Pathophysiological role of poly(ADP-ribose) polymerase (PARP) activation during acetaminophen-induced liver cell necrosis in mice.

DNA fragmentation in hepatocytes occurs early after acetaminophen (AAP) overdose in mice. DNA strandbreaks can induce excessive activation of poly(ADP-ribose) polymerases (PARP), which may lead to oncotic necrosis. Based on controversial findings with chemical PARP inhibitors, the role of PARP-1 activation in AAP hepatotoxicity remains unclear. To investigate PARP-1 activation and evaluate a pathophysiological role of PARP-1, we used both PARP inhibitors (3-aminobenzamide; 5-aminoisoquinolinone) and PARP gene knockout mice (PARP-/-). Treatment of C3Heb/FeJ mice with 300 mg/kg AAP resulted in DNA fragmentation and alanine aminotransferase (ALT) release as early as 3 h, with further increase of these parameters up to 12 h. Few nuclei of hepatocytes stained positive for poly-ADP-ribosylated nuclear proteins (PAR) as indicator for PARP-1 activation at 4.5 h. However, the number of PAR-positive cells and staining intensity increased substantially at 6 and 12 h. Pretreatment with 500 mg/kg 3-aminobenzamide before AAP attenuated hepatic glutathione depletion and completely eliminated DNA fragmentation and liver injury. Delayed treatment several hours after AAP was still partially protective. On the other hand, liver injury was not attenuated in PARP-/- mice compared to wild-type animals. Similarly, the specific PARP-1 inhibitor 5-aminoisoquinolinone (5 mg/kg) was not protective. However, 3-aminobenzamide attenuated liver injury in WT and PARP-/- mice. In summary, PARP-1 activation is a consequence of DNA fragmentation after AAP overdose. However, PARP-1 activation is not a relevant event for AAP-induced oncotic necrosis. The protection of 3-aminobenzamide against AAP-induced liver injury was due to reduced metabolic activation and potentially its antioxidant effect but independent of PARP-1 inhibition.     

聚腺苷二磷酸核糖聚合酶的功能及其抑制剂潜在的临床应用

聚腺苷二磷酸核糖聚合酶（PARP）是人体重要的酶之一，参与染色质松弛、信号转录、DNA修复和细胞凋亡等生理过程。PABP过度激活则引起细胞坏死，从而介导多种病理过程。因此，抑制PARP可能会起到对某些疾病的治疗作用。本文综述了PARP的功能及PARP抑制剂的潜在临床应用。     

New inhibitors of poly(ADP-ribose) polymerase (PARP)

Poly(ADP-ribose) polymerase-1 (PARP-1), the most prominent member of the PARP family, is a DNA-binding protein that is activated by nicks in DNA occurring during inflammation, ischaemia, neurodegeneration or cancer therapy. Activated PARP-1 consumes NAD⁺ that is cleaved into nicotinamide and ADP-ribose and polymerises the latter onto nuclear acceptor proteins. This highly energy consuming process is pivotal for the maintenance of genomic stability although over-activation can culminate in cell dysfunction and necrosis. Therefore, PARP-1 is regarded as a promising target for the development of drugs useful in various forms of inflammation, ischaemia–reperfusion injury and as an adjunct in cancer therapy. This review summarises the structural classes of known PARP-1 inhibitors, with a focus on new inhibitors published for this target, between 2002 and July 2004. The chemistry and biological data disclosed in these patent applications are discussed in light of new structural knowledge of the catalytic domain of the PARP family and recent work with potent inhibitors demonstrating the effects of PARP inhibition in various animal disease models.     

