poly(ADP-ribose) Polymerase-1 Hyperactivation Research Articles

Sevoflurane exposure during the second trimester induces neurotoxicity in offspring rats by hyperactivation of PARP-1.

Fetal exposure to general anesthesia may cause noteworthy neurocognitive impairment, but the mechanisms are unclear. Our study designed to explore the potential mechanism of neurotoxicity in offspring rats after sevoflurane exposure to the pregnant rats during the second trimester. Pregnant rats (G14 day) were administrated with or without 3.5% sevoflurane, 40mg/kg 3-aminobenzamide (3-AB), inhibitor of poly ADP ribose polymerase 1 (PARP-1), or 10mg/kg TC-2153, inhibitor of striatal-enriched phosphatase 61 (STEP61). Afterwards, the effects on expression of β-tubulin (TUJ1), neurite outgrowth inhibitor A (Nogo-A), parthanatos-related and STEP61/proline-rich tyrosine kinase 2 (Pyk2) pathway-associated proteins, and reactive oxygen species (ROS) levels were examined by immunofluorescence staining, Western blot, and dihydroethidium (DHE) staining, respectively. Moreover, morphological changes in the hippocampal CA3 region and neuronal cell death were tested by glycine silver staining and TUNEL and immunofluorescence double staining, respectively. Furthermore, spatial learning and memory functions of rats on postnatal 28-33days (PND 28-33) were evaluated by morris water maze (MWM). Mid-pregnancy exposure to sevoflurane led to excessive PARP-1 activation, poly (ADP-ribose) (PAR) polymer accumulation, apoptosis-inducing factor (AIF) nuclear translocation, and Nogo-A accumulation. Besides, sevoflurane significantly inhibited neurite growth and increased cell death in the fetal rat brain. Additionally, sevoflurane activated STEP61/Pyk2 pathway and increased ROS levels. However, 3-AB or TC-2153 significantly alleviated cell death, promoted neurites growth, and improved sevoflurane-induced spatial learning and memory impairment. This study proposes that sevoflurane exposure during the second trimester incudes neurotoxicity in offspring rats by hyperactivation of PARP-1 via STEP61/Pyk2 pathway.

Molecular Mechanisms of Parthanatos and Its Role in Diverse Diseases.

Differential evolution of apoptosis, programmed necrosis, and autophagy, parthanatos is a form of cell death mediated by poly(ADP-ribose) polymerase 1 (PARP1), which is caused by DNA damage. PARP1 hyper-activation stimulates apoptosis-inducing factor (AIF) nucleus translocation, and accelerates nicotinamide adenine dinucleotide (NAD+) and adenosine triphosphate (ATP) depletion, leading to DNA fragmentation. The mechanisms of parthanatos mainly include DNA damage, PARP1 hyper-activation, PAR accumulation, NAD+ and ATP depletion, and AIF nucleus translocation. Now, it is reported that parthanatos widely exists in different diseases (tumors, retinal diseases, neurological diseases, diabetes, renal diseases, cardiovascular diseases, ischemia-reperfusion injury...). Excessive or defective parthanatos contributes to pathological cell damage; therefore, parthanatos is critical in the therapy and prevention of many diseases. In this work, the hallmarks and molecular mechanisms of parthanatos and its related disorders are summarized. The questions raised by the recent findings are also presented. Further understanding of parthanatos will provide a new treatment option for associated conditions.

KDM6B promotes PARthanatos via suppression of O6-methylguanine DNA methyltransferase repair and sustained checkpoint response.

Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA damage sensor and contributes to both DNA repair and cell death processes. However, how PARP-1 signaling is regulated to switch its function from DNA repair to cell death remains largely unknown. Here, we found that PARP-1 plays a central role in alkylating agent-induced PARthanatic cancer cell death. Lysine demethylase 6B (KDM6B) was identified as a key regulator of PARthanatos. Loss of KDM6B protein or its demethylase activity conferred cancer cell resistance to PARthanatic cell death in response to alkylating agents. Mechanistically, KDM6B knockout suppressed methylation at the promoter of O6-methylguanine-DNA methyltransferase (MGMT) to enhance MGMT expression and its direct DNA repair function, thereby inhibiting DNA damage-evoked PARP-1 hyperactivation and subsequent cell death. Moreover, KDM6B knockout triggered sustained Chk1 phosphorylation and activated a second XRCC1-dependent repair machinery to fix DNA damage evading from MGMT repair. Inhibition of MGMT or checkpoint response re-sensitized KDM6B deficient cells to PARthanatos induced by alkylating agents. These findings provide new molecular insights into epigenetic regulation of PARP-1 signaling mediating DNA repair or cell death and identify KDM6B as a biomarker for prediction of cancer cell vulnerability to alkylating agent treatment.

Therapeutic Potentials of Poly (ADP-Ribose) Polymerase 1 (PARP1) Inhibition in Multiple Sclerosis and Animal Models: Concept Revisiting.

