Figure 1.

Strategies in tumor-targeting bacterial therapy. (A) Bacteria have adequate tissue penetrating ability. Anaerobic bacteria, which only colonize in areas devoid of oxygen, may actively swim away from the vasculature, penetrate deep into tumor tissue and accumulate following systematic injection (pink syringe), a property traditional chemotherapy (green syringe) does not possess. (B) Delivery of anticancer agents. Bacteria have the ability to manufacture and deliver specific materials, which may be coupled with particular anticancer agents. Engineered bacteria kill cancer cells by expressing proteins that act against tumors (e.g. cytotoxic agents, cytokines, antibodies, cytotoxins, antiangiogenic agents and enzymes that convert the nonfunctional prodrug to an active anticancer drug) and transferring eukaryotic expression vectors into infected cancer cells. (C) Bacteria in oncolytic therapy. Anaerobic bacteria swim into tumor tissue, multiply in the hypoxic/necrotic areas and directly kill tumor cells.