PARP inhibitors: new partners in the therapy of cancer and inflammatory diseases

Role of poly(ADP-ribose) polymerases in the regulation of inflammatory processes

PARP enzymes influence the immune system at several key points and thus modulate inflammatory diseases. PARP enzymes affect immune cell maturation and differentiation and regulate the expression of inflammatory mediators such as cytokines, chemokines, inducible nitric oxide synthase and adhesion molecules. Moreover, PARP enzymes are key regulators of cell death during inflammation-related oxidative and nitrosative stress. Here we provide an overview of the different inflammatory diseases regulated by PARP enzymes.

Potential role of poly(ADP-ribose) polymerase (PARP) activation in methotrexate-induced nephrotoxicity and tubular apoptosis

Nephrotoxicity is one of the serious dose-limiting complications of methotrexate (MTX) when used in the treatment of various malignancies and nononcological diseases. The aim of this study was to investigate the role of poly(adenosine diphosphate ribose) polymerase (PARP) activity in MTX-induced nephrotoxicity. Rats were divided into 4 groups as control, MTX treated (MTX, 7 mg/kg per d, intraperitoneally [ip], once daily for 3 consecutive days), MTX plus 1,5-isoquinelinediol (ISO, a PARP inhibitor, 3 mg/kg per d, i.p.) treated, or ISO treated. Histopathology of kidneys was evaluated by light microscopy. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling assay was used to analyze apoptosis in kidney sections. Blood urea nitrogen (BUN), serum creatinine, and urinary N-acetyl-β-d-glucosaminidase (NAG) were used as biochemical markers of MTX-induced renal injury. Our results showed that MTX administration significantly increased BUN, serum creatinine, and urinary NAG levels. The PARP-1 and PAR (a product of PARP activity) expression and apoptotic cell death were also markedly increased in renal tubules after MTX administration. The ISO treatment attenuated MTX-induced renal injury, as indicated by BUN and serum creatinine levels, urinary NAG excretion, and renal histology. The PARP inhibitor treatment reduced PARP-1 and PAR expression to levels similar to that of controls. These results revealed that ISO may have a protective effect against the nephrotoxic effects of MTX by inhibiting PARP activation. This is the first study that demonstrates the role of PARP activation in MTX-induced nephrotoxicity and tubular apoptosis.

Overexpression of chromatin assembly factor-1 p60, poly(ADP-ribose) polymerase 1 and nestin predicts metastasizing behaviour of oral cancer

Aims

The natural history of oral squamous cell carcinomas (OSCCs) is variable and difficult to predict. This study aimed to assess the value of the expression of poly(ADP-ribose) polymerase 1 (PARP-1), chromatin assembly factor-1 (CAF-1)/p60 and the stem cell markers CD133, CD166, CD44, CD44v6 and nestin as markers of outcome and progression-free survival in OSCC patients.

Methods

Clinical data were collected from 66 patients (41 male and 25 female, aged 29–92 years) who underwent surgery for OSCC of the tongue, floor, lips, and palate. During follow-up (range: 12–131 months), 14 patients experienced relapse/metastasis and/or death. The study was performed by immunohistochemistry on paraffin-embedded tumour tissues, western blot analysis of tumour protein lysates and human cell lines, and RNA silencing assays. In addition, the human papillomavirus (HPV) status of primary tumours was evaluated by immunohistochemistry and viral subtyping. Univariate and multivariate analyses were performed to determine the correlation between these parameters and the clinical and pathological variables of the study population.

Results and conclusions

We found that a PARP-1^high/CAF-1 p60^high/nestin^high phenotype characterized the OSCCs with the worst prognosis (all HPV-negative). This may be of benefit in clinical management, since radio-enhancing anti-PARP-1 and/or anti-CAF-1/p60 agents may allow radioresistance to be bypassed in the nestin-overexpressing, metastasizing OSCC cells.

Breast cancer chemoprevention: old and new approaches

In 1976, Sporn has defined chemoprevention as “the use of pharmacologic or natural agents that inhibit the development of invasive breast cancer either by blocking the DNA damage that initiates carcinogenesis, or by arresting or reversing the progression of premalignant cells in which such damage has already occurred.” Although the precise mechanism or mechanisms that promote a breast cancer are not completely established, the success of several recent clinical trials in preventive settings in selected high-risk populations suggests that chemoprevention is a rational and an appealing strategy. Breast cancer chemoprevention has focused heavily on endocrine intervention using selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs). Achieving much success in this particular setting and new approaches as low-dose administration are actually under investigations in several topics. Unfortunately, these drugs are active in prevention of endocrine responsive lesions only and have no effect in reducing the risk of estrogen-negative breast cancer. Thus, recently new pathways, biomarkers, and agents likely are to be effective in this subgroup of cancers and were put under investigation. Moreover, the identification of new potential molecular targets and the development of agents aimed at these targets within cancer have already had a significant impact on advanced cancer therapy and provide a wealth of opportunities for chemoprevention. This paper will highlight current clinical research in both ER-positive and ER-negative breast cancer chemoprevention, explaining the biologic effect of the various agents on carcinogenesis and precancerous lesions, and finally presenting an excursus on the state-of-the-art about new molecular targets under investigations in breast cancer settings.

PARP1 polymorphisms increase the risk of gastric cancer in a Chinese population

BACKGROUND AND OBJECTIVE

Poly(adenosine diphosphate [ADP]-ribose) polymerase 1 (PARP1), a protein involved in the DNA repair mechanism, plays an important role in carcinogenesis. In this study, we investigated whether single nucleotide polymorphisms of PARP1 contribute to gastric cancer (GC) and its precursor lesions (gastric precancerous lesions; GPL) in a case-control study conducted in the Hexi area of China, a high-risk area for GC.

METHODS

PARP1 162C>G (Phe54Leu) and 2819A>G (Lys940Arg) polymorphisms were genotyped by real-time PCR using a TaqMan assay in 140 GC cases, 110 GPL cases, and 120 controls. Data were statistically analyzed using the chi-squared test and a logistic regression model.

