The antitumor mechanism of progesterone antagonists is a receptor mediated antiproliferative effect by induction of terminal cell death

The antiprogesterones Onapristone, ZK 112.993 (Schering AG), and Mifepristone (Roussel-Uclaf) proved to possess progesterone receptor-mediated antiproliferative effects in experimental mammary carcinomas. In this study, the potency and mechanism of the antitumor action of Onapristone and ZK 112.993 is characterized by ovariectomized, progestagen and/or estradiol substituted mice bearing hormone-dependent MXT(+) mammary tumours. Medroxyprogesterone acetate (MPA, 0.8 mg/mouse, 3 times weekly, s.c.) could only induce a poor stimulation of tumour growth (% T/C = 40; intact control % T/C = 100), which was only marginally inhibited (% T/C = 21) by Onapristone (0.2 mg/mouse, 6 times weekly, s.c.) during a 6-week therapy. Therefore, the antitumor mechanism of antiprogesterones cannot preferably depend on a classical progesterone antagonism. In contrary, the pronounced stimulation of tumor growth (% T/C = 152) by estradiol benzoate (EB, 0.33 microgram/mouse, 3 times weekly, s.c.) was completely inhibited (% T/C = 7) by the antiprogesterones. An even more stimulated tumour growth was achieved by a combination of EB and MPA (% T/C = 365 using 0.17 mg; % T/C = 225 using 0.8 mg MPA). Onapristone dramatically blocked tumor growth (% T/C = 7) at the lower dose of MPA; no inhibition (% T/C = 203), however, was detected at the higher dose of MPA. These data and a morphological analysis indicate that the potent antitumor activity of the progesterone antagonists depends on the binding to a number of available progesterone receptors high enough to trigger an antiproliferative effect via the induction of terminal differentiation associated with terminal cell death.     

The antitumor potency of progesterone antagonists is due to their differentiation potential.

A new therapy for the progesterone receptor positive mammary carcinoma may be the treatment with progesterone antagonists. This new class of antihormones causes a strong inhibition of tumor growth comparable to the potency of ovariectomy in a panel of experimental mammary carcinomas. The mechanisms of the strong tumor-inhibiting action of progesterone antagonists on experimental mammary carcinomas mainly depends on a progesterone receptor mediated process leading to induction of terminal differentiation and a blockade of the cell cycle. To further characterize the antitumor mechanism of progesterone antagonists we analyzed the effects of Onapristone and ZK 112.993 on DMBA- and MNU-mammary tumors of the rat and MXT-tumors of the mouse after different therapy intervals. These hormone-dependent mammary tumors normally display intraductal growth in papillary, cribiform or solid formation, whereas after treatment periods of 2-6 weeks with progesterone antagonists they displayed dysplastic ductal and acinous formations, usually filled with secretory material. Whereas tumor size, mitotic index, and the grade of tumor malignancy decreased distinctly, the volume fraction of glandular structures in the tumors as well as the appearance of apoptosis increased 3-fold compared to the controls. In addition, the mammary glands of progesterone antagonist treated animals showed the morphological features of differentiation with the appearance of secretory activity. Interestingly, the staining pattern of some of the lectins used, especially UEA 1 binding pattern, fits to the concept of differentiation since recent studies revealed a higher degree of fucosylation only in benign lesions of human breast cancers. Therefore, these data underline the concept of a differentiation potential of progesterone antagonists on progesterone receptor positive mammary carcinomas.     

