Comparison of the micronucleus and chromosome aberration techniques for the documentation of cytogenetic damage in radiochemotherapy-treated patients with rectal cancer.

PURPOSE: The goal of the interdisciplinary Clinical Research Unit KFO179 (Biological Basis of Individual Tumor Response in Patients with Rectal Cancer) is to develop an individual Response and Toxicity Score for patients with locally advanced rectal cancer treated with neoadjuvant radiochemotherapy. The aim of the present study was to find a reliable and sensitive method with easy scoring criteria and high numbers of cell counts in a short period of time in order to analyze DNA damage in peripheral blood lymphocytes. Thus, the cytokinesis-block micronucleus (CBMN) assay and the chromosome aberration technique (CAT) were tested. MATERIALS AND METHODS: Peripheral blood lymphocytes obtained from 22 patients with rectal cancer before (0 Gy), during (21.6 Gy), and after (50.4 Gy) radiochemotherapy were stimulated in vitro by phytohemagglutinin (PHA); the cultures were then processed for the CBMN assay and the CAT to compare the two methods. RESULTS: A significant increase of chromosomal damage was observed in the course of radiochemotherapy parallel to increasing radiation doses, but independent of the chemotherapy applied. The equivalence of both methods was shown by Westlake's equivalence test. CONCLUSION: The results show that the CBMN assay and the CAT are equivalent. For further investigations, we prefer the CBMN assay, because it is simpler through easy scoring criteria, allows high numbers of cell counts in less time, is reliable, sensitive, and has higher statistical power. In the future, we plan to integrate cytogenetic damage during radiochemotherapy into the planned Response and Toxicity Score within our interdisciplinary Clinical Research Unit.

A putatively functional haplotype in the gene encoding transforming growth factor beta-1 as a potential biomarker for radiosensitivity.

PURPOSE: To determine whether genetic variability in TGFB1 is related to circulating transforming growth factor-ß1 (TGF-ß1) plasma concentrations after radiotherapy and to radiosensitivity of lymphoid cells. PATIENTS AND METHODS: Transforming growth factor-ß1 plasma concentrations (n=79) were measured in patients 1 year after radiotherapy and chromosomal aberrations (n=71) ex vivo before therapy start. Furthermore, TGF-ß1 secretion and apoptosis were measured in isolated peripheral blood mononuclear cells of 55 healthy volunteers. These phenotypes were analyzed in relation to five germline polymorphisms in the 5' region of the TGFB1 gene. Because of high linkage disequilibrium, these five polymorphisms reflect frequent genetic variation in this region. A presumed impact of TGF-ß1 on DNA damage or repair was measured as micronucleus formation in 30 lymphoblastoid cell lines. RESULTS: We identified a hypofunctional genetic haplotype termed H3 tagging the 5' region of the TGFB1 gene encoding TGF-ß1. H3 was associated with lower TGF-ß1 plasma concentrations in patients (p=0.01) and reduced TGF-ß1 secretion in irradiated peripheral blood mononuclear cells (p=0.003). Furthermore, cells with H3 were less prone to induction of chromosomal aberrations (p=0.001) and apoptosis (p=0.003) by irradiation. The hypothesis that high TGF-ß1 could sensitize cells to DNA damage was further supported by increased micronuclei formation in 30 lymphoblastoid cell lines when preincubated with TGF-ß1 before irradiation (p=0.04). CONCLUSIONS: On the basis of TGF-ß1 plasma levels and radiation sensitivity of lymphoid cells, this study revealed a putatively hypofunctional TGFB1 haplotype. The significance of this haplotype and the suggested link between TGF-ß1 function and DNA integrity should be further explored in other cell types, as well as other experimental and clinical conditions.

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

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.