Equol and 6-bromoindirubin-3-oxime modulate invasive activity of prostate cancer cell lines through inhibition of urokinase type plasminogen activator

Cancer metastasis requires controlled extracellular matrix degradation mediated by proteolytic enzymes like the urokinase-type plasminogen activator (uPA)-plasminogen system. Consequently the components of the u-PA system are potential targets for anti-invasive and anti-metastatic therapy. The objective of the present study is to determine the effects of the daidzein metabolite equol, and 6-Bromo-indirubin-3-oxime (6BIO) an indirubin synthetic analog, on u-PA expression and activity in prostate cancer cell lines. Prostate cancer PC3 and DU145 cells were treated for 24h, 48h and 72h with equol or 6BIO and the u-PA activity and protein levels were determined in both the cell lysates and growth media. The effect of equol on invasion was also determined in PC3 cells with the use of Boyden Chambers. The effects of the above agents were compared to those of amyloride (a u-PA inhibitor), 3-hydroxyflavone (previously reported to inhibit u-PA activity) and quercetin. While quercetin was ineffective, 3-hydroxyflavone, 6BIO, Equol and amyloride induced a concentration-depended decrease in u-PA activity in PC3 and DU145 cells. The reduction in uPA activity was accompanied with decreased u-PA protein levels. The invasive ability of equol-treated PC3 cells was significantly reduced in comparison to the controls. Furthermore, 6BIO induced a concentration and -time depended decrease in the survival of DU145 and PC3 cells. In conclusion, Equol and 6-BIO have a potent anti-invasive effect on prostate cancer cells. Furthermore, 6-BIO excerts an anti-proliferative effect on prostate cancer cells. These results suggest that 6BIO and equol may be useful anti-metastatic agents.

Acknowledgements: This research was funded by the Cyprus Research Promotion Foundation and the Leventis Fund.