Ovarian cancer is one of the most lethal gynecologic malignancies reported throughout the world. The initial, standard-of-care, adjuvant chemotherapy in epithelial ovarian cancer is usually a platinum drug, such as cisplatin or carboplatin, combined with a taxane. However, despite surgical removal of the tumor and initial high response rates to first-line chemotherapy, around 80% of women will develop cancer recurrence. Effective strategies, including chemotherapy and new research models, are necessary to improve the prognosis. The replication stress response (RSR) is characteristic of the development of tumors, including ovarian cancer. Hence, RSR pathway and DNA repair proteins have emerged as a new area for anticancer drug development. Although clinical trials have shown poly (ADP-ribose) polymerase inhibitors (PARPi) response rates of around 40% in women who carry a mutation in the BRCA1/2 genes, PARPi is responsible for tumor suppression, but not for complete tumor regression. Recent reports suggest that cells with impaired homologous recombination (HR) activities due to mutations in TP53 gene or specific DNA repair proteins are specifically sensitive to ataxia telangiectasia and Rad3-related protein (ATR) inhibitors. Replication stress activates DNA repair checkpoint proteins (ATR, CHK1), which prevent further DNA damage. This review describes the use of DNA repair checkpoint inhibitors as single agents and strategies combining these inhibitors with DNA-damaging compounds for ovarian cancer therapy, as well as the new platforms used for optimizing ovarian cancer therapy.

Poly (ADP-ribose) polymerase inhibitor (PARPi, olaparib) impairs the repair of DNA single-strand breaks (SSBs), resulting in double-strand breaks (DSBs) that cannot be repaired efficiently in homologous recombination repair (HRR)-deficient cancers such as BRCA1/2-mutant cancers, leading to synthetic lethality. Despite the efficacy of olaparib in the treatment of BRCA1/2 deficient tumors, PARPi resistance is common. We hypothesized that the combination of olaparib with anticancer agents that disrupt HRR by targeting ataxia telangiectasia and Rad3-related protein (ATR) or checkpoint kinase 1 (CHK1) may be an effective strategy to reverse ovarian cancer resistance to olaparib. Here, we evaluated the effect of olaparib, the ATR inhibitor AZD6738, and the CHK1 inhibitor MK8776 alone and in combination on cell survival, colony formation, replication stress response (RSR) protein expression, DNA damage, and apoptotic changes in BRCA2 mutated (PEO-1) and HRR-proficient BRCA wild-type (SKOV-3 and OV-90) cells. Combined treatment caused the accumulation of DNA DSBs. PARP expression was associated with sensitivity to olaparib or inhibitors of RSR. Synergistic effects were weaker when olaparib was combined with CHK1i and occurred regardless of the BRCA2 status of tumor cells. Because PARPi increases the reliance on ATR/CHK1 for genome stability, the combination of PARPi with ATR inhibition suppressed ovarian cancer cell growth independently of the efficacy of HRR. The present results were obtained at sub-lethal doses, suggesting the potential of these inhibitors as monotherapy as well as in combination with olaparib.

The current focus of ovarian cancer (OC) research is the improvement of treatment options through maximising drug effectiveness. OC remains the fifth leading cause of cancer-induced mortality in women worldwide. In recent years, nanotechnology has revolutionised drug delivery systems. Nanoparticles may be utilised as carriers in gene therapy or to overcome the problem of drug resistance in tumours by limiting the number of free drugs in circulation and thereby minimising undesired adverse effects. Cell surface receptors, such as human epidermal growth factor 2 (HER2), folic acid (FA) receptors, CD44 (also referred to as homing cell adhesion molecule, HCAM), and vascular endothelial growth factor (VEGF) are highly expressed in ovarian cancer cells. Generation of active targeting nanoparticles involves modification with ligands that recognise cell surface receptors and thereby promote internalisation by cancer cells. Several poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) are currently used for the treatment of high-grade serous ovarian carcinomas (HGSOC) or platinum-sensitive relapsed OC. However, PARP resistance and poor drug bioavailability are common challenges, highlighting the urgent need to develop novel, effective strategies for ovarian cancer treatment. This review evaluates the utility of nanoparticles in ovarian cancer therapy, with a specific focus on targeted approaches and the use of PARPi nanocarriers to optimise treatment outcomes.

