Comparative study of chromosome aberrations induced with aphidicolin in women affected by breast cancer and cervix uterine cancer

Expression of aphidicolin-induced fragile sites and their relationship between genetic susceptibility in breast cancer, ovarian cancer, and non-small-cell lung cancer patients

Fragile sites are nonrandomly located gaps and/or breaks and their expres-sion can be induced by specific culture conditions. There are many reports in the literature that indicate that these sites can act as factors that predispose to specific chromosome aberrations and other complex rearrangement in the chromosome and their association with cancers. In the present study, the expression of the fragile sites induced by aphidicolin was evaluated on prometaphase chromosomes from peripheral blood lymphocytes of 55 patients with breast cancer patients belonging to different stages of the cancer, 25 patients with epithelial ovarian cancer, and 13 with non-small-cell lung cancer, 100 of their first-degree clinically healthy female relatives, and 100 normal age-matched healthy persons without a familial history of cancer. The frequency of expression of the fragile sites in cancer patients and their first-degree relatives was found to be statistically significant (P<0.05) than those of the controls. In different stages of breast cancer patients, 6q26 is the best-defined fragile site whereas 13q13 is confined to stage II and stage III patients only. The chromosomal aberration rate/cell in breast cancer patients was found to be 0.29+/-0.13, in epithelial ovarian cancer patients 0.38+/-0.14, and in non-small-cell lung cancer 0.29+/-0.11 as compared to 0.07+/-0.03 in controls, and was found to be statistically significant. Therefore, our results indicate that these fragile sites may be the unstable sites in the genome and, hence, can be used as suitable and reliable markers for genetic predisposition to breast cancer, epithelial ovarian cancer, and in non-small-cell lung cancer.

Investigation of genetic susceptibility to non-small cell lung cancer by fragile site expression

Fragile sites are non-staining gaps and breaks in specific points of chromosomes that are inducible by various culture conditions. Previous studies have shown that various clastogenic agents increase expression of fragile sites. In this study, the expression of common fragile sites induced by aphidicolin was evaluated on prometaphase chromosomes obtained from peripheral blood lymphocytes. Chromosomal aberrations and fragile site expression of 60 individuals, including 20 patients with non-small cell lung cancer (NSCLC), 20 of their clinically healthy family members, and 20 age-matched normal healthy controls without history of any cancer type were studied. Both the proportion of damaged cells (P < 0.001) and the mean number of gaps and breaks per cell (P < 0.001) were significantly higher in both the patients and relatives' groups when compared with the control group. However, they were insignificant when the patients were compared to their relatives (P > 0.05). We determined four aphidicolin type common fragile sites in our study. These sites in patients with NSCLC and relatives were the following: 1p21, 2q33, 3p14, and 16q23. In these fragile sites, 2q33, 3p14, and 16q23 sites were statistically significant when compared with control group (P < 0.001, P < 0.0005, and P < 0.05, respectively). Consequently, we believe that fragile site studies may be helpful to detection of cancer risk.

Should gaps be included in chromosomal aberration analysis? Evidence based on the comet assay

This study evaluated DNA damage in human lymphocytes due to occupational exposure to low levels of ionizing radiation using two assays: the comet assay and chromosomal aberration (CA) analysis including and excluding gaps. The results obtained reveal a higher correlation between both methods when chromatid and chromosome gaps were included in the correlation analysis (r=0.78 versus r=0.50). This increased correlation support the hypothesis that the gaps constitute a type of chromosome aberration, and suggest that these events should be scored in this type of analysis.

Chromosomal fragile sites and relationship between genetic predisposition to small cell lung cancer

Fragile sites are non-staining gaps and breaks on mammalian chromosomes. Several investigators have pointed out that these sites may act as factors that predispose to specific chromosomal rearrangements that are present in some cancer cases. The expression of common fragile sites induced by aphidicolin (Apc) was evaluated on prometaphase chromosomes obtained from the peripheral blood lymphocytes of 15 patients with lung cancer, 20 of their clinically healthy family members, and 20 age-matched normal controls. As a result of cytogenetic evaluation carried out by the High Resolution Banding (HRB) technique, 1q21, 2q33, 3p14, 7q32, 13q13, 16q23, 17q21, and 22q12 are defined as fragile sites in patients and relatives. The rate of total fragile sites and 2q33, 3p14, and 16q23 are statistically significant in both patients and relatives when compared with the control group. Therefore, our results showed that common fragile sites might be unstable factors in the human genome and they can be used as suitable markers for genetic predisposition to lung cancer.

Parvovirus-mediated antineoplastic activity exploits genome instability

The generation and accumulation of genetic mutations have been associated with carcinogenesis. Epidemiological and experimental evidence implicate parvoviruses in growth inhibition (oncosuppression) and selective destruction (oncolysis) of tumor cells. It is proposed here that parvoviruses can preferentially target genetically unstable tumor cells, which are deficient in DNA repair mechanisms. This selective strategy may serve as a virus-based therapeutic approach against cancer.

