In the search for antagonists of human growth hormone-releasing hormone (hGHRH) with high activity, 22 analogs were synthesized by solid-phase methods, purified, and tested biologically. Within the N-terminal sequence of 28 or 29 amino acids of hGHRH, all the analogs contained D-Arg2, Phe(4- Cl)6 (para-chlorophenylalanine), Abu15 (α-aminobutyric acid), and Nle27 and most of them had Agm29 (agmatine) substituents. All the peptides, except one, were acylated at the N terminus with different hydrophobic acids- e.g., isobutyric acid (Ibu) or 1-naphthylacetic acid (Nac) in order to study the effect of N-terminal acylation on the antagonistic activity. In the superfused rat pituitary cell system, all the analogs inhibited more powerfully the GHRH-induced growth hormone (GH) release than the standard GHRH antagonist [Ac-Tyr1,D-Arg2]hGHRH-(1-29)NH2. Antagonists [Ibu0,D- Arg2,Phe(4-Cl)6, Abu15,Nle27]hGHRH-(1-28)Agm (MZ-4-71), [Nac0,D- Arg2,Phe(4-Cl)6,Abu15,Nle27]hGHRH-(1-28)Agm (MZ-4-243), [Nac0,D- Arg2,Phe(4-Cl)6,Abu15,Nle27]hGHRH-(1-29)NH2(MZ-4-169), [Nac0-His1,D- Arg2,Phe(4-Cl)6,Abu15,Nle27]-hGHRH-(1-29)NH2 (MZ-4-181), and [Nac0,D- Arg2,Phe(4-Cl)6,Abu15,Nle27,Asp28]hGHRH-(1-28)Agm (MZ-4-209) inhibited GH release at 3 x 10-9 M. Among these peptides, MZ-4-243, MZ-4- 169, and MZ-4-181 were also long acting in vitro. Antagonist MZ-4-243 inhibited GH release 100 times more powerfully than the standard antagonist and was the most potent in vitro among GHRH antagonists synthesized. Analogs with high inhibitory effects in vitro were also found to have high affinities to rat pituitary GHRH receptors. In experiments in vivo, antagonists [Ibu0,D-Arg2,Phe(4-Cl)6,Abu15,Nle27]-hGHRH-(1-28)Agm (MZ-4-71), [Nac0,D-Arg2,Phe(4-Cl)6,Abu15,Nle27]hGHRH-(1-29)NH2 (MZ-4-169), and [Nac0-His1,D-Arg2,Phe(4-Cl)6,Abu15,Nle27]hGHRH-(1-29)NH2 (MZ-4-181) induced a significantly greater inhibition of GH release than the standard antagonist. In view of their high antagonistic activity and prolonged duration of action, some of these antagonists of GHRH may find clinical applications, including treatment of certain endocrine disorders and insulin- like growth factor I-dependent tumors.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Dec 6 1994|
- inhibitory growth hormone-releasing hormone analogs
- structure-activity relationships
ASJC Scopus subject areas