Clinical efficacy of PARP inhibitors in breast cancer

BRCA1 and BRCA2 are key tumor suppressor genes that are essential for the homologous recombination DNA repair pathway. Loss of function mutations in these genes result in hereditary breast and ovarian cancer syndromes, which comprise approximately 5% of cases. BRCA1/2 mutations are associated with younger age of diagnosis and increased risk of recurrences. The concept of synthetic lethality led to the development of PARP inhibitors which cause cell cytotoxicity via the inhibition of PARP1, a key DNA repair protein, in cells with germline BRCA1/2 mutations. Although still poorly understood, the most well-acknowledged proposed mechanisms of action of PARP1 inhibition include the inhibition of single strand break repair, PARP trapping, and the upregulation of non-homologous end joining. Olaparib and talazoparib are PARP inhibitors that have been approved for the management of HER2-negative breast cancer in patients with germline BRCA1/2 mutations. This review article highlights the clinical efficacy of PARP inhibitors in patients with HER2-negative breast cancer in early and advanced settings.

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.

Expanding the Use of PARP Inhibitors as Monotherapy and in Combination in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, and is known to be associated with a poor prognosis and limited therapeutic options. Poly (ADP-ribose) polymerase inhibitors (PARPi) are targeted therapeutics that have demonstrated efficacy as monotherapy in metastatic BRCA-mutant (BRCAMUT) TNBC patients. Improved efficacy of PARPi has been demonstrated in BRCAMUT breast cancer patients who have either received fewer lines of chemotherapy or in chemotherapy-naïve patients in the metastatic, adjuvant, and neoadjuvant settings. Moreover, recent trials in smaller cohorts have identified anti-tumor activity of PARPi in TNBC patients, regardless of BRCA-mutation status. While there have been concerns regarding the efficacy and toxicity of the use of PARPi in combination with chemotherapy, these challenges can be mitigated with careful attention to PARPi dosing strategies. To better identify a patient subpopulation that will best respond to PARPi, several genomic biomarkers of homologous recombination deficiency have been tested. However, gene expression signatures associated with PARPi response can integrate different pathways in addition to homologous recombination deficiency and can be implemented in the clinic more readily. Taken together, PARPi have great potential for use in TNBC patients beyond BRCAMUT status, both as a single-agent and in combination.

Perspectives on PARP inhibitors as pharmacotherapeutic strategies for breast cancer

Introduction Approximately 10% of all breast cancer cases occur in individuals who have germline pathogenic variants of the BRCA 1, BRCA 2, and other genes associated with impaired DNA damage repair that is associated with an increased risk of breast, ovarian, and other cancers. Inhibitors of poly-ADP ribose polymerase (PARP) induce synthetic lethality in cancer cells harboring such pathogenic variants.Area covered In this review, the authors review the mechanisms of action, antitumor activity, and adverse events associated with PARP inhibitors for the treatment of advanced breast cancer. The authors then summarize the area and provide their expert perspectives on the area.Expert opinion Two PARP inhibitors are approved in metastatic breast cancer, including olaparib and talozaparib. Both agents were approved based on phase III trials demonstrating that they were associated with improved progression-free survival compared with treatment of physician's choice in patients receiving second-third line therapy for locally advanced, inoperable, or metastatic breast cancer in patients with germline pathogenic BRCA 1 or BRCA2 variants.

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.

Innovations in targeted therapies for triple negative breast cancer

PURPOSE OF REVIEW

Triple negative breast cancer (TNBC) is defined by a lack of targets, namely hormone receptor (HR) expression and human epidermal growth factor receptor 2 amplification. Cytotoxic chemotherapy remains the mainstay of treatment. Though TNBC constitutes approximately 10-15% of breast cancer, it is disproportionally lethal, but it is hoped that outcomes will improve as targetable oncogenic drivers are identified.

RECENT FINDINGS

Translational work in TNBC has focused on subsets defined by defects in homologous recombination repair, immune cell infiltration, or programmed death ligand receptor 1 expression, an over-active phosphoinositide-3 kinase pathway, or expression of androgen receptors. Though not specific to TNBC, the novel cell surface antigen trophoblast antigen 2 has also been identified and successfully targeted. This work has led to Food and Drug Administration approvals for small molecule poly-ADP-ribosyl polymerase inhibitors in patients with deleterious germline mutations in BRCA1 or BRCA2, the combination of nab-paclitaxel with immune checkpoint inhibitor antibodies in the first-line metastatic setting for programmed death ligand receptor 1+ TNBC, and use of the antibody-drug conjugate sacituzumab govitecan in the later-line metastatic setting.

SUMMARY

Identification of targetable oncogenic drivers in TNBC is an area of intense cancer biology research, hopefully translating to new therapies and improved outcomes.

Poly(ADP-ribose) polymerase inhibition in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with limited treatment options. Recently, the poly(ADP-ribose) polymerase inhibitor (PARPi) olaparib has been approved for maintenance therapy after successful platinum-based chemotherapy in patients with germline mutations in BRCA1 and BRCA2. Approval was based on the POLO study that has shown a significant improvement in progression-free survival for patients with metastatic PDAC after at least 4 months of platinum-based chemotherapy. Hopefully, this first biomarker-directed targeted therapy for a relevant subgroup of pancreatic cancer patients is only the beginning of an era of personalized therapy for pancreatic cancer. The potential role for PARPi in improving survival in patients with pancreatic cancer containing somatic tumor mutations has yet to be established. Multiple studies investigating whether PARPi therapy might benefit a larger group of pancreatic cancer patients with homologous recombination repair deficiency and whether combinations with chemotherapy, immunotherapy, or small molecules can improve efficacy are currently underway. We here review the molecular basis for PARPi therapy in PDAC patients and recent developments in clinical studies.

