Broccoli chemical linked to prevention of cancer

April 12, 1994|By Jonathan Bor | Jonathan Bor,Sun Staff Writer

A chemical found abundantly in some varieties of broccoli appears to prevent or slow the development of breast cancer in laboratory rats -- new evidence that people may find a cheap and effective cancer-fighter on the produce aisle.

The news gets better. While Johns Hopkins University scientists extracted the chemical from broccoli, it also occurs in Brussels sprouts, mustard greens, cabbage and other cruciferous vegetables.

The finding, reported in today's Proceedings of the National Academy of Sciences, adds strength to a widely heralded Hopkins report two years ago in which the scientists found that the chemical -- called sulforaphane -- raised the levels of a cancer-fighting enzyme in human cells grown in the laboratory.

In the latest experiment, the Hopkins team discovered that the chemical appeared to reduce the size and incidence of breast tumors in rats that were fed large quantities of the chemical after receiving a hefty dose of a known carcinogen.

Dr. Paul Talalay, a molecular pharmacologist, said yesterday that he will soon begin experiments in which healthy people will be fed broccoli and possibly other vegetables containing sulforaphane, rather than the chemical extract.

This approach carries dual advantages. First, tests involving vegetables off the shelf do not raise safety concerns and, therefore, don't require a lengthy review process by government regulators. Secondly, this approach emphasizes the concept that benefits can be derived from natural substances.

"This is diet, not drug," Dr. Talalay said. "We are emphasizing the fact that people have . . . something they can control themselves."

For obvious reasons of ethics, the human volunteers will not be exposed to carcinogens in an effort to measure the vegetables' cancer-fighting abilities. Instead, scientists will examine blood samples to see if the dietary regimen boosts the levels of enzymes that block carcinogens from triggering tumor growth.

Not everyone connected with the study shares the view that diet -- not pills -- offers the best hope for cancer protection.

"We have not yet quantified how much sulforaphane is in broccoli and how much is needed for human protection," said Dr. Gary H. Posner, an organic chemist at Johns Hopkins. "Plus, the amount of sulforaphane varies as to climate and the species of broccoli. We want to have something like a pill."

Dr. Posner said the answer may lie in a pure chemical packaged in pill form or a synthetic variation. In the study, Dr. Posner and his students produced three variations. One seemed to offer slightly greater protection than did the natural chemical.

In the study, about 68 percent of the rats that received nothing but the carcinogen developed mammary tumors. This compared with 26 percent of the rats receiving a high dose of sulforaphane. xTC In contrast, 25 percent of the rats given a synthetic variation developed tumors.

Dr. Posner said he will continue to experiment with chemicals that are slightly altered versions of the natural chemical found in broccoli.

The other authors of the research article are Dr. Yuesheng Zhang, Dr. Thomas Kensler and Dr. Cheon-Gyu Cho. The scientists all approach cancer with the same basic strategy: to prevent the disease with agents that neutralize carcinogens before they trigger tumor growth.

Past studies have shown that carcinogens -- such as those found in cigarette smoke -- are harmless substances until they are broken down by chemicals inside the body known as Phase 1 enzymes. These enzymes convert the once-benign chemicals into dangerous compounds that can damage DNA -- the genetic blueprint -- and set off the unrestrained growth of cancer. But other enzymes, known as Phase 2 enzymes, counteract these molecules before they do their damage.

Sulforaphane appears to raise the level of these helpful enzymes.

While the scientists focused on breast tumors, Dr. Talalay said there is no reason to believe the compound wouldn't have the same effect on other cancers. While pleased that sulforaphane reduced the incidence of cancer by more than half, he said the same figure may not apply directly to humans. Among other reasons, this is because the rats were given very high doses of both the carcinogen and the protective agents.

Also, the findings have nothing to do with fighting cancer once it has developed, he said. "We don't want people, especially those afflicted with cancer, [to think] that now we have a cure."

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