Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Departamento de Patologia, Faculdade de Medicina de Botucatu (FMB), Universidade Estadual Paulista (UNESP), Botucatu, SP, BrasilUniversidade Estadual Paulista, Departamento de Patologia, Faculdade de Medicina de Botucat

APVMA

C Sonich-Mullin

João Lauro V de Camargo

MG Nascimento

MS da Rocha

N Carmichael

SM Cohen

SM Ihlaseh

USEPA

BMC Proceedings

English

PubMed

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Camargo, João Lauro Viana de

Acervo Digital da Unesp

Chemical carcinogenesis - mode of action to inform quantitative human risk

Acervo Digital da Universidade Estadual Paulista

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

Camargo, João Lauro Viana de [UNESP]

Repositório Institucional UNESP

Crossref

KEYNOTE LECTURE PRESENTATION Open AccessChemical carcinogenesis – mode of action toinform quantitative human riskJoão Lauro V de CamargoFrom São Paulo Advanced School of Comparative OncologyÁguas de São Pedro, Brazil. 30 September - 6 October 2012The progressive public and governmental awareness thatwe live in a chemical world, where both natural and man-made substances impose specific risks to living organisms,raised the need for regulatory and interventional measuresto protect human health. Naturally, regulatory measuresdepend on identification of the hazard and the riskimposed by suspected chemicals. In the absence of humandata, laboratory models have been used to identify targetorgans, adverse effects, and critical toxicological doses, allof which contribute to subsidize specific regulations.A case study is presented to illustrate how basic researchcan contribute to regulatory measures aiming to controlhuman cancer risk due to environmental contaminants.Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is asubstituted urea herbicide acting through inhibition ofplant photosynthesis. In a 2-yr long experiment, Wistarrats fed diuron at 2,500 ppm (about 157 mg/kg.day forboth sexes) developed urothelial carcinomas in the urinarybladder. The non-observed effect level (NOEL) for carci-nogenicity was 25 ppm (1.35 mg/kg.day), based on urothe-lial hyperplasia and tumors [1]. Accordingly, the U.S.Environmental Protection Agency evaluated diuron as a“known/likely carcinogen to humans” [1,2]. Despite thisclassification, the quantitative risk associated to diuronwas considered of no concern [2] and the herbicide isworldwide applied on main agricultural crops such as soy,cotton and sugar cane, among other uses. The impact ofchronic low-dose exposure to diuron on human health hasnot been determined.The standard procedure for identifying chemical carci-nogens is the long-term bioassay with rodents. Althoughpresenting a 40-year long history of usefulness, this 2-yearassay bears important limitations, such as high cost andoperational complexity, and also because it was notdesigned to provide information about the toxicologicalmode of action (MoA) of chemicals. As for any experi-ment with laboratory animals, extrapolating the results tothe human situation is not a simple task, and may com-promise human risk assessment. To inform risk assess-ment, a framework was proposed for systematic anddetailed evaluation of the MoA in laboratory animals andfor evaluating the human relevance of experimental results[3-5].The genotoxic/mutagenic potentials of diuron areaccepted to be negative [1,6,7]. Therefore, the carcino-genic MoA of diuron in the rat urinary bladder shouldbe predominantly non-genotoxic. In an early study, ratsfed diuron at 2,500 ppm during 20 weeks developedurothelial necrosis – observed ultrastructurally -, regen-erative cell proliferation and urothelial hyperplasia [6].To test the hypothesis that urinary crystals and amor-phous precipitates could act as microabrasives to themucosa causing cell death and regenerative hyperplasiathat lead to urothelial carcinogenesis, rats were fed2,500 ppm of diuron either with or without NH4Cl10,000 to acidify urine during 15 to 30 weeks [7].Groups fed diuron+NH4 showed reduced amount ofurinary solids in the urine; nevertheless, urothelialnecrosis and simple hyperplasia (SH), a stochastic pre-neoplastic urothelial lesion, were observed both indiuron- and diuron+NH4Cl treated animals. Therefore,chemically induced cytotoxicity and not abrasion byurinary solids seems to be the initial key event fordiuron-induced rat urothelial carcinogenesis. Theseurothelial lesions start at the very 1st day of exposure to2,500 ppm and encompass cell swelling followed bynecrosis, exfoliation and piling up of cells indicative ofhyperplasia [8]. A recent study indicated that 500 ppmcan also induce urothelial citotoxicity [9].Regarding dose-response and the molecular pathwaysinvolved, rats were fed diuron at different concentrationsCorrespondence: decam@fmb.unesp.brDepartment of Pathology – Faculty of Medicine, São Paulo State University,UNESP, Botucatu, São Paulo, Brazilde Camargo BMC Proceedings 2013, 7(Suppl 2):K10http://www.biomedcentral.com/1753-6561/7/S2/K10© 2013 de Camargo; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited.from 60 ppm up to 2,500 ppm for 7 days and 20 weeks.After 7 days no significant urothelial lesions were observedby light or electron microscopy but gene expression profile(Affymetrix