Abstract 2255: Inhibition of 5-lipoxygenase interrupts c-Myc oncogenic signaling

Background: Previous studies have demonstrated that prostate cancer cells continuously generate 5(S)-HETE series of metabolites from arachidonic acid via 5-lipoxygenase (5-Lox), and inhibition of 5-Lox blocks production of metabolites and triggers apoptosis both in androgen-sensitive as well as androgen-independent prostate cancer cells. This apoptosis is prevented by 5(S)-HETE and 5-oxoETE, but not by leukotrienes or metabolites of 12-Lox or 15-Lox, which is consistent with the idea that the 5-HETE series of metabolites are essential survival factors for prostate cancer cells. Recently, we found that 5-Lox-mediated survival-signaling involves protein kinase C-epsilon (PKC∈), but not PI3K-Akt, or MEK-ERK. Immunohistochemistry revealed that prostate tumor tissues express high levels of 5-Lox, but the expression of 5-Lox in normal prostate glands is undetectable. Thus, 5-Lox emerges as a novel molecular target for prostate cancer. However, downstream signaling mechanisms of 5-Lox metabolites in prostate cancer cells are yet to be characterized, which may reveal additional targets for prostate cancer management. Thus, we wanted to address this question by gene-expression array, RT-PCR, Western blot, and analysis of prostate glands in transgenic animals. Methods: Prostate cancer cells were treated with MK591 (a specific 5-Lox inhibitor) or by Lentiviral 5-Lox shRNA. Whole genome gene expression was analyzed by Illumina HT-12v4 gene-expression array. Expression of c-Myc was confirmed by RT-PCR and Western blot. Apoptosis was measured by annexin-V binding, PARP-cleavage, and DNA-degradation. Transcriptional activation of c-Myc was analyzed by nuclear localization, DNA-binding and luciferase reporter assays. Results: Gene expression array revealed that MK591 strongly inhibits the expression of the oncogene, c-Myc, in prostate cancer cells. RT-PCR and Western blot confirmed down-regulation of c-Myc. MK591-treatment reduces nuclear localization and DNA-binding activity of c-Myc, and dramatically decreased the luciferase reporter activity of c-Myc which is prevented by 5-oxoETE, a metabolic product of 5-Lox. Moreover, MK591 substantially reduces the expression of c-Myc target genes, such as cyclin D1, CDK4, survivin, Aurora kinase, Gemin4 and MCM10, and blocks the viability and colony-forming ability of transformed prostate cancer cells derived from Hi-Myc transgenic mice. Interestingly, while inhibition of 5-Lox induces apoptosis in prostate cancer cells, non-cancer cells such as NIH3T3 or astrocytes (neither expresses 5-Lox), are not affected. Conclusion: Our findings indicate that expression and oncogenic-function of c-Myc in prostate cancer cells are interrupted by inhibition of 5-Lox, and suggest that 5-Lox may contribute to advanced, aggressive prostate cancer by promoting activation of c-Myc via metabolism of arachidonic acid, an omega-6 polyunsaturated fatty acid plentiful in Western diets. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2255. doi:1538-7445.AM2012-2255