Potent agonists of growth hormone‐releasing hormone

Abstract

Analogs of the 29 amino acid sequence of growth hormone-releasing hormone (GH-RH) with agmatine (Agni) in position 29 have been synthesized by the solid phase method, purified, and tested in itfro and in i i i~i .The majority of the analogs contained desaminotyrosine (Dat) in position I , but a few of them had Tyrl, or N-MeTyr'. Some peptides contained one or more additional L-or D-amino acid substitutions in positions 2. 12. 15, 21, 27, and/or 28. Compared to the natural sequence of GH-RH(1-29)NHz, [Dat',Ala15]GH-RH(1-28)Agm (MZ-3-191) and [~-Ala*,Ala'~]GH-RH(1-28)Agm (MZ-3-201) were 8.2 and 7.1 times more potent iri vitro, respectively. These two peptides contained Metz7. Their Nle'7 analogs. [ Dat',Ala1s,Nle'7]GH-RH( 1-2S)Agm (MZ-2-51), prepared previously (9), and [ D -A~~' , A~~~~, N I~~* ] G H -R H ( 1-28)Agm (MZ-3-195) showed relative if7 iitro potencies of 10.5 and 2.4, respectively. These data indicate that replacement of Met'' by NleZ7 enhanced the GH-releasing activity of the analog when the nlolecule contained Dat1-Ala2 residues at the N-terminus, but peptides containing Tyr'-D-Ala' in addition to Nle27 showed decreased potencies. Replacement of Ser28 with Asp in multi-substituted analogs of GH-RH(1-28)Agm resulted in a decrease in in r i m potencies compared to the parent compound. Thus, the Ser'kontaining MZ-2-5 1, and [ Dat',Alali.D-Lys",NleZ7]GH-RH( 1-28)Agm, its Asp2* homolog (MZ-3-149), possessed relative activities of 10.5 and 5.6, respectively. In iivo after the iv injection, the analogs [ Dat',Ala15,Nle'7,Asp2X]GH-RH( 1-28)Agm (MZ-3-149), [ Dat', Ala'5]GH-RH( 1-28)Agm, (MZ-3-191) and [ D -A~~' , A~~'~] G H -R H ( 1-28)Agm (MZ-3-201) showed a potency equivalent to 7.6, 4.9 and 3.3 times that of GH-RH( 1-29)NH2, respectively, at 5 min and 20.3, 4.3 and 1.7 times higher, respectively, at 15 min. After sc administration, analogs MZ-3-149, were shown to be 63.7, 55.2 and 56.8 times more potent than the parent hormone at 15 min and 57.6. 60.6, and 42.6 times more active. respectively, at 30 min. In addition, MZ-3-149 had prolonged GH-releasing activity as compared to the standard, and proved to be more potent than MZ-2-51, the tnost active member of our previous series (8,9). Our studies indicate that very potent GH-RH analogs can result from the combination of agmatine in position 29 with other substitutions. K q M D Y~T : growth hormone-releasing hormone: GH-RH analogs: solid phase peptide synthesis; structure-activity relationships Growth hormone-releasing hormone (GH-RH) exists in different molecular forms, such as GH-RH( 1-44)NHz (1) and GH-RH( 1-40)OH (2). Structure-activity stud-ies have demonstrated that the amino-terminal region is required for the GH-releasing activity (2, 3). It has been observed that replacement of Tyr' by desNH2-' Present address: Department of medical chemistry, Albert Szent-Gyorgyi Medical School, H-6720 Szeged, Hungary. Abbreviations of the amino acids are in accordance with the recommendations of the IUPAC-IUB JCBN ( J . Biol. Chem. 264.668473:

Synthesis of new potent agonistic analogs of growth hormone-releasing hormone (GHRH) and evaluation of their endocrine and cardiac activities

“…Therefore, in our synthesis strategy for the new analogs, several key features of JI-34, JI-36 and JI-38 were maintained. These include substitutions of Orn 12, 21 , Gln 8 , Nle 27 and Asp 28 , each of which inhibited isomerization or degradation [18,37–40]; and a replacement of Gly by Abu at position 15, which appears to increase affinity for the GHRH receptor [38]. On the basis of their structures, the selected new hGHRH agonists could be classified into three groups (Table 1).…”

“…Five C-terminal Agm GHRH(1–29) analogs (Table 1, Group I) were synthesized on Boc-Agm-SPA-MBHA resin with Boc-chemistry [18,37–40]. Boc amino acid derivatives were used in the synthesis.…”

“…The deletion of Tyr-Ala dramatically reduces the bioactivity of GHRH, virtually to zero [7,15]. Therefore, based on the sites of hydrolysis of GHRH by these enzymes, and the structural and conformational requirements necessary for substrate effect, we and others have developed various degradation-resistant GHRH agonists [6–8,12,13,21,22,24,37,39,40]. …”