Mouse Skin Tumorigenesis and Induction of Aryl Hydrocarbon Hydroxylase by Tobacco Smoke Fractions

Ten fractions separated from the neutral portion of cigarette smoke condensate (CSC) were tested on mouse skin for tumor-initiating activity and for their capacity to induce the enzyme aryl hydrocarbon hydroxylase (AHH). Tumor-initiating activity was confined primarily to the fraction containing more than 90% of the polynuclear aromatic hydrocarbons (PAH) in CSC. One other PAH-containing fraction was active. The combined initiating effect of these fractions was comparable to that of a 40-ppm solution of benzo[a]pyrene (BP), which is about 40 times the BP content of CSC. Some of the neutral fractions that have been demonstrated to cause tumor promotion in mice pretreated with 7,12-dimethylbenz[ a]anthracene were inactive as tumor initiators. The fractions that contained aromatic hydrocarbons induced mouse skin AHH levels twofold to sixfold after a single topical application. AHH-inducing activity was not, however, a reliable indicator of the carcinogenic potential of a fraction