Academic literature on the topic 'OGG1 inhibitors'

Abstract Altered oncogene expression in cancer cells causes loss of redox homeostasis resulting in oxidative DNA damage, e.g. 8-oxoguanine (8-oxoG), repaired by base excision repair (BER). PARP1 coordinates BER and relies on the upstream 8-oxoguanine-DNA glycosylase (OGG1) to recognise and excise 8-oxoG. Here we hypothesize that OGG1 may represent an attractive target to exploit reactive oxygen species (ROS) elevation in cancer. Although OGG1 depletion is well tolerated in non-transformed cells, we report here that OGG1 depletion obstructs A3 T-cell lymphoblastic acute leukemia growth in vitro and in vivo, validating OGG1 as a potential anti-cancer target. In line with this hypothesis, we show that OGG1 inhibitors (OGG1i) target a wide range of cancer cells, with a favourable therapeutic index compared to non-transformed cells. Mechanistically, OGG1i and shRNA depletion cause S-phase DNA damage, replication stress and proliferation arrest or cell death, representing a novel mechanistic approach to target cancer. This study adds OGG1 to the list of BER factors, e.g. PARP1, as potential targets for cancer treatment.

The modified guanine base 8-oxoguanine (8-oxoG) is abundantly produced by oxidative stress, can contribute to carcinogenesis, and can be removed from DNA by 8-oxoguanine DNA glycosylase-1 (OGG1), which acts as an 8-oxoG glycosylase and endonuclease. This study investigated the mechanism by which 7,8-dihydroxyflavone (DHF) inhibits oxidative stress-induced 8-oxoG formation in hamster lung fibroblasts (V79-4). DHF significantly reduced the amount of 8-oxoG induced by hydrogen peroxide (H2O2) and elevated the levels of OGG1 mRNA and protein. DHF increased the binding of nuclear factor erythroid 2-related factor 2 (Nrf2) to antioxidant response element sequences in the upstream promoter region of OGG1. Moreover, DHF increased the nuclear levels of Nrf2, small Maf proteins, and the Nrf2/small Maf complex, all of which are decreased by H2O2treatment. Likewise, the level of phosphorylated Akt, which activates Nrf2, was decreased by H2O2treatment but restored by DHF treatment. The levels of OGG1 and nuclear translocation of Nrf2 protein were decreased upon treatment with PI3K inhibitor or Akt inhibitor, and DHF treatment did not restore OGG1 and nuclear Nrf2 levels in these inhibitor-treated cells. Furthermore, PI3K and Akt inhibitors abolished the protective effects of DHF in cells undergoing oxidative stress. These data indicate that DHF induces OGG1 expression via the PI3K-Akt pathway and protects cells against oxidative DNA base damage by activating DNA repair systems.

Cisplatin can induce peripheral neuropathy, which is a common complication of anti-cancer treatment and negatively impacts cancer survivors during and after completion of treatment; therefore, the mechanisms by which cisplatin alters sensory neuronal function to elicit neuropathy are the subject of much investigation. Our previous work suggests that the DNA repair activity of APE1/Ref-1, the rate-limiting enzyme of the base excision repair (BER) pathway, is critical for neuroprotection against cisplatin. A specific role for 8-oxoguanine DNA glycosylase-1 (OGG1), the glycosylase that removes the most common oxidative DNA lesion, and putative coordination of OGG1 with APE1/Ref-1 in sensory neurons, has not been investigated. We investigated whether inhibiting OGG1 glycosylase activity with the small molecule inhibitor, TH5487, and/or APE1/Ref-1 endonuclease activity with APE Repair Inhibitor III would alter the neurotoxic effects of cisplatin in sensory neuronal cultures. Sensory neuron function was assessed by calcitonin gene-related peptide (CGRP) release, as a marker of sensitivity and by neurite outgrowth. Cisplatin altered neuropeptide release in an inverse U-shaped fashion, with low concentrations enhancing and higher concentrations diminishing CGRP release. Pretreatment with BER inhibitors exacerbated the functional effects of cisplatin and enhanced 8oxo-dG and adduct lesions in the presence of cisplatin. Our studies demonstrate that inhibition of OGG1 and APE1 endonuclease activity enhances oxidative DNA damage and exacerbates neurotoxicity, thus limiting oxidative DNA damage in sensory neurons that might alleviate cisplatin-induced neuropathy.

