DNA Replication Vulnerabilities Render Ovarian Cancer Cells Sensitive to Poly(ADP-Ribose) Glycohydrolase Inhibitors

Abstract

SummaryInhibitors of poly(ADP-ribose) polymerase (PARP) have demonstrated efficacy in women with BRCA-mutant ovarian cancer. However, only 15%–20% of ovarian cancers harbor BRCA mutations, therefore additional therapies are required. Here, we show that a subset of ovarian cancer cell lines and ex vivo models derived from patient biopsies are sensitive to a poly(ADP-ribose) glycohydrolase (PARG) inhibitor. Sensitivity is due to underlying DNA replication vulnerabilities that cause persistent fork stalling and replication catastrophe. PARG inhibition is synthetic lethal with inhibition of DNA replication factors, allowing additional models to be sensitized by CHK1 inhibitors. Because PARG and PARP inhibitor sensitivity are mutually exclusive, our observations demonstrate that PARG inhibitors have therapeutic potential to complement PARP inhibitor strategies in the treatment of ovarian cancer.

(ADP-ribosyl)hydrolases: structure, function, and biology

“…Nevertheless, Parg −/− mouse trophoblast-derived stem cells are able to survive in the presence of chemical inhibitors of PARP1/2, suggesting that the accumulation of PAR chains, due to the absence of PARG activity, represents a cell death signal (Koh et al 2004). Importantly, PARG depletion leads to hypersensitivity to genotoxic and replication stress and, consequently, it was proposed as a novel target for modern chemotherapeutic approaches (James et al 2016;Pillay et al 2019). In addition to its functions in DNA repair, PARG activity seems to be involved in the progression of replication forks and recovery from persistent replication stress (Illuzzi et al 2014;Ray Chaudhuri et al 2015).…”

PARP and PARG inhibitors in cancer treatment

“…Inhibitors of poly(ADP-ribose) glycohydrolase (PARG) joined the stage once structures of the PARG catalytic site became available (Slade et al 2011;Dunstan et al 2012;Kim et al 2012; Barkauskaite et al 2013). Rather than synergizing with deficiencies in DNA repair pathways, PARG inhibitors seem to exploit deficiencies in replication machinery and higher levels of replication stress in cancer cells (Pillay et al 2019).…”

Capitalizing on Cancer Replication Stress by Preventing PAR Chain Turnover: A New Type of Synthetic Lethality

“…PDD00017273, a small molecule inhibitor of PARG (PARGi) developed by James et al, (2016), has been shown to stabilize PAR chains in cells and reduce clonogenic ability when combined with DNA damaging agents in sensitive cell lines. Pillay et al (2019) investigate the mechanism of PARGi sensitivity and identify a subset of ovarian cancer models with underlying replication stress vulnerability that make them susceptible to PARG inhibition. In contrast to the cytotoxic effect seen with PARPi treatment of HR-deficient cells, the authors show that the inhibition of PARG generates a cytostatic effect, as demonstrated by an extended S-phase duration and activation of the G 2 /M checkpoint in PARGi-sensitive cell lines.…”

“…To further elucidate the underlying mechanism of PARGi sensitivity, Pillay et al (2019) developed an siRNA screen for synthetic lethal targets in PARGi-resistant cells using pan nuclear gH2AX as the endpoint marker. The top hits were TIMELESS, HUS1, RFC2, and CHK1, all of which are involved in checkpoint signaling at stalled replication forks (Forment and O'Connor, 2018).…”