DNA damage evaluated by gammaH2AX foci formation by a selective group of chemical/physical stressors

Radiosensitizing effects of CDK4/6 inhibitors in hormone receptor-positive and HER2-negative breast cancer mediated downregulation of DNA repair mechanism and NF-κB-signaling pathway

CDK4/6 inhibitors combined with endocrine therapy prolonged survival in hormone receptor (HR)-positive and HER2-negative advanced breast cancer. We investigated whether CDK4/6 inhibitors enhance radiosensitivity and their underlying mechanisms of this subtype of breast cancer. In vitro and in vivo experiments were conducted using two HR-positive and HER2-negative breast cancer cell lines (MCF-7 and T-47D), CDK4/6 inhibitors (ribociclib and palbociclib) and radiotherapy (RT) to assess the biological functions and mechanisms. The radiation-enhancing effect was assessed using clonogenic assays; γH2AX and 53BP1 levels were assessed by immunofluorescence to evaluate DNA damage. The levels of phospho (p)-ERK, c-Myc, and DNA-double strand break (DSB)-related molecules, p-DNA-PKcs, Rad51, and p-ATM, were assessed by western blotting. We used an NF-κB p65 transcription factor assay kit to evaluate NF-κB activity. We evaluated the antitumor effect of the combination of RT and ribociclib through the MCF-7 orthotopic xenograft model. The synergistic effects of combining RT with ribociclib and palbociclib pretreatment were demonstrated by clonogenic assay. CDK4/6 inhibitors synergistically increased the numbers of RT-induced γH2AX and 53BP1, downregulated the expression of p-DNA-PKcs, Rad51 and p-ATM activated by RT, and reduced RT-triggering p-ERK expression, NF-κB activation, and its down-streaming gene, c-Myc. Combined ribociclib and RT reduced the growth of MCF-7 cell xenograft tumors, and downregulated the immunohistochemical expression of p-ERK, p-NF-κB p65, and c-Myc compared to that in the control group. Combining CDK4/6 inhibitors enhanced radiosensitivity of HR-positive and HER2-negative breast cancer cells at least by reducing DNA-DSB repair and weakening the activation of ERK and NF-κB signaling by RT.

A multi-biomarker micronucleus assay using imaging flow cytometry

Genetic toxicity testing assesses the potential of compounds to cause DNA damage. There are many genetic toxicology screening assays designed to assess the DNA damaging potential of chemicals in early drug development aiding the identification of promising drugs that have low-risk potential for causing genetic damage contributing to cancer risk in humans. Despite this, in vitro tests generate a high number of misleading positives, the consequences of which can lead to unnecessary animal testing and/or the abandonment of promising drug candidates. Understanding chemical Mode of Action (MoA) is vital to identifying the true genotoxic potential of substances and, therefore, the risk translation into the clinic. Here we demonstrate a simple, robust protocol for staining fixed, human-lymphoblast p53 proficient TK6 cells with antibodies against ɣH2AX, p53 and pH3S28 along with DRAQ5™ DNA staining that enables analysis of un-lysed cells via microscopy approaches such as imaging flow cytometry. Here, we used the Cytek® Amnis® ImageStream®X Mk II which provides a high-throughput acquisition platform with the sensitivity of flow cytometry and spatial morphological information associated with microscopy. Using the ImageStream manufacturer's software (IDEAS® 6.2), a masking strategy was developed to automatically detect and quantify micronucleus events (MN) and characterise biomarker populations. The gating strategy developed enables the generation of a template capable of automatically batch processing data files quantifying cell-cycle, MN, ɣH2AX, p53 and pH3 populations simultaneously. In this way, we demonstrate how a multiplex system enables DNA damage assessment alongside MN identification using un-lysed cells on the imaging flow cytometry platform. As a proof-of-concept, we use the tool chemicals carbendazim and methyl methanesulphonate (MMS) to demonstrate the assay's ability to correctly identify clastogenic or aneugenic MoAs using the biomarker profiles established.

Comparison of protective effects of nicotinamide mononucleotide and nicotinamide riboside on DNA damage induced by cisplatin in HeLa cells

Background

Previous studies have shown that the nicotinamide adenine dinucleotide (NAD+) precursors, nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR), protect against endogenously or exogenously induced DNA damage. However, whether the two compounds have the same or different efficacy against DNA damage is not clear. In the current study, we systematically compared the effects of NMN and NR on cisplatin-induced DNA damage in HeLa cells.

Methods

To evaluate the protective effects of NMN or NR, HeLa cells were pretreated with different doses of NMN or NR followed with 10 μM of cisplatin treatment. Cell viability was examined by Trypan blue staining assay. For observing the DNA damage repair process, HeLa cells were treated with 10 μM of cisplatin for 12 h, followed with 10 mM NMN or NR treatment for another 8, 16, 24, or 32 h, DNA damage levels were assessed for each time point by immunofluorescent staining against phosphor-H2AX (γH2AX) and alkaline comet assay. The effects of NMN and NR on intracellular NAD+ and reactive oxygen species (ROS) levels were also determined.

Results

NMN and NR treatment alone did not have any significant effects on cell viability, however, both can protect HeLa cells from cisplatin-induced decrease of cell viability with similar efficacy in a dose-dependent manner. On the other hand, while both can reduce the DNA damage levels in cisplatin-treated cells, NR exhibited better protective effect. However, both appeared to boost the DNA damage repair process with similar efficacy. NMN or NR treatment alone could increase cellular NAD+ levels, and both can reverse cisplatin-induced decrease of NAD+ levels. Finally, while neither NMN nor NR affected cellular ROS levels, both inhibited cisplatin-induced increase of ROS with no significant difference between them.

Conclusion

NR have a better protective effect against cisplatin-induced DNA damage than NMN.

ATM/Chk2 and ATR/Chk1 Pathways Respond to DNA Damage Induced by Movento® 240SC and Envidor® 240SC Keto-Enol Insecticides in the Germarium of Drosophila melanogaster

DNA damage response (DDR) pathways in keto-enol genotoxicity have not been characterized, and few studies have reported genotoxic effects in non-target organisms. The present study shows that concentrations of 11.2, 22.4, 37.3 mg/L of Movento® 240SC and 12.3, 24.6, 41.1 mg/L of Envidor® 240SC for 72 h oral exposure induced DSBs by significantly increasing the percentage of γH2AV expression in regions 2b and 3 from the germarium of wild type females of Drosophila melanogaster Oregon R, compared to the control group (0.0 mg/L of insecticides), via confocal immunofluorescence microscopy. The comparison between both insecticides' reveals that only the Envidor® 240SC induces concentration-dependent DNA damage, as well as structural changes in the germarium. We determined that the DDR induced by Movento® 240SC depends on the activation of the ATMtefu, Chk1grp and Chk2lok kinases by significantly increasing the percentage of expression of γH2AV in regions 2b and 3 of the germarium, and that ATRmei-29D and p53dp53 kinases only respond at the highest concentration of 37.3 mg/L of Movento® 240SC. With the Envidor® 240SC insecticide, we determined that the DDR depends on the activation of the ATRmei-29D/Chk1grp and ATMtefu/Chk2lok kinases, and p53dp53 by significantly increasing the percentage of expression of γH2AV in the germarium.

