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

A microscale 3D organ on a chip for recapitulating reciprocal neuroendocrine crosstalk between the hypothalamus and the pituitary gland

Conventional 2D or even recently developed 3Din vitroculture models for hypothalamus and pituitary gland cannot successfully recapitulate reciprocal neuroendocrine communications between these two pivotal neuroendocrine tissues known to play an essential role in controlling the body's endocrine system, survival, and reproduction. In addition, most currentvitroculture models for neuroendocrine tissues fail to properly reflect their complex multicellular structure. In this context, we developed a novel microscale chip platform, termed the 'hypothalamic-pituitary (HP) axis-on-a-chip,' which integrates various cellular components of the hypothalamus and pituitary gland with biomaterials such as collagen and hyaluronic acid. We used non-toxic blood coagulation factors (fibrinogen and thrombin) as natural cross-linking agents to increase the mechanical strength of biomaterials without showing residual toxicity to overcome drawbacks of conventional chemical cross-linking agents. Furthermore, we identified and verified SERPINB2 as a reliable neuroendocrine toxic marker, with its expression significantly increased in both hypothalamus and pituitary gland cells following exposure to various types of toxins. Next, we introduced SERPINB2-fluorescence reporter system into loaded hypothalamic cells and pituitary gland cells within each chamber of the HP axis on a chip, respectively. By incorporating this SERPINB2 detection system into the loaded hypothalamic and pituitary gland cells within our chip platform, Our HP axis-on-chip platform can better mimic reciprocal neuroendocrine crosstalk between the hypothalamus and the pituitary gland in the brain microenvironments with improved efficiency in evaluating neuroendocrine toxicities of certain drug candidates.

Role of gonadotropin-releasing hormone 2 and its receptor in human reproductive cancers

Gonadotropin-releasing hormone (GnRH1) and its receptor (GnRHR1) drive reproduction by regulating gonadotropins. Another form, GnRH2, and its receptor (GnRHR2), also exist in mammals. In humans, GnRH2 and GnRHR2 genes are present, but coding errors in the GnRHR2 gene are predicted to hinder full-length protein production. Nonetheless, mounting evidence supports the presence of a functional GnRHR2 in humans. GnRH2 and its receptor have been identified throughout the body, including peripheral reproductive tissues like the ovary, uterus, breast, and prostate. In addition, GnRH2 and its receptor have been detected in a wide number of reproductive cancer cells in humans. Notably, GnRH2 analogues have potent anti-proliferative, pro-apoptotic, and/or anti-metastatic effects on various reproductive cancers, including endometrial, breast, placental, ovarian, and prostate. Thus, GnRH2 is an emerging target to treat human reproductive cancers.

GNRH family genes contributed to gender-specific disparity of bladder cancer prognosis through exerting opposite regulatory roles between males and females

PURPOSE

There is gender-specific disparity in bladder cancer (BlCa) prognosis. Female BlCa patients present with more advanced tumor and have higher risks of disease recurrence, progression, and mortality than males. Since gonadotropin-releasing hormone (GNRH) family genes were critical genes in gender-related biological activity and could be detected in BlCa specimens, this study aimed to explore potential roles of GNRH1 and GNRHR in gender disparity of BlCa.

METHODS

RNA-sequencing data from The Cancer Genome Atlas Bladder Urothelial Carcinoma dataset, IMvigor210 immunotherapy cohort and Cancer Cell Line Encyclopedia database were used to compare potential roles of GNRH1 and GNRHR in males and females, respectively. Gene set enrichment analysis was used to analyze the biological functions.

RESULTS

Males with higher GNRH1 and GNRHR have better overall survival (P < 0.05, HR < 1), while females with higher expression have a trend toward worse overall survival (P < 0.05, HR > 1). Gene set enrichment analysis identified GNRH1 and GNRHR exert opposite regulatory roles in myogenesis (M5909), interferon-α response (M5911), interferon-γ response (M5913), inflammatory response (M5932) and TNF-α signaling via NF-κβ (M5890) between males and females. The five functions are up-regulated in females (NES > 0), while down-regulated in males (NES < 0). GNRH1 in females was positively correlated with CD3D (R-value > 0 and P < 0.05), while GNRHR in males was negatively correlated with CD247, CD3D and CD3E (R-value < 0 and P < 0.05).

CONCLUSION

GNRH1 and GNRHR have opposite effects on overall survival in different genders, and exert opposite roles in immune-related functions between different genders, which could emerge as a contributor to gender disparity of BlCa prognosis.

