Targeting EZH2 in Prostate Cancer by Luteolin

Louis Stokes Cleveland Va Medical Center, Cleveland OH

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Abstract

DESCRIPTION (provided by applicant): The overall objective of this study is to assess the efficacy of luteolin in preventing progression of prostate cancer and to uncover the molecular basis of its anticancer effects. Post-translational modification of histones is critical for regulation of chromatin structure and gene expression. Enhancer of Zeste homolog 2 (EZH2) is the catalytic subunit of the polycomb repressive complex (PRC)-2, which is involved in chromatin remodeling and gene silencing through its catalysis of the trimethylation of histone H3 on lysine 27 (H3K27). EZH2- mediated epigenetic gene silencing plays an important role in prostate cancer initiation and progression. Increased EZH2 expression promotes neoplastic transformation of epithelial cells and cancer progression. Mechanistically, EZH2-mediated trimethylation of H3K27 results in silencing of a large number of tumor suppressor genes such as CDKN2A/p16, CDH1/E-cadherin, Disabled homolog 2-interacting protein (DAB2IP) and tissue inhibitor of metalloproteinases (TIMP)-3 in prostate cancer. Functional assays have demonstrated EZH2 to be a bonafide oncogene. Our preliminary data suggest that: i) progressive increase in EZH2 during prostate cancer progression and its differential expression in cancer vs. corresponding normal/benign tissue, ii) from in silico studies, the plant flavone luteolin binds to the active site of EZH2, iii) interactin of luteolin with EZH2 and H3k27me3 proteins-ex vivo studies, iii) luteolin inhibits EZH2 expression and H3K27me3 in prostate cancer cells, iv) luteolin alters transcriptome and miRNA expression, v) luteolin decreases proliferation and invasiveness of prostate cancer cells, and vi) luteolin induces re-expression of tumor suppressor genes. Our working hypothesis is that luteolin-mediated suppression of EZH2 and its histone-lysine N- methyltransferase activity inhibits progression of prostate cancer not only through changes in histone methylation, but also through epigenetic modifications in the promoters of tumor suppressor genes and post-translational changes in the levels of EZH2-regulatory miRNAs. We propose four complementary specific aims to determine: (1) the effects of luteolin on EZH2 and other PRC2 complex proteins, (2) the ability of luteolin to reverse EZH2-mediated epigenetic gene silencing, (3) the effects of luteolin on the regulation of specific miRNAs affecting EZH2-mediated changes in prostate cancer cells, and (4) the effects of luteolin-mediated EZH2 inhibition and associated molecular mechanisms on relevant in vivo situations using the TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model, which recapitulate human disease. Prostate cancer is highly prevalent and the second leading cause of cancer-related deaths in men in the United States. The knowledge generated by completion of these studies has the potential to provide the VA healthcare system with unique opportunities for effective treatment strategies for VA men diagnosed with low- grade, low-volume prostate cancer. Such novel strategies are necessitated by the current realities that histologically identical cancers in different patients cn exhibit widely variant biologic behavior, and prostate cancer patients are more likely to have significant comorbidities than the general population. In conclusion, we will define the 1) role of EZH2-mediated epigenetic reprogramming in driving prostate cancer progression, as the EZH2-H3K27me3 epigenetic pathway appears to be very important for repression of tumor suppressor genes, and 2) the beneficial effects of luteolin, which will set a new paradigm in the management of prostate cancer patients undergoing active surveillance or at risk for biochemical recurrence.