Real-world data of poly (ADP-ribose) polymerase inhibitor response in Japanese patients with ovarian cancer.

BACKGROUND: Poly (ADP-ribose) polymerase (PARP) inhibitors have been increasingly used in the treatment of ovarian cancer, with BRCA positivity and homologous recombination deficiency (HRD) being common biomarkers used for predicting their efficacy. However, given the limitations of these biomarkers, new ones need to be explored. METHODS: This retrospective study included 181 ovarian cancer patients who received olaparib or niraparib at two independent hospitals in Japan between May 2018 and December 2022. Clinical information and blood sampling data were collected. Patient characteristics, treatment history, and predictability of treatment duration based on blood data before treatment initiation were examined. RESULTS: High-grade serous carcinoma, BRCA positivity, HRD, and maintenance therapy after recurrence treatment were observed more frequently in the olaparib group than in the niraparib group. The most common reasons for treatment interruption were anemia, fatigue, and nausea in the olaparib group and thrombocytopenia in the niraparib group. Regarding response to olaparib treatment, complete response to the most recent treatment, maintenance therapy after the first chemotherapy, high-grade serous carcinoma, and germline BRCA positivity were observed significantly more frequently among responders than among non-responders. Furthermore, neutrophil counts were significantly higher among responders than among non-responders. CONCLUSIONS: Inflammation-related blood data, such as neutrophil count, obtained at the initial pre-treatment visit might serve as potential predictors for prolonged olaparib treatment. While this study offers valuable insights into potential indicators for prolonged olaparib treatment, it underscores the need for more expansive research to strengthen our understanding of PARP inhibitors and optimize treatment strategies in ovarian cancer.

Comparison of poly (ADP-ribose) polymerase inhibitors (PARPis) as maintenance therapy for newly-diagnosed and platinum-sensitive recurrent ovarian cancer with BRCA mutational status: a systematic review and network meta-analysis.

BACKGROUND: Poly(adenosine diphosphate [ADP]-ribose) polymerase inhibitors (PARPi) treatment for ovarian cancer (OC) are ever-changing. This study aimed to compare the efficacy and overall safety of available PARPi as maintenance therapy for BRCA mutation status in patients with newly diagnosed and platinum-sensitive recurrent (PSR) OC patients. RESEARCH DESIGN AND METHODS: Relevant RCTs were systematically retrieved from PubMed and Embase until 31 May 2022. Progression-free survival (PFS) and overall survival (OS) based on BRCA mutation status and adverse events (AEs) regardless of mutation were efficacy and safety endpoints. RESULTS: In newly diagnosed BRCAm-OC patients, olaparib (HR: 0.33; 95% confidence interval [CI]: 0.25, 0.43) and other PARPis [niraparib (HR: 0.40; 95% CI: 0.29, 0.55), rucaparib (HR: 0.40; 95% CI: 0.21, 0.76) and veliparib (HR: 0.44; 95% CI: 0.28, 0.69)] had a statistically significant effect on PFS versus placebo. In BRCAm-PSROC patients, Olaparib exhibited significant benefit (HR: 0.69; 95% CI: 0.54, 0.88) for OS compared to other PARPis. In BRCAwt-PSR OC patients, Olaparib showed a favorable OS benefit than other PARPis (HR: 0.84; 95% CI: 0.57,1.22). Overall, safety profile of all PARPis was acceptable. CONCLUSION: All PARPis showed significant benefit, with olaparib showing greater benefit in newly diagnosed and PSR OC women. REGISTRATION: CRD42021288932.

Combining Novel Hormonal Therapies with a Poly (ADP-Ribose) Polymerase Inhibitor for Metastatic Castration-Resistant Prostate Cancer: Emerging Evidence.

