Binding of medroxyprogesterone acetate in human breast cancer

Distinguishing androgen receptor agonists and antagonists: distinct mechanisms of activation by medroxyprogesterone acetate and dihydrotestosterone

Natural and pharmacological androgen receptor (AR) ligands were tested for their ability to induce the AR NH2-terminal and carboxyl-terminal (N/C) interaction in a two-hybrid protein assay to determine whether N/C complex formation distinguishes in vivo AR agonists from antagonists. High-affinity agonists such as dihydrotestosterone, mibolerone, testosterone, and methyltrienolone at concentrations between 0.1 and 1 nM induce the N/C interaction more than 40-fold. The lower affinity anabolic steroids, oxandrolone and fluoxymesterone, require concentrations of 10-100 nM for up to 23-fold induction of the N/C interaction. However no N/C interaction was detected in the presence of the antagonists, hydroxyflutamide, cyproterone acetate, or RU56187, at concentrations up to 1 microM, or with 1 microM estradiol, progesterone, or medroxyprogesterone acetate; each of these steroids at 1-500 nM inhibited the dihydrotestosterone-induced N/C interaction, with medroxyprogesterone acetate being the most effective. In transient and stable cotransfection assays using the mouse mammary tumor virus reporter vector, all ligands displayed concentration-dependent AR agonist activity that paralleled induction of the N/C interaction, with antagonists and weaker agonists failing to induce the N/C interaction. AR dimerization and DNA binding in mobility shift assays and AR stabilization reflected, but were not dependent on, the N/C interaction. The results indicate that the N/C interaction facilitates agonist potency at low physiological ligand concentrations as detected in transcription, dimerization/DNA binding, and stabilization assays. However the N/C interaction is not required for agonist activity at sufficiently high ligand concentrations, nor does its inhibition imply antagonist activity.

Estrogen and androgen receptor mediated stimulation and inhibition of proliferation by androst-5-ene-3 beta,17 beta-diol in human mammary cancer cells

Androst-5-ene-3 beta,17 beta-diol (ADIOL) and 5 alpha-androstane-3 beta,17 beta-diol (5 alpha A), which are metabolites of dehydroepiandrosterone and dihydrotestosterone, are known to have estrogenic properties. This study reevaluates the estrogenic effects of ADIOL and 5 alpha A in MCF-7 cells and demonstrates additionally androgen-like inhibitory properties of these compounds in human hormone-dependent mammary cancer cells. ADIOL and 5 alpha A (10-100 nM) stimulate the proliferation of estrogen-sensitive MCF-7 cells. Binding assays with the estrogen receptor and inhibition of stimulation with the antiestrogen tamoxifen support the involvement of the estrogen receptor. On the other hand, the mammary cancer cell line MFM-223 is strongly inhibited by ADIOL and 5 alpha A in the same concentration range. This cell line is androgen receptor positive and is inhibited by androgens, but unresponsive to estrogens and progestins. The inhibitory effects of ADIOL and 5 alpha A in MFM-223 cells are mediated by the androgen receptor as demonstrated by receptor studies and competition experiments with hormone antagonists. ADIOL and 5 alpha A thus possess estrogen- and androgen-like properties and can stimulate or inhibit proliferation of human mammary cancer cells. The reactions of mammary cancer cells to these steroids depend on the receptor content and the growth properties of the individual cell line.

Medroxyprogesterone acetate inhibits the proliferation of estrogen- and progesterone-receptor negative MFM-223 human mammary cancer cells via the androgen receptor

This study demonstrates for the first time, that medroxyprogesterone acetate (MPA) inhibits the proliferation of the estrogen and progesterone receptor negative mammary cancer cell line MFM-223 via the androgen receptor. MPA is a progestin, which is used in the hormonal treatment of disseminated breast cancer. It binds to the progesterone, androgen, and glucocorticoid receptor and may exert its antiproliferative effects via different receptors. MFM-223 human mammary cancer cells contain a very high level of androgen receptors (160 fmol/mg protein) and low levels of estrogen, progesterone, and glucocorticoid receptors (< 20 fmol/mg protein). This cell line provides therefore a good model system to analyze the possible role of the androgen receptor in the action of MPA avoiding interference with other steroid hormone receptors. Effective inhibition of proliferation is achieved by 10 nM MPA or 1 nM of the androgen dihydrotestosterone, corresponding well to the binding affinities of both compounds (3.6 and 0.18 nM, respectively). The involvement of the androgen receptor was confirmed by competition experiments with antiandrogens. Furthermore, MFM-DHT cells, which are an androgen resistant subline of MFM-223 cells, are also resistant to MPA. This data supports the involvement of the androgen receptor in the action of MPA and additionally rules out direct hormone-independent cytotoxic effects of MPA.

