Stattic对乏氧食管癌细胞放射增敏作用机制的研究

目的 观察Stattic对乏氧人食管癌ECA109细胞的体外放射增敏作用,并探讨其可能机制。方法 应用四甲基偶氮唑盐比色法（MTT）检测Stattic对食管癌ECA109细胞的毒性,细胞克隆形成法确定1.0 μmol Stattic对ECA细胞放疗敏感性的影响,流式细胞法检测细胞的凋亡率,γ-H2AX免疫荧光染色法检测不同时间点下ECA109细胞中双键断裂情况,Western blot检测Stattic照射前后STAT3、pSTAT3、HIF-1α、VEGF蛋白的表达。结果 Stattic对ECA109细胞具有毒性,24 h IC₅₀为5.499 μmol/L,克隆形成实验通过单击多靶模型拟合细胞的存活曲线,计算出1.0 μmol/L Stattic的放射增敏比SER_Do分别为1.20（常氧）和1.28（乏氧）,γ-H2AX荧光染色提示Stattic能增加双键断裂情况,尤其是在照射之后0.5 h最为明显。照射联合给药组的乏氧细胞凋亡率较单独乏氧照射组的细胞凋亡增加（t=7.33,P < 0.05）,Western blot显示乏氧食管癌细胞株pSTAT3、乏氧诱导因子1α（HIF-1α）、血管内皮生长因子（VEGF）蛋白的表达升高,Stattic作用24 h表达显著下调。结论 Stattic对乏氧人食管癌细胞株ECA109细胞的毒性呈剂量依赖性,放射增敏作用明显,随药物剂量的增加而增强,其机制可能与抑制pSTAT3、HIF-1α和VEGF蛋白表达有关。     

盐酸小檗碱对乏氧食管癌细胞的放射增敏作用

目的 研究盐酸小檗碱对乏氧食管癌细胞的放射增敏作用。方法 通过MTT法检测盐酸小檗碱对食管癌ECA-109细胞生长的抑制;克隆集落形成实验观察盐酸小檗碱的放射增敏作用;通过免疫荧光实验观察HIF-1的表达情况;流式细胞仪检测细胞的凋亡情况;Western blot检测细胞内HIF-1表达;γ-H2AX焦点形成检测DNA分子损伤情况。结果 盐酸小檗碱抑制食管癌ECA-109细胞的生长,并且有明显的时间和剂量依赖性;通过单击多靶模型拟合曲线,可见低浓度盐酸小檗碱预处理24 h,相比于照射组,可以增加乏氧ECA-109细胞的辐射敏感性(t=3.69,P<0.05),辐射增敏指数为1.42;与照射组相比,盐酸小檗碱+照射组中的细胞凋亡率明显增加(t=4.74,P<0.05);盐酸小檗碱作用于乏氧食管癌细胞,可以使乏氧相关蛋白HIF-1的表达降低,并且呈现明显的量效关系;相对于照射组,盐酸小檗碱+照射组能够增加DNA双链断裂数目(DSB)。结论 盐酸小檗碱能够提高食管癌细胞的放射敏感性,与其增加食管癌细胞的凋亡率和降低乏氧食管癌ECA-109细胞内HIF-1的表达有关。     