Preclinical and clinical studies have suggested potential synergies of combining poly (ADP-ribose) polymerase (PARP) inhibitors and novel hormonal therapies (NHT) for patients with metastatic castration-resistant prostate cancer (mCRPC). We systematically searched PubMed, ClinicalTrials.gov and ASCO-GU annual meeting abstracts up to March 2023 to identify potential phase III trials reporting the use of combining PARP inhibitors with NHT in the first-line setting for mCRPC. A total of four phase III trials met the criteria for subsequent review. Emerging data suggested that the radiographic progression-free survival (rPFS) was significantly longer in the PARP inhibitor combined with NHT group versus the placebo plus NHT group for the first-line setting of biomarker-unselected mCRPC patients, especially for patients with homologous recombination repair (HRR) mutation (HRR m), and with the greatest benefit for BRCA1/2 mutation (BRCA1/2 m) populations. Final overall survival (OS) data of the PROpel trial indicated a significant improvement in median OS for mCRPC patients with HRR m and BRCA1/2 m receiving olaparib + abiraterone. Prior taxane-based chemotherapy might not influence the efficacy of the combination. Compared with the current standard-of-care therapies, combining NHT with PARP inhibitors could achieve a significant survival benefit in the first-line setting for mCRPC patients with HRR and BRCA1/2 mutations.

Poly (ADP-ribose) Polymerase Inhibitors in Patients with Metastatic Castration-Resistant Prostate Cancer: A Meta-Analysis of Randomized Controlled Trials.

Context: Several recent randomized controlled trials (RCTs) have reported on the survival benefits of poly (ADP-ribose) polymerase inhibitors (PARPi) compared to standard-of-care (SOC) treatment (enzalutamide, abiraterone, or docetaxel) in patients with metastatic castration-resistant prostate cancer (mCRPC). However, there is a limited integrated analysis of high-quality evidence comparing the efficacy and safety of PARPi and SOC treatments in this context. Objective: This study aims to comprehensively analyze the survival benefits and adverse events associated with PARPi and SOC treatments through a head-to-head meta-analysis in mCRPC. Evidence acquisition: A systematic review search was conducted in PubMed, Embase, Clinical trials, and the Central Cochrane Registry in July 2023. RCTs were assessed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. The systematic review was prospectively registered on PROSPERO (CRD42023441034). Evidence synthesis: A total of 8 studies, encompassing 2341 cases in the PARPi treatment arm and 1810 cases in the controlled arm, were included in the qualitative synthesis. The hazard ratio (HR) for radiographic progression-free survival (rPFS) and overall survival (OS) were 0.74 (95% CI, 0.61-0.90) and 0.89 (95% CI, 0.80-0.99), respectively, in the intention-to-treatment patients. For subgroup analysis, HRs for rPFS and OS in the BRCA-mutated subgroup were 0.39 (95% CI, 0.28-0.55) and 0.62 (95% CI, 0.38-0.99), while in the HRR-mutated subgroup, HR for rPFS was 0.57 (95% CI, 0.48-0.69) and for OS was 0.77 (95% CI, 0.64-0.93). The odds ratio (OR) for all grades of adverse events (AEs) and AEs with severity of at least grade 3 were 3.86 (95% CI, 2.53-5.90) and 2.30 (95% CI, 1.63-3.26), respectively. Conclusions: PARP inhibitors demonstrate greater effectiveness than SOC treatments in HRR/BRCA-positive patients with mCRPC. Further research is required to explore ways to reduce adverse event rates and investigate the efficacy of HRR/BRCA-negative patients.

[Combination therapy with poly(adenosine diphosphate-ribose) polymerase (PARPi) and androgen receptor signaling pathway (ARPi) inhibitors for metastatic castration-resistant prostate cancer]. / Kombinationstherapie mit Inhibitoren der Poly(Adenosindiphosphat-Ribose)-Polymerasen (PARPi) und des Androgenrezeptorsignalweges (ARPi) beim metastasierten kastrationsrefraktären Prostatakarzinom.

Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease with varying clinical and molecular subtypes. Almost one-third of patients have abnormalities in homologous recombinant repair genes. Again, about one third of these mutations affect the BReast CAncer 1 or 2 (BRCA 1 or BRCA 2) genes, which generally render tumours receptive to treatment with poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi). In 2020 the PARPi olaparib was approved for the treatment of mCRPC after progression with a new hormonal drug (androgen receptor signaling pathway inhibitors, ARPi). In 2022 and 2023 approval of two combination therapies followed, each combining a PARPi and an ARPi (olaparib plus abiraterone and niraparib plus abiraterone). The combination of talazoparib plus enzalutamide will be approved soon. This article introduces the pivotal clinical trials that led to the approval of the respective substances, reports the side effects that may occur during therapy with PARPi plus ARPi, and offers recommendations for management of these side effects.

