Quantitative predictivity of carcinogenicity of the autoradiographic repair test (primary hepatocyte cultures) for a group of 80 chemicals belonging to different chemical classes (original) (raw)
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Quantitative Correlation with Carcinogenic Potency of Different Short Term Tests
Toxicologic Pathology, 1984
The following short term parameters evaluating essentially genotoxic effects were considered: liver DNA alkaline fragmentation (DFI), morphological transformation in hamster embryo cells (TPI), and mutagenicity in the Ames’ test (MPI). The internal consistency of the carcinogenicity data (OPI) was rather high (r = 0.8). The correlation with OPI of DFI and MPI was statistically significant but rather modest, about 0.4-0.5. The best correlation between OPI and TPI was 0.65. This level of correlation was observed only when some kind of dose-response relationship for transformation could be established. When comparisons were attempted for exactly the same 27 compounds for all three tests, a general decrease in predictability was observed. This could be mainly due to problems of representation of the ideal population of chemicals using small samples. The more general problem of the quantitative approach to the predictability of short term tests was also discussed.
Mutation Research/Environmental Mutagenesis and Related Subjects, 1979
When suspensions of freshly isolated rat hepatocytes were exposed to a number of carcinogenic compounds, it was possible to measure an increased UDS by a rapid procedure via liquid-scintillation counting. For a number of carcinogenic compounds and some of their non,carcinogenic structural analogues a good correlation between the carcinogenic property and the ability to induce UDS was demonstrable. Out of 12 carcinogenic compounds, belonging to several different chemical classes, 10gave rise to an increased UDS, whereas only 2 compounds, the polycyclic aromatic hydrocarbons benzo[a]pyrene and benz[a]anthracene, did not. All 4 noncarcinogenic compounds tested were negative. Possibly this method can be of value as a routine screening test, in combination with other short-term test systems, thus improving the predictive value of screening in vitro with respect to carcinogenicity. There are promising results showing that measurement of DNA excision repair might be used as a method for detecting carcinogenic properties of
Mutagenic and carcinogenic potency indices and their correlation
Teratogenesis, Carcinogenesis, and Mutagenesis, 1990
We have analyzed a significant number of studies existing in the literature, in which the ability of different short-term tests for predicting carcinogenicity in rodents was investigated. We have separated these studies into two groups. In the better known group of studies, qualitative predictivity was investigated (sensitivity and specificity). In the second group of studies (analyzed in greater detail), positive results were examined for the correlation between carcinogenic potency and potency of response in a given short-term test. There is substantial agreement between qualitative and quantitative predictivity; both appear to be situated between a low and moderate level. We have analyzed the interesting possibility of using the quantitative approach not only for positive data but for combined positive and negative data as well. We have stressed that short-term tests of genotoxicity should be asked to predict only initiation and irreversible alterations in the genome and not to predict a combination of these events, including promotion and modulation of differentiation. Even with regard to only initiation, genotoxicity data should be related to comparative metabolism, as well as to considerations of the significance of different end points and structure-activity relationship data. In conclusion, the information coming from short-term tests of genotoxicity is probably useful but should be used in conjunction with other types of information and only for predicting one particular class of events in the entire process of carcinogenesis.
Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 2005
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.
Cancer research, 1982
Technical modifications of the quantitative determination of unscheduled DNA synthesis in cultured hepatocytes are described which allow for the rapid identification of potentially carcinogenic chemicals on a large-scale screening basis. The test is based on the biochemical quantification of [methyl-3H]thymidine incorporation into DNA in the presence of hydroxyurea following isolation of nuclei from hepatocytes treated with the agent under study. This procedure ("nuclei procedure") eliminates most of the background radioactivity which otherwise obscures the stimulation of DNA repair synthesis by agents that induce a relatively weak response. By combining the nuclei procedure with a double-labeling technique, test results can be obtained within a few hr after exposure of hepatocytes to the test agents. A test series involving 41 agents confirmed the reliability of the nuclei procedure for the assay of DNA repair synthesis. In addition, chemicals which had yielded conflictin...
Environmental Mutagenesis, 1981
The autoradiographic identification of unscheduled DNA synthesis (UDS) in primary cultures of adult rat hepatocytes (HPC) has been proposed as a predictive test for mutagens/carcinogens. To assess the predictive value of this test, results in the hepatocyte UDS assay were compared with data for bacterial mutagenicity using a modified Ames test. Over 200 compounds representing a variety of chemical classes consisting of procarcinogens, ultimate carcinogens, and noncarcinogens were tested in each system. The accurate discrimination of many carcinogens/noncarcinogens was demonstrated by both systems. The induction of UDS in hepatocytes showed an excellent correlation with bacterial mutagenesis in response to polycyclic aromatic hydrocarbons, aromatic amines, biphenyls, nitrosamines, carbamates, azo‐compounds, acridines, halogenated compounds, nitrosureas, quinolines, pyridines, purines, pyrimidines, esters and carbamates. Nitrocompounds, although active in bacteria, were poor inducers ...
