The results, published in the 15 September issue of Cancer Research, suggest that these chemicals 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, professor of oncology in the Lombardi Cancer Center at the Georgetown University Medical Center.
"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.
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.
The researchers induced lung tumor development in experimental mice by exposing them to tobacco carcinogens, and then they fed one group of mice the isothiocyanates.
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 into one of the possible mechanisms of action by which the compounds may offer some protection against lung cancer development, the researchers said.