RESULTS

The presence of the PARP1 2819G allele was associated with an increased risk of GC (odds ratio [OR] 2.354; 95% CI 1.140, 4.861; p = 0.018), especially for cardia GC and diffuse-type GC (ORs 2.988 and 3.784, respectively). We also observed an interaction between Helicobacter pylori infection, GC family history, and the presence of the PARP1 2819G allele. In contrast, the PARP1 162C>G polymorphism was not significantly associated with GPL or GC.

CONCLUSION

The study suggests that the PARP1 2819G allele is associated with an increased risk of GC. In addition, H. pylori-positive status and family history jointly contribute to a higher risk of GC.

Streptozotocin-nicotinamide-induced diabetes in the rat. Characteristics of the experimental model

Administration of both streptozotocin (STZ) and nicotinamide (NA) has been proposed to induce experimental diabetes in the rat. STZ is well known to cause pancreatic B-cell damage, whereas NA is administered to rats to partially protect insulin-secreting cells against STZ. STZ is transported into B-cells via the glucose transporter GLUT2 and causes DNA damage leading to increased activity of poly(ADP-ribose) polymerase (PARP-1) to repair DNA. However, exaggerated activity of this enzyme results in depletion of intracellular NAD(+) and ATP, and the insulin-secreting cells undergo necrosis. The protective action of NA is due to the inhibition of PARP-1 activity. NA inhibits this enzyme, preventing depletion of NAD(+) and ATP in cells exposed to STZ. Moreover, NA serves as a precursor of NAD(+) and thereby additionally increases intracellular NAD(+) levels. The severity of diabetes in experimental rats strongly depends on the doses of STZ and NA given to these animals. Therefore, in diabetic rats, blood glucose may be changed in a broad range--from slight hyperglycemia to substantial hyperglycemia compared with control animals. Similarly, blood insulin may be only slightly decreased or substantial hypoinsulinemia may be induced. In vitro studies demonstrated that the insulin-secretory response to glucose is attenuated in STZ-NA-induced diabetic rats compared with control animals. This is due to reduced B-cell mass as well as metabolic defects in the insulin-secreting cells. Results of numerous experiments have demonstrated that this model of diabetes is useful in studies of different aspects of diabetes.

Anti-inflammatory effects of adrenomedullin on acute lung injury induced by Carrageenan in mice

Adrenomedullin (AM) is a 52 amino acid peptide that has shown predominant anti-inflammatory activities. In the present study, we evaluated the possible therapeutic effect of this peptide in an experimental model of acute inflammation, the carrageenan- (CAR-) induced pleurisy. Pleurisy was induced by injection of CAR into the pleural cavity of mice. AM (200 ng/kg) was administered by intraperitoneal route 1 h after CAR, and the animals were sacrificed 4 h after that. AM treatment attenuated the recruitment of leucocytes in the lung tissue and the generation and/or the expression of the proinflammatory cytokines as well as the expression of the intercellular cell adhesion molecules. Moreover, AM inhibited the induction of inducible nitric oxide synthase (iNOS), thereby abating the generation of nitric oxide (NO) and prevented the oxidative and nitroxidative lung tissue injury, as shown by the reduction of nitrotyrosine, malondialdehyde (MDA), and poly (ADP-ribose) polymerase (PARP) levels. Finally, we demonstrated that these anti-inflammatory effects of AM were associated with the inhibition of nuclear factor-κB (NF-κB) activation. All these parameters were markedly increased by intrapleural CAR in the absence of any treatment. We report that treatment with AM significantly reduces the development of acute lung injury by downregulating a broad spectrum of inflammatory factors.

Managing the breast in patients who test positive for hereditary breast cancer

PURPOSE AND METHODS

The patient who tests positive for hereditary breast cancer has several important decisions to make regarding management of the breasts. Before making an informed decision, the physician must first review the screening assessment to make sure that the patient does not harbor an undiagnosed breast malignancy. In the absence of a malignancy, the management options for the breast range from nonoperative surveillance to prophylactic mastectomy to prevent cancer. In the event that a breast malignancy is diagnosed after a positive genetic test, implications for management of both the affected and the unaffected breast must be considered.

RESULTS AND DISCUSSION

The clinical assessment of the patient who tests positive is discussed. If routine pretest mammograms were negative, should additional diagnostic studies be performed to exclude an undetected/occult malignancy, and if so, what are the roles of magnetic resonance imaging, ultrasonography, digital mammogram, and detection of breast cancer circulating tumor cells? Medical management may include increased surveillance and chemopreventative therapy, including tamoxifen and oral contraceptives. Surgical interventions may be undertaken to reduce risk in people with a genetic susceptibility gene for breast or ovarian cancer; risk-reducing surgical options include mastectomy with or without reconstruction and nipple-sparing techniques. Finally, we discuss management decisions for women who test positive and who are diagnosed with a primary breast cancer, compared to women who have no obvious primary tumor but test positive.

Burn and smoke injury activates poly(ADP-ribose)polymerase in circulating leukocytes

The nuclear enzyme poly(ADP-ribose)polymerase (PARP) plays a significant role in the pathogenesis of various forms of critical illness. DNA strand breaks induced by oxidative and nitrative stress trigger the activation of PARP, and PARP, in turn, mediates cell death and promotes proinflammatory responses. Until recently, most studies focused on the role of PARP in solid organs such as heart, liver, and kidney. We investigated the effect of burn and smoke inhalation on the levels of poly(ADP-ribosylated) proteins in circulating sheep leukocytes ex vivo. Adult female merino sheep were subjected to burn injury (2× 20% each flank, 3 degrees) and smoke inhalation injury (insufflated with a total of 48 breaths of cotton smoke) under deep anesthesia. Arterial and venous blood was collected at baseline, immediately after the injury and 1 to 24 h after the injury. Leukocytes were isolated with the Histopaque method. The levels of poly(ADP-ribosyl)ated proteins were determined by Western blotting. The amount of reactive oxygen species was quantified by the OxyBlot method. To examine whether PARP activation continues to increase ex vivo in the leukocytes, blood samples were incubated at room temperature or at 37°C for 3 h with or without the PARP inhibitor PJ34. To investigate whether the plasma of burn/smoke animals may trigger PARP activation, burn/smoke plasma was incubated with control leukocytes in vitro. The results show that burn and smoke injury induced a marked PARP activation in circulating leukocytes. The activity was the highest immediately after injury and at 1 h and decreased gradually over time. Incubation of whole blood at 37°C for 3 h significantly increased poly(ADP-ribose) levels, indicative of the presence of an ongoing cell activation process. In conclusion, PARP activity is elevated in leukocytes after burn and smoke inhalation injury, and the response parallels the time course of reactive oxygen species generation in these cells.

