Expression of a splice variant of the receptor for GHRH in 3T3 fibroblasts activates cell proliferation responses to GHRH analogs

Characterization of Somatotrope Cell Expansion in Response to GHRH in the Neonatal Mouse Pituitary

In humans and mice, loss-of-function mutations in growth hormone-releasing hormone receptor (GHRHR) cause isolated GH deficiency. The mutant GHRHR mouse model, GhrhrLit/Lit (LIT), exhibits loss of serum GH, but also fewer somatotropes. However, how loss of GHRH signaling affects expansion of stem and progenitor cells giving rise to GH-producing cells is unknown. LIT mice and wild-type littermates were examined for differences in proliferation and gene expression of pituitary lineage markers by quantitative reverse transcription polymerase chain reaction and immunohistochemistry at postnatal day 5 (p5) and 5 weeks. At p5, the LIT mouse shows a global decrease in pituitary proliferation measured by proliferation marker Ki67 and phospho-histone H3. This proliferative defect is seen in a pituitary cell expressing POU1F1 with or without GH. SOX9-positive progenitors show no changes in proliferation in p5 LIT mice. Additionally, the other POU1F1 lineage cells are not decreased in number; rather, we observe an increase in lactotrope cell population as well as messenger RNA for Tshb and Prl. In the 5-week LIT pituitary, the proliferative deficit in POU1F1-expressing cells observed neonatally persists, while the number and proliferative proportion of SOX9 cells do not appear changed. Treatment of cultured pituitary explants with GHRH promotes proliferation of POU1F1-expressing cells, but not GH-positive cells, in a mitogen-activated protein kinase-dependent manner. These findings indicate that hypothalamic GHRH targets proliferation of a POU1F1-positive cell, targeted to the somatotrope lineage, to fine tune their numbers.

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.

GH-dependent growth of experimentally induced carcinomas in vivo

Interest in investigating the role of the growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis in the initiation and progression of experimentally induced carcinomas has arisen due to several observations in the human population. First, subjects with Laron syndrome who lack GH signaling have significantly lower rates of cancer than people who have normal GH signaling. Second, epidemiologic studies have found strong associations between elevated circulating IGF-1 and the incidence of several common cancers. Third, women who bear children early in life have a dramatically reduced risk of developing breast cancer, which may be due to differences in hormone levels including GH. These observations have motivated multiple studies that have experimentally altered activity of the GH/IGF-1 axis in the context of experimental carcinoma models in mice and rats. Most of these studies have utilized carcinoma models for four organ systems that are also frequent sites of carcinomas in humans: the mammary gland, prostate gland, liver, and colon. This review focuses on these studies and describes some of the most common genetic models used to alter the activity of the GH/IGF-1 axis in experimentally induced carcinomas. A recurring theme that emerges from these studies is that manipulations that reduce the activity of GH or mediators of GH action also inhibit carcinogenesis in multiple model systems.

Alveolar epithelial cell growth hormone releasing hormone receptor in alveolar epithelial inflammation

Purpose: Growth hormone-releasing hormone (GHRH) is a 44-amino acid peptide that regulates growth hormone (GH) secretion. We hypothesized that GHRH receptor (GHRH-R) in alveolar type 2 (AT2) cells could modulate pro-inflammatory and possibly subsequent pro-fibrotic effects of lipopolysaccharide (LPS) or cytokines, such that AT2 cells could participate in lung inflammation and fibrosis. Methods: We used human alveolar type 2 (iAT2) epithelial cells derived from induced pluripotent stem cells (iPSC) to investigate how GHRH-R modulates gene and protein expression. We tested iAT2 cells' gene expression in response to LPS or cytokines, seeking whether these mechanisms caused endogenous production of pro-inflammatory molecules or mesenchymal markers. Quantitative real-time PCR (RT-PCR) and Western blotting were used to investigate differential expression of epithelial and mesenchymal markers. Result: Incubation of iAT2 cells with LPS increased expression of IL1-β and TNF-α in addition to mesenchymal genes, including ACTA2, FN1 and COL1A1. Alveolar epithelial cell gene expression due to LPS was significantly inhibited by GHRH-R peptide antagonist MIA-602. Incubation of iAT2 cells with cytokines like those in fibrotic lungs similarly increased expression of genes for IL1-β, TNF-α, TGFβ-1, Wnt5a, smooth muscle actin, fibronectin and collagen. Expression of mesenchymal proteins, such as N-cadherin and vimentin, were also elevated after prolonged exposure to cytokines, confirming epithelial production of pro-inflammatory molecules as an important mechanism that might lead to subsequent fibrosis. Conclusion: iAT2 cells clearly expressed the GHRH-R. Exposure to LPS or cytokines increased iAT2 cell production of pro-inflammatory factors. GHRH-R antagonist MIA-602 inhibited pro-inflammatory gene expression, implicating iAT2 cell GHRH-R signaling in lung inflammation and potentially in fibrosis.

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.

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.

Suppression of reactive oxygen species in endothelial cells by an antagonist of growth hormone-releasing hormone

Growth hormone-releasing hormone (GHRH) is a hypothalamic hormone, which regulates the secretion of growth hormone (GH) from the anterior pituitary gland. The effects of GHRH extend beyond the GH-insulin-like growth factor I axis, and that neuropeptide has been involved in the potentiation of several malignancies and other inflammatory disorders. The development of GHRH antagonists (GHRHAnt) delivers an exciting possibility to counteract the pathogenesis of the GHRH-related effects in human pathophysiology, especially when considered that GHRHAnt support endothelial barrier integrity. Those GHRHAnt-mediated effects are exerted at least in part due to the suppression of major inflammatory pathways, and the modulation of major cytoskeletal components. In the present study, we measured the production of reactive oxygen species (ROS) in bovine pulmonary artery endothelial cells, human cerebral microvascular endothelial cells, and human lung microvascular endothelial cells exposed to GHRH or a commercially available GHRHAnt. Our findings reveal the antioxidative effects of GHRHAnt in all three cell lines, which express GHRH receptors. The redox status of NIH/3T3 cells, which do not produce GHRH receptors, was not significantly affected by GHRH or GHRHAnt. Hence, the application of GHRHAnt in pathologies related to increased ROS production should be further investigated.

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.

GHRH antagonists support lung endothelial barrier function

Growth Hormone-Releasing Hormone (GHRH) regulates the release of growth hormone from the anterior pituitary gland. GHRH also acts as a growth and inflammatory factor in a variety of experimental models in oncology. In the current study, we used bovine pulmonary arterial cells in order to investigate the effects of GHRH and its antagonistic and agonistic analogs in key intracellular pathways that regulate endothelial permeability. GHRH antagonists suppressed the activation of MLC2, ERK1/2, JAK2/STAT3 pathway and increased the intracellular P53 and pAMPK levels. In contrast, both GHRH and GHRH agonist MR409 exerted the opposite effects. Furthermore, GHRH antagonists supported the integrity of endothelial barrier, while GHRH and GHRH agonists had the contrary effects, as reflected in measurements of transendothelial resistance. Our observations support the evidence for the anti - inflammatory role of GHRH antagonists in the vasculature. Moreover, our results suggest that GHRH antagonists should be considered as promising therapeutic agents for treating severe respiratory abnormalities, such as the lethal Acute Respiratory Distress Syndrome (ARDS).