Protein tyrosine nitration and poly(ADP-ribose) polymerase activation in N-methyl-N-nitro-N-nitrosoguanidine-treated thymocytes: implication for cytotoxicity

1-Methyl-3-nitro-1-nitrosoguanidine (MNNG) is a DNA alkylating agent. DNA alkylation by MNNG is known to trigger accelerated poly(ADP-ribose) metabolism. Various nitroso compounds release nitric oxide (NO). Therefore, we set out to investigate whether MNNG functions as NO donor and whether MNNG-derived NO or secondary NO metabolites such as peroxynitrite contribute to MNNG-induced cytotoxicity. MNNG in aqueous solutions resulted in time- and concentration-dependent NO release and nitrite/nitrate formation. Moreover, various proteins in MNNG-treated thymocytes were found to be nitrated, indicating that MNNG-derived NO may combine with cellular superoxide to form peroxynitrite, a nitrating agent. MNNG also caused DNA breakage and increased poly(ADP-ribose) polymerase activity and cytotoxicity in thymocytes. MNNG-induced DNA damage (measured by the comet assay) and thymocyte death (measured by propidium iodide uptake) was prevented by the PARP inhibitor PJ-34 and by glutathione (GSH) or N-acetylcysteine (NAC). The cytoprotection provided by PJ-34 against necrotic parameters was paralleled by increased outputs in apoptotic parameters (caspase activity, DNA laddering) indicating that PARP activation diverts apoptotic death toward necrosis. As MNNG-induced cytotoxicity showed many similarities to peroxynitrite-induced cell death, we tested whether peroxynitrite was responsible for at least part of the cytotoxicity induced by MNNG. Cell-permeable enzymic antioxidants (superoxide dismutase and catalase), the NO scavenger cPTIO or the peroxynitrite decomposition catalyst FP15 failed to inhibit MNNG-induced DNA breakage and cytotoxicity. In conclusion, MNNG induces tyrosine nitration in thymocytes. Furthermore, MNNG damages DNA by a radical mechanism that does not involve NO or peroxynitrite.     

PARP抑制剂用于肿瘤治疗的研究进展

聚腺苷酸二磷酸核糖转移酶(poly(ADP-ribose)polymerase,PARP)是当今癌症治疗的一个新靶点,其能够催化ADP-核糖单元从烟酰胺腺嘌呤二核苷酸(nicotinamide adenine dinucleotide,NAD+)转移至各种受体蛋白。PARP参与DNA修复和转录调控,不但在调节细胞存活和死亡过程中具有关键作用,同时也是肿瘤发展和炎症发生过程中的主要转录因子。PARP在碱基切除修复的DNA单链缺口(SSBs)修复中具有关键作用,抑制其活性能够增强放疗和DNA损伤类化疗药物的效果。目前已有至少8个PARP抑制剂进入临床,最新的体内外实验表明PARP抑制剂不但能够作为放化疗增敏剂,单独使用也能选择性杀伤DNA修复缺陷的肿瘤细胞,如BRCA1和BRCA2缺陷的乳腺癌细胞。大量的临床试验证明:该类药物毒副作用小、效果明确且短期耐受性良好,对于癌症治疗前景广阔。本文主要对PARP抑制剂的原理及其研究进展进行综述。     

聚腺苷二磷酸核糖聚合酶抑制剂的临床研究进展

聚腺苷二磷酸核糖聚合酶(PARP)在癌症治疗中是一个非常重要的新靶点,通过碱基切除修复方式对单股DNA进行修复。近年来,新的协同放疗或化疗的PARP抑制剂已经进入了I、II或III期临床试验。众多的试验数据表明PARP抑制剂不仅可以作为化疗和放疗的增敏剂,而且在BRCA1和BRCA2基因突变的乳腺癌中可单独使用,选择性杀死DNA修复缺陷的癌细胞。本文综述了PARP抑制剂的作用机制和临床研究结果,评估了其不良反应和潜在药效,并提出了临床策略中可能存在的问题以及未来发展方向。     

