PARP-1 Research Articles

3-Aminobenzamide protects against cerebral artery injury and inflammation in rats with intracranial aneurysms.

This study aimed to investigate the treatment effects and molecular mechanism of 3-aminobenzamide (3-AB) on intracranial aneurysms (IA). The IA model was established in male Sprague-Dawley (SD) rats and sham group was set up without ligation. The rats were intraperitoneally injected with normal saline in sham and model control groups and 10 mg/kg, 20 mg/kg and 40 mg/kg 3-AB for low, middle and high 3-AB groups for 3 months, respectively. The rates in and blood pressures of caudal artery were measured and anterior cerebral artery and olfactory artery were stained with hematoxylin and eosin (HE) for morphology observation. Besides, the effects of 3-AB on inflammatory cells, macrophages, neutrophils and T cells, were evaluated using immunohistochemistry. Gene expressions of TNF-α, MMP-9, MMP-2, iNOS, TLR4, PARP-1 and p65 were measured using qRT-PCR and the protein levels of TLR4, PARP-1 and p-p65 were evaluated using western blotting. Blood pressures of rats in 3-AB treatment groups were decreased in a dose-dependent manner. The damage of cerebral artery wall was alleviated and the inflammatory cells (macrophages, neutrophils and T cells) were reduced to some extent in 3-AB high-dose groups. The gene expression of TNF-α, MMP-9, MMP-2, iNOS, TLR4, PARP-1 and p65, as well as the protein expression of TLR4, PARP-1 and p-p65 in 3-AB treatment groups were decreased in a dose-dependent manner (P < 0.01).3-AB exhibited therapeutic effects on IA through inhibiting the secretions of inflammatory cytokines and MMPs.

NF-κB and Poly (ADP-ribose) Polymerase 1 Form a Positive Feedback Loop that Regulates DNA Repair in Acute Myeloid Leukemia Cells.

NF-κB mediates acquired resistance in acute myeloid leukemia (AML) cells treated with DNA-damaging agents. Because DNA repair is the major molecular shift that alters sensitivity to DNA-damaging agents, we explored whether activation of the NF-κB pathway promotes AML cell survival by regulating DNA repair after chemotherapy. Our results showed that RELA, an important subunit of NF-κB, regulated DNA repair by binding to the promoter region of the PARP1 gene and affecting PARP1 gene transcription. Conversely, PARP1 knockdown reduced NF-κB activity, indicating that NF-κB and PARP1 create a positive feedback loop in DNA repair. Simultaneous treatment with the NF-κB inhibitor BMS-345541 and the PARP1 inhibitor olaparib resulted in robust killing of AML cells. This dual inhibition significantly suppressed tumor growth and extended survival times in xenograft tumor models. IMPLICATIONS: RELA and PARP1 form a positive feedback loop to regulate DNA damage repair, simultaneous inhibition of NF-κB and PARP1 increases the antileukemic efficacy of daunorubicin in vitro and in vivo, broadening the use of PARP1 inhibitors.

PARP1 gene polymorphisms and neuroblastoma susceptibility in Chinese children.

Neuroblastoma is a heterogeneous cancer frequently occurring in childhood. Germline mutations of PARP1 oncogene are implicated in several types of cancer. However, whether common single nucleotide polymorphisms (SNPs) in PARP1 gene are associated with neuroblastoma risk has received relatively few attentions. In this multi-center study, we aimed to elucidate the contributing role of PARP1 SNPs in neuroblastoma risk. We successfully genotyped three potentially functional PARP1 SNPs (rs1136410 A>G, rs2666428 T>C, rs8679 A>G) in 469 neuroblastoma cases and 998 controls. We did not detect any significant association between the analyzed SNPs and neuroblastoma risk in single SNP analysis. However, stratified analysis revealed that rs1136410 AG/GG carriers were more likely to develop tumors arising from mediastinum (AG/GG vs. AA: adjusted OR=1.65, 95% CI=1.06-2.56, P=0.028). Moreover, rs2666428 TC/CC carriers were at significantly lower risk to develop tumors from “other sites” (TC/CC vs. TT: adjusted OR=0.44, 95% CI=0.20-0.96, P=0.040). Our findings failed to provide evidence of the conferring role of the PARP1 gene polymorphisms in the risk of neuroblastoma. Further investigations of the association between PARP1 gene SNPs and neuroblastoma risk are warranted.