聚腺苷二磷酸核糖聚合酶-1抑制剂对乳腺癌易感基因突变乳腺癌细胞放射敏感性的影响及调控机制

目的 探讨聚腺苷二磷酸核糖聚合酶-1(PARP-1)的抑制剂3-氨基苯甲酰胺(3-aminobenzamide,3-AB)对于乳腺癌易感基因(BRCA)突变及非突变乳腺癌细胞放射敏感性的影响,探讨PARP-1和BRCA基因在照射引起的乳腺癌细胞DNA损伤修复中的作用及调控机制。方法 将BRCA突变乳腺癌细胞(MDA-MB-436)和BRCA非突变乳腺癌细胞(MDA-MB-231)分别分为对照组(CTRL)、单纯照射组(IR)、单纯用药组(3-AB)和药物联合照射组(3-AB+IR)。通过γ-H2AX免疫荧光焦点,检测DNA双链断裂的损伤情况;克隆形成实验检测细胞的放射敏感性;流式细胞仪检测细胞的凋亡率。结果 克隆形成实验显示,MDA-MB-436细胞较MDA-MB-231细胞放射敏感性明显升高,3-AB可增加两种细胞的放射敏感性。γ-H2AX免疫荧光焦点实验显示MDA-MB-436细胞与MDA-MB-231细胞相比DNA双链的损伤情况明显升高(t=4.57,P<0.05),而3-AB可进一步增加照射引起的DNA损伤,IR+3-AB组的MDA-MB-436细胞DNA损伤最明显(t=3.26,P<0.05)。流式细胞术结果显示,IR+3-AB组的凋亡率最高,且差异有统计学意义(t=3.81,P<0.05)。MDA-MB-436细胞相比MDA-MB-231细胞凋亡率明显增加(t=2.96,P<0.05)。结论 照射过程中,MDA-MB-436细胞比MDA-MB-231细胞产生更多的DNA损伤和凋亡,因此BRCA突变的乳腺癌细胞MDA-MB-436放射敏感性更强。而PARP-1抑制剂可进一步阻断照射引起的DNA损伤修复,从而增加MDA-MB-436的放射敏感性。     

LM-1685对人肺腺癌细胞A549的放射增敏作用

目的 观察环氧合酶-2(COX-2)抑制剂对肺癌细胞的放射增敏作用。方法COX-2抑制剂LM-1685作用于体外培养的肺癌细胞A549,噻唑蓝(MTT)法检测其对肺癌细胞的抑制效果,克隆形成法检测放射敏感性,流式细胞术检测细胞周期变化。结果COX-2抑制剂LM-1685具有明显的抑制A549细胞增殖的作用,其效应呈时间和剂量依赖性,50 μmol/L LM-1685在有或没有IL-1β作用下对A549细胞均有放射增敏作用,其放射增敏比分别为1.12、1.06。50 μmol/L LM-1685能去除X射线导致的A549细胞G₂/M期阻滞。结论COX-2抑制剂对肺癌细胞A549具有放射增敏作用,放射增敏机制可能与去除G₂/M期阻滞有关。     

香兰素衍生物BVAN08对人脑胶质瘤细胞的放射增敏作用及机制研究

目的 研究香兰素衍生物6-溴异香兰素(BVAN08)对人脑胶质瘤细胞的增殖影响、放射增敏作用和相关机制,为开发新的放射增敏抗癌药物提供实验依据。方法 采用MTT法、克隆形成率法检测BVAN08对U-251细胞增殖活性和⁶⁰Coγ射线敏感性的影响(照射剂量率为2.3 Gy/min);光学显微镜观察BVAN08作用后细胞形态学变化;透射电镜检测细胞自吞噬死亡;流式细胞术检测细胞周期和凋亡的变化;Western blot检测DNA修复蛋白DNA-PKcs的表达变化。结果 6-溴异香兰素BVAN08对U-251细胞增殖有显著抑制作用(t=1.83～3.07,P＜0.05),在10～100 μmol/L浓度范围内呈剂量和作用时间依赖性,药物作用48和72 h的IC50分别为55.3 和52.7 μmol/L。60 μmol/L BVAN08作用4 h后,U-251细胞产生明显的G₂/M期阻滞, 12 h达到峰值,G₂/M阻滞达到63.3 %,并开始同时出现细胞凋亡和自吞噬死亡。BVAN08对U-251细胞有明显的放射增敏作用,而且在照射前12 h给药的增敏效果最好,20 μmol/L浓度对2 Gy照射杀伤U-251细胞的增强比为3.14。Western blot检测表明BVAN08能显著抑制DNA-PKcs的表达。结论 香兰素衍生物BVAN08具有明显抑制人脑胶质瘤U-251细胞增殖和辐射增敏作用、并同时诱发凋亡和自吞噬死亡。BVAN08对U-251细胞的辐射增敏作用可能与G₂/M期阻滞和DNA双链断裂修复关键蛋白DNA-PKcs表达的抑制敏感性有关。     

