PARP Inhibitors In Patients Research Articles

The current status of PARP inhibitors in ovarian cancer.

Recent advances in our understanding of the molecular biology of epithelial ovarian cancer have led to the development of a number of targeted therapies, including poly-ADP-ribose polymerase (PARP) inhibitors. PARP inhibitors are a novel class of therapeutic agents that target tumors with deficiencies in the homologous recombination DNA repair pathway. Early studies have shown significant efficacy for PARP inhibitors in patients with germline BRCA1/2 mutations. It has become evident that BRCA wild-type patients with other defects in the homologous recombination repair pathway benefit from this therapeutic approach. Importantly, companion homologous recombination deficiency scores are being developed to help guide the selection of patients most likely to gain clinical benefit from PARP inhibition. Olaparib, the first and most extensively investigated PARP inhibitor, is now licensed in Europe for maintenance treatment of patients with platinum-sensitive relapsed BRCA-mutated (germline or somatic) high-grade serous ovarian cancer who have responded to platinum-based chemotherapy. In the United States, olaparib is licensed for treatment of patients with germline BRCA-mutated ovarian cancer who have received 3 or more lines of chemotherapy. There are a number of other PARP inhibitors in late phase clinical development in ovarian cancer including rucaparib, niraparib, veliparib, and talazoparib. This review will focus on the current evidence for PARP inhibitors in ovarian cancer and discuss ongoing clinical trials and future research directions in this rapidly evolving area.

Abstract 3711: Pre-clinical combinations of ATR and PARP inhibitors: Defining target patient populations and dose schedule

Abstract Defective DNA damage repair, leading to genomic instability, is a common event during tumorigenesis. Despite enabling the persistence of mutations, any of which can confer a growth advantage to the nascent tumor, these defects place an Achilles Heel reliance on remaining repair pathways for survival from DNA damage. The protein kinases ataxia telangiectasia mutated (ATM) and ATM and Rad3 related (ATR) are key mediators of a DNA damage response activated by DNA damage during the S and G2 phases of cell cycle. Together they signal a series of cellular responses including activation of checkpoints and repair by homologous recombination. Loss of ATM pathway function frequently occurs in cancer, commonly from loss of function mutations in the tumor suppressor, p53, a substrate of ATM. This leads to a reliance on ATR that can be exploited for therapeutic benefit. Activation of ATR, by generation of S-phase DNA damage (replication stress, [RS]), can arise from treatment with DNA damaging drugs and certain targeted therapies such as inhibitors of poly ADP ribose polymerase (PARP). PARP is an enzyme involved in several DNA repair pathways, including base excision repair. Some PARP inhibitors have been shown to form an irreversible complex with DNA, potentially generating a direct RS lesion. While initial data indicates that inhibition of ATR and PARP is synergistic in some cancer cells, a comprehensive assessment has not been reported. Inhibition of ATR was cytotoxic in combination with PARP inhibitors against many cancer, but not non-cancer, cells. This effect was observed with multiple PARP inhibitors irrespective of their potential to form a DNA complex. In large cell panels of over 100 cancer cell lines, greater synergy was observed for the combination of an ATR and PARP inhibitor in cell lines with mutation of the TP53 gene. This was confirmed in isogenic cell lines depleted for ATM or p53, and is consistent with the profile of ATR and DNA damaging drug combinations. Furthermore, a triple combination of a PARP inhibitor, ATR inhibitor and the DNA damaging drug, cisplatin, retained cancer cell specific cytotoxic activity. In vitro dose-scheduling studies with the doublet of a PARP and ATR inhibitor showed optimal activity was achieved with transient concurrent exposure to both agents. This schedule contrasts with that for ATR inhibitors in combination with DNA damaging drugs where sequential dosing was optimal. In a mouse xenograft model concurrent dosing on a twice-weekly schedule was effective and well-tolerated. These data demonstrate the potential of combining ATR and PARP inhibitors in patients with p53 defective tumors. An optimal dose schedule was defined from cell and mouse studies. Together the data support clinical evaluation of ATR and PARP inhibitor combinations. Citation Format: John Pollard, Phil Reaper, Adele Peek, Stuart Hughes, Hakim Djeha, Steven Cummings, Karen Larbi, Marina Penney, Jim Sullivan, Darin Takemoto, Chris DeFranco. Pre-clinical combinations of ATR and PARP inhibitors: Defining target patient populations and dose schedule. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3711.

