The role of epigenetic modifications in prostate tumourigenesis.

Prostate cancer is the second-leading cause of cancer death in Australian men. Current therapies for advanced prostate cancer are not curative and most patients eventually develop castrate resistant prostate cancer. Epigenetic modifications are heritable and reversible biochemical changes of the chromatin that regulate gene expression and are important in prostate tumourigenesis. There is also evidence that excess foetal nutrition is associated with increased risk of developing prostate cancer. Hence, the aims of this thesis were to determine the involvement of epigenetic modifications in: the early origin of prostate cancer, prostate cancer progression, as prognostic and therapeutic targets in prostate cancer. The first aim of this thesis was to use a rodent model to determine if a maternal high fat diet (MHFD) is associated with increased risk of prostate cancer in offspring. Offspring exposed to a MHFD had increased incidence of prostate abnormalities compared to offspring exposed to a maternal control diet. GSTP1 is hypermethylated and silenced in human prostate cancer and was decreased in these offspring prostates. The MHFD altered the male offspring prostates microRNA expression and provided insights of possible underlying mechanisms that support a link between MHFD and risk of prostate cancer in adult offspring. The second aim was to investigate if specific histone modifications H3K18Ac and H3K4diMe were prognostic markers for prostate cancer. High levels of H3K18Ac and H3K4diMe were associated with increased risk of prostate cancer relapse respectively. To further investigate the underlying mechanisms, epigenetic genes were mined in microarray data, and an epigenetic gene signature was identified which distinguished non-malignant from tumour prostate tissues in an independent prostate cancer cohort. To investigate if the DNA methyltransferase inhibitor (DNMTi) 5-aza-CdR was a potential treatment agent for prostate cancer, proliferation assays were performed in prostate cancer cells. A daily low-dose and prolonged 5-aza-CdR treatment regime was the most effective treatment in prostate cancer cells compared to high doses administered less frequently. Furthermore, GSTP1 DNA methylation and protein status were good indicators of DNMTis efficacy in vitro, where demethylation indicated growth suppression and protein re-expression indicated cell death induction. To investigate if the Kruppel-like-factor 6 (KLF6) prostate cancer susceptibility gene is epigenetically altered during prostate cancer progression, DNA methylation analyses were performed in human and mouse (TRAMP) prostate cancers. Our results suggest that DNA hypermethylation is not responsible for decreased KLF6 expression in human and TRAMP prostate cancers in our study. Collectively, the findings of this thesis further support the importance of epigenetic modifications in prostate tumourigenesis. We demonstrated the potential of using epigenetic modifications as prognostic markers, therapeutic targets and as a marker of treatment efficacy. Lastly, we provide evidence, for the first time, that MHFD is a risk factor for prostate cancer and that miRNAs are involved. This finding is important and suggests the potential of early prevention/ intervention of prostate cancer by targeting epigenetic modifications and diet intervention.Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 201