Anti-Cancer Prodrug Cyclophosphamide Exerts Thrombogenic Effects on Human Venous Endothelial Cells Independent of CYP450 Activation-Relevance to Thrombosis

Cancer patients are at a very high risk of serious thrombotic events, often fatal. The causes discussed include the detachment of thrombogenic particles from tumor cells or the adverse effects of chemotherapeutic agents. Cytostatic agents can either act directly on their targets or, in the case of a prodrug approach, require metabolization for their action. Cyclophosphamide (CPA) is a widely used cytostatic drug that requires prodrug activation by cytochrome P450 enzymes (CYP) in the liver. We hypothesize that CPA could induce thrombosis in one of the following ways: (1) damage to endothelial cells (EC) after intra-endothelial metabolization; or (2) direct damage to EC without prior metabolization. In order to investigate this hypothesis, endothelial cells (HUVEC) were treated with CPA in clinically relevant concentrations for up to 8 days. HUVECs were chosen as a model representing the first place of action after intravenous CPA administration. No expression of CYP2B6, CYP3A4, CYP2C9 and CYP2C19 was found in HUVEC, but a weak expression of CYP2C18 was observed. CPA treatment of HUVEC induced DNA damage and a reduced formation of an EC monolayer and caused an increased release of prostacyclin (PGI2) and thromboxane (TXA) associated with a shift of the PGI2/TXA balance to a prothrombotic state. In an in vivo scenario, such processes would promote the risk of thrombus formation.

Mesenchymal stem cell-derived exosomes attenuate DNA damage response induced by cisplatin and bleomycin

Stem cell-derived exosomes (SC-Exos) have been shown to protect cells from chemical-induced deoxyribonucleic acid (DNA) damage. However, there has been no systematic comparison of the efficacy of exosomes against different types of DNA damage. Therefore, in this study, we assessed the protective effect of exosomes derived from human embryonic stem cell-induced mesenchymal stem cells (hESC-MSC-Exos) on two types of DNA damage, namely, intra-/inter-strand crosslinks and DNA double-strand breaks induced by cisplatin (Pt) and bleomycin (BLM), respectively, in HeLa cells. The alkaline comet assay demonstrated that hESC-MSC-Exos effectively inhibited Pt- and BLM-induced DNA damage in a dose-dependent manner. When the concentration of hESC-MSC-Exos reaches 2.0 × 10⁶ and 4.0 × 10⁶ particles/mL in Pt- and BLM-treated groups, respectively, there was a significant decrease in tail DNA percentage (Pt: 20.80 ± 1.61 vs 9.40 ± 1.14, p < 0.01; BLM: 21.80 ± 1.31 vs 6.70 ± 0.60, p < 0.01), tail moment (Pt: 10.00 ± 1.21 vs 2.08 ± 0.51, p < 0.01; BLM: 12.00 ± 0.81 vs 2.00 ± 0.21, p < 0.01), and olive tail moment (Pt: 6.01 ± 0.55 vs 2.09 ± 0.25, p < 0.01; BLM: 6.03 ± 0.37 vs 1.53 ± 0.13, p < 0.01). Phospho-histone H2AX (γH2AX) immunofluorescence and western blotting showed an over 50 % decrease in γH2AX expression when the cells were pretreated with hESC-MSC-Exos. As reactive oxygen species (ROS) are important mediators of Pt- and BLM-induced DNA damage, dichloro-dihydro-fluorescein diacetate staining indicated that hESC-MSC-Exos inhibited the increase in intracellular ROS in drug-treated cells. In conclusion, our findings suggest that hESC-MSC-Exos can protect cells from the two types of DNA-damaging drugs and that reduced intracellular ROS is involved in this effect.

Early detection of urinary bladder carcinogens in rats by immunohistochemistry for γ-H2AX: a review from analyses of 100 chemicals

In safety evaluations of chemicals, there is an urgent need to develop short-term methods to replace long-term carcinogenicity tests. We have reported that immunohistochemistry for γ-H2AX, a well-established biomarker of DNA damage, can detect bladder carcinogens at an early stage using histopathological specimens from 28-day repeated-dose oral toxicity studies in rats. Given the markedly low level of γ-H2AX formation in the bladder urothelium of untreated rats, an increase in γ-H2AX-positive cells following chemical exposure can be relatively easy to identify. Among the 100 compounds examined to date, bladder carcinogens can be detected with high sensitivity (33/39; 84.6%) and specificity (58/61; 95.1%). As expected, γ-H2AX formation levels tended to be high following exposure to genotoxic bladder carcinogens, whereas nongenotoxic bladder carcinogens also increased the number of γ-H2AX-positive cells, probably through secondary DNA damage associated with sustained proliferative stimulation. γ-H2AX formation in the bladder urothelium reflects species differences in susceptibility to bladder carcinogenesis between rats and mice and shows a clear dose-dependency associated with the intensity of tumor development as well as high reproducibility. Some of the bladder carcinogens that showed false-negative results in the evaluation of γ-H2AX alone could be detected by combined evaluation with immunostaining for bladder stem cell markers, including aldehyde dehydrogenase 1A1. This method may be useful for the early detection of bladder carcinogens, as it can be performed by simple addition of conventional immunostaining using formalin-fixed paraffin-embedded tissues from 28-day repeated-dose toxicity studies in rodents, which are commonly used in safety evaluations of chemical substances.

Evaluation of DNA double-strand break repair capacity in human cells: Critical overview of current functional methods

DNA double-strand breaks (DSBs) are highly deleterious lesions, responsible for mutagenesis, chromosomal translocation or cell death. DSB repair (DSBR) is therefore a critical part of the DNA damage response (DDR) to restore molecular and genomic integrity. In humans, this process is achieved through different pathways with various outcomes. The balance between DSB repair activities varies depending on cell types, tissues or individuals. Over the years, several methods have been developed to study variations in DSBR capacity. Here, we mainly focus on functional techniques, which provide dynamic information regarding global DSB repair proficiency or the activity of specific pathways. These methods rely on two kinds of approaches. Indirect techniques, such as pulse field gel electrophoresis (PFGE), the comet assay and immunofluorescence (IF), measure DSB repair capacity by quantifying the time-dependent decrease in DSB levels after exposure to a DNA-damaging agent. On the other hand, cell-free assays and reporter-based methods directly track the repair of an artificial DNA substrate. Each approach has intrinsic advantages and limitations and despite considerable efforts, there is currently no ideal method to quantify DSBR capacity. All techniques provide different information and can be regarded as complementary, but some studies report conflicting results. Parameters such as the type of biological material, the required equipment or the cost of analysis may also limit available options. Improving currently available methods measuring DSBR capacity would be a major step forward and we present direct applications in mechanistic studies, drug development, human biomonitoring and personalized medicine, where DSBR analysis may improve the identification of patients eligible for chemo- and radiotherapy.

Depletion of DNA Polymerase Theta Inhibits Tumor Growth and Promotes Genome Instability through the cGAS-STING-ISG Pathway in Esophageal Squamous Cell Carcinoma

Simple Summary

DNA polymerase theta, encoded by the human POLQ gene, is upregulated in several cancers and is associated with poor clinical outcomes. The importance of POLQ, however, has yet to be elucidated in esophageal cancer. In this study, we explored the functional impacts of POLQ and looked into its underlying mechanisms. POLQ was overexpressed in esophageal squamous cell carcinoma (ESCC) tumors associated with unfavorable prognosis and contributed to malignant phenotypes by promoting genome stability, suggesting that targeting polymerase theta may provide a potential therapeutic approach for improving ESCC management.

