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.     

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.     

Potential clinical applications of poly(ADP-ribose) polymerase (PARP) inhibitors.

Poly(ADP-ribose) polymerases (PARPs) are defined as cell signaling enzymes that catalyze the transfer of ADP-ribose units from NAD(+)to a number of acceptor proteins. PARP-1, the best characterized member of the PARP family, that presently includes six members, is an abundant nuclear enzyme implicated in cellular responses to DNA injury provoked by genotoxic stress (oxygen radicals, ionizing radiations and monofunctional alkylating agents). Due to its involvement either in DNA repair or in cell death, PARP-1 is regarded as a double-edged regulator of cellular functions. In fact, when the DNA damage is moderate, PARP-1 participates in the DNA repair process. Conversely, in the case of massive DNA injury, elevated PARP-1 activation leads to rapid NAD(+)/ATP consumption and cell death by necrosis. Excessive PARP-1 activity has been implicated in the pathogenesis of numerous clinical conditions such as stroke, myocardial infarction, shock, diabetes and neurodegenerative disorders. PARP-1 could therefore be considered as a potential target for the development of pharmacological strategies to enhance the antitumor efficacy of radio- and chemotherapy or to treat a number of clinical conditions characterized by oxidative or NO-induced stress and consequent PARP-1 activation. Moreover, the discovery of novel functions for the multiple members of the PARP family might lead in the future to additional clinical indications for PARP inhibitors.     

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。     

Imidazoquinolinone, imidazopyridine, and isoquinolindione derivatives as novel and potent inhibitors of the poly(ADP-ribose) polymerase (PARP): a comparison with standard PARP inhibitors

We have identified three novel structures for inhibitors of the poly(ADP-ribose) polymerase (PARP), a nuclear enzyme activated by strand breaks in DNA and implicated in DNA repair, apoptosis, organ dysfunction or necrosis. 2-[4-(5-Methyl-1H-imidazol-4-yl)-piperidin-1-yl]-4,5-dihydro-imidazo[4,5,1-i,j]quinolin-6-one (BYK49187), 2-(4-pyridin-2-yl-phenyl)-4,5-dihydro-imidazo[4,5,1-i,j]quinolin-6-one (BYK236864), 6-chloro-8-hydroxy-2,3-dimethyl-imidazo-[1,2-alpha]-pyridine (BYK20370), and 4-(1-methyl-1H-pyrrol-2-ylmethylene)-4H-isoquinolin-1,3-dione (BYK204165) inhibited cell-free recombinant human PARP-1 with pIC(50) values of 8.36, 7.81, 6.40, and 7.35 (pK(i) 7.97, 7.43, 5.90, and 7.05), and murine PARP-2 with pIC(50) values of 7.50, 7.55, 5.71, and 5.38, respectively. BYK49187, BYK236864, and BYK20370 displayed no selectivity for PARP-1/2, whereas BYK204165 displayed 100-fold selectivity for PARP-1. The IC(50) values for inhibition of poly(ADP-ribose) synthesis in human lung epithelial A549 and cervical carcinoma C4I cells as well in rat cardiac myoblast H9c2 cells after PARP activation by H(2)O(2) were highly significantly correlated with those at cell-free PARP-1 (r(2) = 0.89-0.96, P < 0.001) but less with those at PARP-2 (r(2) = 0.78-0.84, P < 0.01). The infarct size caused by coronary artery occlusion and reperfusion in the anesthetized rat was reduced by 22% (P < 0.05) by treatment with BYK49187 (3 mg/kg i.v. bolus and 3 mg/kg/h i.v. during 2-h reperfusion), whereas the weaker PARP inhibitors, BYK236864 and BYK20370, were not cardioprotective. In conclusion, the imidazoquinolinone BYK49187 is a potent inhibitor of human PARP-1 activity in cell-free and cellular assays in vitro and reduces myocardial infarct size in vivo. The isoquinolindione BYK204165 was found to be 100-fold more selective for PARP-1. Thus, both compounds might be novel and valuable tools for investigating PARP-1-mediated effects.     

Poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors in cancer chemotherapy

Poly(ADP-ribose) polymerases (PARPs) are defined as a family of cell signaling enzymes present in eukaryotes, which are involved in poly(ADP-ribosylation) of DNA-binding proteins. The best studied of these enzymes (PARP-1) is involved in the cellular response to DNA damage so that in the event of irreparable DNA damage overactivation of PARP-1 leads to necrotic cell death. Inhibitors of PARP-1 activity in combination with DNA-binding antitumor drugs may constitute a suitable strategy in cancer chemotherapy. When DNA is moderately damaged, PARP-1 participates in the DNA repair process and the cell survives. However, in the case of extensive DNA damage PARP-1 overactivation induces a decrease of NAD+ and ATP levels leading to cell dysfunction or even to necrotic cell death. So, due to PARP-1 involvement in cell death, pharmacological inhibition of PARP-1 activity by PARP-1 inhibitors may constitute a suitable target to enhance the activity of antitumor drugs through inhibition of necrosis and activation of apoptosis. PARP-1 inhibitors such as 3-aminobenzamide, 1,5-dihydroxyisoquinolinone and the recently patented tryciclic benzimidazoles have shown potent inhibitory effects of PARP-1 activity in tumor cells. The present review gives an update of the state-of-the-art of inhibition of PARP-1 activity as adjuvant therapy in cancer treatment.     

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。     

Poly(ADP-ribose)polymerase 1 (PARP-1) and postischemic brain damage

Poly(ADP-ribose)polymerases (PARPs) are enzymes that are able to catalyze the transfer of ADP-ribose units from NAD to substrate proteins and are particularly abundant in cell nuclei where they play key roles in the maintenance of genomic integrity, control of cell cycle and gene expression. Brain ischemia overactivates PARPs and PARP-deficient mice or animal treated with PARP inhibitors have a drastically reduced brain damage in various stroke models. PARP 'overactivation' occurs not only in neurons but also in astrocytes, microglial cells, endothelia, and infiltrating leukocytes. The ensuing cell death occurs through various molecular mechanisms: a) excessive ATP use for NAD synthesis and inhibition of mitochondrial function with subsequent energy failure (particularly important in neurons); b) apoptosis-inducing factor (AIF) translocation from the mitochondria to the nucleus (present in neurons, endothelial, and other cells); c) excessive expression of inflammatory mediators (well demonstrated in glial cells) or d) reduced expression of prosurvival factors. Thus PARPs seem to play key roles in postischemic brain damage and are now considered interesting targets for therapies aimed at reducing stroke pathology.     

Triple-negative breast cancer and poly(ADP-ribose) polymerase inhibitors

Recent gene profiling studies have identified at least 5 major subtypes of breast cancer, including normal type, luminal A type, luminal B type, human epidermal growth factor receptor (HER)-2 positive type, and basal-like type. Triple-negative breast cancer (TNBC), showing no or low expressions of estrogen receptor (ER), progesterone receptor (PgR), and HER2, considered important clinical biomarkers, accounts for 10% to 20% of all breast cancers. Hormonal therapy and molecular targeted therapy are not indicated for the management of TNBC, resulting in poor outcomes. Because TNBC lacks clear-cut therapeutic targets, effective treatment strategies remain to be established. However, TNBC is known to share similar biologic characteristics with basal-like type breast cancer and is often accompanied by loss of functional BRCA, a gene-modifying enzyme. Breast cancer with BRCA1 or BRCA2 mutations is accompanied by activation of the enzyme poly(ADP-ribose) polymerase (PARP). PARP, a DNA base-excision repair enzyme, is known to play a central role in gene repair, along with BRCA. Because some breast cancers with BRCA1 or BRCA2 mutations are TNBC, the suppression of PARP has attracted attention as a new treatment strategy for TNBC. In this article, we review the clinical characteristics of TNBC, discuss problems in treatment, and briefly summarize the international development status of PARP inhibitors.     

