Key Questions Direct Next Steps in Diet-Cancer Research

Source: American Institute for Cancer Research; Newsletter 81, Fall 2003

Before scientists can use human trials to study how certain foods influence the cancer process, they must first know some basic things about those foods. This research answers essential questions so scientists can take the next step — designing human trials.

At the heart of every scientific study lies a hypothesis, a single question that must be answered. In the diet-cancer field these questions can be narrowly focused (“Do polyphenols found in green tea inhibit the signal transduction pathways of human cancer cells in vivo?”) or broad in scope (“Does drinking green tea lower cancer risk?”).

These questions are not unrelated: an answer to the first can contribute to answering the second in a clearly defined way. That’s why scientists funded by AICR are studying so many different foods (and food components) in laboratories. They’re experimenting to see how cancer cells react when exposed to different potentially cancer-fighting foods, at different amounts and at different times. Getting these answers allows scientists to design human trials that build on previous studies. Let’s look at one example.

Green Tea Inhibits Tumors in Mice

C.S. Yang, Ph.D., at Rutgers University, is an authority on tea consumption and cancer. He is conducting studies that show that polyphenols – natural substances found in green tea – may prevent the formation of cancer tumors.

Green tea polyphenols are believed to fight against cancer in several ways. For example, they seem to make it more difficult for a cancer cell to respond to growth signals. Thus it slows cancer cell growth. Polyphenols may not be the only chemicals in tea providing cancer prevention benefits, Dr. Yang notes. Dr. Allan H. Cooney’s lab, also at Rutgers, is studying skin cancer. It has found that green tea’s caffeine, rather than its polyphenols, is mainly responsible for the inhibition of tumor formation.

The many previous studies that have compared the green tea consumption of a given country or region to the cancer rates among its population have shown conflicting results, Dr. Yang says. This may indicate that tea is not strong enough to overcome the risk-raising influence of other factors.

“The current method of assessing tea consumption is inadequate,” he says.

Dr. Yang’s lab is developing biomarkers for tea consumption and studying the bioavailability of tea constituents. Bioavailability refers to how well a substance is absorbed into the blood and distributed to different organ tissue. Because polyphenols are not well absorbed and easily eliminated from the blood, green tea seems potentially more useful in preventing oral, stomach and colon cancer than cancer of an internal organ such as the liver, Dr. Yang says.

Dr. Yang’s work on the bioavailability and anti-cancer potential of green tea polyphenols allows researchers to design human trials to find out: How much green tea should human subjects drink to get the most cancer-fighting benefit? Can the tea be used in a way that makes its polyphenols more bioavailable? When should it be consumed, and how long do the effects last?

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