Chemical carcinogens. A review and analysis of the literature of selected chemicals and the establishment of the Gene-Tox Carcinogen Data Base. A report of the U.S. Environmental Protection Agency Gene-Tox Program

Ouabain Induces DNA Damage in Human Osteosarcoma U-2 OS Cells and Alters the Expression of DNA Damage and DNA Repair-associated Proteins

BACKGROUND/AIM

Ouabain, isolated from natural plants, exhibits anticancer activities; however, no report has presented its mechanism of DNA damage induction in human osteosarcoma cancer cells in vitro. The aim of this study was to investigate whether ouabain induces DNA damage and repair, accompanied with molecular pathways in human osteosarcoma cancer U-2 OS cells in vitro.

MATERIALS AND METHODS

The percentage of viable cell number was measured by flow cytometric assay; DNA damage was assayed by DAPI staining, comet assay, and agarose gel electrophoresis. DNA damage and repair associated protein expressions were assayed by western blotting assays.

RESULTS

Ouabain reduced total cell viability, induced chromatin condensation, DNA fragmentation, and DNA damage in U-2 OS cells. Ouabain increased p-ATM^Ser1981, p-ATR^Ser428, and p53 at 2.5-10 μM, increased p-p53^Ser15 at 10 μM; however, it decreased p-MDM2^Ser166 at 2.5-10 μM. Ouabain increased p-H2A.X^Ser139, MDC-1, and PARP at 2.5-10 μM and BRCA1 at 5-10 μM; however, it decreased DNA-PK and MGMT at 2.5-10 μM in U-2 OS cells at 48 h treatment. Ouabain promoted expression and nuclear translocation of p-H2A.X^Ser139 in U-2 OS cells and this was confirmed by confocal laser microscopy.

CONCLUSION

Ouabain reduced total viable cell number through triggering DNA damage and altering the protein expression of DNA damage and repair system in U-2 OS cells in vitro.

Follow-up genotoxicity assessment of Ames-positive/equivocal chemicals using the improved thymidine kinase gene mutation assay in DNA repair-deficient human TK6 cells

Genotoxicity testing plays an important role in the safety assessment of pharmaceuticals, pesticides, and chemical substances. Among the guidelines for various genotoxicity tests, the in vitro genotoxicity test battery comprises the bacterial Ames test and mammalian cell assays. Several chemicals exhibit conflicting results for the bacterial Ames test and mammalian cell genotoxicity studies, which may stem from the differences in DNA repair capacity or metabolism, between different cell types or species. For better understanding the mechanistic implications regarding conflict outcomes between different assay systems, it is necessary to develop in vitro genotoxicity testing approaches with higher specificity towards DNA-damaging reagents. We have recently established an improved thymidine kinase (TK) gene mutation assay (TK assay) that is deficient in DNA excision repair system using human lymphoblastoid TK6 cells lacking XRCC1 and XPA (XRCC1 -/-/XPA -/-), the core factors of base excision repair and nucleotide excision repair, respectively. This DNA repair-deficient TK6 cell line is expected to specifically evaluate the genotoxic potential of chemical substances based on the DNA damage. We focused on four reagents, N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA), p-phenylenediamine (PPD), auramine, and malachite green (MG) as the Ames test-positive chemicals. In our assay, assessment using XRCC1 -/-/XPA -/- cells revealed no statistically significant increase in the mutant frequencies after treatment with NEDA, PPD, and MG, suggesting the chemicals to be non-genotoxic in humans. The observations were consistent with that of the follow-up in vivo studies. In contrast, the mutant frequency was markedly increased in XRCC1 -/-/XPA -/- cells after treatment with auramine. The results suggest that auramine is the genotoxic reagent that preferentially induces DNA damages resolved by BER and/or NER in mammals. Taken together, BER/NER deficient cell-based genotoxicity testing will contribute to elucidate the mechanism of genotoxicity and therefore play a pivotal role in the accurate safety assessment of chemical substances.

Casticin Induces DNA Damage and Affects DNA Repair Associated Protein Expression in Human Lung Cancer A549 Cells (Running Title: Casticin Induces DNA Damage in Lung Cancer Cells)

Casticin was obtained from natural plants, and it has been shown to exert biological functions; however, no report concerns the induction of DNA damage and repair in human lung cancer cells. The objective of this study was to investigate the effects and molecular mechanism of casticin on DNA damage and repair in human lung cancer A549 cells. Cell viability was determined by flow cytometric assay. The DNA damage was evaluated by 4',6-diamidino-2-phenylindole (DAPI) staining and electrophoresis which included comet assay and DNA gel electrophoresis. The protein levels associated with DNA damage and repair were analyzed by western blotting. The expression and translocation of p-H2A.X were observed by confocal laser microscopy. Casticin reduced total viable cell number and induced DNA condensation, fragmentation, and damage in A549 cells. Furthermore, casticin increased p-ATM at 6 h and increased p-ATR and BRCA1 at 6-24 h treatment but decreased p-ATM at 24-48 h, as well as decreased p-ATR and BRCA1 at 48 h. Furthermore, casticin decreased p-p53 at 6-24 h but increased at 48 h. Casticin increased p-H2A.X and MDC1 at 6-48 h treatment. In addition, casticin increased PARP (cleavage) at 6, 24, and 48 h treatment, DNA-PKcs and MGMT at 48 h in A549 cells. Casticin induced the expressions and nuclear translocation of p-H2AX in A549 cells by confocal laser microscopy. Casticin reduced cell number through DNA damage and condensation in human lung cancer A549 cells.

Meeting report, ICH M7 relevant workshop: use of (Q)SAR systems and expert judgment

Use of Quantitative Structure-Activity Relationships ((Q)SAR) prediction tools has been increasing since the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) M7 guideline was issued in June 2014. The Japanese Environmental Mutagen Society and the Bacterial Mutagenicity Study Group took the initiative of the workshop on (Q)SAR in 2016 to discuss using (Q)SAR to predict mutagenicity. The aim of the workshop was to form a common understanding on the current use of (Q)SAR tools in industry and for regulatory purposes and on the process of expert judgment. This report summarizes the general session that reviewed the use of (Q)SAR tools and the case study session that discussed expert judgment.

A Novel Strategy to Predict Carcinogenicity of Antiparasitics Based on a Combination of DNA Lesions and Bacterial Mutagenicity Tests

Genotoxicity and carcinogenicity testing of pharmaceuticals prior to commercialization is requested by regulatory agencies. The bacterial mutagenicity test was considered having the highest accuracy of carcinogenic prediction. However, some evidences suggest that it always results in false-positive responses when the bacterial mutagenicity test is used to predict carcinogenicity. Along with major changes made to the International Committee on Harmonization guidance on genotoxicity testing [S2 (R1)], the old data (especially the cytotgenetic data) may not meet current guidelines. This review provides a compendium of retrievable results of genotoxicity and animal carcinogenicity of 136 antiparasitics. Neither genotoxicity nor carcinogenicity data is available for 84 (61.8%), while 52 (38.2%) have been evaluated in at least one genotoxicity or carcinogenicity study, and only 20 (14.7%) in both genotoxicity and carcinogenicity studies. Among 33 antiparasitics with at least one old result in in vitro genotoxicity, 15 (45.5%) are in agreement with the current ICH S2 (R1) guidance for data acceptance. Compared with other genotoxicity assays, the DNA lesions can significantly increase the accuracy of prediction of carcinogenicity. Together, a combination of DNA lesion and bacterial tests is a more accurate way to predict carcinogenicity.