Modeling of poly(ADP-ribose)polymerase (PARP) inhibitors. Docking of ligands and quantitative structure-activity relationship analysis.

Poly(ADP-ribose)polymerase-1 (PARP-1) is a nuclear enzyme that has recently emerged as an important player in the mechanisms leading to postischemic neuronal death, and PARP inhibitors have been proposed as potential neuroprotective agents. With the aim of clarifying the structural basis responsible for PARP inhibition, we carried out a computational study on 46 inhibitors available through the literature. Our computational approach is composed of three parts. In the first one, representative PARP inhibitors have been docked into the crystallographic structure of the catalytic domain of PARP by using the Autodock 2.4 program. The docking studies thus carried out have provided an alignment scheme that has been instrumental for superimposing all the remaining inhibitors. Upon the basis of this alignment scheme, a quantitative structure-activity relationship (QSAR) analysis has been carried out after electrostatic and steric interaction energies have been computed with the RECEPTOR program. The QSAR analysis yielded a predictive model able to explain much of the variance of the 46-compound data set. The inspection of the QSAR coefficients revealed that the major driving force for potent inhibition is given by the extension of the contact surface between enzyme and inhibitors while electrostatic energy and hydrogen bonding capability play a minor role. Finally, the projection of the QSAR coefficients back onto the X-ray structure of the catalytic domain of PARP provides insights into the role played by specific amino acid residues. This information will be useful to address the design of new selective and potent PARP inhibitors.     

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。     

Role of poly(ADP-ribose) polymerase in sulfur mustard toxicity

Sulfur mustard (SM) is a chemical warfare agent leading to severe blistering of skin and mucosal surfaces, and as a long-term effect, to an increased risk for malignancies. At the molecular level, SM acts as a bifunctional alkylating agent, leading to DNA mono-adducts and di-adducts. This review is focussed on the role of poly(ADP-ribosyl)ation in the cell and tissue responses to SM-induced damage and potential role of inhibitors of poly(ADP-ribosyl)ation as therapeutic agents for SM injury.     

PCB-induced endothelial cell dysfunction: Role of poly(ADP-ribose) polymerase

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants implicated in the development of pro-inflammatory events critical in the pathology of atherosclerosis and cardiovascular disease. PCB exposure of endothelial cells results in increased cellular oxidative stress, activation of stress and inflammatory pathways leading to increased expression of cytokines and adhesion molecules and ultimately cell death, all of which can lead to development of atherosclerosis. To date no studies have been performed to examine the direct effects of PCB exposure on the vasculature relaxant response which if impaired may predispose individuals to hypertension, an additional risk factor for atherosclerosis. Overactivation of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP) following oxidative/nitrosative stress in endothelial cells and subsequent depletion of NADPH has been identified as a central mediator of cellular dysfunction. The aim therefore was to investigate whether 2,2′,4,6,6′-pentachlorobiphenyl (PCB 104) directly causes endothelial cell dysfunction via increased oxidative stress and subsequent overactivation of PARP. Exposure of ex vivo rat aortic rings to PCB 104 impaired the acetylcholine-mediated relaxant response, an effect that was dependent on both concentration and exposure time. In vitro exposure of mouse endothelial cells to PCB 104 resulted in increased cellular oxidative stress through activation of the cytochrome p450 enzyme CYP1A1 with subsequent overactivation of PARP and NADPH depletion. Pharmacological inhibition of CYP1A1 or PARP protected against the PCB 104-mediated endothelial cell dysfunction. In conclusion, the environmental contaminants, PCBs, can activate PARP directly impairing endothelial cell function that may predispose exposed individuals to development of hypertension and cardiovascular disease.     

