The luteinizing hormone-releasing hormone receptor in human prostate cancer cells: messenger ribonucleic acid expression, molecular size, and signal transduction pathway

Anti-metastatic effect of GV1001 on prostate cancer cells; roles of GnRHR-mediated Gαs-cAMP pathway and AR-YAP1 axis

BACKGROUND

Gonadotropin-releasing hormone receptor (GnRHR) transmits its signal via two major Gα-proteins, primarily Gαq and Gαi. However, the precise mechanism underlying the functions of Gαs signal in prostate cancer cells is still unclear. We have previously identified that GV1001, a fragment of the human telomerase reverse transcriptase, functions as a biased GnRHR ligand to selectively stimulate the Gαs/cAMP pathway. Here, we tried to reveal the potential mechanisms of which GV1001-stimulated Gαs-cAMP signaling pathway reduces the migration and metastasis of prostate cancer (PCa) cells.

METHODS

The expression of epithelial-mesenchymal transition (EMT)-related genes was measured by western-blotting and spheroid formation on ultra-low attachment plate was detected after GV1001 treatment. In vivo Spleen-liver metastasis mouse model was used to explore the inhibitory effect of GV1001 on metastatic ability of PCa and the transwell migration assay was performed to identify whether GV1001 had a suppressive effect on cell migration in vitro. In order to demonstrate the interaction between androgen receptor (AR) and YAP1, co-immunoprecipitation (co-IP), immunofluorescence (IF) staining, chromatin immunoprecipitation (ChIP) were performed in LNCaP cells with and without GV1001 treatment.

RESULTS

GV1001 inhibited expression of EMT-related genes and spheroid formation. GV1001 also suppressed in vivo spleen-liver metastasis of LNCaP cells as well as cell migration in vitro. GV1001 enhanced the phosphorylation of AR and transcription activity of androgen response element reporter gene through cAMP/protein kinase A pathway. Moreover, GV1001 increased Ser-127 phosphorylation of YAP1 and its ubiquitination, and subsequently decreased the levels of AR-YAP1 binding in the promoter region of the CTGF gene. In contrast, both protein and mRNA levels of NKX3.1 known for tumor suppressor gene and AR-coregulator were upregulated by GV1001 in LNCaP cells. YAP1 knockout using CRISPR/Cas9 significantly suppressed the migration ability of LNCaP cells, and GV1001 did not affect the cell migration of YAP1-deficient LNCaP cells. On the contrary, cell migration was more potentiated in LNCaP cells overexpressing YAP5SA, a constitutively active form of YAP1, which was not changed by GV1001 treatment.

CONCLUSIONS

Overall, this study reveals an essential role of AR-YAP1 in the regulation of PCa cell migration, and provides evidence that GV1001 could be a novel GnRHR ligand to inhibit metastasis of PCa via the Gαs/cAMP pathway.

Anti-metastatic effect of GV1001 on prostate cancer cells; roles of GnRHR-mediated Gαs-cAMP pathway and AR-YAP1 axis

Background

Gonadotropin-releasing hormone receptor (GnRHR) transmits its signal via two major Gα-proteins, primarily Gαq and Gαi. However, the precise mechanism underlying the functions of Gαs signal in prostate cancer cells is still unclear. We have previously identified that GV1001, a fragment of the human telomerase reverse transcriptase, functions as a biased GnRHR ligand to selectively stimulate the Gαs/cAMP pathway. Here, we tried to reveal the potential mechanisms of which GV1001-stimulated Gαs-cAMP signaling pathway reduces the migration and metastasis of prostate cancer (PCa) cells.

Methods

The expression of epithelial-mesenchymal transition (EMT)-related genes was measured by western-blotting and spheroid formation on ultra-low attachment plate was detected after GV1001 treatment. In vivo Spleen-liver metastasis mouse model was used to explore the inhibitory effect of GV1001 on metastatic ability of PCa and the transwell migration assay was performed to identify whether GV1001 had a suppressive effect on cell migration in vitro. In order to demonstrate the interaction between androgen receptor (AR) and YAP1, co-immunoprecipitation (co-IP), immunofluorescence (IF) staining, chromatin immunoprecipitation (ChIP) were performed in LNCaP cells with and without GV1001 treatment.

Results

GV1001 inhibited expression of EMT-related genes and spheroid formation. GV1001 also suppressed in vivo spleen-liver metastasis of LNCaP cells as well as cell migration in vitro. GV1001 enhanced the phosphorylation of AR and transcription activity of androgen response element reporter gene through cAMP/protein kinase A pathway. Moreover, GV1001 increased Ser-127 phosphorylation of YAP1 and its ubiquitination, and subsequently decreased the levels of AR-YAP1 binding in the promoter region of the CTGF gene. In contrast, both protein and mRNA levels of NKX3.1 known for tumor suppressor gene and AR-coregulator were upregulated by GV1001 in LNCaP cells. YAP1 knockout using CRISPR/Cas9 significantly suppressed the migration ability of LNCaP cells, and GV1001 did not affect the cell migration of YAP1-deficient LNCaP cells. On the contrary, cell migration was more potentiated in LNCaP cells overexpressing YAP5SA, a constitutively active form of YAP1, which was not changed by GV1001 treatment.

Conclusions

Overall, this study reveals an essential role of AR-YAP1 in the regulation of PCa cell migration, and provides evidence that GV1001 could be a novel GnRHR ligand to inhibit metastasis of PCa via the Gαs/cAMP pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00704-3.

Membrane translocation and activation of GnRH receptor sensitize prostate cancer cells to radiation

BACKGROUND

GnRH analogs are widely used as neoadjuvant agents for radiotherapy in prostate cancer (PCa) patients, with well-documented effects in reducing tumor bulk and increasing progression-free survival. GnRH analogs act locally in the prostate by triggering apoptosis of PCa cells via activation of the GnRH receptor (GnRHR). During PCa progression, the distribution of GnRHR within the cell is altered, with reduced expression in the cell membrane and remaining sequestered in the endoplasmic reticulum. Pharmacoperone IN3 is able to relocalize GnRHR to the cell membrane. The aim of this study was to evaluate the effect of radiation on PCa cells pretreated with leuprolide, alone or in combination with IN3, as radiosensitizers.

MATERIAL AND METHODS

PC3 and human PCa primary cell cultures were treated with IN3 for 24 h, followed by different doses of leuprolide for 48 h and, finally, single doses of radiation (3, 6, and 9 Gy). After radiation, cell survival, apoptosis, cell cycle distribution, and colony growth were evaluated.

RESULTS

Radiation reduced cell survival and increased apoptosis in a dose-dependent manner. This effect was also directly related to leuprolide concentration. Pretreatment with IN3 enhanced apoptosis and decreased cell survival, also observing a higher proportion of cells arrested in G2.

CONCLUSION

Neoadjuvant leuprolide increases radiation-mediated apoptosis of PCa cells. This effect was enhanced by pretreatment with pharmacoperone IN3. Clinical use of IN3 as a radiosensitizer combined with androgen deprivation therapy to improve survival of patients with PCa remains to be evaluated.

Dissecting the Hormonal Signaling Landscape in Castration-Resistant Prostate Cancer

Understanding the molecular mechanisms underlying prostate cancer (PCa) progression towards its most aggressive, castration-resistant (CRPC) stage is urgently needed to improve the therapeutic options for this almost incurable pathology. Interestingly, CRPC is known to be characterized by a peculiar hormonal landscape. It is now well established that the androgen/androgen receptor (AR) axis is still active in CRPC cells. The persistent activity of this axis in PCa progression has been shown to be related to different mechanisms, such as intratumoral androgen synthesis, AR amplification and mutations, AR mRNA alternative splicing, increased expression/activity of AR-related transcription factors and coregulators. The hypothalamic gonadotropin-releasing hormone (GnRH), by binding to its specific receptors (GnRH-Rs) at the pituitary level, plays a pivotal role in the regulation of the reproductive functions. GnRH and GnRH-R are also expressed in different types of tumors, including PCa. Specifically, it has been demonstrated that, in CRPC cells, the activation of GnRH-Rs is associated with a significant antiproliferative/proapoptotic, antimetastatic and antiangiogenic activity. This antitumor activity is mainly mediated by the GnRH-R-associated Gαi/cAMP signaling pathway. In this review, we dissect the molecular mechanisms underlying the role of the androgen/AR and GnRH/GnRH-R axes in CRPC progression and the possible therapeutic implications.