Abstract IA10: Angiopoietin/Tie2 as predictive biomarkers for bevacizumab in ovarian cancer

Abstract Ovarian cancer1 is the commonest cause of gynecological cancer death in the West accounting for approximately 7,000 lives in the UK and 22,000 women in the US each year. Surgery and platinum-based chemotherapy have remained the principal treatment modalities for several decades but in the last few years critical improvements in therapy have been made. These have been based on the implementation of PARP inhibitors in patients whose disease harbors BRCA gene mutations and the deployment of anti-angiogenic agents. Several trials have validated the tumor vasculature as a target in the treatment of ovarian cancer, through the addition of VEGF pathway inhibitors to cytotoxic chemotherapy followed by single agent VEGF inhibitors until a year after chemotherapy or until progression. Trials have been carried out in the first line2-4, second line platinum sensitive5 setting and in the platinum-resistant setting6 with the general observation that the addition of VEGF inhibitors to treatment improves progression free survival (PFS) and, in a pre-planned subgroup analysis of one trial, an improvement in overall survival (OS). ICON72 was a first line randomized, controlled trial in which over 1500 patients with FIGO stage Ic to IV ovarian cancer were randomly allocated to receive treatment with carboplatin and paclitaxel or the same regimen supplemented with the anti-VEGF monoclonal antibody, bevacizumab, which was continued for a year in total. The results demonstrated an improvement in PFS in patients at high risk of progression and an overall survival advantage in the same group. Patients with early stage disease did not benefit. VEGF inhibitors have improved PFS in a statistically significant manner in multiple clinical trials yet the effects remain clinically somewhat modest. Taken in conjunction with their moderate toxicity and expense, there was a clear need to identify predictive biomarkers that would allow oncologists to prescribe these agents to the patients most likely to benefit. We therefore validated a multiplex ELISA assay7 to quantify the concentration of several angiogenesis-related molecules in plasma samples taken from patients before treatment, on treatment and at progression. Examining pre-treatment concentrations of plasma angiogenesis-related molecules, while taking into account established clinical prognostic factors, we detected and validated a biomarker signature in which we showed that patients with supra-median concentrations of Ang1 and infra-median concentrations of Tie2 benefitted from bevacizumab. We have now extended this analysis to the blood samples taken from patients on treatment and at the development of progressive disease. The data show that the plasma concentration of Tie2 decreases during treatment with bevacizumab but that this is not seen in patients receiving treatment with cytotoxic therapy alone suggesting that plasma Tie2 is potentially a marker of vascular response. In keeping with this hypothesis, we saw an increase in Tie2 concentrations in patients developing progressive disease and have developed a model to combine changes in Ang1, Tie2 and Ca-125 to determine if these parameters can be used as early detectors of progressive disease. Such a tool would be useful in determining when to stop VEGF inhibitors and/or to change anti-angiogenic therapy to drugs with an alternative anti-vascular mode of action. Acknowledgements: This work was funded by Cancer Research UK and the ICON7 trial was overseen by the MRC (UK) Clinical Trials Unit. Roche (Basel, Switzerland) funded the international sample collection.

Delivering on the promise: poly ADP ribose polymerase inhibition as targeted anticancer therapy.

