How a bacterium from our mouth accelerates the progression of colon cancers

New players are emerging from the shadows on the cancerology battlefields. This microscopic army has a major surprise in store: it does not have a human identity, even though the conflict which opposes the offensives of evil to the defenses of the organism is played out in our flesh. This treacherous army, in fact, recruits battalions of bacteria that work furtively, lurking in the tumors where they have sneaked.

An American team reveals its fatal secrets in two studies, published in journals Cell Reports November 15 and Nature the day after. The authors, from the Fred Hutchinson Cancer Center in Seattle, looked at a bacterium naturally present in our oral cavity, Fusobacterium nucleatum. “It is found in everyone’s dental plaque”says Professor Laurence Zitvogel, oncologist at the Gustave-Roussy Institute, in Villejuif.

F.nucleatum is one of the most abundant bacteria found in oral and colon cancers. The authors show that within the same tumour, it takes refuge in micro-niches. There, it boosts the migration capacities of infected cancer cells. From then on, these become more apt to sow metastases – dragging the microbe with them. Another wrongdoing, F.nucleatum thwarts the action of “killer lymphocytes”, these soldiers of anti-cancer immunity. For this, she recruits allies, traitors to their homeland: human macrophages and neutrophils. By infecting this other category of immune cells, it perverts them. These renegades then block the rise to the front of killer lymphocytes.

The role of the microbiota

The authors also show that a chemotherapy frequently used against colon cancer, 5-fluorouracil (5-FU), not only destroys cancer cells, but also F. nucleatum. On the other hand, this chemotherapy is powerless to kill another bacterium which infiltrates these cancers, Escherichia coli. As a result, it will protect cancer cells against 5-FU. These bacteria form a ” conspiracy “according to Laurence Zitvogel, which act in synergy.

“Intratumoral microbes are not innocent bystanders as the disease progresses, underlines one of the authors, Christopher Johnston. The microbiota should be considered when thinking about optimal cancer treatments. » The study also highlights possible links between oral health and cancer risk.

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