Abstract

Overexpression of the specialized DNA polymerase theta (POLQ) is frequent in breast, colon and lung cancers and has been correlated with unfavorable clinical outcomes. Here, we aimed to determine the importance and functional role of POLQ in esophageal squamous cell carcinoma (ESCC). Integrated analysis of four RNA-seq datasets showed POLQ was predominantly upregulated in ESCC tumors. High expression of POLQ was also observed in a cohort of 25 Hong Kong ESCC patients and negatively correlated with ESCC patient survival. POLQ knockout (KO) ESCC cells were sensitized to multiple genotoxic agents. Both rH2AX foci staining and the comet assay indicated a higher level of genomic instability in POLQ-depleted cells. Double KO of POLQ and FANCD2, known to promote POLQ recruitment at sites of damage, significantly impaired cell proliferation both in vitro and in vivo, as compared to either single POLQ or FANCD2 KOs. A significantly increased number of micronuclei was observed in POLQ and/or FANCD2 KO ESCC cells. Loss of POLQ and/or FANCD2 also resulted in the activation of cGAS and upregulation of interferon-stimulated genes (ISGs). Our results suggest that high abundance of POLQ in ESCC contributes to the malignant phenotype through genome instability and activation of the cGAS pathway.

Applicability of flow cytometry γH2AX assay in population studies: suitability of fresh and frozen whole blood samples

Phosphorylation of H2AX histone (γH2AX) represents an early event in the DNA damage response against double-strand breaks (DSB); hence, its measurement provides a surrogate biomarker of DSB. Recently, we reported initial steps in the standardization of γH2AX assay in peripheral blood leukocytes (PBL), addressing the possibility of using cryopreserved samples, and the need of phytohaemagglutinin (PHA) stimulation prior analysis (Toxicol Sci 2015, 144:406-13). Validating the use of whole blood samples as cell specimen for this assay would be particularly useful for human population studies. Hence, in the current study we determined for the first time the feasibility of whole blood samples, both fresh and frozen, to be used in the γH2AX assay, evaluated by flow cytometry, and the convenience of PHA stimulation. Freshly collected and cryopreserved whole blood samples were treated with bleomycin (BLM), actinomycin-D (Act-D) and mitomycin C (MMC); half of the samples were previously incubated with PHA. Results were compared with those from PBL. Negative responses in MMC treatments were probably due to the quiescence of unstimulated cells, or to the short treatment time in PHA stimulated cells. Fresh whole blood samples exhibited a more intense response to BLM and Act-D treatments in stimulated cells, probably due to DSB indirectly produced from other less relevant types of DNA damage. Results obtained in frozen whole blood samples indicate that PHA stimulation is not advisable. In conclusion, this study demonstrates that whole blood samples can be used to assess DSB-related genotoxicity by the flow cytometry γH2AX assay.

DNA damage and growth hormone hypersecretion in pituitary somatotroph adenomas

Drivers of sporadic benign pituitary adenoma growth are largely unknown. Whole-exome sequencing of 159 prospectively resected pituitary adenomas showed that somatic copy number alteration (SCNA) rather than mutation is a hallmark of hormone-secreting adenomas and that SCNAs correlate with adenoma phenotype. Using single-gene SCNA pathway analysis, we observed that both cAMP and Fanconi anemia DNA damage repair pathways were affected by SCNAs in growth hormone-secreting (GH-secreting) somatotroph adenomas. As somatotroph differentiation and GH secretion are dependent on cAMP activation and we previously showed DNA damage, aneuploidy, and senescence in somatotroph adenomas, we studied links between cAMP signaling and DNA damage. Stimulation of cAMP in C57BL/6 mouse primary pituitary cultures using forskolin or a long-acting GH-releasing hormone (GHRH) analog increased GH production and DNA damage measured by H2AX phosphorylation and a comet assay. Octreotide, a somatostatin receptor ligand that targets somatotroph adenoma GH secretion in patients with acromegaly, inhibited cAMP and GH and reversed DNA damage induction. In vivo long-acting GHRH treatment also induced pituitary DNA damage in mice. We conclude that cAMP, which induces somatotroph proliferation and GH secretion, may concomitantly induce DNA damage, potentially linking hormone hypersecretion to SCNA and genome instability. These results elucidating somatotroph adenoma pathophysiology identify pathways for targeted treatment.

Proteomic changes by radio-mitigative thrombopoietin receptor agonist romiplostim in the blood of mice exposed to lethal total-body irradiation

PURPOSE

The thrombopoietin receptor agonist romiplostim (RP) is a therapeutic agent for immune thrombocytopenia that can achieve complete survival in mice exposed to a lethal dose of ionizing radiation. The estimated mechanism of the radio-protective/mitigative effects of RP has been proposed; however, the detailed mechanism of action remains unclear. This study aimed to elucidate the mechanism of the radio-protective/mitigative effects of RP, the fluctuation of protein in the blood was analyzed by proteomics.

MATERIALS AND METHODS

Eight-week-old female C57BL/6J mice were randomly divided into 5 groups; control at day 0, total-body irradiation (TBI) groups at day 10 and day 18, and TBI plus RP groups at day 10 and day18, consisting of 3 mice per group, and subjected to TBI with 7 Gy of ¹³⁷Cs γ-rays at a dose rate of 0.74 Gy/min. RP was administered intraperitoneally to mice at a dose of 50 µg/kg once daily for 3 days starting 2 hours after TBI. On day 10 and day 18 after TBI, serum collected from each mouse was analyzed by liquid chromatography tandem mass spectrometry.

RESULTS

Nine proteins were identified by proteomics methods from 269 analyzed proteins detected in mice exposed to a lethal dose of TBI: keratin, type II cytoskeletal 1 (KRT1), fructose-1, 6-bisphosphatase (FBP1), cytosolic 10-formyltetrahydrofolate dehydrogenase (ALDH1L1), peptidyl-prolyl cis-trans isomerase A (PPIA), glycine N-methyltransferase (GNMT), glutathione S-transferase Mu 1 (GSTM1), regucalcin (RGN), fructose-bisphosphate aldolase B (ALDOB) and betain-homocysteine S-methyltransferase 1 (BHMT). On the 10th day after TBI, KRT1 was significantly increased (p < 0.05) by 4.26-fold compared to the control group in the TBI group and significantly inhibited in the TBI plus RP group (p < 0.05). Similarly, the expression levels of other 8 proteins detected at 18th day after TBI were significantly increased by 4.29 to 27.44-fold in the TBI group, but significantly decreased in the TBI plus RP group compared to the TBI group, respectively.

CONCLUSION

Nine proteins were identified by proteomics methods from 269 analyzed proteins detected in mice exposed to a lethal dose of TBI. These proteins are also expected to be indicators of the damage induced by high-dose radiation.

High-content imaging analyses of γH2AX-foci and micronuclei in TK6 cells elucidated genotoxicity of chemicals and their clastogenic/aneugenic mode of action

Background

The in vitro micronucleus (MN) test is an important component of a genotoxicity test battery that evaluates chemicals. Although the standard method of manually scoring micronucleated (MNed) cells by microscope is a reliable and standard method, it is laborious and time-consuming. A high-throughput assay system for detecting MN cells automatically has long been desired in the fields of pharmaceutical development or environmental risk monitoring. Although the MN test per se cannot clarify whether the mode of MN induction is aneugenic or clastogenic, this clarification may well be made possible by combining the MN test with an evaluation of γH2AX, a sensitive marker of DNA double strand breaks (DSB). In the present study, we aimed to establish a high-content (HC) imaging assay that automatically detects micronuclei (MNi) and simultaneously measures γH2AX foci in human lymphoblastoid TK6 cells.

