Paclitaxel - Production

Production

From 1967 to 1993, almost all paclitaxel produced was derived from bark from the Pacific yew, the harvesting of which kills the tree in the process. The processes used were descendants of the original isolation method of Wall and Wani; by 1987, the NCI had contracted Hauser Chemical Research of Boulder, Colorado, to handle bark on the scale needed for Phase II and III trials. While there was considerable uncertainty about how large the wild population of Taxus brevifola was and what the eventual demand for taxol would be, it had been clear for many years that an alternative, sustainable source of supply would be needed. Initial attempts used needles from the tree, or material from other related Taxus species, including cultivated ones, but these attempts were bedevilled by the relatively low and often highly variable yields obtained. It was not until the early 1990s, at a time of increased sensitivity to the ecology of the forests of the Pacific Northwest, that taxol was successfully extracted on a clinically useful scale from these sources.

From the late 1970s, chemists in the US and France had been interested in taxol. A number of US groups, including one led by Robert A. Holton, attempted a total synthesis of the molecule, starting from petrochemical-derived starting materials. This work was primarily motivated as a way of generating chemical knowledge, rather than with any expectation of developing a practical production technique. By contrast, the French group of Pierre Potier at the CNRS quickly recognized the problem of yield. His laboratory was on a campus populated by the related yew Taxus baccata, so needles were available locally in large quantity. By 1981, he had shown that it was feasible to isolate relatively large quantities of the compound 10-deacetylbaccatin, a plausible first step for a semisynthetic production route to taxol. By 1988 he copublished such a semisynthetic route from needles of T. baccata. The view of the NCI, however, was even this route was not practical.

By 1988, and particularly with Potier's publication, it was clear to Holton as well a practical semisynthetic production route would be important. By late 1989, Holton's group had developed a semisynthetic route to paclitaxel with twice the yield of the Potier process. Florida State University, where Holton worked, signed a deal with Bristol-Myers Squibb to license this and future patents. In 1992, Holton patented an improved process with an 80% yield. BMS took the process in-house and started to manufacture paclitaxel in Ireland from 10-deacetylbaccatin isolated from the needles of the European yew. In early 1993, BMS was able to announce that it would cease reliance on Pacific yew bark by the end of 1995, effectively terminating the ecological controversy over its use. This announcement also made good their commitment to develop an alternative supply route, made to the NCI in their CRADA application of 1989.

Another group, led by K.C. Nicolaou of the Scripps Research Institute, announced the complete synthesis of paclitaxel at the same time (in February 1994) as Holton's group at Florida State University. Holton argued that his technique was superior to Nicolaou because of the higher yield, whereas Nicolaou said that their yields would be similar if Holton had calculated the yield at every step instead of at an intermediate point of his synthesis.

Currently, all paclitaxel production for BMS uses plant cell fermentation (PCF) technology developed by the German and Canadian biotechnology company Phyton Biotech, Inc and carried out at their plant in Germany. PCF uses a specific Taxus cell line propagated in aqueous medium in large fermentation tanks with the endophytic fungus Penicillium raistrickii. Paclitaxel is then extracted directly, purified by chromatography and isolated by crystallization. Compared to the semisynthesis, PCF eliminates the need for many hazardous chemicals and saves a considerable amount of energy.

In 1993, taxol was discovered to be produced in a newly described endophytic fungus living in the yew tree. It has since been found in a number of other endophytic fungi, including Nodulisporium sylviforme, Alternaria taxi, Cladosporium cladosporioides MD2, Metarhizium anisopliae, Aspergillus candidus MD3, Mucor rouxianus sp., Chaetomella raphigera, Phyllosticta tabernaemontanae, Phomopsis, Pestalotiopsis pauciseta, Phyllosticta citricarpa, Podocarpus,Fusarium solani, Pestalotiopsis terminaliae, Pestalotiopsis breviseta, Botryodiplodia theobromae Pat., Gliocladium sp., Alternaria alternata var. monosporus, Cladosporium cladosporioides, Nigrospora sp., Pestalotiopsis versicolor, and Taxomyces andreanae.