Gonadotropin-releasing hormone receptor expression in the human prostate

Gonadotropin-Releasing Hormone Receptor (GnRHR) and Hypogonadotropic Hypogonadism

Human sexual and reproductive development is regulated by the hypothalamic-pituitary-gonadal (HPG) axis, which is primarily controlled by the gonadotropin-releasing hormone (GnRH) acting on its receptor (GnRHR). Dysregulation of the axis leads to conditions such as congenital hypogonadotropic hypogonadism (CHH) and delayed puberty. The pathophysiology of GnRHR makes it a potential target for treatments in several reproductive diseases and in congenital adrenal hyperplasia. GnRHR belongs to the G protein-coupled receptor family and its GnRH ligand, when bound, activates several complex and tissue-specific signaling pathways. In the pituitary gonadotrope cells, it triggers the G protein subunit dissociation and initiates a cascade of events that lead to the production and secretion of the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) accompanied with the phospholipase C, inositol phosphate production, and protein kinase C activation. Pharmacologically, GnRHR can be modulated by synthetic analogues. Such analogues include the agonists, antagonists, and the pharmacoperones. The agonists stimulate the gonadotropin release and lead to receptor desensitization with prolonged use while the antagonists directly block the GnRHR and rapidly reduce the sex hormone production. Pharmacoperones include the most recent GnRHR therapeutic approaches that directly correct the misfolded GnRHRs, which are caused by genetic mutations and hold serious promise for CHH treatment. Understanding of the GnRHR's genomic and protein structure is crucial for the most appropriate assessing of the mutation impact. Such mutations in the GNRHR are linked to normosmic hypogonadotropic hypogonadism and lead to various clinical symptoms, including delayed puberty, infertility, and impaired sexual development. These mutations vary regarding their mode of inheritance and can be found in the homozygous, compound heterozygous, or in the digenic state. GnRHR expression extends beyond the pituitary gland, and is found in reproductive tissues such as ovaries, uterus, and prostate and non-reproductive tissues such as heart, muscles, liver and melanoma cells. This comprehensive review explores GnRHR's multifaceted role in human reproduction and its clinical implications for reproductive disorders.

Peptides as multifunctional players in cancer therapy

Peptides exhibit lower affinity and a shorter half-life in the body than antibodies. Conversely, peptides demonstrate higher efficiency in tissue penetration and cell internalization than antibodies. Regardless of the pros and cons of peptides, they have been used as tumor-homing ligands for delivering carriers (such as nanoparticles, extracellular vesicles, and cells) and cargoes (such as cytotoxic peptides and radioisotopes) to tumors. Additionally, tumor-homing peptides have been conjugated with cargoes such as small-molecule or chemotherapeutic drugs via linkers to synthesize peptide-drug conjugates. In addition, peptides selectively bind to cell surface receptors and proteins, such as immune checkpoints, receptor kinases, and hormone receptors, subsequently blocking their biological activity or serving as hormone analogs. Furthermore, peptides internalized into cells bind to intracellular proteins and interfere with protein-protein interactions. Thus, peptides demonstrate great application potential as multifunctional players in cancer therapy.

Conventional and new proposals of GnRH therapy for ovarian, breast, and prostatic cancers

For many years, luteinizing hormone-releasing hormone or gonadotropin-releasing hormone (GnRH) analogs have been used to treat androgen or estrogen-dependent tumors. However, emerging evidence shows that the GnRH receptor (GnRH-R) is overexpressed in several cancer cells, including ovarian, endometrial, and prostate cancer cells, suggesting that GnRH analogs could exert direct antitumoral actions in tumoral tissues that express GnRH-R. Another recent approach based on this knowledge was the use of GnRH peptides for developing specific targeted therapies, improving the delivery and accumulation of drugs in tumoral cells, and decreasing most side effects of current treatments. In this review, we discuss the conventional uses of GnRH analogs, together with the recent advances in GnRH-based drug delivery for ovarian, breast, and prostatic cancer cells.

LHRH-Targeted Redox-Responsive Crosslinked Micelles Impart Selective Drug Delivery and Effective Chemotherapy in Triple-Negative Breast Cancer

Systemic chemotherapy is efficacious against triple-negative breast cancer (TNBC), but it is often associated with serious side effects. Here, a luteinizing hormone-releasing hormone (LHRH) receptor-targeted and tumor microenvironment-responsive nanoparticle system to selectively deliver chemotherapeutic drugs to TNBC cells, is reported. This delivery system (termed "LHRH-DCMs") contains poly(ethylene glycol) and dendritic cholic acid as a micellar carrier, reversible intra-micellar disulfide bond as a redox-responsive crosslink, and synthetic high-affinity (D-Lys)-LHRH peptide as a targeting moiety. LHRH-DCMs exhibit high drug loading efficiency, optimal particle size, good colloidal stability, and glutathione-responsive drug release. As expected, LHRH-DCMs are more efficiently internalized into human TNBC cells through receptor-mediated endocytosis, resulting in stronger cytotoxicity against these cancer cells than the non-targeted counterpart when encapsulated with paclitaxel (PTX). Furthermore, near-infrared fluorescence and magnetic resonance imaging demonstrate that LHRH-DCMs facilitate the tumor distribution and penetration of payloads in three different animal models of breast cancer, including cell line-derived xenograft (CDX), patient-derived xenograft (PDX), and transgenic mammary carcinoma. Finally, in vivo therapeutic studies show that PTX-LHRH-DCMs outperform both the corresponding nontargeted PTX-DCMs and the current clinical formulation (Taxol) in an orthotopic TNBC model. These results provide new insights into approaches for precise drug delivery of TNBC.

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.

The targeted LHRH analog AEZS-108 alters expression of genes related to angiogenesis and development of metastasis in uveal melanoma

Uveal melanoma (UM) is the most common malignant tumor of the eye. Recently, we have established that 46% of UM specimens express LHRH receptors. This finding supports the idea of a LHRH receptor-targeted therapy of UM patients. Cytotoxic analog of LHRH, AEZS-108 exhibits effective anti-cancer activity in LHRH-receptor positive cancers. AEZS-108 is a hybrid molecule, composed of a synthetic peptide carrier and the cytotoxic doxorubicin (DOX). In the present study, we investigated AEZS-108 induced cytotoxicity and the altered mRNA expression profile of regulatory factors related to angiogenesis and metastasis in LHRH receptor positive OCM3 cells. Our results show that AEZS-108 upregulates the expression of MASPIN/SERPINB5 tumor suppressor gene, which is downregulated in normal uvea and UM specimens independently from the LHRH receptor-ligand interaction. AEZS-108 also substantially downregulates hypoxia-inducible factor 1 alpha (HIF1A) expression. In order to investigate the mechanism of the induction of MASPIN by AEZS-108, OCM3 cells were treated with free DOX, D-Lys⁶ LHRH analog, or AEZS-108. qRT- PCR analysis revealed in OCM3 cells that AEZS-108 is a more potent inducer of MASPIN than free DOX. In conclusion, we show for the first time that AEZS-108 has a major impact in the regulation of angiogenesis thus plays a potential role in tumor suppression. Taken together, our results support the development of novel therapeutic strategies for UM focusing on LHRH receptors.