Results

TK6 cells were fixed on the bottom of each well in 96-well plates hypotonically, which spreads the cells thinly to detach MNi from the primary nuclei. Then, the number of MNi and immunocytochemically-stained γH2AX foci were measured using an imaging analyzer. The system correctly judged 4 non-genotoxins and 13 genotoxins, which included 9 clastogens and 4 aneugens representing various genotoxic mechanisms, such as DNA alkylation, cross-linking, topoisomerase inhibition, and microtubule disruption. Furthermore, all the clastogens induced both γH2AX foci and MNi, while the aneugens induced only MNi, not γH2AX foci; therefore, the HC imaging assay clearly discriminated the aneugens from the clastogens. Additionally, the test system could feasibly analyze cell cycle, to add information about a chemical’s mode of action.

Conclusions

A HC imaging assay to detect γH2AX foci and MNi in TK6 cells was established, and the assay provided information on the aneugenic/clastogenic mode of action.

Electronic supplementary material

The online version of this article (10.1186/s41021-019-0117-8) contains supplementary material, which is available to authorized users.

Microbial metabolites of proanthocyanidins reduce chemical carcinogen-induced DNA damage in human lung epithelial and fetal hepatic cells in vitro

Seven selected microbial metabolites of proanthocyanidins (MMP), 3-phenylpropionic, 4-hydroxyphenyl acetic, 3-(4-hydroxyphenyl) propionic, p-coumaric, benzoic acid, pyrogallol (PG), and pyrocatechol (PC) were evaluated for their ability to reduce chemical carcinogen-induced toxicity in human lung epithelial cells (BEAS-2B) and human fetal hepatic cells (WRL-68). Cells pre-treated with MMP were exposed to a known chemical carcinogen, 4-[(acetoxymethyl) nitrosamino]-1-(3-pyridyl)-1-butanone (NNKOAc) to assess MMP-mediated cytoprotection and reduction of DNA damage. PG in BEAS-2B and PC in WRL-68 cells mitigated the NNKOAc-induced cytotoxicity. Pre-incubation of PG depicted significant protection against NNKOAc-induced DNA damage in BEAS-2B cells. PC in WRL-68 cells showed similar activity. To understand the mechanisms of PG- and PC-mediated DNA damage reduction, the effect on DNA damage response (DDR) proteins, cellular reactive oxygen species (ROS), total antioxidant capacity (TAC), glutathione peroxidase (GPx), and caspase activity were studied. PG and PC alter the DDR and may promote ATR-Chk1 and ATM-Chk2 pathways, respectively. Cellular oxidative stress induced by NNKOAc was mitigated by PG and PC through enhanced GPx expression and TAC. PG and PC suppressed the activation of the extrinsic apoptotic pathway (caspase 3 and 8) provoked by NNKOAc. MMP are beneficial in chemoprevention by reducing cellular DNA damage.

Zingerone Nanotetramer Strengthened the Polypharmacological Efficacy of Zingerone on Human Hepatoma Cell Lines

We base this study on the concept of drug repositioning to reconstitute the natural product of zingerone as zingerone nanoparticles (zingerone NPs) through a one-pot synthesized process. The as-fabricated zingerone NPs were characterized; they possessed a particle size of 1.42 ± 0.67 nm and a reconstituted structure of zingerone nanotetramer. We further validate the effects of zingerone NPs on the antitumor activity and investigate the relative underlying mechanisms on the human hepatoma SK-Hep-1 and Huh7 cell lines. Our results demonstrated that zingerone NPs significantly inhibit Akt activity and NFκB expression as well as activate the caspases cascade signaling pathway which are involved in the antiproliferation, antitumorigenicity, disturbing cell cycle progression, and induction of DNA damage as well as cell apoptosis. These findings were promising to provide a "Nano-chemoprevention" strategy in future cancer therapeutics and medical and clinical applications.

The thrombopoietin mimetic romiplostim leads to the complete rescue of mice exposed to lethal ionizing radiation

For the primary treatment of emergency exposure to high-dose radiation, such as in the event of a radiation accident, the top priority is the reconstitution and restoration of haematopoiesis. In most radiation accidents, drug therapy is chosen as the most suitable treatment; the chosen drug should already be approved domestically, stably supplied and regularly stockpiled. In the present study, a single administration of romiplostim (RP), an approved thrombopoietin receptor agonist, produced a 100% survival rate in C57BL/6 J mice exposed to a lethal dose (7 Gy) of ¹³⁷Cs γ-rays, and all irradiated mice survived for more than 30 days with both 3- and 5-day consecutive administrations. By day 30, the peripheral blood cells, bone marrow cells and haematopoietic progenitor cells of the RP-administered irradiated mice had all recovered to a level that was not significantly different from that in non-irradiated mice. In contrast to myelosuppression, which did not fully recover until day 30, the expression of several bone marrow cell surface antigens recovered sooner, and DNA repair concurrently increased in haematopoietic cells, speeding the resolution of double strand breaks and reducing the rates of apoptosis. These findings suggest that RP may be a clinic-ready countermeasure to treat victims of radiation accidents.

Familial Esophageal Squamous Cell Carcinoma with damaging rare/germline mutations in KCNJ12/KCNJ18 and GPRIN2 genes

In Iran, esophageal cancer is the fourth common cancers in women and sixth common cancers in men. Here we evaluated the importance of familial risk factors and the role of genetic predisposition in Esophageal Squamous Cell Carcinoma (ESCC) using Whole-Exome Sequencing (WES). Germline damaging mutations were identified in WES data from 9 probands of 9 unrelated ESCC pedigrees. Mutations were confirmed with Sanger sequencing and evaluated amplification-refractory mutation system-Polymerase Chain Reaction (ARMS-PCR) in 50 non-related ethnically matched samples and in complete genomics database. Sixteen candidate variants were detected in ESCC 9 probands. Four of these 16 variants were rare damaging mutations including novel mutations in KCNJ12/KCNJ18, and GPRIN2 genes. This WES study in Iranian patients with ESCC, provides insight into the identification of novel germline mutations in familial ESCC. Our data suggest an association between specific mutations and increased risk of ESCC.

Intestinal exposure to PCB 153 induces inflammation via the ATM/NEMO pathway

BACKGROUND

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that adversely affect human health. PCBs bio-accumulate in organisms important for human consumption. PCBs accumulation in the body leads to activation of the transcription factor NF-κB, a major driver of inflammation. Despite dietary exposure being one of the main routes of exposure to PCBs, the gut has been widely ignored when studying the effects of PCBs.

OBJECTIVES

We investigated the effects of PCB 153 on the intestine and addressed whether PCB 153 affected intestinal permeability or inflammation and the mechanism by which this occurred.

METHODS

Mice were orally exposed to PCB 153 and gut permeability was assessed. Intestinal epithelial cells (IECs) were collected and evaluated for evidence of genotoxicity and inflammation. A human IEC line (SW480) was used to examine the direct effects of PCB 153 on epithelial function. NF-кB activation was measured using a reporter assay, DNA damage was assessed, and cytokine expression was ascertained with real-time PCR.

