Effects of estrogens and antiestrogens on estrogen receptor dynamics and the induction of progesterone receptor in MCF-7 human breast cancer cells

Antiestrogens appear to be useful in the treatment of endo-crine-resuponsive breast cancers in humans. In an attempt to understand their interactions with breast cancer cells, we have examined the effects of estrogens (estradiol and diethylstilbestrol), and antiestrogens with a range of affinities for estrogen receptor (ER), on intracellular ER dynamics and biological resuponse (progesterone receptor) induction in MCF-7 human breast cancer cells. The triphenylethylene antiestrogens studied are α-{p-[2-(1-pyrrolidino)ethoxy]phenyl}-4-methoxy-α'-nitrostilbene (CI628), α-{p-{2-(1-pyrrolidino)ethoxy]phenyl}-4-hydroxy-α'-nitrostilbene (CI628M), cis-{3-[p-(1,2,3,4,-tetrahydro-6-methoxy-2-phenyl-1 -naphthyl)phenoxy]-1,2-propanediol} (U23,469), and cis-{3-{p-(1,2,3,4-tetrahydro-6-hydroxy-2-phenyl-1 -naphthyl)phenoxy]-1,2, propanediol} (U23.469M). The relative binding affinities of the antiestrogens CI628, CI628M, U23,469, and U23,469M for cytoplasmic ER (ERC) were 1.0,17, 0.04, and 34%, resupectively, in which the affinity of estradiol is considered 100%. Receptor-saturating concentrations of CI628, CI628M, estradiol, and diethylstilbestrol (200, 10, 10, and 10 nM, resupectively) caused complete ERC depletion and peak nuclear ER accumulation within 1 hr. The nuclear receptor (ERN) sites declined thereafter and stabilized at near-control levels (1.2 pmol ERN per mg DNA) by 2 to 5 hr, resulting in a net loss (processing) of approximately 50% of total cellular ER. In contrast, U23,469 (2000 nM) promoted complete depletion of ERC and quantitative accumulation as ERN within 5 min, but the total ER content remained constant thereafter (no processing). U23,469M (60 nM) promoted complete ERC depletion and quantitative nuclear accumulation, but the number of ERN sites subsequently declined slowly to reach the control level by Day 5. Among these compounds, estradiol and diethylstilbestrol (0.1 to 1000 nM) promoted a 600% increase in cytoplasmic progesterone receptor (5 days, control = 0.2 pmol/mg DNA). CI628M and U23.469M (1 to 10 nM) produced only a 300% increase, and 1123,469 and CI628 (0.1 to 1000 nM) did not promote any increase. These results indicate that: (a) ER translocation to the nucleus and progesterone receptor induction appear to be related to ligand affinity; (b) antiestrogens can differ substantially from one another in their dynamics of interaction with ER and in their abilities to stimulate increases in cellular progesterone receptor; (c) processing of ER by antiestrogens such as CI628.