The article presents the rationale, clinical development, and current status of poly (ADP ribose) polymerase inhibitors (PARPis) as anticancer agents. The recent approval of olaparib in heavily pretreated patients with advanced ovarian cancer carrying a BRCA1/2 mutation represents a significant therapeutic advance for patients with this difficult to treat disease. Though olaparib is the first agent in this class to be approved, multiple PARPis are in various stages of clinical development, including in combination with other treatment modalities such as radiation, antiangiogenic agents, and cytotoxic chemotherapies. Clinical benefit has been observed with PARPis in patients with advanced BRCA1/2 mutant ovarian and breast cancers. Various PARPis, either as single agents or in combination, are being evaluated in the neoadjuvant, adjuvant, and metastatic settings.

Effectiveness and safety of poly (ADP-ribose) polymerase inhibitors in cancer therapy: A systematic review and meta-analysis.

Poly (ADP-ribose) polymerase (PARP) inhibitors are a class of small-molecule drugs suppressing PARP enzymes activity, inducing the death of cells deficient in homologous recombination repair (HRR). HRR deficiency is common in tumor cells with BRCA gene mutation. Since their first clinical trial in 2003, PARP inhibitors have shown benefit in the treatment of HRR-deficient tumors. Recently, several randomized clinical trials (RCTs) have been conducted to investigate the potential benefit of administration of PARP inhibitors in cancer patients. However, the results remain controversial. To evaluate the efficiency and safety of PARP inhibitors in patients with cancer, we performed a comprehensive meta-analysis of RCTs. According to our study, PARP inhibitors could clearly improve progression-free survival (PFS), especially in patients with BRCA mutation. However, our study showed no significant difference in overall survival (OS) between the PARP inhibitors and controls, even in the BRCA mutation group. Little toxicity was reported in the rate of treatment correlated adverse events (AEs) in PARP inhibitor group compared with controls. In conclusion, PARP inhibitors do well in improving PFS with little toxicity, especially in patients with BRCA deficiency.

An update on PARP inhibitors for the treatment of cancer.

The development of poly (adenosine diphosphate [ADP]) ribose polymerase (PARP) inhibitors (PARPi) has progressed greatly over the last few years and has shown encouraging results in the BRCA1/2 mutation–related cancers. This article attempts to summarize the rationale and theory behind PARPi, the clinical trials already reported, as well as ongoing studies designed to determine the role of PARPi in patients with and without germline mutations of BRCA genes. Future plans for PARPi both as monotherapy and in combination with standard cytotoxics, other biological agents, and as radiosensitizers are also covered. The widening scope of PARPi adds another important targeted agent to the growing list of molecular inhibitors; future and ongoing trials will identify the most effective role for PARPi, including for patients other than BRCA germline mutation carriers.

Molecular features of BRCA1/2 and PALB2 mutation associated pancreatic cancer (PAC).

206 Background: Several clinical reports have indicated increased sensitivity to DNA damaging agents and PARP inhibitors in patients with PAC arising on a background of known BRCA1/2 or PALB2 germline mutation. While the mechanism of tumorigenesis in these cancer remains unclear, it appears likely that BRCA1/2germline mutations can predispose to PAC via 2 mechanisms, only one of which requires loss of the second allele. Determination as to whether biallelic inactivation of these genes is present in the tumor may have important therapeutic implications in predicting sensitivity to PARP inhibitors and other strategies targeting DNA repair. Methods: Following approval by the IRB and human bio specimen utilization committee at MSKCC, full exon sequencing of coding regions of 28 genes including BRCA1, 2 and PALB2 using exon capture by hybridization and next generation sequencing was performed on DNA extracted from 135 PAC samples. In addition, samples were analyzed for the presence of BRCA1 promotor methylation, KRAS hotspot mutations, and genome wide loss of heterozygosity (LOH) as an exploratory assessment of number and length of LOH as a marker of homologous repair deficiency / genomic instability. All patients underwent surgery for PAC at MSKCC after year 2000. Patients were selected on the basis of survival and included if they suffered a cancer-specific death within 1 year of resection or survived at least 30 months. Results: 7 tumors had mutations in BRCA2, 1 in BRCA1 and 1 in PALB2. Of 4 BRCA2 mutated samples evaluated for LOH at the BRCA2 locus, 2 demonstrated LOH while 2 did not. There was no LOH at PALB2 in the sample where a mutation was identified. Activating KRAS mutations were identified in BRCA2 mutated tumors with and without LOH. Methylation of the BRCA1promotor regions was not identified. Conclusions: The frequency of BRCA1/2 mutation carriers was as anticipated in this population. Biallelic loss of BRCA2 or PALB2 are not required for pancreatic tumorigenesis. The benefit of PARP inhibitors in BRCA1 / 2 mutated PAC may be limited to tumors with LOH of these genes. Inactivation of BRCA1 through promoter methylation is not identified in sporadic PAC.

