Setting limits for N-nitrosamines in drugs: A defined approach based on read-across and structure-activity relationship for N-nitrosopiperazine impurities.

This paper describes DARAN (Defined Approach for Risk Assessment of New Nitrosamines), an new defined approach that uses lines of reasoning based on structure-activity relationship (SAR) patterns and Read-Across (RAx) to set transparent and acceptable limits for new N-nitrosamines for which no toxicological data exist. We selected the compound 1-methyl-4-nitrosopiperazine (MeNP) as a target to calculate a new acceptable limit on the basis of a more transparent and scientifically reasoned RAx. We used publicly available databases and datasets to retrieve experimental in vitro mutagenicity and in vivo carcinogenicity data for N-nitrosopiperazine compounds and to form the chemical category for an RAx. We carried out SAR analyses to try to understand patterns and to obtain interpretable inferences of variation in carcinogenic potency among the N-nitrosopiperazines compounds and their differences with the potent nitrosamines NDMA (N-nitrosodimethylamine) and NDEA (N-nitrosodiethylamine). To estimate an acceptable limit for the target MeNP, we used the scientifically based hypotheses and the evidence lines of about the influence of structural attributes for a robust RAx. On the basis of the criteria proposed in the Assessment Report EMA/369136/20202 and by using the SAR hypotheses obtained by the analysis, we obtained a robust RAx, scientifically supported assumptions, which resulted in TD values predicted from the closest structurally related compounds and a worst-case approach.