Age-related changes in the radiosensitivity of animals and critical cell systems. Survival of stem cells of the small intestine epithelium 4-5 days after death in mice of various ages

Mice of three strains exhibited similar changes in radiosensitivity tested with a reference to "intestinal" death: juvenile and old animals were more radiosensitive. No age-related changes were detected in radiosensitivity of stem cells of the small intestine epithelium estimated with a reference to average lethal dose D0.     

Breast Cancer Stem Cell-Like Cells Are More Sensitive to Ionizing Radiation than Non-Stem Cells: Role of ATM

There are contradictory observations about the different radiosensitivities of cancer stem cells and cancer non-stem cells. To resolve these contradictory observations, we studied radiosensitivities by employing breast cancer stem cell (CSC)-like MDA-MB231 and MDA-MB453 cells as well as their corresponding non-stem cells. CSC-like cells proliferate without differentiating and have characteristics of tumor-initiating cells [1]. These cells were exposed to γ-rays (1.25–8.75 Gy) and survival curves were determined by colony formation. A final slope, D₀, of the survival curve for each cell line was determined to measure radiosensitivity. The D₀ of CSC-like and non-stem MDA-MB-453 cells were 1.16 Gy and 1.55 Gy, respectively. Similar results were observed in MDA-MB-231 cells (0.94 Gy vs. 1.56 Gy). After determination of radiosensitivity, we investigated intrinsic cellular determinants which influence radiosensitivity including cell cycle distribution, free-radical scavengers and DNA repair. We observed that even though cell cycle status and antioxidant content may contribute to differential radiosensitivity, differential DNA repair capacity may be a greater determinant of radiosensitivity. Unlike non-stem cells, CSC-like cells have little/no sublethal damage repair, a low intracellular level of ataxia telangiectasia mutated (ATM) and delay of γ-H2AX foci removal (DNA strand break repair). These results suggest that low DNA repair capacity is responsible for the high radiosensitivity of these CSC-like cells.     

Comprehensive profiling of radiosensitive human cell lines with DNA damage response assays identifies the neutral comet assay as a potential surrogate for clonogenic survival

In an effort to explore the possible causes of human radiosensitivity and identify more rapid assays for cellular radiosensitivity, we interrogated a set of assays that evaluate cellular functions involved in recognition and repair of DNA double-strand breaks: (1) neutral comet assay, (2) radiation-induced γ-H2AX focus formation, (3) the temporal kinetics of structural maintenance of chromosomes 1 phosphorylation, (4) intra-S-phase checkpoint integrity, and (5) mitochondrial respiration. We characterized a unique panel of 19 "radiosensitive" human lymphoblastoid cell lines from individuals with undiagnosed diseases suggestive of a DNA repair disorder. Radiosensitivity was defined by reduced cellular survival using a clonogenic survival assay. Each assay identified cell lines with defects in DNA damage response functions. The highest concordance rate observed, 89% (17/19), was between an abnormal neutral comet assay and reduced survival by the colony survival assay. Our data also suggested that the neutral comet assay would be a more rapid surrogate for analyzing DNA repair/processing disorders.     

The influence of chromatin structure on initial DNA damage and radiosensitivity in CHO-K1 and xrs1 cells at low doses of irradiation 1-10 Gy

Mitotic compaction of chromatin was generated by treatment of cells with nocodazole. Alternatively, chromatin structure was altered by incubating cells in 500 mM NaCl. The irradiation response in the dose range of 1-10 Gy was measured by colony assay and by a modified fluorometric analysis of DNA unwinding (FADU) assay which measures the amount of undamaged DNA by EtBr fluorescence. Cell survival curves of irradiated CHO-K1 cells showed that treatment with nocodazole increases radiosensitivity as indicated by a decrease of the mean inactivation dose (D) from 4.446 to 4.376. Nocodazole treatment increased the initial radiation-induced DNA damage detected by the FADU assay from 7% to 13%. In repair-defective xrs1 cells, the same conditions increased the radiosensitivity from 1.209 to 0.7836 and the initial DNA damage from 43% to 57%. Alterations to chromatin structure by hypertonic medium increased radiosensitivity in CHO-K1 cells from of 4.446 to 3.092 and the initial DNA damage from 7% to 15%. In xrs1 cells these conditions caused radiosensitivity to decrease from 1.209 to 1.609 and the initial DNA damage to decrease from 43% to 36%. Disruption of chromatin structure by hypertonic treatment was found to be time-dependent. A threefold increase of exposure time to hypertonic medium from 40 to 120 min increased the initial DNA damage in CHO-K1 cells from 7% to 18% but decreased initial DNA damage in xrs1 cells from 43% to 21%. Perturbation of chromatin structure with hypertonic treatment has been shown to increase the radiosensitivity and the initial DNA damage in repair-competent CHO-K1 cells and decrease the radiosensitivity and DNA damage in repair-defective xrs1 cells. Hypertonic treatment thus abolishes differences in chromatin structure between cell lines and differences in initial DNA damage. Radiosensitivity and initial DNA damage are correlated ( r(2)=0.92; p=0.0026) and this correlation also holds when chromatin compaction is altered. The experiments demonstrate that initial DNA damage and chromatin structure are major determinants of radiosensitivity.     

Genomic instability in both wild-type and telomerase null MEFs

To examine chromosome instability in the absence of telomerase, we established mouse embryonic fibroblast (MEF) lines from late generation mTR–/– and wild-type animals and examined metaphases using telomere fluorescence in situ hybridization (FISH) and spectral karyotyping (SKY). In early passages, mTR–/– G6 cell lines showed more chromosome ends with no telomere signal, more chromosome end-to-end fusions and greater radiosensitivity than wild-type lines. At later passages, however, the rate of genomic instability in the wild-type MEFs increased to a level similar or higher than seen in the mTR–/– G6 cell lines. This high degree of instability in wild-type MEF lines suggests that post-crisis MEFs should not be considered genetically defined cell lines. Surprisingly, the increased radiosensitivity seen in early passage mTR–/– G6 cultures was lost after crisis. Both post-crisis mTR–/– G6 MEFs and wild-type MEFs showed loss of p53 and -H2AX phosphorylation in response to irradiation, indicating a loss of DNA damage checkpoints.Electronic Supplementary Material Supplementary material is available for this article at .     

Role for DNA polymerase beta in response to ionizing radiation

Evidence for a role of DNA polymerase beta in determining radiosensitivity is conflicting. In vitro assays show an involvement of DNA polymerase beta in single strand break repair and base excision repair of oxidative damages, both products of ionizing radiation. Nevertheless the lack of DNA polymerase beta has been shown to have no effect on radiosensitivity. Here we show that mouse embryonic fibroblasts deficient in DNA polymerase beta are considerably more sensitive to ionizing radiation than wild-type cells, but only when confluent. The inhibitor methoxyamine renders abasic sites refractory to the dRP lyase activity of DNA polymerase beta. Methoxyamine did not significantly change radiosensitivity of wild-type fibroblasts in log phase. However, DNA polymerase beta deficient cells in log phase were radiosensitized by methoxyamine. Alkaline comet assays confirmed repair inhibition of ionizing radiation induced damage by methoxyamine in these cells, indicating both the existence of a polymerase beta-dependent long patch pathway and the involvement of another methoxyamine sensitive process, implying the participation of a second short patch polymerase(s) other than DNA polymerase beta. This is the first evidence of a role for DNA polymerase beta in radiosensitivity in vivo.     

Circadian and seasonal rhythms in the radiosensitivity of mongrel white rats

From experiments in albino mongrel rats it is shown that the radiosensitivity of gamma-irradiated (60Co) animals follows a daily rhythm. A synchronization of the daily rhythms in radiosensitivity was noted in winter and during the first spring month which was impaired in April. Established were the rhythms of radiosensitivity for three seasons, i. e. winter, spring and summer, with the extremes in the dependence upon mean annual values varying significantly.     

