Veliparib and topotecan for patients with platinum-resistant or partially platinum-sensitive relapse of epithelial ovarian cancer with BRCA negative or unknown BRCA status

An Overview of PARP Resistance in Ovarian Cancer from a Molecular and Clinical Perspective

Epithelial ovarian cancer (EOC), a primarily high-grade serous carcinoma (HGSOC), is one of the major causes of high death-to-incidence ratios of all gynecological cancers. Cytoreductive surgery and platinum-based chemotherapy represent the main treatments for this aggressive disease. Molecular characterization of HGSOC has revealed that up to 50% of cases have a deficiency in the homologous recombination repair (HRR) system, which makes these tumors sensitive to poly ADP-ribose inhibitors (PARP-is). However, drug resistance often occurs and overcoming it represents a big challenge. A number of strategies are under investigation, with the most promising being combinations of PARP-is with antiangiogenetic agents and immune checkpoint inhibitors. Moreover, new drugs targeting different pathways, including the ATR-CHK1-WEE1, the PI3K-AKT and the RAS/RAF/MEK, are under development both in phase I and II-III clinical trials. Nevertheless, there is still a long way to go, and the next few years promise to be exciting.

Combined inhibition of BADSer99 phosphorylation and PARP ablates models of recurrent ovarian carcinoma

Background

Poly (ADP-ribose) polymerase inhibitors (PARPis) have been approved for the treatment of recurrent epithelial ovarian cancer (EOC), regardless of BRCA status or homologous recombination repair deficiency. However, the low response of platinum-resistant EOC, the emergence of resistance in BRCA-deficient cancer, and therapy-associated toxicities in patients limit the clinical utility of PARPis in recurrent EOC.

Methods

The association of phosphorylated (p) BADS99 with clinicopathological parameters and survival outcomes in an EOC cohort was assessed by immunohistochemistry. The therapeutic synergy, and mechanisms thereof, between a pBADS99 inhibitor and PARPis in EOC was determined in vitro and in vivo using cell line and patient-derived models.

Results

A positive correlation between pBADS99 in EOC with higher disease stage and poorer survival is observed. Increased pBADS99 in EOC cells is significantly associated with BRCA-deficiency and decreased Cisplatin or Olaparib sensitivity. Pharmacological inhibition of pBADS99 synergizes with PARPis to enhance PARPi IC₅₀ and decreases survival, foci formation, and growth in ex vivo culture of EOC cells and patient-derived organoids (PDOs). Combined inhibition of pBADS99 and PARP in EOC cells or PDOs enhances DNA damage but impairs PARPi stimulated DNA repair with a consequent increase in apoptosis. Inhibition of BADS99 phosphorylation synergizes with Olaparib to suppress the xenograft growth of platinum-sensitive and resistant EOC. Combined pBADS99-PARP inhibition produces a complete response in a PDX derived from a patient with metastatic and chemoresistant EOC.

Conclusions

A rational and efficacious combination strategy involving combined inhibition of pBADS99 and PARP for the treatment of recurrent EOC is presented.

Ovarian cancer is difficult to successfully treat because it often recurs as the cancer becomes resistant to drugs used to treat it. As such, new drugs or combinations of drugs are needed to treat patients with recurrent ovarian cancer. Here, a drug combination is reported that is effective in experimental models of ovarian cancer, including those derived from patients. The combination approach uses drugs that have previously been approved for use in patients, known as PARP inhibitors, and another drug to inhibit cancer cell survival by targeting activation of a specific protein involved in cancer cell survival. The net effect of this drug combination in ovarian cancer models is greater than the sum of the drugs used individually. With further testing, this combination may offer a potential strategy to treat patients with recurrent ovarian cancer.

Zhang et al. test the therapeutic potential of an inhibitor of BAD phosphorylation, NPB, in epithelial ovarian cancer. The authors show that the small molecule synergises with PARP inhibition to kill patient-derived ovarian cancer organoids and suppress the growth of xenograft tumours, including a cisplatin-resistant model.

