Food poisoning bacteria shrink tumours in mice

The bacterium commonly behind food poisoning may be an unlikely hero in cancer treatment. Researchers from South Korea, the US and China engineered a weak strain of Salmonella to invade cancerous colon tissue and release a protein to trigger an immune response in mice.

This successfully shrank tumours and prevented relapse. Their findings were published in Science Translational Medicine.

One of the most effective ways of treating a patient’s tumour is with their own immune system, Thomas Cox, a cancer biologist at the Garvan Institute of Medical Research in Sydney, Australia, and who was not involved in the study, says.

The problem is cancer cells fly under the immune system’s radar. So researchers try to find ways to draw immune attention to a tumour, such as pathogenic microbes such as Salmonella strains.

As a tumour expands it can outgrow its blood supply, leaving oxygen-deprived patches. And 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 – and the tumour.

Enlisting Salmonella to draw the body’s immune system’s attention to tumours isn’t particularly new. But Chonnam National University’s Jin Hai Zheng and colleagues took the concept a step further and hit tumours with a double blow.

They genetically modified the Salmonella typhimurium bacterium to release the protein FlaB. FlaB is normally secreted from a marine-dwelling bacterium related to cholera and also stimulates an immune response.

Just three days after the researchers infected mice with colon tumours with FlaB-secreting Salmonella, they noticed the bacteria almost solely invaded cancerous tissue. The tumours hosted 10,000 times more bacteria than vital organs.

And for more than half of the FlaB-Salmonella-treated mice, tumours shrank to be almost invisible. The mice also lived longer and the cancer didn’t spread to other parts of the body.

Cox says while it’s still in its preliminary phase, the work will likely progress to clinical trials.

“It’s 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,” he says.

This therapy has the potential to join the arsenal of cancer-fighting weapons already in place, such as chemotherapy, Cox adds.

For instance, the method could be a way to shrink a tumour before it’s safe to surgically remove it, or even eradicate tumours from surgically inaccessible areas.