Heterogeneous Nucleation of Trichloroethylene Ozonation Products in the Formation of New Fine Particles

Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O₂, NO, NO_2, SO₂ and H₂O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH₄)₂SO₄-H₂O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles.

Final Report on the Safety Assessment of 4-Methoxy-m-Phenylenediamine, 4-Methoxy-m-Phenylenediamine Sulfate, and 4-Methoxy-m-Phenylenediamine-HCl

The hair dye ingredient 4-Methoxy-m-Phenylenediamine Sulfate (4-MMPDS) prior to 1978 was used extensively used in the United States. Concerns raised because of studies which showed the hair dye to be an animal carcinogen prompted the voluntary reformulation and deletion of 4-MMPD in hair dyes containing this ingredient. No reports were made on the use of this ingredient until 1989 when 17 uses were reported. Assays on volunteers indicate that less than 0.2% of the dye penetrates the scalp and that about 3.9% is absorbed through the skin of the forearm. The dye is metabolized and excreted in the urine; a major metabolic product was 4-acetylamino-2-aminoanisole. The LD50 range in rats of aqueous solutions of 4-MMPD was 400–500 mg/kg. No gross tissue abnormalities were reported in subchronic feeding or dermal studies. 4-MMPD was not an ocular irritant when tested at 2.5%, but was a mild skin irritant when tested at the same concentration. The dermal application of hair dye formulations containing up to 4.0% 4-MMPD were negative for both embryotonic toxicity and teratogenic effects. The results of numerous mutagenic studies vary between the assay system used. 4-MMPD was noncarcinogenic in four dermal carcinogenic studies, but was carcinogenic to both rats and mice in feeding studies. On the basis of the information included in this report, it is concluded that 4-Methoxy-m-Phenylenediamine, 4-Methoxy-m-Phenylenediamine Sulfate, and 4-Methoxy-m-Phenylenediamine HCl are unsafe for use in cosmetic products.

Update of carcinogenicity studies in animals and humans of 535 marketed pharmaceuticals

This survey is a compendium of information retrieved on carcinogenicity in animals and humans of 535 marketed pharmaceuticals whose expected clinical use is continuous for at least 6 months or intermittent over an extended period of time. Of the 535 drugs, 530 have the result of at least one carcinogenicity assay in animals, and 279 (52.1%) of them gave a positive response in at least one assay. Only 186 drugs (34.8%) have retrievable information on carcinogenicity in humans, and 104 of them gave to a variable extent evidence of a potential carcinogenic activity. Concerning the correlation between results obtained in animals and epidemiological findings, 58 drugs gave at least one positive result in carcinogenicity assays performed in animals and to a variable extent displayed evidence of carcinogenicity in humans, but 97 drugs tested positive in animals and were noncarcinogenic in humans or vice versa. Our findings, which are in agreement with previous studies, indicate that the evaluation of the benefit/carcinogenic risk ratio should be always made in prescribing a drug.

Genotoxic effects of chlorpyrifos, cypermethrin, endosulfan and 2,4-D on human peripheral lymphocytes cultured from smokers and nonsmokers

Pesticides often cause environmental pollution and adverse effects on human health. We have chosen four structurally different pesticides (endosulfan, an organochlorine pesticide; chlorpyrifos, an organophosphate insecticide; cypermethrin, type II pyrethroid insecticide, and 2,4-dichlorophenoxyacetic acid, a chlorinated aromatic hydrocarbon acid pesticide) to examine and compare their effects on DNA damage in acutely cultured human lymphocytes by the comet assay. In addition, possible differences in response between smoking and nonsmoking subjects were also investigated. Venous blood samples were obtained from healthy male nonsmoker (n = 7) and smoker (n = 8) donors. Primary cultures of lymphocytes were prepared and test groups were treated with three different concentrations (1, 5, and 10 μM) of endosulfan, chlorpyrifos, cypermehrin, and 2,4-D. DNA damage was assessed by alkaline comet assay. We determined an increase in the ratio of DNA migration in human lymphocyte cell cultures as a result of treatment with cypermethrin, 2,4-D and chlorpyrifos at high concentration. Endosulfan had no significant genotoxic effect even at 10 μM concentration. We suggest that chlorpyrifos and cypermethrin are more potentially genotoxic than endosulfan and 2,4-D. Our findings also indicate that the only significant DNA damage between smokers and nonsmokers was observed in the 2,4-D-treated group.

DNA repair decline during mouse spermiogenesis results in the accumulation of heritable DNA damage

The postmeiotic phase of mouse spermatogenesis (spermiogenesis) is very sensitive to the genomic effects of environmental mutagens because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage. We hypothesized that repeated exposures to mutagens during this repair-deficient phase result in the accumulation of heritable genomic damage in mouse sperm that leads to chromosomal aberrations in zygotes after fertilization. We used a combination of single or fractionated exposures to diepoxybutane (DEB), a component of tobacco smoke, to investigate how differential DNA repair efficiencies during the 3 weeks of spermiogenesis affected the accumulation of DEB-induced heritable damage in early spermatids (21-15 days before fertilization (dbf)), late spermatids (14-8dbf) and sperm (7-1dbf). Analysis of chromosomal aberrations in zygotic metaphases using PAINT/DAPI showed that late spermatids and sperm are unable to repair DEB-induced DNA damage as demonstrated by significant increases (P<0.001) in the frequencies of zygotes with chromosomal aberrations. Comparisons between single and fractionated exposures suggested that the DNA repair-deficient window during late spermiogenesis may be less than 2 weeks in the mouse and that during this repair-deficient window there is accumulation of DNA damage in sperm. Finally, the dose-response study in sperm indicated a linear response for both single and repeated exposures. These findings show that the differential DNA repair capacity of postmeiotic male germ cells has a major impact on the risk of paternally transmitted heritable damage and suggest that chronic exposures that may occur in the weeks prior to fertilization because of occupational or lifestyle factors (i.e., smoking) can lead to an accumulation of genetic damage in sperm and result in heritable chromosomal aberrations of paternal origin.

Efficacy of a plant extract (Chelidonium majus L.) in combating induced hepatocarcinogenesis in mice

Ethanolic whole plant extract of Chelidonium majus, extensively used in traditional systems of medicine against various liver ailments, has been tested for its possible anti-tumor, hepato-protective and anti-genotoxic effects in p-dimethylaminoazobenzene (p-DAB) induced hepatocarcinogenesis in mice through multiple assays: cytogenetical, biochemical, histological and electron microscopical. Different sets of mice, 5 (for 7, 15 and 30 days' treatment) or 10 (for 60, 90 and 120 days) each, were chronically fed a diet suitably mixed with p-DAB and phenobarbital to develop liver tumors. One sub-group of carcinogen fed mice was also fed C. majus extract; 0.1 ml daily (drug-treated) while the other equal amount of dilute ethyl alcohol ("vehicle" of plant extract) (positive control). A separate group of mice was maintained with normal diet without any carcinogen treatment (negative control). Data of several cytogenetical endpoints and biochemical assay of some toxicity marker enzymes at all fixation intervals and histology of liver sections through ordinary, scanning and transmission electron microscopy at 60 and 120 days and that of spleen and kidney at 90 days were critically analyzed in the treated lots vis-a-vis controls. The results suggest anti-tumor, anti-genotoxic and hepato-protective effects of the plant extract, showing potentials for use in cancer therapy.

