Isolation and sequencing of cDNAs for splice variants of growth hormone-releasing hormone receptors from human cancers

The Role of Receptor-Ligand Interaction in Somatostatin Signaling Pathways: Implications for Neuroendocrine Tumors

Neuroendocrine tumors (NETs) arise from neuroendocrine cells and manifest in diverse organs. Key players in their regulation are somatostatin and its receptors (SSTR1-SSTR5). Understanding receptor-ligand interactions and signaling pathways is vital for elucidating their role in tumor development and therapeutic potential. This review highlights SSTR characteristics, localization, and expression in tissues, impacting physiological functions. Mechanisms of somatostatin and synthetic analogue binding to SSTRs, their selectivity, and their affinity were analyzed. Upon activation, somatostatin initiates intricate intracellular signaling, involving cAMP, PLC, and MAP kinases and influencing growth, differentiation, survival, and hormone secretion in NETs. This review explores SSTR expression in different tumor types, examining receptor activation effects on cancer cells. SSTRs' significance as therapeutic targets is discussed. Additionally, somatostatin and analogues' role in hormone secretion regulation, tumor growth, and survival is emphasized, presenting relevant therapeutic examples. In conclusion, this review advances the knowledge of receptor-ligand interactions and signaling pathways in somatostatin receptors, with potential for improved neuroendocrine tumor treatments.

Molecular basis of signal transduction mediated by the human GIPR splice variants

Glucose-dependent insulinotropic polypeptide receptor (GIPR) is a potential drug target for metabolic disorders. It works with glucagon-like peptide-1 receptor and glucagon receptor in humans to maintain glucose homeostasis. Unlike the other two receptors, GIPR has at least 13 reported splice variants (SVs), more than half of which have sequence variations at either C or N terminus. To explore their roles in endogenous peptide-mediated GIPR signaling, we determined the cryoelectron microscopy (cryo-EM) structures of the two N terminus-altered SVs (referred as GIPR-202 and GIPR-209 in the Ensembl database, SV1 and SV2 here, respectively) and investigated the outcome of coexpressing each of them in question with GIPR in HEK293T cells with respect to ligand binding, receptor expression, cAMP (adenosine 3,5-cyclic monophosphate) accumulation, β-arrestin recruitment, and cell surface localization. It was found that while both N terminus-altered SVs of GIPR neither bound to the hormone nor elicited signal transduction per se, they suppressed ligand binding and cAMP accumulation of GIPR. Meanwhile, SV1 reduced GIPR-mediated β-arrestin 2 responses. The cryo-EM structures of SV1 and SV2 showed that they reorganized the extracellular halves of transmembrane helices 1, 6, and 7 and extracellular loops 2 and 3 to adopt a ligand-binding pocket-occupied conformation, thereby losing binding ability to the peptide. The results suggest a form of signal bias that is constitutive and ligand-independent, thus expanding our knowledge of biased signaling beyond pharmacological manipulation (i.e., ligand specific) as well as constitutive and ligand-independent (e.g., SV1 of the growth hormone-releasing hormone receptor).

GNRH2 Polymorphism in Men With Prostate Cancer Treated With Androgen Deprivation Therapy

BACKGROUND/AIM

Gonadotropin-releasing hormone 2 (GNRH2) is a poorly-studied peptide hormone that is widely distributed in the central nervous system and expressed in peripheral tissues of mammals. The non-synonymous rs6051545 variant in GNRH2 (A16V) has been linked to higher serum testosterone concentrations. This study investigated whether the A16V variant is associated with altered androgen-deprivation therapy (ADT) progression-free survival (PFS) and overall survival (OS).

PATIENTS AND METHODS

We examined the expression of GNRH2 in prostate tissue microarrays comprising normal tissue, prostatic hyperplasia, and prostate cancer using immunofluorescence. We also evaluated the GNRH2 genotype in 131 patients with prostate cancer who received ADT and compared PFS and OS between the variant and wild-type genotypes.

RESULTS

GNRH2 was detected in all prostate tissues, although expression did not vary with Gleason grade or disease stage (p=0.71). The GNRH2 A16V genotype was not associated with PFS or OS; however, univariate and multivariate analyses revealed Gleason score and definitive local therapy were each associated with PFS (p≤0.0074), whereas age and Gleason score were associated with OS (p≤0.0046).

CONCLUSION

GNRH2 is expressed in normal, hyperplastic, and neoplastic prostate tissues; the A16V variant is not related to treatment outcome or survival.

Signaling mechanism of growth hormone-releasing hormone receptor

The hypothalamic peptide growth hormone-releasing hormone (GHRH) stimulates the secretion of growth hormone (GH) from the pituitary through binding and activation of the pituitary type of GHRH receptor (GHRH-R), which belongs to the family of G protein-coupled receptors with seven potential membrane-spanning domains. Splice variants of GHRH-Rs (SV) in human tumors and other extra pituitary tissues were identified and their cDNA was sequenced. Among the SVs, splice variant 1 (SV1) possesses the greatest similarity to the full-length GHRH-R and remains functional by eliciting cAMP signaling and mitogenic activity upon GHRH stimulation. A large body of work have evaluated potential clinical applications of agonists and antagonists of GHRH in diverse fields, including endocrinology, oncology, cardiology, diabetes, obesity, metabolic dysfunctions, Alzheimer's disease, ophthalmology, wound healing and other applications. In this chapter, we briefly review the expression and potential function of GHRH-Rs and their SVs in various tissues and also elucidate and summarize the activation, molecular mechanism and signalization pathways of these receptors. Therapeutic applications of GHRH analogs are also discussed.

Updates in neuroendocrine neoplasms: From mechanisms to the clinic

Scientific advances constantly improve our understanding of the mechanisms underlying tumorigenesis, allowing us now to analyze cancer in a more precise manner and to identify at an earlier stage the tumors that have greater risk of aggressive behavior. Understanding neuroendocrine neoplasms at molecular level has enabled increasingly targeted treatments, with safety and efficacy validated in large randomized trials. Moreover, the first studies of targeted therapies after molecular profiling of neuroendocrine neoplasms have shown encouraging results, allowing us to foresee ever more personalized medical treatments in the future. This literature review aims to summarize recent advances in the study of neuroendocrine neoplasms and to show how identification of new mechanisms underlying tumorigenesis can be of benefit in clinical practice.

Expression of Growth Hormone-Releasing Hormone and Its Receptor Splice Variants in Primary Human Endometrial Carcinomas: Novel Therapeutic Approaches

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the growth of various tumors, including endometrial carcinomas (EC). However, tumoral receptors that mediate the antiproliferative effects of GHRH antagonists in human ECs have not been fully characterized. In this study, we investigated the expression of mRNA for GHRH and splice variants (SVs) of GHRH receptors (GHRH-R) in 39 human ECs and in 7 normal endometrial tissue samples using RT-PCR. Primers designed for the PCR amplification of mRNA for the full length GHRH-R and SVs were utilized. The PCR products were sequenced, and their specificity was confirmed. Nine ECs cancers (23%) expressed mRNA for SV1, three (7.7%) showed SV2 and eight (20.5%) revealed mRNA for SV4. The presence of SVs for GHRH-Rs could not be detected in any of the normal endometrial tissue specimens. The presence of specific, high affinity GHRH-Rs was also demonstrated in EC specimens using radioligand binding studies. Twenty-four of the investigated thirty-nine tumor samples (61.5%) and three of the seven corresponding normal endometrial tissues (42.9%) expressed mRNA for GHRH ligand. Our findings suggest the possible existence of an autocrine loop in EC based on GHRH and its tumoral SV receptors. The antiproliferative effects of GHRH antagonists on EC are likely to be exerted in part by the local SVs and GHRH system.

Modulating effects of RAMPs on signaling profiles of the glucagon receptor family

Receptor activity-modulating proteins (RAMPs) are accessory molecules that form complexes with specific G protein-coupled receptors (GPCRs) and modulate their functions. It is established that RAMP interacts with the glucagon receptor family of GPCRs but the underlying mechanism is poorly understood. In this study, we used a bioluminescence resonance energy transfer (BRET) approach to comprehensively investigate such interactions. In conjunction with cAMP accumulation, Gα_q activation and β-arrestin1/2 recruitment assays, we not only verified the GPCR–RAMP pairs previously reported, but also identified new patterns of GPCR–RAMP interaction. While RAMP1 was able to modify the three signaling events elicited by both glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), and RAMP2 mainly affected β-arrestin1/2 recruitment by GCGR, GLP-1R and glucagon-like peptide-2 receptor, RAMP3 showed a widespread negative impact on all the family members except for growth hormone-releasing hormone receptor covering the three pathways. Our results suggest that RAMP modulates both G protein dependent and independent signal transduction among the glucagon receptor family members in a receptor-specific manner. Mapping such interactions provides new insights into the role of RAMP in ligand recognition and receptor activation.

