H. Frank Stack

Evaluation of the genetic activity profiles of 65 pesticides

We have previously reported the qualitative results of a major study on 65 pesticides (Waters et al., 1982). Dose information from this investigation (either lowest effective or highest ineffective dose tested) has now been incorporated into a computerized data management system. This report focuses on the qualitative profiles of genetic activity produced by these pesticides and our efforts to classify them according to their genotoxic effects and chemical structures. Three main categories may be distinguished based on the qualitative results: Category 1 pesticides were active in most of the in vitro and in vivo assays employed. These 9 compounds include the structurally similar organophosphate insecticides, acephate, demeton, monocrotophos and trichlorfon; the phthalimide fungicide analogues, captan and folpet; and the thiocarbamate herbicide analogues, diallate, sulfallate and triallate. The 26 Category 2 compounds demonstrated fewer positive results and may be subdivided into two parts, one of which contains 12 halogenated aromatic or heterocyclic ring compounds, including the phenoxy herbicides, 2,4-D, 2,4-DB and 2,4,5-T. The remaining part of Category 2 (14 compounds) consists of structurally similar organophosphate insecticides, azinphos-methyl, crotoxyphos, disulfoton, methyl parathion; three similar ethylenebisdithiocarbamate fungicides, maneb, mancozeb, and zineb; three similar pyrethroid insecticides, allethrin, chrysanthemic acid, and ethyl chrysanthemate; and four structurally diverse compounds, cacodylic acid, dinoseb, sec.-butylamine and benomyl. The third category of 30 pesticides gave negative results in all tests and represents structurally diverse compounds. Using the computerized profile matching methodology, from 2080 possible pairwise chemical combinations of the 65 pesticides, 20 statistically significant pairs were selected, 6 groups of pesticides were identified which were substantially similar to groups of pesticides we had formed previously (Waters et al., 1982) based on genetic activity and chemical structure. The matches showed excellent qualitative and, in most cases, excellent quantitative agreement. Hence it appears that specific patterns of test results present in the genetic activity profiles are related directly to chemical structure. Conversely, the data suggests that certain groups of compounds may be recognized by a well defined series of concordant tests results. As additional data is added, comparison of test results for new chemicals with existing data for known genotoxicants should aid in the evaluation of potential genetic health hazards.

A survey of EPA/OPP and open literature on selected pesticide chemicals: II. Mutagenicity and carcinogenicity of selected chloroacetanilides and related compounds

With this effort, we continue our examination of data on selected pesticide chemicals and their related analogues that have been presented to the U.S. Environmental Protection Agencys (USEPAs) Office of Pesticide Programs (OPP). This report focuses on a group of selected chloroacetanilides and a few related compounds. As part of the registration process for pesticidal chemicals, interested parties (registrants) must submit toxicity information to support the registration including both mutagenicity and carcinogenicity data. Although this information is available to the public via Freedom of Information (FOI) requests to the OPP, publication in the scientific literature allows greater dissemination and examination of the data. For this Special Issue, graphic profiles have been prepared of the mutagenicity and carcinogenicity data available in the submissions to OPP. Also, a discussion is presented about how toxicity data are used to help establish tolerances (limits of pesticide residues in foods). The mutagenicity results submitted by registrants are supplemented by data on these chemicals from the open literature to provide a full perspective of their genetic toxicology. The group of chloroacetanilides reviewed here display a consistent pattern of mutagenic activity, probably mediated via metabolites. This mutagenic activity is a mechanistically plausible factor in the development of tumors seen in experimental animals exposed to this class of chemicals.

Use of computerized data listings and activity profiles of genetic and related effects in the review of 195 compounds

Computer-generated listings of data from short-term tests for genetic and related effects (activity profile listings) were prepared for 195 compounds that included for each compound, the test system (identified by a three-letter code word), qualitative results and the lowest effective dose (LED) or highest ineffective dose (HID) tested. A corresponding bar or line graph (activity profile) was also generated, in which test systems are displayed along the x-axis and the LED or HID values along the y-axis. The listings were reviewed and the data summarized by an IARC Working Group. The methodology used to generate these listings and plots is described, and results are given for one compound, benzene. The entire data base contains approximately 7000 entries from 4000 references.

Activity profiles of antimutagens: in vitro and in vivo data

In this review, retinol, chlorophyllin, and N-acetylcysteine are examined and compared with regard to their antimutagenic activity against some promutagens and a group of direct-acting alkylating agents. The promutagens included aflatoxin B1, certain polycyclic aromatic hydrocarbons (e.g., benzo[a]pyrene), and certain heterocyclic amines (e.g., food pyrolysates). Results of antimutagenicity testing selected from data surveyed in the published literature are displayed graphically as activity profiles of antimutagens showing both the doses tested and the extent of inhibition or enhancement of mutagenic activity. All three antimutagens are discussed in terms of their putative mechanisms of action in vitro and in vivo with emphasis on the xenobiotic metabolizing enzyme systems.

