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Product made from soy and mushroom may aid in prostate cancer treatment

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Cancer answer-Shitake mushrooms are one of the ingredients in a natural compound called GCP, shown in VA lab studies to extend the benefits of a common treatment for metastatic prostate cancer. (Photo: iStockPhoto)
Cancer answer—Shitake mushrooms are one of the ingredients in a natural compound called GCP, shown in VA lab studies to extend the benefits of a common treatment for metastatic prostate cancer. (Photo: iStockPhoto)

A natural, nontoxic product called genistein-combined polysaccharide, or GCP, which is sold in health stores, could help extend life for certain prostate cancer patients, suggested a study by researchers with VA and the University of California, Davis. The study published in December 2012 in Endocrine-Related Cancer, was conducted in human prostate cancer cells and in mice.

Based on the lab findings, the researchers believe GCP could potentially help men with prostate cancer that has metastasized, or spread to other parts of the body. The scientists believe it could also help those who have had their testosterone lowered with drug therapy.

Lowering of testosterone, also known as androgen-deprivation therapy, is the standard of care for men with metastatic prostate cancer. But outcomes from the treatment vary widely.

The research team used GCP, a proprietary extract made from soybeans and shiitake mushrooms and marketed by a Japanese company. The study showed that the combination of genistein and daidzein, two compounds found in GCP, helps block prostate cancer cells' ability to survive when they are starved of testosterone.

The research team had earlier shown that when androgen levels fall, cancerous prostate cells go into self-preservation mode by ejecting a protein known as filamin A. When androgen is plentiful, the protein binds to the androgen receptor in the cell nucleus. The androgen receptor regulates the growth of prostate cancer cells. The exit of filamin A from the nucleus is a game changer: It enables the cell to survive without androgens. As a result, androgen deprivation no longer works as a therapy, and the cancer keeps on spreading.

The new study showed that GCP keeps filamin A in the nucleus. As long as the protein remains attached to the androgen receptor, the cancer cells continue to need androgens to survive and grow. Starved of androgens, they die. In theory, this should prolong the effects of androgen deprivation, in turn extending the patient's life.

The researchers' hypothesis is that metastatic prostate cancer patients with the weakest response to androgen-deprivation therapy could be given GCP as an adjunct. The group is now looking to begin human clinical trials to test the theory.

The lab work was supported by VA and the National Cancer Institute.

Adapted from a news release from the University of California, Davis.



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