Evaluation of a mutation test using S49 mouse lymphoma cells and monitoring simultaneously the induction of dexamethasone resistance, 6-thioguanine resistance and ouabain resistance

Investigations into the mechanisms of carcinogen-induced nuclear enlargement in HeLa S3 cells in vitro

Carcinogen-induced nuclear enlargement has been reported both in vitro and in vivo, but the mechanism, and whether it is causally related to carcinogenesis, has not yet been established. This study was designed to investigate the role of increased DNA content, such as might occur in polyploidy, in induction of nuclear enlargement. The effects of two genotoxic carcinogens, N-methyl-N-nitrosourea and adriamycin, were compared with the effects induced by diethylstilboestrol, which is arguably a non-genotoxic carcinogen but is known to induce polyploidy. HeLa S3 cells were used as the model system for comparison with previous studies. N-methyl-N-nitrosourea and adriamycin both induced a concentration-related increase in nuclear size 24 to 72 hr after a 30 min pulse-treatment. This was accompanied by an increase in the proportions of cells in the G(2) + M stage of the cell cycle, possibly due to a G(2) block. There was some evidence of polyploidy with adriamycin but not with N-methyl-N-nitrosourea. The distributions of nuclear areas indicated that increases in ploidy contributed to, but did not totally account for, the nuclear enlargement. In contrast, diethylstilboestrol increased the range of nuclear areas and DNA content, to both less than and greater than that of control cells, but only after a prolonged exposure period of 48 hr. These data were consistent with diethylstilboestrol inducing spindle damage. These results demonstrate that carcinogen-induced nuclear enlargement is only partially explained by increased nuclear DNA content, and that certain classes of non-genotoxic carcinogen may produce a completely different pattern to that from genotoxic carcinogens.

Lower mutation frequencies are induced by ENU in undifferentiated embryonic cells than in differentiated cells of the mouse in vitro

The pluripotent embryonic carcinoma cells of line P19 established from undifferentiated cells of the early mouse embryo and their differentiated progeny, the epithelioid ectoderm-like EPI-7 cells, were investigated for the induction of mutations at the HPRT locus by the alkylating agent N-ethyl-N-nitrosourea (ENU). We showed that the cytotoxic effects of ENU after a 5-h treatment were lower in undifferentiated P19 cells than in differentiated EPI-7 cells. The IC50 values of ENU in the two cell lines amounted to 0.6 mg/ml and 0.09 mg/ml for P19 and EPI-7 cells, respectively. The induction of 6-thioguanine-resistant mutants by ENU (1.0 mg/ml) determined after an expression time of 8 days for both cell lines resulted in similar mutation frequencies. Using expression times of 8 days for P19 and 11.75 days for EPI-7 cells, taking into account the longer generation time of differentiated EPI-7 cells (13.7 +/- 3.6 h) in comparison to undifferentiated P19 cells (9.3 +/- 0.9 h), ENU induced significantly higher mutant frequencies in EPI-7 cells (4865 mutants/10(6) cells) than in P19 cells (282 mutants/10(6) cells). Our results and data from the literature on UV irradiation-induced repair support the idea that the induction of lower mutation frequencies in embryonic cells may correlate with different proliferation capacities, cell cycle parameters and/or different mechanisms of DNA repair in embryonic stem cells and differentiated cells, respectively.

Mutagenicity, metabolism, and DNA interactions of urethane

Urethane, a known animal carcinogen, has been the subject of intensive research efforts spanning 40 years. Recent concerns have focused on the presence of urethane in a variety of fermented foods and alcoholic beverages, although no epidemiological studies or human case reports have been published. Much information is available about the mutagenesis, metabolism, and DNA interactions of urethane in experimental systems. Urethane is generally not mutagenic in bacteria although in some instances it acts as a weak mutagen. Urethane is not mutagenic in Nuerospora but is weakly mutagenic in Saccharomyces. Drosophila appear to be the only organisms that consistently give positive mutagenic results with urethane, but its mutagenicity is weak and in many cases shows no clear dose dependence. Urethane is a good clastogen in mammalian somatic cells in vivo, but it shows variable results with cells in vitro. It efficiently induces sister chromatid exchanges in a variety of cells. Mammalian spermatogenic cells are insensitive to the induction of specific locus and dominant lethal mutations by urethane. Mutational synergism has been reported to occur between ethyl methanesulfonate and urethane when administered two generations apart, and some investigators have suggested possible synergism for cancer-causing mutations in mice exposed to X-rays and urethane one generation apart. These studies are controversial and have not been confirmed. Studies on the induction of cancer-causing dominant mutations by urethane are at variance with results from extensive studies with the specific locus test in mice. Urethane studies with the unscheduled DNA synthesis assay in mouse spermatogenic cells and with the sperm abnormality test have given negative results. Urethane is rapidly and evenly distributed in the body. The rate of elimination of urethane from plasma is a saturable process and varies according to the strain and age of the animal. Recent studies have concentrations similar to those in wine, ethanol inhibits the tissue distribution of urethane in mice. These results are important because they suggest a lower carcinogenic/mutagenic risk than expected from exposure to urethane in alcoholic beverages. Although research on the metabolic activation of urethane has been extensive, no conclusive results have been obtained about its active metabolite, at one time thought to be N-hydroxyurethane. More recently, it has been postulated that urethane is activated to vinyl carbamate and that this metabolite is capable of reacting with DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/1. Genetic effects of ethanol

