Biocompatible low-retention superparamagnetic iron oxide nanoclusters as contrast agents for magnetic resonance imaging of liver tumor

Although superparamagnetic iron oxide (SPIO) nanoparticles have been developed as a contrast agent for magnetic resonance imaging (MRI), acute iron overload due to the persistently high retention of SPIOs in the liver and spleen that are slowly converted to ferroproteins is a serious safety concern. Here, we report that the addition of poly-L-lysine polymers to an SPIO hydroxyethyl starch solution produced tightly controlled, monodispersed nanoparticles in a sizedependent manner as effective contrast agents for the MRI of liver tumors. High MRI contrast was demonstrated with an orthotopic liver tumor model at a low injection dose. Simultaneously, rapid bioclearance of excess iron in the lung and spleen and in blood serum was observed within 24 h post-injection. The full excretion of excess iron was confirmed in urine post-intravenous injection, suggesting that the effective clearance of SPIOs could be achieved with our SPIO nanoclusters as a liver imaging contrast agent to resolve acute iron overload in the clinical usage of SPIOs as a contrast agent.