Activation of Ataxia Telangiectasia Mutated by DNA Strand Break-inducing Agents Correlates Closely with the Number of DNA Double Strand Breaks

Drug repurposing screen for the rare disease ataxia-telangiectasia

Ataxia Telangiectasia (A-T) is a rare, autosomal recessive genetic disorder characterized by a variety of symptoms, including progressive neurodegeneration, telangiectasia, immunodeficiency, and an increased susceptibility to cancer. It is caused by bi-allelic mutations impacting a gene encoding a serine/threonine kinase ATM (Ataxia Telangiectasia Mutated), which plays a crucial role in DNA repair and maintenance of genomic stability. The disorder primarily affects the nervous system, leading to a range of neurological issues, including cerebellar ataxia. The cause of neurodegeneration due to mutations in ATM is still an area of investigation, and currently there is no known treatment to slow down or stop the progression of the neurological problems. In this collaboration of the A-T Children's Project (ATCP) with Charles River Discovery, we successfully developed a high-throughput assay using induced pluripotent stem cells (iPSC) from A-T donors to measure DNA damage response (DDR). By measuring the changes in levels of activated phosphorylated CHK2 (p-CHK2), which is a downstream signaling event of ATM, we were able to identify compounds that restore this response in the DDR pathway in A-T derived patient cells. Over 6,000 compounds from small molecule drug repurposing libraries were subsequently screened in the assay developed, leading to identification of several promising in vitro hits. Using the assay developed and the identified hits opens avenues to investigate potential therapeutics for A-T.

CREB3L1/OASIS: cell cycle regulator and tumor suppressor

Cell cycle checkpoints detect DNA errors, eventually arresting the cell cycle to promote DNA repair. Failure of such cell cycle arrest causes aberrant cell proliferation, promoting the pathogenesis of multiple diseases, including cancer. Endoplasmic reticulum (ER) stress transducers activate the unfolded protein response, which not only deals with unfolded proteins in ER lumen but also orchestrates diverse physiological phenomena such as cell differentiation and lipid metabolism. Among ER stress transducers, cyclic AMP-responsive element-binding protein 3-like protein 1 (CREB3L1) [also known as old astrocyte specifically induced substance (OASIS)] is an ER-resident transmembrane transcription factor. This molecule is cleaved by regulated intramembrane proteolysis, followed by activation as a transcription factor. OASIS is preferentially expressed in specific cells, including astrocytes and osteoblasts, to regulate their differentiation. In accordance with its name, OASIS was originally identified as being upregulated in long-term-cultured astrocytes undergoing cell cycle arrest because of replicative stress. In the context of cell cycle regulation, previously unknown physiological roles of OASIS have been discovered. OASIS is activated as a transcription factor in response to DNA damage to induce p21-mediated cell cycle arrest. Although p21 is directly induced by the master regulator of the cell cycle, p53, no crosstalk occurs between p21 induction by OASIS or p53. Here, we summarize previously unknown cell cycle regulation by ER-resident transcription factor OASIS, particularly focusing on commonalities and differences in cell cycle arrest between OASIS and p53. This review also mentions tumorigenesis caused by OASIS dysfunctions, and OASIS's potential as a tumor suppressor and therapeutic target.

Senataxin Attenuates DNA Damage Response Activation and Suppresses Senescence

Oxidative stress, driven by reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), induces DNA double-strand breaks (DSBs) that compromise genomic integrity. The DNA Damage Response (DDR), primarily mediated by ATM and ATR kinases, is crucial for recognizing and repairing DSBs. Senataxin (SETX), a DNA/RNA helicase, is critical in resolving R-loops, with mutations in SETX associated with neurodegenerative diseases. This study uncovers a novel function of senataxin in modulating DDR and its impact on cellular senescence. Senataxin is shown to be crucial not only for DSB repair but also for determining cell fate under oxidative stress. SETX knockout cells show impaired DSB repair and prolonged ATM/ATR signaling detected by Western blotting, leading to increased senescence, as indicated by elevated β-galactosidase activity following H2O2 exposure and I-PpoI-induced DSBs. Wild-type cells exhibit higher apoptosis levels compared to SETX knockout cells under H2O2 treatment, suggesting that senataxin promotes apoptosis over senescence in oxidative stress. This indicates that senataxin plays a protective role against the accumulation of senescent cells, potentially mitigating age-related cellular decline and neurodegenerative disease progression. These findings highlight senataxin as a critical mediator in DDR pathways and a potential therapeutic target for conditions where cellular senescence contributes to disease pathology.

Crosstalk between the DNA damage response and cellular senescence drives aging and age-related diseases

Cellular senescence is a crucial process of irreversible cell-cycle arrest, in which cells remain alive, but permanently unable to proliferate in response to distinct types of stressors. Accumulating evidence suggests that DNA damage builds over time and triggers DNA damage response signaling, leading to cellular senescence. Cellular senescence serves as a platform for the perpetuation of inflammatory responses and is central to numerous age-related diseases. Defects in DNA repair genes or senescence can cause premature aging disease. Therapeutic approaches limiting DNA damage or senescence contribute to a rescued phenotype of longevity and neuroprotection, thus suggesting a mechanistic interaction between DNA damage and senescence. Here, we offer a unique perspective on the crosstalk between the DNA damage response pathway and senescence as well as their contribution to age-related diseases. We further summarize recent progress on the mechanisms and therapeutics of senescence, address existing challenges, and offering new insights and future directions in the senescence field.

Isolation of a novel quercetin derivative from Terminalia chebula and RT-PCR-assisted probing to investigate its DNA repair in hepatoma cells

Background and purpose

DNA damage can lead to carcinogenesis if replication proceeds without proper repair. This study focused on the purification of a novel quercetin derivative present in Terminalia chebula fruit and studied its protective role in hepatoma cells due to H2O2-DNA damage.

Experimental approach

The pure compound obtained from the silica gel column was subjected to structural characterization using spectroscopic techniques. MTT assay was employed to select a non-toxic concentration of the isolated compounds on HepG2 and Chang liver cells. The antigenotoxic property of the compound on HepG2 and Chang liver cells was carried out by alkaline comet assay. Analyses of expression levels of mRNA for two DNA repair enzymes, OGG1 and NEIL1, in HepG2 and Chang liver cells, were carried out using the RT-PCR method.

Findings/Results

The pure compound obtained from the fraction-5 of diethyl ether extract was identified as a novel quercetin derivative and named 7-(but-2-en-1-yloxy)-2-(4(but-2-en-1-yloxy)-3-hydroxyphenyl)-3- (hexa-2,4-dien-1-yloxy)-6-hydroxy-4H-chromen-4-one. This compound recorded modest toxicity at the highest concentration tested (percentage cell viability at 100 μg/mL was 64.71 ± 0.38 for HepG2 and 45.32 ± 0.07 for Chang liver cells). The compound has demonstrated noteworthy protection against H2O2-induced DNA damage in both cell lines. Analyses of mRNA expression levels for enzymes OGGI and NEIL1 enzymes in HepG2 and Chang liver cells asserted the protective role of the isolated compound against H2O2-induced DNA damage.

Conclusion and implication

The protective effect of a novel quercetin derivative isolated from T. chebula in the hepatoma cells is reported here for the first time.