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.

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.

Growth Hormone-Releasing Hormone and Its Analogues: Significance for MSCs-Mediated Angiogenesis

Mesenchymal stromal cells (MSCs) are promising candidates for regenerative medicine because of their multipotency, immune-privilege, and paracrine properties including the potential to promote angiogenesis. Accumulating evidence suggests that the inherent properties of cytoprotection and tissue repair by native MSCs can be enhanced by various preconditioning stimuli implemented prior to cell transplantation. Growth hormone-releasing hormone (GHRH), a stimulator in extrahypothalamus systems including tumors, has attracted great attentions in recent years because GHRH and its agonists could promote angiogenesis in various tissues. GHRH and its agonists are proangiogenic in responsive tissues including tumors, and GHRH antagonists have been tested as antitumor agents through their ability to suppress angiogenesis and cell growth. GHRH-R is expressed by MSCs and evolving work from our laboratory indicates that treatment of MSCs with GHRH agonists prior to cell transplantation markedly enhanced the angiogenic potential and tissue reparative properties of MSCs through a STAT3 signaling pathway. In this review we summarized the possible effects of GHRH analogues on cell growth and development, as well as on the proangiogenic properties of MSCs. We also discussed the relationship between GHRH analogues and MSC-mediated angiogenesis. The analyses provide new insights into molecular pathways of MSCs-based therapies and their augmentation by GHRH analogues.

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.

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.

Acceleration of wound healing by growth hormone-releasing hormone and its agonists

Despite the well-documented action of growth hormone-releasing hormone (GHRH) on the stimulation of production and release of growth hormone (GH), the effects of GHRH in peripheral tissues are incompletely explored. In this study, we show that GHRH plays a role in wound healing and tissue repair by acting primarily on wound-associated fibroblasts. Mouse embryonic fibroblasts (MEFs) in culture and wound-associated fibroblasts in mice expressed a splice variant of the receptors for GHRH (SV1). Exposure of MEFs to 100 nM and 500 nM GHRH or the GHRH agonist JI-38 stimulated the expression of α-smooth muscle actin (αSMA) based on immunoblot analyses as well as the expression of an αSMA-β-galactosidase reporter transgene in primary cultures of fibroblasts isolated from transgenic mice. Consistent with this induction of αSMA expression, results of transwell-based migration assays and in vitro wound healing (scratch) assays showed that both GHRH and GHRH agonist JI-38 stimulated the migration of MEFs in vitro. In vivo, local application of GHRH or JI-38 accelerated healing in skin wounds of mice. Histological evaluation of skin biopsies showed that wounds treated with GHRH and JI-38 were both characterized by increased abundance of fibroblasts during the early stages of wound healing and accelerated reformation of the covering epithelium at later stages. These results identify another function of GHRH in promoting skin tissue wound healing and repair. Our findings suggest that GHRH may have clinical utility for augmenting healing of skin wounds resulting from trauma, surgery, or disease.

Growth hormone-releasing hormone antagonist induces apoptosis of human endometrial cancer cells through PKCδ-mediated activation of p53/p21

The growth hormone-releasing hormone (GHRH) antagonists have been shown to inhibit growth of human cancer cells, but the underlying molecular mechanisms and their actions have not been fully investigated. In this study, we first showed that GHRH-R splice variant 1 (SV1) was expressed in two human endometrial cancer cell lines, Ishikawa and ECC-1. By using MTT assay, immunoblotting for cleaved caspase-3 and TUNEL assays, we found that cell growth inhibition and apoptosis were induced in GHRH antagonist, JMR-132-treated cells by activating PKCδ and could be inhibited by treatment with PKC inhibitor, GF109203X. In addition, activation and protein expression of p53 as well as the expression of its downstream effector, p21, were increased by JMR-132 treatment. Moreover, JMR-132-induced p53 and p21 expression were diminished by treatment with PKC inhibitor. Knockdown of endogenous p53 and p21 by siRNAs abolished the JMR-132-induced cell growth inhibition and apoptosis. This study demonstrates a novel mechanism in which GHRH antagonist-induced cell growth inhibition and apoptosis through PKCδ-mediated activation of p53/p21 in human endometrial cancer cells. These findings may suggest the feasibility of GHRH antagonists as a therapeutic approach for human cancer.

Antiproliferative effect of growth hormone-releasing hormone (GHRH) antagonist on ovarian cancer cells through the EGFR-Akt pathway

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) are being developed for the treatment of various human cancers.

METHODS

MTT assay was used to test the proliferation of SKOV3 and CaOV3. The splice variant expression of GHRH receptors was examined by RT-PCR. The expression of protein in signal pathway was examined by Western blotting. siRNA was used to block the effect of EGFR.

RESULTS

In this study, we investigated the effects of a new GHRH antagonist JMR-132, in ovarian cancer cell lines SKOV3 and CaOV3 expressing splice variant (SV)1 of GHRH receptors. MTT assay showed that JMR-132 had strong antiproliferative effects on SKOV3 and CaOV3 cells in both a time-dependent and dose-dependent fashion. JMR-132 also induced the activation and increased cleaved caspase3 in a time- and dose-dependent manner in both cell lines. In addition, JMR-132 treatments decreased significantly the epidermal growth factor receptor (EGFR) level and the phosphorylation of Akt (p-Akt), suggesting that JMR-132 inhibits the EGFR-Akt pathway in ovarian cancer cells. More importantly, treatment of SKOV3 and CaOV3 cells with 100 nM JMR-132 attenuated proliferation and the antiapoptotic effect induced by EGF in both cell lines. After the knockdown of the expression of EGFR by siRNA, the antiproliferative effect of JMR-132 was abolished in SKOV3 and CaOV3 cells.

CONCLUSIONS

The present study demonstrates that the inhibitory effect of the GHRH antagonist JMR-132 on proliferation is due, in part, to an interference with the EGFR-Akt pathway in ovarian cancer cells.

GHRH antagonists reduce the invasive and metastatic potential of human cancer cell lines in vitro

We investigated the effect of a GHRH antagonist, MIA-602on the metastatic cascade in vitro of three human cancers, DBTRG-05 glioblastoma, MDA-MB-468 estrogen-independent breast, and ES-2 clear cell ovarian cancer. GHRH receptors and their main splice variant, SV1 were detected on all three cell lines. After treatment with MIA-602, the cell viability decreased significantly, significant inhibition of cell invasion was observed and the release of MMPs was significantly decreased. The attachment of cancer cells to fibronectin and matrigel was severely hindered. Wound-healing experiments demonstrated a reduced cellular motility in all three cell lines. The upregulation of caveolin-1 and E-cadherin,and thepowerful downregulation of NF-kappaB and beta-catenin was detected. Our study suggests that the clinical application of highly potent GHRH antagonists in cancer therapy would be desirable since they inhibit proliferation and metastasis development as well.

Dose-dependent growth inhibition in vivo of PC-3 prostate cancer with a reduction in tumoral growth factors after therapy with GHRH antagonist MZ-J-7-138

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the growth of various cancers and affect tumoral growth factors.

