Measurement Of DNA Double-strand Breaks Research Articles

Gold Nanoparticles Cause Radiosensitization in 4T1 Cells by Inhibiting DNA Double Strand Break Repair: Single Cell Comparisons of DSB Formation and γH2AX Expression.

Metal nanoparticles sensitize cancers to radiotherapy however their mechanisms of action are complex. The conceptual inspiration arose from theories of physical dose deposition however various chemical and biological factors have also been identified. Interpretation of data has been limited by challenges in measuring true DNA damage compared to DNA damage repair factors. Here, we applied a new assay, STRIDE, for the first time to measure DNA double strand breaks (DSBs) in 4T1 cells as a model of triple negative breast cancer exposed to gold nanoparticles and radiation, and compared this to the common γH2AX assay for DSB repair. The STRIDE assay showed no increase in DSB detection 15 mins after irradiation for cells containing nanoparticles compared to cells without. Gold nanoparticles led to prolonged detection of DSBs after irradiation and delayed the DSB repair. The data show no evidence of increased radiation dose deposition with nanoparticles, but rather enhanced radiobiological effects resulting from nanoparticles which includes disruption of the recruitment of essential DDR machinery, thereby impairing DNA repair processes.

Cysteine depletion sensitizes prostate cancer cells to agents that enhance DNA damage and to immune checkpoint inhibition

BackgroundProstate Cancer (PCa) represents one of the most commonly diagnosed neoplasms in men and is associated with significant morbidity and mortality. Therapy resistance and significant side effects of current treatment strategies indicate the need for more effective agents to treat both androgen-dependent and androgen-independent PCa. In earlier studies, we demonstrated that depletion of L-cysteine/cystine with an engineered human enzyme, Cyst(e)inase, increased intracellular ROS levels and inhibited PCa growth in vitro and in vivo. The current study was conducted to further explore the mechanisms and potential combinatorial approaches with Cyst(e)inase for treatment of PCa.MethodsDNA single strand breaks and clustered oxidative DNA damage were evaluated by alkaline comet assay and pulsed field gel electrophoresis, respectively. Neutral comet assay and immunofluorescence staining was used to measure DNA double strand breaks. Cell survival and reactive oxygen species level were measured by crystal violet assay and DCFDA staining, respectively. Western blot was used to determine protein expression. FACS analyses were preformed for immune cell phenotyping. Allograft and xenograft tumor models were used for assessing effects on tumor growth.ResultsPCa cells treated with Cyst(e)inase lead to DNA single and double strand breaks resulted from clustered oxidative DNA damage (SSBs and DSBs). Cyst(e)inase in combination with Auranofin, a thioredoxin reductase inhibitor, further increased intracellular ROS and DNA DSBs and synergistically inhibited PCa cell growth in vitro and in vivo. A combination of Cyst(e)inase with a PARP inhibitor (Olaparib) also increased DNA DSBs and synergistically inhibited PCa cell growth in vitro and in vivo without additional ROS induction. Knockdown of BRCA2 in PCa cells increased DSBs and enhanced sensitivity to Cyst(e)inase. Finally, Cyst(e)inase treatment altered tumor immune infiltrates and PD-L1 expression and sensitized PCa cells to anti-PD-L1 treatment.ConclusionsThe current results demonstrate the importance of oxidative DNA damage either alone or in combination for Cyst(e)inase-induced anticancer activity. Furthermore, cysteine/cystine depletion alters the tumor immune landscape favoring enhanced immune checkpoint inhibition targeting PD-L1. Thus, combinatorial approaches with Cyst(e)inase could lead to novel therapeutic strategies for PCa.

N6-Methyladenosine RNA Modifications Regulate the Response to Platinum Through Nicotinamide N-methyltransferase.

