Long time persistence of residual 53BP1/γ-H2AX foci in human lymphocytes in relationship to apoptosis,chromatin condensation and biological dosimetry

Purpose:?Novel assay for radiosensitivity is based on measurements of residual DNA repair foci produced by several proteins including phosphorylated H2AX (γ-H2AX), recombinase Rad51 (Rad51) and tumour suppressor p53 binding protein 1 (53BP1), which co-localise with radiation-induced DNA double-strand breaks (DSB). Here, we studied dose-response for residual 53BP1, Rad51, and γ-H2AX foci in relationship to apoptosis and chromatin condensation in human G₀-lymphocytes.

Materials and methods:?Residual foci, apoptosis and condensation of chromatin were studied following irradiation with γ-rays at doses of 0.5–10 Gy.

Results:?No clear dose response for residual Rad51 was seen. Residual 53BP1/γ-H2AX foci remained in human lymphocytes up to four weeks after irradiation. No foci formed during radiation-induced apoptosis. We provide evidence that irreversible apoptotic condensation of chromatin is responsible for arrest of residual foci and preventing de novo focus formation. Similar linear dose dependences up to 2 Gy were observed for the 53BP1/γ-H2AX foci at all studied time points. At higher doses, saturation and decline were caused by preferential elimination of apoptotic lymphocytes with residual foci. While primary 53BP1 and γ-H2AX foci almost completely co-localised, co-localisation of residual foci did not exceed 17%, indicating that 53BP1 and γ-H2AX proteins may remain for different times at the locations of DSB repair.

Conclusions:?Prolonged persistence of residual 53BP1/γ-H2AX foci may be used for biological dosimetry within the dose range up to 2 Gy. While foci are not formed during radiation-induced apoptosis in human lymphocytes, elimination of apoptotic cells with residual foci may affect the dose response.     

Kinetics and dose-response of residual 53BP1/γ-H2AX foci: Co-localization,relationship with DSB repair and clonogenic survival

Purpose: Recent studies revealed that some foci produced by phosphorylated histone 2A family member X (γ-H2AX) and tumor suppressor p53 binding protein 1 (53BP1) that co-localize with radiation-induced DNA double-strand breaks (DSB) remain in cells at relatively long times after irradiation and indicated a possible correlation between cellular radiosensitivity and residual foci. In this study, we investigated dose-responses and kinetics for radiation-induced 53BP1/γ-H2AX foci formation in relation to their co-localization, DSB repair and cell survival.

Materials and methods: Cell survival, DSB and foci were analyzed by clonogenic assay, pulsed field gel electrophoresis (PFGE), and confocal laser microscopy, respectively, in normal human fibroblasts (VH-10) and in a cancer cell line (HeLa). Computer analysis was used to determine both the number and the area of foci.

Results: We show that even at doses down to 1 cGy a statistically significant induction of 53BP1 foci is observed. While the number of foci was found to constantly decrease with post-irradiation time, the per-cell normalized area of foci does not change within a time window of approximately 4 h post-irradiation. Co-localization of γ-H2AX and 53BP1 foci is shown to depend on dose and post-irradiation time. No clear correlations were established between radiosensitivity and foci formation because the dose response for 53BP1/γ-H2AX foci may depend on time after irradiation and duration of the cell cycle. We show that the kinetics of foci disappearance within 24 h post-irradiation do not coincide with those of DSB repair.

Conclusions: The data suggest that the post-irradiation time used for estimation of radiosensitivity at therapeutically relevant low doses (e.g., <3 Gy) in proliferating cells by scoring residual foci should be limited by the duration of the cell cycle, and that direct comparison of the kinetics of DSB repair and disappearance of DSB-co-localizing foci is not possible. Therefore, results obtained from the counting of foci should be interpreted with caution in terms of DSB repair.     

