Analogues of growth hormone-releasing factor (1-29) amide containing the reduced peptide bond isostere in the N-terminal region.
Previous peptide structure-activity investigations employing the psi[CH2NH] peptide bond isostere have produced antagonists when inserted into various sequences. These include bombesin, in which the incorporation of Leu13 psi[CH2NH]Leu14 produced a potent antagonist, and tetragastrin, with which Boc-Trp-Leu psi[CH2NH]Asp-Phe-NH2 is an antagonist. In this study, we chose to investigate the effect of this isostere on growth hormone-releasing factor (1-29) amide. Analogues were prepared by solid-phase synthesis and the isosteres incorporated by racemization-free reductive alkylation with a preformed protected amino acid aldehyde in the presence of NaBH3CN. The aldehydes were prepared by the reduction of the protected N,O-dimethyl hydroxamates with LiAlH4 at 0 degrees C. The purified analogues were assayed in a 4-day primary culture of male rat anterior pituitary cells for growth hormone (GH) release. Potential antagonists were retested in the presence of GRF(1-29)NH2. The following results were obtained: At position 5-6, a very weak agonist was produced with much less than 0.01% activity. Incorporation of the isostere in positions 1-2, 2-3, and 6-7 gave weak agonists with approximately 0.1% activity. Agonists with 0.39% and 1.6% activity were produced by incorporation at 10-11 and 3-4, respectively. The analogue [Ser9 psi[CH2NH]Tyr10]GRF(1-29)NH2 was found to be an antagonist in the 10 microM range vs 1 nM GRF and had no agonist activity at doses as high as 0.1 mM.
Hocart
S J
SJ
Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Murphy
W A
WA
Coy
D H
DH
D000595:Amino Acid Sequence; D000818:Animals; D013006:Growth Hormone / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis* / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017337:Sermorelin; D013329:Structure-Activity Relationship
D010446:Peptide Fragments; D017337:Sermorelin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone