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

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.

Synthesis and structure-activity studies on novel analogs of human growth hormone releasing hormone (GHRH) with enhanced inhibitory activities on tumor growth

The syntheses and biological evaluations of new GHRH analogs of Miami (MIA) series with greatly increased anticancer activity are described. In the design and synthesis of these analogs, the following previous substitutions were conserved: D-Arg², Har⁹, Abu¹⁵, and Nle²⁷. Most new analogs had Ala at position 8. Since replacements of both Lys¹² and Lys²¹ with Orn increased resistance against enzymatic degradation, these modifications were kept. The substitutions of Arg at both positions 11 and 20 by His were also conserved. We kept D-Arg²⁸, Har²⁹ -NH₂ at the C-terminus or inserted Agm or 12-amino dodecanoic acid amide at position 30. We incorporated pentafluoro-Phe (Fpa₅), instead of Cpa, at position 6 and Tyr(Me) at position 10 and ω-amino acids at N-terminus of some analogs. These GHRH analogs were prepared by solid-phase methodology and purified by HPLC. The evaluation of the activity of the analogs on GH release was carried out in vitro on rat pituitaries and in vivo in male rats. Receptor binding affinities were measured in vitro by the competitive binding analysis. The inhibitory activity of the analogs on tumor proliferation in vitro was tested in several human cancer cell lines such as HEC-1A endometrial adenocarcinoma, HCT-15 colorectal adenocarcinoma, and LNCaP prostatic carcinoma. For in vivo tests, various cell lines including PC-3 prostate cancer, HEC-1A endometrial adenocarcinoma, HT diffuse mixed β cell lymphoma, and ACHN renal cell carcinoma cell lines were xenografted into nude mice and treated subcutaneously with GHRH antagonists at doses of 1-5μg/day. Analogs MIA-602, MIA-604, MIA-610, and MIA-640 showed the highest binding affinities, 30, 58, 48, and 73 times higher respectively, than GHRH (1-29) NH₂. Treatment of LNCaP and HCT-15 cells with 5μM MIA-602 or MIA-690 decreased proliferation by 40%-80%. In accord with previous tests in various human cancer lines, analog MIA-602 showed high inhibitory activity in vivo on growth of PC-3 prostate cancer, HT-mixed β cell lymphoma, HEC-1A endometrial adenocarcinoma and ACHN renal cell carcinoma. Thus, GHRH analogs of the Miami series powerfully suppress tumor growth, but have only a weak endocrine GH inhibitory activity. The suppression of tumor growth could be induced in part by the downregulation of GHRH receptors levels.

Mechanisms of synergism between antagonists of growth hormone-releasing hormone and antagonists of luteinizing hormone-releasing hormone in shrinking experimental benign prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) affects aging men. Combined therapy with antagonists of growth hormone-releasing hormone (GHRH) and of luteinizing hormone-releasing hormone (LHRH or GnRH) induces prostate shrinkage in rat models. We investigated the mechanisms of action of this combination on cell cycle traverse and expression of prostatic genes.

METHODS

Effects of GHRH antagonist, JMR-132 (40 µg/day), the LHRH antagonist, cetrorelix (0.625 mg/kg), and their combination were evaluated on testosterone-induced benign prostatic hyperplasia in male Wistar rats. Influence of JMR-132, cetrorelix, and their combinations on cell viability was assessed by MTS assay in BPH-1 human prostate epithelial cells and WPMY-1 normal prostate stromal cells. Cell cycle was analyzed by laser flow cytometry. Real-time PCR arrays were performed.

RESULTS

The combination of antagonists caused marked shrinkage of rat prostate (29.5%). In vitro, JMR-132 plus cetrorelix (both 5µM) produced synergistic (57.4%) inhibition of growth of BPH-1 cells, but a lesser inhibition (46%) of WPMY-1 cells. Co-treatment of with JMR-132 plus cetrorelix induced a significant increase of BPH-1 cells blocked in S-phase plus cells with lower G0 /G1 and G2 /M DNA content. Significant changes in expression of >40 gene transcripts related to growth factors, inflammatory cytokines, and signal transduction were identified.