Comprehensive analysis of oxidative stress-related lncRNA signatures in glioma reveals the discrepancy of prognostic and immune infiltration

Oxidative stress refers to the process of reactive oxide species (ROS) increase in human body due to various factors, which leads to oxidative damage in human tissues. Current studies have confirmed that sustained oxidative stress is one of the distinctive features throughout the development of tumors. Numerous reports have shown that lncRNAs can regulate the process of oxidative stress through multiple pathways. However, the relationship between glioma-associated oxidative stress and lncRNAs is not clearly investigated. RNA sequencing data of GBM (glioblastoma) and LGG (low grade glioma) and corresponding clinical data were retrieved from the TCGA database. Oxidative stress related lncRNAs (ORLs) were identified by Pearson correlation analysis. Prognostic models for 6-ORLs were structured in the training cohort by univariate Cox regression analysis, multivariate Cox regression analysis and LASSO regression analysis. We constructed the nomogram and verified its predictive efficacy by Calibration curves and DCA decision curves. The biological functions and pathways of 6-ORLs-related mRNAs were inferred by Gene Set Enrichment Analysis. Immune cell abundance and immune function associated with risk score (RS) were estimated by ssGSEA, CIBERSORT and MCPcounter synthetically. External validation of the signature was completed using the CGGA-325 and CGGA-693 datasets. 6-ORLs signature-AC083864.2, AC107294.1, AL035446.1, CRNDE, LINC02600, and SNAI3-AS1-were identified through our analysis as being predictive of glioma prognosis. Kaplan-Meier and ROC curves indicated that the signature has a dependable predictive efficacy in the TCGA training cohort, validation cohort and CGGA-325/CGGA-693 test cohort. The 6-ORLs signature were verified to be independent prognostic predictors by multivariate cox regression and stratified survival analysis. Nomogram built with risk scores had strong predictive efficacy for patients' overall survival (OS). The outcomes of the functional enrichment analysis revealing potential molecular regulatory mechanisms for the 6-ORLs. Patients in the high-risk subgroup presented a significant immune microenvironment of macrophage M0 and cancer-associated fibroblast infiltration which was associated with a poorer prognosis. Finally, the expression levels of 6-ORLs in U87/U251/T98/U138 and HA1800 cell lines were verified by RT-qPCR. The nomogram in this study has been made available as a web version for clinicians. This 6-ORLs risk signature has the capabilities to predict the prognosis of glioma patients, assist in evaluating immune infiltration, and assess the efficacy of various anti-tumor systemic therapy regimens.

The development of peptide-drug conjugates (PDCs) strategies for paclitaxel

INTRODUCTION

Paclitaxel is a powerful and effective anti-tumor drug with wide clinical application. However, there are still some limitations, including poor water solubility, low specificity, and susceptibility to drug resistance. The peptide-drug conjugates (PDCs) represent a rising class of therapeutic drugs, which combines small-molecule chemotherapeutic drugs with highly flexible peptides through a cleavable or non-cleavable linker. When this strategy is applied, the therapeutic effects of paclitaxel can be improved.

AREAS COVERED

In this review, we discuss the application of the PDCs strategy in paclitaxel, including two parts: the tumor targeting peptide-paclitaxel conjugates and the cell penetrating peptide-paclitaxel conjugates.

EXPERT OPINION

Combining drugs with multifunctional peptides covalently is an effective strategy for delivering paclitaxel to tumors. Depending on different functional peptides, conjugates can increase the water solubility of paclitaxel, tumor permeability of paclitaxel, the accumulation of paclitaxel in tumor tissues, and enhance the antitumor effect of paclitaxel. In addition, due to the change of cell entry mechanism, partial conjugates can restore the therapeutic activity of paclitaxel against resistant tumors. Notably, in order to better translate into the clinical field in the future, more research should be conducted to ensure the safety and effectiveness of peptide-paclitaxel conjugates.

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.

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.

Dual-trigger improves the outcomes of in vitro fertilization cycles in older patients with diminished ovarian reserve: A retrospective cohort study

Background

Dual-trigger for final oocyte maturation has been applied on the women with poor ovarian response or diminished ovarian reserve. However, the results were controversial. The Patient-Oriented Strategies Encompassing IndividualizeD Oocyte Number (POSEIDON) stratification is a set of newly established criteria for low prognosis patients. The aim of this study was to examine the effectiveness of dual-trigger for final oocyte maturation on the in vitro fertilization (IVF) outcomes of patients who fulfill the POSEIDON group 4 criteria.