Binding of Sudan II and IV to lecithin liposomes and E. coli membranes: insights into the toxicity of hydrophobic azo dyes

Background

Sudan red compounds are hydrophobic azo dyes, still used as food additives in some countries. However, they have been shown to be unsafe, causing tumors in the liver and urinary bladder in rats. They have been classified as category 3 human carcinogens by the International Agency for Research on Cancer. A number of hypotheses that could explain the mechanism of carcinogenesis have been proposed for dyes similar to the Sudan red compounds. Traditionally, investigations of the membrane toxicity of organic substances have focused on hydrocarbons, e.g. polycyclic aromatic hydrocarbons (PAHs), and DDT. In contrast to hydrocarbons, Sudan red compounds contain azo and hydroxy groups, which can form hydrogen bonds with the polar head groups of membrane phospholipids. Thus, entry may be impeded. They could have different toxicities from other lipophilic hydrocarbons. The available data show that because these compounds are lipophilic, interactions with hydrophobic parts of the cell are important for their toxicity. Lipophilic compounds accumulate in the membrane, causing expansion of the membrane surface area, inhibition of primary ion pumps and increased proton permeability.

Results

This work investigated the interactions of the amphiphilic compounds Sudan II and IV with lecithin liposomes and live Escherichia coli (E. coli). Sudan II and IV binding to lecithin liposomes and live E. coli corresponds to the Langmuir adsorption isotherm. In the Sudan red compounds – lecithin liposome solutions, the binding ratio of Sudan II to lecithin is 1/31 and that of Sudan IV to 1/314. The binding constant of the Sudan II-lecithin complex is 1.75 × 10⁴ and that of the Sudan IV-lecithin complex 2.92 × 10⁵. Besides, the influences of pH, electrolyte and temperature were investigated and analyzed quantitatively. In the Sudan red compounds – E.coli mixture, the binding ratios of Sudan II and Sudan IV to E.coli membrane phospholipid are 1/29 and 1/114. The binding constants of the Sudan II – and Sudan IV- E.coli membrane phospholipid complexes are 1.86 × 10⁴ and 6.02 × 10⁴. Over 60% of Sudan II and 75% of Sudan IV penetrated into E.coli, in which 90% of them remained in the E.coli membrane.

Conclusion

Experiments of Sudan II and IV binding to lecithin liposomes and live E. coli indicates that amphiphilic compounds may besequestered in thelecithin liposomes and membrane phospholipid bilayer according to the Langmuir adsorption law. Penetration into the cytosol was impeded and inhibited for Sudan red compounds. It is possible for such compounds themselves (excluding their metabolites and by-products)not result directly in terminal toxicity. Therefore, membrane toxicity could be manifested as membrane blocking and membrane expansion. The method established here may be useful for evaluating the interaction of toxins with membranes.

Assessment of hepatocellular damage and hematological alterations in mice chronically fed p-dimethyl aminoazobenzene and phenobarbital

Two sets of mice (Mus musculus) were chronically fed 0.06% p-dimethylaminoazobenzene (p-DAB) and 0.05% Phenobarbital (PB) for 90 and 120 days, respectively, and several cell biological and hematological parameters were studied against normal diet fed controls. The cell biological studies included: (i) matrix metalloproteinase (MMP) and reduced glutathione content (GSH), and (ii) ultra-structural changes in liver through scanning (SEM) and transmission (TEM) electron microscopies. Further, changes in some other parameters like blood glucose level, cholesterol and hemoglobin contents, serum cortisol concentration and rate of viability of lymphocytes were also recorded. The serum hormonal levels of estradiol and testosterone were also measured in view of the observation that mice subjected to chronic feeding of p-DAB and PB had dramatically reduced reproductive abilities. All results clearly indicated that the chronic feeding of the carcinogens induced considerable toxicity and palpable hepato-cellular injuries along with some other changes during the carcinogenetic process in liver.

SFTG international collaborative study on in vitro micronucleus test I. General conditions and overall conclusions of the study

This study, coordinated by the SFTG (French branch of European Environmental Mutagen Society), included 38 participants from Europe, Japan and America. Clastogens (bleomycin, urethane), including base and nucleoside analogs (5-fluorouracil and cytosine arabinoside), aneugens and/or polyploidy inducers (colchicine, diethylstilboestrol, griseofulvin and thiabendazole), as well as non-genotoxic compounds (mannitol and clofibrate), were tested. Four cell types were used, i.e. human lymphocytes in the presence of cytochalasin B and CHO, CHL and L5178Y cell lines, in the presence or absence of cytochalasin B, with various treatment-recovery schedules. Mitomycin C was used as a positive control for all cell types. Mannitol and clofibrate were consistently negative in all cell types and with all treatment-recovery conditions. Urethane, known to induce questionable clastogenicity, was not found as positive. Bleomycin and mitomycin C were found positive in all treatment-recovery conditions. The base and nucleoside analogs were less easy to detect, especially 5-fluorouracil due to the interference with cytotoxicity, while cytosine arabinoside was detected in all cell types depending on the treatment-recovery schedule. Aneugens (colchicine, diethylstilboestrol and griseofulvin) were all detected in all cell types. In this study, the optimal detection was ensured when a short treatment followed by a long recovery was associated with a long continuous treatment without recovery. There was no impact of the presence or absence of cytochalasin B on the detection of micronucleated cells on cell lines. Scoring micronucleated cells in both mononucleated and binucleated cells when using cytochalasin B was confirmed to be useful for the detection and the identification of aneugens. In conclusion, these results, together with previously published validation studies, provide a useful contribution to the optimisation of a study protocol for the detection of both clastogens and aneugens in the in vitro micronucleus test.

Cytotoxic and genotoxic effects of the azo-dye p-dimethylaminoazobenzene in mice: A time-course study

The cytotoxic and genotoxic effects of chronic feeding of the azo-dye p-dimethylaminoazobenzene (p-DAB) during 7, 15, 30, 60, 90 and 120 days have been assessed in mice. The endpoints used for genotoxic analysis were chromosome aberrations (CA), micronuclei (MN) and mitotic index (MI) in bone-marrow cells, and sperm-head abnormality (SHA) in male gonads. The activities of marker enzymes for toxicity, such as glutamate oxalo-acetate transaminase (GOT), glutamate pyruvate transaminase (GPT), acid phosphatase (ACP) and alkaline phosphatase (ALKP) were also assayed periodically, as was lipid peroxidation (LPO). Chronic feeding of p-DAB produced increased numbers of chromosome aberrations, nuclear anomalies and sperm-head abnormalities, as compared with normal untreated controls, generally in a time-dependent manner until 60 days, after which the anomalies persisted, but rather erratically. However, although there was some noticeable modulation in enzyme activities in the corresponding p-DAB-fed mice as well, these were not strictly time-dependent.