Development of resistance to platinum (Pt) in ovarian cancer remains a major clinical challenge. Here we focused on identifying epitranscriptomic modifications linked to Pt resistance. Fat mass and obesity-associated protein (FTO) is a N6-methyladenosine (m6A) RNA demethylase that we recently described as a tumor suppressor in ovarian cancer. We hypothesized that FTO-induced removal of m6A marks regulates the cellular response of ovarian cancer cells to Pt and is linked to the development of resistance. To study the involvement of FTO in the cellular response to Pt, we used ovarian cancer cells in which FTO was knocked down via short hairpin RNA or overexpressed and Pt-resistant (Pt-R) models derived through repeated cycles of exposure to Pt. We found that FTO was significantly downregulated in Pt-R versus sensitive ovarian cancer cells. Forced expression of FTO, but not of mutant FTO, increased sensitivity to Pt in vitro and in vivo (P < 0.05). Increased numbers of γ-H2AX foci, measuring DNA double-strand breaks, and increased apoptosis were observed after exposure to Pt in FTO-overexpressing versus control cells. Through integrated RNA sequencing and MeRIP sequencing, we identified and validated the enzyme nicotinamide N-methyltransferase (NNMT), as a new FTO target linked to Pt response. NNMT was upregulated and demethylated in FTO-overexpressing cells. Treatment with an NNMT inhibitor or NNMT knockdown restored sensitivity to Pt in FTO-overexpressing cells. Our results support a new function for FTO-dependent m6A RNA modifications in regulating the response to Pt through NNMT, a newly identified RNA methylated gene target.

Poly (ADP-ribose) polymerase inhibitors sensitize cancer cells to hypofractionated radiotherapy through altered selection of DNA double-strand break repair pathways

Purpose Poly (ADP-ribose) polymerase inhibitors (PARPi) are known to induce radiosensitization. However, the exact mechanisms of radiosensitization remain unclear. We previously reported that PARPi may have a unique radiosensitizing effect to enhance β-components of the linear-quadratic model. The aim of this study was to evaluate PARPi in combination with high-dose-per-fraction radiotherapy and to elucidate the underlying mechanisms of its radiosensitization. Materials and methods Radiosensitizing effects of PARPi PJ34, olaparib, and veliparib were measured using a colony-forming assay in the human cancer cell lines, HCT116, NCI-H460, and HT29. Six different radiation dose fractionation schedules were examined by tumor regrowth assay using three-dimensional multicellular spheroids of HCT116, NCI-H460, SW620, and HCT15. The mechanisms of radiosensitization were analyzed by measuring DNA double-strand breaks (DSB), DNA damage responses, chromosomal translocations, cellular senescence, and cell cycle analysis. Results Olaparib and PJ34 were found to show radiosensitization preferentially at higher radiation doses per fraction. Similar results were obtained using a mouse model bearing human tumor xenografts. A kinetic analysis of DNA damage responses and repairs showed that olaparib and PJ34 reduced the homologous recombination activity. However, a neutral comet assay showed that PJ34 treatment did not affect the physical rejoining of DNA-DSBs induced by ionizing radiation. Cell cycle analysis revealed that olaparib and PJ34 strikingly increased G1 tetraploid cells following irradiation, leading to premature senescence. The C-banding analysis of metaphase spreads showed that olaparib and PJ34 significantly increased ionizing radiation-induced dicentric chromosomes. The data suggests that PARPi olaparib and PJ34 altered the choice of DNA-DSB repair pathways rather than reducing the total amount of DNA-DSB repair, which resulted in increased repair errors. Increased quadratic misrepair was one of the mechanisms of PARP-mediated radiosensitization, preferentially at the higher dose range compared to the lower dose range. Conclusion PARPi may be a promising candidate to combine with stereotactic hypofractionated radiotherapy, aiming at high-dose region-directed radiosensitization.

1079P - Dose adjustment of chemotherapy in aggressive lymphoma using automated and standardized analysis and evaluation of DNA double strand breaks

BackgroundIn eukaryotic cells treated with chemotherapeutic drugs DNA double strand breaks (DSB) are the most severe form of DNA damage which usually leads to apoptotic cell death. Cytotoxic chemotherapy is still a mainstay of cancer therapy, but there are few established methods to individually predict efficacy and tolerability. In most regimens dosage is based on the body surface area, a dimension of little biological precision, and individual dose adaptions are usually performed by clinical guessing or in response to adverse events. This project sets out to examine biological parameters of cell damage. MethodsIn particular, we measure DNA double strand breaks by an automated yH2AX assay applying the Aklides NUK® system. In preliminary work, PBMCs were stimulated with bendamustine or with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone, the components of the R-CHOP protocol, to induce DSB. Recruitment of lymphoma patients under R-CHOP therapy and its cytotoxic effects on DSB is currently ongoing. ResultsThere was no inter-individual correlation between drug dose and number of foci, whereas does titrations on the cells of each individual donor demonstrated a clear correlation between dose and yH2AX assay result. Measurements of DSB in vivo using PBMCs of lymphoma patients is currently ongoing. First results show a rising number of DSBs in leucocytes under chemotherapy. ConclusionsThe lack of correlation across individuals between yH2AX foci and drug dosage based on standard calculation by body surface area suggests that standardized dosing of chemotherapeutic drugs based on gross physical determinants such as weight or body surface area does not correspond to the individual’s biological response and clinical effect. To confirm our hypothesis, different biomarkers should also to be involved in this project, like microRNAs and telomere length. The future plan of this project is the replacement of standard dosage regimens by biologically based, real-time-adapted individual dosage in lymphoma to reduce toxicity while increasing therapeutic efficacy. Legal entity responsible for the studyThe authors. FundingBrandenburgian Ministry of Science, Research and Culture (MWFK) Federal Ministry of Education and Research. DisclosureAll authors have declared no conflicts of interest.

