Food poisoning bug enlisted to fight cancer
Like a beacon, modified Salmonella draws the immune system’s attention to cancerous cells.
A bacterium that causes food poisoning may be an unlikely hero in cancer treatment. Researchers, led by Jin Hai Zheng at Chonnam National University in South Korea, engineered a weak strain of Salmonella typhimurium, which causes gastroenteritis in humans, to invade cancerous colon tissue in mice and trigger an immune response.
The bacterial incursion caused the tumours to shrink, and prevented relapse, according to findings published in Science Translational Medicine. One of the most effective ways of treating a patient’s tumour is with their own immune system, says Thomas Cox, a cancer biologist at the Garvan Institute of Medical Research in Sydney, Australia, who was not involved in the study.
Cancer cells typically fly under the immune system’s radar, so researchers try to find ways to draw attention to them. Pathogenic microbes such as Salmonella strains might just be one way to do so.
As a tumour expands it can outgrow its blood supply, leaving oxygen-deprived patches. Because Salmonella thrives in low-oxygen environments, it homes in on those regions and sets up shop.
The immune system then fights the bacterial infection – tackling the tumour along with it.
The idea of enlisting bacteria to make
tumours visible to the immune system has a history going back more than a century to physician William Coley, who treated cancer patients by injecting them with bacterial toxins. In the new work the scientists genetically modified the bacterium to release a protein that rouses an immune response, making the tumours even more visible. The protein is called Flab, normally secreted from a marinedwelling bacterium related to cholera.
CANCER CELLS TYPICALLY FLY UNDER THE IMMUNE SYSTEM’S RADAR, SO RESEARCHERS TRY TO FIND WAYS TO DRAW ATTENTION TO THEM.
Just three days after dosing cancerous mice with the Flab-secreting Salmonella, the researchers noticed the bacteria invaded the oxygen-deprived cancerous tissue almost exclusively. In more than half the mice, the tumours shrank significantly.
Cox says the work, while still preliminary, is “something we’ll certainly hear a lot more about, especially given the current hot trend of immunotherapy and the successes we’ve seen with immunotherapy drugs”.