Anthrax to fight cancer?

Anthrax can be disabled and turned into a cancer-fighting weapon that shows real promise against some types of the disease, scientists have announced.

Researchers led by Shihui Liu and Hannah Aaronson at the US National Institutes of Health in Bethesda, Maryland, said the anthrax bacteria -- often considered a biological weapon -- can be turned from a military killer into a potential cure. Their paper is published in the journal Proceedings of the National Academy of Science.

In it, the authors describe how a modified form of anthrax, injected into mice, killed three types of tumours with no apparent toxic effects on other tissue. After only one treatment, the toxin reduced the size of tumours in the mice by between 65 and 92 per cent.

Two treatments completely abolished 88 per cent of fibrosarcomas, or malignant tumours, and 17 per cent of melanomas (skin and peripheral organ tumours). The anthrax was so lethal, tumour cells began dying just 12 hours after treatment first began.

Normally, the toxin produced by a bacterium, Bacillus anthracis, is activated when it comes into contact with furin, an enzyme found in all living cells.

To render it safe, the scientists genetically engineered the furin activation sequence out of the toxin, and replaced it with an artificial peptide sequence that is activated by urokinase. This is a protein found in very high levels in human tumour cells, making it an ideal target for cancer treatment.

Based on the results so far, researchers say that melanoma, colon and breast tumours would be the most susceptible cancers to the anthrax toxin. The team found that the toxin did not damage skin cells or hair follicles surrounding the tumour, suggesting the treatment may not have the same severe side effects as current cancer therapies.

However, given the potent toxic effects of anthrax, it will be several years before any treatment involving the toxin is likely for human trials.

Professor Richard Kefford, a cancer specialist with Sydney's Westmead Hospital, was interested in the results but not overly excited, saying it's far easier to cure cancer in mice than humans. "We've seen it many times with different treatments -- curing cancer in mice is a snap, but regrettably, when you get into humans, it's a lot more complicated."

Kefford said other anti-cancer agents had proved problematic, such as the Onyx virus which targets cells with a mutation in the p53 gene, a gene commonly found in cancer cells.

"There are lots of problems and the treatment can have all sorts of unforeseen side effects on non-specific targets [such as other tissues]," he said. "But having said this, it's still a very interesting new aspect of a potential therapeutic agent."

Courtesy: ABC Science Online

Published on 27th January 2003

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