The cell stress and immunity cycle in cancer: Toward next generation of cancer immunotherapy

The cellular stress and immunity cycle is a cornerstone of organismal homeostasis. Stress activates intracellular and intercellular communications within a tissue or organ to initiate adaptive responses aiming to resolve the origin of this stress. If such local measures are unable to ameliorate this stress, then intercellular communications expand toward immune activation with the aim of recruiting immune cells to effectively resolve the situation while executing tissue repair to ameliorate any damage and facilitate homeostasis. This cellular stress-immunity cycle is severely dysregulated in diseased contexts like cancer. On one hand, cancer cells dysregulate the normal cellular stress responses to reorient them toward upholding growth at all costs, even at the expense of organismal integrity and homeostasis. On the other hand, the tumors severely dysregulate or inhibit various components of organismal immunity, for example, by facilitating immunosuppressive tumor landscape, lowering antigenicity, and increasing T-cell dysfunction. In this review we aim to comprehensively discuss the basis behind tumoral dysregulation of cellular stress-immunity cycle. We also offer insights into current understanding of the regulators and deregulators of this cycle and how they can be targeted for conceptualizing successful cancer immunotherapy regimen.

miR-302d Targeting of CDKN1A Regulates DNA Damage and Steroid Hormone Secretion in Bovine Cumulus Cells

(1) Background: DNA damage in cumulus cells hinders oocyte maturation and affects steroid hormone secretion. It is crucial to identify the key factors that regulate cellular DNA damage and steroid hormone secretion. (2) Methods: Treatment of bovine cumulus cells with bleomycin to induce DNA damage. The effects of DNA damage on cell biology were determined by detecting changes in DNA damage degree, cell cycle, viability, apoptosis, and steroid hormones. It was verified that mir-302d targeted regulation of CDKN1A expression, and then affected DNA damage and steroid hormone secretion in cumulus cells. (3) Results: Bleomycin induced increased DNA damage, decreased G1-phase cells, increased S-phase cells, inhibited proliferation, promoted apoptosis, affected E2 and P4 secretion, increased CDKN1A expression, and decreased miR-302d expression. Knockdown of CDKN1A reduced DNA damage, increased G1-phase cells, decreased G2-phase cells, promoted proliferation, inhibited apoptosis, increased E2 and P4 secretion, and increased the expression of BRCA1, MRE11, ATM, CDK1, CDK2, CCNE2, STAR, CYP11A1, and HSD3B1. The expression of RAD51, CCND1, p53, and FAS was decreased. Overexpression of CDKN1A resulted in the opposite results. miR-302d targets CDKN1A expression to regulate DNA damage and then affects the cell cycle, proliferation, apoptosis, steroid hormone secretion, and the expression of related genes. (4) Conclusions: miR-302d and CDKN1A were candidate molecular markers for the diagnosis of DNA damage in bovine cumulus cells.

p53-independent tumor suppression by cell-cycle arrest via CREB/ATF transcription factor OASIS

CREB/ATF transcription factor OASIS/CREB3L1 is upregulated in long-term-cultured astrocytes undergoing cell-cycle arrest due to loss of DNA integrity by repeated replication. However, the roles of OASIS in the cell cycle remain unexplored. We find that OASIS arrests the cell cycle at G₂/M phase after DNA damage via direct induction of p21. Cell-cycle arrest by OASIS is dominant in astrocytes and osteoblasts, but not in fibroblasts, which are dependent on p53. In a brain injury model, Oasis^-/- reactive astrocytes surrounding the lesion core show sustained growth and inhibition of cell-cycle arrest, resulting in prolonged gliosis. We find that some glioma patients exhibit low expression of OASIS due to high methylation of its promoter. Specific removal of this hypermethylation in glioblastomas transplanted into nude mice by epigenomic engineering suppresses the tumorigenesis. These findings suggest OASIS as a critical cell-cycle inhibitor with potential to act as a tumor suppressor.

Cisplatin Induces Senescent Lung Cancer Cell-Mediated Stemness Induction via GRP78/Akt-Dependent Mechanism

Cellular senescence is linked with chemotherapy resistance. Based on previous studies, GRP78 is a signal transducer in senescent cells. However, the association between GRP78 and stem cell phenotype remains unknown. Cisplatin treatment was clarified to induce cellular senescence leading to stemness induction via GRP78/Akt signal transduction. H460 cells were treated with 5 μM of cisplatin for 6 days to develop senescence. The colony formation assay and cell cycle analysis were performed. SA-β-galactosidase staining indicated senescence. Western blot analysis and RT-PCR were operated. Immunoprecipitation (IP) and immunocytochemistry assays (ICC) were also performed. Colony-forming activity was completely inhibited, and 87.07% of the cell population was arrested in the G2 phase of the cell cycle. mRNA of p21 and p53 increased approximately by 15.91- and 19.32-fold, respectively. The protein level of p21 and p53 was elevated by 9.57- and 5.9-fold, respectively. In addition, the c-Myc protein level was decreased by 0.2-fold when compared with the non-treatment control. Even though, the total of GRP78 protein was downregulated after cisplatin treatment, but the MTJ1 and downstream regulator, p-Akt/Akt ratio were upregulated by approximately 3.38 and 1.44-fold, respectively. GRP78 and MTJ1 were found at the cell surface membrane. Results showed that the GRP78/MTJ1 complex and stemness markers, including CD44, CD133, Nanog, Oct4, and Sox2, were concomitantly increased in senescent cells. MTJ1 anchored GRP78, facilitating the signal transduction of stem-like phenotypes. The strategy that could interrupt the binding between these crucial proteins or inhibit the translocation of GRP78 might beuseful for cancer therapy.

GM-CSF Protects Macrophages from DNA Damage by Inducing Differentiation

At inflammatory loci, pro-inflammatory activation of macrophages produces large amounts of reactive oxygen species (ROS) that induce DNA breaks and apoptosis. Given that M-CSF and GM-CSF induce two different pathways in macrophages, one for proliferation and the other for survival, in this study we wanted to determine if these growth factors are able to protect against the DNA damage produced during macrophage activation. In macrophages treated with DNA-damaging agents we found that GM-CSF protects better against DNA damage than M-CSF. Treatment with GM-CSF resulted in faster recovery of DNA damage than treatment with M-CSF. The number of apoptotic cells induced after DNA damage was higher in the presence of M-CSF. Protection against DNA damage by GM-CSF is not related to its higher capacity to induce proliferation. GM-CSF induces differentiation markers such as CD11c and MHCII, as well as the pro-survival Bcl-2A1 protein, which make macrophages more resistant to DNA damage.

Caspase-2 regulates S-phase cell cycle events to protect from DNA damage accumulation independent of apoptosis

In addition to its classical role in apoptosis, accumulating evidence suggests that caspase-2 has non-apoptotic functions, including regulation of cell division. Loss of caspase-2 is known to increase proliferation rates but how caspase-2 is regulating this process is currently unclear. We show that caspase-2 is activated in dividing cells in G1-phase of the cell cycle. In the absence of caspase-2, cells exhibit numerous S-phase defects including delayed exit from S-phase, defects in repair of chromosomal aberrations during S-phase, and increased DNA damage following S-phase arrest. In addition, caspase-2-deficient cells have a higher frequency of stalled replication forks, decreased DNA fiber length, and impeded progression of DNA replication tracts. This indicates that caspase-2 protects from replication stress and promotes replication fork protection to maintain genomic stability. These functions are independent of the pro-apoptotic function of caspase-2 because blocking caspase-2-induced cell death had no effect on cell division, DNA damage-induced cell cycle arrest, or DNA damage. Thus, our data supports a model where caspase-2 regulates cell cycle and DNA repair events to protect from the accumulation of DNA damage independently of its pro-apoptotic function.

Challenges and Opportunities to Develop Enediyne Natural Products as Payloads for Antibody-Drug Conjugates

Calicheamicin, the payload of the antibody-drug-conjugates (ADCs) gemtuzumab ozogamicin (Mylotarg^®) and inotuzumab ozogamicin (Besponsa^®), belongs to the class of enediyne natural products. Since the isolation and structural determination of the neocarzinostatin chromophore in 1985, the enediynes have attracted considerable attention for their value as DNA damaging agents in cancer chemotherapy. Due to their non-discriminatory cytotoxicity towards both cancer and healthy cells, the clinical utilization of enediyne natural products relies on conjugation to an appropriate delivery system, such as an antibody. Here we review the current landscape of enediynes as payloads of first-generation and next-generation ADCs.

