The idea is to selectively attack these tumours from inside with the bacteria and from the outside with chemotherapy

Dr Bert Vogelstein

However, a team from the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University in Baltimore has found a way to exploit these harsh conditions.

They have done this by attacking the tumour with bacteria that actually thrive in an oxygen-starved environment.

Researcher Dr Bert Vogelstein said: "The idea is to selectively attack these tumours from inside with the bacteria and from the outside with chemotherapy."

Screening

The scientists systematically screened numerous bacterial species to find one that would thrive in an oxygen-poor environment and, at the same time, destroy surrounding tumour cells.

They settled on one spore-forming bacterial species, called Clostridium novyi (C.novyi).

C.novyi is normally found in soil and dust and contains a toxin that can cause lethal side effects in animals.

The scientists genetically modified the bacteria to remove the toxin gene to make them harmless to normal animals.

Then, they injected spores of these bacteria and conventional chemotherapeutic agents into mice with large tumours composed of transplanted human colon cancer cells.

The results achieved with this strategy were dramatic.

More than half of the tumours treated, including very large tumours, were completely destroyed within 24 hours.

Decomposed

Further research will show whether this particular technique can be taken out of the laboratory and into the patient

Nicola Hawe

The tumours decomposed and turned into blackened scars, while the surrounding healthy tissues remained intact.

The tumour scars then gradually disappeared over the next two weeks, leaving healthy tissue behind.

Clinical trials are not planned at this time as it will take several years to determine which chemotherapy agents make the best combinations and to develop strategies to avoid the toxicity associated with rapid destruction of large tumour masses.

Researcher Professor Kenneth Kinzler said: "We hope that this research will add a new dimension to cancer treatment, but realise that the way tumours respond to treatment in mice can be different than in humans."

Major limit

Nicola Hawe, science information manager for the Cancer Research Campaign, said: "Drug resistance and a lack of tumour selectivity are a major limit to the success of current therapies for common cancers.

"Targeted treatments have the potential to overcome these problems. The ability to deliver a concentrated toxic insult directly to the tumour will in the future produce better treatments and could help reduce side effects.

"Targeting treatments is a major priority for cancer researchers and Professor Vogelstein's work is opening up more possibilities in this field.

"Further research will show whether this particular technique can be taken out of the laboratory and into the patient."

Professor Nick Lemoine, of the Imperial Cancer Research Fund, said the strategy of exploiting biological agents to target cancer cells was "very exciting".

His team, based at London's Hammersmith Hospital plan to treat cancer patients next year with a modified strain of the Salmonella bacterium.

"Early evidence suggests that there may be an enhancement of the effect when combined with standard chemotherapy drugs."

The research is published in Proceedings of the National Academy of Sciences.