Preparation of Size-Defined PEG-Grafted Copolymers as a Polymeric Nanoruler for Size Optimization in Passive Targeting.

Size-dependent (or passive) targeting strategies are a major approach for designing nanomedicines (or nanocarriers) that can systemically deliver drugs to lesion sites as well as solid tumors. However, the optimal size range for passive targeting to various noncancerous lesion sites is unclear. Recently, we fabricated poly(ethylene glycol) (PEG)-grafted copolymers (gPEGs) as a size-tunable "polymeric nanoruler" to clarify the optimal size for systemic inflamed/noninflamed muscle tissue targeting. The hydrodynamic diameter (DH) of gPEGs was controlled in the range from 11 nm to 32 nm by varying the molecular weights of grafted PEGs. The biodistribution analyses of gPEGs revealed that 11-15 nm sized gPEG achieved the highest accumulation in the skeletal muscle tissue of healthy mice, which was presumably determined by competition between the renal excretion efficiency and muscle tissue extravasation efficiency. Interestingly, muscular dystrophy model mice (mdx mice) showed two to three times higher levels of gPEG accumulation in the skeletal muscle tissue, compared with healthy mice, due to the enhanced extravasation of gPEGs in inflamed muscle tissues. The results demonstrated the utility of size-tunable gPEGs, i.e., polymeric nanoruler, for optimizing the passive targeting strategy. In the present study, we describe a detailed protocol for the preparation of gPEGs to disseminate the methodology of the polymeric nanoruler.