Newswise — When University of South Florida chemist Bill Baker dives in the frigid waters off Anvers Island, Antarctica, he looks for a cluster of roundish, light-colored blobs called "tunicates," or "sea squirts." He has been bringing one variety - called Synoicum adareanum - back to his Tampa lab and extracting from it ecdysteroids and polyketids that might prove useful in making the next generation of wonder drugs.
Ecdysteroids are the molting hormones of arthropods, explained Baker, and polyketids are protective compounds made by many different species marine animals. Arthropods represent over 90 percent of the animal kingdom and are distinguished from other animals because their skeleton is outside the body. Their bodies are divided into distinct parts, with jointed legs and appendages and the bodies are bilaterally symmetrical " both sides of the body are the same.
"The majority of ecdysteroids have been found in plants," said Baker. "The number of ecdysteroids isolated from marine invertebrates is very small."
Baker and his colleagues have already isolated an ecdysteroid from S. adareanum that he calls "Hyousterone A," taken from 'hyou,' the Japanese word for ice.
"Ours is the first isolation of an ecdysteroid from a tunicate," said Baker. "We found the structure of the compound to be a hydoxylated analogue of Diaulusterol B."
Why go all the way to Antarctica to find substances that might be turned into drugs to cure disease and save lives? Location, location, location, says Baker.
"Sixty percent of the drugs in use today are either natural products or natural product derivatives," says Baker. "Of the 150,000 known natural products, only 10,000 are derived from marine sources. More than 95 percent of marine natural products come from the tropics. Since the Antarctic is a different and relatively unexplored marine ecosystem, we are more than optimistic about finding a new and useful marine natural product there."
That is what Baker thinks he has found in Palmerolide A, a polyketide, which his lab isolated from the same Antarctic tunicate. When tested against a number of cancer cell types by the National Cancer Institute, the compound showed an unusually high affect on melanoma cells. With melanoma one of the most deadly forms of skin cancer and the number of cases rising, Baker and his colleagues are hoping that Palmerolide A will continue along its testing path and emerge as a new weapon against melanoma.
The path from freezing Antarctic waters, to the lab, to the bedside is, however, a long one, Baker said.
"Synoicum adareanum live at depths that range from 15 to over 700 meters," explained Baker. "They grow in colonies and each colony can be from 18 cm high and 12 cm wide. Divers must collect tunicates, freeze dry them and transport them back to our lab."
Because Palomeride A would be time-consuming and labor intensive to bring back in anything but small quantities, Baker's lab has analyzed the compound and is synthesizing it. In a seminar earlier this year, Baker described the chemical properties of Palomeride A and explained how the synthesis would work.Baker adds that future work will be focused on finding the "reactive center" of the compound and manipulating its bioactivity to be more effective.
Baker's work has been funded by the National Science Foundation and supported by the U.S. Antarctic Program.
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