Investigation of G2-phase chromosomal radiosensitivity in hereditary non-polyposis colorectal cancer cells

Purpose: To investigate whether cells from hereditary nonpolyposis colorectal cancer (HNPCC) patients, a genetic condition characterized by constitutional mutations in DNA mismatch repair genes and associated with predisposition to colorectal carcinoma (CRC). could present a higher G2 chromosomal radiosensitivity. It is generally hypothesized that cancer predisposition in HNPCC is associated with the loss of the wild-type allele in somatic cells, resulting in defective DNA mismatch repair but, to dale, no data on G2 radiosensitivity have been reported for HNPCC. Materials and methods: Lymphoblastoid cell lines derived front six HNPCC patients heterozygous for MLH1, one HNPCC: patient carrying a mutant MSH2 allele and three healthy controls were treated with 50 cGy of X-rays and sampled at various harvesting times, monitoring cell-cycle progression by 5-bromo-2'-deoxyuridine (BrdUrd) incorporation in order to analyse chromosomal damage in the homogeneous G2 population. Results: There were no differences between lymphoblasts derived from patients in the frequency of G2 chromosomal aberrations induced by X-rays when compared with control cell lines. However, despite the absence of G2 radiosensitivity in HNPCC cells, lymphoblasts from patients heterozygous for MLH1 mutations showed a higher induction of chromatid exchanges. Conclusions: The observed possible incorrect rejoining of double-strand breaks in MLH1 heterozygotes would be an additional and important factor contributing to loss of heterozygosity in HNPCC: patients.