Progestogenic effects of tibolone on human endometrial cancer cells

Progestagenic Effects of Tibolone are Target Gene—Specific In Human Endometrial Cells

OBJECTIVES

Tibolone (Tib) exhibits progestagenic activities in addition to its tissue-specific estrogenic activities. The purpose of the current study was to determine the progestagenic actions of Tib and its metabolites using target genes known to be regulated by progestins in human endometrial glandular and stromal cells.

METHODS

Human endometrial glandular and stromal cells were isolated from endometrial tissue fragments and separately incubated with Tib and its metabolites. Real-time polymerase chain reaction (PCR) was used to determine the mRNA content of 17betahydroxy steroid dehydrogenase (17betaHSD, type 2) and sulfotransferase (SULT1E1) in endometrial glandular cells, and prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP1) in endometrial stromal cells.

RESULTS

In glandular cells, Tib and Delta4-tibolone (Delta4Tib) significantly increased the content of 17betaHSD and SULT1E1 mRNA. In stromal cells, Tib and Delta4Tib increased PRL mRNA ( approximately 30% of the capacity compared to progesterone) and had little effect on IGFBP1 mRNA. Anti-progestin, RU486, reversed the induction of SULT1E1 and PRL by progesterone or Tib. Also, the two 3 hydroxyl tobolone metabolites, especially 3betaOHTib, showed some progestagenic effects.

CONCLUSIONS

The data showed that Tib and Delta4Tib exhibited clear progestagenic effects in endometrial glandular cells by inducing 17betaHSD and SULT1E1, while in stromal cells the response was weaker in the induction of PRL and had little effect on IGFBP1. In addition, the 3betaOHTib metabolite expressed progestagenic activity. These disparate effects in two types of cells may be beneficial for maintaining endometrial cells in a quiescent state.

Effect of tibolone and its principal metabolites (3α- and 3β-hydroxy, 3α-sulfate, and 4-ene derivatives) on estrone sulfatase activity in normal and cancerous human breast tissue

BACKGROUND

Tibolone (Org-OD14) is the active substance of Livial®, a synthetic steroid with the structure 7α,17α-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one, possessing weak tissue-specific estrogenic, progestogenic, and androgenic properties, used to treat menopausal complaints. After oral administration, tibolone is extensively metabolized into the 3α-(Org-4904) and 3β-(Org-30126) hydroxy derivatives with estrogenic properties, its 4-ene (Org-OM38) isomer with progestogenic/androgenic activities, and the 3α-sulfate (Org-34322) derivative, a major biologically inactive circulating form. We compared the dose response of tibolone and its metabolites on estrone sulfatase activity [conversion of estrone sulfate (E1S) to estrone (E1)] in normal and cancerous human breast tissues.

MATERIALS AND METHODS

Tissue minces were incubated with physiological concentrations of [3H]-E1S (5×10-9M) alone or in the presence of tibolone and its metabolites (concentration range: 5×10-7to 5×10-5M) for 4 h. Tritiated E1, estradiol (E2), and E1S were separated and evaluated quantitatively by thin-layer chromatography.

RESULTS

The sulfatase activity was significantly higher in cancerous breast but strongly inhibited by tibolone and the different metabolites, whereas 3α- and 3β-hydroxy derivatives were the most potent inhibitors.

CONCLUSION

This very significant inhibitory effect of tibolone and its principal metabolites on the enzyme involved in E2biosynthesis in the human breast provides interesting perspectives to study the biological responses of these compounds in trials with breast cancer patients.

Progesterone inhibition of Wnt/beta-catenin signaling in normal endometrium and endometrial cancer

PURPOSE

Wnt signaling regulates the fine balance between stemness and differentiation. Here, the role of Wnt signaling to maintain the balance between estrogen-induced proliferation and progesterone-induced differentiation during the menstrual cycle, as well as during the induction of hyperplasia and carcinogenesis of the endometrium, was investigated.

EXPERIMENTAL DESIGN

Endometrial gene expression profiles from estradiol (E(2)) and E(2) + medroxyprogesterone acetate-treated postmenopausal patients were combined with profiles obtained during the menstrual cycle (PubMed; GEO DataSets). Ishikawa cells were transfected with progesterone receptors and Wnt inhibitors dickkopf homologue 1 (DKK1) and forkhead box O1 (FOXO1), measuring Wnt activation. Expression of DKK1 and FOXO1 was inhibited by use of sequence-specific short hairpins. Furthermore, patient samples (hormone-treated endometria, hyperplasia, and endometrial cancer) were stained for Wnt activation using nuclear beta-catenin and CD44.

RESULTS

In vivo, targets and components of the Wnt signaling pathway (among them DKK1 and FOXO1) are regulated by E(2) and progesterone. In Wnt-activated Ishikawa cells, progesterone inhibits Wnt signaling by induction of DKK1 and FOXO1. Furthermore, using siRNA-mediated knockdown of both DKK1 and FOXO1, progesterone inhibition of Wnt signaling was partly circumvented. Subsequently, immunohistochemical analysis of the Wnt target gene CD44 showed that progesterone acted as an inhibitor of Wnt signaling in hyperplasia and in well-differentiated endometrial cancer.

CONCLUSION

Progesterone induction of DKK1 and FOXO1 results in inhibition of Wnt signaling in the human endometrium. This Wnt inhibitory effect of progesterone is likely to play a rate-limiting role in the maintenance of endometrial homeostasis and, on its loss, in tumor onset and progression toward malignancy.