The utilization of the rabbit alveolar macrophage and Chinese hamster ovary cell for evaluation of the toxicity of particulate materials: I. Model compounds and metal-coated fly ash

Abstract Data are presented which detail the effects of model particulate compounds and fly ash particles on rabbit alveolar macrophage (RAM) and Chinese hamster ovary (CHO) cells. Silica, silicic acid, titanium dioxide, and size-fractionated (0–2, 2–5, and 5–8 μm) fly ash particles with and without coatings of nickel, lead, or cadmium oxides were the experimental particles. Silica was the most toxic particle studied. Cell viability and ATP in the RAM assay and colony survival in the CHO assay showed an almost identical response to silica and silicic acid. Titanium dioxide particles were relatively inert in the RAM and CHO systems, although a pronounced loss of ATP was observed in cells exposed in serum-free medium. Uncoated fly ash was relatively nontoxic in the RAM system when assayed by measurement of cell number and viability, ATP, and total protein. However, toxicity of the uncoated particles was demonstrated in the CHO clonal assay. The number of colonies formed at 1000 μg/ml particulate was reduced to 10.6, 28.5, and 82.2% of the control for the 0 to 2, 2 to 5-, and 5 to 8-μm size ranges. Nickel oxide-coated fly ash was more cytotoxic than the uncoated particles in both the RAM and CHO cell systems. Toxicity of NiO was similar to that obtained for the NiO-coated fly ash although the weight percentage of NiO in the ash was only 3%, suggesting that the particles enhanced toxicity. The lead oxide-coated fly ash was even more toxic than the nickel-coated particles; these particles were used to explore the effect of serum concentration on toxic responses. Cellular ATP was strongly affected in macrophages exposed in serum-free media and treated with PbO-coated fly ash; ATP ranged from 20 to 200 times less than that for the corresponding uncoated fly ash or untreated control. Nickel and lead did not dissociate from the fly ashes into the biological media. However, cadmium was rapidly released from the cadmium oxide-coated fly ash and provided an excellent model for study of the dissociation of toxic compounds from particle surfaces. The rate of dissociation of the metal was correlated with loss of ATP in RAM cultures. Cell numbers were unaltered after treatment with the CdO-coated fly ash as reported previously for soluble cadmium. The CdO-coated fly ash was considerably more toxic than would have been predicted on the basis of the amount of soluble cadmium released into the medium, also indicating that the association of the metal oxide with the fly ash enhanced toxicity.

A survey of EPA/OPP and open literature on selected pesticide chemicals. III. Mutagenicity and carcinogenicity of benomyl and carbendazim.

The known aneuploidogens, benomyl and its metabolite, carbendazim (methyl 2-benzimidazole carbamate (MBC)), were selected for the third in a series of ongoing projects with selected pesticides. Mutagenicity and carcinogenicity data submitted to the US Environmental Protection Agencys (US EPAs) Office of Pesticide Programs (OPP) as part of the registration process are examined along with data from the open literature. Mutagenicity and carcinogenicity profiles are developed to provide a complete overview and to determine whether an association can be made between benomyl- and MBC-induced mouse liver tumors and aneuploidy. Since aneuploidogens are considered to indirectly affect DNA, the framework adopted by the Agency for evaluating any mode of action (MOA) for carcinogenesis is applied to the benomyl/MBC data. Both agents displayed consistent, positive results for aneuploidy induction but mostly negative results for gene mutations. Non-linear dose responses were seen both in vitro and in vivo for aneuploidy endpoints. No evidence was found suggesting that an alternative MOA other than aneuploidy may be operative. The data show that by 14 days of benomyl treatment, events associated with liver toxicity appear to set in motion the sequence of actions that leads to neoplasms. Genetic changes (as indicated by spindle impairment leading to missegregation of chromosomes, micronucleus induction and subsequent aneuploidy in bone marrow cells) can commence within 1-24h after dosing, well within the time frame for early key events. Critical steps associated with frank tumor formation in the mouse liver include hepatotoxicity, increased liver weights, cell proliferation, hypertrophy, and other steps involving hepatocellular alteration and eventual progression to neoplasms. The analysis, however, reveals weaknesses in the data base for both agents (i.e. no studies on mouse tubulin binding, no in vivo assays of aneuploidy on the target tissue (liver), and no clear data on cell proliferation relative to dose response and time dependency). The deficiencies in defining the MOA for benomyl/MBC introduce uncertainties into the analysis; consequently, benomyl/MBC induction of aneuploidy cannot be definitively linked to mouse liver carcinogenicity at this time.

