PARP-1: Friend or Foe of DNA Damage and Repair in Tumorigenesis?

PARP-1 selectively impairs KRAS-driven phenotypic and molecular features in intrahepatic cholangiocarcinoma

OBJECTIVE

Intrahepatic cholangiocarcinoma (iCCA) is the second most common primary liver cancer with limited therapeutic options. KRAS mutations are among the most abundant genetic alterations in iCCA associated with poor clinical outcome and treatment response. Recent findings indicate that Poly(ADP-ribose)polymerase1 (PARP-1) is implicated in KRAS-driven cancers, but its exact role in cholangiocarcinogenesis remains undefined.

DESIGN

PARP-1 inhibition was performed in patient-derived and established iCCA cells using RNAi, CRISPR/Cas9 and pharmacological inhibition in KRAS-mutant, non-mutant cells. In addition, Parp-1 knockout mice were combined with iCCA induction by hydrodynamic tail vein injection to evaluate an impact on phenotypic and molecular features of Kras-driven and Kras-wildtype iCCA. Clinical implications were confirmed in authentic human iCCA.

RESULTS

PARP-1 was significantly enhanced in KRAS-mutant human iCCA. PARP-1-based interventions preferentially impaired cell viability and tumourigenicity in human KRAS-mutant cell lines. Consistently, loss of Parp-1 provoked distinct phenotype in Kras/Tp53-induced versus Akt/Nicd-induced iCCA and abolished Kras-dependent cholangiocarcinogenesis. Transcriptome analyses confirmed preferential impairment of DNA damage response pathways and replicative stress response mediated by CHK1. Consistently, inhibition of CHK1 effectively reversed PARP-1 mediated effects. Finally, Parp-1 depletion induced molecular switch of KRAS-mutant iCCA recapitulating good prognostic human iCCA patients.

CONCLUSION

Our findings identify the novel prognostic and therapeutic role of PARP-1 in iCCA patients with activation of oncogenic KRAS signalling.

Chronic NOD2 stimulation by MDP confers protection against parthanatos through M2b macrophage polarization in RAW264.7 cells

Innate immune cells show enhanced responsiveness to secondary challenges after an initial non-related stimulation (Trained Innate Immunity, TII). Acute NOD2 activation by Muramyl-Dipeptide (MDP) promotes TII inducing the secretion of pro-inflammatory mediators, while a sustained MDP-stimulation down-regulates the inflammatory response, restoring tolerance. Here we characterized in-vitro the response of murine macrophages to lipopolysaccharide (LPS) challenge under NOD2-chronic stimulation. RAW264.7 cells were trained with MDP (1 μg/ml, 48 h) and challenged with LPS (5 μg/ml, 24 h). Trained cells formed multinucleated giant cells with increased phagocytosis rates compared to untrained/challenged cells. They showed a reduced mitochondrial activity and a switch to aerobic glycolysis. TNF-α, ROS and NO were upregulated in both trained and untrained cultures (MDP+, MDP- cells, p > 0.05); while IL-10, IL-6 IL-12 and MHCII were upregulated only in trained cells after LPS challenge (MDP + LPS+, p < 0.05). A slight upregulation in the expression of B7.2 was also observed in this group, although differences were not statistically significant. MDP-training induced resistance to LPS challenge (p < 0.01). The relative expression of PARP-1 was downregulated after the LPS challenge, which may contribute to the regulatory milieu and to the innate memory mechanisms exhibited by MDP-trained cells. Our results demonstrate that a sustained MDP-training polarizes murine macrophages towards a M2b profile, inhibiting parthanatos. These results may impact on the development of strategies to immunomodulate processes in which inflammation should be controlled.

Globospiramine from Voacanga globosa Exerts Robust Cytotoxic and Antiproliferative Activities on Cancer Cells by Inducing Caspase-Dependent Apoptosis in A549 Cells and Inhibiting MAPK14 (p38α): In Vitro and Computational Investigations

Bisindole alkaloids are a source of inspiration for the design and discovery of new-generation anticancer agents. In this study, we investigated the cytotoxic and antiproliferative activities of three spirobisindole alkaloids from the traditional anticancer Philippine medicinal plant Voacanga globosa, along with their mechanisms of action. Thus, the alkaloids globospiramine (1), deoxyvobtusine (2), and vobtusine lactone (3) showed in vitro cytotoxicity and antiproliferative activities against the tested cell lines (L929, KB3.1, A431, MCF-7, A549, PC-3, and SKOV-3) using MTT and CellTiter-Blue assays. Globospiramine (1) was also screened against a panel of breast cancer cell lines using the sulforhodamine B (SRB) assay and showed moderate cytotoxicity. It also promoted the activation of apoptotic effector caspases 3 and 7 using Caspase-Glo 3/7 and CellEvent-3/7 apoptosis assays. Increased expressions of cleaved caspase 3 and PARP in A549 cells treated with 1 were also observed. Apoptotic activity was also confirmed when globospiramine (1) failed to promote the rapid loss of membrane integrity according to the HeLa cell membrane permeability assay. Network pharmacology analysis, molecular docking, and molecular dynamics simulations identified MAPK14 (p38α), a pharmacological target leading to cancer cell apoptosis, as a putative target. Low toxicity risks and favorable drug-likeness were also predicted for 1. Overall, our study demonstrated the anticancer potentials and apoptotic mechanisms of globospiramine (1), validating the traditional medicinal use of Voacanga globosa.

Investigating the Effects of HMGB1 Overexpression on Colorectal Cancer Cell Migration via Oncolytic Herpes simplex Virus Type 1 (oHSV-1)

Background

Colorectal Cancer (CRC) represents a significant global health challenge, and its progression, resistance to therapy, and metastasis are strongly influenced by the tumor microenvironment, including factors like hypoxia. This study explores the impact of High Mobility Group Box 1 (HMGB1) overexpression on CRC cell migration, while identifying potential genes associated with this process.

Methods

To explore this, we developed oncolytic virotherapy, resulting in HSVHMGB1, an oncolytic Herpes simplex virus that expresses HMGB1. HMGB1 is known its role in cancer progression, particularly in the context of cancer cell migration.

Results

Contrary to expectations, our scratch assays indicated that HSV-HMGB1 did not significantly induce migration in CRC cells, suggesting that HMGB1 might not directly contribute to this process. Employing microarray analysis, we investigated gene expression changes linked to CRC cell migration, leading to construction of a Protein-Protein Interaction (PPI) network. This network revealed the presence of hub proteins, including as NDRG1, LGALS1, and ANGPTL4, which are recognized for their roles in cancer cell migration. The differential expression of these genes under hypoxic conditions was further validated using quantitative RT-PCR, aligning with the findings from our microarray data.

Conclusion

Our findings emphasize the complex regulation of CRC cell migration, and provides valuable insights into potential molecular mechanisms and pathways. These findings have implications for further research into cancer progression and the development of therapeutic strategies.

Frontier knowledge and future directions of programmed cell death in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is one of the most common renal malignancies of the urinary system. Patient outcomes are relatively poor due to the lack of early diagnostic markers and resistance to existing treatment options. Programmed cell death, also known as apoptosis, is a highly regulated and orchestrated form of cell death that occurs ubiquitously throughout various physiological processes. It plays a crucial role in maintaining homeostasis and the balance of cellular activities. The combination of immune checkpoint inhibitors plus targeted therapies is the first-line therapy to advanced RCC. Immune checkpoint inhibitors(ICIs) targeted CTLA-4 and PD-1 have been demonstrated to prompt tumor cell death by immunogenic cell death. Literatures on the rationale of VEGFR inhibitors and mTOR inhibitors to suppress RCC also implicate autophagic, apoptosis and ferroptosis. Accordingly, investigations of cell death modes have important implications for the improvement of existing treatment modalities and the proposal of new therapies for RCC. At present, the novel modes of cell death in renal cancer include ferroptosis, immunogenic cell death, apoptosis, pyroptosis, necroptosis, parthanatos, netotic cell death, cuproptosis, lysosomal-dependent cell death, autophagy-dependent cell death and mpt-driven necrosis, all of which belong to programmed cell death. In this review, we briefly describe the classification of cell death, and discuss the interactions and development between ccRCC and these novel forms of cell death, with a focus on ferroptosis, immunogenic cell death, and apoptosis, in an effort to present the theoretical underpinnings and research possibilities for the diagnosis and targeted treatment of ccRCC.

Inhibition of host PARP1 contributes to the anti-inflammatory and antitubercular activity of pyrazinamide

The antibiotic pyrazinamide (PZA) is a cornerstone of tuberculosis (TB) therapy that shortens treatment durations by several months despite being only weakly bactericidal. Intriguingly, PZA is also an anti-inflammatory molecule shown to specifically reduce inflammatory cytokine signaling and lesion activity in TB patients. However, the target and clinical importance of PZA's host-directed activity during TB therapy remain unclear. Here, we identify the host enzyme Poly(ADP-ribose) Polymerase 1 (PARP1), a pro-inflammatory master regulator strongly activated in TB, as a functionally relevant host target of PZA. We show that PZA inhibits PARP1 enzymatic activity in macrophages and in mice where it reverses TB-induced PARP1 activity in lungs to uninfected levels. Utilizing a PZA-resistant mutant, we demonstrate that PZA's immune-modulatory effects are PARP1-dependent but independent of its bactericidal activity. Importantly, PZA's bactericidal efficacy is impaired in PARP1-deficient mice, suggesting that immune modulation may be an integral component of PZA's antitubercular activity. In addition, adjunctive PARP1 inhibition dramatically reduces inflammation and lesion size in mice and may be a means to reduce lung damage and shorten TB treatment duration. Together, these findings provide insight into PZA's mechanism of action and the therapeutic potential of PARP1 inhibition in the treatment of TB.

