ru-58668 and Breast-Neoplasms

Breast cancer, a most common malignancy in women, was known to be associated with steroid hormone estrogen. The discovery of estrogen receptor (ER) gave us not only a powerful predictive and prognostic marker, but also an efficient target for the treatment of hormone-dependent breast cancer with various estrogen ligands. ER consists of two subtypes i.e. ERα and ERβ, that are mostly G-protein-coupled receptors and activated by estrogen, specially 17β-estradiol. The activation is followed by translocation into the nucleus and binding with DNA to modulate activities of different genes. ERs can manage synthesis of RNA through genomic actions without directly binding to DNA. Receptors are tethered by protein-protein interactions to a transcription factor complex to communicate with DNA. Estrogens also exhibit nongenomic actions, a characteristic feature of steroid hormones, which are so rapid to be considered by the activation of RNA and translation. These are habitually related to stimulation of different protein kinase cascades. Majority of post-menopausal breast cancer is estrogen dependent, mostly potent biological estrogen (E2) for continuous growth and proliferation. Estrogen helps in regulating the differentiation and proliferation of normal breast epithelial cells. In this review we have investigated the important role of ER in development and progression of breast cancer, which is complicated by receptor's interaction with co-regulatory proteins, cross-talk with other signal transduction pathways and development of treatment strategies viz. selective estrogen receptor modulators (SERMs), selective estrogen receptor down regulators (SERDs), aromatase and sulphatase inhibitors.

Topics: Aromatase Inhibitors; Breast Neoplasms; Cell Line, Tumor; Estrogen Antagonists; Estrogens; Female; Humans; Ligands; Men; Molecular Structure; Receptors, Estrogen; Selective Estrogen Receptor Modulators; Signal Transduction; Sulfatases

The suppression of oestrogen receptor alpha (ERalpha) functions by silencing RNAs in association with or not with anti-oestrogens (AEs) both in vitro and in breast cancer cell xenografts was assessed. In vitro, a prolonged decrease in ERalpha protein expression and an enhanced AE-induced inhibition of ERalpha-mediated transcription, together with antiproliferative activity, were observed. Incorporation of ERalpha-siRNAs in pegylated nanocapsules (NC) was achieved; and their intravenous injections in MCF-7 xenografts, in contrast to scramble siRNA containing NCs, lead to decrease in ERalpha protein content and Ki67 labelling in tumour cells. The pure AE RU58668 (RU) both free and entrapped in stealth nanospheres (NS) at very low concentration (8 microg/kg/week) had no effect on tumour growth evolution. However, coinjection of the two nanocarriers potentiated the decrease in ERalpha protein, concomitantly with decreasing tumour vasculature and glucose transporter-1. These data support that the targeted delivery of ERalpha-siRNA in breast tumours potentiates the inhibition of E(2)-induced proliferative activity by encapsulated AE through enhanced anti-vascular activity. In the hormone-independent MDA-MB-231 xenograft model, RU-NS at 4 mg/kg/week induce also a strong tumour vascular normalisation. Together, these findings suggest that the anti-oestrogen activity of RU as well as that of targeted ERalpha-siRNA leads to anti-angiogenic activity. Their delivery in stealth nanocarriers may constitute a new anti-cancer therapeutic strategy in solid tumours.

Topics: Adenocarcinoma; Animals; Breast Neoplasms; Cell Division; Cell Line, Tumor; Drug Synergism; Estradiol; Estrogen Receptor alpha; Estrogen Receptor Modulators; Estrogens; Female; Gene Expression Regulation, Neoplastic; Humans; Injections, Intravenous; Mammary Neoplasms, Experimental; Mice; Mice, Nude; Nanocapsules; Nanospheres; Neoplasm Proteins; Neoplasms, Hormone-Dependent; Polyesters; Polyethylene Glycols; RNA Interference; RNA, Small Interfering; Specific Pathogen-Free Organisms; Xenograft Model Antitumor Assays

