Overexpression of enzymes that repair endogenous damage to DNA

C. elegans as a model to study mitochondrial biology and disease

Mitochondria perform a myriad of essential functions that ensure organismal homeostasis, including maintaining bioenergetic capacity, sensing and signalling the presence of pathogenic threats, and determining cell fate. Their function is highly dependent on mitochondrial quality control and the appropriate regulation of mitochondrial size, shape, and distribution during an entire lifetime, as well as their inheritance across generations. The roundworm Caenorhabditis elegans has emerged as an ideal model organism through which to study mitochondria. The remarkable conservation of mitochondrial biology has allowed C. elegans researchers to investigate complex processes that are challenging to study in higher organisms. In this review, we explore the key recent contributions of C. elegans to mitochondrial biology through the lens of mitochondrial dynamics, organellar removal, and mitochondrial inheritance, as well as their involvement in immune responses, various types of stress, and transgenerational signalling.

Horizontal acquisition of a DNA ligase improves DNA damage tolerance in eukaryotes

Bdelloid rotifers are part of the restricted circle of multicellular animals that can withstand a wide range of genotoxic stresses at any stage of their life cycle. In this study, bdelloid rotifer Adineta vaga is used as a model to decipher the molecular basis of their extreme tolerance. Proteomic analysis shows that a specific DNA ligase, different from those usually involved in DNA repair in eukaryotes, is strongly over-represented upon ionizing radiation. A phylogenetic analysis reveals its orthology to prokaryotic DNA ligase E, and its horizontal acquisition by bdelloid rotifers and plausibly other eukaryotes. The fungus Mortierella verticillata, having a single copy of this DNA Ligase E homolog, also exhibits an increased radiation tolerance with an over-expression of this DNA ligase E following X-ray exposure. We also provide evidence that A. vaga ligase E is a major contributor of DNA breaks ligation activity, which is a common step of all important DNA repair pathways. Consistently, its heterologous expression in human cell lines significantly improves their radio-tolerance. Overall, this study highlights the potential of horizontal gene transfers in eukaryotes, and their contribution to the adaptation to extreme conditions.

XRCC3 and NBS1 gene polymorphisms modulate the risk of pre-oral cancer and oral cancer in the North Indian population

BACKGROUND

Oral cancer is alarming disease in the developing countries like India. DNA repair capacity may affect by genetic polymorphisms in DNA repair genes and thus may cause to cancer. XRCC3 involves in homologous recombination repair pathway and repair DNA damage and crosslinks while, NBS1 participate in repair of double strand DNA break and starts the cell-cycle checkpoint signaling.

AIMS AND OBJECTIVES

This study was to conducted to find the association of XRCC3, NBS1 polymorphisms with oral disease.

RESULTS

TT genotype of XRCC3 was associated with high risk of precancerous lesions and oral cancerous lesions (P value=0.0001, OR=9.68, 95% CI=2.82-33.21; and P value=0.0001, OR=13.10, 95% CI=3.38-50.73 respectively). We did not observe any interactions of XRCC3 polymorphism with demographic parameters in influencing the risk of oral diseases. Variant allele genotypes (CG, GG) of NBS1 (C>G) polymorphism showed protective association with Oral submucous fibrosis (OSMF), lichen planus as well as oral cancer (OR=0.31, OR=0.01; OR=0.39, OR=0.03; OR=0.43, OR=0.31 respectively). Particularly, tobacco chewer with CG & GG genotypes were at decrease risk of oral diseases (P value=0.02, OR=0.32, 95% CI=0.12-0.80). Compared to CC/CC combined genotype CG/CC, CG/CT, GG/CC and CG/CT genotypes decreased the risk of oral disease (OR=0.05, 0.47, 0.26 & 0.14 respectively).

CONCLUSION

This study concludes that SNP in XRCC3, NBS1 affects susceptibility to oral disease.

Glucose Increases STAT3 Activation, Promoting Sustained XRCC1 Expression and Increasing DNA Repair

Dysregulation of DNA repair is a hallmark of cancer, though few cancer-specific mechanisms that drive the overexpression of DNA repair proteins are known. We previously identified STAT3 as a novel transcriptional regulator of X-ray cross-complementing group 1 (XRCC1), an essential scaffold protein in base excision repair in triple-negative breast cancers. We also identified an inducible response to IL-6 and epidermal growth factor stimulation in the non-tumorigenic embryonic kidney cell line HEK293T. As IL-6 and EGF signaling are growth and inflammatory-inducible responses, we examined if glucose challenge can increase STAT3 activation, promoting adaptive changes in XRCC1 expression in different cell types. Acute high glucose exposure promoted XRCC1 expression through STAT3 activation, increasing the repair of methyl methanesulfonate-induced DNA damage in HEK293T cells and the osteosarcoma cell line U2OS. Sustained exposure to high glucose promoted the overexpression of XRCC1, which can be reversed upon glucose restriction and down-regulation of STAT3 activation. Thus, we have identified a novel link between XRCC1 expression and STAT3 activation following exogenous exposures, which could play a critical role in dictating a cancer cell’s response to DNA-damaging agents.

DDRugging glioblastoma: understanding and targeting the DNA damage response to improve future therapies

Glioblastoma is the most frequently diagnosed type of primary brain tumour in adults. These aggressive tumours are characterised by inherent treatment resistance and disease progression, contributing to ~ 190 000 brain tumour-related deaths globally each year. Current therapeutic interventions consist of surgical resection followed by radiotherapy and temozolomide chemotherapy, but average survival is typically around 1 year, with < 10% of patients surviving more than 5 years. Recently, a fourth treatment modality of intermediate-frequency low-intensity electric fields [called tumour-treating fields (TTFields)] was clinically approved for glioblastoma in some countries after it was found to increase median overall survival rates by ~ 5 months in a phase III randomised clinical trial. However, beyond these treatments, attempts to establish more effective therapies have yielded little improvement in survival for patients over the last 50 years. This is in contrast to many other types of cancer and highlights glioblastoma as a recognised tumour of unmet clinical need. Previous work has revealed that glioblastomas contain stem cell-like subpopulations that exhibit heightened expression of DNA damage response (DDR) factors, contributing to therapy resistance and disease relapse. Given that radiotherapy, chemotherapy and TTFields-based therapies all impact DDR mechanisms, this Review will focus on our current knowledge of the role of the DDR in glioblastoma biology and treatment. We also discuss the potential of effective multimodal targeting of the DDR combined with standard-of-care therapies, as well as emerging therapeutic targets, in providing much-needed improvements in survival rates for patients.

