Soy may be new weapon against breast cancer

It seems like, there's more to soy than meets the eye as a new research has suggested that it may have the ability to suppress breast cancer tumour growth.

A University of Arizona Cancer Center research team is engaged in a series of studies to investigate how genistein, a component of soy foods, might suppress the development of breast cancer.

The team's most recent study suggested that genistein can protect BRCA1, a gene that plays a pivotal role in thwarting tumor development in breast tissue. The team is led by Donato F. Romagnolo and Ornella I. Selmin.

A normally functioning breast cell has estrogen receptors, into which the body's natural estrogens fit like a key into a lock, regulating cell growth. Doctors can exploit these receptors by using drugs that attach to them, delivering chemotherapy to cancerous cells with drugs like tamoxifen. In many breast tumors, however, this receptor is missing, rendering tamoxifen ineffective.

BRCA1 is a tumor-suppressor gene. When working normally, it helps keep DNA stable, protecting against genetic diseases like cancer; when BRCA1 is performing abnormally, the body's defenses against breast cancer are impaired. Although a small percentage of breast cancers are caused by mutations in BRCA1, many other breast cancer patients have normal copies, but the genes have been "methylated" wrapped in strands of carbon-based molecules that render them unreadable. A BRCA1 gene "silenced" in this manner is unable to do its job as a tumor suppressor.

One receptor, the aromatic hydrocarbon receptor (AhR), activated by environmental carcinogens like dioxins, tobacco smoke, products of UV light exposure and some fatty acid metabolites, is of particular interest to the UA Cancer Center team. AhR silences BRCA1, triggering a cascade of undesirable effects. When BRCA1 is unable to carry out its duties as a tumor suppressor, cancerous cells can proliferate.

One weapon that may be used to target AhR is found in soy, a protein-packed legume that is a major source of compounds called isoflavones.

"Lifetime intake of soy in Asian women has been linked to reduced risk of breast cancer," said Romagnolo. Genistein is the predominant isoflavone found in soy and it may actually block DNA methylation, the silencing of the BRCA1 gene.

The experiments used cells from human breast tumors, including one cell line that originally was derived from a UA Cancer Center patient. With successful cell experiments behind them, the team is immersed in studies using mice specialized for breast cancer research. If their next wave of experiments supports their hypothesis, the team could move on to clinical studies in humans.

Other questions include what types of soy foods, how much and at what stage of life soy might be optimal for human health. The team especially is interested in discovering whether exposure to soy genistein during gestation can affect a developing fetus and confers protective benefits throughout the lifetime of the offspring.

The study is published in Current Developments in Nutrition.