DNA Double-Strand Breaks in Arctic Char (Salvelinus alpinus) from Bjørnøya in the Norwegian Arctic.

High levels of organochlorine contaminants (OCs) have been found in arctic char (Salvelinus alpinus) from Lake Ellasjøen, Bjørnøya (Norwegian Arctic). The aim of the present study was to investigate the potential genotoxic effect of environmental organochlorine contaminant exposure in arctic char from Ellasjøen compared with arctic char from the low-contaminated Lake Laksvatn nearby. Blood was analyzed using agarose gel electrophoresis and image data analysis to quantify the fraction of total DNA that migrated into the gel (DNA-FTM) as a relative measure of DNA double-strand breaks (DSBs). Analysis by GC-MS of muscle samples showed an average 43 times higher concentration of ΣOCs in arctic char from Ellasjøen (n = 18) compared with Laksvatn char (n = 21). Char from Lake Ellasjøen had a much higher frequency of DSBs, as measured by DNA-FTM, than char from Lake Laksvatn. Principal component analysis and multiple linear regressions show that there was a significant positive relationship between DSBs and levels of organochlorine contaminants in the char. In addition, DSBs were less frequent in reproductively mature char than in immature char. The results suggest that organochlorine contaminants are genotoxic to arctic char. Environ Toxicol Chem 2019;38:2405-2413. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

DNA damage in haemocytes of Harpalus (Pseudophonus) rufipes (De Geer, 1774) (Coleoptera, Carabidae) as an indicator of sublethal effects of exposure to herbicides

The carabid beetle Harpalus (Pseudophonus) rufipes is one the most common polyphagous species in the agroecosystem and plays an important role in the natural control of pests. The primary focus of the study was to examine whether exposure to herbicides, used for agricultural productivity, can have genotoxic sublethal effects on this epigean non-target species. The neutral comet assay was carried out to provide a quantitative measure of DNA double-strand breaks in haemocytes of adults. Beetles from a conventional potato field treated with herbicides such as metribuzin-, clomazone-, pendimethalin- and cycloxydim-based commercial formulates were compared with specimens from an organic potato field in which weeds were removed mechanically. Analyses showed that the level of DNA damage recorded as tail DNA percentage in adults from the conventional potato field (11.55 ± 0.47) was significantly higher (p = 9.5 × 10−5) than that in beetles from the organic control site (8.93 ± 0.22). Moreover, DNA damage reduction was recorded in beetles from the conventional field sampled about 12 weeks after the field treatment compared with that in beetles sampled about 8 weeks after the treatment. The genotoxic effect of herbicide commercial formulations used in the conventional potato field before and during sampling was determined. This report provides evidence that exposure to herbicides has a detrimental effect on H. rufipes and confirms that the Comet assay may be a useful tool in determining the potential genotoxicity of pollutants on soil arthropods.

Sex-related differential susceptibility to doxorubicin-induced cardiotoxicity in B6C3F1 mice