RESULTS

Mice orally exposed to PCB 153 had an increase in intestinal permeability and inflammatory cytokine expression in their IECs; inhibition of NF-кB ameliorated both these effects. This inflammation was associated with genotoxic damage and NF-кB activation. Exposure of SW480 cells to PCB 153 led to similar effects as seen in vivo. We found that activation of the ATM/NEMO pathway by genotoxic stress was upstream of NF-kB activation.

CONCLUSIONS

These results demonstrate that oral exposure to PCB 153 is genotoxic to IECs and induces downstream inflammation and barrier dysfunction in the intestinal epithelium.

Identification of essential transcription factors for adequate DNA damage response after benzo(a)pyrene and aflatoxin B1 exposure by combining transcriptomics with functional genomics

DNA damage mediates widespread changes in transcription through activation or repression of transcription factors (TFs). However, the consequences of regulating specific TFs for the outcome of the DNA repair process remain incompletely understood. Here, we combined transcriptomics and TF binding prediction with functional genomics to identify TFs essential for adequate DNA repair in HepG2 liver cells after a non-cytotoxic dose of carcinogens benzo(a)pyrene (BaP) (2μM) and aflatoxin B1 (AFB1) (5μM). BaP and AFB1 induced a largely common transcriptional response, mediated by similar TFs. A lentiviral shRNA screen knocking down the top31 identified TFs, was performed to determine their effect on DNA repair by assessing phosphorylation of H2AX (γ-H2AX). In addition to the top candidate p53, we identified several other interesting TFs that modulated γ-H2AX after BaP and AFB1 treatment. Validation studies confirmed the role of p53 in reducing γ-H2AX formation and DNA breaks measured by COMET assay after BaP and AFB1 exposure. Expression of the cell cycle inhibitor p21 was profoundly impaired upon p53 knock-down. In addition, the expression of 2 genes involved in nucleotide exchange repair, DDB2 and XPC was significantly reduced in p53 knock-down cells. Although p63 knock-down affected DNA damage upon BaP treatment this was not associated with altered expression of DDB2 or XPC. Finally, knock-down of ARNT reduced γ-H2AX in response to BaP, which was associated with reduced CYP1A1 expression. Importantly, our results suggest a new role for ARNT and its dimerization partner AHR in the occurrence of H2AX phosphorylation after AFB1 treatment. These data show that modulation of TF activity impacts on the repair of BaP- and AFB1-induced DNA damage. Our study also demonstrates the potential of combining functional genomics with genome-wide expression analysis to identify yet unknown causal relationships, thereby aiding in the interpretation of complex biological systems.

Combinations of genotoxic tests for the evaluation of group 1 IARC carcinogens

Many of the known human carcinogens are potent genotoxins that are efficiently detected as carcinogens in human populations but certain types of compounds such as immunosuppressants, sex hormones, etc. act via non-genotoxic mechanism. The absence of genotoxicity and the diversity of modes of action of non-genotoxic carcinogens make predicting their carcinogenic potential extremely challenging. There is evidence that combinations of different short-term tests provide a better and efficient prediction of human genotoxic and non-genotoxic carcinogens. The purpose of this study is to summarize the in vivo and in vitro comet assay (CMT) results of group 1 carcinogens selected from the International Agency for Research on Cancer and to discuss the utility of the comet assay along with other genotoxic assays such as Ames, in vivo micronucleus (MN), and in vivo chromosomal aberration (CA) test. Of the 62 agents for which valid genotoxic data were available, 38 of 61 (62.3%) were Ames test positive, 42 of 60 (70%) were in vivo MN test positive and 36 of 45 (80%) were positive for the in vivo CA test. Higher sensitivity was seen in in vivo CMT (90%) and in vitro CMT (86.9%) assay. Combination of two tests has greater sensitivity than individual tests: in vivo MN + in vivo CA (88.6%); in vivo MN + in vivo CMT (92.5%); and in vivo MN + in vitro CMT (95.6%). Combinations of in vivo or in vitro CMT with other tests provided better sensitivity. In vivo CMT in combination with in vivo CA provided the highest sensitivity (96.7%).

Comparative study of human neuronal and glial cell sensitivity for in vitro neurogenotoxicity testing

Cell cultures from neuronal and glial origin have proven to be powerful tools for elucidating cellular and molecular mechanisms of nervous system development and physiology, and as neurotoxicity models to evaluate in vitro the possible effects of chemicals. But cellular heterogeneity of nervous system is considerable and these cells have been shown to respond diversely to neurotoxic insults, leading to disparate results from different studies. To shed more light on suitability of cellular models of nervous origin for neurotoxicity screening, the objective of this study was to compare the sensitivity to genetic damage induction of two nervous cell lines. To this aim, neurons (SH-SY5Y) and glial (A172) cells were treated with differently-acting genotoxic agents (bleomycin, actinomycin-D, methyl methanesulfonate, mitomycin C, and griseofulvin). After discarding cytotoxicity, genotoxicity was evaluated by a battery of assays encompassing detection of different genetic lesions. Results obtained showed that glial cells are generally more resistant to genotoxic damage induced by clastogenic agents, but more sensitive to aneugenic effects. These results highlight the need of proper design of in vitro neurotoxicology studies, especially for neurogenotoxicity screening, emphasizing the importance of employing more than one nervous cell type for testing the potential toxicity of a particular exposure.

Functional analysis of the TMPRSS2:ERG fusion gene in cisplatin‑induced cell death

The TMPRSS2:E‑twenty‑six (ETS) gene fusion occurs frequently in a high proportion of patients with prostate cancer (PCa) in Western countries, and the aberrant expression of TMPRSS2: v‑ETS avian erythroblastosis virus E26 oncogene homolog (ERG), the most common form of the corresponding protein, can regulate cell migration and contribute to tumor invasion and metastasis. However, its association with other cellular events, and in particular, cell death, remain unknown. To examine the function of such fusion genes, an expression plasmid containing the TMPRSS2:ERG (T1/E5) sequence (ΔERG) from a patient sample was constructed and transiently transfected into DU145 cells, which do not express the fusion gene. It was found that the overexpression of ΔERG significantly inhibited the ability of cisplatin to induce apoptosis in DU145 cells. By contrast, VCaP cells, which do contain TMPRSS2:ERG, were sensitized to cisplatin‑induced apoptosis through siRNA inhibition of the fusion gene. To elucidate the underlying mechanism, a stable cell line expressing the ΔERG gene was constructed. Expression of ΔERG did not affect cell migration, but did protect cells from DNA damage and apoptosis induced by cisplatin. Furthermore, knockdown of ΔERG by short interfering RNA resulted in cells regaining their sensitivity to cisplatin. Finally, the gene coding for activating transcription factor 5, which is important for cell survival, may be upregulated by ΔERG. Taken together, these data point to a new function of the TMPRSS2:ERG fusion gene in regulating the apoptotic pathway.

