DNA adduct and mutational profiles reveal a threshold of cellular defenses against N-nitrosodimethylamine administered to mice in drinking water

Nina Gubina, Lindsay B. Volk, Anna Dormitzer, Emily Michelsen, Lee J. Pribyl, Joshua J. Corrigan, Esha Dalvie, Amanda L. Armijo, Nicolette A. Bugher, Kayla Shonvisky, Monét Norales, Desiree L. Plata, Bevin P. Engelward, Robert G. Croy, John M. Essigmann, Bogdan I. Fedeles

DOI:

Abstract: N-Nitrosodimethylamine (NDMA) is an animal and probable human carcinogen. Here DNA adduct and high-resolution mutational spectra were correlated following administration of NDMA to mice in drinking water. Liver adducts were determined by QQQ-LC-MS using 15N-enriched adduct internal standards. In a dose-escalation study, 7-methylguanine (m7G) in-creased linearly with dose of NDMA. By contrast, O6-methylguanine (m6G) stayed near background up to ~1 ppm, above which its level, and mutations attributed to it, rose steeply. Three weeks into the 5 ppm exposure regimen, m7G and m6G were elevated by 3-5x above background. Mutations were measured at ten weeks. While chromosomal rearrangements were not increased over background, point mutations were elevated substantially in both sexes. Mutational analysis over 96 3-base contexts revealed a spectrum dominated by GCAT mutations in 5’-purine-G-3’ contexts in a pattern that showed high similarity to human cancer COSMIC mutational signature SBS11, with secondary features resembling SBS119 (ATGC). Taken together the data pinpoint m6G as the dominant mutagenic adduct under chronic dosing by NDMA. Further, the work defined the m6G level at which its dedicated re-pair protein, MGMT, became saturated. This study coordinates the use of DNA adduct and mutational analyses, providing new approaches for early detection and management of cancer.