Image analysis of DNA content and nuclear morphometry for predicting radiosensitivity of nasopharyngeal carcinoma

OBJECTIVE: To investigate the relationship among nuclear DNA content, nuclear morphology, clinical response, and radiosensitivity in nasopharyngeal carcinoma (NPC) and the suitability of image cytometric analysis of DNA content and nuclear morphology for predicting radiosensitivity of NPC prior to radiotherapy. STUDY DESIGN: Nuclear DNA content and morphology features were detected by image cytometric analysis in 51 biopsy specimens of NPC prior to radiotherapy. The radiotherapeutic effect experienced by the NPC patients was classified as CR (complete response [i.e., complete tumor disappearance]) and PR (partial response [i.e., residual tumor]) according to pathologic analysis of tumor specimens after completion of the scheduled treatment. RESULTS: The mean DNA index; the percentage of cells with the DNA pattern of 2C, 5C, aneuploidy respectively; the mean nuclear area; the mean nuclear perimeter and the mean nuclear diameter in the CR group were significantly higher than they were in the PR group. CONCLUSION: DNA content and nuclear morphometry by image cytometric analysis were significantly correlated with patient outcome and radiosensitivity of NPC. Other measurements of more biomarkers for predicting the radiosensitivity of NPC await further study.     

The potential value of the neutral comet assay and the expression of genes associated with DNA damage in assessing the radiosensitivity of tumor cells

The assessment of tumor radiosensitivity would be particularly useful in optimizing the radiation dose during radiotherapy. Therefore, the degree of correlation between radiation-induced DNA damage, as measured by the alkaline and the neutral comet assays, and the clonogenic survival of different human tumor cells was studied. Further, tumor radiosensitivity was compared with the expression of genes associated with the cellular response to radiation damage. Five different human tumor cell lines were chosen and the radiosensitivity of these cells was established by clonogenic assay. Alkaline and neutral comet assays were performed in γ-irradiated cells (2-8Gy; either acute or fractionated). Quantitative PCR was performed to evaluate the expression of DNA damage response genes in control and irradiated cells. The relative radiosensitivity of the cell lines assessed by the extent of DNA damage (neutral comet assay) immediately after irradiation (4Gy or 6Gy) was in agreement with radiosensitivity pattern obtained by the clonogenic assay. The survival fraction of irradiated cells showed a better correlation with the magnitude of DNA damage measured by the neutral comet assay (r=-0.9; P<0.05; 6Gy) than evaluated by alkaline comet assay (r=-0.73; P<0.05; 6Gy). Further, a significant correlation between the clonogenic survival and DNA damage was observed in cells exposed to fractionated doses of radiation. Of 15 genes investigated in the gene expression study, HSP70, KU80 and RAD51 all showed significant positive correlations (r=0.9; P<0.05) with tumor radiosensitivity. Our study clearly demonstrated that the neutral comet assay was better than alkaline comet assay for assessment of radiosensitivities of tumor cells after acute or fractionated doses of irradiation.     

Biological effectiveness of ionizing radiations of various quality in Escherichia coli bacteria (a theoretical analysis). A cell inactivation model

The dependence of the radiosensitivity of bacteria (the wild type, superresistant and rec-mutants) on linear energy transfer (LET) is considered. A nonformal model of inactivation of different bacterial mutants has been developed on the basis of the experimental data available. The concept of "metastable siles" (MS) is introduced. MS are peculliar DNA lesions arising from the occurrence of large nucleolytic gaps on both strands of DNA. Different mechanisms responsible for MS formation are considered. The kinetic equations of the model are solved and the parameters determined for both sensitive and resistant mutants.     

Radiosensibilité individuelle et risque aux faibles doses médicales

Individual radiosensitivity to high doses of ionizing radiations has been known for a long time by radiation oncologists. It is responsible for the side effects and complications of radiation therapy in the absence of errors in dose delivery. Immunofluorescence techniques have lowered by a factor 100 the threshold of detection of DNA double-strand breaks, to the level of 1 mGy. The effects of a simple radiography, e.g. a mammography, can be measured. Thus the phenomenon of individual radiosensitivity at low-doses has been assessed in mammary epithelium cell cultures exposed in the conditions of mammography. The mechanisms of individual radiosensitivity are linked to abnormalities of DNA damage signalling and repair. This suggests a link between cancer proneness and radiosensitivity. Individual radiosensitivity has a prevalence of 5 to 15% in the population. Thus, it is a key phenomenon to take into account in public health and in future recommendations of the radioprotection system.     

