OREGON STATE UNIVERSITY

Landscape plants yield cancer-fighting substance

09/10/1997

ONTARIO, Ore. - The raw material for an FDA-approved cancer treatment could be grown in your front yard, an experiment here suggests.

Oregon State University and University of Portland researchers are studying landscape plants that produce Taxol, one of the most promising treatments for breast and ovarian cancer.

Taxol is the trade name for a drug first extracted from the bark of the Pacific yew tree and marketed by the Bristol-Myers Squibb company. This led to fears of potential endangerment of slowing-growing wild Pacific yews.

"Reports of people pillaging the forests for Pacific yew bark to sell to pharmaceutical companies are probably more urban legend than truth," said Angela Hoffman, a chemistry professor at the University of Portland. "However, whether the bark is being taken legally or illegally, it is an unsustainable and apparently unnecessary practice. It looks like we could produce all the Taxol we need from leaves harvested from just a few well-managed plantations.

"Taxol, also known as paclitaxel, may actually be as plentiful in the leaves as the bark of the Pacific yew," she added. "We have also found paclitaxel in the leaves of several landscaping yews."

Where and how to grow landscape-type yews is under study at Oregon State University's Malheur Experiment Station near Ontario on the Oregon-Idaho border.

"The experiment is in its second year and looks promising," said Clint Shock, superintendent of the OSU branch experiment station, who is collaborating with Hoffman. "The plant we're working with is 'taxus media hicksii,' a hybrid of the wild tree with a domesticated plant."

The OSU agronomist had a hunch that water stress might increase the paclitaxel content of yew leaves. It turned out he was right.

"Although the purpose paclitaxel serves in plant physiology is unclear, we do know that its levels increase when the plant is stressed," he said. "We're running trials of varying levels of water consumption and finding a 40 percent increase when the plants are deprived of water to the point that where it stresses them, but still allows them to grow."

Hoffman analyzes the leaves grown at the OSU station. She says Shock's experimental plots are producing about 90 to 130 micrograms of paclitaxel per gram dry weight of yew leaves.

To put that into perspective, she said, it takes about 200 micrograms per cancer treatment and patients generally receive eight to 12 treatments over a several-week period. Currently only approved for breast and ovarian cancer treatment, Taxol also is being tested in combination with other cancer drugs.

Producing Taxol from yew leaves looks to be sustainable and cost effective, Hoffman said. Three research groups have made synthetic Taxol in the laboratory, she noted, but the current process is far too expensive and labor intensive to meet the demand.

"We still need to look at the overall economics of growing yews," she said. "On the western side of Oregon they grow faster but contain less paclitaxel per leaf. On the eastern side they grow slower, but the limited rainfall there makes it easier to water stress, thus increasing (paclitaxel) concentration."