GnRH analogs in gynecological oncology: a review

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.

The gonadotropin-releasing hormone (GnRH) neuronal population is normal in size and distribution in GnRH-deficient and GnRH receptor-mutant hypogonadal mice

Hypothalamic GnRH neurons are essential for initiation and regulation of reproductive function. In addition to pituitary gonadotrope stimulation, activity of GnRH through its receptor (GnRHR) has been suggested to include autocrine regulation of the GnRH neuron. Two hypogonadal mouse strains, the Gnrh1 mutant (hpg) mice and Gnrhr mutant mice were used to investigate the potential role of GnRH signaling in the proper development and maintenance of GnRH neurons. Immunocytochemical analysis of heterozygous hpg mice revealed a GnRH neuron population that was normal in size and distribution, indicating no effect from reduced Gnrh1 gene dosage on the neurons themselves. To visualize GnRH neurons in homozygous GnRH-deficient hpg mice, heterozygous hpg mice were crossed with GnRH-green fluorescent protein (GFP) transgenic mice with targeted expression of the GFP reporter gene in GnRH neurons. Analysis of forebrains of homozygous hpg/GFP-positive mice immunostained for GFP revealed a normal population size and appropriate distribution of GnRH neurons in hpg mice, with immunoreactive neuronal processes present at the median eminence. Similarly, adult mice deficient in functional GnRHR possessed a full complement of GnRH neurons in the basal forebrain that was indistinguishable from the distribution of GnRH neurons in their wild-type counterparts. Moreover, hpg/GFP neurons retained the ability to generate spontaneous bursts of action potential firing activity, suggesting that GnRH peptide is not required for this function. These data establish that autocrine-paracrine GnRH-signaling is not a prerequisite for the developmental migration of GnRH neurons into the brain or for the projection of GnRH neurosecretory axons.

Differential role of gonadotropin-releasing hormone on human ovarian epithelial cancer cell invasion

Ovarian cancer is the most lethal of all gynecological cancers. Most deaths from ovarian cancer are due to widespread intraperitoneal metastases and malignant ascites. However, mechanisms of invasion in ovarian cancer remain poorly understood. In this study, we examined the effects of gonadotropin-releasing hormone (GnRH)-I (the classical mammalian GnRH), GnRH-II (a second form of GnRH), and GnRH receptor on invasion using two human ovarian carcinoma cell lines, OVCAR-3 and SKOV-3. Here we demonstrated that in OVCAR-3, GnRH-I and GnRH-II promoted cell invasion, whereas in SKOV-3, GnRH-I and GnRH-II inhibited cell invasion. Transfection of small interfering RNA to abrogate the gene expression of GnRH receptor reversed GnRH-I and GnRH-II-mediated invasion activities, suggesting that the same receptor, type I GnRH receptor, is essential for the effects of GnRH-I and GnRH-II in both OVCAR-3 and SKOV-3. Treatment of SKOV-3 cells with GnRH-I or GnRH-II resulted in a decrease in matrix metalloproteinase 2 but an increase in tissue inhibitor of metalloproteinase 2 secretions. In addition, we found that GnRH-I and GnRH-II interfered with activation of the phosphatidylinositol-3-kinase/AKT pathway that is well documented to stimulate proteolysis and invasion of ovarian cancer cells. Taken together, these observations suggest that GnRH-I and GnRH-II play key regulatory roles in ovarian tumor cell invasion and extracellular matrix degradation.

Endocrine signaling in ovarian surface epithelium and cancer

Ovarian cancer is the sixth most common cancer and the fifth leading cause of cancer-related death among women in developed countries. Greater than 85% of human ovarian cancer arises within the ovarian surface epithelium (OSE), with the remainder derived from granulosa cells or, rarely, stroma or germ cells. The pathophysiology of ovarian cancer is the least understood among all major human malignancies because of a poor understanding of the aetiological factors and mechanisms of ovarian cancer progression. There is increasing evidence suggesting that several key reproductive hormones, such as GnRH, gonadotrophins and sex steroids, regulate the growth of normal OSE and ovarian cancer cells. The objective of this review was to highlight the effects of these endocrine factors on ovarian cancer cell growth and to summarize the signalling mechanisms involved in normal human OSE and its neoplastic counterparts.

Type II gonadotropin-releasing hormone stimulates p38 mitogen-activated protein kinase and apoptosis in ovarian cancer cells

Recent results indicate that a novel second form of GnRH, GnRH-II, has an antiproliferative effect on ovarian and endometrial cancer cells and might be considered as a possible therapy for gynecological tumors. However, the mechanism of the GnRH-II-induced antiproliferative effect is not known. The p38 MAPK, one of the stress-activated protein kinases, is activated by diverse cellular stress and proinflammatory cytokines. In this study, the effect of GnRH-II on the activation of p38 MAPK was investigated, and its possible role in the regulation of cell proliferation and apoptosis was further examined in the human ovarian cancer cell line, OVCAR-3. Treatment with GnRH-II (100 nM) resulted in an activation of p38 MAPK in a time-dependent manner. A significant activation of p38 MAPK was observed at 2, 5, 10, and 15 min after GnRH-II treatment. The activation of p38 MAPK by GnRH-II was reversed in the presence of a specific inhibitor of p38 MAPK, SB203580 (1 microM). The transcription factor, activator protein-1, was activated (1.5-fold) by GnRH-II and attenuated in the presence of SB203580 (1 microM). Treatment with GnRH-II (1 nM, 100 nM, 10 microM) for 2, 4, and 6 d resulted in an inhibition of cell growth in OVCAR-3 cells as determined by thymidine incorporation assay. The effect of GnRH-II (100 nM) on cell proliferation was blocked by pretreatment with SB203580 (1 microM). Furthermore, a significant increase of apoptosis (1.6-fold) was observed after GnRH-II treatment, which was also reversed by pretreatment with SB203580 (1 microM). Taken together, these results indicate that p38 MAPK is involved in the GnRH-II-induced inhibition of cell growth through activator protein-1 activation, which may be related to induction of apoptosis in ovarian cancer cells.

