Cardioprotective effects of poly(ADP-ribose) polymerase inhibition.

Free radical and oxidant production in cardiac myocytes during ischemia/reperfusion, cardiomyopathy, cardiotoxic drug exposure and ageing leads to DNA strand-breakage which activates the nuclear enzyme poly(ADP-ribose) polymerase (PARP) and initiates an energy consuming, inefficient cellular metabolic cycle with transfer of the ADP-ribosyl moiety of NAD+ to protein acceptors. These processes lead to the functional impairment of the myocytes and promote myocyte death. During the last decade a growing number of experimental studies demonstrated the beneficial effects of PARP inhibition in cell cultures through rodent models and more recently in pre-clinical large animal models of regional and global ischemia/reperfusion injury and various forms of heart failure. The current article provides an overview of the experimental evidence implicating PARP as a pathophysiological modulator of cardiac myocyte injury in vitro and in vivo.     

Recent developments on the role of mitochondria in poly(ADP-ribose) polymerase inhibition

Numerous pathophysiological disorders involve some element of oxidative stress and bioenergetic deficit. Poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors have been used recently as a promising new therapeutic strategy aimed at halting the bioenergetic decline associated with oxidative brain insults and other conditions. PARP-1 uses NAD+ as a substrate and is activated during stressful circumstances, mainly in the nucleus. PARP-1 inhibitors are well known for blocking the excessive consumption of NAD+, thereby preserving energy metabolism. But what is the role of mitochondria in this process? Recent investigations have begun to focus on whether mitochondrial function can also be preserved by PARP-1 inhibitors. This review will present some of the latest mechanistic evidence documenting the potential involvement of PARP-1 inhibitors in protecting mitochondrial function and preventing necrosis, apoptosis and mitochondrial calcium cycling.     

Inhibition of poly(ADP-ribose) polymerase in cancer

Inhibition of the DNA repair enzyme poly(ADP-ribose) polymerase-1 (PARP-1) has been extensively investigated in the pre-clinical setting as a strategy for chemo- or radio-potentiation. Recent evidence has suggested that PARP inhibitors might be active as single agents in certain rare inherited cancers that carry DNA repair defects. As a result, potent PARP-1 inhibitors have in the past three years entered early clinical trials in cancer patients, and the final results of these trials are eagerly awaited.     

Novel modulators of poly(ADP-ribose) polymerase

The nuclear enzyme poly(ADP-ribose) polymerase (PARP)-1 has an important role in regulating cell death and cellular responses to DNA repair. Pharmacological inhibitors of PARP have entered clinical testing as cytoprotective agents in cardiovascular diseases and as adjunct antitumor therapeutics. Initially, it was assumed that the regulation of PARP occurs primarily at the level of DNA breakage: recognition of DNA breaks was considered to be the primary regulator (activator) or the catalytic activity of PARP. Recent studies have provided evidence that PARP-1 activity can also be modulated by several endogenous factors, including various kinases, purines and caffeine metabolites. There is a gender difference in the contribution of PARP-1 to stroke and inflammatory responses, which is due, at least in part, to endogenous estrogen levels. Several tetracycline antibiotics are also potent PARP-1 inhibitors. In this article, we present an overview of novel PARP-1 modulators.     

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.     

Role of poly(ADP-ribose) polymerase 1 (PARP-1) in cardiovascular diseases: the therapeutic potential of PARP inhibitors

Accumulating evidence suggests that the reactive oxygen and nitrogen species are generated in cardiomyocytes and endothelial cells during myocardial ischemia/reperfusion injury, various forms of heart failure or cardiomyopathies, circulatory shock, cardiovascular aging, diabetic complications, myocardial hypertrophy, atherosclerosis, and vascular remodeling following injury. These reactive species induce oxidative DNA damage and consequent activation of the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1), the most abundant isoform of the PARP enzyme family. PARP overactivation, on the one hand, depletes its substrate, NAD+, slowing the rate of glycolysis, electron transport, and ATP formation, eventually leading to the functional impairment or death of the endothelial cells and cardiomyocytes. On the other hand, PARP activation modulates important inflammatory pathways, and PARP-1 activity can also be modulated by several endogenous factors such as various kinases, purines, vitamin D, thyroid hormones, polyamines, and estrogens, just to mention a few. Recent studies have demonstrated that pharmacological inhibition of PARP provides significant benefits in animal models of cardiovascular disorders, and novel PARP inhibitors have entered clinical development for various cardiovascular indications. Because PARP inhibitors can enhance the effect of anticancer drugs and decrease angiogenesis, their therapeutic potential is also being explored for cancer treatment. This review discusses the therapeutic effects of PARP inhibitors in myocardial ischemia/reperfusion injury, various forms of heart failure, cardiomyopathies, circulatory shock, cardiovascular aging, diabetic cardiovascular complications, myocardial hypertrophy, atherosclerosis, vascular remodeling following injury, angiogenesis, and also summarizes our knowledge obtained from the use of PARP-1 knockout mice in the various preclinical models of cardiovascular diseases.     

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。     

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.     

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.     

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.     

Role of the poly(ADP-ribose)polymerase activity in vancomycin-induced renal injury

The aim of the present study was to investigate the role of poly(ADP-ribose)polymerase (PARP) activity in vancomycin (VCM)-induced renal injury and to determine whether 1,5-isoquinelinediol (ISO), a PARP inhibitor agent, could be offered as an alternative therapy in VCM-induced renal impairment. Rats were divided into four groups as follows: (i) control (Group 1); (ii) VCM-treated (Group 2); (iii) VCM plus ISO-treated (Group 3); and (iv) ISO-treated (Group 4). VCM (200 mg/kg, i.p., twice daily) was administered to Groups 2 and 3 for 7 days. ISO (3 mg/kg/day, i.p.) treatment was started 24 h before the first administration of VCM and continued for 8 days. After the 14th VCM injection, the animals were placed in metabolic cages to collect urine samples. All the rats were sacrificed by decapitation, blood samples were taken in tubes and kidneys were excised immediately. Blood urea nitrogen (BUN) and plasma creatinine, and urinary N-acetyl-β-d-glucosaminidase (NAG, a marker of renal tubular injury) were used as markers of VCM-induced renal injury in rats. Light microscopy was used to evaluate semi-quantitative analysis of the kidney sections. Poly(ADP-ribose) (PAR, the product of activated PARP) and PARP-1 expressions in renal tissues were demonstrated by immunohistochemistry and Western blot. VCM administration increased BUN levels from 8.07 ± 0.75 mg/dL to 53.87 ± 10.11 mg/dL. The plasma creatinine levels were 0.8 ± 0.04 mg/dL and 3.38 ± 0.51 mg/dL for the control and VCM-treated groups, respectively. Also, urinary excretion of NAG was increased after VCM injection. Besides, there was a significant dilatation of the renal tubules, eosinophilic casts within some tubules, desquamation and vacuolization of renal tubule epithelium, and interstitial tissue inflammation in VCM-treated rats. In VCM-treated rats, both PAR and PARP-1 expressions were increased in renal tubular cells. ISO treatment attenuated VCM-induced renal injury, as indicated by BUN and plasma creatinine levels, urinary NAG excretion, and renal histology. PARP inhibitor treatment also decreased PAR and PARP-1 protein expressions similar to that of controls. Herewith, the overactivation of the PARP pathway may have a role in VCM-induced renal impairment and pharmacological inhibition of this pathway might be an effective intervention to prevent VCM-induced acute renal injury.     

Endothelial dysfunction in aging animals: the role of poly(ADP-ribose) polymerase activation

Recent work has demonstrated the production of reactive oxygen and nitrogen species in the vasculature of aging animals. Oxidant induced cell injury triggers the activation of nuclear enzyme poly(ADP ribose) polymerase (PARP) leading to endothelial dysfunction in various pathophysiological conditions (reperfusion, shock, diabetes). Here we studied whether the loss of endothelial function in aging rats is dependent upon the PARP pathway within the vasculature. Young (3 months-old) and aging (22 months-old) Wistar rats were treated for 2 months with vehicle or the PARP inhibitor PJ34. In the vehicle-treated aging animals there was a significant loss of endothelial function, as measured by the relaxant responsiveness of vascular rings to acetylcholine. Treatment with PJ34, a potent PARP inhibitor, restored normal endothelial function. There was no impairment of the contractile function and endothelium-independent vasodilatation in aging rats. Furthermore, we found no deterioration in the myocardial contractile function in aging animals. Thus, intraendothelial PARP activation may contribute to endothelial dysfunction associated with aging.     