凋亡素2配体对食管癌细胞株Eca-109放射敏感性的影响

目的 研究凋亡素2配体(Apo-2 ligand,Apo2L),又称肿瘤坏死因子相关凋亡诱导配体(tumor necrosis factor-related apoptosis inducing ligand,TRAIL)对体外培养食管癌细胞株Eca-109放射敏感性的影响。方法 MTT法检测TRAIL对Eca-109细胞的毒性;克隆形成实验检测TRAIL对Eca-109细胞的放射增敏作用;流式细胞仪(FCM)技术分析TRAIL对凋亡率及细胞周期的影响。结果 100~800 μg/ml TRAIL随浓度升高对Eca-109细胞的增殖抑制率增大,药物浓度与细胞抑制率正相关(r=0.981,P<0.01),50%抑制浓度(IC₅₀)为637 μg/ml;200 μg/ml TRAIL能增加Eca-109细胞的放射敏感性,放射增敏比为1.219;不同剂量(0~8 Gy)照射后,给药组的凋亡率均高于单照射组(F=16.97、76.65、92.86、209.66,P<0.05),给药组G₂/M期细胞比例较单照射组增加(F=9.40、84.99、87.61、2025.85,P<0.05)。结论 TRAIL可以抑制Eca-109细胞的生长,诱导细胞凋亡和G₂/M期阻滞,后者可能与TRAIL的放射增敏机制有关。     

5-硝基吲唑衍生物对HeLa细胞的放射增敏作用

目的 研究5-硝基吲唑-3-甲酰亚氨基二乙酸的细胞毒性,以及对HeLa细胞的放射增敏作用。方法 取指数生长期的HeLa细胞,接种于96孔板,加入不同浓度的药物作用后,用噻唑蓝比色法(MTT法)测定存活分数,并比较不同药物剂量加照射的实验组与单纯照射组的细胞存活分数。结果 5-硝基吲唑-3-甲酰亚氨基二乙酸对HeLa细胞的毒性较小。该药物对HeLa细胞有放射增敏作用,且乏氧处理的效果优于有氧处理:0、6、12、24、48、96μg/ml药物乏氧处理,存活率分别为0.91、0.87、0.84、0.81、0.76、0.60;48、96μg/ml药物有氧处理,存活率分别为0.85和0.73。结论 5-硝基吲唑-3-甲酰亚氨基二乙酸对HeLa细胞的毒性较小,且具有一定的乏氧放射增敏剂特征。     

葡萄糖耦联纳米金对A549肺癌细胞体外放射增敏作用

目的 研究葡萄糖纳米金颗粒（Glu-GNPs）联合千伏和兆伏级X射线对肺腺癌A549细胞的体外放射增敏作用。方法 取指数生长期的人肺腺癌A549细胞,分为对照组、Glu-GNPs组、单纯照射组（6 MV单纯照射组与160 kV单纯照射组）、纳米金联合照射组（6 MV+Glu-GNPs组、160 kV+Glu-GNPs组）。使用透射电镜（TEM）观察Glu-GNPs在A549细胞中的分布。使用结晶紫测定法测定Glu-GNPs对A549细胞的毒性作用以及Glu-GNPs联合射线对细胞的增殖抑制作用。克隆形成实验评估Glu-GNPs对A549细胞的放射增敏作用。用γ-H2AX免疫荧光法检测A549细胞受照射后的DNA双链断裂焦点（foci）。结果 TEM显示Glu-GNPs主要分布在A549细胞质中,包括内涵体和线粒体内。浓度低于100 nmol/L的Glu-GNPs对A549细胞无明显毒性作用。不同浓度的Glu-GNPs联合不同能量级X射线对A549细胞均具有明显的增殖抑制作用。在160 kV与6 MV X射线条件下,Glu-GNPs联合照射组存活分数较单纯照射组明显降低（P<0.05）,放射增敏比（SER_D0）分别为1.41和1.15。此外Glu-GNPs可显著增加射线诱导的DNA双链断裂点,且Glu-GNPs联合160 kV X射线组与联合6 MV X射线组相比,有更多的DNA双链断裂灶点（t=12.392、14.893、18.947,P<0.05）。结论 Glu-GNPs可增加A549细胞的放射敏感性,且在keV条件下增敏效果更加明显。     