The IRI-DICE hypothesis: ionizing radiation-induced DSBs may have a functional role for non-deterministic responses at low doses

Low-dose ionizing radiation (IR) responses remain an unresolved issue in radiation biology and risk assessment. Accurate knowledge of low-dose responses is important for estimation of normal tissue risk in cancer radiotherapy or health risks from occupational or hazard exposure. Cellular responses to low-dose IR appear diverse and stochastic in nature and to date no model has been proposed to explain the underlying mechanisms. Here, we propose a hypothesis on IR-induced double-strand break (DSB)-induced cis effects (IRI-DICE) and introduce DNA sequence functionality as a submicron-scale target site with functional outcome on gene expression: DSB induction in a certain genetic target site such as promotor, regulatory element, or gene core would lead to changes in transcript expression, which may range from suppression to overexpression depending on which functional element was damaged. The DNA damage recognition and repair machinery depicts threshold behavior requiring a certain number of DSBs for induction. Stochastically distributed persistent disruption of gene expression may explain-in part-the diverse nature of low-dose responses until the repair machinery is initiated at increased absorbed dose. Radiation quality and complexity of DSB lesions are also discussed. Currently, there are no technologies available to irradiate specific genetic sites to test the IRI-DICE hypothesis directly. However, supportive evidence may be achieved by developing a computational model that combines radiation transport codes with a genomic DNA model that includes sequence functionality and transcription to simulate expression changes in an irradiated cell population. To the best of our knowledge, IRI-DICE is the first hypothesis that includes sequence functionality of different genetic elements in the radiation response and provides a model for the diversity of radiation responses in the (very) low dose regimen.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Cell death induced by dorsomorphin in adult T-cell leukemia/lymphoma is AMPK-independent

Adult T-cell leukemia/lymphoma (ATL) is an aggressive T-cell neoplasm with poor prognosis that develops after chronic infection with human T-cell leukemia virus type 1 (HTLV-1). Although AMP-activated protein kinase (AMPK) is a critical cellular energy sensor, it has recently become clear that AMPK can act as a tumor regulator. Here, we assessed the expression of AMPK in primary ATL cells and the effects of dorsomorphin, an AMPK inhibitor, on primary ATL cells and HTLV-1-infected T-cell lines. AMPK expression in acute and chronic ATL patients was significantly higher than in asymptomatic HTLV-1 carriers and healthy donors. Dorsomorphin induced apoptosis in peripheral blood mononuclear cells from ATL patients. Dorsomorphin also induced dose- and time-dependent apoptosis in HTLV-1-infected T-cell lines. Dorsomorphin increased the production of intracellular reactive oxygen species (ROS) and induced ataxia telangiectasia-mutated Ser1981 phosphorylation and p53 accumulation. These results indicated that dorsomorphin induces apoptosis via ROS-mediated DNA damage in HTLV-1-infected T-cell lines. Furthermore, dorsomorphin suppressed the growth of human ATL tumor xenografts in NOD/SCID mice. Together, these data suggest that AMPK could be a candidate therapeutic target for ATL and that dorsomorphin could be a therapeutic agent for ATL.

Auger electrons for cancer therapy - a review

Background

Auger electrons (AEs) are very low energy electrons that are emitted by radionuclides that decay by electron capture (e.g. ¹¹¹In, ⁶⁷Ga, ^99mTc, ^195mPt, ¹²⁵I and ¹²³I). This energy is deposited over nanometre-micrometre distances, resulting in high linear energy transfer (LET) that is potent for causing lethal damage in cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for treatment of cancer. In this review, we describe the radiobiological properties of AEs, their radiation dosimetry, radiolabelling methods, and preclinical and clinical studies that have been performed to investigate AEs for cancer treatment.

Results

AEs are most lethal to cancer cells when emitted near the cell nucleus and especially when incorporated into DNA (e.g. ¹²⁵I-IUdR). AEs cause DNA damage both directly and indirectly via water radiolysis. AEs can also kill targeted cancer cells by damaging the cell membrane, and kill non-targeted cells through a cross-dose or bystander effect. The radiation dosimetry of AEs considers both organ doses and cellular doses. The Medical Internal Radiation Dose (MIRD) schema may be applied. Radiolabelling methods for complexing AE-emitters to biomolecules (antibodies and peptides) and nanoparticles include radioiodination (¹²⁵I and ¹²³I) or radiometal chelation (¹¹¹In, ⁶⁷Ga, ^99mTc). Cancer cells exposed in vitro to AE-emitting radiotherapeutic agents exhibit decreased clonogenic survival correlated at least in part with unrepaired DNA double-strand breaks (DSBs) detected by immunofluorescence for γH2AX, and chromosomal aberrations. Preclinical studies of AE-emitting radiotherapeutic agents have shown strong tumour growth inhibition in vivo in tumour xenograft mouse models. Minimal normal tissue toxicity was found due to the restricted toxicity of AEs mostly on tumour cells targeted by the radiotherapeutic agents. Clinical studies of AEs for cancer treatment have been limited but some encouraging results were obtained in early studies using ¹¹¹In-DTPA-octreotide and ¹²⁵I-IUdR, in which tumour remissions were achieved in several patients at administered amounts that caused low normal tissue toxicity, as well as promising improvements in the survival of glioblastoma patients with ¹²⁵I-mAb 425, with minimal normal tissue toxicity.

Conclusions

Proof-of-principle for AE radiotherapy of cancer has been shown preclinically, and clinically in a limited number of studies. The recent introduction of many biologically-targeted therapies for cancer creates new opportunities to design novel AE-emitting agents for cancer treatment. Pierre Auger did not conceive of the application of AEs for targeted cancer treatment, but this is a tremendously exciting future that we and many other scientists in this field envision.

Extracellular signal-regulated kinase 5 increases radioresistance of lung cancer cells by enhancing the DNA damage response

Radiotherapy is a frequent mode of cancer treatment, although the development of radioresistance limits its effectiveness. Extensive investigations indicate the diversity of the mechanisms underlying radioresistance. Here, we aimed to explore the effects of extracellular signal-regulated kinase 5 (ERK5) on lung cancer radioresistance and the associated mechanisms. Our data showed that ERK5 is activated during solid lung cancer development, and ectopic expression of ERK5 promoted cell proliferation and G2/M cell cycle transition. In addition, we found that ERK5 is a potential regulator of radiosensitivity in lung cancer cells. Mechanistic investigations revealed that ERK5 could trigger IR-induced activation of Chk1, which has been implicated in DNA repair and cell cycle arrest in response to DNA double-strand breaks (DSBs). Subsequently, ERK5 knockdown or pharmacological inhibition selectively inhibited colony formation of lung cancer cells and enhanced IR-induced G2/M arrest and apoptosis. In vivo, ERK5 knockdown strongly radiosensitized A549 and LLC tumor xenografts to inhibition, with a higher apoptotic response and reduced tumor neovascularization. Taken together, our data indicate that ERK5 is a novel potential target for the treatment of lung cancer, and its expression might be used as a biomarker to predict radiosensitivity in NSCLC patients.

Resistance to radiotherapy in patients with lung cancer may be countered by targeting a protein involved in promoting DNA repair. Radiotherapy causes DNA double-stranded breaks in lung cancer cells in order to kill them. However, cancer cells can show improved DNA repair and responses to damage, resulting in resistance to treatment. Zi-Chun Hua, Hongqin Zhuang at Nanjing University in China and co-workers examined the activity of the extracellular signal-related kinase 5 (ERK5) protein in response to the stress of ionizing radiation. They found that after radiation exposure ERK5 increased expression of another protein involved in DNA repair, facilitating cancer cell recovery. Knocking out ERK5 suppressed this resistance to radiotherapy. ERK5 could be a valuable target for treating lung cancer, and ERK5 expression level could be used as a biomarker for patient sensitivity to radiotherapy.

Northern lights assay: a versatile method for comprehensive detection of DNA damage

DNA damage assays have various limitations in types of lesions detected, sensitivity, specificity and samples that can be analyzed. The Northern Lights Assay (NLA) is based on 2D Strandness-Dependent Electrophoresis (2D-SDE), a technique that separates nucleic acids based on length, strandness, structure and conformation changes induced by damage. NLA is run on a microgel platform in 20-25 min. Each specimen is analyzed in pairs of non-digested DNA to detect single- and double-stranded breaks (DSBs) and Mbo I-digested DNA to detect other lesions. We used NLA to evaluate DNA in solution and isolated from human cells treated with various genotoxic agents. NLA detected and distinguished between single- and DSBs, interstrand and intrastrand DNA crosslinks, and denatured single-stranded DNA. NLA was sufficiently sensitive to detect biologically relevant amount of DNA damage. NLA is a versatile, sensitive and simple method for comprehensive and simultaneous analysis of multiple types of damage, both in purified DNA and in DNA isolated from cells and body fluids. NLA can be used to evaluate DNA quality in biosamples, monitor complex molecular procedures, assess genotoxicity, diagnose genome instability, facilitate cancer theranostics and in basic nucleic acids research.

