Health

Dirt against Cancer

Yew growth dirt, rich in medicine chemicals

By Stefan Anitei, Science Editor

25th of April 2007, 07:11 GMT

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Poison can be turned into a cure. This is also the case of the yew trees, extremely toxic gymnosperms, whose only non-toxic part is the comestible seed's aril (resembling a berry). Their bark (in the case of some species) contains a chemical that fights cancer.

A new research shows that the dirt from the place where yew trees grow can be exploited to get the drug, revealing a new commercial source for it. The chemical paclitaxel (traded as Taxol) was discovered in 1967 in the bark of Pacific yew trees (Taxus brevifolia), which grows in the Pacific Northwest of North America, from southernmost Alaska to central California. Other yew's chemicals, taxanes, can be transformed into paclitaxel.
Since then, paclitaxel and taxanes were also found in some fungi and hazelnuts.

The research team at University of Portland, led by biochemist Angela Hoffman, has been growing yew in the lab from cuttings. The scientists found the paclitaxel in the plant's sap, so they suspected the shrubs could release the drug into the soil through their roots. Weyerhaeuser, a company that grows yew trees commercially for the extraction of the taxanes keeps the shrubs for some years and after that replants the fields.

"This means they have acres of soil they could use. Harvesting paclitaxel from the soil can become profitable if the growers can generate more than 20 grams per acre," Hoffman said.

The team found that the top foot of an acre of an ex-yew growth could contain about 35 g of paclitaxel and 70 g of taxanes in the lab. The team mixed for some hours 40 cubic ft of yew growth soil from Weyerhaeuser's fields with alcohol in a cement mixer, as taxanes are soluble in the alcohol and can be easily extracted from it, and found a value of 25-30 g of paclitaxel per acre and roughly 200 g of taxanes.

"On average, a single dose of paclitaxel contains about 10 to 200 millionths of a gram of the drug," Hoffman said.

20 g "would probably be enough to last 30 to 50 people throughout their entire treatment. The reason less paclitaxel was found in the field than in the lab could be because the scientists' lab techniques are currently more efficient than their field methods," Hoffman said.

Paclitaxel could be less resistant than taxanes, which accumulate from previous yew plantings.

TAGS:

yew | drug | bark

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