Significance of amino acid substitution variants of DNA repair genes in radiosusceptibility of cervical cancer patients; a pilot study.

The present pilot study was designed to elucidate the functional significance of amino acid substitution variants of DNA repair genes. Using the peripheral blood lymphocytes (PBLs) from healthy donors and cervical cancer patients, the contribution of four non-synonymous single nucleotide polymorphisms (SNPs) in three base excision repair genes (BER), XRCC1 (Arg194Trp and Arg399Gln), hOGG1 (Ser326Cys), and APE1 (Asp148Glu), to the susceptibility to ionizing radiation were evaluated. The level of initial, oxidative and residual DNA damage produced by 2 Gy was measured by the alkaline single cell gel electrophoresis (the comet assay), and the SNPs were determined by PCR-restriction fragment length polymorphism (RFLP) assay. No significant differences in the allele frequencies between cancer patients and controls for any of these four SNPs were detected. Although the initial DNA damage levels were approximately similar, significantly higher level of Fpg-sensitive sites were found in patients compared with controls (p<0.001) irrespective of genotype distribution. A trend towards increased values of EndoIII-sensitive sites was determined in PBLs from cancer patients compared with healthy women, mainly carriers of the XRCC1 and OGG1 variant alleles; however, the mean value of EndoIII-sensitive sites does not reach any significance. A substantial delay in DNA strand-break rejoining was ascertained in patients who carried APE1 Glu variant allele in comparison with healthy donors 15 and 60 minutes after irradiation (p< 0.05 and p< 0.01, respectively). In contrast, slightly higher but statistically significant level of residual DNA damage was estimated in controls (APE1Asp/Asp) compared with patients. An association between single nucleotide polymorphism (SNP) of two DNA repair genes functioning in the same biochemical pathway and susceptibility to radiation was found. In the combined genotype APE1/XRCC1 and APE1/hOGG1, a decreased level of residual DNA damage was detected in carriers of wild type APE1 genotype. In addition, a possible modulating effect of hOGG1 gene on the kinetics of strand-break rejoining was estimated. The lowest residual DNA damage level was determined in subjects with the combined APE1(Asp/Asp)/hOGG1(Ser/Cys+Cys/Cys) genotypes. Based on these preliminary data we suppose that a combination of several amino acid substitution variants of DNA repair genes involved in the same repair pathway rather than one low-penetrance SNP in a single gene may contribute to DNA repair outcomes. Larger study with more subjects is needed to verify these findings.