Sensitivity and specificity of bioassay of estrogenicity on mammary gland and uterus of female mice

Young intact (18 days of age) and adult ovariectomized (OV-X, ovariectomized between 21 to 24 days of age) C3H/Di mice were used to measure the estrogenicity on the basis of the growth response of mammary epithelial structures and weight of the uterus. The percentage area of the mammary fat pad occupied by mammary epithelial structures was progressively increased by 17beta estradiol from dose 0.001 microg.d(-1). The maximum effective dose of estradiol was 0.01 microg.d(-1) and the dose 10 microg.d(-1) of estradiol decreased mammary size to control levels (inverted-U-shaped dose-response curve). Progesterone alone progressively stimulated mammary growth in young intact females from dose 125 microg.d(-1), in adult OV-X animals from dose 1000 microg.d(-1). Both in young intact and adult OV-X animals, uterine weight progressively increased during estradiol treatment. Progesterone alone had no effect on uterine weight in young intact animals; in adult OV-X animals, uterine weight was increased starting from dose 250 microg.d(-1). Progesterone acted synergistically with estradiol to produce higher mammary growth than that in females treated with estradiol alone. The effects of a combination of estradiol plus progesterone in the mammary gland were mimicked by norethindrone acetate and inhibited by cortisol in both young intact and adult OV-X animals. Testosterone inhibited estradiol plus progesterone stimulated growth of mammary gland only in OV-X animals, but stimulated uterine weights in both young intact and adult OV-X animals. Spleen weight and size of mammary lymph nodes were not affected by estradiol, progesterone, norethindrone acetate or testosterone, but were decreased by cortisol. Cortisol also decreased the percent area of the mammary fat pad occupied by mammary epithelial structures, but had no effect on weight of the uterus. These results show that bioassay of estrogenicity in females is not specific. Mammary and uterine growth is stimulated not only by estrogens but also by progesterone and testosterone, respectively.     

Progesterone antagonists: Tumor-inhibiting potential and mechanism of action

A new approach for the treatment of breast cancer could be the use of progesterone antagonists. These compounds were originally developed for the inhibition of progesterone-dependent processes and have been shown to be effective in inhibition of nidation and interruption of pregnancy. Although the roles of progesterone and the progesterone receptor in control of cell growth remain unclear, it was found in progesterone receptor positive mammary carcinoma cell lines that the antiprogestin, Mifepristone, had an inhibitory effect on cell growth-and a growth-inhibiting action on the DMBA-induced mammary carcinoma of the rat. We have shown that the progesterone antagonists, Onapristone and ZK 112993, which possess a reduced antiglucocorticoid activity compared to Mifepristone, exert a strong tumor-inhibiting effect in a panel of hormone-dependent mammary tumor models. The effects of these compounds were in some systems superior to those of tamoxifen or high dose progestins and comparable to ovariectomy. Although prerequisites for their antiproliferative potency are an affinity to the progesterone receptor as well as a sufficient number of available receptors in the tumors, the strong tumor inhibiting potential of the antiprogestins cannot be explained by a classical antihormonal mechanism. Surprisingly, the antitumor activity is evident in spite of elevated serum levels of ovarian and pituitary hormones. It was established by morphometric procedures that treatment with Onapristone triggers differentiation of the mitotically active polygonal tumor epithelial cell towards secretory active glandular structures and acini. All our quantitative light and electron microscopic data indicate that the antitumor action of antiprogestins is accompanied by the initiation of terminal differentiation leading to (apoptotic) cell death. Finally, our flow cytometry studies revealed an accumulation of the tumor cells in the G₀G₁ phase of the cell cycle, which may result from induction of differentiation since a differentiation-specific G₁ arrest has already been proposed for other stem cell systems. It can be concluded from these data that the progesterone receptor antagonists differ in their mode of action from compounds used in established endocrine treatment strategies for mammary carcinoma. The ability of progesterone antagonists like Onapristone to reduce the number of cells in S-phase may offer a significant clinical advantage, since it is established that the S-phase fraction is a highly significant predictor of disease-free survival among axillary node-negative patients with diploid mammary tumors.     

Induction of mammary prolactin receptors and lactose synthesis after ovariectomy in the pregnant mouse.