Clinical poly(ADP-ribose) polymerase inhibitors for the treatment of cancer

Poly(ADP-ribose) polymerase (PARP) is believed to play a critical role in the detection of DNA damage and initiation of DNA repair. Although inhibition of PARP has received increasing attention for therapeutic application in a wide variety of acute and chronic diseases, most of the current clinical data surrounding PARP inhibition is in the field of oncology. At least eight different PARP inhibitors have been, or are expected to be evaluated in the clinical oncology setting in 2007 and 2008. This review summarizes the most recently presented or published data on these therapeutic molecules, and discusses how these drugs may continue to be developed in the future.     

Effects of abamectin exposure on male fertility in rats: potential role of oxidative stress-mediated poly(ADP-ribose) polymerase (PARP) activation

Despite the known adverse effects of abamectin pesticide, little is known about its action on male fertility. To explore the effects of exposure to abamectin on male fertility and its mechanism, low (1 mg/kg/day) and high dose (4 mg/kg/day) abamectin were applied to male rats by oral gavage for 1 week and for 6 weeks. Weight of testes, serum reproductive hormone levels, sperm dynamics and histopathology of testes were used to evaluate the reproductive efficiency of abamectin-exposed rats. Abamectin level was determined at high concentrations in plasma and testicular tissues of male rats exposed to this pesticide. The testes weights of animals and serum testosterone concentrations did not show any significant changes after abamectin exposure. Abamectin administration was associated with decreased sperm count and motility and increased seminiferous tubule damage. In addition, significant elevations in the 4-hydroxy-2-nonenal (4-HNE)-modified proteins and poly(ADP-ribose) (PAR) expression, as markers for oxidative stress and poly(ADP-ribose) polymerase (PARP) activation, were observed in testes of rats exposed to abamectin. These results showed that abamectin exposure induces testicular damage and affects sperm dynamics. Oxidative stress-mediated PARP activation might be one of the possible mechanism(s) underlying testicular damage induced by abamectin.     

QSAR studies of phthalazinones: novel inhibitors of poly (ADP-ribose) polymerase

Over activation of poly (ADP-ribose) polymerase has been involved in the pathogenesis of several diseases including stroke, myocardial infarction, diabetes, shock, neurodegenerative disorder, allergy, and several other inflammatory processes. Owing to the dual response of PARP-1 to DNA damage and its involvement in cell death, pharmacological modulation of PARP-1 activity may constitute a useful tool to increase the activity of DNA-binding antitumor drugs. Quantitative structure activity relationship (QSAR) study vis-à-vis physico-chemical parameters and forward feed neural network analysis for a series of phthalazinone derivatives as potent inhibitors of poly (ADP-ribose) polymerase was performed. The result of QSAR studies obtained allows us to recognize such physico-chemical parameters of phthalazinone derivatives which can be strictly related to the PARP-1 inhibitory activity.     

Pharmacological inhibition of poly(ADP-ribose) polymerase in cardiovascular disorders: future directions

Poly(ADP-ribose) polymerase (PARP) activation plays a role in the pathogenesis of various cardiovascular and inflammatory diseases. Reactive oxygen and nitrogen species induce DNA single strand breaks, which serve as obligatory triggers for the activation of PARP. Pharmacological inhibitors of PARP attenuate ischemic and inflammatory cell and organ injury, and this property of the PARP inhibitors can be exploited for the experimental therapy of disease. As several classes of PARP inhibitors move towards clinical development, or have already entered clinical trials, we expect that in the upcoming few years, clinical proof of PARP inhibitors' therapeutic effect will be obtained in human disease. Acute, life-threatening cardiovascular diseases (myocardial infarction, cardiopulmonary bypass in high-risk patients, and other, severe forms of ischemia-reperfusion to other organs including stroke and thoracoabdominal aneurysm repair) represent some of the initial development indications for PARP inhibitors.