Methods

This retrospective cohort study investigated 384 cycles fulfilling the POSEIDON group 4 criteria. The patients underwent IVF treatment using the gonadotropin-releasing hormone (GnRH) antagonist protocol. The study group contained 194 cycles that received dual-trigger (human chorionic gonadotropin [hCG] plus GnRH-agonist) for final oocyte maturation. The control group included 114 cycles where final oocyte maturation was performed with only hCG. Baseline characteristics and cycle parameters, as well as IVF outcomes of both groups were compared.

Results

Baseline characteristics were similar between the dual trigger group and the control group. In terms of IVF outcomes, the dual trigger group demonstrated significantly higher number of retrieved oocytes, metaphase II oocytes, fertilized oocytes, day-3 embryos, and top-quality day-3 embryos. A statistically significant improvement in clinical pregnancy rate and live birth rate was also observed in the dual trigger group.

Conclusions

Our data suggests that dual trigger for final oocyte maturation might improve clinical pregnancy rates and live birth rates of IVF cycles in patients fulfilling the POSEIDON group 4 criteria.

Identification of key microRNAs of plasma extracellular vesicles and their diagnostic and prognostic significance in melanoma

Melanoma is one of the most highly metastatic, aggressive and fatal malignant tumors in skin cancer. This study employs bioinformatics to identify key microRNAs and target genes (TGs) of plasma extracellular vesicles (pEVs) and their diagnostic and prognostic significance in melanoma. The gene expression microarray dataset (GSE100508) was downloaded from the Gene Expression Omnibus database. Differential analysis of miRNAs in pEVs was performed to compare melanoma samples and healthy samples. Then, TGs of the differential miRNAs (DE-miRNAs) in melanoma were selected, and differential genes were analyzed by bioinformatics (including Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment, protein–protein interaction network and prognostic analysis). A total of 55 DE-miRNAs were found, and 3,083 and 1,351 candidate TGs were diagnostically correlated with the top ten upregulated DE-miRNAs and all downregulated DE-miRNAs, respectively. Prognostic analysis results showed that high expression levels of hsa-miR-550a-3p, CDK2 and POLR2A and low expression levels of hsa-miR-150-5p in melanoma patients were associated with significantly reduced overall survival. In conclusion, bioinformatics analysis identified key miRNAs and TGs in pEVs of melanoma, which may represent potential biomarkers for the early diagnosis and treatment of this cancer.

Testosterone-androgen receptor: The steroid link inhibiting TRPM8-mediated cold sensitivity

Recent studies have revealed gender differences in cold perception, and pointed to a possible direct action of testosterone (TST) on the cold-activated TRPM8 (Transient Receptor Potential Melastatin Member 8) channel. However, the mechanisms by which TST influences TRPM8-mediated sensory functions remain elusive. Here, we show that TST inhibits TRPM8-mediated mild-cold perception through the noncanonical engagement of the Androgen Receptor (AR). Castration of both male rats and mice increases sensitivity to mild cold, and this effect depends on the presence of intact TRPM8 and AR. TST in nanomolar concentrations suppresses whole-cell TRPM8-mediated currents and single-channel activity in native dorsal root ganglion (DRG) neurons and HEK293 cells co-expressing recombinant TRPM8 and AR, but not TRPM8 alone. AR cloned from rat DRGs shows no difference from standard AR. However, biochemical assays and confocal imaging reveal the presence of AR on the cell surface and its interaction with TRPM8 in response to TST, leading to an inhibition of channel activity.

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.

GnRH-R-Targeted Lytic Peptide Sensitizes BRCA Wild-type Ovarian Cancer to PARP Inhibition

EP-100 is a synthetic lytic peptide that specifically targets the gonadotropin-releasing hormone receptor on cancer cells. To extend the utility of EP-100, we aimed to identify effective combination therapies with EP-100 for ovarian cancer and explore potential mechanisms of this combination. A series of in vitro (MTT assay, immunoblot analysis, reverse-phase protein array, comet assay, and immunofluorescence staining) and in vivo experiments were carried out to determine the biological effects of EP-100 alone and in combination with standard-of-care drugs. EP-100 decreased the viability of ovarian cancer cells and reduced tumor growth in orthotopic mouse models. Of five standard drugs tested (cisplatin, paclitaxel, doxorubicin, topotecan, and olaparib), we found that the combination of EP-100 and olaparib was synergistic in ovarian cancer cell lines. Further experiments revealed that combined treatment of EP-100 and olaparib significantly increased the number of nuclear foci of phosphorylated histone H2AX. In addition, the extent of DNA damage was significantly increased after treatment with EP-100 and olaparib in comet assay. We performed reverse-phase protein array analyses and identified that the PI3K/AKT pathway was inhibited by EP-100, which we validated with in vitro experiments. In vivo experiment using the HeyA8 mouse model demonstrated that mice treated with EP-100 and olaparib had lower tumor weights (0.06 ± 0.13 g) than those treated with a vehicle (1.19 ± 1.09 g), EP-100 alone (0.62 ± 0.78 g), or olaparib alone (0.50 ± 0.63 g). Our findings indicate that combining EP-100 with olaparib is a promising therapeutic strategy for ovarian cancer.

