Pharmacological inhibition of poly(ADP-ribose) polymerase inhibits angiogenesis

Small molecule tractable PARP inhibitors: Scaffold construction approaches, mechanistic insights and structure activity relationship

Diverse drug design strategies viz. molecular hybridization, substituent installation, scaffold hopping, isosteric replacement, high-throughput screening, induction and separation of chirality, structure modifications of phytoconstituents and use of structural templates have been exhaustively leveraged in the last decade to load the chemical toolbox of PARP inhibitors. Resultantly, numerous promising scaffolds have been pinpointed that in turn have led to the resuscitation of the credence to PARP inhibitors as cancer therapeutics. This review briefly presents the physiological functions of PARPs, the pharmacokinetics, and pharmacodynamics, and the interaction profiles of FDA-approved PARP inhibitors. Comprehensively covered is the section on the drug design strategies employed by drug discovery enthusiasts for furnishing PARP inhibitors. The impact of structural variations in the template of designed scaffolds on enzymatic and cellular activity (structure-activity relationship studies) has been discussed. The insights gained through the biological evaluation such as profiling of physicochemical properties andin vitroADME properties, PK assessments, and high-dose pharmacology are covered.

Dual antitumor immunomodulatory effects of PARP inhibitor on the tumor microenvironment: A counterbalance between anti-tumor and pro-tumor

Poly (ADP-ribose)-polymerases (PARPs) play an essential role in the maintenance of genome integrity, DNA repair, and apoptosis. PARP inhibitors (PARPi) exert antitumor effects via synthetic lethality and PARP trapping. PARPi impact the antitumor immune response by modulating the tumor microenvironment, and their effect has dual properties of promoting and inhibiting the antitumor immune response. PARPi promote M1 macrophage polarization, antigen presentation by dendritic cells, infiltration of B and T cells and their killing capacity and inhibit tumor angiogenesis. PARPi can also inhibit the activation and function of immune cells by upregulating PD-L1. In this review, we summarize the dual immunomodulatory effects and possible underlying mechanisms of PARPi, providing a basis for the design of combination regimens for clinical treatment and the identification of populations who may benefit from these therapies.

Successes and failures of angiogenesis blockade in gastric and gastro-esophageal junction adenocarcinoma

Gastric and gastro-esophageal junction adenocarcinoma (GEA) remains a considerable major public health problem worldwide, being the fifth most common cancer with a fatality-to-case ratio that stands still at 70%. Angiogenesis, which is a well-established cancer hallmark, exerts a fundamental role in cancer initiation and progression and its targeting has been actively pursued as a promising therapeutic strategy in GEA. A wealth of clinical trials has been conducted, investigating anti-angiogenic agents including VEGF-directed monoclonal antibodies, small molecules tyrosine kinase inhibitors and VEGF-Trap agents both in the resectable and advanced setting, reporting controversial results. While phase III randomized trials testing the anti-VEGFR-2 antibody Ramucirumab and the selective VEGFR-2 tyrosine kinase inhibitor Apatinib demonstrated a significant survival benefit in later lines, the shift of angiogenesis inhibitors in the perioperative and first-line setting failed to improve patients’ outcome in GEAs. The molecular landscape of disease, together with novel combinatorial strategies and biomarker-selected approaches are under investigation as key elements to the success of angiogenesis blockade in GEA. In this article, we critically review the existing literature on the biological rationale and clinical development of antiangiogenic agents in GEA, discussing major achievements, limitations and future developments, aiming at fully realizing the potential of this therapeutic approach.

Targeting cancer stem cells in the tumor microenvironment: An emerging role of PARP inhibitors

Cancer stem cells (CSCs) constitute a small population of cancer cells in the tumor microenvironment (TME), which are responsible for metastasis, angiogenesis, drug resistance, and cancer relapse. Understanding the key signatures and resistance mechanisms of CSCs may help in the development of novel chemotherapeutic strategies to specifically target CSCs in the TME. PARP inhibitors (PARPi) are known to enhance the chemosensitivity of cancer cells to other chemotherapeutic agents by inhibiting the DNA repair pathways and chromatin modulation. But their effects on CSCs are still unknown. Few studies have reported that PARPi can stall replication fork progression in CSCs. PARPi also have the potential to overcome chemoresistance in CSCs and anti-angiogenic potentiality as well. Previous reports have suggested that epigenetic drugs can synergistically ameliorate the anti-cancer activities of PARPi through epigenetic modulations. In this review, we have systematically discussed the effects of PARPi on different DNA repair pathways with respect to CSCs and also how CSCs can be targeted either as monotherapy or as a part of combination therapy. We have also talked about how PARPi can help in reversal of chemoresistance of CSCs and the role of PARPi in epigenetic modifications to hinder cancer progression. We have also elaborated on the aspects of research that need to be investigated for development of successful therapeutic interventions using PARPi to specifically target CSCs in the TME.

The PARP Enzyme Family and the Hallmarks of Cancer Part 2: Hallmarks Related to Cancer Host Interactions

Poly (ADP-ribose) polymerases (PARPs) modify target proteins with a single ADP-ribose unit or with a poly (ADP-ribose) (PAR) polymer. PARP inhibitors (PARPis) recently became clinically available for the treatment of BRCA1/2 deficient tumors via the synthetic lethality paradigm. This personalized treatment primarily targets DNA damage-responsive PARPs (PARP1-3). However, the biological roles of PARP family member enzymes are broad; therefore, the effects of PARPis should be viewed in a much wider context, which includes complex effects on all known hallmarks of cancer. In the companion paper (part 1) to this review, we presented the fundamental roles of PARPs in intrinsic cancer cell hallmarks, such as uncontrolled proliferation, evasion of growth suppressors, cell death resistance, genome instability, replicative immortality, and reprogrammed metabolism. In the second part of this review, we present evidence linking PARPs to cancer-associated inflammation, anti-cancer immune response, invasion, and metastasis. A comprehensive overview of the roles of PARPs can facilitate the identification of novel cancer treatment opportunities and barriers limiting the efficacy of PARPi compounds.

Poly (ADP-ribose) polymerase inhibitor exposure reduces ovarian reserve followed by dysfunction in granulosa cells

The use of poly (ADP-ribose) polymerase (PARP) inhibitors is expected to increase, but their effect on fertility is still unclear. The aim of this study was to investigate the effect of PARP inhibitors on ovarian function. In an in vitro study, cultures of ovaries and granulosa cells (GCs) exposed to the PARP inhibitor olaparib were evaluated by real-time RT-PCR, histological study, and hormone assays. In an in vivo study, mice were administered olaparib orally and evaluated via in vitro fertilization (IVF), follicle count, immunohistochemical staining, and real-time RT-PCR. In vitro, the gene expression of GC markers decreased in the olaparib-treated group. Olaparib also negatively affected estradiol production and the expression of GC markers in cultured GCs, with abnormal morphology of GCs observed in the treated group. The follicle number indicated depletion of follicles due to atretic changes in the treatment group, both in vitro and in vivo. Also, olaparib reduced the number of retrieved oocytes and the fertilization rate of IVF, but they recovered after 3 weeks of cessation. Our results indicate that olaparib is toxic to ovaries.

