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Burgoon LD, Kluxen FM, Hüser A, Frericks M. The database makes the poison: How the selection of datasets in QSAR models impacts toxicant prediction of higher tier endpoints. Regul Toxicol Pharmacol 2024; 151:105663. [PMID: 38871173 DOI: 10.1016/j.yrtph.2024.105663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2024] [Revised: 05/10/2024] [Accepted: 06/10/2024] [Indexed: 06/15/2024]
Abstract
As the United States and the European Union continue their steady march towards the acceptance of new approach methodologies (NAMs), we need to ensure that the available tools are fit for purpose. Critics will be well-positioned to caution against NAMs acceptance and adoption if the tools turn out to be inadequate. In this paper, we focus on Quantitative Structure Activity-Relationship (QSAR) models and highlight how the training database affects quality and performance of these models. Our analysis goes to the point of asking, "are the endpoints extracted from the experimental studies in the database trustworthy, or are they false negatives/positives themselves?" We also discuss the impacts of chemistry on QSAR models, including issues with 2-D structure analyses when dealing with isomers, metabolism, and toxicokinetics. We close our analysis with a discussion of challenges associated with translational toxicology, specifically the lack of adverse outcome pathways/adverse outcome pathway networks (AOPs/AOPNs) for many higher tier endpoints. We recognize that it takes a collaborate effort to build better and higher quality QSAR models especially for higher tier toxicological endpoints. Hence, it is critical to bring toxicologists, statisticians, and machine learning specialists together to discuss and solve these challenges to get relevant predictions.
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Rahimi D, Sharifi R, Jaberie H, Naghibalhossaini F. Antiproliferative and Antitelomerase Effects of Silymarin on Human Colorectal and Hepatocellular Carcinoma Cells. PLANTA MEDICA 2024; 90:298-304. [PMID: 38219733 DOI: 10.1055/a-2244-8788] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2024]
Abstract
Silymarin, a widely-used hepatoprotective agent, has shown antitumor properties in both in vitro and animal studies. Currently, there is limited knowledge regarding silymarin's antitelomerase effects on human colorectal cancer and hepatocyte carcinoma cells. In this study, we investigated the antiproliferative and antitelomerase effects of silymarin on four human colorectal cancer and HepG2 hepatocyte carcinoma cell lines. The cell viability and telomerase activity were assessed using MTT and the telomerase repeat amplification protocol assay, respectively. We also investigated the effects of silymarin on the expression of human telomerase reverse transcriptase and its promoter methylation in HepG2 cells by real-time RT-PCR and methylation-specific PCR, respectively. Silymarin treatment inhibited cell proliferation and telomerase activity in all cancer cells. After 24 h of treatment, silymarin exhibited IC50 values ranging from 19 - 56.3 µg/mL against these cancer cells. A 30-min treatment with silymarin at the IC50 concentration effectively inhibited telomerase activity in cell-free extracts of both colorectal cancer and hepatocyte carcinoma cells. Treatment of HepG2 cells with 10 and 30 µg/mL of silymarin for 48 h resulted in a decrease in human telomerase reverse transcriptase expression to 75 and 35% of the level observed in the untreated control (p < 0.01), respectively. Treatment with silymarin (10, 30, and 60 µg/mL) for 48 h did not affect human telomerase reverse transcriptase promoter methylation in HepG2 cells. In conclusion, our findings suggest that silymarin inhibits cancer cell growth by directly inhibiting telomerase activity and downregulating its human telomerase reverse transcriptase catalytic subunit. However, silymarin did not affect human telomerase reverse transcriptase promoter methylation at the concentrations of 10 - 60 µg/mL used in this study.
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Affiliation(s)
- Daruosh Rahimi
- Department of Biochemistry, Shiraz University of Medical Sciences, School of Medicine, Shiraz, Iran
| | - Roya Sharifi
- Department of Laboratory Sciences, School of Allied Medical Sciences, Iran University of Medical Sciences, Tehran, Iran
| | - Hajar Jaberie
- Department of Biochemistry, Faculty of Medicine, Bushehr University of Medical Sciences, Bushehr, Iran
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Oh KK, Yoon SJ, Lee SB, Lee SY, Gupta H, Ganesan R, Sharma SP, Won SM, Jeong JJ, Kim DJ, Suk KT. The convergent application of metabolites from Avena sativa and gut microbiota to ameliorate non-alcoholic fatty liver disease: a network pharmacology study. J Transl Med 2023; 21:263. [PMID: 37069607 PMCID: PMC10111676 DOI: 10.1186/s12967-023-04122-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Accepted: 04/09/2023] [Indexed: 04/19/2023] Open
Abstract
BACKGROUND Non-alcoholic fatty liver disease (NAFLD) is a serious public health issue globally, currently, the treatment of NAFLD lies still in the labyrinth. In the inchoate stage, the combinatorial application of food regimen and favorable gut microbiota (GM) are considered as an alternative therapeutic. Accordingly, we integrated secondary metabolites (SMs) from GM and Avena sativa (AS) known as potent dietary grain to identify the combinatorial efficacy through network pharmacology. METHODS We browsed the SMs of AS via Natural Product Activity & Species Source (NPASS) database and SMs of GM were retrieved by gutMGene database. Then, specific intersecting targets were identified from targets related to SMs of AS and GM. The final targets were selected on NAFLD-related targets, which was considered as crucial targets. The protein-protein interaction (PPI) networks and bubble chart analysis to identify a hub target and a key signaling pathway were conducted, respectively. In parallel, we analyzed the relationship of GM or AS─a key signaling pathway─targets─SMs (GASTM) by merging the five components via RPackage. We identified key SMs on a key signaling pathway via molecular docking assay (MDA). Finally, the identified key SMs were verified the physicochemical properties and toxicity in silico platform. RESULTS The final 16 targets were regarded as critical proteins against NAFLD, and Vascular Endothelial Growth Factor A (VEGFA) was a key target in PPI network analysis. The PI3K-Akt signaling pathway was the uppermost mechanism associated with VEGFA as an antagonistic mode. GASTM networks represented 122 nodes (60 GM, AS, PI3K-Akt signaling pathway, 4 targets, and 56 SMs) and 154 edges. The VEGFA-myricetin, or quercetin, GSK3B-myricetin, IL2-diosgenin complexes formed the most stable conformation, the three ligands were derived from GM. Conversely, NR4A1-vestitol formed stable conformation with the highest affinity, and the vestitol was obtained from AS. The given four SMs were no hurdles to develop into drugs devoid of its toxicity. CONCLUSION In conclusion, we show that combinatorial application of AS and GM might be exerted to the potent synergistic effects against NAFLD, dampening PI3K-Akt signaling pathway. This work provides the importance of dietary strategy and beneficial GM on NAFLD, a data mining basis for further explicating the SMs and pharmacological mechanisms of combinatorial application (AS and GM) against NAFLD.
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Affiliation(s)
- Ki-Kwang Oh
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Sang-Jun Yoon
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Su-Been Lee
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Sang Youn Lee
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Haripriya Gupta
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Raja Ganesan
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Satya Priya Sharma
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Sung-Min Won
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Jin-Ju Jeong
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Dong Joon Kim
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea
| | - Ki-Tae Suk
- Institute for Liver and Digestive Diseases, College of Medicine, Hallym University, Chuncheon, 24252, Korea.
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A new approach to the classification of carcinogenicity. Arch Toxicol 2022; 96:2419-2428. [PMID: 35701604 PMCID: PMC9325845 DOI: 10.1007/s00204-022-03324-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 05/25/2022] [Indexed: 11/02/2022]
Abstract
Concern over substances that may cause cancer has led to various classification schemes to recognize carcinogenic threats and provide a basis to manage those threats. The least useful schemes have a binary choice that declares a substance carcinogenic or not. This overly simplistic approach ignores the complexity of cancer causation by considering neither how the substance causes cancer, nor the potency of that mode of action. Consequently, substances are classified simply as "carcinogenic", compromising the opportunity to properly manage these kinds of substances. It will likely be very difficult, if not impossible, to incorporate New Approach Methodologies (NAMs) into binary schemes. In this paper we propose a new approach cancer classification scheme that segregates substances by both mode of action and potency into three categories and, as a consequence, provides useful guidance in the regulation and management of substances with carcinogenic potential. Examples are given, including aflatoxin (category A), trichlorethylene (category B), and titanium dioxide (category C), which demonstrate the clear differentiation among these substances that generate appropriate levels of concern and management options.
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5
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The effect of benzo[alpha]pyrene on DNA methylation and telomerase activity in human normal and cancer cells. Toxicol In Vitro 2022; 80:105331. [DOI: 10.1016/j.tiv.2022.105331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 01/31/2022] [Accepted: 02/08/2022] [Indexed: 11/19/2022]
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Borgert CJ, Fuentes C, Burgoon LD. Principles of dose-setting in toxicology studies: the importance of kinetics for ensuring human safety. Arch Toxicol 2021; 95:3651-3664. [PMID: 34623454 PMCID: PMC8536606 DOI: 10.1007/s00204-021-03155-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 09/02/2021] [Indexed: 01/11/2023]
Abstract
Regulatory toxicology seeks to ensure that exposures to chemicals encountered in the environment, in the workplace, or in products pose no significant hazards and produce no harm to humans or other organisms, i.e., that chemicals are used safely. The most practical and direct means of ensuring that hazards and harms are avoided is to identify the doses and conditions under which chemical toxicity does not occur so that chemical concentrations and exposures can be appropriately limited. Modern advancements in pharmacology and toxicology have revealed that the rates and mechanisms by which organisms absorb, distribute, metabolize and eliminate chemicals-i.e., the field of kinetics-often determine the doses and conditions under which hazard, and harm, are absent, i.e., the safe dose range. Since kinetics, like chemical hazard and toxicity, are extensive properties that depend on the amount of the chemical encountered, it is possible to identify the maximum dose under which organisms can efficiently metabolize and eliminate the chemicals to which they are exposed, a dose that has been referred to as the kinetic maximum dose, or KMD. This review explains the rationale that compels regulatory toxicology to embrace the advancements made possible by kinetics, why understanding the kinetic relationship between the blood level produced and the administered dose of a chemical is essential for identifying the safe dose range, and why dose-setting in regulatory toxicology studies should be informed by estimates of the KMD rather than rely on the flawed concept of maximum-tolerated toxic dose, or MTD.