Poly (ADP-ribose) Polymerase Inhibition in Patients with Breast Cancer and BRCA 1 and 2 Mutations

The poly-(ADP-ribose) polymerase (PARP) inhibitors olaparib and talazoparib, have recently been approved for use in patients with metastatic breast cancer (BC) and germline BRCA 1 or 2 mutations due to improved progression-free survival compared to chemotherapy. An increasing number of clinical trials are evaluating the role of PARP inhibitors (PARPi) in BC, alone and in combination with other therapies (including immunotherapy), as well as in earlier stages of the disease. This review describes the unique mechanism of action of these drugs and puts into clinical context the results of pivotal clinical trials. We also discuss the future development of PARPi in BC, their potential combination with other strategies, including chemotherapy and immune-checkpoint inhibitors, and the impact of these treatments in current genetic counselling.

First-in-human study of the PARP/tankyrase inhibitor E7449 in patients with advanced solid tumours and evaluation of a novel drug-response predictor

Background

This phase 1 study examined the safety, maximum-tolerated dose (MTD) and antitumour activity of E7449, a novel PARP 1/2 and tankyrase 1/2 inhibitor.

Methods

E7449 was orally administered once daily in 28-day cycles to patients with advanced solid tumours (50–800-mg doses). Archival tumour samples from consenting patients were evaluated for the expression of 414 genes in a biomarker panel (2X-121 drug-response predictor [DRP]) found to be predictive of the response to E7449 in cell lines.

Results

Forty-one patients were enrolled (13 pancreatic, 5 ovarian, 4 each with breast, lung or colorectal cancer and 11 with other tumour types). The most common grade ≥3 treatment-related adverse event was fatigue (n = 7, 17.1%). Five patients experienced a dose-limiting toxicity (fatigue, n = 4, 800 mg; anaphylaxis, n = 1, 600 mg) for an MTD of 600 mg. E7449 exhibited antitumour activity in solid tumours, including 2 partial responses (PRs), and stable disease (SD) in 13 patients, which was durable (>23 weeks) for 8 patients. In 13 patients, the 2X-121 DRP identified those achieving PR and durable SD. E7449 showed good tolerability, promising antitumour activity and significant concentration-dependent PARP inhibition following 50–800-mg oral dosing.

Conclusion

The results support further clinical investigation of E7449 and its associated biomarker 2X-121 DRP.

Clinical trial registration

www.ClinicalTrials.gov code: NCT01618136.

The evolving management of metastatic triple negative breast cancer

Advanced triple negative breast cancer (TNBC) is an incurable disease classified by its lack of expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2. Due to its lack of therapeutic targets, it has historically been treated with single agent chemotherapy, with combination cytotoxic therapy typically reserved for patients with high disease burdens, symptomatic disease, and/or impending visceral crisis. Recent molecular analyses have revealed that this clinical group of TNBCs is in fact quite biologically heterogeneous, with multiple TNBC subtypes defined by distinct biology and clinical behavior. Building on this biology, 2 targeted strategies are now approved for selected patients with advanced TNBC: the poly (ADP-ribose) polymerase inhibitors for advanced TNBC with a germline mutation in BRCA1/2, and the combination of the programmed death ligand 1-specific antibody atezolizumab with nab-paclitaxel for advanced TNBC that expresses programmed death ligand 1 on immune cells within the tumor. These targeted agents tend to be associated with a more favorable side effect profile and longer disease control than standard chemotherapy. A number of other targeted therapies have shown promise in early clinical trials, and several are now in definitive phase 3 testing for advanced TNBC. These include the antiapoptotic kinase inhibitors ipatisertib and capivasertib, and the antibody-drug conjugate sacituzumab govitecan-hziy. Approved biomarker-driven treatment options for this disease are thus likely to expand in the near-term. Here we review current treatment options and emerging targeted therapies for advanced TNBC. For patients who do not meet criteria for approved targeted therapies, participation in clinical trials evaluating precision medicines with candidate predictive biomarkers in advanced TNBC should be encouraged.

Phase I Pharmacokinetic Study of Niraparib in Chinese Patients with Epithelial Ovarian Cancer

LESSONS LEARNED

Pharmacokinetics characteristics of niraparib in Chinese patients were similar to those in white patients. Niraparib could be well tolerated by Chinese patients, and adverse events were manageable in this study. Population pharmacokinetics analysis indicated that baseline body weight had a modest impact on pharmacokinetics parameters of niraparib; however, it was not considered clinically important.

BACKGROUND

This randomized, open-label, single-arm, phase I study was designed to investigate the pharmacokinetics (PK) and safety of niraparib in Chinese patients with epithelial ovarian cancer.

METHODS

Eligible patients were randomized in a 1:1:1 ratio to receive 100, 200, or 300 mg of niraparib once daily. PK parameters were analyzed after single and multiple dose administrations.

RESULTS

Thirty-six Chinese patients were enrolled in total. Niraparib was rapidly absorbed after administration, and median time-to-peak (Tmax ) was 3 hours. The long terminal elimination half-life (T1/2 ∼ 35 hours) supports once-daily dosing regimen. The exposure to niraparib showed linear and dose-proportional pharmacokinetics, whereas other PK parameters such as Tmax , T1/2 , and accumulation ratio were dose independent. Population PK analysis indicated that there was no effect of race on niraparib PK parameters, whereas baseline body weight had a modest impact on niraparib exposure. Grade 3/4 treatment-emergent adverse events (TEAEs; reported in ≥10% of patients) included platelet count decreased (a total of five patients who were all from the 300-mg group) and neutrophil count decreased. The TEAEs were manageable after dose modification.

CONCLUSION

The PK profile of niraparib in Chinese patients is consistent with that in white patients. Niraparib is safe and well tolerated in Chinese patients with ovarian cancer.

