onapristone and Breast-Neoplasms

Antiprogestins represent a relatively new and promising class of therapeutic agents that could have significant impact on human health and reproduction. In the present work, the pharmacodynamics, pharmacokinetics, and metabolism of mifepristone (MIF), lilopristone (LIL), and onapristone (ONA) in humans are reviewed, and characteristics bearing important clinical implications are discussed. Although MIF has gained notoriety as an "abortion pill," antiprogestins may more importantly prove effective in the treatment of endometriosis, uterine leiomyoma, meningioma, cancers of the breast and prostate, and as contraceptive agents. MIF pharmacokinetics display nonlinearities associated with saturable plasma protein (alpha 1-acid glycoprotein, AAG) binding and characterized by lack of dose dependency for parent drug plasma concentrations (for doses greater than 100 mg) and a zero-order phase of elimination. LIL and ONA pharmacokinetics are less well characterized but ONA does not appear to bind AAG and displays a much shorter t1/2 than the other agents. The three antiprogestins are substrates of cytochrome P450 (CYP) 3A4, an enzyme exceedingly important in human xenobiotic metabolism. Even more implicative of likely drug-drug interactions subsequent to their long-term administration are recent data from our laboratory indicating that they inactivate CYP3A4 in a cofactor- and time-dependent manner, suggesting that complexation and induction of the enzyme may occur in vivo via protein stabilization. Moreover, it has been demonstrated that MIF increases CYP3A4 mRNA levels in human hepatocytes in primary culture, indicative of message stabilization and/or transcriptional activation of CYP3A4 expression. Finally, MIF has also been shown to inhibit P-glycoprotein function. Whether LIL and ONA share these latter two characteristics with MIF has not yet been determined but they illustrate properties that, in addition to diminished antiglucocorticoid activities and altered pharmacokinetic characteristics, warrant consideration during the development of these and never antiprogestational agents.

Topics: Abortifacient Agents; Adult; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Contraceptives, Postcoital, Synthetic; Endometriosis; Estrenes; Female; Gonanes; Hormone Antagonists; Humans; Mifepristone; Progestins

Topics: Animals; Antineoplastic Agents; Breast Neoplasms; Female; Gonanes; Hormone Antagonists; Humans; Mice; Mifepristone; Progesterone

Antiprogestogens, which block the action of progesterone at the cellular level through binding to the progesterone receptor, are proving to be one of the most significant developments in endocrinology in recent years. Several hundreds of such compounds have been synthesized, but only a few of them have been evaluated to any significant extent in biological screening models and, to our knowledge, only three compounds, namely mifepristone, lilopristone (ZK 98.734) and onapristone (ZK 98.299) have been given to humans. Most of the clinical research to date has focused on the use of mifepristone given in combination with prostaglandin for termination of early pregnancy, an indication for which the compound is being used routinely in four countries so far, i.e. China, France, the UK and Sweden. The gynaecological and obstetrical applications in which antiprogestogens have been shown to be of value to date include ripening of the pregnant cervix prior to pregnancy termination, sensitization of the uterus to prostaglandins in second-trimester abortion, and induction of labour. Available data suggest that antiprogestogens have no place in the conservative treatment of ectopic pregnancy or in the treatment of premenstrual tension. In fertility regulation, the sequential combination regimen of mifepristone plus prostaglandin as used for inducing abortion has proved to be effective also for menses induction and can be expected to be an efficacious once-a-month contraceptive. Mifepristone alone, without adjuvant prostaglandin, has yielded promising results as an anti-implantation agent and in emergency contraception. Other potential uses include once-a-week contraception, ovulation inhibition (in a sequential regimen with a progestogen), and as a daily mini-pill. Mifepristone, and other antiprogestogens for which biological data have been reported also bind to the cellular receptors for glucocorticoid hormones and, consequently, possess antiglucocorticoid in addition to their antiprogestational activity. Because of this antiglucocorticoid effect, mifepristone has been employed successfully in the palliative treatment of hypercortisolism due to Cushing's syndrome, and its use has been proposed for treating certain forms of depression and of glaucoma, and in wound healing. However, for scientific and practical reasons, it would be preferable if molecules were developed that have only the antiprogestational or the antiglucocorticoid activity rather than both.

Topics: Abortion, Induced; Antineoplastic Agents; Breast Neoplasms; Contraception; Contraceptives, Oral, Synthetic; Endometrial Neoplasms; Endometriosis; Estrenes; Female; Gonanes; Humans; Labor, Induced; Mifepristone; Pregnancy; Pregnancy Trimester, Second; Progestins; Prostaglandins; Receptors, Progesterone

The molecular mechanisms by which progestins and antiprogestins inhibit human breast cancer cell growth are essentially unknown. The mechanisms by which they mediate growth inhibition in human breast cancer cells and the expression of the putative autocrine/paracrine growth factors, epidermal growth factor and transforming growth factors alpha and beta-1 were studied under conditions in which progestin and antiprogestin inhibit the growth of T-47D human breast cancer cells in culture. Under the same conditions, the expression of genes such as c-myc, c-jun and c-fos, which are known to have important roles in growth and differentiation, has been measured. The results indicate that progestins and antiprogestins differentially regulate expression of these genes. The data are consistent with the conclusion that the mechanism of growth inhibition of these two agents differs, although an initial interaction with the progesterone receptor is a necessary first step in initiating the as yet ill-defined cascade of events leading to growth inhibition.

Topics: Breast Neoplasms; Cell Division; Epidermal Growth Factor; ErbB Receptors; Gene Expression Regulation, Neoplastic; Genes, fos; Genes, jun; Genes, myc; Gonanes; Humans; Medroxyprogesterone Acetate; Mifepristone; Neoplasm Proteins; Progestins; Transforming Growth Factors; Tumor Cells, Cultured