Poly (ADP‐ribose) polymerase 1 (PARP1) plays a fundamental role in DNA repair and gene expression. Excessive PARP1 hyperactivation, however, has been associated with cell death. PARP1 and/or its activity are dysregulated in the immune and central nervous system of multiple sclerosis (MS) patients and animal models. Pharmacological PARP1 inhibition is shown to be protective against immune activation and disease severity in MS animal models while genetic PARP1 deficiency studies reported discrepant results. The inconsistency suggests that the function of PARP1 and PARP1‐mediated PARylation may be complex and context‐dependent. The article reviews PARP1 functions, discusses experimental findings and possible interpretations of PARP1 in inflammation, neuronal/axonal degeneration, and oligodendrogliopathy, three major pathological components cooperatively determining MS disease course and neurological progression, and points out future research directions. Cell type specific PARP1 manipulations are necessary for revisiting the role of PARP1 in the three pathological components prior to moving PARP1 inhibition into clinical trials for MS therapy.

Sevoflurane Exposure Induces Neuronal Cell Parthanatos Initiated by DNA Damage in the Developing Brain via an Increase of Intracellular Reactive Oxygen Species

The safety of volatile anesthetics in infants and young children has been drawing increasing concern due to its potential neurotoxicity in the developing brain. Neuronal death is considered a major factor associated with developmental neurotoxicity after exposure to volatile anesthetics sevoflurane, but its mechanism remains elusive. Parthanatos, a new type of programmed cell death, resulting from poly (ADP-ribose) polymerase 1 (PARP-1) hyperactivation in response to DNA damage, was found to account for the pathogenesis of multiple neurological disorders. However, the role of Parthanatos in sevoflurane-induced neonatal neuronal cell death has not been investigated. To test it, neuronal cells treated with 2, 4, and 8% sevoflurane for 6, 12, and 24 h and postnatal day 7 rats exposed to 2.5% sevoflurane for 6 h were used in the present study. Our results found sevoflurane exposure induced neuronal cell death, which was accompanied by PARP-1 hyperactivation, cytoplasmic polymerized ADP-ribose (PAR) accumulation, mitochondrial depolarization, and apoptosis-inducing factor (AIF) nuclear translocation in the neuronal cells and hippocampi of rats. Pharmacological or genetic inhibition of PAPR-1 significantly alleviated sevoflurane-induced neuronal cell death and accumulation of PAR polymer and AIF nuclear translocation, which were consistent with the features of Parthanatos. We observed in vitro and in vivo that sevoflurane exposure resulted in DNA damage, given that 8-hydroxydeoxyguanosine (8-OHdG) and phosphorylation of histone variant H2AX (γH2AX) were improved. Moreover, we detected that sevoflurane exposure was associated with an overproduction of intracellular reactive oxygen species (ROS). Inhibition of ROS with antioxidant NAC markedly alleviated DNA damage caused by sevoflurane, indicating that ROS participated in the regulation of sevoflurane-induced DNA damage. Additionally, sevoflurane exposure resulted in upregulation of Parthanatos-related proteins and neuronal cell death, which were significantly attenuated by pretreatment with NAC. Therefore, these results suggest that sevoflurane exposure induces neuronal cell Parthanatos initiated by DNA damage in the developing brain via the increase of intracellular ROS.

Role of b‐lapachone treatment mediated base excision repair protein PARylation in colorectal cancer cells.

Poly (ADP‐ribose) PAR is a protein post‐translational modification catalyzed by a family of enzymes known as PARPs. Most solid tumors overexpress NAD(P)H;Quinone Oxidoreductase 1 (NQO1), which catalyzes a futile redox cycle of b‐lapachone during exposure, resulting in the formation of high levels of reactive oxygen species (ROS). Futile cycle b‐lapachone recycling produces elevated superoxide levels, resulting in massive levels of hydrogen peroxide that lead to substantial DNA damage and endoplasmic reticulum Ca2+ release. DNA damage and Ca+2 entry into the nucleus leads to the hyperactivation of poly(ADP‐ribose) polymerase 1 (PARP1). A majority of parylation is noted when hyperactivated PARP1 self‐parylates, forming extensive Poly(ADP) ribosylated PAR‐PARP1 levels are noted within 5 mins of exposure to 4 μM β‐lap in A549 cells, as noted by Western blotting using an antibody specific for PARylated moieties. PAR‐PARP1 is a protein post‐translational modification catalyzed by a family of enzymes known as PARPs. DNA single strand breaks along with base‐damage and abasic sites together with nuclear Ca2+ levels lead to hyperactivation of PARP1, a DNA repair enzyme that utilizes NAD+ to generate PAR moieties. This is followed by dramatic NAD+/ATP losses and tumor cells die of a special programmed necrosis process, referred to as NAD+‐keresis. PAR‐PARP1 is rapidly degraded by poly(ADP‐ribose) glycohydrolase (PARG) a exo‐ and endoglycosidase.PARG‐knockdown HCT116 cells were used to gain insight into the function of PARG and whether PARG depletion would enhance b‐lapachone induced cell death by blocking PAR recycling. Proteomic screening after b‐lapachone treatment in colorectal cancer cell line revealed the PARylation landscape of base excision, mismatch and nucleotide excision repair proteins. Twenty (20) of the proteins were found to overlap with H2O2 treatments (200 μM or 2 mM), while one protein (i.e., SPSF) was unique to b‐lapachone treatment. b‐Lapachone treatment affects BER pathways and qualitative analysis of the human Asp‐ and Glu‐ADP‐ribosylated proteome after b‐lapachone treatment indicate major alterations in BER pathways. We confirmed that b‐lapachone mediated cytotoxicity was independent of PARG knockdown or TOPO I or II protein losses. In contrast, RFC1 and PCNA siRNA‐mediated protein knock downs significantly enhanced b‐lapachone lethality, whereas knockdown of Topo I or Topo IIalpha did not affect b‐lapachone lethality. Taken together, these results demonstrated that knockdown of RFC1 enhances lethality of b‐lapachone and could serve as an effective treatment strategy in cancer conditions.Support or Funding InformationThis work was funded by NIH/NCI 5 R01 CA102792‐16 to DAB.