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.

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.

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.

Expression and Role of Gonadotropin-Releasing Hormone 2 and Its Receptor in Mammals

Gonadotropin-releasing hormone 1 (GnRH1) and its receptor (GnRHR1) drive mammalian reproduction via regulation of the gonadotropins. Yet, a second form of GnRH (GnRH2) and its receptor (GnRHR2) also exist in mammals. GnRH2 has been completely conserved throughout 500 million years of evolution, signifying high selection pressure and a critical biological role. However, the GnRH2 gene is absent (e.g., rat) or inactivated (e.g., cow and sheep) in some species but retained in others (e.g., human, horse, and pig). Likewise, many species (e.g., human, chimpanzee, cow, and sheep) retain the GnRHR2 gene but lack the appropriate coding sequence to produce a full-length protein due to gene coding errors; although production of GnRHR2 in humans remains controversial. Certain mammals lack the GnRHR2 gene (e.g., mouse) or most exons entirely (e.g., rat). In contrast, old world monkeys, musk shrews, and pigs maintain the coding sequence required to produce a functional GnRHR2. Like GnRHR1, GnRHR2 is a 7-transmembrane, G protein-coupled receptor that interacts with G_αq/11 to mediate cell signaling. However, GnRHR2 retains a cytoplasmic tail and is only 40% homologous to GnRHR1. A role for GnRH2 and its receptor in mammals has been elusive, likely because common laboratory models lack both the ligand and receptor. Uniquely, both GnRH2 and GnRHR2 are ubiquitously expressed; transcript levels are abundant in peripheral tissues and scarcely found in regions of the brain associated with gonadotropin secretion, suggesting a divergent role from GnRH1/GnRHR1. Indeed, GnRH2 and its receptor are not physiological modulators of gonadotropin secretion in mammals. Instead, GnRH2 and GnRHR2 coordinate the interaction between nutritional status and sexual behavior in the female brain. Within peripheral tissues, GnRH2 and its receptor are novel regulators of reproductive organs. GnRH2 and GnRHR2 directly stimulate steroidogenesis within the porcine testis. In the female, GnRH2 and its receptor may help mediate placental function, implantation, and ovarian steroidogenesis. Furthermore, both the GnRH2 and GnRHR2 genes are expressed in human reproductive tumors and represent emerging targets for cancer treatment. Thus, GnRH2 and GnRHR2 have diverse functions in mammals which remain largely unexplored.

Peptides and Drug Delivery

Peptides have been used as drugs to treat various health conditions, and they are also being developed as diagnostic agents. Due to their receptor selectivity, peptides have recently been utilized for drug delivery to target drug molecules to specific types of cells (i.e. cancer cells, immune cells) to lower the side effects of the drugs. In this case, the drug is conjugated to the carrier peptide for directing the drug to the target cells (e.g. cancer cells) with higher expression of a specific receptor that recognizes the carrier peptide. As a result, the drug is directed to the target diseased cells without affecting the normal cells. Peptides are also being developed for improving drug delivery through the intestinal mucosa barrier (IMB) and the blood-brain barrier (BBB). These peptides were derived from intercellular junction proteins such as occludins, claudins, and cadherins and improve drug delivery through the IMB and BBB via the paracellular pathways. It is hypothesized that the peptides modulate protein-protein interactions in the intercellular junctions of the IMB and BBB to increase the porosity of paracellular pathways of the barriers. These modulator peptides have been shown to enhance brain delivery of small molecules and medium-sized peptides as well as a large protein such as 65 kDa albumin. In the future, this method has the potential to improve oral and brain delivery of therapeutic and diagnostic peptides and proteins.