Correlation between poly (ADP-ribose) polymerase (PARP) and phospho-p65 expression in human breast cancer.

623 Background: Despite the efficacy of targeted agents in patients with HER2+ breast cancer, resistance often develops necessitating novel treatment strategies. Poly (ADP-ribose) polymerase inhibitors (PARPi) are known to target tumors with aberrant DNA repair. We previously reported sensitivity of HER2+ breast cancer cells to PARPi independent of a DNA repair deficiency but rather due to attenuation of NF-kB signaling. In this study, we investigated the expression of PARP and the active NF-kB subunit phospho-p65, indicators of activity for these pathways, in human HER2+ breast tumors and compared to HER2- tumors. Methods: Patients with breast cancer treated at the University of Alabama at Birmingham between the years 1999 and 2012 were identified. Formalin-fixed, paraffin-embedded tissue blocks were stained for PARP and phospho-p65 and evaluated independently by two blinded physicians, including a board-certified pathologist. An H-score was calculated by multiplying the percent of tumor cells with staining intensity of 0, 1, 2, and 3 and subsequently adding these together for a final score of 0-300. Nuclear and cystosolic staining were scored separately for both proteins. Results: Forty-six HER2+ and 38 HER2- patients with available tissue were identified; however, only 41 HER2+ and 32 HER2- cases had tumoral tissue at the time of analysis. PARP and phospho-p65 were found to be almost exclusively nuclear in both groups. The mean nuclear PARP score was 122.3 in HER2+ cases compared to 61.6 in HER2- cases (p value <0.0001). Mean nuclear phospho-p65 scores were 89.0 and 59.4 in HER2+ and HER2- groups, respectively (p value 0.0008). Additionally, a significantly positive correlation was observed between PARP and phospho-p65 levels. Conclusions: Our study suggests that HER2+ breast cancers have elevated PARP and NF-kB activity compared to HER2- cancers. Furthermore, a direct correlation between PARP and phospho-p65 levels was found. When combined with our previously published preclinical findings, the current research supports the potential clinical utility of PARPi in patients with this aggressive form of breast cancer.

Abstract B37: Increased expression of poly (ADP-ribose) polymerase (PARP) and phospho-p65 in human HER2+ breast cancer

