Low androgen levels induce the development of androgen-hypersensitive cell clones in Shionogi mouse mammary carcinoma cells in culture

The influence of the concentration of androgen present on the development of heterogeneous growth responsiveness to androgens was studied in an androgen-sensitive clone (SEM-1) of the Shionogi mammary carcinoma cell line incubated for up to 6 months in the presence of 0, 0.01, 0.3, or 100 nM dihydrotestosterone (DHT). In the absence of added androgen, there was a rapid increase in spontaneous cell growth, the increase being delayed by 2, 4, and 6 months when the cells were incubated with 0.01, 0.3, and 100 nM DHT, respectively. Conversely, the mitogenic effect of DHT decreased rapidly when originally androgen-sensitive cells were incubated with less than maximal concentrations of DHT. The most significant finding was the marked heterogeneity in the androgen sensitivity of the clones obtained after incubation for 2 months in the presence of less than maximal concentrations of DHT. In cells exposed to a maximal concentration of DHT (100 nM), only 2 of 22 clones were more sensitive to DHT (lower Km value) than the original clone, while 8 subclones were hyposensitive to DHT. On the other hand, when the cells were incubated for 2 months with a low (0.3 nM) concentration of DHT, 29% (7 of 24) of the clones were hypersensitive to DHT. Clones derived from cells treated with 0 or 0.1 nM DHT lost most of their responsiveness to DHT during the same time interval, with a simultaneous increase in spontaneous growth rate. The present data show that incubation of a clone of androgen-sensitive Shionogi carcinoma cells in the presence of a low DHT concentration, comparable to the circulating levels of DHT in castrated men, induces the development of androgen-hypersensitive cell clones that are able to grow on minute amounts of androgens. Such androgen-hypersensitive cells are likely to be unresponsive or resistant to antihormonal therapy. The present data emphasize the major importance of the hormonal environment on the maintenance, loss, and increase of tumor cell responsiveness to androgens.