The development of prolactin receptors in the mammary gland after ovariectomy was investigated in pregnant KA mice. Mice were ovariectomized on day 13 of pregnancy and used for the determination of the amount of specific binding of 125I-labelled prolactin to the mammary tissue, and the contents of lactose and nucleic acids in the mammary gland 0, 8, 24, and 72 hr after the operation. The specific binding of 125I-labelled prolactin, lactose and RNA contents in the mammary gland remained low until 8 hr, sharply increased 24 hr and decreased 72 hr after ovariectomy. When ovariectomized mice were treated with 0.2 mg progesterone, pregnancy was maintained and an increase (1.5-fold) in the amount of specific binding was observed with an increase of lactose content. Five mg progesterone completely inhibited lactose synthesis. Cortisol administered with progesterone did not show any specific change at the dose used (0.5 to 10 mg). Although the amount of specific binding was also increased after hysterectomy, this increase (2-fold) did not fully cover the increase after ovariectomy (3-fold). These results suggest that the recepter site for prolactin is induced before the initiation of lactose synthesis caused by ovariectomy during pregnancy.     

A role for the androgen receptor in the endometrial antiproliferative effects of progesterone antagonists

In women and nonhuman primates, treatment with progesterone antagonists suppresses estrogen-dependent mitotic activity in the endometrial glands. This antiproliferative effect is paradoxical, because progesterone antagonists do not bind to the estrogen receptor (ER). While this phenomenon has been termed a "functional noncompetitive antiestrogenic effect," it does not occur in all species or in all regions of the primate reproductive tract, so is best referred to as an "endometrial antiproliferative effect." Recent studies of ours in both women and macaques revealed that the endometrial androgen receptor (AR) was increased by progesterone antagonist treatment. Because androgens are known to suppress estrogen-dependent endometrial proliferation, we hypothesized that the AR was involved in the antiproliferative effects induced by progesterone antagonists. In a test of this hypothesis, we administered the antiandrogen, flutamide, along with progesterone antagonists to ovariectomized, estrogen-treated macaques. Flutamide counteracted the suppressive effects of the progesterone antagonists on endometrial wet weight, thickness, stromal compaction, and mitotic index. Hyaline degeneration of the spiral arteries was also blocked by flutamide. These data implicate the AR as a functional component of the mechanism through which progesterone antagonists induce endometrial antiproliferative effects in the presence of estrogens.     

Secretion of estradiol-17beta by porcine mammary gland of ovariectomized steroid-treated sows

Although the mammary gland of many species secretes estradiol (E(2)), nothing is known of E(2) secretion in the porcine gland. The present study was designed to investigate whether porcine mammary gland was a source of E(2), and to test the influence of individual and combined effects of exogenous progesterone and estradiol benzoate (EB) on the secretion of E(2). Immature crossbred gilts were ovariectomized at 7 months of age followed by 4 weeks later by steroid hormone replacement therapy to produce estradiol and progesterone (P(4)) blood concentrations similar to those observed during a normal estrous cycle. Arterial and venous blood plasma (from carotid artery and anterior mammary vein, respectively) were sampled for 2h at 10 min intervals. Plasma concentrations of progesterone, androstenedione (A(4)), testosterone (T), estrone (E(1)) and estradiol were determined by RIA. In all gilts treated with progesterone alone or in combination with EB, concentrations of P(4), A(4) and E(1) in blood collected from venous outflow were lower compared to concentrations in arterial blood, whereas concentrations of E(2) were higher in blood plasma from the anterior mammary vein compared to plasma from the carotid artery. The results indicated that the porcine mammary gland secreted E(2). Increased concentrations of plasma E(2) collected only from P(4)-treated animals suggested that progesterone activated enzymes involved in steroidogenesis in porcine mammary gland, or those utilized in its metabolism.     