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Affiliation(s)
- C J Borgert
- Applied Pharmacology and Toxicology, Inc., Gainesville, FL, USA.
- Center for Environmental and Human Toxicology (CEHT), Department of Physiological Sciences, University of Florida College of Veterinary Medicine, Gainesville, FL, USA.
| | - C Fuentes
- Department of Statistics, Oregon State University, Corvallis, OR, USA
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Harrison DJ, Doe JE. The modification of cancer risk by chemicals. Toxicol Res (Camb) 2021; 10:800-809. [PMID: 34484671 DOI: 10.1093/toxres/tfab064] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Revised: 05/13/2021] [Accepted: 06/17/2021] [Indexed: 12/30/2022] Open
Abstract
Advances in understanding of the process of carcinogenesis have undermined the concept of chemicals being classifiable as either carcinogens or non-carcinogens. Elements of carcinogenesis are happening all the time and a proportion of cancers cannot be prevented, the 'bad luck hypothesis'. Although the proportion that can be prevented is disputed, it is important to continue efforts to reduce it. Factors that increase cancer risk have been grouped into intrinsic factors that cannot be modified, and endogenous and exogenous factors that can be modified. Chemicals are exogenous factors that can be modified by risk management measures. Chemicals can alter three key rates that influence cancer risk: cell division, mutation rate per cell division, transformation rate of mutated cells to cancer. These rates can form the basis of a dynamic cancer risk model, a generic, adverse outcome pathway for carcinogenesis where chemicals are considered for their ability to modify cancer risk rather than simply whether they are classed as carcinogens or non-carcinogens. This allows the development of different strategies for assessing cancer risk that use a range of data sources and are not dependent on using long-term bioassays and epidemiology to identify carcinogens. The framework will also allow difficult questions such as the effect of less than lifetime exposures and the effect of exposures to more than one chemical to be addressed.
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Affiliation(s)
- David J Harrison
- School of Medicine, University of St Andrews, North Haugh, St Andrews KY16 9TF, UK
| | - John E Doe
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK
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Batke M, Afrapoli FM, Kellner R, Rathman JF, Yang C, Cronin MTD, Escher SE. Threshold of Toxicological Concern—An Update for Non-Genotoxic Carcinogens. FRONTIERS IN TOXICOLOGY 2021; 3:688321. [PMID: 35295144 PMCID: PMC8915827 DOI: 10.3389/ftox.2021.688321] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Accepted: 05/25/2021] [Indexed: 11/22/2022] Open
Abstract
The Threshold of Toxicological Concern (TTC) concept can be applied to organic compounds with the known chemical structure to derive a threshold for exposure, below which a toxic effect on human health by the compound is not expected. The TTC concept distinguishes between carcinogens that may act as genotoxic and non-genotoxic compounds. A positive prediction of a genotoxic mode of action, either by structural alerts or experimental data, leads to the application of the threshold value for genotoxic compounds. Non-genotoxic substances are assigned to the TTC value of their respective Cramer class, even though it is recognized that they could test positive in a rodent cancer bioassay. This study investigated the applicability of the Cramer classes specifically to provide adequate protection for non-genotoxic carcinogens. For this purpose, benchmark dose levels based on tumor incidence were compared with no observed effect levels (NOELs) derived from non-, pre- or neoplastic lesions. One key aspect was the categorization of compounds as non-genotoxic carcinogens. The recently finished CEFIC LRI project B18 classified the carcinogens of the Carcinogenicity Potency DataBase (CPDB) as either non-genotoxic or genotoxic compounds based on experimental or in silico data. A detailed consistency check resulted in a dataset of 137 non-genotoxic organic compounds. For these 137 compounds, NOEL values were derived from high quality animal studies with oral exposure and chronic duration using well-known repositories, such as RepDose, ToxRef, and COSMOS DB. Further, an effective tumor dose (ETD10) was calculated and compared with the lower confidence limit on benchmark dose levels (BMDL10) derived by model averaging. Comparative analysis of NOEL/EDT10/BMDL10 values showed that potentially bioaccumulative compounds in humans, as well as steroids, which both belong to the exclusion categories, occur predominantly in the region of the fifth percentiles of the distributions. Excluding these 25 compounds resulted in significantly higher but comparable fifth percentile chronic NOEL and BMDL10 values, while the fifth percentile EDT10 value was slightly higher but not statistically significant. The comparison of the obtained distributions of NOELs with the existing Cramer classes and their derived TTC values supports the application of Cramer class thresholds to all non-genotoxic compounds, such as non-genotoxic carcinogens.
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Affiliation(s)
- Monika Batke
- Fraunhofer Institute for Toxicology and Experimental Medicine (ITEM), Hannover, Germany
| | | | - Rupert Kellner
- Fraunhofer Institute for Toxicology and Experimental Medicine (ITEM), Hannover, Germany
| | - James F. Rathman
- Altamira, LLC, Columbus, OH, United States
- Molecular Networks GmbH, Nuremberg, Germany
| | - Chihae Yang
- Altamira, LLC, Columbus, OH, United States
- Molecular Networks GmbH, Nuremberg, Germany
| | - Mark T. D. Cronin
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Sylvia E. Escher
- Fraunhofer Institute for Toxicology and Experimental Medicine (ITEM), Hannover, Germany
- *Correspondence: Sylvia E. Escher
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9
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The 2-year rodent bioassay in drug and chemical carcinogenicity testing: Performance, utility, and configuration for cancer hazard identification. J Pharmacol Toxicol Methods 2021; 110:107070. [PMID: 33905862 DOI: 10.1016/j.vascn.2021.107070] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 04/19/2021] [Indexed: 12/13/2022]
Abstract
For several intended uses of chemicals, the 2-year rodent bioassay (RCB) has been the benchmark method to screen the carcinogenicity to humans of substances, according to the hazard identification sphere. Despite the ongoing controversy around this traditional testing, the RCB is in force and being used by stakeholders. After assembling the RCB's ability to forecast the carcinogenicity to humans of substances, the current review aimed to provide a discussion on the RCB's (1) sensitivity and specificity; (2) utility; (3) configuration, and (4) provisional role in the regulatory policy. In general, RCBs conducted at maximum tolerated doses (MTDs) exhibited a functional ability to (1) not missing the great majority of human carcinogens, and to (2) not responding to the large majority of human non-carcinogens. There is citable evidence supporting the use of MTDs to render RCBs as sensitive as possible, particularly provided the ethically-justified small samples used in RCBs. The literature shows that rodent-specific mechanisms of chemical carcinogenesis contribute significant unspecificity to RCBs. Nonetheless, the paradox between a functional sensitivity and a significant unspecificity can be predictively resolved through the application of Bayesian forecasting. In terms of performance to forecast the carcinogenicity to humans of either genotoxic or non-genotoxic substances, 2-species-RCBs added no value over the rat-RCB. Nevertheless, there is preliminary evidence cautioning that 15% of the rodent carcinogens probably carcinogenic to humans could be missed if mouse-RCBs are indiscriminately discontinued. More than thirteen RCB-related issues relevant to regulatory pharmacology and toxicology were discussed and summarized in this review.
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10
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Smith CJ, Perfetti TA, Berry SC, Brash DE, Bus J, Calabrese E, Clemens RA, Fowle JRJ, Greim H, MacGregor JT, Maronpot R, Pressman P, Zeiger E, Hayes AW. Bruce Nathan Ames - Paradigm shifts inside the cancer research revolution. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2020; 787:108363. [PMID: 34083041 DOI: 10.1016/j.mrrev.2020.108363] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 12/21/2020] [Accepted: 12/22/2020] [Indexed: 11/26/2022]
Abstract
Dr. Bruce Ames turned 92 on December 16, 2020. He considers his most recent work linking adequate consumption of 30 known vitamins and minerals with successful aging to be his most important contribution. With the passage of time, it is not uncommon for the accomplishments of a well-known scientist to undergo a parsimonious reductionism in the public mind - Pasteur's vaccine, Mendel's peas, Pavlov's dogs, Ames' test. Those of us in the research generation subsequent to Dr. Ames' are undoubtedly affected by our own unconscious tendencies toward accepting the outstanding achievements of the past as commonplace. In doing so, seminal advances made by earlier investigators are often inadvertently subsumed into common knowledge. But having followed Ames' work since the mid-1970s, we are cognizant that the eponymous Ames Test is but a single chapter in a long and rich narrative. That narrative begins with Ames' classic studies on the histidine operon of Salmonella, for which he was elected to the National Academy of Sciences. A summary of the historical progression of the understanding of chemical carcinogenesis to which Ames and his colleagues contributed is provided. Any summary of a topic as expansive and complex as the ongoing unraveling of the mechanisms underlying chemical carcinogenesis will only touch upon some of the major conceptual advances to which Ames and his colleagues contributed. We hope that scientists of all ages familiar with Ames only through the eponymous Ames Test will further investigate the historical progression of the conceptualization of cancer caused by chemical exposure. As the field of chemical carcinogenesis gradually moves away from primary reliance on animal testing to alternative protocols under the rubric of New Approach Methodologies (NAM) an understanding of where we have been might help to guide where we should go.
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Affiliation(s)
| | | | | | - Douglas E Brash
- Yale University School of Medicine, Senior Research Scientist, Clinical Professor of Therapeutic Radiology, Professor of Genetics and Dermatology, New Haven, CT, USA
| | | | - Edward Calabrese
- University of Massachusetts, School of Public Health and Health Sciences, Professor of Toxicology, Amherst, MA, USA
| | - Roger A Clemens
- University of Southern California, Adjunct Professor of Pharmaceutical Sciences, Associate Director, Regulatory Science Program, USC School of Pharmacy, Los Angeles, CA, USA
| | | | - Helmut Greim
- Professor Emeritus of Toxicology and Environmental Hygiene, Technical University of Munich, Munich, Germany
| | | | | | | | | | - A Wallace Hayes
- University of South Florida College of Public Health Tampa, FL, USA; Institute for Integrative Toxicology, Michigan State University East Lansing, MI, USA
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11
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Murray FJ, Monnot AD, Jacobson-Kram D, Cohen SM, Hardisty JF, Bandara SB, Kovochich M, Deore M, Pitchaiyan SK, Gelotte CK, Lai JCK, Atillasoy E, Hermanowski-Vosatka A, Kuffner E, Unice KM, Yang K, Gebremichael Y, Howell BA, Eichenbaum G. A critical review of the acetaminophen preclinical carcinogenicity and tumor promotion data and their implications for its carcinogenic hazard potential. Regul Toxicol Pharmacol 2020; 118:104801. [PMID: 33039518 DOI: 10.1016/j.yrtph.2020.104801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 09/11/2020] [Accepted: 10/06/2020] [Indexed: 12/22/2022]
Abstract
In 2019 the California Office of Environmental Health Hazard Assessment (OEHHA) initiated a review of the carcinogenic hazard potential of acetaminophen, including an assessment of the long-term rodent carcinogenicity and tumor initiation/promotion studies. The objective of the analysis herein was to inform this review process with a weight-of-evidence assessment of these studies and an assessment of the relevance of these models to humans. In most of the 14 studies, there were no increases in the incidences of tumors in any organ system. In the few studies in which an increase in tumor incidence was observed, there were factors such as absence of a dose response and a rodent-specific tumor supporting that these findings are not relevant to human hazard identification. In addition, we performed qualitative analysis and quantitative simulations of the exposures to acetaminophen and its metabolites and its toxicity profile; the data support that the rodent models are toxicologically relevant to humans. The preclinical carcinogenicity results are consistent with the broader weight of evidence assessment and evaluations of multiple international health authorities supporting that acetaminophen is not a carcinogenic hazard.