One subclass of antiestrogens, the selective estrogen receptor down-regulators (SERDs), have received considerable attention of late as they competitively inhibit estrogen binding and induce a rapid, proteasome-dependent degradation of the receptor. Contained within this class of molecules is the steroidal antiestrogen ICI182,780 (faslodex), recently approved for the treatment of metastatic cancer, and GW5638/DPC974, a SERD that is currently being evaluated in the clinic. Given that mechanistic differences between different selective estrogen receptor modulators have been translated into important clinical profiles, it was of interest to determine if the SERD subclass of ligands were likewise functionally or mechanistically distinguishable. In this study, we show that although the steroidal and nonsteroidal SERDs target ERalpha for degradation, the underlying mechanism(s) are different. Of note was the identification of a specific protein-protein interaction surface presented on ERalpha in the presence of the ICI182,780-activated receptor which is required for degradation. Interestingly, this surface is also presented on ERalpha in the presence of RU58,668, a SERD that is chemically distinct from ICI182,780. This surface is not required for GW5638-mediated degradation, and thus, this SERD seems to affect ERalpha down-regulation by a different mechanism. These data suggest that sequencing of therapies using drugs of this class is likely to be possible. Finally, because of the unmet need for orally active SERDS that function similarly to ICI182,780, we have used the insights from these mechanistic studies to develop and validate a high-throughput screen for compounds of this class with improved pharmaceutical properties.

Topics: Amino Acid Sequence; Binding Sites; Breast Neoplasms; Cell Line, Tumor; Cinnamates; Estradiol; Estrogen Antagonists; Estrogen Receptor alpha; Estrogen Receptor Modulators; Fulvestrant; HeLa Cells; Humans; Molecular Sequence Data; Protein Conformation; Stilbenes; Subcellular Fractions

Antiestrogens target the estrogen receptor and counteract the growth stimulatory action of estrogen on human breast cancer. However, acquired resistance to antiestrogens is a major clinical problem in endocrine treatment of breast cancer patients. To mimic acquired resistance, we have used a model system with the antiestrogen sensitive human breast cancer cell line MCF-7 and several antiestrogen resistant cell lines derived from the parental MCF-7 cell line. This model system was used to study the expression and possible involvement in resistant cell growth of insulin-like growth factor binding protein 2 (IGFBP-2). By an oligonucleotide based microarray, we compared the expression of mRNAs encoding insulin-like growth factor binding protein 1,2,3,4,5 and 6 (IGFBP-1 to -6) in the parental MCF-7 cell line to three human breast cancer cell lines, resistant to the antiestrogen ICI 182,780 (Faslodex/Fulvestrant). Only IGFBP-2 mRNA was overexpressed in all three resistant cell lines. Thus, we compared the IGFBP-2 protein expression in MCF-7 cells to nine antiestrogen resistant breast cancer cell lines, resistant to either ICI 182,780 or tamoxifen or RU 58,668 and found that IGFBP-2 was overexpressed in all nine resistant cell lines. Three of the resistant cell lines, resistant to different antiestrogens, were selected for further studies and IGFBP-2 overexpression was demonstrated at the mRNA level as well as the intra- and extracellular protein level. The objective of this study was to examine if IGFBP-2 is involved in growth of antiestrogen resistant human breast cancer cells. Therefore, IGFBP-2 expression was inhibited by antisense oligonucletides and siRNA. Specific inhibition of IGFBP-2 protein expression was achieved in MCF-7 and the three selected antiestrogen resistant cell lines, but no effect on resistant cell growth was observed. Thus, we were able to establish IGFBP-2 as a marker for antiestrogen resistant breast cancer cell lines, although IGFBP-2 was not a major contributor to the resistant cell growth.

Topics: Biomarkers, Tumor; Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Down-Regulation; Drug Resistance, Neoplasm; Estradiol; Estrogen Antagonists; Estrogens; Fulvestrant; Gene Expression Regulation, Neoplastic; Humans; Insulin-Like Growth Factor Binding Protein 2; Insulin-Like Growth Factor Binding Proteins; Oligonucleotide Array Sequence Analysis; Oligonucleotides, Antisense; Polyunsaturated Alkamides; Receptor, IGF Type 1; Tamoxifen