CONCLUSIONS

GHRH antagonist and LHRH antagonist combination potentiates rat prostate weight reduction and synergistically inhibits of growth of BPH-1 leading to cell cycle arrest in S-phase. These effects were lesser in normal stromal prostate cell line, WPMY-1. Our findings suggest that GHRH antagonists could be useful for BPH therapy, possibly in combination with LHRH antagonists.

Inhibitory effects of antagonists of growth hormone releasing hormone on experimental prostate cancers are associated with upregulation of wild-type p53 and decrease in p21 and mutant p53 proteins

BACKGROUND

The tumor suppressor gene p53 is implicated in cell cycle control and apoptosis. Antagonists of growth hormone-releasing hormone (GHRH) have been shown to inhibit human experimental prostate cancers.

METHODS

We investigated the involvement of p53 apoptotic pathways in this effect. Nude mice bearing xenografted PC-3, DU-145, and MDA-PCa-2b human prostate cancer lines were treated with a new potent GHRH antagonist MZ-J-7-138. To determine whether tumor inhibition by MZ-J-7-138 involves apoptotic mechanisms such as p53 and p21, we evaluated by Western Blot the expression of mutant mt-p53 in PC-3 and DU-145 and of wild type (wt-p53) in MDA-PCa-2b prostate cancers as well as p21.

RESULTS

MZ-J-7-138 significantly inhibited the growth of PC-3, DU-145, and MDA-PCa-2b xenografts in nude mice. Androgen deprivation with the LHRH antagonist Cetrorelix enhanced the anti-proliferative effect of GHRH antagonist MZ-J-7-138 on MDA-PCa-2b tumors. The expression of mutant (mt-p53) and p21 protein in PC-3 and DU-145 tumors was significantly decreased by treatment with MZ-J-7-138, whereas wild type wt-p53 expression in MDA-PCA-2b tumors was up regulated by treatment with Cetrorelix. All three models investigated expressed specific, high affinity GHRH receptors.

CONCLUSIONS

Our findings indicate that the anti-proliferative effects of GHRH antagonist MZ-J-7-138 and LHRH antagonist Cetrorelix on prostate cancers involve p53 and p21 signaling.

Combining growth hormone-releasing hormone antagonist with luteinizing hormone-releasing hormone antagonist greatly augments benign prostatic hyperplasia shrinkage

PURPOSE

Benign prostatic hyperplasia often affects aging men. Antagonists of the neuropeptide growth hormone-releasing hormone reduced prostate weight in an androgen induced benign prostatic hyperplasia model in rats. Luteinizing hormone-releasing hormone antagonists also produce marked, protracted improvement in lower urinary tract symptoms, reduced prostate volume and an increased urinary peak flow rate in men with benign prostatic hyperplasia. We investigated the influence of a combination of antagonists of growth hormone-releasing hormone and luteinizing hormone-releasing hormone on animal models of benign prostatic hyperplasia.

MATERIALS AND METHODS

We evaluated the effects of the growth hormone-releasing hormone antagonist JMR-132, given at a dose of 40 μg daily, the luteinizing hormone-releasing hormone antagonist cetrorelix, given at a dose of 0.625 mg/kg, and their combination on testosterone induced benign prostatic hyperplasia in adult male Wistar rats in vivo. Prostate tissue was examined biochemically and histologically. Serum levels of growth hormone, luteinizing hormone, insulin-like growth factor-1, dihydrotestosterone and prostate specific antigen were determined.

RESULTS

Marked shrinkage of the rat prostate (30.3%) occurred in response to the combination of growth hormone-releasing hormone and luteinizing hormone-releasing hormone antagonists (p<0.01). The combination strongly decreased prostatic prostate specific antigen, 6-transmembrane epithelial antigen of the prostate, interleukin-1β, nuclear factor-κβ and cyclooxygenase-2, and decreased serum prostate specific antigen.

CONCLUSIONS

A combination of growth hormone-releasing hormone antagonist with luteinizing hormone-releasing hormone antagonist potentiated a reduction in prostate weight in an experimental benign prostatic hyperplasia model. Results suggest that this shrinkage in prostate volume was induced by the direct inhibitory effects of growth hormone-releasing hormone and luteinizing hormone-releasing hormone antagonists exerted through their respective prostatic receptors. These findings suggest that growth hormone-releasing hormone antagonists and/or their combination with luteinizing hormone-releasing hormone antagonists should be considered for further development as therapy for benign prostatic hyperplasia.

