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Strupp C, Corvaro M, Cohen SM, Corton JC, Ogawa K, Richert L, Jacobs MN. Increased Cell Proliferation as a Key Event in Chemical Carcinogenesis: Application in an Integrated Approach for the Testing and Assessment of Non-Genotoxic Carcinogenesis. Int J Mol Sci 2023; 24:13246. [PMID: 37686053 PMCID: PMC10488128 DOI: 10.3390/ijms241713246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Revised: 08/17/2023] [Accepted: 08/24/2023] [Indexed: 09/10/2023] Open
Abstract
In contrast to genotoxic carcinogens, there are currently no internationally agreed upon regulatory tools for identifying non-genotoxic carcinogens of human relevance. The rodent cancer bioassay is only used in certain regulatory sectors and is criticized for its limited predictive power for human cancer risk. Cancer is due to genetic errors occurring in single cells. The risk of cancer is higher when there is an increase in the number of errors per replication (genotoxic agents) or in the number of replications (cell proliferation-inducing agents). The default regulatory approach for genotoxic agents whereby no threshold is set is reasonably conservative. However, non-genotoxic carcinogens cannot be regulated in the same way since increased cell proliferation has a clear threshold. An integrated approach for the testing and assessment (IATA) of non-genotoxic carcinogens is under development at the OECD, considering learnings from the regulatory assessment of data-rich substances such as agrochemicals. The aim is to achieve an endorsed IATA that predicts human cancer better than the rodent cancer bioassay, using methodologies that equally or better protect human health and are superior from the view of animal welfare/efficiency. This paper describes the technical opportunities available to assess cell proliferation as the central gateway of an IATA for non-genotoxic carcinogenicity.
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Affiliation(s)
| | | | - Samuel M. Cohen
- Department of Pathology and Microbiology and Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - J. Christopher Corton
- Center for Computational Toxicology and Exposure, United States Environmental Protection Agency (US EPA), Research Triangle Park, NC 27711, USA;
| | - Kumiko Ogawa
- Division of Pathology, National Institute of Health Sciences, Kawasaki 210-9501, Japan
| | | | - Miriam N. Jacobs
- United Kingdom Health Security Agency (UK HSA), Radiation, Chemicals and Environmental Hazards, Harwell Innovation Campus, Dicot OX11 0RQ, UK
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Cohen SM. Screening for human urinary bladder carcinogens: two-year bioassay is unnecessary. Toxicol Res (Camb) 2018; 7:565-575. [PMID: 30090607 PMCID: PMC6061447 DOI: 10.1039/c7tx00294g] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Accepted: 01/22/2018] [Indexed: 11/21/2022] Open
Abstract
Screening for carcinogens in general, and for the urinary bladder specifically, traditionally involves a two-year bioassay in rodents, the results of which often do not have direct relevance to humans with respect to mode of action (MOA) and/or dose response. My proposal describes a multi-step short-term (90 day) screening process that characterizes known human urinary bladder carcinogens, and identifies those reported in rodent two-year bioassays. The initial step is screening for urothelial proliferation, by microscopy or by increased Ki-67 labeling index. If these are negative, the agent is not a urinary bladder carcinogen. If either of these is positive, an MOA and dose response analysis are performed. DNA reactivity is evaluated. If the chemical is non-DNA reactive, evaluation for cytotoxicity is performed. This involves examination of the urothelium and urine, the latter to identify the generation of urinary solids (e.g. calculi). If urinary solids are the cause of cytotoxicity, the MOA is not relevant to human cancer, but dose response becomes essential for evaluating potential toxicity to humans. If cytotoxicity occurs but no urinary solids are detected, urinary concentrations of the chemical and its metabolites are evaluated, and compared to in vitro cytotoxicity against rodent and human immortalized urothelial cell lines. Based on this process, a screen for urinary bladder carcinogenicity is reliable, and more importantly, can be based on MOA and dose response analyses useful in the overall risk assessment for possible human bladder cancer. The proposed procedure is shorter, less expensive and more relevant than the two-year bioassay.
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Affiliation(s)
- Samuel M Cohen
- Havlik-Wall Professor of Oncology , Department of Pathology and Microbiology , University of Nebraska Medical Center , Omaha , NE 68198-3135 , USA .
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Schrenk D. What is the meaning of 'A compound is carcinogenic'? Toxicol Rep 2018; 5:504-511. [PMID: 29854622 PMCID: PMC5977538 DOI: 10.1016/j.toxrep.2018.04.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 03/14/2018] [Accepted: 04/06/2018] [Indexed: 01/08/2023] Open
Abstract
Chemical Carcinogens are compounds which can cause cancer in humans and experimental animals. This property is attributed to many chemicals in the public discussion, resulting in a widespread perception of danger and threat. In contrast, a scientific analysis of the wide and non-critical use of the term 'carcinogenic' is warranted. First, it has to be clarified if the compound acts in a genotoxic or non-genotoxic manner. In the latter case, an ineffective (safe) threshold dose without cancer risk can be assumed. In addition, it needs to be investigated if the mode-of-action causing tumors in laboratory animals is relevant at all for humans. In case the compound is clearly directly genotoxic, an ineffective threshold dose cannot be assumed. However, also in this case it is evident that high doses of the compound are generally associated with a high cancer risk, low doses with a lower one. Based on dose-response data from animal experiments, quantification of the cancer risk is carried out by mathematical modeling. If the safety margin between the lowest carcinogenic dose in animals and the relevant level of exposure in humans exceeds 10,000, the degree of concern is classified as low. Cases, where the compound turns out to be genotoxic in one study or one test only but not in others or only in vitro but not in vivo, are particularly difficult to explain and cause controversial discussions. Also for indirectly genotoxic agents, an ineffective (threshold) dose must be assumed. The situation is aggravated by the use of doubtful epidemiological studies in humans such as in the case of glyphosate, where data from mixed exposure to various chemicals were used. If such considerations are mixed with pure hazard classifications such as 'probably carcinogenic in humans' ignoring dose-response behavior and mode-of-action, the misinformation and public confusion are complete. It appears more urgent but also more difficult than ever to return to a scientifically based perception of these issues.
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Abstract
The sequencing of the human and mouse genomes, and soon that of the rat, offers a foundation to evaluate biological phenomena, including toxicologic effects. Numerous tools are being developed to evaluate aspects of biology based on the DNA sequence. These tools can be utilized to evaluate absorption, distribution, metabolism and excretion, and effects of the toxicologically active product on the target organ. The genes involved can be broadly categorized as those affecting susceptibility to a toxicologic effect and those that are involved in the biologic response. For risk assessment to be performed in a rational manner, fundamental mechanisms of toxicologic processes must be ascertained. Based on successes already achieved, such as development of transgenic and knockout mouse strains, the application of aspects of the genomics revolution could be useful in developing a better understanding of mechanisms, and possibly in identifying specific markers of responses. In addition, genomics are likely to be useful in translating effects between species. However, genomics are being portrayed as the ultimate solution to all of toxicology. This is hardly the case. Basic chemistry, biochemistry, toxicokinetics, pharmacology, and pathology will continue to be needed in the overall weight of evidence approach to risk assessment. Genomics are likely to be of limited usefulness in predicting individual, in contrast to population susceptibility to various toxicological responses. Concordance of various diseases in identical twins, for example, different cancers, is rarely greater than 20% over the lifetime of these individuals. Similarly, genomics are likely to be of limited usefulness in screening for toxicologic end points. As with other tools of biology, those to be developed based on the genome are likely to provide greater usefulness in dissecting the mechanistic processes involved and defining the basis for susceptibility.
