HALF of all cancers may soon be prevented simply by taking a pill once a
week, say researchers working on drugs that activate our body鈥檚 natural defence
mechanisms.
One such drug, called oltipraz, is already being tested. Developed and
approved for treating schistosomiasis, oltipraz was found to stimulate the body
to make an enzyme called glutathione S-transferase. GST neutralises carcinogens
such as benzene, preventing them damaging DNA and allowing the body to get rid
of the by-products. Tests in animals have shown it can prevent cancer.
Toxicologist Thomas Kensler of Johns Hopkins University in Maryland is
carrying out trials of oltipraz in China, where as many as 1 in 10 adults die
from liver cancer caused mainly by a chemical called aflatoxin, which is found
in moulds growing on rice and cereal grains. Kensler gave oltipraz once a week
for two months to volunteers in Qidong.
Advertisement
They excreted over twice as much neutralised aflatoxin in their urine as
volunteers given a placebo, he told a meeting in San Diego last month. 鈥淕ST was
boosted in these people,鈥� says Kensler. 鈥淭he carcinogen interacts with GST
rather than with their DNA.鈥� Kensler is now analysing the results of a longer
study. If the results are good, trials will take place over many years to see if
oltipraz really reduces cases of liver cancer.
GST and related enzymes detoxify a broad range of carcinogens, so the
approach should protect against other types of cancer too. Raymond Bergan 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 3 months, to see if the drug can alter the level of carcinogens
in their lungs.
Clive Bates of the British anti-smoking group ASH fears the drug will give
smokers an excuse not to quit. But Bergan argues the drug would help those who
can鈥檛 kick the habit. 鈥淲hat we鈥檙e looking to do is decrease the side effects for
people who can鈥檛 quit,鈥� he says.
High-risk groups will be the first to benefit from such 鈥渃hemoprotective鈥�
drugs, but the ultimate aim of researchers is to find ways to lower cancer risk
for everyone. 鈥淭he cancer problem can鈥檛 be solved by simply devising treatments
[for people who鈥檝e already got it],鈥� says pharmacologist Paul Talalay of Johns
Hopkins University, who studies how enzymes such as GST work.
In the immediate future, the best general approach is likely to be a dietary
one. Chemicals that boost the production of enzymes such as GST are present in
vegetables such as broccoli and Brussels sprouts, so Talalay and others are
developing vegetables that contain larger quantities. 鈥淔ruit and vegetables
aren鈥檛 just good for you because of vitamin C. It鈥檚 much more profound than
that,鈥� says Raymond Wolf, a researcher for the Imperial Cancer Research Fund at
Dundee University. 鈥淎 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.鈥�
Yongping Bao of the Institute of Food Research in Norwich predicts that in
three years鈥� time we will be able to use chemicals isolated from vegetables in
pills or to fortify food. Changing our diet, he says, may prevent up to half of
all cancers. 鈥淚f we can isolate these chemicals, there is the potential for a
huge impact on cancer,鈥� agrees Wolf.
He also raises the tantalising possibility that protecting our DNA from
damaging chemicals will not only prevent cancer but also slow the ageing
process. 鈥淚n animals, you can keep switching on these enzymes for life, and the
only side effect is increased longevity,鈥� Wolf says.