Fascinating article about extracting taxanes from the dirt that
Pacific Yew trees grow in.

http://www.livescience.com/humanbiology/070424_soil_drugs.html

The bark of certain yew trees can yield a medicine that fights cancer.
Now scientists find the dirt that yew trees grow in can supply the
drug as well, suggesting a new way to commercially harvest the
medicine.

Scientists originally isolated the drug paclitaxel-now commonly known
as Taxol-in 1967 from the bark of Pacific yew trees (Taxus brevifolia)
in a forest near the Mount St. Helens in Washington. This yew also
yields related compounds known as taxanes that can be converted to
paclitaxel. Research since then has revealed other yew species
generate paclitaxel and taxanes as well, as do some fungi and certain
hazelnut varieties.

A decade ago, University of Portland biochemist Angela Hoffman and her
colleagues were interested in growing yew in the lab from cuttings.
They discovered small yew branches could secrete paclitaxel into plant
food, raising the possibility that yew trees might release the drug
into the soil .

Tree farming

The scientists collaborated with Weyerhaeuser, a forest-products
company that grows yew trees to extract taxanes. Their research now
suggests yew trees might secrete paclitaxel and other taxanes from
their roots. The scientists recently presented their findings at the
American Chemical Society meeting in Chicago and will detail the
results in June at a joint meeting in Boise of the Northwest Region of
the American Chemical Society and the American Association for the
Advancement of Science Pacific Division.

Weyerhaeuser grows yew trees for several years before pulling them up
and replanting the fields. "This means they have acres of soil they
could use," Hoffman said. She estimated harvesting paclitaxel from the
soil can become profitable if the growers can generate more than 20
grams per acre.

Based on lab experiments, Hoffman and her colleagues calculated that
the top foot of an acre of yew dirt should yield roughly 35 grams of
paclitaxel and some 70 grams of related taxanes, "stuff that would
have just gone to waste anyhow," Hoffman told LiveScience.

In the field

To field test their ideas, the scientists took nearly 40 cubic feet of
yew soil from a Weyerhaeuser field and mixed it with a few gallons of
rubbing alcohol in a cement mixer for several hours. The taxanes
dissolve in the alcohol, which the scientists then filter off and
extract taxanes from. The field results suggest an acre of soil would
yield about 25 to 30 grams of paclitaxel and about 200 grams of
related taxanes.

On average, a single dose of paclitaxel contains about 10 to 200
millionths of a gram of the drug, Hoffman said. Twenty grams of the
medicine "would probably be enough to last 30 to 50 people throughout
their entire treatment," she estimated.

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. Also, paclitaxel
could have broken down when left out too long in the field. In
contrast, the reason more taxanes were found in the field than in the
lab could be because they are left over from previous yew plantings.