An Intracellular pH-Actuated Polymer for Robust Cytosolic Protein Delivery

Abstract

Robust cytosolic protein delivery requires both efficient protein binding with delivery vehicles and effective protein release after cell internalization. Although a variety of stimuli-responsive carriers have been designed, simultaneously integrating these two functions in one versatile carrier is challenging. Herein, we developed a polyamidoamine (PAMAM)-based polymer with an intracellular pH-actuated hydrophobic-to-hydrophilic transition for this purpose. The polymer (designated as G5-C4) was synthesized by appending N,Ndibutylaminoethyl moieties to the peripheral amino groups of PAMAM dendrimer generation 5. Assisted by hydrophobic interactions, G5-C4 formed condensed nanoparticles with proteins and remained stable under physiological conditions. After efficient cell internalization, G5-C4 underwent a hydrophobic-to-hydrophilic transition at acidic endosomal pH, and thus promoted protein release and endosomal escape, which was verified by structure–activity relationship studies. Furthermore, both in vitro and in vivo studies indicated that G5-C4 achieved superior antitumor effect. This study provides a simple but effective design for stimuli-responsive cytosolic protein delivery.