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Affiliation(s)
- Samuel M Cohen
- Department of Pathology and Microbiology and the Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, Nebraska 68198-3135, USA.
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Cohen SM, Arnold LL. Critical role of toxicologic pathology in a short-term screen for carcinogenicity. J Toxicol Pathol 2016; 29:215-227. [PMID: 27821906 PMCID: PMC5097964 DOI: 10.1293/tox.2016-0036] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2016] [Accepted: 05/09/2016] [Indexed: 12/28/2022] Open
Abstract
Carcinogenic potential of chemicals is currently evaluated using a two year bioassay in rodents. Numerous difficulties are known for this assay, most notably, the lack of information regarding detailed dose response and human relevance of any positive findings. A screen for carcinogenic activity has been proposed based on a 90 day screening assay. Chemicals are first evaluated for proliferative activity in various tissues. If negative, lack of carcinogenic activity can be concluded. If positive, additional evaluation for DNA reactivity, immunosuppression, and estrogenic activity are evaluated. If these are negative, additional efforts are made to determine specific modes of action in the animal model, with a detailed evaluation of the potential relevance to humans. Applications of this approach are presented for liver and urinary bladder. Toxicologic pathology is critical for all of these evaluations, including a detailed histopathologic evaluation of the 90 day assay, immunohistochemical analyses for labeling index, and involvement in a detailed mode of action analysis. Additionally, the toxicologic pathologist needs to be involved with molecular evaluations and evaluations of new molecularly developed animal models. The toxicologic pathologist is uniquely qualified to provide the expertise needed for these evaluations.
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Affiliation(s)
- Samuel M. Cohen
- Department of Pathology and Microbiology, University of Nebraska Medical Center, 983135 Omaha, NE 68198-3135, USA
| | - Lora L. Arnold
- Department of Pathology and Microbiology, University of Nebraska Medical Center, 983135 Omaha, NE 68198-3135, USA
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Dodmane PR, Arnold LL, Pennington KL, Cohen SM. Orally administered nicotine induces urothelial hyperplasia in rats and mice. Toxicology 2013; 315:49-54. [PMID: 24269753 DOI: 10.1016/j.tox.2013.11.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Revised: 10/30/2013] [Accepted: 11/07/2013] [Indexed: 12/31/2022]
Abstract
Tobacco smoking is a major risk factor for multiple human cancers including urinary bladder carcinoma. Tobacco smoke is a complex mixture containing chemicals that are known carcinogens in humans and/or animals. Aromatic amines a major class of DNA-reactive carcinogens in cigarette smoke, are not present at sufficiently high levels to fully explain the incidence of bladder cancer in cigarette smokers. Other agents in tobacco smoke could be excreted in urine and enhance the carcinogenic process by increasing urothelial cell proliferation. Nicotine is one such major component, as it has been shown to induce cell proliferation in multiple cell types in vitro. However, in vivo evidence specifically for the urothelium is lacking. We previously showed that cigarette smoke induces increased urothelial cell proliferation in mice. In the present study, urothelial proliferative and cytotoxic effects were examined after nicotine treatment in mice and rats. Nicotine hydrogen tartrate was administered in drinking water to rats (52 ppm nicotine) and mice (514 ppm nicotine) for 4 weeks and urothelial changes were evaluated. Histopathologically, 7/10 rats and 4/10 mice showed simple hyperplasia following nicotine treatment compared to none in the controls. Rats had an increased mean BrdU labeling index compared to controls, although it was not statistically significantly elevated in either species. Scanning electron microscopic visualization of the urothelium did not reveal significant cytotoxicity. These findings suggest that oral nicotine administration induced urothelial hyperplasia (increased cell proliferation), possibly due to a mitogenic effect of nicotine and/or its metabolites.
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Affiliation(s)
- Puttappa R Dodmane
- Department of Pathology and Microbiology, University of Nebraska Medical Center, 983135 Nebraska Medical Center, Omaha, NE 68198-3135, USA.
| | - Lora L Arnold
- Department of Pathology and Microbiology, University of Nebraska Medical Center, 983135 Nebraska Medical Center, Omaha, NE 68198-3135, USA.
| | - Karen L Pennington
- Department of Pathology and Microbiology, University of Nebraska Medical Center, 983135 Nebraska Medical Center, Omaha, NE 68198-3135, USA.
| | - Samuel M Cohen
- Department of Pathology and Microbiology, University of Nebraska Medical Center, 983135 Nebraska Medical Center, Omaha, NE 68198-3135, USA; Havlik-Wall Professor of Oncology.
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Cohen SM. Urinary Bladder Carcinogenesis by DNA Reactive and Non-Reactive Chemicals: Non-Linearities and Thresholds. Genes Environ 2012. [DOI: 10.3123/jemsge.34.165] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Abstract
Understanding the relationship of chemicals to carcinogenesis has progressed significantly since the initial observations of Hill and Pott in the 1700's. Distinguishing between DNA-reactive chemicals and those which increase cancer risk by increasing cell proliferation has been a major breakthrough in delineating overall mechanisms. Competing processes for activation versus inactivation of chemicals occur at many levels, including metabolism, DNA repair, and cellular repair processes. These processes can be affected by other agents to decrease carcinogenesis (chemoprevention). Increasing knowledge of the multiple steps of carcinogenesis is leading to improved methods for screening chemicals for carcinogenic activity and for regulatory decision making. Improvements in assessment of modes of action involved in animal and in vitro models have led to more rational approaches to assessing relevance to humans. The advent of genomics and high-throughput technologies have contributed to investigations of mechanisms and is beginning to impact development of better methods for screening chemicals. Based on developments in basic research, epidemiology, and astute clinical observations, the major risk factors and etiologic agents have been identified for a majority of cancers, which is beginning to lead to methods to decrease cancer incidence overall and identify targets for early detection and treatment.
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Affiliation(s)
- Samuel M Cohen
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-3135, USA.