METHODS

We investigated the effect of a new GHRH antagonist MZ-J-7-138 at doses of 1.25, 2.5, 5 and 10 microg/day s.c. on the growth of PC-3 human androgen independent prostate cancers xenografted s.c. into nude mice. Binding assays were used to investigate GHRH receptors. The levels of IGF-II and VEGF in tumors were measured by radioimmunoassays.

RESULTS

Treatment with 2.5, 5, and 10 microg/day MZ-J-7-138 caused a significant dose-dependent growth reduction of PC-3 tumors. The greatest inhibition of 78% was obtained with 10 microg/day. The suppression of IGF-II protein levels in tumors was seen at all doses of MZ-J-7-138, but only 10 microg dose induced a significant inhibition. MZ-J-7-138 also reduced VEGF protein levels, the inhibition being significant at doses of 5 and 10 microg. Specific high affinity binding sites for GHRH were found on PC-3 tumors using (125)I-labeled GHRH antagonist JV-1-42. MZ-J-7-138 displaced radiolabeled JV-1-42 with an IC(50) of 0.32 nM indicating its high affinity to GHRH receptors. Real-time PCR analyses detected splice variant 1 (SV1) of GHRH receptor (GHRH-R) as well as pituitary type of GHRH-R and GHRH ligand.

CONCLUSION

Our results demonstrate the efficacy of GHRH antagonist MZ-J-7-138 in suppressing growth of PC-3 prostate cancer at doses lower than previous antagonists. The reduction of levels of growth factors such as VEGF and IGF-II in tumors by GHRH antagonist was correlated with the suppression of tumor growth.

Expression and possible implication of growth hormone-releasing hormone receptor splice variant 1 in endometriosis

OBJECTIVE

To determine possible involvement of splice variant 1 (SV1), a variant of the pituitary growth hormone-releasing hormone (GHRH) receptor, in the development of endometriosis.

DESIGN

Comparative and laboratory study.

SETTING

University teaching hospital reproductive endocrinology and infertility practice.

PATIENT(S)

Eutopic and ectopic endometrial tissues, and peritoneal bone marrow-derived cells were collected from women with or without endometriosis. Normal ovarian tissues were collected from women without endometriosis.

INTERVENTION(S)

Ectopic endometrial stromal cells (ESC) were isolated and cultured with or without GHRH.

MAIN OUTCOME MEASURE(S)

Gene expression of GHRH and SV1 in the sample tissues was determined by reverse transcriptase (RT) nested polymerase chain reaction (PCR). Cyclic adenosine monophosphate (cAMP) production and 5-bromo-2'-deoxyuridine (BrdU) incorporation in ESC were measured using specific assay systems.

RESULT(S)

We detected SV1 messenger RNA (mRNA) in 17 out of 27 (63%) ectopic endometrial tissues, which was statistically significantly higher than that detected in eutopic endometrial tissues (2 out of 47, 4%) and normal ovarian tissues (0 out of 14). A relatively low rate of GHRH mRNA was detected in ectopic endometrial tissues (6 out of 27, 24%) and in eutopic endometrial tissues (12 out of 47, 26%). In contrast, relatively high rates were detected in normal ovarian tissues (14 out of 14, 100%) and peritoneal bone marrow-derived cells (13 out of 16, 81%). We found that GHRH stimulated the production of cAMP and the incorporation of BrdU in SV1-expressing ESC.

CONCLUSION(S)

GHRH and SV1 may play a role in promoting the development of endometriosis.

Expression of growth hormone-releasing hormone receptor splice variant 1 in primary human melanomas

Growth hormone-releasing hormone (GHRH) is secreted by the hypothalamus and upon binding to specific GHRH receptors in the pituitary stimulates growth hormone production and release. In addition to its neuroendocrine action GHRH plays a role in tumorigenesis. Consistently with this latter role, the splice variant 1 (SV1) of GHRH receptor, which is widely expressed in non-pituitary normal tissues and cancers, can mediate the proliferative effects of GHRH and even in the absence of GHRH is capable of eliciting mitogenic signals in the tissues in which it is expressed. The aim of the present study was to investigate the expression of GHRH and its tumoral receptor SV1 in primary human melanomas and dysplastic nevi by immunohistochemistry. None of the specimens tested expressed GHRH. Only 1 of 12 (8%) dysplastic nevi expressed SV1 but 14 of 23 (61%) melanomas showed moderate or strong staining for SV1 (association p<0.005). This is the first report demonstrating the involvement of SV1 in the pathogenesis of melanomas. Our work implies that the progression from a state of dysplasia into malignancy is accompanied by expression of SV1 receptor. Our findings also suggest that treatment with GHRH antagonists should be further explored for the management of malignant melanomas.

The combination of antagonists of LHRH with antagonists of GHRH improves inhibition of androgen sensitive MDA-PCa-2b and LuCaP-35 prostate cancers

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) could extend the duration of response of androgen sensitive prostate cancers to androgen deprivation.

METHODS

We investigated the effect of new GHRH antagonists MZ-J-7-118 and MZ-J-7-138 and luteinizing hormone-releasing hormone (LHRH) antagonist Cetrorelix or castration on androgen sensitive MDA-PCa-2b and LuCaP-35 prostate cancer models xenografted into nude mice. Animals bearing androgen-independent LuCaP-35V prostatic cancer model were also treated with MZ-J-7-118.

RESULTS

Receptors for LHRH and GHRH were present in MDA-PCA-2b, LuCaP-35, and LuCaP-35V tumors. GHRH antagonists increased the inhibitory effect of surgical castration and LHRH antagonists on androgen sensitive MDA-PCa-2b and LuCaP-35 tumors. The time to relapse of androgen-dependent LuCaP-35 tumors was extended by GHRH antagonists. Growth of androgen-independent LuCaP-35V xenografts was also significantly inhibited by MZ-J-7-118. In MDA-PCa-2b tumors treatment with MZ-J-7-118 caused a significant decrease of VEGF and Cetrorelix or its combination with MZ-J-7-118 reduced EGF. The B(max) of EGF receptors was significantly reduced by Cetrorelix, MZ-J-7-118 and their combination.

CONCLUSIONS

Our findings suggest that the use of a combination of antagonists of GHRH and LHRH could improve the therapy for androgen sensitive prostate cancer. Antagonists of GHRH could be also considered for treatment of androgen-independent prostate cancers.

Stimulation of proliferation of MCF-7 breast cancer cells by a transfected splice variant of growth hormone-releasing hormone receptor

Recent evidence indicates that growth hormone-releasing hormone (GHRH) functions as an autocrine/paracrine growth factor for various human cancers. A splice variant (SV) of the full-length receptor for GHRH (GHRHR) is widely expressed in various primary human cancers and established cancer cell lines and appears to mediate the proliferative effects of GHRH. To investigate in greater detail the role of SV1 in tumorigenesis, we have expressed the full-length GHRHR and its SV1 in MCF-7 human breast cancer cells that do not possess either GHRHR or SV1. In accordance with previous findings, the expression of both GHRHR and SV1 restored the sensitivity to GHRH-induced stimulation of cell proliferation, with SV1 being more potent than the GHRHR. Furthermore, MCF-7 cells transfected with SV1 proliferated more quickly than the controls, even in the absence of exogenously added GHRH, suggesting the existence of intrinsic, ligand-independent activity of SV1 after its transfection. In agreement with the stimulation of cell proliferation, the levels of proliferation markers cyclin D1, cyclin E, and proliferating cell nuclear antigen were elevated in MCF-7 cells treated with GHRH, cultured in both serum-free and serum-containing media. In addition, SV1 caused a considerable stimulation of the ability of MCF-7 cells to grow in semisolid medium, an assay considered diagnostic for cell transformation. Collectively, our findings show that the expression of SV1 confers oncogenic activity and provide further evidence that GHRH operates as a growth factor in breast cancer and probably other cancers as well.

