Cancer is the second leading cause of death in the United States today. The search for the therapeutic drugs among the compounds produced by plants began in the 1950s under the direction of the National Cancer Institute. Since then, many thousands of plants have been screened for anticancer activity. But many more remain untested and, with the present rate of extinction of species, life-saving compounds may vanish before they can be discovered.
Two major success stories are the Madagascar periwinkle, Catharanthus roseus, and the Pacific yew tree, Taxus brevifolia. The Madagascar periwinkle is a tropical perennial herb used by traditional healers as a treatment for diabetes. Investigated in the 1950s, this herb was found to have no use in treating diabetes; but extracts contained substances that were effective against leukemia cells. Today these substances, known as vinblastine and vincristine, are widely used in chemotherapy. Vincristine is especially used in the treatment of childhood leukemia. Vinblastine is used in treating cancers of the lymphatic system such as Hodgkin’s disease.
In the 1960s the Pacific yew tree yielded another promising anticancer drug called taxol. Taxol was found in the extracts of the tree’s bark. At first supply of taxol was a problem because the Pacific yew tree is rare, and a large quantity of bark is required for taxol extraction. Other species of yew trees were subsequently found to have taxol in bark and leaves. Cell cultures may also be used to generate taxol, which has recently been synthesized in the lab. Taxol is especially promising for the treatment of advanced ovarian and breast cancers. No one can say what rare or seemingly unimportant plant might yield the next anticancer the next anticancer drug.
— Source: Book of Plant Biology —