A mucosal oxidative burst is a hallmark response to pollen exposure that promotes allergic inflammatory responses. Reactive species constituents of oxidative stress signal via the modification of cellular molecules including nucleic acids. One of the most abundant forms of oxidative genomic base damage is 8-oxo-7,8-dihydroguanine (8-oxoG), which is removed from DNA by 8-oxoguanine DNA glycosylase 1 (OGG1). OGG1 in complex with 8-oxoG acts as a GDP-GTP exchange factor and induces acute inflammation; however, the mechanism(s) by which OGG1 signaling regulates allergic airway inflammation is not known. Here, we postulate that the OGG1 signaling pathway differentially altered the levels of small regulatory RNAs and increased the expression of T helper 2 (Th2) cytokines in ragweed pollen extract (RWPE)-challenged lungs. To determine this, the lungs of sensitized mice expressing or lacking OGG1 were challenged with RWPE and/or with OGG1’s excision product 8-oxoG. The responses in lungs were assessed by next-generation sequencing, as well as various molecular and histological approaches. The results showed that RWPE challenge induced oxidative burst and damage to DNA and activated OGG1 signaling, resulting in the differential expression of 84 micro-RNAs (miRNAs), which then exacerbated antigen-driven allergic inflammation and histological changes in the lungs. The exogenous administration of the downregulated let-7b-p3 mimetic or inhibitors of upregulated miR-23a or miR-27a decreased eosinophil recruitment and mucus and collagen production via controlling the expression of IL-4, IL-5, and IL-13. Together, these data demonstrate the roles of OGG1 signaling in the regulation of antigen-driven allergic immune responses via differential expression of miRNAs upstream of Th2 cytokines and eosinophils.

Abstract Epstein–Barr virus (EBV) immortalizes human B-lymphocytes and is implicated in the pathogenesis of lymphoid and epithelial cell malignancies. The EBV nuclear antigen (EBNA)-1 induces the accumulation of reactive oxygen species (ROS), which enables B-cell immortalization but causes oxidative DNA damage and triggers antiproliferative DNA damage responses. By comparing pairs of EBV-negative and -positive tumor cell lines we found that, while associated with the accumulation of oxidized nucleotides, EBV carriage promotes the concomitant activation of oxo-dNTP sanitization and purging pathways, including upregulation of the nucleoside triphosphatase mut-T homolog 1 (MTH1) and the DNA glycosylases 8-oxoguanine-glycosylase-1 (OGG1) and mut-Y homolog (MUTYH). Expression of EBNA1 was reversibly associated with transcriptional activation of this cellular response. DNA damage and apoptosis were preferentially induced in EBNA1-positive cell lines by treatment with MTH1 inhibitors, suggesting that virus carriage is linked to enhanced vulnerability to oxidative stress. MTH1, OGG1, and MUTYH were upregulated upon EBV infection in primary B-cells and treatment with MTH1 inhibitors prevented B-cell immortalization. These findings highlight an important role of the cellular antioxidant response in sustaining EBV infection, and suggests that targeting this cellular defense may offer a novel approach to antiviral therapy and could reduce the burden of EBV associated cancer.