Potentiation of mammary cancer inhibition by combination of antagonists of growth hormone-releasing hormone with docetaxel

Antagonists of growth hormone-releasing hormone (GHRH) are being developed for the treatment of various cancers. In this study, we investigated the effectiveness of treatment with GHRH antagonist JMR-132 alone and in combination with docetaxel chemotherapy in nude mice bearing MX-1 human breast cancers. Specific high-affinity binding sites for GHRH were found on MX-1 tumor membranes using ligand competition assays with (125)I-labeled GHRH antagonist JV-1-42. JMR-132 displaced radiolabeled JV-1-42 with an IC(50) of 0.14 nM, indicating a high affinity of JMR-132 to GHRH receptors. Treatment of nude mice bearing xenografts of MX-1 with JMR-132 at 10 microg per day s.c. for 22 days significantly (P < 0.05) inhibited tumor volume by 62.9% and tumor weight by 47.8%. Docetaxel given twice at a dose of 20 mg/kg i.p. significantly reduced tumor volume and weight by 74.1% and 58.6%, respectively. Combination treatment with JMR-132 (10 microg/day) and docetaxel (20 mg/kg i.p.) led to growth arrest of most tumors as shown by an inhibition of tumor volume and weight by 97.7% and 95.6%, respectively (P < 0.001). Because no vital cancer cells were detected in some of the excised tumors, a total regression of the tumors was achieved in some cases. Treatment with JMR-132 also strongly reduced the concentration of EGF receptors in MX-1 tumors. Our results demonstrate that GHRH antagonists might provide a therapy for breast cancer and could be combined with docetaxel chemotherapy to enhance the efficacy of treatment.

Expression of growth hormone-releasing hormone (GHRH) and splice variant of GHRH receptors in normal mouse tissues

Growth hormone-releasing hormone (GHRH) stimulates the production and release of growth hormone in the pituitary and induces cell proliferation in a variety of peripheral tissues and tumors. These extrapituitary effects of GHRH are in many cases mediated by a splice variant of GHRH receptor designated SV1 that differs from the pituitary GHRH receptor in a small portion of its amino-terminal region. While SV1 has been detected in several primary tumors and many cancer cell lines its expression in normal tissues remains unclear. In this study we report the results of an immunohistochemical analysis for SV1 and GHRH expression in normal mouse tissues. For the detection of SV1 immunoreactivity we used a polyclonal antiserum against segments 1-25 of the SV1 receptor protein. Mouse heart, colon, lungs, small intestine, stomach and kidneys exhibited increased SV1 immunoreactivity. These tissues were also positive for GHRH expression, however, tissues such as the endometrium were positive only for GHRH and not for SV1 expression. On the contrary, testis were positive for SV1 and not for GHRH expression. These results indicate that SV1 may play a role in normal physiology.

Immunocytochemical localisation of plasma membrane GHRH receptors in human tumours using a novel anti-peptide antibody

Antagonists of growth hormone releasing hormone (GHRH) directly inhibit the growth of a variety of human neoplasms. However, the plasma membrane receptor mediating these effects has not been immunocytochemically visualised in primary tumour cells. Given that previous attempts using an antibody to the amino-terminal region did not result in the visualisation of plasma membrane receptors, we have developed and characterised an anti-peptide antibody to the carboxy-terminal region 403-422 of the human pituitary GHRH receptor. This sequence is identical to residues 339-358 of splice variant 1 (SV1) of tumoural GHRH receptors. Specificity of the antibody was demonstrated by (1) immunocytochemical staining of GHRH receptor-transfected cells, (2) detection of a broad glycosylated protein band migrating at Mr 50,000-60,000 in Western blots of membranes from human pituitary, and (3) abolition of tissue immunostaining by preadsorbtion of the antibody with its immunising peptide. The distribution of GHRH receptors was investigated in 69 formalin-fixed, paraffin-embedded human tumours showing that GHRH receptors were frequently expressed in breast, ovarian and prostate carcinomas. Immunoreactive GHRH receptors were clearly confined to the plasma membrane and uniformly present on nearly all tumour cells. In Western blots of membranes prepared from human tumours, the anti-GHRH receptor antibody detected a non-glycosylated protein band migrating at Mr 40,000, which corresponds to the expected molecular weight of splice variant 1 of tumoural GHRH receptors. Together, our findings provide direct evidence for the presence of GHRH receptor protein on the plasma membrane of primary human tumour cells. The GHRH receptor visualisation could be of value for a rapid immunohistochemical identification of those tumours which could be a target for diagnostic or therapeutic intervention using GHRH analogues.

The expression of the pituitary growth hormone-releasing hormone receptor and its splice variants in normal and neoplastic human tissues

Various attempts to detect human pituitary growth hormone-releasing hormone receptor (pGHRH-R) in neoplastic extrapituitary tissues have thus far failed. Recently, four splice variants (SVs) of GHRH-R have been described, of which SV1 has the highest structural homology to pGHRH-R and likely plays a role in tumor growth. The aim of this study was to reinvestigate whether human tumors and normal human extrapituitary tissues express the pGHRH-R and to corroborate our previous findings on its SVs. Thus, we developed a real-time PCR method for the detection of the mRNA for the pGHRH-R, its SVs, and the GHRH peptide. Using real-time PCR, Western blotting, and radioligand-binding assays, we detected the mRNA for pGHRH-R and pGHRH-R protein in various human cancer cell lines grown in nude mice and in surgical specimens of human lung cancers. The expression of mRNA for SVs of pGHRH-R and GHRH was likewise found in xenografts of human non-Hodgkin's lymphomas, pancreatic cancer, glioblastoma, small-cell lung carcinomas, and in human nonmalignant prostate, liver, lung, kidney, and pituitary. Western blots showed that these normal and malignant human tissues contain SV1 protein and immunoreactive GHRH. Our results demonstrate that some normal human tissues and tumors express mRNA and protein for the pGHRH-R and its splice variants. These findings confirm and extend the concept that GHRH and its receptors play an important role in the pathophysiology of human cancers.

Antagonists of growth hormone releasing hormone and bombesin inhibit the expression of EGF/HER receptor family in H-69 small cell lung carcinoma

Effects of in vivo treatment with antagonists of growth hormone-releasing hormone (GHRH), JV-1-65 and MZ-J-7-110, and bombesin/gastrin-releasing peptide antagonist RC-3940-II, on the EGF receptor (EGFR) family, were investigated in H-69 SCLC. Tumors were analyzed by RT-PCR, immunoblotting and binding assays. Treatment with these analogs reduced the binding capacity of EGFR by 18-64%, and inhibited the mRNA expression for EGFR, HER-2 and -3 by 27-75.4, 17-26.3, and 13.8-46.6%, respectively. The antagonists also decreased the protein levels for EGFR by 21-34%, HER-2 by 36-68% and HER-3 by 43-49%. This is the first demonstration that antiproliferative effects of GHRH antagonists are associated with a downregulation of EGF/HER receptors.

