A β-hairpin peptide with pH-controlled affinity for tumor cells.

Considering that the pH in the tumor microenvironment is dysregulated, we designed a β-hairpin peptide (SSRFEWEFESSDPRGDPSSRFEWEFESS). The configuration of the peptide switched from a flexible linear to a rigid loop structure under weakly acidic conditions. The peptide internalized by tumor cells increased significantly under weakly acidic conditions.