Trypsin resistance of a decapeptide KISS1R agonist containing an Nω-methylarginine substitution

Metastin/kisspeptin is an amidated peptide with 54 amino acid residues isolated from human placental tissues as a ligand of the orphan G-protein-coupled receptor KISS1R that is expressed throughout the central nervous system and in a variety of endocrine and gonadal tissues. Compared to the full-length metastin protein, the N-terminal truncated peptide metastin(45-54) has 3-10 times higher receptor affinity and enhanced ability to increase intracellular calcium concentration which is essential for activation of protein kinases involved in intracellular signaling in a number of pathways that affect reproduction and cell migration. However, metastin(45-54) is rapidly inactivated in serum. In this study, we designed and synthesized a number of metastin(45-54) analogs and evaluated their agonistic activity and trypsin resistance. Among analogs with substitutions of arginine at position 53, N(ω)(-)methylarginine analog 8 showed 3-fold more potent agonistic activity compared with metastin(45-54). Furthermore, analog 8 was shown to resist trypsin cleavage between positions 53 and 54. This substitution may be useful in the development of other Arg-containing peptides for which the avoidance of cleavage is desired.