Effect of diethylstilbestrol on the transformable mouse embryo fibroblast C3H/10T1/2C18 cells. Tumor promotion, cell growth, DNA synthesis, and ornithine decarboxylase.

Transformable mouse embryo fibroblasts, C3H/10T1/2C18, have been used to study the carcinogenic effect of diethylstilbestrol (DES) in vitro. DES did not show any carcinogenic potential under standard assay conditions. Continuous treatment of the target cells for 5 weeks with 5 micro M DES resulted in 1 transformed focus from 32 dishes. However, DES was active as a co-carcinogen in the two-stage transformation assay at concentrations as low as 50 nM. Under identical conditions, 0.17 micro M 12-O-tetradecanoyl phorbol-13-acetate produced approximately twice as many transformed foci. DES was not toxic to the C3H/10T1/2C18 cells over a range of 0.05 to 5 micro M, and total DNA synthesis was not significantly altered up to 5 micro M DES. 1 micro M DES did not influence the doubling time of the C3H/10T1/2C18 cells. DES did not induce ornithine decarboxylase enzyme activity in this test system.