PARP inhibition causes premature loss of cohesion in cancer cells

Abstract

Poly(ADP-ribose) polymerases (PARPs) regulate various aspects of cellular function including mitotic progression. Although PARP inhibitors have been undergoing various clinical trials and the PARP1/2 inhibitor olaparib was approved as monotherapy for BRCA-mutated ovarian cancer, their mode of action in killing tumour cells is not fully understood. We investigated the effect of PARP inhibition on mitosis in cancerous (cervical, ovary, breast and osteosarcoma) and non-cancerous cells by live-cell imaging. The clinically relevant inhibitor olaparib induced strong perturbations in mitosis, including problems with chromosome alignment at the metaphase plate, anaphase delay, and premature loss of cohesion (cohesion fatigue) after a prolonged metaphase arrest, resulting in sister chromatid scattering. PARP1 and PARP2 depletion suppressed the phenotype while PARP2 overexpression enhanced it, suggesting that olaparib-bound PARP1 and PARP2 rather than the lack of catalytic activity causes this phenotype. Olaparib-induced mitotic chromatid scattering was observed in various cancer cell lines with increased protein levels of PARP1 and PARP2, but not in non-cancer or cancer cell lines that expressed lower levels of PARP1 or PARP2. Interestingly, the sister chromatid scattering phenotype occurred only when olaparib was added during the S-phase preceding mitosis, suggesting that PARP1 and PARP2 entrapment at replication forks impairs sister chromatid cohesion. Clinically relevant DNA-damaging agents that impair replication progression such as topoisomerase inhibitors and cisplatin were also found to induce sister chromatid scattering and metaphase plate alignment problems, suggesting that these mitotic phenotypes are a common outcome of replication perturbation.

PARP and PARG inhibitors in cancer treatment

“…Such replication catastrophe results in fork collapse. loss of cohesion or anaphase DNA bridges, which are not observed upon PARP depletion (Murai et al 2012;Shen et al 2015;Kukolj et al 2017;Schoonen et al 2017). Therefore, the cytotoxicity of PARP inhibitors seems to arise from an accumulation of replication problems, which are carried over into mitosis resulting in death by mitotic catastrophe (Slade 2019).…”

“…Furthermore, PARP inhibition during S phase causes weakening of sister chromatid cohesion, resulting in premature loss of cohesion ("cohesion fatigue") and chromosome alignment problems in metaphase ( Fig. 6; Kukolj et al 2017).…”

“…It is clear that mitotic defects in PARP-inhibitor treated cells arise from destabilization of replication forks and DNA damage acquired during S phase. Replication stress-induced mitotic defects result in death by mitotic catastrophe (Dale Rein et al 2015;Gemble et al 2015;Majuelos-Melguizo et al 2015;Colicchia et al 2017;Kukolj et al 2017;Schoonen et al 2017;Maya-Mendoza et al 2018;Michelena et al 2018). Mitotic catastrophe is a special type of cell death whereby cells die by apoptosis or slip out of mitosis through multinucleation or macronucleation due to chromosome missegregation, as well as micronucleation that results from lagging or acentric chromosomes (Galluzzi et al 2018).…”

“…While HR-deficient cancer cells were shown to respond better to PARP inhibitors, PARP inhibitors are also effective in HR-proficient cells that experience high levels of oxidative and replication stress. Indeed, anaphase DNA bridges, lagging chromosomes, micronuclei, ultrafine anaphase DNA bridges, and premature loss of cohesion occur in HR-proficient cells exposed to PARP inhibitors (Majuelos-Melguizo et al 2015;Kukolj et al 2017;Schoonen et al 2017;Michelena et al 2018). Moreover, PARP inhibitor efficacy was shown to correlate with basal levels of replication stress in cancer cells .…”

“…The expression levels of PARP1 itself may also determine PARP inhibitor response. PARP1 expression is increased in different cancer types, particularly at advanced stages (Ossovskaya et al 2010;Domagala et al 2011;Mascolo et al 2012;Bi et al 2013;Bieche et al 2013;Gan et al 2013;Salemi et al 2013;Dziaman et al 2014;Park et al 2015;Zhai et al 2015;Li et al 2016;Hou et al 2018), and in some cases correlates positively with the cytotoxic effects of PARP inhibition (Byers et al 2012;Kukolj et al 2017).…”