DNA methylation is an epigenetic determinant of gene expression. Cytochrome P450 (CYP1A1) is a phase 1 xenobiotic metabolizing enzyme. Glutathione S-transferase P1 (GSTP1) detoxifies metabolites and regulates cellular chemical stress and death. Methylation changes in these genes could play a role in the incidence of cancer. Our aims were to analyze DNA-methylation of selected CpG islands in the CYP1A1 and GSTP1 genes at baseline in subjects who had incident cancer and paired controls, and to determine if DNA methylation in cancer patients changed from baseline to the time close to cancer diagnosis.
We followed-up 1094 subjects (aged: 67±6years) of the PREDIMED-Valencia study prospectively from 2003 to 2014. Cancer incidence was a secondary outcome in our trial. We analyzed 69 cases of incident cancer (lung, breast and colon) during this follow-up period, and 69 paired controls free of cancer. We analyzed DNA-methylation levels of the CYP1A1 and GSTP1 genes at baseline in both groups. Quantitative DNA methylation analysis was undertaken by MALDI-TOF mass spectrometry. We evaluated methylation levels on chromosome 15 (region: 74726090 -74726460 base pairs from promoter) and chromosome 11 (region: 67583556-67583896 base pairs from promoter).
We detected statistically significant differences in DNA methylation levels at baseline in the CYP1A1 and GSTP1 genes between cancer cases and controls (P=0.008 for the CpG site 26-27 of the CYP1A1 gene and P=0.049 for the CpG 10-11 island at the GSTP1 gene). We detected statistically significant changes in DNA methylation prospectively in cancer patients. DNA methylation at the CpG 4 (CYP1A1 gene) was 0.020±0.034 at baseline vs 0.006±0.013 close to cancer diagnosis (P=0.044). For the GSTP1 gene, methylation of the CpG 34-39 prospectively increased from 0.327±0.046 at baseline to 0.345±0.053 (P=0.014) close to cancer diagnosis.
We have detected differences in DNA-methylation of selected CpG Islands of the CYP1A1 and GSTP1 genes at baseline, between future diagnosed cancer subjects and cancer-free controls. Moreover, in patients subsequently diagnosed with cancer, a change in DNA methylation was observed between baseline and close to the time of cancer diagnosis. This suggests a dynamic influence of DNA methylation that could be modulated for prevention.
Clinical trial identification
Controlled-trials.com number ISRCTN35739639
Legal entity responsible for the study
Spanish Government's Instituto de Salud Carlos III and University of Valencia
Instituto de Salud Carlos III
All authors have declared no conflicts of interest.