Combining Poly (ADP-Ribose) Polymerase (PARP) Inhibitors with Chemotherapeutic Agents: Promise and Challenges.

Better understanding of molecular drivers and dysregulated pathways has furthered the concept of precision oncology and rational drug development. The role of DNA damage response (DDR) pathways has been extensively studied in carcinogenesis and as potential therapeutic targets to improve response to chemotherapy or overcome resistance. Treatment with small molecule inhibitors of PARP has resulted in clinical response and conferred survival benefit to patients with ovarian cancer, BRCA-mutant breast cancer, HRD-deficient prostate cancer and BRCA-mutant pancreatic cancer, leading to US Food and Drug Administration (FDA) approvals. However, the observed clinical benefit with single agent PARP inhibitors is limited to few tumor types within the relevant genetic context. Since DDR pathways are essential for repair of damage caused by cytotoxic agents, PARP inhibitors have been evaluated in combination with various chemotherapeutic agents to broaden the therapeutic application of this class of drugs. In this chapter, we discuss the combination of PARP inhibitors with different chemotherapeutics agents, clinical experience to date, lessons learnt, and future directions for this approach.

Efficacy of poly (ADP-ribose) polymerase inhibitors monotherapy and the impact to subsequent platinum-based chemotherapy in breast cancer susceptibility genes1/2-mutated ovarian cancer patients with secondary platinum-sensitive relapse.

BACKGROUND: The therapeutic effect of poly (ADP-ribose) polymerase inhibitors (PARPi) monotherapy compared with platinum-based chemotherapy, and the impact to subsequent platinum-based chemotherapy after PARPi resistance were inconclusive in breast cancer susceptibility genes (BRCA)1/2-mutated ovarian cancer patients with secondary platinum-sensitive relapse. METHODS: BRCA1/2-mutated patients with secondary platinum-sensitive relapse included in this study did not receive any maintenance regimen after first- and second-line platinum-based chemotherapy, and the secondary platinum-free interval (PFI) was more than 6 months. Patients in study group were treated with PARPi monotherapy until disease progression, and patients in control group were treated with platinum-based chemotherapy without restriction. Progression-free survival (PFS) was defined as the time from third-line therapy to disease progression or death, PFS2 was defined as the time from platinum-based chemotherapy after PARPi resistance to next subsequent therapy or death. Post-recurrence survival (PRS) refers to the survival time after secondary platinum-sensitive relapse. RESULTS: A total of 119 patients were retrospectively analyzed, including 71 (59.7%) in study group and 48 (40.3%) in control group. The objective response rate (ORR: 77.5% vs. 80.0%, p=0.766) and PFS (median: 11.2 vs. 11.0 months, p=0.962) were comparable. The benefit of subsequent platinum-based chemotherapy after PARPi resistance was more pronounced in patients with PARPi treatment for more than 12 months (median PFS2: 8.6 vs. 4.3 months, p=0.040). PARPi monotherapy had no adverse effect on PRS compared with platinum-based chemotherapy (median PRS:41.2 vs. 42.8 months, p=0.323). Compared to patients in control group who had never received PARPi, PARPi monotherapy (median PRS: 41.2 vs. 33.7 months, p=0.019) and post-line treatment with PARPi in the control group (median PRS: 48.1 vs. 33.7 months, p=0.002) could prolong PRS for patients with secondary platinum-sensitive relapse. CONCLUSIONS: PARPi monotherapy was similar to platinum-based chemotherapy for BRCA1/2-mutated ovarian cancer patients with secondary platinum-sensitive recurrence, and could improve prognosis.

Pan-Cancer Analysis of Copy-Number Features Identifies Recurrent Signatures and a Homologous Recombination Deficiency Biomarker to Predict Poly (ADP-Ribose) Polymerase Inhibitor Response.

