At present Taxol is obtained mainly from the bark of the Yew tree but scientists have found that the substance can be extracted from the needles of tree. However, the drug is only one-eighth as concentrated compared to the bark and this process leaves room for impurities within it. Other species of the Yew tree also contain Taxol and these are currently under investigation.
The European Yew, Taxotere, which is more abundant than the Pacific Yew, contains a compound that is more soluble and efficient than Taxol in killing lab-grown cancer cells. The needles of the English Yew contain a compound that is ten times more concentrated than the Taxol found in the Pacific Yew. A garden variety of the Yew tree, Taxus media Hicksii, which has needles with high Taxol yield, are being investigated for commercial viability.
For more general information on the different Yew trees click here,
Biotechnologists have now joined the race and are growing masses of tiny Taxol-producing Yew cells that originate in the needles, bark and stems of several Yew species. If these cells are grown in a bath of nutrients small amounts of Taxol are able to be obtained. The hope is that one day vast quantities could be cultured in factory tanks and tapped for the life saving substance. Plant cell tissue culture offers numerous advantages over field-grown material including reliable production from a renewable source and the possibility of enhanced productivity due to metabolic manipulation through strategies as precursor feeding, elicitation of enzyme systems, or metabolic engineering. Little is known about Taxol metabolism, specifically biosynthesis, storage, transport, release,and degradation. However, a better understanding of these cellular functions is required before an optimal plant cell culture system can be designed.
At the moment research is focused on characterising the "fate" of Taxol after synthesis. By applying appropriate metabolic and transport inhibitors(including cytochalasin b, brefeldin A, phenylarsineoxide) in conjunction with transmission electron microscopy, it is possible to study the localization of Taxol and mechanism of Taxol release.
Calcium has been identified as an important compound in affecting Taxol partitioning. The addition of extra-cellular calcium to the medium results in a rapid accumulation of Taxol intra-cellularly. Studies have shown that Taxol degradation does occur in our cell cultures, is first order, and that significant Taxol is lost with time. The results from these experiments have helped formulate a metabolic model for the "fate" of Taxol after synthesis. A corresponding kinetic model is concurrently being formulated and will ultimately be used to identify rate limiting steps in the overall production of Taxol and to predict the effects of various productivity enhancement strategies.