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

Breast cancer is the most common cancer disease in women in the western world. Tamoxifen has been the standard first line endocrine therapy for patients with estrogen receptor (ER) positive tumors. Unfortunately, almost all patients with advanced disease develop tamoxifen resistance. This has lead to a search for new potent antiestrogens. One of the new compounds under development is the pure antiestrogen RU 58,668. To study the mechanisms behind acquired resistance to RU 58,668, the RU 58,668-resistant cell line MCF-7/RU58(R)-1 (RU58(R)-1) was developed. The RU58(R)-1 cell line was responsive to tamoxifen, but cross-resistant to ICI 182,780 and the estrogen-sensitivity was reduced compared to the parental MCF-7 cell line. The protein levels of ERalpha, IGF-I Receptor (IGF-IR) and Bcl-2 were severely reduced, when RU58(R)-1 cells were cultured with RU 58,668 and the expression of progesterone receptor (PR) was lost. The ERalpha level increased upon withdrawal of RU 58,668 and the ERalpha protein was destabilized by RU 58,668 in both cell lines. Regulation of most of the investigated estrogen-sensitive mRNAs was found to be normal in the resistant cells. The protein levels of IGF-IR, Bcl-2 and the IGF Binding Protein 2 (IGFBP2) reverted towards MCF-7 levels upon RU 58,668 withdrawal, but the resistant phenotype was maintained. Thus, it appears as acquired resistance to RU 58,668 is not a result of loss of the ERalpha expression or function and we suggest that in the presence of RU 58,668, the RU58(R)-1 cell line probably uses other mitogenic pathways than the ERalpha pathway for growth and survival.

Topics: Analysis of Variance; Breast Neoplasms; Cell Culture Techniques; Cell Line, Tumor; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Estradiol; Estrogen Receptor Modulators; Female; Humans; Receptors, Estrogen

Death-associated protein (DAP)-kinase is a new Ser/Thr kinase involved in cell apoptosis and tumor suppression, the expression of which has been correlated to invasive potential and metastasis in several human neoplastic tissues. We analyzed the level of DAP-kinase expression in breast cancer specimens and its correlation with survival.. One hundred twenty-eight breast cancer specimens were analyzed by immunohistochemistry. Patient records were studied retrospectively for demographic characteristics, clinical data, hormonal treatment, outcome, and survival. DAP-kinase protein expression was also studied in normal breast cells primary cultures under estrogen and antiestrogen treatment.. Among the 128 patients, 30 showed a DAP-kinase staining < or = 20%, whereas 98 had a staining over 20%. Mean follow-up time was 62 months. The association between tumor Scarff-Bloom and Richardson grade (P = 0.009), estrogen receptor and progesterone receptor expression (P = 0.002 and 0.001, respectively), tumor size (P = 0.05), Bcl-2 expression (P = 0.004), and DAP-kinase immunostaining in the ductal carcinoma group was highly significant. Overall (64 months) and disease-free (63 months) survival in the high DAP-kinase expression group were significantly longer compared with the women whose tumors showed a loss of DAP-kinase expression (51 and 43 months, respectively). DAP-kinase protein was strongly expressed in normal breast tissue and in human breast epithelial cells primary cultures. Estradiol decreased DAP-kinase expression in these cells, arguing for hormonal regulation of the protein.. Loss of DAP-kinase expression negatively correlates to survival and positively correlates to the probability of recurrence in a very significant manner. DAP-kinase thus constitutes a novel and independent prognosis marker for breast cancer.

Topics: Antineoplastic Agents, Hormonal; Apoptosis; Apoptosis Regulatory Proteins; Biomarkers, Tumor; Breast; Breast Neoplasms; Calcium-Calmodulin-Dependent Protein Kinases; Cell Division; Cell Line, Tumor; Cells, Cultured; Death-Associated Protein Kinases; Epithelial Cells; Estradiol; Estrogen Receptor Modulators; Female; Humans; Immunohistochemistry; Prognosis; Proportional Hazards Models; Proto-Oncogene Proteins c-bcl-2; Receptors, Estrogen; Receptors, Progesterone; Survival Analysis; Tamoxifen