Onapristone is a type I progesterone receptor (PR) antagonist, which prevents PR- mediated DNA transcription. Onapristone is active in multiple preclinical models and two prior studies demonstrated promising activity in patients with breast cancer. We conducted a study of extended release (ER) Onapristone to determine a recommended dose and explore the role of transcriptionally-activated PR (APR), detected as an aggregated subnuclear distribution pattern, as a predictive biomarker.. An open-label, multicenter, randomized, parallel-group, phase 1 study (target n = 60; NCT02052128) included female patients ≥18 years with PRpos tumors. APR analysis was performed on archival tumor tissue. Patients were randomized to five cohorts of extended release (ER) onapristone tablets 10, 20, 30, 40 or 50 mg BID, or immediate release 100 mg QD until progressive disease or intolerability. Primary endpoint was to identify the recommended phase 2 dose. Secondary endpoints included safety, clinical benefit and pharmacokinetics.. The phase 1 dose escalation component of the study is complete (n = 52). Tumor diagnosis included: endometrial carcinoma 12; breast cancer 20; ovarian cancer 13; other 7. Median age was 64 (36-84). No dose limiting toxicity was observed with reported liver function test elevation related only to liver metastases. The RP2D was 50 mg ER BID. Median therapy duration was 8 weeks (range 2-44), and 9 patients had clinical benefit ≥24 weeks, including 2 patients with APRpos endometrial carcinoma.. Clinical benefit with excellent tolerance was seen in heavily pretreated patients with endometrial, ovarian and breast cancer. The data support the development of Onapristone in endometrial endometrioid cancer. Onapristone should also be evaluated in ovarian and breast cancers along with APR immunohistochemistry validation.

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Biomarkers, Tumor; Breast Neoplasms; Delayed-Action Preparations; Female; Gonanes; Half-Life; Humans; Middle Aged; Nausea; Neoplasm Metastasis; Neoplasm Recurrence, Local; Receptors, Progesterone

The progesterone receptor antagonist, Onapristone, is an effective endocrine agent in experimental breast cancer models. This study aimed to investigate this agent as first-line endocrine therapy in patients with breast cancer. However, owing to the recognition in this and other clinical studies that some patients on Onapristone developed liver function test abnormalities, the development of this drug and recruitment to the study stopped in 1995. 19 patients either with locally advanced breast cancer (n = 12) or who were elderly, unfit patients with primary breast cancer (n = 7) received Onapristone 100 mg/day. Seventeen of the 19 tumours expressed oestrogen receptors (ER) whilst 12 of the 18 tumours tested expressed progesterone receptors (PgR). Tumour remission was categorised by International Union Against Cancer criteria. One patient was withdrawn after 4.5 months while her disease was static. Of the remaining 18 patients, 10 (56%) showed a partial response and 2 (11%) durable static disease (> or = 6 months), giving an overall tumour remission rate of 67%. The median duration of remission was 70 weeks. Transient liver function test abnormalities developed in a number of patients, mainly during the first 6 weeks of treatment. In conclusion Onapristone can induce tumour responses in human breast cancer.

Topics: Antineoplastic Agents; Breast Neoplasms; Female; Follow-Up Studies; Gonanes; Hormone Antagonists; Humans; Receptors, Estrogen; Receptors, Progesterone; Remission Induction

Type I (IFNα/β) interferon signaling represents a critical transduction pathway involved in recognition and destruction of nascent tumor cells. Downregulation of this pathway to promote a more immunosuppressed microenvironment contributes to the ability of tumor cells to evade the immune system, a known Hallmark of Cancer. The present study investigates the progesterone receptor (PR), which is expressed in the vast majority of breast cancers, and its ability to inhibit efficient interferon signaling in tumor cells. We have shown that PR can block the interferon signaling cascade by promoting ubiquitination and degradation of STAT2. Targeting STAT2 is critical, as we show that it is an essential protein in inducing transcription of interferon-stimulated genes (ISG); shRNA-mediated knockdown of STAT2 severely abrogates the interferon response

Topics: Antineoplastic Agents; Breast Neoplasms; Female; Gonanes; Humans; Interferons; Receptors, Progesterone; Signal Transduction; STAT2 Transcription Factor; Tumor Microenvironment

Antiprogestins have demonstrated promising activity against breast and gynecological cancers, but liver-related safety concerns limited the advancement of this therapeutic class. Onapristone is a full progesterone receptor antagonist originally developed as an oral contraceptive and later evaluated in phase II studies for metastatic breast cancer. Because of liver enzyme elevations identified during clinical studies, further development was halted. Evaluation of antiprogestin pharmacology and pharmacokinetic data suggested that liver enzyme elevations might be related to off-target or metabolic effects associated with clinical drug exposure.. We explored whether the use of a pharmaceutic strategy targeting efficacious systemic dose concentrations, but with diminished peak serum concentrations and/or total drug exposure would mitigate hepatotoxicity. Twice-daily dosing of an extended-release formulation of onapristone was developed and clinically evaluated in light of renewed interest in antiprogestin therapy for treating progesterone receptor-positive breast and gynecologic cancers. The hepatotoxic potential of extended-release onapristone was assessed from two phase I-II studies involving patients with breast, ovarian, endometrial, and prostate cancer.. Among the 88 patients in two phase I-II studies in progesterone receptor-positive malignancies treated with extended-release onapristone, elevated alanine aminotransferase/aspartate aminotransferase levels were found in 20% of patients with liver metastases compared with 6.3% without metastases. Of five patients with grade 3 or higher alanine aminotransferase elevations with or without bilirubin elevations (four with breast cancer and one with endometrial cancer), four were assessed as unrelated to extended-release onapristone by the safety data review committee. Furthermore, while the fifth patient's liver enzyme elevations were considered possibly drug related by the study investigator, they were adjudicated as unlikely to be related (< 25% likelihood) by a subsequent independent hepatologist.. These results suggest that the extended-release formulation by reducing drug exposure may be associated with a reduced risk of hepatotoxicity, and supports the continued clinical evaluation of extended-release onapristone for treating progesterone receptor-positive cancers.

Topics: Adult; Aged; Aged, 80 and over; Breast Neoplasms; Chemical and Drug Induced Liver Injury; Clinical Trials, Phase I as Topic; Clinical Trials, Phase II as Topic; Delayed-Action Preparations; Female; Genital Neoplasms, Female; Gonanes; Hormone Antagonists; Humans; Male; Middle Aged; United States

Progestins induce lipid accumulation in progesterone receptor (PR)-positive breast cancer cells. We speculated that progestin-induced alterations in lipid biology confer resistance to chemotherapy. To examine the biology of lipid loaded breast cancer cells, we used a model of progestin-induced lipid synthesis. T47D (PR-positive) and MDA-MB-231 (PR-negative) cell lines were used to study progestin response. Oil red O staining of T47D cells treated with progestin showed lipid droplet formation was PR dependent, glucose dependent and reduced sensitivity to docetaxel. This protection was not observed in PR-negative MDA-MB-231 cells. Progestin treatment induced stearoyl CoA desaturase-1 (SCD-1) enzyme expression and chemical inhibition of SCD-1 diminished lipid droplets and cell viability, suggesting the importance of lipid stores in cancer cell survival. Gas chromatography/mass spectroscopy analysis of phospholipids from progestin-treated T47D cells revealed an increase in unsaturated fatty acids, with oleic acid as most abundant. Cells surviving docetaxel treatment also contained more oleic acid in phospholipids, suggesting altered membrane fluidity as a potential mechanism of chemoresistance mediated in part by SCD-1. Lastly, intact docetaxel molecules were present within progestin induced lipid droplets, suggesting a protective quenching effect of intracellular lipid droplets. Our studies suggest the metabolic adaptations produced by progestin provide novel metabolic targets for future combinatorial therapies for progestin-responsive breast cancers.

