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-Arg(2), Har(9), Abuls(15), and Nle(27). Most new analogs had Ala at position 8. Since replacements of both Lys(12) and Lys(21) 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-Arg(28), Har(29) -NH2 at the C-terminus or inserted Agm or 12-amino dodecanoic acid amide at position 30. We incorporated pentafluoro-Phe (Fpa(s)), instead of Cpa, at position 6 and Tyr(Me) at position 10 and omega-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 beta cell lymphoma, and ACHN renal cell carcinoma cell lines were xenografted into nude mice and treated subcutaneously with GHRH antagonists at doses of 1-5 mu g/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 5 mu M 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 beta 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. Published by Elsevier Inc.

Background We previously showed that growth hormone-releasing hormone (GHRH) agonists are cardioprotective following myocardial infarction (MI). Here, our aim was to evaluate the in vitro and in vivo activities of highly potent new GHRH agonists, and elucidate their mechanisms of action in promoting cardiac repair. Methods and Results H9c2 cells were cultured in serum-free medium, mimicking nutritional deprivation. GHRH agonists decreased calcium influx and significantly improved cell survival. Rats with cardiac infarction were treated with GHRH agonists or placebo for four weeks. MI size was reduced by selected GHRH agonists (JI-38, MR-356, MR-409); this accompanied an increased number of cardiac c-kit+ cells, cellular mitotic divisions, and vascular density. One week post-MI, MR-409 significantly reduced plasma levels of IL-2, IL-6, IL-10 and TNF-α compared to placebo. Gene expression studies revealed favorable outcomes of MR-409 treatment partially result from inhibitory activity on pro-apoptotic molecules and pro-fibrotic systems, and by elevation of bone morphogenetic proteins. Conclusions Treatment with GHRH agonists appears to reduce the inflammatory responses post-MI and may consequently improve mechanisms of healing and cardiac remod eling by regulating pathways involved in fibrosis, apoptosis and cardiac repair. Patients with cardiac dysfunction could benefit from treatment with novel GHRH agonists.

Malignant melanoma is the deadliest form of skin cancer; the treatment of advanced and recurrent forms remains a challenge. It has recently been reported that growth hormone-releasing hormone (GHRH) receptor is involved in the pathogenesis of melanoma. Therefore, we investigated the effects of our new GHRH antagonists on a human melanoma cancer cell line. Antiproliferative effects of GHRH antagonists, MIA-602, MIA-606 and MIA-690, on the human melanoma cell line, A-375, were studied in vitro using the MTS assay. The effect of MIA-690 (5 μg/day 28 d) was further evaluated in vivo in nude mice bearing xenografts of A-375. Subcellular localization of p27 was detected with Western blot and immunofluorescent staining. MIA-690 inhibited the proliferation of A-375 cells in a dose-dependent manner (33% at 10 μM, and 19.2% at 5 μM, P < 0 .05 vs. control), and suppressed the growth of xenografted tumors by 70.45% (P < 0.05). Flow cytometric analysis of cell cycle effects following the administration of MIA-690 revealed a decrease in the number of cells in G2/M phase (from 19.7% to 12.9%, P < 0.001). Additionally, Western blot and immunofluorescent studies showed that exposure of A-375 cells to MIA-690 triggered the nuclear accumulation of p27. MIA-690 inhibited tumor growth in vitro and in vivo, and increased the translocation of p27 into the nucleus thus inhibiting progression of the cell cycle. Our findings indicate that patients with malignant melanoma could benefit from treatment regimens, which combine existing chemotherapy agents and novel GHRH-antagonists.