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

In MCF-7 breast cancer cells, hydroxytamoxifen (OH-Tam) up-regulates the estrogen receptor (ER) in a form unable to bind [(3)H]estradiol (E(2)). We show here that this property is not restricted to this antiestrogen. [(3)H]E(2) binding assays (whole cell assays, DCC assays on cell extracts) and enzyme immunoassays (Abbott) performed in parallel, establish the permanent presence of such unusual ERs in the absence of any exposure of the cells to a ligand. E(2) and the pure antiestrogen RU 58 668, which down-regulate ER, also decrease [(3)H]E(2) binding. In control cells, these ERs represent about the half of the whole receptor population; they also display a tendency to stabilize within the cell nucleus. Loss of E(2) binding ability appears irreversible, since we failed to label receptor accumulated under OH-Tam with [(3)H]E(2) or [(3)H]tamoxifen aziridine (TAZ). Cycloheximide (CHX), which blocks E(2)-induced down regulation of ER, failed to stabilize [(3)H]E(2) binding (whole cell assay) after an [(3)H]E(2) pulse (1 h), confirming that regulation of E(2) binding and peptide level are related to different regulatory mechanisms. Loss of binding ability could not be ascribed to any ER cleavage as demonstrated by Western blotting with a panel of ER antibodies raised against its various domains (67 kDa ER solely detected). We propose that loss of E(2) binding ability is related to the aging process of the receptor, i.e. it is progressively converted to a form devoted to degradation after it has accomplished its physiological role. Ligands may favor (E(2), RU 58 668) or impede (OH-Tam) this elimination process.

Topics: Antineoplastic Agents, Hormonal; Blotting, Western; Breast Neoplasms; Cell Nucleus; Cycloheximide; Cytosol; Down-Regulation; Estradiol; Estrogen Antagonists; Estrogen Receptor Modulators; Female; Humans; Ligands; Protein Binding; Protein Synthesis Inhibitors; Receptors, Estrogen; Tamoxifen; Time Factors; Tritium; Tumor Cells, Cultured; 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

Data from immunocytochemical assessment of estrogen receptor (ER) regulation in MCF-7 cells under estrogenic and anti-estrogenic stimulation were compared with those obtained by enzyme immunoassay (Abbott ER-EIA). Similar trends were observed, although ER level variations were less marked when assessed immunocytochemically. We confirmed reports of ER disappearance in the presence of estrogens (Es; E2 and DES) and pure anti-estrogens (AEs; RU 58,668 and ICI 164,384) as well as its increase with partial AEs (4-OH-TAM and RU 39,119). E2-induced ER down-regulation was partly blocked by actinomycin D (AMD), okadaic acid (OK) and cycloheximide (CHX) when assessed by these 2 methods. Down-regulation by pure AEs was not impeded by CHX, indicating that they operate differently from Es (i.e., transformation of ER to a form sensitive to constitutive degradation activity). In situ pre-labeling of the cells with [3H]TAZ indicated that all investigated ligands eliminate pre-existing ER through binding to newly synthetized receptors, since [3H]TAZ co-valently associates with ER; E2 and RU 58,668 were more effective than 4-OH-TAM in this regard. CHX blocked ER disappearance even in the presence of pure AEs, which is in contrast to the data established with cells not pre-exposed to [3H]TAZ. Nuclear location of [3H]TAZ-ER complexes may explain this discrepancy, since pure AE-ER complexes were reported to be incapable of nuclear translocation.

Topics: Breast Neoplasms; Cycloheximide; Dactinomycin; Down-Regulation; Estradiol; Estrogen Antagonists; Estrogens; Humans; Immunoenzyme Techniques; Immunohistochemistry; Kinetics; Okadaic Acid; Polyunsaturated Alkamides; Receptors, Estrogen; Tamoxifen; Time Factors; 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

Previous studies with the pure antiestrogen RU 58668 showed that this compound proved to be highly antiproliferative in vitro, and to be the only antiestrogenic compound so far known to induce long-term regression of MCF-7 tumours implanted into nude mice. In order to obtain more insight into the therapeutic potential of this molecule, we performed a new set of experiments in vitro and in vivo in comparison with tamoxifen and/or ICI 182,780. In vitro, 1 nM RU 58668 induced an accumulation of MCF-7 cells in G0/G1 phases of the cell cycle within 48 h and, in contrast to trans-4-hydroxy-tamoxifen, blocked the invasiveness of ras-transfected MCF-7 cells into the chick embryo heart during the three weeks of co-culture. An in vivo dose-effect relationship study showed that RU 58668 induced a regression of MCF-7 tumour with as low a dose as 10 mg/kg/week, and that such an effect can not be obtained either with a sublethal dose of adriamycin or with ICI 182,780, (2-250 mg/kg/week). This reduction in the tumour volumes accords with histological modifications of the tumours, which showed a decrease in the ratio of epithelial cells over the tumoral mass, and with a concomitant decrease in their regrowth potential when reimplanted into naive nude mice. Taken together, these results suggest a promising usefulness for RU 58668 in the treatment of metastatic breast cancer in women.

