Micronucleus formation in human tumour cells: lack of correlation with radiosensitivity.

The micronucleus (MN) test has been carefully characterized in four human tumour cell lines of widely differing radiosensitivity. Two radioresistant bladder carcinoma cell lines (MGH-U1 and RT112), one sensitive medulloblastoma cell line (D283MED) and a sensitive neuroblastoma cell line (HX142) were used. The number of MN per Gy of ionising radiation was 0.13 for HX142, 0.17 for D283MED, 0.21 for RT112 and 0.26 for MGH-U1. This does not rank the cell lines in the same order of radiosensitivity as clonogenic cell survival where the surviving fraction at 2 Gy (SF2) was 0.11 for HX142, 0.2 for D283MED, 0.62 for RT112 and 0.53 for MGH-U1. This discrepancy between MN formation and cell death leaves doubt as to the potential usefulness of the MN test as a rapid assay of radiosensitivity but it has potential implications for the mechanistic basis of radiosensitivity in these cells.     

Fibroblast radiosensitivity measured using the comet DNA-damage assay correlates with clonogenic survival parameters

A study was made of the neutral comet assay as a potential method for measuring normal cell radiosensitivity. Eleven fibroblast strains were studied comprising nine derived from vaginal biopsies from pretreatment cervical cancer patients and two strains from radiosensitive individuals. DNA double strand break (dsbs) dose-response curves for both initial and residual (20-h repair time) damage were obtained over the dose range 0-240 Gy, with slopes varying 3.2 and 8-fold respectively. Clonogenic cell survival parameters were available for all the cell strains following both high- and low-dose rate irradiation. There were no correlations between the dose-response slope of the initial level of DNA dsbs and parameters that mainly describe the initial portion of clonogenic radiation survival curves (SF2, alpha, D). A significant correlation (r = -0.63, P = 0.04) was found between the extent of residual DNA dsbs and clonogenicity for all 11 fibroblast strains. The parameter showing the highest correlation with fibroblast cell killing (D) for the nine normal fibroblasts alone was the ratio of initial/residual DNA dsb dose-response slope (r = 0.80, P = < 0.01). A significant correlation (r = -0.67, P = 0.03) with clonogenic radiosensitivity was also found for all 11 cell strains when using the ratio of initial/residual DNA dsb damage at a single dose of 180 Gy. This study shows that fibroblast radiosensitivity measured using the neutral comet assay correlates with clonogenic radiation survival parameters, and therefore may have potential value in predictive testing of normal tissue radiosensitivity.     

The increment of micronucleus frequency in cervical carcinoma during irradiation in vivo and its prognostic value for tumour radiocurability.

A potential usefulness of micronucleus assay for prediction of tumour radiosensitivity has been tested in 64 patients with advanced stage (II B-IV B) cervical carcinoma treated by radiotherapy. The study of cellular radiosensitivity in vitro was conducted in parallel with the study of cellular damage after tumour irradiation in vivo. Radiosensitivity of in vitro cultured primary cells isolated from tumour biopsies taken before radiotherapy was evaluated using cytokinesis-block micronucleus assay. Frequency of micronuclei per binucleated cell (MN/BNC) at 2 Gy was used as a measure of radiosensitivity. Radiation sensitivity in vivo was expressed as per cent increment of micronucleus frequency in cells isolated from biopsy taken after 20 Gy (external irradiation, 10 x 2 Gy) over the pre-treatment spontaneous micronucleus level and was called MN20. Very low correlation (r = 0.324) was observed between micronucleus frequency in vitro and in vivo. Although micronucleus frequency at 2 Gy differed widely between tumours evaluated (mean MN/BNC was 0.224; range 0.08-0.416), no significant correlation was observed between this parameter and clinical outcome. The average increment of micronucleus frequency after 20 Gy amounted to 193% of spontaneous level (range 60-610%) and was independent of spontaneous micronucleation before radiotherapy. In contrast to in vitro results, these from in vivo assay seem to have a predictive value for radiotherapy of cervix cancer. The micronucleus increment in vivo that reached at least 117.5% of pretreatment value (first quartile for MN20 data set) correlated significantly with better tumour local control (P < 0.008) and overall survival (P < 0.045). Our results suggest that evaluation of increment of micronucleus frequency during radiotherapy (after fixed tested dose of 20 Gy) offers a potentially valuable approach to predicting individual radioresponsiveness and may be helpful for individualization of treatment strategy in advanced stage cervical cancer.     