Role of Gonadotropin-Releasing Hormone (GnRH) in Ovarian Cancer

The hypothalamus–pituitary–gonadal (HPG) axis is the endocrine regulation system that controls the woman’s cycle. The gonadotropin-releasing hormone (GnRH) plays the central role. In addition to the gonadotrophic cells of the pituitary, GnRH receptors are expressed in other reproductive organs, such as the ovary and in tumors originating from the ovary. In ovarian cancer, GnRH is involved in the regulation of proliferation and metastasis. The effects on ovarian tumors can be indirect or direct. GnRH acts indirectly via the HPG axis and directly via GnRH receptors on the surface of ovarian cancer cells. In this systematic review, we will give an overview of the role of GnRH in ovarian cancer development, progression and therapy.

Gonadotropin-Releasing Hormone Receptors in Prostate Cancer: Molecular Aspects and Biological Functions

Pituitary Gonadotropin-Releasing Hormone receptors (GnRH-R) mediate the activity of the hypothalamic decapeptide GnRH, thus playing a key role in the regulation of the reproductive axis. Early-stage prostate cancer (PCa) is dependent on serum androgen levels, and androgen-deprivation therapy (ADT), based on GnRH agonists and antagonists, represents the standard therapeutic approach for PCa patients. Unfortunately, the tumor often progresses towards the more aggressive castration-resistant prostate cancer (CRPC) stage. GnRH receptors are also expressed in CRPC tissues, where their binding to both GnRH agonists and antagonists is associated with significant antiproliferative/proapoptotic, antimetastatic and antiangiogenic effects, mediated by the Gαi/cAMP signaling cascade. GnRH agonists and antagonists are now considered as an effective therapeutic strategy for CRPC patients with many clinical trials demonstrating that the combined use of these drugs with standard therapies (i.e., docetaxel, enzalutamide, abiraterone) significantly improves disease-free survival. In this context, GnRH-based bioconjugates (cytotoxic drugs covalently linked to a GnRH-based decapeptide) have been recently developed. The rationale of this treatment is that the GnRH peptide selectively binds to its receptors, delivering the cytotoxic drug to CRPC cells while sparing nontumor cells. Some of these compounds have already entered clinical trials.

LHRH-Conjugated Drugs as Targeted Therapeutic Agents for the Specific Targeting and Localized Treatment of Triple Negative Breast Cancer

Bulk chemotherapy and drug release strategies for cancer treatment have been associated with lack of specificity and high drug concentrations that often result in toxic side effects. This work presents the results of an experimental study of cancer drugs (prodigiosin or paclitaxel) conjugated to Luteinizing Hormone-Releasing Hormone (LHRH) for the specific targeting and treatment of triple negative breast cancer (TNBC). Injections of LHRH-conjugated drugs (LHRH-prodigiosin or LHRH-paclitaxel) into groups of 4-week-old athymic female nude mice (induced with subcutaneous triple negative xenograft breast tumors) were found to specifically target, eliminate or shrink tumors at early, mid and late stages without any apparent cytotoxicity, as revealed by in vivo toxicity and ex vivo histopathological tests. Our results show that overexpressed LHRH receptors serve as binding sites on the breast cancer cells/tumor and the LHRH-conjugated drugs inhibited the growth of breast cells/tumor in in vitro and in vivo experiments. The inhibitions are attributed to the respective adhesive interactions between LHRH molecular recognition units on the prodigiosin (PGS) and paclitaxel (PTX) drugs and overexpressed LHRH receptors on the breast cancer cells and tumors. The implications of the results are discussed for the development of ligand-conjugated drugs for the specific targeting and treatment of TNBC.

Treatment of Breast Cancer With Gonadotropin-Releasing Hormone Analogs

Although significant progress has been made in the implementation of new breast cancer treatments over the last three decades, this neoplasm annually continues to show high worldwide rates of morbidity and mortality. In consequence, the search for novel therapies with greater effectiveness and specificity has not come to a stop. Among the alternative therapeutic targets, the human gonadotropin-releasing hormone type I and type II (hGnRH-I and hGnRH–II, respectively) and its receptor, the human gonadotropin-releasing hormone receptor type I (hGnRHR-I), have shown to be powerful therapeutic targets to decrease the adverse effects of this disease. In the present review, we describe how the administration of GnRH analogs is able to reduce circulating concentrations of estrogen in premenopausal women through their action on the hypothalamus–pituitary–ovarian axis, consequently reducing the growth of breast tumors and disease recurrence. Also, it has been mentioned that, regardless of the suppression of synthesis and secretion of ovarian steroids, GnRH agonists exert direct anticancer action, such as the reduction of tumor growth and cell invasion. In addition, we discuss the effects on breast cancer of the hGnRH-I and hGnRH-II agonist and antagonist, non-peptide GnRH antagonists, and cytotoxic analogs of GnRH and their implication as novel adjuvant therapies as antitumor agents for reducing the adverse effects of breast cancer. In conclusion, we suggest that the hGnRH/hGnRHR system is a promising target for pharmaceutical development in the treatment of breast cancer, especially for the treatment of advanced states of this disease.

Synthesis, in vitro stability, and antiproliferative effect of d-cysteine modified GnRH-doxorubicin conjugates

Overexpression of gonadotropin-releasing hormone (GnRH) receptor in many tumors but not in normal tissues makes it possible to use GnRH analogs as targeting peptides for selective delivery of cytotoxic agents, which may help to enhance the uptake of anticancer drugs by cancer cells and reduce toxicity to normal cells. The GnRH analogs [d-Cys⁶ , desGly¹⁰ , Pro⁹ -NH₂ ]-GnRH, [d-Cys⁶ , desGly¹⁰ , Pro⁹ -NHEt]-GnRH, and [d-Cys⁶ , α-aza-Gly¹⁰ -NH₂ ]-GnRH were conjugated with doxorubicin (Dox), respectively, through N-succinimidyl-3-maleimidopropionate as a linker to afford three new GnRH-Dox conjugates. The metabolic stability of these conjugates in human serum was determined by RP-HPLC. The antiproliferative activity of the conjugates was examined in GnRH receptor-positive MCF-7 human breast cancer cell line by MTT assay. The three GnRH-Dox conjugates showed improved metabolic stability in human serum in comparison with AN-152. The antiproliferative effect of conjugate II ([d-Cys⁶ , desGly¹⁰ , Pro⁹ -NHEt]-GnRH-Dox) on MCF-7 cells was higher than that of conjugate I ([d-Cys⁶ , desGly¹⁰ , Pro⁹ -NH₂ ]-GnRH-Dox) and conjugate III ([d-Cys⁶ , α-aza-Gly¹⁰ -NH₂ ]-GnRH-Dox), and the cytotoxicity of conjugate II against GnRH receptor-negative 3T3 mouse embryo fibroblast cells was decreased in comparison with free Dox. GnRH receptor inhibition test suggested that the antiproliferative activity of conjugate II might be due to the cellular uptake mediated by the targeting binding of [d-Cys⁶ -des-Gly¹⁰ -Pro⁹ -NHEt]-GnRH to GnRH receptors. Our study indicates that targeting delivery of conjugate II mediated by [d-Cys⁶ -des-Gly¹⁰ -Pro⁹ -NHEt]-GnRH is a promising strategy for chemotherapy of tumors that overexpress GnRH receptors.