Human prostate cancer xenografts in lit/lit mice exhibit reduced growth and androgen-independent progression

BACKGROUND

The growth hormone/insulin-like growth factor I (GH/IGF-I) axis has been linked to prostate cancer (PCa) risk. Although previous studies indicate that human breast cancers and a murine PCa model develop more slowly in murine hosts homozygous for a missense mutation in the GH-releasing hormone receptor (lit/lit) whose "little" dwarfed phenotype is caused by suppressed GH and IGF-I production, the role of these two hormones remains controversial.

METHODS

To assess how the GH/IGF-I axis influences androgen-responsive, castration-resistant (CR), and androgen-independent (AI) growth of human PCa, we compared xenograft growth of the androgen-responsive human PCa cells, LNCaP, and AI human PCa cells, PC3, in intact and castrate Nod/SCID lit/lit and lit/+ mice, and in vitro growth of these cell lines in lit/lit and lit/+ serum-containing media supplemented with GH or IGF-I.

RESULTS

Tumor growth and PSA accumulation rates were suppressed in LNCaP tumor-bearing lit/lit mice pre- and post-castration. Growth of PC3 xenografts in lit/lit mice was also suppressed. In vitro proliferation of LNCaP and PC3 cells cultured in media containing lit/lit mouse serum was decreased as compared to growth in media containing lit/+ serum. Suppressed growth in lit/lit serum could be restored by the addition of IGF-I, and to a lesser extent, GH. Differences in growth correlated with differences in steady-state AKT and ERK1/2 activation.

CONCLUSIONS

This study demonstrates that circulating GH and IGF-I can promote androgen-responsive growth, CR progression, and AI expansion of PTEN-deficient human PCa cell xenografts and indicates that IGF-I can promote PCa growth in a suppressed GH environment.

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.

Serially heterotransplanted human prostate tumours as an experimental model

* Introduction * Serially heterotransplanted human tumours in immunosuppressed mice: similarity to the tumour of origin - Cytological and histological analysis - Karyotype - Marker expression - Other PC markers - Tumour cell proliferation and frequency of mitosis - Vasculature - Stromal compartment - Heterotransplant hormone dependency - Androgen dependent - Partially androgen dependent - Androgen independent - Metastases * Conclusions Preclinical research on prostate cancer (PC) therapies uses several models to represent the human disease accurately. A common model uses patient prostate tumour biopsies to develop a cell line by serially passaging and subsequent implantation, in immunodeficient mice. An alternative model is direct implantation of patient prostate tumour biopsies into immunodeficient mice, followed by serial passage in vivo. The purpose of this review is to compile data from the more than 30 years of human PC serial heterotransplantation research. Serially heterotransplanted tumours are characterized by evaluating the histopathology of the resulting heterotransplants, including cellular differentiation, karyotype, marker expression, hormone sensitivity, cellular proliferation, metastatic potential and stromal and vascular components. These data are compared with the initial patient tumour specimen and, depending on available information, the patient's clinical outcome was compared with the heterotransplanted tumour. The heterotansplant model is a more accurate preclinical model than older generation serially passaged or genetic models to investigate current and newly developed androgen-deprivation agents, antitumour compounds, anti-angiogenic drugs and positron emission tomography radiotracers, as well as new therapeutic regimens for the treatment of PC.

Stimulatory effect of growth hormone-releasing hormone (GHRH(1-29)NH2) on the proliferation, VEGF and chromogranin A secretion by human neuroendocrine tumor cell line NCI-H727 in vitro

Growth hormone-releasing hormone (GHRH) and its receptors have been implicated in a variety of cellular processes like cell survival, proliferation, apoptosis, angiogenesis and neoplastic transformation of various non-pituitary tissues. Here, we investigated for the first time the in vitro effect of GHRH(1-29)NH2 on the proliferation and the secretion of vascular endothelial growth factor (VEGF) and chromogranin A by the human bronchial neuroendocrine tumor cells NCI-H727. GHRH(1-29)NH2 at the concentrations of 10(-8)-10(-6)M increased the proliferation of these cells and this effect was associated with a statistically significant increase in VEGF and chromogranin A secretion into the supernatants of the tested cells. Our findings indicate that GHRH functions as a trophic hormone for bronchial neuroendocrine (NET) tumors.