Deficiency in the repair of UV-induced DNA damage in human skin fibroblasts compromised for the ATM gene

Ataxia-telangiectasia (A-T), is an autosomal recessive disease characterized by neurological and immunological symptoms, radiosensitivity and cancer predisposition. A-T cells exhibit a greatly decreased survival and a reduction in DNA synthesis inhibition as well as p53 induction in response to ionizing radiation. Occasionally, some strains of A-T cells have been reported to manifest a slightly enhanced sensitivity with no consistent observations of a deficiency in either cell cycle control or the repair of DNA damage after treatment with ultraviolet (UV) light. In the present study it is shown that skin fibroblasts from four A-T patients, compared with the control, display enhanced sensitivity to the killing effect of UV-light, moderate radioresistant DNA synthesis, and a reduction in viral recovery in the host cell reactivation (HCR) assay. PCR based analysis indicated that three of these UV-sensitive A-T cell strains bear a large deletion in the ATM gene, and no ATM polypeptide was detected in their cell free extracts. Moreover, it is shown that, in non-replicative conditions, these A-T cells are less efficient than normal cells in repairing the T4 endonuclease V sensitive sites. These results constitute the first clear evidence showing the deficiency of A-T cells in the repair of UV-induced DNA damage, and provide further information on the relationship between cell cycle control and DNA repair in human cells.     

Prediction of radiosensitivity by micronucleus assay

The correlation between cell survival curve and dose response curve of MN frequency following irradiations was studied using cytokinesis-block method. Both dose response curves were analyzed by linear quadratic model, i.e. SF = exp (- alpha D - beta D2) and MN frequency = aD + bD2 + c. A good correlation between alpha/beta and a/b ratios was observed in repeated paired experiments (gamma = 0.97). When the cells were treated with BUdR, alpha-type radiosensitizer, a value in dose response curve of MN frequency increased but b value did not. In 10 renal cell carcinomas, the linear correlations between cell surviving fractions and MN frequencies were observed. When radioresponses of 5 esophageal cancer cell lines were evaluated with MN assay, wide range of a/b ratios was found. These data present that MN frequency assay using CB method is available as a tool of rapid assay of radiosensitivity of cells.     

Lack of a correlation between micronucleus formation and radiosensitivity in established and primary cultures of human tumours.

The radiation-induced genotoxic damage in three established cell lines and 15 primary cultures of human malignant melanoma and ovarian carcinoma showing different radiosensitivity was tested by the cytokinesis-block micronucleus assay. A dose-related increase in micronucleus frequency was observed in all the cell systems. The mean number of micronuclei per Gy of ionising radiation per binucleated cell was respectively 0.44 +/- 0.0075 and 0.43 +/- 0.04 for M14 and JR8 malignant melanoma cell lines and 0.19 +/- 0.013 for the A2780 ovarian cancer cell line. The number of micronuclei did not rank the cell lines in the same order of radiosensitivity as clonogenic cell survival, which showed a surviving fraction at 2 Gy of 0.38 +/- 0.02 for JR8, 0.34 +/- 0.05 for M14 and 0.22 +/- 0.007 for A2780. As regards primary tumour cultures, no correlation was observed between micronucleus induction and surviving fraction at 2 Gy. In conclusion, the discrepancy we observed between micronucleus formation and cell death raises doubts about the potential of the micronucleus assay as a preclinical means to predict radiosensitivity.     

In vitro radiosensitivity of skin fibroblasts can identify a group of patients with complications in various health tissues after radiotherapy]

PURPOSE: A retrospective study of the in vitro radiosensitivity of skin fibroblasts derived from two groups of patients treated by definitive radiotherapy for a variety of tumors who either displayed or did not display severe complications. PATIENTS AND METHODS: Seven radiotherapy patients were selected: three were treated for head and neck, prostate and non-Hodgkin lymphoma tumors, and did not develop any significant complications (control group); four patients were treated for bladder, thyroid, head and neck and anal canal tumors and developed serious acute and especially late reactions (hypersensitive group). Primary cell cultures of skin fibroblasts were established and their radiosensitivity studied by the clonogenic assay after exposing to single radiation doses ranging between 1 and 8 Gy. RESULTS: The survival fraction at 2 Gy (SF2) ranged from 0.27 to 0.38, with a mean of 0.33 for the control group, and from 0.10 to 0.20 with a mean of 0.17 for the hypersensitive group. The Mann-Whitney non-parametric test showed that the difference between the two means was statistically significant (p = 0.03). CONCLUSION: The data are in favor of a correlation between the radiosensitivity of patients' fibroblasts and the reactions of different normal tissues to radiotherapy. This association supports the use of the clonogenic survival, or a surrogate test, as a predictive assay. The multiplicity of normal tissues and organs implicated in this association suggests the existence of genetic factors that determine, at least in part, the radiosensitivity of target cells involved in the expression of normal tissues complications following radiotherapy.     

