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Soy Component May Block Immune Killing of Cancer Cells

Estrogenic compound in soy products inhibits killing by natural killer cells

FRIDAY, Oct. 24 (HealthDay News) -- High consumption of soy-containing products may block the ability of the immune system to kill cancer cells, according to research published in the November issue of Endocrinology.

Xinguo Jiang, and colleagues from the University of Illinois at Urbana-Champaign investigated the effect of the soy isoflavone genistein, which structurally mimics 17-beta-estradiol, on human breast cancer cells. The consumption of soy-based products has increased in the United States, and the researchers had previously shown that estrogens can block the ability of the immune system to induce cell death in cancer cells.

The researchers found that 10 nM genistein induced proteinase inhibitor 9 (PI-9), which inhibits the protease granzyme B used by natural killer cells to kill target cells and blocked their ability to kill breast cancer cells. Induction of PI-9 and resistance to killing were also observed in breast cancer cells producing high levels of estrogen receptor-alpha (ERα) treated with only 100 pM genistein. Further experiments showed that genistein induced PI-9 via ERα, the authors note. PI-9 was also induced in breast cancers grown in ovariectomized athymic mice fed moderate levels of genistein and soy flour, the report indicates.

"A significant population consumes levels of genistein in soy products that may be high enough to induce PI-9, perhaps potentiating the survival of some pre-existing breast cancers by enabling them to evade immunosurveillance," Jiang and colleagues conclude.

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