蒿甲醚对人鼻咽癌细胞CNE-1放射敏感性的影响及其机制研究

目的 研究蒿甲醚(artemether)对人鼻咽癌CNE-1细胞放射敏感性的影响及其作用机理。方法 用MTT法检测蒿甲醚对CNE-1细胞生长的抑制效应;克隆形成法检测蒿甲醚对CNE-1细胞放射敏感性的影响;流式细胞仪检测不同处理因素对CNE-1细胞的细胞周期的影响;Western blot分析蒿甲醚对电离辐射诱导的CNE-1细胞中的细胞周期调控蛋白Cyclin B1和Wee1表达水平的影响。结果 蒿甲醚可抑制CNE-1细胞的增殖,且药物浓度和作用时间相关;20 μmol/L蒿甲醚对CNE-1细胞有放射增敏作用,其放射增敏作用随作用时间的延长而延长,作用24 h 后增敏作用最强,放射增敏比(SER)为1.481。流式细胞仪分析表明,单纯⁶⁰Co γ射线照射后G₂/M期细胞比例上升,而G₀/G₁期细胞比例下降;药物和射线联合作用后,与单纯照射组相比,G₀/G₁期细胞比例上升(t=4.59,P<0.05),G₂/M期细胞比例下降(t=10.60,P<0.05)。蒿甲醚可降低照射后CNE-1细胞内Wee1蛋白表达水平,提高Cyclin B1蛋白表达水平。结论 低浓度蒿甲醚对CNE-1 细胞有放射增敏作用;蒿甲醚通过改变细胞周期调控蛋白Cyclin B1和 Wee1表达水平,诱导G₂/M 期阻滞而发挥放射增敏作用。     

RNA干扰抑制端粒酶反转录酶联合γ射线对人喉癌细胞的作用

目的 观察人端粒酶反转录酶特异性干扰载体(pshRNA-hTERT)联合放射线在细胞和动物模型水平上对人喉鳞癌Hep-2细胞株的生长抑制作用,研究抑制hTERT在放射增敏中的作用。方法 细胞水平:联合pshRNA-hTERT和γ射线作用于人喉癌细胞Hep-2,用TRAP-PCR-ELISA法检测端粒酶活性,彗星电泳检测DNA损伤;动物水平:建立Hep-2和Hep-2R移植瘤模型,瘤内注射pshRNA-hTERT并联合放射线观察对移植瘤的抑制作用,TUNEL法检测肿瘤细胞的凋亡,免疫组织化学法检测肿瘤内hTERT蛋白的表达。 结果 转染pshRNA-hTERT后Hep-2细胞hTERT的mRNA表达抑制率为60.78%;pshRNA-hTERT不仅能抑制Hep-2细胞的端粒酶活性,而且抑制照射后DNA损伤的修复;在移植瘤模型中,pshRNA-hTERT与放射线有协同抑制移植瘤生长的作用(Hep-2:EPO＝1.79;Hep-2R:EPO＝2.01)。结论 pshRNA-hTERT在细胞和动物实验水平均具有放射增敏作用,表明抑制端粒酶及其亚单位可以增加在体肿瘤的放射敏感性,这为喉癌的基因放疗研究提供了依据。     