Potential use of the alkaline comet assay as a predictor of bladder tumour response to radiation

Bladder tumours show a variable response to radiotherapy with only about 50% showing good local control; currently there is no test to predict outcome prior to treatment. We have used five bladder tumour cell lines (T24, UM-UC-3, TCC-SUP, RT112, HT1376) to investigate the potential of the alkaline comet assay (ACA) to predict radiosensitivity. Radiation-induced DNA damage and repair were compared to clonogenic survival. When the five cell lines were irradiated and initial DNA damage was plotted against cell survival, at all doses (0-6 Gy), a significant correlation was found (r2=0.9514). Following 4 Gy X-irradiation, all cell lines, except T24, showed a correlation between SF2 vs half-time for repair and SF2 vs residual damage at 5, 10, 20 and 30 min. The T24 cell line showed radioresistance at low doses (0-2 Gy) and radiosensitivity at higher doses (4-6 Gy) using both cell survival and ACA end points, explaining the lack of correlation observed for this cell line. These data indicate that initial DNA damage and residual damage can be used to predict for radiosensitivity. Our data suggest that predictive tests of radiosensitivity, appropriate to the clinical situation, may require the use of test doses in the clinical range.     

人喉鳞癌细胞端粒长度与放射敏感性的关系探讨

 目的 探讨人喉鳞癌细胞端粒长度与放射敏感性的关系,以寻求能够预测肿瘤细胞内在放射敏感性的分子标志物. 方法 体外长期传代的人喉鳞癌细胞系Hep-2经0、2、4、8、12Gy剂量照射3次后的存活后代体外培养20代,以克隆形成实验测定其放射敏感性参数SF2,用Southern-blotting法测定其端粒长度(TRF). 结果 体外长期传代的Hep-2细胞系随着受照剂量的增加, 其放射存活后代的SF2逐渐升高(P<0.05),其TRF逐渐缩短(P<0.01);而且,SF2与TRF呈现明显的正相关关系(r=0.921, P<0.01). 结论 通过不同放射剂量处理体外长期传代的人喉鳞癌细胞系可获得不同放射敏感性的细胞存活后代,且放射存活后代的放射敏感性与其细胞端粒长度具有较好的负相关关系,提示端粒长度检测有望成为预测肿瘤细胞内在放射敏感性的分子标志物.     

Fractionated irradiation of five human lung cancer cell lines and prediction of survival according to a radiobiology model

BACKGROUND: This study evaluates a predictive radiobiology model by measurements of surviving fraction (SF) by the clonogenic assay or the extrapolation method and the proliferation rate in vitro. It is hypothesized that incorporating proliferation to intrinsic radiosensitivity, measured by SF, to predict radiation responsiveness after fractionated irradiation adds to the model's accuracy. Materials and Methods. Five lung cancer cell lines with known SF after 1 Gy (SF1), and also SF2 and SF5, were irradiated with three different fractionation regimes; 10 × 1 Gy, 5 × 2 Gy or 2 × 5 Gy during the same total time to achieve empirical SF. In addition, the SF1, SF2 and SF5 after fractionated irradiation was calculated for each cell line based on the already known single fraction SF and with or without a proliferation factor. The results were compared to the empirical data. Results and Discussion: By using the clonogenic assay to measure radiosensitivity, prediction of radiosensitivity was improved after fractionated radiotherapy when proliferation was used in the radiobiology model. However, this was not the case in the cell lines where the extrapolation method was used to calculate SF. Thus, a radiobiology model including intrinsic radiosensitivity, measured by the clonogenic assay, as well as proliferation, is better at predicting survival after fractionated radiotherapy, compared to the use of intrinsic radiosensitivity alone.     

