Broccoli curbs cancer-spreading proteins

Eating foods like broccoli and soy has been linked to lower cancer rates.

California researchers say they now understand the biological mechanism behind the protective effect.

Using cells in a lab dish, researchers at the University of California, Los Angeles, found that diindolymethane (DIM), a compound resulting from digestion of cruciferous vegetables, and genistein, an isoflavone in soy, reduce the production of two proteins needed for breast and ovarian cancers to spread.

"We think these compounds might slow or prevent the metastasis of breast and ovarian cancer, which would greatly increase the effectiveness of current treatments," said Erin Hsu, a UCLA graduate student in molecular toxicology.

The UCLA team, which reported its finding at a meeting of the American Association for Cancer Research, will next test the theory in mice.

The findings highlight "an entirely unique mechanism ... Preventing the invasion and metastasis of cancer cells is crucial," said Dr Alan Kristal, associate head of the cancer prevention program at the Fred Hutchinson Cancer Research Centre in Seattle.

Cancer cells express very high levels of a surface receptor known as CXCR4, while the organs to which the cancers spread secrete high levels of CXCL12, a ligand that binds to that particular receptor.

This attraction stimulates the invasive properties of cancer cells and acts like a homing device, drawing the cancer cells to organs like the liver or brain.

The study found that when cancer cells were treated with either DIM or genistein, movement toward CXCL12 is reduced by at least 80 per cent compared to untreated cells.

Hsu says that this same chemotactic attraction is thought to play a role in the development of more than 23 different types of cancer.

The amount of DIM and genistein used in the study is probably comparable to use of a high dose of supplements, and is likely not achievable through consumption of food alone, the researchers said.

Both DIM and genistein are already being developed for use as a preventive, and a chemotherapy treatment for breast cancer, although more extensive toxicological studies are needed, they added.