administration of phosphate-buffered saline (PBS), unmodified S. typhimurium or S. typhimurium expressing empty vector (S. typhimurium [Vec]) in a natural killer (NK) cell-dependent manner. Moreover, genetically modified Salmonella, including S. typhimurium (IFN-γ), showed little toxicity to normal tissues with no observable adverse effects. However, S. typhimurium (IFN-γ)-mediated tumour suppression was attributed to direct killing of tumour cells rather than to stable anti-tumour immunity. Collectively, these results suggest that tumour-targeted therapy using S. typhimurium (IFN-γ) has potential for melanoma treatment.