Daly's Adventure

In a claustrophobic hallway nook of Building 8 on the campus of the National Institutes of Health in Bethesda, Md., stands an aging General Electric freezer crammed with hundreds of vials. Housed in this single appliance is the most comprehensive and hard-won collection of frog skin secretions in the world. The chemicals in some of these vials have sparked research wildfires. One inspired an analgesic drug development program at a major pharmaceutical company. Some became workhorse molecular tools for biologists studying cell receptors and ion channels. The structures and value of others remain unknown.

They are the trophies that chemist, pharmacologist, and chemical ecologist John W. Daly has been finding around the world for more than 40 years, and they have made him famous in the field of natural product chemistry. "For amphibian natural products, his work is simply the best there is," says Jon Clardy of Harvard Medical School, where Clardy investigates, among other things, chemicals made by marine sponges, moths, and microbes.

Even so, Daly—a chemist's Indiana Jones of sorts who has trekked in rain forests and other amphibian-rich venues from Colombia to Thailand to Madagascar to Australia−now finds himself at the most perilous crossroads of his career. In May, Daly was told by Marvin C. Gershengorn, the scientific director of the National Institute of Diabetes & Digestive & Kidney Diseases (NIDDK), that funding for his laboratory there would be zeroed out at the end of this fiscal year because of budgetary constraints. Ever since, Daly and many of his collaborators and colleagues have been desperately trying to convince the leadership at NIDDK and NIH to reverse the decision. At press time, there was talk of relocating Daly's research program to another NIH institute, but there's still no final verdict on whether this will be Daly's last summer of research at NIH.

What bothers Daly most about these troubling times is that it has placed a hold on his relentless quest to uncover some of nature's most ostentatious chemical inventions: molecules with often scientifically useful and sometimes deadly biological consequences that he and others have found in frogs and other amphibians as well as arthropods and the occasional bird. Evidence of Daly's productivity is all over his cramped office. Every shelf and surface is overfilled with laboratory and field notebooks with dates spanning a half-century, manuscripts in various stages of completion, posters with frogs overlaid with chemical structures, stacks of current reprints, and chemical samples and biological specimens.

At 73, Daly is lanky with a gray-bearded face often framed by his gigantic, black-frame reading glasses. On a warm day earlier this month, his choice of sandals and shorts showed off athletic legs that have taken him to many faraway places in search of nature's chemistry. Daly retired in 2002—without really retiring—and is now a scientist emeritus at NIDDK.

With written assurance from Gershengorn and approval by NIH leadership, Daly arranged to retain an office, lab space, secretarial assistance, and the continued collaboration of two longtime staff chemists. H. Martin Garraffo and Thomas F. Spande have been with Daly, elucidating structures of hundreds of natural products, for 19 and 26 years, respectively.

This arrangement is how Daly has kept himself in the game when most scientists his age really do retire. His love for biology showed up as a kid in Portland, Ore., where he collected frogs and garter snakes in his backyard. His mastery of chemistry came later when he earned degrees in biochemistry and organic chemistry at Oregon State University and then at Stanford University. For his Ph.D. dissertation at Stanford, he worked out the structure of a terpene alcohol in peppermint oil. After that, in 1958, his supervisor helped him secure a postdoctoral position at NIH in the Laboratory of Chemistry led by Bernhard Witkop.

There, Daly had two career-defining experiences: He developed experimental skills in pharmacology while working under the tutelage of the late Julius Axelrod, who would share a Nobel Prize for his research on the neurotransmitter norepinephrine. Equally fateful was Witkop's request to Daly in 1963 to run a research errand: Go to the Colombian rain forests to harvest and chemically characterize skin secretions of frogs that Indians there were using to poison their darts. From this came the discovery of the batrachotoxins, a unique class of sodium-channel activators.

After reading about that discovery in Medical World News in 1966, Charles W. Myers, then a herpetology graduate student studying the reptiles and amphibians of Panama, wrote to Daly. He suggested the two collaborate on a study of poison frogs in Panama. "Myers became my mentor in the field," Daly says. He adds that Myers helped him appreciate the biological, ecological, and evolutionary contexts that go along with the pure chemistry of natural products. Seeking to understand these contexts and to find new agents for biomedical research has driven Daly's work ever since.