Significance of combined analysis of PARP1 and EZH2 expression as potentially targetable biomarkers in breast cancer

BackgroundPARP inhibitor (PARPi) is a new class of anticancer therapy and is currently used for the treatment of advanced BRCA-mutant breast cancer (BC). However, a significant number of patients with BRCA-deficient tumors do not respond well to PARPi treatment, and may develop resistance. So, it is

Laminar Flow Inhibits ER Stress-Induced Endothelial Apoptosis through PI3K/Akt-Dependent Signaling Pathway.

Atherosclerosis preferentially involves in prone area of low and disturbed blood flow while steady and high levels of laminar blood flow are relatively protected from atherosclerosis. Disturbed flow induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). ER stress is caused under stress that disturbs the processing and folding of proteins resulting in the accumulation of misfolded proteins in the ER and activation of the UPR. Prolonged or severe UPR leads to activate apoptotic signaling. Recent studies have indicated that disturbed flow significantly up-regulated p-ATF6α, p-IRE1α, and its target spliced XBP-1. However, the role of laminar flow in ER stress-mediated endothelial apoptosis has not been reported yet. The present study thus investigated the role of laminar flow in ER stress-dependent endothelial cell death. The results demonstrated that laminar flow protects ER stress-induced cleavage forms of PARP-1 and caspase-3. Also, laminar flow inhibits ER stress-induced p-eIF2α, ATF4, CHOP, spliced XBP-1, ATF6 and JNK pathway; these effects are abrogated by pharmacological inhibition of PI3K with wortmannin. Finally, nitric oxide affects thapsigargin-induced cell death in response to laminar flow but not UPR. Taken together, these findings indicate that laminar flow inhibits UPR and ER stress-induced endothelial cell death via PI3K/Akt pathway.

Synthetically Lethal BMN 673 (Talazoparib) Loaded Solid Lipid Nanoparticles for BRCA1 Mutant Triple Negative Breast Cancer.

The purpose of the study was to produce BMN 673 loaded solid lipid nanoparticles (SLNs) to improve its therapeutic index, to minimize toxicity and to overcome homologous recombination (HR)-mediated resistance. Firstly, BMN 673-SLNs were characterized using Nano Zeta Sizer. After treatment with different concentrations of BMN 673 and BMN 673-SLNs, cell viability of HCC1937(BRCA1-/-), HCC1937-R (BMN 673-resistant) TNBC and MCF-10A normal human mammary breast epithelial cell line was analyzed by WST-1 assay. In an attempt to assess the therapeutic synthetic lethality efficacy of SLNs formulation, cell cycle arrest, DNA damage, mRNA expression levels of PARP1, H2AFX, RAD51 and BRCA1 gene were investigated. Then, PARP, ɣH2AX, RAD51 and BRCA1 protein expression and nuclear localization were analyzed by western blot and immunofluorescence analysis. When compared with BMN 673, BMN 673-SLNs showed remarkably a decrease in HCC1937 and HCC1937-R cells with less damage to MCF-10A cells. BMN 673-SLNs significantly induced toxicity through double-stranded DNA breaks, G2/M cell cycle arrest and PARP cleavage in TNBC cells. Additionally, BMN 673-resistance was mediated by miR-107, miR-193b and miR-1255b targeting BRCA1 and RAD51 in HCC1937 and HCC1937-R cells. However, BMN 673-SLNs treatment could overcome HR-mediated resistance in TNBC cells. As a result, our findings suggest that SLNs formulation strongly provides a synthetic lethal therapeutic potential in BRCA1 mutated sensitive and resistant TNBC cells.