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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, USA
| | | | | | | | | | | | | | | | | | | | | | | | - Kyunghee Yang
- DILIsym Services Inc., Research Triangle Park, NC, USA
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12
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Suarez‐Torres JD, Jimenez‐Orozco FA, Ciangherotti CE. Drug excipients, food additives, and cosmetic ingredients probably not carcinogenic to humans reveal a functional specificity for the 2‐year rodent bioassay. J Appl Toxicol 2020; 40:1113-1130. [DOI: 10.1002/jat.3971] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 02/26/2020] [Indexed: 12/17/2022]
Affiliation(s)
- Jose D. Suarez‐Torres
- Department of Toxicology, Department of PharmacyUniversidad Nacional de Colombia Bogotá Colombia
- Institute of Pharmaceutical Research, School of PharmacyUniversidad Central de Venezuela Caracas Venezuela
| | - Fausto A. Jimenez‐Orozco
- Department of Pharmacology, Faculty of MedicineUniversidad Nacional Autonoma de Mexico Ciudad de Mexico Mexico
| | - Carlos E. Ciangherotti
- Laboratory of Neuropeptides, School of PharmacyUniversidad Central de Venezuela Caracas Venezuela
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13
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Felter SP, Boobis AR, Botham PA, Brousse A, Greim H, Hollnagel HM, Sauer UG. Hazard identification, classification, and risk assessment of carcinogens: too much or too little? - Report of an ECETOC workshop. Crit Rev Toxicol 2020; 50:72-95. [PMID: 32133908 DOI: 10.1080/10408444.2020.1727843] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) organized a workshop "Hazard Identification, Classification and Risk Assessment of Carcinogens: Too Much or Too Little?" to explore the scientific limitations of the current binary carcinogenicity classification scheme that classifies substances as either carcinogenic or not. Classification is often based upon the rodent 2-year bioassay, which has scientific limitations and is not necessary to predict whether substances are likely human carcinogens. By contrast, tiered testing strategies founded on new approach methodologies (NAMs) followed by subchronic toxicity testing, as necessary, are useful to determine if a substance is likely carcinogenic, by which mode-of-action effects would occur and, for non-genotoxic carcinogens, the dose levels below which the key events leading to carcinogenicity are not affected. Importantly, the objective is not for NAMs to mimic high-dose effects recorded in vivo, as these are not relevant to human risk assessment. Carcinogenicity testing at the "maximum tolerated dose" does not reflect human exposure conditions, but causes major disturbances of homeostasis, which are very unlikely to occur at relevant human exposure levels. The evaluation of findings should consider biological relevance and not just statistical significance. Using this approach, safe exposures to non-genotoxic substances can be established.
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Affiliation(s)
| | | | | | - Alice Brousse
- European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC), Brussels, Belgium
| | | | | | - Ursula G Sauer
- Scientific Consultancy - Animal Welfare, Neubiberg, Germany
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14
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Smith CJ, Perfetti TA. High-dose exposure to synthetic chemicals, hormones, or homeostatic substances in experimental animals or humans can induce artefactual pathology. TOXICOLOGY RESEARCH AND APPLICATION 2020. [DOI: 10.1177/2397847320940557] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The maximum tolerated dose (MTD) provides the highest probability of a positive result in a toxicology bioassay. The assumption underlying the MTD in animal bioassays is that adverse effects at very high doses are qualitatively the same as those occurring at low doses. In contrast with the MTD, the optimal top dose in a toxicology animal study is the highest dose that does not produce a pathological end point that presents no risk at lower doses, for example, the dose below which cytotoxicity induces tumors in the absence of genotoxicity or other carcinogenic mechanisms. Normal concentrations or biological activity levels of many substances necessary for normal physiological function induce pathology when found at high levels. For example, the demonstration that ingestion of abnormally high levels of certain dietary fats can cause or exacerbate atherosclerosis in relevant animal models like rhesus macaques does not demonstrate that normal levels of these fats should be considered as toxic. Excessive estrogenic stimulation is associated with breast, ovarian, and endometrial cancers. This does not imply that normal age-appropriate levels of estrogen are toxic. Normal wound healing is associated with transforming growth factors beta 1 and 2. Excessive stimulation of fibroblasts by these growth factors results in hypertrophic scarring and keloid formation. An understanding of the mode of action of a test substance can facilitate the selection of dose levels much higher than those expected to be experienced by humans, but not beyond a dose level at which pathology is an experimental artefact of the high-dose level.
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Tryndyak V, Borowa-Mazgaj B, Beland FA, Pogribny IP. Gene expression and cytosine DNA methylation alterations in induced pluripotent stem-cell-derived human hepatocytes treated with low doses of chemical carcinogens. Arch Toxicol 2019; 93:3335-3344. [PMID: 31555880 DOI: 10.1007/s00204-019-02569-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 09/04/2019] [Indexed: 12/15/2022]
Abstract
The increasing number of man-made chemicals in the environment that may pose a carcinogenic risk emphasizes the need to develop reliable time- and cost-effective approaches for carcinogen detection. To address this issue, we have investigated the utility of human hepatocytes for the in vitro identification of genotoxic and non-genotoxic carcinogens. Induced pluripotent stem-cell (iPSC)-derived human hepatocytes were treated with the genotoxic carcinogens aflatoxin B1 (AFB1) and benzo[a]pyrene (B[a]P), the non-genotoxic liver carcinogen methapyrilene, and the non-carcinogens aflatoxin B2 (AFB2) and benzo[e]pyrene (B[e]P) at non-cytotoxic concentrations for 7 days, and transcriptomic and DNA methylation profiles were examined. 1569, 1693, and 2061 differentially expressed genes (DEGs) were detected in cells treated with AFB1, B[a]P, and methapyrilene, respectively, whereas no DEGs were found in cells treated with AFB2 or B[e]P. In contrast to the profound cellular transcriptomic responses, exposure of iPSC-derived hepatocytes to the test chemicals resulted in minor random alterations in global DNA methylome, most of which were not associated with changes in gene expression. Overall, our results demonstrate that the major non-genotoxic effect of exposure to carcinogens, regardless of their mode of action, is a profound global transcriptomic response rather than global DNA methylome alterations, indicating the significance of transcriptomic alterations as an informative endpoint in short-term in vitro carcinogen testing.
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Affiliation(s)
- Volodymyr Tryndyak
- Division of Biochemical Toxicology, FDA-National Center for Toxicological Research, Jefferson, AR, USA
| | - Barbara Borowa-Mazgaj
- Division of Biochemical Toxicology, FDA-National Center for Toxicological Research, Jefferson, AR, USA
| | - Frederick A Beland
- Division of Biochemical Toxicology, FDA-National Center for Toxicological Research, Jefferson, AR, USA
| | - Igor P Pogribny
- Division of Biochemical Toxicology, FDA-National Center for Toxicological Research, Jefferson, AR, USA.
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16
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Maertens A, Hartung T. Green Toxicology-Know Early About and Avoid Toxic Product Liabilities. Toxicol Sci 2019; 161:285-289. [PMID: 29267930 DOI: 10.1093/toxsci/kfx243] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Toxicology uniquely among the life sciences relies largely on methods which are more than 40-years old. Over the last 3 decades with more or less success some additions to and few replacements in this toolbox took place, mainly as alternatives to animal testing. The acceptance of such new approaches faces the needs of formal validation and the conservative attitude toward change in safety assessments. Only recently, there is growing awareness that the same alternative methods, especially in silico and in vitro tools can also much earlier and before validation inform decision-taking in the product life cycle. As similar thoughts developed in the context of Green Chemistry, the term of Green Toxicology was coined to describe this change in approach. Here, the current developments in the alternative field, especially computational and more organo-typic cell cultures are reviewed, as they lend themselves to front-loaded chemical safety assessments. The initiatives of the Center for Alternatives to Animal Testing Green Toxicology Collaboration are presented. They aim first of all for forming a community to promote this concept and then for a cultural change in companies with the necessary training of chemists, product stewards and later regulators.
