Abstract 1379: Entinostat induces PARPi sensitivity across multiple ovarian cancer models
Authors: Gupta Vijayalaxmi G. , Petersen Shariska , Hirst Jeff , Roby Katherine , Pathak Harsh , Kusch Meghan , Wilson Andrew , Godwin Andrew , Khabele Dineo 
Published: September 2020

Introduction: Ovarian cancer is a rare, but fatal disease and a leading cause of gynecologic cancer death, in the United States. Poly ADP ribose polymerase inhibitors (PARPi) are promising drugs, most effective in patients with tumors deficient in homologous recombination (HR) genes, mainly BRCA1/2. Our group has published that histone deacetylase inhibitors (HDACi) sensitized HR proficient BRCA wild-type ovarian cancer cells to PARPi, however the mechanism still remains elusive and the efficacy needed to be tested across multiple models. We recently tested Entinostat with and without Olaparib in three different ovarian cancer models, including human/mouse established cell lines, PDX derived primary cell lines and immune-competent/immune-compromised xenograft as well as PDX-derived preclinical mouse models.

Objective: To delineate the efficacy of Entinostat to sensitize ovarian tumors to Olaparib across multiple models and determine the underlying mechanism.

Methods: HR proficient BRCA wild-type ID8/SKOV3 and PDX derived primary cell lines were treated with Entinostat and Olaparib, alone or in combination and analyzed for cell proliferation. DNA damage was studied using Comet assay. Expression of cell proliferation, DNA damage and repair protein were studied using Western blot analysis and immunofluorescence. Further, ID8-treated immune-competent mouse models, SKOV3-treated immune-compromised mouse model and HGSOC patient derived PDX mouse model generated in our lab were treated with vehicle, Entinostat, Olaparib, or the combination. The mice were monitored for toxicity and body weight measured twice weekly, till tissue harvest or survival.

Results: Cell proliferation was significantly decreased (p&lt0.05) in Entinostat-Olaparib combination treated groups in all cell lines tested. Comet assay showed significantly longer comet tail length in combination treated cells compared to control (p&lt0.05). Western blot and Immunofluorescence showed that combination treatment significantly decreased BRCA1, PCNA, RAD51 and increased cleaved PARP, ΓH2AX (p&lt0.05). Further, SKOV3- xenograft mouse model showed decreased tumor burden ((p&lt0.07), ID8-xenograft mouse tumors showed decreased Ki67 (p&lt0.05) and HGSOC derived PDX model showed longer survival when treated with Entinostat-Olaparib combination therapy.

Conclusion: Entinostat in combination with Olaparib decreased cell proliferation, increased DNA damage, induced HR deficiency in vitro, reduced tumor burden, decreased Ki67 in xenograft mouse model, and improved survival of HGSOC derived PDX mice, thereby potentially sensitizing homologous recombination proficient ovarian cancer to PARPi across multiple models.

Citation Format: Vijayalaxmi G. Gupta, Shariska Petersen, Jeff Hirst, Katherine Roby, Harsh Pathak, Meghan Kusch, Andrew Wilson, Andrew Godwin, Dineo Khabele. Entinostat induces PARPi sensitivity across multiple ovarian cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1379.