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Harding C, Pompei F, Wilson R. Corrections to: ‘‘Age distribution of cancer in mice’’. Toxicol Ind Health 2010; 27:265-70. [DOI: 10.1177/0748233710386410] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
We found a crucial error in an earlier paper on cancer in elderly mice, Age distribution of cancer in mice: the incidence turnover at old age (Pompei et al., 2001). That paper’s principal data set, the ED01 records, was scrambled when read and analyzed with a statistical software package. Having done our best to correct the error, and having subjected the data to a more exact extension of originally published methods, we arrive at conclusions significantly different from those proposed in the original article. What appeared to be a dramatic fall off of the cancer mortality rate in mice over 2 years of age is now found to be a continuation or flattening of approximately exponential growth. This new finding is entirely at odds with the old, and does not support our later work on humans. Two of this paper’s authors, F Pompei and R Wilson, contributed to the original article. We are informing authors who have cited our paper in the past and apologize deeply for any wasted time or lost work. We should have subjected the ED01 records to more error checks. We thank Jennifer Blank for helping us discover and correct this error. The ED01 records and our earlier research are available http://physics.harvard.edu/∼wilson/cancer&chemicals/ED01.
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Affiliation(s)
- Charles Harding
- Department of Physics, Harvard University, Jefferson Laboratories, Cambridge, MA 02138, USA
| | - Francesco Pompei
- Department of Physics, Harvard University, Jefferson Laboratories, Cambridge, MA 02138, USA,
| | - Richard Wilson
- Department of Physics, Harvard University, Jefferson Laboratories, Cambridge, MA 02138, USA
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Cohen SM. Evaluation of Possible Carcinogenic Risk to Humans Based on Liver Tumors in Rodent Assays. Toxicol Pathol 2010; 38:487-501. [DOI: 10.1177/0192623310363813] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The two-year rodent bioassay remains the mainstay for carcinogenicity testing, although numerous difficulties have been identified. Fundamentally, a chemical can increase the risk of cancer (1) by damaging DNA directly (DNA reactive) or (2) indirectly by increasing the number of DNA replications (non–DNA reactive). Mechanistic research has identified numerous precursor lesions in the sequence of key events necessary for neoplasia development. Based on these concepts, the author has proposed a short-term (thirteen-week) assay for screening for carcinogenic potential based on a mode of action analysis and on readily available, identifiable preneoplastic changes. A screening assay that detects all potential rodent hepatocarcinogens has been previously identified ( Toxicol Pathol32 [2004], 393–401) including increased liver weight, hepatocellular necrosis, hypertrophy, and cytomegaly. Labeling index for DNA replication might supply additional support. These markers have high sensitivity but low specificity. However, most chemicals can be appropriately classified as to their mode(s) of action for hepatocarcinogenesis with follow-up mechanistic studies, and a rational evaluation of their relevance to humans can be made. A similar process can be envisioned for other tissues for evaluation for carcinogenic potential.
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Affiliation(s)
- Samuel M. Cohen
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE
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de Moura NA, Grassi TF, Rodrigues MAM, Barbisan LF. Potential effects of the herbicide Diuron on mammary and urinary bladder two-stage carcinogenesis in a female Swiss mouse model. Arch Toxicol 2009; 84:165-73. [DOI: 10.1007/s00204-009-0477-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Accepted: 10/08/2009] [Indexed: 11/29/2022]
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Cohen SM, Boobis AR, Meek MEB, Preston RJ, McGregor DB. 4-Aminobiphenyl and DNA Reactivity: Case Study Within the Context of the 2006 IPCS Human Relevance Framework for Analysis of a Cancer Mode of Action for Humans. Crit Rev Toxicol 2008; 36:803-19. [PMID: 17118730 DOI: 10.1080/10408440600977651] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The IPCS Human Relevance Framework was evaluated for a DNA-reactive (genotoxic) carcinogen, 4-aminobiphenyl, based on a wealth of data in animals and humans. The mode of action involves metabolic activation by N-hydroxylation, followed by N-esterification leading to the formation of a reactive electrophile, which binds covalently to DNA, principally to deoxyguanosine, leading to an increased rate of DNA mutations and ultimately to the development of cancer. In humans and dogs, the urinary bladder urothelium is the target organ, whereas in mice it is the bladder and liver; in other species, other tissues can be involved. Differences in organ specificity are thought to be due to differences in metabolic activation versus inactivation. Based on qualitative and quantitative considerations, the mode of action is possible in humans. Other biological processes, such as toxicity and regenerative proliferation, can significantly influence the dose response of 4-aminobiphenyl-induced tumors. Based on the IPCS Human Relevance Framework, 4-aminobiphenyl would be predicted to be a carcinogen in humans, and this is corroborated by extensive epidemiologic evidence. The IPCA Human Relevance Framework is useful in evaluating DNA-reactive carcinogens.
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Affiliation(s)
- Samuel M Cohen
- Department of Pathology and Microbiology and Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, Nebraska, USA.
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Rhomberg LR, Baetcke K, Blancato J, Bus J, Cohen S, Conolly R, Dixit R, Doe J, Ekelman K, Fenner-Crisp P, Harvey P, Hattis D, Jacobs A, Jacobson-Kram D, Lewandowski T, Liteplo R, Pelkonen O, Rice J, Somers D, Turturro A, West W, Olin S. Issues in the Design and Interpretation of Chronic Toxicity and Carcinogenicity Studies in Rodents: Approaches to Dose Selection. Crit Rev Toxicol 2008; 37:729-837. [DOI: 10.1080/10408440701524949] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Bogen KT. An adjustment factor for mode-of-action uncertainty with dual-mode carcinogens: the case of naphthalene-induced nasal tumors in rats. RISK ANALYSIS : AN OFFICIAL PUBLICATION OF THE SOCIETY FOR RISK ANALYSIS 2008; 28:1033-1051. [PMID: 18564993 DOI: 10.1111/j.1539-6924.2008.01066.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The U.S. Environmental Protection Agency (USEPA) guidelines for cancer risk assessment recognize that some chemical carcinogens may have a site-specific mode of action (MOA) involving mutation and cell-killing-induced hyperplasia. The guidelines recommend that for such dual MOA (DMOA) carcinogens, judgment should be used to compare and assess results using separate "linear" (genotoxic) versus "nonlinear" (nongenotoxic) approaches to low-level risk extrapolation. Because the guidelines allow this only when evidence supports reliable risk extrapolation using a validated mechanistic model, they effectively prevent addressing MOA uncertainty when data do not fully validate such a model but otherwise clearly support a DMOA. An adjustment-factor approach is proposed to address this gap, analogous to reference-dose procedures used for classic toxicity endpoints. By this method, even when a "nonlinear" toxicokinetic model cannot be fully validated, the effect of DMOA uncertainty on low-dose risk can be addressed. Application of the proposed approach was illustrated for the case of risk extrapolation from bioassay data on rat nasal tumors induced by chronic lifetime exposure to naphthalene. Bioassay data, toxicokinetic data, and pharmacokinetic analyses were determined to indicate that naphthalene is almost certainly a DMOA carcinogen. Plausibility bounds on rat-tumor-type-specific DMOA-related uncertainty were obtained using a mechanistic two-stage cancer risk model adapted to reflect the empirical link between genotoxic and cytotoxic effects of the most potent identified genotoxic naphthalene metabolites, 1,2- and 1,4-naphthoquinone. Bound-specific adjustment factors were then used to reduce naphthalene risk estimated by linear extrapolation (under the default genotoxic MOA assumption), to account for the DMOA exhibited by this compound.