Topics: Antineoplastic Agents; Breast Neoplasms; Cell Line, Tumor; Cell Proliferation; Docetaxel; Drug Resistance, Neoplasm; Fatty Acids, Nonesterified; Female; Gene Expression; Glucose; Gonanes; Humans; Lipogenesis; Medroxyprogesterone Acetate; Phospholipids; Progestins; Receptors, Progesterone; Stearoyl-CoA Desaturase; Taxoids; Triglycerides

Progesterone receptor (PR) isoforms (PRA and PRB) are implicated in the progression of breast cancers frequently associated with imbalanced PRA/PRB expression ratio. Antiprogestins represent potential antitumorigenic agents for such hormone-dependent cancers. To investigate the mechanism(s) controlling PR isoforms degradation/stability in the context of agonist and antagonist ligands, we used endometrial and mammary cancer cells stably expressing PRA and/or PRB. We found that the antiprogestin RU486 inhibited the agonist-induced turnover of PR isoforms through active mechanism(s) involving distinct MAPK-dependent phosphorylations. p42/44 MAPK activity inhibited proteasome-mediated degradation of RU486-bound PRB but not PRA in both cell lines. Ligand-induced PRB turnover required neosynthesis of a mandatory down-regulating partner whose interaction/function is negatively controlled by p42/44 MAPK. Such regulation strongly influenced expression of various endogenous PRB target genes in a selective manner, supporting functional relevance of the mechanism. Interestingly, in contrast to PRB, PRA stability was specifically increased by MAPK kinase kinase 1-induced p38 MAPK activation. Selective inhibition of p42/p44 or p38 activity resulted in opposite variations of the PRA/PRB expression ratio. Moreover, MAPK-dependent PR isoforms stability was independent of PR serine-294 phosphorylation previously proposed as a major sensor of PR down-regulation. In sum, we demonstrate that MAPK-mediated cell signaling differentially controls PRA/PRB expression ratio at posttranslational level through ligand-sensitive processes. Imbalance in PRA/PRB ratio frequently associated with carcinogenesis might be a direct consequence of disorders in MAPK signaling that might switch cellular responses to hormonal stimuli and contribute towards pathogenesis.

Topics: Breast Neoplasms; Cell Line, Tumor; Endometrial Neoplasms; Female; Gonanes; Humans; Ligands; MAP Kinase Kinase Kinase 1; Mifepristone; Mitogen-Activated Protein Kinase 1; Models, Biological; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Phosphoserine; Promegestone; Proteasome Endopeptidase Complex; Protein Isoforms; Protein Stability; Receptors, Progesterone; Transcription, Genetic

Phosphorylation of the tumor suppressor protein, retinoblastoma (pRb), regulates the progression of the cell cycle. Previous work from this laboratory had shown that estradiol (E(2)) regulates tumor suppressor proteins, p53 and retinoblastoma in breast cancer cells. In the present study, we have examined the phosphorylation of pRB in T47D breast cancer cells following treatments with R5020 and antiprogestins. In growth medium containing serum depleted of endogenous steroids by charcoal treatment, pRb appeared mainly in its hypophosphorylated form. Addition of 10 nM R5020 to the culture medium caused hyperphosphorylation of pRb within 24 h, but the hypophosphorylated form of pRb began to accumulate after 72 h. Upon prolonged R5020 treatment (72-96 h), pRb was detected exclusively in its hypophosphorylated form. While treatment of cells with R5020 caused a transient increase in the level of cyclin D1, E(2) addition caused a sustained increase in the level of cyclin D1 consistent with its role in stimulating pRb phosphorylation. Antagonists of both estrogen receptor (ER) and progesterone receptor (PR) blocked the E(2) and R5020-induced pRb phosphorylation, respectively. These results suggest that R5020 induces pRb phosphorylation via a transient increased expression of cyclin D1, whereas E(2) treatment results in sustained expression of cyclin D1 and increased pRb phosphorylation. Furthermore, R5020 effects on pRb phosphorylation appear PR-mediated as no cross-antagonism of pRb phosphorylation was observed: the R5020 effects were blocked by RU486 and ZK98299, but not by the pure ER antagonist, ICI 182, 780 (ICI).

Topics: Breast Neoplasms; Estradiol; Estrogen Receptor Modulators; Estrogens; Fulvestrant; Gonanes; Humans; Mifepristone; Phosphorylation; Progesterone; Promegestone; Receptors, Estrogen; Receptors, Progesterone; Retinoblastoma Protein; Tumor Cells, Cultured

Progesterone antagonist RU486 (mifepristone) has been implicated for many anti-neoplastic and obstetrical applications. But the compound has demonstrated undesired agonist-like effect depending on cell, tissue and species studied. Using PR-transfected breast cancer cells MDA-MB-231, this report describes the similarities and differences between progesterone- and RU486-mediated effects on cell growth, cell differentiation and, at the molecular level, on the activation of p44/p42 MAP kinases (MAPK). Like progesterone, RU486 inhibited cells growth by arresting the cells in G0/G1 phase of the cell cycle. In contrast to progesterone that induced cell spreading, RU486 induced a multipolar, stellate morphology. RU486-treated cells showed no increase of stress fibers, nor was there any increase of focal adhesions as progesterone-treated cells did. Furthermore, despite of the fact that both compounds inhibited cell growth, RU486 significantly stimulated the activation of p44/p42 MAP kinases whereas progesterone markedly inhibited the activation. Nonetheless, the effects of RU486 were PR-mediated and RU486 was able to antagonize the effect of progesterone on cell growth and focal adhesion. In conclusion, RU486 can act not only as a progesterone antagonist, a progesterone agonist but also induced morphological and molecular changes that were distinct from progesterone-mediated effects in PR-transfected MDA-MB-231 cells. The non-progesterone-like effect of RU486 may be mediated through a pathway that is different from the progesterone-mediated pathway, or it is the result of a blockade of certain critical step(s) in the progesterone-mediated pathway. In any case, undesired side effects of antiprogestin may create clinical complications. PR-transfected MDA-MB-231 breast cancer cells provide a model for studying the functions of progesterone analogues.

