Cellular vitamins, DNA methylation and cancer risk.

The overall goal of this research is to evaluate interactions among cellular vitamin levels and global DNA hypomethylation and the impact of these variables on human cancer risk. Global DNA methylation was determined by two methods: a radiolabeled methyl incorporation (RMI) assay and an immunohistochemical assay using an antibody to 5-methylcytosine (5-MC). The RMI assay is useful for evaluating methylation of DNA in tissue samples, whereas the 5-MC assay clearly reveals DNA methylation in specific types of cells and has minimal day-to-day variability. We have observed significant interactions among cancer-protective vitamins and global DNA methylation at the level of tissues. A significant positive association was observed between global DNA methylation in buccal mucosal cells and malignant tissues, but not between global DNA methylation in peripheral leukocytes and malignant tissues of the lung. These results suggest that changes in global methylation in buccal mucosal cells may reflect changes in tissues at high risk of developing lung cancer. With the antibody technique, we have demonstrated that alterations in global DNA methylation are associated with epigenetic differences in susceptibility for development of lung cancer, which is involved in the progression of the disease. The effect of race on these relationships also is discussed. Significant associations observed between expression of epidermal growth factor receptor and global DNA methylation, as assessed by the 5-MC assay but not by the RMI assay, indicate that evaluation of global methylation and biomarkers in specific types of cells may shed light on the associations between global DNA methylation and other intermediate endpoint biomarkers in the future.