microarrays) indicated altered pathwaysrelated to cell-to-cell interactions in a dose-response man-ner, suggesting that the early influence of diuron and/orits metabolites on the urothelium may result in loss ofcell-to-cell adhesion and local tissue disorganization [10].By the week 20th, rats fed 1,250 or 2,500 ppm, but notthose fed 125 ppm or lower, developed SH [11]. Accord-ingly, gene expression data suggested that low levels ofdiuron induced pathways involved in the maintenance ofcellular homeostasis while higher levels were associated toincreased cell metabolism, oxidative stress and cell deathfollowed by sustained hyperplasia. Although based on pre-neoplastic alterations, these data allow indicating diuron at1,250 ppm as potentially carcinogenic as 2,500 ppm andassuming 125 ppm as a no effect level (NOEL) for urothe-lial alterations [11].This case study illustrates how translational non-clinicalresearch can help to understand and eventually controlenvironmentally-related human cancer hazards. Opticaland ultrastructural microscopies, genotoxicity assays, cellproliferation assays, and genome-wide transcriptional pro-filing disclosed key events of diuron-induced rat urothelialcytotoxicity and potential carcinogenesis. They also indi-cated that a threshold dose may exist below which no car-cinogenic process is launched. Data still missing tosupport sound quantitative human risk assessment refersto the evaluation of human relevance of the key eventsverified in rodents and the identification of the exposurelevels to which people are exposed.AcknowledgmentsBrazilian funding agencies FAPESP and CNPq provided grants to supportthese studies. Researchers at the Nebraska University Medical Center(UNMC), under Dr. S.M. Cohen, at the National Health and EnvironmentalEffects Research Laboratories (NHEERL), USEPA, under Dr. D.C. Wolf, and atthe Sao Paulo State Univ (UNESP), under Dr. J.L.V. de Camargo, gave supportand co-authored the studies described.Published: 4 April 2013References1. APVMA: Diuron. Human health assessment. Australian Pesticides andVeterinary Medicines Authority. Australian Government; 2011, 76.2. USEPA: Registration Eligibility Decision (RED) for Diuron. USEnvironmental Protection Agency. Office of Prevention, Pesticides and ToxicSubstances; 2003 [http://www.epa.gov/oppsrrd1/REDs/diuron_red.pdf],Accessed on September 12th, 2012.3. Sonich-Mullin C, Fielder R, Wiltse J, Baetcke K, Dempsey J, Fenner-Crisp P,Grant D, Hartley M, Knaap A, Kroese D, Mangelsdorf I, Meek E, Rice JM,Younes M, International Programme on Chemical Safety: IPCS conceptualframework for evaluating a mode of action for chemical carcinogenesis.Regulatory Toxicology and Pharmacology 2001, 34:146-152.4. Cohen SM, Klaunig J, Meek ME, Hill RN, Pastoor T, Lehman-McKeeman L,Bucher J, Longfellow DG, Seed J, Dellarco V, Fenner-Crisp P, Patton D:Evaluating the human relevance of chemically induced animal tumors.Toxicol Sci 2004, 78(2):181-6.5. Carmichael N, Bausen M, Boobis AR, Cohen SM, Embry M, Fruijtier-Pölloth C,Greim H, Lewis R, Bette Meek ME, Mellor H, Vickers C, Doe J: Using modeof action information to improve regulatory decision-making: anECETOC/ILSI RF/HESI workshop overview. Crit Rev Toxicol 2011, 41:175-186.6. Nascimento MG, de Oliveira ML, Lima AS, de Camargo JL: Effects of diuron[3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the urinary bladder of maleWistar rats. Toxicology 2006, 224:66-73.7. da Rocha MS, Nascimento MG, Cardoso AP, de Lima PL, Zelandi EA, deCamargo JL, de Oliveira ML: Cytotoxicity and regenerative proliferation asthe mode of action for diuron-induced urothelial carcinogenesis in therat. Toxicol Sci 2010, 113(1):37-44.8. da Rocha MS, Arnold LL, Pennington KL, Muirhead D, Dodmane PR,Anwar MM, Battalora M, De Camargo JL, Cohen SM: Diuron-induced ratbladder epithelial cytotoxicity. Toxicol Sci 2012.9. Cardoso , et al: Dose-response study of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) on the urinary bladder of male Wistar rats., inpreparation.10. Ihlaseh , et al: Gene expression profiling of urinary bladder urotheliumfrom rats treated with diuron for seven days., in preparation.11. Ihlaseh SM, Bailey KA, Hester SD, Jones C, Ren H, Cardoso AP, Oliveira ML,Wolf DC, de Camargo JL: Transcriptional profile of diuron-induced toxicityon the urinary bladder of male Wistar rats to inform mode of action.Toxicol Sci 2011, 122(2):330-338.doi:10.1186/1753-6561-7-S2-K10Cite this article as: de Camargo: Chemical carcinogenesis – mode ofaction to inform quantitative human risk. BMC Proceedings 20137(Suppl 2):K10.Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color figure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionSubmit your manuscript at www.biomedcentral.com/submitde Camargo BMC Proceedings 2013, 7(Suppl 2):K10http://www.biomedcentral.com/1753-6561/7/S2/K10Page 2 of 2

Chemical carcinogenesis – mode of action to inform quantitative human risk

Jo�o Lauro V de Camargo

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Chemical carcinogenesis � mode of action to inform quantitative human risk

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Chemical carcinogenesis – mode of action to inform quantitative human risk

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