Nature's Gifts: The Hidden Medicine Chest

By Mark J. Plotkin

It's always exciting for a biologist to find an animal species for the first time, but the 1974 discovery made by Michael Tyler of the University of Adelaide was even more fascinating than usual. Searching a boulder-strewn, fast-flowing creek in an Australian rain forest, Tyler spotted a frog unlike any he'd ever encountered. While its appearance--brown back and cream-colored underside--was nothing special, its reproductive behavior proved to be downright bizarre. The female swallowed her own eggs, incubated them in her stomach and gave birth through her mouth. A single mother coughed up 21 offspring in the same litter.

How is that possible? How could this amphibian, christened the Australian gastric-brooding frog, carry the eggs (and then the tadpoles) inside her stomach without having the offspring digested by stomach acid? To his amazement, Tyler found that the mother frog had the ability to turn off her stomach acids while carrying her precious cargo.

It doesn't take a pharmaceutical marketing manager to figure out the potential here. Excess stomach acid causes great misery in millions of human beings. Perhaps the frog secreted a compound that could help chemists develop a new drug to relieve some human stomach ailments. Maybe so, but we'll never know. The Australian gastric-brooding frog went extinct in 1980, long before a drug company could uncover its secret.

At the dawn of the 21st century, with technology evolving at an ever increasing rate, many people mistakenly believe the natural world has nothing left to offer us in the way of new medicines. This could not be further from the truth. Mother Nature has been creating weird and wonderful chemicals for more than 3 billion years, and we're only beginning to sift through these hidden treasures. New technologies enable us to find, analyze and manipulate molecules as never before. While today's laboratory scientists can synthesize new molecules from scratch at a pace unimaginable just a few decades back, promising compounds produced by nature's most creative creatures increasingly provide the optimum starting points.

Time and again, we find that plants and animals make strange molecules that chemists would never devise in their wildest dreams (and chemists do dream of chemicals in their wildest dreams). For example, researchers could not have invented the anticancer compound taxol, taken from the Pacific yew tree. It is too fiendishly complex a chemical structure, says natural-products chemist Gordon Cragg, of the U.S. National Cancer Institute.

Some of the most promising natural wonder drugs come from compounds not usually associated with healing: poisons. Merck is marketing a blood thinner based on the venom of the deadly saw-scaled viper. A protein from another Asian pit viper is being studied because it appears to inhibit the spread of melanoma cells, and a compound called SNX-482 from the venom of the Cameroon red tarantula may lead to new treatments for neurological disorders.

Every species everywhere has the potential to teach us something new. How tragic then that just as innovative technologies give us the ability to take advantage of natural compounds as never before, we continue to threaten the world's species and the habitats on which they depend. The European leech, source of a new blood thinner, was almost wiped out by overzealous collectors. The same is true for poison dart frogs, producers of many intriguing chemicals. Tropical cone snails and sponges, known to harbor analgesic and anticancer compounds, respectively, live on coral reefs, one of the planet's most endangered marine ecosystems.

History teaches us the folly of destroying species that could benefit humanity. John Riddle, a classics scholar at North Carolina State University, has written about a female contraceptive used by the ancient Greeks and Romans and reputed to be safe and effective. Known as silphion to the Greeks and silphium to the Romans, it was the economic staple of the Greek city-state of Cyrene, which apparently encompassed most of the plant's natural habitat. The plant was mentioned in the writings of Pliny, Hippocrates, Dioscorides and even in a play by Aristophanes. Highly prized, it was worth more than its weight in silver and was portrayed on Cyrenian coins.

Riddle and his colleagues have reported that experiments on lab rats with common fennel (a close relative of silphium's) did indeed show contraceptive activity. Unfortunately, they were unable to test the efficacy of silphium itself. Because of the insatiable demand for it in the ancient world, silphium went extinct about 1,500 years ago.

This article is adapted from Plotkin's new book, Medicine Quest: In Search of Nature's Healing Secrets (Viking)