Cellular bioenergetics is regulated by PARP1 under resting conditions and during oxidative stress

PURPOSE

The goal of the current studies was to elucidate the role of the principal poly(ADP-ribose)polymerase isoform, PARP1 in the regulation of cellular energetics in endothelial cells under resting conditions and during oxidative stress.

METHODS

We utilized bEnd.3 endothelial cells and A549 human transformed epithelial cells. PARP1 was inhibited either by pharmacological inhibitors or by siRNA silencing. The Seahorse XF24 Extracellular Flux Analyzer was used to measure indices of mitochondrial respiration (oxygen consumption rate) and of glycolysis (extracellular acidification rate). Cell viability, cellular and mitochondrial NAD(+) levels and mitochondrial biogenesis were also measured.

RESULTS

Silencing of PARP1 increased basal cellular parameters of oxidative phosphorylation, providing direct evidence that PARP1 is a regulator of mitochondrial function in resting cells. Pharmacological inhibitors of PARP1 and siRNA silencing of PARP1 protected against the development of mitochondrial dysfunction and elevated the respiratory reserve capacity in endothelial and epithelial cells exposed to oxidative stress. The observed effects were unrelated to an effect on mitochondrial biogenesis. Isolated mitochondria of A549 human transformed epithelial cells exhibited an improved resting bioenergetic status after stable lentiviral silencing of PARP1; these effects were associated with elevated resting mitochondrial NAD+ levels in PARP1 silenced cells.

CONCLUSIONS

PARP1 is a regulator of basal cellular energetics in resting endothelial and epithelial cells. Furthermore, endothelial cells respond with a decrease in their mitochondrial reserve capacity during low-level oxidative stress, an effect, which is attenuated by PARP1 inhibition. While PARP1 is a regulator of oxidative phosphorylation in resting and oxidatively stressed cells, it only exerts a minor effect on glycolysis.

MK-4827, a PARP-1/-2 inhibitor, strongly enhances response of human lung and breast cancer xenografts to radiation

The poly-(ADP-ribose) polymerase (PARP) inhibitor, MK-4827, is a novel potent, orally bioavailable PARP-1 and PARP-2 inhibitor currently in phase I clinical trials for cancer treatment. No preclinical data currently exist on the combination of MK-4827 with radiotherapy. The current study examined combined treatment efficacy of MK-4827 and fractionated radiotherapy using a variety of human tumor xenografts of differing p53 status: Calu-6 (p53 null), A549 (p53 wild-type [wt]) and H-460 (p53 wt) lung cancers and triple negative MDA-MB-231 human breast carcinoma. To mimic clinical application of radiotherapy, fractionated radiation (2 Gy per fraction) schedules given once or twice daily for 1 to 2 weeks combined with MK-4827, 50 mg/kg once daily or 25 mg/kg twice daily, were used. MK-4827 was found to be highly and similarly effective in both radiation schedules but maximum radiation enhancement was observed when MK-4827 was given at a dose of 50 mg/kg once daily (EF = 2.2). MK-4827 radiosensitized all four tumors studied regardless of their p53 status. MK-4827 reduced PAR levels in tumors by 1 h after administration which persisted for up to 24 h. This long period of PARP inhibition potentially adds to the flexibility of design of future clinical trials. Thus, MK-4827 shows high potential to improve the efficacy of radiotherapy.

Increased poly(ADP-ribosyl)ation in skeletal muscle tissue of pediatric patients with severe burn injury: prevention by propranolol treatment

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) has been shown to promote cellular energetic collapse and cellular necrosis in various forms of critical illness. Most of the evidence implicating the PARP pathway in disease processes is derived from preclinical studies. With respect to PARP and burns, studies in rodent and large animal models of burn injury have demonstrated the activation of PARP in various tissues and the beneficial effect of its pharmacological inhibition. The aims of the current study were to measure the activation of PARP in human skeletal muscle biopsies at various stages of severe pediatric burn injury and to identify the cell types where this activation may occur. Another aim of the study was to test the effect of propranolol (an effective treatment of patients with burns) on the activation of PARP in skeletal muscle biopsies. Poly(ADP-ribose) polymerase activation was measured by Western blotting for its product, poly(ADP-ribose) (PAR). The localization of PARP activation was determined by PAR immunohistochemistry. The results showed that PARP becomes activated in the skeletal muscle tissue after burns, with the peak of the activation occurring in the middle stage of the disease (13-18 days after burns). Even at the late stage of the disease (69-369 days after burn), an elevated degree of PARP activation persisted in some of the patients. Immunohistochemical studies localized the staining of PAR primarily to vascular endothelial cells and occasionally to resident mononuclear cells. There was a marked suppression of PARP activation in the skeletal muscle biopsies of patients who received propranolol treatment. We conclude that human burn injury is associated with the activation of PARP. We hypothesize that this response may contribute to the inflammatory responses and cell dysfunction in burns. Some of the clinical benefit of propranolol in burns may be related to its inhibitory effect on PARP activation.

Molecular markers for cancer prognosis and treatment: have we struck gold?

The last decade has witnessed an emerging role for molecular or biochemical markers indicating a specific cellular mechanism or tissue function, often called 'biomarkers'. Biomarkers such as altered DNA, proteins and inflammatory cytokines are critical in cancer research and strategizing treatment in the clinic. In this review we look at the application of biological indicators to cancer research and highlight their roles in cancer detection and treatment. With technological advances in gene expression, genomic and proteomic analysis, biomarker discovery is expanding fast. We focus on some of the predominantly used markers in different types of malignancies, their advantages, and their limitations. Finally we conclude by looking at the future of biomarkers, their utility in the tumorigenic studies, and the progress towards personalized treatment strategies.