Genotoxicity test system based on p53R2 gene expression in human cells: examination with 80 chemicals

p53R2, which encodes a subunit of ribonucleotide reductase, is activated by DNA damage induced by gamma-ray and ultraviolet irradiation, and also by genotoxic chemicals such as adriamycin. For the purpose of constructing an easy-operating genotoxicity test system using human cell lines, we developed a p53R2-dependent luciferase reporter gene assay, and demonstrated dose-dependent luminescence caused by adriamycin in two human cell lines that express wild-type p53, MCF-7 and HepG2. The performance of this assay system was evaluated with 80 chemicals including those known in the Ames test as genotoxic or non-genotoxic. When the luciferase activity of cells treated with the test sample was over 200% to that of control cells in a dose-dependent increasing manner, the sample was judged positive as a genotoxic chemical. Forty of 43 Ames-positive chemicals induced luciferase activity in this assay system. Eight Ames-negative chemicals also induced luciferase activity. These eight chemicals are genotoxic in other in vitro test systems using mammalian cells. It is suggested that this assay system can be applied to rapid screening of chemicals for potential human genotoxicity.

Evaluation of the ability of a battery of three in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens I. Sensitivity, specificity and relative predictivity

The performance of a battery of three of the most commonly used in vitro genotoxicity tests--Ames+mouse lymphoma assay (MLA)+in vitro micronucleus (MN) or chromosomal aberrations (CA) test--has been evaluated for its ability to discriminate rodent carcinogens and non-carcinogens, from a large database of over 700 chemicals compiled from the CPDB ("Gold"), NTP, IARC and other publications. We re-evaluated many (113 MLA and 30 CA) previously published genotoxicity results in order to categorise the performance of these assays using the response categories we established. The sensitivity of the three-test battery was high. Of the 553 carcinogens for which there were valid genotoxicity data, 93% of the rodent carcinogens evaluated in at least one assay gave positive results in at least one of the three tests. Combinations of two and three test systems had greater sensitivity than individual tests resulting in sensitivities of around 90% or more, depending on test combination. Only 19 carcinogens (out of 206 tested in all three tests, considering CA and MN as alternatives) gave consistently negative results in a full three-test battery. Most were either carcinogenic via a non-genotoxic mechanism (liver enzyme inducers, peroxisome proliferators, hormonal carcinogens) considered not necessarily relevant for humans, or were extremely weak (presumed) genotoxic carcinogens (e.g. N-nitrosodiphenylamine). Two carcinogens (5-chloro-o-toluidine, 1,1,2,2-tetrachloroethane) may have a genotoxic element to their carcinogenicity and may have been expected to produce positive results somewhere in the battery. We identified 183 chemicals that were non-carcinogenic after testing in both male and female rats and mice. There were genotoxicity data on 177 of these. The specificity of the Ames test was reasonable (73.9%), but all mammalian cell tests had very low specificity (i.e. below 45%), and this declined to extremely low levels in combinations of two and three test systems. When all three tests were performed, 75-95% of non-carcinogens gave positive (i.e. false positive) results in at least one test in the battery. The extremely low specificity highlights the importance of understanding the mechanism by which genotoxicity may be induced (whether it is relevant for the whole animal or human) and using weight of evidence approaches to assess the carcinogenic risk from a positive genotoxicity signal. It also highlights deficiencies in the current prediction from and understanding of such in vitro results for the in vivo situation. It may even signal the need for either a reassessment of the conditions and criteria for positive results (cytotoxicity, solubility, etc.) or the development and use of a completely new set of in vitro tests (e.g. mutation in transgenic cell lines, systems with inherent metabolic activity avoiding the use of S9, measurement of genetic changes in more cancer-relevant genes or hotspots of genes, etc.). It was very difficult to assess the performance of the in vitro MN test, particularly in combination with other assays, because the published database for this assay is relatively small at this time. The specificity values for the in vitro MN assay may improve if data from a larger proportion of the known non-carcinogens becomes available, and a larger published database of results with the MN assay is urgently needed if this test is to be appreciated for regulatory use. However, specificity levels of <50% will still be unacceptable. Despite these issues, by adopting a relative predictivity (RP) measure (ratio of real:false results), it was possible to establish that positive results in all three tests indicate the chemical is greater than three times more likely to be a rodent carcinogen than a non-carcinogen. Likewise, negative results in all three tests indicate the chemical is greater than two times more likely to be a rodent non-carcinogen than a carcinogen. This RP measure is considered a useful tool for industry to assess the likelihood of a chemical possessing carcinogenic potential from batteries of positive or negative results.

Toxicological characteristics of endocrine-disrupting chemicals: developmental toxicity, carcinogenicity, and mutagenicity

It is generally accepted that endocrine-disrupting chemicals (EDCs) play a role in a variety of adverse health effects in an intact organism or its progeny as a consequence of changes in the endocrine system. Primary toxic effects of EDCs were reported to be related to infertility, reduction in sperm count, and teratogenicity, but other important toxic effects of EDCs such as carcinogenicity and mutagenicity have also been demonstrated. The aim of the present study was to systematically analyze the toxicological characteristics of EDCs in pesticides, industrial chemicals, and metals. A comprehensive literature survey on the 48 EDCs classified by the Centers for Disease Control and Prevention (CDC) was conducted using a number of databases which included Medline, Toxline, and Toxnet. The survey results revealed that toxicological characteristics of EDCs were shown to produce developmental toxicity (81%), carcinogenicity (79%, when positive in at least one animal species; 48%, when classified based on IARC evaluation), mutagenicity (79%), immunotoxicity (52%), and neurotoxicity (50%). Regarding the hormone-modulating effects of the 48 EDCs, estrogenic effects were the most predominant in pesticides, while effects on thyroid hormone were found for heavy metals. EDCs showing estrogen-modulating effects were closely related to carcinogenicity or mutagenicity with a high degree of sensitivity. Systematic information on the toxicological characteristics of the EDCs will be useful for future research directions on EDCs, the development of new screening methods, legal regulation, and for investigations of their mechanism of action.

Evaluation of genotoxicity of captan, maneb and zineb in the wing spot test of Drosophila melanogaster: role of nitrosation

The wing spot test in Drosophila melanogaster is a suitable system for the analysis of genotoxic activity of compounds that need metabolic transformation to render them active. We have analysed the genotoxicity of three fungicides for which it was reported that the metabolic processes taking place in vivo may determine their activity. The compounds analysed are captan, maneb, zineb and ethylenethiourea (ETU) (a metabolic derivative of ethylenebisdithiocarbamates like maneb and zineb). We have also evaluated the ability of ETU to form genotoxic derivatives in vivo analysing this compound in combined treatments with sodium nitrite. Both standard and high bioactivation NORR strains have been used. Captan, usually considered a mutagen in vitro but a non-mutagen in vivo, gave negative results in the wing spot test with both crosses. Positive results were obtained for maneb in the standard cross and for ETU in both the standard and the high bioactivation cross. The genotoxicities of maneb and ETU were higher when treatments were made on media in which nitrosation is favoured. A low absorption of the fungicide and an inefficient availability of the compound in the target may explain negative results obtained with zineb in both crosses. The results obtained in this study with the wing spot test demonstrate once again the suitability of this in vivo assay, in which absorption, distribution and metabolism processes take place, for the evaluation of genotoxicity of compounds to which humans are exposed.

Toxic effects of the herbicide 2,4-dichlorophenoxyacetic acid on lymphoid organs of the rat

We investigated the toxicity of the widely used herbicide dimethylammonium salt of 2,4-dichlorophenoxyacetic acid (DMA-2,4-D) on the lymphoid system of rats after a single dose oral administration using histological, cytochemical and molecular methods. DMA-2,4-D destroyed in a dose- and time-dependent manner the vascular integrity of the thymus and caused cell depletion in the white pulp of the spleen and in the cortex of the thymus, which was at least partly due to programmed cell death. DMA-2,4-D appeared to have hemolytic activity and caused intravascular hemolysis of erythrocytes. An increased hemosiderin content in macrophages of the spleen indicated phagocytosis of lysed erythrocytes. We conclude that acute DMA-2,4-D herbicide poisoning results in severe damage of the lymphatic organs thymus and spleen.