Association between polymorphisms rs2228001 and rs2228000 in XPC and genetic susceptibility to preeclampsia: a case control study

BACKGROUND

Xeroderma pigmentosum complementation group C (XPC) is a DNA damage recognition protein that plays an important role in nucleotide excision repair and can reduce oxidative stress, which may be involved in the development of preeclampsia (PE). Therefore, the aim of this study was to explore whether XPC polymorphisms were relevant to the genetic susceptibility to PE in Chinese Han women.

METHOD

A total of 1276 healthy pregnant women were included as the control group and 958 pregnant women with PE as the case group. DNA was extracted from peripheral blood samples to perform genotyping of loci rs2228001 and rs2228000 in XPC through real-time quantitative polymerase chain reaction (PCR). The relationship between XPC and susceptibility to PE was evaluated by comparing the genotypic and allelic frequencies between the two groups of pregnant women.

RESULTS

Polymorphism of rs2228000 may be associated with PE risk and allele T may play a protective role (genotype, χ2 = 38.961, P < 0.001 and allele χ2 = 21.746 P < 0.001, odds ratio (OR) = 0.885, 95% confidence interval (CI) = 0.840-0.932). No significant difference was found between the two groups in rs2228001,(genotype χ2 = 3.148, P = 0.207 and allele χ2 = 0.59, P = 0.442, OR = 1.017, 95% CI = 0.974-1.062). When the frequencies of genotypes and alleles for early- and late-onset PE, mild PE and severe PE were compared with those of controls, the results were consistent with the large clinical sample.

CONCLUSION

Our data suggest that the genetic variant rs2228000 in XPC may be associated with PE risk in Chinese Han women, and that pregnant women with the TT genotype have a reduced risk of PE. Further investigations are needed to confirm these findings in other regions or larger prospective populations.

Contemporary biomedical engineering perspective on volitional evolution for human radiotolerance enhancement beyond low-earth orbit

A primary objective of the National Aeronautics and Space Administration (NASA) is expansion of humankind's presence outside low-Earth orbit, culminating in permanent interplanetary travel and habitation. Having no inherent means of physiological detection or protection against ionizing radiation, humans incur capricious risk when journeying beyond low-Earth orbit for long periods. NASA has made large investments to analyze pathologies from space radiation exposure, emphasizing the importance of characterizing radiation's physiological effects. Because natural evolution would require many generations to confer resistance against space radiation, immediately pragmatic approaches should be considered. Volitional evolution, defined as humans steering their own heredity, may inevitably retrofit the genome to mitigate resultant pathologies from space radiation exposure. Recently, uniquely radioprotective genes have been identified, conferring local or systemic radiotolerance when overexpressed in vitro and in vivo. Aiding in this process, the CRISPR/Cas9 technique is an inexpensive and reproducible instrument capable of making limited additions and deletions to the genome. Although cohorts can be identified and engineered to protect against radiation, alternative and supplemental strategies should be seriously considered. Advanced propulsion and mild synthetic torpor are perhaps the most likely to be integrated. Interfacing artificial intelligence with genetic engineering using predefined boundary conditions may enable the computational modeling of otherwise overly complex biological networks. The ethical context and boundaries of introducing genetically pioneered humans are considered.

Base excision repair causes age-dependent accumulation of single-stranded DNA breaks that contribute to Parkinson disease pathology

Aging, genomic stress, and mitochondrial dysfunction are risk factors for neurodegenerative pathologies, such as Parkinson disease (PD). Although genomic instability is associated with aging and mitochondrial impairment, the underlying mechanisms are poorly understood. Here, we show that base excision repair generates genomic stress, promoting age-related neurodegeneration in a Caenorhabditis elegans PD model. A physiological level of NTH-1 DNA glycosylase mediates mitochondrial and nuclear genomic instability, which promote degeneration of dopaminergic neurons in older nematodes. Conversely, NTH-1 deficiency protects against α-synuclein-induced neurotoxicity, maintaining neuronal function with age. This apparent paradox is caused by modulation of mitochondrial transcription in NTH-1-deficient cells, and this modulation activates LMD-3, JNK-1, and SKN-1 and induces mitohormesis. The dependance of neuroprotection on mitochondrial transcription highlights the integration of BER and transcription regulation during physiological aging. Finally, whole-exome sequencing of genomic DNA from patients with idiopathic PD suggests that base excision repair might modulate susceptibility to PD in humans.

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Incomplete base excision repair is a source of genomic stress during aging

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The NTH-1 DNA glycosylase is a key mediator of age-dependent genomic instability

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Compromised NTH-1 activity promotes neuroprotection in PD nematodes

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NTH-1 deficiency triggers LMD-3/JNK-1/SKN-1-dependent mitohormetic response

Cellular response to endogenous DNA damage: DNA base modifications in gene expression regulation

The integrity of the genetic information is continuously challenged by numerous genotoxic insults, most frequently in the form of oxidation, alkylation or deamination of the bases that result in DNA damage. These damages compromise the fidelity of the replication, and interfere with the progression and function of the transcription machineries. The DNA damage response (DDR) comprises a series of strategies to deal with DNA damage, including transient transcriptional inhibition, activation of DNA repair pathways and chromatin remodeling. Coordinated control of transcription and DNA repair is required to safeguardi cellular functions and identities. Here, we address the cellular responses to endogenous DNA damage, with a particular focus on the role of DNA glycosylases and the Base Excision Repair (BER) pathway, in conjunction with the DDR factors, in responding to DNA damage during the transcription process. We will also discuss functions of newly identified epigenetic and regulatory marks, such as 5-hydroxymethylcytosine and its oxidative products and 8-oxoguanine, that were previously considered only as DNA damages. In light of these resultsthe classical perception of DNA damage as detrimental for cellular processes are changing. and a picture emerges whereDNA glycosylases act as dynamic regulators of transcription, placing them at the intersection of DNA repair and gene expression modulation.

Yeast Rpn4 Links the Proteasome and DNA Repair via RAD52 Regulation

Environmental and intracellular factors often damage DNA, but multiple DNA repair pathways maintain genome integrity. In yeast, the 26S proteasome and its transcriptional regulator and substrate Rpn4 are involved in DNA damage resistance. Paradoxically, while proteasome dysfunction may induce hyper-resistance to DNA-damaging agents, Rpn4 malfunction sensitizes yeasts to these agents. Previously, we proposed that proteasome inhibition causes Rpn4 stabilization followed by the upregulation of Rpn4-dependent DNA repair genes and pathways. Here, we aimed to elucidate the key Rpn4 targets responsible for DNA damage hyper-resistance in proteasome mutants. We impaired the Rpn4-mediated regulation of candidate genes using the CRISPR/Cas9 system and tested the sensitivity of mutant strains to 4-NQO, MMS and zeocin. We found that the separate or simultaneous deregulation of 19S or 20S proteasome subcomplexes induced MAG1, DDI1, RAD23 and RAD52 in an Rpn4-dependent manner. Deregulation of RAD23, DDI1 and RAD52 sensitized yeast to DNA damage. Genetic, epigenetic or dihydrocoumarin-mediated RAD52 repression restored the sensitivity of the proteasome mutants to DNA damage. Our results suggest that the Rpn4-mediated overexpression of DNA repair genes, especially RAD52, defines the DNA damage hyper-resistant phenotype of proteasome mutants. The developed yeast model is useful for characterizing drugs that reverse the DNA damage hyper-resistance phenotypes of cancers.

