The findings add to the argument for eating whole foods, as synergy between the compounds is key to their success against the enzyme.
The enzyme, known as human DNA topoisomerase II, is necessary for the spread of cancer and commonly used in cancer research to screen plant chemicals.
Flavonoids found in significant quantities in red wine, tea and dark chocolate, are considered responsible for the protection these foods have been shown to offer over heart disease and cancers.
But scientists at the University of Illinois at Urbana-Champaign dispel the theory that single flavonoids could be offered in supplements to protect against disease.
In an early online edition of the Journal of Agricultural and Food Chemistry (pp 2489 - 2498;DOI: 10.1021/jf048524w), they describe a dozen new constituents in grape-cell culture extracts.
They report that new chemicals from the proanthocyanidin and anthocyanin classes of the flavonoid family worked together to have a greater effect against topoisomerase II than the previously identified flavonoids quercetin and resveratrol. Alone, the individual components had less effect on the enzyme.
"It's very clear that the synergy is critical. When a cell becomes malignant that enzyme is expressed 300 times more than in a normal cell. If we can find a compound or mixture of compounds that can reduce the activity of that enzyme, the cancerous cells will die," said author Elvira Gonzalez de Mejia, a professor in food science and human nutrition.
"We definitely had very potent activity against the particular antibody system we were using, which was that of the critical proliferation stage of carcinogenesis," added Mary Ann Lila, a professor in the department of natural resources and environmental sciences.
"In our subsequent studies now under way in animal models, we are getting direct evidence that these components in grapes work synergistically in fighting cancer. They have to work together to obtain the potency that works."
The researchers have also found these compounds to be highly bioavailable in a study that tracks the flavonoids moving around the bloodstream of rats.
"By eating the fruit, we know that the bioactive component involved goes into your bloodstream and relocates to other regions. Before now, we didn't really know that," said de Mejia.
Eventually, Lila said, researchers may be able to determine reasonable dosages for therapeutic consumption of flavonoid-rich grapes. Supplements containing specific flavonoids will probably not result in desired benefits because complementary components required for synergistic activity may be missing.