By Lisa Seachrist

Washington Editor

Privately held Dendreon Corp. has begun treating patients in the first of two Phase III clinical trials testing its vaccine therapy in patients with metastatic prostate cancer.

The double-blind, placebo-controlled study, which will include 240 men suffering from advanced prostate cancer, will evaluate the ability of Dendreon's immunotherapeutic vaccine to stop the progression of the disease. The first study is being conducted in the Western part of the U.S. The second Phase III clinical study will be conducted in the Midwest and Northeast.

"We are doing this trial without the help of a partner," said Martin Simonetti, chief financial officer for Seattle-based Dendreon. "We just completed a $17 million Series E financing so we are pretty confident we have sufficient funds for our Phase III program."

Dendreon's therapeutic vaccine, APC8015, is designed to jump-start the immune system by relying on the patient's own dendritic cells to stimulate an immune reaction to cancer. Dendreon isolates the patient's dendritic cells - specialized immune cells that serve as watchdogs by identifying foreign proteins - from peripheral blood. The cells are then activated with a recombinant prostate tumor vaccine in order to trigger an immune reaction to a prostate-specific antigen known as prostate alkaline phosphatase, which is found in most prostate cancer cells.

The treated dendritic cells are then returned to the patient's bloodstream, where they initiate the production of killer T cells in an attempt to rid the body of prostate tumor cells. Phase I/II studies suggested the treatment delivers a long-lasting immunity and could delay tumor progression.

The Phase III studies, which are identical in design, will enroll men with metastatic prostate cancer who've failed hormone therapy. In addition, the men must be free of any pain related to cancer. The participants in the study will receive three immunotherapy treatments over 30 days. Patients assigned to the placebo arm of the trial may enter a "crossover study" if their disease progresses during the study. Patients will be followed for at least one year.

"We will be monitoring progression using bone scans," said David Urdal, chief scientific officer for Dendreon. "We're requiring patients to be pain-free because that will be a secondary endpoint - delay of the onset of cancer-related pain. It's really difficult to quantify the change from some pain to worse pain; it's easier to quantify the onset of pain, and the FDA agrees."

In Phase II trials, APC8015 provided a median delay in disease progression of more than 300 days. In men receiving placebo, disease progression time occurred between 90 and 120 days. Some men experienced tumor regression or stabilization measured by changes in serum PSA levels over time and tumor shrinkage seen on X-rays.

The company is currently conducting Phase II studies of the therapy in less advanced cases of prostate cancer.

"The ideal population for this therapy would be men with a smaller disease burden," Urdal said. "We are working on developing this product for men with earlier-stage disease as well as those with late-stage disease."

Founded in 1992, Dendreon is focused on the development of cell-based therapies for the treatment of cancer and infectious disease. It has developed a platform for the isolation and activation of peripheral blood dendritic cells that allows the production of therapeutic agents.