The activated DNA double-strand break repair pathway in cumulus cells from aging patients may be used as a convincing predictor of poor outcomes after in vitro fertilization-embryo transfer treatment

Women with advanced maternal age exhibit low anti-Müllerian hormone (AMH) levels and an altered follicular environment, which is associated with poor oocyte quality and embryonic developmental potential. However, the underlying mechanism is poorly understood. The present study aimed to assesswhether aging patients exhibit an activated DNA double-strandbreak (DSB) repair pathway in cumulus cells and thus, an association with poor outcomes after in vitro fertilization-embryo transfer (IVF-ET) treatment. Cumulus cells from young (≤29 y) and aging (≥37 y) human female patients were collected after oocyte retrieval. Our results indicated that aging patients showed a higher rate of γ-H2AX-positive cells than in young patients (24.33±4.55 vs.12.40±2.31, P<0.05). We also found that the mRNA expression levels of BRCA1, ATM, MRE11 and RAD51 were significantly elevated in aging cumulus cells. Accordingly, significantly increased protein levels of phospho-H2AX, BRCA1, ATM, MRE11 and RAD51 could be observed in aging cumulus cells. Moreover, aging cumulus cells showed a more frequent occurrence of early apoptosis than young cumulus cells. This study found that increases in DSBs and the activation of the repair pathway are potential indicators that may be used to predictoutcomes after IVF-ET treatment.

DNA Ligase C and Prim-PolC participate in base excision repair in mycobacteria

Prokaryotic Ligase D is a conserved DNA repair apparatus processing DNA double-strand breaks in stationary phase. An orthologous Ligase C (LigC) complex also co-exists in many bacterial species but its function is unknown. Here we show that the LigC complex interacts with core BER enzymes in vivo and demonstrate that together these factors constitute an excision repair apparatus capable of repairing damaged bases and abasic sites. The polymerase component, which contains a conserved C-terminal structural loop, preferentially binds to and fills-in short gapped DNA intermediates with RNA and LigC ligates the resulting nicks to complete repair. Components of the LigC complex, like LigD, are expressed upon entry into stationary phase and cells lacking either of these pathways exhibit increased sensitivity to oxidising genotoxins. Together, these findings establish that the LigC complex is directly involved in an excision repair pathway(s) that repairs DNA damage with ribonucleotides during stationary phase.

Ligase D is a conserved DNA repair protein complex that repairs double-strand breaks in stationary phase prokaryotes. Here the authors show that orthologous Ligase C has a role in base excision repair during stationary phase.

Enhancement of apoptotic activities on brain cancer cells via the combination of γ-tocotrienol and jerantinine A

BACKGROUND

γ-Tocotrienol, a vitamin E isomer possesses pronounced in vitro anticancer activities. However, the in vivo potency has been limited by hardly achievable therapeutic levels owing to inefficient high-dose oral delivery which leads to subsequent metabolic degradation. Jerantinine A, an Aspidosperma alkaloid, originally isolated from Tabernaemontana corymbosa, has proved to possess interesting anticancer activities. However, jerantinine A also induces toxicity to non-cancerous cells.

PURPOSE

We adopted a combinatorial approach with the joint application of γ-tocotrienol and jerantinine A at lower concentrations in order to minimize toxicity towards non-cancerous cells while improving the potency on brain cancer cells.

METHODS

The antiproliferative potency of individual γ-tocotrienol and jerantinine A as well as combined in low-concentration was firstly evaluated on U87MG cancer and MRC5 normal cells. Morphological changes, DNA damage patterns, cell cycle arrests and the effects of individual and combined low-concentration compounds on microtubules were then investigated. Finally, the potential roles of caspase enzymes and apoptosis-related proteins in mediating the apoptotic mechanisms were investigated using apoptosis antibody array, ELISA and Western blotting analysis.

RESULTS

Combinatorial study between γ-tocotrienol at a concentration range (0-24µg/ml) and fixed IC₂₀ concentration of jerantinine A (0.16µg/ml) induced a potent antiproliferative effect on U87MG cells and led to a reduction on the new half maximal inhibitory concentration of γ-tocotrienol (i.e._tIC₅₀=1.29µg/ml) as compared to that of individual γ-tocotrienol (i.e. IC₅₀=3.17µg/ml). A reduction on undesirable toxicity to MRC5 normal cells was also observed. G0/G1 cell cycle arrest was evident on U87MG cells receiving IC₅₀ of individual γ-tocotrienol and combined low-concentration compounds (1.29µg/ml γ-tocotrienol + 0.16µg/ml jerantinine A), whereas, a profound G2/M arrest was evident on cells treated with IC₅₀ of individual jerantinine A. Additionally, individual jerantinine A and combined compounds (except individual γ-tocotrienol) caused a disruption of microtubule networks triggering Fas- and p53-induced apoptosis mediated via the death receptor and mitochondrial pathways.

CONCLUSIONS

These findings demonstrated that the combined use of lower concentrations of γ-tocotrienol and jerantinine A induced potent cytotoxic effects on U87MG cancer cells resulting in a reduction on the required individual concentrations and thereby minimizing toxicity of jerantinine A towards non-cancerous MRC5 cells as well as probably overcoming the high-dose limiting application of γ-tocotrienol. The multi-targeted mechanisms of action of the combination approach have shown a therapeutic potential against brain cancer in vitro and therefore, further in vivo investigations using a suitable animal model should be the way forward.

Linking loss of sodium-iodide symporter expression to DNA damage

Radiotherapy of thyroid cancer with I-131 is abrogated by inherent loss of radioiodine uptake due to loss of sodium iodide symporter (NIS) expression in poorly differentiated tumor cells. It is also known that ionizing radiation per se down-regulates NIS (the stunning effect), but the mechanism is unknown. Here we investigated whether loss of NIS-mediated iodide transport may be elicited by DNA damage. Calicheamicin, a fungal toxin that specifically cleaves double-stranded DNA, induced a full scale DNA damage response mediated by the ataxia-telangiectasia mutated (ATM) kinase in quiescent normal thyrocytes. At sublethal concentrations (<1nM) calicheamicin blocked NIS mRNA expression and transepithelial iodide transport as stimulated by thyrotropin; loss of function occurred at a much faster rate than after I-131 irradiation. KU-55933, a selective ATM kinase inhibitor, partly rescued NIS expression and iodide transport in DNA-damaged cells. Prolonged ATM inhibition in healthy cells also repressed NIS-mediated iodide transport. ATM-dependent loss of iodide transport was counteracted by IGF-1. Together, these findings indicate that NIS, the major iodide transporter of the thyroid gland, is susceptible to DNA damage involving ATM-mediated mechanisms. This uncovers novel means of poor radioiodine uptake in thyroid cells subjected to extrinsic or intrinsic genotoxic stress.

Dynamic monitoring of oxidative DNA double-strand break and repair in cardiomyocytes

DNA double-strand breaks (DSBs) are most dangerous lesions. To determine whether oxidative stress can induce DSBs and how they are repaired in cardiomyocytes (CMs), cultured neonatal rat CMs were treated with different doses of H2O2 and followed for up to 72 h for monitoring the spatiotemporal dynamics of DNA repair protein assembly/disassembly at DSB foci. The protein levels and foci numbers of histone H2AX phosphorylated at serine 139 (γ-H2AX) increased proportionally to 50, 100, and 200 μmol/L H2O2 after 30 min treatment. When H2O2 was at or above 400 μmol/L, γ-H2AX became predominantly pannuclear. After 30 min, 200 μmol/L of H2O2 treatment, γ-H2AX levels were highest within the first hour and then gradually declined during the recovery and returned to basal levels at 48 h. Among DNA damage transducer kinases, ataxia telangiectasia mutated (ATM) was significantly activated by H2O2 in contrast to mild activation of ATR (ATM and Rad3-related). A DSB binding protein, p53 binding protein 1, formed distinct nuclear foci that colocalized with γ-H2AX foci and phosphorylated ATM. Our findings indicate that DSBs can be induced by H2O2 and ATM is the main kinase to mediate DSB repair in CMs. Therefore, monitoring DSB repair can assess oxidative injury and response in CMs.

