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Killing Caner with Genetically modified Bacteria

Researchers employ a genetically modified bacteria to eliminate tumors in mice.

The report published in February issue of the Science Translational Medicine discloses an immunological mechanism that contributes to bacteria-driven, cancer–killing activity claiming that a genetically altered Salmonella typhimurium a gastroenteritis-causing bacteria, is an effective destroyer of mouse tumors.

The reasoning behind most bacteria-driven cancer therapies is the fact that oxygen-starved and necrotic cores of tumors are attractive environments for anaerobic bacteria such as Salmonella, Clostridium, and Listeria, and an infection can lead to tumor colonization by these bugs. By means of active multiplication, the bacteria can directly kill the cancer cells and also attract the attention of the body’s immune system (which is generally suppressed within tumors), leading to further tumor destruction.

Things are not so easy and there are safety issues in implementation for patients. In a recent trial, researchers found attenuated Salmonella bacteria to be safe, but they were unable to create a strong response. To overcome the issue researchers tried to boost the potency of the Salmonella by engineering the bacteria to overexpress a protein proven to induce a strong immune response—flagellin B. As per the new report, intravenous injections of the flagellin expressing Salmonella eliminated the experimental tumors in 55 percent of mice, which then remained healthy until the end of the four-month observation period. Without overexpression of flagellin, the tumors in the mice tended to regrow after initial shrinking by the Salmonella. 

Some scientist agrees that current study extends our understanding of bacterial-based cancer therapy at a molecular level but one of the problems with developing bacterial cancer treatments has been that “these bacteria are almost a black box.” They promote cancer destruction, but no one is exactly sure how.

Source: J.H. Zheng et al., “Two-step enhanced cancer immunotherapy with engineered Salmonella typhimurium secreting heterologous flagellin,” Science Translational Medicine, 9, eaak9537, 2017.

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