Development of a mouse model of mammary gland versus uterus tissue selectivity using estrogen- and progesterone-regulated gene markers

We have identified mRNA markers of estradiol and progesterone action in the mouse mammary gland and uterus to establish an in vivo model for the evaluation of novel and potentially tissue selective estrogens and progestins. Gene chip analysis of mRNA from ovariectomized (OVX) mice treated with vehicle (V), 17beta-estradiol (E2), progesterone (P) or E2+P for 7 days identified defensinbeta1 (Defbeta1) and indoleamine-pyrrole 2,3 dioxygenase (INDO) as markers of E2 and P action in the mammary gland, and serine protease inhibitor, Kazal type 3 (Spink3) and G protein-coupled receptor 105 (GPR105) as markers in the uterus. Defbeta1 and Spink3 are both upregulated by E2+P, whereas INDO and GPR105 have a complementary profile of upregulation by E2 alone and suppression of the E2 effect by P. Quantitative RT-PCR analysis of mammary gland markers was concordant with histological changes. Using this model, medroxyprogesterone acetate (MPA) and tanaproget (TNPR), a novel nonsteroidal progesterone receptor agonist, were evaluated and found to have no marked tissue selectivity relative to progesterone. In addition, the ERalpha selective ligand propyl pyrazole triol (PPT) and the ERbeta selective ligands ERB-041 and WAY-202196 were evaluated on the mammary gland endpoints of histology and Defbeta1 mRNA expression, and showed that ERalpha stimulation is necessary and sufficient for eliciting estradiol-mediated changes in the mammary gland.     

Physiologic role of relaxin on mammary gland growth in rats

The role of relaxin in stimulating growth of the mammary gland was assessed in ovariectomized and intact male rats for a period of 20 days. In addition to relaxin alone, the ovarian mammogenic hormones estradiol and progesterone were used in combination with relaxin and with each other to evaluate responses of mammae. Indices for mammary growth included wet weight, dry fat-free tissue, DNA, RNA, total protein, and collagen. Quantitative estimates of DNA and collagen represented the best indicators of parenchymal and stromal growth, respectively. Because changes in body weights were significantly different among hormonally administered groups, these were included as well. In Ovariectomized young rats, relaxin alone and in combination with estradiol and progesterone increased all indices significantly (P less than 0.01). The collagenous portion of total protein was high for the group receiving relaxin alone (62%) compared with the control group (46%). Relaxin administered along with estradiol and progesterone increased collagen accumulation to 73%, compared with 54% in the estradiol + progesterone group. Relaxin did not significantly increase growth indices when administered to male rats at 10 and 20 micrograms/day, while 30 micrograms stimulated a significant increase in total protein (P less than 0.05), suggesting that 30 micrograms of relaxin/day may be considered the basal concentration needed to induce a physiologic response in males. Relaxin induced a growth effect on mammae by synergizing with progesterone and estradiol in order to stimulate parenchymal proliferation, as noted by a DNA increase, and to increase stromal distensibility of the mammary pad by invoking accumulation of collagen and total protein in substituting for mammary adipose tissue.     

Metastasis-associated protein 1 deregulation causes inappropriate mammary gland development and tumorigenesis

Emerging data suggest that metastasis-associated protein 1 (MTA1) represses ligand-dependent transactivation functions of estrogen receptor-alpha in cultured breast cancer cells and that MTA1 is upregulated in human breast tumors. However, the role of MTA1 in tumorigenesis in a physiologically relevant animal system remains unknown. To reveal the role of MTA1 in mammary gland development, transgenic mice expressing MTA1 under the control of the mouse mammary tumor virus promoter long terminal repeat were generated. Unexpectedly, we found that mammary glands of these virgin transgenic mice exhibited extensive side branching and precocious differentiation because of increased proliferation of ductal and alveolar epithelial cells. Mammary glands of virgin transgenic mice resemble those from wild-type mice in mid-pregnancy and inappropriately express beta-casein, cyclin D1 and beta-catenin protein. Increased ductal growth was also observed in the glands of ovariectomized female mice, as well as of transgenic male mice. MTA1 dysregulation in mammary epithelium and cancer cells triggered downregulation of the progesterone receptor-B isoform and upregulation of the progesterone receptor-A isoform, resulting in an imbalance in the native ratio of progesterone receptor A and B isoforms. MTA1 transgene also increased the expression of progesterone receptor-A target genes Bcl-XL (Bcl2l1) and cyclin D1 in mammary gland of virgin mice, and, subsequently, produced a delayed involution. Remarkably, 30% of MTA1 transgenic females developed focal hyperplastic nodules, and about 7% exhibited mammary tumors within 18 months. These studies establish, for the first time, a potential role of MTA1 in mammary gland development and tumorigenesis. The underlying mechanism involves the upregulation of progesterone receptor A and its targets, Bcl-XL and cyclin D1.     