Gonadotropin-releasing hormone stimulates biliary proliferation by paracrine/autocrine mechanisms

During cholestatic liver disease, there is dysregulation in the balance between biliary growth and loss in bile duct-ligated (BDL) rats modulated by neuroendocrine peptides via autocrine/paracrine pathways. Gonadotropin-releasing hormone (GnRH) is a trophic peptide hormone that modulates reproductive function and proliferation in many cell types. We evaluated the autocrine role of GnRH in the regulation of cholangiocyte proliferation. The expression of GnRH receptors was assessed in a normal mouse cholangiocyte cell line (NMC), sham, and BDL rats. The effect of GnRH administration was evaluated in normal rats and in NMC. GnRH-induced biliary proliferation was evaluated by changes in intrahepatic bile duct mass and the expression of proliferation and function markers. The expression and secretion of GnRH in NMC and isolated cholangiocytes was assessed. GnRH receptor subtypes GnRHR1 and GnRHR2 were expressed in cholangiocytes. Treatment with GnRH increased intrahepatic bile duct mass as well as proliferation and function markers in cholangiocytes. Transient knockdown and pharmacologic inhibition of GnRHR1 in NMC decreased proliferation. BDL cholangiocytes had increased expression of GnRH compared with normal rats, accompanied by increased GnRH secretion. In vivo and in vitro knockdown of GnRH decreased intrahepatic bile duct mass/cholangiocyte proliferation and fibrosis. GnRH secreted by cholangiocytes promotes biliary proliferation via an autocrine pathway. Disruption of GnRH/GnRHR signaling may be important for the management of cholestatic liver diseases.

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.

Noradrenaline modulates the presence of gonadotropin-releasing hormone in ovary. The importance of its interrelation on the ovarian steroidogenesis and apoptosis on dioestrus II in rat

The aim of this work was to investigate if noradrenaline (NA), added in the coeliac ganglion -superior ovarian nerve- ovary system (CG-SON-O) and in ovary incubation, modifies the release of ovarian progesterone (P4), gonadotropin-releasing hormone (GnRH) and oestradiol (E2), and the expression of 3β-HSD and 20α-HSD and proapoptotic bax and antiapoptotic bcl-2 on dioestrus II in the rat. The CG-SON-O system and the ovary were removed and placed in one cuvette containing Krebs-Ringer solution (control groups), and NA was added to the ganglion compartment in the ex vivo system and in the ovary compartment in the ovary incubation (experimental groups). P4, GnRH and E2 were measured by RIA, and gene expression was measured by RT-PCR. In the ex-vivo system, the release of ovarian P4 and GnRH and the expression of 3β-HSD and bax decreased; E2 and bcl-2 increased, and the bax/bcl-2 ratio decreased. However, in the ovary incubation, P4, GnRH, the expression of 3β-HSD and bax increased; E2, the expression of 20α-HSD and bcl-2 decreased while the bax/bcl-2 ratio increased, thus favoring apoptosis. The peripheral nervous system protected the ovary from the apoptotic mechanisms while in the ovary incubation the effect was reverted. Our results indicate that NA regulates ovarian steroidogenesis and apoptosis by modulating GnRH release from the coeliac ganglion and ovary, being NA a possible generator of a GnRH-gonadotropins axis in the ovary. This work is expected to contribute with new evidence of the clinical importance of catecholamines and GnRH in therapy and prevention of ovarian pathologies.

Multipronged quantitative proteomic analyses indicate modulation of various signal transduction pathways in human meningiomas

Meningiomas (MGs) are frequent tumors of the CNS originating from the meningeal layers of the spinal cord and the brain. In this study, comparative tissue proteomic analysis of low and high grades of MGs was performed by using iTRAQ-based quantitative proteomics in combination with ESI-quadrupole-TOF and Q-Exactive MS, and results were validated by employing ELISA. Combining the results obtained from two MS platforms, we were able to identify overall 4308 proteins (1% false discover rate), among which 2367 exhibited differential expression (more than and equal to 2 peptide and ≥ 1.5-fold in at least one grade) in MGs. Several differentially expressed proteins were found to be associated with diverse signaling pathways, including integrin, Wnt, Ras, epidermal growth factor receptor, and FGR signaling. Proteins, such as vinculin or histones, which act as the signaling activators to initiate multiple signaling pathways, were found to be upregulated in MGs. Quite a few candidates, such as protein S-100A6, aldehyde dehydrogenase mitochondrial, AHNAK, cytoskeleton-associated protein 4, and caveolin, showed sequential increase in low- and high-grade MGs, whereas differential expressions of collagen alpha-1 (VI), protein S100-A9, 14 kDa phosphohistidine phosphatase, or transgelin-2 were found to be grade specific. Our findings provide new insights regarding the association of various signal transduction pathways in MG pathogenesis and may introduce new opportunities for the early detection and prognosis of MGs.

