March 24, 1994
Media Contact: Joann Rodgers
Phone: (410) 955-8659
Researchers at Johns Hopkins have now shown that a chemical found in broccoli protects animals against the development of cancer.
The same is true, the researchers report, for synthetic compounds closely related to the broccoli chemical.
The finding is the next step in a quest widely reported two years ago to find substances in edible plants that prevent or lessen the risk of cancer in humans. That earlier study, led by Hopkins molecular pharmacologist Paul Talalay, M.D., showed that the plant chemical sulforaphane boosts production of anti-cancer enzymes in lab cultures of human cells.
In the new study, published in the April 5 issue of the Proceedings of the National Academy of Sciences, the researchers found that sulforaphane and several related compounds synthesized in the lab blocked mammary (breast) cancer formation in rats treated with a potent cancer-causing molecule called DMBA.
"We strongly suspected that sulforaphane would turn out to be an effective anti- cancer agent, based on the earlier studies," says Talalay, "but seeing changes in a culture dish isn't the same as proving cancer formation is blocked in animals."
Human epidemiological studies have shown repeatedly that eating large quantities of fruits and vegetables, especially those in the class of broccoli and brussels sprouts and cabbage, lowers the risk of developing some types of cancer. Some varieties of broccoli are especially rich in sulforaphane.
The results are quite dramatic," says Talalay. 'They showed that when the rats were treated with sulforaphane, far fewer animals developed tumors. Also, the number of tumors and their size was greatly reduced, and their appearance was delayed."
The observations were true for both sulforaphane and for the synthetic relatives designed by a Hopkins chemistry professor, Gary H. Posner, Ph.D. "The synthetic versions are easier to produce than sulforaphane and are more stable," says Posner.
"We still do not understand precisely how sulforaphane protects animal tissues," says Talalay. "But based on earlier research, we believe that much of sulforaphane's 'chemoprotective' nature is based on its ability to heighten the activity of a group of enzymes, called Phase 2 enzymes. The body uses these to detoxify foreign substances including cancer-causing agents.
This "disarming" of carcinogens makes them less reactive and able to damage a cell's DNA, a crucial step in cancer development, Talalay says.
"The next step," he adds, "is to pick out the plants that are the most protective and then go on to clinical trials with humans." Not all varieties of broccoli, for example, are equally protective, and handling and storage also can affect their abilities.
The researchers say future work will take two paths: identifying plants that are particularly able to raise Phase 2 enzymes and devising even more potent synthetic compounds with the anti-cancer effect.
The dietary approach to protecting against cancer ñ Finding plants that people are already eating and that are rich in chemoprotective activity ñ is probably simplest," says Talalay. "Yet vegetables, even of a single type like broccoli, vary enormously in their protective power. Our studies will focus on maximizing that power."
Synthetic forms of the protective cbemicals will require extensive safety testing before they can be administered to healthy populations, Talalay adds. Other authors of the research article are Yuesheng Zhang, M.D.; Thomas Kensler, Ph.D.; and Cheon-Gyu Cho, Ph.D. Funding was from the National Cancer Institute and the American Institute for Cancer Research.