Direct effects of GnRH agonists in human hormone-sensitive endometrial cells

Progestin-based pharmacotherapy in fertility preservation in early endometrial cancer

Endometrial cancer is a common tumor of the female reproductive system. In recent years, as the age of onset of the disease has gradually become younger, this has caused distress to some young patients with reproductive needs, and the active search for methods of preserving reproductive function has gradually attracted attention. In this paper, we will systematize the current status of progestin-based pharmacotherapy in combination with other drug therapies in the conservative management of early-stage endometrial cancer. With the expectation of providing a reference for the treatment of early stage endometrial cancer patients in China and for the in-depth development of related research in this field.

The Role of Gonadotropin-Releasing Hormone (GnRH) in Endometrial Cancer

Endometrial cancer (EC) is one of the most common gynecological malignancies. Gonadotropin releasing hormone (GnRH) is a decapeptide first described to be secreted by the hypothalamus to regulate pituitary gonadotropin secretion. In this systematic review, we analyze and summarize the data indicating that most EC express GnRH and its receptor (GnRH-R) as part of an autocrine system regulating proliferation, the cell cycle, and apoptosis. We analyze the available data on the expression and function of GnRH-II, its putative receptor, and its signal transduction. GnRH-I and GnRH-II agonists, and antagonists as well as cytotoxic GnRH-I analogs, have been shown to inhibit proliferation and to induce apoptosis in human EC cell lines in pre-clinical models. Treatment with conventional doses of GnRH-agonists that suppress pituitary gonadotropin secretion and ovarian estrogen production has become part of fertility preserving therapy of early EC or its pre-cancer (atypical endometrial hyperplasia). Conventional doses of GnRH-agonists had marginal activity in advanced or recurrent EC. Higher doses or more potent analogs including GnRH-II antagonists have not yet been used clinically. The cytotoxic GnRH-analog Zoptarelin Doxorubicin has shown encouraging activity in a phase II trial in patients with advanced or recurrent EC, which expressed GnRH-R. In a phase III trial in patients with EC of unknown GnRH-R expression, the cytotoxic GnRH doxorubicin conjugate was not superior to free doxorubicin. Further well-designed clinical trials exploiting the GnRH-system in EC might be useful.

Leuprorelin acetate long-lasting effects on GnRH receptors of prostate cancer cells: an atomic force microscopy study of agonist/receptor interaction

High cell-surface GnRH receptor (GnRH-R) levels have been shown to have a major influence on the extent of GnRH agonist-mediated tumor growth inhibition. The ability of the GnRH agonist leuprorelin acetate (LA) to induce a post-transcriptional upregulation of GnRH-R at the plasma membrane of androgen-sensitive (LNCaP) and -insensitive (PC-3) prostate cancer (PCa) cells has been previously demonstrated by Western blotting. Here we performed single molecule force spectroscopy by using Atomic Force Microscopy (AFM), which has proven to be a powerful tool allowing for investigation of living cell surface biological features, such as the so far unclear GnRH agonist/receptor interaction. Thus, in the hormone-insensitive PC-3 cells, we characterized the strength of the LA-receptor binding, and the amount and distribution of the functional receptor molecules on the cell surface. The effect of a long and continuous treatment (up to 30 days) with the agonist (10⁻¹¹ and 10⁻⁶ M) on the same parameters was also investigated. A GnRH-R increase was observed, reaching the maximum (∼80%) after 30 days of treatment with the highest dose of LA (10⁻⁶ M). The analogue-induced increase in GnRH-R was also demonstrated by Western blotting. In addition, two different receptor bound strengths were detected by AFM, which suggests the existence of two GnRH-R classes. A homogeneous distribution of the unbinding events has been found on untreated and treated PC-3 cell surfaces. The persistence of high receptor levels at the membrane of these living cells may warrant the maintenance of the response to LA also in androgen-unresponsive PCa. Moreover, the determination of ligand/receptor bond strength could shed light on the poorly understood event of LA/GnRH-R interaction and/or address structural/chemical agonist optimizations.

