Differential inhibitory effects on human endometrial carcinoma cell growth of luteinizing hormone-releasing hormone analogues

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.

Gonadotropin-releasing hormone (GnRH)-I and GnRH-II induce cell growth inhibition in human endometrial cancer cells: involvement of integrin beta3 and focal adhesion kinase

Endometrial carcinoma is the most common neoplasm of the female genital tract, accounting for nearly one half of all gynecologic cancers in the Western world. Although intensive research on pathological phenomena of endometrial cancer is currently going on, but exact cause and biological aspects of this disease are not well described yet. In addition to well-documented roles of gonadotropin-releasing hormone (GnRH) in hypopituitary ovarian (HPO) axis, the agonistic or antagonistic analogs (or both) of GnRH have been shown to inhibit the proliferation of a variety of human gynecologic cancers. Thus, in the present study, we further examined the possibility that GnRH induces integrin beta3 and activation of focal adhesion kinase (FAK) through mitogen-activated protein kinases (MAPKs), ERK1/2 and p38, to inhibit the growth of HEC1A endometrial cancer cell line. As a result, both GnRH-I and GnRH-II resulted in a significant increase in integrin beta3 expression and evoked the activation of FAK in a time-dependent manner in these cells. In addition, these analogs induced an activation of ERK1/2 and p38 MAPK in a time-dependent manner as downstream pathways of FAK. It appears that GnRH-II has much greater effect on the activation of FAK, ERK1/2 and p38 compared to GnRH-I in these cells. Further, we demonstrated that the growth inhibition of HEC1A cells by GnRH-I or GnRH-II is involved in the activation of integrin-FAK and ERK1/2 and p38 MAPK pathways. Taken together, these results suggest that GnRH may be involved in the inhibition of endometrial cancer cell growth via activation of integrin beta3 and FAK as a direct effect. This knowledge could contribute to a better understanding of the mechanisms implicated in the therapeutic action of GnRH and its biomedical application for the treatment against endometrial cancer.

A crucial role for Galphaq/11, but not Galphai/o or Galphas, in gonadotropin-releasing hormone receptor-mediated cell growth inhibition

GnRH acts on its cognate receptor in pituitary gonadotropes to regulate the biosynthesis and secretion of gonadotropins. It may also have direct extrapituitary actions, including inhibition of cell growth in reproductive malignancies, in which GnRH activation of the MAPK cascades is thought to play a pivotal role. In extrapituitary tissues, GnRH receptor signaling has been postulated to involve coupling of the receptor to different G proteins. We examined the ability of the GnRH receptor to couple directly to Galpha(q/11), Galpha(i/o), and Galpha(s), their roles in the activation of the MAPK cascades, and the subsequent cellular effects. We show that in Galpha(q/11)-negative cells stably expressing the GnRH receptor, GnRH did not induce activation of ERK, jun-N-terminal kinase, or P38 MAPK. In contrast to Galpha(i) or chimeric Galpha(qi5), transfection of Galpha(q) cDNA enabled GnRH to induce phosphorylation of ERK, jun-N-terminal kinase, and P38. Furthermore, no GnRH-mediated cAMP response or inhibition of isoproterenol-induced cAMP accumulation was observed. In another cellular background, [35S]GTPgammaS binding assays confirmed that the GnRH receptor was unable to directly couple to Galpha(i) but could directly interact with Galpha(q/11). Interestingly, GnRH stimulated a marked reduction in cell growth only in cells expressing Galpha(q), and this inhibition could be significantly rescued by blocking ERK activation. We therefore provide direct evidence, in multiple cellular backgrounds, that coupling of the GnRH receptor to Galpha(q/11), but not to Galpha(i/o) or Galpha(s), and consequent activation of ERK plays a crucial role in GnRH-mediated cell death.

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.

Expression of receptors for luteinizing hormone-releasing hormone in human ovarian and endometrial cancers: frequency, autoregulation, and correlation with direct antiproliferative activity of luteinizing hormone-releasing hormone analogues

OBJECTIVE

Several recent reports have demonstrated the expression of luteinizing hormone-releasing hormone receptors by human ovarian and endometrial cancers. Controversy persists on the relevance of this finding, in particular whether these receptors mediate direct antiproliferative effects of luteinizing hormone-releasing hormone analogues. We correlated the expression of luteinizing hormone-releasing hormone receptors by well-characterized ovarian and endometrial cancer cell lines with the ability of luteinizing hormone-releasing hormone analogues to reduce their proliferation and studied the autoregulation of luteinizing hormone-releasing hormone receptor expression by luteinizing hormone-releasing hormone agonist triptorelin and antagonist cetrorelix. The expression of luteinizing hormone-releasing hormone receptors was assessed in a series of specimens from primary ovarian and endometrial cancers.

STUDY DESIGN

Luteinizing hormone-releasing hormone receptor expression was assessed by semiquantitative reverse transcriptase-polymerase chain reaction and radioligand binding assay. Antiproliferative effects were ascertained by proliferation assays in the absence or presence of luteinizing hormone-releasing hormone analogues.