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Affiliation(s)
- Kenneth T Bogen
- Exponent Inc., Health Sciences Group, 500 1th Street, Oakland, CA 94607, USA.
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Application of mode-of-action considerations in human cancer risk assessment. Toxicol Lett 2008; 180:75-80. [PMID: 18588958 DOI: 10.1016/j.toxlet.2008.05.021] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2008] [Revised: 05/28/2008] [Accepted: 05/28/2008] [Indexed: 10/22/2022]
Abstract
The distinction between carcinogens with DNA-reactive and epigenetic modes of action and the application of mode-of-action considerations to risk assessment is reviewed. A bioindicator-based risk assessment strategy is described. This approach involves the use of mechanistic data to establish a "toxicologically insignificant daily intake".
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Affiliation(s)
- Samuel M. Cohen
- Department of Pathology and Microbiology and the Eppley Institute for Research on Cancer, University of Nebraska Medical Center
| | - Lora L. Arnold
- Department of Pathology and Microbiology and the Eppley Institute for Research on Cancer, University of Nebraska Medical Center
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17
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Cohen SM. Thresholds in Genotoxicity and Carcinogenicity: Urinary Bladder Carcinogenesis. Genes Environ 2008. [DOI: 10.3123/jemsge.30.132] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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18
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Ohnishi T, Arnold LL, He J, Clark NM, Kawasaki S, Rennard SI, Boyer CW, Cohen SM. Inhalation of tobacco smoke induces increased proliferation of urinary bladder epithelium and endothelium in female C57BL/6 mice. Toxicology 2007; 241:58-65. [PMID: 17897767 DOI: 10.1016/j.tox.2007.08.088] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Revised: 07/30/2007] [Accepted: 08/05/2007] [Indexed: 11/16/2022]
Abstract
Cigarette smoking is the major environmental risk factor for bladder cancer in humans. Aromatic amines, potent DNA-reactive bladder carcinogens present in cigarette smoke, contribute significantly. However, increased cell proliferation, caused by direct mitogenesis or in response to cytotoxicity, may also play a role since urothelial hyperplasia has been observed in human cigarette smokers. We examined the urothelial effects of cigarette smoke (whole body inhalation exposure (Teague) system) in female C57BL/6 mice at various times in two studies, including reversibility evaluations. In both studies, no urothelial hyperplasia was observed by light microscopy in any group. However, in study 1, the Ki-67 labeling index (LI) of the urothelium was significantly increased in the smoke exposed group compared to controls through 3 months, but was not present at 6, 9 or 12 months even with continued exposures. In the groups that discontinued smoke exposure, it returned to the same levels as controls or lower. In study 2, the bromodeoxyuridine LI was similar to controls on day 1 but significantly increased at 5 days in the smoke exposed group. In the group that discontinued smoke exposure for 2 days, the LI was increased compared to controls but not significantly. Superficial urothelial cell cytotoxicity and necrosis were detectable by scanning electron microscopy at 5 days. Changes in LI of submucosal endothelial cells generally followed those of the urothelium and effects were reversible upon cessation of exposure. The increased urothelial proliferation appeared to be due to superficial cell cytotoxicity with consequent regeneration.
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Affiliation(s)
- Takamasa Ohnishi
- Department of Pathology and Microbiology, Eppley Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198-3135, United States
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Cohen SM, Ohnishi T, Clark NM, He J, Arnold LL. Investigations of rodent urinary bladder carcinogens: collection, processing, and evaluation of urine and bladders. Toxicol Pathol 2007; 35:337-47. [PMID: 17455081 DOI: 10.1080/01926230701197115] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Examination of the urine and the bladder epithelium are essential to the investigation of mechanisms of urinary bladder carcinogens in rodents. However, urine and bladder tissue specimens must be collected and processed properly if accurate data are to be derived. The optimum specimen for analysis of urinary constituents is fresh void urine collected from nonfasting animals. Fasting the animal prior to urine collection changes the normal composition, including pH. Many of the normal urinary constituents can influence the mode of action of bladder carcinogens, especially for non-genotoxic agents. Light microscopy is routinely used to examine the bladder epithelium. However, it is often necessary to use more sensitive techniques, such as scanning electron microscopy (SEM) to detect subtle cytotoxic changes in the superficial cell layer of the urothelium, and bromodeoxyuridine (BrdU) incorporation, PCNA, or Ki-67 immunohistochemistry to determine the labeling index for cell proliferation. The urinary bladder must be handled gently and inflated with fixative in situ before the animal dies to avoid artifactual autolytic damage to the bladder epithelium that is visible by SEM and may be mistaken for treatment-related changes. The purpose of this paper is to provide information for the proper collection and examination of urine and the urinary bladder.
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Affiliation(s)
- Samuel M Cohen
- Department of Pathology and Microbiology, and the Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, NE 68198-3135, USA.
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Abstract
The distinction between DNA-reactive and epigenetic carcinogens and their roles in oncogenesis is reviewed. An approach to cancer hazard assessment based upon mechanisms is described.
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Affiliation(s)
- G M Williams
- Department of Pathology, Basic Sciences Building, New York Medical College, Valhalla, NY 10595, USA
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Culp SJ, Warbritton AR, Smith BA, Li EE, Beland FA. DNA adduct measurements, cell proliferation and tumor mutation induction in relation to tumor formation in B6C3F1 mice fed coal tar or benzo[a]pyrene. Carcinogenesis 2000. [DOI: 10.1093/carcin/21.5.433] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Culp SJ, Warbritton AR, Smith BA, Li EE, Beland FA. DNA adduct measurements, cell proliferation and tumor mutation induction in relation to tumor formation in B6C3F1 mice fed coal tar or benzo[ a ]pyrene. Carcinogenesis 2000. [DOI: 10.1093/carcin/21.7.1433] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Smith CJ, Perfetti TA, Rumple MA, Rodgman A, Doolittle DJ. "IARC group 2A Carcinogens" reported in cigarette mainstream smoke. Food Chem Toxicol 2000; 38:371-83. [PMID: 10722891 DOI: 10.1016/s0278-6915(99)00156-8] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
As a follow-up to an earlier study on IARC Group I compounds, further efforts have been made to evaluate the international literature on cigarette mainstream smoke for reports on constituents classified as IARC "Group 2A: probably carcinogenic to humans" and IARC "Group 2B: possibly carcinogenic to humans." IARC classifies 59 agents, mixtures and exposures as Group 2A. Of the overall list of 59, 50 represent chemical entities or complex mixtures ( [IARC,] ). When only chemical entities which have their origin from cigarette components (tobacco and paper) are considered, further searching of the international literature has revealed that nine chemical compounds of the 50 Group 2A listings have been reported in cigarette mainstream smoke ( Table 1 ). In micrograms/cigarette (mug/cig), the ranges reported for each of the nine compounds are as follows: formaldehyde (3.4-283); benzo[a]pyrene (B[a]P) (0.004-0. 108); dibenz[a,h]anthracene (DB[a,h]A) (0.004-0.076); N-nitrosodiethylamine (DEN) (non-detectable-0.0076); benz[a]anthracene (B[a]A) (trace-0.08); N-nitrosodimethylamine (DMN) (non-detectable-0.7-1.62); acrylamide (1.1-2.34); 1,3-butadiene (16-77); and 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) (0. 00026-0.00049).