Proteomic screening reveals the PARylation landscape of base excision repair proteins after Beta‐Lapachone treatment in colorectal cancer cells

Colorectal cancer (CRC) is a leading cause of cancer death and the third most common type of cancer worldwide. In early cases, surgery is the mainstay of treatment, but often patients are primarily diagnosed in an advanced stage of disease and may have distant metastases. Most solid tumors overexpress NAD(P)H;Quinone Oxidoreductase 1 (NQO1), which catalyzes a futile redox cycle of b‐lapachone during exposure, resulting in the formation of high levels of reactive oxygen species (ROS). Futile cycle b‐lapachone recycling produces elevated superoxide levels, resulting in massive levels of hydrogen peroxide that lead to substantial DNA damage and endoplasmic reticulum Ca2+ release. DNA damage and Ca+2 entry into the nucleus leads to the hyperactivation of poly(ADP‐ribose) polymerase 1 (PARP1). A majority of parylation is noted when hyperactivated PARP1 self‐parylates, forming extensive Poly(ADP) ribosylated PAR‐PARP1 levels are noted within 5 mins of exposure to 4 μM β‐lap in A549 cells, as noted by Western blotting using an antibody specific for PARylated moieties. PAR‐PARP1 is a protein post‐translational modification catalyzed by a family of enzymes known as PARPs. DNA single strand breaks along with base‐damage and abasic sites together with nuclear Ca2+ levels lead to hyperactivation of PARP1, a DNA repair enzyme that utilizes NAD+ to generate PAR moieties. This is followed by dramatic NAD+/ATP losses and tumor cells die of a special programmed necrosis process, referred to as NAD+‐keresis.PAR‐PARP1 is rapidly degraded by poly(ADP‐ribose) glycohydrolase (PARG) a exo‐ and endoglycosidase. PARG‐knockdown HCT116 cells were used to gain insight into the function of PARG and whether PARG depletion would enhance b‐lapachone induced cell death by blocking PAR recycling. Proteomic screening after b‐lapachone treatment in colorectal cancer cell line revealed the PARylation landscape of base excision, mismatch and nucleotide excision repair proteins. Twenty (20) of the proteins were found to overlap with H2O2 treatments (200 μM or 2 mM), while one protein (i.e., SPSF) was unique to b‐lapachone treatment. b‐Lapachone treatment affects BER pathways and qualitative analysis of the human Asp‐ and Glu‐ADP‐ribosylated proteome after b‐lapachone treatment indicate major alterations in BER pathways. We confirmed that b‐lapachone mediated cytotoxicity was independent of PARG knockdown or TOPO I or II protein losses. In contrast, RFC1 and PCNA siRNA‐mediated protein knock downs significantly enhanced b‐lapachone lethality, whereas knockdown of Topo I or Topo IIalpha did not affect b‐lapachone lethality. Taken together, these results demonstrated that knockdown of RFC1 enhances lethality of b‐lapachone and could serve as an effective treatment strategy in CRC. We are currently delineating the mechanism of enhanced lethality of β‐lapachone by loss of RFC1.Support or Funding InformationThis work was funded by NIH/NCI 5 R01 CA102792‐16 to DAB.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

OGG1-initiated base excision repair exacerbates oxidative stress-induced parthanatos

Oxidative stress-induced DNA damage has been well acknowledged as a major cause leading to cell death, which is etiologically linked to ischemic injury and degenerative alterations. The most common oxidation product of DNA is base lesion 8-oxo-7,8-dihydroguanine (8-oxoG), which is repaired by 8-oxoG glycosylase1 (OGG1)-initiated baseexcision repair (BER) pathway (OGG1-BER); however, the role of OGG1-BER in oxidative stress-induced cell death is poorly investigated. DNA strand breaks and apurinic/apyrimidinic (AP) sites are effective substrates to activate DNA damage sensor poly(ADP-ribose) polymerase 1 (PARP1). Overactivation of PARP1 is associated with apoptosis-inducing factor (AIF)-mediated and caspase-independent cell death (parthanatos). We hypothesized that after an excessive oxidative insult, OGG1-BER-generated strand breaks result in hyperactivation of PARP1 and consequently cell death. To test, wild type, knockout, siRNA-depleted MEFs and neuroblastoma cells, or those expressing repair-deficient OGG1 mutants were oxidatively stressed and the role of OGG1 was examined. Results showed that OGG1-BER further increases the levels of ROS-induced DNA damage by generating repair intermediates, leading to PARP1 overactivation and cell death. Cells lacking or expressing repair-deficient OGG1 showed lower levels of DNA strand lesions, PARP1 activation, and nuclear translocation of apoptosis-inducing factor, resulting in the increased resistance to ROS-induced parthanatos. These results suggested that OGG1 guards genome integrity through either lesion repair or elimination of cells with malignant potential, to maintain the homeostasis of the host, which might depend on the magnitude of guanine oxidation.