Biological Basis for Threshold Responses to Methylating Agents

The cellular outcomes of chemical exposure are as much about the cellular response to the chemical as it is an effect of the chemical. We are growing in our understanding of the genotoxic interaction between chemistry and biology. For example, recent data has revealed the biological basis for mutation induction curves for a methylating chemical, which has been shown to be dependent on the repair capacity of the cells. However, this is just one end point in the toxicity pathway from chemical exposure to cell death. Much remains to be known in order for us to predict how cells will respond to a certain dose. Methylating agents, a subset of alkylating agents, are of particular interest, because of the variety of adverse genetic end points that can result, not only at increasing doses, but also over time. For instance, methylating agents are mutagenic, their potency, for this end point, is determined by the cellular repair capacity of an enzyme called methylguanine DNA-methyltransferase (MGMT) and its ability to repair the induceed methyl adducts. However, methyl adducts can become clastogenic. Erroneous biological processing will convert mutagenic adducts to clastogenic events in the form of double strand breaks (DSBs). How the cell responds to DSBs is via a cascade of protein kinases, which is called the DNA damage response (DDR), which will determine if the damage is repaired effectively, via homologous recombination, or with errors, via nonhomologous end joining, or whether the cell dies via apoptosis or enters senescence. The fate of cells may be determined by the extent of damage and the resulting strength of DDR signaling. Therefore, thresholds of damage may exist that determine cell fate. Such thresholds would be dependent on each of the repair and response mechanisms that these methyl adducts stimulate. The molecular mechanism of how methyl adducts kill cells is still to be fully resolved. If we are able to quantify each of these thresholds of damage for a given cell, then we can ascertain, of the many adducts that are induced, what proportion of them are mutagenic, what proportion are clastogenic, and how many of these clastogenic events are toxic. This review examines the possibility of dose and damage thresholds for methylating agents, from the perspective of the underlying evolutionary mechanisms that may be accountable.

A DNA Repair Pathway Polymorphism (rs25487) and Angiographically Proven Coronary Artery Patients in a Population of Southern Iran

BACKGROUND

Coronary Artery Disease (CAD), which is a multifactorial genetic disease, is known as one of the most common causes of death worldwide. In this regard, X-ray Repair Cross-Complementing group 1 (XRCC1), a DNA repair protein involved in Single-Strand Breaks (SSBs), and Base Excision Repair (BER) pathways have been reported to be responsible for the efficient repair of single strand breaks and damaged bases in DNA.

OBJECTIVES

In the current study, we analyzed Arg399Gln (rs25487), which is one of the most common polymorphisms of XRCC1 gene that might be associated with the increased risk for CAD.

METHODS

This case-control study was performed to investigate the relationship between this polymorphism and CAD development. In this study, 290 patients and 216 controls were diagnosed by cardiac angiography and then screened for the above-mentioned polymorphism using Restriction Fragment Length Polymorphisms (RFLP) method.

RESULTS

The frequency of the GA genotype of XRCC1 Arg399Gln (rs25487) was significantly higher in CAD patients compared to the controls (p=0.002, OR: 1.21, 95% CI: 1.06-1.37). Moreover, its dominant mode (AA + GA) genotype had a 1.851-fold increase in the risk of CAD (p = 0.005).

CONCLUSION

Our findings demonstrated that Arg399Gln polymorphism of XRCC1 (rs25487) has a significant relationship with CAD and also plays a probable predisposing role in that. Our results support the role of DNA damages and the malfunctions of DNA repair system in the patients with CAD.

MSH2 Overexpression Due to an Unclassified Variant in 3'-Untranslated Region in a Patient with Colon Cancer

Background: The loss or low expression of DNA mismatch repair (MMR) genes can result in genomic instability and tumorigenesis. One such gene, MSH2, is mutated or rearranged in Lynch syndrome (LS), which is characterized by a high risk of tumor development, including colorectal cancer. However, many variants identified in this gene are often defined as variants of uncertain significance (VUS). In this study, we selected a variant in the 3′ untranslated region (UTR) of MSH2 (c*226A > G), identified in three affected members of a LS family and already reported in the literature as a VUS. Methods: The effect of this variant on the activity of the MMR complex was examined using a set of functional assays to evaluate MSH2 expression. Results: We found MSH2 was overexpressed compared to healthy controls, as determined by RTqPCR and Western blot analyses of total RNA and proteins, respectively, extracted from peripheral blood samples. These results were confirmed by luciferase reporter gene assays. Conclusions: We therefore speculated that, in addition to canonical inactivation via a gene mutation, MMR activity may also be modulated by changes in MMR gene expression.

Fluoroquinolone antibiotics show genotoxic effect through DNA-binding and oxidative damage

The fluoroquinolones (FQs) are one the most successful class of synthetic antibiotics that primarily target the type II topoisomerases. With a pursuit to evaluate their genotoxicity, the present work established moderate to good DNA-damaging properties of some of the well-known and clinically prescribed fluoroquinolone antibiotics (2^nd and 3^rd generation). Hypochromic shift in UV-Vis absorption titration, fluorescence quenching in competitive ethidium bromide displacement assay (with calf-thymus DNA) and in-silico studies established DNA-intercalation with binding constants of the order 10⁴. A basic Structure Activity Relationship (SAR) has been derived from the docking results. MTT assay has been also done to evaluate the effect of these antibiotics on cell viability. The expression level of specific DNA-glycosylase enzymes responsible for repairing the oxidized DNA bases are quantified through western blot analysis. The studies revealed that fluoroquinolone antibiotics initiate the genotoxic effect at a concentration of above 50 μg/mL. Recruitment of APE1 and NEIL1 was found to be significantly increased to remove the oxidized nucleobases.

Interaction between XRCC 1 gene polymorphisms and diabetes on susceptibility to primary open-angle glaucoma

IMPACT STATEMENT

Some studies have suggested that diabetes and XRCC gene may be risk factors for glaucoma; however, no studies have focused on the interaction between the XRCC gene and T2DM with respect to POAG risk. Therefore, the present study evaluated the initiative gene-environment interactions in POAG.

