Injected bacteria could provide a potent new weapon against inoperable hard-to-treat cancers, new research suggests. Scientists have resurrected an idea from more than a century ago to turn bugs into "biosurgeons" that can target and destroy deadly tumours. The radical approach has already shown astounding results in pet dogs that were being treated for naturally-occurring tumours, completely eradicating the cancer in three animals.
In a pilot clinical trial, it also significantly reduced the size of a tumour in one human patient. Work investigating whether the treatment is suitable for humans is still going on. The bacterium used is a modified de-toxified version of the soil bug Clostridium novyi-NT which can cause tissue-damaging infections in cattle, sheep and humans. Because the microbe thrives only in oxygen-poor environments, it is able to target the oxygen-starved hearts of aggressive tumours.
US lead scientist Dr Saurabh Saha, from BioMed Valley Discoveries, a Kansas-based biotech company that specialises in unusual medical advances, said: "We have encouraging signs that this bacteria could be used to treat certain inoperable tumours, and that could give hope to some patients who don't have any other options."
Solid tumour cancers become especially dangerous when they alter their metabolism to survive in the absence of oxygen. They then become resistant to radiotherapy and anti-cancer drugs, and are more likely to spread, or metastasise, around the body. This can occur when a tumour outgrows its blood supply, leading to "hypoxia" - or oxygen starvation - in its inner regions.
The idea of using bacteria to combat cancer dates back to the 1890s when American researcher William Coley noticed that some cancer patients with post-surgical infections went into remission or were even cured. The medical establishment remained unconvinced by the approach, which was largely overshadowed by new developments in radiotherapy.
Over a decade ago the potential of bacterial cancer treatment was explored again, using C. novyi. Scientists experimented with "infecting" the blood of animals, but the results were not encouraging. For the new research Dr Saha's team instead injected the bacterial spores directly into tumours, on the basis that not enough of them were reaching their target via the bloodstream.
Of 16 pet dogs volunteered by their owners for the trial, six demonstrated an anti-tumour response after 21 days. Tumours were wiped out completely in three of the six, while in the others they shrank by at least 30%, the researchers reported in the journal Science Translational Medicine. Next, a preliminary Phase I trial was set up to study the treatment in humans. The first patient recruited was a 53-year-old woman with an aggressive abdominal cancer that had spread to her liver, lungs, upper arm and shoulder despite multiple cycles of chemo and radiotherapy.
A total of 10,000 bacterial spores were injected into a tumour growing in her right shoulder and within days the bugs were infiltrating and destroying the cancer cells. Weeks later a magnetic resonance imaging (MRI) scan showed that a significant amount of the tumour had gone. As a result, the pain in the patient's shoulder subsided and she was able to move her arm again.
Previous studies have suggested that as well as directly attacking tumours, the bacteria also trigger a powerful localised immune response against the cancer. "The hope is that C. novyi-NT will be a useful adjuvant (addition) to the new immune checkpoint inhibitors that can block the ability of tumours to evade a host mediated immune response," said Dr Saha. "It will be interesting to see if a combination of the two approaches could destroy tumours not just at the injection site, but also at any other sites where the cancer may have spread to throughout the body."
One downside of the treatment is that it produces side-effects associated with infection, including fever, abscesses and inflammation. Dr Saha stressed that the team was still awaiting the results of early clinical trials involving other patients. "We are still in the early stages, and need to further assess the safety and efficacy of the treatment, as well as explore how well it works in combination with other cancer therapies," he said.