Sex is a risk factor for development of cardiotoxicity, induced by the anti-cancer drug, doxorubicin (DOX), in humans. To explore potential mechanisms underlying differential susceptibility to DOX between sexes, 8-week old male and female B6C3F1 mice were dosed with 3mg/kg body weight DOX or an equivalent volume of saline via tail vein once a week for 6, 7, 8, and 9 consecutive weeks, resulting in 18, 21, 24, and 27mg/kg cumulative DOX doses, respectively. At necropsy, one week after each consecutive final dose, the extent of myocardial injury was greater in male mice compared to females as indicated by higher plasma concentrations of cardiac troponin T at all cumulative DOX doses with statistically significant differences between sexes at the 21 and 24mg/kg cumulative doses. A greater susceptibility to DOX in male mice was further confirmed by the presence of cytoplasmic vacuolization in cardiomyocytes, with left atrium being more vulnerable to DOX cardiotoxicity. The number of TUNEL-positive cardiomyocytes was mostly higher in DOX-treated male mice compared to female counterparts, showing a statistically significant sex-related difference only in left atrium at 21mg/kg cumulative dose. DOX-treated male mice also had an increased number of γ-H2A.X-positive (measure of DNA double-strand breaks) cardiomyocytes compared to female counterparts with a significant sex effect in the ventricle at 27mg/kg cumulative dose and right atrium at 21 and 27mg/kg cumulative doses. This newly established mouse model provides a means to identify biomarkers and access potential mechanisms underlying sex-related differences in DOX-induced cardiotoxicity.

The Role of miR-34a in Tritiated Water Toxicity in Human Umbilical Vein Endothelial Cells.

In this work, we investigated the toxic effects of tritiated water (HTO) on the cardiovascular system. We examined the role of microRNA-34a (miR-34a) in DNA damage and repair in human umbilical vein endothelial cells (HUVECs) exposed to HTO. Cell proliferation capacity was evaluated by cell counting, and miR-34a expression was detected using quantitative PCR (QT-PCR). The Comet assay and γ-H2AX immunostaining were used to measure DNA double-strand breaks (DSBs). Reverse transcription polymerase chain reaction was used to measure the expression level of c-myc messenger RNA (mRNA). The cells exposed to HTO showed significantly lower proliferation than the control cells over 3 days. The DNA damage in the HTO group was more severe than that in the control group, at each time point examined. The expression of miR-34a mimics caused increased DNA DSBs whereas that of the miR-34a inhibitor caused decreased DNA DSBs. The proliferation viability was the opposite for the miR-34a mimics and inhibitor groups. The expression levels of c-myc mRNA in cells transfected with miR-34a mimics were lower than that in cells transfected with the miR-34a-5p inhibitor, at 0.5 hours and 2 hours after transfection. In summary, miR-34a mediates HTO toxicity in HUVECs by downregulating the expression of c-myc.

Histone H2AX phosphorylation as a measure of DNA double-strand breaks and a marker of environmental stress and disease activity in lupus

ObjectiveDefective or inefficient DNA double-strand break (DSB) repair results in failure to preserve genomic integrity leading to apoptotic cell death, a hallmark of systemic lupus erythematosus (SLE). Compelling evidence linked...

Abstract 3872: Genotoxicity of zinc oxid nanoparticles and the activation of ATM-Chk2 DNA-damage-response pathway are caused by zinc-ions

Abstract Zinc oxide nanoparticles (ZnO-NP) are used in a variety of applications including cosmetics and pharmaceuticals. The common utilization of ZnO-NPs results in an increasing environmental release with unknown health effects. Recent studies have shown that ZnO-NP exposure cause cellular toxicity including DNA-damages. Discussed mechanisms are interactions of the ZnO-NP with intracellular structures and molecules after internalization, extracellular or intracellular dissociation of the particles, and the generation of ROS. In the present study we evaluated the genotoxic properties of ZnO-NP as well as the cellular DNA damage response in dependence of oxidative distress and ZnO-NP dissociation into Zn2+. For this purpose, we exposed the human epithelial cell line A549 to defined ZnO-NP (100μg/ml). Genotoxic effects of the particles were evaluated by Comet assay and γH2AX-foci, measuring DNA double-strand breaks (DNA-DSBs). Dissociation of ZnO-NP and the intracellular increase of Zn2+ were performed with spectrofluorimetric and cLSM measurements by the use of FluoZin3. Oxidative distress was determined by the compound dihydrodichlorofluorescein diacetate (H2DCF-DA). The Activation of the DNA damage response pathway was proven by analyses of H2AX-, ATM-, Chk1- and Chk2 phosphorylation, and p21, p53 up-regulation after ZnO-NP exposure by western blot or ELISA. To figure out, if the genotoxic potential of ZnO-NP is dependent of released Zn2+ or the generation of ROS we inhibited oxidative distress by the antioxidant N-acetyl-L-cysteine (NAC) and Zn2+ were extracellular chelated by diethylene triamine pentaacetic acid (DTPA). We found a fast extracellular dissociation of ZnO-NP and a quick intracellular increase of Zn2+. Furthermore, we ascertained an activation of H2AX induced by ZnO-NP; this phosphorylation is totally inhibited by DTPA. ZnO-NP activated the DSB-damage response indicated by ATM-, Chk2-phosphorylation as well as an up-regulation of p53 and p21. Pretreatment with NAC scavenging ROS leads to a reduced and Zn2+ complexation to no activation of ATM-Chk2-DNA damage pathway. The ATR/Chk1 pathway was not activated by ZnO-NP. We demonstrated ZnO-NP induced DNA-damages and the activation of the ATM/Chk2 DNA damage response pathway but not the ATR/Chk1 pathway, indicating that ZnO-NP exposure induces DNA-DSBs. Scavanging of ROS leads to a slight reduction of DNA-DSBs but extracellular Zn2+ compelxation to a complete impairment suggesting that the mechanism of ZnO-NP genotoxicity is not mediated via ROS-generation but rather a direct interaction of dissociated Zn-ions with the DNA. Citation Format: Julia Heim, Nawaz Muhammad Tahir, Anke Kaltbeitzel, Volker Mailänder, Hartmut Lüddens, Wolfgang Tremel, Jürgen Brieger. Genotoxicity of zinc oxid nanoparticles and the activation of ATM-Chk2 DNA-damage-response pathway are caused by zinc-ions. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3872. doi:10.1158/1538-7445.AM2015-3872