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Affiliation(s)
- Alexandra Maertens
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland
| | - Thomas Hartung
- Center for Alternatives to Animal Testing (CAAT), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland.,Department of Biology, Center for Alternatives to Animal Testing-Europe, University of Konstanz, Konstanz, Germany
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17
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Tryndyak V, Kindrat I, Dreval K, Churchwell MI, Beland FA, Pogribny IP. Effect of aflatoxin B 1, benzo[a]pyrene, and methapyrilene on transcriptomic and epigenetic alterations in human liver HepaRG cells. Food Chem Toxicol 2018; 121:214-223. [PMID: 30157460 DOI: 10.1016/j.fct.2018.08.034] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 08/15/2018] [Accepted: 08/22/2018] [Indexed: 12/16/2022]
Abstract
The increasing number of man-made chemicals in the environment that may pose a carcinogenic risk highlights the need for developing reliable time- and cost-effective approaches for carcinogen detection and identification. To address this issue, we investigated the utility of high-throughput microarray gene expression and next-generation genome-wide DNA methylation sequencing for the in vitro identification of genotoxic and non-genotoxic carcinogens. Terminally differentiated and metabolically competent human liver HepaRG cells were treated at minimally cytotoxic concentrations of (i) the genotoxic human liver carcinogen aflatoxin B1 (AFB1) and its structural non-carcinogenic analog aflatoxin B2 (AFB2); (ii) the genotoxic human lung carcinogen benzo[a]pyrene (B[a]P) and its non-carcinogenic isomer benzo[e]pyrene (B[e]P); and (iii) the non-genotoxic liver carcinogen methapyrilene for 72 h and transcriptomic and DNA methylation profiles were examined. Treatment of HepaRG cells with the liver carcinogens AFB1 and methapyrilene generated distinct gene-expression profiles, whereas B[a]P had only a slight effect on gene expression. In contrast to transcriptomic alterations, treatment of HepaRG cells with the carcinogenic and non-carcinogenic chemicals resulted in profound changes in the DNA methylation footprint; however, the correlation between gene-specific DNA methylation and gene expression changes was minimal. Among the carcinogen-altered genes, transferrin (TF) emerged as sensitive marker for an initial screening of chemicals for their potential liver carcinogenicity. Potential liver carcinogens (i.e., chemicals causing altered TF gene expression) could then be subjected to gene-expression analyses to differentiate genotoxic from non-genotoxic liver carcinogens. This approach may substantially enhance the identification and assessment of potential liver carcinogens.
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Affiliation(s)
- Volodymyr Tryndyak
- Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Rd, Jefferson, AR, 72079, USA
| | - Iryna Kindrat
- Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Rd, Jefferson, AR, 72079, USA
| | - Kostiantyn Dreval
- Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Rd, Jefferson, AR, 72079, USA; Department of Internal Medicine, Division of Molecular Medicine, Program in Cancer Genetics, Epigenetics and Genomics, University of New Mexico Comprehensive Cancer Center, Albuquerque, NM, 87131, USA
| | - Mona I Churchwell
- Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Rd, Jefferson, AR, 72079, USA
| | - Frederick A Beland
- Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Rd, Jefferson, AR, 72079, USA
| | - Igor P Pogribny
- Division of Biochemical Toxicology, National Center for Toxicological Research, 3900 NCTR Rd, Jefferson, AR, 72079, USA.
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18
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Goodman JI. Goodbye to the bioassay. Toxicol Res (Camb) 2018; 7:558-564. [PMID: 30090606 PMCID: PMC6062362 DOI: 10.1039/c8tx00004b] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 01/31/2018] [Indexed: 12/30/2022] Open
Abstract
It is time to say goodbye to the standard two-year rodent bioassay. While a few, primarily genotoxic, compounds which are clearly associated with human cancer test positive in the bioassay, there is no science-based, sound foundation for presuming it provides either a valid broad (across different chemicals) capability for discerning potential human carcinogens or a valid starting point for making human risk assessment decisions. The two basic assumptions underlying the bioassay are: (1) rodent carcinogens are human carcinogens; and (2) results obtained at high doses are indicative of results that will occur at lower, environmentally relevant, doses. Both of these assumptions are not correct. Furthermore, a reevaluation of National Toxicology Program bioassay data has revealed that if the dose group size were increased from 50 to 200 rodents per group the number of bioassays deemed to be positive would increase from approximately 50% to very close to 100%. Thus, under the extreme conditions of the bioassay (e.g., high doses, lifetime exposure and, at times, a non-physiological route of administration) virtually all chemicals tested could be made into rodent carcinogens. In recent years there have been a number of proposals to move away from the standard bioassay. In particular, a recently formulated decision tree (Cohen, 2017), which places an emphasis on dose-response relationships and invites the use of MOA information, provides a sound basis for moving on from the bioassay and towards a rational approach to both identify chemicals which appear to have the potential to cause cancer in humans and take dose-response relationships into consideration in order to place the extent, if any, of the risk they might pose into proper perspective.
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Affiliation(s)
- Jay I Goodman
- Department of Pharmacology and Toxicology , Michigan State University , East Lansing , MI 48824 , USA . ; Tel: +1-517-353-9346
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19
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Thompson CM, Suh M, Proctor DM, Chappell G, Borghoff S, Ellis-Hutchings R, Wiench K, Finch L. Assessment of the mode of action underlying development of forestomach tumors in rodents following oral exposure to ethyl acrylate and relevance to humans. Regul Toxicol Pharmacol 2018; 96:178-189. [PMID: 29738809 DOI: 10.1016/j.yrtph.2018.05.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 04/22/2018] [Accepted: 05/02/2018] [Indexed: 02/07/2023]
Abstract
Chronic repeated gavage dosing of high concentrations of ethyl acrylate (EA) causes forestomach tumors in rats and mice. For two decades, there has been general consensus that these tumors are unique to rodents because of: i) lack of carcinogenicity in other organs, ii) specificity to the forestomach (an organ unique to rodents which humans do not possess), iii) lack of carcinogenicity by other routes of exposure, and iv) obvious site of contact toxicity at carcinogenic doses. In 1986, EA was classified as possibly carcinogenic to humans by the International Agency for Research on Cancer (IARC). However, by applying a MOA analyses and human relevance framework assessment, the weight-of-evidence supports a cytotoxic MOA with the following key events: i) bolus delivery of EA to forestomach lumen and subsequent absorption, ii) cytotoxicity likely due to saturation of enzymatic detoxification, iii) chronic regenerative hyperplasia, and iv) spontaneous mutation due to increased cell replication and cell population. Clonal expansion of initiated cells thus results in late onset tumorigenesis. The key events in this 'wound and healing' MOA provide high confidence in the MOA as assessed by evolved Bradford-Hill Criteria. The weight-of-evidence supported by the proposed MOA, combined with a unique tissue that does not exist in humans, indicates that EA is highly unlikely to pose a human cancer hazard.
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Affiliation(s)
| | - Mina Suh
- ToxStrategies, Inc., Mission Viejo, CA 92692, United States
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20
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Smirnova L, Kleinstreuer N, Corvi R, Levchenko A, Fitzpatrick SC, Hartung T. 3S - Systematic, systemic, and systems biology and toxicology. ALTEX 2018; 35:139-162. [PMID: 29677694 PMCID: PMC6696989 DOI: 10.14573/altex.1804051] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 04/06/2018] [Indexed: 12/11/2022]
Abstract
A biological system is more than the sum of its parts - it accomplishes many functions via synergy. Deconstructing the system down to the molecular mechanism level necessitates the complement of reconstructing functions on all levels, i.e., in our conceptualization of biology and its perturbations, our experimental models and computer modelling. Toxicology contains the somewhat arbitrary subclass "systemic toxicities"; however, there is no relevant toxic insult or general disease that is not systemic. At least inflammation and repair are involved that require coordinated signaling mechanisms across the organism. However, the more body components involved, the greater the challenge to reca-pitulate such toxicities using non-animal models. Here, the shortcomings of current systemic testing and the development of alternative approaches are summarized. We argue that we need a systematic approach to integrating existing knowledge as exemplified by systematic reviews and other evidence-based approaches. Such knowledge can guide us in modelling these systems using bioengineering and virtual computer models, i.e., via systems biology or systems toxicology approaches. Experimental multi-organ-on-chip and microphysiological systems (MPS) provide a more physiological view of the organism, facilitating more comprehensive coverage of systemic toxicities, i.e., the perturbation on organism level, without using substitute organisms (animals). The next challenge is to establish disease models, i.e., micropathophysiological systems (MPPS), to expand their utility to encompass biomedicine. Combining computational and experimental systems approaches and the chal-lenges of validating them are discussed. The suggested 3S approach promises to leverage 21st century technology and systematic thinking to achieve a paradigm change in studying systemic effects.
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Affiliation(s)
- Lena Smirnova
- Johns Hopkins University, Bloomberg School of Public Health, Center for Alternatives to Animal Testing (CAAT), Baltimore, MD, USA
| | | | - Raffaella Corvi
- European Commission, Joint Research Centre (JRC), EU Reference Laboratory for Alternatives to Animal Testing (EURL ECVAM), Ispra, (VA), Italy
| | - Andre Levchenko
- Yale Systems Biology Institute and Biomedical Engineering Department, Yale University, New Haven, CT, USA
| | - Suzanne C Fitzpatrick
- Food and Drug Administration (FDA), Center for Food Safety and Applied Nutrition, College Park, MD, USA
| | - Thomas Hartung
- Johns Hopkins University, Bloomberg School of Public Health, Center for Alternatives to Animal Testing (CAAT), Baltimore, MD, USA.
- CAAT-Europe, University of Konstanz, Konstanz, Germany
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21
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Modernizing Human Cancer Risk Assessment of Therapeutics. Trends Pharmacol Sci 2017; 39:232-247. [PMID: 29242029 DOI: 10.1016/j.tips.2017.11.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/17/2017] [Accepted: 11/17/2017] [Indexed: 12/14/2022]
Abstract
Cancer risk assessment of therapeutics is plagued by poor translatability of rodent models of carcinogenesis. In order to overcome this fundamental limitation, new approaches are needed that enable us to evaluate cancer risk directly in humans and human-based cellular models. Our enhanced understanding of the mechanisms of carcinogenesis and the influence of human genome sequence variation on cancer risk motivates us to re-evaluate how we assess the carcinogenic risk of therapeutics. This review will highlight new opportunities for applying this knowledge to the development of a battery of human-based in vitro models and biomarkers for assessing cancer risk of novel therapeutics.
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Gengenbacher N, Singhal M, Augustin HG. Preclinical mouse solid tumour models: status quo, challenges and perspectives. Nat Rev Cancer 2017; 17:751-765. [PMID: 29077691 DOI: 10.1038/nrc.2017.92] [Citation(s) in RCA: 193] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Oncology research in humans is limited to analytical and observational studies for obvious ethical reasons, with therapy-focused clinical trials being the one exception to this rule. Preclinical mouse tumour models therefore serve as an indispensable intermediate experimental model system bridging more reductionist in vitro research with human studies. Based on a systematic survey of preclinical mouse tumour studies published in eight scientific journals in 2016, this Analysis provides an overview of how contemporary preclinical mouse tumour biology research is pursued. It thereby identifies some of the most important challenges in this field and discusses potential ways in which preclinical mouse tumour models could be improved for better relevance, reproducibility and translatability.
