Experimental data indicate that antagonists of growth hormone-releasing hormone (GHRH) could be used clinically in disorders characterized by excessive GHRH/growth hormone (GH) secretion, but direct evidence for the effectiveness of GHRH antagonists on human pituitary tissue is still lacking. In this study, we investigated the inhibitory effect of our GHRH antagonists MZ-4-71 and JV-1-36 and the somatostatin (SST) analog RC-160 on superfused pituitary cells obtained from a human GH-secreting adenoma. Using Western blot analysis and immunohistochemistry, we demonstrated profuse expression of the GHRH receptor and its major splice variant SV1 and an increase in the expression of Gsa protein in the adenoma tissue. Exposure of the tumor cells to exogenous pulses of GHRH induced definite GH responses, causing a 3- to 5-fold elevation of the basal GH level. The antagonists MZ-4-71 and JV-1-36 did not alter basal GH secretion, indicating that the adenoma cells did not secrete GHRH in an autocrine manner. However, both antagonists prevented the stimulatory effect of exogenous GHRH. Similarly to the GHRH antagonists, neither SST-14 nor the SST analog RC-160 had an effect on the basal GH secretion of the tumor cells, but both peptides inhibited the stimulatory effect of exogenous GHRH, with RC-160 being more potent than SST. Our study provides direct evidence for the effectiveness of potent GHRH antagonists such as MZ-4-71 and JV-1-36 on human pituitary GH-secreting adenoma tissue and strongly suggests that these drugs could be used for therapy of GHRH-associated forms of acromegaly, particularly for those patients in whom surgery fails or is not an option.

Keywords:
Human GHRH receptor, Gsa protein, MZ-4-71, JV-1-36, Somatostatin
1.
Kanashiro-Takeuchi RM, Tziomalos K, Takeuchi LM, Treuer AV, Lamirault G, Dulce R, Hurtado M, Song Y, Block NL, Rick F, Klukovits A, Hu Q, Varga JL, Schally AV, Hare JM: Cardioprotective effects of growth hormone-releasing hormone agonist after myocardial infarction. Proc Natl Acad Sci USA 2010;107:2604–2609.
2.
Ludwig B, Ziegler CG, Schally AV, Richter C, Steffen A, Jabs N, Funk RH, Brendel MD, Block NL, Ehrhart-Bornstein M, Bornstein SR: Agonists of growth hormone-releasing hormone as a potential effector for survival and proliferation of pancreatic islets. Proc Natl Acad Sci USA 2010;107:12623–12628.
3.
Dioufa N, Schally AV, Chatzistamou I, Moustou E, Block NL, Owens GK, Papavassiliou AG, Kiaris H: Acceleration of wound healing by growth hormone-releasing hormone and its agonists. Proc Natl Acad Sci USA 2010;107:18611–18615.
4.
Schally AV, Varga JL, Engel JB. Antagonists of growth hormone-releasing hormone: an emerging therapy for cancer. Nat Clin Endocrinol Metab 2008;1:33–43.
5.
Kovacs M, Schally AV, Varga JL, Zarandi M: Endocrine and antineoplastic actions of growth hormone-releasing hormone antagonists. Curr Med Chem 2008;15:314–321.
6.
Kovacs M, Kineman RD, Schally AV, Zarandi M, Groot K, Frohman LA: Effects of antagonists of growth hormone-releasing hormone (GHRH) on GH and insulin-like growth factor-I levels in transgenic mice overexpressing the human GHRH gene, an animal model of acromegaly. Endocrinology 1997;138:4536–4542.
7.
Kovacs M, Schally AV, Lee EJ, Busto R, Armatis P, Groot K, et al: Inhibitory effects of antagonistic analogs of GHRH receptor pituitary cells overexpressing the human GHRH receptor. J Endocrinol 2002;175:425–434.
8.
Kovacs M, Schally AV, Zarandi M, Groot K: Inhibition of GH release of rats by new potent antagonists of growth hormone-releasing hormone (GH-RH). Peptides 1997;18:431–438.
9.
Zarandi M, Kovacs M, Horvath JE, Toth K, Halmos G, Groot K, Nagy A, Kele Z, Schally AV: Synthesis and in vitro evaluation of new potent antagonists of growth hormone-releasing hormone (GH-RH). Peptides 1997;18:423–430.
10.
Kovacs M, Zarandi M, Halmos G, Groot K, Schally AV: Effects of acute and chronic administration of a new potent antagonist of growth hormone-releasing hormone in rats: mechanisms of action. Endocrinology 1996;137:5364–5369.
11.
Zarandi M, Horvath JE, Halmos G, Pinski J, Nagy A, Groot K, Rekasi Z, Schally AV: Synthesis and biological activities of highly potent antagonists of growth hormone-releasing hormone. Proc Natl Acad Sci USA 1994;91:12298–12302.
12.
Varga JL, Schally AV, Csernus VJ, Zarandi M, Halmos G, Groot K, Rekasi Z: Synthesis and biological evaluation of antagonists of growth hormone-releasing hormone with high and protracted in vivo activities. Proc Natl Acad Sci USA 1999;96:692–697.
13.
Csernus VJ, Schally AV: The dispersed cell superfusion system; in Greenstein BD (ed): Neuroendocrine Research Methods. London, Harwood, 1991, pp 71–109.