The expression frequency of common fragile sites and genetic predisposition to colon cancer

The expression frequency of common fragile sites induced by aphidicolin (Apc), bromodeoxyuridine (BrdU), and caffeine was evaluated on prometaphase chromosomes obtained from the peripheral blood lymphocytes of 32 patients with colon cancer, 30 of their clinically healthy family members and 30 age-matched normal controls. The proportion of damaged cells (P < 0.001), the mean number of chromosomal aberrations and the expression frequencies of fragile sites were significantly higher in the patient and relative groups compared to the control group. Our findings show an increased genetic instability in patients with colon cancer and their first-degree relatives. In addition, common fragile sites can be used as a suitable marker for determining genetic predisposition to cancer.

The expression of fragile sites in lymphocytes of patients with rectum cancer and their first-degree relatives

Fragile sites are non-staining gaps and breaks in specific points of chromosomes. These sites also include acentric fragments, triradial figures and several rearrangements. Although this issue has been controversial recently, they may be related to structural chromosomal rearrangement in some neoplasms. In this study, the expression of fragile sites induced by aphidicolin (Apc), 5-bromodeoxyuridine (BrdU) and caffeine was investigated on prometaphase chromosomes obtained from the peripheral blood lymphocytes of 36 patients with rectum cancer, 30 first-degree relatives and 30 normal healthy controls. The results of the structural chromosome aberrations determined in patients and their first-degree relatives were significantly higher than those in control subjects (P<0.001). We determined aphidicolin type common fragile sites (1p36, 1p31, 1p21, 1q21, 1q25, 1q44, 2p24, 2q21, 2q33, 2q37, 3p14, 5q21, 5q33, 13q13, 14q24, 16q23 and 18q21). When the rates of sites such as 1p21, 1q25, 2q33, 3p14, 5q21 and 14q24 in patients and in their first-degree relatives were compared with the control group, the difference was statistically significant. Our results indicated an increased genetic instability in patients with rectum cancer and their first-degree relatives. Therefore, the increase of fragile site expression may be an important marker showing genetic predisposition to rectum cancer.

The expression of common fragile sites in peripheral blood lymphocytes of breast and colorectal cancer patients with aphidicolin

The frequency and distribution of aphidicolin induced common fragile sites was evaluated on chromosomes of peripheral blood lymphocytes in 10 breast and 10 colorectal cancer patients, and 10 healthy controls to determine correlation between specific fragile sites and cancer breakpoints. Fifty complete metaphases were screened from each culture and the results were evaluated by Student's t-test. The total number of fragile sites was found as 933 in breast cancer patients, 950 in colorectal cancer patients and 501 in control group. Both the number of aberrations per cell and number of aberrations per damaged cell were significantly higher in the patient groups. These findings indicate that genetic instability in the breast and colorectal cancer patients increased and fragile sites may play a critical role in the pathogenesis of breast and colorectal cancer.

Cell cycle control, checkpoint mechanisms, and genotoxic stress

The ability of cells to maintain genomic integrity is vital for cell survival and proliferation. Lack of fidelity in DNA replication and maintenance can result in deleterious mutations leading to cell death or, in multicellular organisms, cancer. The purpose of this review is to discuss the known signal transduction pathways that regulate cell cycle progression and the mechanisms cells employ to insure DNA stability in the face of genotoxic stress. In particular, we focus on mammalian cell cycle checkpoint functions, their role in maintaining DNA stability during the cell cycle following exposure to genotoxic agents, and the gene products that act in checkpoint function signal transduction cascades. Key transitions in the cell cycle are regulated by the activities of various protein kinase complexes composed of cyclin and cyclin-dependent kinase (Cdk) molecules. Surveillance control mechanisms that check to ensure proper completion of early events and cellular integrity before initiation of subsequent events in cell cycle progression are referred to as cell cycle checkpoints and can generate a transient delay that provides the cell more time to repair damage before progressing to the next phase of the cycle. A variety of cellular responses are elicited that function in checkpoint signaling to inhibit cyclin/Cdk activities. These responses include the p53-dependent and p53-independent induction of Cdk inhibitors and the p53-independent inhibitory phosphorylation of Cdk molecules themselves. Eliciting proper G1, S, and G2 checkpoint responses to double-strand DNA breaks requires the function of the Ataxia telangiectasia mutated gene product. Several human heritable cancer-prone syndromes known to alter DNA stability have been found to have defects in checkpoint surveillance pathways. Exposures to several common sources of genotoxic stress, including oxidative stress, ionizing radiation, UV radiation, and the genotoxic compound benzo[a]pyrene, elicit cell cycle checkpoint responses that show both similarities and differences in their molecular signaling.

Novel putative fragile sites observed in feline fibroblasts treated with aphidicolin and fluorodeoxyuridine

Fragile sites are non-randomly distributed chromosomal breaks and gaps observed in the cells cultivated under certain conditions. Feline fragile sites were analyzed using skin fibroblast strains after the treatments with aphidicolin and fluorodeoxyuridine in combination with caffeine. Three aphidicolin-induced fragile sites (A1q21, C2q13 and E1p21) as well as a folate-sensitive site (B1q14) were observed in all the 3 fibroblast strains tested for each treatment group. The loci in A1q21 and B1q14 are very close to that reported previously for peripheral blood lymphocytes and lung cells. Two chromosomal break points in C2q13 and E1p21 seem to be new fragile sites. Fifteen candidates for feline fragile sites were also assigned their locations in feline chromosomes. Both the incidence and distribution of feline fragile sites in skin fibroblasts seem to be different at least in part from those in lymphocytes.