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Affiliation(s)
- Nicolas Gengenbacher
- Division of Vascular Oncology and Metastasis, German Cancer Research Center (DKFZ-ZMBH Alliance), 69120 Heidelberg, Germany
| | - Mahak Singhal
- Division of Vascular Oncology and Metastasis, German Cancer Research Center (DKFZ-ZMBH Alliance), 69120 Heidelberg, Germany
- Department of Vascular Biology and Tumor Angiogenesis (CBTM), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Hellmut G Augustin
- Division of Vascular Oncology and Metastasis, German Cancer Research Center (DKFZ-ZMBH Alliance), 69120 Heidelberg, Germany
- Department of Vascular Biology and Tumor Angiogenesis (CBTM), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
- German Cancer Consortium, 69120 Heidelberg, Germany
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23
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Kindrat I, Dreval K, Shpyleva S, Tryndyak V, de Conti A, Mudalige TK, Chen T, Erstenyuk AM, Beland FA, Pogribny IP. Effect of methapyrilene hydrochloride on hepatic intracellular iron metabolism in vivo and in vitro. Toxicol Lett 2017; 281:65-73. [DOI: 10.1016/j.toxlet.2017.09.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 08/22/2017] [Accepted: 09/17/2017] [Indexed: 12/20/2022]
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24
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Thompson CM, Young RR, Dinesdurage H, Suh M, Harris MA, Rohr AC, Proctor DM. Assessment of the mutagenic potential of hexavalent chromium in the duodenum of big blue® rats. Toxicol Appl Pharmacol 2017; 330:48-52. [DOI: 10.1016/j.taap.2017.07.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 07/01/2017] [Accepted: 07/03/2017] [Indexed: 02/07/2023]
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25
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Tarazona JV, Court-Marques D, Tiramani M, Reich H, Pfeil R, Istace F, Crivellente F. Glyphosate toxicity and carcinogenicity: a review of the scientific basis of the European Union assessment and its differences with IARC. Arch Toxicol 2017; 91:2723-2743. [PMID: 28374158 PMCID: PMC5515989 DOI: 10.1007/s00204-017-1962-5] [Citation(s) in RCA: 189] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2017] [Accepted: 03/21/2017] [Indexed: 11/29/2022]
Abstract
Glyphosate is the most widely used herbicide worldwide. It is a broad spectrum herbicide and its agricultural uses increased considerably after the development of glyphosate-resistant genetically modified (GM) varieties. Since glyphosate was introduced in 1974, all regulatory assessments have established that glyphosate has low hazard potential to mammals, however, the International Agency for Research on Cancer (IARC) concluded in March 2015 that it is probably carcinogenic. The IARC conclusion was not confirmed by the EU assessment or the recent joint WHO/FAO evaluation, both using additional evidence. Glyphosate is not the first topic of disagreement between IARC and regulatory evaluations, but has received greater attention. This review presents the scientific basis of the glyphosate health assessment conducted within the European Union (EU) renewal process, and explains the differences in the carcinogenicity assessment with IARC. Use of different data sets, particularly on long-term toxicity/carcinogenicity in rodents, could partially explain the divergent views; but methodological differences in the evaluation of the available evidence have been identified. The EU assessment did not identify a carcinogenicity hazard, revised the toxicological profile proposing new toxicological reference values, and conducted a risk assessment for some representatives uses. Two complementary exposure assessments, human-biomonitoring and food-residues-monitoring, suggests that actual exposure levels are below these reference values and do not represent a public concern.
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Affiliation(s)
- Jose V Tarazona
- Pesticides Unit, European Food Safety Authority, Via Carlo Magno 1/A, 43126, Parma, Italy.
| | - Daniele Court-Marques
- Pesticides Unit, European Food Safety Authority, Via Carlo Magno 1/A, 43126, Parma, Italy
| | - Manuela Tiramani
- Pesticides Unit, European Food Safety Authority, Via Carlo Magno 1/A, 43126, Parma, Italy
| | - Hermine Reich
- Pesticides Unit, European Food Safety Authority, Via Carlo Magno 1/A, 43126, Parma, Italy
| | - Rudolf Pfeil
- Federal Institute for Risk Assessment (BfR), Berlin, Germany
| | - Frederique Istace
- Pesticides Unit, European Food Safety Authority, Via Carlo Magno 1/A, 43126, Parma, Italy
| | - Federica Crivellente
- Pesticides Unit, European Food Safety Authority, Via Carlo Magno 1/A, 43126, Parma, Italy
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26
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Galloway SM. International regulatory requirements for genotoxicity testing for pharmaceuticals used in human medicine, and their impurities and metabolites. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2017; 58:296-324. [PMID: 28299826 DOI: 10.1002/em.22077] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 02/05/2017] [Indexed: 06/06/2023]
Abstract
The process of developing international (ICH) guidelines is described, and the main guidelines reviewed are the ICH S2(R1) guideline that includes the genotoxicity test battery for human pharmaceuticals, and the ICH M7 guideline for assessing and limiting potentially mutagenic impurities and degradation products in drugs. Key aspects of the guidelines are reviewed in the context of drug development, for example the incorporation of genotoxicity assessment into non-clinical toxicity studies, and ways to develop and assess weight of evidence. In both guidelines, the existence of "thresholds" or non-linear dose responses for genotoxicity plays a part in the strategies. Differences in ICH S2(R1) protocol recommendations from OECD guidelines are highlighted and rationales explained. The use of genotoxicity data during clinical development and in assessment of carcinogenic potential is also described. There are no international guidelines on assessment of potentially genotoxic metabolites, but some approaches to safety assessment are discussed for these. Environ. Mol. Mutagen. 58:296-324, 2017. © 2017 Wiley Periodicals, Inc.
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27
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Luijten M, Olthof ED, Hakkert BC, Rorije E, van der Laan JW, Woutersen RA, van Benthem J. An integrative test strategy for cancer hazard identification. Crit Rev Toxicol 2016; 46:615-39. [PMID: 27142259 DOI: 10.3109/10408444.2016.1171294] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Assessment of genotoxic and carcinogenic potential is considered one of the basic requirements when evaluating possible human health risks associated with exposure to chemicals. Test strategies currently in place focus primarily on identifying genotoxic potential due to the strong association between the accumulation of genetic damage and cancer. Using genotoxicity assays to predict carcinogenic potential has the significant drawback that risks from non-genotoxic carcinogens remain largely undetected unless carcinogenicity studies are performed. Furthermore, test systems already developed to reduce animal use are not easily accepted and implemented by either industries or regulators. This manuscript reviews the test methods for cancer hazard identification that have been adopted by the regulatory authorities, and discusses the most promising alternative methods that have been developed to date. Based on these findings, a generally applicable tiered test strategy is proposed that can be considered capable of detecting both genotoxic as well as non-genotoxic carcinogens and will improve understanding of the underlying mode of action. Finally, strengths and weaknesses of this new integrative test strategy for cancer hazard identification are presented.
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Affiliation(s)
- Mirjam Luijten
- a Centre for Health Protection, National Institute for Public Health and the Environment (RIVM) , Bilthoven , the Netherlands
| | - Evelyn D Olthof
- a Centre for Health Protection, National Institute for Public Health and the Environment (RIVM) , Bilthoven , the Netherlands
| | - Betty C Hakkert
- b Centre for Safety of Substances and Products, National Institute for Public Health and the Environment (RIVM) , Bilthoven , the Netherlands
| | - Emiel Rorije
- b Centre for Safety of Substances and Products, National Institute for Public Health and the Environment (RIVM) , Bilthoven , the Netherlands
| | | | - Ruud A Woutersen
- d Netherlands Organization for Applied Scientific Research (TNO) , Zeist , the Netherlands
| | - Jan van Benthem
- a Centre for Health Protection, National Institute for Public Health and the Environment (RIVM) , Bilthoven , the Netherlands
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28
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Anthony Tony Cox L, Popken DA, Kaplan AM, Plunkett LM, Becker RA. How well can in vitro data predict in vivo effects of chemicals? Rodent carcinogenicity as a case study. Regul Toxicol Pharmacol 2016; 77:54-64. [PMID: 26879462 DOI: 10.1016/j.yrtph.2016.02.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 02/03/2016] [Accepted: 02/07/2016] [Indexed: 12/31/2022]
Abstract
A recent research article by the National Center for Computational Toxicology (NCCT) (Kleinstreuer et al., 2013), indicated that high throughput screening (HTS) data from assays linked to hallmarks and presumed pathways of carcinogenesis could be used to predict classification of pesticides as either (a) possible, probable or likely rodent carcinogens; or (b) not likely carcinogens or evidence of non-carcinogenicity. Using independently developed software to validate the computational results, we replicated the majority of the results reported. We also found that the prediction model correlating cancer pathway bioactivity scores with in vivo carcinogenic effects in rodents was not robust. A change of classification of a single chemical in the test set was capable of changing the overall study conclusion about the statistical significance of the correlation. Furthermore, in the subset of pesticide compounds used in model validation, the accuracy of prediction was no better than chance for about three quarters of the chemicals (those with fewer than 7 positive outcomes in HTS assays representing the 11 histopathological endpoints used in model development), suggesting that the prediction model was not adequate to predict cancer hazard for most of these chemicals. Although the utility of the model for humans is also unclear because a number of the rodent responses modeled (e.g., mouse liver tumors, rat thyroid tumors, rat testicular tumors, etc.) are not considered biologically relevant to human responses, the data examined imply the need for further research with HTS assays and improved models, which might help to predict classifications of in vivo carcinogenic responses in rodents for the pesticide considered, and thus reduce the need for testing in laboratory animals.
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Affiliation(s)
| | | | - A Michael Kaplan
- A. Michael Kaplan & Associates, LLC, 23 Wilkinson Drive, Landenberg, PA, 19350, USA.
| | - Laura M Plunkett
- Integrative Biostrategies LLC, 1127 Eldridge Parkway, Suite 300-335, Houston, TX, 77077, USA.
| | - Richard A Becker
- American Chemistry Council, 700 Second Street NE, Washington, D.C. 20002, USA.
