Sublethal concentrations of 17-AAG suppress homologous recombination DNA repair and enhance sensitivity to carboplatin and olaparib in HR proficient ovarian cancer cells

Oncotarget. 2014 May 15;5(9):2678-87. doi: 10.18632/oncotarget.1929.


The promise of PARP-inhibitors(PARPis) in the management of epithelial ovarian cancer(EOC) is tempered by the fact that approximately 50% of patients with homologous recombination (HR)-proficient tumors do not respond well to these agents. Combination of PARPis with agents that inhibit HR may represent an effective strategy to enhance their activity in HR-proficient tumors. Using a bioinformatics approach, we identified that heat shock protein 90 inhibitors(HSP90i) may suppress HR and thus revert HR-proficient to HR-deficient tumors. Analysis of publicly available gene expression data showed that exposure of HR-proficient breast cancer cell lines to HSP90i 17-AAG(17-allylamino-17-demethoxygeldanamycin) downregulated HR, ATM and Fanconi Anemia pathways. In HR-proficient EOC cells, 17-AAG suppressed HR as assessed using the RAD51 foci formation assay and this was further confirmed using the Direct Repeat-GFP reporter assay. Furthermore, 17-AAG downregulated BRCA1 and/or RAD51 protein levels, and induced significantly more γH2AX activation in combination with olaparib compared to olaparib alone. Finally, sublethal concentrations of 17-AAG sensitized HR-proficient EOC lines to olaparib and carboplatin but did not affect sensitivity of the HR-deficient OVCAR8 line arguing that the 17-AAG mediated sensitization is dependent on suppression of HR. These results provide a preclinical rationale for using a combination of olaparib/17-AAG in HR-proficient EOC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • BRCA1 Protein / metabolism
  • Benzoquinones / pharmacology*
  • Blotting, Western
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology
  • Carboplatin / administration & dosage
  • Carcinoma, Ovarian Epithelial
  • Drug Resistance, Neoplasm / drug effects*
  • Enzyme Inhibitors / pharmacology
  • Female
  • Flow Cytometry
  • Fluorescent Antibody Technique
  • Humans
  • Immunoenzyme Techniques
  • Lactams, Macrocyclic / pharmacology*
  • Neoplasms, Glandular and Epithelial / drug therapy*
  • Neoplasms, Glandular and Epithelial / genetics
  • Neoplasms, Glandular and Epithelial / pathology
  • Ovarian Neoplasms / drug therapy*
  • Ovarian Neoplasms / genetics
  • Ovarian Neoplasms / pathology
  • Phthalazines / administration & dosage
  • Piperazines / administration & dosage
  • Poly(ADP-ribose) Polymerase Inhibitors
  • Poly(ADP-ribose) Polymerases / metabolism
  • Recombinational DNA Repair / drug effects*
  • Recombinational DNA Repair / genetics
  • Tumor Cells, Cultured


  • BRCA1 Protein
  • Benzoquinones
  • Enzyme Inhibitors
  • Lactams, Macrocyclic
  • Phthalazines
  • Piperazines
  • Poly(ADP-ribose) Polymerase Inhibitors
  • tanespimycin
  • Carboplatin
  • Poly(ADP-ribose) Polymerases
  • olaparib