Evaluation of genotoxicity using automated detection of γH2AX in metabolically competent HepaRG cells

The in situ detection of γH2AX was recently reported to be a promising biomarker of genotoxicity. In addition, the human HepaRG hepatoma cells appear to be relevant for investigating hepatic genotoxicity since they express most of drug metabolizing enzymes and a wild type p53. The aim of this study was to determine whether the automated in situ detection of γH2AX positive HepaRG cells could be relevant for evaluation of genotoxicity after single or long-term repeated in vitro exposure compared to micronucleus assay. Metabolically competent HepaRG cells were treated daily with environmental contaminants and genotoxicity was evaluated after 1, 7 and 14 days. Using these cells, we confirmed the genotoxicity of aflatoxin B1 and benzo(a)pyrene and demonstrated that dimethylbenzanthracene, fipronil and endosulfan previously found genotoxic with comet or micronucleus assays also induced γH2AX phosphorylation. Furthermore, we showed that fluoranthene and bisphenol A induced γH2AX while no effect had been previously reported in HepG2 cells. In addition, induction of γH2AX was observed with some compounds only after 7 days, highlighting the importance of studying long-term effects of low doses of contaminants. Together, our data demonstrate that automated γH2AX detection in metabolically competent HepaRG cells is a suitable high-through put genotoxicity screening assay.

Evaluation of four human cell lines with distinct biotransformation properties for genotoxic screening

In a previous study, we validated an in vitro genotoxicity assay based on γH2AX quantification using the In-Cell Western (ICW) method in HepG2 cells. The assay demonstrated high sensitivity and specificity but failed to detect genotoxicity for few compounds that require specific metabolic bioactivation not sufficiently covered by HepG2 cells. The aim of the present study was to assess γH2AX ICW sensitivity using a broader range of genotoxic molecules with HepG2 cells and three additional human cell lines with distinct biotransformation properties: two cell lines expressing some phase I and II bioactivation capabilities (LS-174T and Hep3B), and one with poor general bioactivation properties (ACHN). We evaluated the four cell lines by testing 24 compounds recommended by European Centre for the Validation of Alternative Methods and a set of 24 additional chemicals with different mode of genotoxic action (MOA) (aneugenicity, DNA adducts formation, induction of oxidative stress), including some known to require specific cytochrome P450 metabolic bioactivation. Results for the 48 compounds tested showed that the γH2AX ICW assay was more sensitive with LS-174T and HepG2 cells than with Hep3B or ACHN cell lines. Among the 38 compounds tested with positive or equivocal carcinogenicity data, 36 (95%) showed a positive genotoxic response with the γH2AX ICW assay compared to only 27 (71%) using the Ames assay. We confirm that the γH2AX ICW assay on HepG2 cells, without an exogenous metabolic activation system, may be a suitable test to predict the in vivo genotoxicity of chemicals with different genotoxic MOA. Moreover, the use of the ACHN cell line in combination with LS-174T and HepG2 cells may permit in many cases to discriminate direct from bioactivated genotoxins. Overall, our results confirm the high sensitivity of the γH2AX ICW assay which, in turn, should reduce the number of animals used for genotoxicity assessment.

DNA breaks and chromosomal aberrations arise when replication meets base excision repair

DNA double-strand breaks and chromosomal aberrations after treatment with N-alkylating agents likely arise as a result of replication fork collision with single-strand breaks generated during base excision repair.

Exposures that methylate DNA potently induce DNA double-strand breaks (DSBs) and chromosomal aberrations, which are thought to arise when damaged bases block DNA replication. Here, we demonstrate that DNA methylation damage causes DSB formation when replication interferes with base excision repair (BER), the predominant pathway for repairing methylated bases. We show that cells defective in the N-methylpurine DNA glycosylase, which fail to remove N-methylpurines from DNA and do not initiate BER, display strongly reduced levels of methylation-induced DSBs and chromosomal aberrations compared with wild-type cells. Also, cells unable to generate single-strand breaks (SSBs) at apurinic/apyrimidinic sites do not form DSBs immediately after methylation damage. In contrast, cells deficient in x-ray cross-complementing protein 1, DNA polymerase β, or poly (ADP-ribose) polymerase 1 activity, all of which fail to seal SSBs induced at apurinic/apyrimidinic sites, exhibit strongly elevated levels of methylation-induced DSBs and chromosomal aberrations. We propose that DSBs and chromosomal aberrations after treatment with N-alkylators arise when replication forks collide with SSBs generated during BER.

Paraspeckle protein 1 (PSPC1) is involved in the cisplatin induced DNA damage response--role in G1/S checkpoint

Paraspeckle protein 1 (PSPC1) was first identified as a structural protein of the subnuclear structure termed paraspeckle. However, the exact physiological functions of PSPC1 are still largely unknown. Previously, using a proteomic approach, we have shown that exposure to cisplatin can induce PSPC1 expression in HeLa cells, indicating the possible involvement for PSPC1 in the DNA damage response (DDR). In the current study, the role of PSPC1 in DDR was examined. First, it was found that cisplatin treatment could indeed induce the expression of PSPC1 protein. Abolishing PSPC1 expression by siRNA significantly inhibited cell growth, caused spontaneous cell death, and increased DNA damage. However, PSPC1 did not co-localize with γH2AX, 53BP1, or Rad51, indicating no direct involvement in DNA repair pathways mediated by these molecules. Interestingly, knockdown of PSPC1 disrupted the normal cell cycle distribution, with more cells entering the G2/M phase. Furthermore, while cisplatin induced G1/S arrest in HeLa cells, knockdown of PSPC1 caused cells to escape the G1/S checkpoint and enter mitosis, and resulted in more cell death. Taken together, these observations indicate a new role for PSPC1 in maintaining genome integrity during the DDR, particularly in the G1/S checkpoint.

Base excision DNA repair defect in thioredoxin-1 (Trx1)-deficient cells

Thioredoxin-1 (Trx1) is an antioxidant enzyme with a protective role in the removal of oxidative stress. We investigated the mechanism by which the redox modulator Trx1 affects base excision repair (BER) activity to understand the protective role of Trx1. We constructed a Trx1 knockdown system to demonstrate the specific mechanism of Trx1 shRNA cells compared with that in the wild type cells, leading to increased cellular susceptibility to a sublethal dose of BER-inducible toxicant, nitrosomethylurea (NMU). In addition, we observed a modulatory role of Trx1 in the BER pathway via the p53 downstream gene, growth arrest, and DNA-damage-inducible protein 45 α (Gadd45a). The protein level and function of p53, a Trx1 downstream gene, coincidently decreased in the Trx1 shRNA cells. Futhermore, Trx1 shRNA cells showed decreased Gadd45a expression and interaction of Gadd45a with apurinic/apyrimidinic endonuclease 1 (APE1) as well as APE activity. In conclusion, Trx1 might cooperate in the control of APE1 function by modulating the p53-mediated BER via the protein-protein interaction between Gadd45a and APE1, providing insight into the novel role of redox factor Trx1 in modulation of BER.

Proteomic analysis of cellular response induced by multi-walled carbon nanotubes exposure in A549 cells

The wide application of multi-walled carbon nanotubes (MWCNT) has raised serious concerns about their safety on human health and the environment. However, the potential harmful effects of MWCNT remain unclear and contradictory. To clarify the potentially toxic effects of MWCNT and to elucidate the associated underlying mechanisms, the effects of MWCNT on human lung adenocarcinoma A549 cells were examined at both the cellular and the protein level. Cytotoxicity and genotoxicity were examined, followed by a proteomic analysis (2-DE coupled with LC-MS/MS) of the cellular response to MWCNT. Our results demonstrate that MWCNT induces cytotoxicity in A549 cells only at relatively high concentrations and longer exposure time. Within a relatively low dosage range (30 µg/ml) and short time period (24 h), MWCNT treatment does not induce significant cytotoxicity, cell cycle changes, apoptosis, or DNA damage. However, at these low doses and times, MWCNT treatment causes significant changes in protein expression. A total of 106 proteins show altered expression at various time points and dosages, and of these, 52 proteins were further identified by MS. Identified proteins are involved in several cellular processes including proliferation, stress, and cellular skeleton organization. In particular, MWCNT treatment causes increases in actin expression. This increase has the potential to contribute to increased migration capacity and may be mediated by reactive oxygen species (ROS).