Antagonists of growth hormone releasing hormone (GHRH) and of bombesin/gastrin releasing peptide (BN/GRP) suppress the expression of VEGF, bFGF, and receptors of the EGF/HER family in PC-3 and DU-145 human androgen-independent prostate cancers

BACKGROUND

Antagonists of growth hormone releasing hormone (GHRH) as well as antagonists of bombesin/gastrin releasing peptide (BN/GRP) inhibit the growth of various malignancies (cancers) including prostate cancer.

METHODS

We investigated the effects of GHRH antagonists MZ-J-7-118 and RC-J-29-18, BN/GRP antagonists RC-3940-II and RC-3940-Et and the combination of MZ-J-7-118 and RC-3940-II on the growth of PC-3 and DU-145 human androgen independent prostate cancers xenografted s.c. into nude mice. To elucidate the mechanisms of action of these analogs, growth factors like IGF-II (insulin-like growth factor-II), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and epidermal growth factor receptor/human epidermal growth factor receptor (EGF-R/HER) family were measured in tumors as well as IGF-I in serum.

RESULTS

Antagonists of GHRH and BN/GRP alone or in combination significantly inhibited growth of PC-3 and DU-145 tumors, the greatest inhibition of tumor volume being achieved by combination of MZ-J-7-118 (5 microg/day) and RC-3940-II (10 microg/day). BN/GRP and GHRH antagonists and their combination also decreased the expression of VEGF significantly in PC-3 and non-significantly in DU-145, as measured by radioimmunoassay for VEGF protein and RT-PCR for mRNA levels of VEGF. GHRH and BN/GRP antagonists reduced bFGF concentrations and the maximal binding capacity of EGF receptors, and their mRNA levels in PC-3 and DU-145 tumors. mRNA levels for HER-2 and -3 were also diminished in PC-3 tumors by GHRH and BN/GRP antagonists. No changes in HER-4 were found after treatment. Serum IGF-I and tumoral IGF-II levels were not affected by the analogs.

CONCLUSIONS

BN/GRP and GHRH antagonists inhibit growth of PC-3 and DU-145 prostate cancers by suppressing the expression of tumoral growth factors such as VEGF and bFGF as well as the receptors for EGF and related HER-2 and -3. Additive effects on tumor inhibition (TI) in vivo, but not on VEGF, bFGF, or members of the EGF/HER receptor family, can be achieved by the joint administration of both classes of analogs.

Effective treatment of experimental human non-Hodgkin's lymphomas with antagonists of growth hormone-releasing hormone

Antagonists of growth hormone-releasing hormone (GHRH) were shown to inhibit the growth of various cancers. We investigated the antitumor activity and the mechanism of action of GHRH antagonists in human non-Hodgkin's lymphomas (NHL). Nude mice bearing xenografts of RL and HT human NHL were treated with GHRH antagonists MZ-5-156 and MZ-J-7-138 at a dose of 40 microg twice daily. The concentrations of serum IGF-1 and GHRH, bFGF, and VEGF in tumor tissue were measured by radioimmunoassays. Expression of GHRH and splice variant 1 of the GHRH receptor in both cell lines was examined by RT-PCR. The effects of MZ-5-156, MZ-J-7-138 and GHRH on cell proliferation were evaluated in vitro. Treatment with MZ-5-156 and MZ-J-7-138 significantly (P < 0.05) inhibited the growth of RL and HT tumors by 59.9-73.9%. High-affinity binding sites for GHRH and mRNA for GHRH and splice variant-1 of the GHRH receptors were found on RL and HT tumors. RL and HT cells contained GHRH peptide, and their growth in vitro was significantly inhibited by both antagonists. IGF-I levels in serum of mice were significantly decreased by antagonist MZ-5-156. Therapy with GHRH antagonists also significantly reduced tumoral bFGF, whereas VEGF levels were not suppressed. Our findings suggest that GHRH antagonists inhibit the growth of RL and HT lymphomas by direct effects mediated by tumoral receptors for GHRH. GHRH antagonists could offer a new therapeutic modality for the management of advanced NHL.

Expression of growth hormone-releasing hormone receptor splicing variants in human primary adrenocortical tumours

OBJECTIVE

Several splice variants (SVs) of GHRH receptor (GHRH-R) have been identified in various human cancers through which GHRH antagonists may exert their IGF-II-mediated antiproliferative action. Because the overexpression of the IGF-II gene is a frequent feature of adrenal carcinoma, we searched for the presence of GHRH-R SVs in these tumours.

METHODS AND RESULTS

The expression of GHRH-R SVs was assessed by nested PCR in 45 human adrenocortical tumours. We have amplified 720-, 566- and 335-bp PCR products only in carcinomas. Their sequence revealed three open reading frames, corresponding to SV1, SV2 and SV4 of GHRH-R. SV2 was detected in five of 24 cancers examined, whereas the incidence of SV1 and SV4 was lower. Their simultaneous expression was observed in one carcinoma. No PCR products for SV3 or wild-type GHRH-R were found in carcinomas; mRNA for wild-type GHRH-R or SVs of GHRH-R were not observed either in adenomas or in normal adrenal or in NCI-H295R cells. Interestingly, all carcinomas which expressed SVs were also positive for the presence of GHRH mRNA.

CONCLUSION

This is the first time that the expression of splice variants of GHRH-R has been demonstrated in human adrenal carcinoma. This study raises the possibility that splice variants might play a role in adrenal carcinogenesis and might offer the possibility for new therapeutic strategies at least in a subgroup of adrenal carcinomas.

Antagonist of growth hormone-releasing hormone induces apoptosis in LNCaP human prostate cancer cells through a Ca2+-dependent pathway

Antagonists of growth hormone-releasing hormone (GHRH) exert antiproliferative effects directly on cancer cells, which are mediated by the tumoral GHRH receptors. However, the signal transduction pathways involved in antiproliferative effect of GHRH antagonists have not yet been elucidated. We used flow cytometry to investigate whether GHRH antagonist JV-1-38 can induce changes in the cytosolic free Ca2+ concentration leading to apoptosis in LNCaP human prostate cancer cells. JV-1-38 evoked prompt Ca2+ signal in a dose-dependent way (1-10 microM) and induced early stage of apoptosis in LNCaP human prostate cancer cells at a concentration effective in suppression of cell proliferation (10 microM) peaking after 3 h. Unexpectedly, agonist GHRH(1-29)NH2, which elevates cytosolic free Ca2+ concentration in pituitary somatotrophs at nanomolar concentrations, failed to induce Ca2+ signal or apoptosis even at a 10-fold higher concentration (100 microM). However, agonist GHRH(1-29)NH2 inhibited JV-1-38-induced Ca2+ signals in a dose-dependent way without affecting the antagonist-induced apoptosis. Peptides unrelated to GHRH did not induce Ca2+ signals in LNCaP human prostate cancer cells. EDTA (10 mM) or nifedipine (10 microM) significantly reduced the Ca2+ signal and early stage of apoptosis induced by JV-1-38, supporting the view that the increase in intracellular Ca2+ in response to JV-1-38 occurs primarily through extracellular Ca2+ entry through voltage-operated Ca2+ channels. In conclusion, GHRH antagonists activate tumoral GHRH receptors and are able to induce apoptosis in LNCaP human prostate cancer cells through a Ca2+-dependent pathway. Treatment with GHRH antagonists may offer a new approach to the therapy of prostate and other hormone-sensitive cancers.