Inhibition of heme oxygenase-1 enhances the radiosensitivity in human nonsmall cell lung cancer a549 cells

Abstract undergoing radiotherapy or chemotherapy failed to respond. The aim of this study was to evaluate whether Inhibitor of HO-1, zinc protoporphyrin IX (Znpp), enhances the radiosensitivity in human nonsmall cell lung cancer (NSCLC) A549 Cells. A549 cells were induced by Znpp and irradiated by X-rays. Then, expression of HO-1 was measured by real-time polymerase chain reaction. Cell survival was evaluated using the MTS assay and the clonogenic survival assay; apoptosis and cell cycle distribution were monitored by flow cytometry. First, overexpression of the HO-1 mRNA was found in treatment with irradiation alone in A549 cells, and expression of the HO-1 mRNA was reduced after combined treatments with 12?μmol/L of Znpp and irradiation. Second, diminished cell viability percentage, decreased cell clonogenic survival fraction, enhanced cell apoptotic index, and increased percentage of cells in the G1 phase were found after combined treatments with 12?μmol/L of Znpp and irradiation compared to either treatment alone (p<0.05). Inhibitor of HO-1, Znpp, can increase the radiosensitivity of human NSCLC A549 cells.     

Rapid fluorescence-based assay for radiosensitivity and chemosensitivity testing in mammalian cells in vitro

An efficient and rapid cytotoxicity assay has been developed, particularly for radiobiological studies, utilizing 96-well microtiter plates. Several days after treatment, cell numbers per well were measured by fluorescent intensity using an automatic reader after staining with the DNA specific dye Hoechst 33258. For radiobiological applications, a microtiter plate irradiation box was designed and built which allowed a variable number of wells (minimum 4, maximum 16) to be irradiated at one time. In this manner, complete dose-response curves could be obtained from one plate. The assay depends on the growth of surviving and untreated cells, and by appropriate choice of conditions (cell numbers plated, time of assay), cell survival curves for this quick fluorescence assay were in reasonable agreement with those from a clonogenic assay for cisplatin and X-ray-induced cell killing. The assay can span 1.5-2 decades of cell survival and is suitable for any cell line which grows as a monolayer. Radiobiological applications were tested using agents or conditions which modified radiation damage. Firstly, sublethal damage repair could be demonstrated in RIF1 mouse tumor cells by comparing the survival curve for a single X-ray dose with that for two fractions separated by 4 h. Secondly, incorporation of 5-iodo-2'-deoxyuridine into cellular DNA was shown to radiosensitize Chinese Hamster cells, with similar enhancement ratios obtained from the fluorescence and clonogenic assays. Thirdly, radiosensitization by cisplatin and radioprotection by cysteamine could be readily measured using the quick fluorescence assay. The ability to have multiple dose groups per plate makes it an efficient assay for both radiosensitivity and chemosensitivity testing.     

Relationship between clonogenic radiosensitivity, radiation-induced apoptosis and DNA damage/repair in human colon cancer cells

The intrinsic radiation sensitivity of normal and tumour tissue is a major determinant of the outcome of radiotherapy. There is currently no established test that can be used routinely to measure the radiosensitivity of the cells in an individual patient's cancer in a manner that can inform treatment planning. The purpose of this study was to evaluate, in four human colorectal adenocarcinoma cell lines, two possible end points as surrogate markers of radiation response--apoptosis and induction of DNA single-strand breaks--and to compare the results with those of a conventional clonogenic assay. Cell lines (SW707 SW480, SW48 and HT29) known to differ in radiosensitivity were exposed to single doses of X-rays ranging from 0.5 to 5 Gy and cell survival was measured using the clonogenic assay. Apoptosis was determined on the basis of morphology under fluorescent microscopy and DNA damage/repair was measured, as tail moment, using an adaptation of the alkaline comet assay. The relationship between surviving fraction at 2 Gy (SF2) and the percentage of apoptotic cells 24 h after the same dose was complex, but apoptosis accurately predicted the order of radiosensitivities as measured by SF2. Initial damage measured after 2 Gy using the alkaline comet assay gave a close correlation with SF2 (r2=0.95), whereas there was no correlation between initial DNA damage repair rate and SF2.     

Does skin fibroblast radiosensitivity predict squamous cancer cell radiosensitivity of the same individual?