Background: Triple negative breast cancer (TNBC) is a distinct subtype of breast cancer burdened with a dismal prognosis due to the lack of effective therapeutic agents. Receptors for LHRH (luteinizing hormone-releasing hormone) can be successfully targeted with AEZS-108 [AN-152], an analog of LHRH conjugated to doxorubicin. Our study evaluates the presence of this target LHRH receptor in human specimens of TNBC and investigates the efficacy and toxicity of AEZS-108 in vivo. We also studied in vitro activity of AEZS-125, a new LHRH analog conjugated with the highly potent natural compound, Disorazol Z.Methods: 69 human surgical specimens of TNBC were investigated for LHRH-R expression by immunohistochemistry. Expression of LHRH-R in two TNBC cell lines was evaluated by real time RT-PCR. Cytotoxicity of AEZS-125 was evaluated by Cell Titer Blue cytoxicity assay. LHRH-receptor expression was silenced with an siRNA in both cell lines. For the in vivo experiments an athymic nude mice model xenotransplanted with the cell lines, MDA-MB-231 and HCC 1806, was used. The animals were randomised to three groups receiving solvent only (d 1, 7, 14, i.v.) for control, AEZS-108 (d 1, 7, 14, i.v.) or doxorubicin at an equimolar dose (d 1, 7, 14, i.v.).Results: In human clinical specimens of TNBC, expression of the LHRH-receptor was present in 49% (n = 69). HCC 1806 and MDA-MB-231 TNBC cells expressed mRNA for the LHRH-receptor. Silencing of the LHRH-receptor significantly decreased the cytotoxic effect of AEZS-108. MDA-MB-231 and HCC 1806 tumors xenografted into nude mice were significantly inhibited by treatment with AEZS-108; doxorubicin at equimolar doses was ineffective. As compared to AEZS 108, the Disorazol Z - LHRH conjugate, AEZS-125, demonstrated an increased cytotoxicity in vitro in HCC 1806 and MDA-MB-231 TNBC; this was diminished by receptor blockade with synthetic LHRH agonist (triptorelin) pretreatment.Conclusion: The current study confirms that LHRH-receptors are expressed by a significant proportion of TNBC and can be successfully used as homing sites for cytotoxic analogs of LHRH, such as AEZS-108 and AEZS-125.

Management of castration-resistant prostate cancer (CRPC) is challenging due to lack of efficacious therapy. Luteinizing hormone-releasing hormone (LHRH) analogs appear to act directly on cells based on the LHRH receptors on human prostate adenocarcinoma cells. We explored anticancer activity of a cytotoxic analog of LHRH, AEZS-108, consisting of LHRH agonist linked to doxorubicin. Nude mice bearing DU-145 tumors were used to compare antitumor effects of AEZS-108 with its individual constituents or their unconjugated combination. The tumor growth inhibition of conjugate was greatest among treatment groups (90.5% inhibition vs. 41% by [D-Lys(6)]LHRH+DOX). The presence of LHRH receptors on DU-145 cells was confirmed by immunocytochemistry. In vitro, AEZS-108 significantly inhibited cell proliferation (61.2% inhibition) and elevated apoptosis rates (by 46%). By the detection of the inherent doxorubicin fluorescence, unconjugated doxorubicin was seen in the nucleus; the conjugate was perinuclear and at cell membrane. Autophagy, visualized by GFP-tagged p62 reporter, was increased by AEZS-108 (7.9-fold vs. 5.3-fold by DOX+[D-Lys(6)]LHRH. AEZS-108 more effectively increased reactive oxygen species (ROS, 2-fold vs. 1.4-fold by DOX+[D-Lys(6)]LHRH) and levels of the apoptotic regulator p21 in vivo and in vitro. We demonstrate robust inhibitory effects of the targeted cytotoxic LHRH analog, AEZS-108, on LHRHR positive castration-resistant prostate cancer cells.

