Cell Genesys, Medarex Drugs Fight Prostate Cancer

Cell Genesys Inc., the developer of the GVAX immune system-booster, said its treatment reduced a common sign of prostate cancer when used with an experimental treatment from Medarex Inc.

The two drugs may work well together because GVAX stimulates immune system cells to fight cancer and the Medarex treatment unleashes the cells from controls that keep them in check, researchers said today a medical meeting. Five of six patients on GVAX and high doses of the Medarex drug cut their PSA scores, a measurement of disease, in half, researchers said.

Cell Genesys, based in South San Francisco, California, is conducting late-stage clinical trials enrolling more than 1,200 patients to see whether GVAX can help prostate-cancer patients live longer. The first study is expected to offer results in the second half of 2009. If successful, it could be the first approved immune-boosting therapy for cancer in the U.S. An estimated 28,000 men will die of prostate tumors this year, according to the American Cancer Society.

The combination is ``showing a lot of success in increasing anti-tumor activity in these patients,'' said Saskia Santegoets, a cancer researcher at Vrije University Medical Center in Amsterdam, in a statement.

The findings were presented today at the American Association for Cancer Research meeting in San Diego.

Shares Fall

Cell Genesys fell 2 cents to $3.16 at 4 p.m. New York time in Nasdaq Stock Market composite trading. The stock has gained 37 percent this year.

Cell Genesys, which has no marketed products, had an accumulated deficit of $491 million at the end of 2007, the company said in its annual report filed with the Securities and Exchange Commission. The company was founded in 1988.

Medarex, based in Princeton, New Jersey, dropped 42 cents, or 5.4 percent, to $7.37. It has dropped 29 percent this year. The company, founded in 1987, had an accumulated deficit of $990 million at the end of 2007, the company said in its annual report.

The study looked at 12 patients who took GVAX every other week for six months, and were broken into four groups who took different doses of the Medarex drug, ipilimumab. Patients had a terminal form of prostate cancer that resisted standard hormone-blocking therapy.

Highest Doses

The anti-tumor responses, measured by PSA or prostate-specific antigen, scores, were seen at the two highest doses of the Medarex treatment. Four of the five patients who responded had their PSA scores stay low for six months. Two patients had multiple lesions on their bones disappear. One person had an improvement in bone pain, researchers said.

GVAX is made of whole tumor cells that have been dosed with radiation to prevent them from multiplying in the body. The cells carry markers of prostate cancer that are supposed to ``teach'' the immune system to recognize them as foreign and mount an attack.

Cell Genesys is conducting a late-stage study of 626 patients, called Vital-1, to determine whether GVAX can help people live longer than those taking Sanofi-Aventis SA (SAN)'s Taxotere, a chemotherapy.

Last month, Cell Genesys formed a global alliance with Osaka, Japan-based Takeda Pharmaceutical Co. (4502) to develop and market GVAX for prostate cancer. Takeda agreed to pay $50 million upfront, as much as $270 million in milestone payments, and royalties on sales, the companies said.

Many investors are betting Cell Genesys will fail. About 16.8 million shares of the company were in a short position at the end of March, up from 6.89 million on March 15, 2007, according to data compiled by Bloomberg. Short-sellers try to profit on a falling stock by selling borrowing shares and buying them back later at a lower price.

To contact the reporter on this story: Luke Timmerman in San Francisco at ltimmerman@bloomberg.net

To contact the editor responsible for this story: Reg Gale in New York at rgale5@bloomberg.net

Press spacebar to pause and continue. Press esc to stop.

Bloomberg reserves the right to remove comments but is under no obligation to do so, or to explain individual moderation decisions.

Please enable JavaScript to view the comments powered by Disqus.