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Anti-cancer compound found to block late-stage breast-cancer cell growth

01.09.2004

A well known anti-cancer agent in certain vegetables has just had its reputation enhanced. The compound, in broccoli and other cruciferous vegetables, has been found to be effective in disrupting late stages of cell growth in breast cancer.

Keith Singletary and doctoral student Steven Jackson of the University of Illinois at Urbana-Champaign report their finding involving sulforaphane (SUL), which they say could ultimately be used to enhance the prevention and treatment of breast cancer, in the September issue of the Journal of Nutrition.

“This is the first report to show how the naturally occurring plant chemical sulforaphane can block late stages of the cancer process by disrupting components of the cell called microtubules,” said Singletary, a professor in the department of food science and human nutrition. “We were surprised and pleased to find that SUL could block the growth of breast cells that were already cancerous.”

SUL is abundant in such vegetables as broccoli, brussels sprouts and kale. Chewing causes the cell walls of these vegetables to break, and SUL is released into the body.

Singletary, a researcher in phytochemicals and cancer chemoprevention, and Jackson exposed cultures of malignant human breast cancer cells to SUL. Within hours, SUL blocked cell division and disrupted microtubules, which are long, slender cylinders made up of tubulin (protein), that are essential for the separation of duplicated chromosomes during cell division.

“It is not yet clear whether the doses required to produce inhibition of tubulin polymerization are higher than those achievable via dietary intakes,” wrote Jackson and Singletary. “However, the results show that tubulin disruption may be an important explanation for SUL’s antiproliferative action.” “These findings are significant since SUL’s actions appear similar to a group of anticancer drugs currently in use, such as Taxol,” Singletary said.

SUL is studied extensively for its effects against cancer. Previous reports have shown that SUL induces defensive mechanisms that are effective in protecting normal cells from the initiation of cancer. “More than 10 years ago, researchers at Johns Hopkins University reported that SUL is a potent inducer of enzyme systems that can defend against carcinogens,” Singletary said. Such defense mechanisms are effective during the early stage of cancer.

The Illinois research extends the 1992 discovery at Johns Hopkins and pinpoints how SUL works during later stages of cancer, such that SUL can suppress the orderly division process in human breast cancer cells. “The findings may be helpful in the development of new breast cancer prevention and treatment strategies,” Singletary said. “For example, it may be possible that ingesting SUL in combination with certain natural compounds or drugs could enhance their anticancer effectiveness and reduce side effects.”

According to the American Cancer Society, breast cancer this year will account for 15 percent of all cancer deaths in women, and approximately 275,000 new breast cancer cases of various forms will be diagnosed.

Improvements in treatments such as chemotherapy have led to an 88 percent survival rate in Caucasian women and a 74 percent survival rate in African-American women, according to the most recent ACS survey in 2003.

However, some current chemotherapy drugs have side effects that have the ACS and other organizations seeking new strategies that combine chemotherapy drugs with other treatments to potentially lessen the toxic effects.

The new Illinois study confirms a previous study in mice. In the February 2004 issue of the journal Carcinogenesis, Singletary and Jackson reported that SUL treatments in mice with implanted cancer cells resulted in decreased tumor size.

More research is needed to assess SUL’s potential in countering breast cancer development, Singletary said. “What we do not know is how specific SUL and other similar phytochemicals are toward cancer cells compared to normal cells,” he said. “We also do not know against which cancers SUL’s microtubule-targeting actions are most effective.”

Future studies in Singletary’s lab will address those issues. The University of Illinois Agricultural Experiment Station and the U.S. Department of Agriculture funded the research.