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Stopping cancer before it
starts
LONDON -- Apr. 7, 2001
-- Could half of all cancers be prevented simply by taking a
pill once a week? That's the question cancer prevention researchers
are asking about a new class of drugs that activate the body's
natural defense mechanisms.
In an article in the
April 7, New Scientist several researchers talk about
their efforts to harness these cancer-prevention chemicals.
Unlike the antioxidants
such as vitamin C or E, the chemicals these researchers are studying
act on the genetic level says Dr. Raymond Wolf, a researcher
for the Imperial Cancer Research Fund in the United Kingdom.
"Fruit and vegetables
aren't just good for you because of vitamin C. It's much more
profound than that," Wolf said in the article.
"A key difference
between drugs like oltipraz and antioxidants such as vitamin
C is that with agents that induce gene expression, the effects
are long-lasting. If we can isolate these chemicals, there is
the potential for a huge impact on cancer," he says.
The drug oltipraz,
is already being tested in China among workers at risk for liver
cancer and soon will be tested in the United States in smokers
to see if it can reduce lung cancer.
Developed and approved
for treating schistosomiasis, a tropical disease caused by a
blood-borne parasite, oltipraz was found to stimulate production
of an enzyme called glutathione S-transferase (GST). This enzyme
neutralizes carcinogens such as benzene, preventing them from
damaging DNA and allowing the body to rid itself of the by-products.
Tests in animals have shown it can prevent cancer.
Dr. Thomas Kensler,
a toxicologist at Johns Hopkins University in Baltimore, is conducting
trials of oltipraz in China, where as many as 1 in 10 adults
die from liver cancer caused mainly by a chemical called aflatoxin,
found in molds growing on rice and cereal grains. Kensler gave
oltipraz once a week for two months to volunteers in Qidong.
Kensler's team reported
at a scientific meeting in San Diego last month that those taking
the oltipraz excreted over twice as much neutralised aflatoxin
in their urine as volunteers given a placebo.
"GST was boosted
in these people," Kensler told the New Scientist. "The carcinogen interacts
with GST rather than with their DNA."
Kensler is now analysing
the results of a longer study. If the results hold, a multi-year
trial will investigate whether oltipraz can not just neutralize
aflatoxin, but actually reduce the incidence of liver cancer.
GST and related enzymes
detoxify a broad range of carcinogens, so the approach should
protect against other types of cancer too. Dr. Raymond Bergan,
a cancer prevention researcher at Northwestern University in
Illinois is now enlisting volunteers for a trial to investigate
whether oltipraz can protect smokers against lung cancer.
People smoking more
than one pack per day will take either a placebo or an oltipraz
pill weekly for three months, to see if the drug can alter the
level of carcinogens in their lungs.
Taking a different
approach from developing pills, Dr. Paul Talalay, a pharmacologist
at Johns Hopkins University and others are developing vegetables
that contain larger quantities of the naturally occurring chemicals
in vegetables such as broccoli and Brussels sprouts that boost
production of anti-cancer enzymes like GST.
"The cancer problem
can't be solved by simply devising treatments [for people who've
already got it]," says Talalay.
The researchers agree
that high-risk groups will be the first to benefit from such
"chemoprotective" drugs, but the ultimate aim is to
find ways to lower cancer risk for everyone.
SOURCE: New Scientist
issue: 7th April 2001
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