Tests on the drug, derived from the bark of the African bush willow, have shown that it attacks the blood supply to the cancer instead of the cancer cells themselves. A single dose can kill up to 95 per cent of solid tumour cells by starving them of their blood supply.
Dr Dai Chaplin, who led the research at the Cancer Research Campaign's Gray laboratories at Mount Vernon Hospital, Middlesex, said the drug's new type of action could have wide application. "As more than 90 per cent of cancers are solid tumours or lumps, we are very excited about its potential. It opens the door for the development of other drugs working on the same principle. Cancer is a war and we are opening up a new battlefront."
Announcing the findings at a press conference to mark National Cancer Day today, Professor Gordon McVie, director of the campaign, said cancer research had come full circle with a renewed interest in natural compounds after the fashionable swing away from them in the Seventies in favour of designer molecules dreamed up in the laboratory.
Professor Alan McGown of the Paterson Institute at the Christie hospital in Manchester, which is testing the anti-cancer properties of a range of natural compounds, said: "These are big complicated molecules - too big for a chemist to sit down and say `I am going to design that.' They would never have been discovered if we had not looked at nature. The world's greatest chemist of all time is nature."
Dr Chaplin said that most cancer treatments were targeted at killing the cancer cells. One centimetre of tumour can contain hundreds of millions of cells, making it a slow process requiring high doses of toxic drugs.
The new drug, combretastatin, destroys endothelial cells lining the blood vessels which supply the tumour. In laboratory studies, Dr Chaplin found that damaging one of these endothelial cells killed more than 1,000 tumour cells. The findings, published in the US journal, Cancer Research, showed only small doses were required reducing side-effects.
Dr Chaplin said: "The response can be dramatic. In some tumours it shuts down the blood supply in two hours. We may have a new class of drugs here. It is a great start."
Human trials could begin within 18 months. Dr Chaplin admitted there were many tests of safety and efficacy to be done before it could used on patients. The drug acts selectively, for reasons that are not understood, only targeting blood vessels in the tumour leaving others elsewhere in the body unaffected. It is not known, however, whether it will hinder the growth of blood vessels in other parts of the body, for example during wound healing or in the reproductive tract during ovulation and pregnancy.
Dr Chaplin also said that the drug killed the centre of the tumour but left the rim unaffected, and would therefore need to be used in conjunction with conventional radiotherapy or chemotherapy.
Combretastatin was discovered 10 years ago by Professor Bob Pettit of the Arizona State University in the US. Professor Pettit, who sits on the Cancer Research Campaign's drug committee, mentioned it to Dr Chaplin who decided to investigate its anti-cancer properties.
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