Olaparib Suppresses MDSC Recruitment via SDF1α/CXCR4 Axis to Improve the Anti-tumor Efficacy of CAR-T Cells on Breast Cancer in Mice

A hostile tumor microenvironment is one of the major obstacles for the efficacy of chimeric antigen receptor modified T (CAR-T) cells, and combination treatment might be a potential way to overcome this obstacle. Poly(ADP-ribose) polymerase inhibitor (PARPi) has demonstrated tremendous potential in breast cancer. In this study, we explored the possible combination of the PAPRi olaparib with EGFRvIII-targeted CAR (806-28Z CAR) T cells in immunocompetent mouse models of breast cancer. The results indicated that the administration of olaparib could significantly enhance the efficacy of 806-28Z CAR-T cells in vivo. Interestingly, we observed that olaparib could suppress myeloid-derived suppressor cell (MDSC) migration and promote the survival of CD8⁺ T cells in tumor tissue. Mechanistically, olaparib was shown to reduce the expression of SDF1α released from cancer-associated fibroblasts (CAFs) and thereby decreased MDSC migration through CXCR4. Taken together, this study demonstrated that olaparib could increase the antitumor activities of CAR-T cell therapy at least partially through inhibiting MDSC migration via the SDF1α/CXCR4 axis. These findings uncover a novel mechanism of PARPi function and provide additional mechanistic rationale for combining PARPi with CAR-T cells for the treatment of breast cancer.

Novel Poly(Adenosine Diphosphate-Ribose) Polymerase (PARP) Inhibitor, AZD2461, Down-Regulates VEGF and Induces Apoptosis in Prostate Cancer Cells

Background

Prostate cancer (Pca) is a heterogeneous disease, and current treatments are not based on molecular stratification. Poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitors have recently been found to be remarkably toxic to cells with defects in homologous recombination, particularly cells with BRCA-mutated backgrounds. Therefore, this preliminary study was designed to evaluate whether PTEN expression status could have an impact on the sensitivity of invasive Pca cells to the PARP inhibitor, AZD2461.

Methods

MTT viability test, Annexin V‐FITC/propidium iodide double staining, and caspase3 activity assay were used to evaluate the apoptosis and relative expression of PTEN and VEGF in PC-3 and DU145 cell lines using real-time PCR.

Results

MTT results showed that the inhibitory effects of AZD2461 were higher in PC-3 than DU145 cells (with IC50 of 36.48 and 59.03 µM at 48 hours of treatment, respectively). Flow cytometric analysis also showed the same results. When exposed to 40 µM of AZD2461, PC-3 (38.8%) and DU145 (28%) cells underwent apoptosis (p < 0.05). Treatment of cells by AZD2461 also caused a significant increase in apoptosis through caspase3 activation in both cell lines. VEGF mRNA levels in PC-3 cells significantly decreased compared to adjusted untreated cells (p < 0.05) in all measured times while displaying different alteration patterns in DU145 cells (p < 0.05).

Conclusion

AZD2461 suppresses the growth of prostate tumor cells since AZD2461 monotherapy could prove to be efficacious, especially against cells not expressing PTEN besides activating the possible apoptosis-independent cell death pathways.

Nanoformulation of Talazoparib Delays Tumor Progression and Ascites Formation in a Late Stage Cancer Model

Talazoparib, a potent PARP inhibitor, induces synthetic lethality in BRCA-deficient cancers making it an attractive candidate for ovarian cancer treatment. However, its potency lends itself to side effects associated more closely with traditional chemotherapeutics than other clinically approved PARP inhbitors. We sought to formulate Talazoparib in a nanoparticle delivery system, which allows the drug to be administered intraperitoneally. This was done to specifically target peritoneal dissemination of late stage metastatic ovarian cancer and increase talazoparib's therapeutic efficacy while minimizing toxic side effects. NanoTalazoparib was developed and characterized with regard to its size, loading, and surface charge. Talazoparib and NanoTalazoparib were tested on a panel of murine and human BRCA cell lines and the dose response was compared to Olaparib's, the currently used PARP inhibitor. Therapeutic efficacy was tested in vivo in a Brca peritoneal cancer model that mimics late stage disseminated disease. NanoTalazoparib has a diameter of about 70 nm with a neutral surface charge and ~75% encapsulation efficiency, which slowly releases the drug over several hours. Dose response analysis indicated that the murine cell lines with conditional BRCA1/2, PTEN, and TP53 deletions had the lowest IC50s. NanoTalazoparib administered on a schedule of three doses weekly slowed disease progression and resulted in significantly less mice with ascites at the end point compared to controls. These results indicate that the slow release nanoformulation, NanoTalazoparib, effectively delivers PARP inhibitor therapy to the peritoneal cavity for disseminated cancer treatment. The ability to decrease ascites formation with the introduction of intraperitoneal NanoTalazoparib suggests this treatment may be an effective way to treat ovarian cancer-associated ascites and slow disease progression.

Vitamin E improves testicular damage in streptozocin-induced diabetic rats, via increasing vascular endothelial growth factor and poly(ADP-ribose) polymerase-1

The precise mechanism by which diabetes impairs spermatogenesis and testicular function is not exactly known. Vascular endothelial growth factor (VEGF) and poly(ADP-ribose) polymerase-1 (PARP-1) are important for germ cell homeostasis and repair of DNA respectively. The aim of this study was to investigate the correlation between diabetes-induced testicular damage and testicular VEGF and PARP-1 expression and the possible protective role of vitamin E supplementation. A total of 45 male Wistar albino rats were randomly divided into three groups: Group I (nondiabetic rats), Group II (streptozocin-induced diabetic rats) and Group III (streptozocin-induced diabetic rats treated orally with 0.4 mg/kg vitamin E). Five weeks later, testicular tissue was used for assessment of MDA concentration by colorimetry, histopathological examination and immunostaining for PARP-1 and VEGFIn diabetic rats, testicular weight, seminiferous tubule diameter and germinal epithelial thickness were decreased, basement membrane was thickened and Johnsen score decreased. Reduced VEGF and PARP-1 immunostaining were associated with decreased Johnsen score in diabetic rats. Vitamin E administration was protective against oxidative stress-associated damage evidenced by lower MDA levels, improved testicular weight, spermatogenesis and higher immunostaining for VEGF and PARP-1. Testicular VEGF and PARP-1 might therefore be helpful biomarkers for diabetic testicular damage. Administration of vitamin E may have a protective role against diabetes-induced testicular damage.