Downregulation of MDC1 and 53BP1 by short hairpin RNA enhances radiosensitivity in laryngeal carcinoma cells

DNA double-strand breaks (DSBs) induced by ionizing radiation (IR) are among the most cytotoxic types of DNA damage. The DNA damage response (DDR) may be a reason for the cancer cell resistance to radiotherapy using IR. Identified as critical upstream mediators of the phosphorylation of ataxia telangiectasia-mutated (ATM) pathway, mediator of DNA damage checkpoint 1 (MDC1) and p53-binding proteins 1 (53BP1) may affect the radiosensitivity of tumor cells. In the present study, we generated two HEP-2 cell lines with a stable knockdown of MDC1 or 53BP1 with short hairpin RNA (shRNA), respectively, and investigated the effect of MDC1 and 53BP1 on cell radiosensitivity, cell cycle distribution and the formation of cell foci. Downregulation of the two proteins reduced the number of clonogenic cells that treated with IR. Accumulation of G2/M phase cells was detected after the MDC1 and 53BP1 downregulation. These results indicated that the expression of MDC1 or 53BP1 limited tumor cell sensitivity to radiotherapy and may play an important role in the DNA repair progression. Furthermore, the MDC1 foci was identified and presented in the 53BP1-inhibited cells. By contrast, the 53BP1 foci was absent from the MDC1-inhibited cells. The results confirmed that the recruitment of 53BP1 into the foci occurred in an MDC1-dependent manner.

Bora downregulation results in radioresistance by promoting repair of double strand breaks

Following DNA double-strand breaks cells activate several DNA-damage response protein kinases, which then trigger histone H2AX phosphorylation and the accumulation of proteins such as MDC1, p53-binding protein 1, and breast cancer gene 1 at the damage site to promote DNA double-strand breaks repair. We identified a novel biomarker, Bora (previously called C13orf34), that is associated with radiosensitivity. In the current study, we set out to investigate how Bora might be involved in response to irradiation. We found a novel function of Bora in DNA damage repair response. Bora down-regulation increased colony formation in cells exposed to irradiation. This increased resistance to irradiation in Bora-deficient cells is likely due to a faster rate of double-strand breaks repair. After irradiation, Bora-knockdown cells displayed increased G2-M cell cycle arrest and increased Chk2 phosphorylation. Furthermore, Bora specifically interacted with the tandem breast cancer gene 1 C-terminal domain of MDC1 in a phosphorylation dependent manner, and overexpression of Bora could abolish irradiation induced MDC1 foci formation. In summary, Bora may play a significant role in radiosensitivity through the regulation of MDC1 and DNA repair.

Cytotoxicity and apoptotic activities of alpha-, gamma- and delta-tocotrienol isomers on human cancer cells

Background

Tocotrienols, especially the gamma isomer was discovered to possess cytotoxic effects associated with the induction of apoptosis in numerous cancers. Individual tocotrienol isomers are believed to induce dissimilar apoptotic mechanisms in different cancer types. This study was aimed to compare the cytotoxic potency of alpha-, gamma- and delta-tocotrienols, and to explore their resultant apoptotic mechanisms in human lung adenocarcinoma A549 and glioblastoma U87MG cells which are scarcely researched.

Methods

The cytotoxic effects of alpha-, gamma- and delta-tocotrienols in both A549 and U87MG cancer cells were first determined at the cell viability and morphological aspects. DNA damage types were then identified by comet assay and flow cytometric study was carried out to support the incidence of apoptosis. The involvements of caspase-8, Bid, Bax and mitochondrial membrane permeability (MMP) in the execution of apoptosis were further expounded.

Results

All tocotrienols inhibited the growth of A549 and U87MG cancer cells in a concentration- and time-dependent manner. These treated cancer cells demonstrated some hallmarks of apoptotic morphologies, apoptosis was further confirmed by cell accumulation at the pre-G₁ stage. All tocotrienols induced only double strand DNA breaks (DSBs) and no single strand DNA breaks (SSBs) in both treated cancer cells. Activation of caspase-8 leading to increased levels of Bid and Bax as well as cytochrome c release attributed by the disruption of mitochondrial membrane permeability in both A549 and U87MG cells were evident.

Conclusions

This study has shown that delta-tocotrienol, in all experimental approaches, possessed a higher efficacy (shorter induction period) and effectiveness (higher induction rate) in the execution of apoptosis in both A549 and U87MG cancer cells as compared to alpha- and gamma-tocotrienols. Tocotrienols in particular the delta isomer can be an alternative chemotherapeutic agent for treating lung and brain cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/1472-6882-14-469) contains supplementary material, which is available to authorized users.

Antiproliferation and induction of caspase-8-dependent mitochondria-mediated apoptosis by β-tocotrienol in human lung and brain cancer cell lines

The pure vitamin isomer, β-tocotrienol has the least abundance among the other vitamin E isomers that are present in numerous plants. Hence, it is very scarcely studied for its bioactivity. In this study, the antiproliferative effects and primary apoptotic mechanisms of β-tocotrienol on human lung adenocarcinoma A549 and glioblastoma U87MG cells were investigated. It was evidenced that β-tocotrienol had inhibited the growth of both A549 (GI50=1.38±0.334μM) and U87MG (GI50=2.53±0.604μM) cells at rather low concentrations. Cancer cells incubated with β-tocotrienol were also found to exhibit hallmarks of apoptotic morphologies including membrane blebbing, chromatin condensation and formation of apoptotic bodies. The apoptotic properties of β-tocotrienol in both A549 and U87MG cells were the results of its capability to induce significant (P<0.05) double-strand DNA breaks (DSBs) without involving single-strand DNA breaks (SSBs). β-Tocotrienol is said to induce activation of caspase-8 in both A549 and U87MG cells guided by no activation when caspase-8 inhibitor, z-IETD-fmk was added. Besides, disruption on the mitochondrial membrane permeability of the cells in a concentration- and time-dependent manner had occurred. The induction of apoptosis by β-tocotrienol in A549 and U87MG cells was confirmed to involve both the death-receptor mediated and mitochondria-dependent apoptotic pathways. These findings could potentiate the palm oil derived β-tocotrienol to serve as a new anticancer agent for treating human lung and brain cancers.

Polycomb-group histone methyltransferase CLF is required for proper somatic recombination in Arabidopsis

Homologous recombination (HR) is a key process during meiosis in reproductive cells and the DNA damage repair process in somatic cells. Although chromatin structure is thought to be crucial for HR, only a small number of chromatin modifiers have been studied in HR regulation so far. Here, we investigated the function of CURLY LEAF (CLF), a Polycomb-group (PcG) gene responsible for histone3 lysine 27 trimethylation (H3K27me3), in somatic and meiotic HR in Arabidopsis thaliana. Although fluorescent protein reporter assays in pollen and seeds showed that the frequency of meiotic cross-over in the loss-of-function mutant clf-29 was not significantly different from that in wild type, there was a lower frequency of HR in clf-29 than in wild type under normal conditions and under bleomycin treatment. The DNA damage levels were comparable between clf-29 and wild type, even though several DNA damage repair genes (e.g. ATM, BRCA2a, RAD50, RAD51, RAD54, and PARP2) were expressed at lower levels in clf-29. Under bleomycin treatment, the expression levels of DNA repair genes were similar in clf-29 and wild type, thus CLF may also regulate HR via other mechanisms. These findings expand the current knowledge of PcG function and contribute to general interests of epigenetic regulation in genome stability regulation.

Alpha particle induced DNA damage and repair in normal cultured thyrocytes of different proliferation status

Childhood exposure to ionizing radiation increases the risk of developing thyroid cancer later in life and this is suggested to be due to higher proliferation of the young thyroid. The interest of using high-LET alpha particles from Astatine-211 ((211)At), concentrated in the thyroid by the same mechanism as (131)I [1], in cancer treatment has increased during recent years because of its high efficiency in inducing biological damage and beneficial dose distribution when compared to low-LET radiation. Most knowledge of the DNA damage response in thyroid is from studies using low-LET irradiation and much less is known of high-LET irradiation. In this paper we investigated the DNA damage response and biological consequences to photons from Cobolt-60 ((60)Co) and alpha particles from (211)At in normal primary thyrocytes of different cell cycle status. For both radiation qualities the intensity levels of γH2AX decreased during the first 24h in both cycling and stationary cultures and complete repair was seen in all cultures but cycling cells exposed to (211)At. Compared to stationary cells alpha particles were more harmful for cycling cultures, an effect also seen at the pChk2 levels. Increasing ratios of micronuclei per cell nuclei were seen up to 1Gy (211)At. We found that primary thyrocytes were much more sensitive to alpha particle exposure compared with low-LET photons. Calculations of the relative biological effectiveness yielded higher RBE for cycling cells compared with stationary cultures at a modest level of damage, clearly demonstrating that cell cycle status influences the relative effectiveness of alpha particles.

