ru-58668 and afimoxifene

Estrogen receptor alpha (ER) turnover in MCF-7 cells was assessed by pulse chase analysis and measurement of ER steady-state level. In untreated cells, degradation of (35)S-labeled ER was characterized by a slow phase followed by a more rapid decline. Without ligand, ER elimination was totally compensated by synthesis which maintained receptor homeostasis. Estradiol (E(2)) and the pure antiestrogen RU 58,668 abolished the slow phase of ER breakdown and enhanced the degradation of neosynthesized ER, producing a low ER steady-state level. By contrast, the partial antiestrogen OH-Tam was ineffective in this respect and caused ER accumulation. Regardless of the conditions, ER breakdown was abolished by proteasome inhibition (MG-132). ER ligands decreased cell capacity to bind [(3)H]E(2), even in the presence of MG-132, indicating that the regulation of ER level and E(2) binding capacity occurs through distinct mechanisms. MG-132 partially blocked the basal transcription of an ERE-dependent reporter gene and modified the ability of E(2) to induce the expression of the latter: the hormone was unable to restore the transactivation activity measured without MG-132. RU 58,668 and OH-Tam failed to enhance the inhibitory action of MG-132, suggesting that a loss of basal ER-mediated transactivation mainly affects the stimulatory effect of estrogens. Overall, our findings reveal that ER steady state level, ligand binding capacity and transactivation potency fit in a complex regulatory scheme involving distinct mechanisms, which may be dissociated from each other under various treatments.

Topics: Breast Neoplasms; Cell Line, Tumor; Cycloheximide; Down-Regulation; Enzyme Inhibitors; Estradiol; Estrogen Receptor alpha; Genes, Reporter; Humans; Leupeptins; Ligands; Luciferases; Methionine; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Sulfur Radioisotopes; Tamoxifen; Transcription, Genetic; Tritium

Estrogen receptor-alpha (ER) is down-regulated in the presence of its cognate ligand, estradiol (E2), as well as in the presence of antiestrogens, through the ubiquitin proteasome pathway. Here, we show that, at pharmacological concentrations, the degradation rate of pure antagonist/endogenous ER complexes from human breast cancer MCF-7 cells is 10 times faster than that of ER-E2 complexes, while 4-hydroxy-tamoxifen (4-OH-T)-ER complexes are stable. Whereas pure antagonist-ER complexes are firmly bound to a nuclear compartment from which they are not extractable, the 4-OH-T-ER accumulates in a soluble cell compartment. No difference was observed in the fate of ER whether bound to pure antiestrogens ICI 182,780 or RU 58668. Cycloheximide experiments showed that, while the proteasome-mediated destruction of E2-ER (unlike that of RU 58668- and ICI 182,780-ER) complexes could implicate (or not) a protein synthesis-dependent process, both MAPKs (p38 and ERKs p44 and p42) are activated. By using a panel of kinase inhibitors/activators to study the impact of phosphorylation pathways on ER degradation, we found that protein kinase C is an enhancer of proteasome-mediated degradation of both ligand-free and ER bound to either E2, 4-OH-T, and pure antagonists. On the contrary, protein kinase A, MAPKs, and phosphatidyl-inositol-3 kinase all impede proteasome-mediated destruction of ligand free and E2-bound ER while only MAPKs inhibit the degradation of pure antiestrogens/ER species. In addition, no correlation was found between the capacity of kinase inhibitors to affect ER stability and the basal or E2-induced transcription. These results suggest that, in MCF-7 breast cancer cells, ER turnover, localization, and activity are maintained by an equilibrium between various phosphorylation pathways, which are differently modulated by ER ligands and protein kinases.

Topics: Antineoplastic Agents, Hormonal; Breast Neoplasms; Cell Line, Tumor; Cyclic AMP-Dependent Protein Kinases; Cysteine Endopeptidases; Dose-Response Relationship, Drug; Estradiol; Estrogen Antagonists; Estrogen Receptor alpha; Estrogen Receptor Modulators; Female; Fulvestrant; Gene Expression Regulation, Neoplastic; Humans; Kinetics; Ligands; MAP Kinase Kinase Kinases; Multienzyme Complexes; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proteasome Endopeptidase Complex; Protein Kinase C; Protein Kinase Inhibitors; Protein Kinases; Receptors, Estrogen; Tamoxifen; Transcription, Genetic

