title: Comparison of in vivo genotoxic and carcinogenic potency to augment mode of action analysis: Case study with hexavalent chromium.
abstract: Recent analyses-highlighted by the International Workshops on Genotoxicity Testing Working Group on Quantitative Approaches to Genetic Toxicology Risk Assessment-have identified a correlation between (log) estimates of a carcinogen's in vivo genotoxic potency and in vivo carcinogenic potency in typical laboratory animal models, even when the underlying data have not been matched for tissue, species, or strain. Such a correlation could have important implications for risk assessment, including informing the mode of action (MOA) of specific carcinogens. When in vivo genotoxic potency is weak relative to carcinogenic potency, MOAs other than genotoxicity (e.g., endocrine disruption or regenerative hyperplasia) may be operational. Herein, we review recent in vivo genotoxicity and carcinogenicity data for hexavalent chromium (Cr(VI)), following oral ingestion, in relevant tissues and species in the context of the aforementioned correlation. Potency estimates were generated using benchmark doses, or no-observable-adverse-effect-levels when data were not amenable to dose-response modeling. While the ratio between log values for carcinogenic and genotoxic potency was ≥1 for many compounds, the ratios for several Cr(VI) datasets (including in target tissue) were less than unity. In fact, the ratios for Cr(VI) clustered closely with ratios for chloroform and diethanolamine, two chemicals posited to have non-genotoxic MOAs. These findings suggest that genotoxicity may not play a major role in the cancers observed in rodents following exposure to high concentrations of Cr(VI) in drinking water-a finding consistent with recent MOA and adverse outcome pathway (AOP) analyses concerning Cr(VI). This semi-quantitative analysis, therefore, may be useful to augment traditional MOA and AOP analyses. More case examples will be needed to further explore the general applicability and validity of this approach for human health risk assessment.
authors.affiliation: ToxStrategies, Inc., Katy, TX, United States. Electronic address: cthompson@toxstrategies.com.
authors.forename: Chad M
authors.initials: CM
authors.lastname: Thompson
authors.affiliation: ToxStrategies, Inc., Austin, TX, United States.
authors.forename: Anne
authors.initials: A
authors.lastname: Bichteler
authors.affiliation: ToxStrategies, Inc., Austin, TX, United States.
authors.forename: Julia E
authors.initials: JE
authors.lastname: Rager
authors.affiliation: ToxStrategies, Inc., Mission Viejo, CA, United States.
authors.forename: Mina
authors.initials: M
authors.lastname: Suh
authors.affiliation: ToxStrategies, Inc., Mission Viejo, CA, United States.
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Proctor
authors.affiliation: ToxStrategies, Inc., Austin, TX, United States.
authors.forename: Laurie C
authors.initials: LC
authors.lastname: Haws
authors.affiliation: ToxStrategies, Inc., Katy, TX, United States.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Harris
mesh_terms: D000284:Administration, Oral; D000818:Animals; D015197:Carcinogenicity Tests; D002274:Carcinogens, Environmental / Q000008:administration & dosage / Q000633:toxicity; D002857:Chromium / Q000008:administration & dosage / Q000633:toxicity*; D004379:Duodenal Neoplasms / Q000139:chemically induced*; D005260:Female; D008297:Male; D015201:Meta-Analysis as Topic; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009062:Mouth Neoplasms / Q000139:chemically induced*; D009152:Mutagenicity Tests; D011916:Rats, Inbred F344; D012196:Review Literature as Topic; D018570:Risk Assessment / Q000379:methods; D014874:Water Pollutants, Chemical / Q000008:administration & dosage / Q000633:toxicity*
chemical_list: D002274:Carcinogens, Environmental; D014874:Water Pollutants, Chemical; D002857:Chromium; C074702:chromium hexavalent ion
keywords: Carcinogenicity; Genotoxicity; Hexavalent chromium; Mode of action; Risk assessment