Food and Chemical Toxicology, 1986
The interdisciplinary evaluation of risks from carcinogens utilizes, inter alia, data on the activities of the compounds in short-term assays. A systematic approach is being used to determine (a) mutagenesis in bacteria (the study of direct activities and specific modes of metabolic activation), (b) DNA damage within primary mammalian cells (DNA single-strand breaks and persistence of damage, by a method extendable to the in vivo situation) and (c) amplified DNA sequences in cultured cells (as an endpoint probably relevant to carcinogenesis). This test combination was expected to reduce some of the shortcomings of other batteries of tests, which suffer from a lack of appropriate metabolic conversion of compounds, irrelevancy of genetic endpoints and pharmacokinetic limitations. Furthermore, as each assay in the test strategy differs from the others only by one of the parameters described above, a reasonable understanding of divergent test results from assay to assay was anticipated. Several substances were investigated to elucidate why their activities in short-term assays and in carcinogenesis experiments do not correlate. The substances were N-nitrodimethylamine, for which formaldehyde is the reactive intermediate in bacterial mutagenesis but not in mammalian cells or in vivo, N-nitrosodiethanolamine, a carcinogen that must be activated by external alcohol dehydrogenase to be mutagenic in bacteria, N-nitrosodialkylamines, with unique organotropism in vivo for which organ-specific activation was studied in vitro, N-nitroso compounds that are inactivated in vivo but not in vitro, and components of the aristolocbic acid mixture which may be metabolized oxidatively or reductively, as well as numerous miscellaneous compounds that were expected to be genotoxins on account of their chemical structure. In addition to the assessment of genotoxicity, the results obtained in individual tests of this strategy yield important data on mechanisms of activity, such as organ-specific activation and deactivation, species variations, in vitro~in vivo correlation and persistence or repair of damage.
Mutagenesis
Genotoxicity testing is an important part of standard safety testing strategies. Animal studies have always been a key component, either as a mandatory part of the regulatory test battery, or to follow-up questionable in vitro findings. The strengths and weaknesses of in vivo assays is a continuous matter of debate, including their capacity to predict (human) carcinogenicity. We have therefore analysed the sensitivity of five routinely used in vivo tests to determine, in addition to other aspects, which tests or combination of tests best identify 73 chemicals classified as IARC Group 1 and 2A carcinogens. The in vivo tests included the micronucleus (MN), unscheduled DNA synthesis (UDS), comet, Pig-a and transgenic rodent assays (TGR). The individual assays detect 74.2% (49/66, MN), 64.3% (9/14, UDS), 92.1% (35/38, comet), 82.4% (14/17, Pig-a) and 90.3% (28/31, TGR) of the probable and confirmed human carcinogens that were tested in these assays. Combining assays that cover different genotoxicity endpoints and multiple tissues, e.g. the bone marrow MN and the liver comet assays, increases the sensitivity further (to 94%). Correlations in terms of organ-specificity for these assays with human cancer target organs revealed only a limited correlation for the hematopoietic system but not for other organs. The data supports the use of the comet and TGR assays for detection of 'site-of-first-contact' genotoxicants, but these chemicals were generally also detected in assays that measure genotoxicity in tissues not directly exposed, e.g. liver and the hematopoietic system. In conclusion, our evaluation confirmed a high sensitivity of the five in vivo genotoxicity assays for prediction of human carcinogens, which can be further increased by combining assays. Moreover, the addition of the comet to the in vivo MN test would identify all DNA reactive human carcinogens. Importantly, integration of some of the study readouts into one experiment is an animal-saving alternative to performing separate experiments.
Data selection and treatment of chemicals tested for genotoxicity and carcinogenicity
Environmental Health Perspectives, 1991
A datbase contaning q live and qu e Of Arlmenl in tbe fikofgenniy and carcinogenicity has boee deped. By a zg resultofthesde performed by the U.& Natonullsckgy Program, or by a simia program develped inapn, orrepretdinthesentc l e, amsull perfmonedbg priat oag dons, Infomation has bo e d reling o3389 chmcls, Ideried by their CAS number. Th studies consdered for the database Indude three gnotkicty/mug dty short-term test (STl), namely, twoin Wtv (Samonella, gene muation amy, andmu mmaliacelsh/man cy roosome abe r amy) and onein Wvo, the rodent bone murew moceuns asy. lb ipte the pome value ofthoe SIT a forr n the rut ofannalllong-term ayse so beencolected. V* hae re-evauatedan the genety sesand the majorityofthose casestudied In diferent labotoris con resultshasbeen resolved; a pro orn questionable cases is, however, stil present in the da e. In total, 289 (85S%) of the che ahave been tested in the Salmonella amy; 399(413%) have beept In the in vit caberdon amy; 319 (9A%) hae been tested in the in Wwo rodent bon nawel mi rmkclensI ay; 71 (2L2%) ofthechenulcaw b haeenested In theix Wso Ianial long-term biosy. For 1lll ch as tested in the Salmn a , 30,650 qustudies have been Included in the d thus alowing a possble la n ofmut i ding tother mutagenic potency. One thousn nnebnddchb (5.1%) vesbown positive rnts hi at leone ofthe four d ass, thus leaving 1$89 chemical (43.9%) with neptive result By ng the oat between gsy,siown by the thrme STIs condered, and n w have demonstrated that the podtive peitivity nreas to a value of 95.6% if the three ST1b are conidered together (two Ui itrv and oneix wvoSTIT); sibmiry, the negAive p reichtivity risestoavalueof89.6% with the sam three assys. The accuracy, or the dance, of the SIT sand the cacin_!-t resuts was92.5% for the three SM Abough the results colected are of high interest for sdentific and practil actons, the aim of the present study is to prepare a genotoodcity/cardnogenicity database for a further quantitat scture-activity relationship (QSAR) study based on a computer cbemistry analysis.