Colorectal cancer cells Caco-2 and HCT116 resist epigenetic effects of isothiocyanates and selenium in vitro

It is relatively unknown how different dietary components, in partnership, regulate gene expression linked to colon pathology. It has been suggested that the combination of various bioactive components present in a plant-based diet is crucial for their potential anticancer activities. This study employed a combinatorial chemopreventive strategy to investigate the impact of selenium and/or isothiocyanates on DNA methylation processes in colorectal carcinoma cell lines. To gain insights into the epigenetic-mediated changes in gene expression in response to these dietary constituents cultured Caco-2 and HCT116 cells were exposed for up to 12 days to different concentrations of selenium methylselenocysteine and selenite (ranging from 0.2 to 5 mu M) either alone or in combination with sulforaphane and iberin (ranging from 6 to 8 mu M), and changes to gene-specific (p16 (INK4A) and ESR1), global (LINE-1) methylation and DNMT expression were quantified using real-time PCR-based assays. No effects on the methylation of CpG islands in ESR1, p16 (INK4A) or of LINE-1, a marker of global genomic methylation, were observed after exposure of Caco-2 and HCT116 cells to selenium or isothiocyanates. Only transient changes in DNMT mRNA expression, which occurred mostly in the treatment groups containing isothiocyanates, were observed, and these occurred only for specific DNMT transcripts and did not lead to the modification of the aberrant methylation status present in these cells. These data suggest that treatment for colon cancer cells with selenium and/or isothiocyanates, either individually or in combination does not impact abnormal methylation patterns of key genes involved in the complex multistep process of colon carcinogenesis in vitro.