Exploring the Effect of Drug Loading on the Biological Fate of Polymer-Coated Solid Nanoparticles

Polymer-coated inorganic nanoparticles (NPs) have attracted great attention in drug delivery fields due to their unique magnetic, optical, and thermal properties. Recent studies have shown that the surface physicochemical properties of these NPs, including the size, shape, shell hydration, protein corona, and so forth, affect their biological fate. However, there has been less attention on the effect of the drug loading amount on the biological activity of inorganic NPs. Here, we used upconverting NPs (UCNPs) as an inorganic nanocarrier model, coated them with a triblock terpolymer poly(poly(ethylene glycol) methyl ether methacrylate)-block-polymethacrylic acid-block-ethylene glycol methacrylate phosphate (PPEGMEMA-b-PMAA-b-PEGMP), and loaded them with different amounts of anticancer drug doxorubicin (DOX) by electrostatic interactions. Our results show that the UCNPs with the lowest DOX loading amount (1.32%) have the best biological behavior. We find that the effect of DOX loading on the biological behavior of UCNPs is dominated by polymer shell hydration and the protein corona. The lowest drug-loading UCNPs are more hydrated and have more albumin coronas around, which leads to an increasing effect on the association with cancer cells and drug accumulation in the mouse tumor area. Our findings highlight the importance of optimizing the drug loading amounts in polymer-coated inorganic drug delivery systems as the amount and type of drug will alter the physical properties of the polymer shell.