Development of esterase-resistant and highly active ghrelin analogs via thiol-ene click chemistry

The orexigenic peptide ghrelin exerts important functions in energy metabolism and cellular homeostasis by activating the growth hormone secretagogue receptor type 1a (GHSR1a), and thus has therapeutic potential to treat certain diseases. Native ghrelin carries an essential O-fatty acyl moiety at the side-chain of its third Ser residue; however, this posttranslational modification is susceptible to hydrolysis by certain esterases in circulation, representing a major route of in vivo inactivation of ghrelin. In the present study, we developed a novel approach to prepare various esterase-resistant ghrelin analogs via photo-induced thiol-ene click chemistry. A recombinant unacylated human ghrelin mutant carrying a unique Cys residue at the third position was reacted with commercially available end alkenes, thus various alkyl moieties were introduced to the side-chain of its unique Cys residue via a thioether bond. Among eleven S-alkylated ghrelin analogs, analog 11, generated by reacting with 2-methyl-1-octene, not only acquired much higher stability in human serum and fetal bovine serum, but also acquired moderately higher activity compared with native human ghrelin. Thus, the present study not only provided an efficient approach to prepare various esterase-resistant ghrelin analogs, but also produced a novel highly stable and highly active ghrelin analog with therapeutic potential.