Spontaneous and radiation-induced chromosomal instability and persistence of chromosome aberrations after radiotherapy in lymphocytes from prostate cancer patients

Abstract

The aim of the study was to compare the spontaneous and ex vivo radiation-induced chromosomal damage in lymphocytes of untreated prostate cancer patients and age-matched healthy donors, and to evaluate the chromosomal damage, induced by radiotherapy, and its persistence. Blood samples from 102 prostate cancer patients were obtained before radiotherapy to investigate the excess acentric fragments and dicentric chromosomes. In addition, in a subgroup of ten patients, simple exchanges in chromosomes 2 and 4 were evaluated by fluorescent in situ hybridization (FISH), before the onset of therapy, in the middle and at the end of therapy, and 1 year later. Data were compared to blood samples from ten age-matched healthy donors. We found that spontaneous yields of acentric chromosome fragments and simple exchanges were significantly increased in lymphocytes of patients before onset of therapy, indicating chromosomal instability in these patients. Ex vivo radiation-induced aberrations were not significantly increased, indicating proficient repair of radiation-induced DNA double-strand breaks in lymphocytes of these patients. As expected, the yields of dicentric and acentric chromosomes, and the partial yields of simple exchanges, were increased after the onset of therapy. Surprisingly, yields after 1 year were comparable to those directly after radiotherapy, indicating persistence of chromosomal instability over this time. Our results indicate that prostate cancer patients are characterized by increased spontaneous chromosomal instability. This instability seems to result from defects other than a deficient repair of radiation-induced DNA double-strand breaks. Radiotherapy-induced chromosomal damage persists 1 year after treatment.

Fig. 1

a Spontaneous yields of excess acentric fragments per 100 cells (peripheral lymphocytes) in prostate cancer patients compared to healthy donors. Prostate cancers patients are divided into patients with prostate only (open circles) and patients with prostate and nodal disease (open triangles). Yields of excess acentric fragments (y _ac (ex)) were determined in Giemsa-stained metaphases. Data are presented as individual data points plotted depending on age (open symbols = patients; closed diamonds = healthy donors). b Spontaneous yields of chromosome aberrations per cell (peripheral lymphocytes) in prostate cancer patients compared to healthy donors. Yields of dicentric chromosomes (y _dic) and excess acentric fragments (y _ac (ex)) were determined in Giemsa-stained metaphases. Yields of simple exchanges (y _SE), representing sums of dicentric chromosomes and reciprocal translocations, were evaluated in metaphases with painted chromosomes 2 and 4. Data are presented as box plots with each box enclosing 50% of the overall data. The corresponding median value of the variable is displayed as a horizontal line. The top and the bottom of the box mark the limits of ±25% of the variable population. The vertical lines extending from the top and bottom of each box denote the minimum and maximum values within the data set that are located within an acceptable range (points with values either greater than the upper quartile +1.5x interquartile distance or less than lower quartile −1.5x interquartile distance); outliers that are not included are represented by circles

Fig. 2

Chromosome aberration yields per cell (peripheral lymphocytes) in prostate cancer patients compared to healthy donors after ex vivo irradiation with D = 3 Gy. Blood samples of cancer patients were taken before radiotherapy. Yields of dicentric chromosomes (y _dic) and excess acentric fragments (y _ac (ex)) were determined in Giemsa-stained metaphases. Yields of simple exchanges (y _SE), representing sums of dicentric chromosomes and reciprocal translocations were evaluated in metaphases with painted chromosomes 2 and 4. Data are presented as box plots with each box enclosing 50% of the overall data. Median value of the variable is displayed as a horizontal line. The top and the bottom of the box mark the limits of ±25% of the variable population. The lines extending from the top and bottom of each box denote the minimum and maximum values within the data set that are located within an acceptable range (points with values either greater than the upper quartile +1.5x interquartile distance or less than lower quartile −1.5x interquartile distance); outliers that are not included are represented by circles

Fig. 3

a–c Genomic yields of excess acentric fragments (a), dicentric chromosomes (b), and partial yields of simple exchanges (c) per cell as observed at different times in peripheral lymphocytes of prostate cancer patients. Genomic aberration yields were determined in Giemsa-stained metaphases; partial yields of simple exchanges (dicentric chromosomes plus reciprocal translocations) were evaluated in metaphases with painted chromosomes 2 and 4. Blood samples of cancer patients were obtained before radiotherapy, in the middle and at the end of the treatment, as well as 1 year after treatment. Blood samples, obtained before treatment, were irradiated ex vivo with D = 3 Gy. Data are presented as box plots with each box enclosing 50% of the data, and the median value of the variable displayed as a horizontal line. The top and the bottom of the box mark the limits of ±25% of the variable population. The vertical lines extending from the top and bottom of each box denote the minimum and maximum values within the data set located within an acceptable range (points whose values is either greater than upper quartile +1.5x interquartile distance or less than lower quartile −1.5x interquartile distance); outliers that are not included are represented by circles