Impact of growth hormone-releasing hormone (GHRH) antagonist on Decidual stromal cell growth and apoptosis in vitro

Endometrial stromal cells remodeling is critical during human pregnancy. GHRH and its functional receptor have been shown to be expressed in gynecological cancer cells and eutopic endometrial stromal cells. Recent studies have demonstrated the potential clinical uses of antagonists of GHRH as effective antitumor agents because of its directly antagonistic effect on the locally produced GHRH in gynecological tumors. However, the impact of GHRH antagonists on normal endometrial stromal cell growth remained to be elucidated. The aim of this study was to investigate the effect of a GHRH antagonist (JMR-132) on cell proliferation and apoptosis of human decidual stromal cells and the underlying molecular mechanisms. Our results showed that GHRH and the splice variant 1 (SV1) of GHRH receptor (GHRH-R SV1) are expressed in human decidual stromal cells isolated from the decidual tissues of early pregnant women receiving surgical abortion. In addition, treatment of stroma cells with JMR-132 induced cell apoptosis with increasing cleaved caspase-3 and caspase-9 activities, and decrease cell viability in a time- and dose-dependent manner. Using a dual inhibition approach (pharmacological inhibitors and siRNA-mediated knockdown), we showed that JMR-132-induced activation of apoptotic signals are mediated by the activation of ERK1/2 and JNK signaling pathways and the subsequent upregulation of GADD45α. Taken together, JMR-132 suppresses cell survival of decidual stromal cells by inducing apoptosis through the activation of ERK1/2- and JNK-mediated upregulation of GADD45α in human endometrial stromal cells. Our findings provide new insights into the potential impact of GHRH antagonist on the decidual programming in humans.

Constitutive signal bias mediated by the human GHRHR splice variant 1

The mechanism of functional changes induced by alternative splicing of GHRHR is largely unknown. Here, we demonstrate that GHRH-elicited signal bias toward β-arrestin recruitment is constitutively mediated by SV1. The cryogenic electron microscopy structures of SV1 and molecular dynamics simulations reveal the different functionalities between GHRHR and SV1 at the near-atomic level (i.e., the N termini of GHRHR and SV1 differentiate the downstream signaling pathways, G_s versus β-arrestins). Our findings provide valuable insights into the functional diversity of class B1 GPCRs that may aid in the design of better therapeutic agents against certain cancers.

Alternative splicing of G protein–coupled receptors has been observed, but their functions are largely unknown. Here, we report that a splice variant (SV1) of the human growth hormone–releasing hormone receptor (GHRHR) is capable of transducing biased signal. Differing only at the receptor N terminus, GHRHR predominantly activates G_s while SV1 selectively couples to β-arrestins. Based on the cryogenic electron microscopy structures of SV1 in the apo state or GHRH-bound state in complex with the G_s protein, molecular dynamics simulations reveal that the N termini of GHRHR and SV1 differentiate the downstream signaling pathways, G_s versus β-arrestins. As suggested by mutagenesis and functional studies, it appears that GHRH-elicited signal bias toward β-arrestin recruitment is constitutively mediated by SV1. The level of SV1 expression in prostate cancer cells is also positively correlated with ERK1/2 phosphorylation but negatively correlated with cAMP response. Our findings imply that constitutive signal bias may be a mechanism that ensures cancer cell proliferation.

Prognostic Alternative Splicing Signatures in Esophageal Carcinoma

Alternative splicing (AS) is a method of increasing the number of proteins that the genome is capable of coding for, by altering the pre-mRNA during its maturation. This process provides the ability of a broad range of proteins to arise from a single gene. AS events are known to occur in up to 94% of human genes. Cumulative data have shown that aberrant AS functionality is a major factor in human diseases. This review focuses on the contribution made by aberrant AS functionality in the development and progression of esophageal cancer. The changes in the pattern of expression of alternately spliced isoforms in esophageal cancer can be used as diagnostic or prognostic biomarkers. Additionally, these can be used as targets for the development of new treatments for esophageal cancer.

Splice variant of growth hormone-releasing hormone receptor drives esophageal squamous cell carcinoma conferring a therapeutic target

An explanation has been lacking for the suppressive action of antagonists of growth hormone-releasing hormone receptors (GHRH-Rs) on cancers that do not express GHRH-Rs, an established target of the antagonists. We demonstrate here that esophageal squamous cell carcinoma (ESCC), a representative cancer type that barely expresses GHRH-Rs, responds to GHRH-R antagonists. Hypoxia induces GHRH-R splice variant 1 (SV1) and activates a key glycolytic enzyme. Glycolytic metabolism and tumor progression are promoted by activation of SV1 and reversed by the GHRH-R antagonist MIA-602. A high expression of SV1 in ESCC patients predicts a poor prognosis. These findings document the importance of SV1 as a target of GHRH-R antagonists and underline the therapeutic potential of GHRH-R antagonists against SV1-expressing cancers.

The extrahypothalamic growth hormone-releasing hormone (GHRH) and its cognate receptors (GHRH-Rs) and splice variants are expressed in a variety of cancers. It has been shown that the pituitary type of GHRH-R (pGHRH-R) mediates the inhibition of tumor growth induced by GHRH-R antagonists. However, GHRH-R antagonists can also suppress some cancers that do not express pGHRH-R, yet the underlying mechanisms have not been determined. Here, using human esophageal squamous cell carcinoma (ESCC) as a model, we were able to reveal that SV1, a known splice variant of GHRH-R, is responsible for the inhibition induced by GHRH-R antagonist MIA-602. We demonstrated that GHRH-R splice variant 1 (SV1) is a hypoxia-driven promoter of tumor progression. Hypoxia-elevated SV1 activates a key glycolytic enzyme, muscle-type phosphofructokinase (PFKM), through the nuclear factor kappa B (NF-κB) pathway, which enhances glycolytic metabolism and promotes progression of ESCC. The malignant actions induced by the SV1–NF-κB–PFKM pathway could be reversed by MIA-602. Altogether, our studies demonstrate a mechanism by which GHRH-R antagonists target SV1. Our findings suggest that SV1 is a hypoxia-induced oncogenic promoter which can be an alternative target of GHRH-R antagonists.

Growth hormone releasing hormone in the unfolded protein response context

The effects of Growth Hormone Releasing Hormone in human pathophysiology are not limited to those mediated by the Growth Hormone Releasing Hormone-Growth Hormone-Insulin-like Growth Factor-I axis. Receptors specific for this neuropeptide are expressed in a diverse variety of human tissues, to initiate multifarious signaling cascades, regulators of cellular homeostasis and survival. The Unfolded Protein Response is in charge of adaptive responses towards a plethora of challenges, able to trigger cellular repair or death. The possible involvement of Growth Hormone Releasing Hormone and its agonistic and antagonistic analogs in those events, may deliver exciting possibilities in the treatment of human disease, including the Acute Respiratory Distress Syndrome.

The Microenvironment of Pituitary Tumors-Biological and Therapeutic Implications

The tumor microenvironment (TME) includes resident and infiltrative non-tumor cells, as well as blood and lymph vessels, extracellular matrix molecules, and numerous soluble factors, such as cytokines and chemokines. While the TME is now considered to be a prognostic tool and a therapeutic target for many cancers, little is known about its composition in pituitary tumors. This review summarizes our current knowledge of the TME within pituitary tumors and the strong interest in TME as a therapeutic target. While we cover the importance of angiogenesis and immune infiltrating cells, we also address the role of the elusive folliculostellate cells, the emerging literature on pituitary tumor-associated fibroblasts, and the contribution of extracellular matrix components in these tumors. The cases of human pituitary tumors treated with TME-targeting therapies are reviewed and emerging concepts of vascular normalization and combined therapies are presented. Together, this snapshot overview of the current literature pinpoints not only the underestimated role of TME components in pituitary tumor biology, but also the major promise it may offer for both prognosis and targeted therapeutics.