Poly(ADP-ribose) polymerase-1 is a key mediator of cisplatin-induced kidney inflammation and injury

Cisplatin is a commonly used chemotherapeutic drug, the clinical use of which is limited by the development of dose-dependent nephrotoxicity. Enhanced inflammatory response, oxidative stress, and cell death have been implicated in the development of cisplatin-induced nephropathy; however, the precise mechanisms are elusive. Overactivation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) by oxidative DNA damage under various pathological conditions promotes cell death and up-regulation of key proinflammatory pathways. In this study, using a well-established model of nephropathy, we have explored the role of PARP-1 in cisplatin-induced kidney injury. Genetic deletion or pharmacological inhibition of PARP-1 markedly attenuated the cisplatin-induced histopathological damage, impaired renal function (elevated serum BUN and creatinine levels), and enhanced inflammatory response (leukocyte infiltration; TNF-α, IL-1β, F4/80, adhesion molecules ICAM-1/VCAM-1 expression) and consequent oxidative/nitrative stress (4-HNE, 8-OHdG, and nitrotyrosine content; NOX2/NOX4 expression). PARP inhibition also facilitated the cisplatin-induced death of cancer cells. Thus, PARP activation plays an important role in cisplatin-induced kidney injury, and its pharmacological inhibition may represent a promising approach to preventing the cisplatin-induced nephropathy. This is particularly exciting because several PARP inhibitors alone or in combination with DNA-damaging anticancer agents show considerable promise in clinical trials for treatment of various malignancies (e.g., triple-negative breast cancer).

PPARα mediates the anti-inflammatory effect of simvastatin in an experimental model of zymosan-induced multiple organ failure

BACKGROUND AND PURPOSE

Zymosan-induced non-septic shock is a multi-factorial pathology that involves several organs including the kidneys, liver and lungs. Its complexity and diversity presents a continuing therapeutic challenge. Given their pleiotropic effect, statins could be beneficial in non-septic shock. One of the molecular mechanisms underlying the anti-inflammatory effect of statins involves the peroxisome proliferator-activated receptor (PPAR) α. We used a zymosan-induced non-septic shock experimental model to investigate the role of PPARα in the anti-inflammatory effects of simvastatin.

EXPERIMENTAL APPROACH

Effects of simvastatin (5 or 10 mg·kg(-1) i.p.) were analysed in PPARα knock-out (KO) and PPARα wild type (WT) mice after zymosan or vehicle administration. Organ injury in lung, liver, kidney and intestine was evaluated by immunohistology. PPARα mRNA expression and nuclear factor-κB activation were evaluated in all experimental groups, 18 h after study onset. Cytokine levels were measured in plasma, and nitrite/nitrate in plasma and peritoneal exudate. Nitric oxide synthase, nitrotyrosine and poly ADP-ribose were localized by immunohistochemical methods.

KEY RESULTS

Simvastatin significantly and dose-dependently increased the zymosan-induced expression of PPARα levels in all tissues analysed. It also dose-dependently reduced systemic inflammation and the organ injury induced by zymosan in lung, liver, intestine and kidney. These effects were observed in PPARαWT mice and in PPARαKO mice.

CONCLUSIONS AND IMPLICATIONS

Simvastatin protected against the molecular and cellular damage caused by systemic inflammation in our experimental model. Our results also provide new information regarding the role of PPARα in the anti-inflammatory effects of statins.

SNPs in DNA repair genes associated to meningitis and host immune response

In vitro and in animal models, APE1, OGG1, and PARP-1 have been proposed as being involved with inflammatory response. In this work, we have investigated if the SNPs APE1 Asn148Glu, OGG1 Ser326Cys, and PARP-1 Val762Ala are associated to meningitis. The patient genotypes were investigated by PIRA-PCR or PCR-RFLP. DNA damages were detected in genomic DNA by Fpg treatment. IgG and IgA were measured from plasma and the cytokines and chemokines were measured from cerebrospinal fluid samples using Bio-Plex assays. A higher frequency (P<0.05) of APE1 Glu allele in bacterial meningitis (BM) and aseptic meningitis (AM) patients was observed. The genotypes Asn/Asn in control group and Asn/Glu in BM group was also higher. For the SNP OGG1 Ser326Cys, the genotype Cys/Cys was more frequent (P<0.05) in BM group. The frequency of PARP-1 Val/Val genotype was higher in control group (P<0.05). The occurrence of combined SNPs is significantly higher in BM patients, indicating that these SNPs may be associated to the disease. Increasing in sensitive sites to Fpg was observed in carriers of APE1 Glu allele or OGG1 Cys allele, suggesting that SNPs affect DNA repair activity. Alterations in IgG production were observed in the presence of SNPs APE1 Asn148Glu, OGG1 Ser326Cys or PARP-1 Val762Ala. Moreover, reduction in the levels of IL-6, IL-1Ra, MCP-1/CCL2 and IL-8/CXCL8 was observed in the presence of APE1 Glu allele in BM patients. In conclusion, we obtained indications of an effect of SNPs in DNA repair genes on the regulation of immune response in meningitis.

Signaling mechanism of poly(ADP-ribose) polymerase-1 (PARP-1) in inflammatory diseases

Poly(ADP-ribosyl)ation, attaching the ADP-ribose polymer chain to the receptor protein, is a unique posttranslational modification. Poly(ADP-ribose) polymerase-1 (PARP-1) is a well-characterized member of the PARP family. In this review, we provide a general update on molecular structure and structure-based activity of this enzyme. However, we mainly focus on the roles of PARP-1 in inflammatory diseases. Specifically, we discuss the signaling pathway context that PARP-1 is involved in to regulate the pathogenesis of inflammation. PARP-1 facilitates diverse inflammatory responses by promoting inflammation-relevant gene expression, such as cytokines, oxidation-reduction-related enzymes, and adhesion molecules. Excessive activation of PARP-1 induces mitochondria-associated cell death in injured tissues and constitutes another mechanism for exacerbating inflammation.

New insights into the prevention and treatment of familial breast cancer

Individuals who inherit a deleterious mutation in BRCA1 or BRCA2 are at very high risk for breast cancer but there are several strategies available for successfully managing this risk. Breast cancers that develop in the context of germline BRCA gene mutation present challenges for management but also opportunities. DNA damaging agents, like cisplatin, and the new class of drugs called PARP inhibitors exploit the underlying defect in DNA damage repair to great effect.

