The purine scaffold Hsp90 inhibitor PU-H71 sensitizes cancer cells to heavy ion radiation by inhibiting DNA repair by homologous recombination and non-homologous end joining.
PU-H71 is a purine-scaffold Hsp90 inhibitor developed to overcome limitations of conventional Hsp90 inhibitors. This study was designed to investigate the combined effect of PU-H71 and heavy ion irradiation on human tumor and normal cells.



The effects of PU-H71 were determined by monitoring cell survival by colony formation, and DNA double-strand break (DSB) repair by γ-H2AX foci and immuno-blotting DSB repair proteins. The mode of cell death was evaluated by sub-G1 DNA content (as an indicator for apoptosis), and mitotic catastrophe.



PU-H71 enhanced heavy ion irradiation-induced cell death in three human cancer cell lines, but the drug did not radiosensitize normal human fibroblasts. In irradiated tumor cells, PU-H71 increased the persistence of γ-H2AX foci, and it reduced RAD51 foci and phosphorylated DNA-PKcs, key DSB repair proteins involved in homologous recombination (HR) and non-homologous end joining (NHEJ). In some tumor cell lines, PU-H71 altered the sub-G1 cell fraction and mitotic catastrophe following carbon ion irradiation.



Our results demonstrate that PU-H71 sensitizes human cancer cells to heavy ion irradiation by inhibiting both HR and NHEJ DSB repair pathways. PU-H71 holds promise as a radiosensitizer for enhancing the efficacy of heavy ion radiotherapy.
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan.
Younghyun
Y
Lee
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan; Graduate School of Medical and Pharmaceutical Sciences, Chiba University, Japan.
Huizi Keiko
HK
Li
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan.
Aya
A
Masaoka
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan; Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Japan.
Shigeaki
S
Sunada
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan.
Hirokazu
H
Hirakawa
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan.
Akira
A
Fujimori
Department of Environmental and Radiological Health Sciences, Colorado State University, USA.
Jac A
JA
Nickoloff
Dept. of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba, Japan. Electronic address: okayasu.ryuichi@qst.go.jp.
Ryuichi
R
Okayasu
D000072283:A549 Cells; D017209:Apoptosis / Q000187:drug effects; D052117:Benzodioxoles / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006367:HeLa Cells; D063193:Heavy Ion Radiotherapy; D006657:Histones / Q000378:metabolism; D059765:Homologous Recombination / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D011687:Purines / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014410:Tumor Stem Cell Assay
D052117:Benzodioxoles; C468783:H2AX protein, human; D018841:HSP90 Heat-Shock Proteins; D006657:Histones; D011687:Purines; D011838:Radiation-Sensitizing Agents; C526550:9H-purine-9-propanamine, 6-amino-8-((6-iodo-1,3-benzodioxol-5-yl)thio)-N-(1-methylethyl)-; D004247:DNA
DNA repair; Heavy ion radiotherapy; Hsp90; PU-H71; Radiosensitization
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