Elucidating the Therapeutic Utility of Olaparib in Sulfatide-Induced Human Astrocyte Toxicity and Neuroinflammation

Metachromatic leukodystrophy (MLD) is a severe demyelinating, autosomal recessive genetic leukodystrophy, with no curative treatment. The disease is underpinned by mutations in the arylsulfatase A gene (ARSA), resulting in deficient activity of this lysosomal enzyme, and consequential accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the brain. Most of the effects in the brain have been attributed to the accumulation of sulfatides in oligodendrocytes and their cell damage. In contrast, less is known regarding sulfatide toxicity in astrocytes. Poly (ADP-ribose) polymerase (PARP) inhibitors are anti-cancer therapeutics that have proven efficacy in preclinical models of many neurodegenerative and inflammatory diseases, but have never been tested for MLD. Here, we examined the toxic effect of sulfatides on human astrocytes and restoration of this cell damage by the marketed PARP-1 inhibitor, Olaparib. Cultured human astrocytes were treated with increasing concentrations of sulfatides (5-100 μM) with or without Olaparib (100 nM). Cell viability assays were used to ascertain whether sulfatide-induced toxicity was rescued by Olaparib. Immunofluorescence, calcium (Ca2+) imaging, ROS, and mitochondrial damage assays were also used to explore the effects of sulfatides and Olaparib. ELISAs were performed and chemotaxis of peripheral blood immune cells was measured to examine the effects of Olaparib on sulfatide-induced inflammation in human astrocytes. Here, we established a concentration-dependent (EC50∼20 μM at 24 h) model of sulfatide-induced astrocyte toxicity. Our data demonstrate that sulfatide-induced astrocyte toxicity involves (i) PARP-1 activation, (ii) pro-inflammatory cytokine release, and (iii) enhanced chemoattraction of peripheral blood immune cells. Moreover, these sulfatide-induced effects were attenuated by Olaparib (IC50∼100 nM). In addition, sulfatide caused impairments of ROS production, mitochondrial stress, and Ca2+ signaling in human astrocytes, that were indicative of metabolic alterations and that were also alleviated by Olaparib (100 nM) treatment. Our data support the hypothesis that sulfatides can drive astrocyte cell death and demonstrate that Olaparib can dampen many facets of sulfatide-induced toxicity, including, mitochondrial stress, inflammatory responses, and communication between human astrocytes and peripheral blood immune cells. These data are suggestive of potential therapeutic utility of PARP inhibitors in the sphere of rare demyelinating diseases, and in particular MLD. Graphical abstract. Proposed mechanism of action of Olaparib in sulfatide-treated astrocytes. Human astrocytes treated for 24 h with sulfatides increase PARP-1 expression and die. PARP-1 overexpression is modulated by Ca2+ release from the endoplasmic reticulum, thus enhancing intracellular Ca2+ concentration. PARP-1 inhibition with Olaparib reduces Ca2+ influx and cell death. Olaparib also decreases IL-6, IL-8, IL-17, and CX3CL1 release from sulfatide-stimulated astrocytes, suggesting that PARP-1 plays a role in dampening neuroinflammation in MLD. This is confirmed by the reduction of immune cell migration such as lymphocytes, NK cells, and T cells towards sulfatide-treated astrocytes. Moreover, mitochondrial stress and ROS production induced by sulfatides are rescued by PARP-1 inhibition. Future studies will focus on the signaling cascades triggered by PARP-1-mediated currents in reactive astrocytes and Olaparib as a potential therapeutic target for MLD.

An insight into the structure-activity relationship studies of anticancer medicinal attributes of 7-azaindole derivatives: a review

In the current portfolio, there is a lot of interest in the 7-azaindole building block for drug discovery. The creation of synthetic, sophisticated methods for the modification of 7-azaindoles is a promising area of research. This review covers the structure-activity relationship of 7-azaindole analogs, which have been shown to be effective anticancer agents in the literature of the past two decades. Positions 1, 3 and 5 of the 7-azaindole ring are the most active sites. Disubstitution is used for the synthesis of a new analog of the 7-azaindole moiety. All positions are used to create novel molecules that are effective anticancer agents. The alkyl, aryl carboxamide group and heterocyclic ring are the most successful types of substitution.

Olaparib Attenuates Demyelination and Neuroinflammation in an Organotypic Slice Culture Model of Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a severe demyelinating, autosomal recessive genetic leukodystrophy. The disease is underpinned by mutations in the arylsulfatase A gene (ARSA), resulting in deficient activity of the arylsulfatase A lysosomal enzyme and consequential accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the brain. Using an ex vivo murine-derived organotypic cerebellar slice culture model, we demonstrate that sulfatide induces demyelination in a concentration-dependent manner. Interestingly, our novel data demonstrate that sulfatide-induced demyelination is underpinned by PARP-1 activation, oligodendrocyte loss, pro-inflammatory cytokine expression, astrogliosis, and microgliosis. Moreover, such sulfatide-induced effects can be attenuated by the treatment with the poly (ADP-ribose) polymerase 1 (PARP-1) inhibitor Olaparib (IC50∼100 nM) suggesting that this small molecule may be neuroprotective and limit toxin-induced demyelination. Our data support the idea that sulfatide is a key driver of demyelination and neuroinflammation in MLD and suggest that PARP-1 inhibitors have therapeutic utility in the sphere of rare demyelinating disease.

Regulation of Biomolecular Condensates by Poly(ADP-ribose)

Biomolecular condensates are reversible compartments that form through a process called phase separation. Post-translational modifications like ADP-ribosylation can nucleate the formation of these condensates by accelerating the self-association of proteins. Poly(ADP-ribose) (PAR) chains are remarkably transient modifications with turnover rates on the order of minutes, yet they can be required for the formation of granules in response to oxidative stress, DNA damage, and other stimuli. Moreover, accumulation of PAR is linked with adverse phase transitions in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In this review, we provide a primer on how PAR is synthesized and regulated, the diverse structures and chemistries of ADP-ribosylation modifications, and protein-PAR interactions. We review substantial progress in recent efforts to determine the molecular mechanism of PAR-mediated phase separation, and we further delineate how inhibitors of PAR polymerases may be effective treatments for neurodegenerative pathologies. Finally, we highlight the need for rigorous biochemical interrogation of ADP-ribosylation in vivo and in vitro to clarify the exact pathway from PARylation to condensate formation.

DNA Repair Inhibitors: Potential Targets and Partners for Targeted Radionuclide Therapy

The present review aims to explore the potential targets/partners for future targeted radionuclide therapy (TRT) strategies, wherein cancer cells often are not killed effectively, despite receiving a high average tumor radiation dose. Here, we shall discuss the key factors in the cancer genome, especially those related to DNA damage response/repair and maintenance systems for escaping cell death in cancer cells. To overcome the current limitations of TRT effectiveness due to radiation/drug-tolerant cells and tumor heterogeneity, and to make TRT more effective, we propose that a promising strategy would be to target the DNA maintenance factors that are crucial for cancer survival. Considering their cancer-specific DNA damage response/repair ability and dysregulated transcription/epigenetic system, key factors such as PARP, ATM/ATR, amplified/overexpressed transcription factors, and DNA methyltransferases have the potential to be molecular targets for Auger electron therapy; moreover, their inhibition by non-radioactive molecules could be a partnering component for enhancing the therapeutic response of TRT.

Mycotoxins Have a Potential of Inducing Cell Senescence: A New Understanding of Mycotoxin Immunotoxicity

Mycotoxins result in immune dysfunction and cause immune diseases in animals and humans. However, the mechanisms of immunotoxicity involved in mycotoxins have not been fully explored, and emerging evidence suggests that these toxins may promote their immunotoxicity via cellular senescence. Mycotoxins induce cell senescence after DNA damage, and activate signaling via the NF-κB and JNK pathways to promote the secretion of senescence-associated secretory phenotype (SASP) cytokines including IL-6, IL-8, and TNF-α. DNA damage can also over-activate or cleave poly (ADP-ribose) polymerase-1 (PARP-1), increase the expression of cell cycle inhibitory proteins p21, and p53, and induce cell cycle arrest and then senescence. These senescent cells further down-regulate proliferation-related genes and overexpress inflammatory factors resulting in chronic inflammation and eventual immune exhaustion. Here we review the underlying mechanisms by which mycotoxins trigger cell senescence and the potential roles of SASP and PARP in these pathways. This work will help to further understand the mechanisms of immunotoxicity involved in mycotoxins.