Low-Density Lipoprotein Receptor-Related Protein-1 Signaling in Angiogenesis

Low-density lipoprotein receptor-related protein-1 (LRP1) plays multifunctional roles in lipid homeostasis, signaling transduction, and endocytosis. It has been recognized as an endocytic receptor for many ligands and is involved in the signaling pathways of many growth factors or cytokines. Dysregulation of LRP1-dependent signaling events contributes to the development of pathophysiologic processes such as Alzheimer’s disease, atherosclerosis, inflammation, and coagulation. Interestingly, recent studies have linked LRP1 with endothelial function and angiogenesis, which has been underappreciated for a long time. During zebrafish embryonic development, LRP1 is required for the formation of vascular network, especially for the venous development. LRP1 depletion in the mouse embryo proper leads to angiogenic defects and disruption of endothelial integrity. Moreover, in a mouse oxygen-induced retinopathy model, specific depletion of LRP1 in endothelial cells results in abnormal development of neovessels. These loss-of-function studies suggest that LRP1 plays a pivotal role in angiogenesis. The review addresses the recent advances in the roles of LRP1-dependent signaling during angiogenesis.

Predictors and Modulators of Synthetic Lethality: An Update on PARP Inhibitors and Personalized Medicine

Poly(ADP-ribose) polymerase (PARP) inhibitors have proven to be successful agents in inducing synthetic lethality in several malignancies. Several PARP inhibitors have reached clinical trial testing for treatment in different cancers, and, recently, Olaparib (AZD2281) has gained both United States Food and Drug Administration (USFDA) and the European Commission (EC) approval for use in BRCA-mutated advanced ovarian cancer treatment. The need to identify biomarkers, their interactions in DNA damage repair pathways, and their potential utility in identifying patients who are candidates for PARP inhibitor treatment is well recognized. In this review, we detail many of the biomarkers that have been investigated for their ability to predict both PARP inhibitor sensitivity and resistance in preclinical studies as well as the results of several clinical trials that have tested the safety and efficacy of different PARP inhibitor agents in BRCA and non-BRCA-mutated cancers.

LRP1 Regulates Retinal Angiogenesis by Inhibiting PARP-1 Activity and Endothelial Cell Proliferation

OBJECTIVE

We recently demonstrated that low-density lipoprotein receptor-related protein 1 (LRP1) is required for cardiovascular development in zebrafish. However, what role LRP1 plays in angiogenesis remains to be determined. To better understand the role of LRP1 in endothelial cell function, we investigated how LRP1 regulates mouse retinal angiogenesis.

APPROACH AND RESULTS

Depletion of LRP1 in endothelial cells results in increased retinal neovascularization in a mouse model of oxygen-induced retinopathy. Specifically, retinas in mice lacking endothelial LRP1 have more branching points and angiogenic sprouts at the leading edge of the newly formed vasculature. Increased endothelial proliferation as detected by Ki67 staining was observed in LRP1-deleted retinal endothelium in response to hypoxia. Using an array of biochemical and cell biology approaches, we demonstrate that poly(ADP-ribose) polymerase-1 (PARP-1) directly interacts with LRP1 in human retinal microvascular endothelial cells. This interaction between LRP1 and PARP-1 decreases under hypoxic condition. Moreover, LRP1 knockdown results in increased PARP-1 activity and subsequent phosphorylation of both retinoblastoma protein and cyclin-dependent kinase 2, which function to promote cell cycle progression and angiogenesis.

CONCLUSIONS

Together, these data reveal a pivotal role for LRP1 in endothelial cell proliferation and retinal neovascularization induced by hypoxia. In addition, we demonstrate for the first time the interaction between LRP1 and PARP-1 and the LRP1-dependent regulation of PARP-1-signaling pathways. These data bring forth the possibility of novel therapeutic approaches for pathological angiogenesis.

Genomic instability in human cancer: Molecular insights and opportunities for therapeutic attack and prevention through diet and nutrition

Genomic instability can initiate cancer, augment progression, and influence the overall prognosis of the affected patient. Genomic instability arises from many different pathways, such as telomere damage, centrosome amplification, epigenetic modifications, and DNA damage from endogenous and exogenous sources, and can be perpetuating, or limiting, through the induction of mutations or aneuploidy, both enabling and catastrophic. Many cancer treatments induce DNA damage to impair cell division on a global scale but it is accepted that personalized treatments, those that are tailored to the particular patient and type of cancer, must also be developed. In this review, we detail the mechanisms from which genomic instability arises and can lead to cancer, as well as treatments and measures that prevent genomic instability or take advantage of the cellular defects caused by genomic instability. In particular, we identify and discuss five priority targets against genomic instability: (1) prevention of DNA damage; (2) enhancement of DNA repair; (3) targeting deficient DNA repair; (4) impairing centrosome clustering; and, (5) inhibition of telomerase activity. Moreover, we highlight vitamin D and B, selenium, carotenoids, PARP inhibitors, resveratrol, and isothiocyanates as priority approaches against genomic instability. The prioritized target sites and approaches were cross validated to identify potential synergistic effects on a number of important areas of cancer biology.

Enhancing tumor-targeting monoclonal antibodies therapy by PARP inhibitors

Monoclonal antibodies (mAbs) have become a successful therapeutic approach in cancer. However, some patients do not achieve long-term clinical benefit and most mAbs only exert modest effects as monotherapies. Therefore, combinations with chemotherapy are currently being investigated. Emerging studies have shown a synergistic therapeutic effect of PARP inhibitors and mAbs in cancer. PARP enzymes catalytically cleave β-NAD⁺ and transfer the ADP-ribose moiety to acceptor proteins, modifying their function. In here, we update recent data about the therapeutic effect of the combination of PARP inhibitors with mAbs in cancer treatment and discuss the molecular mechanisms involved in this synergy.

Genomic profiling in locally advanced and inflammatory breast cancer and its link to DCE-MRI and overall survival

PURPOSE

We have previously reported that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) perfusion patterns obtained from locally advanced breast cancer (LABC) patients prior to neoadjuvant therapy predicted pathologic clinical response. Genomic analyses were also independently conducted on the same patient population. This retrospective study was performed to test two hypotheses: (1) gene expression profiles are associated with DCE-MRI perfusion patterns, and (2) association between long-term overall survival data and gene expression profiles can lead to the identification of novel predictive biomarkers.

METHODS

We utilised RNA microarray and DCE-MRI data from 47 LABC patients, including 13 inflammatory breast cancer (IBC) patients. Association between gene expression profile and DCE-MRI perfusion patterns (centrifugal and centripetal) was determined by Wilcoxon rank sum test. Association between gene expression level and survival was assessed using a Cox rank score test. Additional genomic analysis of the IBC subset was conducted, with a period of follow-up of up to 11 years. Associations between gene expression and overall survival were further assessed in The Cancer Genome Atlas Data Portal.

RESULTS

Differences in gene expression profiles were seen between centrifugal and centripetal perfusion patterns in the sulphotransferase family, cytosolic, 1 A, phenol-preferring, members 1 and 2 (SULT1A1, SULT1A2), poly (ADP-ribose) polymerase, member 6 (PARP6), and metastasis tumour antigen1 (MTA1). In the IBC subset our analyses demonstrated that differential expression of 45 genes was associated with long-term survival.

CONCLUSIONS

Here we have demonstrated an association between DCE-MRI perfusion patterns and gene expression profiles. In addition we have reported on candidate prognostic biomarkers in IBC patients, with some of the genes being significantly associated with survival in IBC and LABC.