Topics: Animals; Antineoplastic Agents; Breast Neoplasms; Carcinogenicity Tests; Cell Cycle; Cell Division; Chick Embryo; Dose-Response Relationship, Drug; Estradiol; Estrogen Antagonists; Female; Fulvestrant; Genes, ras; Heart; Humans; Kinetics; Mice; Mice, Inbred BALB C; Mice, Nude; Myocardium; Neoplasm Invasiveness; Tamoxifen; Tumor Cells, Cultured

The recently described pure antiestrogen RU 58668 displayed potent antiproliferative activities in vitro on several ER+ human mammary cell lines, stimulated either by estradiol or by endogenous or exogenous growth factors. Moreover, when administered to nude mice it proved to be the only antiestrogen to induce regression (at least 10 weeks) of estradiol-stimulated MCF-7 tumors, whereas tamoxifen only stabilized the tumor volume for 4 to 8 weeks. So the first purpose of this work was to study the effect of RU 58668 for 6 months and to evaluate its activity on tumors which escaped from the tamoxifen treatment. On the other hand, we looked for its effect on models more related to frequently described clinical observations, such as the overexpression of an oncogene or the implication of autocrine or paracrine growth factors. Long-term studies of RU 58668 on the estradiol-stimulated MCF-7 model showed that this compound induced a shrinking of tumor volumes for at least 25 weeks (3 to 6 times longer than the stabilization induced by tamoxifen) and was able to reduce the volume of tumors which escaped from, or even were stimulated by, tamoxifen. On models of spontaneously growing tumors, where the overexpression of an oncogene or the production of growth factors was involved, RU 58668 induced the same tumor shrinking that was previously observed on estradiol- or tamoxifen-stimulated models. Finally, when MCF-7 cells were injected in the uteri, a spontaneous tumor take was observed (in about 80-90% of the animals), leading to a more than twofold increase in uterus weight. This growth is largely stimulated by estradiol and tamoxifen. On this model, histological examination showed that only 30% of the animals receiving RU 58668 displayed tumoral microfoci. These studies suggest that RU 58668 may be used for the treatment of ER+ patients which are primarily resistant to or which escaped from tamoxifen treatment. Its preventive activity on tumor take also suggests its use as an adjuvant to prevent the development of metastases.

Topics: Animals; Breast Neoplasms; Drug Resistance; Estradiol; Estrogen Antagonists; Female; Genes, ras; Humans; Mice; Mice, Inbred BALB C; Mice, Nude; Neoplasm Transplantation; Receptors, Estrogen; Tamoxifen; Transfection; Transplantation, Heterologous; Transplantation, Heterotopic; Tumor Cells, Cultured; Uterus

Two 11 beta-derivatives of estradiol (E2) were tested for their potential antiestrogenic activity in the MCF-7 breast cancer model: one contained a phenoxydimethylaminoethyl side-chain (RU 39,411), the other a pentafluoropentylsulfinyl side-chain (RU 58,668). The former compound displayed mixed estrogenic/antiestrogenic properties, while the latter indicated only an antiestrogenic activity. Both the compounds produced a growth inhibition of MCF-7 cells at doses related to their binding affinity for the estrogen receptor (ER); E2 suppressed this inhibition. The compounds also down-regulated the estrogen binding capacity of the cells but failed to reduce ER mRNA levels, indicating that the grafting of their side-chains prevented this antagonistic effect usually observed with steroidal estrogens. Assessment of ER levels by enzyme immunoassay revealed a marked increase with RU 39,411 and a decrease with RU 58,668; different mechanisms of action should, therefore, be considered. Finally, the estrogenic activity of RU 39,411 was demonstrated by its strong ability to induce synthesis of the progesterone receptor; RU 58,668 failed to display this agonistic activity.

Topics: Antineoplastic Agents; Breast Neoplasms; Down-Regulation; Estradiol; Estrogen Antagonists; Humans; Structure-Activity Relationship; Tumor Cells, Cultured