14.
Havt A, Schally AV, Halmos G, Varga JL, Toller GL, Horvath JE, Szepeshazi K, Köster F, Kovitz K, Groot K, Zarandi M, Kanashiro CA: The expression of the pituitary growth hormone-releasing hormone receptor and its splice variants in normal and neoplastic human tissues. Proc Natl Acad Sci USA 2005;102:17424–17429.
15.
Schulz S, Röcken C, Schulz S: Immunocytochemical localization of plasma membrane GHRH receptors in human tumors using a novel anti-peptide antibody. Eur J Cancer 2006;42:2390–2396.
16.
Melmed S: Acromegaly pathogenesis and treatment. J Clin Invest 2009;119:3189–3202.
17.
Reubi JC, Landolt AM: The growth hormone responses to octreotide in acromegaly correlate with adenoma somatostatin receptor status. J. Clin Endocrinol Metab 1989;68:844–855.
18.
Lancranjan I, Atkinson AB: Results of a European multicentre study with Sandostatin LAR in acromegalic patients. Sandostatin LAR Group. Pituitary 1999;1:105–114.
19.
Jaffe CA, Pan W, Brown MB, DeMott-Friberg R, Barkan AL: Regulation of GH secretion in acromegaly: reproducibility of daily GH profiles and attenuated negative feedback by IGF-I. J Clin Endocrinol Metab 2001;86:4364–4370.
20.
Christensen SE, Weeke J, Orskov H, Jørgensen JO, Esmann J, Doxey JC: Plasma growth hormone in acromegalic patients. Demonstration of highly reproducible diurnal profiles in individual patients. Acta Endocrinol 1987;116:49–52.
21.
Semer M, Faria AC, Nery M, Salgado LR, Knoepfelmacher M, Wajchenberg BL, Liberman B: Growth hormone pulsatility in active and cured acromegalic subjects. J Clin Endocrinol Metab 1995;80:3767–3770.
22.
Ho PJ, Jaffe CA, Friberg RD, Chandler WF, Barkan AL: Persistence of rapid growth hormone (GH) pulsatility after successful removal of GH-producing pituitary tumors. J Clin Endocrinol Metab 1994;78:1403–1410.
23.
Dimaraki EV, Chandler WF, Brown MB, Jaffe CA, Kim SY, Taussig R, Padmanabhan V, Barkan AL: The role of endogenous growth hormone-releasing hormone in acromegaly. J Clin Endocrinol Metab 2006;91:2185–2190.
24.
Adams EF, Law H, Buchfelder M, Fahlbusch R, Lightman S, Levy A: Presence of GHRH mRNA in human pituitary somatotrophinomas and its relationship to in vitro effect of a GHRH-antagonist on GH secretion and cAMP production. Pituitary 1998;1:7–12.
25.
Miller TL, Godfrey PA, Dealmeida VI, Mayo KE: The rat growth hormone-releasing hormone receptor gene: structure, regulation, and generation of receptor isoforms with different signaling properties. Endocrinology 1999;140:4152–4165.
26.
Billestrup N, Swanson LW, Vale W: Growth hormone-releasing factor stimulates proliferation of somatotrophs in vitro. Proc Natl Acad Sci USA 1986;83:6854–6857.
27.
Asa SL, Kovacs K, Stefaneanu L, Horvath E, Billestrup N, Gonzalez-Manchon C, Vale W: Pituitary adenomas in mice transgenic for growth hormone-releasing hormone. Endocrinology 1992;131:2083–2089.
28.
Melmed S: Extrapituitary acromegaly. Endocrinol Metab Clin North Am 1991;20:507–518.
29.
Biermasz NR, Smit JW, Pereira AM, Frölich M, Romijn JA, Roelfsema F: Acromegaly caused by growth hormone-releasing hormone-producing tumors: long-term observational studies in three patients. Pituitary 2007;10:237–249.
30.
Cai RZ, Szoke B, Lu R, Fu D, Redding TW, Schally AV: Synthesis and biological activity of highly potent octapeptide analogs of somatostatin. Proc Natl Acad Sci USA 1986;83:1896–1900.
31.
Hofland LJ, van Koetsveld PM, Waaijers M, Zuyderwijk J, Lamberts SW: Relative potencies of the somatostatin analogs octreotide, BIM-23014, and RC-160 on the inhibition of hormone release by cultured human endocrine tumor cells and normal rat anterior pituitary cells. Endocrinology 1994;134:301–306.
32.
Hamacher C, Bröcker M, Adams EF, Lei T, Fahlbusch R, Buchfelder M, Derwahl M: Overexpression of stimulatory G protein α-subunit is a hallmark of most human somatotrophic pituitary tumours and is associated with resistance to GH-releasing hormone. Pituitary 1998;1:13–23.
33.
Picard C, Silvy M, Gerard C, Buffat C, Lavaque E, Figarella-Branger D, Dufour H, Gabert J, Beckers A, Brue T, Enjalbert A, Barlier A: Gs α overexpression and loss of Gs α imprinting in human adenomas: association with tumor size and response to pharmacologic treatment. Int J Cancer 2007;121:1245–1252.
© 2012 S. Karger AG, Basel
2012
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.