Research from the Human Biology Division provides insight on the cancer-fighting mechanisms of PC-SPES, a well-known herbal supplement taken by men with advanced prostate cancer to slow progression of the disease.
What's more, the study suggests that PC-SPES could compromise the effectiveness of the chemotherapy agent Taxol, which is commonly prescribed for men with prostate cancer.
PC-SPES has long been known to act as an estrogen, blocking male hormones that fuel prostate cancer.
Michael Bonham, a graduate student in Dr. Peter Nelson's laboratory, and colleagues found that PC-SPES also effectively thwarts cancer growth by inhibiting the assembly of specific structural components within prostate-cancer cells, killing the cells and blocking tumor growth.
The researchers also found that the supplement contains compounds that behave much differently from estrogens. More research is needed to identify these compounds and understand how they work.
The study, published in the Nov. 6 Journal of the National Cancer Institute, also involved collaborators at Cedars-Sinai Prostate Cancer Center in Los Angeles and at Veterans Affairs Puget Sound Health System. CaP CURE and the National Cancer Institute funded the work.
Just as PC-SPES blocks the assembly of structural components that provide support for a cancer cell, several traditional chemotherapy agents, such as Taxol, work in the opposite way by inhibiting the breakdown of the same components. Either way, the cell dies.
The researchers found that while PC-SPES and Taxol effectively kill cancer cells independently, the drugs are less effective when combined. They act against each other, which could decrease the effectiveness of therapy.
Nelson said that although this drug interaction has not been demonstrated in humans, it does raise concern.
"Studies in the laboratory don't always translate to what actually happens in humans," he said. "But it's information that should probably be out there so that people can be aware of it."
The findings underscore the importance of open communication between cancer patients who take supplements and their oncologists.
"Most of my patients are taking a lot of different supplements," Nelson said. "Many of these preparations will do no harm, but because some could cause problems I encourage them to talk with me so that we can negotiate their use."
PC-SPES is a Chinese dietary supplement consisting of eight herbs, including licorice and saw palmetto, which has been shown in preliminary studies to be effective against prostate cancer. In February, PC-SPES was voluntarily recalled by its manufacturer, BotanicLab, due to concerns that it was tainted with undeclared prescription-drug ingredients such as DES (an estrogenic agent) and coumadin, a blood-thinning agent.
Cancer-prevention team includes naturopath Heather Greenlee
Naturopathic physicians and cancer-prevention researchers alike feel that the best way to counteract disease is to stop it before it starts.
That mutual conviction is what drew naturopath Dr. Heather Greenlee to Fred Hutchinson, where she conducts prevention research with Dr. Johanna Lampe in the Public Health Sciences Division.
Greenlee, the division's first naturopathic postdoctoral fellow, is the recent recipient of a three-year training grant from the National Center for Complementary and Alternative Medicine, a recently established branch of the National Institutes of Health.
"Ideally, we shouldn't have to treat disease at all," Greenlee said. "The fundamentals of naturopathic medicine are focused on disease prevention, and I see my research in the Cancer Prevention Research Program as a good fit with the naturopathic approach."
Greenlee and Lampe plan to evaluate the impact of natural "alternatives" - including dietary changes and herbal supplements - on estrogen metabolism in premenopausal women.
Greenlee eventually plans to study these effects in women at high risk of developing breast cancer. Estrogen is a known risk factor for the disease.
In clinical practice, naturopaths use combinations of many of these natural remedies to regulate hormone levels, said Greenlee, who maintains a clinical practice at the Bastyr Center for Natural Health in Seattle.
"We know many of these interventions can have potent biologic effects on different hormonal pathways in the body," she said.
"While researchers have focused on some of the individual therapies, no one has investigated the effects of the multidimensional approach used routinely by naturopathic physicians on estrogen metabolism."