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Affiliation(s)
- C J Smith
- Research and Development, Bowman Gray Technical Center, R.J. Reynolds Tobacco Company, Winston-Salem, NC 27102, USA
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24
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Bitsch A, Klöhn PC, Hadjiolov N, Bergmann O, Neumann HG. New insights into carcinogenesis of the classical model arylamine 2-acetylaminofluorene. Cancer Lett 1999; 143:223-7. [PMID: 10503908 DOI: 10.1016/s0304-3835(99)00129-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
2-Acetylaminofluorene (AAF) is a complete carcinogen in rat liver. The genotoxic effects of reactive metabolites are considered necessary but not sufficient to explain tumor formation. An overview is given of an AAF-feeding experiment designed to demonstrate early effects, preceding the development of enzyme-altered foci to support the hypothesis that toxic effects lead to a cirrhosis-like transformation as a prerequisite for the expansion of initiated foci and how those effects influence the dose-time-response relationship of tumor formation. Male Wistar rats were fed 0.005, 0.01, 0.02, 0.04 and 0.08% AAF in the diet for 2, 4, 8, and 16 weeks. GST-P-positive foci developed more than proportionately only at 16 weeks. As a first sign of morphological alterations the number of apoptoses increased (2 weeks), the proliferation rate followed with some delay and was maximal at 4 weeks. The most sensitive parameter for adaptive responses was the inhibition of the mitochondrial permeability transition, studied ex vivo. All parameters increased dose-dependently at low doses. A threshold could not be detected, but effects developed much more gradually with the lowest, non-toxic dose. The situation of massive development of foci observed with the higher doses at 16 weeks was not reached. Apoptosis and proliferation rate reach a plateau between 4 and 8 weeks with some of the doses indicating a period in which some balance between adaptation and stress response exists.
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Affiliation(s)
- A Bitsch
- Department of Toxicology, University of Würzburg, Germany
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25
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Affiliation(s)
- G M Williams
- New York Medical College, Valhalla, New York 10595, USA.
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26
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Affiliation(s)
- S M Cohen
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha 68198-3135, USA
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27
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Abstract
Urinary bladder carcinogenesis in rodents bears numerous similarities to the diseases in humans. In rats, the process progresses through the morphologic stages of simple hyperplasia, papillary and nodular hyperplasia, papilloma, noninvasive, and invasive carcinoma. In mice, the pathogenesis can be similar or can follow a sequence of marked dysplasia with or without hyperplasia, leading to carcinoma in situ and ultimately to high-grade invasive carcinoma. Although the papillary and nonpapillary diseases appear to be related in rodents and in humans, they are distinct morphologically, biologically, and molecularly. Numerous classes of genotoxic chemicals have been identified as bladder carcinogens in rodents, and some of these have also been identified as carcinogenic in humans, most notably, aromatic amines, nitrosamines, and cyclophosphamide. In contrast, nongenotoxic chemicals appear to be highly specific with respect to species, strain, diet, agent, dose, and mechanism. For some, it is unclear whether the results at high doses in rodents can be extrapolated to low doses or to humans, e.g., chemicals that cause bladder cancer only at high doses related to the formation of calculi. Numerous observations in rodents can assist in identifying possible mechanisms involved for these nongenotoxic chemicals and therefore can be important for a rational evaluation of human risk.
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Affiliation(s)
- S M Cohen
- University of Nebraska Medical Center, Department of Pathology and Microbiology, Omaha 68198-3135, USA
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28
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Abstract
We investigate the determinability of model parameters for a two-stage cancer model, using as an example chemically induced skin cancer in mice. When the time course of the papilloma number and cancer rate are known, the rate of creation of initiated cells and their net-growth rate can be uniquely determined. These two high-level parameters are sufficient to uniquely simulate the experimental papilloma data. However, the mitotic and death rates of initiated and transformed cells cannot be determined from the available experimental data. The rate of creation of transformed cells and their net-growth rate cannot be determined independently. Thus, although the deterministic two-stage cancer model can simulate the kinetics of papilloma formation and skin cancer data, many of the basic underlying biological parameters (i.e., mitotic and death rates) cannot be uniquely determined from the usually available biological data.
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Affiliation(s)
- D Wiarda
- University of Tennessee, Knoxville, USA
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29
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Maynard RL, Cameron KM, Fielder R, McDonald A, Wadge A. Setting air quality standards for carcinogens: an alternative to mathematical quantitative risk assessment-discussion paper. Regul Toxicol Pharmacol 1997; 26:S60-70. [PMID: 9380838 DOI: 10.1006/rtph.1997.1140] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
It has been accepted in many countries that the regulation of ambient air quality should involve the use of health-based air quality standards. Setting standards for air pollutants which are genotoxic carcinogens presents difficult problems to the regulator, in that the prediction of the effects on health of low levels of exposure is suspected to be inaccurate, and is not currently amenable to either experimental or epidemiological verification. In some countries, techniques of mathematical quantitative risk assessment have been adopted to calculate acceptable levels of exposure to, or the unit risk factors for, genotoxic carcinogens. We regard these approaches as unsatisfactory. An alternative approach, based upon a number of argued premises, a strategy which identifies decision points and the cautious application of uncertainty factors, is described.