Homology-directed repair is required for the development of radioresistance during S phase: interplay between double-strand break repair and checkpoint response

The S-phase-dependent radioresistance to killing uniformly seen in eukaryotic cells is absent in radiosensitive mutants with defects in genes involved in the repair of DNA double-strand breaks (DSBs) by homologous recombination (homologous recombination repair: HRR). This implicates, for the first time, a concrete DNA repair process in the radiosensitivity of a specific cell cycle phase. The cell cycle-dependent fluctuations in radiosensitivity reflect a fundamental and well-documented radiobiological phenomenon that still awaits a detailed molecular characterization. The underlying mechanisms are likely to combine aspects of DNA repair and cell cycle regulation. Advances in both fields allow a first dissection in the cell cycle of the molecular interplay between DSB repair and DNA damage checkpoint response and its contribution to cell survival. Here we review the available literature on the topic, speculate on the ramifications of this information for our understanding of cellular responses to DNA damage, and discuss future directions in research. An effort is made to integrate relevant phenomena of radiation action, such as low-dose radiosensitivity and the G(2) assay in this scheme.     

Non-homologous end-joining defect in fanconi anemia hematopoietic cells exposed to ionizing radiation

Fanconi anemia is a genetically heterogeneous recessive disease characterized mainly by bone marrow failure and cancer predisposition. Although it is accepted that Fanconi cells are highly sensitive to DNA crosslinking agents, their response to ionizing radiation is still unclear. Using pulsed-field gel electrophoresis, we have observed that radiation generates a similar number of DNA double-strand breaks in normal and Fanconi cells from three (FA-A, FA-C and FA-F) of the 11 complementation groups identified. Nonsynchronized as well as nonproliferating Fanconi anemia cells showed an evident defect in rejoining the double-strand breaks generated by ionizing radiation, indicating defective non-homologous end-joining repair. At the cellular level, no difference in the radiosensitivity of normal and FA-A lymphoblast cells was noted, and a modest increase in the radiosensitivity of Fanca-/- hematopoietic progenitor cells was observed compared to Fanca+/+ cells. Finally, when animals were exposed to a fractionated total-body irradiation of 5 Gy, a similar hematopoietic syndrome was observed in wild-type and Fanca-/- mice. Taken together, our observations suggest that Fanconi cells, in particular those having nonfunctional Fanconi proteins upstream of FANCD2, have a defect in the non-homologous end-joining repair of double-strand breaks produced by ionizing radiation, and that compensatory mechanisms of DNA repair and/or stem cell regeneration should limit the impact of this defect in irradiated organisms.     

Radiosensitivity of coding and noncoding DNA sequences of various organisms]

Relationship between pyrimidine distribution patterns and radiosensitivity (Z) of DNA molecules of different species was derived by computer analysis of recurrence frequency of pyrimidine clusters. Blocking factors (beta) and Z for coding and non-coding DNA sequences of species from different taxonomic classes have been calculated within a new model. The radiosensitivity of coding DNA sequences practically does not vary whereas Z values were increased during evolution from simplest to higher organisms. The beta and Z values calculated for several groups of individual genes were shown to vary considerably.     

Characteristics of the development of interphase death of hematopoietic tissue in dogs in response to gamma irradiation

In experiments with 2-3 week dogs it was shown that whole-body gamma-irradiation with a dose of 3 Gy causes an insignificant absolute rise in the amount of degrading chromatin of the haemopoietic organs during the first 24 h following irradiation. After 48 h, this cell death parameter is normalized. A considerably lower radiosensitivity of lymphoid cells of dogs compared to small laboratory animals is indicated by a stable DNA content per 1 g of thymus, intactness of its structure after irradiation, and the absence of an increase in thymidine content of blood of young and adult dogs under the effect of 3-3.7 Gy radiation.     