Kinetics and dose-response of residual 53BP1/gamma-H2AX foci: co-localization, relationship with DSB repair and clonogenic survival

PURPOSE: Recent studies revealed that some foci produced by phosphorylated histone 2A family member X (gamma-H2AX) and tumor suppressor p53 binding protein 1 (53BP1) that co-localize with radiation-induced DNA double-strand breaks (DSB) remain in cells at relatively long times after irradiation and indicated a possible correlation between cellular radiosensitivity and residual foci. In this study, we investigated dose-responses and kinetics for radiation-induced 53BP1/gamma-H2AX foci formation in relation to their co-localization, DSB repair and cell survival. MATERIALS AND METHODS: Cell survival, DSB and foci were analyzed by clonogenic assay, pulsed field gel electrophoresis (PFGE), and confocal laser microscopy, respectively, in normal human fibroblasts (VH-10) and in a cancer cell line (HeLa). Computer analysis was used to determine both the number and the area of foci. RESULTS: We show that even at doses down to 1 cGy a statistically significant induction of 53BP1 foci is observed. While the number of foci was found to constantly decrease with post-irradiation time, the per-cell normalized area of foci does not change within a time window of approximately 4 h post-irradiation. Co-localization of gamma-H2AX and 53BP1 foci is shown to depend on dose and post-irradiation time. No clear correlations were established between radiosensitivity and foci formation because the dose response for 53BP1/gamma-H2AX foci may depend on time after irradiation and duration of the cell cycle. We show that the kinetics of foci disappearance within 24 h post-irradiation do not coincide with those of DSB repair. CONCLUSIONS: The data suggest that the post-irradiation time used for estimation of radiosensitivity at therapeutically relevant low doses (e.g., <3 Gy) in proliferating cells by scoring residual foci should be limited by the duration of the cell cycle, and that direct comparison of the kinetics of DSB repair and disappearance of DSB-co-localizing foci is not possible. Therefore, results obtained from the counting of foci should be interpreted with caution in terms of DSB repair.     

Underestimation of the small residual damage when measuring DNA double-strand breaks (DSB): is the repair of radiation-induced DSB complete?

PURPOSE: To overcome the underestimation of the small residual damage when measuring DNA double-strand breaks (DSB) as fraction of activity released (FAR) by pulsed-field gel electrophoresis. MATERIALS AND METHODS: The techniques used to assess DNA damage (e.g. pulsed-field gel electrophoresis, neutral elution, comet assay) do not directly measure the number of DSB. The Bl?cher model can be used to express data as DSB after irradiation at 4 degrees C by calculating the distribution of all radiation-induced DNA fragments as a function of their size. We have used this model to measure the residual DSB (irradiation at 4 degrees C followed by incubation at 37 degrees C) in untransformed human fibroblasts. RESULTS: The DSB induction rate after irradiation at 4 degrees C was 39.1+/-2.0 Gy(-1). The DSB repair rate obtained after doses of 10 to 80 Gy followed by repair times of 0 to 24 h was expressed as unrepaired DSB calculated from the Bl?cher formula. All the damage appeared to be repaired at 24h when the data were expressed as FAR, whereas 15% of DSB remained unrepaired. The DSB repair rate and the chromosome break repair rate assessed by premature condensation chromosome (PCC) techniques were similar. CONCLUSION: The expression of repair data in terms of FAR dramatically underestimates the amount of unrepaired DNA damage. The Bl?cher model that takes into account the size distribution of radiation-induced DNA fragments should therefore be used to avoid this bias. Applied to a normal human fibroblast cell line, this model shows that DSB repair is never complete.     

Radiation response of apoptosis in C57BL/6N mouse spleen after whole-body irradiation

Purpose : Primary conditioning low dose irradiation suppresses the molecular responses against secondary challenge high dose irradiation; this phenomenon has been termed the radioadaptive response. The mechanism of the radioadaptive response is not yet clear. This study was undertaken to elucidate the radiation response of apoptosis in mouse spleen after whole-body irradiation. Materials and methods : The induction of apoptosis was analysed in the spleens of C57BL/6N mice after chronic irradiation with γ-rays at 1.5 Gy (0.001 Gy/min for 25 h) followed by challenge irradiation with X-rays at 3.0Gy (1 Gy/min). Results : Accumulation of p53 and Bax, and the induction of apoptosis were observed dose-dependently in mouse spleen 12 h after acute irradiation at a high dose-rate. However, it was found that there was significant suppression of the accumulation of p53 and Bax, and induction of apoptosis 12 h after challenge irradiation at 3.0Gy at a high dose-rate following chronic preirradiation at 1.5Gy at a low dose-rate. In addition, the combination of pre-irradiation at 1.5Gy at a high dose-rate and challenge irradiation at 3.0Gy at a high dose-rate could not suppress the accumulation of p53 and Bax or the induction of apoptosis. Conclusions : Chronic pre-irradiation at a low dose-rate suppressed Bax-mediated apoptosis. These findings suggest that the radioadaptive response in mouse spleen may be due to a suppression of p53-mediated apoptosis.     

Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiated in vacuum

Purpose : To measure action spectra for the induction of single-strand breaks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photons and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage. Materials and methods : Plasmid pMSG-CAT was irradiated as a monolayer, under vacuum, with 7-150 eV photons produced by a synchrotron source. Yields of SSB and DSB were determined by the separation of the three plasmid forms by gel electrophoresis. Results : The yields of SSB per incident photon increased from 1.4 x 10 -15 SSB per plasmid per photon/cm 2 at 7 eV to 7.5 x 10 -14 SSB per plasmid per photon/cm 2 at 150 eV. Direct induction of DSB was also detected increasing from 3.4 x 10 -17 DSB per plasmid per photon/cm 2 at 7 eV to 4.1 x 10 -15 DSB per plasmid per photon/cm 2 at 150 eV. When the absorption cross-section of the DNA was considered, the quantum efficiency for break formation increased over the energy range studied. Over the entire energy range, the ratio of SSB to DSB remained constant. Conclusions : These studies provide evidence for the ability of photons as low as 7 eV to induce both SSB and DSB. The common action spectrum for both lesions suggests that they derive from the same initial photoproducts under conditions where the DNA is irradiated in vacuum and a predominantly direct effect is being observed. The spectral and dose-effect behaviour indicates that DSB are induced predominantly by single-event processes in the energy range covered.     

Radiation-induced genomic instability in repair deficient mutants of Chinese hamster cells

PURPOSE: To determine the role of single (SSB) and double strand break (DSB) repair in the induction and propagation of radiation-induced instability. MATERIALS AND METHODS: Two defined hamster cell lines with known DNA repair deficiencies in DSB repair (XR-C1) and base excision repair (EM-C11) and the parental wild-type line (CHO-9) were used. The rate of micronucleus formation, apoptosis and survival were measured at 0, 7 and 14 days after X-ray radiation. RESULTS: An enhanced rate of production of damaged cells was observed in wild type and the repair deficient mutants after irradiation. This was cell type, dose and time-dependent. All cells demonstrated delayed death up to day 14 after irradiation along with an elevated apoptosis frequency. The yield of micronuclei was not significantly increased in the wild-type cells, but was in the mutant cells, over the dose and time range studied. For all three endpoints the increase in damage was most pronounced in the SSB deficient cell line. CONCLUSIONS: SSB and/or oxidized base damage play a major role, rather than DSB, in radiation induced instability.     

Low-dose hyper-radiosensitivity of progressive and regressive cells isolated from a rat colon tumour: impact of DNA repair

PURPOSE: To ask whether highly metastatic sublines show more marked low-dose hyper-radiosensitivity (HRS) response than poorly metastatic ones. MATERIALS AND METHODS: The progressive (PRO) subline showing tumourigenicity and metastatic potential and the regressive (REG) subline showing neither tumourigenicity nor metastatic potential were both isolated from a parental rat colon tumour. Clonogenic survival, micronuclei and apoptosis, cell cycle distribution, DNA single- (SSB) and double-strand breaks (DSB) induction and repair were examined. RESULTS: HRS phenomenon was demonstrated in PRO subline. Before irradiation, PRO cells show more spontaneous damage than REG cells. After 0.1 Gy, PRO cells displayed: (i) More DNA SSB 15 min post-irradiation, (ii) more unrepaired DNA DSB processed by the non-homologous end-joining (NHEJ) and by the RAD51-dependent recombination pathways, (iii) more micronuclei, than REG cells while neither apoptosis nor p53 phosphorylation nor cell cycle arrest was observed in both sublines. CONCLUSIONS: HRS response of PRO subline may be induced by impairments in NHEJ repair that targets G(1) cells and RAD51-dependent repair that targets S-G(2)/M cells. The cellular consequences of such impairments are a failure to arrest in cell cycle, the propagation of damage through cell cycle, mitotic death but not p53-dependent apoptosis. Tumourigenic cells with high metastatic potential may preferentially show HRS response.     