Background: The relationship between depression and increased oxidative stress is well known. DNA damage by oxidation factors is an important cause of the aging process in psychiatric disorders. Aims: Owing to the scarcity of human studies and high inconsistencies in studies of the effects of antidepressants on DNA damage, the current study was undertaken to investigate the effects of depression and its treatment on DNA damage. Methods: In a 15-week open-label study of citalopram ( n = 25) and sertraline ( n = 20), levels of DNA damage were measured by comet assay, proinflammatory (Interlukin-6 (IL-6)) and oxidative DNA damage (8-hydroxy-2’-deoxyguanosine (8-OHdG)) markers by ELISA, and gene expression of base excision repair enzymes (8-oxoguanine glycosylase (OGG1) and poly (ADP)-ribose polymerase-1 (PARP1)) by quantitative real-time polymerase chain reaction in healthy control patients ( n = 14), with depression at the baseline and the same patients after week 15. Results: DNA damage, 8-OHdG, IL-6 and expression of PARP1 were elevated in patients with depression compared with the healthy controls ( p < 0.001). Selective serotonin reuptake inhibitor (SSRI) therapy could significantly reduce the depression score ( p < 0.01), DNA damage ( p < 0.001), as well as 8-OHdG and IL-6 ( p < 0.0001). Nevertheless, the expression of PARP1 and OGG1 showed no significant changes after treatment. Conclusions: This is the first study on the effect of SSRIs on the DNA damage and some of the repair enzymes in depression. Based on the results, depression can cause increased DNA damage. This damage is followed by activation of compensatory mechanisms whereby the expression of DNA damage repair enzymes is elevated. Finally, the treatment of psychiatric disorder by antidepressants can lower the level of oxidative DNA damage.

Abstract Abstract 520 Tyrosine kinase inhibitors (TKIs) such as imatinib, dasatinib and nilotinib revolutionized the treatment of BCR-ABL1 kinase-positive chronic myeloid leukemia in chronic phase (CML-CP). Unfortunately, 15–25% of patients initially responding favorably to imatinib will develop acquired drug resistance, which in 40–90% of cases is caused by genomic instability resulting in the appearance of clones expressing TKI resistant BCR-ABL1 kinase mutants. We reported that CML-CP leukemia stem and progenitor cell populations accumulate high amounts of reactive oxygen species (ROS) resulting in excessive oxidative DNA damage such as oxidized DNA bases (8-oxoguanine and 5-hydroxycytosine→uracil) (Nieborowska-Skorska et al., Blood, 2012). Unfaithful and/or inefficient repair of these lesions generates TKI resistant point mutations in BCR-ABL1 kinase. Oxidative DNA lesions may be removed by base excision repair (BER) or, if not removed, will create mismatches, which are repaired by mismatch repair (MMR). Since we found that MMR is inhibited in CML-CP (Stoklosa et al., Cancer Res., 2008), the activity of BER is critical to prevent the accumulation of point mutations. Using an array of specific substrates and inhibitors/blocking antibodies we found that two major glycosylases, uracil-DNA glycosylase UNG2 and 8-oxoguanine glycosylase (OGG1) responsible for the excision of uracil (product of oxidation of cytosine) and 8-oxoguanine (8-oxoG) from DNA, respectively, were inhibited in BCR-ABL1 –transformed cell lines and CD34+ CML cells. The inhibitory effect was even more pronounced in CML blast phase (CML-BP) in comparison to CML-CP, it depended on BCR-ABL1 kinase activity and was not accompanied by deregulation of nuclear expression and/or chromatin association of these glycosylases. The effect was BCR-ABL1 kinase-specific because several other fusion tyrosine kinases such as TEL-ABL1, TEL-PDGFbetaR and NPM-ALK did not reduce UNG2 activity. Using UNG2-specific inhibitor UGI we found that UNG2 activity diminished the number of oxidized DNA bases detected by modified comet assay and prevented accumulation of point mutations in reporter gene Na+/K+ATPase, which encode resistance to ouabain. In conclusion, we hypothesize that inhibition of UNG2 and OGG1, accompanied by reduced MMR activity is responsible for accumulation of TKI-resistant BCR-ABL1 kinase point mutations and perhaps also other point mutations facilitating malignant progression of CML. Disclosures: No relevant conflicts of interest to declare.