Peptides derived from the extracellular domain of the somatostatin receptor splicing variant SST5TMD4 increase malignancy in multiple cancer cell types

Extracellular fragments derived from plasma membrane receptors can play relevant roles in the development/progression of tumor pathologies, thereby offering novel diagnostic or therapeutic opportunities. The truncated variant of somatostatin receptor subtype-5, SST5TMD4, is an aberrantly spliced receptor with 4 transmembrane domains, highly overexpressed in several tumor types, whose C-terminal tail is exposed towards the extracellular matrix, and could therefore be the substrate for proteolytic enzymes. In silico analysis implemented herein predicted 2 possible cleavage sites for metalloproteases MMP2, 9, 14, and 16 in its sequence, which could generate 3 releasable peptides. Of note, expression of those MMPs was directly correlated with SST5TMD4 in several cancer-derived cell lines (ie neuroendocrine tumors and prostate, breast, and liver cancers). Moreover, incubation with SST5TMD4-derived peptides enhanced malignancy features in all cancer cell types tested (ie proliferation, migration, etc.) and blunted the antiproliferative response to somatostatin in QGP-1 cells, acting probably through PI3K/AKT and/or MEK/ERK signaling pathways and the modulation of key cancer-associated genes (eg MMPs, MKI67, ACTR2/3, CD24/44). These results suggest that SST5TMD4-derived peptides could contribute to the strong oncogenic role of SST5TMD4 observed in multiple tumor pathologies, and, therefore, represent potential candidates to identify novel diagnostic, prognostic, or therapeutic targets in cancer.

Actions and Potential Therapeutic Applications of Growth Hormone-Releasing Hormone Agonists

In this article, we briefly review the identification of GHRH, provide an abridged overview of GHRH antagonists, and focus on studies with GHRH agonists. Potent GHRH agonists of JI and MR class were synthesized and evaluated biologically. Besides the induction of the release of pituitary GH, GHRH analogs promote cell proliferation and exert stimulatory effects on various tissues, which express GHRH receptors (GHRH-Rs). A large body of work shows that GHRH agonists, such as MR-409, improve pancreatic β-cell proliferation and metabolic functions and facilitate engraftment of islets after transplantation in rodents. Accordingly, GHRH agonists offer a new therapeutic approach to treating diabetes. Various studies demonstrate that GHRH agonists promote repair of cardiac tissue, producing improvement of ejection fraction and reduction of infarct size in rats, reduction of infarct scar in swine, and attenuation of cardiac hypertrophy in mice, suggesting clinical applications. The presence of GHRH-Rs in ocular tissues and neuroprotective effects of GHRH analogs in experimental diabetic retinopathy indicates their possible therapeutic applications for eye diseases. Other effects of GHRH agonists, include acceleration of wound healing, activation of immune cells, and action on the central nervous system. As GHRH might function as a growth factor, we examined effects of GHRH agonists on tumors. In vitro, GHRH agonists stimulate growth of human cancer cells and upregulate GHRH-Rs. However, in vivo, GHRH agonists inhibit growth of human cancers xenografted into nude mice and downregulate pituitary and tumoral GHRH-Rs. Therapeutic applications of GHRH analogs are discussed. The development of GHRH analogs should lead to their clinical use.

Agonists of growth hormone-releasing hormone (GHRH) inhibit human experimental cancers in vivo by down-regulating receptors for GHRH

The effects of the growth hormone-releasing hormone (GHRH) agonist MR409 on various human cancer cells were investigated. In H446 small cell lung cancer (SCLC) and HCC827 and H460 (non-SCLC) cells, MR409 promoted cell viability, reduced cell apoptosis, and induced the production of cellular cAMP in vitro. Western blot analyses showed that treatment of cancer cells with MR409 up-regulated the expression of cyclins D1 and D2 and cyclin-dependent kinases 4 and 6, down-regulated p27^kip1, and significantly increased the expression of the pituitary-type GHRH receptor (pGHRH-R) and its splice-variant (SV1). Hence, in vitro MR409 exerts agonistic action on lung cancer cells in contrast to GHRH antagonists. However, in vivo, MR409 inhibited growth of lung cancers xenografted into nude mice. MR409 given s.c. at 5 μg/day for 4 to 8 weeks significantly suppressed growth of HCC827, H460, and H446 tumors by 48.2%, 48.7%, and 65.6%, respectively. This inhibition of tumor growth by MR409 was accompanied by the down-regulation of the expression of pGHRH-R and SV1 in the pituitary gland and tumors. Tumor inhibitory effects of MR409 in vivo were also observed in other human cancers, including gastric, pancreatic, urothelial, prostatic, mammary, and colorectal. This inhibition of tumor growth parallel to the down-regulation of GHRH-Rs is similar and comparable to the suppression of sex hormone-dependent cancers after the down-regulation of receptors for luteinizing hormone-releasing hormone (LHRH) by LHRH agonists. Further oncological investigations with GHRH agonists are needed to elucidate the underlying mechanisms.

A new approach to the treatment of acute myeloid leukaemia targeting the receptor for growth hormone-releasing hormone

Growth hormone-releasing hormone (GHRH) is secreted by the hypothalamus and acts on the pituitary gland to stimulate the release of growth hormone (GH). GHRH can also be produced by human cancers, in which it functions as an autocrine/paracrine growth factor. We have previously shown that synthetic antagonistic analogues of GHRH are able to successfully suppress the growth of 60 different human cancer cell lines representing over 20 cancers. Nevertheless, the expression of GHRH and its receptors in leukaemias has never been examined. Our study demonstrates the presence of GHRH receptor (GHRH-R) on 3 of 4 human acute myeloid leukaemia (AML) cell lines-K-562, THP-1, and KG-1a-and significant inhibition of proliferation of these three cell lines in vitro following incubation with the GHRH antagonist MIA-602. We further show that this inhibition of proliferation is associated with the upregulation of pro-apoptotic genes and inhibition of Akt signalling in leukaemic cells. Treatment with MIA-602 of mice bearing xenografts of these human AML cell lines drastically reduced tumour growth. The expression of GHRH-R was further confirmed in 9 of 9 samples from patients with AML. These findings offer a new therapeutic approach to this malignancy and suggest a possible role of GHRH-R signalling in the pathology of AML.

Growth hormone-releasing hormone antagonist inhibits the invasiveness of human endometrial cancer cells by down-regulating twist and N-cadherin expression

More than 25% of patients diagnosed with endometrial carcinoma have invasive primary cancer accompanied by metastases. Growth hormone-releasing hormone (GHRH) plays an important role in reproduction. Here, we examined the effect of a GHRH antagonist on the motility of endometrial cancer cells and the mechanisms of action of the antagonist in endometrial cancer. Western blotting and immunohistochemistry (IHC) were used to determine the expression of the GHRH receptor protein. The activity of Twist and N-cadherin was determined by Western blotting. Cell motility was assessed by an invasion and migration assay. GHRH receptor siRNA was applied to knockdown the GHRH receptor in endometrial cancer cells. The GHRH antagonist inhibited cell motility in a dose-dependent manner. The GHRH antagonist inhibited cell motility and suppressed the expression of Twist and N-cadherin, and the suppression was abolished by GHRH receptor siRNA pretreatment. Moreover, the inhibition of Twist and N-cadherin with Twist siRNA and N-cadherin siRNA, respectively, suppressed cell motility. Our study indicates that the GHRH antagonist inhibited the cell motility of endometrial cancer cells through the GHRH receptor via the suppression of Twist and N-cadherin. Our findings represent a new concept in the mechanism of GHRH antagonist-suppressed cell motility in endometrial cancer cells and suggest the possibility of exploring GHRH antagonists as potential therapeutics for the treatment of human endometrial cancer.

Agonistic analogs of growth hormone releasing hormone (GHRH) promote wound healing by stimulating the proliferation and survival of human dermal fibroblasts through ERK and AKT pathways

Decreased or impaired proliferation capability of dermal fibroblasts interferes with successful wound healing. Several growth factors tested failed to fully restore the growth of fibroblasts, possibly due to their rapid degradation by proteases. It is therefore critical to find new agents which have stimulatory effects on fibroblasts while being highly resistant to degradation. In such a scenario, the activities of two agonistic analogs of growth hormone releasing hormone (GHRH), MR-409 and MR-502, were evaluated for their impact on proliferation and survival of primary human dermal fibroblasts. In vitro, both analogs significantly stimulated cell growth by more than 50%. Under serum-depletion induced stress, fibroblasts treated with MR-409 or MR-502 demonstrated better survival rates than control. These effects can be inhibited by either PD98059 or wortmannin. Signaling through MEK/ERK1/2 and PI3K/AKT in an IGF-1 receptor-independent manner is required. In vivo, MR-409 promoted wound closure. Animals treated topically with MR-409 healed earlier than controls in a dose-dependent manner. Histologic examination revealed better wound contraction and less fibrosis in treated groups. In conclusion, MR-409 is a potent mitogenic and anti-apoptotic factor for primary human dermal fibroblasts. Its beneficial effects on wound healing make it a promising agent for future development.