Targeted Therapies for Triple-Negative Breast Cancer

OPINION STATEMENT

Triple-negative breast cancer (TNBC) is a particularly aggressive subtype of breast cancer. TNBC is a heterogenous subtype of breast cancer that is beginning to be refined by its molecular characteristics and clinical response to a targeted therapeutic approach. Until recently the backbone of therapy against TNBC has been cytotoxic chemotherapy. However, the breast oncology community is now seeing encouraging clinical activity from molecularly targeted approaches to TNBC. Recently, we have seen 3 newly approved targeted therapies for TNBC, including the PARP inhibitors olaparib and talazoparib for germline BRCA mutation associated breast cancer (gBRCAm-BC) and most recently the checkpoint inhibitor, atezolizumab in combination with nab-paclitaxel for programmed death-ligand 1 (PD-L1+) advanced TNBC. Improved biomarkers are needed to inform better patient selection for treatment with checkpoint inhibition. Higher response rates are seen when checkpoint inhibitors are combined with chemotherapy in the first-line setting and the use of these agents at an earlier stage of the disease does show promise. Antibody-drug conjugates are generating much excitement and may allow re-examination of prior cytotoxics that failed in development due to toxicity. Tumor sequencing is identifying potential molecular targets and ongoing studies are evaluating novel small molecule agents in this field such as AKT inhibition and many others. The treatment paradigm of chemotherapy as "one size fits all" approach for management of TNBC is changing based on molecular subtyping. Soon, the term TNBC may no longer be appropriate, as this heterogenous subtype of breast cancer is further refined by its molecular characteristics and clinical response to a targeted therapeutic approach.

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.

Advances in Targeted Therapies for Triple-Negative Breast Cancer

While the outcomes for patients diagnosed with hormone receptor positive (HR+) and/or human epidermal growth factor receptor 2-positive (HER2+) breast cancers have continued to improve with the development of targeted therapies, the same cannot be said yet for those affected with triple-negative breast cancer (TNBC). Currently, the mainstay of treatment for the 10-15% of patients diagnosed with TNBC remains cytotoxic chemotherapy, but it is hoped that through an enhanced characterization of TNBC biology, this disease will be molecularly delineated into subgroups with targetable oncogenic drivers. This review will focus on recent therapeutic innovations for TNBC, including poly-ADP-ribosyl polymerase (PARP) inhibitors, phosphoinositide 3-kinase (PI3K) pathway inhibitors, immune checkpoint inhibitors, and cyclin-dependent kinase (CDK) inhibitors.

Druggable Molecular Targets for the Treatment of Triple Negative Breast Cancer

Breast cancer (BC) is still the most common cancer among women worldwide. Amongst the subtypes of BC, triple negative breast cancer (TNBC) is characterized by deficient expression of estrogen, progesterone, and human epidermal growth factor receptor 2 receptors. These patients are therefore not given the option of targeted therapy and have worse prognosis as a result. Consequently, much research has been devoted to identifying specific molecular targets that can be utilized for targeted cancer therapy, thereby limiting the progression and metastasis of this invasive tumor, and improving patient outcomes. In this review, we have focused on the molecular targets in TNBC, categorizing these into targets within the immune system such as immune checkpoint modulators, intra-nuclear targets, intracellular targets, and cell surface targets. The aim of this review is to introduce and summarize the known targets and drugs under investigation in phase II or III clinical trials, while introducing additional possible targets for future drug development. This review brings a tangible benefit to cancer researchers who seek a comprehensive comparison of TNBC treatment options.

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.

PARP Inhibitors in Ovarian Cancer: The Route to "Ithaca"

Poly (ADP-ribose) polymerase (PARP) inhibitors are a novel class of therapeutic agents that target tumors with deficiencies in the homologous recombination DNA repair pathway. Genomic instability characterizes high-grade serous ovarian cancer (HGSOC), with one half of all tumors displaying defects in the important DNA repair pathway of homologous recombination. Early studies have shown significant efficacy for PARP inhibitors in patients with germline breast related cancer antigens 1 and 2 (BRCA1/2) mutations. It has also become evident that BRCA wild-type patients with other defects in the homologous recombination repair pathway benefit from this treatment. Companion homologous recombination deficiency (HRD) scores are being developed to guide the selection of patients that are most likely to benefit from PARP inhibition. The choice of which PARP inhibitor is mainly based upon the number of prior therapies and the presence of a BRCA mutation or HRD. The identification of patients most likely to benefit from PARP inhibitor therapy in view of HRD and other biomarker assessments is still challenging. The aim of this review is to describe the current evidence for PARP inhibitors in ovarian cancer, their mechanism of action, and the outstanding issues, including the rate of long-term toxicities and the evolution of resistance.

Advances in the use of PARP inhibitors for BRCA1/2-associated breast cancer: talazoparib

Poly-ADP-ribosyl polymerase (PARP) enzymes PARP-1 and PARP-2 recognize DNA damage and set off a cascade of cellular mechanisms required for multiple types of DNA damage repair. PARP inhibitors are small molecule mimetics of nicotinamide which bind to PARP’s catalytic domain to inhibit poly-ADP-ribosylation (PARylation) of target proteins, including PARP-1 itself. PARP inhibitors olaparib, veliparib, talazoparib, niraparib and rucaparib have predominantly been studied in women with breast or ovarian cancers associated with deleterious germline mutations in BRCA1 and BRCA2 (gBRCA1/2+). The BRCA1 and BRCA2 proteins are involved in DNA repair by homologous recombination. This review will focus on talazoparib, a PARP inhibitor approved by the US FDA for the treatment of metastatic gBRCA1/2+ breast cancers in October 2018.

