The aim of this study was to deliver ribonuclease A (RNase A) intracellularly using dextran nanogels for cancer treatment. To this end, positively charged RNase A was electrostatically loaded in anionic dextran nanogels with an average size of 205 nm, which were prepared by an inverse mini-emulsion technique. To chemically immobilize the loaded protein in the nanogels and prevent its unwanted release in the extracellular environment, the protein was covalently linked to the nanogel network via disulfide bonds, which are cleavable in the reductive cytosolic environment. A high loading efficiency and loading content of RNase A (75% and 20%, respectively) were obtained. Coating of the nanogels with the cationic polymer polyethyleneimine reversed the zeta potential of nanogels from −31.6 mV to +7.6 mV. The nanogels showed a fast and triggered release of RNase in the presence of glutathione. Negatively charged RNase A loaded nanogels did not show cytotoxicity, likely due to their limited cellular uptake. In contrast, PEI coated RNase A loaded nanogels showed high uptake by MDA-MB 231 breast cancer cells and exhibited a concentration-dependent cytotoxic effect by apoptosis. The results demonstrate that PEI coated nanogels are promising nano-carriers for intracellular protein delivery, encouraging further evaluation of this formulation in preclinical models.
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