Quantum Mechanical Assessment of Nitrosamine Potency

Area of Science:

• Computational Chemistry
• Toxicology
• Medicinal Chemistry

Background:

• Nitrosamines are a class of compounds of concern due to their potent carcinogenic properties.
• Novel nitrosamine drug substance-related impurities (NDSRIs) require risk assessment for carcinogenicity.
• Current regulatory guidance necessitates limiting nitrosamines below a threshold of toxicological concern (1.5 μg/day).

Purpose of the Study:

• To utilize quantum mechanical (QM) analysis to understand structure-reactivity relationships in nitrosamine carcinogenicity.
• To predict the carcinogenic potency of NDSRIs lacking specific carcinogenicity data.
• To compare QM-based predictions with the Carcinogenic Potency Characterization Approach (CPCA) framework.

Main Methods:

• Quantum mechanical (QM) calculations to determine activation energies for key metabolic pathways.
• Analysis of diverse nitrosamine structures, including N-nitroso pyrrolidines, piperidines, piperazines, morpholines, thiomorpholine, aromatic, and aliphatic nitrosamines.
• Comparison of QM results with the CPCA framework for estimating acceptable intakes (AI).

Main Results:

• QM modeling identified trends in nitrosamine potency through activation energies of metabolic activation pathways.
• The study found instances where CPCA either underestimated or overestimated AI compared to QM predictions.
• QM modeling provides a more analytical method to estimate AI for NDSRIs, especially when CPCA indicates high potency.

Conclusions:

• A combined mechanistic understanding of nitrosamine metabolism (e.g., α-hydroxylation, hydrolysis, DNA interaction) is crucial for predicting potency.
• QM modeling offers a valuable analytical tool to refine AI estimations for novel NDSRIs.
• This work supports and enhances existing regulatory frameworks like CPCA for managing nitrosamine impurities.