The researchers incubated breast and liver cancer cells with lycopene and found that natural chemical stimulated production of phase II detoxification enzymes, which remove harmful carcinogens from the cells and the body.
As expression of phase II enzymes is regulated by the 'antioxidant response element' (ARE), the new research suggests that this could be the mechanism behind the cancer-preventive effect of tomatoes, said Dr Joseph Levy and colleagues from Ben-Gurion University of the Negev, Beer-Sheva, Israel, speaking at the American Association for Cancer Research annual meeting this week.
A number of epidemiological studies looking at consumption of tomato products, shows that they can reduce risk of certain types of cancer when consumed regularly. It has also been proposed that this is due to a number of different compounds in tomatoes, rather than lycopene alone.
Testing other carotenoids for expression of phase II enzymes revealed that they were inferior to lycopene however. Beta-carotene had a lesser effect, while asataxanthin and another tomato carotenoid called phytoene had no impact on the cancer cells.
"The transactivation was dose-dependent and unexpectedly specific forlycopene, since astaxanthin, beta-carotene and phytoene had no effect. This specificity suggests that activation of ARE-mediated transcription by carotenoids is not related solely to their antioxidant properties," noted the researchers.
But the findings do not rule out the role of other compounds in tomatoes, Dr Yoav Sharoni told NutraIngredients.com.
"Beta-carotene did not activate the ARE transcription but there are probably other pathways to enhance the phase 2 enzymes," he said.
"We have seen that when you combine lycopene with other carotenoids there is a synergistic effect and all of the epidemiological evidence comes from consumption of tomato products rather than pure lycopene."
Despite this, a number of companies are currently developing synthetic or fungus-derived lycopene for sale to supplement companies. Lycopene has also been linked to reduced risk of heart disease and protection against breast cancer.
A meta-analysis of 21 studies in this month's Cancer Epidemiology Biomarkers and Prevention (2004, vol.13, 340-345), concluded that high amounts of tomato-based products may significantly reduce the risk of prostate cancer but noted that further research is needed to determine the type and quantity of tomato products and their role in preventing prostate cancer.