Poly(ADP)-ribose polymerase inhibition: frequent durable responses in BRCA carrier ovarian cancer correlating with platinum-free interval

BRCA2 Germline Mutations Identify Gastric Cancers Responsive to PARP Inhibitors

Despite negative results of clinical trials conducted on the overall population of patients with gastric cancer, PARP inhibitor (PARPi) therapeutic strategy still might represent a window of opportunity for a subpopulation of patients with gastric cancer. An estimated 7% to 12% of gastric cancers exhibit a mutational signature associated with homologous recombination (HR) failure, suggesting that these patients could potentially benefit from PARPis. To analyze responsiveness of gastric cancer to PARPi, we exploited a gastroesophageal adenocarcinoma (GEA) platform of patient-derived xenografts (PDX) and PDX-derived primary cells and selected 10 PDXs with loss-of-function mutations in HR pathway genes. Cell viability assays and preclinical trials showed that olaparib treatment was effective in PDXs harboring BRCA2 germline mutations and somatic inactivation of the second allele. Olaparib responsive tumors were sensitive to oxaliplatin as well. Evaluation of HR deficiency (HRD) and mutational signatures efficiently stratified responder and nonresponder PDXs. A retrospective analysis on 57 patients with GEA showed that BRCA2 inactivating variants were associated with longer progression-free survival upon platinum-based regimens. Five of 7 patients with BRCA2 germline mutations carried the p.K3326* variant, classified as "benign." However, familial history of cancer, the absence of RAD51 foci in tumor cells, and a high HRD score suggest a deleterious effect of this mutation in gastric cancer. In conclusion, PARPis could represent an effective therapeutic option for BRCA2-mutated and/or high HRD score patients with GEA, including patients with familial intestinal gastric cancer.

SIGNIFICANCE

PARP inhibition is a potential strategy for treating patients with gastric cancer with mutated BRCA2 or homologous repair deficiency, including patients with familial intestinal gastric cancer, for whom BRCA2 germline testing should be recommended.

PARP inhibitors: risk factors for toxicity and matching patients to the proper poly (ADP-ribose) polymerase inhibitor (PARPi) therapy

The past 5 years have seen several fundamental advances in ovarian cancer, with important new insights towards novel therapeutic opportunities within the DNA repair pathway. With the incorporation of poly (ADP-ribose) polymerase inhibitors (PARPi) into maintenance treatment regimens, the management of short- and long-term adverse events are key clinical priorities. Currently, three different PARPi are clinically beneficial and have been approved for primary and recurrent ovarian cancer: olaparib, niraparib, and rucaparib. The duration of treatment with PARPi in patients with ovarian cancer varies; patients can receive treatment for up to 2 or 3 years in first-line setting, or continue treatment until unacceptable toxicity or progression occurs in recurrent disease. Despite their similar mechanisms of action, these three inhibitors have specific toxicity profiles, which may lead to dose interruptions or discontinuation of treatment. This review summarizes the current indications for PARPi, including their role in recurrent and first-line maintenance treatment for advanced ovarian cancer. We also outline dose modifications leading to treatment disruption and potential changes in quality of life after prolonged treatment. Finally, we highlight the patient groups most likely to benefit from each of the three different PARPi.

PARP Inhibitors in Breast and Ovarian Cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors are one of the most successful examples of clinical translation of targeted therapies in medical oncology, and this has been demonstrated by their effective management of BRCA1/BRCA2 mutant cancers, most notably in breast and ovarian cancers. PARP inhibitors target DNA repair pathways that BRCA1/2-mutant tumours are dependent upon. Inhibition of the key components of these pathways leads to DNA damage triggering subsequent critical levels of genomic instability, mitotic catastrophe and cell death. This ultimately results in a synthetic lethal relationship between BRCA1/2 and PARP, which underpins the effectiveness of PARP inhibitors. Despite the early and dramatic response seen with PARP inhibitors, patients receiving them often develop treatment resistance. To date, data from both clinical and preclinical studies have highlighted multiple resistance mechanisms to PARP inhibitors, and only by understanding these mechanisms are we able to overcome the challenges. The focus of this review is to summarise the underlying mechanisms underpinning treatment resistance to PARP inhibitors and to aid both clinicians and scientists to develop better clinically applicable assays to better select patients who would derive the greatest benefit as well as develop new novel/combination treatment strategies to overcome these mechanisms of resistance. With a better understanding of PARP inhibitor resistance mechanisms, we would not only be able to identify a subset of patients who are unlikely to benefit from therapy but also to sequence our treatment paradigm to avoid and overcome these resistance mechanisms.

Chemotherapy-free treatment of recurrent advanced ovarian cancer: myth or reality?

Advanced ovarian cancer remains a leading cause of death from gynecologic malignancy. Surgery and, in most cases, platinum-based chemotherapy with or without maintenance with bevacizumab and/or poly-ADP ribose polymerase inhibitors (PARPi) represent the mainstay of treatment, but the disease typically recurs. The treatment of these patients represents a clinical challenge because sequential chemotherapy regimens are often used, with suboptimal outcomes and cumulative toxicity. Chemotherapy-free regimens, based on combinations of PARPi, vascular endothelial growth factor receptor inhibitors, anti-programmed cell death protein-1/programmed death-ligand 1, and anti-cytotoxic T-lymphocyte-associated protein-4 antibodies, among others, represent a valid option, with manageable toxicity profile and ease of administration. This review addresses this new strategy in the management of recurrent ovarian cancer and discusses its feasibility in the treatment landscape of the disease.

Therapeutic targeting of DNA damage repair pathways guided by homologous recombination deficiency scoring in ovarian cancers

The susceptibility of cells to DNA damage and their DNA repair ability are crucial for cancer therapy. Homologous recombination is one of the major repairing mechanisms for DNA double-strand breaks. Approximately half of ovarian cancer (OvCa) cells harbor homologous recombination deficiency (HRD). Considering that HRD is a major hallmark of OvCas, scholars proposed HRD scoring to evaluate the HRD degree and guide the choice of therapeutic strategies for OvCas. In the last decade, synthetic lethal strategy by targeting poly (ADP-ribose) polymerase (PARP) in HR-deficient OvCas has attracted considerable attention in view of its favorable clinical effort. We therefore suggested that the uses of other DNA damage/repair-targeted drugs in HR-deficient OvCas might also offer better clinical outcome. Here, we reviewed the current small molecule compounds that targeted DNA damage/repair pathways and discussed the HRD scoring system to guide their clinical uses.

PROTAC'ing oncoproteins: targeted protein degradation for cancer therapy

Molecularly targeted cancer therapies substantially improve patient outcomes, although the durability of their effectiveness can be limited. Resistance to these therapies is often related to adaptive changes in the target oncoprotein which reduce binding affinity. The arsenal of targeted cancer therapies, moreover, lacks coverage of several notorious oncoproteins with challenging features for inhibitor development. Degraders are a relatively new therapeutic modality which deplete the target protein by hijacking the cellular protein destruction machinery. Degraders offer several advantages for cancer therapy including resiliency to acquired mutations in the target protein, enhanced selectivity, lower dosing requirements, and the potential to abrogate oncogenic transcription factors and scaffolding proteins. Herein, we review the development of proteolysis targeting chimeras (PROTACs) for selected cancer therapy targets and their reported biological activities. The medicinal chemistry of PROTAC design has been a challenging area of active research, but the recent advances in the field will usher in an era of rational degrader design.

Exposure-Response Analyses of Olaparib in Real-Life Patients with Ovarian Cancer

BACKGROUND

Olaparib is given in a fixed dose of twice-daily 300 mg in patients who are diagnosed with ovarian cancer, breast cancer, prostate cancer or pancreas cancer and has a high interpatient variability in pharmacokinetic exposure. The objective of this study was to investigate whether pharmacokinetic exposure of olaparib is related to efficacy and safety in a real-life patient' cohort.

METHODS

A longitudinal observational study was conducted in patients who received olaparib for metastatic ovarian cancer of whom pharmacokinetic samples were collected. A Kaplan-Meier analyses was used to explore the relationship between olaparib exposure, measured as (calculated) minimum plasma concentrations (C_min), and efficacy, Univariate and multivariate cox-regression analyses were performed. Also, the C_min of patients who experienced toxicity was compared with patients who did not experience any toxicity.