Luteinizing Hormone-Releasing Hormone I (LHRH-I) and Its Metabolite in Peripheral Tissues

Luteinizing hormone-releasing hormone (LHRH) was first isolated in the mammalian hypothalamus and shown to be the primary regulator of the reproductive system through its initiation of pituitary gonadotropin release. Since its discovery, this form of LHRH (LHRH-I) has been shown to be one of many structural variants with a variety of roles in both the brain and peripheral tissues. Enormous interest has been focused on LHRH-I and LHRH-II and their cognate receptors as targets for designing therapies to treat cancers of the reproductive system. LHRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15) that cleaves the hormone at the fifth and sixth bond of the decapeptide (Tyr5-Gly6) to form LHRH-( 1 – 5 ). We have previously reported that the autoregulation of LHRH gene expression can also be mediated by its processed peptide, LHRH-( 1 – 5 ). Furthermore, LHRH-( 1 – 5 ) has also been shown to be involved in cell proliferation. This review will focus on the possible roles of LHRH and its processed peptide, LHRH-( 1 – 5 ), in non-hypothalamic tissues.

A processed metabolite of luteinizing hormone-releasing hormone has proliferative effects in endometrial cells

OBJECTIVE

The purpose of this study is to determine the possible role of the processed peptide of LHRH, LHRH-(1-5), in regulating growth of endometrial cancer cells.

STUDY DESIGN

An endometrial cancer cell line, the Ishikawa cell line, was cultured under standard conditions and treated in a dose-dependent manner with 1 of 2 hormones, LHRH and LHRH-(1-5) to determine the ability of these peptides to regulate cellular growth. A tetrazolium-based assay was used to determine the effect these peptides have on cell proliferation. Furthermore, enzyme-linked immunosorbent assay (ELISA)-based assays were used to determine the expression of caspase-3/7 and pERK-1/2. Statistical analyses were conducted using an analysis of variance followed by Fisher LSD as the post-hoc test.

RESULTS

The results show that LHRH is anti-proliferative whereas LHRH-(1-5) is proliferative on the cells. Furthermore, LHRH-(1-5) decreased caspase-3/7 and pERK1/2 expression.

CONCLUSION

This is the first time LHRH-(1-5) is shown to have proliferative effects on cells.

Effect of GnRH analogues on apoptosis and expression of Bcl-2, Bax, Fas and FasL proteins in endometrial epithelial cell cultures from patients with endometriosis and controls

BACKGROUND

Our purpose was to evaluate the effect of the GnRH agonist (GnRHa), leuprolide acetate (LA), and the GnRH antagonist (GnRHant), Antide, on apoptosis and expression of apoptosis-related proteins in endometrial epithelial cell (EEC) cultures from patients with endometriosis and controls (infertile women without endometriosis).

METHODS

Biopsy specimens of eutopic endometrium were obtained from 22 patients with endometriosis and from 14 women that served as controls. Apoptosis was examined in EEC after incubation with LA and Antide. Bax, Bcl-2, Fas and FasL expression was evaluated after exposure to LA, Antide or a combination of both. The percentage of apoptotic cells (%ApC) was assessed by the acridine orange-ethidium bromide technique, and protein expression was evaluated by western blot and immunocytochemistry.

RESULTS

LA 100 and 1000 ng/ml increased the %ApC in EEC from patients with endometriosis (both P < 0.05) and controls (p < 0.05 and P < 0.01, respectively). Antide 10(-5) M increased the %ApC in EEC from patients with endometriosis and controls (P < 0.01). In EEC from women with endometriosis, Bax expression increased after treatment with LA, Antide and LA + Antide (P < 0.05, P < 0.001 and P < 0.001), whereas Bcl-2 expression decreased after exposure to LA and Antide (P < 0.001 and P < 0.01). FasL expression increased after LA, Antide and LA + Antide treatments (P < 0.01, P < 0.001 and P < 0.01). No significant changes were observed on Fas expression.

CONCLUSIONS

GnRH analogues enhanced apoptosis in EEC, and this was accompanied by an increase in expression of the pro-apoptotic proteins Bax and FasL and a decrease in expression of the anti-apoptotic protein Bcl-2.

Effect of tibolone and its metabolites on vascular endothelial growth factor isoforms 121 and 165 and thrombospondin-1 mRNA in Ishikawa cells

OBJECTIVE

To compare the mRNA expression of vascular endothelial growth factor (VEGF) 121 and 165 isoforms and thrombospondin-1 (TSP-1) after incubation with tibolone and tibolone metabolites 3alpha-hydroxytibolone, 3beta-hydroxytibolone, Delta4-tibolone, and 17beta-estradiol (E2) in cultured Ishikawa cells.