Methyltransferase Set7/9 as a Multifaceted Regulator of ROS Response

Reactive oxygen species (ROS) induce multiple signaling cascades in the cell and hence play an important role in the regulation of the cell's fate. ROS can cause irreversible damage to DNA and proteins resulting in cell death. Therefore, finely tuned regulatory mechanisms exist in evolutionarily diverse organisms that are aimed at the neutralization of ROS and its consequences with respect to cellular damage. The SET domain-containing lysine methyltransferase Set7/9 (KMT7, SETD7, SET7, SET9) post-translationally modifies several histones and non-histone proteins via monomethylation of the target lysines in a sequence-specific manner. In cellulo, the Set7/9-directed covalent modification of its substrates affects gene expression, cell cycle, energy metabolism, apoptosis, ROS, and DNA damage response. However, the in vivo role of Set7/9 remains enigmatic. In this review, we summarize the currently available information regarding the role of methyltransferase Set7/9 in the regulation of ROS-inducible molecular cascades in response to oxidative stress. We also highlight the in vivo importance of Set7/9 in ROS-related diseases.

DNA damage and up-regulation of PARP-1 induced by columbin in vitro and in vivo

Columbin (CLB) is the most abundant (>1.0%) furan-containing diterpenoid lactone in herbal medicine Tinospora sagittate (Oliv.) Gagnep. The furano-terpenoid was found to be hepatotoxic, but the exact mechanisms remain unknown. The present study demonstrated that administration of CLB at 50 mg/kg induced hepatotoxicity, DNA damage and up-regulation of PARP-1 in vivo. Exposure to CLB (10 μM) induced GSH depletion, over-production of ROS, DNA damage, up-regulation of PARP-1 and cell death in cultured mouse primary hepatocytes in vitro. Co-treatment of mouse primary hepatocytes with ketoconazole (10 μM) or glutathione ethyl ester (200 μM) attenuated the GSH depletion, over-production of ROS, DNA damage, up-regulation of PARP-1, and cell death induced by CLB, while co-exposure to L-buthionine sulfoximine (BSO, 1000 μM) intensified such adverse effects resulting from CLB exposure. These results suggest that the metabolic activation of CLB by CYP3A resulted in the depletion of GSH and increase of ROS formation. The resultant over-production of ROS subsequently disrupted the DNA integrity and up-regulated the expression of PARP-1 in response to DNA damage, and ROS-induced DNA damage was involved in the hepatotoxicity of CLB.

Multi-therapies Based on PARP Inhibition: Potential Therapeutic Approaches for Cancer Treatment

The nuclear enzymes called poly(ADP-ribose)polymerases (PARPs) are known to catalyze the process of PARylation, which plays a vital role in various cellular functions. They have become important targets for the discovery of novel antitumor drugs since their inhibition can induce significant lethality in tumor cells. Therefore, researchers all over the world have been focusing on developing novel and potent PARP inhibitors for cancer therapy. Studies have shown that PARP inhibitors and other antitumor agents, such as EZH2 and EGFR inhibitors, play a synergistic role in cancer cells. The combined inhibition of PARP and the targets with synergistic effects may provide a rational strategy to improve the effectiveness of current anticancer regimens. In this Perspective, we sum up the recent advance of PARP-targeted agents, including single-target inhibitors/degraders and dual-target inhibitors/degraders, discuss the fundamental theory of developing these dual-target agents, and give insight into the corresponding structure-activity relationships of these agents.

The protective effect of 17 β-estradiol on human uterosacral ligament fibroblasts from postmenopausal women with pelvic organ prolapse

This study aims to explore the protective effects of 17 β-estradiol on the human uterosacral ligament fibroblasts (hUSLFs) under static or stretched conditions. The experiments were performed on hUSLFs derived from pelvic organ prolapse (POP) and non-POP patients. Fibroblasts were cultured after collagenase digestion and identified by morphological observation and immunocytochemical methods. 17 β-estradiol (10⁻¹⁰ M and 10⁻⁹ M) and mechanical stress induced by the FX-5000 T-cell stress loading system under a loading strain of 1/2 sin waveform uniaxial cyclic stress with a tensile strain of 20% and a frequency of 0.5 Hz were either or both applied on hUSLFs. Cell proliferation was measured by CCK8, and cell apoptosis and death were detected using Annexin V/7-AAD staining and flow cytometric analysis. We found that the fibroblasts growth rate of POP patients was significantly lower than controls. The cell apoptosis and death rate increased as the mechanical load intensifying. After 20% mechanical stretching for 24 h, the dead cell rate was higher in POP than control. Notably, 17 β-estradiol treatment reversed mechanical stress induced hUSLFs apoptosis and death in both POP and Control cells. The protein and mRNA levels of anti-apoptotic PARP1 (poly-ADP-ribose polymerase) and Bcl-2 were increased by estrogen treatment. Meanwhile, expression of estrogen receptor α, a target of Poly-ADP-Ribosylation of PARP1, was also enhanced by 17 β-estradiol under the mechanical load. In conclusion, estrogen application ameliorates the mechanical strain induced cell apoptosis and death in hUSLFs from POP patients. PARP1 might be involved in this protective process, providing novel insights into the mechanical biology of and possible therapies for POP.

Network Pharmacology-Based Analysis on the Potential Biological Mechanisms of Yinzhihuang Oral Liquid in Treating Neonatal Hyperbilirubinemia

Objective

Neonatal hyperbilirubinemia is caused by the excessive production of bilirubin and decreased excretion ability in the neonatal period. It leads to a concentration of blood bilirubin that exceeds a certain threshold. Yinzhihuang oral liquid (YZH) is a traditional Chinese medicine mixture used in the treatment of neonatal hyperbilirubinemia in China. This article systematically explores the pharmacological mechanisms by which YZH acts in the treatment of neonatal hyperbilirubinemia through network pharmacology at the molecular level.

Methods

We adopted the method of network pharmacology, which includes active component prescreening, target gene prediction, gene enrichment analysis, and network analysis.

Results

According to the network pharmacological analysis, 8 genes (STAT3, AKT1, MAPK14, JUN, TP53, MAPK3, ESR1, and RELA) may be targets of YZH in the treatment of neonatal hyperbilirubinemia. In addition, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that YZH may regulate antioxidation, modulate lipid metabolism, and have anti-infective properties.

Conclusion

In this study, the pharmacological action and molecular mechanisms of YZH were predicted as a whole. It was found that YZH is a promising drug for treating oxidative stress due to bilirubin, as it reduces immunosuppression and helps to eliminate virus infection.

Oxidative Stress Markers Are Associated with a Poor Prognosis in Patients with Pancreatic Cancer

Pancreatic cancer is a malignancy of rising prevalence, especially in developed countries where dietary patterns and sedentariness favor its onset. This malady ranks seventh in cancer-related deaths in the world, although it is expected to rank second in the coming years, behind lung cancer. The low survival rate is due to the asymptomatic course of the early stages, which in many cases leads to metastases when becoming evident in advanced stages. In this context, molecular pathology is on the way towards finding new approaches with biomarkers that allow a better prognosis and monitoring of patients. So the present study aims to evaluate a series of molecular biomarkers, PARP1, NOX1, NOX2, eNOS and iNOS, as promising candidates for prognosis and survival by using immunohistochemistry. The analysis performed in 41 patients with pancreatic cancer showed a correlation between a high expression of all these components with a low survival rate, with high statistical power for all. In addition, a 60-month longitudinal surveillance program was managed, accompanied by several clinical parameters. The derivative Kaplan–Meier curves indicated a low cumulative survival rate as well. Ultimately, our research emphasized the value of these molecules as survival-associated biomarkers in pancreatic cancer, offering new gates for clinical management.

Recent Progress of the research on the benzimidazole PARP-1 inhibitors

Poly (ADP-ribose) polymerase-1 (PARP-1) is a multifunctional protein that plays an important role in DNA repair and genome integrity. PARP-1 inhibitors can be used as effective drugs not only to treat BRCA-1/2 deficient cancers because of the effect of synthetically lethal, but also to treat non-BRCA1/2 deficient tumours because of the effect of PARP capture. Therefore, the PARP inhibitors have become a focus of compelling research. Among these inhibitors, substituted benzimidazole derivatives were mainly concerned lead compounds. However, the commercial available benzimidazole PARP-1 inhibitors have some shortcomings such as serious toxicity in combination with chemotherapy drugs, in vivo cardiovascular side effects such as anemia. Therefore it's crucial for scientists to explore more structure-activity relationships of the benzimidazole PARP-1 inhibitors and access safer and more effective PARP inhibitors. As the binding region of PARP-1 and the substrates is usually characterized as NI site and AD site, the modification of benzimidazoles mainly occurs on the benzimidazole skeleton (NI site), and the side chain of benzimidazole on 2-C position (AD site). Herein, the recent progresses of the researches of benzamides PARP inhibitors were introduced. We noticed that even though many efforts were taken to the modification of NI sites, there were still lacks of optimistic and impressive results. However, the structure-activity relationships of the modification of AD sites have not thoroughly discovered yet. We hope that enlightened by the previous researches, more researches of AD site should be occurred and more effective benzimidazole PARP-1 inhibitors could be designed, synthesized, and applied to clinics.

