Natural substances in fruits and vegetables may be potential treatment for prostate cancer
ROCHESTER, MINN. — Quercetin (kwer-se-ten), a natural substance found in apples, onions, tea and red wine, may be a potentially novel approach for preventing and treating prostate cancer, according to a laboratory research study conducted at Mayo Clinic in Rochester.
The results of the study were presented today, March 26, at the 92nd annual meeting of the American Association for Cancer Research (AACR) in New Orleans. The study also is published in this month’s issue of the cancer journal Carcinogenesis.
“Our laboratory results showed quercetin blocks the androgen (hormone) activity in androgen-responsive human prostate cancer cell lines,” says Nianzeng Xing, Ph.D., the Mayo Clinic researcher who presented the results of the study at AACR.
“By blocking the androgen activity, the growth of prostate cancer cells can be prevented or stopped,” he said. “Our study suggests quercetin may be a potential non-hormonal approach to accomplishing that goal.”
Prostate cancer is the second leading cause of cancer death in men in the United States. It annually claims about 31,500 men, accounting for about 11 percent of male cancer-related deaths.
The findings may lead to another treatment option for the nearly 200,000 men diagnosed with prostate cancer annually in the United States. It also may mean that eventually some men may not have to undergo castration, the current, commonly used treatment for advanced prostate cancer.
However, Dr. Xing cautions, more research is required to determine whether the preliminary laboratory findings about quercetin translate into actual benefit for men either at risk or diagnosed with prostate cancer.
Quercetin is an abundant, naturally occurring flavonoid compound. In addition to apples, onions, black and green tea, and red wine, the compound is found in green leafy vegetables, beans and citrus fruits.
Quercetin has been studied scientifically for the past 30 years. It’s documented as safe and having relatively low toxicity.
The compound is currently used in therapeutic treatments for allergic conditions such as asthma, hay fever, eczema and hives. It’s also used clinically to treat several inflammatory conditions, including gout, pancreatitis and prostatitis.
The Mayo Clinic study is the first research indicating quercetin has significant activity against the androgen receptor in the human prostate cancer cell lines.
Androgens are male hormones, the most common being testosterone. Androgens also are involved in the development, progression and growth of prostate cancer.
The biological effects of androgens in the prostate are mediated by the androgen receptor, says Dr. Xing. An activated androgen receptor can turn on or off critical genes, which affect the biology and pathology of the prostate.
“Our laboratory data showed that androgen receptor expression was inhibited by quercetin and the rate of response was dose-dependent,” says Dr. Xing. “Our study also delineated the mechanism by which quercetin reduced the androgen receptor.”
Androgen deprivation or suppression therapy by surgery or medication to remove or reduce the androgens is the cornerstone of current treatment for advanced prostate cancer.
“Unfortunately, the cancer recurs in about 80 percent of men within one to two years after undergoing the therapy, and this may be correlated with mutations in the androgen receptor,” says Dr. Xing.
“The androgen receptor may function with either a small of amount of androgen or independently of androgens,” he says. “As a result, the cancer learns to grow in the prostate with less hormone or even without the need of the hormones.”
In view of that fact, Dr. Xing says, “A more effective strategy in the fight against prostate cancer may be to minimize or eliminate the amount of the androgen receptor.”
The Mayo Clinic research study indicated that this strategy may be possible with quercetin.
The next step in the research process is to study the effects of quercetin in a laboratory mouse model with prostate cancer.
###DESCRIPTION OF ANDROGENS AND ANDROGEN RECEPTOR Androgens are hormones that enter the prostate cell and bind to the androgen receptor protein. The function of the androgen receptor is similar to a light switch in that the receptor turns on certain genes in the prostate. These certain genes promote the growth of prostate cancer cells. By knocking out the androgen receptor switch, as suggested by the Mayo Clinic study, prostate cancer cells are prevented from growing.
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