Investigation of potential early key events and mode of action for 1,2‐dichloroethane‐induced mammary tumors in female rats

• Published in: Journal of applied toxicology 2021-03, Vol.41 (3), p.362-374
• Main Authors: LeBaron, Matthew J., Hotchkiss, Jon A., Zhang, Fagen, Koehler, Matthew W., Boverhof, Darrell R.
• Format: Article
• Language: English
• Subjects: Adducts; Animal tissues; Bioassays; Breast cancer; Carcinogens; Cell growth; Cell proliferation; Chemical synthesis; Chlorinated hydrocarbons; Comet assay; Damage detection; DCE; Deoxyribonucleic acid; Dichloroethane; DNA; DNA adducts; DNA damage; EDC; Epithelial cells; Estrus; Exposure; Genotoxicity; Glutathione; In vivo methods and tests; Mammary gland; Mammary glands; mammary tumors; MoA; Mode of action; Mutagenicity; nongenotoxic; Polyvinyl chloride; Prolactin; Toxicity; Tumors; Vapors; Weight
• ISSN: 0260-437X; 1099-1263
• DOI: 10.1002/jat.4048

1,2‐dichloroethane (DCE or EDC) is a chlorinated hydrocarbon used as a chemical intermediate, including in the synthesis of polyvinyl chloride. Although DCE has induced tumors in both rats and mice, the overall weight‐of‐evidence suggests a lack of in vivo mutagenicity. The present study was conducted to explore a potential mode of action further for tumor formation in rat mammary tissue. Fischer 344 rats were exposed to target concentrations of 0 or 200 ppm of DCE vapors (6 hours/day, 7 days/week) for at least 28 days; 200 ppm represents a concentration of ~20% higher than that reported to induce mammary tumors. Endpoints examined included DNA damage (via Comet assay), glutathione (reduced, oxidized and conjugated), tissue DNA adducts, cell proliferation and serum prolactin levels. Exposure to DCE did not alter serum prolactin levels with consistent estrous stage, did not cause cell proliferation in mammary epithelial cells, nor result in histopathological alterations in the mammary gland. DNA adducts were identified, including the N7‐guanylethyl glutathione adduct, with higher adduct levels measured in liver (nontumorigenic target) compared with mammary tissue isolated from the same rats; no known mutagenic adducts were identified. DCE did not increase the Comet assay response in mammary epithelial cells, whereas DNA damage in the positive control (N‐nitroso‐N‐methylurea) was significantly increased. Although the result of this study did not identify a specific mode of action for DCE‐induced mammary tumors in rats, the lack of any exposure‐related genotoxic responses further contributes to the weight‐of‐evidence suggesting that DCE is a nongenotoxic carcinogen. 1,2‐dichloroethane (DCE or EDC) is a chlorinated hydrocarbon used as a chemical intermediate, including in the synthesis of polyvinyl chloride. The present study was conducted to explore further the potential mode of action for tumor formation in rat mammary tissue. Although the results of this study do not identify a specific mode of action for DCE‐induced mammary tumors in rats, the lack of any exposure‐related genotoxic responses further contributes to the weight‐of‐evidence suggesting that DCE is a nongenotoxic carcinogen.