Abstract Poly(ADP-ribose) polymerases (PARPs) facilitate the repair of DNA single-strand breaks (SSBs). When PARPs are inhibited, unrepaired SSBs colliding with replication forks give rise to cytotoxic double-strand breaks. These are normally rescued by homologous recombination (HR), but, in cells with suboptimal HR, PARP inhibition leads to genomic instability and cell death, a phenomenon currently exploited in the therapy of ovarian cancers in BRCA1/2 mutation carriers. In spite of their promise, resistance to PARP inhibitors (PARPis) has already emerged. In order to identify the possible underlying causes of the resistance, we set out to identify the endogenous source of DNA damage that activates PARPs. We argued that if the toxicity of PARPis is indeed caused by unrepaired SSBs, these breaks must arise spontaneously, because PARPis are used as single agents. We now show that a significant contributor to PARPi toxicity is oxygen metabolism. While BRCA1-depleted or -mutated cells were hypersensitive to the clinically approved PARPi olaparib, its toxicity was significantly attenuated by depletion of OGG1 or MYH DNA glycosylases, as well as by treatment with reactive oxygen species scavengers, growth under hypoxic conditions or chemical OGG1 inhibition. Thus, clinical resistance to PARPi therapy may emerge simply through reduced efficiency of oxidative damage repair.

OGG1 est une ADN glycosylase de la voie de réparation par excision de base (BER) qui excise spécifiquement la guanine oxydée 8oxoG. La voie BER est bien connue pour son rôle dans la maintenance du génome nucléaire mais elle est également la principale voie de réparation de l'ADN mitochondrial. La déficience de l'activité d'OGG1 entraîne une mutagenèse importante lors de la réplication de l'ADN nucléaire, ce qui n'a pas été détecté au niveau de l'ADNmt. Malgré cela, la déficience d'OGG1 induit une augmentation des ROS mitochondriaux, une perte du potentiel de la membrane mitochondriale et une augmentation des niveaux d'apoptose. Différentes études ont montré une augmentation de l'oxydation de l'ADNmt suite à la déficience en OGG1 et l'ont associée au phénotype mentionné précédemment. Dans le présent travail, nous avons évalué si le défaut de réparation de l'ADN mitochondrial dans les cellules déficientes en OGG1 était à l'origine de la production accrue de ROS mitochondriaux à la suite d'un stress oxydatif. Suite à un stress oxydatif, nous avons détecté une oxydation plus importante de l'ADNmt dans les cellules U2OS OGG1 KO. Grace à l'utilisation de biosenseurs de ROS couplés à la microscopie en temps réel et à la cytométrie en flux, nous avons également pu observer des niveaux de ROS mitochondriaux plus élevés. De manière surprenante, la même expérience réalisée dans des cellules dépourvues d'ADNmt n'a pas modifié la différence de niveaux de ROS entre les cellules WT et les cellules déficientes en OGG1, ce qui suggère que la réparation de l'ADNmt n'est pas responsable des défauts mitochondriaux observés dans les modèles cellulaires déficients en OGG1.Outre son activité de réparation, OGG1 joue un rôle dans la modulation de l'expression des gènes. Suite à un stress oxydatif, les promoteurs de gènes riches en GC, notamment pouvant former des G-quadruplexes, sont oxydés et la liaison d'OGG1 peut activer l'expression des gènes par le recrutement de facteurs de transcription. Nous montrons ici que les niveaux d'ARNm de SIRT3, un des prrincipaux régulateurs de la détoxification des ROS mitochondriaux, sont réduits dans les modèles cellulaires déficients en OGG1 et qu'un mutant d'OGG1 localisé uniquement dans le noyau suffit à rétablir les niveaux de SIRT3. L'analyse du promoteur de SIRT3 a révélé la présence de plusieurs séquences G-quadruplex potentielles (PQS) dans le brin codant. L'inhibition de SIRT3 ou d'OGG1 entraîne une augmentation des niveaux de ROS mitochondriaux et de l'expression du facteur de transcription FOXO3A et de SOD2, impliqués dans la détoxification des ROS. L'ensemble de ces résultats suggère un rôle nucléaire d'OGG1 dans la régulation des voies de détoxification des ROS mitochondriaux. Nos résultats montrent que SIRT3 module également les