The evaluation of cellular uptake efficiency and tumor-targeting ability of MPEG–PDLLA micelles: effect of particle size

In this study, we successfully prepared MPEG–PDLLA polymer micelles with two different particle sizes, A and B. DLS and TEM assays demonstrated that the particle sizes of the polymer micelles A and polymer micelles B were about 25 nm and 150 nm respectively. The stability of the MPEG–PDLLA polymer micelles in vitro revealed that the free Cy5.5 dye had been successfully loaded into the polymer micelles as a fluorescence marker and the fluorescence wasn’t quenched until 72 h. The cellular uptake of the polymer micelles was time-dependent and micelles A (particle size 25 nm) showed a higher efficiency to be internalized into the cytoplasm of MCF-7 cells than micelles B (particle size 150 nm). Furthermore, in vivo and in vitro biodistribution and tumor-targeting of polymer micelles MPEG–PDLLA were investigated in female MCF-7 tumor-bearing balb/cA-nu mice with an IVIS imaging system. The results showed that polymer micelles A (particle size 25 nm) had a time dependent biodistribution and tumor site accumulation in mice bearing MCF-7 tumors. Meanwhile, the NIR fluorescence intensity of polymer micelles B (particle size 150 nm) in tumor sites showed a pattern of a rise, a peak and then a decline. What’s more, the distribution of the polymer micelles in the tissue slices demonstrated the same results. Consequently, the results indicated that the micelles with a smaller particle size (25 nm) could be more efficiently internalized into cells and increase the enhanced permeation and retention (EPR) effect in tumor tissue. Therefore, a reasonable small size of micelles may be a key factor for a high-performance anti-cancer drug delivery system.