DNA repair foci and late apoptosis/necrosis in peripheral blood lymphocytes of breast cancer patients undergoing radiotherapy

Abstract

Purpose: Double-strand breaks (DSB) repair and apoptosis are assumed to be key factors in the determination of individual variability in response to radiation treatment. In this study we investigated tumor protein p53 (TP53) binding protein 1 (53BP1) and phosphorylated histone 2A family member X (γH2AX) foci, γH2AX pan-staining and late apoptosis/necrosis (LAN) in lymphocytes from breast cancer (BC) patients undergoing radiotherapy.

Materials and methods: BC patients were subjected to local radiotherapy with fractionated doses using linear accelerator. Adverse reactions of patients were classified according to the Radiation Therapy Oncology Group (RTOG)/European Organization for Research and Treatment of Cancer (EORTC) criteria. Blood samples were collected before treatment, at various time-points during and after radiotherapy. Residual 53BP1 and γH2AX foci, γH2AX pan-staining were analyzed in peripheral blood lymphocytes (PBL) using the Metafer system and confocal laser scanning microscopy. LAN cells were counted by the trypan blue (TB) exclusion assay. Statistical analysis was performed using Mann–Whitney test, Spearman rank correlation test and analysis of covariance (ANCOVA).

Results: No statistically significant changes were observed in the levels of γH2AX foci during radiotherapy. In contrast, radiation-induced residual 53BP1 were detected already after the first fraction. Increased individual variability in the 53BP1 focus formation was observed during treatment. The background level of DNA repair foci and its individual variability in response to radiotherapy decreased after the end of radiotherapy indicating successful removal of DNA-damaging effects. A correlation between stage of cancer and 53BP1 focus formation was established which suggests the prognostic value of this test. We show that the fraction of LAN cells negatively correlates with the level of 53BP1 and positively correlates with individual radiosensitivity. Only weak correlation was observed between γH2AX pan-staining and LAN cells. Due to large interindividual variability, both in vivo assays, LAN and focus formation, have shown relatively low predictive power at the individual level.

Conclusions: It is likely that radiosensitive patients have less efficient mechanisms of elimination of apoptotic cells with DNA damage resulting in accumulation of LAN cells and facilitating adverse reactions. Our data suggested that the grade of adverse reaction may positively correlate with LAN cells in PBL before and during radiotherapy.     

γ-H2AX分析电离辐射诱发小鼠神经元DNA双链断裂及修复

目的 观察临床剂量的电离辐射后小鼠神经元DNA双链的断裂及修复, 探讨γ-H2AX是否能作为衡量体内正常脑组织神经元DNA双链断裂(DSB)形成和修复的指标。方法 电离辐射诱导DSB形成试验,C57BL/6小鼠行0.1、0.5和1.0 Gy全身照射后10 min,收集脑组织进行分析;DSB修复试验,修复功能正常小鼠(C57BL/6)和修复缺陷鼠(BALB/c, A-T 和SCID)在全身照射2 Gy后0.5、2.5、5、24和48 h收集脑组织进行分析。未照射的小鼠作为对照组。γ-H2AX和NeuN免疫荧光双重染色和免疫组织化学染色分析脑组织神经元DSB形成和修复。结果 DSB形成试验,在对照组脑组织皮质区神经元的细胞核内仅有数目很少的γ-H2AX焦点,而受照射后细胞核内γ-H2AX焦点数目显著增加,并显示出明显的剂量相关。通过分析不同放射敏感性的小鼠电离辐射后脑组织皮质区神经元的DSB修复动力学,发现C57BL/6小鼠细胞核内γ-H2AX焦点随时间的延长迅速减少,在照射后24和48 h仅有很低水平DSB未修复;而免疫缺陷SCID鼠在照射后所有的时间点都显示出γ-H2AX焦点的明显增加,A-T小鼠表现出较低的修复缺陷,主要表现在较晚的时间点(≥5 h)γ-H2AX焦点的中度增加;放射敏感的BALB/c小鼠与C57BL/6小鼠相比γ-H2AX焦点数量轻度增加。结论 γ-H2AX焦点分析可以作为一项精确的量化指标,在体内衡量临床相关剂量电离辐射诱导的DSB形成和修复。     

Persistence of γ-H2AX and 53BP1 foci in proliferating and non-proliferating human mammary epithelial cells after exposure to γ-rays or iron ions

Purpose:?To investigate γ-H2AX (phosphorylated histone H2AX) and 53BP1 (tumour protein 53 binding protein No. 1) foci formation and removal in proliferating and non-proliferating human mammary epithelial cells (HMEC) after exposure to sparsely and densely ionising radiation under different cell culture conditions.

