PC-SPES Story Not Over Yet

Until recently, PC-SPES was a popular over-the-counter herbal preparation used by many men with prostate cancer. Men reported it helped them feel better, and clinical studies demonstrated PSA (prostate-specific antigen) responses and even some responses measurable by imaging studies. But then several lots of PC-SPES capsules were found to contain DES, which might account for its clinical activity. PC-SPES was removed from the market, and the future of this controversial herbal product appeared bleak indeed.

Now in a report from Cancer Research (2002;62:3920–3924), Michael Bonham and colleagues from the Fred Hutchinson Cancer Research Center and the University of Washington in Seattle have shown that PC-SPES alone may be active against prostate cancer, and that its herbs act by mechanisms that differ from those of DES.

Using cDNA microarrays, Bonham looked at the effects of PC-SPES (carefully checked and found to be free of DES) on expression of more than 3,000 genes in prostate cancer cell cultures. The same methods were also used to determine the effects of DES on gene expression.

PC-SPES increased the activity of 144 genes, and decreased the activity of 175 other genes. Many of these genes are thought to have a part in the growth and regulation of prostate cancer cells. The researchers found that, for the most part, PC-SPES and DES acted on different prostate cancer-related genes.

David Rosenthal, MD, Professor of Medicine at Harvard Medical School and Medical Director of the Zakin Center for Integrative Therapies at the Dana-Farber Cancer Institute in Boston was encouraged by the results of this study. “There is something different and valuable here,” said Rosenthal, who is also Chair of the American Cancer Society's Alternative and Complementary Methods of Cancer Management Advisory Group.

The example of PC-SPES illustrates the need for proper manufacturing and testing of herbal products, said Rosenthal. “We didn't study this the right way at the beginning. We should have studied it first, then done the clinical trials. We have learned something from PC-SPES.”

Peter Nelson, MD, a medical oncologist at the Fred Hutchinson Cancer Research Center and co-author of the report, said that he was first interested in PC-SPES when he became aware that many of his prostate cancer patients were taking the herbal supplement. Now he believes there may be something in PC-SPES that is unique to the compound and works against prostate cancer. “There is really something in that mixture that has activity against prostate cancer,” said Nelson.