e13125 Background: Epithelial ovarian cancer (EOC) is the second most common gynecologic cancer in the United States, and carries the highest mortality in this category in the West. The progression free survival and overall survival depend greatly on tumor sensitivity to a platinum chemotherapy. Once platinum resistance is encountered, response rates of only 6–30% are achieved. A relatively new modality in EOC that would allow targeted treatments is a PARP inhibitor, a drug that inhibits the enzyme poly (ADP-ribose) polymerase (PARP), which is showing promise for the treatment of EOC with mutations in the BRCA1 or BRCA2 tumor suppressors. Triapine, a novel small-molecule drug developed in our laboratory, potently inhibits the activity of ribonucleotide reductase involved in the key step of DNA synthesis and replication. Methods: 1. Cell sensitivity to varying ratios of treating drug combinations (Triapine with cisplatin; PARP inhibitor, olaparib) was carried out by clonogenic survival assays using multiple EOC cell lines (A2780, Caov-3, EFO, IGROV-1, BG-1, PEO1, SKOV3). 2. AKT level was measured in the cell lines before and after treatment. 3. BRCA1 wild-type and BRCA1-knockdown EOC cells were treated with cisplatin or PARP alone and in combination with Triapine. Drug-induced DNA damage was assessed by the levels of g-H2AX, the marker of double stranded breaks (DSBs), and of Rad51 foci, a marker of HR repair of DSBs. Results: Treatment with Triapine leads to synergistic sensitization of BRCA1 wild-type EOC cells to platinum drugs and to olaparib. Both platinum drugs and olaparib induce DNA damage that is repaired by HR. This suggests that Triapine inhibits HR and sensitizes EOC cells to these drugs. Triapine attenuates olaparib-induced Rad51 foci in BRCA1-wild type cells, which resembles the impairment of such foci formation in BRCA1-knockdown cells. Triapine causes down-regulation of AKT activity in EOC cells. Conclusions: Triapine produces synthetic lethality by inhibiting both DNA repair and pro-survival pathways. Combination of Triapine and platinum drugs/PARP inhibitors represents a rational and innovative therapy that targets EOC with a high level of AKT activity.
Early responses of the STAT3 pathway to platinum drugs are associated with cisplatin resistance in epithelial ovarian cancer
