Abstract A35: Olaparib causes premature loss of cohesion in cancer cells

Abstract

Although it has been decades since PARP inhibitors were initially discovered and various clinical trials have been performed, their mode of action in killing tumor cells subsequent to PARP inhibition is still not fully understood. We have recently identified poly(ADP-ribosyl)ation (PARylation) as a new post-translational modification of the cohesin complex, a key player in chromosome segregation during mitosis. We investigated the effect of PARP inhibition on mitosis in a panel of cells of cancer (cervical, breast, ovarian) and normal tissue origin. We treated cancerous and non-cancerous cell lines labelled with chromatin markers with a selected set of PARP inhibitors and imaged them with fluorescence live microscopy. Out of 5 tested inhibitors, a well-known and clinically relevant PARP inhibitor olaparib, induced strongest perturbations in mitotic progression. Olaparib induced a delay in entering anaphase, problems aligning chromosomes at the metaphase plate and premature loss of cohesion (cohesion fatigue) after a prolonged metaphase arrest. Cohesion fatigue, leading to cell death, was observed in cancer cell lines exhibiting S-phase stalling or G2/M arrest with increased protein levels of PARP1. Olaparib is known to entrap PARP1 at replication forks and thereby perturb replication fork movement. While its addition before the onset of mitosis did not result in mitotic defects, addition of olaparib only in S-phase was sufficient to cause mitotic phenotypes. Our results indicate that PARP inhibition by olaparib in S phase has downstream effects on mitotic progression. PARP1 RNAi in addition to olaparib treatment rescues the cohesion fatigue phenotype, suggesting that entrapment of PARP1 at the replication fork upon its inhibition is the main cause of cohesion fatigue. Cohesion fatigue was observed only in highly aneuploid cancer cells that are described to have an increased rate of chromosome mis-segregation. In conclusion, higher susceptibility of aneuploid cancer to cohesion fatigue and cell death upon olaparib treatment relative to normal cells would support its use as anti-mitotic chemotherapy. Citation Format: Eva Kukolj, Tanja Kaufmann, Amalie E. Dick, Robert Zeillinger, Daniel W. Gerlich, Dea Slade. Olaparib causes premature loss of cohesion in cancer cells. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Targeting the Vulnerabilities of Cancer; May 16-19, 2016; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(1_Suppl):Abstract nr A35.