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 and Evaluation of 18F-Labeled Peptide for Gonadotropin-Releasing Hormone Receptor Imaging

The gonadotropin-releasing hormone (GnRH) receptor is overexpressed in the majority of tumors of the human reproductive system. The purpose of this study was to develop an ¹⁸F-labeled peptide for tumor GnRH receptor imaging. In this study, the GnRH (pGlu¹-His²-Trp³-Ser⁴-Tyr⁵-Gly⁶-Leu⁷-Arg⁸-Pro⁹-Gly¹⁰-NH₂) peptide analogues FP-d-Lys⁶-GnRH (FP = 2-fluoropropanoyl) and NOTA-P-d-Lys⁶-GnRH (P = ethylene glycol) were designed and synthesized. The IC₅₀ values of FP-d-Lys⁶-GnRH and NOTA-P-d-Lys⁶-GnRH were 2.0 nM and 56.2 nM, respectively. 4-Nitrophenyl-2-[¹⁸F]fluoropropionate was conjugated to the ε-amino group of the d-lysine side chain of d-Lys⁶-GnRH to yield the new tracer [¹⁸F]FP-d-Lys⁶-GnRH with a decay-corrected yield of 8 ± 3% and a specific activity of 20−100 GBq/µmol (n=6). Cell uptake studies of [¹⁸F]FP-d-Lys⁶-GnRH in GnRH receptor-positive PC-3 cells and GnRH receptor-negative CHO-K1 cells indicated receptor-specific accumulation. Biodistribution and PET studies in nude mice bearing PC-3 xenografted tumors showed that [¹⁸F]FP-d-Lys⁶-GnRH was localized in tumors with a higher uptake than in surrounding muscle and heart tissues. Furthermore, the metabolic stability of [¹⁸F]FP-d-Lys⁶-GnRH was determined in mouse blood and PC-3 tumor homogenates at 1 h after tracer injection. The presented results indicated a potential of the novel tracer [¹⁸F]FP-d-Lys⁶-GnRH for tumor GnRH receptor imaging.

Small molecule targeted NIR dye conjugate for imaging LHRH receptor positive cancers

Overexpression of Luteinizing Hormone Releasing Hormone Receptor (LHRH-R) in various cancers and restricted expression of the receptor in healthy cells qualifies it as a valuable cancer biomarker. Previously, LHRH-R targeted peptides have been utilized to deliver attached payloads to LHRH-R expressing cancers. We report here for the first time the utilization of a small molecule non-peptidic ligand (BOEPL) of LHRH-R to deliver attached payloads to LHRH-R positive tumors. For this purpose, we linked the BOEPL ligand to a near infrared dye via various linkers. In vitro, these conjugates demonstrated low nanomolar binding affinity and in vivo they exhibited receptor-mediated uptake specifically in tumor tissue. Moreover, tumor uptake could be blocked by administration of excess unlabeled conjugate, and time course experiments showed retention of the dye conjugate in the tumor up to 12 h post injection. Because uptake of BOEPL-targeted NIR dye conjugates by nonmalignant organs/tissues was negligible and since the transient presence of targeted NIR dye in the kidneys was a result of clearance mechanism, we suggest that a BOEPL-targeted NIR dye might constitute a useful agent for fluorescence-guided surgery of LHRH-R positive cancers. Moreover, our results also provide proof of concept that BOEPL can be successfully used to deliver attached payloads to LHRH-R positive tumors in vivo.

Double-edged sword of gonadotropin-releasing hormone (GnRH): A novel role of GnRH in the multiple beneficial functions of endometrial stem cells

Gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of gonadotropins, which induce estrogen production and subsequent ovulation. Therefore, long-term GnRH exposure to regulate ovarian hyperstimulation is recognized as the gold standard for most in vitro fertilization (IVF) strategies. However, one of the most disappointing aspects of current IVF technology is relatively low rate (between 35 and 50%) of positive pregnancy outcomes, and the major reason for this high cancellation rate has not yet been revealed. Previous studies have demonstrated that resident stem cell deficiency limits the cyclic regenerative capacity of the endometrium and subsequently increases pregnancy failure rates. Therefore, we hypothesized that long-term GnRH exposure directly damages endometrial stem cells and consequently negatively affects pregnancy outcomes in GnRH-based IVF. In addition to their well-known roles in regulating the hypothalamus-pituitary-gonadal axis, GnRH and its receptors also localize in the extra-hypothalamic endometrium, suggesting a possible non-canonical role in endometrial stem cells. Consistent with our hypothesis, we show for the first time that GnRH suppresses the multiple beneficial functions of endometrial stem cells via the PI3K/Akt signaling pathway in vitro and in vivo. To the best of our knowledge, this is the first study to focus on the direct effects of GnRH on the regenerative potential of stem cells, and the findings will facilitate the development of more promising IVF strategies.

Buserelin alleviates chloride transport defect in human cystic fibrosis nasal epithelial cells

Cystic fibrosis (CF) is the most common autosomal recessive disease in Caucasians caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) chloride (Cl-) channel regulated by protein kinases, phosphatases, divalent cations and by protein-protein interactions. Among protein-protein interactions, we previously showed that Annexin A5 (AnxA5) binds to CFTR and is involved in the channel localization within membranes and in its Cl- channel function. The deletion of phenylalanine at position 508 (F508del) is the most common mutation in CF which leads to an altered protein (F508del-CFTR) folding with a nascent protein retained within the ER and is quickly degraded. We previously showed that AnxA5 binds to F508del-CFTR and that its increased expression due to a Gonadoliberin (GnRH) augments Cl- efflux in cells expressing F508del-CFTR. The aim of the present work was to use the GnRH analog buserelin which is already used in medicine. Human nasal epithelial cells from controls and CF patients (F508del/F508del) were treated with buserelin and we show here that the treatment alleviates Cl- channel defects in CF cells. Using proteomics we highlighted some proteins explaining this result. Finally, we propose that buserelin is a potential new pharmaceutical compound that can be used in CF and that bronchus can be targeted since we show here that they express GnRH-R.

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.