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Affiliation(s)
- R L Maynard
- Health Aspects of Environment and Food Division, Department of Health, Skipton House, Elephant and Castle, London, SE1 6LW, United Kingdom
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30
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Poirier MC, Beland FA. Aromatic amine DNA adduct formation in chronically-exposed mice: considerations for human comparison. Mutat Res 1997; 376:177-84. [PMID: 9202754 DOI: 10.1016/s0027-5107(97)00041-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Lifetime chronic exposure of mice to the aromatic amines 4-aminobiphenyl (ABP) and 2-acetylaminofluorene (AAF) produces liver and urinary bladder tumors. In parallel experiments, DNA adduct levels in target tissues reach a steady-state (a balance between adduct formation and removal) after about four weeks of either AAF or ABP ingestion. For these and other carcinogens, steady-state DNA adduct levels most frequently increase linearly with dose, but the formation of tumors also depends upon a variety of factors, including the proliferative capacity of the target tissue, the sex of the animal, genotoxic properties of the specific adducts formed, and other unknown events. Chronic dosing experiments in animal models are of interest for human risk assessment because human exposure is typically intermittent, involving repeated exposures. However, it is to be expected that in a genetically-diverse human population, where the lifetime averages > 70 years, the relationship between tumorigenesis and DNA adduct formation will be relatively more complex than that observed in mice. From our studies of chronic ABP exposure in male mice, we have obtained the daily dose of ABP and the steady-state level of N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) adduct associated with a 50% mouse bladder tumor incidence. Our attempt at a human extrapolation for adducts and urinary bladder cancer in smoking males (20-40 cigarettes/day) is based on the ABP dose per cigarette, values for the dG-C8-ABP adduct in bladder biopsies of lifetime heavy smokers at age approximately 70, and the smoking-related bladder tumor incidence (absolute lifetime risk) for Caucasian males in the United States aged 65-84 years. The extrapolation has produced two major predictions, one related to adduct formation and the other related to tumorigenesis. First, the observed level of smoking-related dG-C8-ABP in DNA of human bladder epithelium, expressed as a function of daily ABP intake, is about 3500-times higher than similar data for mice, which suggests that humans may perform the biotransformation of ABP more efficiently than mice. Second, at a similar bladder tumor incidence, mouse bladder contained adduct concentrations that were much higher than those observed in human bladder; for example, at a 2.6% tumor incidence, mouse bladder contained an average of 55.5 fmol dG-C8-ABP/microgram DNA (1850 adducts/10(8) nucleotides), while bladders from Caucasian male smokers contained an average of 0.036 fmol dG-C8-ABP/microgram DNA (1.2 adducts/10(8) nucleotides). This suggests that factors other than ABP-DNA adducts, such as adducts of other carcinogens, the influence of promoters, and synergistic effects of all of these factors contribute substantially to smoking-related bladder cancer in humans.
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Affiliation(s)
- M C Poirier
- National Cancer Institute, NIH, Bethesda, MD 20892-4255, USA.
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31
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Affiliation(s)
- J R Foster
- Research Pathology Group, Pathology Section, Zeneca Central Toxicology Laboratory, Macclesfield, Cheshire, UK
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32
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Kitchin KT, Brown JL. Dose-response relationship for rat liver DNA damage caused by 1,2-dimethylhydrazine. Toxicology 1996; 114:113-24. [PMID: 8947610 DOI: 10.1016/s0300-483x(96)03478-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
An experimental approach was taken to the question of dose-response curves for chemical carcinogenesis, using DNA damage as a biomarker. Female rats were give 13 different doses of 1,2-dimethylhydrazine (from 1.4 to 135,000 micrograms/kg) and the subsequent hepatic DNA damage was determined by the alkaline elution technique. DMH doses below 450 micrograms/kg did not significantly damage DNA; all DMH doses of 1000 micrograms/kg or higher damaged rat hepatic DNA (P < 0.05). In this study the x values (dose) ranged over five orders of magnitude and the y values (DNA damage) ranged 30-fold. Ten different regression models (linear, quadratic, cubic, power, and six nonlinear transition models) were compared in their ability to fit the experimental data. With respect to log transformed dose, the six nonlinear transition equations fit the data considerably better than the four power type of equations. A sigmoid model fit to the log transformed dose of 1,2-dimethylhydrazine had an r2 of 0.9979, a degree of freedom adjusted r2 of 0.9969, a F-statistic of 1,457, and a fit standard error of 0.50. With respect to untransformed dose, only three equations (sigmoid, cascade and gaussian cumulative) could creditably fit the DMH data. The experimental results are interpreted with respect to hormesis, use of log transformed dose, sigmoid dose-response models, thresholds of biological response and cancer risk assessment.
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Affiliation(s)
- K T Kitchin
- Biochemistry and Pathobiology Branch, US EPA, Research Triangle Park, NC 27711, USA.
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33
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Culp SJ, Gaylor DW, Sheldon WG, Goldstein LS, Beland FA. DNA Adduct Measurements in Relation to Small Intestine and Forestomach Tumor Incidence during the Chronic Feeding of Coal TAR or Benzo[A]Pyrene to Mice. Polycycl Aromat Compd 1996. [DOI: 10.1080/10406639608544662] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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La DK, Swenberg JA. DNA adducts: biological markers of exposure and potential applications to risk assessment. Mutat Res 1996; 365:129-46. [PMID: 8898994 DOI: 10.1016/s0165-1110(96)90017-2] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
DNA adducts have been investigated extensively during the past decade. This research has been advanced, in part, by the development of ultrasensitive analytical methods, such as 32P-postlabeling and mass spectrometry, that enable detection of DNA adducts at concentrations as low as one adduct per 10(9) to 10(10) normal nucleotides. Studies of mutations in activated oncogenes such as ras, inactivated tumor suppressor genes such as p53, and surrogate genes such as hprt provide linkage between DNA adducts and carcinogenesis. The measurement of DNA adducts, or molecular dosimetry, has important applications for cancer risk assessment. Cancer risk assessment currently involves estimating the probable effects of carcinogens in humans based on results of animal bioassays. Estimates of risk are then derived from mathematical models that fit data of tumor incidence at the high animal exposures and extrapolate to probable human exposures that may be orders of magnitude lower. Molecular dosimetry could extend the observable range of mechanistic data several orders of magnitude lower than can be achieved in carcinogenesis bioassays. This measurement also compensates automatically for individual and species differences in toxicokinetic factors, as well as any nonlinearities that affect the quantitative relationships between exposure and molecular dose. As a result, molecular dosimetry can provide a basis for conducting high- to low-dose, route-to-route, and interspecies extrapolations. The incorporation of such data into risk assessment promises to reduce uncertainties and produce more accurate estimates of risk compared to current methods.
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Affiliation(s)
- D K La
- Curriculum in Toxicology, University of North Carolina, Chapel Hill 27599, USA
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35
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Abstract
DNA replication does not have 100% fidelity. Consequently, a chemical can increase the risk of cancer either by directly damaging DNA (genotoxic) or by increasing the number of cell replications, or both. Increased cell proliferation can be produced by increasing cell births (by direct mitogenesis or regeneration following toxicity), or decreasing cell deaths (by inhibiting apoptosis or differentiation). Cell proliferation can affect the dose-response curve for genotoxic carcinogens and is the basis for carcinogenicity by nongenotoxic agents. Bladder carcinogens will be used to illustrate these mechanisms, and their implications with respect to human risk assessment will be presented.
