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Groene thee goed ter voorkoming en ter bestrijding van
kanker.*
Green tea: prevention and
treatment of cancer by nutraceuticals
Editor’s note: The following
independently written article was originally published in the September 18,
2004, issue of the British medical journal The Lancet [Elsevier Lancet 2004 Sep
18;364(9439):1021-2.]
Green tea1 has always been considered by the Chinese and Japanese
peoples as a potent medicine for the maintenance of health, endowed with the
power to prolong life. Recently, Yean Lee and colleagues2 looked at the effects of the main active green tea
constituent, epigallocatechin-3 gallate (EGCG) on chronic lymphocytic leukaemia
B cells isolated from leukaemic patients. These cells are characterised by their
resistance to apoptosis because they secrete and bind vascular endothelial
growth factor (VEGF), a potent angiogenic cytokine that also acts as a crucial
survival factor for tumour cells. The researchers showed that addition of EGCG
to these cells markedly decreased VEGF-receptor phosphorylation, leading to the
disruption of the VEGF-dependent autocrine pathway that protects the cells from
apoptosis and cell death.
These results support our
observations3 on the potent inhibition of
the activity of VEGF-receptor tyrosine kinase by components of green tea, and
provide strong evidence that this inhibitory effect may have profound
repercussions on tumours that depend on this cytokine for progression. Of
considerable importance is the low concentration of EGCG required to trigger the
observed biological effects, because VEGF-receptor activity can be inhibited3 and apoptosis of leukaemia B
cells can be induced2 with concentrations of EGCG
in the plasma after moderate drinking of green tea (2-4 cups a day).4 Although more extensive investigation on the effects
of this compound in patients with chronic lymphocytic leukaemia B is required,
these findings nevertheless raise the interesting possibility that green tea
could be used as a combination agent for treating leukaemia.
VEGF is also crucially
important to tumour angiogenesis, the process by which tumours grow and invade
surrounding host tissues.5 In the
initial phases of tumour growth, angiogenesis by low-dose delivery of EGCG, as
seen in vitro,3-7 could thus have beneficial
in-vivo effects against several other types of cancer. This mechanism also
provides a strong scientific basis for the chemopreventive property of green tea
that has been inferred from several epidemiological studies which showed that
frequent drinking of green tea is inversely associated with the risk of
developing several types of human cancer, such as oesophageal cancer.8
With the notable exception of
the use of retinoic acid for the treatment of promyelocytic leukaemia,9 the importance of nutraceuticals in cancer prevention
and treatment remains largely under-exploited despite increasing evidence
showing that these molecules have chemopreventive and chemotherapeutic ability.
Notwithstanding the considerable progress made in the design of novel anticancer
drugs in recent years, one clear lesson from the past decades of research into
cancer is that, although we can treat cancer and induce remission, survival
rates have changed little in most cancers. Moreover, most anticancer drugs have
several toxic side effects that may produce a poor quality of life for patients
and considerable cost in supportive care. Green tea and other diet-dervived
compounds, such as curcumin, phyto-estrogens and carotenoids,10 offer several advantages as
anticancer products, because these compounds are non-toxic, produce few side
effects, are widely available, and are cheap. It would thus be interesting to
examine the beneficial effects of including green tea in the diet of patients
undergoing treatment for cancer as well as in patients at high risk of
recurrence, such as those in remission after treatment and those at risk for a
second neoplasm.
We believe that anticancer
agents designed by nature and used for several thousands of years with little
toxicity may prove useful in treating and preventing cancer. Results such as
those obtained by Lee and co-workers2 show that
food derived chemicals constitute a complementary source of anticancer agents.
Richard Béliveau, Denis
Gingras
Laboratoire de Médecin Moléculaire, Hospital
Ste-Justin-UQAM, Centre de Cancérologie
Charles-Bruneau, Montréal, Quebec, Canada H3T 1C (Jan. 2005)