An in vivo-in vitro short term carcinogenicity test using rat peritoneal cells.

A new short-term mammalian carcinogenicity test system is presented in which an in vivo application in rats is followed after 2 weeks by an in vitro culture of the peritoneal cells. One week of culture was sufficient to induce colony growth in soft agar in some cultures of the dimethylnitrosamine (DMNA)-treated, but not in those of control, rats. The results proved to be reproducible and dose-related. Suspended colony growth was not observed in cultures of control rats stimulated successively by the 2 mitogens: thioglycollate and Al(OH)3. The incidence of rats showing transformed colonies in their cultures after a single DMNA dose of 20 mg/kg was nearly double that reported for rats developing tumors after a higher single dose of 30 mg/kg DMNA. More recent experiments have shown that whereas the carcinogen benzo[a]pyrene was positive, its non-carcinogenic analog benzo[e]pyrene was negative; both applied at a single oral dose of 15 mg/kg. A similar result was observed with the acetylaminofluorene (AAF) analogs: 2-AAF and 4-AAF, where the former, a carcinogen, proved positive and the latter, a non-carcinogen, negative. Both analogs were applied at a single oral dose of 50 mg/kg. 2-AAF was also positive at a dose of 25 mg/kg corresponding to 2.5% of the highest tolerable dose of this carcinogen. These results suggest a high structure-related specificity of our test system. Many more similar tests with carcinogen/non-carcinogen analogs will be needed however, before this specificity can be sufficiently established.