N-Nitrosobenzylmethylamine is activated to a DNA benzylating agent in rats

The ability of rat tissues to activate the esophageal carcinogen, N- nitrosobenzylmethylamine (NBzMA), to a DNA benzylating intermediate was investigated. [3-³H]NBzMA was prepared and given to male F344 rats. Tissues were harvested 4 h after treatment, and DNA was isolated. HPLC analysis with radiochemical detection of chemical and enzymatic hydrolysates of DNA from liver and lung revealed the formation of benzyl adducts. Benzyl alcohol, N²- benzylguanine, 3-benzyladenine, N⁶-benzyladenine, and 7-benzylguanine were the major radioactive components in the hydrolysates. An unknown adduct was also observed. The adduct distribution was similar to that observed in [3- ³H]benzylnitroseurea ([3-³H]BzNU)treated calf thymus DNA. However, enzymatic hydrolysates of [3-³H]BzNU-treated DNA also contained significant levels of O⁶-benzyl-2'-deoxyguanosine (O⁶-BzdG). This radioactive adduct disappeared upon incubation of the DNA with a crude preparation of the repair protein, O⁶-alkylguanine-DNA alkyltransferase isolated from rat liver. These data provide evidence that O⁶-BzdG is probably rapidly repaired in vivo. No benzylation of esophageal mucosal DNA was detected. The level of DNA benzylation observed in tissues from [3-³H]NBzMA-treated rats was several orders of magnitude lower than the level of DNA methylation in these same tissues. Therefore, these data indicate that DNA benzylation plays a minor role, if any, in the carcinogenic activity of NBzMA.