Evaluation of the Biological Properties and the Enzymatic Stability of Glycosylated Luteinizing Hormone-Releasing Hormone Analogs

The enzymatic stability, antitumor activity, and gonadotropin stimulatory effects of glycosylated luteinizing hormone-releasing hormone (LHRH) analogs were investigated in this study. Conjugation of carbohydrate units, including lactose (Lac), glucose (GS), and galactose (Gal) to LHRH peptide protected the peptide from proteolytic degradation and increased the peptides' half-lives in human plasma, rat kidney membrane enzymes, and liver homogenate markedly. Among all seven modified analogs, compound 1 (Lac-[Q(1)][w(6)]LHRH) and compound 6 (GS(4)-[w(6)]LHRH) were stable in human plasma during 4 h of experiment. The half-lives of compounds 1 and 6 improved significantly in kidney membrane enzymes (from 3 min for LHRH to 68 and 103 min, respectively). The major cleavage sites for most of the glycosylated compounds were found to be at Trp(3)-Ser(4) and Ser(4)-Tyr(5) in compounds 1-5. Compound 6 was hydrolyzed at Ser(4)-Tyr(5) and the sugar conjugation site. The antiproliferative activity of the glycopeptides was evaluated on LHRH receptor-positive prostate cancer cells. The glycosylated LHRH derivatives had a significant growth inhibitory effect on the LNCaP cells after a 48-h treatment. It was demonstrated that compound 1 significantly increased the release of luteinizing hormone (LH) at 5 and 10 nM concentrations and compound 5 (GS-[Q(1)]LHRH) stimulated the release of follicle-stimulating hormone (FSH) at 5 nM concentration in dispersed rat pituitary cells (p < 0.05). In our studies, compound 1-bearing lactose and D-Trp was the most stable and active and is a promising candidate for future preclinical investigations in terms of in vitro biological activity and metabolic stability.

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.

Novel peptidomimetics related to gonadotropin-releasing hormone (GnRH)

Novel GnRH I and II analogues were designed and synthesized by Solid Phase Peptides Synthesis (SPPS), since GnRH has antiproliferative properties, but poor metabolic stability.

Regulation of local steroidogenesis in the brain and in prostate cancer: lessons learned from interdisciplinary collaboration

Sex steroids play critical roles in the regulation of the brain and many other organs. Traditionally, researchers have focused on sex steroid signaling that involves travel from the gonads via the circulation to intracellular receptors in target tissues. This classic concept has been challenged, however, by the growing number of cases in which steroids are synthesized locally and act locally within diverse tissues. For example, the brain and prostate carcinoma were previously considered targets of gonadal sex steroids, but under certain circumstances, these tissues can upregulate their steroidogenic potential, particularly when circulating sex steroid concentrations are low. We review some of the similarities and differences between local sex steroid synthesis in the brain and prostate cancer. We also share five lessons that we have learned during the course of our interdisciplinary collaboration, which brought together neuroendocrinologists and cancer biologists. These lessons have important implications for future research in both fields.

Nonreproductive role of gonadotropin-releasing hormone in the control of ascidian metamorphosis

BACKGROUND

Gonadotropin-releasing hormones (GnRHs) are neuropeptides that play central roles in the reproduction of vertebrates. In the ascidian Ciona intestinalis, GnRHs and their receptors are expressed in the nervous systems at the larval stage, when animals are not yet capable of reproduction, suggesting that the hormones have non-reproductive roles.

RESULTS

We showed that GnRHs in Ciona are involved in the animal's metamorphosis by regulating tail absorption and adult organ growth. Absorption of the larval tail and growth of the adult organs are two major events in the metamorphosis of ascidians. When larvae were treated with GnRHs, they completed tail absorption more frequently than control larvae. cAMP was suggested to be a second messenger for the induction of tail absorption by GnRHs. tGnRH-3 and tGnRH-5 (the "t" indicates "tunicate") inhibited the growth of adult organs by arresting cell cycle progression in parallel with the promotion of tail absorption.

CONCLUSIONS

This study provides new insights into the molecular mechanisms of ascidian metamorphosis conducted by non-reproductive GnRHs.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Long-term pituitary downregulation before frozen embryo transfer could improve pregnancy outcomes in women with adenomyosis