Existing Evidence for the Repurposing of PARP-1 Inhibitors in Rare Demyelinating Diseases

Simple Summary

Poly (ADP-ribose) polymerase-1 (PARP-1) inhibitors are successful cancer therapeutics that impair DNA repair machinery, leading to an accumulation of DNA damage and consequently cell death. The shared underlying mechanisms driving malignancy and demyelinating disease, together with the success of anticancer drugs as repurposed therapeutics, makes the repurposing of PARP-1 inhibitors for demyelinating diseases a worthy concept to consider. In addition, PARP-1 inhibitors demonstrate notable neuroprotective effects in demyelinating disorders, including multiple sclerosis which is considered the archetypical demyelinating disease.

Abstract

Over the past decade, Poly (ADP-ribose) polymerase-1 (PARP-1) inhibitors have arisen as a novel and promising targeted therapy for breast cancer gene (BRCA)-mutated ovarian and breast cancer patients. Therapies targeting the enzyme, PARP-1, have since established their place as maintenance drugs for cancer. Here, we present existing evidence that implicates PARP-1 as a player in the development and progression of both malignancy and demyelinating disease. These findings, together with the proven clinical efficacy and marketed success of PARP-1 inhibitors in cancer, present the repurposing of these drugs for demyelinating diseases as a desirable therapeutic concept. Indeed, PARP-1 inhibitors are noted to demonstrate neuroprotective effects in demyelinating disorders such as multiple sclerosis and Parkinson’s disease, further supporting the use of these drugs in demyelinating, neuroinflammatory, and neurodegenerative diseases. In this review, we discuss the potential for repurposing PARP-1 inhibitors, with a focus on rare demyelinating diseases. In particular, we address the possible use of PARP-1 inhibitors in examples of rare leukodystrophies, for which there are a paucity of treatment options and an urgent need for novel therapeutic approaches.

Pleiotropic role of PARP1: an overview

Poly (ADP-ribose) polymerase 1 (PARP1) protein is encoded by the PARP1 gene located on chromosome 1 (1q42.12) in human cells. It plays a crucial role in post-translational modification by adding poly (ADP-ribose) (PAR) groups to various proteins and PARP1 itself by utilizing nicotinamide adenine dinucleotide (NAD +) as a substrate. Since the discovery of PARP1, its role in DNA repair and cell death has been its identity. This is evident from an overwhelmingly high number of scientific reports in this regard. However, PARP1 also plays critical roles in inflammation, metabolism, tumor development and progression, chromatin modification and transcription, mRNA stability, and alternative splicing. In the present study, we attempted to compile all the scattered scientific information about this molecule, including the structure and multifunctional role of PARP1 in cancer and non-cancer diseases, along with PARP1 inhibitors (PARPis). Furthermore, for the first time, we have classified PARP1-mediated cell death for ease of understanding its role in cell death pathways.

Poly(ADP)-Ribosylation Inhibition: A Promising Approach for Clear Cell Renal Cell Carcinoma Therapy

Poly(ADP-ribose) polymerase 1 (PARP-1) and glycohydrolase (PARG) enzymes regulate chromatin structure, transcription activation, and DNA repair by modulating poly(ADP-ribose) (pADPr) level. Interest in PARP-1 inhibitors has soared recently with the recognition of their antitumor efficacy. We have shown that the development of clear cell renal cell carcinoma (ccRCC) is associated with extreme accumulation of pADPr caused by the enhanced expression of PARP-1 and decreased PARG levels. The most severe misregulation of pADPr turnover is found in ccRCC specimens from metastatic lesions. Both, classical NAD-like and non-NAD-like PARP-1 inhibitors reduced viability and clonogenic potential of ccRCC cell lines and suppressed growth of ccRCC xenograft tumors. However, classical NAD-like PARP-1 inhibitors affected viability of normal kidney epithelial cells at high concentrations, while novel non-NAD-like PARP-1 inhibitors exhibited activity against malignant cells only. We have also utilized different approaches to reduce the pADPr level in ccRCC cells by stably overexpressing PARG and demonstrated the prominent antitumor effect of this "back-to-normal" intervention. We also generated ccRCC cell lines with stable overexpression of PARG under doxycycline induction. This genetic approach demonstrated significantly affected malignancy of ccRCC cells. Transcriptome analysis linked observed phenotype with changes in gene expression levels for lipid metabolism, interferon signaling, and angiogenesis pathways along with the changes in expression of key cancer-related genes.

A375 melanoma cells are sensitized to cisplatin-induced toxicity by a synthetic nitro-flavone derivative 2-(4-Nitrophenyl)-4H-chromen-4-one through inhibition of PARP1

BACKGROUND

Cisplatin has been extensively used in therapeutics for its broad-spectrum anticancer activity and frequently used for the treatment of solid tumors. However, it presents several side-effects and several cancers develop resistance. Combination therapy of cisplatin with poly (ADP-ribose) polymerase 1 (PARP1) inhibitors has been effective in increasing its efficacy at lower doses.

METHODS AND RESULTS

In this work, we have shown that the nitro-flavone derivative, 2-(4-Nitrophenyl)-4H-chromen-4-one (4NCO), can improve the sensitivity of cancer cells to cisplatin through inhibition of PARP1. The effect of 4NCO on cisplatin toxicity was studied through combination therapy in both exponential and density inhibited A375 melanoma cells. Combination index (CI) was determined from isobologram analysis. The mechanism of cell killing was assessed by lactate dehydrogenase (LDH) assay. Temporal nicotinamide adenine dinucleotide (NAD⁺) assay was done to show the inhibition of PARP1. We also performed in silico molecular modeling studies to know the binding mode of 4NCO to a modeled PARP1-DNA complex containing cisplatin-crosslinked adduct. The results from both in silico and in cellulo studies confirmed that PARP1 inhibition by 4NCO was most effective in sensitizing A375 melanoma cells to cisplatin. Isobologram analysis revealed that 4NCO reduced cell viability both in exponential and density inhibited A375 cells synergistically. The combination led to cell death through apoptosis.

CONCLUSION

The synthetic nitro-flavone derivative 4NCO effectively inhibited the important nuclear DNA repair enzyme PARP1 and therefore, could complement the DNA-damaging anticancer drug cisplatin in A375 cells and thus, could act as a potential adjuvant to cisplatin in melanoma therapy.

PARP Power: A Structural Perspective on PARP1, PARP2, and PARP3 in DNA Damage Repair and Nucleosome Remodelling

Poly (ADP-ribose) polymerases (PARP) 1-3 are well-known multi-domain enzymes, catalysing the covalent modification of proteins, DNA, and themselves. They attach mono- or poly-ADP-ribose to targets using NAD⁺ as a substrate. Poly-ADP-ribosylation (PARylation) is central to the important functions of PARP enzymes in the DNA damage response and nucleosome remodelling. Activation of PARP happens through DNA binding via zinc fingers and/or the WGR domain. Modulation of their activity using PARP inhibitors occupying the NAD⁺ binding site has proven successful in cancer therapies. For decades, studies set out to elucidate their full-length molecular structure and activation mechanism. In the last five years, significant advances have progressed the structural and functional understanding of PARP1-3, such as understanding allosteric activation via inter-domain contacts, how PARP senses damaged DNA in the crowded nucleus, and the complementary role of histone PARylation factor 1 in modulating the active site of PARP. Here, we review these advances together with the versatility of PARP domains involved in DNA binding, the targets and shape of PARylation and the role of PARPs in nucleosome remodelling.

Host-Directed Therapies: Modulating Inflammation to Treat Tuberculosis

Following infection with Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), most human hosts are able to contain the infection and avoid progression to active TB disease through expression of a balanced, homeostatic immune response. Proinflammatory mechanisms aiming to kill, slow and sequester the pathogen are key to a successful host response. However, an excessive or inappropriate pro-inflammatory response may lead to granuloma enlargement and tissue damage, which may prolong the TB treatment duration and permanently diminish the lung function of TB survivors. The host also expresses certain anti-inflammatory mediators which may play either beneficial or detrimental roles depending on the timing of their deployment. The balance between the timing and expression levels of pro- and anti-inflammatory responses plays an important role in the fate of infection. Interestingly, M. tuberculosis appears to manipulate both sides of the human immune response to remodel the host environment for its own benefit. Consequently, therapies which modulate either end of this spectrum of immune responses at the appropriate time may have the potential to improve the treatment of TB or to reduce the formation of permanent lung damage after microbiological cure. Here, we highlight host-directed TB therapies targeting pro- or anti-inflammatory processes that have been evaluated in pre-clinical models. The repurposing of already available drugs known to modulate these responses may improve the future of TB therapy.