lncRNA CCAT1靶向miR-130b-3p对人胰腺癌细胞PANC-1放射敏感性的影响

目的 探讨lncRNA CCAT1和miR-130b-3p对体外培养的胰腺癌细胞PANC-1放射敏感性的影响。方法 采用Real-time PCR检测胰腺癌组织及其细胞系和2 Gy X射线照射后PANC-1细胞中CCAT1和miR-130b-3p的相对表达水平。沉默CCAT1表达、抑制miR-130b-3p表达后,应用流式细胞仪、Caspase 3活性检测试剂盒及克隆形成实验检测细胞凋亡率、Caspase 3活性和细胞存活分数,并绘制单击多靶模型拟合曲线;利用starBase v2.0在线预测、荧光素酶报告基因、RNA结合蛋白免疫沉淀实验（RIP）及Real-time PCR实验,验证CCAT1和miR-130b-3p的靶向关系。结果 在放射抵抗的胰腺癌组织、胰腺癌细胞系和2 Gy照射的PANC-1细胞中,CCAT1表达均上调（t=6.322~8.555,P<0.05）,miR-130b-3p表达下调（t=3.950~18.795,P<0.05）。2 Gy照射并沉默CCAT1,PANC-1细胞存活分数降低（t=2.929、5.047、5.234、5.125,P<0.05）,细胞凋亡率增加（t=6.953,P<0.05）,Caspase 3活性升高（t=6.836,P<0.05）。发现CCAT1能靶向调控miR-130b-3p表达,抑制miR-130b-3p表达,PANC-1细胞存活分数增大（t=4.564、6.736、8.656,P<0.05）,细胞凋亡减少（t=5.234,P<0.05）,Caspase 3活性降低（t=10.440,P<0.05）。结论 沉默CCAT1表达能够促进miR-130b-3p表达,从而增加PANC-1细胞放射敏感性。     

尼妥珠单抗及西妥昔单抗增强照射对人食管癌细胞系的作用

目的 观察尼妥珠单抗（h-R3）、西妥昔单抗（C225）联合照射对人食管鳞癌细胞系TE-13的作用。方法 分为无药对照组、h-R3组、C225组、单纯照射组、h-R3联合照射组、C225联合照射组,采用MTS法观察处理组对食管癌细胞增殖的影响,并计算细胞增殖率;采用克隆形成实验检测h-R3、C225对食管癌细胞系放射敏感性的影响,多靶单击模型拟合细胞存活曲线;通过流式细胞仪分析细胞周期分布及细胞凋亡变化。结果 与单纯照射组相比,单抗联合照射组的细胞增殖率明显降低（F=325.59,P<0.05）,细胞凋亡率明显升高（F=120.59,P<0.05）, SF₂、D₀、D_q及N值均显著降低,G₀/G₁、G₂/M期细胞比例均增加,S期细胞比例减少。C225联合照射组的细胞凋亡率高于h-R3联合照射组（F=120.59,P<0.05）,C225联合照射组SER（1.83）高于h-R3联合照射组SER（1.46）。结论 h-R3与C225均能提高照射对食管鳞癌细胞系TE-13的抗肿瘤作用,C225的杀伤作用略优于h-R3。     

Biological outcomes of γ-radiation induced DNA damages in breast and lung cancer cells pretreated with free radical scavengers

Abstract

Purpose: Investigation of effects on DNA of γ-irradiated human cancer cells pretreated with free radical scavengers is aimed to create reference data which would enable assessment of the relative efficiency of high linear energy transfer (LET) radiations used in hadron therapy, i.e. protons and carbon ions.

Materials and methods: MCF-7 breast and HTB177 lung cancer cells are irradiated with γ-rays. To minimize indirect effects of irradiation, dimethyl sulfoxide (DMSO) or glycerol are applied as free radical scavengers. Biological response to irradiation is evaluated through clonogenic cell survival, immunocytochemical and cell cycle analysis, as well as expression of proteins involved in DNA damage response.

Results: Examined cell lines reveal similar level of radioresistance. Application of scavengers leads to the rise of cell survival and decreases the number of DNA double strand breaks in irradiated cells. Differences in cell cycle and protein expression between the two cell lines are probably caused by different DNA damage repair mechanisms that are activated.