Extrapituitary Effects of the Growth Hormone-Releasing Hormone

Growth hormone-releasing hormone (GHRH) is a neuropeptide secreted by the hypothalamus that stimulates the synthesis and release of growth hormone (GH) in the pituitary. Accumulating evidence suggests that in addition to GHRH's neuroendocrine action, GHRH is present in several extrahypothalamic tissues and is involved in a variety of cellular processes. Its function is related to the regulation of cell proliferation and differentiation of various nonpituitary cell types. In certain cases, ectopic production of GHRH has also been implicated in carcinogenesis. The mechanisms by which GHRH affects the peripheral extrapituitary tissues remain poorly understood, but it is likely that classic neuroendocrine action as well as paracrine and autocrine pathways are involved. Some headway has been made in the identification of extrapituitary receptors for GHRH and cDNA as splice variants of these GHRH receptors found in various tumors. The fact that the nonpituitary GHRH receptors are not fully identified, however, remains the major obstacle in studying, at a more mechanistic level, the action of local GHRH. This review summarizes the information available regarding the role of GHRH in the extrapituitary tissues with emphasis on its potential therapeutic and diagnostic applications.

Inhibitory Effect of Antagonists of Bombesin and Growth Hormone-Releasing Hormone on Orthotopic and Intraosseous Growth and Invasiveness of PC-3 Human Prostate Cancer in Nude Mice

Purpose: To determine whether antagonists of growth hormone-releasing hormone (GHRH) and bombesin/gastrin-releasing peptide (BN/GRP) can inhibit the orthotopic and metastatic growth of PC-3 human androgen-independent prostate cancers.

Experimental Design: The effects of administration of GHRH antagonist MZ-J-7-118, BN/GRP antagonist RC-3940-II, and their combination on the growth and metastatic spread of PC-3 tumors implanted orthotopically into nude mice were evaluated. The efficacy of this treatment on PC-3 tumors implanted intratibially and s.c. was also determined.

Results: Treatment with MZ-J-7-118, RC-3940-II, or their combination significantly inhibited the growth of PC-3 tumors implanted orthotopically, intraosseously, and s.c. The combination of the two antagonists had the greatest effect, inhibiting orthotopic tumor growth by 77%, intratibially implanted tumors by 86%, and s.c. tumors by 86%. The therapy with BN/GRP and GHRH antagonists, especially in combination, also reduced the local tumor spread and distant metastases in animals bearing orthotopic tumors. Combination therapy was likewise the most effective in reducing the incidence and severity of tibial osteolytic lesions and pathologic fractures in intraosseously implanted tumors. High-affinity binding sites for BN/GRP and GHRH were found in s.c. and orthotopic PC-3 tumor samples. MZ-J-7-118, RC-3940-II, and the combination of both compounds inhibited in vitro growth of PC-3 cells.

Conclusions: Our findings show the efficacy of BN/GRP antagonists and GHRH antagonists for the treatment of advanced prostate cancer in preclinical metastatic models. As BN/GRP antagonists are already in clinical trials and GHRH antagonists are effective in androgen-independent prostate cancer models, these analogues could be considered for the management of advanced prostate carcinoma.

Development of a polyclonal antiserum for the detection of the isoforms of the receptors for human growth hormone-releasing hormone on tumors

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the growth of various human cancers by multiple mechanisms, which include direct effects on tumor cells through the splice variants (SV) of the GHRH receptor. Our findings suggest that the tumoral protein encoded by SV 1 (SV1) is a likely functional receptor. The aim of this study was to develop a polyclonal antiserum against a polypeptide analog of segment 1-25 of the putative SV1 receptor protein. Rabbits were immunized with [Ala-23]SV1 (1-25)-Tyr-26-Cys-27-NH2 as a hapten, conjugated to BSA or keyhole limpet hemocyanin. The antisera thus generated were evaluated by RIA for binding to the radiolabeled hapten. The specificity and sensitivity of the antisera were studied on xenografts of RL and HT human non-Hodgkin's lymphomas. The sera raised against keyhole limpet hemocyanin-SV1 hapten, showed binding values of 50-75% at a 1:56,000 dilution. In Western blot analyses, the purified polyclonal antibody recognized a specific signal with a molecular mass of approximately 40 kDa in RL and HT lymphomas. This band corresponds to the estimated molecular mass of the GHRH receptor isoform encoded by SV1. RT-PCR and ligand binding studies also revealed the expression of SV1 and the presence of high-affinity binding sites for GHRH on RL and HT tumors. Because the antiserum developed recognizes the tumoral GHRH receptor protein encoded by SV1, it should be of value in various investigations.

Cdk4 is indispensable for postnatal proliferation of the anterior pituitary

For proper development and tissue homeostasis, cell cycle progression is controlled by multilayered mechanisms. Recent studies using knock-out mice have shown that animals can develop relatively normally with deficiency for each of the G1/S-regulatory proteins, D-type and E-type cyclins, cyclin-dependent kinase 4 (Cdk4), and Cdk2. Although Cdk4-null mice show no embryonic lethality, they exhibit specific endocrine phenotypes, i.e. dwarfism, infertility, and diabetes. Here we have demonstrated that Cdk4 plays an essential non-redundant role in postnatal proliferation of the anterior pituitary. Pituitaries from wild-type and Cdk4-null embryos at embryonic day 17.5 are morphologically indistinguishable with similar numbers of cells expressing a proliferating marker, Ki67, and cells expressing a differentiation marker, growth hormone. In contrast, anterior pituitaries of Cdk4-null mice at postnatal 8 weeks are extremely hypoplastic with markedly decreased numbers of Ki67+ cells, suggesting impaired cell proliferation. Pituitary hyperplasia induced by transgenic expression of human growth hormone-releasing hormone (GHRH) is significantly diminished in the Cdk4+/- genetic background and completely abrogated in the Cdk4-/- background. Small interfering RNA (siRNA)-mediated knockdown of Cdk4 inhibits GHRH-induced proliferation of GH3 somato/lactotroph cells with restored expression of GHRH receptors. Cdk4 siRNA also inhibits estrogen-dependent cell proliferation in GH3 cells and closely related GH4 cells. In contrast, Cdk6 siRNA does not diminish proliferation of these cells. Furthermore, Cdk4 siRNA does not affect GHRH-induced proliferation of mouse embryonic fibroblasts or estrogen-dependent proliferation of mammary carcinoma MCF-7 cells. Taken together, Cdk4 is dispensable for prenatal development of the pituitary or proliferation of other non-endocrine tissues but indispensable specifically for postnatal proliferation of somato/lactotrophs.

