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The question of whether growth under low glucose conditions leads to a reduced amount of cell hypoxia was investigated using an in vitro tumour analogue, the sandwich system. In this multicellular system, the interplay between diffusion and consumption of oxygen and nutrients results in spatial gradients of these environmental factors. Gradients in the environment lead to biological heterogeneity within the cell population. A necrotic centre, surrounded by a viable cell border, subsequently develops. Cells adjacent to the necrotic centre in sandwiches are hypoxic and are in an environment somewhat analogous to that of cells adjacent to necrotic regions in solid tumours. Using sandwiches of the 9L and V79 cell lines, the effects of growth under low glucose conditions on the degree of hypoxia in regions adjacent to the necrotic centre were investigated. Per-cell binding of 3H-misonidazole, assessed by autoradiography, was used as an indicator of oxygen deprivation. It was found that the extent of the hypoxic region and the severity of hypoxia were considerably reduced by growing sandwiches in a glucose concentration of 0.6 mM rather than 6.5 mM. This reduction was found in conjunction with a smaller viable border; it occurred despite the fact that the average per-cell oxygen consumption is higher in the low glucose sandwiches. The data are qualitatively consistent with a joint oxygen-glucose deprivation model for cell necrosis.

Purpose: To analyse spectra of chromosome aberrations induced in vitro by low LET radiation, in order to characterize radiation damage mechanisms quantitatively. Methods: Multiplex fluorescence in situ hybridization (mFISH) allows the simultaneous identification of each homologous chromosome pair by its own colour. mFISH data, specifying number distributions for colour junctions in metaphases of human peripheral blood lymphocytes 72 hours after exposure in vitro to a 3 Gy γ-ray dose, were combined with similar, previously published results. Monte Carlo computer implementations of radiobiological models for chromosome aberration production guided quantitative analyses, which took into account distribution of cells among different metaphases and lethal effects or preferential elimination of some aberrations at cell division. Results and Conclusions: Standard models of DNA damage induction/repair/misrepair explain the main trends of the data as regards the fraction of metaphases having a particular number of colours involved in colour junctions. However, all standard models systematically under-predict the observed fraction of metaphases where a large number of different chromosomes participate in aberrations. An early appearance of chromosomal instability could explain most of the discrepancies. [ABSTRACT FROM AUTHOR]

Abstract. Purpose: Using published FISH data for chromosome aberration production in human fibroblasts by hard X-rays to test a breakage-and-reunion model. Methods : The model assumed pairwise misrejoining, random apart from proximity e ffects, of DNA double-strand break (DSB) free ends. CAS (chromosome aberration simulator) Monte Carlo computer software implementing the model was modified to use a distance algorithm for misrejoining instead of using DSB interaction sites. The modification (called CAS2) allowed a somewhat more realistic approach to large-scale chromatin geometry, chromosome territories and proximity effects. It required adding a third adjustable parameter, the chromosome territory intersection factor, quantifying the amount of intertwining among different chromosomes. Results: CAS2 gave somewhat better results than CAS. A reasonable fit with a few discrepancies was obtained for the frequencies at three different radiation doses of many different aberration types and of aberrations involving various specific chromosomes in a large data set using one-paint FISH scoring. The optimal average chromosome territory intersection factor was ~1.1, indicating that, for an arbitrarily chosen location in the nucleus, on average slightly more than two chromosomes have very nearby loci. Without changing the three parameter values, a fit was also obtained for a corresponding, smaller, two-paint data set. Conclusions: A random breakage-and-reunion model incorporating proximity effects by using a distance algorithm gave acceptable approximations for many details of hard X-ray aberration patterns. However, enough discrepancies were found that the possibility of an additional or alternate formation mechanism remains. [ABSTRACT FROM AUTHOR]

Purpose: Published low-LET FISH data were used to test two models of chromosome aberration production based on breakage-and-reunion or recombinational repair. Materials and methods: Randomness of DNA double strand break induction and misrejoining is analyzed comprehensively and adopted as a working hypothesis. Proximity effects are approximated by using interaction sites. Model results are calculated using CAS (chromosome aberration simulator) Monte Carlo computer software with two adjustable parameters. CAS can emulate the specifics of any experimental painting protocol, allowing very detailed tests of the models. Results: To reasonable approximation, breakage-and-reunion model predictions are consistent with low-LET FISH results, including two large, elaborate, one-paint data sets. An explicitly specified version of the recombinational-repair model severely underpredicts the frequency of the visibly complex aberration patterns most commonly observed with one-paint FISH, and is inconsistent with some observed multi-paint patterns. When high-dose effects (distortion and saturation) are taken into account quantitatively, a dose-response relation for apparently simple interchanges slightly favours the breakage-and-reunion model over the recombinational-repair model, despite being approximately linear over the dose range 2-6Gy. Conclusions: The random breakage-and-reunion model gives comprehensive baseline predictions that are sufficiently accurate for the organization of experimental results. The data speak against complex aberrations being formed by the random recombinational repair pathway discussed here. [ABSTRACT FROM AUTHOR]