Survey of tumorigenic sensitivity in 6-month rasH2-Tg mice studies compared with 2-year rodent assays

• Published in: Journal of Toxicologic Pathology Vol. 35; no. 1; pp. 53 - 73
• Main Authors: Hisada, Shigeru, Tsubota, Kenjiro, Inoue, Kenji, Yamada, Hisaharu, Ikeda, Takanori, Sistare, Frank D.
• Format: Journal Article
• Language: English
• Published: Japan JAPANESE SOCIETY OF TOXICOLOGIC PATHOLOGY 01.01.2022; Japan Science and Technology Agency; Japanese Society of Toxicologic Pathology
• Subjects: Animal models; Carcinogenicity; Carcinogens; Genotoxicity; high dose selection; Hyperplasia; ICH S1C guideline; maximum recommended human dose; Mice; Original; pharmacokinetic parameters; Pharmacokinetics; Polls & surveys; rasH2-Tg mouse; Risk analysis; Risk factors; Rodents; Tumorigenesis; Tumors; high dose selection; maximum recommended human dose; ICH S1C guideline; rasH2-Tg mouse; pharmacokinetic parameters; carcinogenicity
• ISSN: 0914-9198; 1881-915X; 1347-7404
• DOI: 10.1293/tox.2021-0031

The pharmacokinetic endpoint of a 25-fold increase in human exposure is one of the specified criteria for high-dose selection for 2-year carcinogenicity studies in rodents according to ICH S1C(R2). However, this criterion is not universally accepted for 6-month carcinogenicity tests in rasH2-Tg mice. To evaluate an appropriate multiple for rasH2-Tg mice, we evaluated data for 53 compounds across five categories of rasH2-Tg mouse-positive [(1) genotoxic and (2) non-genotoxic] carcinogens and rasH2-Tg mouse-negative [(3) non-genotoxic carcinogens with clear or uncertain human relevance; (4) non-genotoxic rodent-specific carcinogens; and (5) non-carcinogens], and surveyed their tumorigenic activities and high doses in rasH2-Tg mice and 2-year rodent models. Our survey indicated that area under the curve (AUC) margins (AMs) or body surface area-adjusted dose ratios (DRs) of tumorigenesis in rasH2-Tg mice to the maximum recommended human dose (MRHD) were 0.05- to 5.2-fold in 6 category (1) compounds with small differences between models and 0.2- to 47-fold in 7 category (2) including three 2-year rat study-negative compounds. Among all 53 compounds, including 40 compounds of the rasH2-Tg mouse-negative category (3), (4), and (5), no histopathologic risk factors for rodent neoplasia were induced only at doses above 50-fold AM or DR in rasH2-Tg mice except for two compounds, which induced hyperplasia and had no relationship with the tumors observed in the rasH2-Tg mouse or 2-year rodent studies. From the results of these surveys, we confirmed that exceeding a high dose level of 50-fold AM in rasH2-Tg mouse carcinogenicity studies does not appear to be of value.