Regulation of prostate cancer by hormone-responsive G protein-coupled receptors

Regulation of prostate cancer by androgen and androgen receptor (AR), and blockade of AR signaling by AR antagonists and steroidogenic enzyme inhibitors have been extensively studied. G protein-coupled receptors (GPCRs) are a family of membrane receptors that regulate almost all physiological processes. Nearly 40% of FDA-approved drugs in the market target GPCRs. A variety of GPCRs that mediate reproductive function have been demonstrated to be involved in the regulation of prostate cancer. These GPCRs include gonadotropin-releasing hormone receptor, luteinizing hormone receptor, follicle-stimulating hormone receptor, relaxin receptor, ghrelin receptor, and kisspeptin receptor. We highlight here GPCR regulation of prostate cancer by these GPCRs. Further therapeutic approaches targeting these GPCRs for the treatment of prostate cancer are summarized.

Differential roles of PKC isoforms (PKCs) in GnRH stimulation of MAPK phosphorylation in gonadotrope derived cells

The role of protein kinase C (PKC) isoforms (PKCs) in GnRH-stimulated MAPK [ERK1/2, JNK1/2 and p38) phosphorylation was examined in gonadotrope derived cells. GnRH induced a protracted activation of ERK1/2 and a slower and more transient activation of JNK1/2 and p38MAPK. Gonadotropes express conventional PKCα and PKCβII, novel PKCδ, PKCε and PKCθ, and atypical PKC-ι/λ. The use of green fluorescent protein (GFP)-PKCs constructs revealed that GnRH induced rapid translocation of PKCα and PKCβII to the plasma membrane, followed by their redistribution to the cytosol. PKCδ and PKCε localized to the cytoplasm and Golgi, followed by the rapid redistribution by GnRH of PKCδ to the perinuclear zone and of PKCε to the plasma membrane. The use of dominant negatives for PKCs and peptide inhibitors for the receptors for activated C kinase (RACKs) has revealed differential role for PKCα, PKCβII, PKCδ and PKCε in ERK1/2, JNK1/2 and p38MAPK phosphorylation in a ligand-and cell context-dependent manner. The paradoxical findings that PKCs activated by GnRH and PMA play a differential role in MAPKs phosphorylation may be explained by persistent vs. transient redistribution of selected PKCs or redistribution of a given PKC to the perinuclear zone vs. the plasma membrane. Thus, we have identified the PKCs involved in GnRH stimulated MAPKs phosphorylation in gonadotrope derived cells. Once activated, the MAPKs will mediate the transcription of the gonadotropin subunits and GnRH receptor genes.

GnRH in the Human Female Reproductive Axis

Gonadotropin-releasing hormone (GnRH) is recognized as the central regulator of the functions of the pituitary-gonadal axis. The increasing knowledge on the mechanisms controlling the development and the function of GnRH-producing neurons is leading to a better diagnostic and therapeutic approach for hypogonadotropic hypogonadisms and for alterations of the puberty onset. During female life span, the function of the GnRH pulse generator may be affected by a number of inputs from other neuronal systems, offering alternative strategies for diagnostic and therapeutic interventions. Moreover, the identification of a GnRH/GnRH receptor system in both human ovary and endometrium has widened the spectrum of action of the peptide outside its hypothalamic functions. The pharmacological use of GnRH itself or its synthetic analogs (agonists and antagonists) provides a valid tool to either stimulate or block gonadotropin secretion and to modulate the female fertility in several reproductive disorders and in assisted reproduction technology. The use of GnRH agonists in young female patients undergoing chemotherapy is also considered a promising therapeutic approach to counteract iatrogenic ovarian failure.

Double-receptor-targeting multifunctional iron oxide nanoparticles drug delivery system for the treatment and imaging of prostate cancer

As an alternative therapeutic treatment to reduce or eliminate the current side effects associated with advanced prostate cancer (PCa) chemotherapy, a multifunctional double-receptor-targeting iron oxide nanoparticles (IONPs) (luteinizing hormone-releasing hormone receptor [LHRH-R] peptide- and urokinase-type plasminogen activator receptor [uPAR] peptide-targeted iron oxide nanoparticles, LHRH-AE105-IONPs) drug delivery system was developed. Two tumor-targeting peptides guided this double-receptor-targeting nanoscale drug delivery system. These peptides targeted the LHRH-R and the uPAR on PCa cells. Dynamic light scattering showed an increase in the hydrodynamic size of the LHRH-AE105-IONPs in comparison to the non-targeted iron oxide nanoparticles (NT-IONPs). Surface analysis showed that there was a decrease in the zeta potential values for drug-loaded LHRH-AE105-IONPs compared to the NT-IONPs. Prussian blue staining demonstrated that the LHRH-AE105-IONPs were internalized efficiently by the human PCa cell line, PC-3. In vitro, magnetic resonance imaging (MRI) results confirmed the preferential binding and accumulation of LHRH-AE105-IONPs in PC-3 cells compared to normal prostate epithelial cells (RC77N/E). The results also showed that LHRH-AE105-IONPs significantly maintained T2 MRI contrast effects and reduced T2 values upon internalization by PC-3 cells. These paclitaxel-loaded double-receptor-targeting IONPs also showed an approximately twofold reduction in PC-3 cell viability compared to NT-IONPs.

Synthesis, characterization and systematic comparison of FITC-labelled GnRH-I, -II and -III analogues on various tumour cells

Targeted tumour therapy is the focus of recent cancer research. Gonadotropin-releasing hormone (GnRH) analogues are able to deliver anticancer agents selectively into tumour cells, which highly express GnRH receptors. However, the effectiveness of different analogues as targeting moiety in drug delivery systems is rarely compared, and the investigated types of cancer are also limited. Therefore, we prepared selectively labelled, fluorescent derivatives of GnRH-I, -II and -III analogues, which were successfully used for drug targeting. In this manuscript, we investigated these analogues' solubility, stability and passive membrane permeability and compared their cellular uptake by various cancer cells. We found that these labelled GnRH conjugates provide great detectability, without undesired cytotoxicity and passive membrane permeability. The introduced experiments with these conjugates proved their reliable tracking, quantification and comparison. Cellular uptake efficiency was studied on human breast, colon, pancreas and prostate cancer cells (MCF-7, HT-29, BxPC-3, LNCaP) and on dog kidney cells (Madin-Darby canine kidney). Each of the three conjugates was taken up by GnRH-I receptor-expressing cells, but the different cells preferred different analogues. Furthermore, we demonstrated for the first time the high cell surface expression of GnRH-I receptors and the effective cellular uptake of GnRH analogues on human pharynx tumour (Detroit-562) cells. In summary, our presented results detail that the introduced conjugates could be innovative tools for the examination of the GnRH-based drug delivery systems on various cells and offer novel information about these peptides. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Differential roles of PKC isoforms (PKCs) and Ca2+ in GnRH and phorbol 12-myristate 13-acetate (PMA) stimulation of p38MAPK phosphorylation in immortalized gonadotrope cells

We examined the role of PKCs and Ca²⁺ in GnRH-stimulated p38MAPK phosphorylation in the gonadotrope derived αT3-1 and LβT2 cell lines. GnRH induced a slow and rapid increase in p38MAPK phosphorylation in αT3-1 and LβT2 cells respectively, while PMA gave a slow response. The use of dominant negatives for PKCs and peptide inhibitors for the receptors for activated C kinase (RACKs), has revealed differential role for PKCα, PKCβII, PKCδ and PKCε in p38MAPK phosphorylation in a ligand-and cell context-dependent manner. The paradoxical findings that PKCs activated by GnRH and PMA play a differential role in p38MAPK phosphorylation may be explained by differential localization of the PKCs. Basal, GnRH- and PMA- stimulation of p38MAPK phosphorylation in αT3-1 cells is mediated by Ca²⁺ influx via voltage-gated Ca²⁺ channels and Ca²⁺ mobilization, while in the differentiated LβT2 gonadotrope cells it is mediated only by Ca²⁺ mobilization. p38MAPK resides in the cell membrane and is relocated to the nucleus by GnRH (∼5 min). Thus, we have identified the PKCs and the Ca²⁺ pools involved in GnRH stimulated p38MAPK phosphorylation.

