TY - JOUR
T1 - Evaluation of the mode of action and human relevance of liver tumors in male mice treated with epyrifenacil
AU - Fukunaga, Satoki
AU - Ogata, Keiko
AU - Eguchi, Ayumi
AU - Matsunaga, Kohei
AU - Sakurai, Kengo
AU - Abe, Jun
AU - Cohen, Samuel M.
AU - Asano, Hiroyuki
N1 - Funding Information:
This study was supported by the Sumitomo Chemical Co., Ltd.
Funding Information:
A framework for analyzing MOAs of toxicity observed in experimental animals, including tumorigenesis, and their relevance to humans has been developed by the International Programme on Chemical Safety (IPCS) of the World Health Organization (Boobis et al., 2006, 2008; Sonich-Mullin et al., 2001) and the International Life Sciences Institute (ILSI) (Meek et al., 2003; Seed et al., 2005) sponsored by the United States Environmental Protection Agency (U.S. EPA) and Health Canada. It is widely used as a template to elucidate the human relevance of a carcinogenic MOA observed in experimental animals. The postulated MOA is generally considered qualitatively to be plausible in humans if the key events of this MOA in mice have similarities with those of an MOA for porphyria-mediated liver tumorigenesis in humans (Holsapple et al., 2006; Smith and Foster, 2018). In the case of a mouse carcinogenicity MOA that is qualitatively relevant to humans, a more quantitative assessment is required for purposes of human relevance analysis within the IPCS Human Relevance Framework (Boobis et al., 2006). Therefore, it is important to characterize the MOA in the mouse and also evaluate an effect of epyrifenacil on these key events in human liver, which enables more accurate quantitative assessment and human relevance analysis.This study was supported by the Sumitomo Chemical Co., Ltd.
Publisher Copyright:
© 2022 The Authors
PY - 2022/12
Y1 - 2022/12
N2 - Epyrifenacil (trademark name: Rapidicil®), a novel protoporphyrinogen oxidase (PPO)-inhibiting herbicide, induces hepatocellular adenomas and carcinomas in male CD-1 mice after 78 weeks treatment. The mode of action (MOA) of these mouse liver tumors and their relevance to humans was assessed based on the 2006 International Programme on Chemical Safety (IPCS) Human Relevance Framework. Epyrifenacil is not genotoxic and induced liver tumors via the postulated porphyria-mediated cytotoxicity MOA with the following key events: (#1) PPO inhibition; (#2) porphyrin accumulation; (#3) hepatocellular injury; with (#4) subsequent regenerative cell proliferation; and ultimately (#5) development of liver tumors. This article evaluates the weight of evidence for this MOA based on the modified Bradford Hill criteria. The MOA data were aligned with the dose and temporal concordance, biological plausibility, coherence, strength, consistency, and specificity for a porphyria-mediated cytotoxicity MOA while excluding other alternative MOAs. Although the postulated MOA could qualitatively potentially occur in humans, we demonstrate that it is unlikely to occur in humans because of quantitative toxicodynamic and toxicokinetic differences between mice and humans. Therefore, this MOA is considered not relevant to humans, utilizing the IPCS Human Relevance Framework; consequently, a nonlinear, threshold dose response would be appropriate for human risk assessment.
AB - Epyrifenacil (trademark name: Rapidicil®), a novel protoporphyrinogen oxidase (PPO)-inhibiting herbicide, induces hepatocellular adenomas and carcinomas in male CD-1 mice after 78 weeks treatment. The mode of action (MOA) of these mouse liver tumors and their relevance to humans was assessed based on the 2006 International Programme on Chemical Safety (IPCS) Human Relevance Framework. Epyrifenacil is not genotoxic and induced liver tumors via the postulated porphyria-mediated cytotoxicity MOA with the following key events: (#1) PPO inhibition; (#2) porphyrin accumulation; (#3) hepatocellular injury; with (#4) subsequent regenerative cell proliferation; and ultimately (#5) development of liver tumors. This article evaluates the weight of evidence for this MOA based on the modified Bradford Hill criteria. The MOA data were aligned with the dose and temporal concordance, biological plausibility, coherence, strength, consistency, and specificity for a porphyria-mediated cytotoxicity MOA while excluding other alternative MOAs. Although the postulated MOA could qualitatively potentially occur in humans, we demonstrate that it is unlikely to occur in humans because of quantitative toxicodynamic and toxicokinetic differences between mice and humans. Therefore, this MOA is considered not relevant to humans, utilizing the IPCS Human Relevance Framework; consequently, a nonlinear, threshold dose response would be appropriate for human risk assessment.
KW - Chemical-induced porphyria
KW - Chimeric mouse with humanized liver
KW - Epyrifenacil
KW - Mode of action
KW - Mouse liver tumors
KW - Porphyria-mediated cytotoxicity
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U2 - 10.1016/j.yrtph.2022.105268
DO - 10.1016/j.yrtph.2022.105268
M3 - Article
C2 - 36210011
AN - SCOPUS:85141005262
SN - 0273-2300
VL - 136
JO - Regulatory Toxicology and Pharmacology
JF - Regulatory Toxicology and Pharmacology
M1 - 105268
ER -