Material and methods:?HMEC cells were grown either as monolayers (2D) or in extracellular matrix to allow the formation of acinar structures in vitro (3D). Foci numbers were quantified by image analysis at various time points after exposure.

Results:?Our results reveal that in non-proliferating cells under 2D and 3D cell culture conditions, iron-ion induced γ-H2AX foci were still present at 72?h after exposure, although 53BP1 foci returned to control levels at 48?h. In contrast in proliferating HMEC, both γ-H2AX and 53BP1 foci decreased to control levels during the 24–48?h time interval after irradiation under 2D conditions. Foci numbers decreased faster after γ-ray irradiation and returned to control levels by 12?h regardless of marker, cell proliferation status, and cell culture condition.

Conclusions:?The disappearance of radiation-induced γ-H2AX and 53BP1 foci in HMEC has different dynamics that depend on radiation quality and proliferation status. Notably, the general patterns do not depend on the cell culture condition (2D versus 3D). We speculate that the persistent γ-H2AX foci in iron-ion irradiated non-proliferating cells could be due to limited availability of double-strand break (DSB) repair pathways in G0/G1-phase, or that repair of complex DSB requires replication or chromatin remodelling.     

Radiation-induced genomic instability in repair deficient mutants of Chinese hamster cells

Purpose: To determine the role of single (SSB) and double strand break (DSB) repair in the induction and propagation of radiation-induced instability.

Materials and methods: Two defined hamster cell lines with known DNA repair deficiencies in DSB repair (XR-C1) and base excision repair (EM-C11) and the parental wild-type line (CHO-9) were used. The rate of micronucleus formation, apoptosis and survival were measured at 0, 7 and 14 days after X-ray radiation.

Results: An enhanced rate of production of damaged cells was observed in wild type and the repair deficient mutants after irradiation. This was cell type, dose and time-dependent. All cells demonstrated delayed death up to day 14 after irradiation along with an elevated apoptosis frequency. The yield of micronuclei was not significantly increased in the wild-type cells, but was in the mutant cells, over the dose and time range studied. For all three endpoints the increase in damage was most pronounced in the SSB deficient cell line.

Conclusions: SSB and/or oxidized base damage play a major role, rather than DSB, in radiation induced instability.     

DNA double-strand break signalling: X-ray energy dependence of residual co-localised foci of γ-H2AX and 53BP1

Purpose:?The application of ionising radiation for medical purposes requires the investigation of induced and persistent DNA damages, especially for soft X-rays that are assumed to be more effective than higher energy photons. Therefore, we examined the energy dependent time and dose response of residual DNA damage foci for soft X-rays in comparison to 200 kV photons.

Materials and methods:?DNA damage present in cell line 184A1 within 48?h after irradiations with 10 kV, 25 kV and 200 kV photons was analysed by immunochemical detection of co-localised γ-H2AX (phosphorylated histone H2AX) and 53BP1 (tumour protein 53 binding protein) foci.

Results:?The dose dependencies of the colocated foci revealed significant energy dependent differences with increasing amounts of residual foci at decreasing X-ray energy independent on postirradiation time. Dose-dependent RBE (relative biological effectiveness) values ranging from 4 to 7 were determined for 10 kV relative to 200 kV X-rays based on the 24 hour dose responses. For 25 kV photons, ratios considerably higher than one were obtained only for doses above 2 Gy.

Conclusions:?The expected energy dependence with increasing DNA damage at decreasing photon energy was confirmed for the residual co-localised foci measured at different time points after irradiation.     

Low-dose hyper-radiosensitivity of progressive and regressive cells isolated from a rat colon tumour: Impact of DNA repair

Purpose: To ask whether highly metastatic sublines show more marked low-dose hyper-radiosensitivity (HRS) response than poorly metastatic ones.

Materials and methods: The progressive (PRO) subline showing tumourigenicity and metastatic potential and the regressive (REG) subline showing neither tumourigenicity nor metastatic potential were both isolated from a parental rat colon tumour. Clonogenic survival, micronuclei and apoptosis, cell cycle distribution, DNA single- (SSB) and double-strand breaks (DSB) induction and repair were examined.

