Researchers have found a way to load bacteria with a cancer-killing treatment and get them to self-destruct inside a tumour, delivering the toxin.
A few surviving bacteria are left that keep growing and then self-destruct again, continuing the cycle so that cancer gets treated on a regular schedule.
The discovery was carried out by scientists from the University of California at San Diego, led by Prof Jeff Hasty.
"We welcome news of any positive therapeutic advance in the battle against cancer. Research into preventing, diagnosing and treating cancer is vital to fight this disease and eventually find a cure," Dr Robert O'Connor, head of research at the Irish Cancer Society said.
Researchers first tested the bacteria by treating cervical cancer cells in the laboratory, and saw that the cancer cells were effectively killed by the toxin.
They then gave the bacteria to mice with incurable metastatic colorectal cancer. Mice which had been treated with bacteria plus regular chemotherapy survived longer than mice treated with either chemotherapy or bacteria alone.
They also tried loading the bacteria with other agents, such as compounds that stimulate the immune system to fight against the tumour. These experiments also showed encouraging results, the scientists found, describing their findings in the journal Nature.
The scientists used genetic engineering to change the DNA of the bacteria. These changes cause them to self-destruct when they reach certain numbers. But self-destruction is not complete and a few bacteria are left alive and will continue to grow.
Once they get to large numbers again, they repeat the self-destruction mechanism and a cycle is established.
Since dead bacteria release all their contents, the scientists also loaded them with an anti-tumour toxin called haemolysin E.
Because the bacteria prefer environments with low levels of oxygen, they initially spread everywhere but end up concentrating inside the tumour. Tumours grow very fast and don’t have a good blood supply, resulting in low oxygen levels, the scientists say.
This novel therapy takes advantage of a known way used by bacteria to change their behaviour in unison when food is scarce. In this case, when bacteria grew in large numbers, they increased their levels of the anti-tumour toxin and another substance which caused them to self-destruct.
This mechanism, called quorum sensing, has been known for some time, but this is the first time it has been used to administer an anti-cancer therapy in controlled cycles.
Prestigious scientists such as Bert Vogelstein, from Johns Hopkins’ Sidney Kimmel Cancer Center in Baltimore, have hailed the work as highly innovative. They have remarked that “weaponizing bacteria” could be a new way of treating cancer in the near future.
Vanesa Martinez is on placement at The Irish Times under the BSA/SFI media fellowship programme