Highly Reproducible Hyperthermia Response in Water, Agar, and Cellular Environment by Discretely PEGylated Magnetite Nanoparticles

Abstract

Local heat generation from magnetic nanoparticles(MNPs) exposed to alternating magneticfields can revolutionizecancer treatment. However, the application of MNPs as anticanceragents is limited by serious drawbacks. Foremost among these arethe fast uptake and biodegradation of MNPs by cells and theunpredictable magnetic behavior of the MNPs when theyaccumulate within or around cells and tissues. In fact, severalstudies have reported that the heating power of MNPs is severelyreduced in the cellular environment, probably due to a combinationof increased viscosity and strong NP agglomeration. Herein, wepresent an optimized protocol to coat magnetite (Fe3O4) NPs largerthan 20 nm (FM-NPs) with high molecular weight PEG moleculesthat avoid collective coatings, prevent the formation of large clustersof NPs and keep constant their high heating performance in environments with very different ionic strengths and viscosities (distilledwater, physiological solutions, agar and cell culture media). The great reproducibility and reliability of the heating capacity of thisFM-NP@PEG system in such different environments has been confirmed by AC magnetometry and by more conventionalcalorimetric measurements. The explanation of this behavior has been shown to lie in preserving as much as possible the magneticsingle domain-type behavior of nearly isolated NPs.In vitroendocytosis experiments in a colon cancer-derived cell line indicate thatFM-NP@PEG formulations with PEGs of higher molecular weight (20 kDa) are more resistant to endocytosis than formulationswith smaller PEGs (5 kDa), showing quite large uptake mean-life (τ> 5 h) in comparison with other NP systems. Thein vitromagnetic hyperthermia was performed at 21 mT and 650 kHz during 1 h in a pre-endocytosis stage and complete cell death wasachieved 48 h posthyperthermia. These optimal FM-NP@PEG formulations with high resistance to endocytosis and predictablemagnetic response will aid the progress and accuracy of the emerging era of theranostics.