Zyflamend^®-mediated inhibition of human prostate cancer PC3 cell proliferation: Effects on 12-LOX and Rb protein phosphorylation . Free

B97

Chronic inflammation has been considered as a causative factor for development of various cancers, including lung, colon, prostate and H & N cancer. It is therefore understandable why treatment or even prevention of chronic inflammation is a worthwhile target for therapeutic agents. The potential of the multiherb product Zyflamend as an anti-inflammatory agent and as a product capable of inhibiting the proliferation of human cancer cells has recently been reported. Here Zyflamend was investigated for its antiproliferative effects on PC3 human prostate cancer cells and specifically for its effects on eicosanoid metabolism in this prostate cancer cell line. Zyflamend was observed to produce a concentration-dependent inhibition of cloned COX-1, COX-2, and 5-LOX enzyme activities, with inhibition of 5-HETE production being greater than that of PGE₂ formation. Applied to intact PC3 cells, Zyflamend was able to inhibit 50% of the formation of 12-HETE at a concentration as low as 0.25 μl/ml, whereas a similar inhibitory effect of Zyflamend on formation of PGE2 and 5-HETE was observed at concentration of 1 μl/ml, suggesting Zyflamend was most potent against 12-LOX, followed by 5-LOX and then COX activities. The concentration-dependent inhibition of PC3 cell proliferation was associated with a selective G₂/M arrest of the cell cycle and induction of apoptosis, as evidenced by flow cytometric staining of PC3 cells with annexin V. Zyflamend also produced a concentration-dependent down-regulation of 5-LOX and 12-LOX expression. Determination of cell signal transduction proteins demonstrated that Zyflamend produced an increase in p21 phosphorylation but down-regulated phosphorylation of retinoblastoma (Rb) protein at multiple phosphorylation sites. The decrease in pRb proteins was shown to be due to 12-LOX inhibition and a decline in 12-HETE levels in the cells. Replenishing 12-HETE in Zyflamend-treated cells overcame the ability of this multiple herb product to inhibit cell proliferation, and concordantly, 12-HETE blocked Zyflamend's ability to down-regulate phosphorylation of Rb protein. We conclude that the effective control of human prostate cancer cell proliferation with Zyflamend is multi-mechanistic but, in part, involves regulation of aberrant tumor cell eicosanoid metabolism, especially on 5- and 12-LOX, as well as restoration of Rb tumor suppressor protein function through regulation of its phosphorylation status. This study is supported in part by NewChapter Inc.