A major clinical translational challenge in nanomedicine is the potential of toxicity associated with the uptake and long-term retention of non-degradable nanoparticles (NPs) in major organs. The development of inorganic NPs that undergo renal clearance could potentially resolve this significant biosafety concern. However, it remains unclear whether inorganic NPs that can be excreted by the kidneys remain capable of targeting tumors with poor permeability. Glioblastoma multiforme, the most malignant orthotopic brain tumor, presents a unique challenge for NP delivery because of the blood-brain barrier and robust blood-tumor barrier of reactive microglia and macroglia in the tumor microenvironment. Herein, we used an orthotopic murine glioma model to investigate the passive targeting of glutathione-coated gold nanoparticles (AuNPs) of 3 nm in diameter that undergo renal clearance and 18-nm AuNPs that fail to undergo renal clearance. Remarkably, we report that 3-nm AuNPs were able to target intracranial tumor tissues with higher efficiency (2.3× relative to surrounding non-tumor normal brain tissues) and greater specificity (3.0×) than did the larger AuNPs. Pharmacokinetics studies suggested that the higher glioma targeting ability of the 3-nm AuNPs may be attributed to the longer retention time in circulation. The total accumulation of the 3-nm AuNPs in major organs was significantly less (8.4×) than that of the 18-nm AuNPs. Microscopic imaging of blood vessels and renal-clearable AuNPs showed extravasation of NPs from the leaky blood-tumor barrier into the tumor interstitium. Taken together, our results suggest that the 3-nm AuNPs, characterized by enhanced permeability and retention, are able to target brain tumors and undergo renal clearance.
Keywords: brain tumor; enhanced permeability and retention; gold nanoparticles; passive targeting; renal clearance.