title: RETRACTED: Combining PARP-1 inhibition and radiation in Ewing sarcoma results in lethal DNA damage.
abstract: Ewing sarcomas (ES) harbor a chromosomal translocation that fuses the EWS gene to an ETS transcription factor, most commonly Friend leukemia integration 1 (FLI1). The EWS-FLI1 fusion protein acts in a positive feedback loop to maintain the expression of PARP-1, which is involved in repair of DNA damage. Here, we examine the effects of PARP-1 inhibition and radiation therapy on Ewing sarcomas. In proliferation assays, the Ewing sarcoma cell lines RD-ES and SK-N-MC were much more sensitive than non-Ewing sarcoma cell lines to the PARP-1 inhibitor olaparib (Ola; IC50 0.5-1 μmol/L vs. >5 μmol/L) and to radiation (IC50 2-4 Gy vs. >6 Gy). PARP-1 inhibition with short hairpin RNA (shRNA) or Ola sensitized Ewing sarcoma cells, but not non-Ewing sarcoma cells, to radiation therapy in both proliferation and colony formation assays. Using the Comet assay, radiation of Ewing sarcoma cells with Ola, compared to without Ola, resulted in more DNA damage at 1 hour (mean tail moment 36-54 vs. 26-28) and sustained DNA damage at 24 hours (24-29 vs. 6-8). This DNA damage led to a 2.9- to 4.0-fold increase in apoptosis and a 1.6- to 2.4-fold increase in cell death. The effect of PARP-1 inhibition and radiation therapy on Ewing sarcoma cells was lost when EWS-FLI1 was silenced by shRNA. A small dose of radiation therapy (4 Gy), when combined with PARP-1 inhibition, stopped the growth of SK-N-MC flank tumors xenografts. In conclusion, PARP-1 inhibition in Ewing sarcomas amplifies the level and duration of DNA damage caused by radiation therapy, leading to synergistic increases in apoptosis and cell death in a EWS-FLI1-dependent manner.
authors: Corresponding Author: Sam S. Yoon, Department of Surgery, Memorial Sloan-Kettering Cancer Center, H-1209, 1275 York Avenue, New York, NY 10065. yoons@mskcc.org.
authors: Hae-June
authors: HJ
authors: Lee
authors: Changhwan
authors: C
authors: Yoon
authors: Benjamin
authors: B
authors: Schmidt
authors: Do Joong
authors: DJ
authors: Park
authors: Alexia Y
authors: AY
authors: Zhang
authors: Hayriye V
authors: HV
authors: Erkizan
authors: Jeffrey A
authors: JA
authors: Toretsky
authors: David G
authors: DG
authors: Kirsch
authors: Sam S
authors: SS
authors: Yoon
mesh_terms: D000818:Animals; D016923:Cell Death; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D004249:DNA Damage; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D015514:Oncogene Proteins, Fusion / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010793:Phthalazines / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D051789:Proto-Oncogene Protein c-fli-1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D034802:RNA-Binding Protein EWS / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012512:Sarcoma, Ewing / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000532:radiotherapy*; D023041:Xenograft Model Antitumor Assays
chemical_list: C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D051789:Proto-Oncogene Protein c-fli-1; D034741:RNA, Small Interfering; D034802:RNA-Binding Protein EWS; C531550:olaparib
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