Chemoprevention in prostate cancer

Dietary genistein inhibits metastasis of human prostate cancer in mice

Dietary genistein has been linked to lower prostate cancer (PCa) mortality. Metastasis is the ultimate cause of death from PCa. Cell detachment and invasion represent early steps in the metastatic cascade. We had shown that genistein inhibits PCa cell detachment and cell invasion in vitro. Genistein-mediated inhibition of activation of focal adhesion kinase (FAK) and of the p38 mitogen-activated protein kinase (MAPK)-heat shock protein 27 (HSP27) pathway has been shown by us to regulate PCa cell detachment and invasion effects, respectively. To evaluate the antimetastatic potential of genistein, we developed an animal model suited to evaluating antimetastatic drug efficacy. Orthotopically implanted human PC3-M PCa cells formed lung micrometastasis by 4 weeks in >80% of inbred athymic mice. Feeding mice dietary genistein before implantation led to blood concentrations similar to those measured in genistein-consuming men. Genistein decreased metastases by 96%, induced nuclear morphometric changes in PC3-M cells indicative of increased adhesion (i.e., decreased detachment) but did not alter tumor growth. Genistein increased tumor levels of FAK, p38 MAPK, and HSP27 "promotility" proteins. However, the ratio of phosphorylated to total protein trended downward, indicating a failure to increase relative amounts of activated protein. This study describes a murine model of human PCa metastasis well suited for testing antimetastatic drugs. It shows for the first time that dietary concentrations of genistein can inhibit PCa cell metastasis. Increases in promotility proteins support the notion of cellular compensatory responses to antimotility effects induced by therapy. Studies of antimetastatic efficacy in man are warranted and are under way.

Genistein inhibits p38 map kinase activation, matrix metalloproteinase type 2, and cell invasion in human prostate epithelial cells

Epidemiologic studies associate consumption of genistein, in the form of dietary soy, with lower rates of metastatic prostate cancer. We have previously shown that genistein inhibits prostate cancer cell detachment in vitro, that it is well tolerated in an older cohort of men with prostate cancer, and that it alters cell signaling in that same cohort. We have also shown that p38 mitogen-activated protein kinase (MAPK) is necessary for transforming growth factor beta (TGF-beta)-mediated increases in prostate cancer adhesion. Although cell invasion is closely linked to metastatic behavior, little is known about how this process is regulated in prostate cancer or what effect, if any, genistein has on associated processes. We now show that genistein inhibits matrix metalloproteinase type 2 (MMP-2) activity in six of seven prostate cell lines tested, blocks MMP-2 induction by TGF-beta, and inhibits cell invasion. Efficacy was seen at low nanomolar concentrations, corresponding to blood concentrations of free genistein attained after dietary consumption. Inhibition of p38 MAPK by either SB203580 or dominant-negative construct blocked induction of MMP-2 and cell invasion by TGF-beta. Genistein exerted similar effects and was found to block activation of p38 MAPK by TGF-beta. This study shows that p38 MAPK is necessary for TGF-beta-mediated induction of MMP-2 and cell invasion in prostate cancer and that genistein blocks activation of p38 MAPK, thereby inhibiting processes closely linked to metastasis, and does so at concentrations associated with dietary consumption. Any potential causal link to epidemiologic findings will require further investigation.