PJ-34 inhibits PARP-1 expression and ERK phosphorylation in glioma-conditioned brain microvascular endothelial cells

Inhibitors of PARP-1(Poly(ADP-ribose) polymerase-1) act by competing with NAD(+), the enzyme physiological substrate, which play a protective role in many pathological conditions characterized by PARP-1 overactivation. It has been shown that PARP-1 also promotes tumor growth and progression through its DNA repair activity. Since angiogenesis is an essential requirement for these activities, we sought to determine whether PARP inhibition might affect rat brain microvascular endothelial cells (GP8.3) migration, stimulated by C6-glioma conditioned medium (CM). Through wound-healing experiments and MTT analysis, we demonstrated that PARP-1 inhibitor PJ-34 [N-(6-Oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide] abolishes the migratory response of GP8.3 cells and reduces their viability. PARP-1 also acts in a DNA independent way within the Extracellular-Regulated-Kinase (ERK) signaling cascade, which regulates cell proliferation and differentiation. By western analysis and confocal laser scanning microscopy (LSM), we analyzed the effects of PJ-34 on PARP-1 expression, phospho-ERK and phospho-Elk-1 activation. The effect of MEK (mitogen-activated-protein-kinase-kinase) inhibitor PD98059 (2-(2-Amino-3-methoxyphenyl)-4 H-1-benzopyran-4-one) on PARP-1 expression in unstimulated and in CM-stimulated GP8.3 cells was analyzed by RT-PCR. PARP-1 expression and phospho-ERK activation were significantly reduced by treatment of GP8.3 cells with PJ-34 or PD98059. By LSM, we further demonstrated that PARP-1 and phospho-ERK are coexpressed and share the same subcellular localization in GP8.3 cells, in the cytoplasm as well as in nucleoplasm. Based on these data, we propose that PARP-1 and phospho-ERK interact in the cytosol and then translocate to the nucleus, where they trigger a proliferative response. We also propose that PARP-1 inhibition blocks CM-induced endothelial migration by interfering with ERK signal-transduction pathway.

Deciphering the insights of poly(ADP-ribosylation) in tumor progression

Poly (ADP-ribose) polymerase (PARP) inhibitors are particularly efficient against tumors with defects in the homologous recombination repair pathway. Nonetheless poly(ADP-ribosylation) (PARylation) modulates prometastasic activities and adaptation of tumor to a hostile microenvironment. Modulation of metastasis-promoting traits is possible through the alteration of key transcription factors involved in the regulation of the hypoxic response, the recruitment of new vessels (or angiogenesis), and the stimulation of epithelial to mesenchymal transition (EMT). In this review, we summarized some of the findings that focalize on PARP-1's action on tumor aggressiveness, suggesting new therapeutic opportunities against an assembly of tumors not necessarily bearing DNA repair defects. Metastasis accounts for the vast majority of mortality derived from solid cancer. PARP-1 is an active player in tumor adaptation to metastasis and PARP inhibitors, recognized as promising therapeutic agents against homologous recombination deficient tumors, has novel properties responsible for the antimetastatic actions in different tumor settings.

Activation of poly(ADP-ribose) polymerase-1 delays wound healing by regulating keratinocyte migration and production of inflammatory mediators

Poly(ADP-ribosyl)ation (PARylation) is a protein modification reaction regulating various diverse cellular functions ranging from metabolism, DNA repair and transcription to cell death. We set out to investigate the role of PARylation in wound healing, a highly complex process involving various cellular and humoral factors. We found that topically applied poly[ADP-ribose] polymerase (PARP) inhibitors 3-aminobenzamide and PJ-34 accelerated wound closure in a mouse model of excision wounding. Moreover, wounds also closed faster in PARP-1 knockout mice as compared with wild-type littermates. Immunofluorescent staining for poly(ADP-ribose) (PAR) indicated increased PAR synthesis in scattered cells of the wound bed. Expression of interleukin (IL)-6, tumor necrosis factor (TNF)-α, inducible nitric oxide synthase and matrix metalloproteinase-9 was lower in the wounds of PARP-1 knockout mice as compared with control, and expression of IL-1β, cyclooxygenase-2, TIMP-1 and -2 also were affected. The level of nitrotyrosine (a marker of nitrating stress) was lower in the wounds of PARP-1 knockout animals as compared with controls. In vitro scratch assays revealed significantly faster migration of keratinocytes treated with 3-aminobenzamide or PJ34 as compared with control cells. These data suggest that PARylation by PARP-1 slows down the wound healing process by increasing the production of inflammatory mediators and nitrating stress and by slowing the migration of keratinocytes.

Parp-1 genetic ablation in Ela-myc mice unveils novel roles for Parp-1 in pancreatic cancer

Pancreatic cancer has a dismal prognosis and is currently the fourth leading cause of cancer-related death in developed countries. The inhibition of poly(ADP-ribose) polymerase-1 (Parp-1), the major protein responsible for poly(ADP-ribosy)lation in response to DNA damage, has emerged as a promising treatment for several tumour types. Here we aimed to elucidate the involvement of Parp-1 in pancreatic tumour progression. We assessed Parp-1 protein expression in normal, preneoplastic and pancreatic tumour samples from humans and from K-Ras- and c-myc-driven mouse models of pancreatic cancer. Parp-1 was highly expressed in acinar cells in normal and cancer tissues. In contrast, ductal cells expressed very low or undetectable levels of this protein, both in a normal and in a tumour context. The Parp-1 expression pattern was similar in human and mouse samples, thereby validating the use of animal models for further studies. To determine the in vivo effects of Parp-1 depletion on pancreatic cancer progression, Ela-myc-driven pancreatic tumour development was analysed in a Parp-1 knock-out background. Loss of Parp-1 resulted in increased tumour necrosis and decreased proliferation, apoptosis and angiogenesis. Interestingly, Ela-myc:Parp-1(-/-) mice displayed fewer ductal tumours than their Ela-myc:Parp-1(+/+) counterparts, suggesting that Parp-1 participates in promoting acinar-to-ductal metaplasia, a key event in pancreatic cancer initiation. Moreover, impaired macrophage recruitment can be responsible for the ADM blockade found in the Ela-myc:Parp-1(-/-) mice. Finally, molecular analysis revealed that Parp-1 modulates ADM downstream of the Stat3-MMP7 axis and is also involved in transcriptional up-regulation of the MDM2, VEGFR1 and MMP28 cancer-related genes. In conclusion, the expression pattern of Parp-1 in normal and cancer tissue and the in vivo functional effects of Parp-1 depletion point to a novel role for this protein in pancreatic carcinogenesis and shed light into the clinical use of Parp-1 inhibitors.