Abstract 2555: The mechanism of action of bendamustine alone or in combination with nucleoside analogs in chronic lymphocytic leukemia

Abstract Bendamustine (BEN) is a promising new treatment for chronic lymphocytic leukemia (CLL) and is believed to function as an alkylating agent (eg, chlorambucil, CLB) while sharing structural similarities to a nucleoside analogue (eg, fludarabine, FLU). Enhanced cell death has been observed with the combination of BEN and FLU in primary CLL cells in vitro, likely due to the inhibition of repair of BEN DNA cross-linking by FLU. However, both BEN and FLU are marrow-toxic, limiting the use of this combination in the clinic. The nucleoside analog, pentostatin (PEN), is an adenosine deaminase inhibitor that causes the accumulation of deoxyadenosine (dADO) and is less marrow-suppressive than FLU. However, the cytotoxic effectiveness of dADO/PEN in combination with BEN is not known. Flow cytometry analysis using annexin V/7-ADD and the MTT assay were performed to determine the effectiveness of BEN treatment in primary CLL cells as compared to or in combination with CLB, FLU, or dADO/PEN at varying drug concentrations and time points. Using the MTT assay, there was a linear relationship between cytotoxicity and drug concentration, similar to that seen with CLB. In vitro treatment of CLL cells with BEN, CLB, FLU, or dADO/PEN induced apoptosis, the degree being time- and concentration-dependent. However, the sensitivity of CLL cells to BEN or CLB varied, suggesting different mechanisms of action. Enhanced cell kill was seen with the combination of BEN or CLB with FLU or dADO/PEN, with the extent of increased cytotoxicity being similar for FLU or dADO/PEN. Cell death mechanisms were analyzed via staining for surface expression of death receptors (DR4 and DR5) and mitochondrial stress (DICO6 and DHE). γ-H2AX staining was used to measure DNA double-strand breaks (DSBs) and the alkaline comet assay was used to measure both DNA DSBs and single-strand breaks (SSBs). An increase in DR4 and DR5 surface expression, loss of mitochondrial membrane potential, and increased reactive oxygen species production was observed with all agents. There was an increase in DNA SSB and DSB following FLU, as compared to BEN and CLB, while a combination of BEN and FLU further increased the number of breaks (especially SSBs) compared to FLU alone. Thus, BEN has the properties of an alkylating agent, rather than a nucleoside analog, but has a different spectrum of antitumor activity to CLB. BEN induces apoptosis through both the death receptor and mitochondrial pathways. Increased cell kill is seen on combining BEN with dADO/PEN suggesting that this might be a useful combination in the clinic. Citation Format: Sara E.F. Kost, Eric D.J. Bouchard, William S. Liang, Versha Banerji, Spencer B. Gibson, Sachin Katyal, James B. Johnston. The mechanism of action of bendamustine alone or in combination with nucleoside analogs in chronic lymphocytic leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2555. doi:10.1158/1538-7445.AM2015-2555