Poly(ADP-ribose) polymerase-1 inhibition: preclinical and clinical development of synthetic lethality

The hereditary forms of breast cancer identified by BRCA1 and BRCA2 genes have a defect in homologous DNA repair and demonstrate a dependence on alternate DNA repair processes by base excision repair, which requires poly(ADP-ribose) polymerase 1 (PARP-1). siRNA and deletion mutations demonstrate that interference with PARP-1 function results in enhanced cell death when the malignancy has a defect in homologous recombination. These findings resulted in a plethora of agents in clinical trials that interfere with DNA repair, and these agents offer the potential of being more selective in their effects than classic chemotherapeutic drugs. An electronic search of the National Library of Medicine for published articles written in English used the terms "PARP inhibitors" and "breast cancer" to find prospective, retrospective and review articles. Additional searches were done for articles dealing with mechanism of action. A total of 152 articles dealing with breast cancer and PARP inhibition were identified. PARP inhibition not only affects nonhomologous repair, but also has several other nongenomic functions. Mutational resistance to these agents was seen in preclinical studies. To date, PARP-1 inhibitors were shown to enhance cytotoxic effects of some chemotherapy agents. This new class of agents may offer more therapeutic specificity by exploiting a DNA repair defect seen in some human tumors with initial clinical trials demonstrating antitumor activity. Although PARP inhibitors may offer a therapeutic option for selected malignancies, the long-term effects of these agents have not yet been defined.

Age-related loss of stress-induced nuclear proteasome activation is due to low PARP-1 activity

Changes in protein turnover are among the dominant metabolic changes during aging. Of special importance is the maintenance of nuclear protein homeostasis to ensure a coordinated cellular metabolism. Therefore, in the nucleus a special PARP-1-mediated mechanism of proteasomal activation exists to ensure a rapid degradation of oxidized nuclear proteins. It was already demonstrated earlier that the cytosolic proteasomal system declines dramatically with aging, whereas the nuclear proteasome remains less affected. We demonstrate here that the stress-mediated proteasomal activation in the nucleus declines during replicative senescence of human fibroblasts. Furthermore, we clearly show that this decline in the PARP-1-mediated proteasomal activation is due to a decline in the expression and activity of PARP-1 in senescent fibroblasts. In a final study we show that this process also happens in vivo, because the protein expression level of PARP-1 is significantly lower in the skin of aged donors compared to that of young ones. Therefore, we conclude that the rate-limiting factor in poly(ADP-ribose)-mediated proteasomal activation in oxidative stress is PARP-1 and not the nuclear proteasome itself.

Oxidative stress initiates DNA damager MNNG-induced poly(ADP-ribose)polymerase-1-dependent parthanatos cell death

The alkylating agent N-methyl-N'-nitro-N'-nitrosoguanidine (MNNG) can cause excess DNA strand breaks that lead to poly(ADP-ribose)polymerase-1 (PARP-1) overactivation and cell death (parthanatos). However, the detail mechanism of MNNG-induced parthanatos was not well-investigated. In this study, we used MNNG-treated mouse embryonic fibroblasts (MEFs) to elucidate the signaling pathways of MNNG-induced parthanatos. We found that MNNG-induced cell death accompanied by rapid PARP-1 activation, c-Jun N-terminal kinase (JNK) activation, biphasic reactive oxygen species (ROS) production and intracellular calcium increase. The early ROS production occurring at 1 min and peaking at 5-15 min after MNNG treatment partially resulted from NADPH oxidase. In contrast, the late phase of ROS production occurring at 30 min and time-dependently increasing up to 6h after MNNG treatment was generated by mitochondria. The antioxidant, NAC can abrogate all phenomena caused by MNNG. Results indicate that the calcium rise was downstream of early ROS production, and was involved in PARP-1 and JNK activation. Moreover, the PARP inhibitor was able to reduce MNNG-induced late-phase ROS production, calcium elevation, and cell death. Results further indicated the involvement of RIP1 in sustained ROS production and calcium increase. We characterized the interactive roles of ROS, calcium, JNK, and RIP1 in MNNG-induced cell death. We found that in addition to the alkylating property previously demonstrated, ROS production triggered by MNNG results in enhanced DNA damage and PARP-1 activation. Moreover, intracellular calcium elevation and ROS production have mutual amplification effects and thus contribute to PARP-1-mediated parthanatos.

Cooperative role of NF-{kappa}B and poly(ADP-ribose) polymerase 1 (PARP-1) in the TNF-induced inhibition of PHEX expression in osteoblasts

Reduced bone mass is a common complication in chronic inflammatory diseases, although the mechanisms are not completely understood. The PHEX gene encodes a zinc endopeptidase expressed in osteoblasts and contributes to bone mineralization. The aim of this study was to determine the molecular mechanism involved in TNF-mediated down-regulation of Phex gene transcription. We demonstrate down-regulation of the Phex gene in two models of colitis: naive T-cell transfer and in gnotobiotic IL-10(-/-) mice. In vitro, TNF decreased expression of Phex in UMR106 cells and did not require de novo synthesis of a transrepressor. Transfecting UMR-106 cells with a series of deletion constructs of the proximal Phex promoter identified a region located within -74 nucleotides containing NF-κB and AP-1 binding sites. After TNF treatment, the RelA/p50 NF-κB complex interacted with two cis-elements at positions -70/-66 and -29/-25 nucleotides in the proximal Phex promoter. Inhibition of NF-κB signaling increased the basal level of Phex transcription and abrogated the effects of TNF, whereas overexpression of RelA mimicked the effect of TNF. We identified poly(ADP-ribose) polymerase 1 (PARP-1) binding immediately upstream of the NF-κB sites and showed that TNF induced poly(ADP-ribosyl)ation of RelA when bound to the Phex promoter. TNF-mediated Phex down-regulation was completely abrogated in vitro by PARP-1 inhibitor and overexpression of poly(ADP-ribose) glucohydrolase (PARG) and in vivo in PARP-1(-/-) mice. Our results suggest that NF-κB signaling and PARP-1 enzymatic activity cooperatively contribute to the constitutive and inducible suppression of Phex. The described phenomenon likely contributes to the loss of bone mass density in chronic inflammatory diseases, such as inflammatory bowel disease.