PARP inhibitor olaparib increases the oncolytic activity of dl922-947 in in vitro and in vivo model of anaplastic thyroid carcinoma

PARP inhibitors are mostly effective as anticancer drugs in association with DNA damaging agents. We have previously shown that the oncolytic adenovirus dl922-947 induces extensive DNA damage, therefore we hypothesized a synergistic antitumoral effect of the PARP inhibitor olaparib in association with dl922-947. Anaplastic thyroid carcinoma was chosen as model since it is a particularly aggressive tumor and, because of its localized growth, it is suitable for intratumoral treatment with oncolytic viruses. Here, we show that dl922-947 infection induces PARP activation, and we confirm in vitro and in vivo that PARP inhibition increases dl922-947 replication and oncolytic activity. In vitro, the combination with olaparib exacerbates the appearance of cell death markers, such as Annexin V positivity, caspase 3 cleavage, cytochrome C release and propidium iodide permeability. In vivo, we also observed a better viral distribution upon PARP inhibition. Changes in CD31 levels suggest a direct effect of olaparib on tumor vascularization and on the viral distribution within the tumor mass. The observation that PARP inhibition enhances the effects of dl922-947 is highly promising not only for the treatment of anaplastic thyroid carcinoma but, in general, for the treatment of other tumors that could benefit from the use of oncolytic viruses.

Inhibition of poly(ADP-ribosyl)ation in cancer: old and new paradigms revisited

Inhibitors of poly(ADP-ribose) polymerases actualized the biological concept of synthetic lethality in the clinical practice, yielding a paradigmatic example of translational medicine. The profound sensitivity of tumors with germline BRCA mutations to PARP1/2 blockade owes to inherent defects of the BRCA-dependent homologous recombination machinery, which are unleashed by interruption of PARP DNA repair activity and lead to DNA damage overload and cell death. Conversely, aspirant BRCA-like tumors harboring somatic DNA repair dysfunctions (a vast entity of genetic and epigenetic defects known as "BRCAness") not always align with the familial counterpart and appear not to be equally sensitive to PARP inhibition. The acquisition of secondary resistance in initially responsive patients and the lack of standardized biomarkers to identify "BRCAness" pose serious threats to the clinical advance of PARP inhibitors; a feeling is also emerging that a BRCA-centered perspective might have missed the influence of additional, not negligible and DNA repair-independent PARP contributions onto therapy outcome. While regulatory approval for PARP1/2 inhibitors is still pending, novel therapeutic opportunities are sprouting from different branches of the PARP family, although they remain immature for clinical extrapolation. This review is an endeavor to provide a comprehensive appraisal of the multifaceted biology of PARPs and their evolving impact on cancer therapeutics.

Combination of AZD2281 (Olaparib) and GX15-070 (Obatoclax) results in synergistic antitumor activities in preclinical models of pancreatic cancer

In this study, we explored the antitumor activities of the PARP inhibitor AZD2281 (Olaparib) and the pan-Bcl-2 inhibitor GX15-070 (Obatoclax) in six pancreatic cancer cell lines. While both agents were able to cause growth arrest and limited apoptosis, the combination of the two was able to synergistically cause growth arrest and non-apoptotic cell death. Furthermore, in an in vivo xenograft model, the combination caused substantially increased tumor necrosis compared to either treatment alone. Our results support further investigation of the combination of Bcl-2 and PARP inhibitors for the treatment of pancreatic cancer.

Inhibition of proliferation and invasiveness of ovarian cancer C13* cells by a poly(ADP-ribose) polymerase inhibitor and the role of nuclear factor-κB

Objective

To investigate the effect of the poly(ADP-ribose) polymerase-1 (PARP-1) inhibitor PJ34 on the proliferation and invasiveness of ovarian cancer C13* cells and the role of nuclear factor-κB (NF-κB).

Methods

Proliferation of C13* cells was measured using a 3 -(4,5-dimethylthazol-2-yl)-2,5-diphenyl tetrazolium bromide assay after incubation with PJ34 at different concentrations and for different treatment durations. In addition, expression of PARP-1 and the NF-κB p65 subunit after treatment with PJ34 was measured using Western blot and immunocytochemistry. The effect of PJ34 on cell invasiveness was examined using a transwell invasion assay.

Results

PJ34 inhibited proliferation of C13* cells in a time- and dose-dependent manner. PJ34 treatment was also associated with a dose-dependent decrease in PARP-1 and NF-κB p65 expression and attenuated invasiveness of C13* cells. PARP-1 expression was positively correlated with NF-κB p65 expression.

Conclusion

The PARP-1 inhibitor PJ34 can markedly inhibit the proliferation and invasiveness of C13* cells, possibly due to PARP-1-mediated attenuation of NF-κB activity.

The Role of PARP Inhibitors in the Treatment of Gynecologic Malignancies

Gynecologic malignancies annually account for over 91,000 new cancer cases and approximately 28,000 deaths in the United States. Although there have been advancements in cytotoxic chemotherapies, there has not been significant improvement in overall survival in these patients. While targeted therapies have shown some benefit in many solid tumors, further development of these agents is needed for the treatment of gynecologic malignancies. Poly(ADP-ribose) polymerase (PARP) catalyzes the polyADP-ribosylation of proteins involved in DNA repair. Inhibitors of PARP were originally developed for cancers with homologous recombination deficiencies, such as those harboring mutations in BRCA1 or BRCA2 genes. However, pre-clinical research and clinical trials have suggested that the activity of PARP inhibitors is not limited to those with BRCA mutations. PARP inhibitors may have activity in cancers deficient in other DNA repair genes, signaling pathways that mitigate DNA repair, or in combination with DNA-damaging agents independent of DNA repair dysfunction. Currently there are seven different PARP inhibitors in clinical development for cancer. While there has been promising clinical activity for some of these agents, there are still significant unanswered questions regarding their use. Going forward, specific questions that must be answered include timing of therapy, use in combination with cytotoxic agents or as single-agent maintenance therapy, and whether there is a predictive biomarker that can be used with PARP inhibition. Even with large strides in the treatment of many gynecologic malignancies in recent years, it is imperative that we develop newer agents and methods to identify patients that may benefit from these compounds. The focus of this review will be on pre-clinical data, current clinical trials, and the future of PARP inhibitors in the treatment of ovarian, endometrial, and cervical cancer.

Molecular pathways: targeting PARP in cancer treatment

Poly (ADP-ribose) polymerases (PARP) are a family of nuclear protein enzymes involved in the DNA damage response. The role of PARP-1 in base excisional repair has been extensively characterized. More recent in vitro studies additionally implicate a role for PARP-1 in facilitating homologous recombination and nonhomologous end-joining. The more faithful process of homologous recombination repair of double-stranded DNA breaks involves localization of BRCA-1 and BRCA-2 to sites of DNA damage, resection of the double-stranded break, and gap-filling DNA synthesis using the homologous sister chromatid as a template. Simultaneous dysfunction of both DNA repair pathways decreases the ability of cells to compensate, and forms the basis for the concept of synthetic lethality. Treatment strategies, thus far, have focused on two main principles: (i) exploitation of the concept of synthetic lethality in homologous recombination-deficient tumors, primarily in breast and ovarian cancer patients with BRCA mutation, and (ii) as radiosensitizers and chemosensitizers. BRCA deficiency accounts for only a fraction of dysfunction in homologous recombination repair. Epigenetic alterations of BRCA function and defects within the Fanconi anemia pathway also result in defective DNA repair. Rational therapeutic combinations exploiting alternate mechanisms of defective DNA repair, abrogation of cell-cycle checkpoints, and additional functions of PARP-1 present novel opportunities for further clinical development of PARP inhibitors. On the basis of the results of clinical studies of PARP inhibitors thus far, it is imperative that future development of PARP inhibitors take a more refined approach, identifying the unique subset of patients that would most benefit from these agents, determining the optimal time for use, and identifying the optimal combination partner in any particular setting.

