DNA Alkylation with N-Methylquinolinium Quinone Methide to N2-dG Adducts Resulting in Extensive Stops in Primer Extension with DNA Polymerases and Subsequent Suppression of GFP Expression in A549 Cells

Abstract

Quinone methides (QMs) are involved in the metabolism of many drugs and carcinogens as reactive intermediates to form covalent nucleobase adducts in DNA that associate with high mutagenicity. Recently, a plethora of synthetic QM DNA alkylating agents have been developed to form various nucleobase adducts as potential antitumor agents. However, the mutagenic potential of these synthetic QM alkylating agents has not been fully investigated. In this report, N-methylquinolinium QM was developed as a synthetic model to study biological consequences of the formation of nucleobase adducts in a DNA target. N-Methylquinolinium QM was generated in situ via an elimination process from a bis-quaternary ammonium precursor that was synthesized from a quinoline derivative. Alkylation with N-methylquinolinium QM on a DNA target produced mostly a stable N(2)-dG adduct as revealed by gel electrophoresis and DNA digestion assays and confirmed by mass and NMR analyses. The formation of N(2)-dG adducts of a DNA target was found to cause extensive stops in the primer extension with high fidelity DNA polymerase T7 and even low fidelity error prone Dpo4. The direct biological impact of a prealkylated green fluorescence protein plasmid with N-methylquinolinium QM was demonstrated as significant suppression of protein expression in A549 cells. Overall, our results suggested that nucleobase-QM adducts could potentially block nucleobase mismatch/translesion in the error-prone process to reduce the mutagenic potential if designed carefully.