An international team of researchers has discovered that certain bacteria in pancreatic tumors have the potential to break down gemcitabine, a common chemotherapy drug. The team believes this could be one of the many reasons why chemo sometimes fails.

The study, published in Science, focused on a class of microbes known as Gammaproteobacteria and looked at how an enzyme they produce can neutralize the chemo drug. They think that using antibiotics in conjunction with cancer-fighting drugs might help treat tumors more effectively.

“Because the topic is so new, we first used different methods to prove that there really were bacteria inside the tumors. Then we decided to look at the effect that these bacteria might have on chemotherapy,” study author Dr Ravid Straussman, of the Weizmann Institute in Israel, said in a statement.

The researchers examined more than 100 human pancreatic tumors and discovered that bacteria with a long form of the cytidine deaminase (CDD) gene live both around and inside cancer cells. They also found that the long CDD gene was key to making gemcitabine ineffective. The team carefully ensured that the bacteria were actually from the tumors rather than external contamination.

Funnily enough, external contamination is what started the research. The team was studying chemotherapy resistance but they were looking to see if healthy neighboring cells might be unwittingly helping the tumor grow. They discovered that skin cells seemed to be making pancreatic cancer cells impervious to the drug.

When the researchers looked for the more minute cause of this resistance they discovered that the skin cells were contaminated. “We nearly threw it away,” said Straussman, “but then we decided to follow it up, instead.”

The next step was to identify how these bacteria were capable of stopping the drug from working.

The scientists conducted experiments using mice with cancer. The tumor cells of half the mice were infected with bacteria that had the CDD gene, whilst the other half were exposed to bacteria that didn't have the gene. Only the first group showed resistance to the chemotherapy drug but when treated with antibiotics, the mice responded to the chemotherapy as hoped.

This is a very early study and many questions still remain. The team is now interested in finding out whether bacteria inhabit different types of cancer and if so, how they effect chemotherapy resistance.