Design, Synthesis, and Biological Evaluation of Arginine <i>N</i>-Glycosylation Stapled Peptides with Potent Antitumor Activity <i>In Vivo</i>

The host defense peptide PP-1 has attracted attention for its strong antitumor activity. However, its potential for clinical use is hindered by its poor proteolytic stability. In this study, a series of stapled PP-1 derivatives were obtained by an all-hydrocarbon stapling strategy and arginine <i>N</i>-glycosylation, and five rounds of peptide libraries containing more than 60 stapled and/or arginine <i>N</i>-glycosylated peptides were rationally constructed. PP-60 exhibited superior <i>in vitro</i> antitumor activities and low hemolytic toxicity. Compared with the parent peptide PP-1, PP-60 exhibited improved proteolytic and serum stability and, importantly, significantly weakened hemolysis and potential toxicity to liver tissue. Confocal microscopy revealed the superior cell permeability of PP-60. Flow cytometry revealed that PP-60 could exert its antitumor effects by inducing apoptosis. Notably, PP-60 displayed a potent therapeutic effect without obvious side effects in a nude mouse model. PP-60 holds promise for further development as a lead antitumor agent.