The Role of Gonadotropin-Releasing Hormone in Cancer Cell Proliferation and Metastasis

In several human malignant tumors of the urogenital tract, including cancers of the endometrium, ovary, urinary bladder, and prostate, it has been possible to identify expression of gonadotropin-releasing hormone (GnRH) and its receptor as part of an autocrine system, which regulates cell proliferation. The expression of GnRH receptor has also been identified in breast cancers and non-reproductive cancers such as pancreatic cancers and glioblastoma. Various investigators have observed dose- and time-dependent growth inhibitory effects of GnRH agonists in cell lines derived from these cancers. GnRH antagonists have also shown marked growth inhibitory effects on most cancer cell lines. This indicates that in the GnRH system in cancer cells, there may not be a dichotomy between GnRH agonists and antagonists. The well-known signaling mechanisms of the GnRH receptor, which are present in pituitary gonadotrophs, are not involved in forwarding the antiproliferative effects of GnRH analogs in cancer cells. Instead, the GnRH receptor activates a phosphotyrosine phosphatase (PTP) and counteracts with the mitogenic signal transduction of growth factor receptors, which results in a reduction of cancer cell proliferation. The PTP activation, which is induced by GnRH, also inhibits G-protein-coupled estrogen receptor 1 (GPER), which is a membrane-bound receptor for estrogens. GPER plays an important role in breast cancers, which do not express the estrogen receptor α (ERα). In metastatic breast, ovarian, and endometrial cancer cells, GnRH reduces cell invasion in vitro, metastasis in vivo, and the increased expression of S100A4 and CYR61. All of these factors play important roles in epithelial-mesenchymal transition. This review will summarize the present state of knowledge about the GnRH receptor and its signaling in human cancers.

Augmentation of gonadotropin-releasing hormone receptor expression in the post-lactational mammary tissues of rats

Gonadotropin-releasing hormone (GnRH) is a neurohormone of the hypothalamus controlling pituitary gonadotropin secretion and hence gametogenesis. While it has also been believed that GnRH is synthesized and functions in various peripheral tissues, the expression of GnRH receptor (GnRH-R) in peripheral tissues is not well-described. We previously found that annexin A5, which is increased in the pituitary gonadotropes by GnRH, is dramatically increased in rat mammary epithelial cells after weaning, suggesting that local GnRH is responsible for this increase. Annexin A5 is a member of the annexin family of proteins and is thought to be involved in various regulatory mechanisms, including apoptosis. In the present study, we examined GnRH-R expression in the mammary tissues after weaning. Although GnRH-R mRNA was not detected in the mammary tissues during lactation, it was dramatically increased after weaning. Forced weaning at mid-lactation (day 10) also promoted the expression of GnRH-R transcripts in mammary tissues within 2 days. Furthermore, western blotting analysis with anti-GnRH-R showed that the expression of an immuno-positive 60-kDa protein, whose size was equivalent to that of rat GnRH-R, was confirmed to increase after weaning. These findings clarified the induction of GnRH-R in the mammary tissues after weaning and suggest that GnRH is involved in the involution and tissue remodeling of post-lactating rat mammary tissues.

GnRH-(1-5) activates matrix metallopeptidase-9 to release epidermal growth factor and promote cellular invasion

In the extracellular space, the gonadotropin-releasing hormone (GnRH) is metabolized by the zinc metalloendopeptidase EC3.4.24.15 (EP24.15) to form the pentapeptide, GnRH-(1-5). GnRH-(1-5) diverges in function and mechanism of action from GnRH in the brain and periphery. GnRH-(1-5) acts on the orphan G protein-coupled receptor 101 (GPR101) to sequentially stimulate epidermal growth factor (EGF) release, phosphorylate the EGF receptor (EGFR), and facilitate cellular migration. These GnRH-(1-5) actions are dependent on matrix metallopeptidase (MMP) activity. Here, we demonstrated that these GnRH-(1-5) effects are dependent on increased MMP-9 enzymatic activity in the Ishikawa and ECC-1 cell lines. Furthermore, the effects of GnRH-(1-5) mediated by GPR101 and the subsequent increase in MMP-9 enzymatic activity lead to an increase in cellular invasion. These results suggest that GnRH-(1-5) and GPR101 regulation of MMP-9 may have physiological relevance in the metastatic potential of endometrial cancer cells.

GnRH participates in the self-renewal of A549-derived lung cancer stem-like cells through upregulation of the JNK signaling pathway

Lung cancer is the leading cause of cancer-related mortality in humans. Exploration of the mechanisms underlying the self-renewal and stemness maintenance of cancer stem-like cells (CSLCs) will open new avenues in lung cancer diagnosis and therapy. Here, we isolated and identified a subpopulation of lung cancer stem-like cells (LCSLCs) from non-small cell lung carcinoma (NSCLC) A549 cells with features including self-renewal capacity in vitro, elevated tumorigenic activity in vivo, and high expression of stemness markers CD44, CD133, aldehyde dehydrogenase 1 (ALDH1) and Sox2, using a serum-free suspension sphere-forming culture method. We then found a higher expression level of gonadotropin-releasing hormone (GnRH) in the LCSLCs using a microarray assay, suggesting that GnRH may play a role in the self-renewal capacity and stemness maintenance in lung cancer cells. In addition, the suppression of GnRH capacity negatively regulated self-renewal and stemness maintenance in the LCSLCs. Overexpression of GnRH promoted stemness properties of A549-derived LCSLCs, indicating that GnRH expression is essential for the self-renewal and stemness maintenance in LCSLCs. Moreover, further investigations demonstrated that the promotion of GnRH functions of self-renewal and stemness maintenance in LCSLCs was associated with the JNK signaling pathway. Therefore, our results showed that GnRH participates in the self-renewal capacity and stemness maintenance of LCSLCs by upregulating the JNK signaling pathway, and GnRH may be useful as an alternative LCSLC therapy.

A phenotypic high throughput screening assay for the identification of pharmacoperones for the gonadotropin releasing hormone receptor

We describe a phenotypic high throughput screening (HTS) calcium flux assay designed to identify pharmacoperones for the gonadotropin releasing hormone receptor (GnRHR). Pharmacoperones are target-specific, small molecules that diffuse into cells, rescue misfolded protein mutants, and restore them to function. Rescue is based on correcting the trafficking of mutants that would otherwise be retained in the endoplasmic reticulum and unable to function correctly. This approach identifies drugs with a significant degree of novelty, relying on cellular mechanisms that are not currently exploited. Development of such assays is important, since the extensive use of agonist/antagonist screens alone means that useful chemical structures may be present in existing libraries but have not been previously identified using existing methods. Our assay utilizes cell lines stably expressing a GnRHR mutant under the control of a tetracycline (OFF) transactivator. This allows us to quantitate the level of functional and properly trafficked G protein coupled receptors present in each test well. Furthermore, since we are able to turn receptor expression on and off, we can rapidly eliminate the majority of false positives from our screening results. Our data show that this approach is likely to be successful in identifying hits from large chemical libraries.