Gemcitabine Based Peptide Conjugate with Improved Metabolic Properties and Dual Mode of Efficacy

Gemcitabine is a clinically established anticancer agent potent in various solid tumors but limited by its rapid metabolic inactivation and off-target toxicity. We have previously generated a metabolically superior to gemcitabine molecule (GSG) by conjugating gemcitabine to a gonadotropin releasing hormone receptor (GnRH-R) ligand peptide and showed that GSG was efficacious in a castration resistant prostate cancer (CRPC) animal model. The current article provides an in-depth metabolic and mechanistic study of GSG, coupled with toxicity assays that strengthen the potential role of GSG in the clinic. LC-MS/MS based approaches were employed to delineate the metabolism of GSG, its mechanistic cellular uptake, and release of gemcitabine and to quantitate the intracellular levels of gemcitabine and its metabolites (active dFdCTP and inactive dFdU) resulting from GSG. The GnRH-R agonistic potential of GSG was investigated by quantifying the testosterone levels in animals dosed daily with GSG, while an in vitro colony forming assay together with in vivo whole blood measurements were performed to elucidate the hematotoxicity profile of GSG. Stability showed that the major metabolite of GSG is a more stable nonapeptide that could prolong gemcitabine's bioavailability. GSG acted as a prodrug and offered a metabolic advantage compared to gemcitabine by generating higher and steadier levels of dFdCTP/dFdU ratio, while intracellular release of gemcitabine from GSG in DU145 CRPC cells depended on nucleoside transporters. Daily administrations in mice showed that GSG is a potent GnRH-R agonist that can also cause testosterone ablation without any observed hematotoxicity. In summary, GSG could offer a powerful and unique pharmacological approach to prostate cancer treatment: a single nontoxic molecule that can be used to reach the tumor site selectively with superior to gemcitabine metabolism, biodistribution, and safety while also agonistically ablating testosterone levels.

Cardiovascular risk with androgen deprivation therapy for prostate cancer: potential mechanisms

Androgen deprivation therapy (ADT) is frequently used for the treatment of advanced prostate cancer. ADT is associated with numerous side effects related to its mode of action, namely the suppression of testosterone to castrate levels. Recently, several large retrospective studies have also reported an increased risk of diabetes and cardiovascular disease in men receiving ADT, although these risks have not been confirmed by prospective randomized trials. We review the literature to consider the risk of cardiovascular disease with different forms of ADT and examine in detail potential mechanisms by which any such risk could be mediated. Mechanisms discussed include the metabolic syndrome resulting from low testosterone level and the potential roles of testosterone flare, gonadotropin-releasing hormone receptors outside the pituitary gland, and altered levels of follicle-stimulating hormone. Finally, the clinical implications for men prescribed ADT for the treatment of advanced prostate cancer are considered.

Comparative in vitro biological evaluation of daunorubicin containing GnRH-I and GnRH-II conjugates developed for tumor targeting

Hormone based drug targeting is a promising tool for selective tumor therapy. In this study, synthesis and systematic comparative biological evaluation of novel drug containing analogs of gonadotropin-releasing hormone GnRH-I and GnRH-II is reported demonstrating their suitability for tumor targeting. The cytotoxic conjugates were prepared by the attachment of the chemotherapeutical agent daunorubicin (Dau) to GnRH analogs directly or through an enzyme-labile spacer with oxime linkage. All conjugates were found to be proteolytically stable under circumstances applied in biological assays. Both GnRH-I and GnRH-II were able to bind similarly to high-affinity GnRH-I receptors on human pituitary and human prostate cancer cells. The in vitro long-term cytotoxic effect of the conjugates was comparable with that of the free drug in human breast and colon cancer cell lines. Furthermore, a concentration-dependent cellular uptake profile was observed. The in vitro apoptotic effect of the compounds was evaluated by flow cytometry analysis using annexin-V. Our results show that both the GnRH-I and the GnRH-II based analogs might be applied for targeted tumor therapy.

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.

Improvement of chloride transport defect by gonadotropin-releasing hormone (GnRH) in cystic fibrosis epithelial cells

Cystic fibrosis (CF), the most common autosomal recessive disease in Caucasians, is due to mutations in the CFTR gene. F508del, the most frequent mutation in patients, impairs CFTR protein folding and biosynthesis. The F508del-CFTR protein is retained in the endoplasmic reticulum (ER) and its traffic to the plasma membrane is altered. Nevertheless, if it reaches the cell surface, it exhibits a Cl⁻ channel function despite a short half-life. Pharmacological treatments may target the F508del-CFTR defect directly by binding to the mutant protein or indirectly by altering cellular proteostasis, and promote its plasma membrane targeting and stability. We previously showed that annexine A5 (AnxA5) directly binds to F508del-CFTR and, when overexpressed, promotes its membrane stability, leading to the restoration of some Cl⁻ channel function in cells. Because Gonadotropin-Releasing Hormone (GnRH) increases AnxA5 expression in some cells, we tested it in CF cells. We showed that human epithelial cells express GnRH-receptors (GnRH-R) and that GnRH induces an AnxA5 overexpression and an increased Cl⁻ channel function in F508del-CFTR cells, due to an increased stability of the protein in the membranes. Beside the numerous physiological implications of the GnRH-R expression in epithelial cells, we propose that a topical use of GnRH is a potential treatment in CF.

Baculoviruses as gene therapy vectors for human prostate cancer

Prostate cancer is the most commonly diagnosed cancer in ageing men in the western world. While the primary cancers can be treated with androgen ablation, radiotherapy and surgery, recurrent castration resistant cancers have an extremely poor prognosis, hence promoting research that could lead to a better treatment. Targeted therapeutic gene therapy may provide an attractive option for these patients. By exploiting the natural ability of viruses to target and transfer their genes into cancer cells, either naturally or after genetic manipulation, new generations of biological control can be developed. In this review we present the advantages and practicalities of using baculovirus as a vector for prostate cancer gene therapy and provide evidence for the potential of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) as a safer alternative vehicle for targeting cancer cells. Strategies to target baculovirus binding specifically to prostate cell surfaces are also presented. The large insertion capacity of baculoviruses also permits restricted, prostate-specific gene expression of therapeutic genes by cloning extended human transcriptional control sequences into the baculovirus genome.

