Abstract:

The Pacific Yew (Taxus brevifolia) and the English Yew (Taxus baccata) are used as active plant ingredients for the anti-cancer drug Taxol, which is produced by the Bristol-Myers Squibb Company. Paclitaxel, another name for Taxol, works against cancer by interfering with mitosis, where it breaks down the mitotic spindle during cell division, which prevents the cell from dividing into daughter cells.

The production of Taxol caused problems, when after harvesting the bark of the Pacific Yew, the trees died. Because of this, the Bristol-Myers Squibb Company had to find a new source to get the active ingredient, which they found in the English Yew. Taxus baccata is not only more effective, but also not harmful to the trees because only the needles and twigs are used to produce Taxol.

The Pacific Yew is found in the Northwestern part of the United States and Canada, the English Yew in parts of Vermont.

When researching for 10 prescription drugs that contain active plant ingredients, Taxol was one of the most interesting medicines. During the history of this drug the active plant ingredient changed from the bark of the Pacific Yew (Taxus brevifolia) to the needles and twigs of the English Yew (Taxus baccata). The reason behind this change was that when the bark of the Pacific Yew was harvested, not only the plant itself died, but also the lives of animals like the spotted owl that lived in the same habitat were threatened.

The Pacific Yew or Taxus brevifolia is a small evergreen tree with indistinct growth form. It grows in moist soils in British Columbia, Alaska, California, Idaho, Montana, Oregon, and Washington. The Pacific Yew can reach up to 50 feet in height and two feet in diameter. The needles are single, linear, and spirally arranged, about one inch long, yellow- green to dark green above and paler below. The male flowers are small, round, and yellow and are borne on the underside of the leaves, while female flowers are solitary. The fruits of the Pacific yew are round, fleshy, and of an orange-red color.

The English Yew or Taxus baccata is also a small evergreen tree or large shrub with numerous limbed boles and a short trunk. Its leaves are alternate, simple, two-ranked linear, and approximately one inch long. They appear dark green and shiny on top, yellow or pale green on the bottom. The fruit is a naked ovoid seed about ¼ inch long, surrounded by a bright red, fleshy aril. The English Yew matures in the late summer. Taxus baccata is native to England, but has been introduced to some parts in the Northeastern United States, mainly Vermont.

Historically, Native American tribes used yew brews to treat rheumatism, fever, and arthritis. The Japanese used yew leaves to treat diabetes and to induce abortion.

Information and pictures used in the report on Taxol®, English yew (Taxus baccata), and Pacific yew (Taxus brevifolia) was obtained from web sites off of the Internet. To view the web pages used, see the reference section of this report. Taxol is a registered trademark of Bristol-Myers Squibb.

Figure 1. Taxol molecular structure

Paclitaxel, which is sold as Taxol by Bristol-Myers Squibb, binds to microtubules and inhibits their depolymerization (molecular disassembly) into tubulin. This means that paclitaxel blocks a cell's ability to break down the mitotic spindlem during mitosis (cell division). With the spindle still in place the cell can't divide into daughter cells (this is in contrast to drugs like colchicine and the Vinca alkaloids, which block mitosis by keeping the spindle from being formed in the first place).

Figure 2. Pacific yew (Taxus brevifolia)

Pacific yew (Taxus brevifolia) characteristics:

Leaf: Needles single, linear, and spirally arranged (although they appear 2-ranked), 1 inch long, yellow-green to dark green above and paler below (but without bloom), apex pointed but not sharp, each needle has a distinct petiole that parallels the twig for a short distance.

Flower: Dioecious, male flowers are small, round, and yellow and are borne on the undersides of the leaves; Female flowers are solitary.

Fruit: A round, fleshy, orange-red aril about 1/4 inch long containing one hard seed, exposed at the end.

Twig: Round, slender, and remaining green for many years, relatively few lateral branches.

Bark: Always thin (about 1/4 inch), reddish-brown, and scaly, inner bark is reddish-purple.

Form: Small evergreen understory tree with indistinct growth form. Can reach 50 feet tall and 2 feet in diameter, but usually much smaller. Trunks are usually fluted and asymmetrical. Very slow growing but can reach a very old age.

Figure 3. English yew (Taxus baccata)

English yew (Taxus baccata)characteristics:

Leaf: Evergreen, alternate, simple, 2-ranked, linear, approximately 1 inch long, dark green and shiny above, yellow or pale green below.

Flower: Male is a globose strobili; female is a small stalked bud in leaf axils.

Fruit: A naked ovoid seed 1/4 inch long, surrounded by a bright red, fleshy aril. Maturing late summer, persistent through autumn.

Twig: Light green in color, turning brown after several years.

Bark: Dark, usually red-purple, and scaly or somewhat peeling.

Form: Small tree or large shrub with many limbed boles and a short trunk.

The purpose of Taxol (paclitaxel) is to help fight cancer, especially ovarian carcinomas and advanced breast cancer. The medication interferes with mitosis by breaking down the mitotic spindle, which prevents the cell from dividing into daughter cells. Taxol is an intravenous drug that is administered by a doctor over a 24-hour period in 21-day intervals. This drug not only has benefits, but also severe side effects, including anaphylactic reactions, which can be life threatening, if not treated shortly after the injection. Other less serious side effects include the loss of hair, pain in joints, painful urination, nausea, and vomiting among many others.

Unfortunately, controversy surrounded the use of the Pacific Yew in Taxol. Taxus brevifolia is the plant that was originally used in Taxol. This tree is found in the Pacific Northwest of the United States and Canada. The drug was harvested from the bark of this rare species. However, by removing the bark of the Pacific Yew, the tree was killed, which led to another problem. By killing the tree, environmental groups felt that it also threatened the home of a federally protected and endangered species, the spotted owl.

Bristol-Myers, the maker of the drug, felt compelled to find an alternative source of paclitaxel for commercial production. Researchers found that the needles and twigs of another type of yew, the English Yew or Taxus Baccata, can be used to produce a semisynthetic form of the drug, which requires less raw material and also protects the yew tree. Over the past few years Bristol-Myers has received the approval to collect twigs and needles from the plant in both public and private gardens. This is a big step forward because by using cultivated trees improves the consistency and quality of the raw material. In the end, environmental improvements in the production of Taxol, gives patients more opportunities to extend their lives.

• Taxol is use to help fight ovarian carcinomas and advanced breast cancer.
• Taxol is derived from twigs and needles of the English Yew

Description and Natural History of the English and Pacific Yew.

English Yew Fact Sheet: English Yew-Taxaceae-Taxus Baccata.

Pacific Yew Fact Sheet: Pacific Yew-Taxaceae-Taxus Brevifolia.

Pharmacology of Paclitaxel and Docetaxel.

The Environmental Story.