This study examined the effect of combination treatment with the poly (ADP-ribose) polymerase inhibitor olaparib and metformin on homologous recombination (HR)-proficient epithelial ovarian cancer (EOC). Ovarian cancer cell lines (OV-90 and SKOV-3) were treated with olaparib, metformin, or a combination of both. Cell viability was assessed by MTT and colony formation assays. The production of reactive oxygen species (ROS) and changes in mitochondrial membrane potential were examined using the specific fluorescence probes, DCFH2-DA (2′,7′-dichloro-dihydrofluorescein diacetate) and JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolcarbocyanine). Apoptotic and necrotic changes were measured by double staining with Hoechst 33258 and propidium iodide, orange acridine and ethidium bromide staining, phosphatidylserine externalization, TUNEL assay, caspase 3/7 activity, and cytochrome c and p53 expression. Compared with single-drug treatment, the combination of olaparib and metformin significantly inhibited cell proliferation and colony formation in HR-proficient ovarian cancer cells. ROS production preceded a decrease in mitochondrial membrane potential. The changes in ROS levels suggested their involvement in inducing apoptosis in response to combination treatment. The present results indicate a shift towards synergism in cells with mutant or null p53, treated with olaparib combined with metformin, providing a new approach to the treatment of gynecologic cancers. Taken together, the results support the use of metformin to sensitize EOC to olaparib therapy.

Olaparib is a poly (ADP-ribose) polymerase inhibitor (PARPi) that inhibits PARP1/2, leading to replication-induced DNA damage that requires homologous recombination repair. Olaparib is often insufficient to treat BRCA-mutated (BRCA^MUT) and BRCA wild-type (BRCA^WT) high-grade serous ovarian carcinomas (HGSOCs). We examined the short-term (up to 48 h) efficacy of PARPi treatment on a DNA damage response pathway mediated by ATR and CHK1 kinases in BRCA^MUT (PEO-1) and BRCA^WT (SKOV-3 and OV-90) cells. The combination of ATRi/CHK1i with PARPi was not more cytotoxic than ATR and CHK1 monotherapy. The combination of olaparib with inhibitors of the ATR/CHK1 pathway generated chromosomal abnormalities, independent on BRCA^MUT status of cells and formed of micronuclei (MN). However, the beneficial effect of the PARPi:ATRi combination on MN was seen only in the PEO1 BRCA^MUT line. Monotherapy with ATR/CHK1 inhibitors reduced BrdU incorporation due to a slower rate of DNA synthesis, which resulted from elevated levels of replication stress, while simultaneous blockade of PARP and ATR caused beneficial effects only in OV-90 cells. Inhibition of ATR/CHK1 increased the formation of double-strand breaks as measured by increased γH2AX expression at collapsed replication forks, resulting in increased levels of apoptosis. Our findings indicate that ATR and CHK1 inhibitors provoke premature mitotic entry, leading to genomic instability and ultimately cell death.

Genomic alterations and aberrant DNA damage signaling are hallmarks of ovarian cancer (OC), the leading cause of mortality among gynecological cancers worldwide. Owing to the lack of specific symptoms and late-stage diagnosis, survival chances of patients are significantly reduced. Poly (ADP-ribose) polymerase (PARP) inhibitors and replication stress response inhibitors present attractive therapeutic strategies for OC. Recent research has focused on ovarian cancer-associated microRNAs (miRNAs) that play significant regulatory roles in various cellular processes. While miRNAs have been shown to participate in regulation of tumorigenesis and drug responses through modulating the DNA damage response (DDR), little is known about their potential influence on sensitivity to chemotherapy. The main objective of this review is to summarize recent findings on the utility of miRNAs as cancer biomarkers, in particular, ovarian cancer, and their regulation of DDR or modified replication stress response proteins. We further discuss the suppressive and promotional effects of various miRNAs on ovarian cancer and their participation in cell cycle disturbance, response to DNA damage, and therapeutic functions in multiple cancer types, with particular focus on ovarian cancer. Improved understanding of the mechanisms by which miRNAs regulate drug resistance should facilitate the development of effective combination therapies for ovarian cancer.