多聚二磷酸腺苷核糖聚合酶抑制剂对顺铂在肺癌治疗中增敏的作用研究

目的探讨多聚二磷酸腺苷核糖聚合酶(PARP-1)抑制剂4-氨基-1,8-萘二胺(4-AN)对顺铂在肺腺癌治疗中的增敏作用及相关机制。方法应用MTT法和克隆形成试验检测4-AN与顺铂联合作用对A549细胞的细胞毒性作用;应用单细胞凝胶电泳和微核试验检测4-AN与顺铂联合作用对A549细胞的遗传毒性作用。结果 4-AN可以增加顺铂对A549细胞的杀伤作用,且杀伤作用随4-AN浓度增加而增强;4-AN可以增加顺铂导致的DNA单双链断裂和染色体损伤,而且随药物浓度的增加,损伤作用增强。结论抑制PARP-1可以有效的增加A549对顺铂的敏感性,其作用机制可能是通过抑制A549细胞DNA单双链损伤修复,继而引起染色体损伤,导致细胞的生长和克隆受到抑制。     

苯并咪唑类聚腺苷二磷酸核糖聚合酶抑制剂的合成及初步活性研究

目的 设计合成一系列苯并咪唑类衍生物,并测定其聚腺苷二磷酸核糖聚合酶(PARP)抑制活性.方法 以3-硝基邻苯二甲酸酐为基本原料,经开环、Hofmann重排、酰胺化或酯化、还原得到邻二氨基苯化合物,再与相应的苯甲醛及其衍生物环合得到目标分子;采用体外抑酶试验初步筛选目标分子的PARO抑制活性.结果与结论 合成了22个苯...     

Poly(ADP-ribose) polymerase inhibitors as promising cancer therapeutics

The year of 2005 was a watershed in the history of poly(ADP-ribose) polymerase (PARP) inhibitors due to the important findings of selective killing in BRCA-deficient cancers by PARP inhibition. The findings made PARP inhibition one of the most promising new therapeutic approaches to cancers, especially to those with specific defects. With AZD2281 and BSI-201 entering phase III clinical trials, the final application of PARP inhibitors in clinic would come true soon. This current paper will review the major advances in targeting PARP for cancer therapy and discuss the existing questions, the answers to which may influence the future of PARP inhibitors as cancer therapeutics.     

New inhibitors of poly(ADP-ribose) polymerase and their potential therapeutic targets

Poly(ADP-ribose) polymerase (PARP) is a DNA-binding protein that is activated by nicks in the DNA molecule. It regulates the activity of various enzymes, including itself, that are involved in the control of DNA metabolism. Evidence obtained with both benzamide and isoquinolinone PARP inhibitors and the PARP-1(^-/-) phenotype, clearly indicate that PARP plays an important role in NO/ROS-induced cell damage during inflammation, ischaemia and neurodegeneration. PARP is involved in the maintenance of genomic stability and PARP inhibition may also potentiate the cytotoxic action of agents used in cancer therapy. Benzamides, although not very potent (IC₅₀ ~ 20 – 50 μM) PARP inhibitors, have been widely used to probe PARP functions, because of their lack of toxicity both in vitro and in vivo, even at high doses. In the early 1990s, a new class of very potent PARP inhibitors (i.e., at least 100-fold more potent thatn benzamide), the dihydroisoquinolinones, benzamide derivatives with the carbamoyl group constrained into the antiorientation, was discovered. At the same time, a large structure–activity surevey identified over 13 chemical classes of PARP inhibitors, the most potent calss sharing a common structural feature, the presence of a carbonyl group built into a polyaromatic heterocyclic skeleton or a carbamoyl group attached to an aromatic ring. Recently, a better knowledge of the PARP catalytic domain and the use of its crystal structure have led to the design and synthesis of the tricyclic lactam indoles, active at low nanomolar concentrations, and with favourable physical properties and in vivo characteristics. In the last few years the interest in PARP as a therapeutic target has been rapidly growing. This article reviews the patents filed for new PARP inhibitors over the last three years, up to February 2002, and their development status.     