Previously, we have shown that the targeted cytotoxic somatostatin (sst) analogue AN-162 [AZSE-124] inhibits the growth of MDA-MB-231 human breast cancers xenografted into nude mice. In this study, we examined the trafficking of AN-162 into the cell, the expression of the somatostatin receptors (sstr) in specimens of human triple-negative breast cancers (TNBC), and the effect of AN-162 on HCC 1806 human TNBC xenografts. The expression of sstr in TNBC tumor samples was investigated by immunohistochemical staining. The expression of sstr in HCC 1806 was evaluated by reverse transcription PCR. Internalization studies with 125I-labeled AN-162 were carried out and the autofluorescence sign of doxorubicin moiety in the cell nucleus after incubation with AN-162 was measured using a fluorescence assay. The effects of AN-162 on the growth of HCC 1806 xenografted into nude mice were studied. A fluorescence microscopy cytotoxicity assay in vitro to detect cell death after treatment with AN-162 was also carried out. About 28% of TNBC tumor specimens showed a positive staining for sstr subtype 2a. HCC 1806 expresses all five subtypes of sstr. In the fluorescence cytotoxicity assay, dead HCC 1806 cells were found 24 h after incubation with AN-162. The growth of HCC 1806 tumors in nude mice was significantly inhibited by treatment with AN-162. AN-162 was internalized into the HCC 1806 cells and doxorubicin moiety was detected in the cell nuclei. This study is the first to show that the trafficking of the cytotoxic sst analogue AN-162 into the cell is mediated by sstr. Our work shows that the growth of xenografted HCC 1806 TNBCs can be effectively inhibited in vivo with AN-162. This investigation provides information on the mechanism of action and efficacy of this new targeted cytotoxic sst analogue and identifies in this relation the sstr as a favorable therapeutic target in TNBC.

The dismal prognosis of malignant brain tumors drives the development of new treatment modalities. In view of the multiple activities of growth hormone-releasing hormone (GHRH), we hypothesized that pretreatment with a GHRH agonist, JI-34, might increase the susceptibility of U-87 MG glioblastoma multiforme (GBM) cells to subsequent treatment with the cytotoxic drug, doxorubicin (DOX). This concept was corroborated by our findings, in vivo, showing that the combination of the GHRH agonist, JI-34, and DOX inhibited the growth of GBM tumors, transplanted into nude mice, more than DOX alone. In vitro, the pretreatment of GBM cells with JI-34 potentiated inhibitory effects of DOX on cell proliferation, diminished cell size and viability, and promoted apoptotic processes, as shown by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide proliferation assay, ApoLive-Glo multiplex assay, and cell volumetric assay. Proteomic studies further revealed that the pretreatment with GHRH agonist evoked differentiation decreasing the expression of the neuroectodermal stem cell antigen, nestin, and up-regulating the glial maturation marker, GFAP. The GHRH agonist also reduced the release of humoral regulators of glial growth, such as FGF basic and TGFβ. Proteomic and gene-expression (RT-PCR) studies confirmed the strong proapoptotic activity (increase in p53, decrease in v-myc and Bcl-2) and anti-invasive potential (decrease in integrin α3) of the combination of GHRH agonist and DOX. These findings indicate that the GHRH agonists can potentiate the anticancer activity of the traditional chemotherapeutic drug, DOX, by multiple mechanisms including the induction of differentiation of cancer cells.

236 Background: Management of castration-resistant prostate cancer (CRPC) is challenging because of limitations in efficacy of current therapies. Somatostatin receptors are expressed in human CRPC. Here we tested targeted somatostatin AN-162 analog consisting of doxorubicin (DOX) conjugated to octapeptide RC-121, acting as a carrier, in human androgen-independent prostate cancer cell lines in vitro and in vivo. Methods: Expression of mRNA for the five subtypes of the somatostatin receptor in PC-3 and DU-145 human prostate cancer cell lines was evaluated by RT-PCR. Somatostatin receptor binding was measured with radioligand assays. The effect of AN-162 and DOX on the viability of PC-3 and DU-145 cells was assessed by MTS assay. Nude mice bearing PC-3 and DU-145 tumors were randomized to 5 groups (control, AN-162, DOX, somatostatin analog RC-160 as a control, and DOX + RC-160). Treatment consisted i.v. injections of AN-162, DOX, RC-160, DOX + RC-160, or vehicle once a week for 4 weeks. Tumor volume was measured every week; the study lasted 28 days. The doses of AN-162 were equivalent to 1.45 mg/kg DOX (2.5 μmol/kg). Results: The PC-3 and DU-145 cell lines were positive for the five subtypes of the somatostatin receptor. AN-162 and DOX (0.10–10 µM) inhibited the proliferation of PC-3 and DU-145 prostate cancer cells in a dose-dependent manner. AN-162 exerted a stronger inhibition of proliferation than DOX alone, but in vitro the difference was not significant. In vivo, AN-162 significantly inhibited growth of both tumor models’ compared with the controls and the groups given equimolar doses of doxorubicin, RC-160, or doxorubicin unconjugated to RC-160. Conclusions: Our work demonstrates potent inhibitory effects of AN-162 on somatostatin receptor positive androgen-independent prostate cancers, which were greater than any of the components of AN-162. The mechanisms of action of targeted cytotoxic analog of somatostatin AN-162 in CRPC should be explored. Our findings suggest the possible use of AN-162 in patients with CRPC.