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29
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Wikoff DS, Rager JE, Haws LC, Borghoff SJ. A high dose mode of action for tetrabromobisphenol A-induced uterine adenocarcinomas in Wistar Han rats: A critical evaluation of key events in an adverse outcome pathway framework. Regul Toxicol Pharmacol 2016; 77:143-59. [PMID: 26828025 DOI: 10.1016/j.yrtph.2016.01.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2015] [Revised: 01/23/2016] [Accepted: 01/25/2016] [Indexed: 10/22/2022]
Abstract
TBBPA is a non-genotoxic flame retardant used to improve fire safety in a wide variety of consumer products. Estimated human exposures to TBBPA are very low (<0.000084 mg/kg-day), relative to the doses (500 and 1000 mg/kg-day of TBBPA) administered in a recent bioassay that resulted in uterine tumors in Wistar Han rats following chronic exposure. As part of an effort to characterize the relevance of the uterine tumors to humans, data and biological knowledge relevant to the progression of events associated with TBBPA-induced uterine tumors in female rats were organized in an adverse outcome pathway (AOP) framework. Based on a review of possible MOAs for chemically induced uterine tumors and available TBBPA data sets, a plausible molecular initiating event (MIE) was the ability of TBBPA to bind to and inhibit estrogen sulfotransferases, the enzymes responsible for sulfation of estradiol. Subsequent key events in the AOP, including increased bioavailability of unconjugated estrogens in uterine tissue, would occur as a result of decreased sulfation, leading to a disruption in estrogen homeostasis, increased expression of estrogen responsive genes, cell proliferation, and hyperplasia. Available data support subsequent key events, including generation of reactive quinones from the metabolism of estrogens, followed by DNA damage that could contribute to the development of uterine tumors. Uncertainties associated with human relevance are highlighted by potential strain/species sensitivities to development of uterine tumors, as well as the characterization of a dose-dependent MIE. For the latter, it was determined that the TBBPA metabolic profile is altered at high doses (such as those used in the cancer bioassay), and thus an MIE that is only operative under repeated high dose, administration. The MIE and subsequent key events for the development of TBBPA-induced uterine tumors are not feasible in humans given differences in the kinetic and dynamic factors associated with high dose exposures in rats relative to human exposure levels to TBBPA.
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Affiliation(s)
- D S Wikoff
- ToxStrategies, Austin, TX, United States.
| | - J E Rager
- ToxStrategies, Austin, TX, United States
| | - L C Haws
- ToxStrategies, Austin, TX, United States
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Borgert CJ, Wise K, Becker RA. Modernizing problem formulation for risk assessment necessitates articulation of mode of action. Regul Toxicol Pharmacol 2015; 72:538-51. [DOI: 10.1016/j.yrtph.2015.04.018] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 04/17/2015] [Accepted: 04/18/2015] [Indexed: 10/23/2022]
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Thompson CM, Seiter J, Chappell MA, Tappero RV, Proctor DM, Suh M, Wolf JC, Haws LC, Vitale R, Mittal L, Kirman CR, Hays SM, Harris MA. Synchrotron-based imaging of chromium and γ-H2AX immunostaining in the duodenum following repeated exposure to Cr(VI) in drinking water. Toxicol Sci 2015; 143:16-25. [PMID: 25352572 PMCID: PMC4274380 DOI: 10.1093/toxsci/kfu206] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Current drinking water standards for chromium are for the combined total of both hexavalent and trivalent chromium (Cr(VI) and Cr(III)). However, recent studies have shown that Cr(III) is not carcinogenic to rodents, whereas mice chronically exposed to high levels of Cr(VI) developed duodenal tumors. These findings may suggest the need for environmental standards specific for Cr(VI). Whether the intestinal tumors arose through a mutagenic or non-mutagenic mode of action (MOA) greatly impacts how drinking water standards for Cr(VI) are derived. Herein, X-ray fluorescence (spectro)microscopy (µ-XRF) was used to image the Cr content in the villus and crypt regions of duodena from B6C3F1 mice exposed to 180 mg/l Cr(VI) in drinking water for 13 weeks. DNA damage was also assessed by γ-H2AX immunostaining. Exposure to Cr(VI) induced villus blunting and crypt hyperplasia in the duodenum--the latter evidenced by lengthening of the crypt compartment by ∼2-fold with a concomitant 1.5-fold increase in the number of crypt enterocytes. γ-H2AX immunostaining was elevated in villi, but not in the crypt compartment. µ-XRF maps revealed mean Cr levels >30 times higher in duodenal villi than crypt regions; mean Cr levels in crypt regions were only slightly above background signal. Despite the presence of Cr and elevated γ-H2AX immunoreactivity in villi, no aberrant foci indicative of transformation were evident. These findings do not support a MOA for intestinal carcinogenesis involving direct Cr-DNA interaction in intestinal stem cells, but rather support a non-mutagenic MOA involving chronic wounding of intestinal villi and crypt cell hyperplasia.
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Affiliation(s)
- Chad M Thompson
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Jennifer Seiter
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Mark A Chappell
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Ryan V Tappero
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Deborah M Proctor
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Mina Suh
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Jeffrey C Wolf
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Laurie C Haws
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510 ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Rock Vitale
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510 ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510 ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Liz Mittal
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Christopher R Kirman
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510 ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510 ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510 ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc
| | - Sean M Hays
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
| | - Mark A Harris
- ToxStrategies, Inc., Katy, Texas 77494, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180, Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11973, ToxStrategies, Inc., Mission Viejo, California 92692, Experimental Pathology Laboratories, Sterling, Virginia 20166, ToxStrategies, Inc., Austin, Texas 78731, Environmental Standards, Inc., Valley Forge, Pennsylvania 19482, Summit Toxicology, LLP, Orange Village, Ohio 44022 and Summit Toxicology, LLP, Allenspark, Colorado 80510
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Thompson CM, Kirman CR, Proctor DM, Haws LC, Suh M, Hays SM, Hixon JG, Harris MA. A chronic oral reference dose for hexavalent chromium-induced intestinal cancer. J Appl Toxicol 2014; 34:525-36. [PMID: 23943231 PMCID: PMC4282340 DOI: 10.1002/jat.2907] [Citation(s) in RCA: 109] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Revised: 05/15/2013] [Accepted: 06/02/2013] [Indexed: 01/18/2023]
Abstract
High concentrations of hexavalent chromium [Cr(VI)] in drinking water induce villous cytotoxicity and compensatory crypt hyperplasia in the small intestines of mice (but not rats). Lifetime exposure to such cytotoxic concentrations increases intestinal neoplasms in mice, suggesting that the mode of action for Cr(VI)-induced intestinal tumors involves chronic wounding and compensatory cell proliferation of the intestine. Therefore, we developed a chronic oral reference dose (RfD) designed to be protective of intestinal damage and thus intestinal cancer. A physiologically based pharmacokinetic model for chromium in mice was used to estimate the amount of Cr(VI) entering each intestinal tissue section (duodenum, jejunum and ileum) from the lumen per day (normalized to intestinal tissue weight). These internal dose metrics, together with corresponding incidences for diffuse hyperplasia, were used to derive points of departure using benchmark dose modeling and constrained nonlinear regression. Both modeling techniques resulted in similar points of departure, which were subsequently converted to human equivalent doses using a human physiologically based pharmacokinetic model. Applying appropriate uncertainty factors, an RfD of 0.006 mg kg(-1) day(-1) was derived for diffuse hyperplasia-an effect that precedes tumor formation. This RfD is protective of both noncancer and cancer effects in the small intestine and corresponds to a safe drinking water equivalent level of 210 µg l(-1). This concentration is higher than the current federal maximum contaminant level for total Cr (100 µg l(-1)) and well above levels of Cr(VI) in US drinking water supplies (typically ≤ 5 µg l(-1)).
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Affiliation(s)
| | | | | | | | - Mina Suh
- ToxStrategies, Inc.Rancho Santa Margarita, CA, 92688, USA
| | - Sean M Hays
- Summit Toxicology, LLPAllenspark, CO, 80510, USA
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Marone PA, Hall WC, Hayes AW. Reassessing the two-year rodent carcinogenicity bioassay: a review of the applicability to human risk and current perspectives. Regul Toxicol Pharmacol 2013; 68:108-18. [PMID: 24287155 DOI: 10.1016/j.yrtph.2013.11.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Revised: 11/15/2013] [Accepted: 11/17/2013] [Indexed: 12/16/2022]
Abstract
The 2-year rodent carcinogenicity test has been the regulatory standard for the prediction of human outcomes for exposure to industrial and agro-chemicals, food additives, pharmaceuticals and environmental pollutants for over 50 years. The extensive experience and data accumulated over that time has spurred a vigorous debate and assessment, particularly over the last 10 years, of the usefulness of this test in terms of cost and time for the information obtained. With renewed interest in the United States and globally, plus new regulations in the European Union, to reduce, refine and replace sentinel animals, this review offers the recommendation that reliance on information obtained from detailed shorter-term, 6 months rodent studies, combined with genotoxicity and chemical mode of action can realize effective prediction of human carcinogenicity instead of the classical two year rodent bioassay. The aim of carcinogenicity studies should not be on the length of time, and by obligation, number of animals expended but on the combined systemic pathophysiologic influence of a suspected chemical in determining disease. This perspective is in coordination with progressive regulatory standards and goals globally to utilize effectively resources of animal usage, time and cost for the goal of human disease predictability.
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Affiliation(s)
| | - William C Hall
- Hall Consulting, Inc., 110 Shady Brook Circle #300, St. Simons Island, GA 31522, USA.
| | - A Wallace Hayes
- Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
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Edler L, Hart A, Greaves P, Carthew P, Coulet M, Boobis A, Williams GM, Smith B. Selection of appropriate tumour data sets for Benchmark Dose Modelling (BMD) and derivation of a Margin of Exposure (MoE) for substances that are genotoxic and carcinogenic: considerations of biological relevance of tumour type, data quality and uncertainty assessment. Food Chem Toxicol 2013; 70:264-89. [PMID: 24176677 DOI: 10.1016/j.fct.2013.10.030] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Revised: 10/17/2013] [Accepted: 10/17/2013] [Indexed: 10/26/2022]
Abstract
This article addresses a number of concepts related to the selection and modelling of carcinogenicity data for the calculation of a Margin of Exposure. It follows up on the recommendations put forward by the International Life Sciences Institute - European branch in 2010 on the application of the Margin of Exposure (MoE) approach to substances in food that are genotoxic and carcinogenic. The aims are to provide practical guidance on the relevance of animal tumour data for human carcinogenic hazard assessment, appropriate selection of tumour data for Benchmark Dose Modelling, and approaches for dealing with the uncertainty associated with the selection of data for modelling and, consequently, the derived Point of Departure (PoD) used to calculate the MoE. Although the concepts outlined in this article are interrelated, the background expertise needed to address each topic varies. For instance, the expertise needed to make a judgement on biological relevance of a specific tumour type is clearly different to that needed to determine the statistical uncertainty around the data used for modelling a benchmark dose. As such, each topic is dealt with separately to allow those with specialised knowledge to target key areas of guidance and provide a more in-depth discussion on each subject for those new to the concept of the Margin of Exposure approach.
