Self-cleaving protein linkers with modulated pH-responsiveness: A new platform for selective control of protein drug function

In this study, we propose a self-cleaving protein that responds to acidic pH, pH intein_N150, as a pH-responsive linker for the selective delivery of protein-based drugs. Being stable at neutral and degradable at weakly acidic pH, pH intein_N150 can be obtained by mutating key amino acids of pH intein, thus stimulating self-cleavage. Unlike chemical linkers, which require additional conjugation steps, protein linkers can be incorporated into protein pharmaceuticals during protein expression. As proof-of-concepts, intracellular penetration of proteins can be selectively turned on or off by cleaving pH intein_N150 near the cell-penetrating peptide sequence at weakly acidic pH. Furthermore, the apoptosis-inducing activity of human tumor necrosis factor-related apoptosis-inducing ligand (hTRAIL) can be selectively activated by cleaving pH intein_N150 adjacent to the albumin binding domain (ABD) at weakly acidic pH. Thus, we expect that this new protein linker can be used for actively controlling various protein-based drugs responding to delicate pH variations around inflammatory or cancerous tissues. These findings have been revealed in an in vivo tumor xenograft mouse model showing elongated systemic circulation and selective induction of tumor toxicity by ABD-pH intein_N150-hTRAIL.