RESULTS

Thirty-five patients were included in the exposure-efficacy analyses, with a median olaparib C_min of 1514 ng/mL. There was no statistical significant difference in PFS of patients below and above the median C_min concentration of olaparib, with a hazard ratio of 1.06 (95% confidence interval: 0.46-2.45, p = 0.9)). For seven patients pharmacokinetic samples were available before toxicity occurred, these patients had a higher C_min of olaparib in comparison with patients who had not experienced any toxicity (n = 33), but it was not statistically significant (p = 0.069).

CONCLUSIONS

Our study shows that exposure of olaparib is not related to PFS. This suggests that the approved dose of olaparib yields sufficient target inhibition in the majority of patients.

Ovarian Cancer—Insights into Platinum Resistance and Overcoming It

Ovarian cancer is the most lethal gynecologic malignancy. Platinum-based chemotherapy is the backbone of treatment for ovarian cancer, and although the majority of patients initially have a platinum-sensitive disease, through multiple recurrences, they will acquire resistance. Platinum-resistant recurrent ovarian cancer has a poor prognosis and few treatment options with limited efficacy. Resistance to platinum compounds is a complex process involving multiple mechanisms pertaining not only to the tumoral cell but also to the tumoral microenvironment. In this review, we discuss the molecular mechanism involved in ovarian cancer cells’ resistance to platinum-based chemotherapy, focusing on the alteration of drug influx and efflux pathways, DNA repair, the dysregulation of epigenetic modulation, and the involvement of the tumoral microenvironment in the acquisition of the platinum-resistant phenotype. Furthermore, we review promising alternative treatment approaches that may improve these patients’ poor prognosis, discussing current strategies, novel combinations, and therapeutic agents.

Overcoming PARP inhibitor resistance in ovarian cancer

Ovarian cancer (OC) is one of the most lethal tumors in women, mostly diagnosed at advanced stages. Standard of care is based on surgery and platinum-based chemotherapy which provides high rates of response, although most patients will relapse. Poly(ADP-ribose) polymerase inhibitors (PARPi) have recently been incorporated in the treatment strategy for high-grade OC, particularly for those with defects in DNA repair pathways (homologous repair deficiency (HRd)). However, some tumor cells may not respond and some others will develop mechanisms of resistance to adapt. The most known mechanism of PARPi resistance is the reversion of HRd to homologous repair proficiency driven by epigenetic and genetic changes. Ongoing research is exploring different agents that are trying to re-sensitize tumor cells,overcome or bypass resistance to PARPi. Current investigations are focused on agents that target replication stress and DNA repair pathways, improve drug delivery, and target other cross-talk pathways. A crucial challenge in practice will be to identify and select patients for the appropriate therapy or combination strategies. However, efforts are needed to decrease overlapping toxicity and define the correct schedule timing of dosing to maximize the therapeutic index.

Efficacy and Safety of Mirvetuximab Soravtansine in Patients With Platinum-Resistant Ovarian Cancer With High Folate Receptor Alpha Expression: Results From the SORAYA Study

PURPOSE

Single-agent chemotherapies have limited activity and considerable toxicity in patients with platinum-resistant epithelial ovarian cancer (PROC). Mirvetuximab soravtansine (MIRV) is an antibody-drug conjugate targeting folate receptor α (FRα). SORAYA is a single-arm, phase II study evaluating efficacy and safety of MIRV in patients with PROC.

METHODS

SORAYA enrolled FRα-high patients with PROC who had received one to three prior therapies, including required bevacizumab. The primary end point was confirmed objective response rate (ORR) by investigator; duration of response was the key secondary end point.

RESULTS

One hundred six patients were enrolled; 105 were evaluable for efficacy. All patients had received prior bevacizumab, 51% had three prior lines of therapy, and 48% received a prior poly ADP-ribose polymerase inhibitor. Median follow-up was 13.4 months. ORR was 32.4% (95% CI, 23.6 to 42.2), including five complete and 29 partial responses. The median duration of response was 6.9 months (95% CI, 5.6 to 9.7). In patients with one to two priors, the ORR by investigator was 35.3% (95% CI, 22.4 to 49.9) and in patients with three priors was 30.2% (95% CI, 18.3 to 44.3). The ORR by investigator was 38.0% (95% CI, 24.7 to 52.8) in patients with prior poly ADP-ribose polymerase inhibitor exposure and 27.5% (95% CI, 15.9 to 41.7) in those without. The most common treatment-related adverse events (all grade and grade 3-4) were blurred vision (41% and 6%), keratopathy (29% and 9%), and nausea (29% and 0%). Treatment-related adverse events led to dose delays, reductions, and discontinuations in 33%, 20%, and 9% of patients, respectively.

CONCLUSION

MIRV demonstrated consistent clinically meaningful antitumor activity and favorable tolerability and safety in patients with FRα-high PROC who had received up to three prior therapies, including bevacizumab, representing an important advance for this biomarker-selected population.

Current status and future promise of next-generation poly (ADP-Ribose) polymerase 1-selective inhibitor AZD5305

The family of poly (ADP-ribose) polymerases (PARPs) consists of 17 members, which have been demonstrated as having effects on a series of cellular processes, including DNA replication and repair. PARP inhibitors (PARPi) suppress DNA repair through "PARP trapping", thus, constitute an important treatment option for cancer nowadays. In addition, PARP inhibition and homologous recombination repair (HRR) defects are synthetically lethal, giving a promising therapeutic for homologous recombination repair deficient (HRD) tumors including BRCA mutation. However, overlapping hematologic toxicity causes PARPi to fail in combination with some first-line chemotherapies. Furthermore, recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for antitumor activity in HRD cancer models. Currently approved PARPi have shown varying levels of selectivity for the entire 17-member PARP family, hence contribute to toxicity. Together, these findings above have provided the necessity and feasibility of developing next-generation PARPi with improved selectivity for PARP1, expanding significant clinical values and wide application prospects both in monotherapy and combination with other anticancer agents. In this review, we summery the latest research of current approved PARPi, discuss the current status and future promise of next-generation PARP1-selective inhibitor AZD5305, including its reported progress up to now and anticipated impact on clinical.

Resistance to PARP Inhibitors After First-Line Platinum-Based Chemotherapy in a Patient with Advanced Ovarian Cancer with a Pathogenic Somatic BRCA1 Mutation

PARP inhibitors (PARPi) are the maintenance therapy after first line platinum-based chemotherapy for patients with advanced epithelial ovarian cancer (EOC) with germline and pathogenic somatic BRCA1/2 mutations. However, as with chemotherapy, patients can develop resistance to PARPi. The selective pressure generated by heterogeneous somatic BRCA mutations may give rise to chemotherapy or PARPi resistant tumors. Here, we present the case of a patient harboring a pathogenic p.Glu143* (c.427G>T) somatic BRCA1 mutation conferring resistance to olaparib following cytoreductive surgery and platinum-based chemotherapy. We ordered a plasma ctDNA analysis (tissue biopsy of recurrent lesions was contraindicated due to their anatomical location) to figure out the possible resistance mechanism. Analysis of ctDNA did not detect the pathogenic somatic BRCA1 p.Glu143* (c.427G>T) mutation seen before. The tumor cells harboring the pathogenic BRCA1 mutation were probably eliminated by the platinum-based chemotherapy, leaving only those without BRCA mutations to proliferate.

Strategies for the Management of Patients with Pancreatic Cancer with PARP Inhibitors

A subset of patients with pancreatic adenocarcinomas (PDAC) harbor mutations that are exploitable in the context of DNA-damage response and repair (DDR) inhibitory strategies. Between 8-18% of PDACs harbor specific mutations in the DDR pathway such as BRCA1/2 mutations, and a higher prevalence exists in high-risk populations (e.g., Ashkenazi Jews). Herein, we will review the current trials and data on the treatment of PDAC patients who harbor such mutations and who appear sensitive to platinum and/or poly ADP ribose polymerase inhibitor (PARPi) based therapies due to a concept known as synthetic lethality. Although this current best-in-class precision treatment shows clinical promise, the specter of resistance limits the extent of therapeutic responses. We therefore also evaluate promising pre-clinical and clinical approaches in the pipeline that may either work with existing therapies to break resistance or work separately with combination therapies against this subset of PDACs.