Validation of high-throughput genotoxicity assay screening using γH2AX in-cell western assay on HepG2 cells

In vitro genotoxicity tests used in regulatory toxicology studies are sensitive, but the occurrence of irrelevant positive results is high compared with carcinogenicity studies in rodents. Current in vitro genotoxicity tests are also often limited by relatively low throughput. The aim of this study was to validate an in vitro genotoxic assay in a 96-well plate format that allows the simultaneous examination of cytotoxicity and genotoxicity. The test is based on the quantification of the phosphorylation of the histone H2AX (γH2AX), which reflects a global genotoxic insult, using the In-Cell Western technique. The assay was evaluated on HepG2 cells by testing a list of 61 compounds recommended by the European Center for the Validation of Alternative Methods (ECVAM), whose genotoxic potential has already been characterized. The γH2AX assay on HepG2 cell line was highly sensitive: 75% of the genotoxic compounds gave a positive result, and specific: 90-100% of nongenotoxic compounds gave negative results. Compared with the micronucleus genotoxicity assay using the same cell line and test compounds, the γH2AX assay was more sensitive and specific. In sum, the high-throughput γH2AX assay described here can accurately detect simultaneously the genotoxic and the cytotoxic potential of compounds with different modes of mutagenic action, notably those who required metabolic activation. The use of this assay in the early discovery phase of drug development may prove to be a valuable way to assess the genotoxic potential of xenobiotics.

Assessment of the in vitro γH2AX assay by High Content Screening as a novel genotoxicity test

The γH2AX assay is widely used as a marker of DNA damage in multiple scientific fields such as cancer biomarker, clinical studies and radiation biology. In particular, the in vitro γH2AX assay has been suggested as a novel in vitro genotoxicity test with potential as a pre-screening tool. However, to date, limited assessments have been carried out to evaluate the sensitivity, specificity and accuracy of the in vitro γH2AX assay. In this study, the microscopy-based system combining automated cellular image acquisition with software quantification for High Content Screening (HCS) has been used for the first time to evaluate the in vitro γH2AX assay. A panel of well-characterised genotoxic and non-genotoxic compounds was selected to assess the performance of the in vitro γH2AX assay in the human bronchial epithelial cell line BEAS-2B. The results obtained during this preliminary assessment indicate that the in vitro γH2AX assay has a high accuracy (86%) as a result of high sensitivity and specificity (86-92% and 80-88% respectively). Our data highlight the potential for γH2AX detection in HCS as a complement to the current regulatory genotoxicity battery of in vitro assays. We therefore recommend more comprehensive assessments to confirm the performance of the in vitro γH2AX assay by HCS with a more extensive set of compounds.

Multiwall carbon nano-onions induce DNA damage and apoptosis in human umbilical vein endothelial cells

Growing evidence has indicated the potential adverse effects on cardiovascular system of some nanomaterials, including fullerenes. In this study, we have evaluated the biological effects of multiwall carbon nano-onions (MWCNOs) (average size of 31.2 nm, ζ potential of 1.6 mV) on human umbilical vein endothelial cells (HUVECs). It was found that MWCNOs exhibited a dose-dependent inhibitory effect on cell growth; EC50 was 44.12 μg/mL. Thus, three concentrations were chosen (0.2, 1, and 5 μg/mL) for further experiments. Flow cytometry analysis revealed that 1 and 5 μg/mL MWCNOs could induce apoptosis in HUVECs, the apoptotic rates were 12% and 24% at 24 h after exposure. On the other hand, MWCNOs did not affect the cell cycle distribution during 24 h period. Using γH2AX foci formation as an indicator for DNA damage, it was shown that 5 μg/mL MWCNOs can induce γH2AX foci formation in HUVECs at 6, 12, and 24 h after treatment, whereas 0.2 μg/mL MWCNOs induced γH2AX foci formation only at 6 h after treatment. In addition, all three concentrations of MWCNOs induced the generation of reactive oxygen species (ROS), and inhibition of ROS generation can partially decrease the γH2AX foci formation induced by MWCNOs. Taken together, these data first suggested that MWCNOs can induce DNA damage and apoptosis in HUVECs, and that ROS might be involved in this process.

Role of reactive oxygen species in the radiation response of human hematopoietic stem/progenitor cells

Hematopoietic stem/progenitor cells (HSPCs), which are present in small numbers in hematopoietic tissues, can differentiate into all hematopoietic lineages and self-renew to maintain their undifferentiated phenotype. HSPCs are extremely sensitive to oxidative stressors such as anti-cancer agents, radiation, and the extensive accumulation of reactive oxygen species (ROS). The quiescence and stemness of HSPCs are maintained by the regulation of mitochondrial biogenesis, ROS, and energy homeostasis in a special microenvironment called the stem cell niche. The present study evaluated the relationship between the production of intracellular ROS and mitochondrial function during the proliferation and differentiation of X-irradiated CD34⁺ cells prepared from human placental/umbilical cord blood HSPCs. Highly purified CD34⁺ HSPCs exposed to X-rays were cultured in liquid and semi-solid medium supplemented with hematopoietic cytokines. X-irradiated CD34⁺ HSPCs treated with hematopoietic cytokines, which promote their proliferation and differentiation, exhibited dramatically suppressed cell growth and clonogenic potential. The amount of intracellular ROS in X-irradiated CD34⁺ HSPCs was significantly higher than that in non-irradiated cells during the culture period. However, neither the intracellular mitochondrial content nor the mitochondrial superoxide production was elevated in X-irradiated CD34⁺ HSPCs compared with non-irradiated cells. Radiation-induced gamma-H2AX expression was observed immediately following exposure to 4 Gy of X-rays and gradually decreased during the culture period. This study reveals that X-irradiation can increase persistent intracellular ROS in human CD34⁺ HSPCs, which may not result from mitochondrial ROS due to mitochondrial dysfunction, and indicates that substantial DNA double-strand breakage can critically reduce the stem cell function.