Treating vasomotor symptoms of menopause: the nurse practitioner's perspective

PURPOSE

This article reviews the pathophysiology of vasomotor symptoms (VMS) of menopause and current management options.

DATA SOURCES

Current scientific literature.

CONCLUSIONS

In most menopausal women, loss of ovarian function results in VMS, including hot flashes, night sweats, and mood and sleep disturbances. Hormone therapy (HT) has been the mainstay of VMS treatment for many years, but safety concerns raised by publication of the Women's Health Initiative (WHI) results have dramatically reduced the use of this treatment. Since the WHI published its findings, attention has focused on other novel treatments for menopausal symptoms, including low-dose oral or transdermal HT and agents such as selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, gabapentin, and clonidine. Many women also use complementary and alternative medications to manage VMS, but little evidence from controlled clinical trials supports their efficacy.

IMPLICATIONS FOR PRACTICE

The increasing number of alternative treatments for VMS requires improvement in patient-provider communication about treatment risks and benefits, individualization of treatment to meet patient needs and attitudes, and careful follow-up to ensure adherence to potentially effective therapy. Nurse practitioners play a leading role in patient evaluation, discussions, and management to help women achieve control over bothersome VMS that dramatically impact their quality of life.

Effects of tibolone metabolites on human endometrial cell lines in co-culture

In human endometrium, cell proliferation is regulated by ovarian steroids through heterotypic interactions between stromal and epithelial cells populating this tissue. The authors test the proliferative effects of tibolone and its metabolites using endometrial co-cultures that mimic the normal proliferative response to hormones. They found that both the Delta(4)-tibolone metabolite and the pure progestin ORG2058 counteract estradiol-driven epithelial cell proliferation. Surprisingly, the estrogen receptor binding 3-hydroxyl-metabolites of tibolone also counteracted estradiol-driven proliferation. Inhibition of proliferation by 3beta-OH-tibolone was abrogated by low doses of the progesterone receptor antagonist mifepristone. This suggests that 3beta-OH-tibolone is converted to a progestagenic metabolite. The authors found that the stromal cells used in the co-cultures express high levels of the ketosteroid dehydrogenase AKR1C2, which is able to oxidize 3beta-OH-tibolone back to tibolone. Thus, the unexpected progestagenic effect of 3beta-OH-tibolone in these co-cultures may be due to metabolic activity present in the stromal cells of the co-cultures.

3-ketosteroid reductase activity and expression by fetal rat osteoblasts

In addition to reproductive tissue, sex hormones induce transcriptional events in many connective tissue cells, including osteoblasts. Some sex hormone receptor modulators with bone sparing effects selectively target estrogen or androgen receptors, whereas others appear more promiscuous, in part through enzymatic metabolism. Rat osteoblasts express significant oxidative 3alpha-hydroxysteroid dehydrogenase activity, which can convert precursor substrates to potent androgen receptor agonists. Here we show that they also express 3-ketosteroid reductase activity, exemplified by 7-methyl-17-ethynyl-19-norandrostan-5 (10)en-3-one (tibolone) conversion to potent estrogen receptor alpha agonists. Conversion was rapid and quantitative, with 3alpha-hydroxytibolone as the primary metabolite. Consistently, tibolone induced estrogen receptor alpha-dependent gene promoter activity through cis-acting estrogen response elements, increased the stimulatory effect of TGF-beta on Smad-dependent gene promoter activity, and enhanced prostaglandin E2-induced activity of transcription factor Runx2. Rat osteoblasts express the 3-ketosteroid reductase AKR1C9, an aldo-keto reductase gene family member. Exposure to prostaglandin E2 increased AKR1C9 gene promoter activity and mRNA expression. AKR1C9 promoter activity was also enhanced by overexpression of protein kinase A catalytic subunit or transcription factor C/EBPdelta, and the effect of PGE2 was reduced by dominant negative C/EBPdelta competition or C/EBPdelta antisense expression. Moreover, prostaglandin E2 increased the amount of functional endogenous nuclear C/EBPdelta that could bind specifically to a distinct domain approximately 1.8-kb upstream from the start site of AKR1C9 transcription. In summary, in addition to 3alpha-hydroxysteroid dehydrogenase, rat osteoblasts express significant and regulatable 3-ketosteroid reductase activity. Through these enzymes, they may selectively metabolize precursor compounds into potent steroid receptor agonists locally within bone.

Effects of tibolone and its metabolites on Angiopoietin-1, Tie-2 and tumor necrosis factor-alpha mRNA in Ishikawa cells. Implication for tibolone's effects on the endometrium

OBJECTIVE

To determine the effect of 17beta-estradiol, medroxyprogesterone acetate, tibolone and tibolone metabolites on Angiopoietin-1, Tie-2, and tumor necrosis factor-alpha in Ishikawa cells, in vitro. We hypothesized that differential effects on angiogenic factors or inflammatory cytokines by individual hormones may be related to the endometrial bleeding in postmenopausal women using hormone therapy.