Topics: Breast Neoplasms; Cell Cycle; Cell Division; Cell Size; Enzyme Activation; Female; Focal Adhesions; Gonanes; Hormone Antagonists; Humans; MAP Kinase Signaling System; Mifepristone; Progesterone; Receptors, Progesterone; Recombinant Fusion Proteins; Stress Fibers; Transfection; Tumor Cells, Cultured

Synthesis and biological evaluation of 6-thiophene 1,2-dihydro or 1,2,3,4-tetrahydroquinoline derivatives resulted in a number of potent nonsteroidal antiprogestins.

Topics: Animals; Breast Neoplasms; Cell Line; Cross Reactions; Fibroblasts; Haplorhini; Humans; Mice; Quinolines; Receptors, Progesterone; Structure-Activity Relationship; Thiophenes; Transfection; Tumor Cells, Cultured

T47D cells, cultured in medium containing serum stripped of endogenous steroids, proliferate in response to treatment with the progesterone receptor (PR) agonist, R5020 or the PR agonist/antagonist, RU486, whereas the full PR antagonist, ZK98299 has no proliferative effects. Under estrogenized conditions, all of the PR ligands tested inhibit cell growth [23]. In order to determine whether the levels or phosphorylation state of PR are reflected in the growth patterns of T47D cells, we monitored the effects of these PR ligands on the immunoblotted PR band intensities, the relative intensities of PR-A and PR-B, and their phosphorylation states that are reflected in their altered mobility during SDS-PAGE. Under conditions where the PR ligands inhibit cell proliferation, each ligand had distinctively different qualitative and quantitative effects on PR. Short term treatment of the cells with R5020 or RU486 induced a characteristic phosphorylation-dependent upshift of both PR-A and PR-B. The phosphorylated PR was stable for up to 4 days after treatment of the cells with RU486, but was down regulated between 6-24 h after treatment with R5020. No replenishment of PR in cells treated with R5020 was detected. ZK98299, at concentrations tested, had no qualitative or quantitative effects on PR. Culturing cells for 8 days in medium containing steroid-depleted serum caused a significant reduction in the PR band intensity without causing a change in the ratio of PR-A and PR-B or their phosphorylation states. This decrease in the PR band intensity was reversed by maintaining the cells in 1 nM estrogen, but was potentiated by RU486 or ZK98299. These observations support the view that decreased PR levels may play a role in the stimulatory effects of R5020 and RU486 when cells are cultured under non-estrogenized conditions.

Topics: Blotting, Western; Breast Neoplasms; Cell Division; Charcoal; Culture Media; Electrophoresis, Polyacrylamide Gel; Estradiol; Female; Gonanes; Hormone Antagonists; Humans; Mifepristone; Phosphorylation; Progesterone Congeners; Promegestone; Receptors, Progesterone; Tumor Cells, Cultured

Interactions between transcription factors are an important means of regulating gene transcription, leading to modifications in the pattern of gene expression and cell fate. In this study, we report that the progesterone receptor (PR) can strongly interfere with transactivation mediated by the arylhydrocarbon receptor (AhR) in T47D breast cancer cells. This interference was not only demonstrated by induction of a transfected dioxin-responsive reporter plasmid but also on the AhR-mediated up-regulation of the endogenous cytochrome P450-1A1 activity. The interference was not mutual, as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent activator of the AhR, did not inhibit progestin-induced promoter activity. When the isoforms of the human PR, hPR-A and hPR-B, were expressed separately in HepG-2 hepatocarcinoma cells, both negatively interfered with the AhR signaling, indicating that the effect is not restricted to T47D cells. In addition, results obtained from studies with both antiprogestins and mutant receptors indicate differences in the underlying molecular mechanisms of repression for both PR isoforms. The suppression by hPR-A does not require additional gene expression or a full transcriptional competent conformation of the receptor. For the repressive effects of hPR-B, however, additional gene expression seems to be involved, as only the agonist-bound, wild-type hPR-B could clearly repress the TCDD-induced response. In conclusion, these studies highlight different mechanisms of repression for the progesterone receptor isoforms on the AhR-mediated trans-activation and underscore the importance of interactions between transcription factors of different families in the regulation of gene transcription.

Topics: Breast Neoplasms; Cytochrome P-450 CYP1A1; Female; Gene Expression Regulation, Enzymologic; Gonanes; Hormone Antagonists; Humans; Mifepristone; Polychlorinated Dibenzodioxins; Pregnenediones; Progesterone Congeners; Receptors, Aryl Hydrocarbon; Receptors, Progesterone; Recombinant Proteins; Signal Transduction; Transcriptional Activation; Transfection; Tumor Cells, Cultured; Up-Regulation

This is the first report demonstrating an in vivo antitumor activity of antiprogestins (mifepristone, onapristone) alone and in combination with tamoxifen in the MCF-7 human breast cancer model. The MCF-7 cells produced progressive growing tumors in female nude mice supplemented with 17beta-estradiol. Tumor regression was observed following either estrogen ablation alone or estrogen ablation in combination with tamoxifen. Monotherapy with tamoxifen or antiprogestins caused a retardation of estrogen-induced tumor progression. Complete inhibition or prevention of tumor growth occurred as a result of simultaneous administration of mifepristone and tamoxifen. The addition of mifepristone in this combination treatment was also effective in delaying or preventing tumor escape (relapse) from the antiestrogenic (antitumor) effect of tamoxifen. These results suggest a potential clinical benefit of adding an antiprogestin to antiestrogen therapy of breast cancer patients.

