The Role of Sulforaphane in Epigenetic Mechanisms, Including Interdependence between Histone Modification and DNA Methylation.

Carcinogenesis as well as cancer progression result from genetic and epigenetic changes of the genome that leads to dysregulation of transcriptional activity of genes. Epigenetic mechanisms in cancer cells comprise (i) post-translation histone modification (i.e., deacetylation and methylation); (ii) DNA global hypomethylation; (iii) promoter hypermethylation of tumour suppressor genes and genes important for cell cycle regulation, cell differentiation and apoptosis; and (iv) posttranscriptional regulation of gene expression by noncoding microRNA. These epigenetic aberrations can be readily reversible and responsive to both synthetic agents and natural components of diet. A source of one of such diet components are cruciferous vegetables, which contain high levels of a number of glucosinolates and deliver, after enzymatic hydrolysis, sulforaphane and other bioactive isothiocyanates, that are involved in effective up-regulation of transcriptional activity of certain genes and also in restoration of active chromatin structure. Thus a consumption of cruciferous vegetables, treated as a source of isothiocyanates, seems to be potentially useful as an effective cancer preventive factor or as a source of nutrients improving efficacy of standard chemotherapies. In this review an attempt is made to elucidate the role of sulforaphane in regulation of gene promoter activity through a direct down-regulation of histone deacetylase activity and alteration of gene promoter methylation in indirect ways, but the sulforaphane influence on non-coding micro-RNA will not be a subject of this review.

Sulforaphane Alone and in Combination with Clofarabine Epigenetically Regulates the Expression of DNA Methylation-Silenced Tumour Suppressor Genes in Human Breast Cancer Cells.

BACKGROUND/AIM: Sporadic breast cancer is frequently associated with aberrant DNA methylation patterns that are reversible and responsive to environmental factors, including diet. In the present study, we investigated the effects of sulforaphane (SFN), a phytochemical from cruciferous vegetables, on the methylation and expression of PTEN and RARbeta2 tumour suppressor genes as well as on the expression of regulators of DNA methylation reaction, DNMT1 , p53 , and p21 , in MCF-7 and MDA-MB-231 human breast cancer cells with different invasive potential. We also evaluate the role of SFN epigenetic effects in support of therapy with clofarabine (ClF) that was recently shown to modulate the epigenome as well. METHODS: Promoter methylation and gene expression were estimated using methylation-sensitive restriction analysis and real-time PCR, respectively. RESULTS: In both MCF-7 and MDA-MB-231 cells, SFN at IC 50 (22 and 46 µ M , respectively) and a physiologically relevant 10 µ M concentration lead to hypomethylation of PTEN and RARbeta2 promoters with concomitant gene upregulation. The combination of SFN and ClF enhances these effects, resulting in an increase in cell growth arrest and apoptosis at a non-invasive breast cancer stage. CONCLUSIONS: Our findings provide evidence that SFN activates DNA methylation-silenced tumour suppressor genes in breast cancer cells and may contribute to SFN-mediated support of therapy with an anti-cancer drug, ClF, increasing its applications in solid tumours.

The role of lipid droplets and adipocytes in cancer. Raman imaging of cell cultures: MCF10A, MCF7, and MDA-MB-231 compared to adipocytes in cancerous human breast tissue.

We have studied live non-malignant (MCF10A), mildly malignant (MCF7) and malignant (MDA-MB-231) breast cancer cells and human breast cancer tissue. We demonstrate the first application of Raman imaging and spectroscopy in diagnosing the role of lipid droplets in cell line cultures that closely mimic an in vivo environment of various stages in human breast cancer tissue. We have analyzed the composition of the lipid droplets in non-malignant and malignant human breast epithelial cell lines and discussed the potential of lipid droplets as a prognostic marker in breast cancer. To identify any difference in the lipid droplet-associated biochemistry and to correlate it with different stages of breast cancer, the PCA method was employed. The chemical composition of lipids and proteins, both in the cell line models and in human breast tissue has been analyzed. The paper shows the alterations in lipid metabolism that have been reported in cancer, at both the cellular and tissue levels, and discusses how they contribute to the different aspects of tumourigenesis.

