Xi Shu

Camptotheca acuminata

COMMON NAMES

• Cancer Tree
• Happy Tree
• Tree of Joy
• Xi Shu

Xi shu is a large tree of up to 25 m in height with slender reddish brown bark and a few branches near the top. It has glossy green, leathery leaves and rounded heads of small, whitish flowers. Cultivars with higher yields of active compounds are being developed. Indigenous to China; it is nowadays grown as ornamental tree and crop plant in India, Japan and the USA. The tree has been placed on the endangered list in China, so that exports from China are now regulated.

PARTS USED

Wood, bark, leaf, fruit.

USES

Camptotheca goes by many names in its native lands. Xi shu translates as "happy tree" and has been called this by people whom it cured of colds and other illnesses. Its other names include long shu (dragon tree), ,jia shu (fine tree), and tian zi shu (heaven wood tree). The Chinese have also used this tree for firewood and as an ornamental plant. All American specimens of the Camptotheca are descendants of two trees germinated from seeds brought from China in the 1930s.

The Chinese have used xi shu for traditional medication purposes for hundreds, and possibly thousands, of years. They have employed xi shu against psoriasis and in the treatment of diseases of the liver, gallbladder, spleen, and stomach. Xi shu has also been used to treat leukemia. In fact, one common name for Camptotheca is the "cancer tree". For treating cancer its primary constituent is camptothecin, which inhibits topoisomerase I, an enzyme linked with cell division and DNA replication. By inhibiting this enzyme, camptothecin appears to stunt tumor growth. A host of other anticancer medications have been modified from camptothecin, two of which are approved by the U.S. Food and Drug Administration. Topotecan is used to treat ovarian and small lung cancers. Irinotecan is used to treat metastatic colorectal cancer, the second leading cause of cancer deaths in the United States. Other camptothecin related medications are no longer in use because of their severe toxicity.

HABITAT AND CULTIVATION

Xi shu, indigenous to China and Tibet, grows best in warm zones.

CONSTITUENTS

Camptothecine, a pentacyclic quinoline alkaloid, is the major compound (about 0.01% in stem bark, 0.02% in root bark and 0.03% in fruits). Camptothecine is poorly soluble in water and causes severe side effects such as diarrhea and haemorrhagic cystitis. As a result, various semi synthetic analogues have been developed, including 9-amino-20S-camptothecine, irinotecan (also known as irinotecan hydrochloride trihydrate, CPT-II or Camptosar) and topotecan (Hyacamptin).

Camptothecine has proven cytostatic and antitumour activity but is also quite toxic. The anticancer effect is due to the unique ability of camptothecine and related compounds to inhibit the nuclear DNA topoisomerase I enzyme so that replication and transcription are interrupted.

USUAL DOSAGE

Pure alkaloids are administered by intravenous drip (in the case of irinotecan, 100 mg per m² of body surface in a weekly treatment repeated six or more times). Weak infusions are used in folk medicine.

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