title: Nontoxic concentration of DNA-PK inhibitor NU7441 radio-sensitizes lung tumor cells with little effect on double strand break repair.
abstract: High-linear energy transfer (LET) heavy ions have been increasingly employed as a useful alternative to conventional photon radiotherapy. As recent studies suggested that high LET radiation mainly affects the nonhomologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair, we further investigated this concept by evaluating the combined effect of an NHEJ inhibitor (NU7441) at a non-toxic concentration and carbon ions. NU7441-treated non-small cell lung cancer (NSCLC) A549 and H1299 cells were irradiated with X-rays and carbon ions (290 MeV/n, 50 keV/μm). Cell survival was measured by clonogenic assay. DNA DSB repair, cell cycle distribution, DNA fragmentation and cellular senescence induction were studied using a flow cytometer. Senescence-associated protein p21 was detected by western blotting. In the present study, 0.3 μM of NU7441, nontoxic to both normal and tumor cells, caused a significant radio-sensitization in tumor cells exposed to X-rays and carbon ions. This concentration did not seem to cause inhibition of DNA DSB repair but induced a significant G2/M arrest, which was particularly emphasized in p53-null H1299 cells treated with NU7441 and carbon ions. In addition, the combined treatment induced more DNA fragmentation and a higher degree of senescence in H1299 cells than in A549 cells, indicating that DNA-PK inhibitor contributes to various modes of cell death in a p53-dependent manner. In summary, NSCLC cells irradiated with carbon ions were radio-sensitized by a low concentration of DNA-PK inhibitor NU7441 through a strong G2/M cell cycle arrest. Our findings may contribute to further effective radiotherapy using heavy ions.
authors.affiliation: Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Tokyo, Japan.|Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Shigeaki
authors.initials: S
authors.lastname: Sunada
authors.affiliation: Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Tokyo, Japan.|Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kanai
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Younghyun
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Research Center for Radiation Emergency Medicine, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yasuda
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Hirakawa
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Cuihua
authors.initials: C
authors.lastname: Liu
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Fujimori
authors.affiliation: Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo, Tokyo, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Uesaka
authors.affiliation: Research Center for Radiation Protection, National Institute of Radiological Sciences, Chiba, Japan. rokayasu@nirs.go.jp.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Okayasu
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002867:Chromones / Q000494:pharmacology*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000187:drug effects* / Q000528:radiation effects; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors*; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D018499:Linear Energy Transfer; D008175:Lung Neoplasms; D009025:Morpholines / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: C499693:8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one; D002867:Chromones; D009025:Morpholines; D011838:Radiation-Sensitizing Agents; D051747:DNA-Activated Protein Kinase
keywords: DNAPK protein; G2 cell cycle arrest; heavy ions; non-small cell lung cancer; p53 genes