Topics: Animals; Antineoplastic Agents, Hormonal; Antineoplastic Combined Chemotherapy Protocols; Breast Neoplasms; Female; Gonanes; Hormone Antagonists; Humans; Mice; Mice, Nude; Mifepristone; Receptors, Estrogen; Receptors, Progesterone; Tamoxifen; Tumor Cells, Cultured

The influence of the novel antiprogestin onapristone on the serum insulin-like growth factor (IGF) system was studied in a group of 13 postmenopausal women with metastatic breast cancer. Blood samples were obtained before treatment and subsequently after 1, 2 and 3 months on therapy. IGF-I, IGF-II and IGF-binding protein (IGFBP)-2 were measured by radioimmunoassay (RIA). In addition, the IGFBP profile was evaluated by Western ligand blotting (WLB), and IGFBP-3 fragmentation determined by immunoblotting. A moderate (29%) but significant increase in IGF-I was observed after 3 months on treatment (p < 0.05). IGFBP-2 showed a significant, progressive increase during treatment when evaluated both by WLB (44% increase over baseline at 3 months) and by RIA (33% increase over baseline at 3 months). There was a non-significant trend towards an initial decrease in IGFBP-3 fragmentation. No significant alterations were observed in IGF-II or any of the binding proteins (except IGFBP-2) determined by Western ligand blotting. Due to the observation that onapristone treatment caused a moderate suppression of serum cortisol and androstenedione, we postulate the observed increase in IGF-I to be due to a slight glucocorticoid agonistic effect of the drug. On the contrary, the increase in IGFBP-2 may be related to disease progression as has been observed in patients suffering from prostatic cancer.

Topics: Adult; Aged; Androstenedione; Antineoplastic Agents; Blotting, Western; Breast Neoplasms; Female; Gonanes; Hormone Antagonists; Humans; Hydrocortisone; Insulin-Like Growth Factor Binding Protein 2; Insulin-Like Growth Factor Binding Protein 3; Insulin-Like Growth Factor Binding Protein 4; Insulin-Like Growth Factor Binding Proteins; Insulin-Like Growth Factor I; Insulin-Like Growth Factor II; Middle Aged; Neoplasm Metastasis; Postmenopause

Estrogenic activities of testosterone (T) and 5a-dihydrotestosterone (DHT) were detected and measured by using their specific stimulatory effects on alkaline phosphatase (AP) activity in human endometrial adenocarcinoma cells of the Ishikawa Var-1 line. These two physiologic androgens were able to induce, at microM concentrations, estrogenic effect believed to be mediated by the estrogen receptor (ER) since the antiestrogens ICI-164384 and 4-hydroxytamoxifen (OHTam), but not the antiandrogens hydroxyflutamide (OHFl) or cyproterone acetate (CPA), reversed that effect. By using another in vitro bioassay, based on the progestin-specific stimulation of AP activity in cells of the T47D human breast cancer line, progestagenic activity was detected and measured in T, DHT and three synthetic androgens: nandrolone (19-nortestosterone). 7 alpha-methyl 19-nortestosterone (MENT) and mibolerone (7 alpha, 17 alpha-dimethyl 19-nortestosterone) (DMNT). While progestagenic effects of T and DHT required relatively high concentrations (microM levels), the synthetic androgens stimulated AP activity at nM or pM levels. These effects seem to be mediated by the progesterone receptor (PR), since they are completely abolished by the antiprogestins RU-486, ZK-98299 and ZK-112993, but not by the antiandrogen OHFl. These simple in vitro bioassays, expressing biological effects of the test compounds in human cells in culture, revealed dual or multiple hormonal activities coexisting in a single compound and provide quantitative information of considerable pharmacological importance concerning the complex actions of drugs.

Topics: Adenocarcinoma; Alkaline Phosphatase; Androgen Antagonists; Androgens; Breast Neoplasms; Cyproterone Acetate; Endometrial Neoplasms; Estradiol; Estrogen Antagonists; Female; Flutamide; Gonanes; Humans; Mifepristone; Polyunsaturated Alkamides; Progestins; Tamoxifen; Testosterone; Testosterone Congeners; Tumor Cells, Cultured

Depending on the tissue, progesterone is classified as a proliferative or a differentiative hormone. To explain this paradox, and to simplify analysis of its effects, we used a breast cancer cell line (T47D-YB) that constitutively expresses the B isoform of progesterone receptors. These cells are resistant to the proliferative effects of epidermal growth factor (EGF). Progesterone treatment accelerates T47D-YB cells through the first mitotic cell cycle, but arrests them in late G1 of the second cycle. This arrest is accompanied by decreased levels of cyclins D1, D3, and E, disappearance of cyclins A and B, and sequential induction of the cyclin-dependent kinase (cdk) inhibitors p21 and p27(Kip1). The retinoblastoma protein is hypophosphorylated and extensively down-regulated. The activity of the cell cycle-dependent protein kinase, cdk2, is regulated biphasically by progesterone: it increases initially, then decreases. This is consistent with the biphasic proliferative increase followed by arrest produced by one pulse of progesterone. A second treatment with progesterone cannot restart proliferation despite adequate levels of transcriptionally competent PR. Instead, a second progesterone dose delays the fall of p21 and enhances the rise of p27(Kip1), thereby intensifying the progesterone resistance in an autoinhibitory loop. However, during the progesterone-induced arrest, the cell cycling machinery is poised to restart. The first dose of progesterone increases the levels of EGF receptors and transiently sensitizes the cells to the proliferative effects of EGF. We conclude that progesterone is neither inherently proliferative nor antiproliferative, but that it is capable of stimulating or inhibiting cell growth depending on whether treatment is transient or continuous. We also suggest that the G1 arrest after progesterone treatment is accompanied by cellular changes that permit other, possibly tissue-specific, factors to influence the final proliferative or differentiative state.

Topics: Breast Neoplasms; CDC2-CDC28 Kinases; Cell Cycle Proteins; Cell Division; Cyclin A; Cyclin B; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase Inhibitor p16; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Cyclin-Dependent Kinases; Cyclins; Drug Synergism; Epidermal Growth Factor; ErbB Receptors; G1 Phase; Gene Expression Regulation; Gonanes; Hormone Antagonists; Humans; Microtubule-Associated Proteins; Mifepristone; Progesterone; Promegestone; Protein Serine-Threonine Kinases; Tumor Cells, Cultured; Tumor Suppressor Proteins

This study reports on factors predicting response to second-line endocrine therapy in 250 patients with breast cancer for which they were assessable for response by the International Union Against Cancer (UICC) criteria. Clinical details relating to first-line endocrine therapy were available for all patients. We have not included in this study patients who received first-line endocrine therapy but did not or have not yet proceeded to second-line hormone therapy--e.g. died from rapidly progressive disease, started chemotherapy for rapidly progressive disease, or remained in long-term remission on first-line endocrine therapy. One hundred and fifty nine patients (72%) achieved remission (objective response and static disease [OR + SD]) on first-line endocrine therapy with a median duration of 19 months. For second-line endocrine therapy the remission rate was 53% (132/225) with a median duration of 15 months. Tumour grade and oestrogen receptor status of the primary tumour were shown to be independent predictors of response to second-line endocrine therapy while response to first-line endocrine therapy was a predictor of the duration of response to second-line endocrine therapy. In the sub-group of patients who showed OR or SD to both first and second-line therapies, there was no correlation between the time to progression (TTP) on first and second-line therapies.

