Will sea animals help treat cancer?

Will sea animals help treat cancer?

Last week, two groups of researchers announced advances that may lead to anticancer medications from the sea.

Researchers at the University of Illinois at Urbana-Champaign have reproduced the first such marine product to be tested on humans, and researchers at Arizona State University (ASU) in Tempe have determined the structure of another substance that has had successful results in animal studies. Their findings appear in the Oct. 28 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

The Illinois group has manufactured didemnin B, which naturally occurs in the pancake-shaped, backbone-less tunicate, Trididemnun solidum, more commonly known as a sea squirt. The group, however, has had difficulty closing the nine-unit cyclic peptide, which is a shortchain protein. So far they have produced only 20 milligrams total. It will be at least another year before the synthesis is perfected, organic chemist Kenneth L. Rinehart told SCIENCE NEWS.

In 1982, Rinehart isolated 25 grams of naturally occurring didemnin B from 600 pounds of tunicates for a phase I trial conducted by the National Cancer Institute at the University of Texas in San Antonio and at the University of Vermont in Burlington. The trial, which found the substance to be safe for humans, was completed last year. Phase II trials, which will determine didemnin B's effectiveness against various cancers, have just begun and will be finished in about one year, says Matthew Suffness, chief of the institute's natural products branch.

The other potential anticancer medication, dolastatin 10, is about 18 months away from clinical trials, says Arizona's G. Robert Pettit. He says his group is several weeks from synthesizing the five-unit peptide that naturally occurs in the sea hare, Dolabella auricularia, which resembles a large snail.

Pettit says he first looked to the sea 22 years ago because "we didn't know of any marine invertebrates with cancer and we assumed we can discover new types of drugs.' Since 1972, he has isolated more than 40 dolastatins, 10 of which have been tested on animals. Dolastatin 10 has been the most successful. Pettit says it has cured mice with melanoma and has doubled the lifetimes of mice with leukemia.

If the substances prove effective in humans, researchers expect to mass-produce them by harvesting and breeding the animals or plugging the substances' genes into bacteria. The researchers, however, may not have to worry about any technique. Blue-green algae live near the animals and may produce the substances. If that's true, Suffness says, "we'll just ferment the algae.'