Abstract Background: Despite the efficacy of targeted agents against the HER2 receptor, many patients with HER2+ breast cancer will develop resistance, thus necessitating novel treatment strategies. Poly (ADP-ribose) polymerase inhibitors (PARPi) are a well-tolerated class of drugs that target tumors with defective DNA repair pathways. Interestingly, we previously reported that HER2+ breast cancer cells are sensitive to PARPi alone both in vitro and in vivo independent of a basal or induced DNA repair defect (Nowsheen et al., Cancer Research 2012). Further, we found that attenuation of NF-κB signaling may account for this intriguing susceptibility. To further substantiate the potential utility of PARPi in HER2+ breast cancer, we investigated the expression and cellular location of PARP and phospho-p65, indicators of activity of the PARP and NF-κB pathways, respectively, in human HER2+ breast cancer specimens and compared to HER2- breast tumors. Methods: Breast cancer patients treated at UAB with available stored tissue blocks between the years 1999 and 2012 were identified. Formalin-fixed, paraffin-embedded tissue blocks were stained for PARP and phospho-p65 and evaluated independently by two blinded physicians, including a board-certified pathologist. An H-score was calculated by multiplying the percent of tumor cells with staining intensity of 0, 1, 2, and 3+ and subsequently adding these together for a final score of 0-300. Nuclear and cystosolic staining were scored separately for both proteins. The number of samples with 2 or 3+ staining of PARP or phospho-p65 in each group was also assessed. Results: Forty-one HER2+ and 32 HER2- cases were examined. PARP and phospho-p65 were found to be almost exclusively nuclear in both groups. The mean H-score for nuclear PARP was 122.3 in HER2+ cases compared to 61.6 in HER2- cases (p value <0.0001). Mean H-scores for nuclear phospho-p65 were 89.0 and 59.4 in HER2+ and HER2- groups, respectively (p value 0.0008). Further, a statistically significant positive correlation was observed between PARP and phospho-p65 levels. Interestingly, a significant difference was also observed between the percent of HER2+ and HER2- tumors with ≥2+ staining of PARP and phospho-p65. Seventy-three percent of HER2+ patients had ≥2+ PARP staining compared to 37% of the HER2- group (p value 0.0039). Likewise, 61% versus 16% of the HER2+ and HER2- patients, respectively, had ≥2+ phospho-p65 staining (p value 0.0001). Conclusions: Our study suggests that HER2+ breast cancers have elevated markers for PARP and NF-κB activity compared to HER2- cancers. A direct correlation between PARP and phospho-p65 levels was also found. Furthermore, staining of ≥2+ for either protein was significantly different between the two groups suggesting this as a potential biomarker for clinical application. When combined with our previously published preclinical findings, the current research supports the potential clinical utility of PARPi in patients with this aggressive form of breast cancer. Citation Format: Lisa Klepczyk, Shi Wei, Jason Brazelton, Kimberly Keene, Yufeng Li, James Bonner, Andres Forero, Albert LoBuglio, William Grizzle, Eddy Yang. Increased expression of poly (ADP-ribose) polymerase (PARP) and phospho-p65 in human HER2+ breast cancer. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr B37.

Abstract LB-174: Translation of preclinical predictive sensitivity of Ewing sarcoma to PARP inhibition: Phase II study of olaparib in adult patients with recurrent/metastatic Ewing sarcoma following failure of prior chemotherapy.

Abstract Based on preclinical biology (1, 2), this translational trial aimed to assess the efficacy and tolerability of the PARP inhibitor, olaparib, in patients with advanced Ewing sarcoma progressing after prior chemotherapy. In this uncontrolled phase II pilot, adult participants with radiographically measureable disease received 400 mg of olaparib capsules, twice daily, until disease progression or drug intolerance. Tumor measurements were determined by CT or MRI, at 6 and 12 weeks after starting olaparib administration, and then every 8 weeks thereafter. Tumor response determinations were made according to RECIST 1.1, and adverse event determinations were made according to CTCAE, version 4.0. A total of 22 participants were planned to be enrolled using a conventional 2-step phase II study design. If no objective responses were observed after 12 participants had been followed for at least 3 months, further accrual would be stopped. 12 participants were enrolled, and all were evaluable. A single case each of grade 3 anemia and grade 3 thrombocytopenia was observed (see Table One). Otherwise, no significant or unexpected toxicities were observed while participants were receiving study drugs. There were 0 PR/CR, 4 SD (duration 10.9, 11.4, 11.9, and 18.4 wks), and 8 PD as best response. Of the SD, 2 had minor responses (-16.7% and -11.7% by RECIST 1.1). The median time to disease progression was 5.7 weeks. Further enrollment was therefore discontinued. This study is the first report of a prospective phase II trial to evaluate the safety and efficacy of a PARP inhibitor in patients with Ewing sarcoma. Olaparib tablets were safe and well tolerated when administered to this small cohort at the 400 mg BID dose, although the median duration of dosing was for only 5.7 weeks. However, no significant responses were seen, and the short average interval to disease progression underscores the aggressiveness of this disease. Preclinical modeling supports exquisite in vivo sensitivity of this pathway in combination with chemotherapy, and such a trial of olaparib with temozolomide will begin shortly at our Center. Toxicity Type # of Patients Grade 1 2 3 4 Anemia 1 0 0 0 0 Blood and lymphatic systems disorders: other 1 1 0 0 0 Fatigue 1 1 0 0 0 Fever 1 1 0 0 0 Pain 2 1 0 1 0 Rash maculo-papular 1 1 0 0 0 Nausea 1 1 1 0 0 Vomiting 1 1 0 0 0 Urinary tract infection 1 1 0 0 0 Platelet count decreased 2 1 1 0 Hypoglycemia 1 1 0 0 0 Metabolism and nutrition disorders: other 1 1 0 0 0 Arthritis 1 1 0 0 0 Musculoskeletal and connective tissue disorder: other 1 1 0 0 0 Dizziness 1 1 0 0 0 Nervous system disorders: other 1 1 1 0 0 Cough 3 3 0 0 0 Postnasal drip 1 1 0 0 0 Respiratory, thoracic and mediastinal disorders: other 1 1 0 0 0 Hypertension 1 1 0 0 0 Total 25 19 3 0 0 Citation Format: Edwin Choy, James Butrynski, David Harmon, Jeffrey Morgan, Suzanne George, Andrew Wagner, David D'Adamo, Greg Cote, Yael Rubinstein, Cyril Benes, Daniel Haber, Jose Baselga, George Demetri. Translation of preclinical predictive sensitivity of Ewing sarcoma to PARP inhibition: Phase II study of olaparib in adult patients with recurrent/metastatic Ewing sarcoma following failure of prior chemotherapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-174. doi:10.1158/1538-7445.AM2013-LB-174