Vive la radiorésistance!: converging research in radiobiology and biogerontology to enhance human radioresistance for deep space exploration and colonization

While many efforts have been made to pave the way toward human space colonization, little consideration has been given to the methods of protecting spacefarers against harsh cosmic and local radioactive environments and the high costs associated with protection from the deleterious physiological effects of exposure to high-Linear energy transfer (high-LET) radiation. Herein, we lay the foundations of a roadmap toward enhancing human radioresistance for the purposes of deep space colonization and exploration. We outline future research directions toward the goal of enhancing human radioresistance, including upregulation of endogenous repair and radioprotective mechanisms, possible leeways into gene therapy in order to enhance radioresistance via the translation of exogenous and engineered DNA repair and radioprotective mechanisms, the substitution of organic molecules with fortified isoforms, and methods of slowing metabolic activity while preserving cognitive function. We conclude by presenting the known associations between radioresistance and longevity, and articulating the position that enhancing human radioresistance is likely to extend the healthspan of human spacefarers as well.

Neuraminidase-1: a novel therapeutic target in multistage tumorigenesis

Several of the growth factors and their receptor tyrosine kinases (RTK) such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), vascular endothelial growth factor (VEGF), nerve growth factor (NGF) and insulin are promising candidate targets for cancer therapy. Indeed, tyrosine kinase inhibitors (TKI) have been developed to target these growth factors and their receptors, and have demonstrated dramatic initial responses in cancer therapy. Yet, most patients ultimately develop TKI drug resistance and relapse. It is essential in the clinical setting that the targeted therapies are to circumvent multistage tumorigenesis, including genetic mutations at the different growth factor receptors, tumor neovascularization, chemoresistance of tumors, immune-mediated tumorigenesis and the development of tissue invasion and metastasis. Here, we identify a novel receptor signaling platform linked to EGF, NGF, insulin and TOLL-like receptor (TLR) activations, all of which are known to play major roles in tumorigenesis. The importance of these findings signify an innovative and promising entirely new targeted therapy for cancer. The role of mammalian neuraminidase-1 (Neu1) in complex with matrix metalloproteinase-9 and G protein-coupled receptor tethered to RTKs and TLRs is identified as a major target in multistage tumorigenesis. Evidence exposing the link connecting growth factor-binding and immune-mediated tumorigenesis to this novel receptor-signaling paradigm will be reviewed in its current relationship to cancer.

Characterization of Trypanosoma cruzi MutY DNA glycosylase ortholog and its role in oxidative stress response

Trypanosoma cruzi is a protozoan parasite and the causative agent of Chagas disease. Like most living organisms, it is susceptible to oxidative stress, and must adapt to distinct environments. Hence, DNA repair is essential for its survival and the persistence of infection. Therefore, we studied whether T. cruzi has a homolog counterpart of the MutY enzyme (TcMYH), important in the DNA Base Excision Repair (BER) mechanism. Analysis of T. cruzi genome database showed that this parasite has a putative MutY DNA glycosylase sequence. We performed heterologous complementation assays using this genomic sequence. TcMYH complemented the Escherichia coli MutY- strain, reducing the mutation rate to a level similar to wild type. In in vitro assays, TcMYH was able to remove an adenine that was opposite to 8-oxoguanine. We have also constructed a T. cruzi lineage that overexpresses MYH. Although in standard conditions this lineage has similar growth to control cells, the overexpressor is more sensitive to hydrogen peroxide and glucose oxidase than the control, probably due to accumulation of AP sites in its DNA. Localization experiments with GFP-fused TcMYH showed this enzyme is present in both nucleus and mitochondrion. QPCR and MtOX results reinforce the presence and function of TcMYH in these two organelles. Our data suggest T. cruzi has a functional MYH DNA glycosylase, which participates in nuclear and mitochondrial DNA Base Excision Repair.

Increased Oxidative DNA Damage in Placenta Contributes to Cadmium-Induced Preeclamptic Conditions in Rat

To explore the possible mechanisms of cadmium (Cd)-induced preeclamptic conditions in rats. In the present study, we introduced the in vivo model of preeclampsia by giving intraperitoneal injections of cadmium chloride (CdCl2) to pregnant rats from gestational day (GD) 4 to 19. Maternal body weights were recorded on GD 0, 14, and 20, while their systolic blood pressures (SBPs) monitored on GD 3, 11, and 18. On GD 20, rats were sacrificed and the specimens were collected. The morphological changes of placenta and kidney tissues of pregnant rats were examined by hematoxylin and eosin staining assay. Blood Cd level was detected by inductively coupled plasma mass spectrometry. Total antioxidant capacity (TAC) was evaluated using FRAP method and total nitrite (NOx) was detected with Griess reagent. Antioxidative factors and DNA damage/repair biomarkers were measured by real-time qPCR, western blot or immunohistochemistry study. The current results showed that CdCl2-treated pregnant rats developed preeclampsia (PE)-like manifestations, such as hypertension, albuminuria, with decreased TAC and increased blood Cd level, and pro-oxidative/antioxidative or DNA damage/repair biomarkers. Our study demonstrated that increased oxidative DNA damage in placenta could contribute to Cd-induced preeclamptic conditions in rat.

Inhibition of FoxM1-Mediated DNA Repair by Imipramine Blue Suppresses Breast Cancer Growth and Metastasis

PURPOSE

The approaches aimed at inhibiting the ability of cancer cells to repair DNA strand breaks have emerged as promising targets for treating cancers. Here, we assessed the potential of imipramine blue (IB), a novel analogue of antidepressant imipramine, to suppress breast cancer growth and metastasis by inhibiting the ability of breast cancer cells to repair DNA strand breaks by homologous recombination (HR).

EXPERIMENTAL DESIGN

The effect of IB on breast cancer growth and metastasis was assessed in vitro as well as in preclinical mouse models. Besides, the therapeutic efficacy and safety of IB was determined in ex vivo explants from breast cancer patients. The mechanism of action of IB was evaluated by performing gene-expression, drug-protein interaction, cell-cycle, and DNA repair studies.

RESULTS

We show that the systemic delivery of IB using nanoparticle-based delivery approach suppressed breast cancer growth and metastasis without inducing toxicity in preclinical mouse models. Using ex vivo explants from breast cancer patients, we demonstrated that IB inhibited breast cancer growth without affecting normal mammary epithelial cells. Furthermore, our mechanistic studies revealed that IB may interact and inhibit the activity of proto-oncogene FoxM1 and associated signaling that play critical roles in HR-mediated DNA repair.