Development of Homologous Recombination Functional Assays for Targeting the DDR

Identification of tumours that have homologous recombination deficiency (HRD) has become of increasing interest following the licensing of PARP inhibitors. Potential methods to assess HRD status include; clinical selection for platinum sensitive disease, mutational/methylation status, genomic scars/signature and functional RAD51 assays. Homologous recombination (HR) is a dynamic process with the potential to evolve over a disease course, particularly in relation to previous treatment. This is one of the major drawbacks of genomic scars/signatures, as they only demonstrate historic HR status. Functional HR assays have the benefit of giving a real time HR status readout and therefore have the potential for clearer identification of patients who may benefit from PARP inhibitors at that specific time point. However, the development of RAD51 foci assays ready for clinical practice has been challenging. Pre-clinical considerations have included; controlling for variation in tumour proliferation, tissue type and whether DNA damage induction is required. Furthermore, the assays require correlation with clinical outcomes, an understanding of how they complement current testing modalities and validation of test performance in large cohorts. Despite these challenges, given the profound benefit from PARP inhibitors seen in those with an HRD phenotype to date, the ongoing development and validation of these functional HR assays remains of high clinical importance.

Olaparib and advanced ovarian cancer: Summary of the past and looking into the future

Ovarian cancer (OC) is women's eighth most common cancer, bearing the highest mortality rates of all female reproductive system malignancies. Poly (ADP-ribose) polymerase inhibitors (PARPis) have reshaped the treatment scenario of metastatic OC as a maintenance post platinum-based chemotherapy. Olaparib is the first PARPi developed for this disease. Results from Study 42, Study 19, SOLO2, OPINION, SOLO1, and PAOLA-1 clinical trials, led to the FDA and EMA approval of olaparib for the maintenance treatment of women with high-grade epithelial ovarian, fallopian tube, or primary peritoneal cancer without platinum progression: in the platinum-sensitive recurrent OC; in the newly diagnosed setting in case Breast Cancer (BRCA) mutations and, in combination with bevacizumab, in case of BRCA mutation or deficiency of homologous recombination genes. In this review, we synthetized olaparib's pharmacokinetic and pharmacodynamic properties and its use in special populations. We summarized the efficacy and safety of the studies leading to the current approvals and discussed the future developments of this agent.

CA-125 KELIM as a Potential Complementary Tool for Predicting Veliparib Benefit: An Exploratory Analysis From the VELIA/GOG-3005 Study

PURPOSE

In VELIA trial, veliparib combined with carboplatin-paclitaxel, followed by maintenance (veliparib-throughout) was associated with improved progression-free survival (PFS) compared with carboplatin-paclitaxel alone in patients with high-grade ovarian carcinomas. We explored the prognostic value of the modeled cancer antigen (CA)-125 elimination rate constant K (KELIM), which is known to be an indicator of the intrinsic tumor chemosensitivity (the faster the rate of CA-125 decline, the higher the KELIM and the higher the chemosensitivity), and its association with benefit from veliparib.

PATIENTS AND METHODS

Individual KELIM values were estimated from longitudinal CA-125 kinetics. Patients were categorized as having favorable (≥ median) or unfavorable (< median) KELIM. The prognostic value of KELIM for veliparib-related PFS benefit was explored in cohorts treated with primary or interval debulking surgery, according to the surgery completeness, the disease progression risk group, and the homologous recombination (HR) status (BRCA mutation, HR deficiency [HRD], or HR proficiency [HRP]).

RESULTS

The data from 854 of 1,140 enrolled patients were analyzed (primary debulking surgery, n = 700; interval debulking surgery, n = 154). Increasing KELIM values were associated with higher benefit from veliparib in HRD cancer, as were decreasing KELIM values in HRP cancer. The highest PFS benefit from veliparib was observed in patients with both favorable KELIM and BRCA mutation (hazard ratio, 0.28; 95% CI, 0.13 to 0.61) or BRCA wild-type HRD cancer (hazard ratio, 0.43; 95% CI, 0.26 to 0.70), consistent with the association between poly (adenosine diphosphate-ribose) polymerase inhibitor efficacy and platinum sensitivity. In contrast, seventy-four percent of patients with a BRCA mutation and unfavorable KELIM progressed within 18 months while on veliparib. The patients with HRP cancer and unfavorable KELIM might have benefited from the veliparib chemosensitizing effect.

CONCLUSION

In addition to HRD/BRCA status, the tumor primary chemosensitivity observed during the first-line chemotherapy might be another complementary determinant of poly (adenosine diphosphate-ribose) polymerase inhibitor efficacy.

Implementation of Comprehensive Genomic Profiling in Ovarian Cancer Patients: A Retrospective Analysis

Comprehensive genomic profiling (CGP) allows for the detection of driver alterations at high resolution, but the limited number of approved targeted therapies and their high costs have contributed to its limited clinical utilization. We retrospectively compared data of 946 women with ovarian cancer (11.4% were referred to CGP, and 88.6% served as control) to examine whether CGP provides a prognosis benefit. Patient baseline parameters were similar between the groups. Cox regression analysis adjusted for age, disease stage at diagnosis, and recurrence status showed statistically significantly longer median overall survival (mOS) in the CGP group versus the control (73.4 versus 54.5 months, p < 0.001). Fifty-four patients (52.9%) had actionable mutations with potential treatments; twenty-six (48.2%) were treated with matched targeted therapy, showing a trend for longer mOS than the eighty-six women in the CGP group who were not given a suggested treatment (105.5 versus 63.6 months, p = 0.066). None of the genomic alterations predicted metastasis location. CCNE1 amplification and KRAS mutations were associated with shorter mOS. Patients with tumor mutation burden ≥4 mutations/megabase had longer mOS. High loss of heterozygosity was associated with longer mOS (99.0 versus 48.2 months, p = 0.004). CGP testing may provide both prognostic and predictive insights for treatment of patients with ovarian cancer. Prospective studies of larger cohorts are warranted.

PARP-1 genetic polymorphism associated with radiation sensitivity of non-small cell lung cancer

About 70% of non-small cell lung cancer (NSCLC) patients require radiotherapy. However, due to the difference in radiation sensitivity, the treatment outcome may differ for the same pathology and choice of treatment. Poly (ADP-ribose) polymerase 1 (PARP-1) is a key gene responsible for DNA repair and is involved in base excision repair as well as repair of single strand break induced by ionizing radiation and oxidative damage. In order to investigate the relationship between PARP-1 gene polymorphism and radiation sensitivity in NSCLC, we collected 141 primary NSCLC patients undergoing three-dimensional conformal radiotherapy. For each case, the gross tumor volumes (GTV) before radiation and that after 40 Gy radiation were measured to calculate the tumor regression rate. TaqMan real-time polymerase chain reaction was performed to genotype the single-nucleotide polymorphisms (SNPs). Genotype frequencies for PARP-1 genotypes were 14.2% for C/C, 44.7% for C/G and 41.1% for G/G. The average tumor regression rate after 40 Gy radiation therapy was 35.1% ± 0.192. Tumor regression rate of mid-term RT of C/C genotype was 44.6% ± 0.170, which was higher than that of genotype C/G and G/G (32.4% ± 0.196 and 34.8% ± 0.188, respectively) with statistical significance (F = 3.169 p = 0.045). The higher tumor regression rate in patients with C/C genotype suggested that G allele was a protective factor against radiation therapy. Using the median tumor regression rate of 34%, we divided the entire cohort into two groups, and found that the frequency distribution of PARP-1 gene rs3219073 had significant difference between these two groups (p < 0.05). These results showed that PARP-1 gene polymorphism may affect patient radiation sensitivity and predict the efficacy of radiotherapy. It therefore presents an opportunity for developing new therapeutic targets to improve radiotherapy outcome.

