Role of 12-lipoxygenase in regulation of ovarian cancer cell proliferation and survival

Eicosanoid-related enzymes have been implicated in the pathogenesis of various cancers. Little is known about the relevance of lipoxygenase pathway to ovarian cancer growth. In this study, we examined the role of 12-lipoxygenase (12-LOX), the main human 12-HETE generating enzyme, in the regulation of proliferation and survival in epithelial ovarian cancer. Immunohistological analysis of 12-LOX expression in high-grade serous ovarian carcinoma and normal ovarian epithelium tissues was performed. The presence of 12-LOX-12-HETE system was confirmed in two epithelial ovarian cancer (EOC) cell lines, OVCAR-3 and SK-OV-3, using RT-PCR, Western blot and LC/MS analysis. The effects of N-benzyl-N-hydroxy-5-phenyl-pentanamide (BMD-122), a specific 12-LOX inhibitor, on cell growth, survival, apoptosis, and cell signaling were determined. We found that a significantly higher level of 12-LOX expression in high-grade serous ovarian carcinoma compared to normal ovarian epithelium. OVCAR-3 and SK-OV-3 were found to express high level of 12-LOX mRNA and protein. Both EOC increased their 12-HETE production when incubated with arachidonic acid. BMD-122 inhibited the EOC growth in a dose-dependent fashion. Purified 12-HETE significantly reversed such inhibitory effects of BMD-122. In addition, BMD-122 blocked the MAPK signaling pathway by inhibiting the phosphorylation of ERK and induced a similar to 20-30% increase in the EOC apoptosis. Down-regulation of the 12-LOX expression using 12-LOX siRNA also resulted in markedly reduction in cell growth. These data suggest that 12-LOX is involved in the regulation of ovarian cancer cell growth and survival and is a potential new therapeutic target.