pH-controllable cell-penetrating polypeptide that exhibits cancer targeting

Helical peptides were naturally-occurring ordered conformations that mediated various biological functions essential for biotechnology. However, it was difficult for natural helical polypeptides to be applied in biomedical fields due to low bioavailability. To avoid these problems, synthetic alpha-helical polypeptides have recently been introduced by further modifying pendants in the side chain. In spite of an attractive biomimetic helical motif, these systems could not be tailored for targeted delivery mainly due to nonspecific binding events. To address these issues, we created a conformation-transformable polypeptide capable of eliciting a pH-activated cell-penetrating property solely at the cancer region. The developed novel polypeptide showed that the bare helical conformation had a function at physiological conditions while the pH-induced helical motif provided an active cell-penetrating characteristic at a tumor extracellular matrix pH. The unusual conformation-transformable system can elicit bioactive properties exclusively at mild acidic pH.

Statement of significance: We developed pH-controllable cell-penetrating polypeptides (PCCPs) undergoing pH-induced conformational transitions. Unlike natural cell-penetrating peptides, PCCPs was capable of penetrating the plasma membranes dominantly at tumor pH, driven by pH-controlled helicity. The conformation of PCCPs at neutral pH showed low helical propensity because of dominant electrostatic attractions within the side chains. However, the helicity of PCCPs was considerably augmented by the balance of electrostatic interactions, thereby inducing selective cellular penetration. Three polypeptides undergoing different conformational transitions were prepared to verify the selective cellular uptake influenced by their structures. The PCCP undergoing low-to-high helical conformation provided the tumor specificity and enhanced uptake efficiency. pH-induced conformation-transformable polypeptide might provide a novel platform for stimuli-triggered targeting systems.