Oxime bond-linked daunorubicin-GnRH-III bioconjugates exert antitumor activity in castration-resistant prostate cancer cells via the type I GnRH receptor

It is well established that gonadotropin-releasing hormone receptors (GnRH-R) are expressed in different types of cancers, including castration-resistant prostate cancer (CRPC) and mediate the antiproliferative effect of GnRH analogs. Thus, these compounds are employed as targeting moieties to selectively deliver chemotherapeutic agents to cancer cells. GnRH-III, the decapeptide isolated from the sea lamprey brain, has lower potency than GnRH in stimulating gonadotropin secretion, but it exerts antiproliferative effects on many tumors expressing the GnRH-R. GnRH-III-based peptides are considered promising targeting moieties for the preparation of anticancer drug delivery systems. These studies were aimed at i) evaluating the antitumor activity of two cytotoxic oxime bond-linked daunorubicin (Dau)-GnRH-III derivative bioconjugates (Dau-GnRH-III, in which daunorubicin was coupled to the 8Lys in the native form of GnRH-III, and Dau-[4Lys(Ac)]-GnRH-III, in which daunorubicin was attached to the 8Lys of a GnRH-III derivative where 4Ser was replaced by an acetylated lysine) on CRPC cells; and ii) to elucidate the involvement of the classical GnRH-R (type I GnRH-R) in this antitumor activity. Our results demonstrated that both Dau-GnRH-III and Dau-[4Lys(Ac)]-GnRH-III were rapidly internalized into DU145 prostate cancer cells and exerted a significant cytostatic effect. Both bioconjugates increased the levels of the active form of caspase-3, indicating the involvement of apoptosis in their antitumor activity. The antiproliferative effect of both Dau-GnRH-III and Dau-[4Lys(Ac)]-GnRH-III was counteracted by the simultaneous treatment of the cells with Antide, an antagonist of the GnRH-R. Moreover, after silencing the type I GnRH-R the antitumor activity of both bioconjugates was completely abolished. These data demonstrate that in CRPC cells, daunorubicin-GnRH-III derivative bioconjugates: i) inhibit tumor cell proliferation, by triggering the apoptosis process; ii) exert their antitumor effect through the activation of the type I GnRH-R expressed on these cells. Cytotoxic-GnRH-III derivative may represent promising targeted chemotherapeutics for the treatment of CRPC patients.

Chaperoning G protein-coupled receptors: from cell biology to therapeutics

G protein-coupled receptors (GPCRs) are membrane proteins that traverse the plasma membrane seven times (hence, are also called 7TM receptors). The polytopic structure of GPCRs makes the folding of GPCRs difficult and complex. Indeed, many wild-type GPCRs are not folded optimally, and defects in folding are the most common cause of genetic diseases due to GPCR mutations. Both general and receptor-specific molecular chaperones aid the folding of GPCRs. Chemical chaperones have been shown to be able to correct the misfolding in mutant GPCRs, proving to be important tools for studying the structure-function relationship of GPCRs. However, their potential therapeutic value is very limited. Pharmacological chaperones (pharmacoperones) are potentially important novel therapeutics for treating genetic diseases caused by mutations in GPCR genes that resulted in misfolded mutant proteins. Pharmacoperones also increase cell surface expression of wild-type GPCRs; therefore, they could be used to treat diseases that do not harbor mutations in GPCRs. Recent studies have shown that indeed pharmacoperones work in both experimental animals and patients. High-throughput assays have been developed to identify new pharmacoperones that could be used as therapeutics for a number of endocrine and other genetic diseases.

Prostate cancer relevant antigens and enzymes for targeted drug delivery

Chemotherapy is one of the most widely used approaches in combating advanced prostate cancer, but its therapeutic efficacy is usually insufficient due to poor specificity and associated toxicity. Lack of targeted delivery to prostate cancer cells is also the primary obstacles in achieving feasible therapeutic effect of other promising agents including peptide, protein, and nucleic acid. Consequently, there remains a critical need for strategies to increase the selectivity of anti-prostate cancer agents. This review will focus on various prostate cancer-relevant antigens and enzymes that could be exploited for prostate cancer targeted drug delivery. Among various targeting strategies, active targeting is the most advanced approach to specifically deliver drugs to their designated cancer cells. In this approach, drug carriers are modified with targeting ligands that can specifically bind to prostate cancer-specific antigens. Moreover, there are several specific enzymes in the tumor microenvironment of prostate cancer that can be exploited for stimulus-responsive drug delivery systems. These systems can specifically release the active drug in the tumor microenvironment of prostate cancer, leading to enhanced tumor penetration efficiency.

Gonadotropin-releasing hormone agonists sensitize, and resensitize, prostate cancer cells to docetaxel in a p53-dependent manner

Gonadotropin-releasing hormone (GnRH) receptors are expressed in prostate cancer, specifically in the most aggressive stage of the tumor (castration-resistant prostate cancer, CRPC) for which the standard treatment, docetaxel-based chemotherapy, can only improve the median survival time by few months. We previously showed that GnRH agonists exert an antitumor activity in CRPC cells; however, a link between GnRH receptors and the apoptotic machinery remains to be defined. Aim of this study was to evaluate whether, in CRPC cells, GnRH agonists might affect the expression/activity of apoptosis-related proteins and might sensitize, or resensitize, cancer cells to chemotherapeutics. We demonstrated that, in p53-positive DU145 cells, GnRH agonists: a) increase the expression of the proapoptotic protein Bax; this effect is mediated by the phosphorylation (activation) of p53, triggered by the p38 MAPK; b) potentiate the antiproliferative/proapoptotic activity of docetaxel; c) resensitize docetaxel-resistant cells to the antitumor activity of the cytotoxic drug. These data indicate that GnRH agonists sensitize and, more importantly, resensitize DU145 CRPC cells to chemotherapy in a p53-dependent manner. To confirm the crucial role of p53 in the activity of GnRH agonists, experiments were performed in p53-null PC3 cells. We found that GnRH agonists fail to increase Bax expression and do not potentiate the cytotoxic activity of docetaxel. These results may provide a rationale for novel combination treatment strategies, especially for docetaxel-resistant CRPC patients expressing a functional p53 protein.

Differential signaling of the GnRH receptor in pituitary gonadotrope cell lines and prostate cancer cell lines

The GnRH receptor (GnRHR) mediates the pituitary functions of GnRH, as well as its anti-proliferative effects in sex hormone-dependent cancer cells. Here we compare the signaling of GnRHR in pituitary gonadotrope cell lines vs. prostate cancer cell lines. We first noticed that the expression level of PKCα, PKCβII and PKCε is much higher in αT3-1 and LβT2 gonadotrope cell lines vs. LNCaP and DU-145 cell lines, while the opposite is seen for PKCδ. Activation of PKCα, PKCβII and PKCε by GnRH is relatively transient in αT3-1 and LβT2 gonadotrope cell lines and more prolonged in LNCaP and DU-145 cell lines. On the otherhand, the activation and re-distribution of the above PKCs by PMA was similar for both gonadotrope cell lines and prostate cancer cell lines. Activation of ERK1/2 by GnRH and PMA was robust in the gonadotrope cell lines, with a smaller effect observed in the prostate cancer cell lines. The Ca(2+) ionophore A23187 stimulated ERK1/2 in gonadotrope cell lines but not in prostate cancer cell lines. GnRH, PMA and A23187 stimulated JNK activity in gonadotrope cell lines, with a more sustained effect in prostate cancer cell lines. Sustained activation of p38 was observed for PMA and A23187 in Du-145 cells, while p38 activation by GnRH, PMA and A23187 in LβT2 cells was transient. Thus, differential expression and re-distribution of PKCs by GnRH and the transient vs. the more sustained nature of the activation of the PKC-MAPK cascade by GnRH in gonadotrope cell lines vs. prostate cancer cell lines respectively, may provide the mechanistic basis for the cell context-dependent differential biological responses observed in GnRH interaction with pituitary gonadotropes vs. prostate cancer cells.