Enzymatic stability, solution structure, and antiproliferative effect on prostate cancer cells of leuprolide and new gonadotropin-releasing hormone peptide analogs

Analogs of GnRH, including [DLeu6, desGly1o]-GnRH-NHEt (leuprolide, commercial product), have been widely used in oncology to induce reversible chemical castration. Several studies have provided evidence that, besides their pituitary effects, GnRH analogs may exert direct antiproliferative effects on tumor cells. To study the effect of modifications in positions 4 and 6 of leuprolide on prostate cancer cell proliferation, we synthesized 12 new leuprolide analogs. All GnRH analogs lacked the carboxy-terminal Gly10-amide of GnRH, and an ethylamide residue was added to Pro9. Gly6 was substituted by DLys, Nepsilon-modified DLys, Glu, and DGlu. To improve the enzymatic stability, NMeSer was incorporated in position 4, and the rate of hydrolysis by alpha-chymotrypsin and subtilisin was investigated. Our results demonstrate that this incorporation increases enzymatic stability in all analogs of GnRH, whereas the antiproliferative effect on PC3 and LNCaP prostate cancer cells is similar to that of leuprolide. Conformational studies were performed to elucidate structural changes occurring on substitution of native residues and to study structure-activity relationship for these analogs. The solution models of [DLeu6, desGly10]-GnRH-NHEt (leuprolide), [NMeSer4, DGlu6, desGly10]-GnRH-NHEt, [Glu6, desGly10]-GnRH-NHEt, and [DGIu6, desGly10]-GnRH-NHEt peptides were determined through two-dimensional nuclear magnetic resonance spectroscopy in dimethylsulfoxide. Nuclear magnetic resonance data provide experimental evidence for the U-turn-like structure appeared in all four analogs, which could be characterized as beta-hairpin conformation. The most stable analog [NMeSer4, DGlu6, desGly10]-GnRH-NHEt against proteolytic cleavage forms a second extra backbone turn observed for residues 1-4.

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.

Elevated GnRH receptor expression plus GnRH agonist treatment inhibits the growth of a subset of papillomavirus 18-immortalized human prostate cells

BACKGROUND AND AIMS

Human metastatic prostate cancer cell growth can be inhibited by GnRH analogs but effects on virus-immortalized prostate cells have not been investigated.

METHODS

Virus-immortalized prostate cells were stably transfected with rat GnRH receptor cDNA and levels of GnRH binding were correlated with GnRH effects on signaling, cell cycle, growth, exosome production, and apoptosis.

RESULTS

High levels of cell surface GnRH receptor occurred in transfected papillomavirus-immortalized WPE-1-NB26 epithelial cells but not in non-tumourigenic RWPE-1, myoepithelial WPMY-1 cells, or SV40-immortalized PNT1A. Endogenous cell surface GnRH receptor was undetectable in non-transfected cells or cancer cell lines LNCaP, PC3, and DU145. GnRH receptor levels correlated with induction of inositol phosphates, elevation of intracellular Ca(2+) , cytoskeletal actin reorganization, modulation of ERK activation and cell growth-inhibition with GnRH agonists. Hoechst 33342 DNA staining-cell sorting indicated accumulation of cells in G2 following agonist treatment. Release of exosomes from transfected WPE-1-NB26 was unaffected by agonists, unlike induction observed in HEK293([SCL60]) cells. Increased PARP cleavage and apoptotic body production were undetectable during growth-inhibition in WPE-1-NB26 cells, contrasting with HEK293([SCL60]) . EGF receptor activation inhibited GnRH-induced ERK activation in WPE-1-NB26 but growth-inhibition was not rescued by EGF or PKC inhibitor Ro320432. Growth of cells expressing low levels of GnRH receptor was not affected by agonists.

CONCLUSIONS

Engineered high-level GnRH receptor activation inhibits growth of a subset of papillomavirus-immortalized prostate cells. Elucidating mechanisms leading to clone-specific differences in cell surface GnRH receptor levels is a valuable next step in developing strategies to exploit prostate cell anti-proliferation using GnRH agonists.

The heart: a novel gonadotrophin-releasing hormone target

Gonadotrophin-releasing hormone (GnRH) is a hypothalamic hormone transported by the hypophyseal portal bloodstream to the pituitary gland, where it binds to GnRH receptors. However, GnRH receptors are expressed in multiple extrapituitary tissues, although their physiological relevance is not fully understood. GnRH agonists are employed extensively in steroid deprivation therapy, especially to suppress testosterone in prostate cancer. Because GnRH agonist treatment is associated with increased coronary heart disease and myocardial infarction, we investigated the impact of GnRH on cardiomyocyte contractile function. Cardiomyocytes were isolated from mouse hearts and mechanical and intracellular Ca(2+) properties were evaluated, including peak shortening amplitude (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90) ), maximal velocity of shortening/relengthening (± dLdt), electrically-stimulated rise in Fura-2 fluorescence intensity (ΔFFI) and Ca(2+) decay. GnRH (1 ng/ml) increased PS, ± dL/dt, resting FFI and ΔFFI, and prolonged TPS, TR(90) and Ca(2+) decay time, whereas 1 pg/ml GnRH affected all these cardiomyocyte variables, except TPS, resting FFI and ΔFFI. A concentration of 1 fg/ml GnRH and the GnRH cleavage product, GnRH-[1-5] (300 pg/ml), had no effect on any cardiomyocyte parameter. The 1 pg/ml GnRH-elicited responses were attenuated by the GnRH receptor antagonist cetrorelix (10 μm), the protein kinase A (PKA) inhibitor H89 (1 μm) but not the protein kinase C inhibitor chelerythrine chloride (1 μm). These data revealed that GnRH is capable of regulating cardiac contractile function via a GnRH receptor/PKA-dependent mechanism. If present in the human heart, dysfunction of such a system may play an important role in cardiac pathology observed in men treated with GnRH agonists for prostate cancer.

Dose-ranging study of the luteinizing hormone-releasing hormone receptor antagonist cetrorelix pamoate in the treatment of patients with symptomatic benign prostatic hyperplasia

OBJECTIVE

To compare the efficacy of 4 dosage regimens of cetrorelix pamoate, a sustained release formulation that allows for more convenient dosing, in patients with symptomatic benign prostatic hyperplasia (BPH). Repeated dosing with cetrorelix acetate was shown to be active in the treatment of BPH symptoms.

METHODS

Double-blind, randomized, multicenter study was undertaken among patients with International Prostate Symptom Score (IPSS) ≥ 13. After a single-blind placebo run-in phase of 4 weeks, treatment was administered at 2-week intervals as follows: 30 + 30 mg, 30 + 30 + 30 mg, 60 + 30, 60 + 60 mg cetrorelix pamoate, or matching placebo. Patients were followed-up for 28 weeks after randomization.

RESULTS

A statistically significant overall difference was found with respect to the primary variable, the IPSS (P ≤ .001). Optimal results, a 4-point improvement in IPSS in excess of the changes observed in the placebo group, were achieved with a starting dose of 60 mg cetrorelix pamoate followed by a dose of 30 mg 2 weeks later. In all dosage groups, the symptomatic improvement was paralleled by an increase in uroflow. There was a marked dissociation between only moderate and transient testosterone suppression and the persisting effects on BPH signs and symptoms. Tolerability was good at all cetrorelix dosages.

CONCLUSIONS

Intramuscular injections of 60 and 30 mg of cetrorelix pamoate within 2 weeks provide rapid symptomatic improvements of BPH that are sustained for the following 6 months.

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.

Is the metalloendopeptidase EC 3.4.24.15 (EP24.15), the enzyme that cleaves luteinizing hormone-releasing hormone (LHRH), an activating enzyme?