This study aimed at a better understanding of estrogen receptor alpha (ER) up regulation induced by partial estrogen antagonists. Effect of treatment with hydroxytamoxifen (OH-Tam) on ER level in MCF-7 cells was investigated by an approach combining ER measurement (enzyme immunoassay) and morphological demonstration (immunofluorescence). Furthermore, the influence of drug exposure on the rates of ER synthesis and degradation was assessed by determining [35S]methionine incorporated into the receptor in different experimental conditions (measurement of synthesis or pulse-chase experiments). ER up regulation was already induced by a 1-h pulse treatment with OH-Tam, thus a continuous exposure was not required. This process appeared reversible (i.e. ER accumulation due to OH-Tam rapidly vanished upon subsequent exposure to 17beta-estradiol (E2) or the pure antiestrogen RU 58668). While OH-Tam did not affect the rate of [35S]methionine incorporation into ER, it clearly caused an impairment of ER degradation (pulse-chase experiments) indicating that up regulation results from a stabilization of the receptor associated with the maintenance of its synthesis. Various tamoxifen derivatives, as well as a few related partial antiestrogens, were compared on the basis of binding ability and propensity to induce ER up regulation. A close relationship was found between both properties. Structure-activity analysis revealed that the capacity of these compounds to induce ER up regulation is associated with characteristics of their aminoalkyle side-chain, similar to those required for antiestrogenicity.

Topics: Breast Neoplasms; Cell Line, Tumor; Cell Nucleus; Cytosol; Down-Regulation; Enzyme-Linked Immunosorbent Assay; Estradiol; Estrogen Receptor alpha; Estrogen Receptor Modulators; Fluorescent Antibody Technique; Gene Expression Regulation, Neoplastic; Humans; Phenols; Radioligand Assay; Receptors, Estrogen; Structure-Activity Relationship; Tamoxifen; Up-Regulation

Nonsteroidal antiestrogens, such as tamoxifen, are well established in the treatment of breast cancer. The development of new steroidal compounds without partial agonist activity allows deeper insights into the mechanism of antiestrogen action, but thus far, the combined use of steroidal and nonsteroidal antiestrogens has not been studied extensively. We compared the nonsteroidal 4-trans-hydroxytamoxifen (OHT) with the two steroidal antiestrogens, ICI 182780 and RU 58668, in the estrogen receptor-positive human breast cancer cell lines MCF-7 and T47D. The effect of each compound alone or of OHT in combination with one of the steroidal antiestrogens was studied in regard to cell proliferation, expression of estrogen receptors (ERs) and progesterone receptors, and secretion of transforming growth factor beta2 (TGF-beta2). All antiestrogens examined led to enhanced secretion of TGF-beta2, which is correlated with their individual growth-inhibitory potential. OHT partially counteracts the larger growth inhibition of human breast cancer cells exerted by the steroidal antiestrogens ICI 182780 and RU 58668. Also, OHT antagonizes the higher induction of TGF-beta2 seen after treatment of MCF-7 cells with steroidal antiestrogens. The loss of ER and down-regulation of progesterone receptor under treatment with the steroidal antiestrogens is prevented by OHT, whereas the steroidal antiestrogens prevent the ability of hydroxytamoxifen to increase the ER content. These results indicate that TGF-beta2 is a marker of action for both types of compounds, but steroidal and nonsteroidal antiestrogens partially antagonize each other in blocking ER-mediated cellular events. It would appear that no additive or synergistic effect of the two types of antiestrogens can be expected in the treatment of breast cancer.

Topics: Antineoplastic Combined Chemotherapy Protocols; Breast Neoplasms; Cell Division; Drug Interactions; Estradiol; Estrogen Antagonists; Female; Fulvestrant; Humans; Receptors, Estrogen; Receptors, Progesterone; Tamoxifen; Transforming Growth Factor beta; Tumor Cells, Cultured