PURPOSE: Copy-number (CN) features reveal the molecular state of cancers and may have predictive and prognostic value in the treatment of cancer. We sought to apply published CN analysis methods to a large pan-cancer data set and characterize ubiquitous CN signatures across tumor types, including potential utility for treatment selection. METHODS: We analyzed the landscape of CN features in 260,333 pan-cancer samples. We examined the association of 10 signatures with genomic alterations and clinical characteristics and trained a machine learning classifier using CN and insertion and deletion features to detect homologous recombination deficiency signature (HRDsig) positivity. Clinical outcomes were assessed using a real-world clinicogenomic database (CGDB) of comprehensive genomic profiling linked to deidentified, electronic health record-derived clinical data. RESULTS: CN signatures were prevalent across cancer types and associated with diverse processes including focal tandem duplications, seismic amplifications, genome-wide loss of heterozygosity (gLOH), and HRD. Our novel HRDsig outperformed gLOH in predicting BRCAness and effectively distinguished biallelic BRCA and homologous recombination-repair wild-type (HRRwt) samples pan-tumor, demonstrating high sensitivity to detect biallelic BRCA in ovarian (93%) and other HRD-associated cancers (80%-87%). Pan-tumor prevalence of HRDsig was 6.4%. HRRwt cases represented a significant fraction of the HRDsig-positive cohort, likely reflecting a population with nongenomic mechanisms of HRD. In ovarian and prostate CGDBs, HRDsig identified more patients than gLOH and had predictive value for poly (ADP-ribose) polymerase inhibitor (PARPi) benefit. CONCLUSION: Tumor CN profiles are informative, revealing diverse processes active in cancer. We describe the landscape of 10 CN signatures in a large pan-cancer cohort, including two associated with HRD. We trained a machine learning-based HRDsig that robustly identified BRCAness and associated with biallelic BRCA pan-tumor, and was predictive of PARPi benefit in real-world ovarian and prostate data sets.

ShallowHRD status acts as an effective prognostic predictor in ovarian cancer patients treated by poly (ADP-ribose) polymerase inhibitors (PARPis).

PURPOSE: Homologous recombination deficiency (HRD) plays a crucial role in ovarian cancer patients who are treated with Poly (ADP-ribose) polymerase inhibitors (PARPis). It could be defined as a prognosis biomarker. However, many high throughput sequencing methods for evaluating HRD, including HRDetect (WGS 10X), SigMA (WGS 40X or panel 1000X), and scarHRD (WGS 30X), are technically complex, time and data-storage consuming, and costly. Herein, we aimed to develop a low-cost method by low sequencing coverage to identify HRD status for precision medication. METHODS: We utilized ShallowHRD, a software tool to evaluate tumor HRD based on whole genome sequencing (WGS) at low coverage (1X), and established a novel scoring system, ShallowHRD score system. RESULTS: Compared with negative ShallowHRD status (ShallowHRD score < 15 or BRCAwild), positive ShallowHRD status (ShallowHRD score ≥ 15 or BRCAmut) presented favorable survival after being treated with PARPis. CONCLUSION: The ShallowHRD status is a good biomarker for predicting prognosis, which could help guide the clinical application of PARPis in ovarian cancer patients by a cost-effective, time and data-storage saving method.

Poly (ADP-Ribose) Polymerase Inhibitors in Patients With Urothelial Cancer.

Poly ADP-ribose polymerase inhibitors (PARPis) have clinical activity in several cancers. The rationale of their therapeutic use in urothelial cancer (UC) resides in the high homologous-recombination repair (HRR) deficiency (HRD) prevalence and potential cross-sensitivity with platinum-based chemotherapy (PBCT). This review aims to summarize and analyze trials exploring the activity of PARPis in UC, focusing on patients who may benefit from those agents, the best clinical setting for the treatment and the benefit of the association with immune-checkpoint inhibitors (ICIs). We included all the available trials analyzing the activity of PARPis in UC in neoadjuvant, adjuvant, first or subsequent lines, and maintenance setting. We included PARPis in monotherapy and in association with other agents. The results in the maintenance setting are intriguing: ATLANTIS trial showed signals of improved progression-free survival in patients with known HRR aberrations, although the Meet-URO12 trial, with its negative results, suggested the failure of clinical selection based on platinum sensitivity only. Single-agent PARPis in pretreated patients showed discouraging results in an unselected population of chemo-refractory patients. Concerning the association of PARPis with ICIs, several trials are exploring their role in platinum-naïve setting; the results in the advanced setting were globally negative. Prior selection of HRD status is essential to identify patients who might benefit from PARPis. The ideal clinical settings seem to be the maintenance treatment and the combination with ICIs in platinum-naïve patients. Definitive results of ongoing and further trials will delineate the position for PARPis, if any, in UC therapy.