A comparison of plasma prolactin levels in young female Long-Evans and Holtzman rats as measured by Nb2 lymphoma bioassay and radioimmunoassay

This study was conducted to determine the plasma levels of prolactin in prepubertal and young, postpubertal, proestrus rats of mammary tumor-susceptible (Sprague-Dawley) and tumor-resistant (Long-Evans) strains using a sensitive bioassay-Nb2 lymphoma cell replication. Prepubertal Long-Evans rats had significantly higher levels of prolactin than did Holtzman Sprague-Dawley rats of the same age. Likewise, Long-Evans rats secreted significantly more prolactin into the blood on the afternoon and evening of proestrus than did Holtzman rats. Finally, ovariectomized Long-Evans rats released more prolactin into the blood at 1 day, but not at 8 or 15 days, of treatment with diethylstilbestrol. Prolactin levels determined by conventional radioimmunoassay and by bioassay were similar except on the afternoon of proestrus, when, in both strains of rats, the bioassay to radioimmunoassay ratio increased significantly above 1.0 during the late evening. In addition, the ratio was significantly less than 1.0 in the early and late afternoon in the Holtzman rats, but not Long-Evans rats. These data indicate that a strain of rats that is resistant to experimentally induced mammary cancer has higher prolactin levels in the blood than does a strain that is susceptible to mammary cancer at a time when mammary gland growth is rapid. Furthermore, there are times during the proestrus prolactin surge when the bioassay yielded higher and lower values of prolactin than radioimmunoassay of the same samples, suggesting functional heterogeneity of prolactin that may impact on mammary gland or other target tissue function.     

Detection of estrogenicity by bioassay on the mouse mammary gland in vivo

The wide chemical diversity of estrogenic compounds precludes an accurate prediction of estrogenic activity on the basis of chemical structure or radioimmunological assay and thus requires that the potency of these compounds is defined by bioassay. The mammary duct growth response in intact prepubertal and adult gonadectomized female and male mice of the C3H/Di strain was used to assess the estrogenicity of synthetic compounds or their derivatives. The vehicle for tested compounds should be free of estrogenic and other hormonal effects. Olive oil or sunflower oil exerted estrogenic activities and were thus unsuitable as vehicles for the tested compounds. The absence of estrogenic activity, high solubility of different steroid hormones, and the low incidence of the inflammatory reactions at the injection site were achieved by using a vehicle containing benzyl alcohol, benzyl benzoate, butylhydroxyanisole, butylhydroxytoluene, ethyl oleate and ethanol. The bioassay was primarily designed to examine the effect of tested compounds on mammogenesis. The duration of hormone treatment was chosen to be long enough for induction of duct growth but too short to induce lobuloalveolar differentiation. Females were treated for 10 days, males for 15 days. The proportional volume occupied by mammary epithelial structures was estimated by the modified Chalkley's technique. The mean coefficient of variation of quantitative evaluation of 10 different mammary glands obtained by two operators varied between 3.2 and 17.4%. The mean coefficient of variation of quintuplicate determinations of each mammary gland by one operator was 10.1%, and 11.1% by the other. The correlation coefficient between results of two operators was 0.994. Estrogens are primarily defined by their ability to increase the mitotic activity of female secondary sex organs. However, our results have shown that progesterone alone, if administered in a high dose, stimulates mammary growth in both intact prepubertal and OV-X female mice similarly as the synthetic progestatial steroid norethindrone with inherent estrogenic properties. In contrast, progesterone alone had no effect, in young intact or adult castrated males, but norethindrone did stimulate mammary growth. These results demonstrated that the mammary gland of males is a suitable model for estrogen screening.     