Targeted next-generation sequencing (NGS) of advanced prostate cancer (PCA) using formalin-fixed tissue.

4649 Background: The genomic landscape of advanced PCA is not well characterized, partly due to limited availability of frozen metastatic tissue. This has created a gap in our knowledge of treatment related and potentially targetable genomic alterations. The purpose of this study was to demonstrate feasibility of performing NGS to molecularly characterize advanced PCA using formalin-fixed paraffin embedded (FFPE) tissue. Methods: 25 metastatic CRPC, 4 metastatic hormone naïve PCA, 3 primary localized PCA, and 18 benign matched prostates were evaluated (40mm FFPE tissue per case). High-density foci were captured and sequenced for 3230 exons of 182 cancer-related genes and 37 introns of 14 genes often rearranged in cancer to an average depth of >800x in a CLIA lab (Foundation Medicine). Recurrent mutations, copy number alterations, and fusions were validated using PCR and FISH. Results: In >90% of samples, there was sufficient DNA (≥50 ng) for analysis. Recurrent high confidence cancer alterations in CRPC included: TMPRSS2-ERG fusion (44%), PTEN loss (44%), TP53 mutation (40%), AR mutation (24%), AR gain (24%), RB mutation (28%), MYC gain (12%), and BRCA2 loss (12%). Overall 48% of CRPC harbored AR gene alterations. Additionally, there were mutations in CTNNB1 (12%), ATM (8%) and PIK3CA (4%). Copy number alterations not previously described in PCA included CCND1, CDK4/6 gains and CDKN2A/CDKN2B deletions. Hormone naïve metastatic and high risk localized PCA demonstrated similar frequency of TMPRSS2-ERG gene fusion, BRCA2 deletion, and TP53 mutations as CRPC, but AR alterations and MYC gain were not seen. Conclusions: This study demonstrates feasibility of in-depth, NGS based DNA analysis using FFPE tissue, even biopsy material. Frequent AR alterations in CRPC, mutations associated with disease progression, and potential drug targets were identified. Focused NGS has clinical potential to identify actionable genomic alterations in advanced PCA that can impact patient participation in trials as well as treatment and outcome. Treatment options include PARP inhibitors for patients with BRCA2 and ATM alterations (20% of cases) and PI3K/AKT inhibitors for PIK3CA mutations.