A review of the genetic and related effects of 1,3-butadiene in rodents and humans

In this paper, the metabolism and genetic toxicity of 1,3-butadiene (BD) and its oxidative metabolites in humans and rodents is reviewed with attention to newer data that have been published since the latest evaluation of BD by the International Agency for Research on Cancer (IARC). The oxidative metabolism of BD in mice, rats and humans is compared with emphasis on the major pathways leading to the reactive intermediates 1,2-epoxy-3-butene (EB), 1,2:3, 4-diepoxybutane (DEB), and 3,4-epoxy-1,2-butanediol (EBdiol). Results from recent studies of DNA and hemoglobin adducts indicate that EBdiol may play a more significant role in the toxicity of BD than previously thought. All three metabolites are capable of reacting with macromolecules, such as DNA and hemoglobin, and have been shown to induce a variety of genotoxic effects in mice and rats as well as in human cells in vitro. DEB is clearly the most potent of these genotoxins followed by EB, which in turn is more potent than EBdiol. Studies of mutations in lacI and lacZ mice and of the Hprt mutational spectrum in rodents and humans show that mutations at G:C base pairs are critical events in the mutagenicity of BD. In-depth analyses of the mutational spectra induced by BD and/or its oxidative metabolites should help to clarify which metabolite(s) are associated with specific mutations in each animal species and which mutational events contribute to BD-induced carcinogenicity. While the quantitative relationship between exposure to BD, its genotoxicity, and the induction of cancer in occupationally exposed humans remains to be fully established, there is sufficient data currently available to demonstrate that 1,3-butadiene is a probable human carcinogen.

A survey of EPA/OPP and open literature data on selected pesticide chemicals tested for mutagenicity. I: Introduction and first ten chemicals

Parties interested in registering a pesticide chemical with the U.S. Environmental Protection Agencys (USEPAs) Office of Pesticide Programs (OPP) must submit toxicity information to support the registration. Mutagenicity data are a part of the required information that must be submitted. This information is available to the public via Freedom of Information requests to the OPP. However, it is felt that this information would be more effectively and widely disseminated if presented in a published medium. Beginning with this publication, sets of mutagenicity data on pesticide chemicals will be periodically published in the Genetic Activity Profile (GAP) format. In addition, mutagenicity data extracted from the currently available open literature is also presented to provide a more complete database and to allow comparisons between the OPP-submitted data and other publicly available information.

Genetic activity profiles of anticancer drugs

The results from short-term tests for genetic and related effects, abstracted from the open literature for 36 anticancer drugs, are examined in this review. Data for 27 of these agents are available in the EPA/IARC Genetic Activity Profile (GAP) database. Data summaries, including data listings and activity profiles, are presented for nine anticancer drugs added to the GAP database for this analysis. Genetic toxicity data from the recent literature are included for the additional agents to provide a broader representation of the categories of drugs being evaluated. These categories, based on the chemical mode of action, are covalent and noncovalent DNA-binding drugs, topoisomerase II inhibitors, antimetabolites, mitotic spindle inhibitors, and drugs which affect endocrine function. The qualitative data for all 36 drugs are summarized in this report and findings are presented from pair-wise matching of genetic activity profiles, based on test results in common, for some chemical analogs. The significance of germ cell test results for some of these drugs and their implication in assessing risk of heritable genetic disease are discussed.

The genetic toxicology of putative nongenotoxic carcinogens

This report examines a group of putative nongenotoxic carcinogens that have been cited in the published literature. Using short-term test data from the U.S. Environmental Protection Agency/International Agency for Research on Cancer genetic activity profile (EPA/IARC GAP) database we have classified these agents on the basis of their mutagenicity emphasizing three genetic endpoints: gene mutation, chromosomal aberration and aneuploidy. On the basis of results of short-term tests for these effects, we have defined criteria for evidence of mutagenicity (and nonmutagenicity) and have applied these criteria in classifying the group of putative nongenotoxic carcinogens. The results from this evaluation based on the EPA/IARC GAP database are presented along with a summary of the short-term test data for each chemical and the relevant carcinogenicity results from the NTP, Gene-Tox and IARC databases. The data clearly demonstrate that many of the putative nongenotoxic carcinogens that have been adequately tested in short-term bioassays induce gene or chromosomal mutations or aneuploidy.