CONCLUSIONS

These findings highlight the potential of IB to be applied as a safe regimen for treating breast cancer patients. Given that FoxM1 is an established therapeutic target for several cancers, the identification of a compound that inhibits FoxM1- and FoxM1-mediated DNA repair has immense translational potential for treating many aggressive cancers. Clin Cancer Res; 22(14); 3524-36. ©2016 AACR.

Up-regulation of MSH2, XRCC1 and ATM genes in patients with type 2 diabetes and coronary artery disease

AIMS

Coronary artery disease (CAD) is a major problem in some patients with type 2 diabetes mellitus (T2DM). CAD has been suggested to be the main result of reduced efficacy of DNA repair systems. Analysis of the DNA repair system in patients with diabetes can potentially uncover the molecular basis of their susceptibility to the CAD. The aim of the present study was to compare the expression levels of some important DNA repair genes, including ATM, XRCC1 and MSH2, in CAD+ versus CAD- patients with T2DM. Furthermore, the relevance of putative single nucleotide polymorphisms (SNPs) in the promoter regions of these genes with mRNA expression was evaluated.

METHODS

Expression analysis was performed by RT-qPCR on 76 patients with T2DM (41 CAD+ and 35 CAD- individuals confirmed by angiography). The genotypes of the patients were examined by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

Significant up-regulation of the MSH2 (2.49-fold, P=0.001), XRCC1 (2.11-fold, P=0.001) and ATM (2.15-fold, P=0.003) genes was observed in patients with T2DM and CAD. We could not detect any function for SNPs by comparing gene expression. In a receiver operating characteristic (ROC) curve analysis, the area under the ROC curve for sum of relative expressions of all genes reached 0.81 (95% CI: 0.690-0.936, P=0.003), which indicates a potential biomarker for identifying patients with T2DM and CAD.

CONCLUSION

These results suggest that expression levels of DNA repair genes may serve as informative biomarkers for identifying patients with T2DM and CAD.

Multiwall Carbon Nanotube-Induced DNA Damage and Cytotoxicity in Male Human Peripheral Blood Lymphocytes

Carbon nanotubes (CNTs) have been introduced recently as a novel carrier system for both small and large therapeutic molecules. Biotin-functionalized single-wall CNTs have been conjugated with the anticancer agent taxoid using a cleavable linker, and multiwall carbon nanotubes (MWCNTs) conjugated with iron nanoparticles have been efficiently loaded with doxorubicin. The MWCNTs are effective transporters for biological macromolecules and drugs to target cells and tissues, thereby attracting the attention of the biomedical industry. Administrating MWCNTs for medical application invariably involves intravenous administration and ultimate contact with human peripheral blood lymphocytes (HPBLs), yet toxicological studies on the effect of MWCNTs on HPBLs are lacking. Accordingly, this study evaluated the cytotoxic and genotoxic effects of MWCNTs on healthy male HPBLs. Healthy male HPBLs were treated with MWCNTs at 3 different concentrations (12.5, 25, and 50 μg/mL) for 48 hours. Under these conditions, the MWCNTs induced significant cell growth retardation, DNA damage, and cytotoxicity. The MWCNT-treated HPBLs also exhibited an increased intracellular reactive oxygen species level during the experimental period, which leads to cell damage and death, proliferation inhibition, DNA damage, and an inflammatory response.

Esculetin Downregulates the Expression of AML1-ETO and C-Kit in Kasumi-1 Cell Line by Decreasing Half-Life of mRNA

One of the most frequent genetic aberrations in acute myeloid leukemia (AML) is chromosomal translocation between AML1/RUNX1 on chromosome 21 and ETO gene on chromosome 8 resulting in the expression of chimeric oncogene AML1-ETO. Although patients with t(8;21) translocation have good prognosis, 5-year survival is observed only in 50% of the cases. AML1-ETO translocation is usually accompanied by overexpression of mutant C-Kit, a tyrosine kinase, which contributes to uncontrolled proliferation of premature blood cells leading to relapse and poor prognosis. We illustrate the potential use of esculetin on leukemic cell line, Kasumi-1, bearing t(8;21) translocation and mutated C-Kit gene. Esculetin decreases the expression of AML1-ETO at both protein and transcript level within 24 hours of treatment. Half-life of AML1-ETO mRNA was reduced from 7 hours to 1.5 hours. Similarly half-life of C-Kit mRNA was reduced to 2 hours from 5 hours in esculetin treated cells. Esculetin also perturbed the expression of ectopically expressed AML1-ETO in U937 cells. The decreased expression of AML1-ETO chimeric gene was associated with increased expression of LAT1 and RUNX3 genes, targets of AML1. We envisage that discovery of a drug candidate which could target both these mutated genes would be a considerable breakthrough for future application.

DNA damage in cells exhibiting radiation-induced genomic instability

Cells exhibiting radiation-induced genomic instability exhibit varied spectra of genetic and chromosomal aberrations. Even so, oxidative stress remains a common theme in the initiation and/or perpetuation of this phenomenon. Isolated oxidatively modified bases, abasic sites, DNA single strand breaks and clustered DNA damage are induced in normal mammalian cultured cells and tissues due to endogenous reactive oxygen species generated during normal cellular metabolism in an aerobic environment. While sparse DNA damage may be easily repaired, clustered DNA damage may lead to persistent cytotoxic or mutagenic events that can lead to genomic instability. In this study, we tested the hypothesis that DNA damage signatures characterised by altered levels of endogenous, potentially mutagenic, types of DNA damage and chromosomal breakage are related to radiation-induced genomic instability and persistent oxidative stress phenotypes observed in the chromosomally unstable progeny of irradiated cells. The measurement of oxypurine, oxypyrimidine and abasic site endogenous DNA damage showed differences in non-double-strand breaks (DSB) clusters among the three of the four unstable clones evaluated as compared to genomically stable clones and the parental cell line. These three unstable clones also had increased levels of DSB clusters. The results of this study demonstrate that each unstable cell line has a unique spectrum of persistent damage and lead us to speculate that alterations in DNA damage signaling and repair may be related to the perpetuation of genomic instability.

Naturally occurring polyphenol, morin hydrate, inhibits enzymatic activity of N-methylpurine DNA glycosylase, a DNA repair enzyme with various roles in human disease

Interest in the mechanisms of DNA repair pathways, including the base excision repair (BER) pathway specifically, has heightened since these pathways have been shown to modulate important aspects of human disease. Modulation of the expression or activity of a particular BER enzyme, N-methylpurine DNA glycosylase (MPG), has been demonstrated to play a role in carcinogenesis and resistance to chemotherapy as well as neurodegenerative diseases, which has intensified the focus on studying MPG-related mechanisms of repair. A specific small molecule inhibitor for MPG activity would be a valuable biochemical tool for understanding these repair mechanisms. By screening several small molecule chemical libraries, we identified a natural polyphenolic compound, morin hydrate, which inhibits MPG activity specifically (IC50=2.6μM). Detailed mechanism analysis showed that morin hydrate inhibited substrate DNA binding of MPG, and eventually the enzymatic activity of MPG. Computational docking studies with an x-ray derived MPG structure as well as comparison studies with other structurally-related flavonoids offer a rationale for the inhibitory activity of morin hydrate observed. The results of this study suggest that the morin hydrate could be an effective tool for studying MPG function and it is possible that morin hydrate and its derivatives could be utilized in future studies focused on the role of MPG in human disease.

