A strain of harmless bacteria that live in soil could soon be helping to kill cancer tumors, thanks to researchers from the University of Nottingham in the UK and the University of Maastricht in the Netherlands who are presenting their work at a conference in York, England, this week. They said they expect to test the strain in cancer patients in 2013, and if successful, hope the method can be combined with additional approaches to win the battle against cancer.
The bacterium is Clostridium sporogenes, which is widespread in soil. Injected into cancer patients, the bacterium grows in solid tumors and releases an enzyme which triggers a separately injected "pro-drug" to kill cancer cells.
The anti-cancer drug only becomes active when it meets the bacterial enzyme in the tumor and therfore only targets cells nearby.
To take the experimental therapy from the lab stage to be ready for clinical trials, the researchers had to carry out a number of improvements.
One improvement was to insert a gene into the bacterium's DNA that made it produce greater quantities of the trigger enzyme in the tumor. This also improved the enzyme's ability to convert the "pro-drug" into its active form.
But what is it about this bacterium that makes it especially suitable for cancer therapy? The clue lies in the question: how come healthy cells aren't affected? This is an important question for clinical trials: researchers have to show that their candidate therapy will leave healthy cells alone.
The leader of this research is Nigel Minton, Professor of Applied Molecular Microbiology at Nottingham, who set up the Clostridia Research Group (CRG) there in 2004. He explained to the press the reason Clostridium sporogenes makes a good candidate for this type of therapy is because it is an ancient organism that evolved on Earth before it had an oxygen-rich atmosphere, so it only thrives in environments low in oxygen:
"When Clostridia spores are injected into a cancer patient, they will only grow in oxygen-depleted environments, ie the centre of solid tumors. This is a totally natural phenomenon, which requires no fundamental alterations and is exquisitely specific. We can exploit this specificity to kill tumor cells but leave healthy tissue unscathed," said Minton.
The hope is that C. sporogenes will eventually prove to be a simple and safe way to cure a wide range of solid tumors.
Minton said their therapy will kill "all types of tumor cell". He said it was better than surgery, especially for patients at high risk or who have tumors that are difficult to reach.
"We anticipate that the strain we have developed will be used in a clinical trial in 2013 led by Jan Theys and Philippe Lambin at the University of Maastricht in The Netherlands," added Minton, who anticipates if the trial is successful, the therapy will become a frontline treatment for solid tumors.