Ferenc G. Rick,* Andrew V. Schally, Norman L. Block, Andrew Abi-Chaker, Awtar Krishan, and Luca Szalontay Veterans AffairsMedical Centerand South FloridaVeterans Affairs Foundationfor ResearchandEducation, Miami, Florida Departmentof Pathology,UniversityofMiami,Miller SchoolofMedicine,Miami, Florida DivisionsofHematology/OncologyandEndocrinology,DepartmentofMedicine,UniversityofMiami, Miller SchoolofMedicine,Miami, Florida

In view of the recent findings of stimulatory effects of GHRH analogs, JI-34, JI-36 and JI-38, on cardiomyocytes, pancreatic islets and wound healing, three series of new analogs of GHRH(1-29) have been synthesized and evaluated biologically in an endeavor to produce more potent compounds. "Agmatine analogs", MR-356 (N-Me-Tyr(1)-JI-38), MR-361(N-Me-Tyr(1), D-Ala(2)-JI-38) and MR-367(N-Me-Tyr(1), D-Ala(2), Asn(8)-JI-38), in which Dat in JI-38 is replaced by N-Me-Tyr(1), showed improved relative potencies on GH release upon subcutaneous administration in vivo and binding in vitro. Modification with N-Me-Tyr(1) and Arg(29)-NHCH3 as in MR-403 (N-Me-Tyr(1), D-Ala(2), Arg(29)-NHCH3-JI-38), MR-406 (N-Me-Tyr(1), Arg(29)-NHCH3-JI-38) and MR-409 (N-Me-Tyr(1), D-Ala(2), Asn(8), Arg(29)-NHCH3-JI-38), and MR-410 (N-Me-Tyr(1), D-Ala(2), Thr(8), Arg(29)-NHCH3-JI-38) resulted in dramatically increased endocrine activities. These appear to be the most potent GHRH agonistic analogs so far developed. Analogs with Apa(30)-NH2 such as MR-326 (N-Me-Tyr(1), D-Ala(2), Arg(29), Apa(30)-NH2-JI-38), and with Gab(30)-NH2, as MR-502 (D-Ala(2), 5F-Phe(6), Ser(28), Arg(29),Gab(30)-NH2-JI-38) also exhibited much higher potency than JI-38 upon i.v. administration. The relationship between the GH-releasing potency and the analog structure is discussed. Fourteen GHRH agonists with the highest endocrine potencies were subjected to cardiologic tests. MR-409 and MR-356 exhibited higher potency than JI-38 in activating myocardial repair in rats with induced myocardial infarction. As the previous class of analogs, exemplified by JI-38, had shown promising results in multiple fields including cardiology, diabetes and wound healing, our new, more potent, GHRH agonists should manifest additional efficacy for possible medical applications.