DESIGN

Ishikawa cells (immortalized from a well-differentiated human adenocarcinoma cell line) were cultured in vitro to confluence. Tibolone, 3alpha-hydroxytibolone, 3beta-hydroxytibolone, Delta4-tibolone and E2 at concentrations of 1.0, 0.1 and 0.01 micromol/L were added to confluent cells and further cultured for an additional 24 h. Control cells were treated with medium in absence of hormone. Total RNA was extracted from control and treated Ishikawa cells. After reverse transcription, VEGF, TSP-1 and the housekeeping gene, beta-actin cDNAs, were amplified in a polymerase chain reaction spiked with 33p-dCTP. Relative abundance of VEGF 121 and 165 isoforms and TSP-1 mRNA was measured by scintillation spectroscopy.

RESULTS

E2, tibolone, 3alpha-hydroxytibolone, and 3beta-hydroxytibolone increased both VEGF 121 and 165 mRNA compared with the control. However, Delta4-tibolone had no effect on either VEGF 121 or 165 mRNA compared with the control. Delta4-Tibolone increased TSP-1 mRNA expression compared with control levels. E2, tibolone, 3alpha-hydroxytibolone, and 3beta-hydroxytibolone did not increase TSP-1 mRNA expression at any concentration.

CONCLUSIONS

Tibolone and the 3alpha- and 3beta-tibolone metabolites with E2 increased VEGF 121 and 165 isoforms. Conversely, Delta4-tibolone, which is reported to have progestational-like activity, did not stimulate VEGF 121 and VEGF 165 but increased TSP-1 mRNA synthesis in cultured Ishikawa cells. We hypothesize, based on these data, that the clinical finding of no endometrial growth in women using tibolone may be partly related to alterations in these angiogenic factors.

Gonadotropin-releasing hormone receptor-mediated growth suppression of immortalized LbetaT2 gonadotrope and stable HEK293 cell lines

Continuous administration of GnRH analogs results in an inhibition of tumor growth that may be mediated in part by direct activation of GnRH receptors (GnRHRs) expressed on tumor cells. However, it is not fully understood how the GnRHR mediates these growth effects. This study aimed to determine how the presence or absence of this receptor in different cell types might affect the ability of GnRH to directly mediate growth effects. We demonstrate that continuous treatment with GnRH or a GnRH agonist (GnRHA) induces an antiproliferative effect in a gonadotrope-derived cell line (LbetaT2) and also in HEK293 cells stably expressing either the rat or human GnRHR. The antiproliferative effect was time and dose dependent and was verified using [3H]thymidine incorporation, light microscopy, and analysis of cell number. Inhibition was specifically mediated via the GnRHR, as cotreatment of the GnRHR-expressing cell lines with a GnRH antagonist blocked the growth-suppressive effect induced by GnRHA treatment. Cell cycle analysis revealed that GnRHA-treated HEK/GnRHR cell lines induced an accumulation of cells in the G2/M phase, whereas a G0/G1 arrest was observed in LbetaT2 cells. GnRHA treatment also caused a small, but significant, increase in apoptotic cells. This study provides evidence for a direct role for the GnRHR in mediating antiproliferative events in two cell systems, neither of which was derived from extrapituitary reproductive tumors. The ability to induce these effects, regardless of the cell system involved, has implications regarding the use of GnRH analogs for the treatment of endocrine-related disorders and tumors.

Direct effect of a gonadotropin-releasing hormone agonist on the growth of canine mammary tumour cells

Gonadotropin-releasing hormone (GnRH) agonist exert "in vivo" an inhibitory action on the growth of hormone-dependent canine mammary tumours (Lombardi et al. [1999] J. Vet. Pharmacol Ther. 22(1):56-61). The present experiments have been performed "in vitro" in order to investigate the mechanisms involved in this direct antiproliferative action of GnRH agonists. In particular, the aim was to study whether these compounds might exert their antiproliferative effect by interfering with the stimulatory action of epidermal growth factor (EGF). To this purpose, the effects of GnRH agonist, Goserelin (GnRH-A), on the mitogenic action of EGF, on EGF-activated intracellular signaling mechanisms (intracellular calcium and nitric oxide production) as well as on ATP induced cell proliferation and signalling, and on the binding of EGF receptors have been evaluated in primary culture of canine mammary tumour cells. The results of these "in vitro" studies show that GnRH-A counteracts the mitogenic action of EGF and ATP, decreases the EGF/ATP-induced calcium signalling and reduces EGF binding, probably by means of NO-induced [Ca2+]i downregulation. These data suggest that GnRH agonists may inhibit the proliferation of the tumour cells by interfering with the stimulatory action of EGF.