Conclusion: The obtained results show that DMSO and glycerol have good scavenging capacity, and may be used to minimize DNA damage induced by free radicals. Therefore, they will be used as the reference for comparison with high LET irradiations, as well as good experimental data suitable for validation of numerical simulations.     

Anti-apoptotic effect of 3-aminobenzamide,an inhibitor of poly (ADP-ribose) polymerase,against multiple organ damage induced by gamma irradiation in rats

Purpose: This study aimed to investigate the effect of 3-aminobenzamide (3-AB) in doses of 5, 10 and 15?mg/kg on the inhibition of Poly (ADP-ribose) polymerase (PARP) when combined with ionizing radiation (IR).

Material and methods: Rats were treated intraperitonealy, one hour prior to irradiation at a dose level of 6 Gray (Gy) and were sacrificed 24?hours after irradiation. Control groups were run concurrently.

Results: IR led to an increase of thiobarbituric acid reactive substance (TBARS), nitrite as well as a decrease in total antioxidant capacity associated increase in myeloperoxidase (MPO) with the expression of cyclooxygenase-2 (COX-2). Moreover, IR caused an increase in serum lactate dehydrogenase (LDH) activity and cytosolyic Ca⁺² associated with an expression of Caspase-3 as well as a decline in complex-I activity and adenosine triphosphate (ATP) level. Pretreatment with 5 and 10?mg/kg of 3AB guarded against the changes in all the measured parameters, conversely the dose of 15?mg/kg showed no effect on the damage induced by irradiation in the selected tissues. Moreover, 3AB has a dose-dependent effect on viability of Vero cells.

Conclusion: The selected low doses of 3AB rather than the higher dose (15?mg/kg) protected against radiation-induced multiple organ damage.     

内质网应激通路抑制剂Salubrinal增强人头颈部鳞癌细胞的放射敏感性

目的 观察内质网应激通路抑制剂Salubrinal增强人头颈部鳞癌细胞放射敏感性的作用。方法 采用Western blot法检测人头颈部鳞癌细胞系（KB、Fadu、Detroit 562）射线照射后不同时间点（0、20 min、1 h、3 h、6 h、12 h、24 h和48 h）内质网应激通路核心蛋白-葡萄糖调节蛋白78（GRP78）的表达情况;对3种细胞系设立空白对照组和ERS通路抑制剂组（sal组）,同样方法检测GRP78的表达;集落克隆形成法检测3种细胞系不同剂量照射（0、2、4和6 Gy）对10 mmol/L Salburinal处理后不同时间（12、24、36 h）细胞存活分数的影响。结果 Western blot结果显示,照射后20 min~1 h,3种头颈部鳞癌细胞GRP78蛋白表达增加,照射后3 h达到高峰,与0 min组比较,差异有统计学意义（t=12.72、13.37、18.31,P<0.05）。采用Salubrinal处理细胞后,sal组与空白对照组比较,GRP78的表达下调,差异有统计学意义（t=14.25、5.34、3.12,P<0.05）。集落克隆形成实验结果提示,Salubrinal增强射线抑制细胞增殖,3种细胞加药12 h的放射增敏比分别为1.16、1.05和1.06。结论 内质网应激通路抑制剂Salubrinal增强人头颈部鳞癌细胞放射敏感性。     