DESIGN

Ishikawa cells were cultured to 80% confluence, in vitro. After 24h incubation in serum-free media, 1.0, 0.1 and 0.01 microM of 17beta-estradiol, medroxyprogesterone acetate, tibolone, 3alpha-hydroxytibolone, 3beta-hydroxytibolone, and Delta4-tibolone were added to the Ishikawa cells. The cells plus steroids were then incubated for a further 24h. Total RNA was extracted from control and treated Ishikawa cells. After reverse transcription, Angiopoietin-1, Tie-2, tumor necrosis factor-alpha, and beta-actin cDNAs were amplified in a polymerase chain reaction spiked with 33p-dCTP. Relative abundance of Angiopoietin-1, Tie-2, and tumor necrosis factor-alpha mRNA was measured by scintillation spectroscopy.

RESULTS

17Beta-estradiol and medroxyprogesterone acetate increased Angiopoietin-1 mRNA significantly higher than control, tibolone and tibolone hydroxy metabolites. Delta4-Tibolone at all concentrations tested did not increase Angiopoietin-1. None of the steroids tested at any concentration altered Tie-2 mRNA expression compared to control. 17Beta-Estradiol at 1.0 and 0.1 microM increased tumor necrosis factor-alpha mRNA significantly higher than control. Medroxyprogesterone acetate only at 1.0 microM increased tumor necrosis factor-alpha mRNA above control levels. Tibolone, 3alpha-hydroxytibolone, 3beta-hydroxytibolone, and Delta4-tibolone at every concentration had no effect on tumor necrosis factor-alpha mRNA abundance.

CONCLUSIONS

Delta4-Tibolone did not stimulate Angiopoietin-1, while the other steroids had differential effects greater than control. None of the steroids changed the expression of Tie-2 mRNA. Tumor necrosis factor-alpha was increased by 17beta-estradiol and by the highest concentration of medroxyprogesterone acetate. We interpret these results as supportive of our hypothesis that differential effects on angiogenic factors or inflammatory cytokines by individual steroids may be related to the clinical occurrence of endometrial bleeding in postmenopausal women using hormone therapy.

7α-Methyl-ethinyl estradiol is not a metabolite of tibolone but a chemical stress artifact

OBJECTIVE

This study was conducted to establish whether 7alpha-methyl-ethinyl estradiol (7alpha-MEE) in plasma from postmenopausal women treated with tibolone is a metabolite or an artifact.

DESIGN

Clinical samples with known levels of tibolone metabolites, plus plasma samples spiked with tibolone and metabolites, were analyzed for levels of 7alpha-MEE using liquid chromatography-mass spectometry (LC-MS/MS) with and without derivatization.

RESULTS

Approximately 20 to 40 pg/mL 7alpha-MEE was detected using LC-MS/MS with derivatization in plasma samples from postmenopausal women treated with tibolone. In plasma samples spiked with 200 ng/mL tibolone or Delta-tibolone, LC-MS/MS with derivatization revealed the generation of around 200 and 36 pg/mL 7alpha-MEE, respectively, whereas LC-MS/MS without derivatization showed no detectable chemical conversion of tibolone to 7alpha-MEE. Generation of 7alpha-MEE is increased by the "stress conditions" used in the derivatization procedure; simply drying the sample also shows this artifactual conversion. The major active and sulfated 3-hydroxy metabolites of tibolone are not converted to 7alpha-MEE. Without derivatization, and avoiding stress conditions, no detectable levels (<20 pg/mL) of 7alpha-MEE were found in plasma samples from postmenopausal women treated with single (eight participants at 13 time points) or multiple (seven participants at 18 time points) doses of tibolone.

CONCLUSIONS

7alpha-MEE is not a metabolite of tibolone but is a chemical artifact generated during analytical procedures with derivatization. Using LC-MS/MS without derivatization, 7alpha-MEE cannot be demonstrated in plasma from postmenopausal women after single or multiple doses of tibolone.

Regulation of SULT1E1 expression in Ishikawa adenocarcinoma cells by tibolone

Tibolone is used therapeutically as a hormone replacement agent and has beneficial effects on osteoporosis and hot flushes as well as libido in post-menopausal women without stimulatory effects in the breast and endometrium. The lack of effect in the endometrium is due in part to the tissue specific sulfation of tibolone and its active metabolites in endometrial tissues. Tibolone is metabolized into 3alpha-OH and 3beta-OH tibolone as well as the Delta4-isomer. Tibolone and the Delta4-isomer bind and activate progesterone and androgen receptors whereas 3alpha-OH and 3beta-OH tibolone activate the estrogen receptors. Human endometrium and Ishikawa endometrial adenocarcinoma cells express SULT1E1 that efficiently sulfates both 3-OH tibolone metabolites and has trace activity with tibolone but no activity with the Delta4-isomer. Treatment of Ishikawa cells with all four tibolone compounds resulted in the induction of SULT1E1 activity similar to the induction by progesterone. The induction of SULT1E1 was inhibited by RU486 indicating a role for the progesterone receptor. Sulfation of the tibolone compounds by Ishikawa cells and Ishikawa cells expressing physiological levels of SULT1E1 activity resulted in the sulfation of tibolone and the 3-OH metabolites but not Delta4-tibolone. These results indicate that the lack of endometrial stimulation involves induction of SULT1E1 and the selective sulfation and inactivation of the estrogenic 3-OH tibolones and interconversion of the tibolone metabolites to generate the progestagenic non-sulfated Delta4-isomer.

Endometrial cancer patients and tibolone: A matched case–control study

OBJECTIVE

To evaluate whether tibolone had adverse effects on the prognosis of endometrial cancer patients.

