Polymeric mesoscale nanoparticles exhibit dynamin- and macropinocytosis-dependent endocytosis.

Polymeric mesoscale nanoparticles (MNPs) are 300 to 500 nm in diameter with a PEGylated surface that exhibit unique renal tropism as a function of that size range, as described in our prior work, with selectivity toward renal tubular epithelial cells. Despite their well-described therapeutic applications, we do not yet fully understand whether they maintain the unique mesoscale size range under various storage condition, nor do we understand the mechanisms of their internalization in renal tubular epithelial cells. Here, we investigated whether MNPs maintain their size when exposed to freeze-thaw cycles and storage outside their intended -20 °C condition. MNPs demonstrated negligible changes in size and polydispersity up to 4 freeze-thaw cycles, while we found an increase in size elevated temperature as a function of cargo loading. We then performed in vitro studies to evaluate MNP cellular uptake mechanisms using the human renal cell carcinoma tubular epithelial cell line 786-O treated with pharmacological inhibitors of uptake pathways. We found that MNP internalization is almost entirely prevented by dynamin inhibitors, while macropinocytosis inhibition also reduced uptake, suggesting that such standard nanoparticle uptake pathways are robust to the mesoscale size range.