N-NITROSOBENZYLMETHYLAMINE IS ACTIVATED TO A DNA BENZYLATING AGENT INRATS

The ability of rat tissues to activate the esophageal carcinogen, N-ni trosobenzylmethylamine (NBzMA), to a DNA benzylating intermediate was investigated. [3-H-3]NBzMA was prepared and given to male F344 rats. T issues were harvested 4 h after treatment, and DNA was isolated. HPLC analysis with radiochemical detection of chemical and enzymatic hydrol ysates of DNA from liver and lung revealed the formation of benzyl add ucts. Benzyl alcohol, N-2-benzylguanine, 3-benzyladenine, N-6-benzylad enine, and 7-benzylguanine were the major radioactive components in th e hydrolysates. An unknown adduct was also observed. The adduct distri bution was similar to that observed in [3-H-3]benzylnitrosourea ([3-H- 3]BzNU)treated calf thymus DNA. However, enzymatic hydrolysates of [3- H-3]BzNU-treated DNA also contained significant levels of O-6-benzyl-2 '-deoxyguanosine (O-6-BzdG). This radioactive adduct disappeared upon incubation of the DNA with a crude preparation of the repair protein, O-6-alkylguanine-DNA alkyltransferase isolated from rat liver. These d ata provide evidence that O-6-BzdG is probably rapidly repaired in viv o. No benzylation of esophageal mucosal DNA was detected. The level of DNA benzylation observed in tissues from [3-H-3]NBzMA-treated rats wa s several orders of magnitude lower than the level of DNA methylation in these same tissues. Therefore, these data indicate that DNA benzyla tion plays a minor role, if any, in the carcinogenic activity of NBzMA .