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Vegetable compound cuts hormone
action in prostate cancer
NEW ORLEANS, Mar. 26, 2001-A natural substance
found in common fruits and vegetables, significantly reduced
the production of a key protein in hormone-dependent forms of
prostate cancer, investigators reported today at the American
Association of Cancer Researchers (AACR) meeting here.
The protein, called androgen receptor (AR)
acts like an antenna on the surface of prostate cells pulling
in the hormone signals and transmitting them to the cell nucleus
where the signal stimulates cell growth.
In the study led by Dr. Nianzeng Xing, a research
fellow in the Urology Department at Mayo Clinic, Rochester, Minn.,
showed that the natural substance, called quercetin, which can
be found in apples, onions, green and black tea, leafy vegetables,
beans, and red wine, jams the AR protein's ability to receive
the hormone signal.
"We were attracted to quercetin because
it is an abundant natural substance with documented safety,"
said Nianzeng Xing, in a prepared statement. "According
to our preliminary data, quercetin should be a good candidate
for prostate cancer treatment because it inhibits the expression
and function of the androgen receptor, and is a natural compound
with relatively low toxicity."
In this laboratory study, the researchers
compared the AR function of prostate cells grown in a dish after
treating them with various amounts of quercetin. Doses over 10
units of quercetin showed significant reduction androgen receptor
function. A dose of 50 units induced a dramatic reduction in
the levels of two androgen-regulated tumor markers: prostate-specific
antigen (PSA; 6.5 times) and hK2 (11 times).
The same dose also impeded production of the
AR protein by up to 60 percent. This is the first research to
demonstrate that quercetin has significant activity against AR
and that the effect depends on the dose.
Prostate cancer is sensitive to male hormones
known as androgens, which act through the androgen receptor.
Researchers have long been interested in therapeutic approaches
that disarm androgens as carcinogenic factors by shutting down
their enabling receptors or slashing AR levels.
Despite surgical castration - removal of the
testes to eliminate the cancer-stimulating testosterone (an androgen)
they produce -- prostate cancer recurs in approximately 80 percent
of cases of late-stage disease.
The Mayo investigators plan to follow this
in vitro research with a study of quercetin in a mouse model
designed to develop prostate cancer.
The American Cancer Society Prostate cancer
estimates that prostate cancer will strike 198,100 men and will
cause 31,500 deaths in the United States this year.
SOURCE: American Association for Cancer Researchers
press release for 92nd Annual Meeting, New Orleans, La.
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