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Affiliation(s)
- Lutz Edler
- German Cancer Research Centre (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
| | - Andy Hart
- The Food and Environment Research Agency - FERA, Sand Hutton, YO41 1LZ York, United Kingdom.
| | - Peter Greaves
- Department of Cancer Studies and Molecular Medicine, University of Leicester, LE2 7LX Leicester, United Kingdom.
| | - Philip Carthew
- Unilever, Colworth House Sharnbrook, MK44 1LQ Bedfordshire, United Kingdom.
| | - Myriam Coulet
- Nestlé Research Centre, Vers-Chez-Les-Blanc, 1000 Lausanne, Switzerland.
| | - Alan Boobis
- Imperial College, Hammersmith Campus, Ducane Road, W12 0NN London, United Kingdom.
| | - Gary M Williams
- New York Medical College, Basic Science Building, Room 413, Valhalla, NY 10595, United States.
| | - Benjamin Smith
- Firmenich, Rue de la Bergere 7, 1217-Meyrin 2, Switzerland.
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Osimitz TG, Droege W, Boobis AR, Lake BG. Evaluation of the utility of the lifetime mouse bioassay in the identification of cancer hazards for humans. Food Chem Toxicol 2013; 60:550-62. [DOI: 10.1016/j.fct.2013.08.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/08/2013] [Accepted: 08/09/2013] [Indexed: 10/26/2022]
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Thompson CM, Proctor DM, Suh M, Haws LC, Kirman CR, Harris MA. Assessment of the mode of action underlying development of rodent small intestinal tumors following oral exposure to hexavalent chromium and relevance to humans. Crit Rev Toxicol 2013; 43:244-74. [PMID: 23445218 PMCID: PMC3604738 DOI: 10.3109/10408444.2013.768596] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Revised: 01/16/2013] [Accepted: 01/17/2013] [Indexed: 12/13/2022]
Abstract
Abstract Chronic exposure to high concentrations of hexavalent chromium (Cr(VI)) in drinking water causes intestinal adenomas and carcinomas in mice, but not in rats. Cr(VI) causes damage to intestinal villi and crypt hyperplasia in mice after only one week of exposure. After two years of exposure, intestinal damage and crypt hyperplasia are evident in mice (but not rats), as are intestinal tumors. Although Cr(VI) has genotoxic properties, these findings suggest that intestinal tumors in mice arise as a result of chronic mucosal injury. To better understand the mode of action (MOA) of Cr(VI) in the intestine, a 90-day drinking water study was conducted to collect histological, biochemical, toxicogenomic and pharmacokinetic data in intestinal tissues. Using MOA analyses and human relevance frameworks proposed by national and international regulatory agencies, the weight of evidence supports a cytotoxic MOA with the following key events: (a) absorption of Cr(VI) from the intestinal lumen, (b) toxicity to intestinal villi, (c) crypt regenerative hyperplasia and (d) clonal expansion of mutations within the crypt stem cells, resulting in late onset tumorigenesis. This article summarizes the data supporting each key event in the MOA, as well as data that argue against a mutagenic MOA for Cr(VI)-induced intestinal tumors.
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Lack of human tissue-specific correlations for rodent pancreatic and colorectal carcinogens. Regul Toxicol Pharmacol 2012; 64:442-58. [PMID: 23069141 DOI: 10.1016/j.yrtph.2012.10.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 09/12/2012] [Accepted: 10/01/2012] [Indexed: 12/14/2022]
Abstract
To better understand the relationships between chemical exposures and human cancer causation, incidence data for human cancer types were identified and pancreatic and colorectal cancers were studied in-depth to assess whether data supporting the causation of pancreatic or colorectal tumors by chemicals in rodents is predictive of causation by the same chemicals of the same tumors in humans. A search of the Carcinogenic Potency Database, the National Toxicology Program (NTP) technical report database, and the published literature identified 38 and 39 chemicals reported to cause pancreatic and colorectal tumors, respectively, in mice or rats. For each of these chemicals, searches were conducted of the International Agency for Research on Cancer monographs, the NTP Report on Carcinogens, and the published literature for evidence of induction of the same tumors in humans. Based on this evaluation, no conclusive evidence was identified to suggest that chemicals reported to cause pancreatic or colorectal tumors in rodents also cause these tumors in humans. These findings suggest that pancreatic tumor data from mouse and rat bioassays are of limited utility with regard to predicting similar tumor induction in humans. For colorectal cancer, a lack of correlation was noted for the vast majority of chemicals.
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Riebeling C, Hayess K, Peters AK, Steemans M, Spielmann H, Luch A, Seiler AEM. Assaying embryotoxicity in the test tube: current limitations of the embryonic stem cell test (EST) challenging its applicability domain. Crit Rev Toxicol 2012; 42:443-64. [PMID: 22512667 DOI: 10.3109/10408444.2012.674483] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Testing for embryotoxicity in vitro is an attractive alternative to animal experimentation. The embryonic stem cell test (EST) is such a method, and it has been formally validated by the European Centre for the Validation of Alternative Methods. A number of recent studies have underscored the potential of this method. However, the EST performed well below the 78% accuracy expected from the validation study using a new set of chemicals and pharmaceutical compounds, and also of toxicity criteria, tested to enlarge the database of the validated EST as part of the Work Package III of the ReProTect Project funded within the 6th Framework Programme of the European Union. To assess the performance and applicability domain of the EST we present a detailed review of the substances and their effects in the EST being nitrofen, ochratoxin A, D-penicillamine, methylazoxymethanol, lovastatin, papaverine, warfarin, β-aminopropionitrile, dinoseb, furosemide, doxylamine, pravastatin, and metoclopramide. By delineation of the molecular mechanisms of the substances we identify six categories of reasons for misclassifications. Some of these limitations might also affect other in vitro methods assessing embryotoxicity. Substances that fall into these categories need to be included in future validation sets and in validation guidelines for embryotoxicity testing. Most importantly, we suggest conceivable improvements and additions to the EST which will resolve most of the limitations.
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Affiliation(s)
- Christian Riebeling
- German Federal Institute for Risk Assessment (BfR), ZEBET - Alternative Methods to Animal Experiments, Berlin, Germany
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Can estragole in fennel seed decoctions really be considered a danger for human health? A fennel safety update. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2012; 2012:860542. [PMID: 22899959 PMCID: PMC3414240 DOI: 10.1155/2012/860542] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 06/20/2012] [Indexed: 01/11/2023]
Abstract
Fennel (Foeniculum vulgare Mill.) mature fruit (commonly known as seeds) and essential oil of fennel are widely used as flavoring agents in food products such as liqueurs, bread, cheese, and an ingredient of cosmetics and pharmaceutical products. Moreover fennel infusions are the classical decoction for nursing babies to prevent flatulence and colic spasm. Traditionally in Europe and Mediterranean areas fennel is used as antispasmodic, diuretic, anti-inflammatory, analgesic, secretomotor, secretolytic, galactagogue, eye lotion, and antioxidant remedy and integrator. Topically, fennel powder is used as a poultice for snake bites. In Asian cultures fennel was ingested to speed the elimination of poisons. As one of the ancient Saxon people's nine sacred herbs, fennel was credited with the power to cure. Fennel was also valued as a magic herb: in the Middle Ages it was draped over doorways on Midsummer's Eve to protect the household from evil spirits. Recently because of estragole carcinogenicity, fennel has been charged to be dangerous for humans especially if used as decoction for babies. But this allegation do not consider the remedy is prepared as a matrix of substances, and recent researches confirm that pure estragole is inactivated by many substance contained in the decoction.
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Rafferty P, Egenolf D, Brosnan K, Makropoulos D, Jordan J, Meshaw K, Walker M, Volk A, Bugelski PJ. Immunotoxicologic effects of cyclosporine on tumor progression in models of squamous cell carcinoma and B-cell lymphoma in C3H mice. J Immunotoxicol 2012; 9:43-55. [DOI: 10.3109/1547691x.2011.614646] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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Beyer LA, Beck BD, Lewandowski TA. Historical perspective on the use of animal bioassays to predict carcinogenicity: Evolution in design and recognition of utility. Crit Rev Toxicol 2011; 41:321-38. [DOI: 10.3109/10408444.2010.541222] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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McGregor D, Boobis A, Binaglia M, Botham P, Hoffstadt L, Hubbard S, Petry T, Riley A, Schwartz D, Hennes C. Guidance for the classification of carcinogens under the Globally Harmonised System of Classification and Labelling of Chemicals (GHS). Crit Rev Toxicol 2010; 40:245-85. [PMID: 20014893 DOI: 10.3109/10408440903384717] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The United Nations Conference on Environment and Development (UNCED) has developed criteria for a globally harmonised system of classification and labelling of chemicals (GHS). With regard to carcinogenicity, GHS distinguishes between Category 1 ('known or presumed human carcinogens') and Category 2 ('suspected human carcinogens'). Category 1 carcinogens are divided into Category 1A ('known to have carcinogenic potential for humans'), based largely on human evidence, and 1B ('presumed to have carcinogenic potential for humans'), based largely on experimental animal data. Concerns have been raised that the criteria for applying these carcinogenicity classifications are not sufficiently well defined and potentially allow different conclusions to be drawn. The current document describes an attempt to reduce the potential for diverse conclusions resulting from the GHS classification system through the application of a series of questions during the evaluation of data from experiments with rodents; epidemiological data, which could lead to Category 1A, have not been considered. Answers to each question can lead either to a classification decision or to the next question, but this process should only be implemented in an environment of informed scientific opinion. The scheme is illustrated with five case studies. These questions are: (1) Has a relevant form of the substance been tested? (2) Is the study design relevant to human exposure? (3) Is there a substance-related response? (4) Is the target tissue exposure relevant to humans? (5) Can a mode of action be established? (6) Is the mode of action relevant to humans? (7) What is the potency?
