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

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Abstract
Transformable mouse embryo fibroblasts, C3H/10T1/2C18, were 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 wk with 5 .mu.M DES resulted in 1 transformed focus from 32 dishes. DES was active as a co-carcinogen in the 2-stage transformation assay at concentrations as low as 50 nM. Under identical conditions, 0.17 .mu.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 0.05-5 .mu.M, and total DNA synthesis was not significantly altered up to 5 .mu.M DES. One .mu.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.