Determination of the role of PAR‐associated proteins in ROS‐mediated cell death

2,3,5‐Tris‐(glutathion‐S‐yl)hydroquinone (TGHQ) is a nephrotoxic and nephrocarcinogenic metabolite of hydroquinone. TGHQ can redox cycle, generating ROS which cause DNA strand breaks, hyperactivation of poly(ADP‐ribose) polymerase‐1 (PARP‐1), increases in intracellular calcium concentration (i[Ca2+]), and cell death. PARP‐1 is a nuclear protein involved in DNA repair, transcriptional regulation and intracellular trafficking, and catalyzes the attachment of a posttranscriptional modification, consisting of multi branched ADP‐ribose polymers (PAR) on target proteins. ROS stress promotes PARP‐1 hyperactivation and elevations in i[Ca2+] which are reciprocally coupled, resulting in cell death. The molecular mechanism of this interaction is unclear. The aim of the present study was to identify TGHQ‐induced PAR‐associated proteins and their potential role in cell death. Human kidney proximal tubule cells (HK‐2) were treated with 400 μM TGHQ to induce ROS‐stress leading to PARP‐1 hyperactivation. PAR‐associated proteins were immunoprecipitated, followed by subsequent separation by SDS PAGE and proteomic analysis. A relative protein abundance analysis by spectral counts allowed us to obtain fold‐changes in protein abundance relative to control. 361 PAR‐associated proteins were significantly identified as modified by TGHQ treatment. From this cohort, 276 proteins showed an increased PAR association while 85 were decreased. Additionally, 13 targets had Gene Ontology annotations related to calcium. Of these, neuroblast differentiation‐associated protein (AHNAK), calcium homeostasis endoplasmic reticulum protein (CHERP) and general transcription factor II‐I (TFII‐I) are directly involved in modulation of i[Ca2+]. TFII‐I is a transcription factor that regulates i[Ca2+] by sequestering phospholipase C (PLC) in the cytosol. Under basal conditions free PLC binds and promotes the translocation of the transient receptor potential channel (TRPC3) to the plasma membrane leading to increases in i[Ca2+]. TFII‐I increased PAR‐association might therefore lead to calcium influx via TRPC3. Using co‐immunoprecipitation and immunodetection against TFII‐I, we confirmed increased TFII‐I PAR‐association. The effect of a TRPC3 inhibitor on TGHQ‐dependent modulation of i[Ca2+] was determined by live imaging of HK‐2 cells with the calcium sensitive dye fluo‐8 AM. Inhibition of TRPC3 promoted a delayed but higher increase in i[Ca2+]. Cellular compartmentalization of TFII‐I under TGHQ treatment was determined by cellular fractionation. TGHQ induced TFII‐I translocation from the nucleus to the cytosol as well as decreased tyrosine phosphorylation, which might have a functional effect on the transactivation potential of TFII‐I. In summary, LC‐MS/MS identified proteins with altered PARylation under ROS stress. TFII‐I is a novel PAR interacting protein which participates in signaling pathways with potential importance in TGHQ‐mediated cell death. Currently we are investigating the transcriptional and DNA repair effects of PAR‐associated TFII‐I that might be relevant to the mechanism of ROS‐dependent toxicity.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 68: Functional interactions of HPV and PARP-1 in head and neck cancer

Abstract Though the overall incidence of head and neck cancer has been declining over the last several decades, there has been a concomitant and worrisome rise in human-papilloma virus (HPV)-associated head and neck squamous cell carcinoma (HNSCC). HPV infection is a necessary but not sufficient condition for cancer development. Unlike in cervical cancer, where several co-factors including smoking and co-infection with other agents are well established, how HPV drives malignant transformation in head and neck cancer and which cellular factors are required are not well characterized. Recent evidence from our group has shown that poly (ADP-ribose) polymerase-1 (PARP-1) is overexpressed and overactive in HPV-positive (HPV(+)), but not HPV-negative (HPV(-)), oropharyngeal squamous cell carcinoma (OPSCC). The significance of PARP-1 overexpression and hyperactivation in cancer is only beginning to emerge. High levels of PARP-1 are found in a fraction of hepatocellular and breast cancers and correlate with poor prognosis. Recently, PARP-1 was implicated in prostate cancer progression. This study explores the role of PARP-1 in HPV infection and HNSCC carcinogenesis. Biochemical methods were used to determine PARP activity in vitro, in head and neck tumors, and during infection with HPV16 pseudovirus (PsV) or overexpression of HPV16 proteins in epithelial cells. The response to PARP inhibition was evaluated with clonogenic survival assays. HPV L1 mRNA in HNSCC was detected using quantitative real-time PCR and HPV L1 protein levels were determined by immunohistochemistry. Here, we show that the HPV16 major capsid protein L1 directly binds PARP-1 and activates poly(ADP-ribosyl)ation in the absence of DNA damage in vitro and in HPV(-) cells. Using PARP-1 knockout cells, we found that PARP-1 expression and enzymatic activity supports initial HPV infection. Furthermore, HPV(-) cells were sensitized to PARP inhibition both after L1 overexpression and after infection with HPV16 PsV particles. In conclusion, we report functional interactions between the viral capsid and cellular protein, signifying a vital role played by PARP-1 in HPV infection and carcinogenesis. Importantly, our data provide a mechanistic explanation for pharmacological PARP inhibition as an intriguing therapeutic opportunity for HPV(+) head and neck cancers. Citation Format: Cyril S. Gary, Michael Hajek, Asel Biktasova, Andrew Sewell, Yarbrough G. Wendell, Natalia Issaeva. Functional interactions of HPV and PARP-1 in head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 68.