Hormonal defect in maspin heterozygous mice reveals a role of progesterone in pubertal ductal development

Progesterone and PR are mainly thought to affect tertiary ductal side branching and alveologenesis in late stage of mammary gland development. Here, we present evidence that they also play a role in early ductal development. This conclusion derived from our analysis of maspin heterozygous (Mp+/-) mice that showed defective ductal development at puberty. The defect was due to a reduced systemic level of progesterone. We show that treatment of Mp+/- mice with progesterone rescued the defect of ductal development. When both wild-type and Mp+/- mice were ovariectomized at 4 wk of age, treatment with progesterone alone can stimulate their ductal growth. In addition, treatment of wild-type mice with the progesterone inhibitor RU486 slowed ductal development in a dose-dependent manner. To confirm that progesterone receptor (PR) was required for progesterone action in ductal development at pubertal stage, we treated ovariectomized PR-deficient (PRKO) and wild-type mice with progesterone and examined ductal development at 7 wk of age. Whereas wild-type mammary glands displayed abundant ductal growth after progesterone treatment, there was a significant retardation of ductal growth in PRKO mice. Furthermore, we observed reduced ductal development in intact PRKO mice at 7 wk of age compared with that of wild-type mice. However, the defect was rescued at late stage of mammary development in PRKO mice. These data demonstrate that progesterone signaling, which is mediated by PR, plays an important role in early ductal development. In PRKO mice, a compensatory mechanism occurs that rescues the ductal defect at a late stage of mammary development.     

Immunization of ovariectomized ewes against progesterone, oestrogen or cortisol to detect effects of adrenal steroids on reproduction

Ovariectomized ewes were immunized against cortisol, oestrogen or progesterone to determine whether steroids of non-ovarian origin occur in sufficient amounts to influence the reproductive system. Ewes immunized against oestrogen (oestrone + oestradiol) had smaller uteri (P less than 0.05) and a lower concentration of oestradiol in uterine tissue (P less than 0.05), while the adrenal gland was heavier (P less than 0.05). In the peripheral plasma of immunized ewes, the concentration of FSH, but not LH, was increased (P less than 0.05). Ewes immunized against cortisol also had smaller uteri (P less than 0.05) and heavier adrenal glands (P less than 0.05), but gonadotrophins and the concentration of oestradiol in the uterus were unaffected. Immunization against progesterone, or injection with synthetic glucocorticoids, did not affect any of the characteristics measured. We conclude that the adrenal gland of the ewes produced sufficient oestrogen or aromatizable androgen to have significant effects on the reproductive system. In contrast, adrenal production of progesterone did not produce detectable biological effects. Immunization against cortisol did affect the reproductive system, but the mechanism of this action could not be determined.     

Synthesis and antiproliferative potency of 9-beta-D-arabinofuranosyl-2-fluoroadenine phospholipid adducts.

Three novel alkylphospholipid and four novel O-alkylglycerophospholipid derivatives of fludarabine (F-ara-AMP), known as a drug for the clinical treatment of chronic lymphocytic leukemia, were synthesized. The antiproliferative activity was determined in comparison to the parent nucleoside fludarabine in an immortalized but nontumorigenic human mammary epithelial cell line (H 184 A1N4), in two human breast tumor cell lines (MaTu and MCF7), and in two leukemic cell lines (HL 60 and Daudi). Fludarabine inhibited the growth of the leucemic cell lines very effectively. The breast tumor cell lines responded with much less sensitivity. The antiproliferative potency of the new compounds strongly depended on the chemical structure of the lipid component, and derivatives with a high effectiveness against one or both of the breast tumor cell lines were described.     

