Effects of progestins, estrogens, and antihormones on growth and lactate dehydrogenase in the human breast cancer cell line T47D.

We have previously reported progestin stimulation of growth and lactate dehydrogenase (LDH) in the human breast cancer cell line T47D. Our further findings now show that growth stimulation by progestins occurs in a dose-responsive manner at physiological concentrations and is inhibited by the antiprogestin RU486. 17 beta-Estradiol (E2) also stimulates proliferation and LDH, and these stimulations are inhibited by tamoxifen. In addition, tamoxifen alone slightly stimulates proliferation. Surprisingly, RU486 also inhibits stimulation by E2. Thus, RU486 acts not only as an antiprogestin, but also as an antiestrogen. While combined promegestone (R5020) and E2 substantially stimulate proliferation, when RU486 is added to this combination it does not further inhibit, but leads to enhanced stimulation. However, the same addition of RU486 to combined E2 and R5020 diminishes LDH stimulation. This suggests that LDH stimulation and growth stimulation are dissociated. Finally, tamoxifen inhibits growth stimulation by combined R5020 and E2, but addition of the antiprogestin RU486 to this combination does not lead to a further inhibition of proliferation. Even so, this same combination reduces LDH levels to control values, further suggesting that stimulation of growth and LDH are dissociated. All of these findings occurred in the absence of the estrogenic pH indicator phenol red. These results emphasize the potential of LDH as an end point for studying the mechanism of female steroid hormone action. They also reveal antiestrogenic activity in RU486. Further, they shed light on the interaction among estrogens, progestins, antiestrogens, and antiprogestins in their effects on growth. Further understanding of this complex interplay may be helpful in treatment of human breast cancer.

Growth stimulation of T47D human breast cancer cells by the anti-progestin RU486.

Our laboratory has previously reported that physiological levels of progestins stimulate growth of the human breast cancer cell line T47D. We have also determined that the antiprogestin RU486 inhibits this stimulation. Here we present the unexpected finding that RU486 alone also stimulates growth of these breast cancer cells. Thus, RU486 exhibits both antagonist and agonist-like activity, in a manner somewhat reminiscent of the antiestrogen tamoxifen. To our knowledge, this is the first report of stimulation of breast cancer growth by RU486.

Progestin stimulation of lactate dehydrogenase in the human breast cancer cell line T-47D.

We have previously reported that physiological levels of progestins alone stimulate lactate dehydrogenase in a dose-responsive manner in the progesterone-receptor-rich human breast cancer cell line T-47D. Using isozyme electrophoresis, we have not found that lactate dehydrogenase isozyme 5 is the only isozyme detectable in these cells, as has been reported for other human breast cancer cells in long-term tissue culture. Upon treatment with progestins, isozyme 5 remains the only isozyme detectable. T-47D cells were plated in charcoal-stripped serum-containing medium and grown for 2 days before treatment with progestin. Lactate dehydrogenase stimulation then plateaued after around 2-3 days of treatment with progestin and was maintained until around day 5, following which a decline in enzyme activity occurred. The effect is specific for progestins, and inhibited by the anti-progestin RU-38486 (17 beta-hydroxy-11 beta-(4-dimethyl-aminophenyl-1)-17 alpha-(prop-1-ynil)-estra-4,9-dien-3-one). Experiments using actinomycin D and cycloheximide suggests that the effect is dependent on RNA and protein synthesis, respectively. Lactate dehydrogenase stimulation occurs regardless of the presence of the estrogenic pH indicator Phenol red, and of whether it was analyzed per mg DNA or per mg protein.

Progestin effects on growth in the human breast cancer cell line T-47D--possible therapeutic implications.

In order to determine growth effects of the progestin R5020, (promegestone), we have utilized the progesterone-receptor rich human breast cancer cell line T-47D, growing the cells in the absence of the pH indicator phenol red, which has recently been found to be estrogenic. In contrast to reports on cells grown in the presence of phenol red, we find that promegestone alone, at physiological progestin concentration, significantly stimulates growth. Estradiol alone, at physiological concentration, stimulates growth much more. Promegestone in combination with estradiol is antiestrogenic for growth; that is, it significantly decreases the growth stimulatory effect of estradiol. These results raise the possibility that estrogen receptor and progesterone receptor-rich breast cancer patients might benefit more from a combination of anti-progestin and anti-estrogen therapy than from anti-estrogens alone.