Intracellular signaling pathways mediated by the gonadotropin-releasing hormone (GnRH) receptor

The hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator of the reproductive system, triggering the synthesis and release of LH and FSH in the pituitary. GnRH transmits its signal via two specific serpentine receptors that belong to the large group of G-protein coupled receptors (GPCRs). Here we review the intracellular signaling pathways mediated by the GnRH receptor (GnRHR). In pituitary-derived alpha T3-1 cells, a widely used model for GnRH action, GnRHR signaling includes activation of mitogen-activated protein kinase (MAPK) cascades, which provide an important link for the transmission of signals from the cell surface to the nucleus and play a role in the regulation of gonadotropin transcription. Activation of ERK--one of the MAPK cascades--by GnRH in these cells depends mainly on the phosphorylation of Raf1 by PKC, supported by a pathway involving c-Src, dynamin, and Ras. On the other hand, the activation of JNK, another MAPK cascade, involves PKC, c-Src, CDC42/Rac1, and probably MEKK1. The GnRHR is also expressed in non-pituitary cells and was found to be involved in the inhibition of cell proliferation in certain cells. Therefore, GnRHR represents a potential target for GnRH-analogs used for cancer treatment. Interestingly, the signaling mechanism of the GnRHR in other cell types significantly differs from that in pituitary cells. Studies conducted in GnRHR-expressing COS7 cells have shown that GnRHR transmits its signals mainly via Gi, EGF receptor, c-Src, and is not dependent on PKC. Understanding the signaling mechanisms elicited by GnRHR can shed light on the mechanism of action of GnRH in pituitary and extra-pituitary tissues.

Prevention of menstruation with leuprorelin (GnRH agonist) in women undergoing myelosuppressive chemotherapy or radiochemotherapy for hematological malignancies: a pilot study

Vaginal bleeding during aplasia can induce transfusion support, infection and discomfort. Oral and intramuscular hormonotherapy can be toxic and/or difficult to manage (mucositis). This single-center pilot study evaluated the efficacy and safety of leuprorelin (L) in preventing heavy vaginal bleeding in 20 nonmenopausal women with leukemia, lymphoma or myeloma and foreseable therapy-induced thrombocytopenia. Until platelet recovery, patients received subcutaneous injections of L, with concomitant nomegestrol acetate (NA) during the first 35 days to prevent flare-up. Median age was 33 years (18-48). Platelet nadir was < 20 x 10(9)/l in 17 patients; 103 L injections were performed (median per patient: 4 [1-14]). No moderate or severe adverse event was related to hormonal therapy. Seventeen patients did not experience any clinically or therapeutically relevant bleeding. Eleven spottings and 8 metrorrhagias (mean duration: 3 days) occurred in 11 patients, requiring enhanced NA in 3 cases (baseline platelet count was < 20 x 10(9)/l in 1 pt, premature termination of NA [the single platelet transfusion for metrorrhagia] in 1 pt, and endometrial hyperplasia (EH) in the third). In patients without EH, only 5 spottings were observed after the third injection, without neither clinical nor therapeutic impact (63 injections). In conclusion, leuprorelin administration is safe and effective in preventing vaginal bleeding. The sustained-release form and subcutaneous administration offer quality of life advantages.

The role of LH-RH analogues in the adjuvant and palliative treatment of breast cancer

Ovarian ablation has a long-standing history in the treatment of metastatic breast cancer. At the end of the past century, several reports appeared on the beneficial effect of surgical removal of the ovaries in premenopausal women with advanced breast cancer. Subsequently, this treatment became the standard systemic hormone therapy for such patients. However, the disadvantage is that only a minority of patients respond, and the remainder suffer unnecessary treatment morbidity. In a random premenopausal patient population, oophorectomy produced an average 33% objective response rate. In the search for alternatives, analogues of luteinizing hormone-releasing hormone (LH-RH) have been thoroughly investigated in pre- and postmenopausal women. The results obtained have established a place for LH-RH agonists in the treatment of premenopausal women with metastatic breast cancer. In addition, these substances have replaced oophorectomy where indicated in the adjuvant hormonal treatment of premenopausal breast cancer.

A multicenter phase II study with triptorelin (sustained-release LHRH agonist) in advanced or recurrent endometrial carcinoma: a French anticancer federation study

The objective of this phase II multicenter study was to assess the efficacy and tolerance of triptorelin (a sustained-release LHRH agonist) in advanced or recurrent endometrial cancer. A total of 101 monthly intramuscular injections were administered to 24 eligible patients (median number/patient = 3; range 1-12). Mainly due to progression, only 16 patients received 3 or more injections. Among the 23 evaluable patients, 1 complete and 1 partial response (response rate of 8.7%) and 5 disease stabilizations were observed, often of long duration, but never in an irradiated area or after progestogens treatment failure. Median survival for eligible patients was 7.2 months (range: 1-36 months). Only grade 1 toxicities possibly related to the treatment were observed in 4 patients. In conclusion, triptorelin was safe, well tolerated, and easily manageable, and the very low toxicity did not impair the quality of life in these patients with a very poor prognosis. Although the response rate was disappointing, several patients showed early evidence of efficacy which may be of long duration. Response rates range between 0 and 45% in different published studies. Additional studies with stricter inclusion criteria and a larger sample size are necessary to better evaluate the role of LHRH agonists in endometrial adenocarcinomas.