Effect of Medroxyprogesterone Acetate on Immunohistochemical Expression of Estradiol in Endometrial Carcinoma

The effect of medroxyprogesterone acetate (MPA) on the immunohistochemical expression of estradiol (E2) was investigated in 25 cases of endometrial carcinoma. Twenty-three cases of the endometrial carcinomas showed positive Immunoreactivity for E2. The immunohistochemical expression of E2 was more intensive in carcinoma cells than in stromal cells. Although the morphologic alterations induced by MPA treatment were observed only in 2 cases who were administered more than 30,000 mg of MPA, the staining intensity in most cases appeared to decrease after the treatment. The decrease in E2 immunoreactivities of cancer cells as well as of stromal cells in Grade 1 or Grade 2 was significant. These results suggest that MPA might decrease the E2 content in endometrial carcinoma cells as well as in stromal cells.

Down-regulation of androgen receptor by progestins and interference with estrogenic or androgenic stimulation of mammary carcinoma cell growth

The regulatory influence of medroxyprogesterone acetate (MPA) on estrogen and androgen receptors of the human breast cancer cell lines MCF-7 and EFM-19 was explored in conjunction with the growth-promoting properties of these steroids. In the absence of steroidal stimulation, up to 1 microM MPA had no effect on the proliferation of the MCF-7 cell strain used and of EFM-19 cells. Under stimulation with 10 nM 17 beta-estradiol or 1 microM dihydrotestosterone, dose-dependent inhibition of the cell proliferation rates by 0.1-1 microM MPA was observed. Binding of MPA to the androgen receptor (Kd = 2.1 nM) but not to the estrogen receptor was demonstrable. During incubation of MCF-7 or EFM-19 cells with 1 microM MPA for 7 days, the estrogen and androgen receptor contents were down-regulated by approximately 50% and 60%, respectively. Likewise, the number of androgen-binding sites was reduced to 35% of the untreated controls after incubation of MCF-7 cells with 1 microM synthetic progestin R5020 for 7 days. The results indicate down-regulation of estrogen and androgen receptors by progestins in the absence of stimulatory effects on the proliferation of mammary carcinoma cells.

Actions of medroxyprogesterone acetate on the efficacy of cytotoxic drugs: studies with human breast cancer cells in culture

Human breast cancer cells (MCF-7) showed increased responses to methotrexate and vincristine after a 48-hr pre-treatment with medroxyprogesterone acetate. The effect of the hormone, which was detectable at concentrations of between 10 and 100 nM, was independent of its growth-inhibitory action. These findings confirm a previous clinical study and have important implications with regard to the management of advanced breast cancer.

Androgen and glucocorticoid receptor-mediated inhibition of cell proliferation by medroxyprogesterone acetate in ZR-75-1 human breast cancer cells

Medroxyprogesterone acetate (MPA) is a synthetic progestin, currently used in the adjuvant treatment of advanced breast cancer, which induces remission rates (30-40%) comparable to those obtained with other types of endocrine therapies. Since, in addition to its progestin-like action, MPA exhibits androgen- and glucocorticoid-like activities in other tissues, the present study was designed to assess the relative contribution of the different steroid receptor systems in the direct action of MPA on breast cancer cell growth, using the ZR-75-1 human mammary carcinoma cell line as an in vitro model. Unlike pure progestins, MPA potently inhibited the proliferation of ZR-75-1 cells in a concentration-dependent manner either in the presence or in the absence of estrogens, and the addition of insulin had only marginal effects on its growth-inhibitory activity. On the other hand, both hydroxyflutamide (OHF, a non-steroidal monospecific antiandrogen) and RU486 (a potent antiglucocorticoid and antiprogestin also endowed with antiandrogenic activity) competitively reversed MPA antiproliferative effects. MPA further decreased the growth of ZR-75-1 cells co-incubated with maximally inhibitory concentrations of either 5 alpha-dihydrotestosterone (DHT) or dexamethasone (DEX), although at about 300-fold higher MPA concentrations with DHT-treated than with DEX-treated ZR-75-1 cells, thus demonstrating a highly predominant androgenic effect. However, MPA had no effect on the growth of ZR-75-1 cells co-incubated with DHT and DEX simultaneously, thus supporting the predominant role of androgen and glucocorticoid receptors in MPA action. A 12-day preincubation of ZR-75-1 cells with increasing concentrations of MPA (10(-12) to 3 x 10(-6)M) decreased the specific uptake of [3H]estradiol (E2) by intact cell monolayers to the same extent as 10 nM DHT, an effect which was competitively blocked by the addition of OHF (3 microM). MPA action on ZR-75-1 cell growth also significantly differed from that of progestins in being additive to the inhibition of E2-stimulated growth by the steroidal antiestrogen ICI164384. The present data indicate that the main action of MPA on ZR-75-1 human breast cancer cell growth is due to its androgen receptor-mediated inhibitory action, while its glucocorticoid-like activity could play an additional role at high concentrations.