niveaux d'expression d'OGG1 et que les deux protéines jouent un rôle majeur dans le devenir cellulaire. Nous avons observé plusieurs caractéristiques de cellules sénescentes (forme cellulaire, morphologie mitochondriale, niveaux de P21) après une dépletion de SIRT3 qui dépendent de la présence d'OGG1 puisqu'elles sont abolies lors de la co-déplétion de SIRT3 et OGG1 et la réexpression d'OGG1 est suffisante pour les restaurer. Le rôle d'OGG1 dans l'expression des gènes, la modulation de l'inflammation et le cancer en font une cible intéressante pour plusieurs applications thérapeutiques. Des inhibiteurs et des activateurs d'OGG1 ont été récemment développés. Cependant, dans ce travail, nous avons identifié d'importants effets hors cible des inhibiteurs compétitifs d'OGG1 TH5478 et SU0268. Les deux molécules inhibent les pompes d'efflux de la famille ABC à un niveau comparable aux inhibiteurs spécifiques. L'inhibition des pompes d'efflux a été associée à une toxicité élevée, ce qui limite l'utilisation thérapeutique de ces molécules. Il est donc indispensable d'explorer d'autres stratégies afin de développer des inhibiteurs plus spécifiques d'OGG1
OGG1 is a DNA glycosylase from the base excision repair (BER) pathway that specifically excises the oxidized guanine 8oxoG. Besides being active in the nuclear compartment, BER is also the main mitochondrial DNA repair pathway. Deficiency of OGG1 repair activity results in higher mutagenesis following DNA replication in nuclear DNA that has not been detected at the level of mtDNA. Despite that, deficiency of OGG1 results in increased mitochondrial ROS, loss of mitochondrial membrane potential and increased apoptosis levels. Different studies have shown increased mtDNA oxidation following OGG1 deficiency and linked it to the phenotype previously mentioned. In the present work, we evaluated if the mtDNA repair activity of OGG1 is causally involved in higher mitochondrial ROS production following oxidative stress. Following oxidative stress, we detected higher mtDNA oxidation in U2OS OGG1 KO cells. Moreover, by using sensitive ROS biosensors coupled to live time imaging and cytofluorimetry analysis, we could also observe higher mitochondrial ROS levels. Surprisingly, the same experiment carried in cells devoided of mtDNA did not alter the differential in ROS levels between WT and OGG1 deficient cells, suggesting that mtDNA repair is not responsible of higher mitochondrial ROS production observed in OGG1 deficient cell models. Beside its repair activity, OGG1 has a non-canonical role in modulating gene expression. Following oxidative stress, gene promoters rich in GC content are oxidized and the binding of OGG1 can activate gene expression by the recruitment of transcription factors. We show here that the RNA levels of the main regulator of the mitochondrial ROS detoxification pathway, SIRT3, are reduced in OGG1 deficient cell models and that a mutant of OGG1 localising only in the nucleus is enough to rescue normal SIRT3 levels. SIRT3 promoter presents several potential G-quadruplex sequences (PQS) in the coding strand. The binding of OGG1 to oxidized PQS has already been proposed to modulate gene expression for several promoters. Silencing of SIRT3 or OGG1 results in increased mitochondrial ROS levels and expression of oxidative stress responsive transcription factor FOXO3A that upregulates the ROS scavenger SOD2. Together, these results suggest that a nuclear role of OGG1 modulates ROS detoxifying pathways to impact mitochondrial functions. Our results show that SIRT3 also modulates OGG1 expression levels and that both proteins play a major role in cell fate determination. We observed several characteristics of senescent cells (cell shape, mitochondrial morphology, P21 levels) after SIRT3 depletion, which depend on the presence of OGG1, as these characteristics are abolished when both SIRT3 and OGG1 are co-depleted, and the re-expression of OGG1 is sufficient to restore them.OGG1 role in gene expression and its role in modulating inflammation and cancer cell physiology makes of it an interesting target for several therapeutical applications. OGG1 inhibitors and activators have been recently developed. However, in this work, we have identified important off-target effects of two different OGG1 competitive inhibitors, TH5478 and SU0268. Both molecules carry inhibitory activity on efflux pumps of the ABC family at a level comparable to specific inhibitors. The inhibition of efflux pumps has been associated to high toxicity and therefore limits the therapeutical use of those molecules. Our work, suggests that the design of new OGG1 competitive inhibitors should take into account the ABC efflux pump structure and that different approaches to inhibit OGG1 should also be explored