Mutational Profile of Aggressive, Localised Prostate Cancer from African Caribbean Men Versus European Ancestry Men

Causes of high mortality of prostate cancer in men of African ancestry living in the French West Indies are still debated, between suspicions of environmental factors and genetic susceptibility. We report an integrated genomic study of 25 tumour tissues from radical prostatectomy of aggressive (defined by International Society of Urological Pathology ≥3) prostate cancer patients (10 African Caribbean and 15 French Caucasian) using single nucleotide polymorphism arrays, whole-genome sequencing, and RNA sequencing. The results show that African Caribbean tumours are characterised by a more frequent deletion at 1q41-43 encompassing the DNA repair gene PARP1, and a higher proportion of intrachromosomal rearrangements including duplications associated with CDK12 truncating mutations. Transcriptome analyses show an overexpression of genes related to androgen receptor activity in African Caribbean tumours, and of PVT1, a long non-coding RNA located at 8q24 that confirms the strong involvement of this region in prostate tumours from men of African ancestry.Patient summary: Mortality of prostate cancer is higher in African Caribbean men than in French Caucasian men. Specificities of the former could be explained by genomic events linked with key genes such as DNA damage pathway genes PARP1, CDK12, and the oncogenic long non-coding RNA gene PVT1 at the 8q24 prostate cancer susceptibility locus.

DNA is a new acceptor of PARP3 protein

DNA is a new acceptor of PARP3 protein

The CCR4-NOT Complex Maintains ß-Cell Identity through the Repression of ß-Cell Disallowed Genes

Loss of β-cell identity, dedifferentiation and reprogramming are recognized as mechanisms of β-cell dysfunction in diabetes. Molecular β-cell identity is not only defined by the expression of signature functional β-cell specific genes but also the repression of several genes recently identified in β-cell research as β-cell disallowed genes. The molecular mechanisms involved in the repression of β-cell disallowed genes are largely unknown. Here, we show that the CCR4-NOT complex, a major deadenylase conserved in eukaryotes, is involved in post-transcriptional regulation of β-cell disallowed genes. β-cell specific depletion of CNOT3 (CNOT3βKO), a CCR4-NOT complex subunit, in mice promotes deceased insulin secretion, early impaired glucose tolerance and the development of overt diabetes at 12 weeks of age. CNOT3βKO islets display decreased insulin content and decreased glucose responsiveness. Furthermore, CNOT3 depleted ß cells exhibit ultrastructural abnormalities including: degranulated β cells, increased immature insulin granules and abnormal mitochondria. RNAseq and qRT-PCR analyses revealed that CNOT3βKO islets have decreased expression of β-cell functional genes: (Ins1, Ins2, MafA, Pcsk2 and Cpe) and increased expression of 9 of the 11 core β-cell disallowed genes: (Slc16A1, Ldha, Pdgfra, Cxcl12, Igfbp4, Oat, Maf, Smad3 and Cd302) and progenitor-like cells genes: (Nanog and Ngn3) supporting the loss of β-cell identity. Using the total RNAseq data, we assessed mRNA stability by calculating the relative amounts of introns and exons for a given mRNA. RNA immunoprecipitation revealed that the CCR4-NOT complex directly binds several upregulated stabilized β-cell disallowed genes: Slc16A1, Tgm2, Cat and Parp3 genes. The present data highlight deadenylation as a novel molecular mechanism regulating β-cell disallowed genes. Thus, we further propose that the CCR4-NOT complex is essential for maintaining β-cell identity by repressing β-cell disallowed genes. Disclosure D. Mostafa: None. A. Takahashi: None. A. Yanagiya: None. T. Yamamoto: None.

Ectopic microRNAs used to preserve human mesenchymal stem cell potency and epigenetics.

