Combining heavy ion radiation and artificial microRNAs to target the homologous recombination repair gene efficiently kills human tumor cells.
OBJECTIVE
Previously, we demonstrated that heavy ions kill more cells at the same dose than X-rays because DNA-clustered lesions produced by heavy ions affect nonhomologous end-joining (NHEJ) repair but not homologous recombination repair (HRR). We have also shown that our designed artificial microRNAs (amiRs) could efficiently target XRCC4 (an essential factor for NHEJ) or XRCC2 (an essential factor for HRR) and sensitize human tumor cells to X-rays. Based on these data, we were interested in testing the hypothesis that combining heavy ions and amiRs to target HRR but not NHEJ should more efficiently kill human tumor cells.


METHODS
Human tumor cell lines (U87MG, a brain tumor cell line, and A549, a lung cancer cell line) and their counterparts, overexpressed with amiR to target XRCC2, XRCC4 or both, were used in this study. Survival sensitivities were examined using a clonogenic assay after these cells were exposed to X-rays or heavy ions. In addition, these cell lines were subcutaneously injected into nude mice to form xenografts and the tumor size was compared after the tumor areas were exposed to X-rays or heavy ions.


RESULTS
Although targeting either XRCC4 (NHEJ factor) or XRCC2 (HRR factor) sensitized the human tumor cells to X-rays, in vitro and the xenograft animal model, targeting only XRCC2 but not XRCC4 sensitized the human tumor cells to heavy ions in vitro and in the xenograft animal model.


CONCLUSIONS
Combining heavy ions with targeting the HRR pathway, but not the NHEJ pathway, could significantly improve the efficiency of tumor cell death.
Department of Neurosurgery, Provincial Hospital Affiliated to Shandong University, Shandong University, Jinan, China.
Zhiming
Z
Zheng
Ping
P
Wang
Hongyan
H
Wang
Xiangming
X
Zhang
Minli
M
Wang
Francis A
FA
Cucinotta
Ya
Y
Wang
D000818:Animals; D016923:Cell Death / Q000235:genetics / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics / Q000528:radiation effects*; D003131:Combined Modality Therapy / Q000379:methods; D004268:DNA-Binding Proteins / Q000235:genetics / Q000528:radiation effects*; D063193:Heavy Ion Radiotherapy; D006801:Humans; D008297:Male; D051379:Mice; D035683:MicroRNAs / Q000627:therapeutic use*; D011836:Radiation Tolerance; D059767:Recombinational DNA Repair / Q000235:genetics / Q000528:radiation effects*; D047368:Tumor Burden; D023041:Xenograft Model Antitumor Assays / Q000379:methods
D004268:DNA-Binding Proteins; D035683:MicroRNAs; C113187:XRCC2 protein, human; C101467:XRCC4 protein, human