DNA promoter methylation in normal colon mucosa taken from healthy individuals and cancer patients, and evaluated in relation to similar events in colorectal tumors.

B128

We have studied promoter methylation in normal colon mucosa samples from healthy individuals (n = 21) and from cancer patients (n = 19), and compared the pattern with the ones in adenomas (n = 63), carcinomas (n = 53), and colon cancer cell lines (n = 20). To our knowledge, only one previous study has examined promoter methylation in normal mucosa from both healthy individuals and cancer patients. We examined the following eleven genes: ADAMTS1, APC, CDKN2A, CRABP1, HOXA9, MGMT, MLH1, NR3C1, PTEN, RUNX3, and SCGB3A1. In total, 38% "normal-normals", 84% "cancer-normals", 73% adenomas, 89% carcinomas, and 100% cell lines were methylated in one or more of the 11 genes analyzed with an average of 0.7, 2.1, 1.7, 3.4, and 5.3 methylated genes in the five respective tumor groups. The normal samples derived from cancer patients showed significantly more methylation compared with samples from non-cancerous individuals. This was apparent both for the widespread methylation (comparing mean number of methylated genes) (P = 0.002), as well as at the individual gene level (ADAMTS1, P = 0.040; APC, P = 0.009; MGMT, P = 0.051). With few exceptions gene methylation frequencies typically increased with tumor aggressiveness. The most frequently methylated genes in the primary carcinomas were ADAMTS1, CRABP1, and MGMT. To the best of our knowledge three genes, HOXA9, RUNX3, and SCGB3A1 are for the first time reported to be methylated in benign lesions of the large bowel. Three genes, HOXA9, MGMT, and APC showed comparable methylation frequencies in adenomas and carcinomas, suggesting that the inactivation of these occur early in colorectal tumorigenesis. Indeed, these genes were also the three most frequently methylated in normal samples. We confirmed that methylation is most common in carcinomas with MSI and proximal location. For some of the genes methylation status were associated to gender, age, and polyp size. In general, methylation frequencies were higher in cell lines than in primary tumors and statistically significant for CRABP1, CDKN2A, and SCGB3A1. However, the comparable overall methylation profiles between the two groups, suggests that colon cancer cell lines can be considered representative epigenetic models for large bowel carcinomas.