Clinical Impact of Next-Generation Sequencing Multi-Gene Panel Highlighting the Landscape of Germline Alterations in Ovarian Cancer Patients

BRCA1 and BRCA2 are the most frequently mutated genes in ovarian cancer (OC) crucial both for the identification of cancer predisposition and therapeutic choices. However, germline variants in other genes could be involved in OC susceptibility. We characterized OC patients to detect mutations in genes other than BRCA1/2 that could be associated with a high risk of developing OC and permit patients to enter the most appropriate treatment and surveillance program. Next-generation sequencing analysis with a 94-gene panel was performed on germline DNA of 219 OC patients. We identified 34 pathogenic/likely pathogenic variants in BRCA1/2 and 38 in other 21 genes. The patients with pathogenic/likely pathogenic variants in the non-BRCA1/2 genes mainly developed OC alone compared to the other groups that also developed breast cancer or other tumors (p = 0.001). Clinical correlation analysis showed that the low-risk patients were significantly associated with platinum sensitivity (p < 0.001). Regarding PARP inhibitors (PARPi) response, the patients with pathogenic mutations in the non-BRCA1/2 genes had worse PFS and OS. Moreover, a statistically significantly worse PFS was found for every increase of one thousand platelets before PARPi treatment. To conclude, knowledge about molecular alterations in genes beyond BRCA1/2 in OC could allow for more personalized diagnostic, predictive, prognostic, and therapeutic strategies for OC patients.

The genomic and immune landscape of long-term survivors of high-grade serous ovarian cancer

Fewer than half of all patients with advanced-stage high-grade serous ovarian cancers (HGSCs) survive more than five years after diagnosis, but those who have an exceptionally long survival could provide insights into tumor biology and therapeutic approaches. We analyzed 60 patients with advanced-stage HGSC who survived more than 10 years after diagnosis using whole-genome sequencing, transcriptome and methylome profiling of their primary tumor samples, comparing this data to 66 short- or moderate-term survivors. Tumors of long-term survivors were more likely to have multiple alterations in genes associated with DNA repair and more frequent somatic variants resulting in an increased predicted neoantigen load. Patients clustered into survival groups based on genomic and immune cell signatures, including three subsets of patients with BRCA1 alterations with distinctly different outcomes. Specific combinations of germline and somatic gene alterations, tumor cell phenotypes and differential immune responses appear to contribute to long-term survival in HGSC.

Pharmacokinetics and Pharmacodynamics of PARP Inhibitors in Oncology

Olaparib, niraparib, rucaparib, and talazoparib are poly (ADP-ribose) polymerase (PARP) inhibitors approved for the treatment of ovarian, breast, pancreatic, and/or prostate cancer. Poly (ADP-ribose) polymerase inhibitors are potent inhibitors of the PARP enzymes with comparable half-maximal inhibitory concentrations in the nanomolar range. Olaparib and rucaparib are orally dosed twice a day, extensively metabolized by cytochrome P450 enzymes, and inhibitors of several enzymes and drug transporters with a high risk for drug-drug interactions. Niraparib and talazoparib are orally dosed once a day with a lower risk for niraparib and a minimal risk for talazoparib to cause drug-drug interactions. All four PARP inhibitors show moderate-to-high interindividual variability in plasma exposure. Higher exposure is associated with an increase in toxicity, mostly hematological toxicity. For talazoparib, exposure-efficacy relationships have been described, but for olaparib, niraparib, and rucaparib this relationship remains inconclusive. Further studies are required to investigate exposure-response relationships to improve dosing of PARP inhibitors, in which therapeutic drug monitoring could play an important role. In this review, we give an overview of the pharmacokinetic properties of the four PARP inhibitors, including considerations for patients with renal dysfunction or hepatic impairment, the effect of food, and drug-drug interactions. Furthermore, we focus on the pharmacodynamics and summarize the available exposure-efficacy and exposure-toxicity relationships.

CRISPR screens guide the way for PARP and ATR inhibitor biomarker discovery

DNA repair pathways are heavily studied for their role in cancer initiation and progression. Due to the large amount of inherent DNA damage in cancer cells, tumor cells profoundly rely on proper DNA repair for efficient cell cycle progression. Several current chemotherapeutics promote excessive DNA damage in cancer cells, thus leading to cell death during cell cycle progression. However, if the tumor has efficient DNA repair mechanisms, DNA-damaging therapeutics may not be as effective. Therefore, directly inhibiting DNA repair pathways alone and in combination with chemotherapeutics that cause DNA damage may result in improved clinical outcomes. Nevertheless, tumors can acquire resistance to DNA repair inhibitors. It is essential to understand the genetic mechanisms underlying this resistance. Genome-wide CRISPR screening has emerged as a powerful tool to identify biomarkers of resistance or sensitivity to DNA repair inhibitors. CRISPR knockout and CRISPR activation screens can be designed to investigate how the loss or overexpression of any human gene impacts resistance or sensitivity to specific inhibitors. This review will address the role of CRISPR screening in identifying biomarkers of resistance and sensitivity to DNA repair pathway inhibitors. We will focus on inhibitors targeting the PARP1 and ATR enzymes, and how the biomarkers identified from CRISPR screens can help inform the treatment plan for cancer patients.

ATR Inhibitors in Platinum-Resistant Ovarian Cancer

Platinum-resistant ovarian cancer (PROC) is one of the deadliest types of epithelial ovarian cancer, and it is associated with a poor prognosis as the median overall survival (OS) is less than 12 months. Targeted therapy is a popular emerging treatment method. Several targeted therapies, including those using bevacizumab and poly (ADP-ribose) polymerase inhibitor (PARPi), have been used to treat PROC. Ataxia telangiectasia and RAD3-Related Protein Kinase inhibitors (ATRi) have attracted attention as a promising class of targeted drugs that can regulate the cell cycle and influence homologous recombination (HR) repair. In recent years, many preclinical and clinical studies have demonstrated the efficacy of ATRis in PROC. This review focuses on the anticancer mechanism of ATRis and the progress of research on ATRis for PROC.

PARP1 proximity proteomics reveals interaction partners at stressed replication forks

PARP1 mediates poly-ADP-ribosylation of proteins on chromatin in response to different types of DNA lesions. PARP inhibitors are used for the treatment of BRCA1/2-deficient breast, ovarian, and prostate cancer. Loss of DNA replication fork protection is proposed as one mechanism that contributes to the vulnerability of BRCA1/2-deficient cells to PARP inhibitors. However, the mechanisms that regulate PARP1 activity at stressed replication forks remain poorly understood. Here, we performed proximity proteomics of PARP1 and isolation of proteins on stressed replication forks to map putative PARP1 regulators. We identified TPX2 as a direct PARP1-binding protein that regulates the auto-ADP-ribosylation activity of PARP1. TPX2 interacts with DNA damage response proteins and promotes homology-directed repair of DNA double-strand breaks. Moreover, TPX2 mRNA levels are increased in BRCA1/2-mutated breast and prostate cancers, and high TPX2 expression levels correlate with the sensitivity of cancer cells to PARP-trapping inhibitors. We propose that TPX2 confers a mitosis-independent function in the cellular response to replication stress by interacting with PARP1.

Integrated proteomics identifies PARP inhibitor-induced prosurvival signaling changes as potential vulnerabilities in ovarian cancer

BRCA1/2-deficient ovarian carcinoma (OC) has been shown to be particularly sensitive to poly (ADP-ribose) polymerase inhibitors (PARPis). Furthermore, BRCA1/2 mutation status is currently used as a predictive biomarker for PARPi therapy. Despite providing a major clinical benefit to the majority of patients, a significant proportion of BRCA1/2-deficient OC tumors do not respond to PARPis for reasons that are incompletely understood. Using an integrated chemical, phospho- and ADP-ribosylation proteomics approach, we sought here to develop additional mechanism-based biomarker candidates for PARPi therapy in OC and identify new targets for combination therapy to overcome primary resistance. Using chemical proteomics with PARPi baits in a BRCA1-isogenic OC cell line pair, as well as patient-derived BRCA1-proficient and BRCA1-deficient tumor samples, and subsequent validation by coimmunoprecipitation, we showed differential PARP1 and PARP2 protein complex composition in PARPi-sensitive, BRCA1-deficient UWB1.289 (UWB) cells compared to PARPi-insensitive, BRCA1-reconstituted UWB1.289+BRCA1 (UWB+B) cells. In addition, global phosphoproteomics and ADP-ribosylation proteomics furthermore revealed that the PARPi rucaparib induced the cell cycle pathway and nonhomologous end joining (NHEJ) pathway in UWB cells but downregulated ErbB signaling in UWB+B cells. In addition, we observed AKT PARylation and prosurvival AKT-mTOR signaling in UWB+B cells after PARPi treatment. Consistently, we found the synergy of PARPis with DNAPK or AKT inhibitors was more pronounced in UWB+B cells, highlighting these pathways as actionable vulnerabilities. In conclusion, we demonstrate the combination of chemical proteomics, phosphoproteomics, and ADP-ribosylation proteomics can identify differential PARP1/2 complexes and diverse, but actionable, drug compensatory signaling in OC.