Genomic stability in response to high versus low linear energy transfer radiation in Arabidopsis thaliana

Low linear energy transfer (LET) gamma rays and high LET HZE (high atomic weight, high energy) particles act as powerful mutagens in both plants and animals. DNA damage generated by HZE particles is more densely clustered than that generated by gamma rays. To understand the genetic requirements for resistance to high versus low LET radiation, a series of Arabidopsis thaliana mutants were exposed to either 1GeV Fe nuclei or gamma radiation. A comparison of effects on the germination and subsequent growth of seedlings led us to conclude that the relative biological effectiveness (RBE) of the two types of radiation (HZE versus gamma) are roughly 3:1. Similarly, in wild-type lines, loss of somatic heterozygosity was induced at an RBE of about a 2:1 (HZE versus gamma). Checkpoint and repair defects, as expected, enhanced sensitivity to both agents. The "replication fork" checkpoint, governed by ATR, played a slightly more important role in resistance to HZE-induced mutagenesis than in resistance to gamma induced mutagenesis.

Cell cycle stage-specific roles of Rad18 in tolerance and repair of oxidative DNA damage

The E3 ubiquitin ligase Rad18 mediates tolerance of replication fork-stalling bulky DNA lesions, but whether Rad18 mediates tolerance of bulky DNA lesions acquired outside S-phase is unclear. Using synchronized cultures of primary human cells, we defined cell cycle stage-specific contributions of Rad18 to genome maintenance in response to ultraviolet C (UVC) and H(2)O(2)-induced DNA damage. UVC and H(2)O(2) treatments both induced Rad18-mediated proliferating cell nuclear antigen mono-ubiquitination during G(0), G(1) and S-phase. Rad18 was important for repressing H(2)O(2)-induced (but not ultraviolet-induced) double strand break (DSB) accumulation and ATM S1981 phosphorylation only during G(1), indicating a specific role for Rad18 in processing of oxidative DNA lesions outside S-phase. However, H(2)O(2)-induced DSB formation in Rad18-depleted G1 cells was not associated with increased genotoxin sensitivity, indicating that back-up DSB repair mechanisms compensate for Rad18 deficiency. Indeed, in DNA LigIV-deficient cells Rad18-depletion conferred H(2)O(2)-sensitivity, demonstrating functional redundancy between Rad18 and non-homologous end joining for tolerance of oxidative DNA damage acquired during G(1). In contrast with G(1)-synchronized cultures, S-phase cells were H(2)O(2)-sensitive following Rad18-depletion. We conclude that although Rad18 pathway activation by oxidative lesions is not restricted to S-phase, Rad18-mediated trans-lesion synthesis by Polη is dispensable for damage-tolerance in G(1) (because of back-up non-homologous end joining-mediated DSB repair), yet Rad18 is necessary for damage tolerance during S-phase.

A requirement for polymerized actin in DNA double-strand break repair

Nuclear actin is involved in several nuclear processes from chromatin remodeling to transcription. Here we examined the requirement for actin polymerization in DNA double-strand break repair. Double-strand breaks are considered the most dangerous type of DNA lesion. Double-strand break repair consists of a complex set of events that are tightly regulated. Failure at any step can have catastrophic consequences such as genomic instability, oncogenesis or cell death. Many proteins involved in this repair process have been identified and their roles characterized. We discovered that some DNA double-strand break repair factors are capable of associating with polymeric actin in vitro and specifically, that purified Ku70/80 interacts with polymerized actin under these conditions. We find that the disruption of polymeric actin inhibits DNA double strand break repair both in vitro and in vivo. Introduction of nuclear targeted mutant actin that cannot polymerize, or the depolymerization of endogenous actin filaments by the addition of cytochalasin D, alters the retention of Ku80 at sites of DNA damage in live cells. Our results suggest that polymeric actin is required for proper DNA double-strand break repair and may function through the stabilization of the Ku heterodimer at the DNA damage site.

DNA damage caused by metal nanoparticles: involvement of oxidative stress and activation of ATM

Nanotechnology is a fast growing emerging field, the benefits of which are widely publicized. Our current knowledge of the health effects of metal nanoparticles such as nanosized cobalt (Nano-Co) and titanium dioxide (Nano-TiO(2)) is limited but suggests that metal nanoparticles may exert more adverse pulmonary effects as compared with standard-sized particles. To investigate metal nanoparticle-induced genotoxic effects and the potential underlying mechanisms, human lung epithelial A549 cells were exposed to Nano-Co and Nano-TiO(2). Our results showed that exposure of A549 cells to Nano-Co caused reactive oxygen species (ROS) generation that was abolished by pretreatment of cells with ROS inhibitors or scavengers, such as catalase and N-acetyl-L(+)-cysteine (NAC). However, exposure of A549 cells to Nano-TiO(2) did not cause ROS generation. Nano-Co caused DNA damage in A549 cells, which was reflected by an increase in length, width, and DNA content of the comet tail by the Comet assay. Exposure of A549 cells to Nano-Co also caused a dose- and a time-response increased expression of phosphorylated histone H2AX (γ-H2AX), Rad51, and phosphorylated p53. These effects were significantly attenuated when A549 cells were pretreated with catalase or NAC. Nano-TiO(2) did not show these effects. These results suggest that oxidative stress may be involved in Nano-Co-induced DNA damage. To further investigate the pathways involved in the Nano-Co-induced DNA damage, we measured the phosphorylation of ataxia telangiectasia mutant (ATM). Our results showed that phosphorylation of ATM was increased when A549 cells were exposed to Nano-Co, and this effect was attenuated when cells were pretreated with catalase or NAC. Pretreatment of A549 cells with an ATM specific inhibitor, KU55933, significantly abolished Nano-Co-induced DNA damage. Furthermore, pretreatment of A549 cells with ROS scavengers, such as catalase and NAC, significantly abolished Nano-Co-induced increased expression of phosphorylated ATM. Taken together, oxidative stress and ATM activation are involved in Nano-Co-induced DNA damage. These findings have important implications for understanding the potential health effects of metal nanoparticle exposure.

Oxoguanine glycosylase 1 (OGG1) protects cells from DNA double-strand break damage following methylmercury (MeHg) exposure

Methylmercury (MeHg) is a potent neurotoxin, teratogen, and probable carcinogen, but the underlying mechanisms of its actions remain unclear. Although MeHg causes several types of DNA damage, the toxicological consequences of this macromolecular damage are unknown. MeHg enhances oxidative stress, which can cause various oxidative DNA lesions that are primarily repaired by oxoguanine glycosylase 1 (OGG1). Herein, we compared the response of wild-type and OGG1 null (Ogg1(-/-)) murine embryonic fibroblasts to environmentally relevant, low micromolar concentrations of MeHg by measuring clonogenic efficiency, cell cycle arrest, DNA double-strand breaks (DSBs), and activation of the DNA damage response pathway.Ogg1(-/-) cells exhibited greater sensitivity to MeHg than wild-type controls, as measured by the clonogenic assay, and showed a greater propensity for MeHg-initiated apoptosis. Both wild-type and Ogg1(-/-) cells underwent cell cycle arrest when exposed to micromolar concentrations of MeHg; however, the extent of DSBs was exacerbated in Ogg1(-/-) cells compared with that in wild-type controls. Pretreatment with the antioxidative enzyme catalase reduced levels of DSBs in both wild-type and Ogg1(-/-) cells but failed to block MeHg-initiated apoptosis at micromolar concentrations. Our findings implicate reactive oxygen species mediated DNA damage in the mechanism of MeHg toxicity; and demonstrate for the first time that impaired DNA repair capacity enhances cellular sensitivity to MeHg. Accordingly, the genotoxic properties of MeHg may contribute to its neurotoxic and teratogenic effects, and an individual's response to oxidative stress and DNA damage may constitute an important determinant of risk.