Increased activity of antagonists of growth hormone-releasing hormone substituted at positions 8, 9, and 10

Antagonists of human growth hormone-releasing hormone (hGHRH) with increased potency and improved enzymatic and chemical stability are needed for potential clinical applications. We synthesized 21 antagonistic analogs of hGHRH(1-29)NH(2), substituted at positions 8, 9, and 10 of the common core sequence [phenylacetyl-Tyr(1), d-Arg(2,28), para-chloro-phenylalanine 6, Arg(9)/homoarginine 9, Tyr(10)/O-methyltyrosine 10, alpha-aminobutyric acid 15, norleucine 27, Har(29)] hGHRH(1-29)NH(2). Inhibitory effects on hGHRH-induced GH release were evaluated in vitro in a superfused rat pituitary system, as well as in vivo after i.v. injection into rats. The binding affinities of the peptides to pituitary GHRH receptors were also determined. Introduction of para-amidinophenylalanine 10 yielded antagonists JV-1-62 and -63 with the highest activities in vitro and lowest receptor dissociation constants (K(i) = 0.057-0.062 nM). Antagonists JV-1-62 and -63 also exhibited the strongest effect in vivo, significantly (P < 0.05-0.001) inhibiting hGHRH-induced GH release for at least 1 h. Para-aminophenylalanine 10 and O-ethyltyrosine 10 substitutions yielded antagonists potent in vitro, but His(10), 3,3'-diphenylalanine 10, 2-naphthylalanine 10, and cyclohexylalanine 10 modifications were detrimental. Antagonists containing citrulline 9 (in MZ-J-7-72), amidinophenylalanine 9 (in JV-1-65), His(9), d-Arg(9), citrulline 8, Ala(8), d-Ala(8), or alpha-aminobutyric acid 8 substituents also had high activity and receptor affinity in vitro. However, in vitro potencies of analogs with substitution in position 9 correlated poorly with acute endocrine effects in vivo, as exemplified by the weak and/or short inhibitory actions of antagonists JV-1-65 and MZ-J-7-72 on GH release in vivo. Nevertheless, antagonist JV-1-65 was more potent than JV-1-63 in tests on inhibition of the growth of human prostatic and lung cancer lines xenografted into nude mice. This indicates that oncological activity may be based on several mechanisms. hGHRH antagonists with improved efficacy could be useful for treatment of cancers that depend on insulin-like growth factors or GHRH.

Effects of plasmid-mediated growth hormone-releasing hormone supplementation on LL-2 adenocarcinoma in mice

This study was designed to measure the effects of plasmid growth hormone-releasing hormone (GHRH) supplementation on LL-2 (Lewis lung adenocarcinoma) tumor-bearing immunocompetent mice. Male and female mice (n = 20/group/experiment) received 2.5 x 10(6) LL-2 cells in the left flank. One day later, we injected the mice intramuscularly with 20 micro g of a myogenic plasmid, pSP-hGHRH or pSP-betagal, as a control. Mean serum IGF-I was significantly higher in treated animals versus controls (P < 0.05). Male and female mice constitutively expressing GHRH exhibited a decline in tumor growth rate relative to controls (20% for males, P < 0.03, and 11% for females, P < 0.13). Histopathological analysis revealed that treated animals were less likely to develop lung metastases than controls (11%) and had no alternate-organ metastases. The number of metastases/lung was reduced by 57% in female mice with GHRH treatment (P < 0.006). When tumor size exceeded 8% of body weight, GHRH-treated mice showed normal urea, creatinine, and kidney volume, while controls displayed signs of renal insufficiency. This study provides evidence that with plasmid-mediated GHRH supplementation in tumor-bearing mice, tumor growth rate is not increased but is actually attenuated.

Ligand-dependent and -independent effects of splice variant 1 of growth hormone-releasing hormone receptor

Existing evidence indicates that, in addition to its neuroendocrine action, growth hormone-releasing hormone (GHRH) acts directly on several nonpituitary tissues, especially neoplasms, and stimulates cell proliferation. We have recently reported that a splice variant of the receptor (SV1) is expressed in various normal tissues and particularly in tumor tissues, producing mitogenic effects on GHRH binding. By using HEC-1A human endometrial carcinoma cells, which express endogenous SV1, we show that, in addition to its ability to mediate the mitogenic effects of GHRH, SV1 also possesses relatively high intrinsic, ligand-independent activity. By using an antisense RNA-based approach we found that SV1 ablation reduces the efficacy of colony formation and the rate of cell proliferation of HEC-1A cells in the absence of exogenous GHRH, and decreases their sensitivity to GHRH when the neurohormone is added to the culture media. This ligand-independent stimulation of cell proliferation appears to be a characteristic property of the truncated form of the receptor, because the expression of SV1 and not of the full-length GHRH receptor stimulated the proliferation of 3T3 fibroblasts in the absence of exogenous GHRH, whereas both forms mediated the proliferative effects of GHRH. Evaluation of 21 specimens of human primary endometrial carcinoma for expression of SV1 by immunohistochemistry indicated that in contrast to the GHRH receptor, which is absent, SV1 is expressed in approximately 43% of the specimens. These findings indicate that SV1 can operate in a ligand-independent as well as a ligand-dependent manner. The overexpression of this form of GHRH receptor may be associated with carcinogenesis.

Growth hormone-releasing hormone and extra-pituitary tumorigenesis: therapeutic and diagnostic applications of growth hormone-releasing hormone antagonists

Growth hormone-releasing hormone (GHRH) regulates growth hormone release from the pituitary. However, in addition to this neuroendocrine action, much evidence implies an additional role for GHRH in carcinogenesis in non-pituitary tissues. This role of GHRH in cancer development appears to be due to the operation of several mechanisms, which involve the regulation of the growth hormone-dependent hepatic insulin-like growth factor I (IGFI) production, tumoural IGF-I and IGF-II secretion and direct action of GHRH on tumour cells by autocrine and/or paracrine pathways. This review summarises the available information regarding the role of GHRH in tumorigenesis with special emphasis on the direct action of GHRH in primary and experimental cancers.

GH-RH antagonist (MZ-4-71) inhibits VEGF secretion and proliferation of murine endothelial cells

Angiogenesis plays a key role in solid tumor formation, invasiveness and metastasis. Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen that is necessary in the process of neovascularisation. Antagonists of growth hormone-releasing hormone (GH-RH) have been shown to suppress both in vivo and in vitro growth and metastasis of many human cancer cell lines. The mechanisms that mediate the antitumorigenic actions of these antagonists involve direct and indirect pathways, but are not completely elucidated. We have examined the effect of GH-RH antagonist MZ-4-71 on proliferation activity and VEGF release from cultured murine endothelial cells HECa10 in vitro. MZ-4-71 at 10(-8) to 10(-6) M concentrations inhibited the proliferative activity of cultured cells and suppressed the release of VEGF into supernatants of 72 h endothelial cell cultures. To our knowledge this is the first study reporting antiangiogenic properties of GH-RH antagonists.