Microsomal deacetylation of ring-hydroxylated 2-(acetylamino)fluorene isomers: effect of ring position and molecular mechanics considerations

Metabolism of arylamides such as 2-(acetylamino)fluorene to mutagenic products is catalyzed by various liver microsomal and cytosolic enzymes. Deacylation is believed to be a deactivating pathway, and the activity of the microsomal deacetylase toward N-hydroxy-2-AAF is exceedingly greater than toward the parent 2-AAF. Another deactivating pathway is cytochrome P450-catalyzed ring hydroxylation. We have studied the effect of ring hydroxyl substitution on the activity of the liver microsomal deacetylase from Aroclor 1254-treated rats in vitro. The deacetylase activity was generally decreased toward ring-hydroxylated derivatives in the order of 2AAF approximately 1-OH-AAF > 3-OH-AAF > 7-OH-AAF > 5-OH-AAF approximately 9-OH-AAF. The difference in activity between 2-AAF and 5-OH- and 9-OH-AAF was about eightfold. Molecular mechanics calculations reveal that structural and geometrical parameters are more important than the energies associated with the different isomers. We show that the greater the distance of the hydroxyl group on the fluorenyl ring structure from the acetylamino group, the slower the rate of deacetylation. The difference in reactivity between the 1-hydroxy-2-AAF and the other hydroxy-2-AAF isomers is due to the lack of planarity of the 1-hydroxy isomer as compared to the essentially planar configuration of the other isomers. The relative contribution of microsomal ring hydroxylation and deacetylation to detoxification of arylamides remains to be established.

Genotoxicity testing of six insecticides in two crosses of the Drosophila wing spot test

Among the great variety of genotoxicity assays available, the wing spot test in Drosophila melanogaster has some characteristics that make it very suited for the screening of genotoxic activity, i.e., it is an easy and inexpensive assay using a eukaryotic organism in vivo. One of the most interesting characteristics of the assay is its capacity to detect genotoxic activity of promutagens without the necessity of an exogenous metabolic activation system. In this paper we present results obtained with a recently developed high bioactivation cross of the wing spot test (NORR cross). The positive results obtained with the five well-known procarcinogens 7, 12-dimethylbenz[a]anthracene, N-nitrosopyrrolidine, p-dimethylaminoazobenzene, diethylnitrosamine and urethane clearly show that the NORR strains are similar to the other high bioactivation strains previously described, but they lack their methodological disadvantages. We have tested six insecticides, which are characterised by having contradictory results in other genotoxicity tests, using both the standard and the high bioactivation (NORR) cross. The six insecticides analysed are the pyrethroid allethrin, the methylenedioxyphenolic compound piperonyl butoxide, the chlorinated hydrocarbons dieldrin and endrin, and the organophosphates dimethoate and malathion. We obtained negative results for all six compounds. Our results show the suitability of the wing spot test for the evaluation of compounds at the first level of genotoxicity testing.

Interactions between hormones and chemicals in breast cancer

Development of breast cancer in women is dependent on diverse factors, including genetic predisposition, exposure to both exogenous and endogenous chemicals, which can modulate initiation, promotion and progression of this disease, and the timing of exposure to these agents. Several compounds--including 16 alpha-hydroxyestrone (16 alpha-OHE1), catecholestrogens, and aromatic amines--have been proposed as initiators of mammary carcinogenesis in humans; however, their role as genotoxins is unconfirmed. Lifetime exposure to estrogens has been established as an important risk factor for breast cancer, and it has been suggested that xenoestrogens may directly add to the hormonal risk or indirectly increase risk by decreasing 2-hydroxyestrone (2-OHE1)/16 alpha-OHE1 metabolite ratios. Results of recent studies suggest that chemical-induced modulation of 2-OHE1/16 alpha-OHE1 metabolite ratios is not predictive of xenoestrogens or mammary carcinogens. Moreover, based on current known dietary intakes of natural and xenoestrogenic/antiestrogenic chemicals, it is unlikely that xenoestrogens contribute significantly to a woman's overall lifetime exposure to estrogens. More information is required on the identities and serum levels of both natural and xenoendocrine active compounds, their concentrations in serum, and the mammary gland and levels of these compounds at critical periods of exposure.

The L5178Y/tk+/- mouse lymphoma specific gene and chromosomal mutation assay a phase III report of the U.S. Environmental Protection Agency Gene-Tox Program

The L5178Y/tk+/- (-)3.7.2C mouse lymphoma assay (MLA) which detects mutations affecting the heterozygous thymidine kinase (tk) locus is capable of responding to chemicals acting as clastogens as well as point mutagens. Improvements in the assay to enhance detection of this spectrum of genetic events are summarized, and criteria for evaluating the data are defined. Using these criteria, the Phase III Work Group reviewed and evaluated literature containing MLA results published from 1976 through 1993. The data base included 602 chemicals of which 343 were evaluated as positive, 44 negative, 18 equivocal, 54 apparently inappropriate for evaluation in this test system with the published protocols, and 142 that were inadequately tested, and thus a definitive call could not be made. The overall performance of the assay is summarized by chemical class, and the outcome of testing 260 chemicals in the MLA is compared with Gene-Tox and National Toxicology Program evaluations of rodent carcinogenesis bioassay results for the same chemicals. Based on the Work Group's evaluation of published MLA data for chemicals that were considered adequately tested, it is concluded that for most chemicals the L5178Y/tk+/- mouse lymphoma assay is eminently well suited for genotoxicity testing and for predicting the potential for carcinogenicity.

Comparison of the standard and reduced pH Syrian hamster embryo (SHE) cell in vitro transformation assays in predicting the carcinogenic potential of chemicals

A comprehensive review of the Syrian Hamster Embryo (SHE) cell transformation literature was performed in order to catalogue the chemical/physical entities which have been evaluated for in vitro cell transformation potential. Both reduced pH (pH 6.7) and standard pH (pH 7.1-7.3) SHE cell testing protocols were considered. Based upon this analysis, over 472 individual chemical/physical agents and 182 combinations of chemical/physical agents have been tested under the standard pH conditions, while over 56 chemical/physical agents have been tested under reduced pH conditions. Of the 472 chemical/physical agents tested at the standard pH, 213 had in vivo carcinogenicity data available. Of these 213 chemical/physical agents, 177 were carcinogens while 36 were non-carcinogens. The results of testing the SHE transformability of these 213 chemical/physical agents indicates that the standard pH SHE cell transformation assay had a concordance of 80% (171/213), a sensitivity of 82% (146/177), and a specificity of 69% (25/36). Of these 213 chemical/physical agents, 53% (112/213) were tested more than once often in more than one laboratory, with a 82% (92/112) interlaboratory agreement rate, thus providing confirmatory results. Carcinogenicity data were available for 48 of the 56 chemical/physical agents tested for SHE cell transformation under the reduced pH conditions. The SHE cell transformation assay under reduced pH conditions had a concordance of 85% (41/48), a sensitivity of 87% (26/30), and a specificity of 83% (15/18). For Salmonella-negative carcinogens, the standard pH SHE assay correctly predicted carcinogenicity 75% (48/64) of the time while the reduced pH SHE assay correctly predicted carcinogenicity for Salmonella-negative carcinogens 78% (14/18) of the time. For chemical/physical agents tested under both the reduced pH and standard pH conditions, the standard pH and reduced pH SHE cell assays had a 69% (22/32) agreement rate. Under the reduced pH conditions, the SHE assay correctly predicted rodent carcinogenicity in 86% (25/29) of the chemicals tested under both reduced and standard pH conditions. Under standard pH conditions, the SHE assay correctly predicted rodent carcinogenicity in 69% (20/29) of the chemicals tested under both reduced and standard pH conditions. Collectively, these data indicate that the SHE cell transformation assay is predictive for rodent carcinogenicity under either reduced or standard pH conditions. Importantly, the assay displays better performance and appears to have improved carcinogen prediction capability under reduced pH conditions.