Factors controlling the mechanism of NAD(+) non-redox reactions

β-Nicotinamide adenine dinucleotide (NAD(+)) is an indispensable coenzyme or substrate for enzymes involved in catalyzing redox and non-redox reactions. ADP-ribosylating enzymes catalyze cleavage of the nicotinamide-glycosyl bond of NAD(+) and addition of a nucleophilic group from their substrate proteins to the N-ribose anomeric carbon of NAD(+). Although the role of the nicotinamide-ribose fragment in the mechanism of NAD(+) hydrolysis has been examined, the role of the doubly negatively charged, flexible, and chemically reactive NAD(+) diphosphate moiety in the reaction process has largely been neglected. Thus, the participation of the pyrophosphate group in stabilizing intra- and intermolecular interactions in the ground state and transition state has not been explored. Furthermore, the roles of other factors such as the type/nucleophilicity of the attacking nucleophile and the medium in influencing the reaction pathway have not been systematically evaluated. In this study, we endeavor to fill in these gaps and elucidate the role of these factors in controlling the NAD(+) nicotinamide-glycosyl bond cleavage. Using density functional theory combined with continuum dielectric methods, we modeled both S(N)1 and S(N)2 reaction pathways and assessed the role of the diphosphate group in stabilizing the (i) NAD(+) ground state, (ii) oxocarbocation intermediate, (iii) reaction product, and (iv) nucleophile. We also assessed the chemical nature of the attacking nucleophile and the role of the protein matrix in affecting the reaction mechanism. Our results reveal an intricate interplay among various factors in controlling the reaction pathway, which in turn suggests ways in which the enzyme can accelerate the reaction.

Targeting poly(ADP-ribose) polymerase activity for cancer therapy

Poly(ADP-ribosyl)ation is a ubiquitous protein modification found in mammalian cells that modulates many cellular responses, including DNA repair. The poly(ADP-ribose) polymerase (PARP) family catalyze the formation and addition onto proteins of negatively charged ADP-ribose polymers synthesized from NAD(+). The absence of PARP-1 and PARP-2, both of which are activated by DNA damage, results in hypersensitivity to ionizing radiation and alkylating agents. PARP inhibitors that compete with NAD(+) at the enzyme's activity site are effective chemo- and radiopotentiation agents and, in BRCA-deficient tumors, can be used as single-agent therapies acting through the principle of synthetic lethality. Through extensive drug-development programs, third-generation inhibitors have now entered clinical trials and are showing great promise. However, both PARP-1 and PARP-2 are not only involved in DNA repair but also in transcription regulation, chromatin modification, and cellular homeostasis. The impact on these processes of PARP inhibition on long-term therapeutic responses needs to be investigated.

Comparative study of the binding characteristics to and inhibitory potencies towards PARP and in vivo antidiabetogenic potencies of taurine, 3-aminobenzamide and nicotinamide

BACKGROUND

Poly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic beta-cell death and in the development of endothelial dysfunction in humans and experimental animals. PARP activation is also relevant to the development of complications of diabetes. Hence, agents capable of inhibiting PARP may be useful in preventing the development of diabetes and in slowing down complications of diabetes.

METHODS

PARP inhibition was assessed with a colorimetric assay kit. Molecular docking studies on the active site of PARP were conducted using the crystalline structure of the enzyme available as Protein Data Bank Identification No. 1UK1. Type 2 diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ, 60 mg/kg, i.p.). The test compounds (3-aminobenzamide = 3-AB, nicotinamide = NIC, taurine = TAU) were given by the i.p. route 45 min before STZ at 2.4 mM/kg (all three compounds) or 1.2 and 3.6 mM/kg (only NIC and TAU). Blood samples were collected at 24 hr after STZ and processed for their plasma. The plasma samples were used to measure glucose, insulin, cholesterol, triglycerides, malondialdehyde, nitric oxide, and glutathione levels using reported methods.

RESULTS

3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC> or =TAU. Molecular docking studies at the active site of PARP showed 3-AB and NIC to interact with the binding site for the nicotinamide moiety of NAD+ and TAU to interact with the binding site for the adenine moiety of NAD+. While STZ-induced diabetes elevated all the experimental parameters examined and lowered the insulin output, a pretreatment with 3-AB, NIC or TAU reversed these trends to a significant extent. At a dose of 2.4 mm/kg, the protective effect decreased in the approximate order 3-AB>NIC> or =TAU. The attenuating actions of both NIC and TAU were dose-related except for the plasma lipids since NIC was without a significant effect at all doses tested.

CONCLUSIONS

At equal molar doses, 3-AB was generally more potent than either TAU or NIC as an antidiabetogenic agent, but the differences were not as dramatic as would have been predicted from their differences in PARP inhibitory potencies. NIC and TAU demonstrated dose-related effects, which in the case of TAU were only evident at doses > or =2.4 mM/kg. The present results also suggest that in the case of NIC and TAU an increase in dose will enhance the magnitude of their attenuating actions on diabetes-related biochemical alterations to that achieved with a stronger PARP inhibitor such as 3-AB. Hence, dosing will play a critical role in clinical studies assessing the merits of NIC and TAU as diabetes-preventing agents.

Poly ADP-ribose polymerase-1 and health

Niacin (vitamin B(3)) is required to form nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are involved in scores of anabolic and catabolic redox reactions throughout metabolism. It is now understood that NAD(+) is also a substrate for several families of ADP-ribosylation reactions, which control processes like DNA repair, replication and transcription, the activity of G-proteins, chromatin structure and intracellular calcium signalling. Poly(ADP-ribose)polymerase-1 (PARP-1) is the most active of the PARP enzymes, and it has been implicated in both prevention and aggravation of disease processes. Inhibition of poly-ADP-ribose formation will tend to cause genomic instability and tumorigenesis in chronic models of DNA damage, but the same inhibition can prevent many acute disease processes, such as stroke, myocardial infarction and septic shock. In models of acute stress, PARP-1 inhibition may protect cellular NAD pools and prevent nuclear factor-kappaB-dependent inflammatory signalling, while long-term protective roles for PARP-1 include DNA repair and regulation of chromatin structure. Promising new PARP-1 inhibitors may display interactions with dietary niacin status and may have long-term deleterious effects on genomic stability, but may be extremely valuable for the treatment of acute inflammatory conditions.