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Affiliation(s)
- S M Cohen
- University of Nebraska Medical Center, Omaha 68198-3135, USA
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36
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Ito N, Hasegawa R, Imaida K, Hirose M, Asamoto M, Shirai T. Concepts in multistage carcinogenesis. Crit Rev Oncol Hematol 1995; 21:105-133. [PMID: 8822499 DOI: 10.1016/1040-8428(94)00169-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Affiliation(s)
- N Ito
- First Department of Pathology, Nagoya City University Medical School, Japan
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37
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Abstract
Chemicals can increase carcinogenic risk by either directly damaging DNA or increasing cell replication or they can do both. These effects have different implications for a biologically-based extrapolation from rodent bioassays to humans. 2-Acetylaminofluorene (2-AAF) administered at low doses to mice for a lifetime has a different dose-response for the liver (approximately linear) compared to the urinary bladder (apparent no effect dose of 45 ppm with a sigmoidal dose response at 60-150 ppm), which can be explained if carcinogen metabolism, DNA adduct formation and cell proliferation effects are considered. In contrast to 2-AAF and other genotoxic chemicals, chemicals which form calculi in the urine do not generally damage DNA directly but increase cell proliferation dramatically by eroding the bladder surface, leading to regenerative hyperplasia. This occurs only at doses at which calculi form; lower doses do not produce calculi and, therefore, do not increase cell proliferation or cause tumors. Extrapolation to humans from the rodent bioassay should be dependent on dose requirements for formation of calculi rather than any type of statistical extrapolation to lower doses. Saccharin and other sodium salts administered at high doses to rats also produce bladder cancer by increasing cell proliferation. These salts do not affect mice, hamsters, guinea pig or monkeys. Based on dose and mechanistic considerations, saccharin and these other sodium salts are unlikely to be human carcinogens. Extrapolation to possible human cancer risk requires biological determinations rather than simply using statistical formulations.
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Affiliation(s)
- S M Cohen
- University of Nebraska Medical Center, Department of Pathology and Microbiology, Omaha 68198-3135, USA
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38
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Lensing SY, Kodell RL. Fitting the two-stage clonal expansion model based on exact hazard to the ED01 data using SAS NLIN. RISK ANALYSIS : AN OFFICIAL PUBLICATION OF THE SOCIETY FOR RISK ANALYSIS 1995; 15:233-245. [PMID: 7597259 DOI: 10.1111/j.1539-6924.1995.tb00317.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The two-stage clonal expansion model is a popular model for carcinogenesis data. One common form of this model is based on the approximate hazard function. In certain situations, this formulation is not appropriate, and the exact hazard should be applied. However, the difficulty of implementing the model based on the exact hazard has deterred many from using it. This paper presents a program implementing the exact hazard model for piecewise constant dosing using SAS, a package that is readily available to most that are interested in this type of analysis. Also, an analysis of the ED01 data is presented using this program, and comparisons are made to an earlier analysis based on the approximate hazard. By allowing for an independent background tumor mechanism, an excellent fit to the bladder tumor incidence data was obtained.
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Affiliation(s)
- S Y Lensing
- Computer Sciences Corporation, National Center for Toxicological Research (HFT-20), Jefferson, Arkansas 72079-9502, USA
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39
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Cohen SM, Ellwein LB. Relationship of DNA adducts derived from 2-acetylaminofluorene to cell proliferation and the induction of rodent liver and bladder tumors. Toxicol Pathol 1995; 23:136-42. [PMID: 7569667 DOI: 10.1177/019262339502300206] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Pharmacokinetic models have been developed to assist in extrapolating results from rodent bioassays. However, in numerous circumstances, it is necessary to combine such models with cellular response models to fully define interspecies and dose extrapolations. Interactions between pharmacokinetic target tissue end points (DNA adduct formation) and cellular proliferation in liver and urinary bladder carcinogenesis is illustrated with the results from the ED01 study involving 2-acetylaminofluorene administered to female mice. The interaction of genotoxic and cell proliferative effects are also illustrated in a co-carcinogenesis study with low doses of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide and high doses of sodium saccharin. The application of such interactions to humans is illustrated for the case of cigarette smoke-induced bladder cancer.
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Affiliation(s)
- S M Cohen
- University of Nebraska Medical Center, Eppley Institute for Research in Cancer, Omaha 68198-3135, USA
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40
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Maynard RL, Cameron KM, Fielder R, McDonald A, Wadge A. Setting air quality standards for carcinogens: an alternative to mathematical quantitative risk assessment--discussion paper. Hum Exp Toxicol 1995; 14:175-86. [PMID: 7779442 DOI: 10.1177/096032719501400204] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
1. It has been accepted in many countries that the regulation of ambient air quality should involve the use of health-based air quality standards. 2. Setting standards for air pollutants which are genotoxic carcinogens presents difficult problems to the regulator, in that the prediction of the effects on health of low levels of exposure is suspected to be inaccurate, and is not presently amenable to either experimental or epidemiological verification. 3. In some countries, techniques of Mathematical Quantitative Risk Assessment (MQRA) have been adopted to calculate acceptable levels of exposure to, or the unit risk factors for, genotoxic carcinogens. We regard these approaches as unsatisfactory. 4. An alternative approach, based upon a number of argued premises, a strategy which identifies decision points and the cautious application of uncertainty factors, is described.
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Affiliation(s)
- R L Maynard
- Health Aspects of Environment and Food Division, Department of Health, London, UK
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41
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Kitchin KT, Brown JL. Dose-response relationship for rat liver DNA damage caused by 49 rodent carcinogens. Toxicology 1994; 88:31-49. [PMID: 8160204 DOI: 10.1016/0300-483x(94)90109-0] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
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.
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Affiliation(s)
- K T Kitchin
- Carcinogenesis and Metabolism Branch, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
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42
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Goldstein BD. Risk assessment methodology: maximum tolerated dose and two-stage carcinogenesis models. Toxicol Pathol 1994; 22:194-7. [PMID: 7973367 DOI: 10.1177/019262339402200213] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The Committee on Risk Assessment Methodology of the Board on Environmental Studies and Toxicology of the National Academy of Sciences has considered issues related to the use of the maximum tolerated dose (MTD) in carcinogenesis bioassays and of 2-stage models of carcinogenesis. In each case, the goal has been to consider whether sufficient information is available to lead to a change in current methodology used by regulatory agencies in assessing risk. The majority of the committee favored retention of the MTD but recommended that lower doses also be used for cancer bioassays and, if the results are positive, performance of additional mechanistic studies aimed at improved extrapolation to environmentally relevant concentrations. The minority recommended that additional preliminary studies be done in order to obtain information about the highest dose relevant to extrapolation to humans for use in the cancer bioassay. Two-stage carcinogenesis models were found to be an excellent approach to increase understanding but required an extensive toxicological data base beyond that available for most chemicals. These deliberations have highlighted the value of increased understanding of the basic mechanisms of action of potential cancer-causing chemicals in order to advance the methodology of risk assessment.
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Affiliation(s)
- B D Goldstein
- Environmental and Occupational Health Sciences Institute, Piscataway, New Jersey 08855
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43
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Frederick CB. Limiting the uncertainty in risk assessment by the development of physiologically based pharmacokinetic and pharmacodynamic models. Toxicol Lett 1993; 68:159-75. [PMID: 8516762 DOI: 10.1016/0378-4274(93)90128-k] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Analysis of the default cancer risk assessment methodology suggests that the confidence interval usually associated with the prediction of an upper bound on risk underestimates the uncertainty in the risk estimate. This underestimate of uncertainty is based on the use of a large number of policy decisions or professional judgements that are incorporated into the methodology as exact values with no estimate of error. An alternative approach is to develop a comprehensive biologically based risk assessment that provides scientific data to substitute for many of the policy decisions of the default methodology.