METHODS

In this retrospective matched case-control study, out of 396 patients with endometrial cancer from January 1997 to December 2002, 68 patients who underwent complete surgical staging were identified as tibolone users (cases). For each case, one control as tibolone non-user was matched for stage and grade of disease, in this order of priority (ratio users: non-users, 1:1).

RESULTS

There were no significant differences in age (p = 0.11), stage (p = 1.00), grade (p = 0.96) and treatment modality (p = 0.55) between two arms. The mean duration of follow-up for tibolone users and tibolone non-users is 48.0 months and 54.4 months, respectively (p = 0.12). In tibolone users, a total of four patients recurred and two out of four patients died of disease. In tibolone non-users, there were three recurrences and all of three patients died of disease. There were no significant differences in disease free survival (p = 0.52) and overall survival (p = 0.61) between two arms. And there was no significant difference in disease free survival according to the duration of tibolone use (p = 0.14).

CONCLUSION

There was no evidence that tibolone had adverse effects on the disease free survival and overall survival of endometrial cancer patients. So, tibolone could be used in these patients.

Metabolism of tibolone and its metabolites in uterine and vaginal tissue of rat and human origin

In postmenopausal women, tibolone shows clear tissue differences in its stimulatory effects on the vagina and uterus. In rats, however, it has stimulatory effects on both tissues, with a different, more estrogenic, effect on the uterus than in humans. This may be due to differences in local metabolism. Therefore, in the present study, the metabolism of tibolone was analyzed in incubations of uterine and vaginal tissue from postmenopausal women and ovariectomized rats using radiolabeled tibolone in order to understand the tissue- and species-specific metabolism. In the rat, tibolone (50 nM) was mainly 3alpha-reduced to the estrogenic 3alpha-OH-tibolone in the uterus and vagina. The 3beta-OH tibolone can be isomerized to 3alpha-OH-tibolone with tibolone as intermediate. In contrast, in the same tissues from postmenopausal women, the progestagenic Delta4-isomer and estrogenic 3beta-OH-tibolone were the major metabolites of tibolone. The formation of the Delta4-isomer was higher in uterine tissue. The 3beta-hydroxysteroid dehydrogenase (HSD) inhibitor epostane had no effect on tibolone metabolism in human uterine and vaginal tissue microsomes and HEK293 cells expressing the human 3beta-HSD types 1 and 2 isoforms did not metabolize tibolone. Moreover, the 3beta-reduction of tibolone to 3beta-OH-tibolone was NADPH dependent, while the isomerization of tibolone to the Delta4-isomer did not require a cofactor. It was therefore concluded that human 3beta-HSD isoforms are not involved in the metabolism of tibolone, and that the 3beta-reduction and the Delta5-10 to Delta4 isomerization may be catalyzed by different enzymes. In conclusion, we showed that, in hormone therapy target tissues of the rat as compared with the human, different metabolic pathways for tibolone exist and therefore result in metabolites with different pharmacological properties. The rat is therefore a poor model to predict the effects of tibolone on the uterus in postmenopausal women.

Tibolone and metabolites induce prolactin production in human endometrial stromal cells in vitro: evidence for cell-specific metabolism

In this study, we assessed the effects of tibolone and its metabolites on the production of a progesterone sensitive parameter, prolactin, in human endometrium stroma cells in vitro. In addition, the metabolism of the compounds by isolated stromal and epithelial cells was evaluated. The reference compounds, progesterone, Org 2058, and DHT all induced prolactin production. Oestradiol also slightly induced prolactin production and enhanced the response to Org 2058. Tibolone and Delta4-tibolone were similar with regard to potency to induce prolactin levels in the culture supernatant. Their potency was lower than that of Org 2058, similar to that of progesterone and higher than that of DHT. The efficacies of tibolone, Delta4-tibolone and Org 2058 were similar (approximately 200-fold induction). The estrogenic tibolone metabolites 3alpha- and 3beta-OH tibolone also significantly stimulated prolactin production. Their potency, however, was low since significance was reached only at the highest concentrations tested. The PR antagonist Org 31710 inhibited both tibolone- and Delta4-tibolone-induced prolactin production. The responses of tibolone and Delta4-tibolone were not affected by co-incubation with the androgen receptor antagonist OH-flutamide. The effect of tibolone, but not Delta4-tibolone, was antagonized approximately 50% in combination with the highest dose (1 microM) estrogen receptor antagonist, ICI 164384. The induction of prolactin by 3alpha- and 3beta-OH tibolone was antagonized most potently by Org 31710, but also by ICI 164384 and OH-flutamide. Tibolone is metabolized differently in epithelial and stromal cells of the human endometrium. The epithelial cells mostly produce the progestagenic/androgenic Delta4-tibolone. The stromal cells produce predominantly the 3beta-OH tibolone, and some Delta4-tibolone, but the net effect observed with regard to prolactin production is progestagenic. When the metabolites 3alpha-OH, 3beta-OH, and Delta4-tibolone were added to the cultures no conversions were observed. The HPLC analyses showed no evidence for the production of sulfated metabolites. In conclusion, the net effects on endometrial stromal cells are predominantly progestagenic. Tibolone is converted by epithelial cells into Delta4-tibolone which displays progestagenic and androgenic activities, whereas in stromal cells also the estrogenic metabolites 3alpha- and 3beta-OH tibolone are formed.