LHRH (GNRH) was first isolated in the mammalian hypothalamus and shown to be the primary regulator of the reproductive neuroendocrine axis comprising of the hypothalamus, pituitary and gonads. LHRH acts centrally through its initiation of pituitary gonadotrophin release. Since its discovery, this form of LHRH (LHRH-I) has been shown to be one of over 20 structural variants with a variety of roles in both the brain and peripheral tissues. 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 auto-regulation of LHRH-I (GNRH1) gene expression and secretion can also be mediated by itself and its processed peptide, LHRH-(1–5), centrally and in peripheral tissues. In this review, we present the evidence that EP24.15 is the main enzyme of LHRH metabolism. Following this, we look at the metabolism of other neuropeptides where an active peptide fragments is formed during degradation and use this as a platform to postulate that EP24.15 may also produce an active peptide fragment in the process of breaking down LHRH. We close this review by the role EP24.15 may have in regulation of the complex LHRH system.

Targeted drug and gene delivery systems for lung cancer therapy

PURPOSE

To evaluate the efficacy of a novel docetaxel derivative of deslorelin, a luteinizing hormone-releasing hormone (LHRH) agonist, and its combination in vivo with RGD peptide conjugated nanoparticles encapsulating an antiangiogenic, anti-vascular endothelial growth factor (VEGF) intraceptor (Flt23k; RGD-Flt23k-NP) in H1299 lung cancer cells and/or xenografts in athymic nude BALB/c mice.

EXPERIMENTAL DESIGN

The in vitro and in vivo efficacy of the deslorelin-docetaxel conjugate was evaluated in H1299 cells and xenografts in athymic nude mice. Coadministration of deslorelin-docetaxel conjugate and RGD-Flt23k-NP was tested in vivo in mice. Tumor inhibition, apoptosis, and VEGF inhibition were estimated in each of the treatment groups.

RESULTS

The conjugate enhanced in vitro docetaxel efficacy by 13-fold in H1299 cells compared with docetaxel at 24 hours, and this effect was inhibited following reduction of LHRH receptor expression by an antisense oligonucleotide. Combination of the conjugate with the RGD-Flt23k-NP in vivo resulted in an 82- and 15-fold tumor growth inhibition on day 39 following repeated weekly i.v. injections and a single intratumoral (i.t.) injection, respectively. These effects were significantly greater than individual targeted therapies or docetaxel alone. Similarly, apoptotic indices for the combination therapy were 14% and 10% in the i.v. and i.t. groups, respectively, and higher than the individual therapies. Combination therapy groups exhibited greater VEGF inhibition in both the i.v. and i.t. groups.

CONCLUSIONS

Docetaxel efficacy was enhanced by LHRH receptor-targeted deslorelin conjugate and further improved by combination with targeted antiangiogenic nanoparticle gene therapy. Combination of novel targeted therapeutic approaches described here provides an attractive alternative to the current treatment options for lung cancer therapy.

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.

Gonadotropin-releasing hormone: GnRH receptor signaling in extrapituitary tissues

Gonadotropin-releasing hormone (GnRH) has historically been known as a pituitary hormone; however, in the past few years, interest has been raised in locally produced, extrapituitary GnRH. GnRH receptor (GnRHR) was found to be expressed in normal human reproductive tissues (e.g. breast, endometrium, ovary, and prostate) and tumors derived from these tissues. Numerous studies have provided evidence for a role of GnRH in cell proliferation. More recently, we and others have reported a novel role for GnRH in other aspects of tumor progression, such as metastasis and angiogenesis. The multiple actions of GnRH could be linked to the divergence of signaling pathways that are activated by GnRHR. Recent observations also demonstrate cross-talk between GnRHR and growth factor receptors. Intriguingly, the classical G(alphaq)-11-phospholipase C signal transduction pathway, known to function in pituitary gonadotropes, is not involved in GnRH actions at nonpituitary targets. Herein, we review the key findings on the role of GnRH in the control of tumor growth, progression, and dissemination. The emerging role of GnRHR in actin cytoskeleton remodeling (small Rho GTPases), expression and/or activity of adhesion molecules (integrins), proteolytic enzymes (matrix metalloproteinases) and angiogenic factors is explored. The signal transduction mechanisms of GnRHR in mediating these activities is described. Finally, we discuss how a common GnRHR may mediate different, even opposite, responses to GnRH in the same tissue/cell type and whether an additional receptor(s) for GnRH exists.

A multi-hit endocrine model of intrinsic adult-onset asthma

Epidemiological studies indicate that adult-onset asthma is initiated by stress (anxiety and depression), obesity and menopause. Ironically, despite our understanding of the various stressors that promote chronic adult-onset asthma, most of which are known to elevate cortisol production via the hypothalamic-pituitary-adrenal (HPA) axis, inhaled and systemic corticosteroids are the mainstay for the treatment of chronic asthma. This implicates other endocrine or cellular changes independent of cortisol synthesis in non-allergic adult-onset asthma. The mechanism by which corticosteroids are thought to modulate bronchial tone in relieving asthma is via corticosteroid-responsive genes that increase PGE(2) and cAMP production which promote muscle relaxation. Therefore, any physiological condition that suppresses intracellular PGE(2) and cAMP production would counter cortisol-induced muscle relaxation and potentially trigger non-allergic adult-onset asthma. Stress, obesity and menopause act on three interrelated endocrine pathways, the serotonergic, leptinergic and hypothalamic pathways, all of which operate through receptors to modulate cAMP and Ca(2+) metabolism in smooth muscle cells (SMCs). We propose that the level of SMC cAMP, as determined by overall signaling through corticosteroid receptors, leptin receptors and the GPCRs of the HPG and serotonergic pathways, will regulate bronchial tone (i.e. the 'Multi-Hit Endocrine Model of Adult-Onset Asthma'). Thus, decreases in HPG (menopause) and serotonergic (depression) signaling and increases in leptinergic (obesity) signaling relative to HPA signaling would decrease cellular SMC cAMP and promote muscle contraction. This model can explain the discrepant epidemiological data associating stress, obesity, depression and menopause with adult-onset asthma and is supported by basic and clinical data. Treatment of depressed or menopausal asthmatics with selective serotonin reuptake inhibitors or hormone replacement therapy, respectively, alleviates bronchoconstriction. Future therapeutic strategies might therefore target the serotonergic, leptinergic and hypothalamic pathways in regulating cellular cAMP production and bronchoconstriction for the treatment of adult-onset asthma.

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.