Anti-proliferative and pro-apoptotic effects of GHRH antagonists in prostate cancer

Growth hormone-releasing hormone (GHRH) and its receptors have been implicated in the progression of various tumors. In vitro and in vivo studies have demonstrated that GHRH antagonists inhibit the growth of several cancers. GHRH antagonists, JMR-132 and JV-1-38 inhibit the growth of androgen-independent prostate tumors. Here we investigated the involvement of GHRH antagonists in proliferative and apoptotic processes. We used non-tumoral RWPE-1 and tumoral LNCaP and PC3 human prostatic epithelial cells, as well as an experimental model of human tumor PC3 cells. We evaluated the effects of JMR-132 and JV-1-38 antagonists on cell viability and proliferation in the three cell lines by means of MTT and BrdU assays, respectively, as well as on cell cycle and apoptotic process in PC3 cells. The expression levels of PCNA, p53, p21, CD44, Cyclin D1, c-myc, Bax and Bcl2 were determined in both in vivo and in vitro models by means of Western-blot and RT-PCR. GHRH antagonists suppressed cell proliferation and decreased the levels of the proliferation marker, PCNA, in the three cell lines and in PC3 tumor. GHRH antagonists led to an increase of cells in S-phase and a decrease in G1 and G2/M phases, and induced S-phase arrest and increase of apoptotic cells. The effects of GHRH-antagonists on cell cycle could be due to the changes observed in the expression of p21, p53, Bax, Bcl2, CD44, Cyclin D1, c-myc and caspase 3. Present results confirm and extend the role of GHRH antagonists as anti-proliferative and pro-apoptotic molecules in prostate cancer.

Possible Predictive Markers of Response to Therapy in Esophageal Squamous Cell Cancer

The aim of the present study was to investigate the relationship between the intensity of biomarker expression and the response to radiochemotherapy in patients with advanced esophageal squamous cell cancer (ESCC). Ninety-two patients with locally advanced ESCC were examined retrospectively. Pre-treatment tumor samples were stained for proteins SOUL, Hsp 16.2, Growth Hormone-Releasing Hormone Receptor (GHRH-R) and p-Akt using immunhistochemistry methods. Kaplan-Meier curves were used to show the relationship between intensity of expression of biomarkers and clinical parameters and 3-year OS. A significant correlation was found between high intensity staining for Hsp 16.2, p-Akt and SOUL and poor response to NRCT. Application of a higher dose of radiation and higher dose of cisplatin resulted in better clinical and histopathological responses, respectively. Among the clinical parameters, the localization of the tumor in the upper-third of the esophagus and less than 10% weight loss were independent prognostic factors for increased 3-year OS. Hsp16.2, p-Akt and SOUL are predictors of negative response to NRCT, therefore these biomarkers may become promising targets for therapy. Furthermore, level of expression of p-Akt, weight loss and the localization of the tumor are significant factors in the prediction of OS in ESCC.

Inhibitory Effects of Antagonists of Growth Hormone-Releasing Hormone (GHRH) in Thyroid Cancer

Growth hormone-releasing hormone (GHRH) is a peptide hormone secreted by the hypothalamus that regulates the synthesis and secretion of growth hormone (GH) in the pituitary. The extra-hypothalamic GHRH and its cognate receptors (GHRHR and splice variants) play a mitogenic role by stimulating cell proliferation and preventing apoptotic cell death. It is well established that GHRH antagonists inhibit the growth, tumorigenicity, and metastasis of various human malignancies. In this work, we studied the effect of two new GHRH antagonists, MIA602 and MIA690, on thyroid cancer. We studied the effect of MIA602 and MIA690 on thyroid cancer in vitro, using human thyroid cancer cell lines, and in vivo, using chicken embryo chorioallantoic membrane (CAM) assays. We found that mRNA for GHRH and GHRH receptor is expressed in thyroid cell lines and in samples of thyroid tumors. Immunohistochemistry confirmed the expression of GHRHR protein in specimens of thyroid tumor. We observed that GHRH antagonists inhibited the growth and increased apoptosis of thyroid cancer cells. In vivo, the antagonists inhibited growth and angiogenesis of engrafted thyroid tumors. Our results suggest that GHRH expression may play a role in growth of thyroid cancer and that GHRH antagonists can be a therapeutic option for thyroid cancer patients.

Growth hormone-releasing hormone is produced by adipocytes and regulates lipolysis through growth hormone receptor

BACKGROUND

Growth hormone-releasing hormone (GHRH) has a crucial role in growth hormone (GH) secretion, but little is known about its production by adipocytes and its involvement in adipocyte metabolism.

OBJECTIVES

To determine whether GHRH and its receptor (GHRH-R) are present in human adipocytes and to study their levels in obesity. Also, to analyze the effects of GHRH on human adipocyte differentiation and lipolysis.

METHODS

GHRH/GHRH-R and GH/GH-R mRNA expression levels were analyzed in human mature adipocytes from non-obese and morbidly obese subjects. Human mesenchymal stem cells (HMSC) were differentiated to adipocytes with GHRH (10^-14-10^-8 M). Adipocyte differentiation, lipolysis and gene expression were measured and the effect of GH-R silencing was determined.

RESULTS

Mature adipocytes from morbidly obese subjects showed a higher expression of GHRH and GH-R, and a lower expression of GHRH-R and GH than non-obese subjects (P<0.05). A total of 10^-14-10^-10 M GHRH induced an inhibition of lipid accumulation and PPAR-γ expression (P<0.05), and an increase in glycerol release and HSL expression (P<0.05) in human differentiated adipocytes. A total of 10^-12-10^-8 M GHRH decreased GHRH-R expression in human differentiated adipocytes (P<0.05). A total of 10^-10-10^-8 M GHRH increased GH and GH-R expression in human differentiated adipocytes (P<0.05). The effects of GHRH at 10^-10 M on adipocyte differentiation and lipolysis were blocked when GH-R expression was silenced.

CONCLUSIONS

GHRH and GHRH-R are expressed in human adipocytes and are negatively associated. GHRH at low doses may exert an anti-obesity effect by inhibiting HMSC differentiation in adipocytes and by increasing adipocyte lipolysis in an autocrine or paracrine pathway. These effects are mediated by GH and GH-R.

Expression of hypothalamic neurohormones and their receptors in the human eye

Extrapituitary roles for hypothalamic neurohormones have recently become apparent and clinically relevant, based on the use of synthetic peptide analogs for the treatment of multiple conditions including cancers, pulmonary edema and myocardial infarction. In the eye, it has been suggested that some of these hormones and their receptors may be present in the ciliary body, iris, trabecular meshwork and retina, but their physiological role has yet to be elucidated. Our study intends to comprehensively demonstrate the expression of some hypothalamic neuroendocrine hormones and their receptors within different retinal and extraretinal structures of the human eye. Immunofluorescence, Western blot analysis, and RT-PCR were used to evaluate the qualitative and quantitative expression of Luteinizing Hormone Releasing Hormone (LHRH), Growth Hormone Releasing Hormone (GHRH), Thyrotropin Releasing Hormone (TRH), Gastrin Releasing Peptide (GRP) and Somatostatin as well as their respective receptors (LHRH-R, GHRH-R, TRH-R, GRP-R, SST-R1) in cadaveric human eye tissue and in paraffinized human eye tissue sections. The hypothalamic hormones LHRH, GHRH, TRH, GRP and Somatostatin and their respective receptors (LHRH-R, GHRH-R, TRH-R, GRPR/BB2 and SST-R1), were expressed in the conjunctiva, cornea, trabecular meshwork, ciliary body, lens, retina, and optic nerve.

