title: Soy isoflavones augment radiation effect by inhibiting APE1/Ref-1 DNA repair activity in non-small cell lung cancer.
abstract: BACKGROUND
  Soy isoflavones sensitize cancer cells to radiation both in vitro and in vivo. To improve the effect of radiotherapy for non-small cell lung cancer, we assessed the potential of using a complementary approach with soy isoflavones.
  
  
  METHODS
  Human A549 non-small cell lung cancer cells were treated with soy isoflavones, radiation, or both and tested for cell growth. DNA double-strand breaks (DSBs) were detected by immunostaining for γ-H2AX foci. Expressions of γ-H2AX, HIF-1α, and APE1/Ref-1 were assessed by Western blots. DNA-binding activities of HIF-1α and NF-κB transcription factors were analyzed by electrophoretic mobility shift assay.
  
  
  RESULTS
  Soy isoflavones increased A549 cell killing induced by radiation. Multiple γ-H2AX foci were detectable at 1 hour after radiation but decreased at 24 hours after radiation. Soy isoflavones also caused DNA DSBs, but γ-H2AX foci increased over time. Soy isoflavones and radiation caused an increase in γ-H2AX foci, which persisted at 24 hours, indicating both increased DNA damage and inhibition of repair. Soy isoflavones inhibited the radiation-induced activity of the DNA repair/redox enzyme APE1/Ref-1 and the transcription factors NF-κB and HIF-1α. E3330, which inhibits the redox activity of APE1/Ref-1, did not alter the repair of radiation-induced DSBs. Methoxyamine, which inhibits APE1/Ref-1 DNA repair activity, partly blocked the decrease in radiation-induced DSBs at 24 hours, suggesting partial mitigation of radiation-induced DNA repair akin to the effect of soy combined with radiation, in agreement with cytotoxic assays.
  
  
  CONCLUSIONS
  Inhibition of APE1/Ref-1 DNA repair activity by soy could be involved in the mechanism by which soy alters DNA repair and leads to cell killing.
authors.affiliation: Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
authors.forename: Vinita
authors.initials: V
authors.lastname: Singh-Gupta
authors.forename: Michael C
authors.initials: MC
authors.lastname: Joiner
authors.forename: Lindsay
authors.initials: L
authors.lastname: Runyan
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Yunker
authors.forename: Fazlul H
authors.initials: FH
authors.lastname: Sarkar
authors.forename: Steven
authors.initials: S
authors.lastname: Miller
authors.forename: Shirish M
authors.initials: SM
authors.lastname: Gadgeel
authors.forename: Andre A
authors.initials: AA
authors.lastname: Konski
authors.forename: Gilda G
authors.initials: GG
authors.lastname: Hillman
mesh_terms: D016227:Benzoquinones / Q000494:pharmacology; D015153:Blotting, Western; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism* / Q000473:pathology* / Q000517:prevention & control; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects* / Q000528:radiation effects*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000378:metabolism; D006801:Humans; D006898:Hydroxylamines / Q000494:pharmacology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D007529:Isoflavones / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D011422:Propionates / Q000494:pharmacology; D013025:Glycine max / Q000737:chemistry*; D014407:Tumor Cells, Cultured; D014965:X-Rays
chemical_list: D016227:Benzoquinones; C468783:H2AX protein, human; C497442:HIF1A protein, human; D006657:Histones; D006898:Hydroxylamines; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007529:Isoflavones; D016328:NF-kappa B; D011422:Propionates; C075569:E 3330; C005214:methoxyamine; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase