Inhibition of poly(ADP-ribose) polymerase interferes with Trypanosoma cruzi infection and proliferation of the parasite

Novel anti-Acanthamoeba effects elicited by a repurposed poly (ADP-ribose) polymerase inhibitor AZ9482

Introduction

Acanthamoeba infection is a serious public health concern, necessitating the development of effective and safe anti-Acanthamoeba chemotherapies. Poly (ADP-ribose) polymerases (PARPs) govern a colossal amount of biological processes, such as DNA damage repair, protein degradation and apoptosis. Multiple PARP-targeted compounds have been approved for cancer treatment. However, repurposing of PARP inhibitors to treat Acanthamoeba is poorly understood.

Methods

In the present study, we attempted to fill these knowledge gaps by performing anti-Acanthamoeba efficacy assays, cell biology experiments, bioinformatics, and transcriptomic analyses.

Results

Using a homology model of Acanthamoeba poly (ADP-ribose) polymerases (PARPs), molecular docking of approved drugs revealed three potential inhibitory compounds: olaparib, venadaparib and AZ9482. In particular, venadaparib exhibited superior docking scores (-13.71) and favorable predicted binding free energy (-89.28 kcal/mol), followed by AZ9482, which showed a docking score of -13.20 and a binding free energy of -92.13 kcal/mol. Notably, the positively charged cyclopropylamine in venadaparib established a salt bridge (through E535) and a hydrogen bond (via N531) within the binding pocket. For comparison, AZ9482 was well stacked by the surrounding aromatic residues including H625, Y652, Y659 and Y670. In an assessment of trophozoites viability, AZ9482 exhibited a dose-and time-dependent anti-trophozoite effect by suppressing Acanthamoeba PARP activity, unlike olaparib and venadaparib. An Annexin V-fluorescein isothiocyanate/propidium iodide apoptosis assay revealed AZ9482 induced trophozoite necrotic cell death rather than apoptosis. Transcriptomics analyses conducted on Acanthamoeba trophozoites treated with AZ9482 demonstrated an atlas of differentially regulated proteins and genes, and found that AZ9482 rapidly upregulates a multitude of DNA damage repair pathways in trophozoites, and intriguingly downregulates several virulent genes. Analyzing gene expression related to DNA damage repair pathway and the rate of apurinic/apyrimidinic (AP) sites indicated DNA damage efficacy and repair modulation in Acanthamoeba trophozoites following AZ9482 treatment.

Discussion

Collectively, these findings highlight AZ9482, as a structurally unique PARP inhibitor, provides a promising prototype for advancing anti-Acanthamoeba drug research.

Trypanosoma cruzi PARP is enriched in the nucleolus and is present in a thread connecting nuclei during mitosis

Poly (ADP-ribose) polymerase (PARP) is responsible for the synthesis of ADP-ribose polymers, which are involved in a wide range of cellular processes such as preservation of genome integrity, DNA damage signaling and repair, molecular switches between distinct cell death pathways, and cell cycle progression. Previously, we demonstrated that the only PARP present in T. cruzi migrates to the nucleus upon genotoxic stimulus. In this work, we identify the N-terminal domain as being sufficient for TcPARP nuclear localization and describe for the first time that TcPARP is enriched in the parasite's nucleolus. We also describe that TcPARP is present in a thread-like structure that connects two dividing nuclei and co-localizes with nucleolar material and microtubules. Furthermore, ADP-ribose polymers could also be detected in this thread during mitosis. These findings represent a first approach to new potential TcPARP functions inside the nucleus and will help understand its role well beyond the largely described DNA damage response protein in trypanosomatids.

In Silico Investigation of Conserved miRNAs and Their Targets From the Expressed Sequence Tags in Neospora Caninum Genome

Neospora caninum is a protozoan parasite, the etiologic agent of Neosporosis—a common cause of abortion in cattle worldwide. Herd level prevalence of Neosporosis could be as high as 90%. However, there is no approved treatment and vaccines available for Neosporosis. MicroRNA (miRNA) based prophylaxis and therapeutics could be options for Neosporosis in cattle and other animals. The current study aimed to investigate the genome of Neospora caninum to identify and characterize the conserved miRNAs through Expressed Sequence Tags (ESTs) dependent homology search. A total of 1,041 mature miRNAs of reference organisms were employed against 336 non-redundant ESTs available in the genome of Neospora caninum. The study predicted one putative miRNA “nca-miR-9388-5p” of 19 nucleotides with MFEI value -1.51 kcal/mol and (A + U) content% 72.94% corresponding with its pre-miRNA. A comprehensive search for specific gene targets was performed and discovered 16 potential genes associated with different protozoal physiological functions. Significantly, the gene “Protein phosphatase” was found responsible for the virulence of Neospora caninum. The other genes were accounted for gene expression, vesicular transport, cell signaling, cell proliferation, DNA repair mechanism, and different developmental stages of the protozoon. Therefore, this study finding will provide pivotal information to future aspirants upon Bovine Neosporosis. It will also serve as the baseline information for further studies of the bioinformatics approach to identify other protozoal miRNAs.

Tankyrase inhibitors hinder Trypanosoma cruzi infection by altering host-cell signalling pathways

Chagas disease is a potentially life-threatening protozoan infection affecting around 8 million people, for which only chemotherapies with limited efficacy and severe adverse secondary effects are available. The aetiological agent, Trypanosoma cruzi, displays varied cell invading tactics and triggers different host cell signals, including the Wnt/β-catenin pathway. Poly(ADP-ribose) (PAR) can be synthetized by certain members of the poly(ADP-ribose) polymerase (PARP) family: PARP-1/-2 and Tankyrases-1/2 (TNKS). PAR homoeostasis participates in the host cell response to T. cruzi infection and TNKS are involved in Wnt signalling, among other pathways. Therefore, we hypothesized that TNKS inhibitors (TNKSi) could hamper T. cruzi infection. We showed that five TNKSi (FLALL9, MN64, XAV939, G007LK and OULL9) diminished T. cruzi infection of Vero cells. As most TNKSi did not affect the viability of axenically cultivated parasites, our results suggested that TNKSi were interfering with parasite–host cell signalling. Infection by T. cruzi induced nuclear translocation of β-catenin, as well as upregulation of TNF-α expression and secretion. These changes were hampered by TNKSi. Further signals should be monitored in this model and in vivo. As a TNKSi has entered cancer clinical trials with promising results, our findings encourage further studies aiming at drug repurposing strategies.

PARP Inhibitor Olaparib Causes No Potentiation of the Bleomycin Effect in VERO Cells, Even in the Presence of Pooled ATM, DNA-PK, and LigIV Inhibitors

Poly(ADP-ribosyl)polymerase (PARP) synthesizes poly(ADP-ribose) (PAR), which is anchored to proteins. PAR facilitates multiprotein complexes' assembly. Nuclear PAR affects chromatin's structure and functions, including transcriptional regulation. In response to stress, particularly genotoxic stress, PARP activation facilitates DNA damage repair. The PARP inhibitor Olaparib (OLA) displays synthetic lethality with mutated homologous recombination proteins (BRCA-1/2), base excision repair proteins (XRCC1, Polβ), and canonical nonhomologous end joining (LigIV). However, the limits of synthetic lethality are not clear. On one hand, it is unknown whether any limiting factor of homologous recombination can be a synthetic PARP lethality partner. On the other hand, some BRCA-mutated patients are not responsive to OLA for still unknown reasons. In an effort to help delineate the boundaries of synthetic lethality, we have induced DNA damage in VERO cells with the radiomimetic chemotherapeutic agent bleomycin (BLEO). A VERO subpopulation was resistant to BLEO, BLEO + OLA, and BLEO + OLA + ATM inhibitor KU55933 + DNA-PK inhibitor KU-0060648 + LigIV inhibitor SCR7 pyrazine. Regarding the mechanism(s) behind the resistance and lack of synthetic lethality, some hypotheses have been discarded and alternative hypotheses are suggested.

Poly(ADP-ribose) metabolism in human parasitic protozoa

Poly(ADP-ribosyl)ation reactions constitute a post-translational protein modification synthesized in higher eukaryotes by a family of poly(ADP-ribose)polymerases (PARP) and catabolized mainly by poly(ADP-ribose) glycohydrolase (PARG). The best understood role of PARP is the maintenance of genomic integrity via the promotion of DNA repair that leads to cell survival when low levels of genotoxic stress occur. The participation of PARP in unleashing cell death at higher levels of damage has also been broadly studied. The biology of poly(ADP-ribosyl)ation in protozoan parasites, however, still remains a mystery. This review will examine the presence of the key enzyme involved in ADP-ribose polymer (PAR) metabolism in protozoan parasites associated with human diseases. Theoretical and experimental data obtained up to date have revealed the presence of PAR metabolism only in the trypanosomatids Trypanosoma cruzi and T. brucei, the apicomplexan Toxoplasma gondii and Entamoeba histolytica. T. cruzi and T. brucei, as opposed to humans and other organisms, have only one PARP and one PARG with subcellular localizations that are distinct from the ones described for their mammalian counterparts. The topics discussed in this review describe the first studies on PAR metabolism in trypanosomatids, specially the role of PAR on DNA damage response, cell cycle progression and cell death after genotoxic stimuli. The results described show differences in some aspects of PAR metabolism in trypanosomatids in comparison to other eukaryotes. New questions about the function of this metabolic pathway in the parasites under study are open and we hope it encourages the research community to explore this signaling pathway as a new possible target of clinical relevance in these and other disease-causing parasites.

Mechanisms of DNA repair in Trypanosoma cruzi: What do we know so far?

Trypanosoma cruzi is the etiological agent of Chagas Disease, which affects 6-7 million people worldwide. Since the early stages of infection and throughout its life cycle, the parasite is exposed to several genotoxic agents. Furthermore, DNA damage is also part of the mechanism of action of at least a few trypanocidal drugs, including Benznidazole. Thus, it is paramount for the parasite to count on an efficient DNA repair machinery to guarantee genome integrity and survival. The present work provides an up-to-date review of both the conserved and peculiar DNA repair mechanisms described in T. cruzi against oxidative stress, ultraviolet and ionizing radiation, DNA adduct-inducing agents, and Benznidazole. The comprehension of the DNA repair mechanisms of the parasite may shed light on the parasite evolution and possibly pave the way for the development of novel and more effective trypanocidal drugs.

Host NAD+ metabolism and infections: therapeutic implications

Nicotinamide adenine dinucleotide (NAD+) is both a crucial coenzyme and a cosubstrate for various metabolic reactions in all living cells. Maintenance of NAD+ levels is essential for cell energy homeostasis, survival, proliferation and function. Mounting evidence points to NAD+ as one of the major modulators of immuno-metabolic circuits, thus regulating immune responses and functions. Recent studies delineate impaired host NAD+ metabolism during chronic infections and inflammation, suggesting NAD+ replenishment as an avenue to ameliorate deleterious inflammatory responses. Here, we discuss aspects of NAD+ biosynthesis and consumption, NAD+ biology during infections and how NAD+ metabolism can be intervened with pharmacologically to enhance the host's immunological fitness against pathogens.

Genome-wide and protein kinase-focused RNAi screens reveal conserved and novel damage response pathways in Trypanosoma brucei

All cells are subject to structural damage that must be addressed for continued growth. A wide range of damage affects the genome, meaning multiple pathways have evolved to repair or bypass the resulting DNA lesions. Though many repair pathways are conserved, their presence or function can reflect the life style of individual organisms. To identify genome maintenance pathways in a divergent eukaryote and important parasite, Trypanosoma brucei, we performed RNAi screens to identify genes important for survival following exposure to the alkylating agent methyl methanesulphonate. Amongst a cohort of broadly conserved and, therefore, early evolved repair pathways, we reveal multiple activities not so far examined functionally in T. brucei, including DNA polymerases, DNA helicases and chromatin factors. In addition, the screens reveal Trypanosoma- or kinetoplastid-specific repair-associated activities. We also provide focused analyses of repair-associated protein kinases and show that loss of at least nine, and potentially as many as 30 protein kinases, including a nuclear aurora kinase, sensitises T. brucei to alkylation damage. Our results demonstrate the potential for synthetic lethal genome-wide screening of gene function in T. brucei and provide an evolutionary perspective on the repair pathways that underpin effective responses to damage, with particular relevance for related kinetoplastid pathogens. By revealing that a large number of diverse T. brucei protein kinases act in the response to damage, we expand the range of eukaryotic signalling factors implicated in genome maintenance activities.

Damage to the genome is a universal threat to life. Though the repair pathways used to tackle damage can be widely conserved, lineage-specific specialisations are found, reflecting the differing life styles of extant organisms. Using RNAi coupled with next generation sequencing we have screened for genes that are important for growth of Trypanosoma brucei, a diverged eukaryotic microbe and important parasite, in the presence of alkylation damage caused by methyl methanesulphonate. We reveal both repair pathway conservation relative to characterised eukaryotes and specialisation, including uncharacterised roles for translesion DNA polymerases, DNA helicases and chromatin factors. Furthermore, we demonstrate that loss of around 15% of T. brucei protein kinases sensitises the parasites to alkylation, indicating phosphorylation signalling plays widespread and under-investigated roles in the damage response pathways of eukaryotes.

Structural and Biochemical Characterization of Poly-ADP-ribose Polymerase from Trypanosoma brucei

Trypanosoma brucei is a unicellular parasite responsible for African trypanosomiasis or sleeping sickness. It contains a single PARP enzyme opposed to many higher eukaryotes, which have numerous PARPs. PARPs are responsible for a post-translational modification, ADP-ribosylation, regulating a multitude of cellular events. T. brucei PARP, like human PARPs-1-3, is activated by DNA binding and it potentially functions in DNA repair processes. Here we characterized activation requirements, structure and subcellular localization of T. brucei PARP. T. brucei PARP was found to be selectively activated by 5′ phosphorylated and 3′ phosphorylated DNA breaks. Importantly, the N-terminal region is responsible for high-affinity DNA-binding and required for DNA-dependent enzymatic activation. This module is also required for nuclear localization of the protein in response to oxidative stress. Solution structures of activating and non-activating PARP-DNA complexes were determined with small-angle X-ray scattering revealing distinct differences in their DNA-binding modes.

Proximal ADP-ribose Hydrolysis in Trypanosomatids is Catalyzed by a Macrodomain

ADP-ribosylation is a ubiquitous protein modification utilized by both prokaryotes and eukaryotes for several cellular functions, such as DNA repair, proliferation, and cell signaling. Higher eukaryotes, such as humans, utilize various enzymes to reverse the modification and to regulate ADP-ribose dependent signaling. In contrast, some lower eukaryotes, including trypanosomatids, lack many of these enzymes and therefore have a much more simplified ADP-ribose metabolism. Here we identified and characterized ADP-ribose hydrolases from Trypanosoma brucei and Trypanosoma cruzi, which are homologous to human O-acetyl-ADP-ribose deacetylases MacroD1 and MacroD2. The enzymes are capable for hydrolysis of protein linked ADP-ribose and a product of sirtuin-mediated lysine deacetylation, O-acetyl-ADP-ribose. Crystal structures of the trypanosomatid macrodomains revealed a conserved catalytic site with distinct differences to human MacroD1 and MacroD2.

Disrupted ADP-ribose metabolism with nuclear Poly (ADP-ribose) accumulation leads to different cell death pathways in presence of hydrogen peroxide in procyclic Trypanosoma brucei

BACKGROUND

Poly(ADP-ribose) (PAR) metabolism participates in several biological processes such as DNA damage signaling and repair, which is a thoroughly studied function. PAR is synthesized by Poly(ADP-ribose) polymerase (PARP) and hydrolyzed by Poly(ADP-ribose) glycohydrolase (PARG). In contrast to human and other higher eukaryotes, Trypanosoma brucei contains only one PARP and PARG. Up to date, the function of these enzymes has remained elusive in this parasite. The aim of this work is to unravel the role that PAR plays in genotoxic stress response.

METHODS

The optimal conditions for the activity of purified recombinant TbPARP were determined by using a fluorometric activity assay followed by screening of PARP inhibitors. Sensitivity to a genotoxic agent, H2O2, was assessed by counting motile parasites over the total number in a Neubauer chamber, in presence of a potent PARP inhibitor as well as in procyclic transgenic lines which either down-regulate PARP or PARG, or over-express PARP. Triplicates were carried out for each condition tested and data significance was assessed with two-way Anova followed by Bonferroni test. Finally, PAR influence was studied in cell death pathways by flow cytometry.

RESULTS

Abolition of a functional PARP either by using potent inhibitors present or in PARP-silenced parasites had no effect on parasite growth in culture; however, PARP-inhibited and PARP down-regulated parasites presented an increased resistance against H2O2 treatment when compared to their wild type counterparts. PARP over-expressing and PARG-silenced parasites displayed polymer accumulation in the nucleus and, as expected, showed diminished resistance when exposed to the same genotoxic stimulus. Indeed, they suffered a necrotic death pathway, while an apoptosis-like mechanism was observed in control cultures. Surprisingly, PARP migrated to the nucleus and synthesized PAR only after a genomic stress in wild type parasites while PARG occurred always in this organelle.

CONCLUSIONS

PARP over-expressing and PARG-silenced cells presented PAR accumulation in the nucleus, even in absence of oxidative stress. Procyclic death pathway after genotoxic damage depends on basal nuclear PAR. This evidence demonstrates that the polymer may have a toxic action by itself since the consequences of an exacerbated PARP activity cannot fully explain the increment in sensitivity observed here. Moreover, the unusual localization of PARP and PARG would reveal a novel regulatory mechanism, making them invaluable model systems.

VERO cells harbor a poly-ADP-ribose belt partnering their epithelial adhesion belt

Poly-ADP-ribose (PAR) is a polymer of up to 400 ADP-ribose units synthesized by poly-ADP-ribose-polymerases (PARPs) and degraded by poly-ADP-ribose-glycohydrolase (PARG). Nuclear PAR modulates chromatin compaction, affecting nuclear functions (gene expression, DNA repair). Diverse defined PARP cytoplasmic allocation patterns contrast with the yet still imprecise PAR distribution and still unclear functions. Based on previous evidence from other models, we hypothesized that PAR could be present in epithelial cells where cadherin-based adherens junctions are linked with the actin cytoskeleton (constituting the adhesion belt). In the present work, we have examined through immunofluorescence and confocal microscopy, the subcellular localization of PAR in an epithelial monkey kidney cell line (VERO). PAR was distinguished colocalizing with actin and vinculin in the epithelial belt, a location that has not been previously reported. Actin filaments disruption with cytochalasin D was paralleled by PAR belt disruption. Conversely, PARP inhibitors 3-aminobenzamide, PJ34 or XAV 939, affected PAR belt synthesis, actin distribution, cell shape and adhesion. Extracellular calcium chelation displayed similar effects. Our results demonstrate the existence of PAR in a novel subcellular localization. An initial interpretation of all the available evidence points towards TNKS-1 as the most probable PAR belt architect, although TNKS-2 involvement cannot be discarded. Forthcoming research will test this hypothesis as well as explore the existence of the PAR belt in other epithelial cells and deepen into its functional implications.

DNA repair pathways in trypanosomatids: from DNA repair to drug resistance

All living organisms are continuously faced with endogenous or exogenous stress conditions affecting genome stability. DNA repair pathways act as a defense mechanism, which is essential to maintain DNA integrity. There is much to learn about the regulation and functions of these mechanisms, not only in human cells but also equally in divergent organisms. In trypanosomatids, DNA repair pathways protect the genome against mutations but also act as an adaptive mechanism to promote drug resistance. In this review, we scrutinize the molecular mechanisms and DNA repair pathways which are conserved in trypanosomatids. The recent advances made by the genome consortiums reveal the complete genomic sequences of several pathogens. Therefore, using bioinformatics and genomic sequences, we analyze the conservation of DNA repair proteins and their key protein motifs in trypanosomatids. We thus present a comprehensive view of DNA repair processes in trypanosomatids at the crossroads of DNA repair and drug resistance.

Mammalian cellular culture models of Trypanosoma cruzi infection: a review of the published literature

Cellular culture infection with Trypanosoma cruzi is a tool used to dissect the biological mechanisms behind Chagas disease as well as to screen potential trypanocidal compounds. Data on these models are highly heterogeneous, which represents a challenge when attempting to compare different studies. The purpose of this review is to provide an overview of the cell culture infectivity assays performed to date. Scientific journal databases were searched for articles in which cultured cells were infected with any Trypanosoma cruzi strain or isolate regardless of the study’s goal. From these articles the cell type, parasite genotype, culture conditions and infectivity results were extracted. This review represents an initial step toward the unification of infectivity model data. Important differences were detected when comparing the pathophysiology of Chagas disease with the experimental conditions used in the analyzed studies. While Trypanosoma cruzi preferentially infects stromal cells in vivo, most of the assays employ epithelial cell lines. Furthermore, the most commonly used parasite strain (Tulahuen-TcVI) is associated with chagasic cardiomyopathy only in the Southern Cone of South America. Suggestions to overcome these discrepancies include the use of stromal cell lines and parasite genotypes associated with the known characteristics of the natural history of Chagas disease.

NLRP3 controls Trypanosoma cruzi infection through a caspase-1-dependent IL-1R-independent NO production

Trypanosoma cruzi (T. cruzi) is an intracellular protozoan parasite and the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people worldwide. Although the role of TLR and Nod1 in the control of T. cruzi infection is well-established, the involvement of inflammasomes remains to be elucidated. Herein, we demonstrate for the first time that T. cruzi infection induces IL-1β production in an NLRP3- and caspase-1-dependent manner. Cathepsin B appears to be required for NLRP3 activation in response to infection with T. cruzi, as pharmacological inhibition of cathepsin B abrogates IL-1β secretion. NLRP3^−/− and caspase1^−/− mice exhibited high numbers of T. cruzi parasites, with a magnitude of peak parasitemia comparable to MyD88^−/− and iNOS^−/− mice (which are susceptible models for T. cruzi infection), indicating the involvement of NLRP3 inflammasome in the control of the acute phase of T. cruzi infection. Although the inflammatory cytokines IL-6 and IFN-γ were found in spleen cells from NLRP3^−/− and caspase1^−/− mice infected with T. cruzi, these mice exhibited severe defects in nitric oxide (NO) production and an impairment in macrophage-mediated parasite killing. Interestingly, neutralization of IL-1β and IL-18, and IL-1R genetic deficiency demonstrate that these cytokines have a minor effect on NO secretion and the capacity of macrophages to control T. cruzi infection. In contrast, inhibition of caspase-1 with z-YVAD-fmk abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− and caspase-1^−/− macrophages. Taken together, our results demonstrate a role for the NLRP3 inflammasome in the control of T. cruzi infection and identify NLRP3-mediated, caspase-1-dependent and IL-1R-independent NO production as a novel effector mechanism for these innate receptors.

Inflammasomes are cytosolic innate receptors that are emerging as central effectors in the control of infections and inflammatory pathologies. NLRP3 is the most studied member of inflammasomes with established role in the control of bacterial and viral infections. This manuscript describes original studies on the involvement of NLRP3 inflammasome in the control of Trypanosoma cruzi, the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people in the world. T. cruzi activates NLRP3 inflammasome by a mechanism involving cathepsin B. NLRP3^−/− and caspase1^−/− mice display high parasitemia during acute phase of T. cruzi infection, which could be explained by a severe defect in the production of nitric oxide (NO) and in the impairment of their macrophages to control intracellular parasites. Interestingly, inhibition of caspase-1, but not the neutralization of IL-1β and IL-18, the best-studied caspase-1 substrates, abrogated NO production by WT and MyD88^−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3^−/− macrophages. Together, our results indicate a caspase-1-dependent and IL-1β and IL-18-independent pathway for NO production as a new effector mechanism played by NLRP3 to control T. cruzi infection.