Expression of gonadotropin-releasing hormone receptor in cerebral cortical neurons of embryos and adult rats

Mammalian gonadotropin-releasing hormone (GnRH) was initially isolated from hypothalamus and its receptor from anterior pituitary, although extrapituitary GnRH receptors have been reported. The aim of the present study was to investigate whether GnRH receptor and its mRNA are expressed in cerebral cortical neurons of rat embryos and adult rats using immunohistochemical and reverse transcriptase polymerase chain reaction (RT-PCR) techniques. The immunohistochemistry and RT-PCR analysis showed expression of GnRH receptor and presence of its mRNA, in both cerebral cortical neurons of rat embryos and cerebral cortical tissues of adult rats. Additional experiments showed a decrease in the receptor mRNA expression when cultured neurons of rat embryos were treated with GnRH. It is possible that the presence of GnRH receptors in cortical neurons of rat may be involved in other physiological roles such as neurohormone or neuromodulator.

Gonadotropin-releasing hormone in apoptosis of prostate cancer cells

GnRH and its analogs (GnRH-a) are used extensively for the treatment of prostate cancer and other hormone-dependent diseases via the desensitization of pituitary gonadotropes, which consequently leads to the inhibition of gonadotropins, gonadal steroids and tumor growth. The actions of GnRH-a are mediated by the GnRH receptor (GnRHR) that is expressed in both the pituitary and extrapituitary sites, including normal tissues and tumors. Several studies have provided evidence that besides its pituitary effects, GnRH-a may exert direct anti-proliferative and apoptotic effects in tumor cells. These effects are mediated by the GnRHRs via signal transduction mechanisms that are distinct from the classical pituitary mechanisms. Here we describe the direct effects of GnRH-a on prostate cancer and other types of cancer. Interestingly, androgen ablation by GnRH-a is the main treatment for hormone-dependent prostate cancer. However, most of these tumors become eventually hormone-refractory, and are no longer sensitive to the GnRH-a-mediated reduction in androgen levels. Hence, the ability of GnRH-a to induce direct effects such as apoptosis may have large implications regarding the clinical use of GnRH-a. Therefore, an understanding of the cellular mechanisms involved in GnRH-a action may lead to better therapeutic modalities for the treatment of advanced prostate cancer and other malignancies.

Inhibition of human experimental prostate cancers by a targeted cytotoxic luteinizing hormone-releasing hormone analog AN-207

BACKGROUND

Receptors for luteinizing hormone-releasing hormone (LHRH) on human prostate cancers can be used for targeted chemotherapy with cytotoxic analogs of LHRH, such as AN-207, which consists of superactive doxorubicin derivative 2-pyrrolino doxorubicin (AN-201) linked to carrier [D-Lys6] LHRH.

METHODS

The effects of AN-207 and AN-201 were investigated in DU-145 androgen independent and LuCaP-35 androgen sensitive human prostate cancers xenografted into nude mice. Toxicity was evaluated by survival rates, changes in body weights, and leukocyte counts. LHRH receptors on DU-145 and LuCaP-35 tumors were evaluated by radioreceptor assays and RT-PCR. The effects on apoptosis and cell proliferation were investigated by histology and evaluation of apoptotic oncogenes Bcl-2 and Bax by Western Blot analysis.

RESULTS

AN-207 inhibited growth of DU-145 tumors significantly by 75% (P < 0.01) and LuCaP-35 human prostate cancers by 80% (P < 0.01), and was less toxic than AN-201. Receptors for LHRH were expressed on DU-145 and LuCaP-35 tumors. Blockade of LHRH receptors with LHRH agonist Triptorelin nullified the effects of AN-207. Treatment with AN-207, but not with AN-201, decreased Bcl-2/Bax ratio in DU-145 tumors and Bcl-2 in LuCaP-35 tumors indicating an increase in apoptotic activity. AN-207, but not AN-201, decreased cell proliferation in both models.

CONCLUSIONS

Targeted chemotherapy with AN-207 could be considered for treatment of advanced prostate cancer.

Receptors for luteinizing hormone releasing hormone expressed on human renal cell carcinomas can be used for targeted chemotherapy with cytotoxic luteinizing hormone releasing hormone analogues

PURPOSE

To determine the expression of luteinizing hormone releasing hormone (LHRH) receptors in specimens and cell lines of human renal cell carcinoma (RCC) and to evaluate the antitumor efficacy of targeted therapy with a cytotoxic analogue of LHRH, AN-207, in vivo. AN-207, consisting of [D-Lys(6)] LHRH linked to a cytotoxic radical, 2-pyrrolinodoxorubicin (AN-201), binds with high affinity to LHRH receptors and can be targeted to tumors expressing these receptors.

EXPERIMENTAL DESIGN

The expression of LHRH receptors was investigated in 28 surgically removed specimens of human renal cell carcinoma (RCC) by immunohistochemistry and in three human RCC cell lines A-498, ACHN, and 786-0 by radioreceptor assays, Western immunoblotting, and reverse transcription-PCR analysis. Antitumor efficacy of AN-207 was examined in experimental models of these cell lines.

RESULTS

Positive staining for LHRH receptors was found in all (28 of 28) of the examined human RCC specimens. mRNA for LHRH receptor, receptor protein, and LHRH binding sites were detected in all three cell lines. AN-207 significantly (P < 0.05) inhibited the growth of A-498, ACHN, and 786-0 xenografts in vivo producing a 67.8% to 73.8% decrease in tumor volume and a 62.2% to 77.3% reduction in tumor weight. Nontargeted cytotoxic radical AN-201 had no significant antitumor effects. Blockade of LHRH receptors by an excess of LHRH agonist Decapeptyl suppressed tumor inhibitory effects of AN-207.

CONCLUSIONS

Our findings indicate that LHRH receptors are expressed in human RCC specimens and can be used for targeted chemotherapy with cytotoxic LHRH analogues.

Targeting of cytotoxic luteinizing hormone-releasing hormone analogs to breast, ovarian, endometrial, and prostate cancers

Targeted chemotherapy is a modern approach aimed at increasing the efficacy of systemic chemotherapy and reducing its side effects. The peptide receptors expressed primarily on cancerous cells can serve as targets for a selective destruction of malignant tumors. Binding sites for LHRH (now known in genome and microarray databases as GNRH1), were found on 52% of human breast cancers, about 80% of human ovarian and endometrial cancers, and 86% of human prostatic carcinoma specimens. Because LHRH receptors are not expressed on most normal tissues, they represent a specific target for cancer chemotherapy with antineoplastic agents linked to an LHRH vector molecule. To test the efficacy of targeted chemotherapy based on LHRH analogs, we recently developed a cytotoxic analog of LHRH, designated AN-152, which consists of [D-Lys6]LHRH covalently linked to one of the most widely used chemotherapeutic agents, doxorubicin (DOX). In addition, we designed and synthesized a highly active derivative of DOX, 2-pyrrolino-DOX (AN-201), which is 500-1000 times more potent than DOX in vitro. AN-201 is active against tumors resistant to DOX, and noncardiotoxic. As in the case of DOX, AN-201 was coupled to carrier peptide [D-Lys6]LHRH to form a superactive targeted cytotoxic LHRH analog, AN-207. Both AN-152 and AN-207 can effectively inhibit the growth of LHRH receptor-positive human breast, ovarian, endometrial, and prostate cancers xenografted into nude mice. DOX-containing cytotoxic LHRH analog AN-152 is scheduled for clinical phase I/IIa trials in patients with advanced ovarian and breast cancers in 2005.