辐射对恶性脑胶质瘤细胞放射敏感性的影响及其机制

目的 观察辐射对人脑恶性胶质瘤细胞株SHG-44辐射敏感性的影响,并探讨辐射抗性产生的机制.方法 使用胶质瘤细胞株SHG-44及经单次照射10 Gy后连续培养15代的辐射后细胞株SHG-4410 Gy,采用集落形成实验评估辐射对两种细胞株辐射敏感性的影响,流式细胞仪检测两种细胞株的辐射前后细胞周期时相分布及凋亡率,并用RT-PCR法检测cyclin B1 mRNA和miR-21的表达水平,Western blot法检测信号转导子和转录激活子3(Stat3)蛋白表达水平.结果 比较D0、SF2,SHG-44细胞(D0 =2.35、SF2=0.62),低于SHG-4410 Gy细胞(D0=3.22,SF2=0.74).与SHG-44细胞相比,SHG-4410 Gy细胞G2/M期比例减少,S期比例增多(F =22.21,P＜0.05).照射前后SHG-4410 Gy cyclinB1 mRNA相对量大于SHG-44细胞株(t=3.1、4.1,P＜0.05).照射前后的早期凋亡率分别为SHG-44 (17.60±0.26)％和(28.00±0.36)％,SHG-4410 Gy(4.20±0.30)％和(5.17±0.65)％,SHG-4410 Gy细胞与SHG-44细胞相比,早期凋亡率明显下降(t=58.0,P＜0.01).qRT-PCR及Western blot法检测SHG-4410 Gy细胞的miR-21表达及Stat3蛋白表达均较SHG-44升高.结论 照射后SHG-44细胞辐射抗性增加,可能与辐射上调细胞周期信号传导通路中的靶基因cyclinB1导致的G2/M期细胞比例减少有关;同时,辐射导致细胞miR-21表达增高,降低细胞的凋亡.     

Rescue of Marker Phenotypes: Effects of BUdR Sensitization,Hypoxia and High LET

Summary

The survival curve of colony-forming ability of Chinese hamster wg3h cells has been compared with the dose—response curve for the expression of an active thymidine kinase (TK) gene from these cells. The TK⁺ phenotype was measured by hybrid colony formation after fusion of wg3h (TK⁺) cells with Chinese hamster A23 (TK^?) cells. The TK⁺ survival data fitted a multi-target curve up to 3 krad of ¹³⁷Cs irradiation, when a highly resistant fraction of hybrid colonies was seen at about 1 per cent survival. The D₀ of TK⁺ survival for the multi-target region was 3·1–4·0 times greater than that of wg3h survival, even when the D₀ for cell survival varied between 136 and 545 rad by 14 MeV neutrons and hypoxia respectively. This parallel modification of cell and TK⁺ sensitivities suggests that the lesions causing cell inactivation are of the same type as those that cause marker inactivation. Using 14 MeV neutron data the approximate target size for TK inactivation was calculated to be 0·54–0·91 per cent of the DNA content of the cell (or about one-fifth to one-tenth of a chromosome). The data support the idea that marker inactivation results primarily from damage occurring outside the marker gene. BUdR labelling of wg3h cells before irradiation caused slight toxicity (30 per cent reduction in plating efficiency) and a twofold increase in cell sensitivity. However, the sensitivity of the TK⁺ phenotype increases by only 30 per cent. The increased cell sensitivity thus appeared to result from synergism between increased sensitivity of DNA to strand breakage and metabolic toxicity, the latter being largely overcome by fusion with normal cells.     

High levels of chromosome aberrations correlate with impaired in vitro radiation-induced apoptosis and DNA repair in human B-chronic lymphocytic leukaemia cells

PURPOSE: To investigate the relationship between the susceptibility of B-chronic lymphoid leukaemia (B-CLL) cells to DNA damage-induced apoptosis, the kinetics of DNA strand-break rejoining, and chromosome damage after exposure to ionizing irradiation. MATERIALS AND METHODS: Lymphocytes from B-CLL patients were gamma-irradiated in vitro with 0.2-5 Gy and stimulated by Staphylococcus aureus cowan I (SAC I) for estimation of chromosomal damage. Induction of apoptosis after irradiation was studied in 50 patients by two methods: morphological characterization of apoptotic cells after fluorescent staining (Hoechst), and specific quantification of mono- and oligonucleosomes in cytoplasmic cell fractions (ELISA assay). Morphological chromosome damage was scored in the first cell generation after irradiation (13 patients). In parallel, the kinetics of DNA single-strand break rejoining were investigated by the alkaline comet assay (12 patients). RESULTS: Ionizing irradiation did not induce apoptosis in lymphocytes from a subset of B-CLL patients. The results suggest that B-CLL cells resistant to radiation-induced apoptosis could repair DNA strand-breaks more rapidly and showed a higher level of chromosome aberrations than radiation-sensitive B-CLL cells. CONCLUSION: Each of three biological effects observed (apoptosis, kinetics of DNA single-strand-break repair, chromosomal damage) might be explained by different modifications occurring in irradiated B-CLL cells. Their convergence strongly suggests that resistance to apoptotic death initiation by DNA damage may be impeded by a rapid engaging of the DNA repair mechanisms. The higher level of chromosome aberrations observed in these cells suggests that the type of DNA repair system involved may generate inaccurate repair.     

