There are no clinical data to support use of GCP for cancer prevention or treatment.
Genistein Combined Polysaccharide (GCP) is composed of genistein, a soy isoflavone, and polysaccharides derived from Basidiomycetes mushrooms. Although GCP itself has not been studied in the laboratory, genistein and Basidiomycetes mushrooms have, with the following results.
Genistein has been studied extensively in laboratory experiments. These generally show that genistein, when directly applied to several types of cancer cells (including estrogen receptor (ER+) and (ER-) breast cancer, prostate cancer, neuroblastoma and sarcoma), inhibits their growth and replication. Genistein 1) competes with the body’s own estrogen and 2) inhibits the ability of a growth factor called EGF to stimulate its receptor and cause downstream cellular effects. Estrogen and EGF can enhance the growth of certain tumors (such as ER+ breast cancer), so scientists think that genistein might act against them to slow tumor growth. This theory has not been confirmed in humans through clinical studies, however.
Laboratory research has suggested that the polysaccharides in Basidiomycetes mushrooms can slow the growth of tumors, enhance certain activities of immune cells, and kill some bacteria and viruses on contact. It is not clear to what extent these effects occur in the human body.
It is controversial whether patients with estrogen-dependent tumors should take soy products such as genistein, due to its possible estrogenic activity. Patients should ask their doctors.
To prevent and treat cancer
Genistein shows anti-tumor activity in the laboratory setting, but the same has not been shown for GCP.
To treat prostate and bladder cancer
Case reports show benefit of GCP, but clinical trials are lacking.
Do Not Take If
You are undergoing chemotherapy with tamoxifen (Studies in animals suggest that genistein may lessen its effects).
A nutritional supplement prepared by fermenting soy extract with basidiomycetes, genistein combined polysaccharide (GCP) is composed of genistein, a soy isoflavone, and polysaccharides obtained from a variety of mushrooms. Isoflavones have been shown to influence hormone-dependent cancers due to their estrogenic activity. Basidiomycetes express immune-stimulant (1) and antitumor (2)(3) activity in vitro. In prostate cancer cells, GCP was found to reduce androgen receptor and prostate specific antigen levels, induce cell growth arrest, and modestly increase apoptosis (4). GCP was also found to inhibit cell growth and induce apoptosis in androgen-dependent and -independent human prostate cancer cell lines (5). It potentiated the cytostatic and cytotoxic activities of docetaxel, bicalutamide, and the sRC kinase inhibitor, pp2 (5). Another study found that GCP treatment resulted in significant inhibition of cell proliferation and arrested the cell cycle in the G2/M phase in three human lymphoid cell lines (6).
Case reports show complete regression of T3 prostate cancer following treatment with GCP (7); and supplementation with GCP prevented recurrence of transitional cell carcinoma (TCC) of the bladder (10). However, no large scale clinical trials have been performed to verify GCP’s anticancer potential.
Mechanism of Action
In vitro experiments show that genistein inhibits tyrosine-specific protein kinase activity of EGF receptors. Inhibition is competitive with respect to ATP and noncompetitive to a phosphate acceptor, histone H2B. Genistein bears no structural relationship with ATP, so inhibition may not be due to true competition for the same active site as that utilized by ATP (8). Basidiomycetes polysaccharides possess antitumor, antiviral, antibacterial and immune-modulating activities. The fermentation of soy extract with basidiomycetes deglycosylates the soy isoflavones which renders them in a highly absorbable form (7).
In prostate cancer cells, GCP was found to inhibit mammalian target of rapamycin (MTOR) activity (4). MTOR is a downstream effector of Akt, an enzyme which plays an important role in cancer cell proliferation and survival (4). (For more information on the mechanism of genistein action, see our monograph on soy.)
Tamoxifen: Animal studies suggest that genistein, a soy isoflavone, may antagonize the effects of tamoxifen on estrogen-dependent breast cancer. (9)