Yew

Yew is a name for several species of coniferous trees from the families Taxaceae and Cephalotaxaceae, especially those from the genus Taxus. There are two especially notable species: the European or common yew (Taxus baccata) and the Pacific yew (Taxus brevifolia).

Taxus brevifolia

The Pacific yew is notable as the natural origin of the anti-cancer drug paclitaxel, sold under the brand names Taxol (which was formerly its common name in scientific literature) and Abraxane. The drug was extracted from the bark, the harvesting of which kills the tree. It was the first known chemical to interfere with the action of microtubules — tiny protein filaments that pull the components of the cell into the right places during mitosis. The demand for taxol during its clinical trials caused the Pacific yew to be threatened with extinction. Fortunately, an economical partial synthesis from a chemical found in the needles of common yew was developed in 1993. Later, a much more efficient method used a cell culture of a fungus symbiotic with the yew tree, which also produces taxol.

Taxus baccata

An extremely old common yew growing in the Llangernyw village in Wales, thought to be 4000-5000 years old

The common yew, also called European yew or English yew, is notable for achieving extreme ages, due in part to its ability to fragment into smaller parts and keep growing after the central core dies. Several examples older than 1000 years are known, with some dating from before the supposed date of the Biblical flood (2348 BCE according to Ussher).

There are some yews that have become attached to implausible myths due to their considerable age. This includes the Fortingall Yew in Perthshire, Scotland, under which it is claimed Pontius Pilate played as a child: although the tree is ancient enough at probably 2000-3000 years old, the presence of Pilate in central Scotland is implausible. Some people suggest the tree is 5000 years old and the oldest living thing in Europe, although slightly younger estimates have more credibility. Other elderly yews with fewer Biblical connections include the Ashbrittle yew in Somerset, England, which the local council's expert dates to around 2000 BCE. The Llangernyw Yew in Conwy, Wales is often dated as 4000-5000 years old although some claim it is only around 1500. The tendency of yews to fragment, and the desire to preserve fragile trees, means dating is more complex than just chopping it down and counting the rings.

The needles of the common yew are a source of 10-deacetylbaccatin, a chemical used as the starting material in the synthesis of the paclitaxel analogue, docetaxel, sold under the brand name Taxotere. Docetaxel went out of patent in 2010.

Woo

Due to the legitimate drug connection, the case of the Pacific yew tree was a boon to promoters of herbalism and other "natural" medicine. Nobody seems to have tried making yew-based herbal remedies yet, which is a good thing, since all species of yew are poisonous.

External links

• Cancer Research UK: Paclitaxel
• Cancer Research UK: Docetaxel