title: Dual targeting of EWS-FLI1 activity and the associated DNA damage response with trabectedin and SN38 synergistically inhibits Ewing sarcoma cell growth.
abstract: OBJECTIVE
  The goal of this study is to optimize the activity of trabectedin for Ewing sarcoma by developing a molecularly targeted combination therapy.
  
  
  METHODS
  We have recently shown that trabectedin interferes with the activity of EWS-FLI1 in Ewing sarcoma cells. In this report, we build on this work to develop a trabectedin-based combination therapy with improved EWS-FLI1 suppression that also targets the drug-associated DNA damage to Ewing sarcoma cells.
  
  
  RESULTS
  We demonstrate by siRNA experiments that EWS-FLI1 drives the expression of the Werner syndrome protein (WRN) in Ewing sarcoma cells. Because WRN-deficient cells are known to be hypersensitive to camptothecins, we utilize trabectedin to block EWS-FLI1 activity, suppress WRN expression, and selectively sensitize Ewing sarcoma cells to the DNA-damaging effects of SN38. We show that trabectedin and SN38 are synergistic, demonstrate an increase in DNA double-strand breaks, an accumulation of cells in S-phase and a low picomolar IC50. In addition, SN38 cooperates with trabectedin to augment the suppression of EWS-FLI1 downstream targets, leading to an improved therapeutic index in vivo. These effects translate into the marked regression of two Ewing sarcoma xenografts at a fraction of the dose of camptothecin used in other xenograft studies.
  
  
  CONCLUSIONS
  These results provide the basis and rationale for translating this drug combination to the clinic. In addition, the study highlights an approach that utilizes a targeted agent to interfere with an oncogenic transcription factor and then exploits the resulting changes in gene expression to develop a molecularly targeted combination therapy.
authors.affiliation: Authors' Affiliations: Monroe Carrell Jr. Children's Hospital at Vanderbilt and the Vanderbilt Ingram Cancer Center, Nashville, Tennessee; Molecular Oncology Section, Pediatric Oncology Branch; Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland; and Istituto di Ricerche Farmacologiche "Mario Negri" -IRCCS, Milan, Italy.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Grohar
authors.forename: Laure E
authors.initials: LE
authors.lastname: Segars
authors.forename: Choh
authors.initials: C
authors.lastname: Yeung
authors.forename: Yves
authors.initials: Y
authors.lastname: Pommier
authors.forename: Maurizio
authors.initials: M
authors.lastname: D'Incalci
authors.forename: Arnulfo
authors.initials: A
authors.lastname: Mendoza
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Helman
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects*; D004149:Dioxoles / Q000494:pharmacology*; D004195:Disease Models, Animal; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004357:Drug Synergism; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D015514:Oncogene Proteins, Fusion / Q000037:antagonists & inhibitors* / Q000235:genetics; D010641:Phenotype; D051789:Proto-Oncogene Protein c-fli-1 / Q000037:antagonists & inhibitors* / Q000235:genetics; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D034802:RNA-Binding Protein EWS / Q000037:antagonists & inhibitors* / Q000235:genetics; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism; D012512:Sarcoma, Ewing / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D044005:Tetrahydroisoquinolines / Q000494:pharmacology*; D000077606:Trabectedin; D000071657:Werner Syndrome Helicase; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D004149:Dioxoles; C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034741:RNA, Small Interfering; D034802:RNA-Binding Protein EWS; D044005:Tetrahydroisoquinolines; D000077146:Irinotecan; D004317:Doxorubicin; D005090:Exodeoxyribonucleases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; D000077606:Trabectedin; D002166:Camptothecin