Study proves contamination of prostate cancer supplement
advanced prostate cancer which was recalled in the US and Canada
earlier this year, has shown that the supplement was contaminated
with the synthetic drugs warfarin, diethylstilbestrol and
indomethacin.
A chemical analysis of PC-SPES, a recently recalled herbal dietary supplement commonly used to treat advanced prostate cancer, has shown that the supplement was contaminated with the synthetic drugs warfarin, diethylstilbestrol and indomethacin.
Both diethylstilbestrol and indomethacin have known anticancer properties.
Later preparations of PC-SPES, which contained less diethylstilbestrol and indomethacin than earlier preparations, showed a corresponding decrease in anticancer potency by as much as sixfold, researchers have reported in the 4 September issue of the Journal of the National Cancer Institute.
PC-SPES ("PC" stands for prostate cancer, "SPES" is Latin for hope) is a mixture of seven medicinal herbs plus saw palmetto. The compound was introduced in the United States as a dietary supplement in 1996. Early studies suggested that the preparation was effective in reducing levels of prostate-specific antigen (PSA, a marker for prostate cancer) in both hormone-responsive and hormone-resistant prostate cancer patients.
However, concern grew because of evidence that the preparations were being contaminated with synthetic drugs, said Dr Jeffrey White of the National Cancer Institute in an accompanying editorial.
Subsequent studies found that PC-SPES contained the synthetic oestrogen diethylstilbestrol, the anti-inflammatory drug indomethacin, and the blood thinner warfarin.
Earlier this year, BotanicLab, the California-based manufacturer of PC-SPES, voluntarily recalled the product and has since gone out of business.
In this analysis of eight lots of PC-SPES manufactured at different times between 1996 and 2001, Dr Milos Sovak of the Biophysica Foundation in La Jolla, California, Dr Robert Nagourney of Rational Therapeutics, Long Beach, California, and their colleagues found that all lots contained indomethacin and most of the lots contained diethylstilbestrol. Warfarin began appearing in varying amounts in lots manufactured after July 1998.
"The origin of the three potent synthetic drugs in PC-SPES is puzzling," wrote the researchers. They noted that the amount of diethylstilbestrol present in the lots would have been enough to exert anticancer activity. Lots manufactured after the spring of 1999 contained significantly less diethylstilbestrol and indomethacin than earlier lots and had two to six times less anticancer activity.
In his editorial, White said that "herbal research is complicated enough without having to deal with the added problem of potential product adulteration."
He added that preclinical and clinical trial research of promising herbal interventions should continue but he urged investigators to consider regular quality control evaluations by independent laboratories throughout the course of their research.
The lessons from PC-SPES must be learned well, he said, "because the loss of a product that symbolised hope to some should not occur without leading to an ultimate gain for all cancer patients."