Gonadotropin-releasing hormone neuropeptides and receptor in human breast cancer: correlation to poor prognosis parameters

Expression of the two gonadotropin-releasing hormone homologue peptides GnRHI and GnRHII and their receptor GnRHR has been demonstrated in a number of malignancies. In hormone-dependent breast cancer, GnRH analogs are used for therapy in premenopausal women. Gene expression of GnRHI, II and R was studied in breast biopsies from primary breast adenocarcinoma obtained from the tumor and the adjacent benign tissue. Levels were evaluated by a multiplex real-time RT-PCR. GnRHI transcripts were detected in 14.7% of the benign and 29.4% malignant biopsies and GnRHII in 21.2% benign and 44.1% malignant biopsies. GnRHR was also more frequent in the malignant (54.2%) than in the benign (24.0%) biopsies, at similar expression levels. No transcripts were detected in biopsies from healthy individuals. There was a strong correlation between the presence of GnRHI and GnRHII transcripts and their receptor in the benign and the malignant biopsies. GnRHI, II and R expression correlated significantly with poor prognosis pathological parameters. Immunohistochemistry for GnRHR revealed expression in malignant cells and in epithelial cells of mammary ducts of the adjacent area with pre-cancerous features. In contrast, GnRH I and II peptides were rarely expressed at low levels in breast cancer cells. In conclusion GnRH peptides and receptor are expressed more frequently in breast tumors than in the adjacent mammary tissue, representing a malignant feature. Their expression correlated to tumor characteristics of poor prognosis and was therefore related to more aggressive malignancies. Concomitant expression of peptides and receptor supports an autocrine/paracrine regulating role.

Pharmacoperone IN3 enhances the apoptotic effect of leuprolide in prostate cancer cells by increasing the gonadotropin-releasing hormone receptor in the cell membrane

Gonadotropin-releasing hormone (GnRH) agonists are widely used for the treatment of advanced prostate cancer (PCa). Agonists activate the GnRH receptor (GnRH-R), triggering apoptosis in PCa cells. In gonadotropes, the amount of GnRH-R in the plasma membrane is regulated by protein folding and endoplasmic reticulum retention, mechanisms that can be overcome by the pharmacoperone IN3. Our aim was to describe the intracellular distribution of GnRH-R in PCa cells and its relation to response to GnRH analog treatments. The expressions of GnRH-R in PCa biopsies were evaluated by immunohistochemistry and the intracellular distribution was determined by immunofluorescence in primary cell cultures from human PCa samples. Cultured cells were pretreated with IN3 and then with leuprolide. Cell survival was evaluated by 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) thiazolyl blue formazan and cell cycle and apoptosis by flow cytometry. We observed that the expression of GnRH-R decreased according to malignant progression. Most GnRH-R are located inside the cell, colocalizing with endoplasmic reticulum markers. The treatment with IN3 decreased cellular GnRH-R retention, increasing plasma membrane expression in approximately 60%. Pretreatment with IN3 decreased PCa cell survival compared with leuprolide-alone treatment, primarily because of an increase in apoptosis. We conclude that the response of PCa cells to leuprolide is related to the amount of GnRH-R in the plasma membrane. Therefore, pretreatment evaluation of the amount of these receptors may be a predictor of the outcome of leuprolide treatment in PCa patients. Assessment of systemic IN3 effect would be necessary to determine its utility as an adjuvant treatment in hormone-resistant tumors.

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.

Gonadotropin-releasing hormone receptor activates GTPase RhoA and inhibits cell invasion in the breast cancer cell line MDA-MB-231

Background

Gonadotropin-releasing hormone (GnRH) and its receptor (GnRHR) are both expressed by a number of malignant tumors, including those of the breast. In the latter, both behave as potent inhibitors of invasion. Nevertheless, the signaling pathways whereby the activated GnRH/GnRHR system exerts this effect have not been clearly established. In this study, we provide experimental evidence that describes components of the mechanism(s) whereby GnRH inhibits breast cancer cell invasion.

Methods

Actin polymerization and substrate adhesion was measured in the highly invasive cell line, MDA-MB-231 transiently expressing the wild-type or mutant DesK191 GnRHR by fluorometry, flow cytometric analysis, and confocal microscopy, in the absence or presence of GnRH agonist. The effect of RhoA-GTP on stress fiber formation and focal adhesion assembly was measured in MDA-MB-231 cells co-expressing the GnRHRs and the GAP domain of human p190Rho GAP-A or the dominant negative mutant GAP-Y1284D. Cell invasion was determined by the transwell migration assay.

Results

Agonist-stimulated activation of the wild-type GnRHR and the highly plasma membrane expressed mutant GnRHR-DesK191 transiently transfected to MDA-MB-231 cells, favored F-actin polymerization and substrate adhesion. Confocal imaging allowed detection of an association between F-actin levels and the increase in stress fibers promoted by exposure to GnRH. Pull-down assays showed that the effects observed on actin cytoskeleton resulted from GnRH-stimulated activation of RhoA GTPase. Activation of this small G protein favored the marked increase in both cell adhesion to Collagen-I and number of focal adhesion complexes leading to inhibition of the invasion capacity of MDA-MB-231 cells as disclosed by assays in Transwell Chambers.

Conclusions

We here show that GnRH inhibits invasion of highly invasive breast cancer-derived MDA-MB-231 cells. This effect is mediated through an increase in substrate adhesion promoted by activation of RhoA GTPase and formation of stress fibers and focal adhesions. These observations offer new insights into the molecular mechanisms whereby activation of overexpressed GnRHRs affects cell invasion potential of this malignant cell line, and provide opportunities for designing mechanism-based adjuvant therapies for breast cancer.

GnRH receptors in cancer: from cell biology to novel targeted therapeutic strategies

The crucial role of pituitary GnRH receptors (GnRH-R) in the control of reproductive functions is well established. These receptors are the target of GnRH agonists (through receptor desensitization) and antagonists (through receptor blockade) for the treatment of steroid-dependent pathologies, including hormone-dependent tumors. It has also become increasingly clear that GnRH-R are expressed in cancer tissues, either related (i.e. prostate, breast, endometrial, and ovarian cancers) or unrelated (i.e. melanoma, glioblastoma, lung, and pancreatic cancers) to the reproductive system. In hormone-related tumors, GnRH-R appear to be expressed even when the tumor has escaped steroid dependence (such as castration-resistant prostate cancer). These receptors are coupled to a G(αi)-mediated intracellular signaling pathway. Activation of tumor GnRH-R by means of GnRH agonists elicits a strong antiproliferative, antimetastatic, and antiangiogenic (more recently demonstrated) activity. Interestingly, GnRH antagonists have also been shown to elicit a direct antitumor effect; thus, these compounds behave as antagonists of GnRH-R at the pituitary level and as agonists of the same receptors expressed in tumors. According to the ligand-induced selective-signaling theory, GnRH-R might assume various conformations, endowed with different activities for GnRH analogs and with different intracellular signaling pathways, according to the cell context. Based on these consistent experimental observations, tumor GnRH-R are now considered a very interesting candidate for novel molecular, GnRH analog-based, targeted strategies for the treatment of tumors expressing these receptors. These agents include GnRH agonists and antagonists, GnRH analog-based cytotoxic (i.e. doxorubicin) or nutraceutic (i.e. curcumin) hybrids, and GnRH-R-targeted nanoparticles delivering anticancer compounds.

New Agonist- and Antagonist-Based Treatment Approaches for Advanced Prostate Cancer

Increased understanding of prostate cancer biology has led to new treatment strategies and promising new agents for treating prostate cancer, in particular peptide-based agonists and antagonists. In this review article, new therapy modalities and potential approaches for the treatment of advanced prostate cancer are discussed, including agonists and antagonists of luteinizing hormone-releasing hormone, antagonists of bombesin/gastrin-releasing peptide, and growth hormone-releasing hormone and somatostatin analogues. Though the prognosis of patients with prostate cancer is much improved by some of these treatment approaches, including combination treatment methods, extensive side-effects are still reported. These include sexual dysfunction, functional lesions of the liver and renal system, osteoporosis, anaemia and diarrhoea. Future studies should focus on new treatment agents and treatment approaches that can eliminate side-effects and improve quality of life in patients with prostate cancer on the basis of potent treatment efficacy.