Some studies have shown that long-term gonadotropin-releasing hormone (GnRH) agonist administration before in vitro fertilization/intracytoplasmic sperm in infertile women with endometriosis or adenomyosis significantly increases the chances of pregnancy. We were interested in whether long-term GnRH agonist pretreatment could improve pregnancy outcomes in adenomyosis patients undergoing frozen embryo transfer (FET) after preparation of the endometrium with hormone replacement therapy (HRT). Totally, 339 patients with adenomyosis were included in this retrospective study, 194 received long-term GnRH agonist plus HRT (down-regulation + HRT) and 145 received HRT. There were no differences between the groups in characteristic such as age, body mass index, duration or cause of infertility, serum CA-125 level and basal hormone levels. On the day of progesterone administration, mean endometrial thickness and serum progesterone level were significantly greater in HRT patients. Mean score and number of embryos transferred showed no differences. In down regulation + HRT group, clinical pregnancy, implantation and ongoing pregnancy rates were 51.35%, 32.56% and 48.91%, respectively, significantly higher than that of HRT group (24.83%, 16.07% and 21.38%, respectively). So, we concluded that in FET, long-term GnRH agonist pretreatment significantly improved pregnancy outcomes in patients with adenomyosis.

Structure-activity studies of lGnRH-III through rational amino acid substitution and NMR conformational studies

Lamprey gonadotropin-releasing hormone type III (lGnRH-III) is an isoform of GnRH isolated from the sea lamprey (Petromyzon marinus) with negligible endocrine activity in mammalian systems. Data concerning the superior direct anticancer activity of lGnRH-III have been published, raising questions on the structure-activity relationship. We synthesized 21 lGnRH-III analogs with rational amino acid substitutions and studied their effect on PC3 and LNCaP prostate cancer cell proliferation. Our results question the importance of the acidic charge of Asp⁶ for the antiproliferative activity and indicate the significance of the stereochemistry of Trp in positions 3 and 7. Furthermore, conjugation of an acetyl-group to the side chain of Lys⁸ or side chain cyclization of amino acids 1-8 increased the antiproliferative activity of lGnRH-III demonstrating that the proposed salt bridge between Asp⁶ and Lys⁸ is not crucial. Conformational studies of lGnRH-III were performed through NMR spectroscopy, and the solution structure of GnRH-I was solved. In solution, lGnRH-III adopts an extended backbone conformation in contrast to the well-defined β-turn conformation of GnRH-I.

Interactions of the GnRH receptor with heterotrimeric G proteins

G protein-coupled receptors (GPCRs) are the largest class of integral membrane protein receptors in the human genome. We examined here the reports whether the GnRH receptor (GnRHR) interacts with a single or multiple types of G proteins. It seems that the GnRHR, as other GPCRs, alternates between various conformations and is stabilized by its ligands, other modulators and intracellular partners in selective conformations culminating in coupling with a single type or multiple G proteins in a cell- and context-specific manner.

Investigation on chemotactic drug targeting (chemotaxis and adhesion) inducer effect of GnRH-III derivatives in Tetrahymena and human leukemia cell line

GnRH-III has been shown to exert a cytotoxic effect on the GnRH-R positive tumor cells. The chemotactic drug targeting (CDT) represents a new way for drug delivery approach based on selective chemoattractant guided targeting. The major goal of the present work was to develop and investigate various GnRH-III derivatives as potential targeting moieties for CDT. The cell physiological effects (chemotaxis, adhesion, and signaling) induced by three native GnRHs (hGnRH-I, cGnRH-II, and lGnRH-III) and nine GnRH-III derivatives were evaluated in two model cells (Tetrahymena pyriformis and Mono Mac 6 human monocytes). According to our results, the native GnRH-III elicited the highest chemoattractant and adhesion inducer activities of all synthesized peptides in micromolar concentrations in monocytes. With respect to chemoattraction, dimeric derivatives linked by a disulfide bridge ([GnRH-III(C)](2) ) proved to be efficient in both model cells; furthermore, acetylation of the linker region ([GnRH-III(Ac-C)](2) ) could slightly improve the chemotactic and adhesion effects in monocytes. The length of the peptide and the type of N-terminal amino acid could also determine the chemotactic and adhesion modulation potency of each fragment. The application of the chemoattractant GnRH-III derivatives was accompanied by a significant activation of phosphatidylinositol 3-kinase in both model cells. In summary, our work on low-level differentiated model cells of tumors has proved that GnRH-III and some of its synthetic derivatives are promising candidates to be applied in CDT: these compounds might act both as carrier, delivery unit, and antitumor agents.

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.

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.