Human mesenchymal stem cells (hMSCs) have remarkable potential for use in regenerative medicine. However, one of the great challenges is preserving their potency for long time. This study investigated the effect of miRNA ectopic expression on their proliferation and also on the expression level of Parp1 as an epigenetic switch preserving pluripotency in hMSCs. A cationic liposome was prepared as an efficient carrier for miRNA delivery. The miRNA loading efficiency and physical stability of vesicles were measured, and their scanning electron microscopic shapes determined. hMSCs were transfected with miR-302a and miR-34a followed by assessment of their proliferation potency with MTT assay and measurement of the expression of Parp1 by quantitative polymerase chain reaction (QPCR). Cell transfection with miR-302a and miR-34a efficiently and differentially affects the proliferation potency of hMSCs and the expression level of Parp1 as the key epigenetic factor involved in pluripotency. While miR-302a increases Parp1 expression, miR-34a suppresses it significantly, showing differential effects. Our results demonstrated that miRNA-based treatments represent efficient therapeutic systems and hold a great promise for future use in regenerative medicine through modification of hMSC pluripotency and epigenome.

Primary Mutational Landscape Linked with Pre-Docetaxel Lactate Dehydrogenase Levels Predicts Docetaxel Response in Metastatic Castrate-Resistant Prostate Cancer

BackgroundDocetaxel chemotherapy is a standard of care for metastatic castrate-resistant prostate cancer (mCRPC): 40–50% of patients achieve a biochemical response. However, there is a lack of response predictive biomarkers. ObjectiveTo assess lactate dehydrogenase (LDH) as a docetaxel response biomarker in mCRPC and to examine the association of LDH with genomic alterations in primary diagnostic biopsies. Design, setting, and participantsClinical and associated primary tumour-targeted next-generation sequencing data from matched training (n=150) and test (n=120) cohorts of progressive mCRPC patients receiving docetaxel therapy were analysed. Data were correlated with large-scale prostate cancer genomic datasets. Outcome measurements and statistical analysisProstate-specific antigen (PSA) response, radiographic response, biochemical progression-free survival (PFS), overall survival (OS), genomic analysis of primary biopsies, and genomic datasets (Memorial Sloan Kettering Cancer Center [MSKCC] and SU2C/PCF). Results and limitationsSerum LDH ≥450U/l is a reliable prognostic biomarker (area under the curve: 0.757 [standard deviation 0.054, 95% confidence interval [CI] 0.650–0.864, p<0.001]) in progressive mCRPC, predicting PFS at 3 mo. Patients with LDH ≥450U/l were poorer PSA responders, with shorter PFS (213 vs 372 d, hazard ratio [HR] 1.876, 95% CI 1.289–2.7300) and OS (362 vs 563 d, HR 1.630, 95% CI 1.127–2.357). High LDH is an independent surrogate marker for survival following docetaxel and predicts a poor radiological response (p=0.043). Of the 14 patients with LDH ≥450U/l available for next-generation sequencing, nine (64.3%) were more likely to have DNA repair gene mutation(s) (BRCA1/2, ATM, CHEK2, Fanconi anaemia gene) in their primary biopsy. Cross correlation with MSKCC and SU2C/PCF databases revealed a positive correlation between LDHA, PARP1 (r=0.667, p<0.01), and other DNA repair genes. ConclusionsGenomic abnormalities of LDHA and DNA repair in primary biopsies link to high pretreatment LDH and poor response to docetaxel in mCRPC. Patient summaryThe presence of mutations of the lactate dehydrogenase and DNA repair pathways are associated with aggressive prostate cancer and poor response to chemotherapy later in the disease.

Correlation of primary biopsy mutational landscape to pre-docetaxel LDH for prediction of docetaxel therapeutic response.