Individualization of radiation doses is presumed to result in better radiotherapy outcome. Success rate in measuring radiosensitivity is probably the most limiting factor for present radiosensitivity assays to be introduced into clinical routine. To find a simpler predictive parameter, we compared the radiosensitivity of dermal fibroblasts and head and neck squamous cell carcinoma (SCC) cell lines established from the same individuals. The radiosensitivity was tested using the clonogenic 96-well plate assay. The surviving fraction at 2.0 Gy (SF2) was determined, as well as the mean inactivation dose (AUC) of cancer cells. SF2 of SCC cell lines and skin fibroblasts were 0.25-0.44 and 0.11-0.43, respectively. AUC of SCC cells was 1.4-2.1 Gy. Dermal fibroblasts were more radiosensitive than SCC cells in 14 of 15 cases. In 1 patient (UT-SCC-8), cancer cells were found to be more radiosensitive than corresponding dermal fibroblasts. There was a clear tendency to a correlation between radiosensitivities of these 2 cell types, but statistical significance was reached only when the data of UT-SCC-8 was excluded. In our material, the intrinsic radiosensitivity of head and neck SCC cells could in most cases be predicted from the intrinsic radiosensitivity of dermal fibroblasts established from the same individual.     

Enhancement of glioblastoma radioresponse by a selective COX-2 inhibitor celecoxib: inhibition of tumor angiogenesis with extensive tumor necrosis

PURPOSE: Toward improved glioblastoma multiforme treatment, we determined whether celecoxib, a selective cyclooxygenase (COX)-2 inhibitor, could enhance glioblastoma radiosensitivity by inducing tumor necrosis and inhibiting tumor angiogenesis. METHODS AND MATERIALS: U-87MG cells treated with celecoxib, irradiation, or both were assayed for clonogenic survival and angiogenic factor protein analysis (angiopoietin-1, angiopoietin-2, and vascular endothelial growth factor [VEGF]). In vivo, survival of mice intracranially implanted with U-87MG cells and treated with celecoxib and/or irradiation was monitored. Isolated tumors were assessed for tumor necrosis and tumor microvascular density by von Williebrand's factor (vWF) immunohistochemical staining. RESULTS: Celecoxib (4 and 30 microM; 24, 48, and 72 h) enhanced U-87MG cell radiosensitivity by significantly reducing clonogenic survival of irradiated cells. Angiopoietin-1 and VEGF proteins were decreased, whereas angiopoietin-2 expression increased after 72 h of celecoxib alone and when combined with irradiation. In vivo, median survival of control mice intracranially implanted with U-87MG cells was 18 days. Celecoxib (100 mg/kg/day, 2 weeks) significantly extended median survival of irradiated mice (24 Gy total) from 34 to 41 days, with extensive tumor necrosis [24.5 +/- 8.6% of tumor region, compared with irradiation alone (2.7 +/- 1.8%)]. Tumor microvascular density was significantly reduced in combined celecoxib and irradiated tumors (52.5 +/- 2.9 microvessels per mm2 tumor region), compared with irradiated tumors alone (65.4 +/- 4.0 microvessels per mm2). CONCLUSION: Celecoxib significantly enhanced glioblastoma radiosensitivity, reduced clonogenic survival, and prolonged survival of glioblastoma-implanted mice by inhibition of tumor angiogenesis with extensive tumor necrosis.     

The effect of patient-to-patient variability on the accuracy of predictive assays of tumor response to radiotherapy: a theoretical evaluation

Mathematical modeling was used to investigate the relative accuracy that might be expected from predictive assays of tumor response to radiotherapy based on one of the following four tumor characteristics: intrinsic tumor-cell radiosensitivity, doubling time of the clonogenic tumor cells, number of clonogens in the tumor at the start of treatment, and extent of hypoxia in the tumor. In particular, the influence of inter-tumor heterogeneity on predictive accuracy was investigated. Wide patient-to-patient variability in a tumor characteristic contributing to treatment response adds to the accuracy of a predictive assay based on that characteristic, but variability from patient to patient in factors influencing response, but not measured by the assay, has a confounding effect and reduces predictive accuracy. The results of this theoretical study suggest that predictive assays based on intrinsic tumor-cell radiosensitivity are much more likely to be correlated with clinical outcome than are assays based on clonogen doubling time, hypoxic fraction, or clonogen number, since individual differences in tumor radiosensitivity can seriously confound assays based on the other factors. It is concluded that it may be necessary to correct for individual differences in intrinsic radiosensitivity before predictive assays based on other tumor characteristics, such as potential doubling time, might have any detectable clinical significance.     