Clofarabine, a novel adenosine analogue, reactivates DNA methylation-silenced tumour suppressor genes and inhibits cell growth in breast cancer cells.

Clofarabine (2-chloro-2'-fluoro-2'-deoxyarabinosyladenine, ClF) is a second-generation 2'-deoxyadenosine analogue that is structurally related to cladribine (2-chloro-2'-deoxyadenosine, 2CdA) and fludarabine (9-beta-d-arabinosyl-2-fluoroadenine, F-ara-A). It demonstrates potent antitumour activity at much lower doses than parent compounds with high therapeutic efficacy in paediatric blood cancers. Our previous studies in breast cancer cells indicate that 2CdA and F-ara-A are involved in epigenetic regulation of gene transcription. We therefore investigated whether ClF influences methylation and expression of selected tumour suppressor genes, such as adenomatous polyposis coli (APC), phosphatase and tensin homologue (PTEN), and retinoic acid receptor beta 2 (RARbeta2), as well as expression of p53, p21 and DNA methyltransferase 1 (DNMT1) in MCF-7 and MDA-MB-231 breast cancer cell lines with different invasive potential. Promoter methylation and gene expression were estimated using methylation-sensitive restriction analysis (MSRA) and real-time PCR, respectively. ClF demonstrated potent growth inhibitory activity in MCF-7 and MDA-MB-231 cells after 96h treatment with IC50 determined as equal to 640nM and 50nM, respectively. In both breast cancer cell lines, ClF led to hypomethylation and up-regulation of APC, PTEN and RARbeta2 as well as increase in p21 expression. Only in non-invasive MCF-7 cells, these changes were associated with down-regulation of DNMT1. Our results provide first evidence of ClF implications in epigenetic regulation of transcriptional activity of selected tumour suppressor genes in breast cancer. It seems to be a new important element of ClF anticancer activity and may indicate its potential efficacy in epigenetic therapy of solid tumours, especially at early stages of carcinogenesis.

Folic acid enforces DNA methylation-mediated transcriptional silencing of PTEN, APC and RARbeta2 tumour suppressor genes in breast cancer.

Folate, one of the most studied dietary compounds, has recently become the main topic of debates on food fortification. Although low folate levels may be associated with increased risk of cancer development, simultaneously several reports indicate a detrimental effects mediated by high folate concentrations. Using the methylation sensitive restriction analysis (MSRA) and real-time RT-PCR we tested the effect of folic acid on DNA promoter methylation and expression of PTEN, APC and RARbeta2 tumour suppressor genes in MCF-7 and MDA-MB-231 breast cancer cell lines with different invasive capacity. The tested genes encode proteins involved in regulation of oncogenic intracellular signaling pathways. The results show that the increasing concentrations of folic acid lead to a dose-dependent down-regulation of tumour suppressor genes which may be linked to the increased DNA methylation detected within their promoter regions. The effects were more remarkable in non-invasive MCF-7 cells where we also observed 30% up-regulation of DNMT1 expression at the highest folate concentration used. Our findings show that caution need to be used when introducing folic acid supplementation since it may lead to cancer progression.

Influence of clofarabine on transcriptional activity of PTEN, APC, RARB2, ZAP70 genes in K562 cells.

BACKGROUND: In this study, the effect of clofarabine, a new generation 2'-deoxyadenosine analogue, on promoter methylation and transcriptional activity of selected genes (PTEN, APC, RARB2, ZAP70) in K562 cells was assessed. MATERIALS AND METHODS: Promoter methylation was estimated using methylation-sensitive restriction analysis. The mRNA level of the genes was measured with real-time PCR. RESULTS: The inhibitory cytostatic index (IG(50)) for clofarabine in K562 cells cultured for 72 (or 96) h was 8 nM. The drug (20 nM) caused: (i) potent diminution in methylation of PTEN promoter, moderate methylation reduction of APC and RARB2 promoters, and complete methylation of ZAP70 promoter; (ii) significant stimulation of PTEN, APC, RARB, and p21 mRNA expression and (iii) decline in mRNA level of ZAP70 and DNMT1 genes. CONCLUSION: The results indicated that clofarabine is involved in epigenetic regulation of transcriptional activity of the tested tumour suppressor genes and genes encoding proteins involved in DNA methylation process.