Pacific Yew--Taxus Brevifolia

Pacific Yew is an evergreen tree native to the Pacific Northwest. It is famous as the source of Taxol, one of the most effective cancer treatments found in the last fifty years. Its discovery came after many hiccups and false starts, and my summary will make it all look very simple, which it wasn't.

In the 1950s, the National Cancer Institute was screening every synthetic chemical it could get its hands on for anti-tumor activity. In 1960, it started in on natural products. Since they needed an accurate identification to make sure that it knew where the substances were coming from, they turned to USDA botanists. They tested 30,000 samples per year. In 1962, Arthur Barclay collected samples from the Pacific Yew and submitted them to the Research Triangle Institute in North Carolina. Dr Susan Brand Horwitz delineated its mode of action: it encouraged development to such a degree that cell division became uncoordinated and cells died.

It was selected for clinical trials in 1977. However, the trials were delayed for years due to the difficulty of extracting enough Taxol. It is in very low concentrations in the yew, and the highest concentration is found in the bark. When the bark is harvested, the trees die. Since the bark is only 1/8" thick, to treat one patient for one year, several trees were needed.

Environmentalists complained. They pointed out that the slow-growing yews would be decimated withing a few years in order to treat all the people who would want it. In addition, the yew was the habitat of the Northern Spotted Owl.

Scientists looked for another source of Taxol. They were unable to find one. However, they did find a tree with a precursor to Taxol. Not only was a  taxane present in the European Yew, there were reasonable concentrations in the leaves, so that the tree did not need to be sacrificed to extract the chemical. In addition, yews are grown as hedges in Europe, so that trimmings were regularly available.

Synthesizing Taxol from European Yew worked well for awhile. But now it can be made in the lab from plant cell cultures. The yews of the Pacific Northwest were saved by the ingenuity of scientists working together.

It is used to treat breast, lung and ovarian cancer as well as Karposi's Sarcoma. It is one of the most potent chemotherapy agents ever discovered. Yay, trees!

(Rx)