DNA Damage and Energy Crisis are Central in the Mechanism for the Cytotoxicity of Pharmacological Ascorbate in Cancer Treatment

The clinical application of ascorbate in cancer treatment has a long and controversial history. The clinical potential of pharmacological ascorbate (P-AscH‒; IV delivery achieving mM concentrations in blood) as an adjuvant in cancer therapy is being re-evaluated. At mM concentrations, P-AscH‒ is thought to exhibit anti-cancer activity via generation of a flux of H2O2 in tumors. However, a complete understanding of mechanism for P-AscH‒ has not yet been established. Here, we use a cell culture model of pancreatic cancer, MIA PaCa-2 and PANC-1, to examine the effects of P-AscH‒ on DNA damage, and downstream consequences, including changes in bioenergetics. We have found that the high flux of H2O2 produced by P-AscH‒ induces both nuclear and mitochondrial DNA damage. In response to this DNA damage, we observed that poly (ADP-ribose) polymerase-1 (PARP-1) is hyperactivated, as determined by increased formation of poly (ADP-ribose) polymer. Using our unique absolute quantitation, we found that the P-AscH‒-mediated the overactivation of PARP-1, which results in consumption of NAD+, and subsequently depletion of ATP (energy crisis) leading to mitotic cell death. Time-course studies with MIA PaCa-2 cells showed that the level of NAD+ and ATP were reduced by 80% immediately after a 1-h exposure to P-AscH‒ (4 mM; 14 pmol cell-1); both species returned to near basal levels within 24 h. In parallel with these metabolic and energetic restorations, the lesions in nuclear DNA were removed within 3 h; however, even after 24 h, lesions in mitochondrial DNA were only partially repaired. We have also found that the ATR-Chk1 pathway has a major role in the maintenance of genomic integrity following treatment with P-AscH‒. Hence, combinations of P-AscH‒ and Chk1 inhibitors could have potential in the treatment of cancer. Hyperactivation of PARP-1 and DNA repair are ATP-consuming processes. Using a Seahorse XF96 Analyzer, we observed no changes in OCR or ECAR/PPR following treatment with P-AscH‒, indicating that the severe decrease in ATP is due solely to increased demand, not changes in the rate of production. These results clearly indicate that the combination of DNA damage coupled with compromised ATP availability could be a key aspect of the anti-cancer activity of P-AscH‒. These preclinical findings can guide the best use of P-AscH‒ as an adjuvant in cancer therapy.

Mitochondrial Dysfunction Mediated by Poly(ADP-Ribose) Polymerase-1 Activation Contributes to Hippocampal Neuronal Damage Following Status Epilepticus.

Mitochondrial dysfunction plays a central role in the neuropathology associated with status epilepticus (SE) and is implicated in the development of epilepsy. While excitotoxic mechanisms are well-known mediators affecting mitochondrial health following SE, whether hyperactivation of poly(ADP-ribose) polymerase-1 (PARP-1) also contributes to SE-induced mitochondrial dysfunction remains to be examined. Here we first evaluated the temporal evolution of poly-ADP-ribosylated protein levels in hippocampus following kainic acid-induced SE as a marker for PARP-1 activity, and found that PARP-1 was hyperactive at 24 h following SE. We evaluated oxidative metabolism and found decreased NAD+ levels by enzymatic cycling, and impaired NAD+-dependent mitochondrial respiration as measured by polarography at 24 h following SE. Stereological estimation showed significant cell loss in the hippocampal CA1 and CA3 subregions 72 h following SE. PARP-1 inhibition using N-(6-Oxo-5,6-dihydro-phenanthridin-2-yl)- N,N-dimethylacetamide (PJ-34) in vivo administration was associated with preserved NAD+ levels and NAD+-dependent mitochondrial respiration, and improved CA1 neuronal survival. These findings suggest that PARP-1 hyperactivation contributes to SE-associated mitochondrial dysfunction and CA1 hippocampal damage. The deleterious effects of PARP-1 hyperactivation on mitochondrial respiration are in part mediated through intracellular NAD+ depletion. Therefore, modulating PARP-1 activity may represent a potential therapeutic target to preserve intracellular energetics and mitochondrial function following SE.

