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

// Young Eun Choi 1 , Chiara Battelli 2 , Jacqueline Watson 1 , Joyce Liu 3 , Jennifer Curtis 3 , Alexander N. Morse 4 , Ursula A. Matulonis 3 , Dipanjan Chowdhury 1 , Panagiotis A. Konstantinopoulos 1, 3 1 Department of Radiation Oncology, Dana Farber Cancer Institute, Harvard Medical School 2 Maine Center for Cancer Medicine, Scarborough, Maine 3 Department of Medical Oncology, Medical Gynecologic Oncology Program, Dana Farber Cancer Institute, Harvard Medical School 4 New York University Global Institute of Public Health Correspondence: Panagiotis Konstantinopoulos, email: // Keywords : Epithelial ovarian cancer, platinum, PARP inhibitors, Heat Shock Protein 90 inhibitors, homologous recombination Received : February 23, 2014 Accepted : April 30, 2014 Published : April 30, 2014 Abstract 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.