Managing Adverse Effects Associated With Poly (ADP-ribose) Polymerase Inhibitors in Ovarian Cancer: A Synthesis of Clinical Trial and Real-World Data.

The use of poly (ADP-ribose) polymerase (PARP) inhibitor therapy is standard care in the management of patients with various malignancies including ovarian, breast, prostate, and pancreatic cancers. PARP inhibitors have been approved in different settings for patients with specific hereditary pathogenic variants, most notably homologous recombination repair pathways such as BRCA1 and BRCA2 genes. The vast experience with PARP inhibitors (olaparib, niraparib, rucaparib) has been in the management of epithelial ovarian cancer. There have not been any head-to-head comparisons of PARP inhibitors in randomized trials, and we can only perform cross-comparison on the basis of the reported literature. The three approved PARP inhibitors share several common adverse effects because of a class effect including nausea, fatigue, and anemia, but there are notable differences likely because of variations in their poly-pharmacology and off-target effects. Finally, patients included in clinical trials are often younger with a good performance status and less comorbidities than the real-world population, and hence, the potential benefits and adverse effects may not be superimposable. In this review, we describe these differences and discuss strategies to mitigate and manage adverse side effects effectively.

Interstitial lung disease in patients treated with poly (ADP-ribose) polymerase inhibitors (PARPi): analysis of results from clinical trials and the FDA Adverse Events Reporting System database.

OBJECTIVE: To evaluate the risk of interstitial lung disease associated with poly (ADP-ribose) polymerase inhibitors (PARPi) and characterize its clinical features. METHODS: We systematically reviewed phase III randomized clinical trials of interstitial lung disease related to PARPi and calculated Peto odds ratios (ORs) with 95% confidence intervals (CIs). Pharmacovigilance studies were conducted by collecting cases of PARPi-related interstitial lung disease from the FDA Adverse Events Reporting System and assessing disproportionalities by reporting ORs and information components. RESULTS: A total of five randomized clinical trials involving 2980 patients were included. Although PARPi showed a tendency to increase the risk of interstitial lung disease compared with controls, this difference was not significant (Peto OR: 4.92; 95% CI: 0.92 to 26.35). A total of 170 cases of interstitial lung disease related to PARPi were included, with a median latency of 99 days. PARPi had a significantly increased reporting of interstitial lung disease (reporting OR: 2.86; 95% CI: 2.46 to 3.33; information component (IC): 1.49; 95% CI: 1.28 to 1.74). Our sensitivity analyses showed strong robustness of the disproportionalities between PARPi as a class, olaparib, and interstitial lung disease. Some 91.9% of patients experienced discontinuation, 51.6% achieved remission, and no deaths were reported. CONCLUSION: Our pharmacovigilance study suggested increased reporting of interstitial lung disease related to PARPi particularly olaparib.

BCL6B Contributes to Ocular Vascular Diseases via Notch Signal Silencing.

