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From cattle toxin to anti-cancer drug; locoweed, poisonous to livestock, contains a component that destroys malignancies.

From Cattle Toxin to Anti-Cancer Drug

Locoweed, poisonous to livestock, contains a component that destroys malignancies.

Detective work that unmasked a plant toxin poisonous to beef cattle has helped medical science in its search for cancer-fighting weapons.

The toxin, swainsonine, can weaken and eventually kill not only cattle, but also horses, sheep, goats, and other animals that graze on the dozen or so rangeland plants commonly known as locoweeds, says ARS chemist Russell J. Molyneux at Albany, California.

But medical researchers, feeding the compound to laboratory mice, have discovered that swainsonine also stops growth of malignant tumors. Those

scientists used tiny doses, unlikely to harm humans or animals.

Here's how this chemical from cattle-poisoning weeds in the American West ended up in cancer labs. Molyneux and colleague Lynn F. James at the ARS Poisonous Plants Laboratory in Logan, Utah, pinpointed swainsonine as the culprit in locoweed poisonings about 10 years ago. Their finding came about a year after Australian scientists discovered and named the toxin.

An article in Science by Molyneux and James noted swainsonine's effect on animal cells, first described by the Australians. Swainsonine soon captured the interest of medical researchers.

Among them was Kenneth Olden, head of a research team at Howard University Cancer Center in Washington, D.C. He realized that swainsonine might offer a promising new approach to fighting cancer.

Teams like Olden's went on to discover that small doses of swainsonine will indeed stop the spread of malignant tumors in laboratory mice. Swainsonine probably does that by boosting the number and activity of macrophages, helpful cells that fight cancer and other diseases.

Cancer research with swainsonine is continuing in labs in the United States, Canada, and Japan.

Olden's team first used toxin purified and supplied by Molyneux, who extracted it from locoweeds collected by James' staff in Logan. As interest in it grew among medical researchers, companies began making the compound; today, scientists can choose from natural or synthetic swainsonine.

Whatever fame locoweed may earn as the source of a potential cancer-fighting drug, it already has a reputation in cattle country. Animals that eat it may spook easily, withdraw from their companions, or wander aimlessly.

The plants get their name from the word "loco," Spanish for crazy. Poisoned animals may weaken, lose weight, and--if pregnant--abort, or bear young with birth defects.

Every part of the plant--blooms, stems, and leaves--harbors the toxin. Plants remain poisonous even when dead and dry.

Ranchers could protect their animals by herding them away from locoweed-infested pastures and ranges when swainsonine levels climb. That's why Molyneux is tracking swings in the swainsonine content of American locoweeds such as the spotted species (Astragalus lentiginosus) or white locoweed (Oxytropis sericea).

Molyneux and the Logan team also want to find out how much swainsonine an animal normally converts into harmless compounds. "That's so we'll know--more precisely--how much locoweed animals can eat without danger," he says.

Swainsonine is an alkaloid, a class of chemicals that includes caffeine, cocaine, and strychnine. It may be habit-forming.

Poisoned animals, even if moved to safer pastures, will be more susceptible to swainsonine's effects if they ever again graze locoweed.

PHOTO : Chemist Russell Molyneux examines a locoweed plant while working with the structure of locoweed toxin, swainsonine, on the computer.

Russell J. Molyneux is with USDA-ARS Plant Protection Research, Western Regional Research Center, 800 Buchanan St., Albany, CA 94710. Phone (510) 559-5812.
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Author:Wood, Marcia
Publication:Agricultural Research
Date:Jan 1, 1992
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