Erythropoietin-driven signalling and cell migration mediated by polyADP-ribosylation

Background:

Recombinant human erythropoietin (EPO) is the leading biotechnology engineered hormone for treatment of anaemia associated with chronic conditions including kidney failure and cancer. The finding of EPO receptors on cancer cells has raised the concern that in addition to its action in erythropoiesis, EPO may promote tumour cell growth. We questioned whether EPO-induced signalling and consequent malignant cell manifestation is mediated by polyADP-ribosylation.

Methods:

Erythropoietin-mediated PARP (polyADP-ribose polymerase-1) activation, gene expression and core histone H4 acetylation were examined in UT7 cells, using western blot analysis, RT–PCR and immunofluorescence. Erythropoietin-driven migration of the human breast epithelial cell line MDA-MB-435 was determined by the scratch assay and in migration chambers.

Results:

We have found that EPO treatment induced PARP activation. Moreover, EPO-driven c-fos and Egr-1 gene expression as well as histone H4 acetylation were mediated via polyADP-ribosylation. Erythropoietin-induced cell migration was blocked by the PARP inhibitor, ABT-888, indicating an essential role for polyADP-ribosylation in this process.

Conclusions:

We have identified a novel pathway by which EPO-induced gene expression and breast cancer cell migration are regulated by polyADP-ribosylation. This study introduces new possibilities regarding EPO treatment for cancer-associated anaemia where combining systemic EPO treatment with targeted administration of PARP inhibitors to the tumour may allow safe treatment with EPO, minimising its possible undesirable proliferative effects on the tumour.

Nuclear PARP-1 protein overexpression is associated with poor overall survival in early breast cancer

BACKGROUND

Poly(ADP-ribose)polymerase-1 (PARP-1) is a highly promising novel target in breast cancer. However, the expression of PARP-1 protein in breast cancer and its associations with outcome are yet poorly characterized.

PATIENTS AND METHODS

Quantitative expression of PARP-1 protein was assayed by a specific immunohistochemical signal intensity scanning assay in a range of normal to malignant breast lesions, including a series of patients (N = 330) with operable breast cancer to correlate with clinicopathological factors and long-term outcome.

RESULTS

PARP-1 was overexpressed in about a third of ductal carcinoma in situ and infiltrating breast carcinomas. PARP-1 protein overexpression was associated to higher tumor grade (P = 0.01), estrogen-negative tumors (P < 0.001) and triple-negative phenotype (P < 0.001). The hazard ratio (HR) for death in patients with PARP-1 overexpressing tumors was 7.24 (95% CI; 3.56-14.75). In a multivariate analysis, PARP-1 overexpression was an independent prognostic factor for both disease-free (HR 10.05; 95% CI 5.42-10.66) and overall survival (HR 1.82; 95% CI 1.32-2.52).

CONCLUSIONS

Nuclear PARP-1 is overexpressed during the malignant transformation of the breast, particularly in triple-negative tumors, and independently predicts poor prognosis in operable invasive breast cancer.

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).

Vascular endothelial growth factor confers endothelial resistance to apoptosis through poly(ADP-ribose) polymerase

BACKGROUND

Vascular endothelial growth factor (VEGF) inhibits the endothelial apoptosis that is induced by caspases during vascular remodeling; however, the underlying mechanisms have not been completely elucidated.

OBJECTIVES

We hypothesized that VEGF upregulates poly(ADP-ribose) polymerase-1 (PARP) as a caspase mediator, and sought to investigate the link between apoptosis inhibition by VEGF and PARP regulation in the human vasculature.

METHODS

Human endothelial cells (primary cells, macrovascular/microvascular lines) were incubated with 100 pg mL(-1) to 1 μg mL(-1) VEGF-A(165) in the absence or presence of PARP small interfering RNA (siRNA). Apoptosis induced by integrin inhibition was measured by flow cytometry, trypan blue exclusion, and nuclear morphology. PARP expression and activity were determined by real-time RT-PCR, Western blot, and ribosylation assay. VEGF receptors and signal transduction were analyzed by inhibitor experiments, enzyme assays, western blot, and immunofluorescence microscopy. Immunohistochemistry was applied to a vascular culture model and to 24 atherosclerotic and 10 normal human arteries.

RESULTS

VEGF-A(165) induced resistance to apoptosis caused by caspase activation in endothelial cells in a time-dependent manner. VEGF, but not fibroblast growth factor-2 or transforming growth factor-β, time-dependently and dose-dependently induced PARP expression and activity, involving VEGF receptor-2 colocalized with neuropilin-1 as well as the signal transduction molecules c-Jun N-terminal kinase and Akt. The antiapoptotic effect of VEGF was abrogated by PARP siRNA. The relationship between local VEGF influence and endothelial PARP expression was confirmed in human arteries and the vascular culture model.

CONCLUSIONS

 VEGF exerts its antiapoptotic effect on the endothelium through the regulation of PARP expression. PARP has been attributed an ambiguous role in apoptosis; here, we show that PARP promotes vascular endothelial integrity in VEGF-associated processes.

Low doses of 3-aminobenzamide, a poly(ADP-ribose) polymerase inhibitor, stimulate angiogenesis by regulating expression of urokinase type plasminogen activator and matrix metalloprotease 2

Background

Poly(ADP-Ribose) polymerase (PARP) activity has been demonstrated fundamental in many cellular processes, including DNA repair, cell proliferation and differentiation. In particular, PARP activity has been recently found to affect proliferation, migration, and tube formation of human umbilical vein endothelial cells. In recent times, PARP inhibitors have entered in clinical trials to potentiate cancer treatments by preventing DNA repair, but little is known about the effects performed by different drug concentrations on neoangiogenesis, an essential step in tumor growth.

Methods

Human umbilical vein endothelial cells were treated with 3 aminobenzamide (3ABA), a PARP inhibitor, and tested for several different cellular parameters.

Results

Here we present in vitro evidence that a low concentration of 3ABA (50 μM), stimulates angiogenesis by decreasing fibrinolytic activity, carried out by urokinase-type plasminogen activator (uPA), and by enhancing matrix metalloprotease-2 (MMP-2) gelatinolytic activity, in fibroblast growth factor-2-stimulated endothelial cells. These unbalanced pathways modify in vitro angiogenic steps, inhibiting chemoinvasion and stimulating tubulogenic activity.

Conclusions

Our results suggest that the proangiogenic effect of low concentrations of 3ABA alerts on the efficacy of PARP inhibitors to potentiate anticancer therapy. Moreover, they indicate that endothelial chemoinvasion and tubulogenesis depend on distinct proteolytic pathways.