Emerging Novel Therapeutics in Triple-Negative Breast Cancer

The mortality from breast cancer has steadily decreased due in part to early detection and advances in therapy. The treatment options for breast cancer vary considerably depending on the histological subtype. There are a number of very effective targeted therapies available for estrogen receptor-positive disease and for human epidermal growth factor receptor 2-positive disease. However, triple-negative breast cancer is a particularly aggressive subtype. This subtype represents an unmet need for improved therapies. TNBC is a heterogenous subtype of breast cancer that is beginning to be refined by its molecular characteristics and clinical response to a targeted therapeutic approach. Here we review the recent advances in the treatment of TNBC with emphasis on the many emerging novel targeted therapies.

PARP1 Trapping by PARP Inhibitors Drives Cytotoxicity in Both Cancer Cells and Healthy Bone Marrow

PARP inhibitors have recently been approved as monotherapies for the treatment of recurrent ovarian cancer and metastatic BRCA-associated breast cancer, and ongoing studies are exploring additional indications and combinations with other agents. PARP inhibitors trap PARP onto damaged chromatin when combined with temozolomide and methyl methanesulfonate, but the clinical relevance of these findings remains unknown. PARP trapping has thus far been undetectable in cancer cells treated with PARP inhibitors alone. Here, we evaluate the contribution of PARP trapping to the tolerability and efficacy of PARP inhibitors in the monotherapy setting. We developed a novel implementation of the proximity ligation assay to detect chromatin-trapped PARP1 at single-cell resolution with higher sensitivity and throughput than previously reported methods. We further demonstrate that the PARP inhibitor-induced trapping appears to drive single-agent cytotoxicity in healthy human bone marrow, indicating that the toxicity of trapped PARP complexes is not restricted to cancer cells with homologous recombination deficiency. Finally, we show that PARP inhibitors with dramatically different trapping potencies exhibit comparable tumor growth inhibition at MTDs in a xenograft model of BRCA1-mutant triple-negative breast cancer. These results are consistent with emerging clinical data and suggest that the inverse relationship between trapping potency and tolerability may limit the potential therapeutic advantage of potent trapping activity. IMPLICATIONS: PARP trapping contributes to single-agent cytotoxicity of PARP inhibitors in both cancer cells and healthy bone marrow, and the therapeutic advantage of potent trapping activity appears to be limited.

[DNA damage repair: An emerging strategy in metastatic prostate cancer]

Genetic instability is one part of the oncogenic process. Gene mutations involved in DNA repair mechanisms can promote this genetic instability and participate in oncogenesis and metastatic progression. In prostate cancer, DNA repair abnormalities mainly correspond to somatic or constitutional mutations of the BRCA2 and ATM genes. Therapeutic management of metastatic castration-resistant prostate cancer (mCRPC) is currently based on new hormonal therapies (abiraterone, enzalutamide) and taxane-type chemotherapy (docetaxel or cabazitaxel). Preliminary data tend to indicate a specific activity of agents causing DNA breaks (platinum salts) and PARP inhibitors in patients with these DNA repair abnormalities. The frequency of DNA repair gene mutations in patients with prostate cancer (around 20%) and the antitumor response of PARP inhibitors make it a possible short-term therapeutic strategy with several registering clinical trials ongoing.

Emerging therapeutic modalities of PARP inhibitors in breast cancer

Inhibition of Poly (ADP-ribose) polymerase (PARP) has shown marked benefit for breast cancer with homologous recombination deficiency, whether driven by defects in BRCA1, BRCA2, or other pathway components. Since the initial approval of olaparib, a mostly investigated PARP inhibitor (PARPi), the clinical development of PARPi in breast cancer treatment has been a major emphasis. Researches in investigating platinum-PARPi combination use compared with platinum monotherapy demonstrated promising benefit in metastatic BRCA mutated breast cancer or TNBC, while no such superiority was observed in the neoadjuvant setting of TNBC. Moreover, the utility of PARP inhibition in BRCA1/2 mutated breast cancer with different platinum-free interval was investigated. There was a clear association between clinical benefit with PARPi and platinum sensitivity, whereas partial efficacy of PARPi still occurs in platinum-resistant patients. In addition, proof-of-principle studies of immunotherapy combined with PARPi in breast cancer have obtained promising results, indicating the potential benefit of the combination therapy in patients with breast cancer. These efforts, contributing to maximize the utility of PARPi, may drive a new era of this agent after its first routine use. In this review, we summarized the utility of combining platinum-PARPi in BRCA mutated breast cancer or TNBC compared with platinum monotherapy and provided promising prospects of PARPi as maintenance therapy in breast cancer, as well as providing a strong rationale for testing immunotherapy combined with PARPi in breast cancer to expand the clinical utility of PARPi.

PARP inhibitors in breast cancer: Bringing synthetic lethality to the bedside

Individuals with breast and ovarian cancer susceptibility gene 1 (BRCA1) or BRCA2 germline mutations have a significantly increased lifetime risk for breast and ovarian cancers. BRCA-mutant cancer cells have abnormal homologous recombination (HR) repair of DNA. In these tumors, the base excision repair (BER) pathway is important for cell survival. The poly(adenosine diphosphate-ribose) polymerase (PARP) enzymes play a key role in BER, and PARP inhibitors are effective in causing cell death in BRCA-mutant cells while sparing normal cells-a concept called synthetic lethality. PARP inhibitors are the first cancer therapeutics designed to exploit synthetic lethality. Recent clinical trials in BRCA-mutant, metastatic breast cancer demonstrated improved outcomes with single-agent PARP inhibitors (olaparib and talazoparib) over chemotherapy. However, resistance to PARP inhibitors remains a challenge. Primarily due to myelosuppression, the combination of PARP inhibitors with chemotherapy has been difficult. Novel combinations with chemotherapy, immunotherapy, and other targeted therapies are being pursued. In this review, the authors discuss current knowledge of PARP inhibitors in BRCA-mutant breast cancer and potential future directions for these agents. Cancer 2018;124:2498-506. © 2018 American Cancer Society.