Kinetic mechanism for the flipping and excision of 1,N(6)-ethenoadenine by AlkA

Escherichia coli 3-methyladenine DNA glycosylase II (AlkA), an adaptive response glycosylase with a broad substrate range, initiates base excision repair by flipping a lesion out of the DNA duplex and hydrolyzing the N-glycosidic bond. We used transient and steady state kinetics to determine the minimal mechanism for recognition and excision of 1,N⁶-ethenoadenine (εA) by AlkA. The natural fluorescence of this endogenously produced lesion allowed us to directly monitor the nucleotide flipping step. We found that AlkA rapidly and reversibly binds and flips out εA prior to N-glycosidic bond hydrolysis, which is the rate-limiting step of the reaction. The binding affinity of AlkA for the εA-DNA lesion is only 40-fold tighter than for a nonspecific site and 20-fold weaker than for the abasic DNA site. The mechanism of AlkA-catalyzed excision of εA was compared to that of the human alkyladenine DNA glycosylase (AAG), an independently evolved glycosylase that recognizes many of the same substrates. AlkA and AAG both catalyze N-glycosidic bond hydrolysis to release εA, and their overall rates of reaction are within 2-fold of each other. Nevertheless, we find dramatic differences in the kinetics and thermodynamics for binding to εA-DNA. AlkA catalyzes nucleotide flipping an order of magnitude faster than AAG; however, the equilibrium for flipping is almost 3 orders of magnitude more favorable for AAG than for AlkA. These results illustrate how enzymes that perform the same chemistry can use different substrate recognition strategies to effectively repair DNA damage.

Repair mechanisms help glioblastoma resist treatment

Glioblastoma multiforme (GBM) is a malignant and incurable glial brain tumour. The current best treatment for GBM includes maximal safe surgical resection followed by concomitant radiotherapy and adjuvant temozolomide. Despite this, median survival is still only 14-16 months. Mechanisms that lead to chemo- and radio-resistance underpin treatment failure. Insights into the DNA repair mechanisms that permit resistance to chemoradiotherapy in GBM may help improve patient responses to currently available therapies.

Polymorphisms in DNA repair genes (APEX1, XPD, XRCC1 and XRCC3) and risk of preeclampsia in a Mexican mestizo population

Variations in genes involved in DNA repair systems have been proposed as risk factors for the development of preeclampsia (PE). We conducted a case-control study to investigate the association of Human apurinic/apyrimidinic (AP) endonuclease (APEX1) Asp148Glu (rs1130409), Xeroderma Pigmentosum group D (XPD) Lys751Gln (rs13181), X-ray repair cross-complementing group 1 (XRCC) Arg399Gln (rs25487) and X-ray repair cross-complementing group 3 (XRCC3) Thr241Met (rs861539) polymorphisms with PE in a Mexican population. Samples of 202 cases and 350 controls were genotyped using RTPCR. Association analyses based on a χ2 test and binary logistic regression were performed to determine the odds ratio (OR) and a 95% confidence interval (95% CI) for each polymorphism. The allelic frequencies of APEX1 Asp148Glu polymorphism showed statistical significant differences between preeclamptic and normal women (p = 0.036). Although neither of the polymorphisms proved to be a risk factor for the disease, the APEX1 Asp148Glu polymorphism showed a tendency of association (OR: 1.74, 95% CI = 0.96-3.14) and a significant trend (p for trend = 0.048). A subgroup analyses revealed differences in the allelic frequencies of APEX1 Asp148Glu polymorphism between women with mild preeclampsia and severe preeclampsia (p = 0.035). In conclusion, our results reveal no association between XPD Lys751Gln, XRCC Arg399Gln and XRCC3 Thr241Met polymorphisms and the risk of PE in a Mexican mestizo population; however, the results in the APEX1 Asp148Glu polymorphism suggest the need for future studies using a larger sample size.

Redox environment, free radical, and oxidative DNA damage

SIGNIFICANCE

Effective redox homeostasis is critical, and disruption of this process can have important cellular consequences. An array of systems protect the cell from potentially damaging reactive oxygen species (ROS), however if these systems are overwhelmed, for example, in aberrantly functioning cells, ROS can have a number of detrimental consequences, including DNA damage. Oxidative DNA damage can be repaired by a number of DNA repair pathways, such as base excision repair (BER).

RECENT ADVANCES

The role of ROS in oxidative DNA damage is well established, however, there is an emerging role for ROS and the redox environment in modulating the efficiency of DNA repair pathways targeting oxidative DNA lesions.

CRITICAL ISSUES

Oxidative DNA damage and modulation of DNA damage and repair by the redox environment are implicated in a number of diseases. Understanding how the redox environment plays such a critical role in DNA damage and repair will allow us to further understand the far reaching cellular consequence of ROS.

FUTURE DIRECTIONS

In this review, we discuss the detrimental effects of ROS, oxidative DNA damage repair, and the redox systems that exist to control redox homeostasis. We also describe how DNA pathways can be modulated by the redox environment and how the redox environment and oxidative DNA damage plays a role in disease.

Mammalian base excision repair: the forgotten archangel

Base excision repair (BER) is a frontline repair system that is responsible for maintaining genome integrity and thus preventing premature aging, cancer and many other human diseases by repairing thousands of DNA lesions and strand breaks continuously caused by endogenous and exogenous mutagens. This fundamental and essential function of BER not only necessitates tight control of the continuous availability of basic components for fast and accurate repair, but also requires temporal and spatial coordination of BER and cell cycle progression to prevent replication of damaged DNA. The major goal of this review is to critically examine controversial and newly emerging questions about mammalian BER pathways, mechanisms regulating BER capacity, BER responses to DNA damage and their links to checkpoint control of DNA replication.