Validation of the SOS/umu test using test results of 486 chemicals and comparison with the Ames test and carcinogenicity data

The present study gives a comprehensive update of all umu genotoxicity assay results published so far. The available data of 486 chemicals investigated with the umu test are compared with the Ames test (274 compounds) as well as rodent carcinogenicity data (179 compounds). On the whole, there is good agreement between the umu test and the Ames test results, with a concordance of about 90%. The umu test was able to detect 86% of the Ames mutagens, while the Ames test (using at least 5 strains) detected 97% of the umu positive compounds. The elimination of TA102 from the set of Ames tester strains reduced the percentage of detectable umu genotoxins from 97 to 86%. The agreement between carcinogenesis and umu response was 65%, which is comparable to earlier studies concerning rodent carcinogenesis and Salmonella mutagenesis. The present compilation of umu results provides a database that can be used for the comparison of the SOS-inducing activity of chemicals and their mutagenicity, respectively, carcinogenicity. The results presented here clearly demonstrate that a chemical which induces the expression of the umu operon can be regarded a rodent carcinogen with a high degree of certainty (93%).

Induction of Cyp1a-1 and Cyp1a-2 gene expression by a reconstituted mixture of polynuclear aromatic hydrocarbons in B6C3F1 mice

The potential non-additive interactions of polynuclear aromatic hydrocarbon (PAH) mixtures as inducers of Cyp1a-1 and Cyp1a-2 gene expression were investigated in B6C3F1 mice using a reconstituted PAH mixture. The chemical composition (% by weight) of the reconstituted PAH mixture was: 2-ring PAHs--indan (0.22), naphthalene (23.8), 2-methylnaphthalene (23.2) and 1-methylnaphthalene (13.3); 3-ring PAHs--acenaphthylene (7.7), acenaphthene (0.6), dibenzofuran (0.7), fluorene (4.3), phenanthrene (10.5) and anthracene (3.4); > or = 4-ring PAHs--fluoranthene (2.4), pyrene (4.3), benz[a]anthracene (1.4), chrysene (1.5), benzo[b]fluoranthene (0.8), benzo[k]fluoranthene (0.9) and benzo[a]pyrene (0.9). The composition of the 2-, 3- and > or = 4-ring PAH fractions were based on the relative concentration of individual PAHs as noted above. The > or = 4-ring PAH fractions were based on the relative concentration of individual PAHs as noted above. The > or = 4-ring PAH fraction and reconstituted mixture induced hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity and Cyp1a-1 mRNA levels, whereas the 2- and 3-ring PAHs were only weakly active. Direct comparison of the potencies of the reconstituted mixture and > or = 4-ring PAHs showed that the Cyp1a-1 induction activity of the reconstituted mixture was due to the > or = 4-ring PAHs. The reconstituted PAH mixture and > or = 4-ring PAHs also induced Cyp1a-2 hepatic mRNA levels and microsomal methoxyresorufin O-deethylase (MROD) activity; however, their dose-response curves indicated that the reconstituted PAH mixture was more potent as a Cyp1a-2 inducer than the > or = 4 ring PAHs. The differences in potency were due to 3-ring PAHs which were found to be strong inducers of hepatic Cyp1a-2 mRNA levels and microsomal MROD activity at the lowest dose administered (37 mg/kg). The 3-ring mixture caused a maximal 29-fold increase in hepatic MROD activity at a dose of 292 mg/kg, but only 28% of maximal induction of EROD activity. Northern analysis of liver mRNA from mice treated with 3-ring PAHs showed that there was minimal induction of Cyp1a-1 mRNA levels. The 3-ring PAHs did not competitively bind to the mouse hepatic cytosolic aryl hydrocarbon (Ah) receptor suggesting that 3-ring PAHs are a new class of Cyp1a-2 inducers which do not act through the Ah receptor.

Mutagenicity and mutation spectra of 2-acetylaminofluorene at frameshift and base-substitution alleles in four DNA repair backgrounds of Salmonella

We used colony probe hybridization procedures to determine the mutations in approximately 600 revertants of the -1 frameshift allele hisD3052 and approximately 200 revertants of the base-substitution allele hisG46 of Salmonella typhimurium induced by 2-acetylaminofluorene (2-AAF) in the presence of Aroclor-induced rat liver S9. 2-AAF was primarily a frameshift mutagen, exhibiting 5 times more frameshift than base-substitution activity. The only frameshift mutation 2-AAF induced at the hisD3052 allele was a hotspot (-2) deletion within the sequence CGCGCGCG. The addition of the pKM101 plasmid had a small effect on the mutagenic potency of 2-AAF at this allele in a uvr+ background and no effect on the mutation spectra in either a uvr+ or uvr- background. The small amount of base-substitution activity exhibited by 2-AAF at the hisG46 allele required the presence of both the pKM101 plasmid and the uvrB mutation. The base substitutions were G.C-->T.A transversions (86%) and G.C-->A.T transitions (14%), and 85% of the substitutions were at the second position of the CCC target of the hisG46 allele; the remainder were at the first position. We propose that the hotspot frameshift may be initiated by N-acetyl-2-aminofluorene adducts located at the C(8) position of any of the guanines except the first one in the CGCGCGCG hotspot sequence. The mutation might then result from correct incorporation of cytosine opposite the adducted guanine, followed by a 2-base slippage according to our recently proposed correct-incorporation/slippage model. The hotspot mutation may also result from a 2-AAF-induced B- to Z-DNA transition at the repeating GpC site as well as by the action of enzymes involved in DNA metabolism, such as DNA resolvases or topoisomerases, on DNA structures that have been distorted by 2-AAF adducts. The small amount of 2-AAF-induced base-substitution activity may be due to mispairing of adenine opposite the minor aminofluorene adduct at the C(8) position of guanine.

Overview of mutation assays in transgenic mice for routine testing

There is scientific and regulatory interest in using mutation assays in transgenic mice in safety assessments for new chemicals and drugs. Currently these assays are in the process of being validated, and protocols for routine testing are being defined. Some of the issues and results to date with regard to assay validation include reproducibility of the assay results (they are qualitatively reproducible), relevance of the test system (the transgene closely approximates an endogenous mammalian gene as a mutational target for the limited number of compounds tested), and the predictivity of the assay for heritable effects (unknown at this time) or carcinogenicity (the assays show good positive predictivity for carcinogenicity; the negative predictivity of the assay requires further investigation). Definition of appropriate study protocols for routine testing requires that applicable statistical methods are available and that the experimental parameters that affect the detection of mutations are known. Progress made in identifying these parameters is discussed. A proposal is made for the custom design of routine safety studies, which is based on the anticipated use of each individual test agent. A working group has been formed to conduct some of the studies still required for validation of these assays.