Update on PARP Inhibitors in Breast Cancer

OPINION STATEMENT

The single agent activity of PARP inhibitors (PARPi) in germline BRCA mutated (gBRCAm) breast and ovarian cancer suggests untapped potential for this new class of drug in breast cancer. The US Food and Drug Administration has approved three PARPi (olaparib, rucaparib, and niraparib) so far to treat certain ovarian cancers, including those with gBRCAm and olaparib for treatment of gBRCAm breast cancers. Several PARPi are now under clinical development for breast cancer in the various treatment settings. Recently, two phase III trials of olaparib (OlympiaD) and talazoparib (EMBRACA) demonstrated 3-month progression-free survival improvement with PARPi compared to physician's choice single agent chemotherapy in metastatic gBRCAm breast cancer. To date, PARPi seems less efficacious in metastatic breast cancer patients than those with BRCA mutated platinum-sensitive recurrent ovarian cancer, perhaps reflecting the biologic heterogeneity and low somatic BRCA mutation rate in breast cancer. The use of PARPi is gradually evolving, including combination strategies with chemotherapy, targeted agents, radiotherapy, or immunotherapy in women with and without gBRCAm. The role of predictive biomarkers, including molecular signatures and homologous recombination repair deficiency scores based on loss of heterozygosity and other structural genomic aberrations, will be crucial to identify a subgroup of patients who may have benefit from PARPi. An improved understanding of the mechanisms underlying PARPi clinical resistance will also be important to enable the development of new approaches to increase efficacy. This is a field rich in opportunity, and the coming years should see a better understanding of which breast cancer patients we should treat with PARPi and where these agents should come in over the course of treatment.

Phase I combination study of the PARP inhibitor veliparib plus carboplatin and gemcitabine in patients with advanced ovarian cancer and other solid malignancies

OBJECTIVE

Determine the maximum tolerated dose (MTD) and recommended phase II dose (RP2D) of veliparib combined with carboplatin and gemcitabine in patients with advanced ovarian cancer and other nonhematologic malignancies.

METHODS

In this phase I study, patients with metastatic or unresectable solid tumors and ≤2 prior chemotherapy regimens received veliparib combined with carboplatin area under the curve (AUC) 4 on day 1 and gemcitabine 800mg/m² on days 1 and 8 of a 21-day cycle for maximum 10cycles, followed by optional veliparib maintenance therapy. Veliparib dosing commenced twice-daily (BID) continuously on day 1 of cycle 2; granulocyte colony-stimulating factor was permitted. Dose escalation used a Bayesian continual reassessment method. Safety, tolerability, and efficacy were evaluated.

RESULTS

Seventy-five patients were enrolled (ovarian cancer, n=54; breast cancer, n=12). Thirty-six patients with ovarian cancer (67%) had known germline BRCA mutations. Most common treatment-related adverse events (TRAEs; ≥60%) were thrombocytopenia, neutropenia, nausea, and anemia. Most common grade 3/4 TRAEs (≥40%) were neutropenia and thrombocytopenia. Dose-limiting toxicities were thrombocytopenia and neutropenia. The MTD/RP2D was established at veliparib 250mg with carboplatin AUC 4 plus gemcitabine 800mg/m². Responses were observed in 69% of patients with BRCA-deficient ovarian cancer (45% partial, 24% complete responses). Five patients remained on veliparib (80-310mg BID) for >34cycles.

CONCLUSIONS

Veliparib plus carboplatin/gemcitabine is tolerated, with a safety profile similar to carboplatin and gemcitabine alone. Combination therapy demonstrated promising preliminary antitumor activity in platinum-sensitive ovarian cancer patients with germline BRCA mutations. Trial registration ID: NCT01063816.

Pathway-Enriched Gene Signature Associated with 53BP1 Response to PARP Inhibition in Triple-Negative Breast Cancer

Effective treatment of patients with triple-negative (ER-negative, PR-negative, HER2-negative) breast cancer remains a challenge. Although PARP inhibitors are being evaluated in clinical trials, biomarkers are needed to identify patients who will most benefit from anti-PARP therapy. We determined the responses of three PARP inhibitors (veliparib, olaparib, and talazoparib) in a panel of eight triple-negative breast cancer cell lines. Therapeutic responses and cellular phenotypes were elucidated using high-content imaging and quantitative immunofluorescence to assess markers of DNA damage (53BP1) and apoptosis (cleaved PARP). We determined the pharmacodynamic changes as percentage of cells positive for 53BP1, mean number of 53BP1 foci per cell, and percentage of cells positive for cleaved PARP. Inspired by traditional dose-response measures of cell viability, an EC₅₀ value was calculated for each cellular phenotype and each PARP inhibitor. The EC₅₀ values for both 53BP1 metrics strongly correlated with IC₅₀ values for each PARP inhibitor. Pathway enrichment analysis identified a set of DNA repair and cell cycle-associated genes that were associated with 53BP1 response following PARP inhibition. The overall accuracy of our 63 gene set in predicting response to olaparib in seven breast cancer patient-derived xenograft tumors was 86%. In triple-negative breast cancer patients who had not received anti-PARP therapy, the predicted response rate of our gene signature was 45%. These results indicate that 53BP1 is a biomarker of response to anti-PARP therapy in the laboratory, and our DNA damage response gene signature may be used to identify patients who are most likely to respond to PARP inhibition. Mol Cancer Ther; 16(12); 2892-901. ©2017 AACR.