Potential Targeted Therapies in Ovarian Cancer

BACKGROUND

We aimed to identify somatic pathogenic and likely pathogenic mutations using next-generation sequencing (NGS). The mutational findings were held against clinically well-described data to identify potential targeted therapies in Danish patients diagnosed with high-grade serous ovarian cancer (HGSC).

METHODS

We characterized the mutational profile of 128 HGSC patients. Clinical data were obtained from the Danish Gynecological Database and tissue samples were collected through the Danish CancerBiobank. DNA was analyzed using NGS.

RESULTS

47 (37%) patients were platinum-sensitive, 32 (25%) partially platinum-sensitive, 35 (27%) platinum-resistant, and three (2%) platinum-refractory, while 11 (9%) patients did not receive chemotherapy. Overall, 27 (21%) had known druggable targets. Twelve (26%) platinum-sensitive patients had druggable targets for PARP inhibitors: one for tyrosine kinase inhibitors and one for immunotherapy treatment. Eight (25%) partially platinum-sensitive patients had druggable targets: seven were eligible for PARP inhibitors and one was potentially eligible for alpesilib and hormone therapy. Seven (20%) platinum-resistant patients had druggable targets: six (86%) were potentially eligible for PARP inhibitors, one for immunotherapy, and one for erdafitinib.

CONCLUSIONS

PARP inhibitors are the most frequent potential targeted therapy in HGSC. However, other targeted therapies remain relevant for investigation according to our mutational findings.

Small-molecule inhibitors, immune checkpoint inhibitors, and more: FDA-approved novel therapeutic drugs for solid tumors from 1991 to 2021

The United States Food and Drug Administration (US FDA) has always been a forerunner in drug evaluation and supervision. Over the past 31 years, 1050 drugs (excluding vaccines, cell-based therapies, and gene therapy products) have been approved as new molecular entities (NMEs) or biologics license applications (BLAs). A total of 228 of these 1050 drugs were identified as cancer therapeutics or cancer-related drugs, and 120 of them were classified as therapeutic drugs for solid tumors according to their initial indications. These drugs have evolved from small molecules with broad-spectrum antitumor properties in the early stage to monoclonal antibodies (mAbs) and antibody‒drug conjugates (ADCs) with a more precise targeting effect during the most recent decade. These drugs have extended indications for other malignancies, constituting a cancer treatment system for monotherapy or combined therapy. However, the available targets are still mainly limited to receptor tyrosine kinases (RTKs), restricting the development of antitumor drugs. In this review, these 120 drugs are summarized and classified according to the initial indications, characteristics, or functions. Additionally, RTK-targeted therapies and immune checkpoint-based immunotherapies are also discussed. Our analysis of existing challenges and potential opportunities in drug development may advance solid tumor treatment in the future.

Targeting the ALK-CDK9-Tyr19 kinase cascade sensitizes ovarian and breast tumors to PARP inhibition via destabilization of the P-TEFb complex

Poly(ADP-ribose) polymerase (PARP) inhibitors have demonstrated promising clinical activity in multiple cancers. However, resistance to PARP inhibitors remains a substantial clinical challenge. In the present study, we report that anaplastic lymphoma kinase (ALK) directly phosphorylates CDK9 at tyrosine-19 to promote homologous recombination (HR) repair and PARP inhibitor resistance. Phospho-CDK9-Tyr19 increases its kinase activity and nuclear localization to stabilize positive transcriptional elongation factor b and activate polymerase II-dependent transcription of HR-repair genes. Conversely, ALK inhibition increases ubiquitination and degradation of CDK9 by Skp2, an E3 ligase. Notably, combination of US Food and Drug Administration-approved ALK and PARP inhibitors markedly reduce tumor growth and improve survival of mice in PARP inhibitor-/platinum-resistant tumor xenograft models. Using human tumor biospecimens, we further demonstrate that phosphorylated ALK (p-ALK) expression is associated with resistance to PARP inhibitors and positively correlated with p-Tyr19-CDK9 expression. Together, our findings support a biomarker-driven, combinatorial treatment strategy involving ALK and PARP inhibitors to induce synthetic lethality in PARP inhibitor-/platinum-resistant tumors with high p-ALK-p-Tyr19-CDK9 expression.

Olaparib synergizes with arsenic trioxide by promoting apoptosis and ferroptosis in platinum-resistant ovarian cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors are efficacious in treating platinum-sensitive ovarian cancer (OC), but demonstrate limited efficiency in patients with platinum-resistant OC. Thus, further investigations into combined strategies that enhance the response to PARP inhibitors (PARPi) in platinum-resistant OC are required. The present study aimed to investigate the combined therapy of arsenic trioxide (ATO) with olaparib, a common PARPi, and determine how this synergistic cytotoxicity works in platinum-resistant OC cells. Functional assays demonstrated that the combined treatment of olaparib with ATO significantly suppressed cell proliferation and colony formation, and enhanced DNA damage as well as cell apoptosis in A2780-CIS and SKOV3-CIS cell lines. Results of the present study also demonstrated that a combination of olaparib with ATO increased lipid peroxidation and eventually triggered ferroptosis. Consistently, the combined treatment synergistically suppressed tumor growth in mice xenograft models. Mechanistically, ATO in combination with olaparib activated the AMPK α pathway and suppressed the expression levels of stearoyl-CoA desaturase 1 (SCD1). Collectively, results of the present study demonstrated that treatment with ATO enhanced the effects of olaparib in platinum-resistant OC.

Corrected Allele Frequency of BRCA1/2 Mutations Is an Independent Prognostic Factor for Treatment Response to PARP-Inhibitors in Ovarian Cancer Patients

PARP inhibitors (PARPi) have increased treatment options in ovarian cancer, particularly in patients with BRCA1/2 mutations, although there are still marked differences in the duration of patients’ response to this targeted therapy. BRCA testing is routinely performed in tumor tissue of ovarian cancer patients. The resulting molecular pathological findings include the genetic nomenclature of the mutation, the frequency of the mutated allele (variant allele frequency, VAF), and the tumor cell content. VAF measures the percentage of mutated alleles from the total alleles in the cells of the examined tissue. The aim of this study was to investigate the significance of VAF on the therapeutic response to PARPis in ovarian cancer patients. Epithelial ovarian cancer patients harboring BRCA1/2 tumor mutations, who underwent germline testing and received PARPi therapy at the Medical University of Vienna (n = 41) were included in the study. Corrected VAF (cVAF) was calculated based on VAF, tumor cell content, and germline mutation. Patients were divided into two groups based on their cVAF. Median PFS under PARPi in patients with low cVAF was 13.0 months (IQR [10.3-not reached]) and was not reached in the high cVAF group. High cVAF was significantly associated with longer PFS in the multivariate analysis (HR = 0.07; 95% CI [0.01–0.63]; p = 0.017). In conclusion, high cVAF was associated with a significantly better response to PARPi in this study population.

What predicts the clinical benefits of PARP inhibitors in platinum-sensitive recurrent ovarian cancer: A real-world single-center retrospective cohort study from China

Objective

This study assessed the real-world application, effectiveness, and safety of olaparib and niraparib as maintenance therapies in patients with platinum-sensitive recurrent ovarian cancer (PSROC) in China and investigated clinical factors associated with prolonged benefits of poly ADP-ribose polymerase (PARP) inhibitors to help guide clinician treatment-decision making in daily practice.

Methods

This real-world single-center retrospective cohort study was conducted at the Shandong Cancer Hospital and Institute. Archival data of consecutive patients diagnosed with PSROC who achieved a complete response (CR) or partial response (PR) after the last platinum-based chemotherapy and treated with olaparib or niraparib as maintenance therapy from August 2018 to September 2021 were collected.