Effect of cyproterone acetate,d-norgestrel and progesterone on the canine mammary gland

Summary The effects of short-term (8 weeks) treatment with different doses of cyproterone acetate (CPA), d-norgestrel (d-N) and progesterone (PRO) on the mammary gland were studied in cycle-synchronized beagle bitches (first anoestrus). Mammary glands from non-treated primiparous beagle bitches in the 6th and 9th weeks of pregnancy were also included. The results were evaluated using the whole-mount technique, histologic, histochemical and biochemical methods. CPA, d-N and PRO were shown to cause dose-dependent mammary growth accompanied by an increase in the mammary weight, DNA content and activity of several histochemically demonstrable dehydrogenases. These changes resembled in some aspects mammary development observed in the last third of pregnancy. A single human oral contraceptive dose (HCD) of CPA as well as a dose as low as 1.0mg/kg/day subcutaneously of PRO was capable of stimulating complete mammary development. A comparable effect was first observed as a result of treatment with as much as 100 times the HCD of d-N. However, d-N and CPA were shown to be more effective than PRO in stimulating ductal proliferative activity. These structural and biochemical responses indicate that quantitative and/or qualitative differences may exist between PRO, the synthetic progesterone derivative CPA and the synthetic nortestosterone progestagen d-N with regard to their growth-promoting effect on the canine mammary gland. This may be explained by possible differences in their potency and range of biological activity, pharmacodynamics and effects on pituitary hormone secretion.The authors are grateful to Dr. Christel Schöbel and Mrs. P. Kurth for carrying out the experimental work on animals, to Dr. Y. Nishino and Mr. M. Leidecker for biochemical determination of DNA, to Dr. J. Kaufmann for statistical analysis, to Miss E. Fallenbacher, Mrs. B. Schilk, Mrs. G. Soulioti and Miss. U. Tüshaus for their excellent technical assistance, and to Dr. P. Günzel for his advice and encouragement     

Endocrine pharmacological characterization of progesterone antagonists and progesterone receptor modulators with respect to PR-agonistic and antagonistic activity

Studies were conducted to assess progesterone antagonists (PAs) and progesterone receptor modulators (PRMs) with respect to PR agonistic and antagonistic activities in vivo. These properties are not always adequately reflected in transactivation in vitro models. Studies were performed in pregnant rats, estrogen-primed rabbits (McPhail -Test), and cycling and pregnant guinea pigs. Tested compounds included mifepristone (RU486), onapristone, J867, J956, J1042, and ZK137316. J-compounds induced sub-maximum endometrial transformation and, paradoxically, inhibited effects of progesterone in rabbits. Mifepristone, onapristone, and ZK137316 behaved as 'pure' antagonists in this species. Inhibition of uterine PGF(2alpha) secretion and inhibition of luteolysis in cycling guinea pigs were more sensitive parameters of PR-agonistic and antagonistic properties. 'Pure' PAs inhibited uterine PGF(2alpha) secretion and luteal regression completely. The PR agonist R5020 reversed both effects which demonstrates a PR mediation. Agonistic PRMs (J-substances and mifepristone) showed no or blunted antiluteolytic effects compared to the 'pure' PR antagonist onapristone. When tested in pregnant guinea pigs for their labor-inducing potential, PR agonistic PRMs had much reduced or abolished abortifacient activity compared to mifepristone (mifepristone > J956 > J867/J912 > J1042). However, in cycling animals, superior antiovulatory and antiproliferative properties of the J-substances were seen. Antiovulatory effects of 'pure' and agonistic PRMs are probably due to different mechanisms. The relevance of rodent studies for antiovulatory and uterine antiproliferative effects for the human is still uncertain. The non-abortifacient PRM J1042 induced stromal compaction and inhibition of endometrial proliferation in monkeys, but this effect was not stronger than that of the 'purer' PAs. 'Pure' PAs are important pharmacological tools analogous to PRKO models to study the role of PR in the menstrual cycle and in pregnancy.     

