Design and Synthesis of Potent Hexapeptide and Heptapeptide Gonadotropin-Releasing Hormone Antagonists by Truncation of a Decapeptide Analogue Sequence

Abstract

A novel strategy for designing reduced-size analogues of the decapeptide gonadotropin-releasing hormone (GnRH) was developed. As opposed to previous attempts to delete residues from either of the peptide's termini, our approach is based upon the known importance of both C- and N-terminals of GnRH analogues for receptor recognition, whereas the central part of the molecule is replaced by a short spacer. The present truncation strategy was successful for generation of reduced-size hexapeptide and heptapeptide antagonists possessing potent antagonistic capacity. The same methodology was not suitable for the generation of reduced-size agonists, suggesting different conformational characteristics for GnRH agonists and antagonists. A heptapeptide antagonist designed by this method was shown to inhibit serum levels of luteinizing hormone in castrated rats in vivo. Structure-activity studies suggested that the structural preferences for GnRH receptor recognition are similar to those reported for decapeptide antagonists. Our studies resulted in a heptapeptide GnRH antagonist (Ac-D-Nal2-D-Cpa-D-Pal-Gly-Arg-Pro-D-Ala-NH2) with high receptor binding affinity (IC50 = 7 nM), as compared to that of GnRH itself (IC50 = 2 nM). The highest affinity of a hexapeptide antagonist that we have synthesized was somewhat lower (IC50 = 45 nM).

Structure–Function Studies of Linear and Cyclized Peptide Antagonists of the GnRH Receptor

“…To develop orally available small molecule antagonists, peptides with less than 10 amino acids were synthesized. Most studies failed so far but, by deletion of Ser 4 -Tyr 5 and Leu 7 , a potent heptapeptidic antagonist with K D ϭ 7 nM has been described (33,34,43). The cyclic pentapeptide D-49141 (35) with moderate binding affinity of K D ϭ 364 nM, was modified by substituting for side chains known to be important for high binding affinity of linear decapeptides.…”

Neurotrophic Effects of GnRH on Neurite Outgrowth and Neurofilament Protein Expression in Cultured Cerebral Cortical Neurons of Rat Embryos

“…In all cases, Antide was added 1 h before GnRH. The concentration of Atide, was similar to that which antagonized the effect of GnRH on gonadotrophins hormone secretion in dispersed pituitary cells [17] and aT3 cell [18]. Control cultures were treated with vehicle.…”

Bone loss in ovariectomized rats: Dominant role for estrogen but apparently not for FSH

“…LH and FSH concentration in rat serum were measured by radioimmunoassay, using the kits provided by the National Institute of Arthritis, Metabolism and Digestive Diseases, Rat Pituitary Program [Yahalom et al, 2000].…”