PC-SPES, a dietary supplement taken by some men to treat prostate cancer, may compromise the effectiveness of chemotherapeutic drugs for the disease, such as paclitaxel, according to a new study.
The study, published in the November 6 issue of the Journal of the National Cancer Institute, shows that the effects of paclitaxel may be reduced when taken alongside the herbal supplement.
Michael J Bonham and Peter S. Nelson, of the Fred Hutchinson Cancer Research Center in Seattle, US, and their colleagues found that treatment of prostate cancer cells in vitro with PC-SPES altered the expression of numerous cytoskeleton genes, including á-tubulin, a component of microtubules and a target for the chemotherapeutic agent paclitaxel. The authors also found that PC-SPES reduced paclitaxel activity in both laboratory and mouse studies.
PC-SPES is a mixture of seven medicinal herbs plus saw palmetto. The compound was introduced in the United States as a dietary supplement in 1996, but has since been controversial as it has been found to contain other prescription drugs.
The study showed that PC-SPES and paclitaxel seem to work in different ways - the herbal extract slows the growth of cancer cells by inhibiting the assembly of certain cell structures called microtubules, but paclitaxel works by preventing the breakdown of the microtubular structures.
"Our results suggest that PC-SPES and paclitaxel may have conflicting effects if administered together in the clinical setting," the authors concluded.
The study also illustrates growing concerns about the use of botanical compounds alongside conventional drugs.