The expression of GHRH and its receptors in breast carcinomas with apocrine differentiation-further evidence of the presence of a GHRH pathway in these tumors

Apocrine breast carcinomas were evaluated for the expression of components of the growth hormone-releasing hormone (GHRH) autocrine/paracrine pathway: GHRH and its receptors (GHRH-R), as mammary apocrine carcinomas and epithelium seemed to be uniformly positive for GHRH-R in a pilot study. The apocrine phenotype was determined on the basis of hematoxylin-eosin morphology and a congruent immunohistochemical profile (estrogen receptor negativity, androgen receptor and gross cystic disease fluid protein-15 positivity). Thirty-five formalin-fixed, paraffin-embedded apocrine breast cancers in tissue microarrays and 24 cases using whole-tissue sections were evaluated for GHRH-R and GHRH expression by immunohistochemistry using polyclonal antibodies raised against various domains of GHRH-R and one polyclonal antibody specific for GHRH. GHRH-R positivity was detected in the overwhelming majority (ranging from 90% to 100%) of apocrine breast carcinomas with all but one of the antibodies applied. The expression was usually diffuse with only isolated cases showing positivity in less than 50% of tumor cells. With the PA5-33583 antibody, GHRH-R positivity was seen only in 73% of the cases in at least 50% of the tumor cells. GHRH expression was also present in all but one case tested, with more than 50% of the cells expressing it in 30/34 cases. These results support a high rate of GHRH-R and GHRH expression in apocrine breast carcinomas. Whether these findings can be exploited for the targeted treatment of apocrine breast carcinomas with GHRH antagonists requires further study.

New therapies for relapsed castration-resistant prostate cancer based on peptide analogs of hypothalamic hormones

It is a pleasure to contribute our presentation at the International Prostate Forum of the Annual Meeting of the American Urological Association (AUA) to this special issue of the Asian Journal of Andrology.

Preclinical therapy of benign prostatic hyperplasia with neuropeptide hormone antagonists

Benign prostatic hyperplasia (BPH) is a pathologic condition of the prostate described as a substantial increase in its number of epithelial and stromal cells. BPH may significantly reduce the quality of life due to the initiation of bladder outlet obstruction and lower urinary tract syndromes. Current medical therapies mostly consist of inhibitors of 5α-reductase or α₁-adrenergic blockers; their efficacy is often insufficient. Antagonistic analogs of neuropeptide hormones are novel candidates for the management of BPH. At first, antagonists of luteinizing hormone-releasing hormone (LHRH) have been introduced to the therapy aimed to reduce serum testosterone levels. However, they have also been found to produce an inhibitory activity on local LHRH receptors in the prostate as well as impotence and other related side effects. Since then, several preclinical and clinical studies reported the favorable effects of LHRH antagonists in BPH. In contrast, antagonists of growth hormone-releasing hormone (GHRH) and gastrin-releasing peptide (GRP) have been tested only in preclinical settings and produce significant reduction in prostate size in experimental models of BPH. They act at least in part, by blocking the action of respective ligands produced locally on prostates through their respective receptors in the prostate, and by inhibition of autocrine insulin-like growth factors-I/II and epidermal growth factor production. GHRH and LHRH antagonists were also tested in combination resulting in a cumulative effect that was greater than that of each alone. This article will review the numerous studies that demonstrate the beneficial effects of antagonistic analogs of LHRH, GHRH and GRP in BPH, as well as suggesting a potential role for somatostatin analogs in experimental therapies.

Triple negative breast cancers express receptors for LHRH and are potential therapeutic targets for cytotoxic LHRH-analogs, AEZS 108 and AEZS 125

BACKGROUND

Triple negative breast cancer (TNBC) is a distinct subtype of breast cancer burdened with a dismal prognosis due to the lack of effective therapeutic agents. Receptors for LHRH (luteinizing hormone-releasing hormone) can be successfully targeted with AEZS-108 [AN-152], an analog of LHRH conjugated to doxorubicin. Our study evaluates the presence of this target LHRH receptor in human specimens of TNBC and investigates the efficacy and toxicity of AEZS-108 in vivo. We also studied in vitro activity of AEZS-125, a new LHRH analog conjugated with the highly potent natural compound, Disorazol Z.

METHODS

69 human surgical specimens of TNBC were investigated for LHRH-R expression by immunohistochemistry. Expression of LHRH-R in two TNBC cell lines was evaluated by real time RT-PCR. Cytotoxicity of AEZS-125 was evaluated by Cell Titer Blue cytoxicity assay. LHRH- receptor expression was silenced with an siRNA in both cell lines. For the in vivo experiments an athymic nude mice model xenotransplanted with the cell lines, MDA-MB-231 and HCC 1806, was used. The animals were randomised to three groups receiving solvent only (d 1, 7, 14, i.v.) for control, AEZS-108 (d 1, 7, 14, i.v.) or doxorubicin at an equimolar dose (d 1, 7, 14, i.v.).

RESULTS

In human clinical specimens of TNBC, expression of the LHRH-receptor was present in 49% (n = 69).HCC 1806 and MDA-MB-231 TNBC cells expressed mRNA for the LHRH-receptor. Silencing of the LHRH-receptor significantly decreased the cytotoxic effect of AEZS-108. MDA-MB-231 and HCC 1806 tumors xenografted into nude mice were significantly inhibited by treatment with AEZS-108; doxorubicin at equimolar doses was ineffective.As compared to AEZS 108, the Disorazol Z - LHRH conjugate, AEZS-125, demonstrated an increased cytotoxicity in vitro in HCC 1806 and MDA-MB-231 TNBC; this was diminished by receptor blockade with synthetic LHRH agonist (triptorelin) pretreatment.

CONCLUSION

The current study confirms that LHRH-receptors are expressed by a significant proportion of TNBC and can be successfully used as homing sites for cytotoxic analogs of LHRH, such as AEZS-108 and AEZS-125.

Antagonistic analogs of growth hormone-releasing hormone increase the efficacy of treatment of triple negative breast cancer in nude mice with doxorubicin; A preclinical study

Introduction

This study evaluated the effects of an antagonistic analog of growth hormone-releasing hormone, MIA-602, on tumor growth, response to doxorubicin, expression of drug resistance genes, and efflux pump function in human triple negative breast cancers.

Methods

HCC1806 (doxorubicin-sensitive) and MX-1 (doxorubicin-resistant), cell lines were xenografted into nude mice and treated with MIA-602, doxorubicin, or their combination. Tumors were evaluated for changes in volume and the expression of the drug resistance genes MDR1 and NANOG. In-vitro cell culture assays were used to analyze the effect of MIA-602 on efflux pump function.

Results

Therapy with MIA-602 significantly reduced tumor growth and enhanced the efficacy of doxorubicin in both cell lines. Control HCC1806 tumors grew by 435%, while the volume of tumors treated with MIA-602 enlarged by 172.2% and with doxorubicin by 201.6%. Treatment with the combination of MIA-602 and doxorubicin resulted in an increase in volume of only 76.2%. Control MX-1 tumors grew by 907%, while tumors treated with MIA-602 enlarged by 434.8% and with doxorubicin by 815%. The combination of MIA-602 and doxorubicin reduced the increase in tumor volume to 256%. Treatment with MIA-602 lowered the level of growth hormone-releasing hormone and growth hormone-releasing hormone receptors and significantly reduced the expression of multidrug resistance (MDR1) gene and the drug resistance regulator NANOG. MIA-602 also suppressed efflux pump function in both cell lines.

Conclusions

We conclude that treatment of triple negative breast cancers with growth hormone-releasing hormone antagonists reduces tumor growth and potentiates the effects of cytotoxic therapy by nullifying drug resistance.

Protective effect of Growth Hormone-Releasing Hormone agonist in bacterial toxin-induced pulmonary barrier dysfunction

RATIONALE

Antibiotic treatment of patients infected with G(-) or G(+) bacteria promotes release of the toxins lipopolysaccharide (LPS) and pneumolysin (PLY) in their lungs. Growth Hormone-releasing Hormone (GHRH) agonist JI-34 protects human lung microvascular endothelial cells (HL-MVEC), expressing splice variant 1 (SV-1) of the receptor, from PLY-induced barrier dysfunction. We investigated whether JI-34 also blunts LPS-induced hyperpermeability. Since GHRH receptor (GHRH-R) signaling can potentially stimulate both cAMP-dependent barrier-protective pathways as well as barrier-disruptive protein kinase C pathways, we studied their interaction in GHRH agonist-treated HL-MVEC, in the presence of PLY, by means of siRNA-mediated protein kinase A (PKA) depletion.