DNA double-strand breaks in relation to persistent organic pollutants in a fasting seabird

Lipophilic persistent organic pollutants (POPs) are released from fat reserves during fasting, causing increased blood concentrations. Thus, POPs represent a potential anthropogenic stressor during fasting periods. We analysed the blood of female common eiders (Somateria mollissima) by using agarose gel electrophoresis and image data analysis to quantify the DNA-fraction, of total DNA, that migrated into the gel (DNA-FTM) as a relative measure of DNA double strand-breaks (DSBs) during the fasting incubation period in the high arctic. In 2008 and in 2009 blood samples were obtained for analysis of 9 POPs and DNA-FTM at day 5 of the incubation period, and then in the same individuals at day 20. This unique study design gave us the opportunity to analyse the same individuals throughout two points in time, with low and high stress burdens. During the incubation period the body mass (BM) decreased by 21–24%, whereas the POP levels increased by 148–639%. The DNA-FTM increased by 61–67% (being proportional to the increase in DSBs). At day 5, but not day 20, DNA-FTM was positively correlated with most analysed POPs. The increase in DNA-FTM was positively correlated with the decrease in BM (g) during incubation. Thus, we suggest that fasting stress (BM loss) decreases DNA integrity and that stress caused by fasting on BM loss appeared to override the additional stress caused by concurrent increase in levels of the analysed POPs in the eiders. Blood levels of POPs in the eiders in Svalbard were relatively low, and additive and/or synergistic genotoxic effects of fasting stress and POP exposure may occur in populations with higher POP levels.

Effects of dna-dependent protein kinase inhibition by NU7026 on dna repair and cell survival in irradiated gastric cancer cell line N87.

Repair of radiation-induced dna double-strand breaks is a key mechanism in cancer cell radio-resistance. The synthesized compound NU7026 specifically inhibits dna-dependent protein kinase (dna-pk) within the non-homologous end-joining repair mechanism. Earlier studies demonstrated increased radiosensitivity in dna-pk deficient cells compared with wild-type cells. In chronic leukemia cells, NU7026 appears to enhance the cytotoxic effect of chlorambucil. The radio-modifying effects of NU7026 on cell survival, cell cycle, apoptosis, and dna double-strand break repair have yet to be studied in gastric cancer cells. The gastric cancer cell line N87 was treated with 0 Gy or 4 Gy in the presence of NU7026 at a dose range of 0-20 μmol/L. Clonogenic assays were used to assess cell survival after treatment. Cell-cycle distribution was analyzed using propidium iodide with fluorescence-activated cell sorting. Apoptosis was detected using annexin-V and propidium iodide with fluorescence-activated cell sorting. The γH2AX assay was used to measure dna double-strand breaks. Statistically significant increases in G2/M arrest were observed in N87 cells treated with radiation and NU7026 compared with those treated with radiation alone (p = 0.0004). Combined treatment also led to an increase in apoptosis (p = 0.01). At 24 hours, the γH2AX analysis revealed more dna double-strand breaks in N87 cells treated with radiation and NU7026 than in those treated with radiation alone (p = 0.04). Clonogenic assays demonstrated declining cell survival as both the radiation and the NU7026 dose increased. The dose enhancement factor at 0.1 survival fraction was 1.28 when N87 cells were treated with 4 Gy radiation and 5 μmol/L NU7026. In gastric cancer cells, NU7026 appears to enhance the cytotoxic effect of irradiation as assessed by clonogenic assays. This increased cytotoxicity might be the result of an increase in dna double-strand breaks resulting in G2/M cell arrest and possibly higher levels of apoptosis.

Damaging and protective bystander cross-talk between human lung cancer and normal cells after proton microbeam irradiation

Most of the studies of radiation-induced bystander effects (RIBE) have been focused on understanding the radiobiological changes observed in bystander cells in response to the signals from irradiated cells in a normal cell population with implications to radiation risk assessment. However, reports on RIBE with relevance to cancer radiotherapy especially investigating the bidirectional and criss-cross bystander communications between cancer and normal cells are limited. Hence, in present study employing co-culture approach, we have investigated the bystander cross-talk between lung cancer (A549) and normal (WI38) cells after proton-microbeam irradiation using γ-H2AX foci fluorescence as a measure of DNA double-strand breaks (DSBs). We observed that in A549–A549 co-cultures, irradiated A549 cells exert damaging effects in bystander A549 cells, which were found to be mediated through gap junctional intercellular communication (GJIC). However, in A549–WI38 co-cultures, irradiated A549 did not affect bystander WI38 cells. Rather, bystander WI38 cells induced inverse protective signalling (rescue effect) in irradiated A549 cells, which was independent of GJIC. On the other hand, in response to irradiated WI38 cells neither of the bystander cells (A549 or WI38) showed significant increase in γ-H2AX foci. The observed bystander signalling between tumour and normal cells may have potential implications in therapeutic outcome of cancer radiotherapy.

