Molecular disruption of DNA polymerase β for platinum sensitisation and synthetic lethality in epithelial ovarian cancers

Abstract

Targeting PARP1 [Poly(ADP-Ribose) Polymerase 1] for synthetic lethality is a new strategy for BRCA germ-line mutated or platinum sensitive ovarian cancers. However, not all patients respond due to intrinsic or acquired resistance to PARP1 inhibitor. Development of alternative synthetic lethality approaches is a high priority. DNA polymerase β (Polβ), a critical player in base excision repair (BER), interacts with PARP1 during DNA repair. Here we show that polβ deficiency is a predictor of platinum sensitivity in human ovarian tumours. Polβ depletion not only increased platinum sensitivity but also reduced invasion, migration and impaired EMT (epithelial to mesenchymal transition) of ovarian cancer cells. Polβ small molecular inhibitors (Pamoic acid and NSC666719) were selectively toxic to BRCA2 deficient cells and associated with double-strand breaks (DSB) accumulation, cell cycle arrest and increased apoptosis. Interestingly, PARG [Poly(ADP-Ribose) Glycohydrolase] inhibitor (PDD00017273) [but not PARP1 inhibitor (Olaparib)] was synthetically lethal in polβ deficient cells. Selective toxicity to PDD00017273 was associated with poly (ADP-ribose) accumulation, reduced nicotinamide adenine dinucleotide (NAD+) level, DSB accumulation, cell cycle arrest and increased apoptosis. In human tumours, polβ-PARG co-expression adversely impacted survival in patients. Our data provide evidence that polβ targeting is a novel strategy and warrants further pharmaceutical development in epithelial ovarian cancers.

Suppression of DNA Polymerase β Activity Is Synthetically Lethal in BRCA1-Deficient Cells

“…Pol β has been speculated to be a synthetic lethal partner for BRCA1 . Furthermore, while this manuscript was in preparation, it was reported that the suppression of Pol β and BRCA2 activities is synthetically lethal . Our goal was to determine whether deficiencies in Pol β and the tumor suppressor, BRCA1, are synthetically lethal.…”

“…10 Furthermore, while this manuscript was in preparation, it was reported that the suppression of Pol β and BRCA2 activities is synthetically lethal. 27 Our goal was to determine whether deficiencies in Pol β and the tumor suppressor, BRCA1, are synthetically lethal. Pol β deficiency was introduced to the cells in one of two ways.…”

Targeting Mre11 overcomes platinum resistance and induces synthetic lethality in XRCC1 deficient epithelial ovarian cancers

“…Slides were incubated with the primary anti-Mre11 mouse monoclonal antibody (clone ab214, Abcam), at a dilution of 1:800, for 1 h at room temperature. We have recently reported the clinicopathological significance of the expression of NBS1 21 , RAD50 22 , XRCC1 25 , polβ 24 , PARP1 25 , FEN1 26 , LIG1 27 and LIG3 27 in ovarian cancers. For XRCC1 staining 25 , a set of TMA slides were incubated for 15 min at room temperature with 1:200 anti-XRCC1 mouse monoclonal antibody (Ab-1, clone 33-2-5, Thermoscientific, Fremont, CA).…”

“…In addition, Mre11 has roles during BER/SSBR [8][9][10] . We have recently shown that overexpression of NBS1 21 , RAD50 22 , XRCC1 23 , polβ 24 , PARP1 25 , FEN1 26 , LIG1 27 and LIG3 27 predict platinum resistance in ovarian cancer. As expected, we observed a strong positive correlation between the expression of Mre11 protein and the expression of Rad50 and Nbs1 (all ps < 0.001) (Supplementary Table 6).…”

Can Cisplatin Therapy Be Improved? Pathways That Can Be Targeted

“…Mutations in the ATM, RB1 and FANCC genes in muscle-invasive bladder cancer patients (MIBC) correlate with complete response to cisplatin-based neoadjuvant chemotherapy in patients from the clinical trials NCT01031420 and NCT01611662 [81]. In addition, we have previously shown that DNA polymerase beta (Polβ) depletion exquisitely sensitises ovarian cancer cells to cisplatin [82]. We also showed that ovarian tumours with high Polβ expression have poor survival compared to low Polβ expressing tumours.…”