SMURF2-mediated ubiquitin signaling plays an essential role in the regulation of PARP1 PARylating activity, molecular interactions, and functions in mammalian cells

Poly(ADP-ribose) polymerase 1 (PARP1) is a key molecular stress sensor and response mediator implicated in multiple cellular functions in health and diseases. Despite its importance and intrinsic involvement in pivotal molecular and cellular processes, including DNA repair, transcription regulation, chromatin organization, and cell death, the regulatory mechanisms of PARP1 are poorly understood. In this study, we show that SMURF2, a HECT-type E3 ubiquitin ligase and suggested tumor suppressor, physically interacts with PARP1 in different cellular settings, directly ubiquitinates it in vitro and stimulates its PARylation activity in cells, the phenomenon that required SMURF2 E3 ubiquitin ligase function. Intriguingly, in the cellular environment SMURF2 was found to regulate the dynamic exchange of ubiquitin moieties on PARP1, mostly decreasing its monoubiquitination. Through the set of systematic mass spectrometry analyses conducted on SMURF2-modified cells, we identified on PARP1 18 lysine residues (out of 126 present in PARP1) as sites which ubiquitination was considerably affected by SMURF2. Subsequent site-directed mutagenesis coupled with in cellula ubiquitination and PARylation assays unveiled K222 as a critical site enabling a cross talk between SMURF2-modulated monoubiquitination of PARP1 and its activity, and pointed to K498, S507, and a KTR triad (K498/K521/K524) as the main auto-PARylation sites affected by SMURF2. The results also uncovered that SMURF2 controls PARP1 interactome, influencing its functions and expression in a context-dependent manner. Taken together, these findings suggest that SMURF2-mediated ubiquitin signaling plays an essential role in PARP1 regulation, beyond the regulation of its protein expression.

Impact of the Cellular Zinc Status on PARP-1 Activity and Genomic Stability in HeLa S3 Cells

Poly(ADP-ribose) polymerase 1 (PARP-1) is actively involved in several DNA repair pathways, especially in the detection of DNA lesions and DNA damage signaling. However, the mechanisms of PARP-1 activation are not fully understood. PARP-1 contains three zinc finger structures, among which the first zinc finger has a remarkably low affinity toward zinc ions. Within the present study, we investigated the impact of the cellular zinc status on PARP-1 activity and on genomic stability in HeLa S3 cells. Significant impairment of H₂O₂-induced poly(ADP-ribosyl)ation and an increase in DNA strand breaks were detected in the case of zinc depletion by the zinc chelator N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) which reduced the total and labile zinc concentrations. On the contrary, preincubation of cells with ZnCl₂ led to an overload of total as well as labile zinc and resulted in an increased poly(ADP-ribosyl)ation response upon H₂O₂ treatment. Furthermore, the impact of the cellular zinc status on gene expression profiles was investigated via high-throughput RT-qPCR, analyzing 95 genes related to metal homeostasis, DNA damage and oxidative stress response, cell cycle regulation and proliferation. Genes encoding metallothioneins responded most sensitively on conditions of mild zinc depletion or moderate zinc overload. Zinc depletion induced by higher concentrations of TPEN led to a significant induction of genes encoding DNA repair factors and cell cycle arrest, indicating the induction of DNA damage and genomic instability. Zinc overload provoked an up-regulation of the oxidative stress response. Altogether, the results highlight the potential role of zinc signaling for PARP-1 activation and the maintenance of genomic stability.

PARP1 as a Marker of an Aggressive Clinical Phenotype in Cutaneous Melanoma-A Clinical and an In Vitro Study

(1) Background: Poly(ADP-ribose) polymerase 1) (PARP1) is a pleiotropic enzyme involved in several cellular processes, e.g., DNA damage repair, regulation of mitosis, and immune response. Little is known about the role of PARP1 in melanoma development and progression. We aimed to investigate the prognostic significance of PARP1 expression in cutaneous melanoma through evaluation of mRNA and protein levels of PARP1 in normal melanocytes and melanoma cell lines, as well as in patients' tissue material from surgical resections. (2) Methods: An in vitro model was based on two types of normal human melanocytes (HEMn-DP and HEMn-LP) and four melanoma cell lines (A375, WM1341D, Hs294T, and WM9). PARP1 mRNA gene expression was estimated using real-time polymerase chain reaction (RT-PCR), whereas the protein level of PARP1 was evaluated by fluorescence confocal microscopy and then confirmed by Western Blotting analysis. The expression of PARP1 was also assessed by immunohistochemistry in formalin-fixed paraffin-embedded tissues of 128 primary cutaneous melanoma patients and correlated with follow-up and clinicopathologic features. (3) Results: The in vitro study showed that melanoma cells exhibited significantly higher PARP1 expression at mRNA and protein levels than normal melanocytes. High PARP1 expression was also associated with the invasiveness of tumor cells. Elevated nuclear PARP1 expression in patients without nodal metastases strongly correlated with significantly shorter disease-free survival (p = 0.0015) and revealed a trend with shorter cancer-specific overall survival (p = 0.05). High PARP1 immunoreactivity in the lymph node-negative group of patients was significantly associated with higher Breslow tumor thickness, presence of ulceration, and a higher mitotic index (p = 0.0016, p = 0.023, and p < 0.001, respectively). In patients with nodal metastases, high PARP1 expression significantly correlated with the presence of microsatellitosis (p = 0.034), but we did not confirm the prognostic significance of PARP1 expression in these patients. In the entire analyzed group of patients (with and without nodal metastases at the time of diagnosis), PARP1 expression was associated with a high mitotic index (p = 0.001) and the presence of ulceration (p = 0.036). Moreover, in patients with elevated PARP1 expression, melanoma was more frequently located in the skin of the head and neck region (p = 0.015). In multivariate analysis, high PARP1 expression was an independent unfavorable prognosticator in lymph node-negative cutaneous melanoma patients. (4) Conclusions: In vitro molecular biology approaches demonstrated enhanced PARP1 expression in cutaneous melanoma. These results were confirmed by the immunohistochemical study with clinical parameter analysis, which showed that a high level of PARP1 correlated with unfavorable clinical outcome. These observations raise the potential role of PARP1 inhibitor-based therapy in cutaneous melanoma.

Making Connections: p53 and the Cathepsin Proteases as Co-Regulators of Cancer and Apoptosis

Simple Summary

This article describes an emerging area of significant interest in cancer and cell death and the relationships shared by these through the p53 and cathepsin proteins. While it has been demonstrated that the p53 protein can directly induce the leakage of cathepsin proteases from the lysosome, directly triggering cell death, little is known about what factors set the threshold at which the lysosome can become permeabilized. It appears that the expression levels of cathepsin proteases may be central to this process, with some of them being transcriptionally regulated by p53. The consequences of such a mechanism have serious implications for lysosomal-mediated apoptosis and have significant input into the design of therapeutics and their strategic use. In this review, we highlight the importance of extending such findings to other cathepsin family members and the need to assess the roles of p53 isoforms and mutants in furthering this mechanism.

Abstract

While viewed as the “guardian of the genome”, the importance of the tumor suppressor p53 protein has increasingly gained ever more recognition in modulating additional modes of action related to cell death. Slowly but surely, its importance has evolved from a mutated genetic locus heavily implicated in a wide array of cancer types to modulating lysosomal-mediated cell death either directly or indirectly through the transcriptional regulation of the key signal transduction pathway intermediates involved in this. As an important step in determining the fate of cells in response to cytotoxicity or during stress response, lysosomal-mediated cell death has also become strongly interwoven with the key components that give the lysosome functionality in the form of the cathepsin proteases. While a number of articles have been published highlighting the independent input of p53 or cathepsins to cellular homeostasis and disease progression, one key area that warrants further focus is the regulatory relationship that p53 and its isoforms share with such proteases in regulating lysosomal-mediated cell death. Herein, we review recent developments that have shaped this relationship and highlight key areas that need further exploration to aid novel therapeutic design and intervention strategies.

Combining PARP and DNA-PK Inhibitors With Irradiation Inhibits HPV-Negative Head and Neck Cancer Squamous Carcinoma Growth

Novel targeted agents to inhibit DNA repair pathways to sensitize tumors to irradiation (IR) are being investigated as an alternative to chemoradiation for locally advanced human papilloma virus negative (HPV-negative) head and neck squamous cell carcinoma (HNSCC). Two well-characterized targets that, when inhibited, exhibit potent IR sensitization are PARP1 and DNA-PKcs. However, their cooperation in sensitizing HPV-negative HNSCC to IR remains to be explored given that PARP1 and DNA-Pk_CS bind to unresected stalled DNA replication forks and cooperate to recruit XRCC1 to facilitate double-strand break repair. Here, we show that the combination of the DNA-PK inhibitor NU7441 and the PARP inhibitor olaparib significantly decrease proliferation (61–78%) compared to no reduction with either agent alone (p < 0.001) in both SCC1 and SCC6 cell lines. Adding IR to the combination further decreased cell proliferation (91–92%, p < 0.001) in SCC1 and SCC6. Similar results were observed using long-term colony formation assays [dose enhancement ratio (DER) 2.3–3.2 at 4Gy, p < 0.05]. Reduced cell survival was attributed to increased apoptosis and G2/M cell cycle arrest. Kinomic analysis using tyrosine (PTK) and serine/threonine (STK) arrays reveals that combination treatment results in the most potent inhibition of kinases involved in the CDK and ERK pathways compared to either agent alone. In vivo, a significant delay of tumor growth was observed in UM-SCC1 xenografts receiving IR with olaparib and/or NU7441, which was similar to the cisplatin-IR group. Both regimens were less toxic than cisplatin-IR as assessed by loss of mouse body weight. Taken together, these results demonstrate that the combination of NU7441 and olaparib with IR enhances HPV-negative HNSCC inhibition in both cell culture and in mice, suggesting a potential innovative combination for effectively treating patients with HPV-negative HNSCC.

Transmembrane Protein 230 Mediates a Poly(ADP-ribose) Polymerase-1-Linked Apoptosis

Mutations in transmembrane protein 230 (TMEM230) gene are suggested to be associated with the autosomal dominant Parkinson’s disease (PD) with typical movement disorders and Lewy body pathology. However, the normal functions and the pathological roles of TMEM230 are not clear. In this study, we used TMEM230 isoform II constructs including wild-type (WT) and four reported PD-linked mutation constructs (Y92C, R141L, 184Wext*5, and 184PGext*5). Ectopic expression of WT and PD-linked mutant TMEM230 variants in cultured cells dramatically induced apoptotic cell death compared with that of vector control cells. Mutant TMEM230 caused cell toxicity at an increased severity than WT TMEM230. Moreover, expression of TMEM230 increased mitochondrial reactive oxygen species (ROS) levels, decreased cellular ATP, activated caspase 3/7, and increased poly(ADP-ribose) polymerase-1 (PARP1) cleavage. Treatment with N-acetylcysteine (NAC; an ROS scavenger) or Z-VAD-FMK (a caspase inhibitor) significantly attenuated TMEM230-induced apoptosis in both cultured cells and primary neurons. Our results indicated that TMEM230 mediated a PARP1-linked apoptotic cell death pathway. These findings not only provide the novel insight into the biological roles of TMEM230 in the PARP1-linked pathway but also provide a TMEM230-induced cell death mechanism underlying PD pathogenesis.

Histone-dependent PARP-1 inhibitors: A novel therapeutic modality for the treatment of prostate and renal cancers

Clinical interest in poly(ADP-ribose) polymerase 1 (PARP-1) has increased over the past decade with the recognition of its roles in transcription regulation, DNA repair, epigenetic bookmarking, and chromatin restructuring. A number of PARP-1 inhibitors demonstrating clinical efficacy against tumors of various origins have emerged in recent years. These inhibitors have been essentially designed as nicotinamide adenine dinucleotide (NAD⁺) mimetics. However, because NAD⁺ is utilized by many enzymes other than PARP-1, NAD⁺ competitors tend to produce certain off-target effects. To overcome the limitation of NAD-like PARP-1 inhibitors, we have developed a new class of PARP-1 inhibitors that specifically targets the histone-dependent route of PARP-1 activation, a mechanism of activation that is unique to PARP-1. Novel histone-dependent inhibitors are highly specific for PARP-1 and demonstrate promising in vitro and in vivo efficacy against prostate and renal tumors. Our findings suggest that novel PARP-1 inhibitors have strong therapeutic potential for the treatment of urological tumors.

PARP1 V762A polymorphism affects the prognosis of myelodysplastic syndromes

OBJECTIVE

Myelodysplastic syndromes (MDS), caused by various genetic mutations in hematopoietic stem cells, are associated with highly variable outcomes. Poly (ADP-ribose) polymerase-1 (PARP1) plays an important role in DNA damage repair and contributes to the progression of several types of cancer. Here, we investigated the impact of PARP1 V762A polymorphism on the susceptibility to and prognosis of MDS.

METHODS

Samples collected from 105 MDS patients and 202 race-matched healthy controls were subjected to polymerase chain reaction-restriction fragment length polymorphism for genotyping.

RESULTS

The allele and genotype frequencies of PARP1 V762A did not differ between MDS patients and the control group. However, MDS patients with the PARP1 V762A non-AA genotype, which is associated with high gene activity, had shorter overall survival rates (P = .01) than those with the AA genotype. Multivariate analysis of overall survival also revealed PARP1 V762A non-AA genotype as a poor prognostic factor (P = .02). When patients were analyzed according to treatment history, the PARP1 V762A non-AA genotype was only associated with poor survival in patients who had received treatment (P = .02).

CONCLUSION

PARP1 V762A polymorphism may be an independent prognostic factor for MDS, and a predictive biomarker for MDS treatment.

Targeting cervical cancer: Is there a role for poly (ADP-ribose) polymerase inhibition?

Patients with metastatic and recurrent cervical cancer (CC) have a poor prognosis with limited palliative treatment options. Increasing understanding of the cellular aberrations inherent to cancer cells has allowed the development of therapies to target biological pathways, an important step toward the individualization of cancer therapy. The poly (ADP-ribose) polymerase (PARP) family of enzymes is important in several DNA repair pathways. Drugs that inhibit these PARP enzymes have been investigated in many types of cancer and their application in the treatment of gynecologic malignancies has rapidly evolved. Although the majority of data for PARPi in gynecologic malignancies has been specifically regarding ovarian cancer, their role in the treatment of uterine and CC is currently being investigated. This review will examine PARP inhibitors in CC, summarizes the critical clinical trials of PARP inhibitors that have been completed, provides an overview of the on-going trials, presents the confirmed conclusions and notes the issues that need to be addressed in future studies.

Restriction of AID activity and somatic hypermutation by PARP-1

Affinity maturation of the humoral immune response depends on somatic hypermutation (SHM) of immunoglobulin (Ig) genes, which is initiated by targeted lesion introduction by activation-induced deaminase (AID), followed by error-prone DNA repair. Stringent regulation of this process is essential to prevent genetic instability, but no negative feedback control has been identified to date. Here we show that poly(ADP-ribose) polymerase-1 (PARP-1) is a key factor restricting AID activity during somatic hypermutation. Poly(ADP-ribose) (PAR) chains formed at DNA breaks trigger AID-PAR association, thus preventing excessive DNA damage induction at sites of AID action. Accordingly, AID activity and somatic hypermutation at the Ig variable region is decreased by PARP-1 activity. In addition, PARP-1 regulates DNA lesion processing by affecting strand biased A:T mutagenesis. Our study establishes a novel function of the ancestral genome maintenance factor PARP-1 as a critical local feedback regulator of both AID activity and DNA repair during Ig gene diversification.

An Orally Available Tubulin Inhibitor, VERU-111, Suppresses Triple-Negative Breast Cancer Tumor Growth and Metastasis and Bypasses Taxane Resistance

Triple-negative breast cancer (TNBC) accounts for approximately 15% of breast cancer cases in the United States. TNBC has poorer overall prognosis relative to other molecular subtypes due to rapid onset of drug resistance to conventional chemotherapies and increased risk of visceral metastases. Taxanes like paclitaxel are standard chemotherapies that stabilize microtubules, but their clinical efficacy is often limited by drug resistance and neurotoxicities. We evaluated the preclinical efficacy of a novel, potent, and orally bioavailable tubulin inhibitor, VERU-111, in TNBC models. VERU-111 showed potent cytotoxicity against TNBC cell lines, inducing apoptosis and cell-cycle arrest in a concentration-dependent manner. VERU-111 also efficiently inhibited colony formation, cell migration, and invasion. Orally administered VERU-111 inhibited MDA-MB-231 xenograft growth in a dose-dependent manner, with similar efficacies to paclitaxel, but without acute toxicity. VERU-111 significantly reduced metastases originating from the mammary fat pad into lung, liver, and kidney metastasis in an experimental metastasis model. Moreover, VERU-111, but not paclitaxel, suppressed growth of luciferase-labeled, taxane-resistant, patient-derived metastatic TNBC tumors. In this model, VERU-111 repressed growth of preestablished axillary lymph node metastases and lung, bone, and liver metastases at study endpoint, whereas paclitaxel enhanced liver metastases relative to vehicle controls. Collectively, these studies strongly suggest that VERU-111 is not only a potent inhibitor of aggressive TNBC phenotypes, but it is also efficacious in a taxane-resistant model of metastatic TNBC. Thus, VERU-111 is a promising new generation of tubulin inhibitor for the treatment of TNBC and may be effective in patients who progress on taxanes.Results presented in this study demonstrate the efficacy of VERU-111 in vivo and provide strong rationale for future development of VERU-111 as an effective treatment for metastatic breast cancer.

Non-NAD-like PARP-1 inhibitors in prostate cancer treatment

In our previous studies of the molecular mechanisms of poly(ADP-ribose) polymerase 1 (PARP-1)-mediated transcriptional regulation we identified a novel class of PARP-1 inhibitors targeting the histone-dependent route of PARP-1 activation. Because histone-dependent activation is unique to PARP-1, non-NAD-like PARP-1 inhibitors have the potential to bypass the off-target effects of classical NAD-dependent PARP-1 inhibitors, such as olaparib, veliparib, and rucaparib. Furthermore, our recently published studies demonstrate that, compared to NAD-like PARP-1 inhibitors that are used clinically, the non-NAD-like PARP-1 inhibitor 5F02 exhibited superior antitumor activity in cell and animal models of human prostate cancer (PC). In this study, we further evaluated the antitumor activity of 5F02 and several of its novel analogues against PC cells. In contrast to NAD-like PARP-1 inhibitors, non-NAD-like PARP-1 inhibitors demonstrated efficacy against androgen-dependent and -independent routes of androgen receptor signaling activation. Our experiments reveal that methylation of the quaternary ammonium salt and the presence of esters were critical for the antitumor activity of 5F02 against PC cells. In addition, we examined the role of a related regulatory protein of PARP-1, called Poly(ADP-ribose) glycohydrolase (PARG), in prostate carcinogenesis. Our study reveals that PARG expression is severely disrupted in PC cells, which is associated with decreased integrity and localization of Cajal bodies (CB). Overall, the results of our study strengthen the justification for using non-NAD-like PARP-1 inhibitors as a novel therapeutic strategy for the treatment of advanced prostate cancer.