220 Background: There is a lack of biomarkers to predict docetaxel response. Here we assess the potential of pre-treatment LDH, associated to the mutational background of the primary biopsy taken prior to 1st line therapy with ADT, to predict docetaxel response in the castrate resistant setting. Methods: Clinical and associated primary biopsy targeted next-generation sequencing data from matched training (n = 150) and test (n = 120) sets of retrospective progressive mCRPC patients (diagnosed 1996-2006) treated with docetaxel therapy were analyzed. LDH thresholds were determined and validated on the training and test sets respectively. Clinico-pathological associations with LDH were assessed using student t-test, Wilcoxon test and Chi-square test and predictive value of LDH determined by linear regression analysis for PSA and radiologic response. Time to event outcomes (PFS &amp; OS) was evaluated by Kaplan-Meier. Meta-analysis of LDH association with DNA repair genes in the MSKCC and SU2C/PCF was conducted using cBioPortal Results: Using pre-docetaxel serum LDH of ≥450U/L as a prognostic threshold (AUC:0.75 (SD 0.054, 95% CI, 0.650–0.864, P &lt; 0.001)) patients with LDH ≥450U/L were poorer PSA responders, with shorter PFS (213 vs 372 days, HR 1.876 (95% CI, 1.289-2.730)) and OS (362 vs 563 days, HR 1.630 (95% CI, 1.127-2.357)). LDH was also an independent surrogate marker for prediction of poor radiologic response and survival following docetaxel chemotherapy (P = 0.043). Genomic analysis showed that patients with LDH ≥450U/L (9/14 (64.3%)) have a higher tumour mutational burden (TMB) at the point of primary pre-ADT biopsy (mean, 46.2 vs 6.2 mutations/MB; p = 0.129) and that they were more likely to have DNA repair gene mutation(s) (BRCA1/2, ATM, CHEK2 and Fanconi’s anemia gene). Meta-analysis of the large MSKCC and the SU2C-PCF patient genomic databases confirmed the positive correlation between the LDH gene LDHA and PARP1 gene (r = 0.667, p &lt; 0.01) expression and expression of other DNA repair genes. Conclusions: High pre-treatment serum LDH coupled with mutations in the DNA repair pathway in primary pre-ADT biopsy correlates with poor docetaxel response and overall survival in the castrate resistant state.

Targeting the MYCN-PARP-DNA Damage Response Pathway in Neuroendocrine Prostate Cancer.

Purpose: We investigated MYCN-regulated molecular pathways in castration-resistant prostate cancer (CRPC) classified by morphologic criteria as adenocarcinoma or neuroendocrine to extend the molecular phenotype, establish driver pathways, and identify novel approaches to combination therapy for neuroendocrine prostate cancer (NEPC).Experimental Design and Results: Using comparative bioinformatics analyses of CRPC-Adeno and CRPC-Neuro RNA sequence data from public data sets and a panel of 28 PDX models, we identified a MYCN-PARP-DNA damage response (DDR) pathway that is enriched in CRPC with neuroendocrine differentiation (NED) and CRPC-Neuro. ChIP-PCR assay revealed that N-MYC transcriptionally activates PARP1, PARP2, BRCA1, RMI2, and TOPBP1 through binding to the promoters of these genes. MYCN or PARP1 gene knockdown significantly reduced the expression of MYCN-PARP-DDR pathway genes and NED markers, and inhibition with MYCNsi and/or PARPsi, BRCA1si, or RMI2si significantly suppressed malignant activities, including cell viability, colony formation, and cell migration, in C4-2b4 and NCI-H660 cells. Targeting this pathway with AURKA inhibitor PHA739358 and PARP inhibitor olaparib generated therapeutic effects similar to those of gene knockdown in vitro and significantly suppressed tumor growth in both C4-2b4 and MDACC PDX144-13C subcutaneous models in vivoConclusions: Our results identify a novel MYCN-PARP-DDR pathway that is driven by N-MYC in a subset of CRPC-Adeno and in NEPC. Targeting this pathway using in vitro and in vivo CRPC-Adeno and CRPC-Neuro models demonstrated a novel therapeutic strategy for NEPC. Further investigation of N-MYC-regulated DDR gene targets and the biological and clinical significance of MYCN-PARP-DDR signaling will more fully elucidate the importance of the MYCN-PARP-DDR signaling pathway in the development and maintenance of NEPC. Clin Cancer Res; 24(3); 696-707. ©2017 AACR.