Results

Overall, 106 women were included in the cohort. Seventy-two (68%) patients were treated with olaparib, while 34 (32%) received niraparib; 99.1% of the patients were diagnosed with high-grade serous carcinoma, and 73.6% had FIGO stages III–IV. Approximately 71.7% of the patients had received PARP inhibitors after the second platinum-based line and 44.3% of the patients achieved a CR in their last platinum-based therapy. The median platinum-free interval (PFI) after the penultimate platinum-based therapy was 10 (95% CI: 10–13.6) months. The median PFS was 21 (95% CI: 13–24.5) months and the median CFI was 22 (95% CI: 16–26.5) months. Consistent with the univariate analysis, the multivariate analysis identified three independent factors associated with prolonged progression-free survival (PFS) and chemotherapy-free interval (CFI): breast cancer susceptibility gene (BRCA) mutant type (p = 0.005 and p = 0.003); PFI ≥12 months (p = 0.01 and p = 0.006); and CR to last platinum-based therapy (p = 0.016 and p = 0.019). It was found that there was no appreciable difference in any grade 3–4 hematological AE between patients who received olaparib and niraparib.

Conclusion

Maintenance treatment with olaparib and niraparib is effective and well tolerated for PSROC patients in real-world clinical practice. Three clinical factors were identified that predicted prolonged survival under maintenance therapy with PARP inhibitors: BRCA mutant type, PFI ≥12 months, and CR to last platinum-based therapy. These findings should be further confirmed with an appropriately powered analysis in studies with larger sample sizes.

The disruption of the CCDC6 – PP4 axis induces a BRCAness like phenotype and sensitivity to PARP inhibitors in high-grade serous ovarian carcinoma

Background

Treatment with PARP inhibitors (PARPi) is primarily effective against high-grade serous ovarian cancers (HGSOC) with BRCA1/2 mutations or other deficiencies in homologous recombination (HR) repair mechanisms. However, resistance to PARPi frequently develops, mostly as a result of BRCA1/2 reversion mutations. The tumour suppressor CCDC6 is involved in HR repair by regulating the PP4c phosphatase activity on γH2AX. In this work, we reported that in ovarian cancer cells, a physical or functional loss of CCDC6 results synthetic lethal with the PARP-inhibitors drugs, by affecting the HR repair. We also unravelled a role for CCDC6 as predictive marker of PARPi sensitivity in ovarian cancer, and the impact of CCDC6 downregulation in overcoming PARPi resistance in these tumours.

Methods

A panel of HGSOC cell lines (either BRCA-wild type or mutant) were treated with PARPi after CCDC6 was attenuated by silencing or by inhibiting USP7, a CCDC6-deubiquitinating enzyme, and the effects on cell survival were assessed. At the cellular and molecular levels, the processes underlying the CCDC6-dependent modification of drugs’ sensitivity were examined. Patient-derived xenografts (PDXs) were immunostained for CCDC6, and the expression of the protein was analysed statistically after digital or visual means.

Results

HGSOC cells acquired PARPi sensitivity after CCDC6 depletion. Notably, CCDC6 downregulation restored the PARPi sensitivity in newly generated or spontaneously resistant cells containing either wild type- or mutant-BRCA2. When in an un-phosphorylated state, the CCDC6 residue threonine 427 is crucial for effective CCDC6-PP4 complex formation and PP4 sequestration, which maintains high γH2AX levels and effective HR. Remarkably, the PP4-dependent control of HR repair is influenced by the CCDC6 constitutively phosphorylated mutant T427D or by the CCDC6 loss, favouring PARPi sensitivity. As a result, the PP4 regulatory component PP4R3α showed to be essential for both the activity of the PP4 complex and the CCDC6 dependent PARPi sensitivity. It's interesting to note that immunohistochemistry revealed an intense CCDC6 protein staining in olaparib-resistant HGSOC cells and PDXs.

Conclusions

Our findings suggest that the physical loss or the functional impairment of CCDC6 enhances the PP4c complex activity, which causes BRCAness and PARPi sensitivity in HGSOC cells. Moreover, CCDC6 downregulation might overcome PARPi resistance in HGSOCs, thus supporting the potential of targeting CCDC6 by USP7 inhibitors to tackle PARPi resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02459-2.

BRCA Mutations in Ovarian and Prostate Cancer: Bench to Bedside

Simple Summary

DNA damage is one of the hallmarks of cancer. Epithelial ovarian cancer (EOC) —especially the high-grade serous subtype—harbors a defect in at least one DNA damage response (DDR) pathway. Defective DDR results from a variety of lesions affecting homologous recombination (HR) and nonhomologous end joining (NHEJ) for double strand breaks, base excision repair (BER), and nucleotide excision repair (NER) for single strand breaks and mismatch repair (MMR). Apart from the EOC, mutations in the DDR genes, such as BRCA1 and BRCA2, are common in prostate cancer as well. Among them, BRCA2 lesions are found in 12% of metastatic castration-resistant prostate cancers, but very rarely in primary prostate cancer. Better understanding of the DDR pathways is essential in order to optimize the therapeutic choices, and has led to the design of biomarker-driven clinical trials. Poly(ADP-ribose) polymerase (PARP) inhibitors are now a standard therapy for EOC patients, and more recently have been approved for the metastatic castration-resistant prostate cancer with alterations in DDR genes. They are particularly effective in tumours with HR deficiency.

Abstract

DNA damage repair (DDR) defects are common in different cancer types, and these alterations can be exploited therapeutically. Epithelial ovarian cancer (EOC) is among the tumours with the highest percentage of hereditary cases. BRCA1 and BRCA2 predisposing pathogenic variants (PVs) were the first to be associated with EOC, whereas additional genes comprising the homologous recombination (HR) pathway have been discovered with DNA sequencing technologies. The incidence of DDR alterations among patients with metastatic prostate cancer is much higher compared to those with localized disease. Genetic testing is playing an increasingly important role in the treatment of patients with ovarian and prostate cancer. The development of poly (ADP-ribose) polymerase (PARP) inhibitors offers a therapeutic strategy for patients with EOC. One of the mechanisms of PARP inhibitors exploits the concept of synthetic lethality. Tumours with BRCA1 or BRCA2 mutations are highly sensitive to PARP inhibitors. Moreover, the synthetic lethal interaction may be exploited beyond germline BRCA mutations in the context of HR deficiency, and this is an area of ongoing research. PARP inhibitors are in advanced stages of development as a treatment for metastatic castration-resistant prostate cancer. However, there is a major concern regarding the need to identify reliable biomarkers predictive of treatment response. In this review, we explore the mechanisms of DDR, the potential for genomic analysis of ovarian and prostate cancer, and therapeutics of PARP inhibitors, along with predictive biomarkers.

RAD54B mutations enhance the sensitivity of ovarian cancer cells to poly(ADP-ribose) polymerase (PARP) inhibitors

Synthetic lethal targeting of homologous recombination (HR)–deficient ovarian cancers (OvCas) with poly(ADP-ribose) polymerase inhibitors (PARPis) has attracted considerable attention. Olaparib was the first PARPi approved by the Food and Drug Administration, offering significant clinical benefits in BRCA1/2-deficient OvCas. However, only approximately 20% of OvCa patients harbor BRCA1/2 mutations. Given the shared roles that BRCA1/2 have with other HR regulators, alterations in HR genes may also contribute to “BRCAness profiles” in OvCas. RAD54B has been considered a key player in HR repair, although its roles and therapeutic potential in cancers need further investigation. Here, we identified 22 frequently mutated HR genes by whole-exome sequencing of OvCa tissues from 82 patients. To our surprise, 7.3% of patients were found to harbor mutations of RAD54B, the third-highest mutated gene among patients. We determined that RAD54B-mutated tumor tissues harbored more DNA double-strand breaks than normal tissues. Additionally, we found that RAD54B knockdown inhibited HR repair, enhanced sensitivities of OvCa cells with increased DNA double-strand breaks to olaparib, and induced apoptosis. Enhanced inhibitory effects of olaparib on the growth of ES2 xenograft tumors were further demonstrated by RAD54B knockdown. Finally, we show that restoration with wildtype RAD54B rather than RAD54B^N593S and RAD54B^H219Y, identified in patients, abolished the effects of RAD54B knockdown, indicating these RAD54B mutants probably malfunctioned in HR repair. Our investigations may offer insight into the contributions of RAD54B mutations to synthetic lethality with olaparib treatment in OvCas, enrich the gene list for “HR deficiency scoring,” and expand the applications of PARPis.