Mechanism of the radiation effect at the level of the supramolecular structures of eukaryotic DNA

The methods of viscosimetry and light scattering were used to study the radiosensitivity of the supramolecular DNA (SM DNA) structure in vivo. Irreversible lesions were found in SM DNA 2 min after gamma-irradiation of rats with a dose of 10 Gy. They were associated with the damage to the RNA-lipoprotein component (a linker) and with the dissociation of SM DNA to fragments of different molecular weight, that is, 109 +/- 25 X 10(6), 51 +/- 15 X 10(6), and 47 +/- 21 X 10(6) D for liver, spleen, and thymus, respectively, which correlated with the radiosensitivity of these organs.     

Effects of modifying topoisomerase II levels on cellular recovery from radiation damage

Effects of Modifying Topoisomerase II Levels on Cellular Recovery from Radiation Damage. Experiments were performed with the budding yeast, Saccharomyces cerevisiae, to test whether DNA topoisomerase II is involved in repair of DNA damage induced by ionizing radiation. Topoisomerase II was inactivated by use of a temperature-sensitive mutation. Enzyme inactivation increased cellular radiosensitivity, blocked the restitution of broken chromosomes, assayed by pulsed-field gel electrophoresis, and prolonged the induction of a DNA damage-inducible gene (RNR3). Overexpression of the topoisomerase II gene did not alter cellular radiosensitivity. The data support a role for topoisomerase II in the repair of DNA strand breaks.     

Enhancement of radiation-induced cell killing and DNA double-strand breaks in a human tumor cell line using nanomolar concentrations of aclacinomycin A.

Several agents that induce differentiation have previously been shown to induce the terminal differentiation of leukemic cells and enhance the radiosensitivity of certain solid tumor cell lines in vitro using millimolar concentrations. We now report that aclacinomycin A (ACM), a potent inducer of leukemic cell differentiation in vitro, can significantly enhance the radiosensitivity of a human colon tumor cell line (Clone A) at a concentration of 10 nM. Based on colony-forming efficiency, the maximum increase in radiosensitivity was found using 15 nM ACM for 3 days with a dose enhancement factor of 1.4 at a surviving fraction of 0.10. This treatment increased cell doubling time, but had no effect on cell-cycle phase distribution. To gain insight into the mechanisms responsible for this radiosensitization, gamma-ray-induced DNA single- and double-strand breaks were examined. Aclacinomycin A had no effect on the induction of DNA single-strand breaks but significantly enhanced the formation of gamma-ray-induced DNA double-strand breaks. The rate or extent of repair of the induced double-strand breaks was not influenced by ACM treatment. These data suggest that ACM, at achievable plasma concentrations, can enhance the radiosensitivity of a human tumor cell line by increasing the initial level of radiation-induced DNA double-strand breaks.     

Statistical analysis of kinetics,distribution and co-localisation of DNA repair foci in irradiated cells: Cell cycle effect and implications for prediction of radiosensitivity

Detection of γ-H2AX foci as a measure of DNA double strand break induction and repair provides the basis of a rapid approach to establish individual radiosensitivity. However, the assignment of criteria to define increased radiosensitivity is not straightforward. Experimental end points, analytical methods and proliferative status of the cells sampled for analysis are important. All these issues are addressed in the present study, which was prompted by a clinical request to assess the radiosensitivity status of an SCID paediatric patient being considered for bone marrow transplantation.     

Inherited sensitivity to X-rays in man

Ataxia-telangiectasia (A-T), an inherited disorder giving radiation sensitivity and cancer-proneness, is discussed in terms of a defect in ability to repair DNA damage. A new assay using damaged recombinant DNA molecules suggests that the fidelity of repair of DNA double-strand breaks is reduced in an A-T cell line. Specific chromosomal changes in some A-T patients appear to be associated with cancer induction, and it is suggested that these could be linked to a DNA repair-fidelity defect. However, a general correlation between radiosensitivity and cancer-proneness is difficult to establish at present, partly because of diversity in radiosensitivity in the normal population.