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

The multiherb anti-inflammatory product Zyflamend was investigated for its anti proliferative effects on PC3 human prostate cancer cells and eicosanoid metabolism in this prostate cancer cell line. Zyflamend produced 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 PGE(2) formation. Applied to intact PC3 cells, Zyflamend was found to be 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 G(2)/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. The decrease in pRb protein 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.