You have accessJournal of UrologyBenign Prostatic Hyperplasia: Basic Research1 Apr 20131600 COMBINATION OF BOMBESIN/GASTRIN-RELEASING PEPTIDE ANTAGONIST WITH GROWTH-HORMONE-RELEASING HORMONE ANTAGONIST AUGMENTS SHRINKAGE OF BENIGN PROSTATIC HYPERPLASIA IN RATS Ferenc Rick, Andrew Abi-Chaker, Luca Szalontay, Roberto Perez, Norman Block, Gabor Halmos, and Andrew Schally Ferenc RickFerenc Rick Miami, FL More articles by this author , Andrew Abi-ChakerAndrew Abi-Chaker Miami, FL More articles by this author , Luca SzalontayLuca Szalontay Miami, FL More articles by this author , Roberto PerezRoberto Perez Miami, FL More articles by this author , Norman BlockNorman Block Miami, FL More articles by this author , Gabor HalmosGabor Halmos Debrecen, Hungary More articles by this author , and Andrew SchallyAndrew Schally Miami, FL More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.3150AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Benign prostatic hyperplasia (BPH) often affects aging men. Its pathogenesis is incompletely understood. Growth factors, such as growth hormone-releasing hormone (GHRH), and bombesin/gastrin-releasing peptide (BN/GRP) have been implicated in BPH. We showed that antagonists of GHRH and BN/GRP reduce prostate weight in an androgen induced BPH model in rats. We investigated the effects of BN/GRP antagonist, RC-3940-II, in combination with GHRH antagonist, MIA-606, in vitro cell cultures and on animal models of BPH. METHODS Binding to GRP and GHRH receptors was measured with radioligand assays. Effects of the BN/GRP antagonist, RC-3940-II (25μg daily s.c.), the GHRH antagonist MIA-606 (20μg daily), and their combination were evaluated in vivo in male rats with testosterone-induced BPH. Influence of RC-3940-II, MIA-606, 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 A single class of specific, high affinity binding sites for GRP receptors and for GHRH receptors was found in rat prostates as well as in BPH-1 and WPMY-1 cells. The combination of antagonists caused marked shrinkage of rat prostate (27.3%, p<0.01). In vitro, RC-3940-II plus MIA-606 (all 5μM) produced synergistic (56.7%) inhibition of growth of BPH−1 cells, and 47% inhibition of WPMY−1 cells. Combination of RC-3940-II plus MIA-606 significantly increased the amount of BPH-1 cells blocked in S−phase plus cells with lower G0/G1 and G2/M DNA content. Expression of >40 gene transcripts related to growth factors, inflammatory cytokines, and signal transduction changed significantly. CONCLUSIONS Combinations of BN/GRP antagonist with GHRH antagonist augmented the reduction in prostate weight in experimental BPH model. Thus BN/GRP antagonists and/or their combinations with GHRH antagonist could be considered for further development as therapy for BPH. Biochemical and histological evaluation will follow to explore the mechanisms of action of these antagonists in BPH. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e657 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Ferenc Rick Miami, FL More articles by this author Andrew Abi-Chaker Miami, FL More articles by this author Luca Szalontay Miami, FL More articles by this author Roberto Perez Miami, FL More articles by this author Norman Block Miami, FL More articles by this author Gabor Halmos Debrecen, Hungary More articles by this author Andrew Schally Miami, FL More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Glioblastoma multiforme is the most frequent tumor of the central nervous system in adults and has a dismal clinical outcome, which necessitates the development of new therapeutic approaches. We investigated in vivo the action of the targeted cytotoxic analog of luteinizing hormone releasing hormone, AN-152 (AEZS-108) in nude mice (Ncr nu/nu strain) bearing xenotransplanted U-87 MG glioblastoma tumors. We evaluated in vitro the expression of LHRH receptors, proliferation, apoptosis and the release of oncogenic and tumor suppressor cytokines. Clinical and U-87 MG samples of glioblastoma tumors expressed LHRH receptors. Treatment of nude mice with AN-152, once a week at an intravenous dose of 413 nmol/20 g, for six weeks resulted in 76 % reduction in tumor growth. AN-152 nearly completely abolished tumor progression and elicited remarkable apoptosis in vitro. Genomic (RT-PCR) and proteomic (ELISA, Western blot) studies revealed that AN-152 activated apoptosis, as reflected by the changes in p53 and its regulators and substrates, inhibited cell growth, and elicited changes in intermediary filament pattern. AN-152 similarly reestablished contact regulation as demonstrated by expression of adhesion molecules and inhibited vascularization, as reflected by the transcription of angiogenic factors. Our findings suggest that targeted cytotoxic analog AN-152 (AEZS-108) should be considered for a treatment of glioblastomas.

