Explanation for main features of structure-genotoxicity relationships of aromatic amines by theoretical studies of their activation pathways in CYP1A2.

Aromatic and heteroaromatic amines (ArNH2) represent a class of potential mutagens that after being metabolically activated covalently modify DNA. Activation of ArNH2 in many cases starts with N-hydroxylation by P450 enzymes, primarily CYP1A2. Poor understanding of structure–mutagenicity relationships of ArNH2 limits their use in drug discovery programs. Key factors that facilitate activation of ArNH2 are revealed by exploring their reaction intermediates in CYP1A2 using DFT calculations. On the basis of these calculations and extensive analysis of structure–mutagenicity data, we suggest that mutagenic metabolites are generated by ferric peroxo intermediate, (CYP1A2)FeIII–OO–, in a three-step heterolytic mechanism. First, the distal oxygen of the oxidant abstracts proton from H-bonded ArNH2. The subsequent proximal protonation of the resulting (CYP1A2)FeIII–OOH weakens both the O–O and the O–H bonds of the oxidant. Heterolytic cleavage of the O–O bond leads to N-hydroxylation of ArNH– via SN2 mechanism, w...