BACKGROUND: Endothelial cell activation is tightly controlled by the balance between VEGF (vascular endothelial cell growth factor) and Notch signaling pathway. VEGF destabilizes blood vessels and promotes neovascularization, which are common features of sight-threatening ocular vascular disorders. Here, we show that BCL6B (B-cell CLL/lymphoma 6 member B protein), also known as BAZF, ZBTB28, and ZNF62, plays a pivotal role in the development of retinal edema and neovascularization. METHODS: The pathophysiological physiological role of BCL6B was investigated in cellular and animal models mimicking 2 pathological conditions: retinal vein occlusion and choroidal neovascularization. An in vitro experimental system was used in which human retinal microvascular endothelial cells were supplemented with VEGF. Choroidal neovascularization cynomolgus monkey model was generated to investigate the involvement of BCL6B in the pathogenesis. Mice lacking BCL6B or treated with BCL6B-targeting small-interfering ribose nucleic acid were examined for histological and molecular phenotypes. RESULTS: In retinal endothelial cells, the BCL6B expression level was increased by VEGF. BCL6B-deficient endothelial cells showed Notch signal activation and attenuated cord formation via blockage of the VEGF-VEGFR2 signaling pathway. Optical coherence tomography images showed that choroidal neovascularization lesions were decreased by BCL6B-targeting small-interfering ribose nucleic acid. Although BCL6B mRNA expression was significantly increased in the retina, BCL6B-targeting small-interfering ribose nucleic acid suppressed ocular edema in the neuroretina. The increase in proangiogenic cytokines and breakdown of the inner blood-retinal barrier were abrogated in BCL6B knockout (KO) mice via Notch transcriptional activation by CBF1 (C promotor-binding factor 1) and its activator, the NICD (notch intracellular domain). Immunostaining showed that Müller cell activation, a source of VEGF, was diminished in BCL6B-KO retinas. CONCLUSIONS: These data indicate that BCL6B may be a novel therapeutic target for ocular vascular diseases characterized by ocular neovascularization and edema.

Kidney function in patients with ovarian cancer treated with poly (ADP-ribose) polymerase (PARP) inhibitors.

BACKGROUND: Poly (ADP-ribose) polymerase inhibitors (PARPi) have revolutionized the treatment of ovarian cancer; however, real-world data on kidney function among patients treated with PARPi are lacking. METHODS: We identified adults treated with olaparib or niraparib between 2015 and 2021 at a major cancer center in Boston, MA, USA. We determined the incidence of any acute kidney injury (AKI), defined as at least a 1.5-fold rise in serum creatinine from baseline in the first 12 months following PARPi initiation. We calculated the percentage of patients with any AKI and sustained AKI and adjudicated the etiologies by manual chart review. We compared trajectories in estimated glomerular filtration rate (eGFR) among PARPi-treated and carboplatin and paclitaxel-treated patients with ovarian cancer, matched by baseline eGFR. RESULTS: Of 269 patients, 60 (22.3%) developed AKI, including 43 of 194 (22.1%) olaparib-treated patients and 17 of 75 (22.7%) niraparib-treated patients. Only 9 of 269 (3.3%) had AKI attributable to the PARPi. Of the 60 patients with AKI, 21 (35%) had sustained AKI, of whom 6 had AKI attributable to the PARPi (2.2% of the whole cohort). eGFR declined within 30 days post-PARPi initiation by 9.61 (SD = 11.017) mL/min per 1.73 m2 but recovered by 8.39 (SD = 14.05) mL/min per 1.73 m2 within 90 days after therapy cessation. There was no difference in eGFR at 12 months post-therapy initiation in patients receiving PARPi or controls receiving carboplatin and paclitaxel (P = .29). CONCLUSIONS: AKI is common following PARPi initiation as is a transient decline in eGFR; however, sustained AKI directly attributable to the PARPi and long-term eGFR decline are uncommon.

Poly (ADP-ribose) polymerase inhibitors (PARPi) in ovarian cancer: lessons learned and future directions.

Poly (ADP-ribose) polymerase inhibitors (PARPi) represent a new standard of care in the upfront treatment of advanced epithelial ovarian cancer to the point that the vast majority of patients now receive a PARPi, alone or in combination with the anti-angiogenic bevacizumab, as part of their first-line maintenance therapy. The clinical benefit of PARPi is well established; however, much has changed since their introduction and several relevant questions have been raised and remain unresolved in the post-PARPi era. The decision-making process regarding the most appropriate first-line maintenance therapy could be challenging in clinical practice, especially in the homologous recombination-proficient setting, and several other factors need to be considered apart from the mutational status. Concerns regarding post-PARPi progression treatment have emerged, highlighting an unmet need to define a valid algorithm strategy. PARPi may not only compromise the response to further platinum due to cross-resistance mechanisms but the impact on subsequent non-platinum chemotherapy and surgery also remains unclear. Definitive results on the role of PARPi rechallenge are awaited, especially in the case of oligoprogression managed with locoregional treatment. Moreover, the updated overall survival data from the recurrent setting warrant caution in using PARPi as single agents for unselected patients. Several PARPi combination regimens are emerging for overcoming PARPi resistance and may become our new therapeutic armamentarium. This review discusses a set of clinically relevant issues in the PARPi era and provides a glimpse of future challenges and opportunities in ovarian cancer treatment.

