Increased carcinogen metabolism and survival of retrovirus-infected Fischer rat embryo cells following repetitive carcinogen treatment.

Abstract

The carcinogens N-2-acetylaminofluorene (AAF) and diethylnitrosamine (DEN) often give negative results when tested in the Fischer rat embryo cell survival assay with the standard single 72-hour regimen, whereas another carcinogen, benzo(a)pyrene [B(a)P], may yield varied results between different laboratories and may require relatively high concentrations (compared with other polycyclic aromatic hydrocarbons) for a positive result to occur. Enhanced survivals (compared with controls) were 56% or less with these carcinogens. In place of the standard single 72-hour treatment with test chemical, the cells were exposed to three consecutive 24-hour treatments. The amount of B(a)P metabolized during the last of the three 24-hour treatment periods was 3.2 times greater than that during the first 24-hour period, indicating that an induction effect occurred. Furthermore, the total amount of metabolites of B(a)P formed with repetitive treatments was 2.1 times greater than with a single 72-hour treatment. The total amount of AAF metabolites formed with repeated treatments was 1.6 times greater than with the single treatment regimen, although no induction effect was observed between treatment periods. Survival enhancement with the repetitive regimen increased to 181% with B(a)P, 172% with AAF, and 188% with DEN. With benzo(e)pyrene, anthracene, and pyrene, enhanced survival was 14% or less following the single treatment regimen and did not increase following repetitive treatments. When the carcinogen cinnamyl anthranilate was tested using repetitive treatments, survival enhancement was more than 100% at three of six doses, versus less than 0% when the standard single treatment regimen was used.