Topics: Adult; Aged; Aged, 80 and over; Aminoglutethimide; Anastrozole; Antineoplastic Agents, Hormonal; Breast Neoplasms; Female; Gonanes; Goserelin; Humans; Megestrol Acetate; Middle Aged; Nitriles; Ovariectomy; Predictive Value of Tests; Remission Induction; Tamoxifen; Triazoles

In 1986 we reported the appearance of a progestin binding protein in the human breast cancer cell line Evsa-T, originally described as lacking both estrogen and progesterone receptors (ER and PR). In this report we show that PR of this cell line displays a binding affinity for [3H]ORG 2058 and a sucrose gradient sedimentation profile similar to those ascribed to PR from MCF-7 or T47D breast cancer cell lines. PR from Evsa-T cells is down-regulated by the progestin R-5020 as well as by the two antiprogestins, ZK 112.993 and ZK 98.299, but does not confer growth sensitivity to these compounds. ER remains undetectable by ligand binding assay, enzyme immunoassay and northern blotting. Our Evsa-T clone could be a valuable model for assessing the mechanisms leading the ER-/PR+ phenotype occurring occasionally in breast cancers and frequently in meningiomas.

Topics: Breast Neoplasms; Cell Division; Cytosol; Down-Regulation; Female; Gene Expression Regulation, Neoplastic; Gonanes; Hormone Antagonists; Humans; Mifepristone; Pregnenediones; Progestins; Receptors, Estrogen; Receptors, Progesterone; RNA, Messenger; RNA, Neoplasm; Tumor Cells, Cultured

Human progesterone receptor (PR) is phosphorylated on multiple serine residues; three sites (Ser102, Ser294, and Ser345) are inducible by hormone agonist, while at least six others are basally phosphorylated and exhibit a general increase in response to hormone. In this study we have used high performance liquid chromatography phosphopeptide mapping and manual peptide sequencing to investigate how two different progestin antagonists, RU486 and ZK98299, affect site-specific phosphorylation of PR isolated from T47D breast cancer cells. As compared to the progestin agonist R5020, RU486 stimulated a similar increase in overall incorporation of [32P]phosphate per PR molecule (2.5-2.6-fold for PR-A and 2.1-fold for PR-B), and at the site-specific level, RU486 stimulated both the basal and inducible sites to the same extent as R5020. In contrast, ZK98299 produced only a minimal increase in overall phosphorylation (1.2-fold for PR-A and 1.1-fold for PR-B) which was due to a reduced stimulation of the basal sites and failure to induce any of the three hormone-dependent sites. No inappropriate phosphorylation sites were detected in response to either RU486 or ZK98299. In cotreatment studies, ZK98299 blocked the increase in overall phosphorylation of PR induced by R5020, demonstrating that the failure of this antagonist to stimulate specific phosphorylation sites is not due to an inefficient interaction with PR in the intact cell. These results indicate that the biological effects of RU486 are not mediated by an alternation in the phosphorylation state of PR, whereas failure to promote phosphorylation of certain sites may contribute to the antagonist action of ZK98299. Additionally these results support the concept of two mechanistic classes of anti-progestins that affect PR differently in vivo.

Topics: Amino Acid Sequence; Breast Neoplasms; Female; Gonanes; Humans; Mifepristone; Molecular Sequence Data; Phosphorylation; Progestins; Receptors, Progesterone; Signal Transduction; Tumor Cells, Cultured

In addition to their antiprogestational activity, the antiprogestins RU486, ZK98.299 and ZK98.734 possess varying antiglucocorticoid as well as androgen-like or antiandrogen-like properties in human mammary cancer cells. The human mammary cancer cell line MFM-223, which contains only androgen receptors, was used as a model to investigate androgen receptor mediated effects of these antiprogestins. Proliferation of MFM-223 cells is inhibited by androgens and does not respond to oestrogens, progestins and glucocorticoids. As shown in proliferation assays, ZK98.734 was a strong inhibitor of cell proliferation. This effect was antagonised by the antiandrogen hydroxyflutamide. ZK98.734 was found to displace [3H]R1881 from the androgen receptor in MFM-223 cells, substantiating the involvement of the androgen receptor. The antiprogestin ZK98.299 failed to influence the proliferation of MFM-223 cells. ZK98.299 did not bind to the androgen receptor and was devoid of androgenic or antiandrogenic activity. RU486 bound to the androgen receptor. It was a weak inhibitor of MFM-223 cell proliferation, but the inhibition of proliferation by RU486 was not antagonised by hydroxyflutamide. This effect was probably not mediated by the androgen receptor. RU486 had antiandrogenic activity in this cell line, as it antagonised the inhibitory effect of dihydrotestosterone at a 100-molar excess. These results were confirmed by transfection experiments with an MMTV-CAT construct in the same cell line, demonstrating the biological function of the ZK98.734-androgen receptor complex. ZK98.299 and RU486 were not able to induce CAT activity. The different androgenic or antiandrogenic properties of the antiprogestins investigated should be considered when selecting antiprogestational properties of the antiprogestins investigated should be considered when selecting antiprogestational compounds for clinical applications, as a partial androgenic activity may be of benefit in breast cancer but can have undesired side-effects in other diseases.