Veliparib for the treatment of solid malignancies

OBJECTIVE

Veliparib is a poly adenosine diphosphate ribose polymerase (PARP) -1 and -2 inhibitor with chemo-sensitizing and anticancer activities that has shown promising results in early-phase trials. The aim of this comprehensive review is to summarise the profile of veliparib and to provide an overview of its early clinical investigations.

DATA SOURCES

Details of all the completed trials evaluating the profile of veliparib were identified from ClinicalTrials.gov with the relevant keywords. Furthermore, databases such as Google Scholar and PubMed were searched using the National Clinical Trial (NCT) number to retrieve publications of results not listed in the trial registry.

DATA SUMMARY

A total of 25 completed clinical trials indicating the use of veliparib in solid malignancies were identified. The results showed that veliparib is well tolerated, both as a single agent and in combination with standard chemotherapy doses. Being a broad-spectrum potentiator of DNA-damaging agents and radiation, it has shown to improve the clinical outcomes, particularly in solid tumors like ovarian cancer, breast cancer and lung cancer.

CONCLUSIONS

The results from clinical trials indicate that veliparib can be an excellent therapeutic strategy for BRCA mutation associated cancers and tumors bearing deficiencies in the HR pathway as well. Further studies establishing the dosing, sequence of therapy, extended use and compatibility with various anti-cancer drugs are warranted to define its exact role in cancer therapy.

Perspectives on PARP Inhibitor Combinations for Ovarian Cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors constitute an important treatment option for ovarian cancer nowadays. The magnitude of benefit from PARP inhibitors is influenced by the homologous recombination status, with greater benefit observed in patients with BRCA mutated or BRCA wild-type homologous recombination deficient (HRD) tumors. Although some PARP inhibitor activity has been shown in homologous recombination proficient (HRP) ovarian tumors, its clinical relevance as a single agent is unsatisfactory in this population. Furthermore, even HRD tumors present primary or secondary resistance to PARP inhibitors. Strategies to overcome treatment resistance, as well as to enhance PARP inhibitors' efficacy in HRP tumors, are highly warranted. Diverse combinations are being studied with this aim, including combinations with antiangiogenics, immunotherapy, and other targeted therapies. This review discusses the rationale for developing therapy combinations with PARP inhibitors, the current knowledge, and the future perspectives on this issue.

The evolving role of PARP inhibitors in advanced ovarian cancer

The field of ovarian cancer has been revolutionized with the use of poly (ADP-ribose) polymerase (PARP) inhibitors, which present greater inhibition effect in epithelial subtype due to high rates of homologous recombination deficiency. PARP inhibition exploits this cancer pitfall by disrupting DNA repair, leading to genomic instability and apoptosis. Three PARP inhibitors (olaparib, niraparib, and rucaparib) are now approved for use in women with epithelial ovarian cancer, while others are under development. Among women with BRCA1/2 mutations, maintenance PARP therapy has led to a nearly fourfold prolongation of PFS, while those without BRCA1/2 mutations experience an approximately twofold increase in PFS. Differences in trial design, patient selection and primary analysis population affect the conclusions on PARP inhibitors. Limited OS data have been published and there is also limited experience regarding long-term safety. With regard to toxicity profile, there are no differences in serious adverse events between the experimental and control groups. However, combining adverse event data from maintenance phases, a trend towards more events in the experimental group, compared with controls, has been shown. The mechanisms of PARP-inhibitor resistance include restoration of HR through reversion mutations in HR genes, leading to resumed HR function. Other mechanisms that sustain sufficient DNA repair are discussed as well. PARP inhibitors play a pivotal role in the management of ovarian cancer, affecting the future treatment choices. Defining exactly which patients will benefit from them is a challenge and the need for HRD testing to define ‘BRCA-ness’ will add additional costs to treatment.