Metformin and epothilone A treatment up regulate pro-apoptotic PARP-1, Casp-3 and H2AX genes and decrease of AKT kinase level to control cell death of human hepatocellular carcinoma and ovary adenocarcinoma cells

High mortality rates in ovarian and liver cancer are largely a result of resistance to currently used chemotherapy. Here, we investigated genotoxic and pro-oxidant effects of metformin (MET) and epothilone A (A) in combination with respect to apoptosis in HepG2 and SKOV-3 cancer cells. Reactive oxygen species (ROS) was studied using 2′,7′-dichlorodihydrofluoresein diacetate, and samples were analyzed for the presence and absence of the N-acetylcysteine (NAC). Expression of genes involved in programmed cell death, oxidative and alkylating DNA damage was measured. Probes were analyzed in the presence of Akt or nuclear factor-κB inhibitor. Compared to either drug alone, combination of epothilone A and metformin was more potent; decreased Akt level; and elevated percentage of apoptotic cells, induced cell cycle arrest at G1 phase and elevated the sub-G1 cell population by increasing the mRNA level of caspase-3, poly (ADP-ribose) polymerase-1 and H2AX. The anticancer effect of the drug combination was partially reversed by NAC supplementation, suggesting that ROS generation is required to induce apoptosis. The present study demonstrates that novel combination such as epothilone A and MET show promise in expanding ovarian and liver cancer therapy.

MicroRNA-binding site polymorphisms in genes involved in colorectal cancer etiopathogenesis and their impact on disease prognosis.

According to the Vogelstein's model of colorectal carcinogenesis, genetic variations in highly penetrant genes may be involved in the colorectal cancer (CRC) pathogenesis. Similarly, aberrant function and/or altered expression of microRNAs (miRNAs) often occur in CRC. In this context, polymorphisms in miRNA-binding sites (miRSNPs) may affect miRNA/target gene interaction, resulting in differential mRNA/protein expression and increased susceptibility to common diseases. To explore this phenomenon, we have mined the 3' untranslated regions (3'UTRs) of genes known to be frequently mutated in CRC to search for miRSNPs and tested their association with CRC risk and clinical outcome. Eight miRSNPs (rs1804191, rs397768, rs41116 in APC; rs1137918, s227091, rs4585 in ATM; rs712, rs1137282, rs61764370 in KRAS; rs8674 in PARP1 and rs16950113 in SMAD7) were tested for their association with CRC risk in a case-control study (1111 cases and 1469 healthy controls). The role of these miRSNPs was also investigated in relation to clinical outcome on a subset of patients with complete follow-up. rs8679 within PARP1 was associated with CRC risk and patients' survival. In the dominant model, carriers of at least one C allele were at a decreased risk of cancer (P = 0.05). The CC genotype in rs8679 was also associated with an increased risk of recurrence/progression in patients that received 5-FU-based chemotherapy (log-rank test P = 0.03). Carriers of the homozygous variant genotype TT for rs712 in KRAS gene were associated with a decreased risk of rectal cancer (odds ratio (OR) = 0.65, 95% confidence intervals (CI) 0.43-1.00, P = 0.05) while individuals with colon cancer carrying the heterozygous GT genotype showed a longer overall survival (OS) (P = 0.04). We provide the first evidence that variations in potential miRNA-binding target sites in the 3' UTR of PARP1 gene may modulate CRC risk and prognosis after therapy. Further studies are needed to replicate our finding and assess miRSNPs as predictive biomarkers in independent populations.

Downregulation of miR-221-3p and upregulation of its target gene PARP1 are prognostic biomarkers for triple negative breast cancer patients and associated with poor prognosis.