Antischistosomal drugs: past, present ... and future?

The major antischistosomal drugs that have been or still are in use against infections with schistosomes are considered here together with some compounds that have not been in clinical use, but show interesting characteristics. Each individual compound presents aspects that may be enlightening about parasite biochemistry, parasite biology, and host-parasite relationships. Special attention is given to the mechanisms of action, an understanding of which is seen here as a major factor of progress in chemotherapy. Three compounds are currently in use, i.e., metrifonate, oxamniquine, and praziquantel, and all three are included in the World Health Organization list of essential drugs. They are analyzed in some detail, as each one presents advantages and disadvantages in antischistosomal therapy. The reported occurrence of drug-resistant schistosomes after treatment with oxamniquine and praziquantel suggests strict monitoring of such phenomena and encourages renewed efforts toward the development of multiple drugs against this human parasite.

The presence of KCl in the exposure medium strongly influences the mutagenicity of metabolites of polycyclic aromatic hydrocarbons in Escherichia coli

Previous studies demonstrated that the ion composition of the exposure medium may strongly influence the mutagenicity of many compounds in the liquid preincubation modification of the reversion assay with his- Salmonella typhimurium strains. Similar influences were now observed in the reversion assay with trp- Escherichia coli strain WP2 uvrA. The exposure medium was 8 mM sodium phosphate buffer (pH 7.4), containing no other ions or 125 mM KCl. Omission of KCl resulted in an about 10-fold enhancement of the mutagenic activity of 7-methylbenz[a]anthracene 5,6-oxide, but in a strong decrease in the mutagenicity of 1-hydroxymethylpyrene sulphate, close to the limit of detection. The findings with these two representative mutagens are very similar to those previously observed in S. typhimurium, suggesting that unobtrusive medium components may exert strong influences on the results with many test compounds in various bacterial test systems.

A recombination-based transgenic mouse system for genotoxicity testing

It is well established that mutagens induce recombination in cultured cells and experimental organisms. Presumably, this is a consequence of the DNA-damage-triggering cellular-repair mechanisms. The relationship between recombination and mutagenicity has been exploited in submammalian organisms, such as yeast, to assay the ability of chemical agents and radiation to induce a form of recombination called gene conversion--the non-reciprocal transfer of genetic information. This work has demonstrated the efficacy of predicting mutagenicity on the basis of recombination induction. Here, we describe the utilization of a transgenic mouse system for efficient detection of germ-line gene-conversion events as a mutagen-screening tool. These mice contain two mutually defective reporter (lacZ) genes under the regulatory control of a spermatogenesis-specific promoter. A particular intrachromosomal gene conversion event must occur for the generation of functional lacZ activity. Conversion events are visualized by histochemical staining or flow cytometric analysis of transgenic spermatids. The highly mutagenic compound chlorambucil induced a several fold percentage-wise increase of lacZ-positive spermatids, whereas acrylamide, a weak genotoxin, produced no marked increase in converted spermatids. The results indicate that recombination-based transgenic mouse models for genotoxin screening present a viable option for inexpensive and rapid whole-animal mutagen testing. The particular mice we describe may ultimately prove to be a useful tool for identifying agents which can cause heritable genetic mutations in humans.

Induction of adaptive response by nitrofurantoin against oxidative DNA damage in some bacterial cells

Pretreatment with a sublethal dose of nitrofurantoin did not give any protection to Vibrio cholerae OGAWA 154 (wild-type) cells against subsequent treatment with challenging doses of MNNG and vice versa. However, pretreatment with a sublethal dose of nitrofurantoin offered significant protection to the bacterial cells against subsequent treatment with challenging doses of H2O2 and vice versa. Further, sublethal doses of nitrofurantoin or H2O2 produced almost the same degree of protection against challenges by H2O2 or nitrofurantoin. Both the alkylating agent MNNG and the oxidative agent H2O2 induced adaptive responses in Vibrio cholerae OGAWA 154 cells against subsequent challenge by the respective agents. The experiments presented in this communication revealed that nitrofurantoin produced an adaptive response in bacterial cells against oxidative and not alkylating DNA damage.

Dose-response relationship for rat liver DNA damage caused by 49 rodent carcinogens

An experimental approach was taken to the question of dose-response curves for chemical carcinogenesis. DNA damage in female rat liver was chosen as the experimental parameter because all chemicals found to damage hepatic DNA were rodent carcinogens. The lowest dose causing DNA damage was determined for the 12 active chemicals (1,2-dibromoethane, 1,2-dibromo-3-chloropropane, 1,2-dichloroethane, 1,4-dioxane, methylene chloride, auramine O, Michler's ketone, selenium sulfide, 1,3-dichloropropene, 1,2-dimethylhydrazine, N-nitroso-piperidine and butylated hydroxytoluene). The resulting dose-response curves for rat hepatic DNA damage were plotted versus log of the molar dose (all activity was in five orders of magnitude) and versus percent of chemicals' oral rat LD50 (most of the activity was in only two orders of magnitude). Dose-response studies of the active chemicals were analyzed by regression methods. With the exception of butylated hydroxytoluene, the dose-response curves fit a linear model well (r2 = 0.886) and a quadratic model even better (r2 = 0.947). Based on experimental data from 11 DNA-damaging carcinogens (a dose range of 6 orders of magnitude), an equation and graph of the dose-response relationship of an 'average DNA-damaging carcinogen' is presented over the x-axis dose range of eight orders of magnitude.

An in vivo-in vitro replicative DNA synthesis (RDS) test using rat hepatocytes as an early prediction assay for nongenotoxic hepatocarcinogens screening of 22 known positives and 25 noncarcinogens

To evaluate the applicability of an in vivo-in vitro replicative DNA synthesis (RDS) test using rat hepatocytes, we conducted the RDS test with 22 nongenotoxic (Ames-negative) hepatocarcinogens and 25 noncarcinogens under our standardized conditions and judgement criteria. Compared to controls (RDS incidence of under 1.0%), the RDS test gave positive results for 18 hepatocarcinogens (positive sensitivity: 82%), and negative results for 20 noncarcinogens (negative specificity: 80%), and thus the overall concordance was 81%. These findings strongly suggest that the RDS test is an extremely useful method for early detection of nongenotoxic hepatocarcinogens.

Complementarity of genotoxic and nongenotoxic predictors of rodent carcinogenicity

Twenty-one chemicals carcinogenic in rodent bioassays were selected for study. The chemicals were administered by gavage in two dose levels to female Sprague-Dawley rats. The effects of these 21 chemicals on four biochemical assays [hepatic DNA damage by alkaline elution (DD), hepatic ornithine decarboxylase activity (ODC), serum alanine aminotransferase activity (ALT), and hepatic cytochrome P-450 content (P450)] were determined. Available data from seven cancer predictors published by others [the Ames test (AMES), mutation in Salmonella typhimurium TA 1537 (TA 1537), structural alerts (SA), mutation in mouse lymphoma cells (MOLY), chromosomal aberrations in Chinese hamster ovary cells (ABS), sister chromatid exchange in hamster ovary cells (SCE), and the ke test (ke)] were also compiled for these 21 chemical carcinogens plus 28 carcinogens and 62 noncarcinogens already published by our laboratory. From the resulting 111 (chemicals) by 11 (individual cancer predictors) data matrix, the five operational characteristics (sensitivity, specificity, positive predictivity, negative predictivity, and concordance) of each of the 11 individual cancer predictors (four biochemical parameters of this study and seven cancer predictors of others) are presented. Two examples of complementarity or synergy of composite cancer predictors were found. To obtain maximum concordance it was necessary to combine both genotoxic and nongenotoxic cancer predictors. The composite cancer predictor (DD or [ODC and P450] or [ODC and ALT]) had higher concordance than did any of the four individual cancer predictors from which it was constructed. Similarly, the composite cancer predictor (TA 1537 or DD or [ODC and P450] or [ODC and ALT]) had higher concordance than any of its five individual constituent cancer predictors. Complementarity or synergy has been demonstrated both 1) among genotoxic cancer predictors (DD and TA 1537) and 2) between nongenotoxic (ODC, P450, and ALT) and genotoxic cancer predictors (TA 1537 and DD).