Poly (ADP-ribose) polymerase (PARP) as target for the treatment of epithelial ovarian cancer: what to know

INTRODUCTION

Poly (ADP-ribose) polymerase (PARP) inhibitors are being developed in maintenance and recurrence treatment settings of epithelial ovarian cancers (EOCs) with BRCA 1-2 gene mutation. PARP inhibitors are the first example of drugs targeting the loss of a gene suppressor: they block base-excision repair in the cancer cells, which have lost homologous recombination due to BRCA-mutation, resulting in loss of DNA repair and cell death, also known as synthetic lethality.

AREAS COVERED

This article provides an overview of PARP inhibitors in OC treatment and also an extensive section on the combined strategies of PARP inhibitors, including approved as well as currently investigated drugs. It also offers a section on the use of predictive biomarkers for PARP inhibitors treatment. Ongoing trials, including novel combinations, are discussed.

EXPERT OPINION

In recent years, there is increasing evidence that PARP inhibitor therapy can have life-long percussion in the treatment of EOC, even if some questions have to be solved yet, such as its use in combination therapy, the possibility to retreat with a PARP inhibitor, and finally how to overcome a resistance mechanism to this therapy. In this way, PARP inhibitors can obtain an important role in making a personalized therapeutic program in the case of first-line, neoadjuvant, platinum-sensitive, and resistant high-grade serous OC treatment.

Development of new poly(ADP-ribose) polymerase (PARP) inhibitors in ovarian cancer: Quo Vadis?

Epithelial ovarian cancer (EOC) is the fifth leading cause of cancer mortality among women, potentially due to ineffectiveness of screening tests for early detection. Patients typically present with advanced disease at diagnosis, whereas, up to 80% relapse and the estimated median progression-free survival (PFS) is approximately 12–18 months. Increased knowledge on the molecular biology of EOC resulted in the development of several targeted therapies, including poly(ADP-ribose) polymerase (PARP) inhibitors. These agents have changed the therapeutic approach of the EOC and exploit homologous recombination (HR) deficiency through synthetic lethality, especially in breast cancer genes 1 and 2 (BRCA1/2) mutation carriers. Furthermore, BRCA wild-type patients with other defects in the HR repair pathway, or those with platinum-resistant tumors may obtain benefit from this treatment. While PARP inhibitors as a class display many similarities, several differences in structure can translate into differences in tolerability and antitumor activity. Currently, olaparib, rucaparib, and niraparib have been approved by Food and Drug Administration (FDA) and/or European Medicines Agency (EMA) for the treatment of EOC, while veliparib is in the late stage of clinical development. Finally, since October 2018 talazoparib is FDA and EMA approved for BRCA carriers with metastatic breast cancers. In this article, we explore the mechanisms of DNA repair, synthetic lethality, efficiency of PARP inhibition, and provide an overview of early and ongoing clinical investigations of the novel PARP inhibitors veliparib and talazoparib.

PARP inhibitors and epithelial ovarian cancer: Molecular mechanisms, clinical development and future prospective

Epithelial ovarian cancer (EOC) has a poor prognosis. Since the introduction of paclitaxel as antineoplastic agent >20 years ago, only a few phase III randomized trials have shown challenging data regarding different therapeutic options for facing its aggressive clinical course and granting active therapies to patients. Different studies have shown the utility of poly(ADP-ribose) polymerase (PARP) inhibitors in women with EOC with or without BRCA mutations, both germline and somatic. Three PARP inhibitors, olaparib, rucaparib and niraparib, have been recently approved by the Food and Drug Administration for clinical use in EOC patients, though with different clinical indications and profiles of toxicity, while two other molecules, veliparib and talazoparib, are still under clinical investigation. The aim of the present paper is to evaluate the current status of PARP inhibitors in terms of molecular activity, pharmacodynamic properties and clinical applications.