The purpose of this study was to identify microRNAs (miRNAs) closely associated with the prognosis of triple-negative breast cancer (TNBC) and their possible targets. This study recruited 125 early-stage TNBC patients, including 40 cases in the experimental group (20 cases with poor prognoses vs. 20 cases with good prognoses) and 85 cases in the validation group (27 cases with poor prognoses vs. 58 cases with good prognoses). In the experimental group, miRNA microarray showed 34 differentially expressed miRNAs in patients with different prognoses. We selected 5 miRNAs for validation. The differential expression of miR-221-3p was further verified in the experimental and validation groups using real-time polymerase chain reaction (PCR). High miR-221-3p expression was associated with better 5-year disease-free survival (DFS) (HR = 0.480; 95% CI, 0.263–0.879; p = 0.017) of TNBC patients. High expression of its target gene PARP1 predicted poorer 5-year DFS (HR = 2.236, 95% CI, 1.209-4.136, p = 0.010). MiR-221-3p down-regulated PARP1 by targeting its 3'-untranslated region.In conclusion, low miR-221-3p expression may contribute to the poor outcome of TNBC patients through regulating PARP1. MiR-221-3p likely plays a role as a PARP1 inhibitor by directly regulating PARP1 expression, thereby affecting the prognoses of TNBC patients.

PARP inhibitors protect against sex- and AAG-dependent alkylation-induced neural degeneration.

Alkylating agents are commonly used to treat cancer. Although base excision repair (BER) is a major pathway for repairing DNA alkylation damage, under certain conditions, the initiation of BER produces toxic repair intermediates that damage healthy tissues. The initiation of BER by the alkyladenine DNA glycosylase (AAG, a.k.a. MPG) can mediate alkylation-induced cytotoxicity in specific cells in the retina and cerebellum of male mice. Cytotoxicity in both wild-type and Aag-transgenic (AagTg) mice is abrogated in the absence of Poly(ADP-ribose) polymerase-1 (PARP1). Here, we tested whether PARP inhibitors can also prevent alkylation-induced retinal and cerebellar degeneration in male and female WT and AagTg mice. Importantly, we found that WT mice display sex-dependent alkylation-induced retinal damage (but not cerebellar damage), with WT males being more sensitive than females. Accordingly, estradiol treatment protects males against alkylation-induced retinal degeneration. In AagTg male and female mice, the alkylation-induced tissue damage in both the retina and cerebellum is exacerbated and the sex difference in the retina is abolished. PARP inhibitors, much like Parp1 gene deletion, protect against alkylation-induced AAG-dependent neuronal degeneration in WT and AagTg mice, regardless of the gender, but their efficacy in preventing alkylation-induced neuronal degeneration depends on PARP inhibitor characteristics and doses. The recent surge in the use of PARP inhibitors in combination with cancer chemotherapeutic alkylating agents might represent a powerful tool for obtaining increased therapeutic efficacy while avoiding the collateral effects of alkylating agents in healthy tissues.

A common intronic variant of PARP1 confers melanoma risk and mediates melanocyte growth via regulation of MITF.

Previous genome-wide association studies have identified a melanoma-associated locus at 1q42.1 that encompasses a ∼100-kb region spanning the PARP1 gene. Expression quantitative trait locus (eQTL) analysis in multiple cell types of the melanocytic lineage consistently demonstrated that the 1q42.1 melanoma risk allele (rs3219090[G]) is correlated with higher PARP1 levels. In silico fine-mapping and functional validation identified a common intronic indel, rs144361550 (-/GGGCCC; r2 = 0.947 with rs3219090), as displaying allele-specific transcriptional activity. A proteomic screen identified RECQL as binding to rs144361550 in an allele-preferential manner. In human primary melanocytes, PARP1 promoted cell proliferation and rescued BRAFV600E-induced senescence phenotypes in a PARylation-independent manner. PARP1 also transformed TERT-immortalized melanocytes expressing BRAFV600E. PARP1-mediated senescence rescue was accompanied by transcriptional activation of the melanocyte-lineage survival oncogene MITF, highlighting a new role for PARP1 in melanomagenesis.

