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Scientists have discovered
that Prozac, the antidepressant taken by millions of people around the
world, may stimulate the growth of brain tumors by blocking the body's
natural ability to kill cancer cells.
An international team of researchers
led by John Gordon, professor of immunology at Birmingham University,
found evidence to suggest cancer cells can be killed by "positive
thinking", which could be blocked when people take Prozac.
The study examined the effects
of Prozac and other antidepressants on a group of tumor cells growing
in a test tube. The researchers found that the drug prevented the cancer
cells from committing "suicide", thereby leading to a more vigorous
growth of the tumors.
Although an increased risk
of cancer has not so far been detected in Prozac patients, the latest
findings could lead to a global re-evaluation of the drug's long-term
safety.
Prozac, a "happiness pill"
that was first approved in the United States in 1987, is widely used for
the treatment of depression, obsessive-compulsive disorder and bulimia
nervosa.
The research work was designed
to find new ways of treating lymphomas, a type of blood cancer, by investigating
how the brain communicates with the immune system to induce "positive
thinking" through a neuro-transmitter in the brain called serotonin.
Serotonin is a natural chemical
that regulates people's moods, keeping them balanced. Too much serotonin
affects appetite and sleep and too little affects the mood - often causing
depression.
Prozac, along with other members
of the class of antidepressants known as selective serotonin re-uptake
inhibitors (SSRIs), works by preventing serotonin from being quickly reabsorbed
by nerve cells in the brain.
The scientists tested other
SSRIs such as Paxil and Celexa and found they, too, had the same effect
in stimulating the growth of a type of tumour known as Burkitt's lymphoma.
An exciting property of serotonin
is that it can tell some cells to self-destruct. We have found that serotonin
can get inside the lymphoma cells and instruct them to commit suicide,
thereby providing the potential for an effective therapy.
The researchers found that
Prozac blocked the entry of serotonin into the test-tube tumor cells and
therefore stopped them from committing suicide. That raised the question
of whether Prozac can do the same in the brains of people taking the drug.
Further work is underway to
test Prozac further in this field. In particular, the scientists want
to develop drugs that will mimic the cancer-destroying feature of serotonin
that is blocked by Prozac.
Blood,
April 1, 2002, Vol. 99, No. 7, pp. 2545-2553
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