Veliparib in ovarian cancer: a new synthetically lethal therapeutic approach

Epithelial ovarian cancer (EOC) accounts for nearly 90% of all ovarian malignancies. The standard therapeutic strategy includes cytoreductive surgery and neo (adjuvant) platinum-based chemotherapy. Relapse of advanced high grade serous ovarian cancer (HGSOC) is related to the development of drug resistance. A defective DNA damage response is a defining hallmark of HGSOC. Poly (ADP-ribose) polymerase (PARP) inhibitors exploit this deficiency through synthetic lethality and have emerged as promising anticancer therapies, especially in breast cancer gene (BRCA1 or BRCA2) mutation carriers. Apart from inducing synthetic lethality, PARP inhibitors have also been shown to trap PARP1 and PARP2 on DNA, leading to PARP-DNA complexes. This "PARP trapping" potentiates synergism between PARP inhibition and both alkylating agents and platinum-based chemotherapy. However, there are remarkable differences in the ability of PARP inhibitors to trap PARP, based on the size and structure of each separate molecule. Since monotherapy with PARP inhibitors is unlikely to induce cancer cell death in BRCA-proficient tumors, the efficacy of PARP inhibitors could be potentially optimized when combined with DNA-damaging agents, or with molecular targeted agents that also impair mechanisms of DNA repair. Olaparib, rucaparib, and niraparib have all obtained US Food and Drug Administration (FDA) and/or European Medicines Agency (EMA) approval in ovarian cancer in different settings. Veliparib does not yet have an approved label; nevertheless, there are currently promising results available in preclinical and early clinical settings. This comprehensive review summarizes the mechanism of action of veliparib and provides an overview of its early and ongoing clinical investigations.

Choosing wisely: Selecting PARP inhibitor combinations to promote anti-tumor immune responses beyond BRCA mutations

PARP inhibitors have transformed the management of advanced high-grade serous ovarian cancer. Despite the overwhelming success of PARP inhibition, particularly in BRCA-mutated ovarian cancer, several limitations and unanswered questions remain. With PARP inhibitors now being used in earlier treatment settings, the issue of both de novo and acquired resistance mechanisms and appropriate post-PARP management are pressing concerns. In addition, the population appropriate to target with PARP inhibitors and their use in patients without BRCA mutations is controversial and evolving. In this review we will discuss exciting PARP combinations and biologic rationale for the development and selection of PARP inhibitor combinations.

Bioengineered adipose-derived stem cells for targeted enzyme-prodrug therapy of ovarian cancer intraperitoneal metastasis

The objective of this study was to develop a stem cell-based system for targeted suicide gene therapy of recurrent, metastatic, and unresectable ovarian cancer. Malignant cells were obtained from the ascites of a patient with advanced recurrent epithelial ovarian cancer (named OVASC-1). Cancer cells were characterized to determine the percentages of drug-resistant ALDH+ cells, MDR-1/ABCG2 overexpressing cells, and cancer stem-like cells. The sensitivity and resistance of the OVASC-1 cells and spheroids to the metabolites of three different enzyme/prodrug systems were assessed, and the most effective one was selected. Adipose-derived stem cells (ASCs) were genetically engineered to express recombinant secretory human carboxylesterase-2 and nanoluciferase genes for simultaneous disease therapy and quantitative imaging. Bioluminescent imaging, magnetic resonance imaging and immuno/histochemistry results show that the engineered ASCs actively targeted and localized at both tumor stroma and necrotic regions. This created the unique opportunity to deliver drugs to not only tumor supporting cells in the stroma, but also to cancer stem-like cells in necrotic/hypoxic regions. The statistical analysis of intraperitoneal OVASC-1 tumor burden and survival rates in mice shows that the administration of the bioengineered ASCs in combination with irinotecan prodrug in the designed sequence and timeline eradicated all intraperitoneal tumors and provided survival benefits. In contrast, treatment of the drug-resistant OVASC-1 tumors with cisplatin/paclitaxel (standard-of-care) did not have any statistically significant benefit. The histopathology and hematology results do not show any toxicity to major peritoneal organs. Our toxicity data in combination with efficacy outcomes delineate a nonsurgical and targeted stem cell-based approach to overcoming drug resistance in recurrent metastatic ovarian cancer.

