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Antibiotics which kill useful bugs are giving cancer patients a kick in the guts

Friday, November 3rd, 2017

Antibiotics may be impeding our ability to fight cancer, two new studies on gut bacteria suggest.

Bacteria-killing pills such as penicillin already get a bad rap for leading to the rise of the drug-resistant superbugs that create havoc in our hospitals.

Now, two studies suggest they also strip our gut of the healthy bacteria needed to help combat cancer.

The new research might soon lead to doctors prescribing probiotics – or even faecal transplants – before starting a dose of chemotherapy.

What remains unclear is which bacteria out of the millions living inside us are responsible for helping to fight cancer. Each study identified a different bug as being the most important.

Microbiota are the tiny bacterial organisms that live in our gut. The community of these bacteria is called the microbiome.

“This research may be applied by developing strategies to change the microbiome to enhance responses to cancer treatment,” says the University of Texas’ Dr Jennifer Wargo, a co-author of one of the papers.

“But we aren’t yet sure what the right formulations are, so we really need to use caution, as some approaches may not help and could potentially even adversely affect the microbiome.”

The two new studies, published on Friday in the journal Science, looked at the impact of microbiota on immunotherapy, a form of chemotherapy that uses the body’s own immune system to fight cancer.

Immunotherapy is “one of the great hopes for cancer therapy”, says Professor Matthew Brown, director of genomics at the Queensland University of Technology.

Professor Brown is an expert on both the microbiome and immunotherapy, and was not involved in the study.

A large number of patients don’t respond to immunotherapy and researchers have been struggling to discover why.

For the first study, French researchers looked at 249 cancer patients receiving immunotherapy. Of those, 69 had been prescribed broad-spectrum antibiotics at the same time to treat other infections.

Cancer survival rates were significantly lower for patients who had been treated with antibiotics, the researchers found. Analysis of their gut microbiota showed they had a much lower diversity of gut bacteria, presumably caused by the antibiotics.

To cross-check the results, the researchers gave cancerous mice an antibiotic followed by a dose of immunotherapy. They too had failed to respond to the treatment.

The researchers then gave them microbiota transplants from the patients who did best on immunotherapy. The mice immediately began to respond strongly to the treatment.

“That’s something that should translate rapidly into changes in protocols to minimise antibiotic use before or after immunotherapy. That was really quite a strong finding,” said Professor Brown.

In the second study, a team of researchers in America and France reported on 112 melanoma patients undergoing immunotherapy.

The patients who responded the best to treatment tended to have a much higher diversity of microbes in their gut.

The microbiome of the group that performed well seemed to be building a lot of amino acids – known to promote immunity – while the microbiome of the other patients focussed more on breaking down compounds.

In fact, the researchers found, the abundance of a single bug, Faecalibacterium, in a patient’s gut was one of the strongest predictors of whether immunotherapy was successful or not.

However, the other study singled out Akkermansia muciniphila as the bug linked to immunotherapy success.

Dr Wargo said gut bacteria was likely influencing the immune system in a number of ways, including producing chemicals that interacted with and stimulated immune cells.

“But we don’t know all the answers yet and there is still a great deal to learn,” she said.

Henry Sapiecha