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.     

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.     

Metal-based inhibition of poly(ADP-ribose) polymerase--the guardian angel of DNA

The inhibition activity of a series of anticancer metal complexes based on platinum, ruthenium, and gold metal ions was evaluated on the zinc-finger protein PARP-1, either purified or directly on protein extracts from human breast cancer MCF7 cells. Information on the reactivity of the metal complexes with the PARP-1 zinc-finger domain was obtained by high-resolution ESI FT-ICR mass spectrometry. An excellent correlation between PARP-1 inhibition in protein extracts and the ability of the complexes to bind to the zinc-finger motif (in competition with zinc) was established. The results support a model whereby displacement of zinc from the PARP-1 zinc finger by other metal ions leads to decreased PARP-1 activity. In vitro combination studies of cisplatin with NAMI-A and RAPTA-T on different cancer cell lines (MCF7, A2780, and A2780cisR) showed that, in some cases, a synergistic effect is in operation.     

Anti-cancer action of 4-iodo-3-nitrobenzamide in combination with buthionine sulfoximine: inactivation of poly(ADP-ribose) polymerase and tumor glycolysis and the appearance of a poly(ADP-ribose) polymerase protease

E-ras 20 tumorigenic malignant cells and CV-1 non-tumorigenic cells were treated with a drug combination of 4-iodo-3-nitrobenzamide (INO(2)BA) and buthionine sulfoximine (BSO). Growth inhibition of E-ras 20 cells by INO(2)BA was augmented 4-fold when cellular GSH content was diminished by BSO, but the growth rate of CV-1 cells was not affected by the drug combination. Analyses of the intracellular fate of the prodrug INO(2)BA revealed that in E-ras 20 cells about 50% of the intracellular reduced drug was covalently protein-bound, and this binding was dependent upon BSO, whereas in CV-1 cells BSO did not influence protein binding. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was identified as the protein that covalently binds the reduction product of INO(2)BA, which is 4-iodo-3-nitrosobenzamide. Since only the enzymatically reduced drug INOBA bound covalently to GAPDH, the BSO-dependent covalent protein-drug association indicated an apparent nitro-reductase activity present in E-ras 20 cells, but not in CV-1 cells, explaining the selective toxicity. Covalent binding of INOBA to GAPDH inactivated this enzyme in vitro; INO(2)BA+BSO also inactivated cellular glycolysis in E-ras 20 cells because it provided the precursor to the inhibitory species: INOBA. Another event that occurred in INO(2)BA+BSO-treated E-ras 20 cells was the progressive appearance of a poly(ADP-ribose) polymerase protease. This enzyme was partially purified and characterized by the polypeptide degradation product generated from PARP I, which exhibited a 50kDa mass. This pattern of proteolysis of PARP I is consistent with a drug-induced necrotic cell killing pathway.     

Inhibition of ADP-evoked platelet aggregation by selected poly(ADP-ribose) polymerase inhibitors

Pathologic platelet activation has been implicated in the pathogenesis of ischemic heart disease. Since cardiomyocytes can be protected from ischemia-reoxygenation injury by poly(ADP-ribose) polymerase (PARP) inhibitors mimicking the adenine/ADP part of NAD, their structural resemblance to ADP may also enable the blockade of platelet aggregation via binding to ADP receptors.Blood samples drawn from healthy volunteers were pre-incubated with different concentrations of PARP inhibitors: 4-hydroxyquinazoline, 2-mercapto-4(3 H)-quinazolinone, or HO-3089. ADP-, collagen- and epinephrine-induced platelet aggregation was evaluated according to the method described by Born. The effect of PARP inhibitors on thrombocyte aggregation was also examined when platelets were sensitized by heparin and in the presence of incremental concentrations of ADP.All examined PARP inhibitors reduced the ADP-induced platelet aggregation in a dose-dependent manner (significant inhibition at 20 microM for HO-3089 and at 500 microM for the other agents; P < 0.05), even if platelets were sensitized with heparin. However, their hindrance on platelet aggregation waned as the concentration of ADP rose (no effect at 40 microM ADP). PARP inhibitors had minimal effect on both collagen- and epinephrine-induced platelet aggregation.Our study first demonstrates the feasibility of a design for PARP inhibitors that does not only protect against ischemia-reperfusion-induced cardiac damage but may also prevent thrombotic events.     

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.