Magnetic brain tumor targeting and biodistribution of long-circulating PEG-modified, cross-linked starch-coated iron oxide nanoparticles.

Magnetic iron oxide nanoparticles (MNPs) have been studied to circumvent the limitations of status-quo brain tumor therapy and can be targeted by applying an external magnetic field to lesions. To address the pharmacokinetic shortcomings of MNPs that can limit targeting efficiency, we recently reported a long-circulating polyethylene glycol modified, cross-linked starch MNP (PEG-MNP) suitable for magnetic targeting. Using a rat model, this work explores the biodistribution patterns of PEG-MNPs in organs of elimination (liver, spleen, lung, and kidney) and shows proof-of-concept that enhanced magnetic brain tumor targeting can be achieved due to the relatively long circulation lifetime of the nanoparticles. Reductions in liver (∼12-fold) and spleen (∼2.5-fold) PEG-MNP concentrations at 1h compared to parent starch-coated MNPs (D) confirm plasma pharmacokinetics observed previously. While liver concentrations of PEG-MNPs remained considerably lower than those observed for D at 1h through 60 h, spleen values continue to increase and are markedly higher at later time points--a trend also observed with histology. Limited to no distribution of PEG-MNPs was visualized in lung or kidney throughout the 60 h course evaluated. Enhanced, selective magnetic brain tumor targeting (t = 1 h) of PEG-MNPs (12 mg Fe/kg) was confirmed in 9L-glioma tumors, with up to 1.0% injected dose/g tissue nanoparticle delivery achieved--a 15-fold improvement over targeted D (0.07% injected dose/g tissue). MRI and histological analyses visually confirmed enhanced targeting and also suggest a limited contribution of passive mechanisms to tissue retention of nanoparticles. Our results are exciting and justify both further development of PEG-MNP as a drug delivery platform and concurrent optimization of the magnetic brain tumor targeting strategy utilized.