gms | German Medical Science

Objective: A variety of epigenetic lesions such as global DNA hypomethylation and aberrant hypermethylation of gene promoters is associated with the pathogenesis of metastases in human cancers. These epigenetic aberrations lead to a repression of gene expression that confers cancer cells the competence to migrate from the primary organ and growth advantages at the secondary tissue site. We have performed an epigenome-wide DNA methylation analysis of lesions involved in cerebral- and extracerebral metastatic processes by means of microarray and sequencing.

Method: We investigated brain metastases of 14 renal cell (RC) and 17 colorectal cancers (CRC) and their corresponding primary carcinomas as well as 25 hepatic metastases of colorectal- and renal carcinomas. As controls, we used brain tissue (n=7) and normal tissue from kidney, liver and colon (n=6). DNA methylation was quantified using BeadArrays with the Illumina GoldenGate Methylation Panel (807 genes) or Illumina Infinium HumanMethylation (14.475 genes). Bisulphite sequencing of selected genes was performed to validate the array data.

Results: Brain metastases showed a distinct signature when compared with normal tissue and 75 genes were differentially hypermethylated (p<0.01 U- Mann Whitney). Brain metastases evolving from different primary carcinomas showed different methylation profiles. A panel of 33 hypermethylated genes significantly identified brain metastases from CRC when compared to brain metastases from RC (p<0.01). Analyzing cerebral and extracerebral metastases from a specific primary carcinoma revealed different methylation profiles. Genes in which hypermethylation was significantly associated with cerebral metastases from hepatic carcinomas were SFRP1, PODXL and POMC; from colorectal carcinomas FZD9, PDE18, ADCYAP1, CCNA1 and FLI1. Similarly, 15 hypermethylated genes were related to the metastatic process to the brain or alternatively to the liver from colorectal cancers; 4 further genes from renal carcinomas (both p<0.01).

Conclusions: Our results clearly show distinct methylation signatures in cerebral and extracerebral metastases evolving from specific primary carcinomas. Moreover, we demonstrate that different panels of metastasis-associated genes undergoing hypermethylation are putative epigenetic biomarkers of “organs at risk”.