Topics: Androgen Antagonists; Antineoplastic Agents; Binding, Competitive; Breast Neoplasms; Cell Division; Dihydrotestosterone; Estrenes; Flutamide; Gonanes; Humans; Mifepristone; Models, Biological; Progestins; Receptors, Androgen; Transfection; Tumor Cells, Cultured

Antiprogestins appear to be a new approach for the endocrine therapy of breast cancer. Most breast cancer cells are growth inhibited by TGF-beta. Any change of tumorcellular TGF-beta secretion could have some impact on tumorcellular growth. We addressed our question to whether the antiprogestin onapristone can induce TGF-beta secretion in breast cancer cells in vitro and whether a possible induction correlates with the antiproliferative effect and the receptor status of the cells.. We examined the ER and PR positive breast cancer cell lines MCF7 and T-47D and an ER and PR negative variant T-47D/x. Hormone receptor levels were determined by EIA, total (LTGF-beta + active TGF-beta) and active TGF-beta by a radioreceptor assay. All cell biological and antiproliferative effects were measured during basal, not estrogen-stimulated growth.. To our knowledge, we are the first to describe, that the TGF-beta secretion of tumor cells can be increased by an antiprogestin (total: 4.8-fold, active 2.9-fold). A stimulation was found only in the markedly PR positive T-47D cells, in which onapristone proved to have strong antiproliferative potency. In the MCF7 and T-47D/x cells onapristone showed no induction of TGF-beta. Moreover, those cells were not growth inhibited. Whereas onapristone did not influence the ER-content, it dramatically downregulated the PR-content of the T-47D and MCF7 cells (93% and 65%, respectively).. These observations make it likely, that the antiproliferative potency of the antiprogestin onapristone is at least partly due to the ability of onapristone, to stimulate the strong growth inhibitor TGF-beta. In contrast to the antiprogestin RU 486, onapristone showed no estrogenic activity (stimulation of growth and PR), which could be a decisive advantage in the therapy of breast cancer, taking into account, that many breast carcinomas grow estrogen dependent.

Topics: Antineoplastic Agents; Breast Neoplasms; Cell Division; Gonanes; Hormone Antagonists; Humans; Receptors, Estrogen; Receptors, Progesterone; Transforming Growth Factor beta; Tumor Cells, Cultured

Previously we reported the identification of two unique progesterone receptor (PR) messenger RNA transcripts that encode a smaller PR isoform, termed the C-receptor (PRc). These two PR transcripts encode a protein that is N-terminally truncated, so that it lacks the first zinc finger of the DNA binding domain, but still contains a complete hormone binding region with sequences for dimerization and nuclear localization. We also have demonstrated the existence of a 60-kDa progestin-specific binding protein in progestin target cells using a monoclonal antibody directed to the C-terminus of PRs, suggesting that these two novel transcripts generate a truncated form of PR. In this paper, we address the hypothesis that the C-receptor arises from the initiation of translation of a methionine C-terminal to the methionine start sites that generate the larger 94-kDa A and 116-kDa B human PR isoforms. The studies shown here support the postulate that another downstream in-frame methionine within the PR-coding region can serve as a translation initiation site for the generation of a third PR protein. A partial PR complementary DNA, lacking the translation start sites for B- and A-receptors was translated in vitro. The synthetic protein product bound [3H]progestins and unlabeled progestins. The antiprogestin RU486 also competed for this binding. Transfection of this partial PR complementary DNA into PR-negative HeLa cells resulted in progestin-specific binding activity. Because the third PR isoform lacks the first zinc finger of the DNA binding domain, but contains sequences for dimerization, we reasoned that the C-receptor isoform would be transcriptionally in-active and not bind DNA directly. Surprisingly, however, in the presence of A- and/or B-receptors, we found that C-receptors can modulate the transcriptional activity of A- and/or B-receptors using a reporter gene. These studies emphasize that multiple receptor isoforms may have distinct biological properties, and that the truncated C-receptor may play a role in explaining some of the pleiotropic effects of progestins.

Topics: Antineoplastic Agents; Breast Neoplasms; Enhancer Elements, Genetic; Gonanes; HeLa Cells; Hormone Antagonists; Humans; Methionine; Mifepristone; Progesterone Congeners; Progestins; Promegestone; Protein Biosynthesis; Receptors, Progesterone; Transcription, Genetic; Transfection; Tumor Cells, Cultured

We have investigated whether constitutive binding by the progesterone receptor (PR) to a promoter is required for the maintenance of an open chromatin structure in vivo. For these experiments, we used human T47D breast cancer cells in which the mouse mammary tumor virus (MMTV) promoter, stably assembled as chromatin, is constitutively hypersensitive to endonucleolytic cleavage. In vivo footprinting revealed that transcription factors nuclear factor 1 and the PR were constitutively bound to the MMTV promoter in these cells. Treatment of these cells for 1 hr with the steroid antagonist ZK98299 prevented PR binding to chromatin in vivo and reversed hypersensitivity, leading to the loss of transcription factor binding. The reduction in hypersensitivity induced by ZK98299 was readily reversed by treatment with the progestin R5020. The chromatin organization of the promoter could be cycled between the open and closed states by consecutive treatments with agonist or antagonist. The antagonist RU486 also blocked activation of transcription and the assembly of a transcription preinitiation complex, but in contrast to ZK98299, maintained the hypersensitive chromatin state. Taken together, these results suggest that PR binding to chromatin is sufficient to induce hypersensitivity to endonucleolytic cleavage. Furthermore, they indicate that the PR binding to DNA and the resulting chromatin hypersensitivity is functionally separate from transcriptional activation in vivo.

Topics: Animals; Breast Neoplasms; Cell Line, Transformed; Cell Transformation, Viral; Chromatin; Female; Gonanes; Humans; Mammary Tumor Virus, Mouse; Mice; Mifepristone; Promoter Regions, Genetic; Receptors, Progesterone; Signal Transduction; Transcriptional Activation

Because progesterone antagonists are growth inhibitors, they are in Phase III clinical trials for the treatment of breast cancer. However, when cellular cAMP levels are elevated, some antiprogestins inappropriately activate transcription. We have proposed that hormone "resistance" may result from such unintended stimulation of breast cancer by antagonists. In transient expression systems, the two natural isoforms of human progesterone receptors (PR), B-receptors and truncated A-receptors, have dissimilar effects on agonist-mediated transcription. We show here that in the presence of 8-Br-cAMP, antiprogestin-occupied B-receptors but not A-receptors become transcriptional activators. Therefore, we developed new model systems to study each PR isoform independently in a breast cancer setting: (a) a stable PR-negative monoclonal subline (T47D-Y) of PR-positive T47D breast cancer cells was selected by flow cytometric PR screening. T47D-Y cells are PR-negative by immunoassays, by ligand binding assay, by growth resistance to progestins, by failure to bind a progesterone response element (PRE) in vitro, and by failure to transactivate PRE-regulated promoters; and (b) T47D-Y cells were stably transfected with expression vectors encoding one or the other PR isoform, and two monoclonal cell lines were selected that express either B-receptors (T47D-YB) or A-receptors (T47D-YA) at levels equal to those seen in natural T47D cells. The ectopically expressed receptors are properly phosphorylated, and like endogenously expressed receptors, they undergo ligand-dependent down-regulation. The expected B:B or A:A homodimers are present in cell extracts from each cell line, but A:B heterodimers are missing in both. In the presence of agonists, cAMP-dependent, transcriptional synergism of PRE-regulated promoters is seen in both cell lines. By contrast, in the presence of the antiprogestins RU486 or ZK112993, inappropriate transactivation occurs in YB cells but not in YA cells. The class of antiprogestins represented by ZK98299, which blocks PR binding to DNA, does not activate transcription in either cell line. We propose that these new cell lines are physiological models for the study of PR isoform-specific antiprogestin resistance in breast cancer.

