Washington, DC -- A family of compounds found in cruciferous vegetables, such as broccoli, cauliflower, and watercress, blocked lung cancer progression in both animal studies and in tests with human lung cancer cells, report researchers from Georgetown University Medical Center and the Institute for Cancer Prevention.
They say the results, published in a set of papers in the September 15 issue of Cancer Research, suggest that these chemicals -- put into a veggie pill of sorts -- might some day be used to help current and former smokers ward off development of lung cancer, the leading cause of cancer death in Americans.
"These studies provides significant insight into the mechanisms of lung cancer prevention and suggests ways the process can be slowed down after exposure has already occurred," said the study's principal investigator Fung-Lung Chung, Ph.D., Professor of Oncology in the Lombardi Cancer Center at the Georgetown University Medical Center. He worked with researchers from the Institute for Cancer Prevention, in Valhalla, New York, and with other scientists in Illinois, Minnesota and New York on the studies.
"We still need to do more research, but it may be that an agent containing these ingredients could, to some degree, help protect people who have developed early lung lesions due to smoking," Chung said. "In any case, we know that eating vegetables is generally good for us, and that some studies have shown they help lower a person's risk of developing cancer."
One of the two new studies being reported was the first to test whether these compounds, derived from naturally occurring isothiocyanates, could have an impact on the stages of cancer development specifically after exposure to cancer-causing elements . To test that, the researchers induced lung tumor development in experimental mice by exposing them to tobacco carcinogens, and then they fed one group of mice the veggie compounds. They found that, indeed, use of the chemicals resulted in a reduced development of benign (harmless) lung tumors to malignant tumors, compared to mice that did not receive the compound.
Chung cautions, however, that it is difficult to draw any direct comparisons between human consumption of these vegetables and the effects seen in the mice studies. "Because the amount of carcinogens we used to induce tumors was very high, we needed to use a very high dose of isothiocyanates to see any effect," he said. "This animal model will give us data for the potential use of such agents in a human clinical trial."
The second new study looked at the effect of the same compound on human lung cancer cells, which were forced to grow quickly (as cancer does) because of insertion of a gene known to be involved in cell growth and regulation. The laboratory test showed that the derivative of isothiocyanate significantly pushed the human lung cells to commit "suicide," compared to cells that did not have the gene, suggesting that its use may stop fast growing lung cancer cells from the outset. This study provides some insight onto "one of the possible mechanisms of action" by which the compounds may offer some protection against lung cancer development, the researchers said.
These studies were continuation of a 20-year research effort by Chung and his team, much of it conducted while Chung was at the Institute for Cancer Prevention before moving to Georgetown University Medical Center. The body of research they have established on the connection between cruciferous vegetables and lung cancer is one of the most detailed available. Chung earlier identified the isothiocyanates may be responsible for the beneficial effects of these vegetables, and he had shown they were effective in hindering development of lung cancer cells.
The study was funded by a grant from the National Institutes of Health. Co-authors include C. Clifford Conaway, PhD, from the Institute for Cancer Prevention, who served as senior investigator on the mouse study, and Yang-Ming Yang, PhD, also from the Institute, who was first author on the lung cell study. Other co-authors include, from the Institute for Cancer Research, Meena Jhanwar-Uniyal, PhD, Joel Schwartz, MD, Chung-Xiou Wang, MD, and Brian Pittman, MS; Defa Tian, MD, from Georgetown University; H. Dorota Halicka, PhD, and Frank Traganos, PhD, from New York Medical College; and Edward McIntee, PhD, and Stephen Hecht, PhD, from the University of Minnesota.
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