Histological and immunohistochemical evaluation of postmenopausal endometrium after 3 weeks of treatment with tibolone, estrogen only, or estrogen plus progestagen

OBJECTIVE

To evaluate histological and immunohistochemical parameters of short-term (21 days) tibolone, estrogen-only, and estrogen+progestagen treatment in the human postmenopausal endometrium.

DESIGN

An observational, open, nonrandomized, controlled study.

SETTING

Three collaborating centers: Amphia Hospital in Breda, Albert Schweitzer Hospital in Dordrecht, Erasmus Medical Center in Rotterdam, the Netherlands.

PATIENT(S)

Thirty healthy, postmenopausal women.

INTERVENTION(S)

Control group (n = 9), no hormonal treatment; tibolone group (n = 8), patients were treated with 2.5 mg of tibolone (administered orally) every day, starting 21 days before surgery; estrogen group (n = 7), patients were treated with 2 mg of E(2) (Zumenon, administered orally; Zambon, Amerfoort; The Netherlands) every day, starting 21 days before surgery; estrogen+progestagen group (n = 6), patients were treated with 2 mg of E(2) (Zumenon, administered orally) and 5 mg of medroxyprogesterone acetate (administered orally) every day, starting 21 days before surgery.

MAIN OUTCOME MEASURE(S)

Uterine tissues were collected, and two pathologists independently assessed histology. Immunohistochemical parameters measured were estrogen receptor alpha, progesterone receptor A/B, Hoxa10, Ki67, and Bcl-2.

RESULT(S)

On the basis of a number of histological and immunohistochemical parameters measured after 21 days of treatment, it was observed that tibolone displays clearly less stimulation (proliferation) of the human postmenopausal endometrium than estrogen at the beginning of a treatment, but the stimulation is higher than with estrogen+progestagen.

CONCLUSION(S)

Short-term (21 days) tibolone treatment results in a small stimulation of proliferation of the endometrium, and because long-term treatment with tibolone has been demonstrated to lead to an atrophic endometrium, it may be concluded that the stimulatory effect, as observed in this study, is transient in nature. It is hypothesized that tibolone first displays a more estrogenic mode of action, which over time, is counterbalanced by the induction of its progestagenic properties.

Tibolone and its metabolites inhibit invasion of human mammary carcinoma cells in vitro

Tibolone is used in postmenopausal women to alleviate menopausal symptoms and to prevent osteoporosis, but it does not stimulate the endometrium and the breast. Up to date, little data are available on the effect of tibolone on breast cancer initiation and progression.

OBJECTIVE

In the present in vitro study, we investigated the effect of tibolone and its metabolites (3alpha-OH tibolone, 3beta-OH tibolone, the Delta4 isomer and the sulphated isoform) on invasion of human breast cancer cells.

METHODS

The effect on invasion was evaluated in the chick heart invasion assay using MCF-7/6 cells and in the collagen type I invasion assay using T47-D cells. Furthermore, the compounds were tested in aggregation and migration assays.

RESULTS

We observed that, at a concentration of 100 microM, tibolone and its 3beta-OH metabolite possess anti-invasive activities in the two different invasion assays. However, this was neither due to effects on cell-cell adhesion nor on motility. In an attempt to probe the mechanism underlying the anti-invasive effect, we found that pro-MMP-9 release was markedly reduced in the supernatant of MCF-7/6 breast cancer cells treated with tibolone, 3alpha-OH tibolone and the Delta4 isomer but, interestingly, not with the sulphated metabolite.

CONCLUSION

We conclude that tibolone and its 3beta-OH metabolite have an anti-invasive effect on the tested breast cancer cell lines in vitro. This effect on invasion is not correlated with an effect on cell-cell adhesion or motility but coincides with a decreased release of pro-MMP-9 in the medium.

Growth regulation and transcriptional activities of estrogen and progesterone in human endometrial cancer cells

Estrogen-stimulated growth of the malignant human endometrium can be balanced by the differentiating properties of progesterone. To study the molecular basis behind this, gene expression profiling was performed using complementary DNA microarray analysis. In this study, the human endometrial cancer cell lines ECC-1 and PRAB-36 were used as models. The ECC-1 cell line, which expresses high levels of estrogen receptor alpha and is stimulated in growth by estrogens, was used to study estrogen regulation of gene expression. The Ishikawa sub-cell line PRAB-36, expressing both PRA and PRB, progesterone receptor isoforms, and inhibited in growth by progestagens, was used to study progesterone regulation of gene expression. Using these two well-differentiated human endometrial cancer cell lines, 148 estrogen- and 148 progesterone-regulated genes were identified. After functional classification, the estrogen- and progesterone-regulated genes could be categorized in different biologically relevant groups. Within the group of "cell growth and/or maintenance," 81 genes were clustered, from which a number of genes could be involved in arranging the cross talk that exists between estrogen and progesterone signaling. On the basis of analysis of the current findings, it is hypothesized that cross talk between estrogen and progestagen signaling does not occur by counterregulation of single genes, but rather at the level of differential regulation of different genes within the same functional families.