Topics: Base Sequence; Breast Neoplasms; Cyclic AMP; Female; Gonanes; Humans; Mifepristone; Molecular Sequence Data; Progestins; Receptors, Progesterone; Transcription, Genetic; Tumor Cells, Cultured

When steroid hormone antagonists have inappropriate agonist effects, the clinical consequences are grave. Progesterone antagonists bind to two naturally occurring isoforms of human progesterone receptors (hPR), hPRB and the NH2-terminally truncated hPRA, and usually inhibit agonist-stimulated transcription. It is shown here that elevation of cAMP levels in a human breast cancer cell line leads to the functional reversal of progesterone antagonist action. While hPR occupied by the antagonists RU486 and ZK112993 are transcriptionally inactive, the antagonist-occupied receptors become strong activators of transcription in the presence of 8-Br-cAMP. However, this functional switch does not occur with the progesterone antagonist ZK98299, which, unlike RU486 and ZK112993, is unable to induce hPR binding to DNA. This suggests that the 8-Br-cAMP-induced transcriptional reversal requires that the antagonist-occupied receptors be bound to DNA. Even with agonist-occupied hPR, addition of 8-Br-cAMP results in a synergistic increase in transcriptional activity. When hPRA alone are transiently expressed in COS-1 cells, transcription of a reporter gene is stimulated by the agonist R5020 and by 8-Br-cAMP and is synergistic when both are present; but the 8-Br-cAMP-dependent component of transcription proceeds in the absence of hPRA, in the absence of the progesterone response element, and in the presence of a DNA-binding domain mutant of hPRA that cannot bind to the progesterone response element. Additionally, under the intracellular conditions in which 8-Br-cAMP activates antagonist-hPR complexes, there is no protein kinase A-mediated phosphorylation of the receptors. We discuss a model in which a gene that is independently transcribed by cAMP-responsive factors and by hPR can be selected for positive or negative regulation on the transcription complex due to additive or cooperative interactions between the two DNA-bound factors.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Antineoplastic Agents; Base Sequence; beta-Galactosidase; Breast Neoplasms; Cell Line; Chloramphenicol O-Acetyltransferase; Cyclic AMP; DNA-Binding Proteins; Female; Gonanes; Humans; Mifepristone; Molecular Sequence Data; Mutagenesis, Site-Directed; Oligodeoxyribonucleotides; Phosphates; Progesterone; Promegestone; Receptors, Progesterone; Recombinant Proteins; Transcription Factors; Transfection; Tumor Cells, Cultured

In a human breast cancer cell line (ZR-PR-LT) we have found a poor overall correlation between affinity of progestins and anti-progestins for the progesterone receptor (PGR), concentration required for receptor down-regulation and anti-proliferative potency. Medroxyprogesterone acetate (MPA) and the anti-progestin RU 38.486, which possess glucocorticoid and antiglucocorticoid activity, respectively, cause receptor down-regulation at lower concentrations than their Kdi for [3H] ORG 2058 binding sites. In addition dexamethasone markedly down-regulates PGR at concentrations which fail to interact with PGR suggesting that heterospecific modulation of PGR occurs via the glucocorticoid receptor. In contrast the progestin ORG2058 and the anti-progestin ZK 98.299 caused 50% PGR down-regulation at a concentration (EC50) 50-fold higher than their Kdi values. ZK 112.993 was 500-fold more potent at PGR down-regulation than ZK 98.299 but had only a 5-fold higher affinity for PGR. Anti-proliferative concentrations of progestins/anti-progestins showing were generally higher than either Kdi values or EC50 values.

Topics: Binding, Competitive; Breast Neoplasms; Dexamethasone; Down-Regulation; Female; Gonanes; Humans; Medroxyprogesterone Acetate; Mifepristone; Mitosis; Pregnenediones; Progesterone Congeners; Progestins; Receptors, Glucocorticoid; Receptors, Progesterone; Tumor Cells, Cultured

We studied the influence of the antiprogestin onapristone (ZK 98.299) and the progestin medroxyprogesterone acetate (MPA) on the proliferation and hormone receptor levels of the following human breast cancer cell lines: the oestrogen receptor (ER) and progesterone receptor (PR) negative cell line MDA-MB-231 and the ER- and PR-positive cell lines T47-D and SK-BR-3. MPA and onapristone both bind to the cellular PR and can inhibit the proliferation of hormone-dependent cells; PR-negative MDA-MB-231 cells are not inhibited. The growth inhibition of the ER- and PR-positive tumour cells induced by onapristone is accompanied by a significant accumulation of cells in the G0/G1 phase and a reduction of S-phase cells, while MPA does not change the distribution of the cell cycle phases. However, MPA reduces the cellular ER content by 27% and the PR content by more than 80%. Conversely, onapristone does not significantly affect ER and PR levels. The extent of growth inhibition by both drugs differs considerably: onapristone inhibits growth of both receptor positive cell lines (T47-D:39%; SK-BR-3:17%), while MPA affected growth in only SK-BR-3 (61%). These results indicate that even though the two drugs act through the PR, the inhibitory effect on the three cell lines of MPA may depend on ER concentration and its down-regulation, while the inhibitory effect of onapristone is mainly correlated to the PR concentration without significantly affecting ER levels. Since tumour cells with low ER concentration are growth suppressed by onapristone, but not by MPA, it remains to be examined whether antiprogestins should preferably be used in PR-positive tumours with a low ER concentration.

Topics: Breast Neoplasms; Cell Cycle; Cell Division; DNA, Neoplasm; Flow Cytometry; Gonanes; Humans; Medroxyprogesterone Acetate; Receptors, Estrogen; Receptors, Glucocorticoid; Receptors, Progesterone; Receptors, Steroid; Tumor Cells, Cultured