Novel drug targets for the pharmacotherapy of benign prostatic hyperplasia (BPH)

Benign prostatic hyperplasia (BPH) is the major cause of lower urinary tract symptoms in men aged 50 or older. Symptoms are not normally life threatening, but often drastically affect the quality of life. The number of men seeking treatment for BPH is expected to grow in the next few years as a result of the ageing male population. Estimates of annual pharmaceutical sales of BPH therapies range from $US 3 to 10 billion, yet this market is dominated by two drug classes. Current drugs are only effective in treating mild to moderate symptoms, yet despite this, no emerging contenders appear to be on the horizon. This is remarkable given the increasing number of patients with severe symptoms who are required to undergo invasive and unpleasant surgery. This review provides a brief background on prostate function and the pathophysiology of BPH, followed by a brief description of BPH epidemiology, the burden it places on society, and the current surgical and pharmaceutical therapies. The recent literature on emerging contenders to current therapies and novel drug targets is then reviewed, focusing on drug targets which are able to relax prostatic smooth muscle in a similar way to the α(1) -adrenoceptor antagonists, as this appears to be the most effective mechanism of action. Other mechanisms which may be of benefit are also discussed. It is concluded that recent basic research has revealed a number of novel drug targets such as muscarinic receptor or P2X-purinoceptor antagonists, which have the potential to produce more effective and safer drug treatments.

A novel indium-111-labeled gonadotropin-releasing hormone peptide for human prostate cancer imaging

The purpose of this study was to evaluate the tumor targeting and imaging properties of a novel (111)In-labeled gonadotropin-releasing hormone (GnRH) peptide {1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-Ahx-(D-Lys(6)-GnRH1)} for human prostate cancer. The biodistribution and tumor imaging properties of (111)In-DOTA-Ahx-(D-Lys(6)-GnRH1) were determined in DU145 human prostate cancer-xenografted nude mice. (111)In-DOTA-Ahx-(d-Lys(6)-GnRH1) exhibited rapid tumor uptake (1.27 ± 0.40% ID/g at 0.5h post-injection) coupled with fast whole-body clearance through the urinary system. The DU145 human prostate cancer-xenografted tumor lesions were clearly visualized by single photon emission computed tomography (SPECT)/CT at 0.5h post-injection of (111)In-DOTA-Ahx-(D-Lys(6)-GnRH1). The successful imaging of DU145 human prostate cancer-xenografted tumor lesions using (111)In-DOTA-Ahx-(d-Lys(6)-GnRH1) highlighted its potential as a novel imaging probe for human prostate cancer imaging.

Dual targeting of tumor and endothelial cells by gonadotropin-releasing hormone agonists to reduce melanoma angiogenesis

We showed previously that GnRH receptors are expressed in melanoma cells; their activation reduces cell growth and metastatic behavior. Here, we investigated whether GnRH agonists might affect the expression of genes involved in melanoma progression. By genome-wide transcriptomic and real-time PCR analysis, we first observed that GnRH agonists decrease the expression of the pro-angiogenic factor vascular endothelial growth factor (VEGF) (all isoforms) in BLM melanoma cells. Then, we demonstrated that GnRH agonists specifically decrease the expression of the VEGF165 isoform as well as its secretion from BLM cells. These data suggested that activation of GnRH receptors might reduce the pro-angiogenic behavior of melanoma cells. To verify this hypothesis, we treated BLM cells with a GnRH agonist; the conditioned medium from these cells was tested to assess its capability to stimulate human umbilical vein endothelial cell (HUVEC) motility. The migration of HUVECs towards the conditioned medium of GnRH agonist-treated BLM cells was significantly lower than the migration of HUVECs toward the conditioned medium of untreated cells. Thus, GnRH agonists reduce the pro-angiogenic behavior of melanoma cells through a decreased production of bioactive VEGF. We then found that GnRH receptors are also expressed on HUVECs and that GnRH agonists reduce their ability to proliferate and to form capillary-like tubes when stimulated by VEGF. These findings suggest that GnRH agonists exert an anti-angiogenic activity indirectly by decreasing VEGF secretion from tumor cells and directly by counteracting the pro-angiogenic activity of the growth factor. These data might lead to the development of novel targeted approaches for melanoma.

Differential role of PKC isoforms in GnRH and phorbol 12-myristate 13-acetate activation of extracellular signal-regulated kinase and Jun N-terminal kinase

GnRH is the first key hormone of reproduction. The role of protein kinase C (PKC) isoforms in GnRH-stimulated MAPK [ERK and Jun N-terminal kinase (JNK)] was examined in the αT3-1 and LβT2 gonadotrope cells. Incubation of the cells with GnRH resulted in a protracted activation of ERK1/2 and a slower and more transient activation of JNK1/2. Gonadotropes express conventional PKCα and conventional PKCβII, novel PKCδ, novel PKCε, and novel PKCθ, and atypical PKC-ι/λ. The use of green fluorescent protein-PKC constructs revealed that GnRH induced rapid translocation of PKCα and PKCβII to the plasma membrane, followed by their redistribution to the cytosol. PKCδ and PKCε localized to the cytoplasm and Golgi, followed by the rapid redistribution by GnRH of PKCδ to the perinuclear zone and of PKCε to the plasma membrane. Interestingly, PKCα, PKCβII, and PKCε translocation to the plasma membrane was more pronounced and more prolonged in phorbol-12-myristate-13-acetate (PMA) than in GnRH-treated cells. The use of selective inhibitors and dominant-negative plasmids for the various PKCs has revealed that PKCβII, PKCδ, and PKCε mediate ERK2 activation by GnRH, whereas PKCα, PKCβII, PKCδ, and PKCε mediate ERK2 activation by PMA. Also, PKCα, PKCβII, PKCδ, and PKCε are involved in GnRH and PMA stimulation of JNK1 in a cell-context-dependent manner. We present preliminary evidence that persistent vs. transient redistribution of selected PKCs or redistribution of a given PKC to the perinuclear zone vs. the plasma membrane may dictate its selective role in ERK or JNK activation. Thus, we have described the contribution of selective PKCs to ERK and JNK activation by GnRH.

Odors activate dual pathways, a TRPC2 and a AA-dependent pathway, in mouse vomeronasal neurons

Located at the anterior portion of the nose, the paired vomeronasal organs (VNO) detect odors and pheromones. In vomeronasal sensory neurons (VSNs) odor responses are mainly mediated by phospholipase C (PLC), stimulation of which elevates diacylglycerol (DAG). DAG activates a transient receptor potential channel (TRPC2) leading to cell depolarization. In this study, we used a natural stimulus, urine, to elicit odor responses in VSNs and found urine responses persisted in TRPC2(-/-) mice, suggesting the existence of a TRPC2-independent signal transduction pathway. Using perforated patch-clamp recordings on isolated VSNs from wild-type (WT) and TRPC2(-/-) mice, we found a PLC inhibitor blocked urine responses from all VSNs. Furthermore, urine responses were reduced by blocking DAG lipase, an enzyme that produces arachidonic acid (AA), in WT mice and abolished in TRPC2(-/-) mice. Consistently, direct stimulation with AA activated an inward current that was independent of TRPC2 channels but required bath Ca(2+) and was blocked by Cd(2+). With the use of inside-out patches from TRPC2(-/-) VSNs, we show that AA activated a channel that also required Ca(2+). Together, these data from WT and TRPC2(-/-) mice suggest that both DAG and its metabolite, AA, mediate excitatory odor responses in VSNs, by activating two types of channels, a TRPC2 and a separate Ca(2+)-permeable channel.