The toxicity of nitrofuran compounds on melanoma and neuroblastoma cells is enhanced by Olaparib and ameliorated by melanin pigment

Nitrofurans are commonly used for the treatment of trypanosomal diseases including Chagas disease. More recently, following the fortuitous discovery that nifurtimox was clinically active against neuroblastoma, nitrofuran compounds are being investigated for activity against cancer. Herein, we show that nitrofuran compounds are similarly potent to human malignant melanoma and neuroblastoma cells. Furthermore, a recently discovered nitrofuran compound, NFN1, was 50- to 175-fold more potent than nifurtimox against human melanoma and neuroblastoma cell lines. As nitrofuran compounds are known to act as pro-drugs, producing DNA-damaging reactive intermediates upon activation, we investigated the DNA repair pathways involved. We show that, contrary to research in Escherichia coli, the Nucleotide Excision Repair pathway is not required to repair nitrofuran-induced DNA damage in mammalian cells. Instead, we show that inhibiting repair of single-strand DNA breaks with the poly(ADP-ribose) polymerase (PARP) inhibitor, Olaparib, enhances nitrofuran toxicity in melanoma and neuroblastoma cells. We propose that this is due to mammalian cells utilising Type 2 nitroreductases for nitrofuran activation producing Reactive Oxygen Species which cause DNA damage that is repaired by the Single Strand Break Repair and/or Base Excision Repair pathways, whereas in bacteria and trypanosomes, Type 1 nitroreductases are also utilised resulting in different DNA lesions. In addition we show that, consistent with Reactive Oxygen Species being formed upon nitrofuran activation and the ability of melanin to absorb Reactive Oxygen Species, production of melanin in melanoma cells offers some protection from NFN1- and hydrogen peroxide-induced toxicity. Our data suggest that combinations of Olaparib and nitrofuran compounds may be advantageous for the treatment of melanoma and neuroblastoma, but that the protection offered to melanoma cells by their melanin pigment must be taken into account.

Host cell poly(ADP-ribose) glycohydrolase is crucial for Trypanosoma cruzi infection cycle

Trypanosoma cruzi, etiological agent of Chagas’ disease, has a complex life cycle which involves the invasion of mammalian host cells, differentiation and intracellular replication. Here we report the first insights into the biological role of a poly(ADP-ribose) glycohydrolase in a trypanosomatid (TcPARG). In silico analysis of the TcPARG gene pointed out the conservation of key residues involved in the catalytic process and, by Western blot, we demonstrated that it is expressed in a life stage-dependant manner. Indirect immunofluorescence assays and electron microscopy using an anti-TcPARG antibody showed that this enzyme is localized in the nucleus independently of the presence of DNA damage or cell cycle stage. The addition of poly(ADP-ribose) glycohydrolase inhibitors ADP-HPD (adenosine diphosphate (hydroxymethyl) pyrrolidinediol) or DEA (6,9-diamino-2-ethoxyacridine lactate monohydrate) to the culture media, both at a 1 µM concentration, reduced in vitro epimastigote growth by 35% and 37% respectively, when compared to control cultures. We also showed that ADP-HPD 1 µM can lead to an alteration in the progression of the cell cycle in hydroxyurea synchronized cultures of T. cruzi epimastigotes. Outstandingly, here we demonstrate that the lack of poly(ADP-ribose) glycohydrolase activity in Vero and A549 host cells, achieved by chemical inhibition or iRNA, produces the reduction of the percentage of infected cells as well as the number of amastigotes per cell and trypomastigotes released, leading to a nearly complete abrogation of the infection process. We conclude that both, T. cruzi and the host, poly(ADP-ribose) glycohydrolase activities are important players in the life cycle of Trypanosoma cruzi, emerging as a promising therapeutic target for the treatment of Chagas’ disease.