METHODS

Barrier function measurements were done in HL-MVEC monolayers using Electrical Cell substrate Impedance Sensing (ECIS) and VE-cadherin expression by Western blotting. Capillary leak was assessed by Evans Blue dye (EBD) incorporation. Cytokine generation in broncho-alveolar lavage fluid (BALF) was measured by multiplex analysis. PKA and PKC-α activity were assessed by Western blotting.

RESULTS

GHRH agonist JI-34 significantly blunts LPS-induced barrier dysfunction, at least in part by preserving VE-cadherin expression, while not affecting inflammation. In addition to activating PKA, GHRH agonist also increases PKC-α activity in PLY-treated HL-MVEC. Treatment with PLY significantly decreases resistance in control siRNA-treated HL-MVEC, but does so even more in PKA-depleted monolayers. Pretreatment with GHRH agonist blunts PLY-induced permeability in control siRNA-treated HL-MVEC, but fails to improve barrier function in PKA-depleted PLY-treated monolayers.

CONCLUSIONS

GHRH signaling in HL-MVEC protects from both LPS and PLY-mediated endothelial barrier dysfunction and concurrently induces a barrier-protective PKA-mediated and a barrier-disruptive PKC-α-induced pathway in the presence of PLY, the former of which dominates the latter.

Differential immunostaining of various types of breast carcinomas for growth hormone-releasing hormone receptor - Apocrine epithelium and carcinomas emerging as uniformly positive

Different classes of breast cancers were explored for their positivity for growth hormone-releasing hormone receptors (GHRH-R) in this pilot study, as no systematic evaluation of such tumors has been performed to date. Seventy-two small primary breast carcinomas were evaluated for GHRH-R expression by immunohistochemistry using a polyclonal antibody and a cutoff value of 10% staining. GHRH-R positivity was detected in 58% of all cases, 20/23 (87%) of invasive lobular carcinomas (ILC) and 22/46 (48%) of invasive ductal carcinomas (IDC). GHRH-R positivity was more frequent in grade 2 tumors (86%), as compared to grade 1 (18%) or grade 3 (47%) cancers. GHRH-R expression was not associated with mitotic scores, the Ki-67 labeling indices or nodal status. IDCs with casting-type calcifications on the mammogram showed positivity for GHRH-R in 9/12 (75%) cases. Most importantly, apocrine epithelium, and all 10 apocrine carcinomas added later to the study were GHRH-R-positive. These preliminary results suggest a greater than average GHRH-R expression in ILCs and IDCs associated with casting-type calcifications on the mammogram. Apocrine carcinomas seem uniformly positive for GHRH-R. Whether these findings could indicate a potential role of GHRH-antagonists in targeted treatment of these types of breast cancer requires further studies.

Preclinical efficacy of growth hormone-releasing hormone antagonists for androgen-dependent and castration-resistant human prostate cancer

Advanced hormone-sensitive prostate cancer responds to androgen-deprivation therapy (ADT); however, therapeutic options for recurrent castration-resistant disease are limited. Because growth hormone-releasing hormone (GHRH) and GHRH receptor (GHRH-R) are regulated in an autocrine fashion in prostate cancer, inhibition of GHRH-R represents a compelling approach to treatment. We investigated the effects of the latest series of improved, highly potent GHRH antagonists--MIA-602, MIA-606, and MIA-690--on the growth of androgen-dependent as well as castration-resistant prostate cancer (CRPC) cells in vitro and in vivo. GHRH-R and its splice variant, SV1, were present in 22Rv1, LNCaP, and VCaP human prostate cancer cell lines. Androgen-dependent LNCaP and VCaP cells expressed higher levels of GHRH-R protein compared with castration-resistant 22Rv1 cells; however, 22Rv1 expressed higher levels of SV1. In vitro, MIA-602 decreased cell proliferation of 22Rv1, LNCaP, and VCaP prostate cancer cell lines by 70%, 61%, and 20%, respectively (all P < 0.05), indicating direct effects of MIA-602. In vivo, MIA-602 was more effective than MIA-606 and MIA-690 and decreased 22Rv1 xenograft tumor volumes in mice by 63% after 3 wk (P < 0.05). No noticeable untoward effects or changes in body weight occurred. In vitro, the VCaP cell line was minimally inhibited by MIA-602, but in vivo, this line showed a substantial reduction in growth of xenografts in response to MIA-602, indicating both direct and systemic inhibitory effects. MIA-602 also further inhibited VCaP xenografts when combined with ADT. This study demonstrates the preclinical efficacy of the GHRH antagonist MIA-602 for treatment of both androgen-dependent and CRPC.

Mini-review: novel therapeutic strategies to blunt actions of pneumolysin in the lungs

Severe pneumonia is the main single cause of death worldwide in children under five years of age. The main etiological agent of pneumonia is the G+ bacterium Streptococcus pneumoniae, which accounts for up to 45% of all cases. Intriguingly, patients can still die days after commencing antibiotic treatment due to the development of permeability edema, although the pathogen was successfully cleared from their lungs. This condition is characterized by a dramatically impaired alveolar epithelial-capillary barrier function and a dysfunction of the sodium transporters required for edema reabsorption, including the apically expressed epithelial sodium channel (ENaC) and the basolaterally expressed sodium potassium pump (Na+-K+-ATPase). The main agent inducing this edema formation is the virulence factor pneumolysin, a cholesterol-binding pore-forming toxin, released in the alveolar compartment of the lungs when pneumococci are being lysed by antibiotic treatment or upon autolysis. Sub-lytic concentrations of pneumolysin can cause endothelial barrier dysfunction and can impair ENaC-mediated sodium uptake in type II alveolar epithelial cells. These events significantly contribute to the formation of permeability edema, for which currently no standard therapy is available. This review focuses on discussing some recent developments in the search for the novel therapeutic agents able to improve lung function despite the presence of pore-forming toxins. Such treatments could reduce the potentially lethal complications occurring after antibiotic treatment of patients with severe pneumonia.

Interaction of PICK1 with C-terminus of growth hormone-releasing hormone receptor (GHRHR) modulates trafficking and signal transduction of human GHRHR

Release of growth hormone (GH) from the somatotroph is regulated by binding GH-releasing hormone (GHRH) to its cognate receptor (GHRHR), one of the members of the G protein-coupled receptor (GPCR) superfamily. Proteins bound to the carboxy (C)-terminus of GPCR have been reported to regulate intracellular trafficking and function of the receptor; however, no functionally significant protein associated with GHRHR has been reported. We have identified a protein interacting with C-kinase 1 (PICK1) as a binding partner of GHRHR. In vitro binding assay revealed the PDZ-domain of PICK1 and the last four amino acid residues of GHRHR were prerequisite for the interaction. Further, in vivo association of these proteins was confirmed. Immunostaining data of a stable cell line expressing GHRHR with or without PICK1 suggested the C-terminus of GHRHR promoted cell surface expression of GHRHR and PICK1 affected the kinetics of the cell surface expression of GHRHR. Furthermore, cAMP production assay showed the C-terminus of GHRHR is involved in the regulation of receptor activation, and the interaction of GHRHR with PICK1 may influence intensities of the signal response after ligand stimulation. Thus, the interaction of the C-terminus of GHRHR with PICK1 has a profound role in regulating the trafficking and the signaling of GHRHR. [Supplementary Figure: available only at http://dx.doi.org/10.1254/jphs.12287FP].

Antagonists of growth hormone-releasing hormone suppress in vivo tumor growth and gene expression in triple negative breast cancers

This study evaluated the effects of a modern antagonistic analog of GHRH on tumor growth and on expression of inflammatory cytokine genes in two models of human triple negative breast cancers (TNBC). The TNBC subtype is refractory to the treatment options available for other hormone-independent breast cancers. Inflammatory cytokines play a major role in the cellular signaling associated with breast cancer pathogenesis and enhance epithelial-mesenchymal transitions (EMT), drug resistance, and metastatic potential. Growth hormone-releasing hormone (GHRH) is a hypothalamic neuropeptide which regulates the synthesis and release of growth hormone by the pituitary and is an autocrine/paracrine growth factor for multiple human cancers. The effects of analogs of GHRH on tumoral cytokine expression have not been previously investigated. Animals bearing xenografts of the human TNBC cell lines, HCC1806 and MX-1, were treated with MIA-602, an antagonistic analog of GHRH. Treatment with MIA-602 significantly reduced tumor growth. We quantified transcript levels of the genes for several inflammatory cytokines. Expression of INFγ, IL-1α, IL-4, IL-6, IL-8, IL-10, and TNFα, was significantly reduced by treatment with MIA-602. We conclude that treatment of TNBC with GHRH antagonists reduces tumor growth through an action mediated by tumoral GHRH receptors and produces a suppression of inflammatory cytokine signaling. Silencing of GHRH receptors in vitro with siRNA inhibited the expression of GHRH-R genes and inflammatory cytokine genes in HCC1806 and MX-1 cells. Further studies on GHRH antagonists may facilitate the development of new strategies for the treatment of resistant cancers.