RESULTS

Ovarian (4/6 cell lines) and endometrial (5/6 cell lines) cancer cell lines expressed luteinizing hormone-releasing hormone receptors. The proliferation of these luteinizing hormone-releasing hormone receptor-positive cell lines was dose- and time-dependently reduced by agonistic and antagonistic luteinizing hormone-releasing hormone analogues. Luteinizing hormone-releasing hormone receptor density was reduced to 80% of controls (control, 100 %; P <.001) by luteinizing hormone-releasing hormone analogues. Seventy percent of primary ovarian cancers and 83% of primary endometrial cancers expressed luteinizing hormone-releasing hormone receptors.

CONCLUSION

These findings suggest that luteinizing hormone-releasing hormone receptors that are expressed by human ovarian and endometrial cancer cell lines mediate direct antiproliferative effects of luteinizing hormone-releasing hormone analogues. Because most respective primary cancers expressed luteinizing hormone-releasing hormone receptors, these receptors might be used for novel antiproliferative therapeutic approaches and should be further evaluated.

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

The antiproliferative effect of two GnRH agonists (leuprorelin acetate and triptorelin), alone or combined with tamoxifen (TAM) or medroxyprogesterone acetate (MPA), on human estrogen-sensitive endometrial cancer cells (Ishikawa) was investigated. Although ineffective when tested alone in all the culture conditions used, both analogues counteracted or even suppressed the estrogen-stimulated growth of Ishikawa cells. The antiestrogenic effect of TAM or MPA was not modified by their association with high doses of the GnRH analogues, but low concentrations of triptorelin combined with MPA 10(-7) M determined a reduction in cell numbers which was greater than that obtained with the progestin or the analogue alone. In addition, analogue treatment prevented the estrogen-induced decrease in the level of estrogen receptors. Our data provide evidence that GnRH agonists can directly inhibit estrogen-stimulated endometrial cancer cell growth and suggest that they may interfere with steroid-receptor machinery.

The expression and action of granulocyte macrophage-colony stimulating factor and its interaction with TGF-beta in endometrial carcinoma

OBJECTIVE

Previous studies have demonstrated that normal human endometrium expresses granulocyte macrophage-colony stimulating factor (GM-CSF) and GM-CSF receptors. Because GM-CSF is administer to cancer patients following chemotherapy, GM-CSF may directly or through interaction with ovarian steroids and other cytokines alter the behavior of endometrial cancer. The aim of this study was to determine the expression of GM-CSF and receptors in endometrial carcinoma and its direct effect and interaction with transforming growth factor beta (TGF-beta) on Ishikawa cells, a human endometrial carcinoma cell line.

METHODS

GM-CSF, GM-CSF receptors, TGF-beta1, and TGF-beta type II receptor expression were evaluated using quantitative reverse transcription polymerase chain reaction (Q-RT-PCR). The effect of GM-CSF on DNA synthesis, cell proliferation, expression of GM-CSF, TGF-beta1, and TGF-beta receptor, and their regulation by ovarian steroids was determined by the rate of [(3)H]thymidine incorporation, MTT assay, Q-RT-PCR, and ELISA, respectively.

RESULTS

Endometrial carcinomas express significantly higher GM-CSF and GM-CSF alpha and beta receptor mRNA compared with normal postmenopausal endometrium. GM-CSF at various doses had no significant effect on the rate of [(3)H]thymidine incorporation or proliferation of Ishikawa cells, whereas TGF-beta1 inhibited [(3)H]thymidine incorporation. GM-CSF and TGF-beta1 regulate their own expression and the expression of TGF-beta type II receptor, which were both upregulated by 17beta-estradiol and medroxyprogesterone acetate treatment and reversed following cotreatment with their respective receptor antagonists.

CONCLUSION

Endometrial carcinoma expresses an elevated level of GM-CSF and GM-CSF receptors. GM-CSF is not a mitogen for the endometrial cancer cell line; however, either alone or through interaction with TGF-beta1, it regulates its own expression and the expression of TGF-beta1 and TGF-beta type II receptor which inhabits endometrial cancer cells. This interaction may represent a regulatory feedback mechanism that could serve to suppress endometrial carcinoma growth.

Inhibitory effect of luteinising hormone-releasing hormone analogues on human endometrial cancer in vitro

We studied the effects of luteinising hormone-releasing hormone (LHRH) agonist leuproreline (1 microM for 96 h) and LHRH antagonist cetrorelix on the cell growth of primary cultures from nine human endometrial cancers using the sulphorhodamine colorimetric test. Histological examinations and reverse transcription and polymerase chain reaction amplification (RT-PCR) for LHRH receptors were also performed. The endometrial cancers examined had a medium to high degree of proliferative activity and a low degree of apoptotic power; furthermore, they expressed the LHRH receptor RNA variably, detectable in 71% of cases. The addition of leuproreline or cetrorelix to cell cultures inhibited growth in a statistically significant way compared to untreated control cells; nevertheless, the percentage of cell growth inhibition obtained was very variable. These data suggest that LHRH analogues can exert differential inhibitory effects on the growth of endometrial cancer, which seems to be independent of the expression of specific LHRH receptors.