PARP-1 cleavage fragments: signatures of cell-death proteases in neurodegeneration

The normal function of poly (ADP-ribose) polymerase-1 (PARP-1) is the routine repair of DNA damage by adding poly (ADP ribose) polymers in response to a variety of cellular stresses. Recently, it has become widely appreciated that PARP-1 also participates in diverse physiological and pathological functions from cell survival to several forms of cell death and has been implicated in gene transcription, immune responses, inflammation, learning, memory, synaptic functions, angiogenesis and aging. In the CNS, PARP inhibition attenuates injury in pathologies like cerebral ischemia, trauma and excitotoxicity demonstrating a central role of PARP-1 in these pathologies. PARP-1 is also a preferred substrate for several 'suicidal' proteases and the proteolytic action of suicidal proteases (caspases, calpains, cathepsins, granzymes and matrix metalloproteinases (MMPs)) on PARP-1 produces several specific proteolytic cleavage fragments with different molecular weights. These PARP-1 signature fragments are recognized biomarkers for specific patterns of protease activity in unique cell death programs. This review focuses on specific suicidal proteases active towards PARP-1 to generate signature PARP-1 fragments that can identify key proteases and particular forms of cell death involved in pathophysiology. The roles played by some of the PARP-1 fragments and their associated binding partners in the control of different forms of cell death are also discussed.

Making the best of PARP inhibitors in ovarian cancer

Drugs that inhibit the enzyme poly(ADP-ribose)polymerase (PARP) are showing considerable promise for the treatment of cancers that have mutations in the BRCA1 or BRCA2 tumor suppressors. This therapeutic approach exploits a synthetic lethal strategy to target the specific DNA repair pathway in these tumors. High-grade ovarian cancers have a generally poor prognosis, and accumulating evidence suggests that mutations in BRCA1 or BRCA2, or silencing of BRCA1 by promoter methylation, may be common in this disease. Here, we consider how the potential benefit of PARP inhibitors might be maximized in ovarian cancer. We suggest that it will be crucial to explore novel therapeutic trial strategies and drug combinations, and incorporate robust biomarkers predictive of response if these drugs are to reach their full potential.

Albendazole inhibits endothelial cell migration, tube formation, vasopermeability, VEGF receptor-2 expression and suppresses retinal neovascularization in ROP model of angiogenesis

The angiogenic process begins with the cell proliferation and migration into the primary vascular network, and leads to vascularization of previously avascular tissues and organs as well to growth and remodeling of the initially homogeneous capillary plexus to form a new microcirculation. Additionally, an increase in microvascular permeability is a crucial step in angiogenesis. Vascular endothelial growth factor (VEGF) plays a central role in angiogenesis. We have previously reported that albendazole suppresses VEGF levels and inhibits malignant ascites formation, suggesting a possible effect on angiogenesis. This study was therefore designed to investigate the antiangiogenic effect of albendazole in non-cancerous models of angiogenesis. In vitro, treatment of human umbilical vein endothelial cells (HUVECs) with albendazole led to inhibition of tube formation, migration, permeability and down-regulation of the VEGF type 2 receptor (VEGFR-2). In vivo albendazole profoundly inhibited hyperoxia-induced retinal angiogenesis in mice. These results provide new insights into the antiangiogenic effects of albendazole.

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.

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

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, which currently comprises 18 members, is an abundant nuclear enzyme implicated in cellular responses to DNA injury provoked by genotoxic stress. PARP is involved in DNA repair and transcriptional regulation and is now recognized as a key regulator of cell survival and cell death as well as a master component of a number of transcription factors involved in tumor development and inflammation. PARP-1 is essential to the repair of DNA single-strand breaks via the base excision repair pathway. Inhibitors of PARP-1 have been shown to enhance the cytotoxic effects of ionizing radiation and DNA-damaging chemotherapy agents, such as the methylating agents and topoisomerase I inhibitors. There are currently at least five PARP inhibitors in clinical trial development. Recent in vitro and in vivo evidence suggests that PARP inhibitors could be used not only as chemo/radiotherapy sensitizers, but also as single agents to selectively kill cancers defective in DNA repair, specifically cancers with mutations in the breast cancer-associated genes (BRCA1 and BRCA2). PARP becomes activated in response to oxidative DNA damage and depletes cellular energy pools, thus leading to cellular dysfunction in various tissues. The activation of PARP may also induce various cell death processes and promotes an inflammatory response associated with multiple organ failure. Inhibition of PARP activity is protective in a wide range of inflammatory and ischemia-reperfusion-associated diseases, including cardiovascular diseases, diabetes, rheumatoid arthritis, endotoxic shock, and stroke. The aim of this review is to overview the emerging data in the literature showing the role of PARP in the pathogenesis of cancer and inflammatory diseases and unravel the solid body of literature that supports the view that PARP is an important target for therapeutic intervention in critical illness.

Cannabinoid CB1 receptor inhibition decreases vascular smooth muscle migration and proliferation

Vascular smooth muscle proliferation and migration triggered by inflammatory stimuli and chemoattractants such as platelet-derived growth factor (PDGF) are key events in the development and progression of atherosclerosis and restenosis. Cannabinoids may modulate cell proliferation and migration in various cell types through cannabinoid receptors. Here we investigated the effects of CB(1) receptor antagonist rimonabant (SR141716A), which has recently been shown to have anti-atherosclerotic effects both in mice and humans, on PDGF-induced proliferation, migration, and signal transduction of human coronary artery smooth muscle cells (HCASMCs). PDGF induced Ras and ERK 1/2 activation, while increasing proliferation and migration of HCASMCs, which were dose dependently attenuated by CB(1) antagonist, rimonabant. These findings suggest that in addition to improving plasma lipid alterations and decreasing inflammatory cell migration and inflammatory response, CB(1) antagonists may exert beneficial effects in atherosclerosis and restenosis by decreasing vascular smooth muscle proliferation and migration.

An enzyme-linked immunosorbent poly(ADP-ribose) polymerase biomarker assay for clinical trials of PARP inhibitors

Many established cancer therapies involve DNA-damaging chemotherapy or radiotherapy. The DNA repair capacity of the tumor represents a common mechanism used by cancer cells to survive DNA-damaging therapy. Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme that is activated by DNA damage and has critical roles in DNA repair. Inhibition of PARP potentiates the activity of DNA-damaging agents such as temozolomide, topoisomerase inhibitors and radiation in both in vitro and in vivo preclinical models. Recently, several PARP inhibitors have entered clinical trials either as single agents or in combination with DNA-damaging chemotherapy. Because PARP inhibitors are not cytotoxic, a biomarker assay is useful to guide the selection of an optimal biological dose. We set out to develop an assay that enables us to detect 50% PAR reduction in human tumors with 80% power in a single-plate assay while assuring no more than a 10% false-positive rate. We have developed and optimized an enzyme-linked immunosorbent assay (ELISA) to measure PARP activity that meets the above-mentioned criterion. This robust assay is able to detect PAR levels of 30-2000 pg/ml in both tumor and peripheral blood monocyte samples. In a B16F10 mouse syngeneic tumor model, PARP inhibitor ABT-888 potentiates the effect of temozolomide in suppressing tumor growth, and PARP activity is greatly reduced by ABT-888 at efficacious doses. In summary, the ELISA assay described here is suitable for biomarker studies in clinical trials of PARP inhibitors.