Simultaneous occurrence of receptors for estradiol, progesterone, and dihydrotestosterone in canine mammary tumors

Fifty-nine canine mammary tumors have been simultaneously assayed for their histological nature and their content of cytosolic receptors for estradiol (ER), progesterone (PGR), and dihydrotestosterone (DHTR). The tumors were histologically defined as benign tumors, malignant mixed tumors, sarcomas, and simple or complex carcinomas. The tumors exhibited a high incidence of steroid receptors (ER in 61% of the tumors, PGR in 69%, DHTR in 36%). It could be demonstrated that, in cytosols of canine mammary tumors, binding sites for different steroids may simultaneously occur. Twenty four percent of the tumors were able to bind specifically all three hormones tested. No tumor class displayed a specific receptor profile in regard to the receptor incidence, KD, and binding capacity. Also no correlation could be detected between histological grading of carcinomas and receptor incidence. In these tumors, however, the amount of ER and PGR binding showed changes dependent on differentiation. Noteworthy tumors simultaneously removed from the same bitch and with identical histological diagnosis were different in their receptor characteristics.

Estrogen and glucocorticoid receptors in adult canine articular cartilage

The cytoplasmic and crude nuclear fractions of adult mongrel dog articular cartilage contained estradiol- and dexamethasone-binding components which had properties of physiologic steroid receptors. The equilibrium dissociation constants averaged 0.37 nM for estradiol and 2.27 nM for dexamethasone. The concentrations estrogen receptors ranged from below 6 to 101 fmol/mg protein in the cytosols and from below 2.8 to 17.5 fmol/micrograms DNA in the nuclear fractions. Glucocorticoid receptors were detected in only 4 of 13 cytosols (range: 61.2-132 fmol/mg protein), whereas 10 of 13 nuclear fractions contained 0.8 to 46.8 femtomoles of the receptors for each microgram of DNA. There appeared to be no marked difference between the contents of either steroid receptor in female or male dog cartilage. No receptors were detected for androgen and progesterone.

Cytoplasmic progesterone and estradiol receptors in normal, hyperplastic, and carcinomatous endometria: therapeutic implications

This study was designed to determine whether the presence of progesterone receptors (PR) and/or estradiol receptors (ER) could be used to predict progestin responsiveness of recurrent or advanced endometrial cancers. We have demonstrated the presence of physicochemically similar cytoplasmic progesterone and estradiol receptors in normal, hyperplastic, and carcinomatous endometria. All normal endometria contained both PR and ER. Seventy-three percent of endometrial hyperplasias were PR(+) and 93% were ER(+). A decreasing concentration of progesterone receptor activity was observed with increasing tumor anaplasia [grade 1, 84% PR(+); grade 2, 55% PR(+); grade 3, 22% PR(+)] and in irradiated tumors. A statistically significant (p less than 0.001) relationship has been demonstrated between the presence of specific cytoplasmic PR and response to progestin therapy in recurrent or advanced endometrial adenocarcinomas. Thus, we conclude that a PR assay may be used to help select the most appropriate therapy for patients with recurrent or advanced endometrial adenocarcinoma.

Relationship between steroid receptors and response to endocrine therapy and cytotoxic chemotherapy in metastatic breast cancer

The relationship between steroid receptor content and response of metastatic breast cancers to endocrine therapy and cytotoxic chemotherapy has been examined. In 54 advanced breast cancers treated with hormonal therapy, 20 of 29 (69%) ER+, PR+ and 3 of 14 (21%) ER+, PR- tumors responded. Of the nine tumors that lacked both ER and PR, 2 (22%) were hormonally responsive. Based on either the ER or PR content alone, 68% of the PR+ and 54% of the ER+ tumors responded to endocrine therapy. Thus, the addition of PR assay could improve the accuracy of ER assay in selecting a hormonally responsive breast cancer. In 29 advanced breast cancers treated with cytotoxic drugs, the presence of ER and/or PR in the tumors seemed to favor an objective response to cytotoxic chemotherapy. The response rate was about 67% regardless of whether the cancers were ER+ or PR+.