TAXOL CLINICAL TRIAL SUPPLIES MAY HAVE TO INCREASE

TAXOL CLINICAL TRIAL SUPPLIES MAY HAVE TO INCREASE two to three-fold to handle projected demand by 1992, according to preliminary estimates.

Bristol currently plans to produce enough taxol to treat approximately 12,500 patients in clinical trials in 1991. In order to treat that number of patients, the company will have to produce about 25 kg of taxol, which would require about 750,000 pounds of dried yew bark. Approximately 40,000 yew trees would have to be harvested to meet that production goal.

The National Cancer Institute is conducting taxol patient- response studies in an attempt to narrow the population to the patients most likely to respond favorably. NCI Cancer Therapy Evaluation Program Associate Director Michael Friedman told a June 24 forum on taxol that NCI investigators view the drug as a potential "part of a curative package for a certain group of patients and we need to find out which patients those are, and how best to employ the drug."

Correlative studies designed to identify those patients are now being conducted, Friedman said, "in which patients will have their tumors analyzed for certain biochemical features. They will be treated with taxol, and their response monitored. If we're able to define a biologic profile of the kind of tumor that responds well to taxol, we can then use that information in many ways. We can pick patients who are more likely to respond, save the drug that might not help some other patients, and at the same time maximize the chance that the patients who are likely to respond will in fact benefit."

NCI's current policy is that "only patients participating in clinical trials will be offered taxol," Friedman said. He predicted that "we won't have an adequate amount of taxol" for compassionate use availability for the next one or two years in all eligible patients with overian and breast cancer. Under the terms of the CRADA (cooperative research and development agreement) Bristol-Myers signed with NCI last January, the company will provide 1 kg of taxol for compassionate use this year. Horovitz said Bristol-Myers recently sent NCI its first shipment for compassionate use.

BMS said it hopes to file a taxol NDA in 1992 for the treatment of ovarian cancer, which would be an orphan use. Taxol is being investigated as a possible treatment for a wide variety of cancers.

Ongoing NCI-sponsored clinical trials using taxol include: a Phase III trial in Stage II and IV ovarian cancer patients designed to compare the response rate, response duration and survival of patients randomly assigned to treatment with cisplatin/taxol or cisplatin/cyclophosphamide; a Phase II trial with taxol in patients with advanced head and neck cancer, designed to study the toxicity of taxol administered in a 24-hour continuous I.V. infusion every three weeks; Phase II studies of taxol in patients with previously untreated extensive-stage small- cell lung cancer and with adenocarcinoma of the upper gastrointestinal tract using the continuous I.V. regimen; a Phase II trial of taxol in patients with hormone-refractory prostate cancer; a Phase II study in patients with advanced non-small-cell lung cancer using intravenous taxol; a Phase I study of taxol/doxorubicin followed by granulocyte colony stimulating factor (G-CSF) in patients with previously untreated metastatic breast cancer; and a Phase I trial of taxol/cisplatin with G-CSF in patients with advanced malignancies.

While yew bark will necessarily be the primary source of taxol for the immediate future, processes to extract taxol from other biomass, such as needles and twigs, are expected to be developed within the next five years, Horovitz said. Dick Miller, a forest geneticist at the United States Forest Service, said that his agency is conducting research on methods to extract taxol from Pacific yew heartwood. Another promising near-term alternative is semi-synthesis of the drug, which involves chemically converting a taxol precursor, or intermediate, from various taxus sources, which include ornamental yew plants, into taxol.

In the long term, it is anticipated that the Pacific yew tree will be domesticated, Miller said. He noted that a joint NCI/USFS study is analyzing the taxol content of needless and twigs taken from trees that were situated in different forests. Initial results show that the taxol content varies widely, he said. Further research will be done to determine whether those differences are due primarily to genetics or to habitat.

Another possible future source of taxol is production through plant cell tissue culture. San Carlos, Calif.-based ESCAgenetics announced June 25 that it has "successfully expressed taxol in tissue culture less than nine months after initiating our taxol program." The company expects to scale up to commercial production within the next two years.