GnRH receptor expression in human prostate cancer cells is affected by hormones and growth factors

GnRH receptors (GnRH-R) have been found in various malignancies, including prostate cancer (PCa). They mediate the direct antitumor effects of GnRH analogs. Nevertheless, few reports concern drug-induced modulation of GnRH-R levels. In this study, we investigated GnRH-R expression in androgen-sensitive (LNCaP) and -insensitive (PC-3) PCa cells treated for 4 and 6 days with a GnRH agonist (Leuprorelin acetate, LA, 10(-11) or 10(-6) M), Dihydrotestosterone (DHT, 10(-9) M), Cyproterone acetate (CA, 10(-7) M), and Epidermal growth factor (EGF, 10 ng/ml), either alone or combined. The RT-PCR analysis showed no variation in GnRH-R mRNA levels of both treated LNCaP and PC-3 cells. On the contrary, immunoblotting indicated that in LNCaP and PC-3 cells, LA upregulated membrane GnRH-R expression (up to 92%). In androgen-sensitive cells, DHT induced a GnRH-R increase (up to 119%) always comparable to that occurring in the presence of CA. GnRH-R upregulation by LA/DHT or CA/DHT association was similar to that promoted by the single agents. In PC-3 cells, EGF upregulated GnRH-R (up to 110%). A prolonged treatment (for 12 days) determined a greater EGF-induced increase in GnRH-R levels (142%). Lower (or no) receptor enhancement occurred when LA and EGF were associated. Our findings indicate that LA post-transcriptionally upregulates its own membrane receptor in androgen-sensitive and -insensitive PCa cells, counteracting the receptor enhancement produced by DHT and EGF. The effects, obtained with a relatively long and continuous treatment, may have implications in the choice of therapy modality with GnRH analogs and may render the receptor a novel therapeutic target, particularly in hormone-refractory PCa.

Type I gonadotropin-releasing hormone receptor mediates the antiproliferative effects of GnRH-II on prostate cancer cells

BACKGROUND

GnRH-II has been shown to exert a strong antiproliferative action on tumors of the female reproductive system. The data so far reported on the effects of GnRH-II on prostate cancer growth are controversial. Moreover, it is still unclear through which receptor [type I or type II GnRH-receptor (GnRH-R)] GnRH-II might modulate cancer cell proliferation.

OBJECTIVE

The objective of this work was to investigate whether GnRH-II might affect the proliferation of prostate cancer cells and to identify the GnRH-R through which the peptide might exert its activity.

DESIGN

We investigated the effects of GnRH-II on prostate cancer cell proliferation. We then transfected PC3 cells with a small interfering RNA targeted to type I GnRH-R. After receptor silencing we evaluated the effects of GnRH-II on cell proliferation and on forskolin-induced intracellular cAMP accumulation. Similar experiments were performed by silencing type II GnRH-R.

RESULTS

GnRH-II exerted an antiproliferative activity on prostate cancer cells. Transfection of PC3 cells with a type I GnRH-R small interfering RNA resulted in a significant decrease of the expression of this receptor. After type I GnRH-R silencing: 1) the antiproliferative effect of GnRH-II was completely abrogated; and 2) GnRH-II lost its capacity to counteract the forskolin-induced cAMP accumulation. On the contrary, type II GnRH-R silencing did not counteract the antiproliferative effect of GnRH-II.

CONCLUSIONS

GnRH-II exerts a specific and significant antiproliferative action on prostate cancer cells. This antitumor effect is mediated by the activation of type I (but not of type II) GnRH-R and by its coupled cAMP intracellular signaling pathway.

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.

Effect of LHRH-PE40 on target cells via LHRH receptors

OBJECTIVE

To detect the effect and cytotoxicity of luteinizing hormone-releasing hormone-Pseudomonas aeruginosa exotoxin 40 (LHRH-PE40) on target cells using LHRH receptors (LHRHR).

METHODS

The affinity of LHRH-PE40 and LHRH binding to LHRHR on the membrane surface of target cells were measured by enzyme linked immunosorbent assay. Morphological observations with light microscope were used to analyze its receptor pathway, with Spiegelmer, and cytotoxicity. IC(50) values of LHRH-PE40, which caused 50% inhibition of tumor cell growth were evaluated by MTT assay. The target cells were exposed to LHRH-PE40 and its cytotoxicity was analyzed by scanning and transmission electron microscopies, agarose gel electrophoresis, and flow cytometry.

RESULTS

LHRH-PE40 killed target cells by LHRHR pathway. The morphological changes in these cells showed decreased cell size, cytoplasmic membrane blebbing, and chromatin condensation and margination. At a certain concentration and time point, HeLa cells were also induced to undergo programmed cell death.

CONCLUSION

LHRH-PE40 induced target cells apoptosis via LHRHR.

Gonadotropin-releasing hormone analog structural determinants of selectivity for inhibition of cell growth: support for the concept of ligand-induced selective signaling

GnRH and its receptor are expressed in human reproductive tract cancers, and direct antiproliferative effects of GnRH analogs have been demonstrated in cancer cell lines. The intracellular signaling responsible for this effect differs from that mediating pituitary gonadotropin secretion. The GnRH structure-activity relationship is different for the two effects. Here we report a structure-activity relationship study of GnRH agonist antiproliferative action in model cell systems of rat and human GnRH receptors stably expressed in HEK293 cells. GnRH II was more potent than GnRH I in inhibiting cell growth in the cell lines. In contrast, GnRH I was more potent than GnRH II in stimulating inositol phosphate production, the signaling pathway in gonadotropes. The different residues in GnRH II (His(5), Trp(7), Tyr(8)) were introduced singly or in pairs into GnRH I. Tyr(5) replacement by His(5) produced the highest increase in the antiproliferative potency of GnRH I. Tyr(8) substitution of Arg(8) produced the most selective analog, with very poor inositol phosphate generation but high antiproliferative potency. In nude mice bearing tumors of the HEK293 cell line, GnRH II and an antagonist administration was ineffective in inhibiting tumor growth, but D-amino acid stabilized analogs (D-Lys(6) and D-Arg(6)) ablated tumor growth. Docking of GnRH I and GnRH II to the human GnRH receptor molecular model revealed that Arg(8) of GnRH I makes contact with Asp(302), whereas Tyr(8) of GnRH II appears to make different contacts, suggesting these residues stabilize different receptor conformations mediating differential intracellular signaling and effects on gonadotropin and cell growth. These findings provide the basis for the development of selective GnRH analog cancer therapeutics that directly target tumor cells or inhibit pituitary gonadotropins or do both.

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.

Diversity of actions of GnRHs mediated by ligand-induced selective signaling

Geoffrey Wingfield Harris' demonstration of hypothalamic hormones regulating pituitary function led to their structural identification and therapeutic utilization in a wide spectrum of diseases. Amongst these, Gonadotropin Releasing Hormone (GnRH) and its analogs are widely employed in modulating gonadotropin and sex steroid secretion to treat infertility, precocious puberty and many hormone-dependent diseases including endometriosis, uterine fibroids and prostatic cancer. While these effects are all mediated via modulation of the pituitary gonadotrope GnRH receptor and the G(q) signaling pathway, it has become increasingly apparent that GnRH regulates many extrapituitary cells in the nervous system and periphery. This review focuses on two such examples, namely GnRH analog effects on reproductive behaviors and GnRH analog effects on the inhibition of cancer cell growth. For both effects the relative activities of a range of GnRH analogs is distinctly different from their effects on the pituitary gonadotrope and different signaling pathways are utilized. As there is only a single functional GnRH receptor type in man we have proposed that the GnRH receptor can assume different conformations which have different selectivity for GnRH analogs and intracellular signaling proteins complexes. This ligand-induced selective-signaling recruits certain pathways while by-passing others and has implications in developing more selective GnRH analogs for highly specific therapeutic intervention.