Ovarian Cancers Harbor Defects in Nonhomologous End Joining Resulting in Resistance to Rucaparib

Abstract

DNA damage defects are common in ovarian cancer and can be used to stratify treatment. Although most work has focused on homologous recombination (HR), DNA double-strand breaks are repaired primarily by nonhomologous end joining (NHEJ). Defects in NHEJ have been shown to contribute to genomic instability and have been associated with the development of chemoresistance. NHEJ was assessed in a panel of ovarian cancer cell lines and 47 primary ascetic-derived ovarian cancer cultures, by measuring the ability of cell extracts to end-join linearized plasmid monomers into multimers. mRNA and protein expression of components of NHEJ was determined using RT-qPCR and Western blotting. Cytotoxicities of cisplatin and the PARP inhibitor rucaparib were assessed using sulforhodamine B (SRB) assays. HR function was assessed using γH2AX/RAD51 foci assay. NHEJ was defective (D) in four of six cell lines and 20 of 47 primary cultures. NHEJ function was independent of HR competence (C). NHEJD cultures were resistant to rucaparib ( = 0.0022). When HR and NHEJ functions were taken into account, only NHEJC/HRD cultures were sensitive to rucaparib (compared with NHEJC/HRC = 0.034, NHEJD/HRC = 0.0002, and NHEJD/HRD = 0.0045). The DNA-PK inhibitor, NU7441, induced resistance to rucaparib ( = 0.014) and HR function recovery in a BRCA1-defective cell line. This study has shown that NHEJ is defective in 40% of ovarian cancers, which is independent of HR function and associated with resistance to PARP inhibitors in primary cultures..

Acquired resistance of phosphatase and tensin homolog‐deficient cells to poly(ADP‐ribose) polymerase inhibitor and Ara‐C mediated by 53BP1 loss and SAMHD1 overexpression

“…In contrast, some drugs in our test such as cisplatin have been reported to be cross‐resistant to PARPi in both clinical and preclinical studies . However, cisplatin was shown not to be cross‐resistant to rucaparib in ovarian cancers defective for nonhomologous end joining . All our PARPi‐resistant PTEN‐deficient variants are not resistant to cisplatin (resistance factor: 0.62‐0.76) either.…”

“…[31][32][33][34] However, cisplatin was shown not to be cross-resistant to rucaparib in ovarian cancers defective for nonhomologous end joining. 35 [37][38][39][40] or ATM 41 -deficient breast [37][38][39]41 or ovarian cancer cells. 40 For the first time, our results reveal that loss of 53BP1 also dominantly mediates the resistance of PTEN-deficient glioblastoma cells to different PARPi, strongly suggesting that loss of 53BP1 is a relatively universal mechanism responsible for PARPi resistance at different conditions.…”

RBX1 prompts degradation of EXO1 to limit the homologous recombination pathway of DNA double-strand break repair in G1 phase

“…It has been reported that cells depleted of DNA-PKcs or treated with DNA-PK inhibitor induced IR-induced RAD51 foci formation [37]. We found that the effects of a DNA-PK inhibitor on RAD51 nucleofilament formation and HR function mainly occurred in G1-phase cells, while no obvious changes occurred in G2 cells.…”

Rucaparib: the past, present, and future of a newly approved PARP inhibitor for ovarian cancer

“…Resistance to rucaparib has also been demonstrated in ovarian cancer tumor cells possessing NHEJ defects. NHEJ plays a significant role in the repair of double-strand DNA breaks, is independent of HR function, and is associated with resistance to rucaparib in ex vivo primary cultures 46. Other mechanisms of resistance such as hypomorphic activity of mutant BRCA1 alleles, upregulation of drug efflux pumps, and reconfiguration of the cellular DNA damage response are still under study 44…”