Phase 1 dose-escalation study of single-agent veliparib in Japanese patients with advanced solid tumors

Veliparib (ABT‐888) is a potent, orally bioavailable poly(ADP‐ribose) polymerase‐1 and ‐2 inhibitor. This phase 1 study evaluated the tolerability, pharmacokinetic profile, safety, and preliminary antitumor activity of single‐agent veliparib in Japanese patients with advanced solid tumors. Eligible patients were assigned to treatment with veliparib at 200 or 400 mg dose; veliparib was self‐administered orally twice daily on days 1–28 of 28‐day cycles. Dose escalation, following a 3 + 3 design, defined dose‐limiting toxicities, the maximum tolerated dose, and the recommended phase 2 dose. Sixteen patients were enrolled (median age, 59 years). Fourteen patients had high‐grade serous ovarian cancer, one had primary peritoneal cancer, and one had BRCA‐mutated breast cancer. The most frequent treatment‐emergent adverse events were nausea and vomiting (93.8% each), decreased appetite (62.5%), abdominal pain, diarrhea, and malaise (31.3% each). A grade ≥3 toxicity was observed in 50% of patients; one patient each in the 200 mg (n = 4) and 400 mg (n = 12) cohorts experienced serious adverse events. Dose‐limiting toxicities were observed for one patient at the 400 mg dose. No toxicities leading to death were reported. The recommended phase 2 dose was defined as 400 mg twice daily. The veliparib pharmacokinetic profile was consistent with that reported for the Western population. Two patients, both with ovarian cancer, had a RECIST partial response. Veliparib monotherapy showed manageable tolerability and safety profiles and a predictable pharmacokinetic profile at a 400 mg twice‐daily dose, and supports the inclusion of Japanese patients in the multinational phase 3 study (NCT02470585).

Efficacy of the PARP Inhibitor Veliparib with Carboplatin or as a Single Agent in Patients with Germline BRCA1- or BRCA2-Associated Metastatic Breast Cancer: California Cancer Consortium Trial NCT01149083

Purpose: We aimed to establish the MTD of the poly (ADP-ribose) (PAR) polymerase inhibitor, veliparib, in combination with carboplatin in germline BRCA1- and BRCA2- (BRCA)-associated metastatic breast cancer (MBC), to assess the efficacy of single-agent veliparib, and of the combination treatment after progression, and to correlate PAR levels with clinical outcome.Experimental Design: Phase I patients received carboplatin (AUC of 5-6, every 21 days), with escalating doses (50-20 mg) of oral twice-daily (BID) veliparib. In a companion phase II trial, patients received single-agent veliparib (400 mg BID), and upon progression, received the combination at MTD. Peripheral blood mononuclear cell PAR and serum veliparib levels were assessed and correlated with outcome.Results: Twenty-seven phase I trial patients were evaluable. Dose-limiting toxicities were nausea, dehydration, and thrombocytopenia [MTD: veliparib 150 mg po BID and carboplatin (AUC of 5)]. Response rate (RR) was 56%; 3 patients remain in complete response (CR) beyond 3 years. Progression-free survival (PFS) and overall survival (OS) were 8.7 and 18.8 months. The PFS and OS were 5.2 and 14.5 months in the 44 patients in the phase II trial, with a 14% RR in BRCA1 (n = 22) and 36% in BRCA2 (n = 22). One of 30 patients responded to the combination therapy after progression on veliparib. Higher baseline PAR was associated with clinical benefit.Conclusions: Safety and efficacy are encouraging with veliparib alone and in combination with carboplatin in BRCA-associated MBC. Lasting CRs were observed when the combination was administered first in the phase I trial. Further investigation of PAR level association with clinical outcomes is warranted. Clin Cancer Res; 23(15); 4066-76. ©2017 AACR.

Development of PARP inhibitors in gynecological malignancies

PARP inhibitors demonstrate synthetic lethality in tumors with BRCA1/2 mutations and other homologous recombination repair deficiencies by interfering with DNA repair and causing direct toxicity to DNA through PARP trapping. PARP inhibitors have been shown to be beneficial in the treatment of BRCA1/2-mutated ovarian cancers, which has led to a shift in the treatment paradigm of this disease. Further studies to establish the role of PARP inhibitors during earlier stages of treatment are ongoing. The use of PARP inhibitors in other cancers with homologous recombination repair deficiencies, such as breast cancer and prostate cancer, is gradually evolving as well, including their use in the neoadjuvant and adjuvant settings. PARP inhibitor combination strategies with chemotherapy, targeted agents, radiotherapy, and immunotherapy are also being explored. The role of predictive biomarkers, including molecular signatures and homologous recombination deficiency scores based on loss of heterozygosity and other structural genomic aberrations, will be crucial to improved patient stratification to enhance the clinical utility of PARP inhibitors. This may also allow the use of PARP inhibitors to be extended beyond tumors with specific homologous recombination DNA repair gene mutations in the future. An improved understanding of the mechanisms underlying PARP inhibitor resistance will also be important to enable the development of new approaches to increase efficacy. This is a field rich in opportunity, and the coming years should see a better understanding of which patients we should be treating with PARP inhibitors and where these agents should come in over the course of treatment.

Development of a Level A in Vitro-in Vivo Correlation for Veliparib (ABT-888) Extended Release Tablet Formulation

PURPOSE

The aim of the current manuscript is to develop and validate a level A in vitro-in vivo correlation (IVIVC) for veliparib extended-release (ER) tablet formulations.

METHODS

The in vitro release profiles of veliparib formulations were determined using USP Dissolution Apparatus 2 with 900 mL of 0.1 N HCl at 75 rpm. In a clinical study, 24 subjects with solid tumors received one of the ER formulations (200 mg): fast (Formulation A), intermediate (Formulation B), and slow (Formulation C), and two 100 mg immediate release capsules (Formulation D). Blood samples were collected over a period of 48 h and analyzed using LCMS/MS. A linear correlation model was developed using fraction absorbed and fraction dissolved data from formulations A and B. Besides assessing internal predictability, external predictability was evaluated using formation C. Prediction errors were estimated for maximum observed plasma concentration (C_max) and area under the plasma-concentration time curve from zero to last measured time point (AUC_t) to determine the predictive ability of the correlation.

