Correlation between cell reproductive death and chromosome aberrations assessed by FISH for low and high doses of radiation and sensitization by iodo-deoxyuridine in human SW-1573 cells

PURPOSE: To study the relationship between cell reproductive death and exchange frequency in SW-1573 human lung tumour cells with and without incorporated iodo-deoxyuridine (IdUrd) following irradiation of plateau-phase cultures with y-rays. METHOD: Linear-quadratic (LQ) analysis was performed for the data on clonogenic survival and on the frequency of chromosomal exchanges studied with fluorescence in situ hybridization in chromosomes X and 2. RESULTS: Differences in the LQ parameters alpha and beta of both non-sensitized and sensitized chromosomes were found. In both chromosomes an increase in the number of chromosomal exchanges in IdUrd-radiosensitized cells compared with non-sensitized cells was observed. The alpha-enhancement factors of 1.7 and 1.9 for the X-chromosome and for chromosome 2, respectively, are similar. For the X-chromosome, the beta coefficient increased by a factor of 3.9 and for chromosome 2 by a factor of 1.4. After correction to a full genome equivalence, no significant difference in alpha was found between chromosomes X and 2 for both control and sensitized cells. In contrast, an almost 2.8 times higher beta was found for the sensitized X-chromosome compared to this value for chromosome 2. CONCLUSIONS: It can be concluded that the linear-quadratic analysis of dose-response relationships offers insights into the correlation between cell survival and induction of exchanges in non-sensitized and radiosensitized cell

A method for the selective irradiation of part of a genome

We developed a method for partial irradiation of cell nuclei and for highlighting the irradiated chromatin domain(s) in both interphase nuclei and metaphase chromosomes. The method involves the use of the replication program of chromosomes and consists of three major steps: I) selection of a suitable chromatin domain, II) damage induction by 125I, and III) visualization of the domain. Here, the first step of the method, applied to Chinese hamster HA-1 cells, is described. Using pulse labelling with the replication marker IUdR, it was shown that Xq does not replicate at early S-phase and that the replication timing of Xq can be highly effectively synchronized with hydroxyurea in a whole cell population. Thus, the replication timing of Xq may be used to exclude or to incorporate 125I into the Xq. Other chromatin can be selected and targeted with 125I in a similar way. Examples of possible applications of the method are give

Induction of chromosome aberrations in unirradiated chromatin after partial irradiation of a cell nucleus

Purpose: It is generally accepted that chromosome exchanges in irradiated cells the formed through interactions between separate DNA doable-strand breaks (DSB). Here we tested whether non-irradiated DNA participate; in the formation of chromosome aberrations wen complex DNA DSB are induced elsewhere in the nucleus. Materials acid methods: Synchronized Chinese hamster cells containing an X chromosome with a late replicating q arm (X-q domain) were labelled with I-125-iododeoxyuridine ((125)IdUrd) in a period of S-phase when the vast majority of the X-q domain was not replicating. DNA damage froth I-125 decay as accumulated at the G1/S border while the culls were stored in liquid nitrogen. Decay of I-125 induced DSB in the immediate vicinity of the I-125 atom. Chromosome aberrations involving what is essentially the I-125-free X-q domain were scored at the first mitosis after cell thawing. As a positive control, cells were treated with (125)IdUrd at a later period in S-phase when the X-q domain replicates yielding a labelled X-q domain. Results: The I-125-free X-q domain exhibited chromosome aberrations (exchanges and fragments). The frequency of these aberrations seas linearly dependent on the number of I-125 decays elsewhere in the cell nucleus. The efficiency of formation of chromosome aberration by the I-125-free X-q domain teas approximately half of that observed in the I-125-labelled X-q domain. Conclusions: The involvement of the I-125-free X-q domain in chromosome aberration, suggests that DNA trot damaged by the decay of incorporated I-125 can interact with damaged DNA, indicating the existence of an alternative pathway fist, the formation of chromosome aberration