The expression of growth hormone-releasing hormone (GHRH) and its receptor splice variants in human breast cancer lines; the evaluation of signaling mechanisms in the stimulation of cell proliferation

Antagonists of growth hormone-releasing hormone (GHRH) inhibit growth of various human cancers including breast cancer, xenografted into nude mice or cultured in vitro. Splice variants (SVs) of receptors for GHRH have been found in several human cancers and cancer cell lines. The antiproliferative actions of GHRH antagonists could be mediated in part through these SVs of GHRH receptors. In this study we examined the expression of mRNA for GHRH and SVs of its receptors in human breast cancer cell lines MCF-7, MCF-7MIII, MDA-MB-231, MDA-MB-435, MDA-MB-468, and T47D. mRNA for GHRH was present in all lines tested. mRNA for SV1 isoform of GHRH receptors was found in MCF-7MIII, MDA-MB-468, and T47D; and for SV2 isoform in MCF-7MIII and T47D cell lines. In proliferation studies in vitro, the growth of T47D cells was stimulated by GHRH and dose-dependently inhibited by GHRH antagonist JV-1-38. H89 (protein kinase A inhibitor), bisindolylmaleimide I (protein kinase C [PKC] inhibitor) and verapamil (voltage-dependent calcium channel blocker) inhibited the GHRH-stimulated proliferation of T47D cells. The GHRH antagonist JV-1-38 suppressed the T47D cell growth in vitro stimulated by PKC activator (phorbol-12-myristate-13-acetate). The stimulation of T47D cells by GHRH was followed by an increase in cAMP production and GHRH antagonist JV-1-38 competitively inhibited this effect. Our results suggest that SVs of GHRH receptors could mediate the responses to GHRH and GHRH antagonists in breast cancer through Ca2+-, cAMP- and PKC-dependent mechanisms. The presence of SV1 of GHRH receptors in human cancers provides a rationale for antitumor therapy based on the blockade of this receptor by specific GHRH antagonists.

Effects of plasmid-mediated growth hormone-releasing hormone in severely debilitated dogs with cancer

Cachexia is a common manifestation of late stage malignancy and is characterized by anemia, anorexia, muscle wasting, loss of adipose tissue, and fatigue. Although cachexia is disabling and can diminish the life expectancy of cancer patients, there are still no effective therapies for this condition. We have examined the feasibility of using a myogenic plasmid to express growth hormone-releasing hormone (GHRH) in severely debilitated companion dogs with naturally occurring tumors. At a median of 16 days after intramuscular delivery of the plasmid, serum concentrations of insulin-like growth factor I (IGF-I), a measure of GHRH activity, were increased in 12 of 16 dogs (P < 0.01). These increases ranged from 21 to 120% (median, 49%) of the pretreatment values and were generally sustained or higher on the final evaluation. Anemia resolved posttreatment, as indicated by significant increases in mean red blood cell count, hematocrit, and hemoglobin concentrations, and there was also a significant rise in the percentage of circulating lymphocytes. Treated dogs maintained their weights over the 56-day study and did not show any adverse effects from the GHRH gene transfer. We conclude that intramuscular injection of a GHRH-expressing plasmid is both safe and capable of stimulating the release of growth hormone and IGF-I in large animals. The observed anabolic responses to a single dose of this therapy might be beneficial in patients with cancer-associated anemia and cachexia.

Expression of mRNA for growth hormone-releasing hormone and splice variants of GHRH receptors in human malignant bone tumors

Splice variants (SV) of receptors for growth hormone-releasing hormone (GHRH) have been found in several human cancer cell lines. GHRH antagonists inhibit growth of various human cancers, including osteosarcomas and Ewing's sarcoma, xenografted into nude mice or cultured in vitro and their antiproliferative action could be mediated, in part, through these SV of GHRH receptors. In this study, we found mRNA for the SV(1) isoform of GHRH receptors in human osteosarcoma line MNNG/HOS and SK-ES-1 Ewing's sarcoma line. We also detected mRNA for GHRH, which is apparently translated into the GHRH peptide and secreted by the cells, as shown by the presence of GHRH-like immunoreactivity in the conditioned media of cell cultures. In proliferation studies in vitro, the growth of SK-ES-1 and MNNG/HOS cells was dose-dependently inhibited by GHRH antagonist JV-1-38 and an antiserum against human GHRH. Our study indicates the presence of an autocrine stimulatory loop based on GHRH and SV(1) of GHRH receptors in human sarcomas. The direct antiproliferative effects of GHRH antagonists on malignant bone tumors appear to be exerted through the SV(1) of GHRH receptors on tumoral cells.

The expression of growth hormone-releasing hormone (GHRH) and splice variants of its receptor in human gastroenteropancreatic carcinomas

Splice variants (SVs) of receptors for growth hormone-releasing hormone (GHRH) have been found in primary human prostate cancers and diverse human cancer cell lines. GHRH antagonists inhibit growth of various experimental human cancers, including pancreatic and colorectal, xenografted into nude mice or cultured in vitro, and their antiproliferative action could be mediated in part through SVs of GHRH receptors. In this study we examined the expression of mRNA for GHRH and for SVs of its receptors in tumors of human pancreatic, colorectal, and gastric cancer cell lines grown in nude mice. mRNA for both GHRH and SV(1) isoform of GHRH receptors was expressed in tumors of pancreatic (SW1990, PANC-1, MIA PaCa-2, Capan-1, Capan-2, and CFPAC1), colonic (COLO 320DM and HT-29), and gastric (NCI-N87, HS746T, and AGS) cancer cell lines; mRNA for SV(2) was also present in Capan-1, Capan-2, CFPAC1, HT-29, and NCI-N87 tumors. In proliferation studies in vitro, the growth of pancreatic, colonic, and gastric cancer cells was stimulated by GHRH(1-29)NH(2) and inhibited by GHRH antagonist JV-1-38. The stimulation of some gastroenteropancreatic cancer cells by GHRH was followed by an increase in cAMP production, and GHRH antagonist JV-1-38 competitively inhibited this effect. Our study indicates the presence of an autocrine/paracrine stimulatory loop based on GHRH and SV(1) of GHRH receptors in human pancreatic, colorectal, and gastric cancers. The finding of SV(1) receptor in human cancers provides an approach to an antitumor therapy based on the blockade of this receptor by specific GHRH antagonists.

Expression of growth hormone-releasing hormone (GHRH) and splice variants of GHRH receptors in human experimental prostate cancers

The expression of mRNA for GHRH and splice variants (SVs) of GHRH receptors in LNCaP, MDA-PCa-2b and PC-3 human prostate cancers grown in nude mice was investigated by RT-PCR. The expression of mRNA for GHRH was detected in LNCaP and PC-3, but not in MDA-PCa-2b prostatic carcinoma. RT-PCR analyses of mRNA isolated from LNCaP, MDA-PCa-2b and PC-3 cancers, revealed the presence of 720 and 566 bp products, corresponding to SV(1) and SV(2) isoforms of GHRH receptors. In PC-3 tumor membranes a radiolabeled GHRH antagonist [125I]-JV-1-42 was bound to one class of high-affinity binding sites (K(d)=1.81+/-0.47 nM) and maximum binding capacity of 332.7+/-27.8 fmol/mg membrane protein. The in vivo uptake of [125I]-JV-1-42 was observed in all xenografts of human prostate cancer, the tracer accumulation being the highest in PC-3 tumors. These results indicate that GHRH and SVs of its receptors, different from those found in the pituitary, are present in experimental human prostate cancers and may form a local mitogenic loop. The antiproliferative effects of GHRH antagonists on growth of prostate cancer could be exerted in part by an interference with this local GHRH system.