Interdependent genotoxic mechanisms of monomethylarsonous acid: role of ROS-induced DNA damage and poly(ADP-ribose) polymerase-1 inhibition in the malignant transformation of urothelial cells

Exposure of human bladder urothelial cells (UROtsa) to 50 nM of the arsenic metabolite, monomethylarsonous acid (MMA^III), for 12 weeks results in irreversible malignant transformation. The ability of continuous, low-level MMA^III exposure to cause an increase in genotoxic potential by inhibiting repair processes necessary to maintain genomic stability is unknown. Following genomic insult within cellular systems poly(ADP-ribose) polymerase-1 (PARP-1), a zinc finger protein, is rapidly activated and recruited to sites of DNA strand breaks. When UROtsa cells are continuously exposed to 50 nM MMA^III, PARP-1 activity does not increase despite the increase in MMA^III-induced DNA single-strand breaks through 12 weeks of exposure. When UROtsa cells are removed from continuous MMA^III exposure (2 weeks), PARP-1 activity increases coinciding with a subsequent decrease in DNA damage levels. Paradoxically, PARP-1 mRNA expression and protein levels are elevated in the presence of continuous MMA^III indicating a possible mechanism to compensate for the inhibition of PARP-1 activity in the presence of MMA^III. The zinc finger domains of PARP-1 contain vicinal sulfhydryl groups which may act as a potential site for MMA^III to bind, displace zinc ion, and render PARP-1 inactive. Mass spectrometry analysis demonstrates the ability of MMA^III to bind a synthetic peptide representing the zinc-finger domain of PARP-1, and displace zinc from the peptide in a dose-dependent manner. In the presence of continuous MMA^III exposure, continuous 4-week zinc supplementation restored PARP-1 activity levels and reduced the genotoxicity associated with MMA^III. Zinc supplementation did not produce an overall increase in PARP-1 protein levels, decrease the levels of MMA^III-induced reactive oxygen species, or alter Cu-Zn superoxide dismutase levels. Overall, these results present two potential interdependent mechanisms in which MMA^III may increase the susceptibility of UROtsa cells to genotoxic insult and/or malignant transformation: elevated levels of MMA^III-induced DNA damage through the production of reactive oxygen species, and the direct MMA^III-induced inhibition of PARP-1.     

Effects of 3-aminobenzamide on poly(ADP-ribose)polymerase expression,apoptosis and cell cycle progression of HeLa cells after X-ray irradiation

The aim of this paper is to study the changes of apoptosis and cell cycle progression in HeLa cells after the poly (ADP-ribose) polymerase (PARP) was inhibited by its inhibitor 3-aminobenzamide (3-AB) and the mechanisms of PARP action on HeLa cells damaged by irradiation. Flow cytometry (FCM) was used to examine the PARP expression and the percentage of apoptotic cells and cell cycle progression. The percentage of HeLa cells with positive expression of PARP protein 2, 4, 8 and 12 h after administrated with 3-AB was significantly lower than that of the control (P < 0.01). The percentages of apoptotic cells in the 3-AB plus irradiation group at the time points of 2, 8, 12 and 24 h after 2 Gy irradiation were higher than that in the irradiation group (P < 0.01 or P < 0.05) and the percentage of G₂ cells decreased significantly (P < 0.01 or P < 0.05). It indicates that 3-AB can rapidly inhibit PARP expression of HeLa cells, promote cell apoptosis and block G₂ arrest induced by irradiation. __________ Translated from Journal of Jilin University (Medicine Edition), 2007, 33(3): 418–421 [译自: 吉林大学学报(医学版]     

Caffeine metabolites are inhibitors of the nuclear enzyme poly(ADP-ribose)polymerase-1 at physiological concentrations