Determination of the initial DNA damage and residual DNA damage remaining after 12 hours of repair in eleven cell lines at low doses of irradiation

Purpose : To determine the relationship between DNA damage and radiosensitivity at low doses (1-10Gy) for the initial DNA damage and residual DNA damage remaining after 12-h repair. Materials and methods : Eleven cell lines, normal human lung epithelial L132, HT29 human colon carcinoma, ATs4 human ataxia telangiectasia, normal CHO-K1 hamster, repair-deficient xrs1 and xrs5 mutants, repair-deficient SCID rodent cell line, the human normal fibroblast 1BR.3, human ataxia telangiectasia fibroblast AT1BR and the repair-deficient fibroblasts 180BR.B and 46BR.1 were irradiated with 60 Co γ-rays. Radiosensitivity was measured by clonogenic survival assay. DNA damage was measured by fluorometric analysis of DNA unwinding (FADU). Results : The radiosensitivity in the 11 cell lines ranged from SF2 of 0.02-0.61. By FADU assay, the undamaged DNA at 5-Gy ranged from 56 to 93%. The initial DNA damage and radiosensitivity were highly correlated (r 2 =0.81). After 5-Gy irradiation and 12-h repair, two groups of cell lines emerged. Group 1 restored undamaged DNA to a level ranging from 94 to 98%. Group 2 restored the undamaged DNA to a level ranging from 77 to 82%. No correlation was seen between residual DNA damage remaining after 12-h repair and radiosensitivity. Conclusion : It is shown that the initial DNA damage correlates with radiosensitivity at low doses of irradiation. This suggests that the initial DNA damage must be considered as a determinant for radiosensitivity.     

Determination of the initial DNA damage and residual DNA damage remaining after 12 hours of repair in eleven cell lines at low doses of irradiation

PURPOSE: To determine the relationship between DNA damage and radiosensitivity at low doses (1-10 Gy) for the initial DNA damage and residual DNA damage remaining after 12-h repair. MATERIALS AND METHODS: Eleven cell lines, normal human lung epithelial L132, HT29 human colon carcinoma, ATs4 human ataxia telangiectasia, normal CHO-K1 hamster, repair-deficient xrs1 and xrs5 mutants, repair-deficient SCID rodent cell line, the human normal fibroblast 1BR.3, human ataxia telangiectasia fibroblast AT1BR and the repair-deficient fibroblasts 180BR.B and 46BR.1 were irradiated with 60Co gamma-rays. Radiosensitivity was measured by clonogenic survival assay. DNA damage was measured by fluorometric analysis of DNA unwinding (FADU). RESULTS: The radiosensitivity in the 11 cell lines ranged from SF2 of 0.02-0.61. By FADU assay, the undamaged DNA at 5-Gy ranged from 56 to 93%. The initial DNA damage and radiosensitivity were highly correlated (r2 = 0.81). After 5-Gy irradiation and 12-h repair, two groups of cell lines emerged. Group 1 restored undamaged DNA to a level ranging from 94 to 98%. Group 2 restored the undamaged DNA to a level ranging from 77 to 82%. No correlation was seen between residual DNA damage remaining after 12-h repair and radiosensitivity. CONCLUSION: It is shown that the initial DNA damage correlates with radiosensitivity at low doses of irradiation. This suggests that the initial DNA damage must be considered as a determinant for radiosensitivity.