Quantitative, Noninvasive Imaging of Radiation-Induced DNA Double-Strand Breaks In Vivo

DNA double-strand breaks (DSB) are a major form of DNA damage and a key mechanism through which radiotherapy and some chemotherapeutic agents kill cancer cells. Despite its importance, measuring DNA DSBs is still a tedious task that is normally carried out by gel electrophoresis or immunofluorescence staining. Here, we report a novel approach to image and quantify DSBs in live mammalian cells through bifragment luciferase reconstitution. N- and C-terminal fragments of firefly luciferase genes were fused with H2AX and MDC1 genes, respectively. Our strategy was based on the established fact that at the sites of DSBs, H2AX protein is phosphoryated and physically associates with the MDC1 protein, thus bringing together N- and C-luciferase fragments and reconstituting luciferase activity. Our strategy allowed serial, noninvasive quantification of DSBs in cells irradiated with X-rays and (56)Fe ions. Furthermore, it allowed for the evaluation of DSBs noninvasively in vivo in irradiated tumors over 2 weeks. Surprisingly, we detected a second wave of DSB induction in irradiated tumor cells days after radiation exposure in addition to the initial rapid induction of DSBs. We conclude that our new split-luciferase-based method for imaging γ-H2AX-MDC1 interaction is a powerful new tool to study DSB repair kinetics in vivo with considerable advantage for experiments requiring observations over an extended period of time.

Adapting the γ-H2AX Assay for Automated Processing in Human Lymphocytes. 1. Technological Aspects

The immunofluorescence-based detection of γ-H2AX is a reliable and sensitive method for quantitatively measuring DNA double-strand breaks (DSBs) in irradiated samples. Since H2AX phosphorylation is highly linear with radiation dose, this well-established biomarker is in current use in radiation biodosimetry. At the Center for High-Throughput Minimally Invasive Radiation Biodosimetry, we have developed a fully automated high-throughput system, the RABIT (Rapid Automated Biodosimetry Tool), that can be used to measure γ-H2AX yields from fingerstick-derived samples of blood. The RABIT workstation has been designed to fully automate the γ-H2AX immunocytochemical protocol, from the isolation of human blood lymphocytes in heparin-coated PVC capillaries to the immunolabeling of γ-H2AX protein and image acquisition to determine fluorescence yield. High throughput is achieved through the use of purpose-built robotics, lymphocyte handling in 96-well filter-bottomed plates, and high-speed imaging. The goal of the present study was to optimize and validate the performance of the RABIT system for the reproducible and quantitative detection of γ-H2AX total fluorescence in lymphocytes in a multiwell format. Validation of our biodosimetry platform was achieved by the linear detection of a dose-dependent increase in γ-H2AX fluorescence in peripheral blood samples irradiated ex vivo with γ rays over the range 0 to 8 Gy. This study demonstrates for the first time the optimization and use of our robotically based biodosimetry workstation to successfully quantify γ-H2AX total fluorescence in irradiated peripheral lymphocytes.

Abstract 1398: Aurora kinase A inhibition with MLN8054 radiosensitizes prostate cancer by inducing cell cycle arrest leading to increased prolonged DNA damage and apoptosis