Purpose of reviewWe provide new viewpoints of hormonal control of benign prostatic hyperplasia (BPH). The latest treatment findings with 5-alpha reductase inhibitors (5-ARIs) finasteride and dutasteride, refined indications, efficacy, and safety are discussed and compared. We also discuss potential new 5-ARIs and other hormonal treatments. Recent findingsFinasteride and dutasteride have equal efficacy and safety for the treatment and prevention of progression of BPH. 5-ARIs are especially recommended for prostates greater than 40 ml and PSA greater than 1.5 ng/ml. Combination therapy is the treatment of choice in these patients, but with prostate volume greater than 58 ml or International Prostate Symptom Score of at least 20, combinations have no advantage over 5-ARI monotherapy. Updates on the recent developments on BPH therapy with luteinizing hormone-releasing hormone (LHRH) antagonist are also reviewed and analyzed. Preclinical studies suggest that growth hormone-releasing hormone (GHRH) antagonists effectively shrink experimentally enlarged prostates alone or in combination with LHRH antagonists. SummaryNew 5-ARIs seem to be the promising agents that need further study. Preclinical studies revealed that GHRH and LHRH antagonists both can cause a reduction in prostate volume. Recent data indicate that prostate shrinkage is induced by the direct inhibitory action of GHRH and of LHRH antagonists exerted through prostatic receptors. The adverse effects of 5ARIs encourage alternative therapy.

Abstract BACKGROUND: Advances in targeted medical thereapy has demonstrated improved clinical outcomes for patients with metastatic renal cell carcinoma (RCC), however, a complete response is rare and current therapy has various adverse effects that are unfortunately not as rare. Early antagonists of growth hormone-releasing hormone (GHRH) were shown to inhibit experimental RCC cell line, Caki-1, in vitro and in vivo. GHRH itself acts as an autocrine/paracrine growth factor in human cancers, including RCC. Herein, we investigate the effects of novel and highly potent new antagonists of GHRH on the growth of three RCC cell lines with different primary tumor sites. METHODS: The expression of GHRH receptor in all three cell lines was evaluated by ligand competition studies. The in vitro influence of GHRH antagonists designated MIA-602, MIA-604, MIA-606 and MIA-690 on cell viability was assessed by MTS assay in ACHN, A498, and 786-0 human RCC cells. GHRH antagonists were given at a dose of 5μg daily in these three nude-mice xenograft models in vivo. Cell cycle parameters were analyzed by laser flow cytometry. RESULTS: Ligand competition studies revealed specific, high affinity binding sites for GHRH receptor in all three RCC cell lines. GHRH antagonists inhibited the proliferation of all three RCC cells in a dose dependent manner. GHRH antagonists caused significant inhibition of tumor growth of ACHN, A498, and 786-0 RCCs ranging from 53-75% after 35 days of treatment (p<0.001). Treatment of ACHN and A498 cells with 10μM MIA-602 and MIA-690 (5 and 10μM) led to a significant increase in number of cells with subG1 DNA content, suggesting apoptosis. CONCLUSIONS: The effectiveness of the new and novel GHRH antagonists in inhibiting growth of experimental RCC models in vitro and in vivo was demonstrated. The inhibitory effect of GHRH antagonists is mainly due to direct suppressive effects exerted through GHRH receptors. Further biochemical and histological evaluation is warranted to explore the mechanisms of action of GHRH antagonists in RCC. Citation Format: Ferenc G. Rick, Andrew Abi-Chaker, Luca Szalontay, Norman L. Block, Gabor Halmos, Mehrdad Nadji, Andrew V. Schally. Powerful inhibition of human renal cell carcinomas with antagonists of growth hormone-releasing hormone (GHRH): a preclinical study. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 91. doi:10.1158/1538-7445.AM2013-91