Analysis of estrogen agonism and antagonism of tamoxifen, raloxifene, and ICI182780 in endometrial cancer cells: a putative role for the epidermal growth factor receptor ligand amphiregulin

OBJECTIVES

In different tissues, estrogens, selective estrogen receptor modulators (SERMs), and anti-estrogens exert different biologic activities. For the endometrium, estradiol and tamoxifen induce proliferation, and because of this, tamoxifen treatment of breast cancer patients results in a two- to sevenfold increased risk for development of endometrial cancer. Use of raloxifene, or the anti-estrogen ICI182780, does not result in such an increased risk. The objective of the current study was to generate and analyze gene expression profiles that reflect the transcriptional response of the human endometrium to estradiol, SERMs like tamoxifen and raloxifene, and anti-estrogens like ICI182780.

METHODS

Transient transfections were performed to analyze the transcriptional response of ECC-1 cells to estradiol, tamoxifen, raloxifene, and ICI182780. Subsequently, to reveal the molecular mechanism of action, gene expression profiles were generated and some of the observed regulated genes were confirmed by Northern blotting. Biostatistical methods were employed to analyze the expression profile results further, and amphiregulin effects on ECC-1 cell signaling were investigated using Northern and Western blotting, and 3H-thymidine incorporation.

RESULTS

Analysis of the profiles revealed that estradiol, tamoxifen, raloxifene, and ICI182780 influence the same biologic processes, but they do so via regulation of different sets of genes. Upon construction of a genetic network it was observed that the largest possible network centered on epidermal growth factor (EGF) receptor signaling. Furthermore, the EGF receptor ligand amphiregulin was differentially regulated by all four ligands. Next it was shown that amphiregulin indeed could stimulate EGF receptor signaling in ECC-1 cells. Based on these results, it was hypothesized that EGF receptor signaling could differentially be affected by estrogen, tamoxifen, raloxifene, and ICI182780 because these four compounds differentially regulate the EGF receptor ligand amphiregulin.

CONCLUSIONS

Regulation of amphiregulin coincides with the described in vivo effect of the four ligands on the endometrium. Therefore, it is possible that modulation of EGF receptor signaling is a significant player in estrogen-agonistic growth of the endometrium and needs to be investigated further.

Tibolone Metabolism in Human Liver Is Catalyzed by 3α/3β-Hydroxysteroid Dehydrogenase Activities of the Four Isoforms of the Aldo-Keto Reductase (AKR)1C Subfamily

Tibolone [[7alpha,17alpha]-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one] is used to treat climacteric symptoms and prevent osteoporosis. It exerts tissue-selective effects via site-specific metabolism into 3alpha- and 3beta-hydroxymetabolites and a Delta4-isomer. Recombinant human cytosolic aldo-keto reductases 1C1 and 1C2 (AKR1C1 and AKR1C2) produce 3beta-hydroxytibolone, and the liver-specific AKR1C4 produces predominantly 3alpha-hydroxytibolone. These observations may account for the appearance of 3beta-hydroxytibolone in target tissues and 3alpha-hydroxytibolone in the circulation. Using liver autopsy samples (which express AKR1C1-AKR1C4), tibolone was reduced via 3alpha- and 3beta-hydroxysteroid dehydrogenase (HSD) activity. 3beta-Hydroxytibolone was exclusively formed in the cytosol and was inhibited by the AKR1C2-specific inhibitor 5beta-cholanic acid-3alpha, 7alpha-diol. The cytosolic formation of 3alpha-hydroxytibolone was inhibited by an AKR1C4-selective inhibitor, phenolphthalein. The ratio of these stereoisomers was 4:1 in favor of 3beta-hydroxytibolone. In HepG2 cell cytosol and intact cells (which do not express AKR1C4), tibolone was exclusively reduced to 3beta-hydroxytibolone and was blocked by the AKR1C1-AKR1C3 inhibitor flufenamic acid. In primary hepatocytes (which express AKR1C1-AKR1C4), time-dependent reduction of tibolone into 3beta- and 3alpha-hydroxytibolone was observed again in a 4:1 ratio. 3beta-HSD activity was inhibited by both 5beta-cholanic acid-3alpha,7alpha-diol and flufenamic acid, implicating a role for AKR1C2 and AKR1C1. By contrast, the formation of 3alpha-hydroxytibolone was exclusively inhibited by phenolphthalein implicating AKR1C4 in this reaction. 3beta- and 3alpha-Hydroxytibolone were rapidly metabolized into polar metabolites (>85%). The formation of minor amounts of tibolone was also observed followed by AKR1C-catalyzed epimerization. The low hepatic formation of 3alpha-hydroxytibolone suggests that AKR1C4 is not the primary source of this metabolite and instead it maybe formed by an intestinal or enterobacterial 3alpha-HSD.

Steroid-modulated proliferation of human endometrial carcinoma cell lines: any role for insulin-like growth factor signaling?

OBJECTIVES

Estrogen-stimulated proliferation of the normal and malignant human endometrium is balanced by the differentiating properties of progesterone. This study evaluated the role of insulin-like growth factor (IGF) signaling in steroid-induced modulation of endometrial cancer cell proliferation.

METHODS

We used the human endometrial, estrogen-responsive ECC-1 and progesterone-responsive PRAB-36 cell lines. Proliferation studies with IGFs in combination with either estrogen or progesterone were conducted. Furthermore, the mRNA and protein expression of insulin-like growth factor-binding proteins (IGFBPs) was evaluated.