Poly (ADP-ribose) polymerase-1 deficiency does not affect ethylnitrosourea mutagenicity in liver and testis of lacZ transgenic mice

Poly (ADP-ribose) polymerase-1 (Parp1) has been implicated in DNA base excision repair, single- and double-strand break repair pathways, as well as in cell death by apoptosis or necrosis. We used Parp1(-/-) lacZ plasmid-based transgenic mice to investigate whether Parp1 deficiency influences the in vivo mutagenic and clastogenic response to the alkylating agent N-ethyl-N-Nitrosourea (ENU) in somatic and germ-cell tissues. The comparison of the lacZ mutant frequencies (MFs) between Parp1(+/+) and Parp1(-/-) mice showed that the ablation of Parp1 does not affect the spontaneous or ENU-induced MFs in liver and testis. In addition, the spectrum of the ENU-induced mutations was not dependent on the Parp1 status, given that similar spectra, consisting mostly of point mutations and a small fraction of deletions/insertions, wereobserved in organs of both Parp1(-/-) and Parp1(+/+) mice. Sequencing of point mutations revealed a consistent significant increase in A:T --> T:A base substitutions, typically induced by ENU. Overall, we observed that neither the frequency nor the spectrum of ENU-induced mutations demonstrated a specificity that could be attributed to the Parp1 impairment in mice organs. The analysis of micronucleus frequency in peripheral blood reticulocytes showed that ENU was clastogenic in both Parp1(-/-) and Parp1(+/+) mice and had a strong cytotoxic effect in Parp1(-/-) mice only. The present data suggest that, at a whole-organism level, Parp1-independent repair mechanisms may be operative in the removal of ENU-induced DNA lesions or that highly damaged cells may be preferentially committed to death when Parp1 is inactivated.

PARP inhibitors: new tools to protect from inflammation

Poly(ADP-ribosylation) consists in the conversion of β-NAD(+) into ADP-ribose, which is then bound to acceptor proteins and further used to form polymers of variable length and structure. The correct turnover of poly(ADP-ribose) is ensured by the concerted action of poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG) enzymes, which are responsible for polymer synthesis and degradation, respectively. Despite the positive role of poly(ADP-ribosylation) in sensing and repairing DNA damage, generated also by ROS, PARP over-activation could allow NAD depletion and consequent necrosis, thus leading to an inflammatory condition in many diseases. In this respect, inhibition of PARP enzymes could exert a protective role towards a number of pathological conditions; i.e. the combined treatment of tumors with PARP inhibitors/anticancer agents proved to have a beneficial effect in cancer therapy. Thus, pharmacological inactivation of poly(ADP-ribosylation) could represent a novel therapeutic strategy to limit cellular injury and to attenuate the inflammatory processes that characterize many disorders.

Folate deficiency provides protection against colon carcinogenesis in DNA polymerase beta haploinsufficient mice

Aging and DNA polymerase beta deficiency (beta-pol(+/-)) interact to accelerate the development of malignant lymphomas and adenocarcinoma and increase tumor bearing load in mice. Folate deficiency (FD) has been shown to induce DNA damage repaired via the base excision repair (BER) pathway. We anticipated that FD and BER deficiency would interact to accelerate aberrant crypt foci (ACF) formation and tumor development in beta-pol haploinsufficient animals. FD resulted in a significant increase in ACF formation in wild type (WT) animals exposed to 1,2-dimethylhydrazine, a known colon and liver carcinogen; however, FD reduced development of ACF in beta-pol haploinsufficient mice. Prolonged feeding of the FD diet resulted in advanced ACF formation and liver tumors in wild type mice. However, FD attenuated onset and progression of ACF and prevented liver tumorigenesis in beta-pol haploinsufficient mice, i.e. FD provided protection against tumorigenesis in a BER-deficient environment in all tissues where 1,2-dimethylhydrazine exerts its damage. Here we show a distinct down-regulation in DNA repair pathways, e.g. BER, nucleotide excision repair, and mismatch repair, and decline in cell proliferation, as well as an up-regulation in poly(ADP-ribose) polymerase, proapoptotic genes, and apoptosis in colons of FD beta-pol haploinsufficient mice.

PARP and PARG inhibitors--new therapeutic targets in cancer treatment

Today, the number of cancer patients throughout the world is increasing alarmingly and as per the World Health Organisation (WHO) data and statistics the prediction for the year 2020 will be 15 million new cases as compared to only 10 million cases in year 2000 leaving us dumbfounded. A lot of effort has been put in by researchers and scientists over decades to find drugs helpful in the treatment of cancers for the benefit of patients--the latest being the Poly ADP-ribose polymerase (PARP) and the Poly ADP-ribose glycohydrolase (PARG) inhibitors. This review highlights their mechanism of action under the rationale of their use and current development in the field of cancer.

Vitamin B3, the nicotinamide adenine dinucleotides and aging

Organism aging is a process of time and maturation culminating in senescence and death. The molecular details that define and determine aging have been intensely investigated. It has become appreciated that the process is partly an accumulation of random yet inevitable changes, but it can be strongly affected by genes that alter lifespan. In this review, we consider how NAD(+) metabolism plays important roles in the random patterns of aging, and also in the more programmatic aspects. The derivatives of NAD(+), such as reduced and oxidized forms of NAD(P)(+), play important roles in maintaining and regulating cellular redox state, Ca(2+) stores, DNA damage and repair, stress responses, cell cycle timing and lipid and energy metabolism. NAD(+) is also a substrate for signaling enzymes like the sirtuins and poly-ADP-ribosylpolymerases, members of a broad family of protein deacetylases and ADP-ribosyltransferases that regulate fundamental cellular processes such as transcription, recombination, cell division, proliferation, genome maintenance, apoptosis, stress resistance and senescence. NAD(+)-dependent enzymes are increasingly appreciated to regulate the timing of changes that lead to aging phenotypes. We consider how metabolism, specifically connected with Vitamin B3 and the nicotinamide adenine dinucleotides and their derivatives, occupies a central place in the aging processes of mammals.