Tumor-selective use of DNA base excision repair inhibition in pancreatic cancer using the NQO1 bioactivatable drug, β-lapachone.

Base excision repair (BER) is an essential pathway for pancreatic ductal adenocarcinoma (PDA) survival. Attempts to target this repair pathway have failed due to lack of tumor-selectivity and very limited efficacy. The NAD(P)H:Quinone Oxidoreductase 1 (NQO1) bioactivatable drug, ß-lapachone (ARQ761 in clinical form), can provide tumor-selective and enhanced synergy with BER inhibition. ß-Lapachone undergoes NQO1-dependent futile redox cycling, generating massive intracellular hydrogen peroxide levels and oxidative DNA lesions that stimulate poly(ADP-ribose) polymerase 1 (PARP1) hyperactivation. Rapid NAD+/ATP depletion and programmed necrosis results. To identify BER modulators essential for repair of ß-lapachone-induced DNA base damage, a focused synthetic lethal RNAi screen demonstrated that silencing the BER scaffolding protein, XRCC1, sensitized PDA cells. In contrast, depleting OGG1 N-glycosylase spared cells from ß-lap-induced lethality and blunted PARP1 hyperactivation. Combining ß-lapachone with XRCC1 knockdown or methoxyamine (MeOX), an apyrimidinic/apurinic (AP)-modifying agent, led to NQO1-dependent synergistic killing in PDA, NSCLC, breast and head and neck cancers. OGG1 knockdown, dicoumarol-treatment or NQO1- cancer cells were spared. MeOX + ß-lapachone exposure resulted in elevated DNA double-strand breaks, PARP1 hyperactivation and TUNEL+ programmed necrosis. Combination treatment caused dramatic antitumor activity, enhanced PARP1-hyperactivation in tumor tissue, and improved survival of mice bearing MiaPaca2-derived xenografts, with 33% apparent cures. Significance: Targeting base excision repair (BER) alone has limited therapeutic potential for pancreatic or other cancers due to a general lack of tumor-selectivity. Here, we present a treatment strategy that makes BER inhibition tumor-selective and NQO1-dependent for therapy of most solid neoplasms, particularly for pancreatic cancer.

PARP-1 Activation Requires Local Unfolding of an Autoinhibitory Domain

Poly(ADP-ribose) polymerase-1 (PARP-1) creates the posttranslational modification PAR from substrate NAD(+) to regulate multiple cellular processes. DNA breaks sharply elevate PARP-1 catalytic activity to mount a cell survival repair response, whereas persistent PARP-1 hyperactivation during severe genotoxic stress is associated with cell death. The mechanism for tight control of the robust catalytic potential of PARP-1 remains unclear. By monitoring PARP-1 dynamics using hydrogen/deuterium exchange-mass spectrometry (HXMS), we unexpectedly find that a specific portion of the helical subdomain (HD) of the catalytic domain rapidly unfolds when PARP-1 encounters a DNA break. Together with biochemical and crystallographic analysis of HD deletion mutants, we show that the HD is an autoinhibitory domain that blocks productive NAD(+) binding. Our molecular model explains how PARP-1 DNA damage detection leads to local unfolding of the HD that relieves autoinhibition, and has important implications for the design of PARP inhibitors.

Abstract P6-02-02: Exploiting Isobutyl-deoxynyboquinone-induced DNA damage responses and metabolic changes for breast cancer therapy

Abstract During oncogenic or cellular stress new genes are frequently (over)-expressed that could be exploited for targeted cancer therapy. The enzyme, NAD(P)H:quinone oxidoreductase-1 (NQO1) is over-expressed in most solid cancers, including 60% of primary and metastatic breast cancers regardless of subtype. Normally, NQO1 detoxifies quinones resulting in the formation of stable hydroquinones that are subsequently excreted from the cell. However, NQO1 bioreduction can turn certain rare quinones, such as β-lapachone and deoxynyboquinone (DNQ), into potent cell death-inducing compounds. These agents cause severe DNA damage, poly(ADP-ribose)polymerase-1 (PARP1) hyperactivation, NAD+/ATP loss, and programmed necrosis of NQO1-expressing cancer cells. Although ß-lapachone (ARQ761) is in current clinical trials at UTSW, more potent tumor-selective NQO1 compounds are needed. Based on its structure and mode of action, isobutyl-DNQ (IB-DNQ) was recently added to the spectrum of NQO1 substrates as a more selective and potent anti-cancer agent whose mechanism of action remains to be elucidated. Although NQO1 expression is a major determinant of IB-DNQ-induced lethality, previously published results from our group showed that increased catalase expression could cause marked cytoprotection. We conducted a screen for NQO1:Catalase ratios in 266 breast tumor samples, and 143 normal breast samples, for a total of 409 specimens. We found that NQO1 expression was significantly elevated in breast tumors compared to normal tissue. In contrast, catalase expression was suppressed in breast tumors versus adjacent normal tissue. These results predict that normal tissue, which typically has higher catalase levels than cancer cells, could be selectively spared from IB-DNQ-induced toxicity. Thus, NQO1:Catalase ratios favor use of IB-DNQ in breast cancers to exploit this large therapeutic window. Since NQO1 bioactivatable drugs synergize with agents that damage DNA, we hypothesized that certain cancer vulnerabilities (e.g., BRCA1-deficient breast cancers) that have elevated endogenous DNA damage would synergize with IB-DNQ. Exposure of breast cancer cells with IB-DNQ induced DNA damage, PARP1 hyperactivation, dramatic loss of essential nucleotides (NAD+/ATP), and µ-calpain-mediated programmed necrosis with 10X greater potency than ß-lapachone. IB-DNQ-induced DNA double-strand breaks (DSBs) that occurred in cells in S/G2 phases were mainly repaired by error-free homologous recombination (HR), and therefore BRCA1-deficient cancers, being HR defective, would be particularly vulnerable to IB-DNQ treatment. Indeed, HCC1937 breast cancer cells, deficient in BRCA1, were extremely sensitive to low dose IB-DNQ due to the overwhelming levels of IB-DNQ-induced DNA damage and their inability to repair it due to their compromised HR. In fact, IB-DNQ was far superior to PARP inhibitors in targeting BRCA1-deficient cells. Studies in vivo showed equivalent antitumor efficacy of IB-DNQ to β-lapachone and DNQ, but with much greater potency at lower doses. These findings offer preclinical ‘proof-of-concept’ for IB-DNQ as a potent chemotherapeutic agent for the treatment of breast cancers, especially those deficient in BRCA1. This research was supported by grant CA102972 to DAB. Citation Format: Mariya Ilcheva, Lifen Cao, Sandeep Burma, David Boothman. Exploiting Isobutyl-deoxynyboquinone-induced DNA damage responses and metabolic changes for breast cancer therapy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-02-02.

