Cancer Therapeutic Found in Green Tea

Green tea seems to protect against cancer by affecting a "promiscuous” protein that pharmacology researchers are now targeting in an effort to develop a new agent to stop the disease, according to a new study.

The study supports beliefs about the health benefits of green tea with definitive scientific findings. The new findings were incorporated into a thesis by Christine Palermo, a student at the University of Rochester (NY, USA). Whereas it has been reported that green tea protects individuals against various types of cancer, including liver and breast cancer, precisely how it does this is as yet unknown.

"It's important to find out the source of green tea's protective effects,” stated Thomas A. Gasiewicz, Ph.D., a toxicologist from the University of Rochester, who has long studied the harmful effects of dioxin, which eventually led him to explore the protective effects of green tea. "What is exciting here is that a complete new mechanism has been found that very well could be responsible for its protective effects, and that could help us find a compound that is much more potent.”

The University of Rochester researchers have discovered a chaperone protein known as HSP90, found to be involved in conferring green tea's protective effects. Other scientists have demonstrated that many cancer cells have an increase in the level of HSP90 compared to normal cells, and that when HSP90 is blocked, levels of proteins that make cancer cells grow decrease.

Pharmaceutical companies are currently studying ways to block HSP90, which is known as a promiscuous chaperone protein because it binds to many different cells and receptors in the body. It now appears that these scientists are trying to duplicate what green tea does naturally. Dr. Gasiewicz reported that pharmaceutical companies can learn from green tea, which might modulate HSP90 in a manner that scientists have not seen before.
Dr. Gasiewicz has long studied how dioxin and other compounds such as cigarette smoke manipulate a key cancer-causing molecule, the aryl hydrocarbon (AH) receptor, which typically plays a role in activating genes that are frequently harmful.

In 2003, the University of Rochester scientists discovered that AH activity is suppressed by a chemical found in green and white teas, epigallocatechingallate (EGCG), a relative of a flavonoid found in cabbage, broccoli, grapes, and red wine that are known to help prevent cancer. The investigators had been working on other compounds in an attempt to block AH activity.

"We initially hypothesized that EGCG would work in the same way as other AH antagonists, by binding directly to it. We were completely surprised that this isn't the case,” remarked Dr. Gasiewicz. The researchers discovered that EGCG binds to HSP90, a protein that helps other proteins remain stable, serving the same role as a kite's tail. When the two bind, HSP90 no longer activates the AH receptor, blocking the cascade of events that would lead to the activation of several harmful genes.




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