Combination of GHRH antagonists and docetaxel shows experimental effectiveness for the treatment of triple-negative breast cancers

In preclinical studies, antagonists of growth hormone-releasing hormone (GHRH) have demonstrated inhibitory effects on the growth of various types of cancers expressing the pituitary type of GHRH receptors (pGHRH-R) and/or its active splice variant 1 (SV1). In this study, we investigated the effectiveness of the treatment of MDA-MB-231 human triple-negative breast cancer (TNBC) with GHRH antagonist JMR-132 alone or in combination with docetaxel. Receptor expression in the MDA-MB-231 human breast cancer cell line was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Cell viability assays were performed on MDA-MB-231 cells treated with JMR-132, docetaxel or in combination. For studies in vivo, a subcutaneous nude mouse xenograft model was used. JMR-132 was administered s.c. at a dose of 10 µg/day and docetaxel at a dose of 10 mg/kg i.p. given on day 1 and 5. Similar regimens were used for the combination of both substances. At the end of the experiment, an mRNA-based human cancer pathway array including 84 major genes was performed on the tumor tissue of mice treated with JMR-132 to elucidate the mechanism of action of GHRH antagonists in vivo. The in vitro proliferation studies revealed that JMR-132 and docetaxel decreased the cell viability in a dose-dependent manner. The combination of both treatments produced a significantly greater inhibition of cell viability compared to the single agents. Treatment of nude mice bearing MDA-MB-231 xenografts with JMR-132 and docetaxel significantly (p<0.05) inhibited tumor growth by 46 and 50%, respectively. Treatment with the combination of JMR-132 and docetaxel led to an inhibition of tumor volume by 71.6% (p<0.001). Polymerase chain reaction array analysis revealed that JMR-132 interacts with signal transduction pathways involved in proliferation, apoptosis and angiogenesis. Our results suggest that GHRH antagonists in combination with taxanes may enhance the efficacy of treatment for patients with TNBC expressing the SV1 and/or the pGHRH receptor.

Growth hormone-releasing hormone receptor splice variant 1 is frequently expressed in oral squamous cell carcinomas

The expression of growth hormone-releasing hormone (GHRH) splice variant 1 (SV1) receptor in neoplastic lesions of the oral cavity was assessed. The sensitivity of HaCaT keratinocytes to GHRH analogs was also evaluated. Thirty-three benign precancerous oral lesions and 27 squamous cell carcinomas of the oral cavity were evaluated by immunohistochemistry for SV1 expression. SV1 expression in HaCaT keratinocytes was assessed by western blot. HaCaT proliferation was evaluated by cell counting. Anti-SV1 immunoreactivity was detected in only 9% (three of 33) precancerous lesions (one hyperplasia and two dysplasias), while 44% (12 of 27) carcinomas were positive for SV1 (p<0.002). GHRH(1-29)NH(2) and GHRH agonist JI-38 stimulated HaCaT proliferation in vitro, and this effect was blocked by GHRH antagonists. These results indicate that SV1 expression may be associated with the transition of precancerous lesions to carcinomas of the oral epithelium. GHRH antagonists may be useful for the management of the disease.

Improvement of islet function in a bioartificial pancreas by enhanced oxygen supply and growth hormone releasing hormone agonist

Islet transplantation is a feasible therapeutic alternative for metabolically labile patients with type 1 diabetes. The primary therapeutic target is stable glycemic control and prevention of complications associated with diabetes by reconstitution of endogenous insulin secretion. However, critical shortage of donor organs, gradual loss in graft function over time, and chronic need for immunosuppression limit the indication for islet transplantation to a small group of patients. Here we present a promising approach to address these limitations by utilization of a macrochamber specially engineered for islet transplantation. The s.c. implantable device allows for controlled and adequate oxygen supply and provides immunological protection of donor islets against the host immune system. The minimally invasive implantable chamber normalized blood glucose in streptozotocin-induced diabetic rodents for up to 3 mo. Sufficient graft function depended on oxygen supply. Pretreatment with the growth hormone-releasing hormone (GHRH) agonist, JI-36, significantly enhanced graft function by improving glucose tolerance and increasing β-cell insulin reserve in rats thereby allowing for a reduction of the islet mass required for metabolic control. As a result of hypervascularization of the tissue surrounding the device, no relevant delay in insulin response to glucose changes has been observed. Consequently, this system opens up a fundamental strategy for therapy of diabetes and may provide a promising avenue for future approaches to xenotransplantation.

Agonist of growth hormone-releasing hormone reduces pneumolysin-induced pulmonary permeability edema

Aggressive treatment with antibiotics in patients infected with Streptococcus pneumoniae induces release of the bacterial virulence factor pneumolysin (PLY). Days after lungs are sterile, this pore-forming toxin can still induce pulmonary permeability edema in patients, characterized by alveolar/capillary barrier dysfunction and impaired alveolar liquid clearance (ALC). ALC is mainly regulated through Na(+) transport by the apically expressed epithelial sodium channel (ENaC) and the basolaterally expressed Na(+)/K(+)-ATPase in type II alveolar epithelial cells. Because no standard treatment is currently available to treat permeability edema, the search for novel therapeutic candidates is of high priority. We detected mRNA expression for the active receptor splice variant SV1 of the hypothalamic polypeptide growth hormone-releasing hormone (GHRH), as well as for GHRH itself, in human lung microvascular endothelial cells (HL-MVEC). Therefore, we have evaluated the effect of the GHRH agonist JI-34 on PLY-induced barrier and ALC dysfunction. JI-34 blunts PLY-mediated endothelial hyperpermeability in monolayers of HL-MVEC, in a cAMP-dependent manner, by means of reducing the phosphorylation of myosin light chain and vascular endothelial (VE)-cadherin. In human airway epithelial H441 cells, PLY significantly impairs Na(+) uptake, but JI-34 restores it to basal levels by means of increasing cAMP levels. Intratracheal instillation of PLY into C57BL6 mice causes pulmonary alveolar epithelial and endothelial hyperpermeability as well as edema formation, all of which are blunted by JI-34. These findings point toward a protective role of the GHRH signaling pathway in PLY-induced permeability edema.

Antagonists of growth hormone-releasing hormone inhibit growth of androgen-independent prostate cancer through inactivation of ERK and Akt kinases

The management of castration-resistant prostate cancer (CRPC) presents a clinical challenge because of limitations in efficacy of current therapies. Novel therapeutic strategies for the treatment of CRPC are needed. Antagonists of hypothalamic growth hormone-releasing hormone (GHRH) inhibit growth of various malignancies, including androgen-dependent and independent prostate cancer, by suppressing diverse tumoral growth factors, especially GHRH itself, which acts as a potent autocrine/paracrine growth factor in many tumors. We evaluated the effects of the GHRH antagonist, JMR-132, on PC-3 human androgen-independent prostate cancer cells in vitro and in vivo. JMR-132 suppressed the proliferation of PC-3 cells in vitro in a dose-dependent manner and significantly inhibited growth of PC-3 tumors by 61% (P < 0.05). The expression of GHRH, GHRH receptors, and their main splice variant, SV1, in PC-3 cells and tumor xenografts was demonstrated by RT-PCR and Western blot. The content of GHRH protein in PC-3 xenografts was lowered markedly, by 66.3% (P < 0.01), after treatment with JMR-132. GHRH induced a significant increase in levels of ERK, but JMR-132 abolished this outcome. Our findings indicate that inhibition of PC-3 prostate cancer by JMR-132 involves inactivation of Akt and ERK. The inhibitory effect produced by GHRH antagonist can result in part from inactivation of the PI3K/Akt/mammalian target of rapamycin and Raf/MEK/ERK pathways and from the reduction in GHRH produced by cancer cells. Our findings support the role of GHRH as an autocrine growth factor in prostate cancer and suggest that antagonists of GHRH should be considered for further development as therapy for CRPC.

