Ames Concordance with the In Vivo Transgenic Rodent (TGR) Gene Mutation Assay for NDSRIs and Relative In Vivo TGR Potency with Nitrosamines with Robust Dose-Response Carcinogenicity Data

Nitrosamines (NAs) are a diverse class of mutagenic impurities encompassing both small molecules and structurally complex drug-related NAs, referred to as nitrosamine drug substance-related impurities (NDSRIs). NAs display a broad range of carcinogenic potential, from high carcinogenic potency to being weak or even non-carcinogenic. In vitro Ames tests, conducted with both rat and hamster liver-induced S9, and in vivo transgenic rodent (TGR) mutation assays have been used by pharmaceutical sponsors for hazard identification of NDSRIs. A comparative analysis of Ames tests and TGR results for 33 NDSRIs was performed and revealed an accuracy of 79% between the overall mutagenic calls in the two assays. For NDSRIs with positive TGR results, mutagenic potency estimates were calculated and compared to NAs with robust carcinogenicity and TGR dose-response data. Results from these NAs demonstrated a strong correlation between carcinogenic potency (TD₅₀) and TGR mutagenic potency (BMDL₅₀) (r² = 0.95), which supports the use of TGR data for both hazard identification and acceptable intake (AI) determination. By integrating quantitative risk assessment tools with TGR assays, this work contributes to a more robust framework for evaluating NA-associated risks.