ATM kinase is activated by sindbis viral vector infection

Sindbis virus is a prototypic member of the Alphavirus genus, Togaviridae family. Sindbis replication results in cellular cytotoxicity, a feature that has been exploited by our laboratory for treatment of in vivo tumors. Understanding the interactions between Sindbis vectors and the host cell can lead to better virus production and increased efficacy of gene therapy vectors. Here we present studies investigating a possible cellular response to genotoxic effects of Sindbis vector infection. The Ataxia Telangiectasia Mutated (ATM) kinase, a sentinel against genomic and cellular stress, was activated by Sindbis vector infection at 3h post infection. ATM substrates, Mcm3 and the γH2AX histone, were subsequently phosphorylated, however, substrates involved with checkpoint arrest of DNA replication, p53, Chk1 and Chk2, were not differentially phosphorylated compared with uninfected cells. The ATM response suggests nuclear pertubation, resulting from cessation of host protein synthesis, as an early event in Sindbis vector infection.

Acalypha wilkesiana extracts induce apoptosis by causing single strand and double strand DNA breaks

ETHNOPHARMACOLOGICAL RELEVANCE

The seeds of Acalypha wilkesiana have been used empirically by traditional healers in Southwest Nigeria together with other plants as a powder mixture to treat patients with breast tumours and inflammation.

AIM OF THE STUDY

There is an increasing interest among researchers in searching for new anticancer drugs from natural resources, particularly plants. This study aimed to investigate the anticancer properties of Acalypha wilkesiana extracts and the characteristics of DNA damage against brain and lung cancer cells.

MATERIALS AND METHODS

The antiproliferative activity of Acalypha wilkesiana extracts (ethyl acetate, hexane, and ethanol) was examined on human glioma (U87MG), human lung carcinoma (A549), and human lung fibroblast (MRC5) cells.

RESULTS

Cell viability MTT assay revealed that ethyl acetate extract of the plant possessed significant antiproliferative effects against both U87MG (GI(50)=28.03 ± 6.44 μg/ml) and A549 (GI(50)=89.63 ± 2.12 μg/ml) cells (p value<0.0001). The hexane extract was found to exhibit crucial antiproliferative effects on U87MG (GI(50)=166.30 ± 30.50 μg/ml) (p value<0.0001) but not on A549 cells. Neither plant extract possessed noticeable antiproliferative effects on the non-cancerous MRC5 cells (GI(50)>300 μg/ml). The ethanol extract showed no antiproliferative effects on any cell line examined. Haematoxylin & Eosin (H & E) staining and single cell gel electrophoresis (SCGE) comet assay confirmed that plant extract-treated cells underwent apoptosis and not necrosis. SCGE comet assays confirmed that plant extracts caused both single strand (SSB) and double strand (DSB) DNA breaks that led to the execution of apoptosis.

CONCLUSION

The extracts (especially ethyl acetate and hexane) of Acalypha wilkesiana possess valuable cytotoxic effects that trigger apoptosis in U87MG and A549 cancer cells through induction of DNA SSBs and DSBs.

Addressing the complex etiology of Alzheimer’s disease: the role of p25/Cdk5

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder characterized by the progressive loss of forebrain neurons and the deterioration of learning and memory. Therapies for AD have primarily focused upon either the inhibition of amyloid synthesis or its deposition in the brain, but clinical testing to date has not yet found an effective amelioration of cognitive symptoms. Synaptic loss closely correlates with the degree of dementia in AD patients. However, mouse AD models that target the amyloid-β pathway generally do not exhibit a profound loss of synapses, despite extensive synaptic dysfunction. The increased generation of p25, an activator of the cyclin-dependent kinase 5 (Cdk5) has been found in both human patients and mouse models of neurodegeneration. The current work reviews our knowledge, to date, on the role of p25/Cdk5 in Alzheimer’s disease, with a focus upon the interaction of amyloid-β and p25/Cdk5 in synaptic dysfunction and neuronal loss.

A novel synthetic protoapigenone analogue, WYC02-9, induces DNA damage and apoptosis in DU145 prostate cancer cells through generation of reactive oxygen species

The protoapigenone analogue WYC02-9, a novel synthetic flavonoid, has been shown to act against a variety of experimental tumors. However, its effects on prostate cancer and its mechanism of action are unknown. Thus, WYC02-9 was investigated for its cytotoxicity against DU145 prostate cancer cells, as was the underlying mechanisms by which WYC02-9 might induce DNA damage and apoptotic cell death through reactive oxygen species (ROS). WYC02-9 inhibited the cell growth of three prostate cancer cell lines, especially DU145 cells. In DU145 cells, WYC02-9 increased the generation of intracellular ROS, followed by induction of DNA damage and activation of the ATM-p53-H2A.X pathway and checkpoint-related signals Chk1/Chk2, which led to increased numbers of cells in the S and G2/M phases of the cell cycle. Furthermore, WYC02-9 induced apoptotic cell death through mitochondrial membrane potential decrease and activation of caspase-9, caspase-3, and PARP. The above effects were all prevented by the ROS scavenger N-acetylcysteine. Administration of WYC02-9 in a nude mouse DU145 xenograft model further identified the anti-cancer activity of WYC02-9. These findings therefore suggest that WYC02-9-induced DNA damage and mitochondria-dependent cell apoptosis in DU145 cells are mediated via ROS generation.

Inactivation of ataxia telangiectasia mutated gene can increase intracellular reactive oxygen species levels and alter radiation-induced cell death pathways in human glioma cells

PURPOSE

To investigate the effects of ataxia telangiectasia mutated (ATM)-regulated reactive oxygen species (ROS) and cell death pathways on the response of U87MG glioma cells to ionising radiation (IR) and oxidative stress.

MATERIAL AND METHODS

ATM expression was blocked in U87MG glioma cells using a small interfering RNA (siRNA) technique. Cell survival, sub-lethal damage (SLD), and potential lethal damage (PLD) repair following IR were assessed by clonogenic assay while changes in intracellular ROS, the apoptosis, and autophagy were followed by flow cytometry and Western blotting.

RESULTS

Blocking ATM expression in U87MG cells increased intracellular ROS levels and sensitivity to the cytotoxic effects of IR and oxygen stress; effects that could be partly counteracted by the antioxidant N-acetylcysteine (NAC). Knock down of ATM rendered cells unable to repair sub-lethal or potentially lethal damage and DNA double strand breaks (DSB) after IR exposure; something that NAC could not counteract. ATM did control the pathways a cell used to die following IR and this did seem to be ROS-dependent.

CONCLUSION

ATM is involved in redox control but ROS elevations following ATM knock down seem more involved in the decision as to what cell death pathway is utilised after IR than DSB repair and radiosensitivity.

BMI1-mediated histone ubiquitylation promotes DNA double-strand break repair

The polycomb repressor complex ubiquitylates γ-H2AX and other components of the DNA damage response pathway to facilitate genomic repair.

Polycomb group (PcG) proteins are major determinants of cell identity, stem cell pluripotency, and epigenetic gene silencing during development. The polycomb repressive complex 1, which contains BMI1, RING1, and RING2, functions as an E3-ubuiquitin ligase. We found that BMI1 and RING2 are recruited to sites of DNA double-strand breaks (DSBs) where they contribute to the ubiquitylation of γ-H2AX. In the absence of BMI1, several proteins dependent on ubiquitin signaling, including 53BP1, BRCA1, and RAP80, are impaired in recruitment to DSBs. Loss of BMI1 sensitizes cells to ionizing radiation to the same extent as loss of RNF8. The simultaneous depletion of both proteins revealed an additive increase in radiation sensitivity. These data uncover an unexpected link between the polycomb and the DNA damage response pathways, and suggest a novel function for BMI1 in maintaining genomic stability.