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Affiliation(s)
- C B Frederick
- Rohm and Haas Company, Toxicology Department, Spring House, PA 19477
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44
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Cher ML, Milchgrub S, Sagalowsky AI. Transitional cell carcinoma of the ureteral stump 23 years after radical nephrectomy for adenocarcinoma. J Urol 1993; 149:106-8. [PMID: 8417186 DOI: 10.1016/s0022-5347(17)36013-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We report a case of simultaneous invasive transitional cell carcinoma in a ureteral stump and superficial bladder tumor occurring 23 years after ipsilateral radical nephrectomy for adenocarcinoma of the kidney. We review the literature on similar cases and discuss potential etiologies of tumor formation in the ureteral stump.
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Affiliation(s)
- M L Cher
- Department of Surgery, University of Texas Southwestern Medical Center, Dallas
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45
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Abstract
A new simulation model of carcinogenesis is described which, in addition to the features of a standard clonal two-stage model (loss of both copies of a tumor suppressor gene by point mutations, cell division and cell death), includes a quantitative description of mitotic recombination, DNA repair, and cell to cell interactions in all stages. The model is implemented as a discrete event process. The results of a sensitivity analysis of the model are presented. The most sensitive parameters were found to be: the number of normal cells at risk, and the division rate, death rate and DNA repair efficiency for the intermediate stage cells. Accurate information about these parameters is important for a quantitative understanding of carcinogenesis. The sensitivity of the model to the number of normal cells indicates the importance of understanding the nature of the cells at risk, for example, stem cells vs. differentiated cells. The model can be used to assess the importance of chromosomal damage such as mitotic recombination and epigenetic mechanisms such as hyperplasia and cytotoxicity in the onset of malignant tumors.
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Affiliation(s)
- F Y Bois
- Indoor Environment Program, Lawrence Berkeley Laboratory, CA 94720
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46
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Ellwein LB, Purtilo DT. Cellular proliferation and genetic events involved in the genesis of Burkitt lymphoma (BL) in immune compromised patients. CANCER GENETICS AND CYTOGENETICS 1992; 64:42-8. [PMID: 1458449 DOI: 10.1016/0165-4608(92)90321-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A mathematical model simulating lymphomagenesis based on the two-hit theory of carcinogenesis is presented by contrasting the biologic variables responsible for a high risk of developing Burkitt lymphoma (BL) in three immunosuppressed groups with that of nonendemic BL. In this model, the pro-B lymphocyte is considered to be the target for BL-specific translocations such as t(8;14). With repeated mitosis, the target cell pool expands in the high-risk individual, and, thereby, the opportunities for a spontaneous translocation to arise are increased. The chromosomal translocation endows the target cell with survival advantages, and, hence, lymphoma develops. Modeling results demonstrate that this increased cell proliferation is sufficient in accounting entirely for the increase in tumor prevalence. Preventing enhanced cellular proliferation by obviating immune deficiency and treating patients with agents that restore immunity or have antiviral and antiproliferative properties prior to conversion from polyclonal B-cell proliferation to monoclonal malignancy could obviate the development of BL.
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Affiliation(s)
- L B Ellwein
- National Institutes of Health, Bethesda, MD 20892
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Frederick CB, Potter DW, Chang-Mateu MI, Andersen ME. A physiologically based pharmacokinetic and pharmacodynamic model to describe the oral dosing of rats with ethyl acrylate and its implications for risk assessment. Toxicol Appl Pharmacol 1992; 114:246-60. [PMID: 1609417 DOI: 10.1016/0041-008x(92)90075-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A physiologically based pharmacokinetic and pharmacodynamic model has been developed to describe the absorption, distribution, and metabolism of orally dosed ethyl acrylate. The model describes the metabolism of ethyl acrylate in 14 tissues based on in vitro metabolic studies conducted with tissue homogenates. The routes of metabolism included in the model are carboxylesterase-catalyzed ester hydrolysis, conjugation with glutathione, and binding to protein. To adequately describe the rate and extent of glutathione depletion following gavage dosing, the steady-state rate of glutathione synthesis in the organs of interest was included. In vivo validation of the model was conducted by comparing the predictions of the model to the results of a variety of gavage dosing experiments with ethyl acrylate, including (1) the time course of glutathione depletion in a variety of tissues up to 98 hr following dosing at three dose levels, (2) the rate and extent of radiolabeled carbon dioxide excretion, and (3) protein binding in the forestomach. The very rapid metabolism predicted by the model was consistent with the observation that ethyl acrylate was metabolized too rapidly in vivo to be detected by common analytical techniques for tissue metabolite analysis. The validation data indicated that the model provides a reasonable description of the pharmacokinetics and the pharmacodynamic response of specific rat tissues following gavage dosing of ethyl acrylate. A dose surrogate, or measure of delivered dose, for ethyl acrylate was calculated and correlated with the incidence and severity of contact site toxicity (edema, inflammation, ulceration, and hyperplasia). The model provides a quantitative tool for evaluating exposure scenarios for their potential to induce contact-site toxicity, and it provides a quantitative approach for understanding the lack of toxicity in tissues remote from the dosing site.
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Affiliation(s)
- C B Frederick
- Toxicology Department, Rohm and Haas Company, Spring House, Pennsylvania 19477
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Abstract
A discrete-time simulation model of carcinogenesis is described mathematically using recursive relationships between time-varying model variables. The dynamics of cellular behavior is represented within a biological framework that encompasses two irreversible and heritable genetic changes. Empirical data and biological supposition dealing with both control and experimental animal groups are used together to establish values for model input variables. The estimation of these variables is integral to the simulation process as described in step-by-step detail. Hepatocarcinogenesis in male F344 rats provides the basis for seven modeling scenarios which illustrate the complexity of relationships among cell proliferation, genotoxicity, and tumor risk.
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Affiliation(s)
- L B Ellwein
- National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892
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Abstract
Promotion is any factor which results in the increased cellular replication of initiated or transformed cells. We argue that cytotoxicity is not a necessary component of promotion and that, therefore, the existence of a threshold for promotion is unlikely.
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Affiliation(s)
- C C Travis
- Risk Analysis Section, Oak Ridge National Laboratory, TN 37831-6109
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Abstract
Chemicals that induce cancer at high doses in animal bioassays often fail to fit the traditional characterization of genotoxins. Many of these nongenotoxic compounds (such as sodium saccharin) have in common the property that they increase cell proliferation in the target organ. A biologically based, computerized description of carcinogenesis was used to show that the increase in cell proliferation can account for the carcinogenicity of nongenotoxic compounds. The carcinogenic dose-response relationship for genotoxic chemicals (such as 2-acetylaminofluorene) was also due in part to increased cell proliferation. Mechanistic information is required for determination of the existence of a threshold for the proliferative (and carcinogenic) response of nongenotoxic chemicals and the estimation of risk for human exposure.
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Affiliation(s)
- S M Cohen
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha 68198
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