L’ADN de tout organisme est continuellement endommagé par des agents physiques ou chimiques d’origines endogène ou exogène. Les dommages de l’ADN qui en résultent peuvent être à l’origine de l’apparition de mutations ou de mort cellulaire. Pour pallier à ces effets délétères, les organismes ont développé des systèmes de réparation de l’ADN. Le système de réparation par excision de base (BER) est la voie majeure de réparation des bases endommagées et est initié par des ADN glycosylases telles que hOGG1 et hNEIL1. Ces enzymes reconnaissent spécifiquement les bases lésées et les éliminent. Paradoxalement, les réparations initiées par ces protéines peuvent diminuer l’effet thérapeutique de certains traitements, notamment anti-cancéreux. En exploitant le principe de létalité synthétique, le ciblage thérapeutique de hOGG1 et hNEIL1 pourrait être pertinent pour lutter contre certains cancers, mais aussi contre des maladies neurodégénératives (Huntington) ou des processus inflammatoires pathologiques. Au travers du criblage « moyen débit » de banques de petites molécules naturelles ou synthétiques, mon travail de thèse a consisté en l’identification de nouveaux inhibiteurs sélectifs de hNEIL1 et hOGG1 et en la caractérisation de leur mode d’action par des études biochimiques et structurales. Si nous avons pu mettre en lumière des fonctions chimiques essentielles et quelques déterminants structuraux et fonctionnels relatifs à leurs modes d’action, de nombreuses zones d’ombre demeurent et mériterons d’être explorés dans le futur. En revanche, l’utilisation d’un homologue archéen de hOGG1, l’enzyme PabAGOG, a permis de proposer un modèle tridimensionnel cohérent d’un complexe hOGG1/inhibiteur pour l’un des meilleurs inhibiteurs que nous avons identifiés. Finalement, ces nouveaux composés comptent parmi les meilleurs inhibiteurs de hOGG1 et hNEIL1 identifiés à ce jour et certains d’entre eux devraient bénéficier d’une évaluation in cellulo
DNA is continuously damaged by physical or chemical agents from endogenous or exogenous sources. These damages can induce mutation or cell death. To counteract these deleterious effects, organisms have developed DNA repair systems. The Base Excision Repair System (BER) is the major pathway to repair damaged bases. It is initiated by DNA Glycosylases such as hNEIL1 and hOGG1 which specifically recognize and remove oxidized bases. However, in some situation like conventional cancer treatment, the repairs initiated by these enzymes can lead to therapeutic resistance. Therefore, based on the synthetic lethality concept, selective inhibition of hNEIL1 and hOGG1 could be relevant in some pathologic contexts like cancer, but also against neurodegenerative diseases (Huntington) or pathological inflammatory processes. This thesis work aimed to identify new selective inhibitors of hNEIL1 and hOGG1 with a "medium throughput" screening of natural or synthetic small molecule libraries, and to characterize their mode of action through biochemical and structural studies. Although we identified some essentials chemicals functions and some leads to understand the action mode of our inhibitors, many areas remains unveiled and deserve to be explored in the future. However, the use of an archaeal homologue of hOGG1, the enzyme PabAGOG, has allowed us to propose a coherent three-dimensional model of an hOGG1/inhibitor complex for one of the best inhibitors we have identified. Finally, these new inhibitors are among the best inhibitors of hOGG1 and hNEIL1 identified to date and some of them will undergo in cellulo evaluation