Daly's brand of retirement includes publishing papers regularly—13 in the past 18 months. He also hasn't put an end to his lifelong series of dozens of natural-product hunting adventures. Two months ago, he traveled to Costa Rica with herpetologists Maureen A. Donnelly and Ralph A. Saporito of Florida International University to investigate the flow of alkaloids from specific ants and other arthropods to the frogs that feed on the arthropods.

With his name on more than 600 published papers, a handful of patents, and a long list of awards and honors—among them induction into the National Academy of Sciences and the symposium "Roots of Chemistry at NIH," which was dedicated to Daly on his 65th birthday&—it would take a book to chronicle his scientific accomplishments. Consider a paper that Daly, Spande, and Garraffo published in the Journal of Natural Products (2005, 68, 1556). It is titled "Alkaloids from Amphibian Skin: A Tabulation of Over Eight Hundred Compounds," and the authors have had a hand in identifying virtually all of those alkaloids. Amid this bounty of chemical diversity, a few discoveries stand out even to Daly.

"Epibatidine is by far the most important because it has had such an impact on nicotinic receptor research," Daly says, referring to a class of cellular receptors in brain and other tissues. First isolated in tiny quantities from the poison frog Epipedobates tricolor during a 1974 field trip with Myers to Ecuador, Daly observed in a routine pharmacology test that a mouse injected with the extract arched its tail over its back. Daly recognized that this was the "Straub tail," a reaction associated with opioids, not with any of the frog alkaloids he had been working with.

It took a second trip to collect enough frogs to allow isolation of about a milligram of the active principle, which the researchers named epibatidine. Daly showed that epibatidine indeed was not an opioid, yet it was 200 times more potent than morphine as an analgesic. The full structure remained a challenge until years later when the increased sophistication of nuclear magnetic resonance spectrometry techniques allowed Daly and colleagues to establish the nicotine-like structure of epibatidine and report it in 1992.

Within a year, the laboratory of Harvard University organic chemist and Nobel Laureate E. J. Corey had synthesized both enantiomers of epibatidine and offered Daly these and three analogs. The gift enabled Daly and colleagues to determine that epibatidine owed its analgesic activity to its potent stimulatory effect on nicotinic receptors. That finding, along with epibatidine's structure, inspired medicinal chemistry programs aimed at developing powerful new analgesics, including one at Abbott Laboratories from which emerged the promising compound ABT-594. This compound is far more potent than morphine as a painkiller but later proved to have unacceptable side effects. Even so, epibatidine has become one of the most important molecular tools for scientists studying the biological role of nicotinic receptors.

Another research standout for Daly was his isolation of batrachotoxin from poison dart frogs of Colombia. With this isolated alkaloid—and crystallographic data supplied by Isabella Karle of the Naval Research Laboratory—Daly and his first postdoctoral colleague, Takashi Tokuyama, were able to establish the compound's structure. In the 1970s, after Daly and electrophysiologist Edson X. Albuquerque at the University of Maryland, College Park, revealed batrachotoxin to be a potent and specific activator of sodium channels, the agent became a widely used tool for probing interactions of anesthetics, anticonvulsants, and antiarrhythmia agents with these channels.

Daly has always been fascinated by the biological and chemical ecological significance of the compounds he has been discovering. That's why one of his more recent research foci has been to track down the ecological sources of some of the toxins.

"I was originally resistant to the dietary source idea," he says, referring to the possibility that the alkaloids are derived from dietary sources rather than made by some biosynthetic process within the amphibians' own cells. Now for over a decade, he and coworkers have been chronicling how poison frogs accumulate their skin alkaloids from alkaloid-containing arthropods, most notably ants, but also from beetles and millipedes.

As Daly even now forges new collaborations and looks forward to new studies, NIDDK's decision to cancel his research funding leaves a bitter taste, like that of the alkaloids he has at times quickly detected in the field using a taste test. "No good science goes unpunished," reads a note on his office door. With the momentum building at NIH in mid-June to keep his lab up and running, however, he is feeling confident that his days of thrilling chemical sleuthing are not yet so numbered.