Molecular biology of gonadotropin-releasing hormone (GnRH)-I, GnRH-II, and their receptors in humans

In human beings, two forms of GnRH, termed GnRH-I and GnRH-II, encoded by separate genes have been identified. Although these hormones share comparable cDNA and genomic structures, their tissue distribution and regulation of gene expression are significantly dissimilar. The actions of GnRH are mediated by the GnRH receptor, which belongs to a member of the rhodopsin-like G protein-coupled receptor superfamily. However, to date, only one conventional GnRH receptor subtype (type I GnRH receptor) uniquely lacking a carboxyl-terminal tail has been found in the human body. Studies on the transcriptional regulation of the human GnRH receptor gene have indicated that tissue-specific gene expression is mediated by differential promoter usage in various cell types. Functionally, there is growing evidence showing that both GnRH-I and GnRH-II are potentially important autocrine and/or paracrine regulators in some extrapituitary compartments. Recent cloning of a second GnRH receptor subtype (type II GnRH receptor) in nonhuman primates revealed that it is structurally and functionally distinct from the mammalian type I receptor. However, the human type II receptor gene homolog carries a frameshift and a premature stop codon, suggesting that a full-length type II receptor does not exist in humans.

Evidence that prostate gonadotropin-releasing hormone receptors mediate an anti-tumourigenic response to analogue therapy in hormone refractory prostate cancer

Gonadotropin-releasing hormone analogue (GnRHa) therapy is an established method of androgen withdrawal in the treatment of prostate cancer. The present study investigated if the expression of prostate GnRH receptors (GnRHRs) might influence the response to GnRHa. GnRHR protein expression was first studied in a panel of prostate cancer cell lines. In androgen-dependent cells, GnRHR expression was unchanged following acute or chronic androgen withdrawal. In these cells, GnRHa significantly inhibited androgen-induced cell proliferation (p = 0.01). In contrast, GnRHa was unable to further suppress basal levels of cell proliferation induced by androgen withdrawal. In androgen-independent prostate cancer cells, variable levels of GnRHR expression were observed. In these cells, GnRHa treatment blocked cell proliferation (p = 0.001) and invasion (up to 70%) induced by fibroblast growth factor stimulation. Crucially, this effect was only evident in cells that expressed high levels of the GnRHR. GnRHa treatment also significantly inhibited the ability of these cells to recover from a cytotoxic insult (50% inhibition). The clinical significance of prostate GnRHR was tested by immunohistochemistry in a preliminary cohort of patients treated with GnRHa or surgical castration. There was no association between GnRHR expression and pathological grade, clinical stage, time to PSA nadir (p = 0.82) (n = 35) or progression to hormone refractory disease (p = 0.22) (n = 21), irrespective of the treatment method. GnRHa therapy in the presence of high GnRHR expression however, was found to be associated with longer disease-specific survival (mean survival 85 months, p = 0.002). In contrast, high GnRHR expression was not associated with survival among surgically castrated patients (mean survival 50 months, p = 0.7). Taken together, these data support the notion of a functional interaction between GnRHa and the GnRHR, which results in an anti-tumourigenic effect on prostate cancer cells. Findings from this report have direct implications for the use of GnRHR as a novel therapeutic target in hormone refractory prostate cancer.

The biology of gonadotropin hormone-releasing hormone: role in the control of tumor growth and progression in humans

It is now well known that different forms of GnRH coexist in the same vertebrate species. In humans, two forms of GnRH have been identified so far. The first form corresponds to the hypophysiotropic decapeptide, and is now called GnRH-I. The second form has been initially identified in the chicken brain, and it is referred to as GnRH-II. GnRH-I binds to and activates specific receptors, belonging to the 7 transmembrane (7TM) domain superfamily, present on pituitary gonadotropes. These receptors (type I GnRH receptors) are coupled to the Gq/11/PLC intracellular signalling pathway. A receptor specific for GnRH-II (type II GnRH receptor) has been identified in non-mammalian vertebrates as well as in primates, but not yet in humans. In the last 10-15 years experimental evidence has been accumulated indicating that GnRH-I is expressed, together with its receptors, in tumors of the reproductive tract (prostate, breast, ovary, and endometrium). In these hormone-related tumors, activation of type I GnRH receptors consistently decreases cell proliferation, mainly by interfering with the mitogenic activity of stimulatory growth factors (e.g., EGF, IGF). Recent data seem to suggest that GnRH-I might also reduce the migratory and invasive capacity of cancer cells, possibly by affecting the expression and/or activity of cell adhesion molecules and of enzymes involved in the remodelling of the extracellular matrix. These observations point to GnRH-I as an autocrine negative regulatory factor on tumor growth progression and metastatization. Extensive research has been performed to clarify the molecular mechanisms underlying the peculiar antitumor activity of GnRH-I. Type I GnRH receptors in hormone-related tumors correspond to those present at the pituitary level in terms of cDNA nucleotide sequence and protein molecular weight, but do not share the same pharmacological profile in terms of binding affinity for the different synthetic GnRH-I analogs. Moreover, the classical intracellular signalling pathway mediating the stimulatory activity of the decapeptide on gonadotropin synthesis and secretion is not involved in its inhibitory activity on hormone-related tumor growth. In these tumors, type I GnRH receptors are coupled to the Gi-cAMP, rather than the Gq/11-PLC, signal transduction pathway. Recently, we have reported that GnRH-I and type I GnRH receptors are expressed also in tumors not related to the reproductive system, such as melanoma. Also in melanoma cells, GnRH-I behaves as a negative regulator of tumor growth and progression. Interestingly, the biochemical and pharmacological profiles of type I GnRH receptors in melanoma seem to correspond to those of the receptors at pituitary level. The data so far reported on the expression and on the possible functions of GnRH-II in humans are still scanty. The decapeptide has been identified, together with a 'putative' type II GnRH receptor, both in the central nervous system and in peripheral structures, such as tissues of the reproductive tract (both normal and tumoral). The specific biological functions of GnRH-II in humans are presently under investigation.

Real-time quantitative reverse transcriptase-polymerase chain reaction for luteinizing hormone-releasing hormone receptor gene mRNA expression in human prostate cancer

OBJECTIVES

To determine quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) detection of luteinizing hormone-releasing hormone (LHRH) receptor mRNA expressing prostate cancer (CaP) and benign prostatic hyperplasia (BPH) tissue by sequence-specific detection with hybridization probes using the LightCycler. Various in vitro studies have indicated that LHRH agonists and antagonists may have a direct inhibitory effect on CaP mediated by specific LHRH receptors. The incidence of LHRH receptor mRNA expression was demonstrated in 50% to 100% of clinical CaP and BPH tissue by current RT-PCR methods. However, qualitative RT-PCR can only demonstrate the existence of a gene; an exact quantification of LHRH-receptor mRNA expression has not yet been done.