Anti-estrogens like hydroxytamoxifen (OHT) have mixed agonist/antagonist activities, leading to tissue-specific stimulation of cellular proliferation. Partial agonist activity of OHT can be observed in vitro in endometrial carcinoma cells like Ishikawa. Here, we have compared several anti-estrogens (including extensively characterized OHT and pure anti-estrogens such as ICI164, 384 and RU58,668, which are devoid of uterotrophic activity) for their capacity to stimulate promoters containing estrogen response elements (EREs) or AP1-binding sites (12-O-tetradecanoylphorbol-13-acetate response elements, TREs), the two types of DNA motifs known to mediate transcriptional stimulation by estrogen receptors. Assays were performed in Ishikawa cells either by transient transfection or by using cell lines with stably propagated reporter vectors. In transient transfection experiments, none of the anti-estrogens displayed agonist activity on the promoters tested. In contrast, significant transcriptional stimulation was observed with low concentrations of OHT and RU39,411 in Ishikawa cells stably propagating reporter constructs containing a minimal ERE3-TATA promoter. In addition, micromolar concentrations of OHT, but not of RU39,411, stimulated stably propagated AP1-responsive reporter constructs. No transcriptional stimulation of ERE- or TRE-containing promoters was observed with the pure anti-estrogens ICI164,384 and RU58,668. These results indicate that the presence of estrogen response elements in promoters is sufficient to mediate cell-specific agonism of anti-estrogens at the transcriptional level, and that stimulation of AP1 activity may be restricted to a subset of anti-estrogens possessing agonist activity on EREs. In addition, our results suggest that transient transfections do not fully recapitulate in vivo conditions required to observe agonist activity of anti-estrogens.

Topics: Animals; Base Sequence; Cell Line; COS Cells; Electrophoresis, Polyacrylamide Gel; Endometrium; Estradiol; Estrogen Antagonists; Estrogens; Female; Gene Expression Regulation; Humans; Polyunsaturated Alkamides; Promoter Regions, Genetic; Receptors, Progesterone; Tamoxifen; Transcription, Genetic; Tumor Cells, Cultured

Bcl-2 is a key protein involved in the control of apoptosis. Our previous studies on breast and endometrium indicated hormonal regulation of bcl-2 in these tissues. In the present work we have analyzed Bcl-2 and Bax protein expressions in MCF-7 and T47-D, 2 hormone-dependent breast-cancer cell lines, by immunoblots. Estradiol markedly increased Bcl-2 protein content, both in short- and in long-term treatments of MCF-7 cells. Two types of anti-estrogens (4-hydroxytamoxifen and RU 58668) were able to reverse this effect. Also, a synthetic progestin (ORG 2058) was able to decrease the Bcl-2 level in T47-D cells. The level of Bax protein, however, was not affected in the same conditions of hormonal treatments. The level of Bcl-2 expression was 4.5-fold higher in MCF-7 than in MDA-MB 231 (an estradiol-independent cell line). From these results, we infer the existence of hormonal regulation of Bcl-2 expression and evoke a novel role for estradiol and progestin in the genesis of breast cancer.

Topics: bcl-2-Associated X Protein; Blotting, Western; Breast Neoplasms; Estradiol; Estrogen Antagonists; Gene Expression; Humans; Immunoblotting; Pregnenediones; Progestins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Tamoxifen; Tumor Cells, Cultured

RU 58,668, a new steroidal antiestrogen, has been synthesized. Its in vitro and in vivo pharmacological activities have been compared to those of tamoxifen and ICI 182,780. In vitro, it displayed affinities for human and murine estrogen receptors equivalent to those of 4-hydroxy-tamoxifen, along with moderate affinities for progestin and glucocorticoid receptors. RU 58,668 proved to be a potent antiproliferative agent on MCF-7 cells stimulated by estradiol, or by exogenous or endogenous growth factors (IC50, 0.01 nM). It also inhibited the growth of the insulin-stimulated T47D cell line. In vivo, RU 58,668 displayed a total anti-uterotrophic activity in mice or rats without exhibiting any agonistic effect. Moreover, RU 58,668 was the only antiestrogenic compound tested so far to be able to induce a long term regression of human mammary MCF-7 tumors implanted in nude mice, suggesting its potential use for the treatment of advanced breast cancer.

Topics: Animals; Antineoplastic Agents; Cell Division; Estradiol; Estrogen Antagonists; Female; Fulvestrant; Humans; Mammary Neoplasms, Experimental; Mice; Mice, Nude; Neoplasm Transplantation; Progesterone; Rabbits; Rats; Receptors, Estrogen; Tamoxifen; Thymus Gland; Tumor Cells, Cultured; Uterus