title: DNMT (DNA methyltransferase) inhibitors radiosensitize human cancer cells by suppressing DNA repair activity.
abstract: BACKGROUND
  Histone modifications and DNA methylation are two major factors in epigenetic phenomenon. Unlike the histone deacetylase inhibitors, which are known to exert radiosensitizing effects, there have only been a few studies thus far concerning the role of DNA methyltransferase (DNMT) inhibitors as radiosensitizers. The principal objective of this study was to evaluate the effects of DNMT inhibitors on the radiosensitivity of human cancer cell lines, and to elucidate the mechanisms relevant to that process.
  
  
  METHODS
  A549 (lung cancer) and U373MG (glioblastoma) cells were exposed to radiation with or without six DNMT inhibitors (5-azacytidine, 5-aza-2'-deoxycytidine, zebularine, hydralazine, epigallocatechin gallate, and psammaplin A) for 18 hours prior to radiation, after which cell survival was evaluated via clonogenic assays. Cell cycle and apoptosis were analyzed via flow cytometry. Expressions of DNMT1, 3A/3B, and cleaved caspase-3 were detected via Western blotting. Expression of γH2AX, a marker of radiation-induced DNA double-strand break, was examined by immunocytochemistry.
  
  
  RESULTS
  Pretreatment with psammaplin A, 5-aza-2'-deoxycytidine, and zebularine radiosensitized both A549 and U373MG cells. Pretreatment with psammaplin A increased the sub-G1 fraction of A549 cells, as compared to cells exposed to radiation alone. Prolongation of γH2AX expression was observed in the cells treated with DNMT inhibitors prior to radiation as compared with those treated by radiation alone.
  
  
  CONCLUSIONS
  Psammaplin A, 5-aza-2'-deoxycytidine, and zebularine induce radiosensitivity in both A549 and U373MG cell lines, and suggest that this effect might be associated with the inhibition of DNA repair.
authors.affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Hak Jae
authors.initials: HJ
authors.lastname: Kim
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Kim
authors.forename: Eui Kyu
authors.initials: EK
authors.lastname: Chie
authors.forename: Park Da
authors.initials: PD
authors.lastname: Young
authors.forename: In Ah
authors.initials: IA
authors.lastname: Kim
authors.forename: Il Han
authors.initials: IH
authors.lastname: Kim
mesh_terms: D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D002392:Catechin / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor / Q000187:drug effects / Q000528:radiation effects; D003562:Cytidine / Q000031:analogs & derivatives / Q000494:pharmacology; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D000090205:DNA Methyltransferase 3A; D004260:DNA Repair / Q000187:drug effects*; D000077209:Decitabine; D004220:Disulfides / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005909:Glioblastoma / Q000473:pathology; D006657:Histones / Q000032:analysis; D006801:Humans; D006830:Hydralazine / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008175:Lung Neoplasms / Q000473:pathology; D009363:Neoplasm Proteins / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014410:Tumor Stem Cell Assay; D014443:Tyrosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000097584:DNA Methyltransferase 3B
chemical_list: D001374:Azacitidine; D053148:Caspase 3; D002392:Catechin; D003562:Cytidine; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D000077209:Decitabine; D004220:Disulfides; D006657:Histones; D006830:Hydralazine; D009363:Neoplasm Proteins; D011838:Radiation-Sensitizing Agents; D014443:Tyrosine; D000097584:DNA Methyltransferase 3B; C000717967:DNMT3A protein, human; C468783:H2AX protein, human; C098378:psammaplin A; C009131:pyrimidin-2-one beta-ribofuranoside; C045651:epigallocatechin gallate; C000619380:DNMT1 protein, human; C505407:CASP3 protein, human