METHODS

Quantitative real-time RT-PCR for LHRH receptor mRNA was performed using the LightCycler system and the RNA Amplification Kit hybridization probes in 35 patients with CaP and 38 patients with BPH.

RESULTS

Thirty-one (88.6%) of the 35 patients with CaP and 36 (94.7%) of the 38 patients with BPH had positive RT-PCR for LHRH receptor mRNA. The number of positive amplifications per 1 microg total RNA was not significantly lower in CaP at 695,428 +/- 350,860 than in BPH at 1,617,654 +/- 787,874. Patients with CaP evidenced a significant negative correlation between the amplification rate for LHRH receptor mRNA and Gleason score (r = -0.476; P = 0.004).

CONCLUSIONS

In the past, the potential mechanisms acting on LHRH receptors in CaP have been identified as possible antitumor strategies for this type of cancer. Our study is the first to show that CaP does not have a higher expression of LHRH receptor mRNA expression than BPH when using quantitative sequence-specific oligonucleotide hybridization probes that only detect certain PCR products.

Gonadotropin-releasing hormone alters the T helper cytokine balance in the pregnant rat

The interactions between immune-endocrine and reproductive systems are heightened during pregnancy as an adaptive mechanism, and are regulated by a complex array of hormones and cytokines that control the survival of a semiallogeneic conceptus. GnRH can exert direct effects on the immune system via its receptor (GnRH-R) on lymphoid cells. In the present study, we employed in vitro, ex vivo, and in vivo approaches to investigate the role of GnRH in the modulation of T helper cytokines in pregnant rats undergoing termination of pregnancy. Day 8 pregnant rats were infused with a GnRH agonist (GnRH-Ag) for 24 h using an osmotic minipump. Sham control rats were infused with the vehicle, saline. Lymphocytes were isolated from sham and treated rats and polyclonally stimulated with immobilized anti-CD3 antibody. The levels of the signature T helper 1 (Th-1) cytokines (interferon-gamma [IFN-gamma] and interleukin-2 [IL-2]) and Th-2 cytokines (IL-4 and IL-10) were measured in culture supernatants. Using immunoflourescence confocal microscopy, we demonstrated for the first time the spatial localization of GnRH-R protein on the surface of lymphocytes. We observed a marked increase in IFN-gamma and inhibition of IL-4 production from lymphocytes of pregnant rats treated in vitro with different doses of GnRH-Ag. Further, the responsiveness of lymphocytes to produce IFN-gamma was markedly increased in cells cultured ex vivo from GnRH-Ag infused rats, whereas the capacity of lymphocytes to produce IL-4 was significantly inhibited. In addition, GnRH-Ag infusion in pregnant rats induced a shift toward Th-1 cytokines in the serum. We did not observe any significant difference in IL-2 and IL-10 production in response to GnRH-Ag. Our results suggest an additional function for GnRH as a Th-1 inducer and Th-2 inhibitor. GnRH can thus skew the cytokine balance to predominantly Th-1 type in pregnancy, leading to the termination of pregnancy in rats.

The clinical implications of the difference between castration, gonadotrophin releasing-hormone (GnRH) antagonists and agonist treatment on the morphology and expression of GnRH receptors in the rat ventral prostate

OBJECTIVE

To examine the effects of castration and continuous gonadotrophin releasing-hormone (GnRH) agonist and antagonist therapy on the expression of GnRH-receptors type I (GnRH-RI) in rat ventral prostate (VP) and pituitary tissue, and to compare the effects on prostate morphology.

MATERIAL AND METHODS

Mature Sprague-Dawley rats were assigned to four treatment groups: group 1, vehicle only; group 2, GnRH agonist goserelin (100 microg/rat/day); group 3, GnRH antagonist cetrorelix (100 microg/rat/day); and group 4, orchidectomy. After 4 weeks the body weights were recorded and VP and pituitary tissue analysed for GnRH-RI expression using a competitive reverse transcriptase-polymerase chain reaction and immunohistochemistry.

RESULTS

GnRH antagonist and orchidectomy decreased testosterone secretion and VP volume similarly, but the effects were not identical. The involution of the glandular lumina was more pronounced after orchidectomy while the antagonist therapy was more effective in suppressing epithelial cell proliferation. In the VP, GnRH-RI mRNA levels were increased after GnRH analogue therapy, but were unaffected by orchidectomy. In the pituitary, GnRH-RI mRNA expression was higher in response to orchidectomy and decreased after GnRH analogue treatment.

CONCLUSION

Treatment with a GnRH antagonist for 4 weeks is more effective than an agonist in suppressing testosterone and inducing VP involution. The GnRH antagonist was more effective in suppressing VP epithelial cell proliferation than was castration, suggesting that it induces reduced proliferation by interfering with effects of locally produced GnRH. These results suggest that different regulatory mechanisms may operate in the rat VP than in the pituitary to control GnRH-RI mRNA expression.

Receptor gene messenger RNA expression in metastatic lesions of prostate cancer

PURPOSE

There are hardly any options for treating hormone refractory prostate cancer. Some groups have already suggested antitumor therapy of prostate cancer using agonists, antagonists or other concepts acting on luteinizing hormone-releasing hormone (LH-RH) receptor. Few studies have been published to date on the detection of LH-RH receptors in human prostate cancer tissue. However, at this point it is completely unclear in this context whether metastasizing prostate cancer lesions, which may be major potential targets of a type of therapy, have any LH-RH receptors. In this study we examined tumor samples of lymph nodes from patients with prostate cancer obtained during radical prostatectomy and laparoscopic lymphadenectomy for the expression of LH-RH receptor messenger (m)RNA.

MATERIALS AND METHODS

Multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) was done to detect the expression of the mRNA of LH-RH receptor, prostate specific antigen and beta-actin in pelvic lymph nodes from 100 patients with prostate cancer.

RESULTS

In 27 patients at least 1 histopathological metastasis (19) and/or positive RT-PCR for prostate specific antigen (22) was identified. In 7 of these patients (25.9%) RT-PCR revealed LH-RH mRNA expression.

CONCLUSIONS

To our knowledge our study shows for the first time a rather low incidence of LH-RH receptor mRNA in primary pelvic lymph node metastases. However, since other studies show that an increased incidence of LH-RH receptors is typical of the hormone refractory stage of the disease, further studies in this specific patient population may help explain the clinical importance of LH-RH receptors in the development of new therapeutic approaches to advanced prostate cancer.