RESULTS

There was a significant linear relationship (r² = 0.944) between the fraction of drug absorbed and the fraction of drug dissolved. The prediction error using the internal validation for C_max and AUC_t were below 15% for the individual formulations and below 10% for the average. The prediction error in AUC_t and C_max for formulation C was 5% and 11%, respectively.

CONCLUSIONS

A level A IVIVC for the veliparib ER tablet formulation was established. The IVIVC may allow the associated dissolution data to be used as a surrogate for bioavailability.

PARP Inhibitors in Reproductive System Cancers: Current Use and Developments

The repair of DNA damage is a critical cellular process governed by multiple biochemical pathways that are often found to be defective in cancer cells. The poly(ADP-ribose) polymerase (PARP) family of proteins controls response to single-strand DNA breaks by detecting these damaged sites and recruiting the proper factors for repair. Blocking this pathway forces cells to utilize complementary mechanisms to repair DNA damage. While PARP inhibition may not, in itself, be sufficient to cause tumor cell death, inhibition of DNA repair with PARP inhibitors is an effective cytotoxic strategy when it is used in patients who carry other defective DNA-repair mechanisms, such as mutations in the genes BRCA 1 and 2. This discovery has supported the development of PARP inhibitors (PARPi), agents that have proven effective against various types of tumors that carry BRCA mutations. With the application of next-generation sequencing of tumors, there is increased interest in looking beyond BRCA mutations to identify genetic and epigenetic aberrations that might lead to similar defects in DNA repair, conferring susceptibility to PARP inhibition. Identification of these genetic lesions and the development of screening assays for their detection may allow for the selection of patients most likely to respond to this class of anticancer agents. This article provides an overview of clinical trial results obtained with PARPi and describes the companion diagnostic assays being established for patient selection. In addition, we review known mechanisms for resistance to PARPi and potential strategies for combining these agents with other types of therapy.

Effect of veliparib (ABT-888) on cardiac repolarization in patients with advanced solid tumors: a randomized, placebo-controlled crossover study

Purpose

Veliparib (ABT-888) is an orally bioavailable potent inhibitor of poly(ADP-ribose) polymerase (PARP)-1 and PARP-2. This phase 1 study evaluated the effect of veliparib on corrected QT interval using Fridericia’s formula (QTcF).

Methods

Eligible patients with advanced solid tumors received single-dose oral veliparib (200 mg or 400 mg) or placebo in a 6-sequence, 3-period crossover design. The primary endpoint was the difference in the mean baseline-adjusted QTcF between 400 mg veliparib and placebo (∆∆QTcF) at six post-dose time points. Absence of clinically relevant QTcF effect was shown if the 95 % upper confidence bound (UCB) for the mean ∆∆QTcF was <10 ms for all time points. An exposure–response analysis was also performed.

Results

Forty-seven patients were enrolled. Maximum mean ∆∆QTcF of veliparib 400 mg was 6.4 ms, with a 95 % UCB of 8.9 ms; for veliparib 200 mg, the maximum mean ∆∆QTcF was 3.6 ms, with a 95 % UCB of 6.1 ms. No patient had a QTcF value >480 ms or change from baseline in QTcF interval >30 ms. Treatment-emergent adverse events (TEAEs) were experienced by 36.2, 48.9, and 47.8 % of patients while receiving veliparib 200 mg, veliparib 400 mg, and placebo, respectively. Most common TEAEs were nausea (12.8 %) and myalgia (8.5 %) after veliparib 200 mg, nausea (8.5 %) and vomiting (8.5 %) after veliparib 400 mg, and nausea (6.5 %) after placebo.

Conclusions

Single-dose veliparib (200 mg or 400 mg) did not result in clinically significant QTc prolongation and was well tolerated in patients with advanced solid tumors.

Treatment of breast cancer 2 (BRCA2)-mutant follicular dendritic cell sarcoma with a poly ADP-ribose polymerase (PARP) inhibitor: a case report

BACKGROUND

Follicular dendritic cell sarcoma is a rare tumour with clinical behaviour covering a spectrum from indolent to aggressive disease. Treatment recommendations are currently based on case reports and small series describing combinations of surgery, chemotherapy and radiotherapy providing the best patient outcomes. Recent knowledge on molecular aberrations in this disease have not yet impacted on therapeutic decisions.

CASE PRESENTATION

We describe a case of progressive follicular dendritic cell sarcoma of the lung and pleura, treated based on knowledge of the tumour's molecular aberrations. The patient was initially treated with surgery, chemotherapy and radiotherapy and developed disease progression. Mutation testing by Caris molecular intelligence demonstrated a breast cancer 2 gene mutation and further treatment with carboplatin and veliparib achieved disease stabilisation.

CONCLUSION

Understanding of the molecular profile of rare tumours is key to improve therapeutic decision making and patient outcomes.

Phase I Safety, Pharmacokinetic, and Pharmacodynamic Study of the Poly(ADP-ribose) Polymerase (PARP) Inhibitor Veliparib (ABT-888) in Combination with Irinotecan in Patients with Advanced Solid Tumors

PURPOSE

PARP is essential for recognition and repair of DNA damage. In preclinical models, PARP inhibitors modulate topoisomerase I inhibitor-mediated DNA damage. This phase I study determined the MTD, dose-limiting toxicities (DLT), pharmacokinetics (PK), and pharmacodynamics (PD) of veliparib, an orally bioavailable PARP1/2 inhibitor, in combination with irinotecan.