Results: HRS phenomenon was demonstrated in PRO subline. Before irradiation, PRO cells show more spontaneous damage than REG cells. After 0.1 Gy, PRO cells displayed: (i) More DNA SSB 15 min post-irradiation, (ii) more unrepaired DNA DSB processed by the non-homologous end-joining (NHEJ) and by the RAD51-dependent recombination pathways, (iii) more micronuclei, than REG cells while neither apoptosis nor p53 phosphorylation nor cell cycle arrest was observed in both sublines.

Conclusions: HRS response of PRO subline may be induced by impairments in NHEJ repair that targets G₁ cells and RAD51-dependent repair that targets S-G₂/M cells. The cellular consequences of such impairments are a failure to arrest in cell cycle, the propagation of damage through cell cycle, mitotic death but not p53-dependent apoptosis. Tumourigenic cells with high metastatic potential may preferentially show HRS response.     

电离辐射诱导EL-4细胞Caspase-3、P53蛋白表达及其生物学作用

目的研究电离辐射对EL-4细胞中Caspase-3和P53蛋白表达的影响，及其对辐射诱导细胞凋亡及多倍体细胞的作用。方法采用单克隆抗体免疫荧光标记及流式细胞术检测蛋白表达的变化，采用PI荧光标记及流式细胞术检测细胞凋亡及多倍体细胞的变化。结果实验表明，4．0GyX射线照射后8及12h，EL-4细胞中Caspase-3蛋白表达与对照组比较，差异有统计学意义（P〈0．05）；照射后2、4、8、12及24h，P53蛋白表达与对照组比较，差异有统计学意义（P〈0．05或P〈0．01）。实验还表明，4．0Gy照射后2、4、8、12、24、48及72h，EL-4细胞凋亡与对照组比较，差异有统计学意义（P〈0．05～P〈0．001）；而照射后2～48h，多倍体细胞数与对照组比较则未见明显变化。结论电离辐射可诱导EL-4细胞Caspase-3及P53蛋白表达增高，可能在辐射诱导细胞凋亡中起重要作用，而辐射诱导多倍体细胞的分子通路则可能是P53非依赖性的。     

Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiated in vacuum

PURPOSE: To measure action spectra for the induction of single-strand breaks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photons and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage. MATERIALS AND METHODS: Plasmid pMSG-CAT was irradiated as a monolayer, under vacuum, with 7 150eV photons produced by a synchrotron source. Yields of SSB and DSB were determined by the separation of the three plasmid forms by gel electrophoresis. RESULTS: The yields of SSB per incident photon increased from 1.4x 10(-15) SSB per plasmid per photon/cm2 at 7eV to 7.5 x 10(-14) SSB per plasmid per photon/cm2 at 150 eV. Direct induction of DSB was also detected increasing from 3.4 x 10(-17) DSB per plasmid per photon/cm2 at 7eV to 4.1 x 10(-15) DSB per plasmid per photon/cm2 at 150eV. When the absorption cross-section of the DNA was considered, the quantum efficiency for break formation increased over the energy range studied. Over the entire energy range, the ratio of SSB to DSB remained constant. CONCLUSIONS: These studies provide evidence for the ability of photons as low as 7 eV to induce both SSB and DSB. The common action spectrum for both lesions suggests that they derive from the same initial photoproducts under conditions where the DNA is irradiated in vacuum and a predominantly direct effect is being observed. The spectral and dose-effect behaviour indicates that DSB are induced predominantly by single-event processes in the energy range covered.     

DNA-dependent protein kinase: effect on DSB repair,G2/M checkpoint and mode of cell death in NSCLC cell lines

Abstract

Purpose: To evaluate the effect of NU7026, a specific inhibitor of DNA-PKcs, on DNA-double strand break (DSB) repair in a cell cycle specific manner, on the G2/M checkpoint, mitotic progression, apoptosis and clonogenic survival in non-small-cell lung carcinoma (NSCLC) cell lines with different p53 status.

Material and methods: Cell cycle progression, and hyperploidy were evaluated using flow cytometry. Polynucleation as a measure for mitotic catastrophe (MC) was evaluated by fluorescence microscopy. DSB induction and repair were measured by constant-gel electrophoresis and γH2AX assay. The efficiency of DSB rejoining during the cell cycle was assessed by distinguishing G1 and G2/M phase cells on the basis of the DNA content in flow cytometry. The overall effect on cell death was determined by apoptosis and the surviving fraction after irradiation with 2?Gy (SF2) assessed by clonogenic survival.

