title: Combining carbon ion irradiation and non-homologous end-joining repair inhibitor NU7026 efficiently kills cancer cells.
abstract: BACKGROUND
  Our previous data demonstrated that targeting non-homologous end-joining repair (NHEJR) yields a higher radiosensitivity than targeting homologous recombination repair (HRR) to heavy ions using DNA repair gene knockouts (KO) in mouse embryonic fibroblast (MEF). In this study, we determined if combining the use of an NHEJR inhibitor with carbon (C) ion irradiation was more efficient in killing human cancer cells compared with only targeting a HRR inhibitor.
  
  
  METHODS
  The TP53-null human non-small cell lung cancer cell line H1299 was used for testing the radiosensitizing effect of NHEJR-related DNA-dependent protein kinase (DNA-PK) inhibitor NU7026, HRR-related Rad51 inhibitor B02, or both to C ion irradiation using colony forming assays. The mechanism underlying the inhibitor radiosensitization was determined by flow cytometry after H2AX phosphorylation staining. HRR-related Rad54-KO, NHEJR-related Lig4-KO, and wild-type TP53-KO MEF were also included to confirm the suppressing effect specificity of these inhibitors.
  
  
  RESULTS
  NU7026 showed significant sensitizing effect to C ion irradiation in a concentration-dependent manner. In contrast, B02 showed a slight sensitizing effect to C ion irradiation. The addition of NU7026 significantly increased H2AX phosphorylation after C ion and x-ray irradiations in H1299 cells, but not B02. NU7026 had no effect on radiosensitivity to Lig4-KO MEF and B02 had no effect on radiosensitivity to Rad54-KO MEF in both irradiations.
  
  
  CONCLUSIONS
  These results suggest that inhibitors targeting the NHEJR pathway could significantly enhance radiosensitivity of human cancer cells to C ion irradiation, rather than targeting the HRR pathway.
authors.affiliation: Department of Radiation Oncology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. gyoku0508@yahoo.co.jp.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Ma
authors.affiliation: Gunma University Heavy Ion Medical Center, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. a-takahashi@gunma-u.ac.jp.
authors.forename: Akihisa
authors.initials: A
authors.lastname: Takahashi
authors.affiliation: Gunma University Heavy Ion Medical Center, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. yyukari@gunma-u.ac.jp.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Yoshida
authors.affiliation: Department of Radiation Oncology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. minami0127minaminami@yahoo.co.jp.
authors.forename: Akiko
authors.initials: A
authors.lastname: Adachi
authors.affiliation: Gunma University Heavy Ion Medical Center, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. Tkanai@gunma-u.ac.jp.
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Kanai
authors.affiliation: Gunma University Heavy Ion Medical Center, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. tohno@gunma-u.ac.jp.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ohno
authors.affiliation: Department of Radiation Oncology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. tnakano@gunma-u.ac.jp.|Gunma University Heavy Ion Medical Center, 3-39-22 Showa-machi, Maebashi, 371-8511, Gunma, Japan. tnakano@gunma-u.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology*; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology*; D059766:DNA End-Joining Repair / Q000187:drug effects / Q000528:radiation effects; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology*; D009025:Morpholines / Q000494:pharmacology*; D011836:Radiation Tolerance / Q000187:drug effects / Q000528:radiation effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: C479235:2-(morpholin-4-yl)benzo(h)chromen-4-one; D002867:Chromones; D009025:Morpholines; D011838:Radiation-Sensitizing Agents