The activity of the nuclear enzyme poly(ADP-ribose)polymerase-1 (E.C.2.4.2.30), which is highly activated by DNA strand breaks, is associated with the pathophysiology of both acute as well as chronic inflammatory diseases. PARP-1 overactivation and the subsequent extensive turnover of its substrate NAD+ put a large demand on mitochondrial ATP-production. Furthermore, due to its reported role in NF-kappaB and AP-1 mediated production of pro-inflammatory cytokines, PARP-1 is considered an interesting target in the treatment of these diseases. In this study the PARP-1 inhibiting capacity of caffeine and several metabolites as well as other (methyl)xanthines was tested using an ELISA-assay with purified human PARP-1. Caffeine itself showed only weak PARP-1 inhibiting activity, whereas the caffeine metabolites 1,7-dimethylxanthine, 3-methylxanthine and 1-methylxanthine, as well as theobromine and theophylline showed significant PARP-1 inhibiting activity. Further evaluation of these compounds in H2O2-treated A549 lung epithelial and RF24 vascular endothelial cells revealed that the decrease in NAD+-levels as well as the formation of the poly(ADP-ribose)polymer was significantly prevented by the major caffeine metabolite 1,7-dimethylxanthine. Furthermore, H2O2-induced necrosis could be prevented by a high dose of 1,7-dimethylxanthine. Finally, antioxidant effects of the methylxanthines could be ruled out with ESR and measurement of the TEAC. Concluding, caffeine metabolites are inhibitors of PARP-1 and the major caffeine metabolite 1,7-dimethylxanthine has significant PARP-1 inhibiting activity in cultured epithelial and endothelial cells at physiological concentrations. This inhibition could have important implications for nutritional treatment of acute and chronic inflammatory pathologies, like prevention of ischemia-reperfusion injury or vascular complications in diabetes.     

MicroRNA-21 promotes epithelial-mesenchymal transition and migration of human bronchial epithelial cells by targeting poly (ADP-ribose) polymerase-1 and activating PI3K/AKT signaling

Epithelial-mesenchymal transition (EMT) is known to be involved in airway remodeling and fibrosis of bronchial asthma. However, the molecular mechanisms leading to EMT have yet to be fully clarified. The current study was designed to reveal the potential mechanism of microRNA-21 (miR-21) and poly (ADP-ribose) polymerase-1 (PARP-1) affecting EMT through the PI3K/AKT signaling pathway. Human bronchial epithelial cells (16HBE cells) were transfected with miR-21 mimics/inhibitors and PARP-1 plasmid/small interfering RNA (siRNA). A dual luciferase reporter assay and biotin-labeled RNA pull-down experiments were conducted to verify the targeting relationship between miR-21 mimics and PARP-1. The migration ability of 16HBE cells was evaluated by Transwell assay. Quantitative real-time polymerase chain reaction and Western blotting experiments were applied to determine the expression of Snail, ZEB1, E-cadherin, N-cadherin, Vimentin, and PARP-1. The effects of the PI3K inhibitor LY294002 on the migration of 16HBE cells and EMT were investigated. Overexpression of miR-21 mimics induced migration and EMT of 16HBE cells, which was significantly inhibited by overexpression of PARP-1. Our findings showed that PARP-1 was a direct target of miR-21, and that miR-21 targeted PARP-1 to promote migration and EMT of 16HBE cells through the PI3K/AKT signaling pathway. Using LY294002 to block PI3K/AKT signaling pathway resulted in a significant reduction in the migration and EMT of 16HBE cells. These results suggest that miR-21 promotes EMT and migration of HBE cells by targeting PARP-1. Additionally, the PI3K/AKT signaling pathway might be involved in this mechanism, which could indicate its usefulness as a therapeutic target for asthma.     

Poly(ADP-ribose) polymerase inhibitors in the prevention of neuronal cell death

Poly(ADP-ribose) polymerase is a nucleic enzyme that promotes energy-dependent repair of DNA, thus helping to protect against DNA fragmentation. Overactivation of PARP, for example in the context of apoptosis, may contribute to neuronal cell death. This article briefly reviews claims for PARP inhibitors as agents for the prevention of neuronal cell death, registered in the period 1998 – December 2001. Biological data are sparse in these patents, few claims are backed by in vitro biochemical data and fewer still with in vivo animal model data. The latter have used animal models of ischaemia rather than of neurodegeneration. The place of PARP inhibitors as a clinical therapy to prevent neuronal cell death remains to be determined.     

