Progression of prostate carcinogenesis and dietary methyl donors: temporal dependence

The Genomic Impact of DNA CpG Methylation on Gene Expression; Relationships in Prostate Cancer

The process of DNA CpG methylation has been extensively investigated for over 50 years and revealed associations between changing methylation status of CpG islands and gene expression. As a result, DNA CpG methylation is implicated in the control of gene expression in developmental and homeostasis processes, as well as being a cancer-driver mechanism. The development of genome-wide technologies and sophisticated statistical analytical approaches has ushered in an era of widespread analyses, for example in the cancer arena, of the relationships between altered DNA CpG methylation, gene expression, and tumor status. The remarkable increase in the volume of such genomic data, for example, through investigators from the Cancer Genome Atlas (TCGA), has allowed dissection of the relationships between DNA CpG methylation density and distribution, gene expression, and tumor outcome. In this manner, it is now possible to test that the genome-wide correlations are measurable between changes in DNA CpG methylation and gene expression. Perhaps surprisingly is that these associations can only be detected for hundreds, but not thousands, of genes, and the direction of the correlations are both positive and negative. This, perhaps, suggests that CpG methylation events in cancer systems can act as disease drivers but the effects are possibly more restricted than suspected. Additionally, the positive and negative correlations suggest direct and indirect events and an incomplete understanding. Within the prostate cancer TCGA cohort, we examined the relationships between expression of genes that control DNA methylation, known targets of DNA methylation and tumor status. This revealed that genes that control the synthesis of S-adenosyl-l-methionine (SAM) associate with altered expression of DNA methylation targets in a subset of aggressive tumors.

Role of diet in prostate cancer: the epigenetic link

Diet is hypothesized to be a critical environmentally related risk factor for prostate cancer (PCa) development, and specific diets and dietary components can also affect PCa progression; however, the mechanisms underlying these associations remain elusive. As for a maturing organism, PCa's epigenome is plastic and evolves from the pre-neoplastic to the metastatic stage. In particular, epigenetic remodeling relies on substrates or cofactors obtained from the diet. Here we review the evidence that bridges dietary modulation to alterations in the prostate epigenome. We propose that such diet-related effects offer a mechanistic link between the impact of different diets and the course of PCa development and progression.

Folate intake and the risk of prostate cancer: a systematic review and meta-analysis

There is conflicting evidence regarding the role of folate on the risk of developing prostate cancer. We performed a systematic review and quantitative meta-analysis of folate blood levels and folate intake, and the risk of prostate cancer. Four electronic databases (Medline, PubMed, Embase and Current Contents Connect) were searched to 11 October 2013, with no language restrictions for observational studies that measured folate intake or blood levels and the risk of prostate cancer. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using a random effects model. The dietary folate meta-analysis comprising 11 studies with 15 336 cases and a total sample size of 146 782 found no statistically significant association with prostate cancer, with an OR of 0.97 (95% CI 0.89-1.06). The total folate meta-analysis comprising of 5 studies with 7114 cases and a total sample size of 93 781 also found no statistically significant association with prostate cancer, with an OR of 0.99 (95% CI 0.82-1.19). The blood folate meta-analysis comprising of seven studies with 6122 cases and a total sample size of 10 232 found an increased risk of prostate cancer with high blood folate levels, with an OR of 1.43 (95% CI 1.06-1.93). There was significant heterogeneity (I(2)=79.5%, P<0.01). Removal of an outlier study removed the heterogeneity (I(2)=0.0%, P=0.54) and the association remained significant with an OR of 1.14 (95% CI 1.02-1.28). Dietary and total folate intake do not appear to be significantly associated with the risk of prostate cancer. High blood folate levels are associated with an increased risk of prostate cancer. These conclusions are limited by the predominance of included studies originating from developed countries with mostly Caucasian populations. Further research in populations with a high prevalence of non-Caucasian backgrounds is needed.

Trials with 'epigenetic' drugs: an update

Epigenetic inactivation of pivotal genes involved in correct cell growth is a hallmark of human pathologies, in particular cancer. These epigenetic mechanisms, including crosstalk between DNA methylation, histone modifications and non-coding RNAs, affect gene expression and are associated with disease progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. Re-expression of genes epigenetically inactivated can result in the suppression of disease state or sensitization to specific therapies. Small molecules that reverse epigenetic inactivation, so-called epi-drugs, are now undergoing clinical trials. Accordingly, the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment have approved some of these drugs. Here, we focus on the biological features of epigenetic molecules, analyzing the mechanism(s) of action and their current use in clinical practice.