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Cancer killer New Scientist14 mar 98

A hormone in soya beans starves tumour cells to death

BIOCHEMISTS in the US have worked out how a key ingredient in soya beans thwarts cancer. Thev have shown that genistein, a plant oestrogen, plays a pivotal role in suppressing the growth of cancerous cells. Asian diets high in soya have been linked with low incidence of cancers, particularly breast, colon and prostate cancers. This link has been reinforced by evidence that when Asians migrate to the US and abandon the high-soya diet, their risk of developing these cancers increases. Amy Lee of the University of Southern California in Los Angeles has discovered that genistein is a key factor in this. It works by weakenin- cancer cells' response to the stresses that usually impel them to grow faster. "When a cancer cell is growing at full blast, the cells soon run out of oxygen and glucose that are normally supplied in blood," savs Lee. To compensate, they send out a chemical SOS which triggers formation of new vessels to nourish the tumour, a process called angiogenesis.

In earlier experiments on tissue cultures, Lee and others proved that genistein can blunt the response of cancer cells to stress. Now, they know the exact mechanism. She and her colleague Yanhong Zhou have shown that genistein blocks the action of a transcription factor known as CCAAT binding factor. This protein normally binds to an important genetic "motif" in DNA and triggers the stress genes. Genistein adds phosphorus to the binding factor, neutral- ising it before the snvitch is tripped, so the cancer cell starves, withers and dies (journal of the National Cancer Institute, vol 90, p 381). "This is preliminary evidence, but genis- tein really stands out as the ingredient that's most active in stopping cancer growth and angiogenesis," says Lee. Crucially, the researchers found that genistein has no effect on normal, healthy cells which are not dividing rapidly like cancer cells. "It doesn't shut off the normal synthesis of this protein in healthy cells," says Lee. Andy Coghlan

Your very good health New Scientist 21 Mar 98

REGULARLY downing a few pints at your local might make you less likely to get cancer, says a team of scientists in the US. They have shown that beer contains substances that can halt tumour gmwth and help destroy the toxins that cause cancer. The discovery could lead to the development of anticancer drugs with fewer unpleasant side effects. Donald Buhler and Cristobal Miranda of Oregon State University in Corvallis and their colleagues tested nine compounds called flavonoids isolated fmm hops. These bitter-tasting chemicals give beer its distinctive taste. The researchers told the annual meeting of the Society of Toxicology in Seattle earlier this month that some of the flavonoid compounds slowed the growth of human breast and ovarian cancer cells by 50 per cent. Two of the compounds also led to a fourfold boost in production of a detoxifying enzyme called quinone reductase in mouse liver cells. This protein helps rid the body of carcinogens. The results fit in with the suaestion that flavonoids in soya beans am partly responsible for the low incidence of breast cancer in Asia (This Week, 14 March, p 14). Exactly how much beer you have to drink to benefit from its cancer-preventing qualities is not clear. But Miranda says it was encouraging that when isolated, the flavonoids slowed the growth of cancer cells at doses unlikely to have any significant toxic effect. He believes the finding may lead to anticancer drugs with fewer side effects than current treatments. "The ultimate aim is to produce refined versions of some af these chemicals that might be given with existing cancer treatments," he says. Michael Day