DNA damage-related RNA expression to assess individual sensitivity to ionizing radiation

Predictive markers of intrinsic radiosensitivity in healthy individuals are needed in monitoring their occupational or environmental radiation exposure and may predict a patient's response to radiotherapy. Ionizing radiation can induce a large spectrum of DNA lesions, but under optimal DNA repair conditions, the principal residual lesions of importance are misrepaired double-strand breaks. The micronucleus (MN) assay represents a useful test in measuring radiosensitivity since it reflects non-repaired DNA breaks at the time of cell division. Spontaneous and radiation-induced MN vary greatly between individuals, and little is known about the molecular mechanisms of this variability. DNA repair and apoptosis processes are involved in the cellular response to radiation-induced DNA damage, and variation in gene expression related to these cellular pathways could be linked to individual radiosensitivity. In this study we analysed by real-time quantitative RT-PCR the basal expression of 12 genes involved both in DNA repair and apoptosis in a series of blood samples obtained from 32 healthy male donors. Relationships between basal RNA expressions and MN frequency and distribution per bi-nucleated cell were studied after ex vivo irradiation of total blood samples. Our results indicate that the variability of mRNA gene expression among the 32 subjects appears to be of the same magnitude or higher than that found for spontaneous or radiation-induced MN frequency and that RAD51 gene expression is negatively correlated with radiation-induced MN frequency.     

Studies of the in vivo radiosensitivity of human skin fibroblasts.

BACKGROUND AND PURPOSE: To examine the radiosensitivity of skin cells obtained directly from the irradiated skin of patients undergoing fractionated radiation treatment prior to surgery for treatment of soft tissue sarcoma (STS) and to determine if there was a relationship with the development of wound healing complications associated with the surgery post-radiotherapy. METHODS: Micronucleus (MN) formation was measured in cells (primarily dermal fibroblasts) obtained from human skin at their first division after being removed from STS patients during post-radiotherapy surgery (2-9 weeks after the end of the radiotherapy). At the time of radiotherapy (planned tumor dose - 50Gy in 25 daily fractions) measurements were made of surface skin dose at predetermined marked sites. Skin from these sites was obtained at surgery and cell suspensions were prepared directly for the cytokinesis-blocked MN assay. Cultured strains of the fibroblasts were also established from skin nominally outside the edge of the radiation beam and DNA damage (MN formation) was examined following irradiation in vitro for comparison with the results from the in situ irradiations. RESULTS: Extensive DNA damage (MN) was detectable in fibroblasts from human skin at extended periods after irradiation (2-9 weeks after the end of the 5-week fractionated radiotherapy). Analysis of skin receiving a range of doses demonstrated that the level of damage observed was dose dependent. There was no clear correlation between the level of damage observed after irradiation in situ and irradiation of cell strains in culture. Similarly, there was no correlation between the extent of MN formation following in situ irradiation and the propensity for the patient to develop wound healing complications post-surgery. CONCLUSIONS: Despite the presence of DNA damage in dermal fibroblasts weeks after the end of the radiation treatment, there was no relationship between this damage and wound healing complications following surgery post-irradiation. These results suggest that factors other than the radiosensitivity of the skin fibroblasts likely also play a role in wound healing in deep wound sites associated with surgery for STS following radiation therapy.     

Radiation induced DNA damage and damage repair in human tumor and fibroblast cell lines assessed by histone H2AX phosphorylation

PURPOSE: To analyze the radiation-induced levels of gammaH2AX and its decay kinetics in 10 human cell lines covering a wide range of cellular radiosensitivity (SF2, 0.06-0.63). METHODS AND MATERIALS: Five tumor cell lines included Colo-800 melanoma, two glioblastoma (MO59J and MO59K), fibrosarcoma HT 1080, and breast carcinoma MCF7. Five primary skin fibroblasts lines included two normal strains, an ataxia telangiectasia strain, and two fibroblast strains from breast cancer patients with an adverse early skin reaction to radiotherapy. Cellular radiosensitivity was assessed by colony-forming test. Deoxyribonucleic acid damage and repair were analyzed according to nuclear gammaH2AX foci intensity, with digital image analysis. RESULTS: The cell lines tested showed a wide degree of variation in the background intensity of immunostained nuclear histone gammaH2AX, which was higher for the tumor cell lines compared with the fibroblast strains. It was not possible to predict clonogenic cell survival (SF2) for the 10 cell lines studied from the radiation-induced gammaH2AX intensity. In addition, the slopes of the dose-response (0-4 Gy) curves, the rates of gammaH2AX disappearance, and its residual expression (相似文献