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Tree that provides paclitaxel is put on list of endangered species

BMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d7411 (Published 15 November 2011) Cite this as: BMJ 2011;343:d7411
  1. Susan Mayor
  1. 1London

Overharvesting of one of the trees that are sources of paclitaxel, a chemotherapy drug used to treat several cancers, has led to its classification as endangered in the latest global list of threatened species, published last week.

The tree, Taxus contorta, a yew that grows in Afghanistan, India, and Nepal, has been classified as endangered by the International Union for Conservation of Nature and Natural Resources, a non-profit organisation funded by governments and other organisations, in its latest “red list” of species at risk of extinction.

Its conservation status has changed from vulnerable to endangered because the estimated global population has declined by more than 50% (but less than 80%) in the past 30 years, explained Philip Thomas, research officer for the International Conifer Conservation Programme at the Royal Botanic Garden Edinburgh and leader of the group that analysed conifer numbers for the latest red list.

Paclitaxel, originally given the generic name taxol, was first discovered in the bark of the Pacific yew tree (Taxus brevifolia) by a US National Cancer Institute researcher in the 1960s, before being developed commercially. It inhibits mitosis so is used to stop cell division in the treatment of a range of cancers, including breast, lung, and ovarian cancers.

Several drug companies have developed methods to manufacture taxanes that do not rely on harvesting yew trees. For example, Bristol-Myers Squibb produces paclitaxel (which it markets as Taxol) by using a Taxus cell line propagated in aqueous medium in large fermentation tanks. However, some drug companies in India and China still use the tree as a source of paclitaxel, Dr Thomas explained.

“In areas where exploitation for taxol production is the primary threat [to Taxus contorta], then the establishment of plantations of cultivated trees is probably the only long term solution unless the development of ‘artificial’ methods (such as cell fermentation) becomes more widespread,” he said.

Craig Hilton-Taylor, manager of the red list unit at the International Union for Conservation of Nature and Natural Resources, said, “The harvesting of the bark kills the trees, but it is possible to extract taxol from clippings, so harvesting, if properly controlled, can be less detrimental to the plants.”

The tree’s decline is also linked to increased harvesting as a result of fuel shortages, population increases, and poverty. “These are very complex issues that require a range of strategies which would include reforestation work and better management of protected areas,” Dr Thomas said.

The red list provides the most authoritative survey of the planet’s species. In the latest list more than 9000 species of animals and plants are classified as critically endangered or endangered. It was first published in 1963 as a report on the conservation status of species globally, highlighting those threatened with extinction. Over the years it has evolved to become a standard for conservation assessment on the basis of the most accurate information available.

Notes

Cite this as: BMJ 2011;343:d7411

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