THURSDAY, Sept. 14, 2005 (HealthDay News) -- A group of compounds found in a wide range of common vegetables may help slow the development of lung cancer, two new studies show.
The compounds -- called isothiocyanates -- are sulphur-containing chemicals that provide much of the flavor found in cruciferous vegetables, which are part of the cabbage family.
Isothiocyanate-rich foods include broccoli, cauliflower, kale, turnips, collards, Brussels sprouts, cabbage, rutabaga, Chinese cabbage, bok choy, horseradish, radishes and watercress.
"The important feature of these studies is that when you treat noncancerous lesions with this compound, the progression of benign lessions into malignancies is actually slowed," said study co-author Fung-Lung Chung, a professor of oncology at Lombardi Cancer Center at Georgetown University Medical Center.
The current research was conducted among mice and in test tubes, rather than in human subjects. However, recent studies have indicated that consuming isothiocyanates may help to prevent cancer in humans by speeding up the removal of carcinogens from the body.
The compound has also demonstrated a potential to inhibit remaining active carcinogens from instigating tumor growth, while actually preventing inactive carcinogens from mobilizing in the first place.
The researchers point out that lung cancer is a leading cause of death among American men and women. Late detection and the general ineffectiveness of chemotherapy contribute to the disease's relatively low survival rate.
In the animal study, Chung and his team exposed a group of mice to an eight-week regimen of carcinogens that are typically found in cigarette smoke and thought to be integral to the development of lung cancer among smokers.
Twenty weeks after the exposure, some of the mice were dissected to determine lung tissue tumor development. The remaining mice were subsequently fed diets containing either high or low doses of phenethyl isothiocyanate and sulforaphane -- two compounds comprised of naturally occurring isothiocynates.
Some of the mice were dissected eight weeks following the start of isothiocyanate treatment, while the remainder was autopsied after either 16 or 22 weeks.
Reporting in the Sept. 15 issue of Cancer Research, the researchers observed that carcinogen-exposed mice placed on the high-dose diet of phenethyl isothiocyanate ultimately developed far fewer malignant tumors than mice not fed such a diet.
Between 13 percent and 19 percent of the high-dose diet mice developed cancerous lung tumors, compared to 42 percent of the mice who were not fed the compound. The lower-dose phenethyl isothiocyanate diet did not, however, provoke a similarly significant reduction in malignant tumor development.
Mice fed sulforaphane diets also experienced low malignancy growth, with between 11 percent and 16 percent developing cancerous lung tumors.
The researchers noted that such lower malignancy growth was associated with both an observed reduction in cancer cell proliferation and an increase in cancer cell "apoptosis" -- or cell suicide -- among the diet-fed mice throughout the treatment period.
Chung and his colleagues emphasized that the stage during which benign lung tumors develop into malignant lung tumors is perhaps the most critical juncture in the progression of lung cancer. And they noted this conversion stage was "strikingly inhibited" in about half the mice that were treated with either of the isothiocyanate compounds.
In a second lab study published in the same journal, the researchers tested the effect that isothiocyanates had on human lung cancer cells in test tubes.
In a laboratory, cell lines of both normal human lung cells and cancerous cells were exposed to phenethyl isothiocyanate compounds similar to the ones used in the mouse study.
Prior to exposure, some of the lung cancer cells had been inserted with a gene that is known to promote fast cell growth, to simulate the normal speedy growth pattern of lung cancer in the body.
The researchers found that the those lung cancer cells that were "designed" for faster growth were also the most affected by exposure to isothiocyanate compounds -- dying off via apoptosis at a significant and faster rate than the non-enhanced cancer cells.
Since the compounds appeared to most effectively target the most active cancer cells, Chung and his team suggested this finding offers up yet another possibly beneficial lung cancer treatment intervention.
In light of both these studies, the authors concluded that future human trials might lead to the development of a regimen of isothiocyanates -- perhaps administered in the form of a "veggie pill" -- to treat both smokers and ex-smokers diagnosed with early lung lesions.
"So this is a very wide range of activity for these compounds, potentially to be used to prevent lung cancer in smokers even before the lesions are present in the lung," Chung added.
"But we need clinical trials to make sure that this benefit can be translated to humans," he stressed.
Bridget Bennett -- a registered dietician and oncology nutritionist with the Continuum Cancer Centers at Beth Israel Medical Center in New York City -- strongly agreed with the need for further research.
"We have no doubts that phytonutrients such as isothiocyanates -- when they're isolated and put in compounds -- can actually kill cancer cells," Bennett said. "But when we isolate them out of the test tube, we don't know what we're losing. So we're not sure if this really works. Are we really getting everything we would get if we ate the whole plant?"
"So it boils down to what we've been telling people for a while -- eat many more fruits and vegetables. Probably double what most of us consume," Bennett said. "Because while it's kind of exciting that putting the chemicals next to the cells kills cancer growth, day to day my advice still is: Eat your broccoli."
In related news, a third journal article discussed the findings of a University College London-led study that found that a compound found in beans, nuts, and cereals seems to inhibit a key enzyme related to tumor growth.
The researchers concluded that a diet rich in such foods might also help in the prevention of cancer, as well as leading to new developments in cancer treatment therapies.
For more on cancer and food, check out the American Cancer Society.