Validation of the cell cycle G(2) delay assay in assessing ionizing radiation sensitivity and breast cancer risk.

Genetic variations in cell cycle checkpoints and DNA repair genes are associated with prolonged cell cycle G(2) delay following ionizing radiation (IR) treatment and breast cancer risk. However, different studies reported conflicting results examining the association between post-IR cell cycle delay and breast cancer risk utilizing four different parameters: cell cycle G(2) delay index, %G(2)-M, G(2)/G(0)-G(1), and (G(2)/G(0)-G(1))/S. Therefore, we evaluated whether different parameters may influence study results using a data set from 118 breast cancer cases and 225 controls as well as lymphoblastoid and breast cancer cell lines with different genetic defects. Our results suggest that cell cycle G(2) delay index may serve as the best parameter in assessing breast cancer risk, genetic regulation of IR-sensitivity, and mutations of ataxia telangiectasia mutated (ATM) and TP53. Cell cycle delay in 21 lymphoblastoid cell lines derived from BRCA1 mutation carriers was not different from that in controls. We also showed that IR-induced DNA-damage signaling, as measured by phosphorylation of H2AX on serine 139 (γ-H2AX) was inversely associated with cell cycle G(2) delay index. In summary, the cellular responses to IR are extremely complex; mutations or genetic variations in DNA damage signaling, cell cycle checkpoints, and DNA repair contribute to cell cycle G(2) delay and breast cancer risk. The cell cycle G(2) delay assay characterized in this study may help identify subpopulations with elevated risk of breast cancer or susceptibility to adverse effects in normal tissue following radiotherapy.

DNA damage levels in prostate cancer cases and controls.

This study used the alkaline Comet assay to evaluate whether basal or H2O2-induced DNA damage is associated with prostate cancer (CaP) risk. Using lymphocyte samples from 158 CaP cases and 128 controls, collected in an ongoing case-control study, our results showed that basal DNA damage did not differ between cases and controls. However, the H2O2-induced DNA damage level was significantly higher in incident cases (mean +/- SD; 6.61 +/- 4.43, n = 102) than controls (5.30 +/- 3.60, n = 128) or prevalent cases (4.47 +/- 3.19; n = 56). Incident cases with a positive smoking history had significantly higher H2O2-induced DNA damage than never-smokers (7.57 +/- 4.82 versus 4.52 +/- 2.40; P < 0.001). Above-median H2O2-induced DNA damage was associated with a 1.61-fold increase in CaP risk [95% confidence interval (CI) = 0.92-2.81], after adjustment for age, race, benign prostatic hyperplasia (BPH), smoking history and family history (FH). Using the lowest quartile of H2O2-induced DNA damage as the referent group, the adjusted ORs for the 25th, 50th and 75th quartiles were 0.90 (95% CI = 0.39-2.05), 1.06 (95% CI = 0.48-2.35) and 2.05 (95% CI = 0.96-4.37), respectively (P = 0.046, test for linear trend). The association between CaP and DNA damage was modified by age, smoking history, family history and body mass index. Our results suggest that DNA damage may be associated with CaP risk. However, larger case-control and follow-up studies are warranted to further evaluate the potential application of the alkaline Comet assay in CaP risk assessment and prevention.

Nucleotide-excision repair and prostate cancer risk.

Prostate cancer (CaP) is the most commonly diagnosed nonskin cancer and the second leading cause of cancer death in American men. Its etiology is not fully understood. Ethnicity/race and family history are associated with it, and incidence increases with age. As with other solid tumors, accumulation of mutations and decline in DNA repair during aging may lead to CaP. However, we believe that conducting a large population screening for every cancer susceptibility gene (e.g. DNA repair) is only meaningful, if we can predict to what extent genetic variants contribute to DNA-repair functional phenotype and CaP risk. This review focuses on the association between CaP and nucleotide excision repair (NER), because some of the DNA adducts generated by CaP-related carcinogens are removed by the NER pathway, and our previous data showed a significant association between lower NER capacity (NERC) and CaP risk. Many laboratories, including ours, have employed a variety of approaches to evaluate the functional significance of DNA-repair single-nucleotide polymorphisms (SNPs) in human cancer risk assessment. Genetic profiling and computational modeling that can predict NERC may have great potential for CaP-risk assessment, because the current NERC assay is quite labor intensive, costly, and therefore not suitable for population-based screening.

The ADPRT V762A genetic variant contributes to prostate cancer susceptibility and deficient enzyme function.

The ADP-ribosyltransferase (ADPRT) gene encodes a zinc-finger DNA-binding protein, poly(ADP-ribose) polymerase-1 (PARP-1), that modifies various nuclear proteins by poly(ADP-ribosyl)ation and functions as a key enzyme in the base excision repair pathway. We have conducted two studies to test whether an amino acid substitution variant, ADPRT V762A (T2444C), is associated with prostate cancer (CaP) risk and decreased enzyme function. The first study used genomic DNA samples from an ongoing, clinic-based case-control study (488 cases and 524 controls) to show that a higher percentage of the CaP cases carried the ADPRT 762 AA genotype than controls (4% versus 2%). In Caucasians, the AA genotype was significantly associated with increased CaP risk [odds ratio (OR), 2.65; 95% confidence interval (CI), 1.08-6.49], and the VA genotype was associated with a slight but not significantly increased CaP risk (OR, 1.18; 95% CI, 0.85-1.64) using VV as the referent group after adjustment for age, benign prostatic hyperplasia, and family history. Furthermore, this association was stronger in younger (<65) men (OR, 4.77; 95% CI, 1.01-22.44) than older (> or =65) men (OR, 1.78; 95% CI, 0.55-5.82). The second study used freshly isolated peripheral lymphocytes from 354 cancer-free subjects to demonstrate that the ADPRT 762 A allele contributed to significantly lower adenosine diphosphate ribosyl transferase (ADPRT)/PARP-1 activities in response to H2O2 in a gene dosage-dependent manner (P < 0.0001, test for linear trend). The PARP-1 activities (mean +/- SD dpm/10(6) cells) were 18,554 +/- 9,070 (n=257), 14,847 +/- 7,082 (n=86), and 12,155 +/- 6,334 (n=11) for VV, VA, and AA genotypes, respectively. This study is the first to provide evidence that the ADPRT V762A-genetic variant contributes to CaP susceptibility and altered ADPRT/PARP-1 enzyme function in response to oxidative damage.