Drug-Loading Content Influences Cellular Uptake of Polymer-Coated Nanocellulose

While the effects of nanoparticle properties such as shape and size on cellular uptake are widely studied, influences exerted by drug loading have so far been ignored. In this work, nanocellulose (NC) coated by Passerini reaction with poly(2-hydroxy ethyl acrylate) (PHEA-g-NC) was loaded with various amounts of ellipticine (EPT) by electrostatic interactions. The drug-loading content was determined by UV-vis spectroscopy to range between 1.68 and 8.07 wt %. Dynamic light scattering and small-angle neutron scattering revealed an increased dehydration of the polymer shell with increasing drug-loading content, which led to higher protein adsorption and more aggregation. The nanoparticle with the highest drug-loading content, NC-EPT8.0, displayed reduced cellular uptake in U87MG glioma cells and MRC-5 fibroblasts. This also translated into reduced toxicity in these cell lines as well as the breast cancer MCF-7 and the macrophage RAW264.7 cell lines. Additionally, the toxicity in U87MG cancer spheroids was unfavorable. The nanoparticle with the best performance was found to have intermediate drug-loading content where the cellular uptake was adequately high while each nanoparticle was able to deliver a sufficiently toxic amount into the cells. Medium drug loading did not hinder uptake into cells while maintaining sufficiently toxic drug concentrations. It was concluded that while striving for a high drug-loading content is appropriate when designing clinically relevant nanoparticles, it needs to be considered that the drug can cause changes in the physicochemical properties of the nanoparticles that might cause unfavorable effects.