Vion Pharmaceuticals Inc. discontinued enrollment of a Phase II study of Triapine as a single agent in patients with prostate cancer in order to focus its resources on the drug's more promising trials - those studying it as a combination therapy.

The company made the decision after it accrued 10 patients in the trial, but also following the release of Phase II data analyzing the drug as a single agent in head and neck cancer.

The company's stock (NASDAQ:VION) fell 35 cents Friday, or 12.2 percent, to close at $2.50.

In the head and neck cancer trial involving a total of 32 patients with recurrent or metastatic disease, one patient had a partial response, while nine patients had stable disease after four courses - approximately eight weeks - of therapy. About 40 percent of the patients had received a prior chemotherapy treatment. Triapine appeared to be well tolerated.

"If the results had given us a very strong signal of Triapine as a single agent in head and neck cancer, of course we would have pursued that," said Howard Johnson, the company's president and chief financial officer. "We got the information we wanted, and then we decided to focus our resources on the combination efforts because that's the main strategy."

The Phase II single-agent trials began a year ago. The company is conducting three clinical studies of Triapine as a combination therapy. It will use the resources saved from stopping the prostate cancer trial partly for two ongoing Phase II studies of Triapine in combination with gemcitabine, which were initiated in May in patients with metastatic or advanced pancreatic cancer and in non-small-cell lung cancer patients. At the American Society of Clinical Oncology meeting in Chicago last year, Vion reported data from a Phase I trial of Triapine in combination with gemcitabine that showed the drug achieves serum concentrations that are capable of enhancing gemcitabine activity in tumor cell lines.

"What we've told the investment community is there should be data on the Phase II Triapine/gemcitabine trials sometime in the first half of this year," Johnson told BioWorld Today.

Vion also is conducting a Phase I trial of Triapine in combination with Ara-C in advanced leukemia. And in addition to the three trials conducted by Vion, the National Cancer Institute (NCI) initiated a trial in January evaluating Triapine as a combination therapy with fludarabine to treat relapsed and refractory hematologic malignancies.

"So there's still multiple trials ongoing and actually the NCI should initiate additional trials in the coming months," Johnson said.

Triapine inhibits the enzyme ribonucleotide reductase, preventing the replication of tumor cells.

In October, Vion entered a license agreement with Beijing Pason Pharmaceuticals Inc. for exclusive rights to develop, manufacture and market Triapine for cancer and antiviral uses in China, Taiwan, Hong Kong and Macao. Vion received an up-front payment of $500,000 for the rights. It is entitled to receive $4.75 million in milestone payments, as well as 11 percent royalties on sales in the territory. Pason will fund all development necessary for regulatory approval in those countries.

Vion's other advanced drug is Cloretazine, or VNP40101M, a sulfonyl hydrazine prodrug. Cloretazine has been evaluated as a single agent in Phase I trials in solid tumors and in advanced leukemia. The drug also is being studied in combination with Ara-C in advanced leukemia. The company plans to begin Phase II trials in leukemia and solid tumors in 2004.

At the preclinical stage, Vion is studying TAPET (Tumor Amplified Protein Expression Therapy), a drug delivery system using modified Salmonella bacteria. The vector is designed to deliver drugs directly to solid tumors. Vion also is evaluating KS119, a hypoxia-selective compound from the sulfonyl hydrazine class.

As of Sept. 30, the company had cash and cash equivalents of $18.4 million. Vion completed an $11.3 million private placement last September, providing it with enough money to take it through December of this year. (See BioWorld Today, Sept. 11, 2003.)

The company said in its quarterly report for the period ended Sept. 30 that it would need to form a partnership or raise additional capital to continue along its operating plan beyond 2004.

About two years ago, the company laid off a third of its employees in order to save cash and support its clinical products. (See BioWorld Today, June 3, 2002.)