Enhanced non-homologous end joining contributes toward synthetic lethality of pathological RAD51C mutants with poly (ADP-ribose) polymerase.

Poly (ADP-ribose) polymerase 1 (PARP1) inhibitors are actively under clinical trials for the treatment of breast and ovarian cancers that arise due to mutations in BRCA1 and BRCA2. The RAD51 paralog RAD51C has been identified as a breast and ovarian cancer susceptibility gene. The pathological RAD51C mutants that were identified in cancer patients are hypomorphic with partial repair function. However, targeting cancer cells that express hypomorphic mutants of RAD51C is highly challenging. Here, we report that RAD51C-deficient cells can be targeted by a 'synthetic lethal' approach using PARP inhibitor and this sensitivity was attributed to accumulation of cells in the G2/M and chromosomal aberrations. In addition, spontaneous hyperactivation of PARP1 was evident in RAD51C-deficient cells. Interestingly, RAD51C-negative cells exhibited enhanced recruitment of non-homologous end joining (NHEJ) proteins onto chromatin and this accumulation correlated with increased activity of error-prone NHEJ as well as genome instability leading to cell death. Notably, inhibition of DNA-PKcs or depletion of KU70 or Ligase IV rescued this phenotype. Strikingly, stimulation of NHEJ by low dose of ionizing radiation (IR) in the PARP inhibitor-treated RAD51C-deficient cells and cells expressing pathological RAD51C mutants induced enhanced toxicity 'synergistically'. These results demonstrate that cancer cells arising due to hypomorphic mutations in RAD51C can be specifically targeted by a 'synergistic approach' and imply that this strategy can be potentially applied to cancers with hypomorphic mutations in other homologous recombination pathway genes.

PARP-1 hyperactivation and reciprocal elevations in intracellular Ca2+ during ROS-induced nonapoptotic cell death.

The generation of reactive oxygen species (ROS) has been implicated in the pathogenesis of renal ischemia/reperfusion injury, and many other pathological conditions. DNA strand breaks caused by ROS lead to the activation of poly(ADP-ribose)polymerase-1 (PARP-1), the excessive activation of which can result in cell death. We have utilized a model in which 2,3,5-tris(glutathion-S-yl)hydroquinone (TGHQ), a nephrotoxic and nephrocarcinogenic metabolite of hydroquinone, causes ROS-dependent cell death in human renal proximal tubule epithelial cells (HK-2), to further elucidate the role of PARP-1 in ROS-dependent cell death. TGHQ-induced ROS generation, DNA strand breaks, hyperactivation of PARP-1, rapid depletion of nicotinamide adenine dinucleotide (NAD), elevations in intracellular Ca(2+) concentrations, and subsequent nonapoptotic cell death in both a PARP- and Ca(2+)-dependent manner. Thus, inhibition of PARP-1 with PJ34 completely blocked TGHQ-mediated accumulation of poly(ADP-ribose) polymers and NAD consumption, and delayed HK-2 cell death. In contrast, chelation of intracellular Ca(2+) with BAPTA completely abrogated TGHQ-induced cell death. Ca(2+) chelation also attenuated PARP-1 hyperactivation. Conversely, inhibition of PARP-1 modulated TGHQ-mediated changes in Ca(2+) homeostasis. Interestingly, PARP-1 hyperactivation was not accompanied by the translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus, a process usually associated with PARP-dependent cell death. Thus, pathways coupling PARP-1 hyperactivation to cell death are likely to be context-dependent, and therapeutic strategies designed to target PARP-1 need to recognize such variability. Our studies provide new insights into PARP-1-mediated nonapoptotic cell death, during which PARP-1 hyperactivation and elevations in intracellular Ca(2+) are reciprocally coupled to amplify ROS-induced nonapoptotic cell death.

