Abstract 5810: Crizotinib and PARP inhibitors act synergistically by triggering apoptosis in high-grade serous ovarian cancer (HGSOC)
Authors: Durmaz Irem , Hedenfalk Ingrid 
Published: August 2018

Abstract
Introduction: Epithelial ovarian cancer is the seventh most common malignancy diagnosed in women, but the fifth most common cause of cancer-related deaths with a relative five-year survival less than 50%. High-grade serous ovarian cancer (HGSOC) is the predominant histological subtype. PARP inhibitors such Olaparib and Niraparib have been approved by the FDA for the maintenance treatment of platinum-sensitive, recurrent HGSOC. However, similar to many other targeted agents, the efficacy of PARP inhibitors is limited by the development of drug resistance. The aim of this study was to investigate new combinatorial treatment strategies to prolong anti-cancer activities of PARP inhibitors using HGSOC cell lines, which might also translate to overcoming resistance in clinical tumors.
Methods: The cytotoxic activities of various drugs (Carboplatin, the PI3K inhibitor LY294002 and the c-met inhibitor Crizotinib) alone or in sequential combination with the PARP inhibitors Niraparib and Olaparib were analyzed using the NCI-SRB assay and xCeLLigence platform and combination index (CI) values were calculated using the Chou-Talalay method. Phospho-H2AX staining was used to address the accumulation of DNA double strand breaks and FACS analysis using propidium iodide was conducted to investigate cell cycle phase distribution. Western blot experiments were performed to reveal the effects of the compounds alone or in combination on the protein level. All experiments were conducted using the OVSAHO (BRCA2 homozygous deletion), KURAMOCHI (BRCA2 mutant) and CAOV3 (BRCA1/2 wild-type) HGSOC cell lines. The clear cell ovarian cancer (CCOC) cell line JHOC5 was used as a reference. Patient-derived primary cells collected from ascites were used for some experiments.
Results: All drugs showed high cytotoxic effects on HGSOC cell lines and on primary cells, however, very low effects were observed in the CCOC cell line. PARP inhibitors and Crizotinib significantly induced accumulation of DNA double strand breaks, which was also observed to a limited extent with LY294002. PARP inhibitors and Carboplatin alone and in combination resulted in G2/M cell cycle arrest. In contrast, Crizotinib alone or in combination with PARP inhibitors induced a SubG1 arrest. Among all sequential combinations, Crizotinib with both of the PARP inhibitors was found to be more strongly synergistic compared to Carboplatin and PARP inhibitor or PARP inhibitor and LY294002 combinations. Treatment of HGSOC cells with a sequential combination of Crizotinib and PARP inhibitors resulted in deregulation of various proteins including ERK, Akt, and p53, all contributing to caspase-3 induced apoptosis.
Conclusion: Our results indicate the possible benefit of combining the c-met inhibitor Crizotinib with PARP inhibitors in HGSOC to enhance the activity of PARP inhibitors as a new therapeutic strategy.
Citation Format: Irem Durmaz, Ingrid Hedenfalk. Crizotinib and PARP inhibitors act synergistically by triggering apoptosis in high-grade serous ovarian cancer (HGSOC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5810.