Abstract LB421: Entinostat alters cell cycle in ovarian cancer cells

Abstract Introduction: We have reported that Class I/II HDACi sensitize PARPi resistant tumors, creating a possibility to expand the use of PARPi beyond homologous recombination deficient tumors. However, the underlying mechanism is still unknown. Here, we report leads obtained from differential gene expression in ovarian cancer cells treated with entinostat and olaparib. Methods: OVCAR3 cells were treated with 0.5 µM entinostat and 10 µM olaparib (alone and combined) for 6h, followed by RNA Seq. Cell cycle was analyzed by flow cytometry in SKOV-3 cells treated with olaparib and entinostat (alone and combined) for 24h, 48h and 72h. Results: RNA-Seq analysis showed reduced expression of genes that regulate G2/M checkpoint progression with both entinostat and olaparib. This correlated with flow cytometry results in SKOV-3 cells, where we observed accumulation of G2/M phase cells when treated with entinostat and olaparib. At 24h post treatment, olaparib and entinostat treated cells had higher population of cells in G2/M phase compared to control (18.5% and 16.7% respectively compared to 14.7% in control). Olaparib combined with entinostat further increased G2/M population to 21.7%. At 48h olaparib treated cells had 17.4% cells in G2/M compared to 14% in control. Entinostat treated cells had 18% G2/M cells. Combination treated cells had 19.7% G2/M cells. At 72h, olaparib and control had similar number of G2/M cells (9.2% and 9.7% respectively). Entinostat treated cells had 12% G2/M cells and combination treated cells had 13.6% cells at G2/M cells. This indicates that entinostat and olaparib disrupt progression of cells from G2/M phase, potentially leading to cell death before they can enter mitosis/cell division. Cell cycle analysis in OVCAR3 cells is in progress. Conclusion: Entinostat and olaparib cause G2/M cell cycle arrest in ovarian cancer cells. Entinostat maintains G2/M cell cycle arrest longer than olaparib, potentially extending the window of efficacy of the combination therapy. Validation of G2/M markers and other gene targets/pathways is in progress. Citation Format: Vijayalaxmi G. Gupta, Heng Liu, Rugang Zhang, Michael Onken, Andrew Wilson, Fiona Yull, Marta Crispens, Mary Mullen, Dineo Khabele. Entinostat alters cell cycle in ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB421.