New drugs from the rain forests

30 New drugs from the rain forests Norman R. Farnsworth Collecting medicinal plants in a rain forest in Cameroon . Plants have always been a "treasure house" of potential new drugs; but emphasis has now turned to tropical rain- forest plants as opposed to the temperate zone plants which previously provided many of the major plant-derived drugs. More than 250 000 species of flowering plants exist on this planet. Of these, about 60% are found in tropical forests and most of the tropical forests of the world are found in developing countries. In recent years, scientists from acade- mic institutions and industrial firms have turned to certain plants from tropical rain forests as a source either of potential new drugs or of compounds from which less toxic or more efficacious drugs can be developed. Plants are selected for study on the basis either of their general scien- tific interest or of their long-standing use in traditional medicine. Among the most important drugs that have been derived from plants over the past half century are the following: ajmalicine, used for circulatory disorders, and reserpine, used for high blood pressure and as a tranquil- lizer, both derived from the Indian Snake Root Rauwolfia se1pentina; atropine and hyoscyamine, which are anticholinergics, and are commer- cially isolated from the Australian cork tree (though originally they were discovered in Atropa belladonna and Hyoseyanus niger ); emetine from Cephaelis ipecacuanha, which is useful as an amoebicide; pilocarpine from the South American rain forest plant Pilocarpus jaborandi, which is widely used for glaucoma; and the skeletal muscle relaxant tubocurarine from the tropical Chondodendron tomentosum. In more recent years, artemisinin from the weed Artemisia annua, was discovered in China to be an effec- tive agent to treat drug-resistant malaria, and is now used-along with several synthetic analogues to treat World Health • 49th Year, No. 2, March-Aprill996 severe types of malaria. Also discov- ered in China from the clubmoss Lycopodium serratum (Huperzia serratum) is the alkaloid huperzine A, currently being studied in China and other countries for the treatment of Alzheimer disease. Tripterygium wilfordii, the Chinese Thunder God Vine, is widely used in China as a standard- ized extract for the treatment of severe cases of arthritis and other autoimmune diseases. It is a power- ful suppressant of the immune sys- tem. Several novel active principles have been isolated from this plant, especially triptolide and tripdiolide. The extract as well as the pure com- pounds also reduce sperm counts in men. Plaunol, isolated from Croton sublyratus (Plau-noi) from Thailand, is being used as an anti-ulcer drug in Japan_ Prospects for new treatments Calanolide A, from the Malaysian tropical rain-forest tree Calophyllum lanigerum var. austrocoriaceum, is currently in pre-clinical development for the treatment of AIDS in the United States. A well-known com- pound, betulinic acid, has recently been isolated from the Zimbabwean tree Ziziphus mauritiana, and has been found to have a selective action against melanoma cells in vitro, and to inhibit melanoma dramatically in laboratory animals. This substance is now being considered for preclinical studies that could lead to a new drug for the treatment of melanoma. Of importance also is a resur- gence in developing and developed countries in the production of stan- dardized crude extracts as drugs. These usually have known active principles that cannot be patented, so the enormous costs of gaining ap- World Health • 49th Yeor, No. 2, Morch-Aprill996 ~, ~~~:?o 7 ' \~· ' '"I .l'il" Echinacea angustifolia is reported to improve the immune system and lessen the symptoms of influenza. proval for the active principles as drugs cannot be recouped by the developer. Some of these include feverfew (Tanacetum parthenium) which has been demonstrated clini- cally to relieve migraine headaches. The leaves of Ginkgo biloba (maid- enhair tree) are widely employed throughout the world as a treatment for memory loss and ringing in the ears, and as a preventive agent for stroke. Numerous clinical studies have shown that extracts of Echinacea angustifolia can improve the immune system and can either prevent or make less severe the symptoms of influenza. Two other plants, Serenoa repens (sabal, sabadilla) fruits and Urtica dioica (nettle) roots, have been clinically investigated and are being used successfully to alleviate benign prostatic hyperplasia. There is increasing evidence from developed countries that tradi- tional medicines (complementary or alternative therapies), which have been used for centuries in developed and developing countries, have In the next issue The May:June issue of World Health is large ly devoted to the elimination of le prosy as a public health problem. The key to elimina ti on is mul tid rug therapy (MDT) Th is issue also foresees the final eradi cation of guinea-worm disease. Achieving these goals wi ll mark two signa l successes for W HO during its first half-cen tu ry of existence. • something positive to offer in the way of healing. In the United States, this area of medicine has been shown to be widely used by the public, and most physicians believe that many of these therapies are effective. The government has now set up an Office of Alternative Medicine within the National Institutes of Health to study this widening area of medical interest. Plants have always been a "trea- sure house" of potential new drugs; but emphasis has now turned to tropical rain-forest plants as opposed to the temperate zone plants which previously provided many of the major plant-derived drugs. Develop- ing country institutions and scientists are becoming more active in plant- derived drug development, and formal cooperative efforts between them and developed country scien- tists and institutions continue to grow. • Professor Norman R. Farnsworth is Research Professor of Pharmacognosy with the Program for Collaborative Research in Pharmaceutical Sciences, of the University of Illinois at Chicago, College of Pharmacy (M/C 877), 833 South Wood Street, Chicago, Illinois 60612, USA Serenoa repens is successful in alleviating benign prostatic hyperplasia. Feverfew (Tanacetum parthenium) has been clinically demonstrated to relieve migraine headaches. Photo Credits Front cover: Page 3: Page 4: Page 5: Page 6: Page 7: Page 8: Page 9: Page 10: Page ll: Page 12: Page 13: Page 14: Page 15: Page 16: Page 17: Page 18: Page 19: Page 20: Page 21: Page 22: Page 23: Page 24: Page 25: Page 26 8. 27: Page 28: Page 29: Page 30: Page 31: Back cover: WHO WHO/ H. Anenden; WHO/ UNESCO/ G. Jocques WHO/ H. Anenden E.P.L./1. Len~ui © Still Pictures; M. Edwords © Still Pictures/M. Edwords ©; WHO/.J. Littlewood L. Sirmon © WHO/ H. Anenden; L. Sirmon © WHO/ H. Anenden WHO/ H. Anenden; Still Pictures/ M. Edwords © WHO/ H. Anenden E.P.L./ N. Dickinson © Still Pictures/ M. Edwords © WHO/P. Almasy; L. Sirmon © WHO L. Sirmon © WHO/ K. Pelzer; WHO/H. Anenden WHO/ J. Mohr; WHO/ P. Almosy Still Pictures/ M. Edwords © WHO/ H. Anenden WHO / E. Schwob E.P.L./ 1. Lengui WHO /B. Chomped WHO/B. Chomped; L. Sirmon © Korolinsko Institute! Still Pictures/ J. 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