LONDON (Reuters) - Scientists said on Tuesday they had gained fresh insight into how a natural anti-fungal agent found in grapes and other crops may help prevent cancer.

Researchers from the School of Pharmacy at De Montfort University in Leicester, central England, reported in the British Journal of Cancer that resveratrol is converted in the body to a known anti-cancer agent which can selectively target and destroy cancer cells.

Although previous studies have suggested plant-estrogen might prevent cancer, they said it was the "first time that scientists had gained an insight into the underlying mechanism of the chemical's anti-cancer properties."

Professor Gerry Potter, the research group leader, said in a statement: "Resveratrol is a defensive molecule against fungus in grapes and other crops, and is found at higher levels in those which have not been treated with man-made fungicides.

"Learning from nature in this way will help in our work to design drugs which are selectively activated in a tumor and can form the basis of anti-cancer treatments."

The researchers found that resveratrol is processed by the enzyme CYP1B1, which is found in a variety of different tumors. This converts resveratol into piceatannol, a closely related plant-estrogen with known anti-cancer activity.

Previous research by the team has shown that this process is restricted to the tumor itself, limiting the toxicity to the cancer cells and serving to selectively destroy them.

Scientists previously believed that CYP1B1 was a cause of cancer, because it is only found in tumors and not in healthy tissue. They now think the enzyme is there to fight it and the team is continuing research into ways to help it in its work.

Potter said: "The belief that CYP1B1 is a cause of cancer is like blaming police for a crime just because they are on the scene.

"We suspected this natural product might be beneficial for health and have cancer preventative properties. This research shows just how it could prevent tumors developing by producing these anti-cancer molecules within the cancer cells themselves."

The team is also looking into the beneficial effects of vegetables such as broccoli and cabbage that contain a molecule that activates the CYP1B1 enzyme.