Abstract B061: Sensitivity and resistance mechanisms of human cancer cell lines treated with PARP, POLθ, and ATR inhibitor combinations in 2D and 3D spheroid cell viability assays

Abstract

Abstract Poly ADP Ribose Polymerase (PARP) inhibitors have changed the landscape of treatment of homologous recombination (HR) -deficient cancers. The combination of PARP targeting agents and genetic alterations in the HR pathway is known to be synthetically lethal. Currently, four PARP inhibitors are approved for treatment of HR-deficient cancers. In combination with DNA damaging agents, PARP inhibitors synergistically kill tumor cells. Occurrence of resistance to PARP inhibitors is a major problem in the clinic. Targeting alternative DNA repair pathways or the use of new drug combinations may overcome PARP inhibitor resistance. We have determined and compared the effect of inhibitors of PARP, POLθ and ATR on cell viability in a large panel of human cancer cell lines (the Oncolines® panel) in 2D cell viability assays, using intracellular ATP content as an indirect read-out of cell number. The relationship between the mutation and expression status of genes involved in the DNA damage response pathway, or known to be involved in PARP inhibitor resistance, was determined. The effect of co-treatment of PARP inhibitors with inhibitors of POLθ, ATR and DNA damaging, cytotoxic agents was determined in BLISS combination matrix experiments in the colorectal adenocarcinoma cell line DLD1 and an isogenic BRCA2-deficient knock-out derivative. Drug combinations were studied in 2D and in 3D spheroid viability assays. To identify novel, potential mechanisms of resistance to PARP inhibitors, BRCA1-deficient ovarian UWB1.289 and BRCA2-deficient DLD1 cells were treated with sequentially increasing concentrations of PARP inhibitors talazoparib or olaparib. Resistant clones were selected and characterized. Our study reveals insight into the genetic determinants of cancer cell line sensitivity to inhibitors of PARP, POLθ and ATR. We also present the first side-by-side comparative study of the effect of drug combinations targeting the DNA damage response pathway in HR-deficient tumors in 2D and 3D spheroid cell viability assays. Citation Format: Janneke J.T.M. Melis, Jeffrey Kooijman, Sabine Wetemans, Suzan Geerdink-Datema, Jelle Dylus, Jeroen A.D.M. de Roos, Wilhelmina E. van Riel, Guido J.R. Zaman. Sensitivity and resistance mechanisms of human cancer cell lines treated with PARP, POLθ, and ATR inhibitor combinations in 2D and 3D spheroid cell viability assays [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B061.