Glucose Deprivation Converts Poly(ADP-ribose) Polymerase-1 Hyperactivation into a Transient Energy-producing Process

Massive poly(ADP-ribose) formation by poly(ADP-ribose) polymerase-1 (PARP-1) triggers NAD depletion and cell death. These events have been invariantly related to cellular energy failure due to ATP shortage. The latter occurs because of both ATP consumption for NAD resynthesis and impairment of mitochondrial ATP formation caused by an increase of the AMP/ADP ratio. ATP depletion is therefore thought to be an inevitable consequence of NAD loss and a hallmark of PARP-1 activation. Here, we challenge this scenario by showing that PARP-1 hyperactivation in cells cultured in the absence of glucose (Glu(-) cells) is followed by NAD depletion and an unexpected PARP-1 activity-dependent ATP increase. We found increased ADP content in resting Glu(-) cells, a condition that counteracts the increase of the AMP/ADP ratio during hyperpoly(ADP-ribosyl)ation and preserves mitochondrial coupling. We also show that the increase of ATP in Glu(-) cells is due to adenylate kinase activity, transforming AMP into ADP which, in turn, is converted into ATP by coupled mitochondria. Interestingly, PARP-1-dependent mitochondrial release of apoptosis-inducing factor (AIF) and cytochrome complex (Cyt c) is reduced in Glu(-) cells, even though cell death eventually occurs. Overall, the present study identifies basal ADP content and adenylate kinase as key determinants of bioenergetics during PARP-1 hyperactivation and unequivocally demonstrates that ATP loss is not metabolically related to NAD depletion.

Catalase Abrogates β-Lapachone–Induced PARP1 Hyperactivation–Directed Programmed Necrosis in NQO1-Positive Breast Cancers

Improving patient outcome by personalized therapy involves a thorough understanding of an agent's mechanism of action. β-Lapachone (clinical forms, Arq501/Arq761) has been developed to exploit dramatic cancer-specific elevations in the phase II detoxifying enzyme NAD(P)H:quinone oxidoreductase (NQO1). NQO1 is dramatically elevated in solid cancers, including primary and metastatic [e.g., triple-negative (ER-, PR-, Her2/Neu-)] breast cancers. To define cellular factors that influence the efficacy of β-lapachone using knowledge of its mechanism of action, we confirmed that NQO1 was required for lethality and mediated a futile redox cycle where ∼120 moles of superoxide were formed per mole of β-lapachone in 2 minutes. β-Lapachone induced reactive oxygen species (ROS), stimulated DNA single-strand break-dependent poly(ADP-ribose) polymerase-1 (PARP1) hyperactivation, caused dramatic loss of essential nucleotides (NAD(+)/ATP), and elicited programmed necrosis in breast cancer cells. Although PARP1 hyperactivation and NQO1 expression were major determinants of β-lapachone-induced lethality, alterations in catalase expression, including treatment with exogenous enzyme, caused marked cytoprotection. Thus, catalase is an important resistance factor and highlights H2O2 as an obligate ROS for cell death from this agent. Exogenous superoxide dismutase enhanced catalase-induced cytoprotection. β-Lapachone-induced cell death included apoptosis-inducing factor (AIF) translocation from mitochondria to nuclei, TUNEL+ staining, atypical PARP1 cleavage, and glyceraldehyde 3-phosphate dehydrogenase S-nitrosylation, which were abrogated by catalase. We predict that the ratio of NQO1:catalase activities in breast cancer versus associated normal tissue are likely to be the major determinants affecting the therapeutic window of β-lapachone and other NQO1 bioactivatable drugs.

Hyperactivation of PARP Triggers Nonhomologous End-Joining in Repair-Deficient Mouse Fibroblasts

Regulation of poly(ADP-ribose) (PAR) synthesis and turnover is critical to determining cell fate after genotoxic stress. Hyperactivation of PAR synthesis by poly(ADP-ribose) polymerase-1 (PARP-1) occurs when cells deficient in DNA repair are exposed to genotoxic agents; however, the function of this hyperactivation has not been adequately explained. Here, we examine PAR synthesis in mouse fibroblasts deficient in the base excision repair enzyme DNA polymerase β (pol β). The extent and duration of PARP-1 activation was measured after exposure to either the DNA alkylating agent, methyl methanesulfonate (MMS), or to low energy laser-induced DNA damage. There was strong DNA damage-induced hyperactivation of PARP-1 in pol β nullcells, but not in wild-type cells. In the case of MMS treatment, PAR synthesis did not lead to cell death in the pol β null cells, but instead resulted in increased PARylation of the nonhomologous end-joining (NHEJ) protein Ku70 and increased association of Ku70 with PARP-1. Inhibition of the NHEJ factor DNA-PK, under conditions of MMS-induced PARP-1 hyperactivation, enhanced necrotic cell death. These data suggest that PARP-1 hyperactivation is a protective mechanism triggering the classical-NHEJ DNA repair pathway when the primary alkylated base damage repair pathway is compromised.