Taxol Revisited

Taxol, the latest cancer-fighting wonder drug, is found in Alaska---growing on trees. Even though Taxol is extremely valuable, it won't replace oil as an income producer for the state. Taxol is derived from the bark of Pacific yew trees, a species found mostly in old-growth forests of the Pacific Northwest, from the Cascades to the Rockies. A few Pacific yews do occur in Alaska, close to the northern limit of their range, but only in Southeast, chiefly near Ketchikan and or Prince of Wales Island.

From the point of view of medical researchers and cancer patients, Pacific yews are too rare everywhere. According to a recent issue of the journal Bioscience, a mature yew will yield between five and 20 pounds of bark. To produce enough Taxol to treat one patient with ovarian cancer, the pharmaceuticals industry must process 60 pounds of bark.

None of the foregoing information is new as regular readers of this column may remember. But the Bioscience report presents some aspects of the Taxol story that scientists have learned only recently. The most important item is that medical researchers now have a much better idea of just how effective Taxol is, at least for some kinds of cancer.

Many species of yew trees have long been a source of so-called bioactive compounds, substances that affect living things. In Europe, the poisonous possibilities of yew extracts gained fame; Macbeth's witches tossed yew slips into their bubbling cauldron. After yew's medicinal properties came to the fore in China and in North America, it was used in herbal medicines.

The National Cancer Institute has a special interest in plant materials used in traditional medicines, and it began testing extracts from Pacific yew in the early 1960s. Because Taxol was found to inhibit the growth of mouse cancer cells in test tubes, it was deemed worthy of further tests. During the 1970s, Taxol showed itself capable of healing tumors in mice, including human skin cancers grafted onto specially bred mice. By 1979, the specific way in which Taxol affected cells had been deciphered: it gums up cell division at the chromosomal level. In 1983, Taxol was approved for limited tests in humans.

Because they appreciated how dangerous Taxol could be, (given yew's long history as a poison and their new understanding of taxol's potent effect on cellular reproduction), the clinical researchers conducting the test accepted as patients only people upon whom best-available medical technology hadn't worked.

Several of these patients with terminal illnesses had fatal allergic reactions to the drug. Others suffered side effects ranging from the dangerous (suppression of blood cell production in bone marrow) to the annoying (tingling feelings in the extremities). Yet, other people began to do better. Tumors shrank. Other symptoms became less severe. Some patients experienced complete remission.

In one study, 30 percent of the patients considered to have terminal ovarian cancer improved instead of dying after they were treated with Taxol. In another study, nearly half the patients suffering from advanced breast cancer experienced partial or full remissions of their disease.

The statistics may not seem impressive because more people died than got better in all cases, but every single survivor is a person probably otherwise doomed. The trials are proceeding with many other types of cancer, again using people who are very likely to die because of the advanced stage of their disease.

Now, 10 years after the human trials began, and after improvements in administering the drug have reduced allergic reactions and side effects, the federal Food and Drug Administration has approved Taxol for general use in advanced ovarian cancer. Doctors can prescribe it for patients who are not yet at death's door. The greatest remaining difficulty may be finding enough Taxol for those patients.