Growth hormone-releasing hormone: not only a neurohormone

Growth hormone-releasing hormone (GHRH) is mostly thought to act by stimulating the production and release of growth hormone from the pituitary. However, this neuropeptide emerges as a rather pleiotropic hormone in view of the identification of various extrapituitary sources for GHRH production, as well as the demonstration of a direct action of GHRH on several tissues other than the pituitary. Non-pituitary GHRH has a wide spectrum of activity, exemplified by its ability to modulate cell proliferation, especially in malignant tissues, to regulate differentiation of some cell types, and to promote healing of skin wounds. These findings extend the role of GHRH and its analogs beyond its accepted regulation of somatotropic activity and indicate new possibilities for therapeutic intervention.

Novel antagonists of growth hormone-releasing hormone inhibit growth and vascularization of human experimental ovarian cancers

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the proliferation of various human cancer cell lines and experimental tumors by mechanisms that include direct action on GHRH receptors in cancer cells.

METHODS

In this study, the effects of newly synthesized GHRH antagonists, MIA-313, MIA-602, MIA-604, and MIA-610, were investigated in 2 human ovarian epithelial adenocarcinoma cell lines, OVCAR-3 and SKOV-3, in vitro and in vivo. The expression of receptors for GHRH was demonstrated by Western blot analysis and ligand competition methods in the OVCAR-3 and SKOV-3 cell lines and in tumors from those cells grown in athymic nude mice. The effects of GHRH antagonists on the secretion of vascular endothelial growth factor (VEGF) by OVCAR-3 cells and on the vascularization of OVCAR-3 xenografts also were evaluated.

RESULTS

Both the pituitary and the splice variant type 1 (SV1) GHRH receptors were detected in the 2 cell lines and in tumor xenografts, and SV1 was expressed at higher levels. Cell viability assays revealed the antiproliferative effect of all GHRH antagonists that were. Maximal tumor growth inhibition was approximately 75% in both models. MIA-313 and MIA-602 decreased VEGF secretion of OVCAR-3 cells, as measured by enzyme-linked immunosorbent assay, and reduced tumor vascularization in a Matrigel plug assay, but caused no change in the expression of VEGF or VEGF receptor in the terminal ileum of mice with OVCAR-3 tumors.

CONCLUSIONS

Results from the current study indicated that a he novel approach based on GHRH antagonists may offer more effective therapeutic alternatives for patients with advanced ovarian cancer and who do not tolerate conventional anti-VEGF therapy.

Somatostatin receptor biology in neuroendocrine and pituitary tumours: part 1--molecular pathways

Neuroendocrine tumours (NETs) may occur at many sites in the body although the majority occur within the gastroenteropancreatic axis. Non-gastroenteropancreatic NETs encompass phaeochromocytomas and paragangliomas, medullary thyroid carcinoma, anterior pituitary tumour, broncho-pulmonary NETs and parathyroid tumours. Like most endocrine tumours, NETs also express somatostatin (SST) receptors (subtypes 1–5) whose ligand SST is known to inhibit endocrine and exocrine secretions and have anti-tumour effects. In the light of this knowledge, the idea of using SST analogues in the treatment of NETs has become increasingly popular and new studies have centred upon the development of new SST analogues. We attempt to review SST receptor (SSTR) biology primarily in neuroendocrine tissues, focusing on pituitary tumours. A full data search was performed through PubMed over the years 2000–2009 with keywords ‘somatostatin, molecular biology, somatostatin receptors, somatostatin signalling, NET, pituitary’ and all relevant publications have been included, together with selected publications prior to that date. SSTR signalling in non-neuroendocrine solid tumours is beyond the scope of this review. SST is a potent anti-proliferative and anti-secretory agent for some NETs. The successful therapeutic use of SST analogues in the treatment of these tumours depends on a thorough understanding of the diverse effects of SSTR subtypes in different tissues and cell types. Further studies will focus on critical points of SSTR biology such as homo- and heterodimerization of SSTRs and the differences between post-receptor signalling pathways of SSTR subtypes.

Truncated somatostatin receptors as new players in somatostatin-cortistatin pathophysiology

Somatostatin (SST) and cortistatin (CORT) act through a family of seven transmembrane domain (TMD) receptors (sst1-5) to govern multiple functions, from growth hormone (GH) secretion to neurotransmission, metabolic homeostasis, gastrointestinal and immune function, and tumor cell growth. Thus, SST analogs are used to treat endocrine/tumoral pathologies. Yet, some SST/CORT actions cannot be explained by their interaction with known ssts. We recently identified novel sst5 variants in human, pig, mouse, and rat that lack one or more TMDs and display unique molecular/functional features: they exhibit distinct tissue distribution, divergent responses to SST/CORT, and intracellular localization as opposed to the typical plasma-membrane distribution of full-length ssts. When coexpressed in the same cell, truncated sst5 variants colocalize and physically interact with full-length ssts, providing a molecular basis to disrupt normal sst2/sst5 functioning. This may explain the inverse correlation between hsst5TMD4 expression in pituitary tumors and octreotide responsiveness in acromegaly. Discovery of these new truncated sst5 variants provides novel insights on SST/CORT/sst pathophysiology and suggests new research avenues for the therapeutic potential of this system.

Antagonists of growth hormone-releasing hormone (GHRH) reduce prostate size in experimental benign prostatic hyperplasia

Growth hormone-releasing hormone (GHRH), a hypothalamic polypeptide, acts as a potent autocrine/paracrine growth factor in many cancers. Benign prostatic hyperplasia (BPH) is a pathologic proliferation of prostatic glandular and stromal tissues; a variety of growth factors and inflammatory processes are inculpated in its pathogenesis. Previously we showed that potent synthetic antagonists of GHRH strongly inhibit the growth of diverse experimental human tumors including prostate cancer by suppressing various tumoral growth factors. The influence of GHRH antagonists on animal models of BPH has not been investigated. We evaluated the effects of the GHRH antagonists JMR-132 given at doses of 40 μg/d, MIA-313 at 20 μg/d, and MIA-459 at 20 μg/d in testosterone-induced BPH in Wistar rats. Reduction of prostate weights was observed after 6 wk of treatment with GHRH antagonists: a 17.8% decrease with JMR-132 treatment; a 17.0% decline with MIA-313 treatment; and a 21.4% reduction with MIA-459 treatment (P < 0.05 for all). We quantified transcript levels of genes related to growth factors, inflammatory cytokines, and signal transduction and identified significant changes in the expression of more than 80 genes (P < 0.05). Significant reductions in protein levels of IL-1β, NF-κβ/p65, and cyclooxygenase-2 (COX-2) also were observed after treatment with a GHRH antagonist. We conclude that GHRH antagonists can lower prostate weight in experimental BPH. This reduction is caused by the direct inhibitory effects of GHRH antagonists exerted through prostatic GHRH receptors. This study sheds light on the mechanism of action of GHRH antagonists in BPH and suggests that GHRH antagonists should be considered for further development as therapy for BPH.

The effect of GHRH antagonists on human glioblastomas and their mechanism of action

The effects of new growth hormone-releasing hormone (GHRH) antagonists JMR-132 and MIA-602 and their mechanism of action were investigated on 2 human glioblastoma cell lines, DBTRG-05 and U-87MG, in vitro and in vivo. GHRH receptors and their main splice variant, SV1 were found on both cell lines. After treatment with JMR-132 or MIA-602, the cell viability decreased significantly. A major decrease in the levels of phospho-Akt, phospho-GSK3β and phosho-ERK 1/2 was detected at 5 and 10 min following treatment with the GHRH antagonists, whereas elevated levels of phospho-p38 were observed at 24 hr. The expression of caspase-3 and poly(ADP-ribose) (PARP), as the downstream executioners of apoptosis were found to be significantly elevated after treatment. Following treatment of the glioblastoma cells with GHRH antagonists, nuclear translocation of apoptosis inducing factor (AIF) and Endonuclease G (Endo G) and the mitochondrial release of cytochrome c (cyt c) were detected, indicating that the cells were undergoing apoptosis. In cells treated with GHRH antagonists, the collapse of the mitochondrial membrane potential was shown with fluorescence microscopy and JC-1 membrane potential sensitive dye. There were no significant differences between results obtained in DBTRG-05 or U-87MG cell lines. After treatment with MIA-602 and JMR-132, the reduction rate in the growth of DBTRG-05 glioblastoma, xenografted into nude mice, was significant and tumor doubling time was also significantly extended when compared with controls. Our study demonstrates that GHRH antagonists induce apoptosis through key proapoptotic pathways and shows the efficacy of MIA-602 for experimental treatment of glioblastoma.