Association between genetic variants of DNA repair genes and coronary artery disease

Polymorphisms in DNA repair genes may be associated with differences in the repair efficiency of DNA damage and may influence an individual's risk of atherosclerosis. Genetic research on coronary artery disease (CAD) has traditionally focused on investigation aimed at identifying disease-susceptibility genes. The aim of this study was to investigate the relationship between AP-endonuclease-1 (Asp148Glu), XRCC1 (Arg399Gln), XRCC3 (Thr241Met), XPD (Lys751Gln), XPG (Asp1104His), and hOGG1 (Ser326Cys), gene polymorphisms and the risk of developing CAD in a Turkish population. The study population consisted of 197 patients with acute coronary syndrome (ACS) with chronic CAD and 135 healthy subjects' age and sex matched. Gene polymorphisms were determined by the polymerase chain reaction-restriction fragment length polymorphism method. We demonstrated for the first time, a positive association of XRCC3 and hOGG1 DNA repair gene variants with CAD risk. XRCC3 Thr/Thr genotype and Thr allele frequencies were significantly increased in ACS and chronic CAD patients compared with the control group (p<0.05). It was also observed that there is a protective role of XRCC3 Met alleles against both ACS and chronic CAD (p<0.05). hOGG1 Cys alleles were found significantly higher in ACS patients than in the control group and carriers of the Cys allele had a 1.7-fold increased risk for ACS. In addition, we confirmed the association of XRCC3 Thr241Met and hOGG1 Ser326Cys gene variants with CAD by haplotype analysis. We found that CAD risk is associated with XRCC3 Thr: hOGG1 Cys haplotype, whereas XRCC3 Met: hOGG1 Ser haplotype was found to be protective against the disease. The preliminary results suggested that XRCC3 and hOGG1 genetic variants may be risk factors by affecting the enzyme's function that may lead to development of CAD.

Ubiquitin ligase UBR3 regulates cellular levels of the essential DNA repair protein APE1 and is required for genome stability

APE1 (Ref-1) is an essential human protein involved in DNA damage repair and regulation of transcription. Although the cellular functions and biochemical properties of APE1 are well characterized, the mechanism involved in regulation of the cellular levels of this important DNA repair/transcriptional regulation enzyme, remains poorly understood. Using an in vitro ubiquitylation assay, we have now purified the human E3 ubiquitin ligase UBR3 as a major activity that polyubiquitylates APE1 at multiple lysine residues clustered on the N-terminal tail. We further show that a knockout of the Ubr3 gene in mouse embryonic fibroblasts leads to an up-regulation of the cellular levels of APE1 protein and subsequent genomic instability. These data propose an important role for UBR3 in the control of the steady state levels of APE1 and consequently error free DNA repair.

Activated leukemic oncogenes AML1-ETO and c-kit: role in development of acute myeloid leukemia and current approaches for their inhibition

Acute myeloid leukemia (AML) is a malignant blood disease caused by different mutations that enhance the proliferative activity and survival of blood cells and affect their differentiation and apoptosis. The most frequent disorders in AML are translocations between chromosomes 21 and 8 leading to production of a chimeric oncogene, AML1-ETO, and hyperexpression of the receptor tyrosine kinase KIT. Mutations in these genes often occur jointly. The presence in cells of two activated oncogenes is likely to trigger their malignization. The current approaches for treatment of oncologic diseases (bone marrow transplantation, radiotherapy, and chemotherapy) have significant shortcomings, and thus many laboratories are intensively developing new approaches against leukemias. Inhibiting expression of activated leukemic oncogenes based on the principle of RNA interference seems to be a promising approach in this field.

Regulation of DNA repair by ubiquitylation

Cellular DNA repair is a frontline system that is responsible for maintaining genome integrity and thus preventing premature aging and cancer by repairing DNA lesions and strand breaks caused by endogenous and exogenous mutagens. However, it is also the principal cellular system in cancer cells that counteracts the killing effect of the major cancer treatments, e.g. chemotherapy and ionizing radiation. Although it is clear that an individual's DNA repair capacity varies, the mechanisms involved in the regulation of repair systems that are responsible for such variations are only just emerging. This knowledge gap is impeding the finding of new cancer therapy targets and the development of novel treatment strategies. In recent years the vital role of post-translational modifications of DNA repair proteins, including ubiquitylation and phosphorylation, has been uncovered. This review will cover recent progress in our understanding of the role of ubiquitylation in the regulation of DNA repair.

hOGG1 Ser326Cys polymorphism and renal cell carcinoma risk in a Chinese population

Oxidative DNA damage caused by reactive oxygen species plays an important role in cancer development. Human 8-oxoguanine DNA glycosylase (hOGG1) is involved in base excision repair of 8-oxoguanine from damaged DNA. We hypothesized that variants in the hOGG1 gene are associated with risk of renal cell carcinoma (RCC). In a hospital-based case-control study of 572 RCC patients and 575 cancer-free controls frequency matched by age and sex, we genotyped the functional polymorphism Ser326Cys (rs1052133) and assessed its associations with risk of RCC in a Chinese population. We found that individuals with the Cys allele were associated with an increased risk of RCC (odds ratio [OR] = 1.40, 95% confidence interval [CI] = 1.02-1.90), compared with those with the Ser/Ser genotype, particularly among subgroups of body mass index >24 kg/m(2) (OR = 1.75, 95% CI = 1.12-2.73) and non-smokers (OR = 1.60, 95% CI = 1.07-2.38). Further, the polymorphism was associated with risk of developing localized stage and well-differentiated RCC. Our results suggested that the polymorphism is involved in the etiology of RCC and thus may be a marker for genetic susceptibility to RCC.

Human base excision repair creates a bias toward -1 frameshift mutations

Frameshift mutations are particularly deleterious to protein function and play a prominent role in carcinogenesis. Most commonly these mutations involve the insertion or omission of a single nucleotide by a DNA polymerase that slips on a damaged or undamaged template. The mismatch DNA repair pathway can repair these nascent polymerase errors. However, overexpression of enzymes of the base excision repair (BER) pathway is known to increase the frequency of frameshift mutations suggesting competition between these pathways. We have examined the fate of DNA containing single nucleotide bulges in human cell extracts and discovered that several deaminated or alkylated nucleotides are efficiently removed by BER. Because single nucleotide bulges are more highly exposed we anticipate that they would be highly susceptible to spontaneous DNA damage. As a model for this, we have shown that chloroacetaldehyde reacts more than 18-fold faster with an A-bulge than with a stable A.T base pair to create alkylated DNA adducts that can be removed by alkyladenine DNA glycosylase. Reconstitution of the BER pathway using purified components establishes that bulged DNA is efficiently processed. Single nucleotide deletion is predicted to repair +1 frameshift events, but to make -1 frameshift events permanent. Therefore, these findings suggest an additional factor contributing to the bias toward deletion mutations.