Ovarian cancer recurrence: is the definition of platinum sensitivity modified by PARPi, bevacizumab or other intervening treatments? : a clinical perspective

In view of the high risk of recurrent disease in stage III and IV ovarian cancer following primary first-line chemotherapy, a variety of maintenance and consolidation treatment strategies have been developed. These have included: radiation, intravenous or intraperitoneal chemotherapy, targeted therapies, and immunotherapy. Popular at this time is the use of Poly-adenosine ribose polymerase (PARP) inhibitors and bevacizumab as maintenance therapy. What effect these maintenance or consolidation therapies have on subsequent response to therapy, specifically platinum-based chemotherapy, is only beginning to be studied. In this manuscript, we review the impact of PARP inhibitors and bevacizumab as well as radiation and maintenance chemotherapy on subsequent response to treatment. Prior use of bevacizumab does not appear to adversely affect subsequent response to platinum-based chemotherapy or platinum-based chemotherapy with bevacizumab. Prior therapy with PARP inhibitors induces platinum resistance to subsequent platinum-based therapy and negates classic predictors of response such as platinum-free interval and breast cancer susceptibility gene (BRCA) mutational status.

Exposure to escalating olaparib does not induce acquired resistance to PARPi and to other chemotherapeutic compounds in ovarian cancer cell lines

Poly (ADP-ribose) polymerase (PARP)-inhibitors (PARPi) such as olaparib and niraparib are currently used as a treatment option for BRCA-deficient tumors and also show efficacy in platinum-sensitive tumors. However, resistance to PARPi occurs in numerous patients and in particular acquired PARPi resistance presents a major obstacle in the treatment of these tumors. In the present study, it was investigated whether stepwise exposure of ovarian cancer cells to escalating concentrations of olaparib produced subcells with acquired resistance to PARPi and/or acquired cross-resistance to platinum compounds, paclitaxel, and doxorubicin. To this aim, the sensitivity of fourteen ovarian cancer cell lines, including nine with TP53-mutations and five carrying BRCA-mutations, to olaparib and niraparib was determined and a subset of seven cell lines was selected to investigate the potential of olaparib to produce resistance. It was identified that escalating olaparib did neither produce subcells with acquired PARPi-resistance nor did it produce acquired cross-resistance to platinum compounds, doxorubicin, and paclitaxel. This finding was independent of the cells' TP53 and BRCA mutation status. CRISPR-Cas9 mediated deletion of PARP1 did not affect sensitivity to PARPi, platinum compounds, doxorubicin, and paclitaxel. In addition, olaparib sensitivity correlated with niraparib sensitivity, but BRCA-mutated cells were not more sensitive to PARPi. Moreover, PARPi sensitivity associated with cross-sensitivity not only to platinum compounds but also to anthracylines, paclitaxel, and inhibitors of histone deacetylases. These in vitro data indicated that olaparib exposure is unlikely to produce an acquired resistance phenotype and that PARPi-sensitive ovarian cancer cells are also cross-sensitive to non-platinum and even to compounds not directly interacting with the DNA.

PARP inhibitors as single agents and in combination therapy: the most promising treatment strategies in clinical trials for BRCA-mutant ovarian and triple-negative breast cancers

INTRODUCTION

Poly (ADP-ribose) polymerase inhibitors (PARPis) are an exciting class of agents that have shown efficacy, particularly for BRCA-mutant triple-negative breast cancer (TNBC) and high-grade serous ovarian cancer (HGSOC). However, most patients who receive PARPi as their standard of care therapy inevitably develop resistance and this underscores the need to identify additional targets that can circumvent such resistance. Combination treatment strategies have been developed in preclinical and clinical studies to address the challenges of efficacy and resistance.

AREAS COVERED

This review examines completed or ongoing clinical trials of PARPi mono- and combination therapies. PARPi monotherapy in HER2 negative breast (HR+ and TNBC subtypes) and ovarian cancer is a focal point. The authors propose potential strategies that might overcome resistance to PARPi and discuss key questions and future directions.

EXPERT OPINION

While the advent of PARPis has significantly improved the treatment of tumors with defects in DNA damage and repair pathways, careful patient selection will be essential to enhance these treatments. The identification of molecular biomarkers to predict disease response and progression is an endeavor.

Ovarian cancer recurrence: is the definition of platinum resistance modified by PARPi and other intervening treatments? The evolving landscape in the management of platinum-resistant ovarian cancer

Definitions of platinum resistance have been questioned and changed over the last five years, even though no predictive biomarker of resistance exists. These have sculpted how we approach platinum retreatment and, consequently, how we devise new treatment strategies for those patients with tumour progression on platinum therapy. Platinum-non-eligible ovarian cancer is treated with single-agent non-platinum drugs. When bevacizumab can be added to chemotherapy, progression-free survival improves significantly. For patients with a BRCA mutation, PARP inhibitor monotherapy is an option compared to chemotherapy. There is currently no clearly identified role for immune-checkpoint inhibition in this patient population. This review describes some of the challenges in treating patients with platinum resistance and suggests refinements in the selection of patients most likely to benefit from targeting a DNA damage response, angiogenesis or immune modulation. It also describes novel agents of interest and possible mechanisms of the synergy of therapeutic combinations.

The Genetic and Molecular Analyses of RAD51C and RAD51D Identifies Rare Variants Implicated in Hereditary Ovarian Cancer from a Genetically Unique Population

To identify candidate variants in RAD51C and RAD51D ovarian cancer (OC) predisposing genes by investigating French Canadians (FC) exhibiting unique genetic architecture. Candidates were identified by whole exome sequencing analysis of 17 OC families and 53 early-onset OC cases. Carrier frequencies were determined by the genetic analysis of 100 OC or HBOC families, 438 sporadic OC cases and 1025 controls. Variants of unknown function were assayed for their biological impact and/or cellular sensitivity to olaparib. RAD51C c.414G>C;p.Leu138Phe and c.705G>T;p.Lys235Asn and RAD51D c.137C>G;p.Ser46Cys, c.620C>T;p.Ser207Leu and c.694C>T;p.Arg232Ter were identified in 17.6% of families and 11.3% of early-onset cases. The highest carrier frequency was observed in OC families (1/44, 2.3%) and sporadic cases (15/438, 3.4%) harbouring RAD51D c.620C>T versus controls (1/1025, 0.1%). Carriers of c.620C>T (n = 7), c.705G>T (n = 2) and c.137C>G (n = 1) were identified in another 538 FC OC cases. RAD51C c.705G>T affected splicing by skipping exon four, while RAD51D p.Ser46Cys affected protein stability and conferred olaparib sensitivity. Genetic and functional assays implicate RAD51C c.705G>T and RAD51D c.137C>G as likely pathogenic variants in OC. The high carrier frequency of RAD51D c.620C>T in FC OC cases validates previous findings. Our findings further support the role of RAD51C and RAD51D in hereditary OC.

Advances and challenges in cancer treatment and nutraceutical prevention: the possible role of dietary phenols in BRCA regulation

Over the years, the attention towards the role of phytochemicals in dietary natural products in reducing the risk of developing cancer is rising. Cancer is the second primary cause of mortality worldwide. The current therapeutic options for cancer treatment are surgical excision, immunotherapy, chemotherapy, and radiotherapy. Unfortunately, in case of metastases or chemoresistance, the treatment options become very limited. Despite the advances in medical and pharmaceutical sciences, the impact of available treatments on survival is not satisfactory. Recently, natural products are a great deal of interest as potential anti-cancer agents. Among them, phenolic compounds have gained a great deal of interest, thanks to their anti-cancer activity. The present review focuses on the suppression of cancer by targeting BRCA gene expression using dietary polyphenols, as well as the clinical aspects of polyphenolic agents in cancer therapy. They regulate specific key processes involved in cancer progression and modulate the expression of oncogenic proteins, like p27, p21, and p53, which may lead to apoptosis, cell cycle arrest, inhibition of cell proliferation, and, consequently, cancer suppression. Thus, one of the mechanisms underlying the anti-cancer activity of phenolics involves the regulation of tumor suppressor genes. Among them, the BRCA genes, with the two forms (BRCA-1 and BRCA-2), play a pivotal role in cancer protection and prevention. BRCA germline mutations are associated with an increased risk of developing several types of cancers, including ovarian, breast, and prostate cancers. BRCA genes also play a key role in the sensitivity and response of cancer cells to specific pharmacological treatments. As the importance of BRCA-1 and BRCA-2 in reducing cancer invasiveness, repairing DNA damages, oncosoppression, and cell cycle checkpoint, their regulation by natural molecules has been examined.

