A chemical found in green tea causes cancer cells to commit suicide

The Journal of the National Cancer Institute Reports: A chemical found in green tea causes cancer cells to commit suicide

Medical researchers at Case Western Reserve University have found a natural component of green tea that triggers a suicidal cell death among cancer cells in living tissue. Researchers led by Dr. Hasan Mukhtar (Dermatology, Oncology), an Indian-born cancer researcher, found that a compound called E-G-C-G (epigallocatechin gallate), commonly found in brewed green tea, signals cancer cells to die or be killed. Dr. Mukhtar says the cancer cells usually oblige by triggering a self-programmed death process called ‘apoptosis’.

Though it’s unclear how cancer cells communicate instructions to self-destruct, cells undergoing apoptosis are visibly altered.

Many foods and cosmetic products now use green tea or green tea extracts as an additive. When applied topically, the extracts, green tea prevents skin cancers associated with sun and chemical exposure. Dr. Mukhtar says green tea and its extracts show promise in fighting cancers of the bladder, oesophagus, and prostrate.

So, how much tea is enough (an average tea bag contains 1 ½ to 2 grams of tea)?

EGCG is capable of blocking UVB-induced skin cancer in mice. At the University of Arizona’s Arizona Cancer Centre, Tucson, researchers are conducting a human clinical trial to analyze the effect of oral and topical formulations of a green tea mixture containing EGCG on skin cancer prevention. Since EGCG cannot be synthesized, David Alberts, M.D., associate dean of research at the University of Arizona College of Medicine, said he expects that chemists will soon initiate programs to develop an EGCG analogue that is more potent but less expensive.

Other human trials involving green tea include an oral cancer prevention trial in China and at the University of Texas M. D. Anderson Cancer Centre, Houston, and a phase III randomized study of the effect of green tea on prostate-specific antigen levels in prostate cancer patients at Memorial Sloan-Kettering Cancer Centre, New York.

A phase II randomized trial is also set to begin soon that will study the effectiveness and toxicity of green tea extract in patients with androgen-independent metastatic prostate cancer.

Several researchers have emphasized the importance of testing green tea in randomized clinical trials. "This is not a one-size-fits-all approach”, Mukhtar said. "What is good for cancer in one population may not be good for another. It is naive to believe that all prostate cancers will be inhibited by green tea."

Tea Polyphenols
In one in-vivo experiment, mice that were fed green tea and exposed to carcinogens prevalent in cigarette smoke developed 45% fewer lung tumours than non-tea-drinking controls. Polyphenolic antioxidants, or catechins, have been identified as the active ingredients in green tea that are responsible for such anti-carcinogenic effects.

The antioxidant activity of these compounds is 25 and 100 times more potent than vitamins E and C, respectively. The most potent of the catechins in green tea is epigallocatechin gallate (EGCG). EGCG is the most powerful antioxidant present in any plant-derived material, said Hasan Mukhtar, Ph.D., professor and director of research at Case Western Reserve University, Cleveland.

Green tea contains greater amounts of polyphenols (30% to 40% of dry weight) than oolong or black teas because it is processed differently, but these teas do also have potential health benefits that are presently also under research investigation.

At a recent American Chemical Society meeting, Roderick Dashwood, Ph.D., principal investigator at Oregon State University’s Linus Pauling Institute, Corvallis, Ore., reported that white tea, which has higher levels of polyphenols, may be even more beneficial than green tea for cancer prevention.

Dashwood is exploring the inhibitory effects and potential mechanisms of action of white tea in vivo, particularly in colorectal cancer.

In parallel with these studies, the Linus Pauling Institute is planning a small clinical trial that will examine the relationship between white tea consumption and colon cancer risk.

Mechanism of Action
The polyphenols present in green tea, particularly EGCG, appear to affect a number of molecular processes, including induction of tumour cell apoptosis (cell self-suicide) and inhibition of tumour growth, invasion, and angiogenesis, and research is still under way to define the precise molecular processes affected.

Yihai Cao, M.D., Ph.D., associate professor at the Karolinska Institute, Stockholm, has found that physiological concentrations of EGCG prevent the proliferation of endothelial cells, thereby inhibiting angiogenesis (cancer cell growth). Furthermore, EGCG inhibited angiogenesis mediated by the potent angiogenic factor vascular endothelial growth factor (VEGF).