RESULTS

Using the ECC-1 cell line, we observed that estrogen-induced proliferation is modulated via the IGF-receptor signaling pathway, and that IGF-1-induced stimulation of proliferation does not influence estrogen receptor signaling. Furthermore, expression of the main modulators of IGF action, the IGFBPs, was found to be regulated by estrogen and progesterone in both cell lines. IGFBP-4 was up-regulated by estrogen in the ECC-1 cell line, and IGFBP-3 and IGFBP-6 were down-regulated by progesterone in the PRAB-36 cell line.

CONCLUSION

Estrogen-induced stimulation of proliferation of ECC-1 endometrial cancer cells is partly achieved via IGF signaling. Furthermore, the IGFBPs are regulated by estrogens as well as progestagens and could potentially play a role in the modulation of endometrial cancer cell proliferation.

EGF signalling in prostate cancer cell lines is inhibited by a high expression level of the endocytosis protein REPS2

In advanced prostate cancer, cellular changes occur leading to a transition from androgen-dependent to androgen-independent growth. During this transition, proliferation of androgen-dependent prostate cancer cells becomes more and more dependent on growth factors, like the epidermal growth factor (EGF). Endocytosis of growth factor receptors, one of the mechanisms that controls growth factor signalling, was observed to be markedly changed in advanced metastatic prostate cancer. Internalisation and signalling of EGF receptors was examined in different prostate cancer cell lines, in relation to the expression level of the endocytosis-related REPS2 gene. It was observed that a high level of REPS2 correlates with reduced EGF-internalisation. To investigate this more thoroughly, prostate cancer cells with inducible REPS2 expression were generated. Using these cells, it was found that REPS2-induction indeed results in reduction of EGF-internalisation. Furthermore, when EGF receptor signalling was evaluated, by examination of mRNA expression for several EGF-responsive genes (EGF receptor, EGR-1, Fos and Jun), it was observed that induced expression of REPS2 exerts an inhibiting effect on this signalling. From these experiments, it is concluded that increased REPS2 expression negatively affects EGF receptor internalisation and subsequent signalling. Therefore, decreased REPS2 expression during prostate cancer progression, observed in earlier work, may result in enhanced EGF receptor expression and signalling, which could add to the androgen-independent state of advanced prostate cancer.

Tibolone Is Metabolized by the 3α/3β-Hydroxysteroid Dehydrogenase Activities of the Four Human Isozymes of the Aldo-Keto Reductase 1C Subfamily: Inversion of Stereospecificity with a Δ5(10)-3-Ketosteroid

Tibolone is used to treat climacteric complaints and prevent osteoporosis. These beneficial effects are exerted via its 3alpha-and 3beta-hydroxymetabolites. Undesirable stimulation of the breast and endometrium is not apparent. Endometrial stimulation is prevented by the progestogenic activity of its Delta4-ene metabolite. The enzymes responsible for the formation of these active metabolites are unknown. Human aldo-keto reductase (AKR)1C isoforms have been shown to act as 3alpha/3beta-hydroxysteroid dehydrogenases (HSDs) on 5alpha-dihydrotestosterone (5alpha-DHT). We show that AKR1Cs also efficiently catalyze the reduction of the Delta(5(10))-3-ketosteroid tibolone to yield 3alpha- and 3beta-hydroxytibolone. Homogeneous recombinant AKR1C1, AKR1C3, and AKR1C4 gave similar catalytic profiles to those observed with 5alpha-DHT. AKR1C1 catalyzed exclusively the formation of 3beta-hydroxytibolone, AKR1C3 showed weak 3beta/3alpha-HSD activity, and AKR1C4 acted predominantly as a 3alpha-HSD. Whereas AKR1C2 acted as a 3alpha-HSD toward 5alpha-DHT, it functioned exclusively as a 3beta-HSD on tibolone. Furthermore, strong substrate inhibition was observed for the AKR1C2 catalyzed reduction of tibolone. Using NAD+, the 3-hydroxymetabolites were efficiently oxidized by homogeneous recombinant AKR1C2 and AKR1C4. However, because of potent inhibition of this activity by NADPH, AKR1Cs will probably act only as 3-ketosteroid reductases in vivo. Molecular docking simulations using crystal structures of AKR1C1 and AKR1C2 explained why AKR1C2 inverted its stereospecificity from a 3alpha-HSD with 5alpha-DHT to a 3beta-HSD with tibolone. The preference for AKR1C1 and AKR1C2 to form 3beta-hydroxytibolone, and the preference of the liver-specific AKR1C4 to form 3alpha-hydroxytibolone, may explain why 3beta-hydroxytibolone is the major metabolite in human target tissues and why 3alpha-hydroxytibolone is the major circulating metabolite.