Role of ubiquitination in the DNA damage response: proteomic analysis to identify new DNA-damage-induced ubiquitinated proteins

The DDR (DNA damage response) is a signalling transduction cascade utilizing many forms of post-translation modification of proteins, including phosphorylation and ubiquitination. The well-known function of ubiquitination is to target proteins for proteasomal degradation; however, it is also involved in the regulation of protein function. The present review describes how ubiquitination regulates the function of certain proteins involved in DDR, in particular FANCD2 (Fanconi's anaemia complementation group D2) and PCNA (proliferating-cell nuclear antigen). Also, the proteomic methods currently used to identify new ubiquitinated proteins in response to DNA damage, including the advantages of using the UBD (ubiquitin-binding domain) beads to purify the ubiquitinated proteins, are considered.

Requirement of ATM for rapid p53 phosphorylation at Ser46 without Ser/Thr-Gln sequences

p53 phosphorylation at Ser46 following DNA damage is important for preferential transactivation of proapoptotic genes. Here, we report that ataxia-telangiectasia mutated (ATM) kinase is responsible for Ser46 phosphorylation of p53 during early-phase response to DNA damage. To elucidate the direct phosphorylation of p53 at Ser46 by ATM, an ATM mutant (ATM-AS) sensitive to ATP analogues was engineered. In vitro kinase assays revealed that p53 was phosphorylated at Ser46 by ATM-AS, even when ATP analogues were used as phosphate donors, although this phosphorylation site is not in an SQ motif, a consensus ATM site. Furthermore, Ser46 phosphorylation by ATM was dependent on the N- and C-terminal domains of p53, unlike Ser15 phosphorylation. Immunofluorescence analyses showed that Ser46-phosphorylated p53 was observed as foci in response to DNA damage and colocalized with gamma-H2AX or Ser1981-phosphorylated ATM. These results suggest that ATM phosphorylates a noncanonical serine residue on p53 by mechanisms different from those for the phosphorylation of Ser15.

Impaired DNA damage response--an Achilles' heel sensitizing cancer to chemotherapy and radiotherapy

Despite the progress in targeting particular molecular abnormalities specific to different cancers (targeted therapy), chemo- and radiotherapies are still the most effective of all anticancer modalities. Induction of DNA damage and inhibition of cell proliferation are the objects of most chemotherapeutic agents and radiation. Their effectiveness was initially thought to be due to the high rate of proliferation of cancer cells. However, normal cell proliferation rate in some tissues often exceeds that of curable tumors. Most tumors have impaired DNA damage response (DDR) and the evidence is forthcoming that this confers sensitivity to chemo- or radiotherapy. DDR is a complex set of events which elicits a plethora of molecular interactions engaging signaling pathways designed to: (a) halt cell cycle progression and division to prevent transfer of DNA damage to progeny cells; (b) increase the accessibility of the damaged sites to the DNA repair machinery; (c) engage DNA repair mechanisms and (d) activate the apoptotic pathway when DNA cannot be successfully repaired. A defective DDR makes cancer cells unable to effectively stop cell cycle progression, engage in DNA repair and/or trigger the apoptotic program when treated with DNA damaging drugs. With continued exposure to the drug, such cells accumulate DNA damage which leads to their reproductive death that may have features of cell senescence. Cancers with nonfunctional BRCA1 and BRCA2 are particularly sensitive to combined treatment with DNA damaging drugs and inhibitors of poly(ADP-ribose) polymerase. Antitumor strategies are being designed to treat cancers having particular defects in their DDR, concurrent with protecting normal cells.

DNA damage response induced by tobacco smoke in normal human bronchial epithelial and A549 pulmonary adenocarcinoma cells assessed by laser scanning cytometry

Cigarette smoke (CS) is a major cause of lung cancer and a contributor to the development of a wide range of other malignancies. There is an acute need to develop a methodology that can rapidly assess the potential carcinogenic properties of the genotoxic agents present in CS. We recently reported that exposure of normal human bronchial epithelial cells (NHBEs) or A549 pulmonary carcinoma cells to CS induces the activation of ATM through its phosphorylation on Ser1981 and phosphorylation of histone H2AX on Ser139 (gammaH2AX) most likely in response to the formation of potentially carcinogenic DNA double-strand breaks (DSBs). To obtain a more complete view of the DNA damage response (DDR) we explored the correlation between ATM activation, H2AX phosphorylation, activation of Chk2 through its phosphorylation on Thr68, and phosphorylation of p53 on Ser15 in NHBE and A549 cell exposed to CS. Multiparameter analysis by laser scanning cytometry made it possible to relate these DDR events, detected immunocytochemically, with cell cycle phase. The CS-dose-dependent induction and increase in the extent of phosphorylation of ATM, Chk2, H2AX, and p53 were seen in both cell types. ATM and Chk2 were phosphorylated approximately 1 h prior to phosphorylation of H2AX and p53. The dephosphorylation of ATM, Chk2, and H2AX was seen after 2 h following CS exposure. The dose-dependency and kinetics of DDR were essentially similar in both cell types, which provide justification for the use of A549 cells in the assessment of genotoxicity of CS in lieu of normal bronchial epithelial cells. The observation that DDR was more pronounced in S-phase cells is consistent with the mechanism of induction of DSBs occurring as a result of collision of replication forks with primary lesions such as DNA adducts that can be caused by CS-generated oxidants. The cytometric assessment of CS-induced DDR provides a means to estimate the genotoxicity of CS and to explore the mechanisms of the response as a function of cell cycle phase and cell type.

gammaH2AX: A potential DNA damage response biomarker for assessing toxicological risk of tobacco products

Differentiation among American cigarettes relies primarily on the use of proprietary tobacco blends, menthol, tobacco substitutes, paper porosity, paper additives, and filter ventilation. These characteristics substantially alter per cigarette yields of tar and nicotine in standardized protocols promulgated by government agencies. However, due to compensatory alterations in smoking behavior to sustain a preferred nicotine dose (e.g., by increasing puff frequency, inhaling more deeply, smoking more cigarettes per day, or blocking filter ventilation holes), smokers actually inhale similar amounts of tar and nicotine regardless of any cigarette variable, supporting epidemiological evidence that all brands have comparable disease risk. Consequently, it would be advantageous to develop assays that realistically compare cigarette smoke (CS)-induced genotoxicity regardless of differences in cigarette construction or smoking behavior. One significant indicator of potentially carcinogenic DNA damage is double strand breaks (DSBs), which can be monitored by measuring Ser 139 phosphorylation on histone H2AX. Previously we showed that phosphorylation of H2AX (defined as gammaH2AX) in exposed lung cells is proportional to CS dose. Thus, we proposed that gammaH2AX may be a viable biomarker for evaluating genotoxic risk of cigarettes in relation to actual nicotine/tar delivery. Here we tested this hypothesis by measuring gammaH2AX levels in A549 human lung cells exposed to CS from a range of commercial cigarettes using various smoking regimens. Results show that gammaH2AX induction, a critical event of the mammalian DNA damage response, provides an assessment of CS-induced DNA damage independent of smoking topography or cigarette type. We conclude that gammaH2AX induction shows promise as a genotoxic bioassay offering specific advantages over the traditional assays for the evaluation of conventional and nonconventional tobacco products.

Candidate protein biodosimeters of human exposure to ionizing radiation

PURPOSE

To conduct a literature review of candidate protein biomarkers for individual radiation biodosimetry of exposure to ionizing radiation.

MATERIALS AND METHODS

Reviewed approximately 300 publications (1973 - April 2006) that reported protein effects in mammalian systems after either in vivo or in vitro radiation exposure.

RESULTS

We found 261 radiation-responsive proteins including 173 human proteins. Most of the studies used high doses of ionizing radiation (>4 Gy) and had no information on dose- or time-responses. The majority of the proteins showed increased amounts or changes in phosphorylation states within 24 h after exposure (range: 1.5- to 10-fold). Of the 47 proteins that are responsive at doses of 1 Gy and below, 6 showed phosphorylation changes at doses below 10 cGy. Proteins were assigned to 9 groups based on consistency of response across species, dose- and time-response information and known role in the radiation damage response.

CONCLUSIONS

ATM (Ataxia telengiectasia mutated), H2AX (histone 2AX), CDKN1A (Cyclin-dependent kinase inhibitor 1A), and TP53 (tumor protein 53) are top candidate radiation protein biomarkers. Furthermore, we recommend a panel of protein biomarkers, each with different dose and time optima, to improve individual radiation biodosimetry for discriminating between low-, moderate-, and high-dose exposures. Our findings have applications for early triage and follow-up medical assessments.