Effect of epostane, ZK 98299, and ZK 98734 on the interruption of pregnancy in the rat

The objective of these studies was to determine whether treatment of 10-day pregnant rats with a combination of epostane (a progesterone biosynthesis inhibitor) and either ZK 98299 or ZK 98734 (progesterone receptor antagonists) would result in additive or synergistic effects on the interruption of pregnancy. When these compounds were tested individually, the order of potency in interrupting pregnancy was ZK 98734 greater than ZK 98299 greater than epostane (50% effective doses 1.3, 4.0, and 35 mg/kg, respectively). Epostane and ZK 98299 were then tested in combination. When epostane was given either 4 h prior to or concurrently with ZK 98299, the combined drug treatment resulted in a significant additive increase in interceptive activity compared to when ZK 98299 was administered alone. In vitro binding studies showed that ZK 98299 and ZK 98734 bound to the rat uterine progesterone receptor in vitro with approximately equal affinity. ZK 98734 bound to the rat thymus glucocorticoid receptor and to the rat ventral prostate androgen receptor with a greater affinity than ZK 98299. The affinity of ZK 98299 for the rat uterine estrogen receptor was weak while the binding of ZK 98734 was not detectable. Thus, the in vitro receptor binding profiles observed were consistent with the known progesterone and glucocorticoid antagonist activities of ZK 98299 and ZK 98734. Overall these findings show that the interceptive activity of epostane and ZK 98299, agents that exert their interceptive activity via different molecular mechanisms, is additive in the 10-day pregnant rat.     

Influence of submandibular salivary glands on hormone responsiveness of mouse mammary glands

Surgical removal of the submandibular salivary glands (sialoadenectomy) of female Balb/c mice significantly (P less than 0.05) reduced mammary development as judged by development scores and mammae DNA levels. Reduction in mammae development score by sialoadenectomy was observed in both mice saline injected and mice treated with estradiol and progesterone. Autografts of submandibular salivary tissue or daily administration of EGF to sialoadenectomized mice partly alleviated the atrophy of the mammary gland induced by sialoadenectomy (P less than 0.05). The results of our studies are consistent with a model of mammary gland developmental regulation that includes the submandibular salivary gland as a mediator of mammogenesis via secretion of EGF.     

Estrogen receptor-beta agonist diarylpropionitrile counteracts the estrogenic activity of estrogen receptor-alpha agonist propylpyrazole-triol in the mammary gland of ovariectomized Sprague Dawley rats

Although estrogen can bind both types of estrogen receptors, estrogen receptor-alpha (ERα) is dominant in mediating estrogenic activity in the mammary gland and uterus. Excessive estrogenic activity such as estrogen-based postmenopausal hormone replacement therapy increases the risk for breast and endometrial cancers. The adverse effect of estrogen on uterine endometrium can be opposed by progestins; however, estrogen-plus-progestin regimen imposes substantially greater risk for breast cancer than estrogen alone. In this study, we used ERα-selective agonist propylpyrazole-triol (PPT) and ERβ-selective agonist diarylpropionitrile (DPN) to activate ERα and estrogen receptor-beta (ERβ) separately in an ovariectomized rat model and determined whether PPT-activated ERα function in the mammary gland can be suppressed by DPN activated ERβ. Ovariectomized rats were randomly divided into six groups and treated with DMSO (control), DPN, PPT, PPT/DPN, PPT/Progesterone, and PPT/Progesterone/DPN, respectively. In the mammary gland, PPT but not DPN increased cell proliferation and amphiregulin gene expression; importantly, the stimulatory effect of PPT on mammary cell proliferation and amphiregulin gene expression can be suppressed by DPN. In the uterus, the effect of PPT on uterine weight and endometrial cell proliferation was not inhibited by DPN but can be inhibited by progesterone. These data provide in vivo evidence that PPT activated ERα activity in the mammary gland can be opposed by ERβ-selective agonist DPN, which may be explored for the development of better hormone replacement therapy regimen with less risk for breast cancer.