Bacteria in cancer therapy: A new generation of weapons

Abstract

Tumors are presently a major threat to human life and health. Malignant tumors are conventionally treated through radiotherapy and chemotherapy. However, traditional therapies yield unsatisfactory results due to high toxicity to the normal cells, inability to treat deep tumor tissues, and the possibility of inducing drug resistance in the tumor cells. This has caused immunotherapy to emerge as an effective and alternate treatment strategy. To overcome the limitations of the conventional treatments as well as to avert the risk of various drug resistance and cytotoxicity, bacterial anti-tumor immunotherapy has raised the interest of researchers. This therapeutic strategy employs bacteria to specifically target and colonize the tumor tissues with preferential accumulation and proliferation. Such bacterial accumulation initiates a series of anti-tumor immune responses, effectively eliminating the tumor cells. This immunotherapy can use the bacteria alone or concomitantly with the other methods. For example, the bacteria can deliver the anti-cancer effect mediators by regulating the expression of the bacterial genes or by synthesizing the bioengineered bacterial complexes. This review will discuss the mechanism of utilizing bacteria in treating tumors, especially in terms of immune mechanisms. This could help in better integrating the bacterial method with other treatment options, thereby, providing a more effective, reliable, and unique treatment therapy for tumors.

Keywords: bacteria-mediated cancer therapy; cancer therapy; immunity; tumor.

FIGURE 1

Bacteria have been shown to inhibit tumor growth through different mechanisms. Bacteria localize to the tumor microenvironment. Interactions between bacteria, cancer cells, and the surrounding microenvironment lead to various changes in tumor‐infiltrating immune cells, cytokines, and chemokines that further promote tumor regression. Different bacteria participate in the immune system in different ways, due to their different structures, they activate specific toll‐like receptor (TLR) family members to elicit distinct innate immune‐signaling cascades that ultimately translate to a comprehensive immune signature unique to each bacterial organism