Abstract The purpose of this study is to investigate a potential new radioenhancer for the treatment of prostate cancer. Despite multiple promising treatment modalities, prostate cancer remains a significant cause of diminished quality of life and cancer death, indicating the need for more aggressive, targeted therapy. Aurora kinase A (AURKA) is a promising treatment target, but its inhibition has never been investigated in combination with radiotherapy in prostate cancer. Using the selective AURKA inhibitor, MLN8054, we performed clonogenic assay to investigate in vitro radiosensitization, cell cycle analysis to observe changes induced by AURKA inhibition, tumor growth delay to study in vivo effects, and histologic active caspase staining to measure apoptosis. We demonstrated radiosensitizing effects in vitro in PC3 and DU145 prostate cancer cell lines, which was confirmed in vivo by tumor growth delay in PC3 xenografts in nude mice. In addition, we investigated a potential mechanism for radiosensitization. We report that MLN8054 induces cell cycle arrest at G2/M and polyploidy in both prostate cancer cell lines, which is associated with sustained DNA damage from radiation as seen by increased immunofluorescence for γ-H2AX, a measure of DNA double-strand breaks. Staining for caspase-3 in xenograft samples showed increased apoptosis in irradiated samples pre-treated with MLN8054 compared to irradiation or inhibitor alone. Our findings support the potential use of AURKA inhibition with MLN8054 to enhance the effectiveness of radiation therapy for the treatment of prostate cancer, and suggest a potential mechanism underlying its radiosensitization effects. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1398.

In VitroandIn VivoOptimization of an Anti-glioma Modality Based on Synchrotron X-Ray Photoactivation of Platinated Drugs

For the past 5 years, a radio-chemotherapy approach based on the photoactivation of platinum atoms (PAT-Plat) consisting of treating tumors with platinated compounds and irradiating them above the platinum K edge (78.4 keV) has been developed at the European Synchrotron Radiation Facility (Grenoble, France). Compared to other preclinical modalities, PAT-Plat provides the highest survivals of rats bearing the rodent F98 glioma. However, further investigations are required to optimize its efficiency and to allow its clinical application. Here we examined in vitro and in vivo whether monochromatic X rays are more efficient than high-energy photons in producing the PAT-Plat effect by measuring DNA double-strand breaks (DSBs) and survival of glioma-bearing rats and whether an increase in the platinum concentration in the tumor results in increased rat survival. DSBs were assessed by pulsed-field gel electrophoresis with different DNA fragment migration programs and with gamma-H2AX immunofluorescence. In vivo, F98 glioma cells were injected intracerebrally, treated with a single intracranial injection of cisplatin or carboplatin 13 days after tumor implantation, and irradiated the day after with 78.8 keV X rays or 6 MV photons. Our results indicate that 78.8 keV X rays are more efficient than high-energy photons at producing the PAT-Plat effect. At low concentrations, cisplatin is more efficient than carboplatin; this is likely due to more efficient DNA binding and DSB repair inhibition. High concentrations of carboplatin inside tumors do not necessarily lead to protracted survival of rats. The therapeutic benefit of anti-glioma synchrotron strategies appears to be correlated with the percentage of unrepaired DSBs but not with the number of DSBs induced.

Retinoblastoma RB94 Enhances Radiation Treatment of Head and Neck Squamous Cell Carcinoma

To assess whether adenovirus-mediated retinoblastoma 94 (Ad-RB94) transgene expression enhances efficacy of radiation therapy (XRT) of human head and neck squamous cell carcinoma (HNSCC). The HNSCC cell lines (JHU006 and JHU012) were treated in vitro and in a nude mouse xenograft model with Ad-RB94, Ad-DL312 control vector, or untreated as mock control. Cell viability and tumor growth were evaluated and combined RB94/XRT antitumor activity was analyzed by measuring DNA double-strand breaks, apoptosis-associated early DNA fragmentation, and levels of RB-regulated cell cycle progression E2F1 transcription factor. Ad-RB94/XRT resulted in significant HNSCC cell growth inhibition compared with XRT alone or Ad-RB94 alone in vitro and caused significant tumor regression compared with XRT alone and Ad-DL312/XRT in JHU006 and with XRT alone, Ad-DL312/XRT and Ad-RB94 alone in JHU012 in vivo. Neutral comet analysis revealed that DNA damage was significantly elevated in cells treated with Ad-RB94 alone and Ad-RB94/XRT. Tumors treated with Ad-RB94 alone showed a striking increase in early apoptosis DNA fragmentation, and DNA fragmentation was further enhanced with XRT. In addition, levels of E2F1 were up-regulated by Ad-RB94/XRT combination, whereas Ad-RB94 alone did not affect E2F1 levels and XRT alone led to down-regulation of E2F1. A potent antitumor effect has been observed after Ad-RB94/XRT combination treatment in HNSCC xenograft tumors. Enhanced tumor regression correlated with increased apoptosis. Ad-RB94 treatment enhances the efficacy of XRT through tumor cell sensitization by arresting the cells at the radiation-sensitive G(2)-M cell cycle and via E2F1 up-regulation.