Using automated imaging to interrogate gonadotrophin-releasing hormone receptor trafficking and function

Gonadotrophin-releasing hormone (GnRH) acts via seven transmembrane receptors on gonadotrophs to stimulate gonadotrophin synthesis and secretion, and thereby mediates central control of reproduction. Type I mammalian GnRHR are unique, in that they lack C-terminal tails. This is thought to underlie their resistance to rapid homologous desensitisation as well as their slow rate of internalisation and inability to provoke G-protein-independent (arrestin-mediated) signalling. More recently it has been discovered that the vast majority of human GnRHR are actually intracellular, in spite of the fact that they are activated at the cell surface by a membrane impermeant peptide hormone. This apparently reflects inefficient exit from the endoplasmic reticulum and again, the absence of the C-tail likely contributes to their intracellular localisation. This review is intended to cover some of these novel aspects of GnRHR biology, focusing on ways that we have used automated fluorescence microscopy (high content imaging) to explore GnRHR localisation and trafficking as well as spatial and temporal aspects of GnRH signalling via the Ca(2+)/calmodulin/calcineurin/NFAT and Raf/MEK/ERK pathways.

Luteinizing Hormone-Releasing Hormone (LHRH)-I antagonist cetrorelix inhibits myeloma cell growth in vitro and in vivo

The objective of this study was to determine the effects of an luteinizing hormone-releasing hormone (LHRH)-I antagonist, Cetrorelix, on human multiple myeloma (MM) cells and to elucidate the mechanisms of action. We showed that LHRH-I and LHRHR-I genes were expressed in MM cell lines and primary MM cells. Treatment with Cetrorelix inhibited growth and colony-forming ability of myeloma cells, including cell lines resistant to arsenic trioxide, bortezomib, or lenalidomide. Cetrorelix induced apoptosis in myeloma cells including primary myeloma cells. In addition, Cetrorelix inhibited the growth of human myeloma cells xenografted into mice without any apparent side effects. Cetrorelix downregulated the nuclear factor-kappa B (NF-κB) pathway activity and the expression of cytokines, including interleukin 6, insulin-like growth factor 1, VEGF-A, and stromal-derived factor 1, important for myeloma cell growth and survival in myeloma cells and/or marrow stromal cells from myeloma patients. Cetrorelix decreased the phosphorylation of extracellular signal regulated kinase 1/2 and STAT3 in myeloma cells, two crucial pathways for myeloma cells growth and survival. Moreover, the expression of p21 and p53 was increased, whereas that of antiapoptotic proteins Bcl-2 and Bcl-x(L) was reduced by Cetrorelix. Our findings indicate that Cetrorelix induces cytotoxicity in myeloma cells through various mechanisms and provide a rationale for investigating Cetrorelix for the treatment of MM.

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.

Peptide-mediated targeted drug delivery

Targeted drug delivery to specific group of cells offers an attractive strategy to minimize the undesirable side effects and achieve the therapeutic effect with a lower dose. Both linear and cyclic peptides have been explored as trafficking moiety due to ease of synthesis, structural simplicity, and low probability of undesirable immunogenicity. Peptides derived from sequence of cell surface proteins, such as intercellular adhesion molecule-1 (ICAM-1), LHRH, Bombesin, and LFA-1, have shown potent binding affinity to the target cell surface receptors. Moreover, peptides derived from ICAM-1 receptor can be internalized by the leukemic T-cells along with the conjugated moiety offering the promise to selectively treat cancers and autoimmune diseases. Systematic analyses have revealed that physicochemical properties of the drug-peptide conjugates and their mechanism of receptor-mediated cellular internalization are important controlling factors for developing a successful targeting system. This review is focused on understanding the factors involved in the development of an effective drug-peptide conjugate with an emphasis on the chemistry and biology of the conjugates. Reported results on several promising drug-peptide conjugates have been critically evaluated. The approaches and results presented here will serve as a guide to systematically approach targeted delivery of cytotoxic drug molecules using peptides for treatment of several diseases.

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.

Trafficking and signalling of gonadotrophin-releasing hormone receptors: an automated imaging approach

Gonadotrophin-releasing hormone (GnRH) is a neuropeptide that mediates central control of reproduction by stimulating gonadotrophin secretion from the pituitary. It acts via 7 transmembrane region (7TM) receptors that lack C-terminal tails, regions that for many 7TM receptors, are necessary for agonist-induced phosphorylation and arrestin binding as well as arrestin-dependent desensitization, internalization and signalling. Recent work has revealed that human GnRH receptors (GnRHR) are poorly expressed at the cell surface. This apparently reflects inefficient exit from the endoplasmic reticulum, which is thought to be increased by pharmacological chaperones (non-peptide GnRHR antagonists that increase cell surface GnRHR expression) or reduced by point mutations that further impair GnRHR trafficking and thereby cause infertility. Here, we review recent work in this field, with emphasis on the use of semi-automated imaging to interrogate compartmentalization and trafficking of these unique 7TM receptors.