Prospect for Application of PARP Inhibitor in Patients with HER2 Negative Breast Cancer

Human epidermal growth factor receptor (HER2) negative metastatic breast cancer (BC) accounts for 73% of BC. The molecular analysis of this disease is essential for potential options for targeted therapy. Several promising clinical strategies are being evaluated which includes endocrine therapy, modified chemotherapy, angiogenesis inhibitors, immune checkpoint inhibitors, and anti-androgens. New therapeutic approaches are being developed that target BC patients with germline mutations in either BRCA1, BRCA2 as well as BRCAness, a condition in which tumors have molecular similarity to BRCA-mutated tumors. Poly (ADP-ribose) polymerase inhibitors (PARPi) which are effective therapy in germline BRCA1 and BRCA2 mutations, are also observed to be effective in somatic mutations. Germline mutations in the homologous recombination pathway genes could also contribute to PARPi sensitivity. PARPi act as chemo- and radio-sensitizers by limiting the DNA-damage response and potentiating the activity of chemo- and radio-therapy when used alone or in combination with chemotherapy. Apart from PARPi as monotherapy, additional researches are ongoing in combination with cytotoxic chemotherapeutics and targeted agents in HER2 negative BC. This review aims at the most recent developments in the targeted therapy, summarizes the recent clinical trials outcomes, along with the overview of ongoing clinical trials in HER2 negative patients with BRCA1/2 mutations and sporadic tumors with BRCAness.

Diastereomeric Recognition of 5',8-cyclo-2'-Deoxyadenosine Lesions by Human Poly(ADP-ribose) Polymerase 1 in a Biomimetic Model

5’,8-Cyclo-2’-deoxyadenosine (cdA), in the 5’R and 5’Sdiastereomeric forms, are typical non strand-break oxidative DNA lesions, induced by hydroxyl radicals, with emerging importance as a molecular marker. These lesions are exclusively repaired by the nucleotide excision repair (NER) mechanism with a low efficiency, thus readily accumulating in the genome. Poly(ADP-ribose) polymerase1 (PARP1) acts as an early responder to DNA damage and plays a key role as a nick sensor in the maintenance of the integrity of the genome by recognizing nicked DNA. So far, it was unknown whether the two diastereomeric cdA lesions could induce specific PARP1 binding. Here, we provide the first evidence of PARP1 to selectively recognize the diastereomeric lesions of 5’S-cdA and 5’R-cdA in vitro as compared to deoxyadenosine in model DNA substrates (23-mers) by using circular dichroism, fluorescence spectroscopy, immunoblotting analysis, and gel mobility shift assay. Several features of the recognition of the damaged and undamaged oligonucleotides by PARP1 were characterized. Remarkably, PARP1 exhibits different affinities in binding to a double strand (ds) oligonucleotide, which incorporates cdA lesions in R and S diastereomeric form. In particular, PARP1 proved to bind oligonucleotides, including a 5’S-cdA, with a higher affinity constant for the 5’S lesion in a model of ds DNA than 5’R-cdA, showing different recognition patterns, also compared with undamaged dA. This new finding highlights the ability of PARP1 to recognize and differentiate the distorted DNA backbone in a biomimetic system caused by different diastereomeric forms of a cdA lesion.

Bilirubin-Induced Oxidative Stress Leads to DNA Damage in the Cerebellum of Hyperbilirubinemic Neonatal Mice and Activates DNA Double-Strand Break Repair Pathways in Human Cells

Unconjugated bilirubin is considered a potent antioxidant when present at moderate levels. However, at high concentrations, it produces severe neurological damage and death associated with kernicterus due to oxidative stress and other mechanisms. While it is widely recognized that oxidative stress by different toxic insults results in severe damage to cellular macromolecules, especially to DNA, no data are available either on DNA damage in the brain triggered by hyperbilirubinemia during the neonatal period or on the activation of DNA repair mechanisms. Here, using a mouse model of neonatal hyperbilirubinemia, we demonstrated that DNA damage occurs in vivo in the cerebellum, the brain region most affected by bilirubin toxicity. We studied the mechanisms associated with potential toxic action of bilirubin on DNA in in vitro models, which showed significant increases in DNA damage when neuronal and nonneuronal cells were treated with 140 nM of free bilirubin (Bf), as determined by γH2AX Western blot and immunofluorescence analyses. Cotreatment of cells with N-acetyl-cysteine, a potent oxidative-stress inhibitor, prevented DNA damage by bilirubin, supporting the concept that DNA damage was caused by bilirubin-induced oxidative stress. Bilirubin treatment also activated the main DNA repair pathways through homologous recombination (HR) and nonhomologous end joining (NHEJ), which may be adaptive responses to repair bilirubin-induced DNA damage. Since DNA damage may be another important factor contributing to neuronal death and bilirubin encephalopathy, these results contribute to the understanding of the mechanisms associated with bilirubin toxicity and may be of relevance in neonates affected with severe hyperbilirubinemia.

Advances in the use of PARP inhibitor therapy for breast cancer

Poly-ADP-ribose polymerase 1 (PARP-1) and PARP-2 are DNA damage sensors that are most active during S-phase of the cell cycle and that have wider-reaching roles in DNA repair than originally described. BRCA1 and BRCA2 (Breast Cancer) proteins are involved in homologous recombination repair (HRR), which requires a homologous chromosome or sister chromatid as a template to faithfully repair DNA double-strand breaks. The small-molecule NAD+ mimetics, olaparib, niraparib, rucaparib, veliparib, and talazoparib, inhibit the catalytic activity of PARP-1 and PARP-2 and are currently being studied in later-stage clinical trials. PARP inhibitor clinical trials have predominantly focused on patients with breast and ovarian cancer with deleterious germline BRCA1 and BRCA2 mutations (gBRCA1/2+) but are now expanding to include cancers with known, suspected, or more-likely-than-not defects in homologous recombination repair. In ovarian cancer, this group also includes women whose cancers are responsive to platinum therapy. Olaparib was FDA-approved in January 2018 for the treatment of gBRCA1/2+ metastatic breast cancers. gBRCA1+ predisposes women to develop triple-negative breast cancers, while women with gBRCA2+ tend to develop hormone-receptor-positive, human epidermal growth factor receptor 2 negative breast cancers. Although PARP inhibitor monotherapy strategies seem most effective in cancers with homologous recombination repair defects, combination strategies may allow expansion into a wider range of cancers. By interfering with DNA repair, PARP inhibitors essentially sensitize cells to DNA-damaging chemotherapies and radiation therapy. Certainly, one could also consider expanding the utility of PARP inhibitors beyond gBRCA1/2+ cancers by causing DNA damage with cytotoxic agents in the presence of a DNA repair inhibitor. Unfortunately, in numerous phase I clinical trials utilizing a combination of cytotoxic chemotherapy at standard doses with dose-escalation of PARP inhibitors, there has generally been failure to reach monotherapy dosages of PARP inhibitors due to myelosuppressive toxicities. Strategies utilizing angiogenesis inhibitors and immune checkpoint inhibitors are generally not hindered by additive toxicities, though the utility of combining PARP inhibitors with treatments that have not been particularly effective in breast cancers somewhat tempers enthusiasm. Finally, there are combination strategies that may serve to mitigate resistance to PARP inhibitors, namely, upregulation of the intracellular PhosphoInositide-3-kinase, AK thymoma (protein kinase B), mechanistic target of rapamycin (PI3K-AKT-mTOR) pathway, or perhaps are more simply meant to interfere with a cell growth pathway heavily implicated in breast cancers while administering relatively well-tolerated PARP inhibitor therapy.

Discriminating radiation injury from recurrent tumor with [18F]PARPi and amino acid PET in mouse models

Background

Radiation injury can be indistinguishable from recurrent tumor on standard imaging. Current protocols for this differential diagnosis require one or more follow-up imaging studies, long dynamic acquisitions, or complex image post-processing; despite much research, the inability to confidently distinguish between these two entities continues to pose a significant dilemma for the treating clinician. Using mouse models of both glioblastoma and radiation necrosis, we tested the potential of poly(ADP-ribose) polymerase (PARP)-targeted PET imaging with [¹⁸F]PARPi to better discriminate radiation injury from tumor.

Results

In mice with experimental radiation necrosis, lesion uptake on [¹⁸F]PARPi-PET was similar to contralateral uptake (1.02 ± 0.26 lesion/contralateral %IA/cc_max ratio), while [¹⁸F]FET-PET clearly delineated the contrast-enhancing region on MR (2.12 ± 0.16 lesion/contralateral %IA/cc_max ratio). In mice with focal intracranial U251 xenografts, tumor visualization on PARPi-PET was superior to FET-PET, and lesion-to-contralateral activity ratios (max/max, p = 0.034) were higher on PARPi-PET than on FET-PET.