Drug targets for traumatic brain injury from poly(ADP-ribose)polymerase pathway modulation

The deleterious pathophysiological cascade induced after traumatic brain injury (TBI) is initiated by an excitotoxic process triggered by excessive glutamate release. Activation of the glutamatergic N-methyl-D-aspartate receptor, by increasing calcium influx, activates nitric oxide (NO) synthases leading to a toxic production of NO. Moreover, after TBI, free radicals are highly produced and participate to a deleterious oxidative stress. Evidence has showed that the major toxic effect of NO comes from its combination with superoxide anion leading to peroxynitrite formation, a highly reactive and oxidant compound. Indeed, peroxynitrite mediates nitrosative stress and is a potent inducer of cell death through its reaction with lipids, proteins and DNA. Particularly DNA damage, caused by both oxidative and nitrosative stresses, results in activation of poly(ADP-ribose) polymerase (PARP), a nuclear enzyme implicated in DNA repair. In response to excessive DNA damage, massive PARP activation leads to energetic depletion and finally to cell death. Since 10 years, accumulating data have showed that inactivation of PARP, either pharmacologically or using PARP null mice, induces neuroprotection in experimental models of TBI. Thus TBI generating NO, oxidative and nitrosative stresses promotes PARP activation contributing in post-traumatic motor, cognitive and histological sequelae. The mechanisms by which PARP inhibitors provide protection might not entirely be related to the preservation of cellular energy stores, but might also include other PARP-mediated mechanisms that needed to be explored in a TBI context. Ten years of experimental research provided rational basis for the development of PARP inhibitors as treatment for TBI.     

Inhibition of poly(ADP-ribose) polymerase prevents vascular hyporesponsiveness induced by lipopolysaccharide in isolated rat aorta

Recent studies clearly show that there is a relationship between endotoxemia and impaired vascular responsiveness. The aim of this study was to investigate whether treatment with the new potent PARP inhibitor PJ34 could prevent the vascular hyporesponsiveness induced by lipopolysaccharide (LPS). Endotoxemia was induced in rats by LPS injection (20 mgkg-1, i.p.). Administration of LPS caused a decrease in mean blood pressure and an increase in heart rate. In endothelium-denuded rings of thoracic aorta from untreated rats, contractile responses to KCl and phenylephrine decreased after LPS injection. Furthermore, there was a significant loss of endothelium-dependent vasodilatation in response to acetylcholine in LPS-treated rats. The animals pretreated with PJ34 (10 mgkg-1, i.p., 30 min before LPS injection), the effect of LPS on vascular responsiveness was lower than the untreated ones. Pretreating the animals with PJ34 before the LPS challenge prevented the decline in mean blood pressure. However, this did not result in significant changes to the heart rate. The inhibitory effect of LPS treatment on both KCl- and phenylephrine-induced contraction responses was significantly antagonized by PJ34. Additionally, pretreatment of the rats with PJ34 attenuated the LPS-induced endothelial dysfunction in endothelium-intact aorta rings. This study demonstrates that PARP activation in the vascular system is an important contributory factor to the impaired vascular responsiveness associated with endotoxic shock. Hence, the pharmacological inhibition of PARP pathway might be an effective intervention to prevent endotoxin-induced vascular hyporesponsiveness.     

Role of poly(ADP-ribose) polymerase activation in endotoxin-induced cardiac collapse in rodents

Reactive oxygen and nitrogen species are overproduced in the cardiovascular system during circulatory shock. Oxidant-induced cell injury involves the activation of poly(ADP-ribose) polymerase (PARP). Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the new potent phenanthridinone PARP inhibitor PJ34 [the hydrochloride salt of N-(oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylacetamide], we studied whether the impaired cardiac function in endotoxic shock is dependent upon the PARP pathway. Escherichia coli endotoxin (lipopolysaccharide, LPS) at 55 mg/kg, i.p., induced a severe depression of the systolic and diastolic contractile function, tachycardia, and a reduction in mean arterial blood pressure in both rats and mice. Treatment with PJ34 significantly improved cardiac function and increased the survival of rodents. In addition, LPS-induced depression of left ventricular performance was significantly less pronounced in PARP-1 knockout mice (PARP(-/-)) as compared with their wild-type littermates (PARP(+/+)). Thus, PARP activation in the cardiovascular system is an important contributory factor to the cardiac collapse and death associated with endotoxin shock.