Paclitaxel chemical structure
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Taxol

Paclitaxel (Taxol®) is a drug used in the treatment of cancer. It was discovered at Research Triangle Institute (RTI) in 1967 when Dr. Monroe E. Wall and Dr. Mansukh C. Wani isolated the compound from the bark of the Pacific yew tree, Taxus brevifolia, and noted its antitumor activity in a broad range of rodent tumors. By 1970, the two scientists had determined the structure of paclitaxel, which is extremely complex. Paclitaxel has since become an effective tool of doctors who treat patients with lung, ovarian, breast cancer, and advanced forms of Kaposi's sarcoma (Saville et al 1995). It is sold under the tradename Taxol®. Together with docetaxel, it forms the drug category of the taxanes. more...

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Paclitaxel is also used for the prevention of restenosis (recurrent narrowing) of coronary stents; locally delivered to the wall of the coronary artery, a paclitaxel coating limits the growth of neointima (scar tissue) within stents (Heldman et al 2001).

History

The history of paclitaxel begins with a 1958 National Cancer Institute study that commissioned Department of Agriculture botanists to collect samples of over 30,000 plants to test for anticancer properties. Arthur S. Barclay, one of those botanists, collected 15 lbs of twigs, needles, and bark from Pacific yew trees in a forest near Mount St. Helens. Months later, in 1963, Monroe E. Wall discovered that bark extract from the Pacific yew possessed antitumor qualities, beginning to reveal the tree's hidden treasure. Soon after, Wall and his colleague Mansukh C. Wani were busy isolating and purifying plant compounds for anticancer tests in Research Triangle Park, North Carolina. In 1967 the team had isolated the active ingredient, announcing their findings at a American Chemical Society meeting in Miami Beach. Wall and Wani published their results, including the chemical structure, in a 1971 issue of the Journal of the American Chemical Society. The paper was noticed immediately by Robert A. Holton who was starting postdoctoral research at Stanford University in natural products synthesis. But, it would be several years before he dedicated his attention to synthesizing pacilitaxel at Florida State University, quelling an emerging environmental controversy; a 40-foot Pacific yew tree, which may have taken 200 years to reach that height, yields only a half gram of paclitaxel, but Holton's group perfected a four-step procedure to convert 10-deacetylbaccatin (a related compound in Pacific yew needles) into paclitaxel. In the late 1970s, Susan B. Horwitz, a molecular pharmacologist at Albert Einstein College of Medicine in New York City, unraveled the key mystery of how paclitaxel works. Largely in part of an enormous research and development effort, starting in government facilities and later in commercial labs, paclitaxel quickly became an all-time best-selling pharmaceutical. Paclitaxel was brought to the market by Bristol-Myers Squibb in 1993 as Taxol®. Annual sales peaked in 2000, reaching US$1.6 billion.

Production

Unfortunately, the Pacific yew is one of the slowest growing trees in the world. Further, the treatment of just one patient requires the cutting down and processing of six 100-year old trees. This supply problem combined with the threat to the endangered spotted owl (Strix occidentalis) has prompted researchers to develop actinobacteria such as Streptomyces coelicolor or Amycolata autotrophica from which paclitaxel-like epothilone compounds can be obtained by fermentation. S. coelicolor produces epothilone A and epothilone B, while A. autotrophica produces epothilone D. Similarly, cultures of the fungus Nodulisporium sylviforme can be used to produce paclitaxel itself.

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Taxol update
From Saturday Evening Post, 11/1/05 by Audrey E. Glass

In the Sept./Oct. 1991 issue of The Saturday Evening Post, you featured a rather extraordinary article about Taxol, an anticancer drug. Bristol-Myers Squibb had a license at that time to use the taxol process.

According to the article, Taxol killed cells in a way that researchers had never seen before--it blocked cells just when they were going to divide, inhibiting the replication of cells. Taxol binds to microtubules in the cell so they can't form spindles necessary to replicate.

Susan Horwitz at Albert Einstein College of Medicine and Dr. Robert Holton at Florida State University were working on creating a totally synthetic form of Bacatin III and Taxol. Whatever happened to that research, and don't you think it's time for an update in the SatEvePost?

I am wondering what happened to all of the 20 million yew trees planted in those nurseries in Rhode Island, Pennsylvania, Ohio, and Michigan?

Every time the telephone rings I get anxious--I am waiting on a pathologist's report on a needle biopsy today on a lump in my breast.

Love your magazine!

Audrey E. Glass

Front Royal, Virginia

Editor's note: The Saturday Evening Post Society planted Pacific yew trees in the hope they might someday yield lifesaving cancer medicines. While the trees have grown beautifully, Dr. Robert Holton and his team at Florida State University discovered a way to produce a synthetic form of Taxol in the lab. As a result, the collection of yew bark--from which the compound was initially extracted--became unnecessary.

Taxol, manufactured and marketed by Bristol-Myers Squibb in the mid-1990s, is FDA-approved for treating ovarian, breast and other cancers. In 1999, the compound reportedly was the top anticancer drug in the world. A generic form (named paclitaxel) was introduced in 2001.

Dr. Holton's success in developing Taxol chemistry has since led to the synthesis of dozens of Taxol derivatives, some of which are showing even more promise in early trials in mice than the parent molecule.

COPYRIGHT 2005 Saturday Evening Post Society
COPYRIGHT 2005 Gale Group

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