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Affiliation(s)
- Douglas McGregor
- Toxicity Evaluation Consultants, Aberdour, Scotland, United Kingdom
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Heller JG, Thornhill PG, Conard BR. New views on the hypothesis of respiratory cancer risk from soluble nickel exposure; and reconsideration of this risk's historical sources in nickel refineries. J Occup Med Toxicol 2009; 4:23. [PMID: 19698165 PMCID: PMC2743697 DOI: 10.1186/1745-6673-4-23] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2009] [Accepted: 08/23/2009] [Indexed: 12/02/2022] Open
Abstract
INTRODUCTION While epidemiological methods have grown in sophistication during the 20th century, their application in historical occupational (and environmental) health research has also led to a corresponding growth in uncertainty in the validity and reliability of the attribution of risk in the resulting studies, particularly where study periods extend back in time to the immediate postwar era (1945-70) when exposure measurements were sporadic, unsystematically collected and primitive in technique; and, more so, to the pre-WWII era (when exposure data were essentially non-existent). These uncertainties propagate with animal studies that are designed to confirm the carcinogenicity by inhalation exposure of a chemical putatively responsible for historical workplace cancers since exact exposure conditions were never well characterized. In this report, we present a weight of scientific evidence examination of the human and toxicological evidence to show that soluble nickel is not carcinogenic; and, furthermore, that the carcinogenic potencies previously assigned by regulators to sulphidic and oxidic nickel compounds for the purposes of developing occupational exposure limits have likely been overestimated. METHODS Published, file and archival evidence covering the pertinent epidemiology, biostatistics, confounding factors, toxicology, industrial hygiene and exposure factors, and other risky exposures were examined to evaluate the soluble nickel carcinogenicity hypothesis; and the likely contribution of a competing workplace carcinogen (arsenic) on sulphidic and oxidic nickel risk estimates. FINDINGS Sharp contrasts in available land area and topography, and consequent intensity of production and refinery process layouts, likely account for differences in nickel species exposures in the Kristiansand (KNR) and Port Colborne (PCNR) refineries. These differences indicate mixed sulphidic and oxidic nickel and arsenic exposures in KNR's historical electrolysis department that were previously overlooked in favour of only soluble nickel exposure; and the absence of comparable insoluble nickel exposures in PCNR's tankhouse, a finding that is consistent with the absence of respiratory cancer risk there. The most recent KNR evidence linking soluble nickel with lung cancer risk arose in a reconfiguration of KNR's historical exposures. But the resulting job exposure matrix lacks an objective, protocol-driven rationale that could provide a valid and reliable basis for analyzing the relationship of KNR lung cancer risk with any nickel species. Evidence of significant arsenic exposure during the processing step in the Clydach refinery's hydrometallurgy department in the 1902-1934 time period likely accounts for most of the elevated respiratory cancer risk observed at that time. An understanding of the mechanism for nickel carcinogenicity remains an elusive goal of toxicological research; as does its capacity to confirm the human health evidence on this subject with animal studies. CONCLUDING REMARKS Epidemiological methods have failed to accurately identify the source(s) of observed lung cancer risk in at least one nickel refinery (KNR). This failure, together with the negative long-term animal inhalation studies on soluble nickel and other toxicological evidence, strongly suggest that the designation of soluble nickel as carcinogenic should be reconsidered, and that the true causes of historical lung cancer risk at certain nickel refineries lie in other exposures, including insoluble nickel compounds, arsenic, sulphuric acid mists and smoking.
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Affiliation(s)
- James G Heller
- James G. Heller Consulting Inc., 1 Berney Crescent, Toronto ON, M4G 3G4, Canada
- Dalla Lana School of Public Health, University of Toronto, 6th Floor, Health Sciences Building, 155 College Street, Toronto ON, M5T 3M7, Canada
| | | | - Bruce R Conard
- Environmental and Health Sciences, Inco Ltd, Toronto, ON, Canada
- BR Conard Consulting, Inc., 153 Balsam Drive, Oakville ON, L6J 3X4, Canada
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Boobis AR, Cohen SM, Doerrer NG, Galloway SM, Haley PJ, Hard GC, Hess FG, Macdonald JS, Thibault S, Wolf DC, Wright J. A Data-Based Assessment of Alternative Strategies for Identification of Potential Human Cancer Hazards. Toxicol Pathol 2009; 37:714-32. [DOI: 10.1177/0192623309343779] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The two-year cancer bioassay in rodents remains the primary testing strategy for in-life screening of compounds that might pose a potential cancer hazard. Yet experimental evidence shows that cancer is often secondary to a biological precursor effect, the mode of action is sometimes not relevant to humans, and key events leading to cancer in rodents from nongenotoxic agents usually occur well before tumorigenesis and at the same or lower doses than those producing tumors. The International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) hypothesized that the signals of importance for human cancer hazard identification can be detected in shorter-term studies. Using the National Toxicology Program (NTP) database, a retrospective analysis was conducted on sixteen chemicals with liver, lung, or kidney tumors in two-year rodent cancer bioassays, and for which short-term data were also available. For nongenotoxic compounds, results showed that cellular changes indicative of a tumorigenic endpoint can be identified for many, but not all, of the chemicals producing tumors in two-year studies after thirteen weeks utilizing conventional endpoints. Additional endpoints are needed to identify some signals not detected with routine evaluation. This effort defined critical questions that should be explored to improve the predictivity of human carcinogenic risk.
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Affiliation(s)
| | | | - Nancy G. Doerrer
- ILSI Health and Environmental Sciences Institute, Washington, D.C., 20005 USA
| | | | | | | | | | | | | | - Douglas C. Wolf
- U.S. Environmental Protection Agency, Research Triangle Park, NC, 27713 USA
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Creton S, Billington R, Davies W, Dent MP, Hawksworth GM, Parry S, Travis KZ. Application of toxicokinetics to improve chemical risk assessment: implications for the use of animals. Regul Toxicol Pharmacol 2009; 55:291-9. [PMID: 19665509 DOI: 10.1016/j.yrtph.2009.08.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Revised: 07/31/2009] [Accepted: 08/03/2009] [Indexed: 11/30/2022]
Abstract
While toxicokinetics has become an integral part of pharmaceutical safety assessment over the last two decades, its use in the chemical industry is relatively new. However, it is recognised as a potentially important tool in human health risk assessment and recent initiatives have advocated greater application of toxicokinetics as part of an improved assessment strategy for crop protection chemicals that could offer greater efficiency, use fewer animals and provide better data for risk assessment purposes. To explore the potential scientific and animal welfare benefits of increased use of toxicokinetic data across the chemical industry, an international workshop was held in 2008. Experts from a wide range of chemical industry sectors, including industrial chemicals, agrochemicals and consumer products, participated in the meeting as well as representatives from relevant regulatory authorities. Pharmaceutical industry experts were also invited, in order to share experiences from the extensive use of toxicokinetics in drug development. Given that increased generation of toxicokinetic data could potentially result in an increased number of animals undergoing testing, technologies and strategies to reduce and refine animal use for this purpose were also considered. This paper outlines and expands upon the key themes that emerged from the workshop.
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Affiliation(s)
- Stuart Creton
- National Centre for the Replacement, Refinement and Reduction of Animals in Research, London W1B 1AL, UK.
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Manuppello J, Willett C. Longer rodent bioassay fails to address 2-year bioassay's flaws. ENVIRONMENTAL HEALTH PERSPECTIVES 2008; 116:A516-A518. [PMID: 19079693 PMCID: PMC2599775 DOI: 10.1289/ehp.11964] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
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Plant N. Can systems toxicology identify common biomarkers of non-genotoxic carcinogenesis? Toxicology 2008; 254:164-9. [PMID: 18674585 DOI: 10.1016/j.tox.2008.07.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2008] [Revised: 06/30/2008] [Accepted: 07/01/2008] [Indexed: 10/25/2022]
Abstract
For the rapid development of safe, efficacious chemicals it is important that any potential liabilities are identified as early as possible in the discovery/development pipeline. Once identified it is then possible to make rational decisions on whether to progress a chemical and/or series further; one such liability is chemical carcinogenesis, a highly undesirable characteristic in a novel chemical entity. Chemical carcinogens may be roughly divided into two classes, those that elicit their actions through direct damage to DNA (genotoxic carcinogens) and those that cause carcinogenesis through mechanisms that involve direct damage of the DNA by the agent (non-genotoxic carcinogens). Whereas the former group can be identified by in vitro screens to a good degree of accuracy, the latter group are far more problematic due to their diverse modes of action. This review will focus on the latter class of chemical carcinogens, examining how modern '-omic' technologies have begun to identify signatures that may represent sensitive, early markers for these processes. In addition to their use in signature generation the role of -omic level approaches to delineating molecular mechanisms of action will also be discussed.
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Affiliation(s)
- Nick Plant
- Centre for Toxicology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK.
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Fielden MR, Brennan R, Gollub J. A gene expression biomarker provides early prediction and mechanistic assessment of hepatic tumor induction by nongenotoxic chemicals. Toxicol Sci 2007; 99:90-100. [PMID: 17557906 DOI: 10.1093/toxsci/kfm156] [Citation(s) in RCA: 141] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
There are currently no accurate and well-validated short-term tests to identify nongenotoxic hepatic tumorigens, thus necessitating an expensive 2-year rodent bioassay before a risk assessment can begin. Using hepatic gene expression data from rats treated for 5 days with one of 100 structurally and mechanistically diverse nongenotoxic hepatocarcinogens and nonhepatocarcinogens, a novel multigenebiomarker (i.e., signature) was derived to predict the likelihood of nongenotoxic chemicals to induce liver tumors in longer term studies. Independent validation of the signature on 47 test chemicals indicates an assay sensitivity and specificity of 86% and 81%, respectively. Alternate short-term in vivo pathological and genomic biomarkers were evaluated in parallel for comparison, including liver weight, hepatocellular hypertrophy, hepatic necrosis, serum alanine aminotransferase activity, induction of cytochrome P450 genes, and repression of Tsc-22 or alpha2-macroglobulin messenger RNA. In contrast to these biomarkers, the gene expression-based signature was more accurate. Unlike existing tests, an understanding of potential modes of action for hepatic tumorigenicity can be derived by comparison of the signature profile of test chemicals to hepatic tumorigens of known mechanism, including regenerative proliferation, proliferation associated with xenobiotic receptor activation, peroxisome proliferation, and steroid hormone-mediated mechanisms. This signature is not only more accurate than current methods, but also facilitates the identification of mode of action to aid in the early assessment of human cancer risk.
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Affiliation(s)
- Mark R Fielden
- Iconix Biosciences, Inc., Mountain View, California 94043, USA.
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