Conclusions

A murine model of radiation necrosis does not demonstrate [¹⁸F]PARPi avidity, and [¹⁸F]PARPi-PET is better than [¹⁸F]FET-PET in distinguishing radiation injury from brain tumor. [¹⁸F]PARPi-PET can be used for discrimination between recurrent tumor and radiation injury within a single, static imaging session, which may be of value to resolve a common dilemma in neuro-oncology.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0399-z) contains supplementary material, which is available to authorized users.

Western diet induces endogen oxidative deoxyribonucleic acid damage and infl ammation in Wistar rats

ABSTRACT Objective Nutritional diseases such as metabolic syndrome, cardiovascular disorder, chronic inflammation or even cancer are observed in people who sustain their lifestyle by Western diet due to high calorie intake. The origin of these diseases are the degraded deoxyribonucleic acid structure. In this study, we investigated whether Western diet produced endogenous oxidative deoxyribonucleic acid damage, apoptosis or inflammation. Methods Twenty-eight male Wistar rats, aged 10-12 weeks, were divided into four groups. The rats in control group received the standard diet and the remaining rats were given one of the following three diets for four weeks: a high-fat diet containing 35% fat, a high-sucrose diet containing 69% sucrose and Western diet comprising both two types of diets. After treatment the serum 8-hydroxy-2-deoxyguanosine, poly (adenosine diphosphate ribose) polymerase-1, chitinase-3-like protein 1, soluble urokinase-type plasminogen activator receptor, Fas ligand and cytochrome c levels were measured. Results It was observed no changes in the serum soluble urokinase-type plasminogen activator receptor, Fas ligand and cytochrome c levels whereas a statistically significant increase in the serum 8-hydroxy-2-deoxyguanosine, poly (adenosine diphosphate ribose) polymerase-1 and chitinase-3-like protein 1 levels were found only in rats that were given Western diet. Conclusion The findings show that Western diet produced endogenous oxidative deoxyribonucleic acid damage, which then increased serum poly (adenosine diphosphate ribose) polymerase-1 levels, eventually leading to inflammation.

An Effective Epigenetic-PARP Inhibitor Combination Therapy for Breast and Ovarian Cancers Independent of BRCA Mutations

Purpose: PARP inhibitors (PARPi) are primarily effective against BRCA1/2-mutated breast and ovarian cancers, but resistance due to reversion of mutated BRCA1/2 and other mechanisms is common. Based on previous reports demonstrating a functional role for DNMT1 in DNA repair and our previous studies demonstrating an ability of DNA methyltransferase inhibitor (DNMTi) to resensitize tumors to primary therapies, we hypothesized that combining a DNMTi with PARPi would sensitize PARPi-resistant breast and ovarian cancers to PARPi therapy, independent of BRCA status.Experimental Design: Breast and ovarian cancer cell lines (BRCA-wild-type/mutant) were treated with PARPi talazoparib and DNMTi guadecitabine. Effects on cell survival, ROS accumulation, and cAMP levels were examined. In vivo, mice bearing either BRCA-proficient breast or ovarian cancer cells were treated with talazoparib and guadecitabine, alone or in combination. Tumor progression, gene expression, and overall survival were analyzed.Results: Combination of guadecitabine and talazoparib synergized to enhance PARPi efficacy, irrespective of BRCA mutation status. Coadministration of guadecitabine with talazoparib increased accumulation of ROS, promoted PARP activation, and further sensitized, in a cAMP/PKA-dependent manner, breast and ovarian cancer cells to PARPi. In addition, DNMTi enhanced PARP "trapping" by talazoparib. Guadecitabine plus talazoparib decreased xenograft tumor growth and increased overall survival in BRCA-proficient high-grade serous ovarian and triple-negative breast cancer models.Conclusions: The novel combination of the next-generation DNMTi guadecitabine and the first-in-class PARPi talazoparib inhibited breast and ovarian cancers harboring either wild-type- or mutant-BRCA, supporting further clinical exploration of this drug combination in PARPi-resistant cancers. Clin Cancer Res; 24(13); 3163-75. ©2018 AACR.

Is inflammation a direct response to dsDNA breaks?

Recent research shows that extra-nuclear cell-free chromatin (cfCh) released from dying cells can freely enter into healthy cells and integrate into their genomes. Genomic integration of cfCh leads to dsDNA breaks and activation of inflammatory cytokines both of which occur concurrently with similar kinetics and that induction of inflammation can be abrogated by preventing DNA breaks with the use of cfCh inactivating agents. The proposal is put forward that inflammatory cytokines are a new family of DDR proteins that are activated following dsDNA breaks inflicted by genomic integration of cfCh.

The Polyphenol Oleuropein Aglycone Modulates the PARP1-SIRT1 Interplay: An In Vitro and In Vivo Study

Poly(ADP-ribose) polymerase-1 (PARP1) activation contributes to the cascade of events initiated by amyloid-β (Aβ) peptide eventually leading to cell death in Alzheimer's disease brain. A significant accumulation of PAR polymers and increase of PARP1 expression were detected in the cortex at the early (3.5 months) and intermediate (6 months) stage of Aβ deposition in the TgCRND8 mouse model. Our previous data highlighted the beneficial effects of oleuropein aglycone (OLE), the main polyphenol found in the olive oil, against neurodegeneration both in cultured cells and in model organisms. Here we found that 8-week OLE treatment (50 mg/kg of diet) to 6-month-old TgCRND8 mice rescued to control values PARP1 activation and the levels of its product, PAR. In N2a neuroblastoma cells, PARP1 activation and PAR formation upon exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were abolished by pretreatment for 24 h with either OLE (100μM) or PARP inhibitors. A significant reduction of the NAD+ content, compared to controls, was found in N2a cells exposed to MNNG (100μM) for 90 min; the latter was slightly attenuated by cell treatment for 24 h with PJ-34 or with OLE. In vitro and in vivo, the OLE-induced reduction of PARP1 activation was paralleled by the overexpression of Sirtuin1 (SIRT1), and, in vivo, by a decrease of NF-κB and the pro-apoptotic marker p53. In N2a cells, we also found that OLE potentiates the MNNG-induced increase of Beclin1 levels. In conclusion, our data show that OLE treatment counteracts neuronal damage through modulation of the PARP1-SIRT1 interplay.

Reciprocal positive selection for weakness - preventing olaparib resistance by inhibiting BRCA2

Human tumor heterogeneity promotes therapeutic failure by increasing the likelihood of resistant cell subpopulations. The PARP-1 inhibitor olaparib is approved for use in BRCA-mutated ovarian cancers but BRCA2-reversion mutations lead to functional homologous recombination repair (HRR) and olaparib resistance. To overcome that resistance and expand use of PARP1 inhibition to cancers with functional HRR, we developed an antisense strategy to render the majority of tumor cells in a population BRCA2-deficient. We predicted that this strategy would render HRR-proficient tumor cells sensitive to olaparib and prevent emergence of resistance in a tumor cell population heterogeneous for HRR proficiency. We report that BRCA2 downregulation sensitized multiple human tumor cell lines (but not non-cancer human kidney cells) to olaparib and, combined with olaparib, increased aneuploidy and chromosomal translocations in human tumor cells. In a mixed HRR-proficient and HRR-deficient cell population, olaparib monotherapy allowed outgrowth of HRR-proficient cells resistant to subsequent olaparib treatment. Combined BRCA2 inhibition and olaparib treatment prevented selection of HRR-proficient cells and inhibited proliferation of the entire population. Treatment with BRCA2 siRNA and olaparib decreased ovarian xenograft growth in mice more effectively than either treatment alone. In vivo use of BRCA2 antisense oligonucleotides may be a viable option to expand clinical use of olaparib and prevent resistance.

Inhibition of the glucocorticoid receptor results in an enhanced miR-99a/100-mediated radiation response in stem-like cells from human prostate cancers

Radiation therapy is a major primary treatment option for both localized early stage prostate cancer, and for advanced, regionally un-resectable, cancer. However, around 30% of patients still experience biochemical recurrence after radiation therapy within 10 years. Thus, identification of better biomarkers and new targets are urgently required to improve current therapeutic strategies. The miR-99 family has been shown to play an important role in the regulation of the DNA damage response, via targeting of the SWI/SNF chromatin remodeling factors, SMARCA5 and SMARCD1 in cell line models. In the present study, we have demonstrated that low expression of miR-99a and miR-100 is present in cell populations which are relatively radiation insensitive, for example in prostate cancer stem cells and in castration-resistant prostate cancer. Additionally, treatment of cells with the synthetic glucocorticoid, Dexamethasone resulted in decreased miR-99a and 100 expression, suggesting a new mechanism of miR-99a and 100 regulation in androgen-independent prostate cells. Strikingly, treatment of prostate cells with the glucocorticoid receptor inhibitor, Mifepristone was found to sensitize prostate cells to radiation by increasing the levels of miR-99a and miR-100. These results qualify the miR99 family as markers of radiation sensitivity and as potential therapeutic targets to improve efficiency of radiotherapy.