Harvesting Drugs from Plants
Stehlin, Dori, FDA Consumer
Harvesting Drugs From Plants
In Samoa, native healers called "taulasea" use the leaves of a small tree to treat back pain and abdominal swelling. They use the roots to treat diarrhea and the wood to treat yellow fever. That same tree is being studied by chemists and biologists with the National Cancer Institute as a possible treatment for AIDS.
Besides the Samoan tree, scientists with NCI's Developmental Therapeutic Program in Frederick, Md., are screening thousands of other plants and animals from around the world looking for treatments for cancer as well as AIDS.
"Natural products drug discovery research is nothing new," says Michael Boyd, M.D., Ph.D., who led the current revival of natural products research at NCI and the development of NCI's new anti-tumor and anti-HIV (AIDS virus) screening tests essential to these efforts. "In cancer chemotherapy, some of the best drugs we have today are natural products. The same is true for almost any class of medicinal agent."
Cancer chemotherapy with naturally derived substances includes:
* Two substances isolated from the Madagascar periwinkle (Vinca rosea): vinblastine sulfate, indicated for several cancers, including Hodgkin's disease; and vincristine sulfate, used especially in childrenwith lymphocytic leukemia.
* A semi-synthetic derivative of the May apple (Podophyllum peltatum), a common woodland plant in the eastern United States, to treat testicular cancer and small cell lung cancer.
Other naturally derived drugs include:
* Digitalis--The dried leaves of Digitalis purpurea, the purple foxglove, are the source of this drug, which is used to treat congestive heart failure and other cardiac disorders.
* Reserpine--This substance, isolated from the roots of tropical shrubs in the genus Rauwolfia, is used as a sedative and to treat high blood pressure.
Although there are no approved anti-cancer drugs derived from marine organisms, the marine environment has tremendous potential as a future source of drugs, according to Boyd. Several novel compounds that show potential anti-tumor activity have been isolated in recent years, and one compound, dideminim B, an extract from an organism known as the sea squirt (Didemnidae species), is the first to enter clinical trials for testing against several kinds of cancer.
Scouring the Globe
While the discovery of medicinal drugs from natural products isn't new, the approach of the NCI program is. "The new thing about this particular program is the degree of emphasis and the novelty of the biological test systems that we are developing," says Boyd.
That "degree of emphasis" means that greatly expanded activity and resources are being concentrated on finding specimens for screening. Since 1988, NIH has had contracts with marine biologists and botanists to collect over a five-year period approximately 15,000 marine organisms, mainly from the Great Barrier Reef off Australia, and 20,000 plants from places such as Samoa and the rain forests of South America and Africa.
Many of the plant collectors are ethnobotanists, who study the relationship between plants and people. In many cultures, that relationship includes using plants to treat disease.
"The search for medicinal plants is a little more difficult than just going into an area and throwing everything you see into a bag," says Michael Balick, Ph.D., director of the Institute of Economic Botany at the New York Botanical Gardens. "First you have to search out healers and others with knowledge of indigenous plants."
Although the preparation for an ethnobotanical search is time-consuming, in the long run this approach saves time, according to botanist Paul Cox in a 1989 article in the journal Economic Botany. "Because ethnobotanical data provide important clues to plants that have pharmacological activity, an ethnobotanical screen of a flora is likely to be far more efficient and productive than a random screen," writes Cox. …