Tissue-selectivity: the mechanism of action of tibolone

Tibolone is effective in preventing bone loss and treating climacteric symptoms, without stimulating the endometrium. The effects on bone, brain and vagina can be accurately explained by the oestrogenic activity of tibolone, but oestrogenic activity is not expressed in the endometrium. Tibolone behaves differently from oestrogen plus progestogen combinations on the breast. Therefore, tibolone can be characterised as a selective oestrogen activity regulator. The objective of this review is to characterise the typical properties of tibolone in order to explain its tissue-selective action. Tibolone is rapidly converted into three major metabolites: 3 alpha- and 3 beta-hydroxy-tibolone, which have oestrogenic effects, and the Delta(4)-isomer, which has progestogenic and androgenic effects. The 3-hydroxy metabolites are present in the circulation, predominantly in their inactive sulphated form. The tissue-selective effects of tibolone are the result of metabolism, enzyme regulation and receptor activation that vary in different tissues. The bone preserving effects are the result of oestradiol receptor activation, whilst other steroid receptors, notably the progesterone and androgen receptor, are not involved. Breast tissue of monkeys is not stimulated, as occurs with oestrogen plus progestogen, because tibolone and its metabolites inhibit sulphatase and 17 beta-hydroxysteroid dehydrogenase (HSD) type I and stimulate sulphotransferase and 17 beta-HSD type II, the combined effects of which prevent conversion to active oestrogens. In addition, tibolone affects cellular homeostasis in the breast by inhibiting proliferation and stimulating apoptosis. Tibolone does not stimulate the endometrium because of the action of the highly stable progestogenic metabolite (Delta(4)-isomer) in combination with an effect on the sulphatase (inhibition)-sulphotransferase (stimulation) system. The oestrogenic metabolites of tibolone have direct favourable effects on the cardiovascular system and, in in vivo models, tibolone has shown no adverse consequences. In conclusion, tibolone shows oestrogenic effects in brain, vagina and bone and has direct oestrogenic effects on the cardiovascular system. In the endometrium, the progestogenic activity of the Delta(4)-metabolite and the effect on oestrogen-inactivating enzymes prevent oestrogenic stimulation. The mammary gland is not stimulated in currently used animal models. Tibolone appears to regulate estrogenic activity in the various tissues by influencing the availability of estrogenic compounds for the estradiol receptor in a tissue-selective manner.

Hormonal suppressive therapy for endometriosis may not improve patient health

OBJECTIVE

To critically examine the possible association between hormonal treatment of endometriosis and ovarian cancer.

RESULT(S)

The malignant potential of endometriosis has been suggested by several clinical studies. Although controversial, ovarian carcinoma of the endometrioid and clear cell subtypes has been associated with endometriosis, particularly among subjects with a longstanding disease. Furthermore, a significantly higher frequency of endometriosis has been found in patients undergoing surgery for endometrioid, clear cell, and mixed subtypes of ovarian carcinoma, as compared with the other subtypes. Changes in the genomic material in endometriotic implants were observed by many investigators in chromosomes 1, 5, 6, 7, 16, and 22 by several methods (fluorescent in situ hybridization, comparative genomic hybridization, and others). Because hormonal ablative treatments may suppress the normal, eukaryotic cells more than the aneuploid cells bearing chromosomal aberrations, it may increase the rate of dyskaryotic cells in the endometriotic implants, possibly augmenting the risk of malignant transformation. A recent published association between Danazol and ovarian cancer suggests that such a theoretical risk may occur.

CONCLUSION(S)

The hormonal ablative treatment of endometriosis may increase the risk of malignant transformation in the endometriotic implants by causing a negative selection and increasing the rate of dyskaryosis and loss of heterozygosity.

Apoptosis in the Endometrium of Postmenopausal Women Receiving Tibolone

BACKGROUND/AIM

Tibolone, a synthetic derivative of the 19-nortestosterone family, induces atrophy of the endometrium, especially via its progestogenic Delta(4) isomer. The aim of the study was to determine whether tibolone induces apoptosis in the endometrium of postmenopausal women.

METHODS

Twenty healthy postmenopausal women (mean age +/- SD 52.4 +/- 4.21 years) who had amenorrhea for at least 1 year and who had no history of any systemic illness and estrogen replacement therapy were enrolled in the study. All patients were offered office endometrial samplings, and then tibolone was prescribed (2.5 mg/day p.o., once daily) to all patients. Repeat endometrial samples were obtained after completion of the 6-month course of tibolone therapy. All samples were immunohistochemically analyzed for the presence of apoptotic cells.

RESULTS

There was no significant difference in the median proportion of apoptotic nuclei between the pre- and posttreatment samples (2 vs. 3%; p > 0.05).

CONCLUSIONS

The results showed that tibolone did not affect the rate of apoptosis in the postmenopausal endometrium. Further studies are needed to clarify the role of apoptosis in overall effects of hormonal compounds on the postmenopausal endometrium.

Progesterone receptors in endometrial cancer invasion and metastasis: development of a mouse model

Progestagens inhibit growth of endometrial cancer cells in vivo and in vitro, and also are reported to inhibit endometrial cancer cell invasion. The progesterone receptor (PR) isotypes PRA and PRB have different transcriptional activity. There are indications that relative over expression of PRB could lead to development of a more invasive phenotype in endometrial cancer. To study the effect of progestagens and the two PR isotypes on tumor dissemination, in vitro and in vivo models should be applied. The Ishikawa endometrial cancer cell line (clone 3H12) was transfected to stably express a high level of human PRB (hPRB), which resulted in the PRB-1 sub-cell line. Ovariectomized athymic NMRI nu/nu mice were injected intraperitoneally with these PRB-1 cells. After 3, 5 and 10 weeks, the animals were sacrificed. Spread of PRB-1 cells in and outside the peritoneal cavity was studied macroscopically and microscopically, and also by PCR detection. After 10 weeks, the PRB-1 cells had formed extensive tumor mass in the peritoneal cavity. Also, cells could be detected outside the peritoneal cavity, indicating metastatic ability of these cells. The present study describes an in vivo model that can provide a valuable tool in studying the influence of progestagens and the two PR isotypes on endometrial cancer cell invasion and metastasis.