Expression of neuropeptide hormone receptors in human adrenal tumors and cell lines: antiproliferative effects of peptide analogues

Peptide analogues targeting various neuropeptide receptors have been used effectively in cancer therapy. A hallmark of adrenocortical tumor formation is the aberrant expression of peptide receptors relating to uncontrolled cell proliferation and hormone overproduction. Our microarray results have also demonstrated a differential expression of neuropeptide hormone receptors in tumor subtypes of human pheochromocytoma. In light of these findings, we performed a comprehensive analysis of relevant receptors in both human adrenomedullary and adrenocortical tumors and tested the antiproliferative effects of peptide analogues targeting these receptors. Specifically, we examined the receptor expression of somatostatin-type-2 receptor, growth hormone-releasing hormone (GHRH) receptor or GHRH receptor splice variant-1 (SV-1) and luteinizing hormone-releasing hormone (LHRH) receptor at the mRNA and protein levels in normal human adrenal tissues, adrenocortical and adrenomedullary tumors, and cell lines. Cytotoxic derivatives of somatostatin AN-238 and, to a lesser extent, AN-162, reduced cell numbers of uninduced and NGF-induced adrenomedullary pheochromocytoma cells and adrenocortical cancer cells. Both the splice variant of GHRH receptor SV-1 and the LHRH receptor were also expressed in adrenocortical cancer cell lines but not in the pheochromocytoma cell line. The GHRH receptor antagonist MZ-4-71 and LHRH antagonist Cetrorelix both significantly reduced cell growth in the adrenocortical cancer cell line. In conclusion, the expression of receptors for somatostatin, GHRH, and LHRH in the normal human adrenal and in adrenal tumors, combined with the growth-inhibitory effects of the antitumor peptide analogues, may make possible improved treatment approaches to adrenal tumors.

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.

Knocking down gene expression for growth hormone-releasing hormone inhibits proliferation of human cancer cell lines

Splice Variant 1 (SV-1) of growth hormone-releasing hormone (GHRH) receptor, found in a wide range of human cancers and established human cancer cell lines, is a functional receptor with ligand-dependent and independent activity. In the present study, we demonstrated by western blots the presence of the SV1 of GHRH receptor and the production of GHRH in MDA-MB-468, MDA-MB-435S and T47D human breast cancer cell lines, LNCaP prostate cancer cell line as well as in NCI H838 non-small cell lung carcinoma. We have also shown that GHRH produced in the conditioned media of these cell lines is biologically active. We then inhibited the intrinsic production of GHRH in these cancer cell lines using si-RNA, specially designed for human GHRH. The knocking down of the GHRH gene expression suppressed the proliferation of T47D, MDA-MB-435S, MDA-MB-468 breast cancer, LNCaP prostate cancer and NCI H838 non-SCLC cell lines in vitro. However, the replacement of the knocked down GHRH expression by exogenous GHRH (1–29)NH₂ re-established the proliferation of the silenced cancer cell lines. Furthermore, the proliferation rate of untransfected cancer cell lines could be stimulated by GHRH (1–29)NH₂ and inhibited by GHRH antagonists MZ-5-156, MZ-4-71 and JMR-132. These results extend previous findings on the critical function of GHRH in tumorigenesis and support the role of GHRH as a tumour growth factor.

The contribution of growth hormone to mammary neoplasia

While the effects of growth hormone (GH) on longitudinal growth are well established, the observation that GH contributes to neoplastic progression is more recent. Accumulating literature implicates GH-mediated signal transduction in the development and progression of a wide range malignancies including breast cancer. Recently autocrine human GH been demonstrated to be an orthotopically expressed oncogene for the human mammary gland. This review will highlight recent evidence linking GH and mammary carcinoma and discuss GH-antagonism as a potential therapeutic approach for treatment of breast cancer.

Antagonists of growth-hormone-releasing hormone: an emerging new therapy for cancer

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.