Therapeutic benefits of niraparib tosylate as radio sensitizer in esophageal squamous cell carcinoma: an in vivo and in vitro preclinical study

PURPOSE

Esophageal squamous cell carcinoma is associated with high morbidity and mortality rate for which radiotherapy is the main treatment modality. Niraparib, a Poly (ADP-ribose) polymerase 1 inhibitors (PARPi) was previously reported to confer radiosensitivity in different malignancies including non-small cell lung cancer. In this study, we assessed the in vivo ability of niraparib in conferring radiosensitivity to esophageal squamous cell carcinoma cells.

MATERIALS AND METHODS

In this study, KYSE-30 and KYSE-150 cell lines were selected as in vivo esophageal squamous cell carcinoma models. The experimental groups were: niraparib tosylate alone, radiotherapy alone, control (no intervention), and combination therapy (radiotherapy + niraparib tosylate). Cell cytotoxicity assay, colony formation assay, flow cytometry, immunofluorescence, Western blotting, immunohistochemistry, lentivirus transfection analysis, and xenograft models were used for confirming radiosensitizing ability of niraparib and to investigate the possible cellular mechanism involved in radiosensitization.

RESULTS

The colony formation efficiency of the combination group was significantly much lower than that of the single radiation group (P < 0.01). Cell cytotoxicity assay demonstrated a significant reduction in proliferation of irradiated cells after treatment with niraparib tosylate compared to niraparib tosylate alone (P < 0.01). Cell apoptosis significantly increased in the combination group compared to either niraparib tosylate or radiotherapy alone (P < 0.01). Rate of tumor suppression rate was significantly high in the combined treatment group (P < 0.01) but, significantly decreased in nude mice. Western blot and lentivirus infection model suggested overexpression of FANCG genes to confer radiosensitivity.

CONCLUSION

These results suggest that the synergistic effect of niraparib tosylate and radiation may be related to the down-regulation of FANCG.

Assessing cognitive toxicity in early phase trials - What are we missing?

OBJECTIVES

Novel therapies, such as, small protein molecule inhibitors and immunotherapies are first tested clinically in Phase I trials. Moving on to later phase trials and ultimately standard practice. A key aim of these early clinical trials is to define a toxicity profile; however, the emphasis is often on safety. The concern is cognitive toxicity is poorly studied in this context and may be under-reported. The aim of this review is to map evidence of cognitive assessment, toxicity, and confounding factors within reports from Phase I trials and consider putative mechanisms of impairment aligned with mechanisms of novel therapies.

METHODS

A scoping review methodology was applied to the search of databases, including Embase, MEDLINE, Clinicaltrials.gov. A [keyword search was conducted, results screened for duplication then inclusion/exclusion criteria applied. Articles were further screened for relevance; data organised into categories and charted in a tabular format]. Evidence was collated and summarised into a narrative synthesis.

RESULTS

Despite the availability of robust ways to assess cognitive function, these are not routinely included in the conduct of early clinical trials. Reports of cognitive toxicity in early Phase I trials are limited and available evidence on this shows that a proportion of patients experience impaired cognitive function over the course of participating in a Phase I trial. Links are identified between the targeted action of some novel therapies and putative mechanisms of cognitive impairment.

CONCLUSION

The review provides rationale for research investigating cognitive function in this context. A study exploring the cognitive function of patients on Phase I trials and the feasibility of formally assessing this within early clinical trials is currently underway at the Royal Marsden.

Targeting of RecQ Helicases as a Novel Therapeutic Strategy for Ovarian Cancer

RecQ helicases are essential for DNA replication, recombination, DNA damage repair, and other nucleic acid metabolic pathways required for normal cell growth, survival, and genome stability. More recently, RecQ helicases have been shown to be important for replication fork stabilization, one of the major mechanisms of PARP inhibitor resistance. Cancer cells often have upregulated helicases and depend on these enzymes to repair rapid growth-promoted DNA lesions. Several studies are now evaluating the use of RecQ helicases as potential biomarkers of breast and gynecologic cancers. Furthermore, RecQ helicases have attracted interest as possible targets for cancer treatment. In this review, we discuss the characteristics of RecQ helicases and their interacting partners that may be utilized for effective treatment strategies (as cancers depend on helicases for survival). We also discuss how targeting helicase in combination with DNA repair inhibitors (i.e., PARP and ATR inhibitors) can be used as novel approaches for cancer treatment to increase sensitivity to current treatment to prevent rise of treatment resistance.

An update on the safety of olaparib for treating ovarian cancer

INTRODUCTION

PARP inhibitors have dramatically improved outcomes for ovarian cancer patients, transforming oncologists' armamentarium and fueling hope for more cures and longer survival.

AREAS COVERED

The recent PARP inhibitor randomized trials of FDA approved PARP inhibitors for ovarian cancer, olaparib, rucaparib and niraparib, and implications for clinical care are discussed with a focus on toxicity and risks. PARP adds NAD polymers to DNA-binding proteins, improving survival of cells after DNA damage, and acting as a scaffold for important DNA Damage Response (DDR) enzymes. If this system is inhibited, PARP activation cannot support DNA repair when there is synthetic lethality from BRCA mutations or homologous repair dysfunction (HRD), and the accumulation of DNA damage can kill cancer and lead to the catastrophic complications of MDS/AML. Although the risk of AML can be a <1% risk, the incidence of MDS/AML presently approaches 10% in patients with BRCA mutations, multiple prior lines of platinum therapy, and protracted exposure to PARP inhibitors.

EXPERT OPINION

PARP inhibitors are a well-tolerated and exciting new class of agents that improve survival despite the risk of AML. Understanding of the biology has led to optimal use and potential new strategies for overcoming PARP resistance.

Toward More Comprehensive Homologous Recombination Deficiency Assays in Ovarian Cancer Part 2: Medical Perspectives

Simple Summary

High-grade serous ovarian cancer (HGSOC—the most frequent and aggressive form of ovarian cancer) represents an important challenge for clinicians. Half of HGSOC cases exhibit homologous recombination deficiency (HRD), mainly through alterations in BRCA1 and BRCA2. This leads to sensitivity to PARP inhibitors, a novel class of breakthrough molecules that improved HGSOC prognoses. To date, three companion diagnostic assays have received FDA approval for the evaluation of HRD status, but their use remains controversial. In this companion review (Part 1: Technical considerations; Part 2: Medical perspectives), we develop an integrative perspective, from translational research to clinical application, that could help physicians and researchers manage HGSOC.

Abstract

High-grade serous ovarian cancer (HGSOC) is the most frequent and aggressive form of ovarian cancer, representing an important challenge for clinicians. Half of HGSOC cases have homologous recombination deficiency (HRD), which has specific causes (mainly alterations in BRCA1/2, but also other alterations encompassed by the BRCAness concept) and consequences, both at molecular (e.g., genomic instability) and clinical (e.g., sensitivity to PARP inhibitor) levels. Based on its prevalence and clinical impact, HRD status merits investigation. To date, three PARP inhibitors have received FDA/EMA approval. For some approvals, the presence of specific molecular alterations is required. Three companion diagnostic (CDx) assays based on distinct technical and medical considerations have received FDA approval to date. However, their use remains controversial due to their technical and medical limitations. In this companion and integrated review, we take a “bench-to-bedside” perspective on HRD definition and evaluation in the context of HGSOC. Part 1 of the review adopts a molecular perspective regarding technical considerations and the development of CDx. Part 2 focuses on the clinical impact of HRD evaluation, primarily through currently validated CDx and prescription of PARP inhibitors, outlining achievements, limitations and medical perspectives.