Article: article from journal or magazin.
Impact of genomic methylation on radiation sensitivity of colorectal carcinoma.
International Journal of Radiation Oncology, Biology, Physics
PURPOSE: To investigate the influence of demethylation with 5-aza-cytidine (AZA) on radiation sensitivity and to define the intrinsic radiation sensitivity of methylation deficient colorectal carcinoma cells. METHODS AND MATERIALS: Radiation sensitizing effects of AZA were investigated in four colorectal carcinoma cell lines (HCT116, SW480, L174 T, Co115), defining influence of AZA on proliferation, clonogenic survival, and cell cycling with or without ionizing radiation. The methylation status for cancer or DNA damage response-related genes silenced by promoter methylation was determined. The effect of deletion of the potential target genes (DNMT1, DNMT3b, and double mutants) on radiation sensitivity was analyzed. RESULTS: AZA showed radiation sensitizing properties at >or=1 micromol/l, a concentration that does not interfere with the cell cycle by itself, in all four tested cell lines with a sensitivity-enhancing ratio (SER) of 1.6 to 2.1 (confidence interval [CI] 0.9-3.3). AZA successfully demethylated promoters of p16 and hMLH1, genes associated with ionizing radiation response. Prolonged exposure to low-dose AZA resulted in sustained radiosensitivity if associated with persistent genomic hypomethylation after recovery from AZA. Compared with maternal HCT116 cells, DNMT3b-defcient deficient cells were more sensitive to radiation with a SER of 2.0 (CI 0.9-2.1; p = 0.03), and DNMT3b/DNMT1-/- double-deficient cells showed a SER of 1.6 (CI 0.5-2.7; p = 0.09). CONCLUSIONS: AZA-induced genomic hypomethylation results in enhanced radiation sensitivity in colorectal carcinoma. The mediators leading to sensitization remain unknown. Defining the specific factors associated with radiation sensitization after genomic demethylation may open the way to better targeting for the purpose of radiation sensitization.
Adaptor Proteins, Signal Transducing/metabolism, Azacitidine/pharmacology, Cell Cycle/drug effects, Cell Cycle/radiation effects, Cell Line, Tumor, Cell Proliferation/drug effects, Cell Proliferation/radiation effects, Cell Survival/drug effects, Cell Survival/radiation effects, Colorectal Neoplasms/genetics, Colorectal Neoplasms/radiotherapy, Cyclin-Dependent Kinase Inhibitor p16/metabolism, DNA (Cytosine-5-)-Methyltransferase/deficiency, DNA (Cytosine-5-)-Methyltransferase/genetics, DNA Methylation/drug effects, DNA Methylation/radiation effects, Gene Deletion, Humans, Nuclear Proteins/metabolism, Radiation Tolerance/drug effects, Radiation Tolerance/genetics, Radiation-Sensitizing Agents/pharmacology
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