This article reviews the potential clinical uses of antagonists of growth-hormone-releasing hormone (GHRH) for tumor therapy. GHRH antagonists suppress the growth of various human cancer lines ...xenografted into nude mice; such tumors include breast, ovarian, endometrial and prostate cancers, lung cancers (small-cell lung carcinomas and non-small-cell lung carcinomas), renal, pancreatic, gastric and colorectal carcinomas, brain tumors (malignant gliomas), osteogenic sarcomas and non-Hodgkin's lymphomas. The antitumor effects of GHRH antagonists are exerted in part indirectly through the inhibition of the secretion of GH from the pituitary and the resulting reduction in the levels of hepatic insulin-like growth factor I (IGF-I). The main effects of the GHRH antagonists are, however, exerted directly on tumors. GHRH ligand is present in various human cancers and might function as an autocrine and/or paracrine growth factor. Pituitary-type GHRH receptors and their splice variants are also found in many human cancers. The inhibitory effects of GHRH antagonists seem to be due to the blockade of action of tumoral GHRH. Antagonists of GHRH can also suppress cancer growth by blocking production of IGF-I and/or IGF-II by the tumor. Further development of GHRH antagonists that are still-more potent should lead to potential therapeutic agents for various cancers.
Whether the growth hormone (GH)/insulin-like growth factor 1(IGF-1) axis exerts cardioprotective effects remains controversial; and the underlying mechanism(s) for such actions are unclear. Here we ...tested the hypothesis that growth hormone-releasing hormone (GHRH) directly activates cellular reparative mechanisms within the injured heart, in a GH/IGF-1 independent fashion. After experimental myocardial infarction (MI), rats were randomly assigned to receive, during a 4-week period, either placebo (n = 14), rat recombinant GH (n = 8) or JI-38 (n = 8; 50 μg/kg per day), a potent GHRH agonist. JI-38 did not elevate serum levels of GH or IGF-1, but it markedly attenuated the degree of cardiac functional decline and remodeling after injury. In contrast, GH administration markedly elevated body weight, heart weight, and circulating GH and IGF-1, but it did not offset the decline in cardiac structure and function. Whereas both JI-38 and GH augmented levels of cardiac precursor cell proliferation, only JI-38 increased antiapoptotic gene expression. The receptor for GHRH was detectable on myocytes, supporting direct activation of cardiac signal transduction. Collectively, these findings demonstrate that within the heart, GHRH agonists can activate cardiac repair after MI, suggesting the existence of a potential signaling pathway based on GHRH in the heart. The phenotypic profile of the response to a potent GHRH agonist has therapeutic implications.
Various attempts to detect human pituitary growth hormone-releasing hormone receptor (pGHRH-R) in neoplastic extra pituitary 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 xenog rafts 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.
Ghrelin synergizes with growth hormone-releasing hormone (GHRH) to potentiate growth hormone (GH) response through a mechanism not yet fully characterized. This study was conducted to analyze the ...role of GHRH as a potential ligand of the ghrelin receptor, GHS-R1a. The results show that hGHRH(1-29)NH₂ (GHRH) induces a dose-dependent calcium mobilization in HEK 293 cells stably transfected with GHS-R1a an effect not observed in wild-type HEK 293 cells. This calcium rise is also observed using the GHRH receptor agonists JI-34 and JI-36. Radioligand binding and cross-linking studies revealed that calcium response to GHRH is mediated by the ghrelin receptor GHS-R1a. GHRH activates the signaling route of inositol phosphate and potentiates the maximal response to ghrelin measured in inositol phosphate turnover. The presence of GHRH increases the binding capacity of ¹²⁵I-ghrelin in a dose dependent-fashion showing a positive binding cooperativity. In addition, confocal microscopy in CHO cells transfected with GHS-R1a tagged with enhanced green fluorescent protein shows that GHRH activates the GHS-R1a endocytosis. Furthermore, the selective GHRH-R antagonists, JV-1-42 and JMR-132, act also as antagonists of the ghrelin receptor GHS-R1a. Our findings suggest that GHRH interacts with ghrelin receptor GHS-R1a, and, in consequence, modifies the ghrelin-associated intracellular signaling pathway. This interaction may represent a form of regulation, which could play a putative role in the physiology of GH regulation and appetite control.
Abstract We investigated the effect of a GHRH antagonist, MIA-602 on 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 the powerful downregulation of NF-κB and β-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.
Potent antagonists of growth hormone-releasing hormone (GHRH) have been developed for the treatment of disorders caused by excessive GHRH or growth hormone (GH) production and for therapy of cancers. ...GHRH antagonists suppressed the release of GH and insulin-like growth factor (IGF)-I in transgenic mice overexpressing human (h) GHRH gene, an animal model of human acromegaly. It was also shown in GH3 rat pituitary tumor cells overexpressing the human pituitary GHRH receptor (pGHRH-R) that GHRH antagonists can inhibit c-AMP production and GH secretion through the human receptor. These observations indicate that GHRH antagonists could be used clinically in disorders characterized by excessive GHRH/GH secretion. Many recent studies demonstrate that GHRH antagonists can inhibit tumor growth by several mechanisms. By indirect action through pGHRH-Rs these antagonists suppress circulating GH/IGF-I level, which results in the inhibition of cancers that depend on GH and/or IGF-I as growth factors. However, GHRH antagonists are also effective inhibitors of tumor IGF-II production, which is a potent mitogen but independent of GH. GHRH antagonists can inhibit tumor cell proliferation by direct action on tumor cell receptors, suppressing the IGF-II and other growth factor production of tumor cells. In addition, various human tumors and tumor cell lines secrete GHRH peptide and respond to GHRH with proliferation. This finding suggests that GHRH functions as an autocrine growth factor and that GHRH antagonists can block its effects on tumor growth. Recently, we demonstrated the expression of hGHRH-R and its splice variants in various human cancers. Antiproliferative action of GHRH antagonists on these cancers indicates that the direct inhibitory effects of GHRH antagonists are mediated by tumoral GHRH receptors.
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.
We investigated the mechanisms of inhibitory effect of growth hormone-releasing hormone (GHRH) antagonist JMR-132 on the growth of HT29, HCT-116 and HCT-15 human colon cancer cells in vitro and in ...vivo. High-affinity binding sites for GHRH and mRNA for GHRH and splice variant-1 (SV1) of the GHRH receptor were found in all three cell lines tested. Proliferation of HT-29, HCT-116 and HCT-15 cells was significantly inhibited in vitro by JMR-132. Time course studies revealed that the treatment of human HCT-116 colon cancer cells with 10μM GHRH antagonist JMR-132 causes a significant DNA damage as shown by an increase in olive tail moment (OTM) and loss of inner mitochondrial membrane potential (∆Ψm). Western blotting demonstrated a time-dependent increase in protein levels of phospho-p53 (Ser46), Bax, cleaved caspase-9, -3, cleavage of poly(ADP-ribose)polymerase (PARP) and a decrease in Bcl-2 levels. An augmentation in cell cycle checkpoint protein p21Waf1/Cip1 was accompanied by a cell cycle arrest in S-phase. DNA fragmentation visualized by the comet assay and the number of apoptotic cells increased time dependently as determined by flow cytometric annexinV and PI staining assays. In vivo, JMR-132 decreased the volume of HT-29, HCT-116 and HCT-15 tumors xenografted into athymic mice up to 75% (p
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