Results: DSB signaling upon treatment with NU7026, as measured by γH2AX signaling, was differently affected in G1 and G2/M cells. The background level of γH2AX was significantly higher in G2/M compared to G1 cells, whereas NU7026 had no effect on the background level. The steepness of the initial dose effect relation at 1?h after irradiation was less pronounced in G2/M compared to G1 cells. NU7026 had no significant effect on the initial dose-effect relation of γH2AX signaling. In comparison, NU7026 significantly slowed down the repair kinetics and increased the residual γH2AX signal at 24?h after irradiation in the G1 phase of all cell lines, but was less effective in G2/M cells. NU7026 significantly increased the fraction of G2/M phase cells upon irradiation. Moreover, NU7026 significantly increased mitotic catastrophe and hyperploidy, as a measure for mitotic failure after low irradiation doses of about 4?Gy, but decreased both at higher doses of 20?Gy. In addition, radiation induced apoptosis increased in A549, H520 and H460 but decreased in H661 upon NU7026 treatment, with a significant reduction of SF2 in all NSCLC cell lines.

Conclusion: Overall, NU7026 significantly influences the cell cycle progression through the G2- and M-phases and thereby determines the fate of cells. The impairment of DNA-PK upon treatment with NU7026 affects the efficiency of the NHEJ system in a cell cycle dependent manner, which may be of relevance for a clinical application of DNA-PK inhibitors in tumor therapy.     

gamma-H2AX foci formation in peripheral blood lymphocytes of tumor patients after local radiotherapy to different sites of the body: dependence on the dose-distribution, irradiated site and time from start of treatment

PURPOSE: To evaluate the relationship between an estimated integral total body radiation dose delivered and phosphorylated histone H2AX protein (gamma-H2AX) foci formation in peripheral blood lymphocytes of cancer patients. MATERIAL AND METHODS: gamma-H2AX formation was quantified as the mean number of foci per lymphocyte (N(meanH2AX)) and the percentage of lymphocytes with > or =n foci. The integrated total body radiation dose was estimated from the dose volume histogram of patient's body corrected for the proportion of the body scanned by computed tomography for 3D treatment planning. RESULTS: There was a strong linear correlation between the mean number of gamma-H2AX foci per lymphocyte in the peripheral blood sample and integrated total body radiation dose (r = 0.83, p < 0.0001). The slope of the relationship was dependent on the site of body irradiated. In comparison to chest irradiation with a slope of 8.7 +/- 0.8 foci Gy(-1), the slopes for brain, upper leg and pelvic sites were significantly shallower by -4.7, -4.3, and -3.8 Gy(-1), respectively (p < 0.0001), while the slope for upper abdomen irradiation was significantly larger by 9.1 +/- 2.6 Gy(-1) (p = 0.0007). There was a slight time effect since the start of radiotherapy on the slopes of the in vivo dose responses leading to shallower slopes (-1.5 +/- 0.7 Gy(-1), p = 0.03) later (> or =10 day) during radiotherapy. After in vitro irradiation, lymphocytes showed 10.41 +/- 0.12 foci per Gy with no evidence of inter-individual heterogeneity. CONCLUSIONS: gamma-H2AX measurements in peripheral lymphocytes after local radiotherapy allow the estimation of the applied integral body dose. The site and time dependence have to be considered.     

慧星电泳用于肿瘤细胞辐射敏感性检测的研究

目的：探讨彗星电泳方法检测肿瘤细胞对γ射线的辐射敏感性的可行性。方法：以自行设计的图像分析系统，用彗星电泳方法检测4种人肿瘤细胞受γ射线照射后细胞初始DNA损伤，以及细胞径30min修复时DNA损伤残余率；用细胞集落存活法检测2Gy γ射线照射后细胞存活率。结果：4种肿瘤细胞初始DNA损伤与辐射敏感性无关，2Gyγ射线照射后4种细胞存活率（SF2）与细胞经30min修复后的DNA损伤残余率相关明显（r=-0.87)，结论：本实验方法有可能成为一种快速、准确检测肿瘤细胞内在辐射敏感性的方法。