The Pacific Yew Tree
The Pacific yew tree (Taxus brevifolia) is a natural source of Taxol®, an anticancer drug widely used in the management of several tumors, including breast, lung, and ovary. How was it discovered? In the 1960s, the National Cancer Institute (NCI) realized that in addition to surgery and radiation therapy, physicians needed a new approach to improve the outcomes of cancer patients. With the Department of Agriculture, the NCI screened thousands of biologic samples derived from plants and animals. Drs M.E. Wall and M. Wani, working under contract for the NCI, discovered that an extract from the Pacific yew tree inhibited cancer cell growth. They named the agent “paclitaxel,” and, subsequently, this compound was found to retard the growth of many different types of cancer cells.
Similar to many other members of the yew family, the Pacific yew is slow growing, and harvesting the bark kills the tree. These two factors led to a critical shortage of the agent, stimulating an effort to develop a synthetic form of the drug, which was finally approved by the US Food and Drug Administration (FDA) in 1993. Now manufactured by cell culture, paclitaxel is listed as an essential drug by the World Health Organization (WHO). Pacific yew is one of many plants now known to have anticancer activity. An unsolved mystery is the relationship between this powerful anticancer agent and the plant. Is the substance beneficial to the plant? If so, how? One novel idea is that the actual source of paclitaxel may not be the plant itself but microbes associated with the plant.