EXPERIMENTAL DESIGN

Patients with advanced solid tumors were treated with 100 mg/m(2) irinotecan on days 1 and 8 of a 21-day cycle. Twice-daily oral dosing of veliparib (10-50 mg) occurred on days 3 to 14 (cycle 1) and days -1 to 14 (subsequent cycles) followed by a 6-day rest. PK studies were conducted with both agents alone and in combination. Paired tumor biopsies were obtained after irinotecan alone and veliparib/irinotecan to evaluate PARP1/2 inhibition and explore DNA damage signals (nuclear γ-H2AX and pNBS1).

RESULTS

Thirty-five patients were treated. DLTs included fatigue, diarrhea, febrile neutropenia, and neutropenia. The MTD was 100 mg/m(2) irinotecan (days 1 and 8) combined with veliparib 40 mg twice daily (days -1-14) on a 21-day cycle. Of 31 response-evaluable patients, there were six (19%) partial responses. Veliparib exhibited linear PK, and there were no apparent PK interactions between veliparib and irinotecan. At all dose levels, veliparib reduced tumor poly(ADP-ribose) (PAR) content in the presence of irinotecan. Several samples showed increases in γ-H2AX and pNBS1 after veliparib/irinotecan compared with irinotecan alone.

CONCLUSIONS

Veliparib can be safely combined with irinotecan at doses that inhibit PARP catalytic activity. Preliminary antitumor activity justifies further evaluation of the combination. Clin Cancer Res; 22(13); 3227-37. ©2016 AACR.

Randomized phase II trial of cyclophosphamide and the oral poly (ADP-ribose) polymerase inhibitor veliparib in patients with recurrent, advanced triple-negative breast cancer

Background In tumors carrying BRCA mutations, DNA damage caused by standard cytotoxic chemotherapy can be potentiated by poly [ADP-ribose] polymerase (PARP) inhibitors, leading to increased cell death through synthetic lethality. Individuals carrying mutations in BRCA have an increased incidence of triple negative breast cancer (TNBC). In order to assess the role of PARP inhibition in the treatment of TNBC, we conducted a randomized phase II trial of the combination of veliparib, a small molecule PARP inhibitor, with the cytotoxic agent cyclophosphamide versus cyclophosphamide alone in patients with refractory TNBC. Methods Adult patients with TNBC were randomized to receive oral cyclophosphamide 50 mg once daily with or without oral veliparib at 60 mg daily in 21-day cycles. Patients on the cyclophosphamide arm could crossover to the combination arm at disease progression. Results Forty-five patients were enrolled; 18 received cyclophosphamide alone and 21 received the combination as their initial treatment regimen. Lymphopenia was the most common grade 3/4 toxicity noted in both arms. One patient in the cyclophosphamide alone arm, and 2 in the combination arm had objective responses. Response rates and median progression free survival did not significantly differ between both treatment arms. Conclusion The addition of veliparib to cyclophosphamide, at the dose and schedule evaluated, did not improve the response rate over cyclophosphamide treatment alone in patients with heavily pre-treated triple-negative breast cancer.

Role of Biomarkers in the Development of PARP Inhibitors

Defects in DNA repair lead to genomic instability and play a critical role in cancer development. Understanding the process by which DNA damage repair is altered or bypassed in cancer may identify novel therapeutic targets and lead to improved patient outcomes. Poly(adenosine diphosphate-ribose) polymerase 1 (PARP1) has an important role in DNA repair, and novel therapeutics targeting PARP1 have been developed to treat cancers with defective DNA repair pathways. Despite treatment successes with PARP inhibitors (PARPi), intrinsic and acquired resistances have been observed. Preclinical studies and clinical trials in cancer suggest that combination therapy using PARPi and platinating agents is more effective than monotherapy in circumventing drug resistance mechanisms. Additionally, identification of biomarkers in response to PARPi will lead to improved patient selection for targeted cancer treatment. Recent technological advances have provided the necessary tools to examine many potential avenues to develop such biomarkers. This review examines the mechanistic rationale of PARP inhibition and potential biomarkers in their development for personalized therapy.

Randomized Trial of Oral Cyclophosphamide and Veliparib in High-Grade Serous Ovarian, Primary Peritoneal, or Fallopian Tube Cancers, or BRCA-Mutant Ovarian Cancer

PURPOSE

Veliparib, a PARP inhibitor, demonstrated clinical activity in combination with oral cyclophosphamide in patients with BRCA-mutant solid tumors in a phase I trial. To define the relative contribution of PARP inhibition to the observed clinical activity, we conducted a randomized phase II trial to determine the response rate of veliparib in combination with cyclophosphamide compared with cyclophosphamide alone in patients with pretreated BRCA-mutant ovarian cancer or in patients with pretreated primary peritoneal, fallopian tube, or high-grade serous ovarian cancers (HGSOC).

EXPERIMENTAL DESIGN

Adult patients were randomized to receive cyclophosphamide alone (50 mg orally once daily) or with veliparib (60 mg orally once daily) in 21-day cycles. Crossover to the combination was allowed at disease progression.

RESULTS

Seventy-five patients were enrolled and 72 were evaluable for response; 38 received cyclophosphamide alone and 37 the combination as their initial treatment regimen. Treatment was well tolerated. One complete response was observed in each arm, with three partial responses (PR) in the combination arm and six PRs in the cyclophosphamide alone arm. Genetic sequence and expression analyses were performed for 211 genes involved in DNA repair; none of the detected genetic alterations were significantly associated with treatment benefit.

CONCLUSION

This is the first trial that evaluated single-agent, low-dose cyclophosphamide in HGSOC, peritoneal, fallopian tube, and BRCA-mutant ovarian cancers. It was well tolerated and clinical activity was observed; the addition of veliparib at 60 mg daily did not improve either the response rate or the median progression-free survival.