Development and impact of the Gene-Tox-Program, genetic activity profiles, and their computerized data bases

This invited historical review traces the development and impact of two major data bases in the field of genetic toxicology. Discussed from a personal perspective are the Environmental Protection Agency (EPA) Gene-Tox Program and the EPA/International Agency for Research on Cancer Genetic Activity Profiles (GAPs) and their respective data bases. Whereas Gene-Tox was focused on the assessment of short-term tests and their role in predicting carcinogens and mutagens, GAPs and the GAP data base were designed specifically to aid in the evaluation of individual chemicals. Both data bases have been computerized. Gene-Tox is available on TOXNET and GAP is available in a personal computer format from the author. The Gene-Tox and GAP data bases appear to have had substantial impact, particularly on hazard identification activities in cancer risk assessment.

Chemical mutagenesis testing in Drosophila. X. Results of 70 coded chemicals tested for the National Toxicology Program

Seventy chemicals were tested for the ability to induce sex-linked recessive lethal (SLRL) mutations in postmeiotic and meiotic germ cells of male Drosophila melanogaster. As in the previous studies in this series, adult feeding was chosen as the first route of administration. If the compound failed to induce mutations by this route, injection exposure was used. Two chemicals, n-butane and propylene, were gaseous and therefore tested only by inhalation. One chemical (dimethylcarbamoyl chloride) was tested only by injection. Those chemicals that were mutagenic in the SLRL assay were further tested for the ability to induce reciprocal translocations. Sixteen of the 70 chemicals tested were mutagenic in the SLRL assay: 3-chloro-2-methylpropene, 3-(chloromethyl)pyridine HCl, dimethylcarbamoyl chloride, HC blue 1,3-iodo-1,2-propanediol, malaoxon, N,N'-methylene-bis-acrylamide, 4,4'-methylenedianiline 2HCl, ziram, cis-dichlorodiaminoplatinum II, 1,2-dibromoethane, dibromomannitol, 1,2-epoxypropane, glycidol, myleran, and toluene diisocyanate. The last seven also induced reciprocal translocations. A comparison of the results from the SLRL assay with other assays for mutagens and carcinogens suggests that the SLRL assay is highly specific, but poorly sensitive, both for mutagens and potential carcinogens.

Genotoxic potency in Drosophila melanogaster of selected aromatic amines and polycyclic aromatic hydrocarbons as assayed in the DNA repair test

Drosophila melanogaster stock consisting of meiotic recombination deficient (Rec-) double mutant mei-9a mei-41D5 males and Rec+ females was exposed at the larval stage to an aromatic amine or a polycyclic aromatic hydrocarbon. After emergence as adult flies, the males and the females were scored separately. When the treatment caused a dose-dependent reduction in the male to female ratio from the control level; the experiment was repeated with a larval stock consisting of Rec+ males and Rec+ females under comparable conditions. A preferential killing effect upon Rec- larvae was taken as evidence of DNA damaging effect of the test compound. Among 16 compounds tested, 1-AP, B(a)P, 2-AF, DAF, 4-AAF, 2-AAF, 1-AA, 2-AA, DMA, B(a)A and DMBA were registered as positive; Py and 3-MC were weakly positive; and B(e)P, Fluo and Ant were negative. The selective killing effects of the compounds in each of the pyrene, fluorene and anthracene series varied drastically as a function of structure in a way similar to that reported for the genotoxicity in Drosophila and the carcinogenicity in rodents. The Drosophila DNA repair assay will serve as a simple adjunct to the already available means for studying the genotoxic potency of aromatic amines and polycyclic aromatic hydrocarbons.

Predicting rodent carcinogenicity of Ames test false positives by in vivo biochemical parameters

28 chemicals known to be mutagenic in the Ames test but not carcinogenic in rodent bioassays were selected for study. The chemicals were administered by gavage in 2 dose levels to female Sprague-Dawley rats. The effects of these 28 chemicals on 4 biochemical assays (hepatic DNA damage by alkaline elution (DD), hepatic ornithine decarboxylase activity (ODC), serum alanine aminotransferase activity (ALT), and hepatic cytochrome P-450 content (P450)) were determined. The scientific approach taken was to either experimentally find individual cancer predictors of high specificity or to mathematically create composite predictors of high specificity. Composite predictive parameters are defined as follows: CP = [ODC and P450], CT = [ALT and ODC], and TS = [DD or CP or CT]. The specificity (percent of rodent noncarcinogens which test negative) of DD, ODC, ALT, P450, CP, CT and TS was 100%, 46%, 89%, 86%, 93%, 93% and 86%, respectively. For these 28 mutagenic noncarcinogens, the specificity of structural alerts (SA) 13%, mutation in mouse lymphoma cells (MOLY) 0%, chromosomal aberrations in Chinese hamster ovary cells (ABS) 13%, and sister-chromatid exchange in Chinese hamster ovary cells (SCE) 0% were much lower. The ke test, an experimental measure of electron attachment, had a specificity of 33%. DD was the only DNA related parameter to predict well the noncarcinogenic rodent bioassay result of Ames false-positive chemicals. 5 nongenotoxic parameters (ALT, P450, CP, CT and [CP or CT]) predicted the rodent bioassay result well. Depending on the prevalence of chemicals carcinogenic to humans, the problem of Ames test false positives for predicting human cancer may be either small or large.

Amphibian micronucleus test(s): a simple and reliable method for evaluating in vivo genotoxic effects of freshwater pollutants and radiations. Initial assessment

A micronucleus test was developed using larvae from two urodele amphibians (Pleurodeles waltl and Ambystoma mexicanum) and an anuran (Xenopus laevis). The methods for maintenance of adults, egg laying, and rearing the larvae are described, and the conditions required for optimal response are given for each of these species. The tests are carried out during a period of intense erythropoiesis when red blood cells are actively dividing in circulating blood. The micronuclei are observed on blood smears. The genotoxic effects of X-rays were evaluated at 12 different doses over a range of 6-1200 rad. All doses, even the very low dose of 6 rad, gave positive results. The test substances were added to the water in which the larvae were reared, and the results obtained after treatment for 12 days and/or 8 days with 47 different chemical compounds are listed. Detailed results are given as the lowest concentration producing a positive response or the highest concentration producing a negative response. The reliability of the test system using the newt is now well established, while the tests using the other two amphibian species are still under evaluation. Integration of this test in a test battery for quality control of water would aid the evaluation of risks to human health, as well as the protection of aquatic ecosystems.