SKH-1 mouse skin painting: a short-term assay to evaluate the tumorigenic activity of cigarette smoke condensate.

The hairless mouse strain SKH-1 was investigated in a short-term assay to assess the tumorigenic activity of mainstream cigarette smoke condensate (CSC). The design chosen was the two-stage dermal tumorigenicity assay (skin painting), with tumor initiation using a single dermal application of the carcinogen/mutagen dimethylbenz(a)anthracene applied to the back at a non-tumorigenic dose and tumor promotion by repeated dermal applications of CSC at the same site. The mice reproducibly developed skin tumors at the application site after 15 weeks at a frequency that allowed comparison of the treatment groups. The histopathological examination revealed the benign nature of the tumors (keratotic papillomas). Prolongation of the application period to 25 weeks resulted in the development of malignant tumors (carcinomas), indicating that the benign tumors after 15 weeks can be taken as surrogate endpoints for malignancies progressing after further treatment. After 15 weeks, tumor incidence (the percentage of tumor-bearing mice), tumor multiplicity (the number of tumors per mouse), and tumor-onset (the duration of the application period that resulted in a meaningful tumor incidence) were positively correlated with the initiating and promoting dose. The reproducibility of this assay was at least comparable to that described for other skin painting models in the literature. When the assay system was used to compare CSCs to which different concentrations of benzo(a)pyrene were added, its ability to distinguish these different condensate preparations was comparable to that of other models. The results obtained with the SKH-1 mouse strain suggest its usefulness in the short-term skin painting assay for the comparative investigation of the tumorigenic activity of different CSCs.

Cytotoxicity, mutagenicity, and tumorigenicity of mainstream smoke from three reference cigarettes machine-smoked to the same yields of total particulate matter per cigarette.

The particle phase of mainstream smoke from three types of cigarettes was investigated in vitro in the Neutral Red cytotoxicity assay and the Salmonella typhimurium Reverse Mutation Assay (Ames Assay) and in vivo in the two-stage dermal tumorigenicity assay (Skin Painting Assay) in SENCAR mice. The cigarettes used were the Reference Cigarettes 1R5F, 2R4F, and 2R1F from the University of Kentucky, USA, which, when smoked according to the smoking regimen defined by the International Standards Organization (ISO), produce a yield of approximately 2, 12, and 26 mg total particulate matter (TPM)/cigarette, respectively. All cigarettes were machine smoked according to ISO and then again in such a way that the TPM yields per cigarette equaled the ISO TPM yields of the other two cigarette types. The TPM from cigarettes with inherently different smoke yields showed similar in vitro toxicity and in vivo toxicity when, with different smoking regimens, these cigarettes were smoked to the same TPM yield. More intensive smoking conditions were associated with lower in vitro and in vivo activity per gram of TPM. The strongest decrease, and the tightest correlation, in this regard was observed for dermal tumorigenicity (tumor incidence).