A novel XPF -357A>C polymorphism predicts risk and recurrence of bladder cancer

Xeroderma pigmentosum group F (XPF) has an essential role in the nucleotide excision repair pathway that removes a wide variety of DNA lesions. We hypothesized that genetic variants in XPF are associated with bladder cancer risk and recurrence. We selected three tagging single nucleotide polymorphisms (tagSNPs) from the HapMap database for the Chinese and genotyped them in a two-stage case-control study to evaluate the association and further examined the functionality of a novel polymorphism in the promoter. The two-stage analysis found that the rs744154 tagSNP in the XPF intron 1, which was linkage disequilibrium with the -357A>C polymorphism in the promoter region, was associated with a protective effect on bladder cancer risk. Electrophoretic mobility shift assay (EMSA) further revealed that the -357C allele decreased the binding ability of transcriptional factors to the XPF promoter. The vector construct containing the -357C allele had a lower luciferase expression than did the -357A allele. The -357C allele in the transcription factor-binding site was also associated with decreased expression levels of both XPF mRNA and protein in bladder cancer tissues. Furthermore, patients with the -357C allele had a shorter overall recurrence-free survival than did patients with the -357A allele. Our results suggest that the XPF promoter -357A>C polymorphism may regulate the expression of XPF and thereby contribute to susceptibility to and prognosis of bladder cancer. Further larger studies with different populations are warranted to confirm these findings.

OGG1 is a novel prognostic indicator in acute myeloid leukaemia

OGG1 (8-oxoguanine DNA glycosylase) constitutes a key component of the DNA base excision repair pathway, catalysing the removal of 8-oxoguanine nucleotides from DNA, thereby suppressing mutagenesis and cell death. We found that OGG1 expression was significantly downregulated by the RUNX1-ETO fusion protein product of the t(8;21) chromosome translocation in normal haematopoietic progenitor cells and in patients with acute myeloid leukaemia (AML). Further examination of OGG1 expression in 174 AML trial patients using Affymetrix microarrays showed that the prevalence rate of OGG1 expression was 33% and correlated strongly with adverse cytogenetics. OGG1-expressing patients had a worse relapse-free survival and overall survival and an increased risk of relapse at 5-years of follow-up. There remained a trend towards increased relapse rate among OGG1-expressing patients, even after adjusting for other known risk factors in comprehensive stratified analyses. We also determined a trend for OGG1 expression to have a more adverse impact on disease outcome in the context of the FLT3-ITD mutation. This study highlights OGG1 as a valuable prognostic marker that could be used to sub-stratify AML patients to predict those likely to fail conventional chemotherapies but those likely to benefit from novel therapeutic approaches that modulate DNA repair activity.

XPD polymorphisms, cigarette smoking, and bladder cancer risk: a meta-analysis

Genetic polymorphisms in DNA repair genes may be involved in increased risk for bladder cancer. Association studies on the XPD Asp312Asn and Lys751Gln polymorphisms with bladder cancer development reported conflicting results. A meta-analysis from eligible cancer case-control studies was performed to assess potential associations. In total, eight studies were used with a fixed effects model or a random effects model to estimate the odds ratio (OR) for XPD polymorphisms and occurrence of bladder cancer. The overall risk for the variant homozygote Asn/Asn and genotype (Asp/Asn + Asn/Asn) of Asp312Asn polymorphism showed a significant correlation with increased bladder cancer occurrence compared to wild genotype Asp/Asp (OR = 1.23, 95% CI = 1.02-1.49 for Asn/Asn vs. Asp/Asp; OR = 1.14, 95% CI = 1.01-1.28 for Asp/Asn + Asn/Asn vs. Asp/Asp). In contrast, no significant association with elevated risk of bladder cancer was found for Lys751Gln polymorphism. In the stratification analysis, there was no significant association between increased risk of bladder cancer in the XPD polymorphisms among Caucasians. Similarly, XPD polymorphisms did not show a significant increased risk among never-smokers or ever-smokers. This meta-analysis suggested that the XPD Asp312Asn but not Lys751Gln polymorphism may be more genetically susceptible to bladder cancer development. Further studies based on larger populations and gene-environment interactions are needed to determine the role of XPD polymorphisms in bladder cancer risk.

Elevated oxidative stress and DNA damage and repair levels in urinary bladder carcinomas associated with schistosomiasis

To cast light on mechanisms underlying development of urothelial carcinomas (UCs) of the urinary bladder associated with Schistosomiasis, we immunohistochemically analyzed the relationship between oxidative stress markers, DNA single strand breaks (ssDNA) which could also measure the levels of base damage and apoptosis in DNA, and expression of DNA repair genes with levels of nitric oxide synthases in bladder carcinomas of Egyptian patients with or without Schistosoma hematobium infection. Marked elevation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels was found in squamous cell carcinomas and UCs associated with Schistosomiasis when compared with non-Schistosomal carcinomas. This was accompanied by strong over expression of the DNA-repair genes, 8-oxoguanine-DNA-glycosylase and apurinic/apyrimidinic endonuclease, as well as increased formation levels of ssDNA. Expression levels of inducible nitric oxide synthase (iNOS) which is known to be indirectly related to oxidative stress was higher in Schistosomal than in the non-Schistosomal carcinomas. However, expression of endothelial nitric oxide synthase was slightly stronger in non-Schistosomal than in the Schistosomal carcinomas. In conclusion, these findings suggest a strong correlation between Schistosoma haematobium infection and increased levels of oxidative stress accompanied by a continuous DNA damage and repair in UCs, all directly correlating with elevated iNOS.

DNA repair and cancer stem-like cells--potential partners in glioma drug resistance?

Glioblastoma is the most malignant and frequent primary brain tumour in adults. Current treatment remains insufficient as these tumours display a diffuse infiltrative growth pattern and tend to recur despite extensive debulking surgery followed by radio- and chemotherapy. The alkylating agents carmustine (1,3-bis-(2-chloroethyl)-1-nitrosourea, or BCNU) and temozolomide (TMZ) are the drugs of choice for adjuvant glioma chemotherapy. However, several independent DNA repair mechanisms can restore the integrity of alkylated DNA bases, and thus contribute to drug resistance and subsequent therapy failure. Recent work suggests that glioblastomas develop as cellular and functional hierarchies through small subpopulations of stem cell-like cancer cells that are responsible for tumour initiation and maintenance. Such cells also appear to possess enhanced DNA repair capacity compared to other cells within the tumours. Challenges in glioblastoma therapy are to determine (1) whether the cancer stem-like cell subpopulations represent a clinically novel target for therapy, and (2) which additional treatment strategies should be applied to improve quality of life and prolong survival of glioblastoma patients. This review addresses clinically relevant mechanisms which contribute to glioma resistance towards current alkylating agent-based chemotherapy, and discusses related mechanisms and treatment strategies in the light of the cancer stem cell hypothesis.