Critical role of poly(ADP-ribose) polymerase-1 in modulating the mode of cell death caused by continuous oxidative stress

Continuously generated hydrogen peroxide (H(2)O(2)) inhibits typical apoptosis and instead initiates a caspase-independent, apoptosis-inducing factor (AIF)-mediated pyknotic cell death. This may be related to H(2)O(2)-mediated DNA damage and subsequent ATP depletion, although the exact mechanisms by which the mode of cell death is decided after H(2)O(2) exposure are still unclear. Accumulated evidence and our previous data led us to hypothesize that continuously generated H(2)O(2), not an H(2)O(2) bolus, induces severe DNA damage, signaling poly(ADP-ribose) polymerase-1 (PARP-1) activation, ATP depletion, and eventually caspase-independent cell death. Results from the present study support that H(2)O(2) generated continuously by glucose oxidase causes excessive DNA damage and PARP-1 activation. Blockage of PARP-1 by a siRNA transfection or by pharmacological inhibitor resulted in the significant inhibition of ATP depletion, loss of mitochondrial membrane potential, nuclear translocation of AIF and endonuclease G, and eventually conversion to caspase-dependent apoptosis. Overall, the current study demonstrates the different roles of PARP-1 inhibition in modulation of cell death according to the method of H(2)O(2) exposure, that is, continuous generation versus a direct addition.

Telomere shortening is associated to TRF1 and PARP1 overexpression in Duchenne muscular dystrophy

Telomere shortening is thought to contribute to premature senescence of satellite cells in Duchenne muscular dystrophy (DMD) muscle. Telomeric repeat binding factor-1 (TRF1) and poly (ADP-ribose) polymerase-1 (PARP1) are proteins known to modulate telomerase reverse transcriptase (TERT) activity, which controls telomere elongation. Here we show that an age-dependent telomere shortening occurs in DMD muscles and is associated to overexpression of mRNA and protein levels of TRF1 and PARP1. TERT expression and activity are detectable in normal control muscles and they slightly increase in DMD. This is the first demonstration of TRF1 and PARP1 overexpression in DMD muscles. They can be directly involved in replicative senescence of satellite cells and/or in the pathogenetic cascade through a cross-talk with oxidative stress and inflammatory response. Modulation of these events by TRF1 or PARP1 inhibition might represent a novel strategy for treatment of DMD and other muscular dystrophies.

A kinetic study on the chemical cleavage of nucleoside diphosphate sugars

Nucleoside diphosphate sugars serve in essential roles in metabolic processes. They have, therefore, been used in mechanistic studies on glycosylation reactions, and their analogues have been synthesised as enzyme and receptor inhibitors. Despite extensive biochemical research, little is known about their chemical reactions. In the present work the chemical cleavage of two different types of nucleoside diphosphate sugars has been studied. UDP-Glc is phosphorylated at the anomeric carbon, whereas in ADP-Rib C-1 is unsubstituted, allowing hence the equilibrium between cyclic hemiacetal and acyclic carbonyl forms. Due to the structural difference, these substrates react via different pathways under slightly alkaline conditions: while UDP-Glc reacts exclusively by a nucleophilic attack of a glucose hydroxyl group on the diphosphate moiety, ADP-Rib undergoes a complex reaction sequence that involves isomerisation processes of the acyclic ribose sugar and results in a release of ADP.

A selective eradication of human nonhereditary breast cancer cells by phenanthridine-derived polyADP-ribose polymerase inhibitors

Introduction

PARP-1 (polyADP-ribose polymerase-1) is known to be activated in response to DNA damage, and activated PARP-1 promotes DNA repair. However, a recently disclosed alternative mechanism of PARP-1 activation by phosphorylated externally regulated kinase (ERK) implicates PARP-1 in a vast number of signal-transduction networks in the cell. Here, PARP-1 activation was examined for its possible effects on cell proliferation in both normal and malignant cells.

Methods

In vitro (cell cultures) and in vivo (xenotransplants) experiments were performed.

Results

Phenanthridine-derived PARP inhibitors interfered with cell proliferation by causing G₂/M arrest in both normal (human epithelial cells MCF10A and mouse embryonic fibroblasts) and human breast cancer cells MCF-7 and MDA231. However, whereas the normal cells were only transiently arrested, G₂/M arrest in the malignant breast cancer cells was permanent and was accompanied by a massive cell death. In accordance, treatment with a phenanthridine-derived PARP inhibitor prevented the development of MCF-7 and MDA231 xenotransplants in female nude mice. Quiescent cells (neurons and cardiomyocytes) are not impaired by these PARP inhibitors.

Conclusions

These results outline a new therapeutic approach for a selective eradication of abundant nonhereditary human breast cancers.

1-methylnicotinamide (MNA) in prevention of diabetes-associated brain disorders

The present study has been designed to establish the potential benefits from 1-methylnicotinamide (MNA) treatment on brain disorders associated with type 1 diabetes. All experiments were carried out after 6 weeks of streptozotocin-induced diabetes (60 mg/kg of body weight, i.p.) in male Wistar rats treated for 5 weeks with or without MNA (100 mg/kg of body weight, per os in drinking water) after 1 week of diabetes induction. Diabetes was shown to reduce monoamine neurotransmitter serotonin transporters activity, as assessed by significant inhibition of [2-(14)C]serotonin uptake, that was accompanied by elevation of spontaneous mediator release in rat brain synaptosomes. Treatment with MNA slightly attenuated diabetes-induced changes in brain serotoninergic system. The precise mechanism underlying MNA action on central serotonin neurotransmission is not known, but appears to be linked to metabolic and signalling pathways involved in controlling synaptic function rather than being associated with direct modulation of serotonin transporters. In particular, MNA action was associated with its partial normalizing effects on such biochemical indices of neuropathy development as decrease in synaptosomal Na(+),K(+)-ATPase activity and plasma membrane depolarization of synaptic endings. Elevated sorbitol formation in brain and NAD(+) deficits resulted from diabetes as major metabolic imbalances were remarkably countered by MNA treatment. However, diabetes-induced decrease in cytosolic NAD(+) to NADH ratio in brain remained unchanged. Notably, MNA supplementation to diabetic rats caused a slight lowering effect on blood glucose level. Accordingly, our findings indicate that neuroprotective properties of MNA are linked to modulation of synaptic activity through multiple mechanisms. In conclusion, we suggest that 1-methylnicotinamide might be a useful agent for treating brain failures related to diabetes.