Alcoholics have a higher frequency of chromosomal aberrations and sister-chromatid exchanges (SCEs) in their peripheral lymphocytes. In human and mammalian cells in vitro, ethanol generally does not induce genetic damage, but it induces SCEs in the presence of an exogenous metabolic system. In human lymphocytes in vitro, ethanol induces SCEs in the presence of alcohol dehydrogenase. In animals in vivo, ethanol induces a variety of genetic effects, including SCEs, micronuclei, dominant lethal mutations and aneuploidy in mouse eggs. There is some indication that ethanol may lead to genetic damage in sperm. In bacteria, ethanol is at best marginally active. Ethanol leads to anomalous chromosome segregation in Aspergillus, to mutations in yeast, to chromosomal aberrations and SCEs in plant root tips and to disturbances of meiosis and micronuclei in tetrads in Zea and Tradescantia respectively. The first metabolite of ethanol, acetaldehyde is mutagenic in a variety of test systems. The mutagenic activity of acetaldehyde in bacteria is questionable, but there is no doubt of its mutagenic activity in a variety of eukaryotic test systems in vitro as well as in vivo.

Sex hormones and neoplasia: genotoxic effects in short term assays

The mechanism of the tumorigenic effects of sex hormones in the liver and in other organs is still unclear. Clues towards an understanding of this action of sex hormones can be gained from short-term assays suitable for revealing adverse effects at different molecular levels relevant to the process of neoplastic transformation. The available data on the effects of sex hormones indicating gene mutations, unscheduled DNA synthesis, sister chromatid exchange, chromosomal anomalies, induction of aneuploidy and cell transformation are reviewed. Although the data base is scant, in particular for androgens and progestins and in systems other than the mutational assays, it can be concluded that sex hormones, in general, fail to induce gene mutations. On the other hand, recent evidence shows that diethylstilbestrol and steroidal estrogens are capable of inducing neoplastic transformation in vitro. In this context, the induction of aneuploidy is discussed as non-mutational but genotoxic effect of estrogens responsible for the neoplastic transformation. Morphological transformation and scoring for chromosomal anomalies can provide useful endpoints for further evaluation of sex hormones with suspected carcinogenic properties.

Induction of malignant transformation by various chemicals in Balb/3T3 clone A31-1-1 cells and biological characterization of some transformants

Balb/c A31-1-1 cells were used for the study of transformation induction by chemicals with different mutagenic specificities. We show that survival of these cells and therefore the calculated transformation frequency per cells at risk is dependent upon the cell density at the time of treatment. It is suggested that equal cell densities should be used for measuring survival values and transformation induction. The quantitative results obtained are discussed in the light of the known mutagenic mechanisms of the chemicals tested. We also characterized morphologically transformed foci induced by different chemicals with respect to some biological properties. Anchorage independence was determined by testing growth in soft agar, loss of contact inhibition was quantitated by measuring maximum cell densities and malignancy was tested by tumor induction in nude mice. Although no very close correlation between these parameters and morphology was observed, the most malignant clones are also the ones with the highest values in the other tests. Our data make one or few genetical targets for transformation induction likely. We therefore speculate that the diverse phenotypes obtained might be due to differential activation of one or very few transforming genes in these cells.

Mutagenicity of methyl 2-benzimidazolecarbamate, diethylstilbestrol and estradiol: structural chromosomal aberrations, sister-chromatid exchanges, C-mitoses, polyploidies and micronuclei

Methyl 2-benzimidazolecarbamate (MBC), diethylstilbestrol (DES) and estradiol were tested with regard to their ability to induce C-mitoses, polyploidies, micronuclei, structural chromosomal aberrations and sister-chromatid exchanges (SCE) in human peripheral lymphocytes in vitro. The compounds did not induce structural chromosomal aberrations either in the presence or absence of metabolic activation. MBC and estradiol were negative in the SCE test. DES induced SCE rates which were not even twice the control level and which were independent of dose and of metabolic activation. All compounds induced C-mitoses, polyploidies and micronuclei. The micronuclei are interpreted as resulting from errors in the anaphase distribution of chromosomes by spindle disturbances rather than from structural chromosomal aberrations.