Role of the peroxynitrite-poly(ADP-ribose) polymerase pathway in human disease

Throughout the last 2 decades, experimental evidence from in vitro studies and preclinical models of disease has demonstrated that reactive oxygen and nitrogen species, including the reactive oxidant peroxynitrite, are generated in parenchymal, endothelial, and infiltrating inflammatory cells during stroke, myocardial and other forms of reperfusion injury, myocardial hypertrophy and heart failure, cardiomyopathies, circulatory shock, cardiovascular aging, atherosclerosis and vascular remodeling after injury, diabetic complications, and neurodegenerative disorders. Peroxynitrite and other 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 depletes its substrate NAD(+), slowing the rate of glycolysis, electron transport, and ATP formation, eventually leading to functional impairment or death of cells, as well as up-regulation of various proinflammatory pathways. In related animal models of disease, peroxynitrite neutralization or pharmacological inhibition of PARP provides significant therapeutic benefits. Therefore, novel antioxidants and PARP inhibitors have entered clinical development for the experimental therapy of various cardiovascular and other diseases. This review focuses on the human data available on the pathophysiological relevance of the peroxynitrite-PARP pathway in a wide range of disparate diseases, ranging from myocardial ischemia/reperfusion injury, myocarditis, heart failure, circulatory shock, and diabetic complications to atherosclerosis, arthritis, colitis, and neurodegenerative disorders.

Stable depletion of poly (ADP-ribose) polymerase-1 reduces in vivo melanoma growth and increases chemosensitivity

Poly(ADP-ribose) polymerase (PARP)-1, which plays a key role in DNA repair, inflammation and transcription, has recently been shown to be involved in angiogenesis. The aim of this study was to investigate PARP-1 role in melanoma aggressiveness and chemoresistance in vivo using clones stably silenced for PARP-1 expression. Whilst the growth characteristics of PARP-1-deficient melanoma cells were comparable to those of PARP-1-proficient cells in vitro, their tumourigenic potential in vivo was significantly compromised. In fact, mice challenged intra-muscle with PARP-1-deficient cells showed a delayed development of measurable tumour nodules, which were also significantly reduced in size with respect to those of mice inoculated with PARP-1-proficient cells. Moreover, animals challenged intra-cranially with PARP-1-deficient cells, a model that mimics CNS localisation of melanoma, showed an increased survival. Immunohistochemical analyses of PARP-1-depleted melanoma grafts indicated a reduced expression of the angiogenesis marker PECAM-1/CD31 and of the pro-inflammatory mediators TNF-alpha and GITR. Notably, PARP-1-silenced melanoma was extremely sensitive to temozolomide, an anticancer agent used for the treatment of metastatic melanoma. These results provide novel evidence for a direct role of PARP-1 in tumour aggressiveness and chemoresistance.

PARP inhibition or gene deficiency counteracts intraepidermal nerve fiber loss and neuropathic pain in advanced diabetic neuropathy

Evidence that poly(ADP-ribose) polymerase (PARP) activation plays an important role in diabetic complications is emerging. This study evaluated the role of PARP in rat and mouse models of advanced diabetic neuropathy. The orally active PARP inhibitor 10-(4-methylpiperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-one (GPI-15427; formulated as a mesilate salt, 30 mg kg(-1) day(-1) in the drinking water for 10 weeks after the first 2 weeks without treatment) at least partially prevented PARP activation in peripheral nerve and DRG neurons, as well as thermal hypoalgesia, mechanical hyperalgesia, tactile allodynia, exaggerated response to formalin, and, most importantly, intraepidermal nerve fiber degeneration in streptozotocin-diabetic rats. These findings are consistent with the lack of small sensory nerve fiber dysfunction in diabetic PARP -/- mice. Furthermore, whereas diabetic PARP +/+ mice displayed approximately 46% intraepidermal nerve fiber loss, diabetic PARP -/- mice retained completely normal intraepidermal nerve fiber density. In conclusion, PARP activation is an important contributor to intraepidermal nerve fiber degeneration and functional changes associated with advanced Type 1 diabetic neuropathy. The results support a rationale for the development of potent and low-toxicity PARP inhibitors and PARP inhibitor-containing combination therapies.

CB2 cannabinoid receptor agonists attenuate TNF-alpha-induced human vascular smooth muscle cell proliferation and migration

BACKGROUND AND PURPOSE

Vascular smooth muscle proliferation and migration triggered by inflammatory stimuli are involved in the development and progression of atherosclerosis and restenosis. Cannabinoids may modulate cell proliferation in various cell types through cannabinoid 2 (CB2) receptors. Here, we investigated the effects of CB2 receptor agonists on TNF-alpha-induced proliferation, migration and signal transduction in human coronary artery smooth muscle cells (HCASMCs).

EXPERIMENTAL APPROACH

HCASMCs were stimulated with TNF-alpha. Smooth muscle proliferation was determined by the extent of BrdU incorporation and the migration was assayed by modified Boyden chamber. CB2 and/or CB1 receptor expressions were determined by immunofluorescence staining, western blotting, RT-PCR, real-time PCR and flow cytometry.

KEY RESULTS

Low levels of CB2 and CB1 receptors were detectable in HCASMCs compared to the high levels of CB2 receptors expressed in THP-1 monocytes. TNF-alpha triggered up to approximately 80% increase (depending on the method used) in CB2 receptor mRNA and/or protein expression in HCASMCs, and induced Ras, p38 MAPK, ERK 1/2, SAPK/JNK and Akt activation, while increasing proliferation and migration. The CB2 agonists, JWH-133 and HU-308, dose-dependently attenuated these effects of TNF-alpha.

CONCLUSIONS AND IMPLICATIONS

Since the above-mentioned TNF-alpha-induced phenotypic changes are critical in the initiation and progression of atherosclerosis and restenosis, our findings suggest that CB2 agonists may offer a novel approach in the treatment of these pathologies by decreasing vascular smooth muscle proliferation and migration.

Poly(ADP-ribose) polymerase (PARP) inhibition or PARP-1 gene deletion reduces angiogenesis

Poly(ADP-ribose) polymerase (PARP)-1 has recently been shown to promote tumour progression. Since angiogenesis is an essential requirement for tumour growth, we examined whether PARP inhibition/deletion might affect endothelial cell functions. To this end, the influence of PARP inhibitors on endothelial cell proliferation, migration, tube formation and angiogenesis in PARP-1 knock-out mice, using an in vivo matrigel plug assay, was investigated. The results indicated that the PARP inhibitor GPI 15427 (IC50 on endothelial PARP: 237 +/- 27 nM), at concentrations devoid of cytotoxic effects (0.5-1 microM), abrogated migration in response to vascular endothelial growth factor or placenta growth factor, hampered formation of tubule-like networks and impaired angiogenesis in vivo. The anti-angiogenic effect of the PARP inhibitor was confirmed in PARP-1 knock-out mice that displayed a defect of angiogenesis induced by growth factors. These results provide evidence for targeting PARP for anti-angiogenesis, adding novel therapeutic implications to the use of PARP inhibitors in cancer treatment.

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.