Abstract 3716: Exploring the significance of PARP-1 expression for therapy and clinical PET/CT imaging of PARP-1 in ovarian cancer

Abstract Introduction: Poly(ADP-ribose) Polymerase 1 (PARP-1) is a multi-faceted enzyme that plays a significant role in DNA single-strand break and double-strand break repair. PARP inhibitors are emerging targeted therapeutics that inhibit the catalytic activity of PARP-1 and trap it on DNA producing poisonous lesions that result in cell death. While there is a vast body of pre-clinical and clinical data supporting the use of PARP inhibitors in cancers that express homologous recombination deficiencies like mutations within BRCA1/2 genes, there is an inadequate characterization of PARP-1 expression patterns in this context. Through pre-clinical studies we have explored the dynamics of PARP-1 expression in response to genotoxic stress, as well as the consequences of PARP-1 deletion for PARP inhibitor therapy in BRCA1 deficient ovarian cancer. In parallel, our group has performed the first clinical PET imaging study in epithelial ovarian cancer measuring PARP-1 in vivo using [18F]FluorThanatrace ([18F]FTT). Methods: CRISPR/Cas9 mediated PARP1 gene deletion was performed in BRCA1 deficient ovarian cancer cell lines. Next, in vitro cell viability assays were performed to evaluate the relative potency of clinically used PARP inhibitors and cisplatin. Following genotoxic stress the dynamics of PARP-1 expression were evaluated. In parallel clinical PET/CT imaging of PARP-1 was performed in epithelial ovarian cancer patients with correlative tissue histology. Results: Our studies indicate there is a spectrum of PARP-1 expression in epithelial ovarian cancer and in vitro BRCA1 mutants show higher PARP-1 expression compared to non-BRCA mutants. In addition, PARP-1 expression is required for PARP inhibitor efficacy in vitro and is either more significant or equal to BRCA1 mutational status. Also, high PARP-1 expression corresponded with platinum sensitivity in vitro. Furthermore, we observed PARP-1 expression increased in response to genotoxic insult relative to DNA damage measured by gH2AX. Lastly, our observations have been further supplemented by clinical [18F]FTT PET/CT images in ovarian cancer patients, which showed a spectrum of PARP-1 expression that corresponded with DNA damage measured by gH2AX. Conclusion: PARP-1 expression has the potential to identify functional DNA repair deficiencies and to provide a biomarker for assessing response to DNA damaging therapies. In complement, clinical PET imaging with [18F]FTT offers a novel technology to determine PARP-1 expression in ovarian cancer patients and warrants further study. Citation Format: Mehran Makvandi, Austin Pantel, Lauren E. Schwartz, Kuiying Xu, Chia-Ju Hsieh, Hyoung Kim, Shi-Hong Li, Robert Doot, Sharon Lee, Fiona Simpkins, Roger A. Greenberg, David A. Mankoff, Robert H. Mach, Lilie Lin. Exploring the significance of PARP-1 expression for therapy and clinical PET/CT imaging of PARP-1 in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3716. doi:10.1158/1538-7445.AM2017-3716

P 034 - By downregulating transcription of PARP1, CDK4/6 inhibitors sensitise human lung cancer cells to oxidative stress-induced DNA damage triggered by WP631 and etoposide

Inhibitors of CDK4/6 – LEE011 and PD0332991 have been tested in clinical trials in combination with other anticancer drugs for their use in cancer treatment. These compounds are documented to arrest cell cycle progression. We show that in human lung cancer cells these agents cause cell accumulation in G1 phase and repression of PARP1 transcription by triggering the recruitment of RB-E2F1-HDAC1-EZH2 repressive complex to the promoter of PARP1 gene, which encodes the protein involved in among other things several mechanisms of DNA damage repair. PARP1 repression could be reversed by administration of inhibitors of histone acetyltransferases and polycomb repressive complex 2 in growth arrested cells. Moreover, cells pre-incubated with LEE011 and PD0332991, in which PARP1 expression was downregulated, were more sensitive to cell death resulting from their treatment with WP631, etoposide and hydrogen peroxide than corresponding cells, in which PARP1 expression was sustained by their stable transfection with an expression vector carrying cDNA for PARP1. Downregulation of PARP1 transcription in the lung cancer cells by treatment with CDK4/6 inhibitors was followed by the increase in DNA damage in consequence of oxidative stress generated by WP631, etoposide and hydrogen peroxide.