A mesoporous silica nanoparticle with charge-convertible pore walls for efficientintracellular protein delivery

Abstract

We report a smart mesoporous silica nanoparticle (MSN) with a pore surface designed toundergo charge conversion in intracellular endosomal condition. The surface of mesoporesin the silica nanoparticles was engineered to have pH-hydrolyzable citraconicamide. Solid-state nuclear magnetic resonance (NMR), Fourier-transform infrared(FT-IR) spectroscopy, and Brunauer–Emmett–Teller (BET) analyses confirmed thesuccessful modification of the pore surfaces. MSNs (MSN–Cit) with citraconicamide functionality on the pore surfaces exhibited a negative zeta potential (−10 mV) at pH 7.4 because of the presence of carboxylate end groups. At cellular endosomal pH (∼5.0), MSN–Cit have a positive zeta potential (16 mV) indicating the dramatic chargeconversion from negative to positive by hydrolysis of surface citraconic amide. Cytochromec (Cyt c) of positive charges could be incorporated into the pores of MSN–Cit byelectrostatic interactions. The release of Cyt c can be controlled by adjusting the pH ofthe release media. At pH 7.4, the Cyt c release was retarded, whereas, at pH 5.0,MSN–Cit facilitated the release of Cyt c. The released Cyt c maintained theenzymatic activity of native Cyt c. Hemolytic activity of MSN–Cit over red blood cells(RBCs) was more pronounced at pH 5.0 than at pH 7.0, indicating the capability ofintracellular endosomal escape of MSN carriers. Confocal laser scanning microscopy(CLSM) studies showed that MSN–Cit effectively released Cyt c in endosomalcompartments after uptake by cancer cells. The MSN developed in this work may serveas efficient intracellular carriers of many cell-impermeable therapeutic proteins.