Detection of γ-H2AX, a Biomarker for DNA Double-strand Breaks, in Urinary Bladders of N -Butyl- N -(4-Hydroxybutyl)-Nitrosamine-Treated Rats

To evaluate the potential role of DNA repair in bladder carcinogenesis, we performed an immunohistochemical analysis of expression of various DNA repair enzymes and γ-H2AX, a high-sensitivity marker of DNA double-strand breaks, in the urothelium of male F344 rats treated with N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN), a bladder-specific carcinogen. Our results clearly demonstrated that γ-H2AX aggregation was specifically generated in nuclei of bladder epithelial cells of BBN-treated rats, which was not found in untreated controls or mesenchymal cells. γ-H2AX-positive cells were detected not only in hyperplastic and neoplastic areas but also in the normal-like urothelium after BBN treatment. These data indicate that γ-H2AX has potential as a useful biomarker for early detection of genotoxicity in the rat urinary bladder. To the best of our knowledge, this is the first report demonstrating expression of γ-H2AX during bladder carcinogenesis.

miR-200c enhances radiosensitivity of human breast cancer cells

Due to the intrinsic resistance of many tumors to radiotherapy, current methods to improve the survival of cancer patients largely depend on increasing tumor radiosensitivity. It is well-known that miR-200c inhibits epithelial-mesenchymal transition (EMT), and enhances cancer cell chemosensitivity. We sought to clarify the effects of miR-200c on the radiosensitization of human breast cancer cells. In this study, we found that low levels of miR-200c expression correlated with radiotolerance in breast cancer cells. miR-200c overexpression could increase radiosensitivity in breast cancer cells by inhibiting cell proliferation, and by increasing apoptosis and DNA double-strand breaks. Additionally, we found that miR-200c directly targeted TANK-binding kinase 1 (TBK1). However, overexpression of TBK1 partially rescued miR-200c mediated apoptosis induced by ionizing radiation. In summary, miR-200c can be a potential target for enhancing the effect of radiation treatment on breast cancer cells.

The stress response resolution assay. I. Quantitative assessment of environmental agent/condition effects on cellular stress resolution outcomes in epithelium

The events or factors that lead from normal cell function to conditions and diseases such as aging or cancer reflect complex interactions between cells and their environment. Cellular stress responses, a group of processes involved in homeostasis and adaptation to environmental change, contribute to cell survival under stress and can be resolved with damage avoidance or damage tolerance outcomes. To investigate the impact of environmental agents/conditions upon cellular stress response outcomes in epithelium, a novel quantitative assay, the "stress response resolution" (SRR) assay, was developed. The SRR assay consists of pretreatment with a test agent or vehicle followed later by a calibrated stress conditions exposure step (here, using 6-thioguanine). Pilot studies conducted with a spontaneously-immortalized murine mammary epithelial cell line pretreated with vehicle or 20 µg N-ethyl-N-nitrososurea/ml medium for 1 hr, or two hTERT-immortalized human bronchial epithelial cell lines pretreated with vehicle or 100 µM zidovudine/lamivudine for 12 days, found minimal alterations in cell morphology, survival, or cell function through 2 weeks post-exposure. However, when these pretreatments were followed 2 weeks later by exposure to calibrated stress conditions of limited duration (for 4 days), significant alterations in stress resolution were observed in pretreated cells compared with vehicle-treated control cells, with decreased damage avoidance survival outcomes in all cell lines and increased damage tolerance outcomes in two of three cell lines. These pilot study results suggest that sub-cytotoxic pretreatments with chemical mutagens have long-term adverse impact upon the ability of cells to resolve subsequent exposure to environmental stressors.

Combined genotoxic effects of a polycyclic aromatic hydrocarbon (B(a)P) and an heterocyclic amine (PhIP) in relation to colorectal carcinogenesis

Colorectal neoplasia is the third most common cancer worldwide. Environmental factors such as diet are known to be involved in the etiology of this cancer. Several epidemiological studies have suggested that specific neo-formed mutagenic compounds related to meat consumption are an underlying factor involved in the association between diet and colorectal cancer. Heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are known mutagens and possible human carcinogens formed at the same time in meat during cooking processes. We studied the genotoxicity of the model PAH benzo(a)pyrene (B(a)P) and HCA 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), alone or in mixture, using the mouse intestinal cell line Apc^Min/+, mimicking the early step of colorectal carcinogenesis, and control Apc^+/+ cells. The genotoxicity of B(a)P and PhIP was investigated using both cell lines, through the quantification of B(a)P and PhIP derived DNA adducts, as well as the use of a genotoxic assay based on histone H2AX phosphorylation quantification. Our results demonstrate that heterozygous Apc mutated cells are more effective to metabolize B(a)P. We also established in different experiments that PhIP and B(a)P were more genotoxic on Apc^Min/+ cells compared to Apc^+/+. Moreover when tested in mixture, we observed a combined genotoxicity of B(a)P and PhIP on the two cell lines, with an increase of PhIP derived DNA adducts in the presence of B(a)P. Because of their genotoxic effects observed on heterozygous Apc mutated cells and their possible combined genotoxic effects, both B(a)P and PhIP, taken together, could be implicated in the observed association between meat consumption and colorectal cancer.

Recruitment of HRDC domain of WRN and BLM to the sites of DNA damage induced by mitomycin C and methyl methanesulfonate

The HRDC (helicase and RNase D C-terminal) domain at the C-terminal of WRNp (Werner protein) (1150-1229 amino acids) and BLMp (Bloom protein) (1212-1292 amino acids) recognize laser microirradiation-induced DNA dsbs (double-strand breaks). However, their role in the recognition of DNA damage other than dsbs has not been reported. In this work, we show that HRDC domain of both the proteins can be recruited to the DNA damage induced by MMS (methyl methanesulfonate) and MMC (methyl mitomycin C). GFP (green fluorescent protein)-tagged HRDC domain produces distinct foci-like respective wild-types after DNA damage induced by the said agents and co-localize with γ-H2AX. However, in time course experiment, we observed that the foci of HRDC domain exist after 24 h of removal of the damaging agents, while the foci of full-length protein disappear completely. This indicates that the repair events are not completed by the presence of protein corresponding to only the HRDC domain. Consequently, cells overexpressing the HRDC domain fail to survive after DNA damage, as determined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. Moreover, 24 h after removal of damaging agents, the extent of DNA damage is greater in cells overexpressing HRDC domain compared with corresponding wild-types, as observed by comet assay. Thus, our observations suggest that HRDC domain of both WRN and BLM can also recognize different types of DNA damages, but for the successful repair they fail to respond to subsequent repair events.

Heat induces gene amplification in cancer cells

BACKGROUND

Hyperthermia plays an important role in cancer therapy. However, as with radiation, it can cause DNA damage and therefore genetic instability. We studied whether hyperthermia can induce gene amplification in cancer cells and explored potential underlying molecular mechanisms.

MATERIALS AND METHODS

(1) Hyperthermia: HCT116 colon cancer cells received water-submerged heating treatment at 42 or 44°C for 30 min; (2) gene amplification assay using N-(phosphoacetyl)-L-aspartate (PALA) selection of cabamyl-P-synthetase, aspartate transcarbarmylase, dihydro-orotase (cad) gene amplified cells; (3) southern blotting for confirmation of increased cad gene copies in PALA-resistant cells; (4) γH2AX immunostaining to detect γH2AX foci as an indication for DNA double strand breaks.

RESULTS

(1) Heat exposure at 42 or 44°C for 30 min induces gene amplification. The frequency of cad gene amplification increased by 2.8 and 6.5 folds respectively; (2) heat exposure at both 42 and 44°C for 30 min induces DNA double strand breaks in HCT116 cells as shown by γH2AX immunostaining.

CONCLUSION

This study shows that heat exposure can induce gene amplification in cancer cells, likely through the generation of DNA double strand breaks, which are believed to be required for the initiation of gene amplification. This process may be promoted by heat when cellular proteins that are responsible for checkpoints, DNA replication, DNA repair and telomere functions are denatured. To our knowledge, this is the first study to provide direct evidence of hyperthermia induced gene amplification.