Recent Advances in Use of Topoisomerase Inhibitors in Combination Cancer Therapy

Inhibitors targeting human topoisomerase I and topoisomerase II alpha have provided a useful chemotherapy option for the treatment of many patients suffering from a variety of cancers. While the treatment can be effective in many patient cases, use of these human topoisomerase inhibitors is limited by side-effects that can be severe. A strategy of employing the topoisomerase inhibitors in combination with other treatments can potentially sensitize the cancer to increase the therapeutic efficacy and reduce resistance or adverse side effects. The combination strategies reviewed here include inhibitors of DNA repair, epigenetic modifications, signaling modulators and immunotherapy. The ongoing investigations on cellular response to topoisomerase inhibitors and newly initiated clinical trials may lead to adoption of novel cancer therapy regimens that can effectively stop the proliferation of cancer cells while limiting the development of resistance.

Veliparib: a new therapeutic option in ovarian cancer?

The role of poly ADP ribose polymerase inhibitors in ovarian cancer is rapidly evolving. Three different poly ADP ribose polymerase inhibitors (olaparib, niraparib and rucaparib) have been already approved as maintenance after response to platinum-based chemotherapy; two of them (olaparib and rucaparib) also as single agents. Veliparib, a novel PARPI, showed promising results in preclinical and early clinical settings. The aim of this review is to discuss veliparib’s mechanisms of action, to provide a clinical update on its safety and activity in ovarian cancer, and to highlight future perspectives for its optimal use. Veliparib favorable toxicity profile encourages its use either as monotherapy or in combination. Its peculiar neuroprotective and radio-sensitizing effect warrant further investigation.

Current status and future prospects of PARP inhibitor clinical trials in ovarian cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors are a class of targeted agents for the treatment of solid tumors. Concurrent PARP inhibition in Breast Cancer Susceptibility Gene (BRCA)-mutated or homologous recombination-deficient tumor cells can induce “synthetic lethality”, which targets two DNA repair pathways and induces serious cytotoxicity to tumor cells without damaging normal cells. Currently, PARP inhibitors such as olaparib, rucaparib and niraparib, which improve progression-free survival, particularly in patients harboring BRCA mutations, are approved by the Food and Drug Administration (FDA) and European Medicine Agency (EMA) for the treatment of ovarian cancers. Based on the results of different clinical trials, the indications for these drugs are slightly different. PARP inhibitors have been studied both as single agents and in combination with chemotherapy, antiangiogenic agents, and ionizing radiation. This review summarizes the critical clinical trials of PARP inhibitors that have been completed, provides an overview of the ongoing trials, presents the confirmed conclusions and notes the issues that need to be addressed in future studies.

Predictors and Modulators of Synthetic Lethality: An Update on PARP Inhibitors and Personalized Medicine

Poly(ADP-ribose) polymerase (PARP) inhibitors have proven to be successful agents in inducing synthetic lethality in several malignancies. Several PARP inhibitors have reached clinical trial testing for treatment in different cancers, and, recently, Olaparib (AZD2281) has gained both United States Food and Drug Administration (USFDA) and the European Commission (EC) approval for use in BRCA-mutated advanced ovarian cancer treatment. The need to identify biomarkers, their interactions in DNA damage repair pathways, and their potential utility in identifying patients who are candidates for PARP inhibitor treatment is well recognized. In this review, we detail many of the biomarkers that have been investigated for their ability to predict both PARP inhibitor sensitivity and resistance in preclinical studies as well as the results of several clinical trials that have tested the safety and efficacy of different PARP inhibitor agents in BRCA and non-BRCA-mutated cancers.