An Update on Poly(ADP-ribose) Polymerase I-A Brief Review.

Poly (ADP-ribose) polymerase 1 (PARP1) plays important roles in both DNA repair and transcription, and the interplay of these processes in relation to cellular function and disease states has not been well defined. The tumor-suppressor effects of PARP inhibitors have attracted significant interest in the development of novel cancer therapies. As PARP1 binding motifs may be readily found in promoter elements of DNA repair genes, the expanding role of PARP1 in DNA repair does not have to be independent of transcription. The discovery of ADP-ribose binding modules that bind to various forms of mono- and poly-ADP-ribose has provided important insights into how ADPribosylation regulates different cellular pathways. Among the four distinct PAR-binding modules discovered so far, it is the macrodomain alone that, in addition to possessing binding activity, in some instances, also supports a catalytic activity toward ADP-ribose derivatives. However, the development of PARP inhibitors as chemopotentiating agents has been limited by an increase in observed toxicity, mainly myelosuppression, necessitating dose reduction of the cytotoxic chemotherapeutic agent and the PARP inhibitor. Hence, it presents an opportunity to rationally develop combinations of PARP inhibitors with new classes of DNA repair inhibitors that are on the horizon and classical cytotoxic agents. Clinical trials of PARP inhibitors are investigating various uses of these approaches in cancer. Recent studies on the clinical significance of PARP1 inhibitors are discussed in this review. These recent research advances will inform the selection of patient populations who can benefit from the PARP inhibitor treatment and the development of effective drug combination strategies.

The Poly (ADP-ribose) polymerase inhibitor olaparib and pan-ErbB inhibitor neratinib are highly synergistic in HER2 overexpressing epithelial ovarian carcinoma in vitro and in vivo.

INTRODUCTION: Ovarian cancer (OC) is associated with the highest gynecologic cancer mortality. The development of novel, effective combinations of targeted therapeutics remains an unmet medical need. We evaluated the preclinical efficacy of the Poly (ADP-ribose) polymerase (PARP) inhibitor (olaparib) and the pan-ErbB inhibitor (neratinib) as single agents and in combination in ovarian cancer cell lines and xenografts with variable HER2 expression. METHODS: In vitro cell viability with olaparib, neratinib, and their combination was assessed using flow-cytometry based assays against a panel of OC primary cell lines with variable HER2 expression. Immunoblotting experiments were performed to elucidate the mechanism of activity and synergism. The in vivo antitumor activity of the olaparib/neratinib combination versus single agents was tested in HER2 positive xenograft OC models. RESULTS: HER2 + OC cell lines demonstrated higher sensitivity to olaparib and neratinib when compared to HER2 negative tumors (i.e., IC50: 2.06 ± 0.33 µM vs. 39.28 ± 30.51 µM, p = 0.0035 for olaparib and 19.42 ± 2.63 nM vs. 235.0 ± 165.0 nM, p = 0.0035 for neratinib). The combination of olaparib with neratinib was more potent when compared to single-agent olaparib or neratinib both in vitro and in vivo, and demonstrated synergy in all primary HER2 + OC models. Western blot experiments showed neratinib decreased pHER2/neu while increased Poly(ADP-ribose) (PAR) enzymatic activity; olaparib increased pHER2/Neu expression and blocked PAR activatio. Olaparib/neratinib in combination decreased both pHER2/Neu as well as PAR activation. CONCLUSION: The combination of olaparib and neratinib is synergistic and endowed with remarkable preclinical activity against HER2+ ovarian cancers. This combination may represent a novel therapeutic option for ovarian cancer patients with HER2+, homologous recombination-proficient tumors resistant to chemotherapy.