Fluorine-19
magnetic resonance imaging (19F MRI) enables
detailed in vivo tracking of fluorine-containing
tracers and is therefore becoming a particularly useful tool in noninvasive
medical imaging. In previous studies, we introduced biocompatible
polymers based on the hydrophilic monomer N-(2-hydroxypropyl)methacrylamide
(HPMA) and the thermoresponsive monomer N-(2,2-difluoroethyl)acrylamide
(DFEA). These polymers have abundant magnetically equivalent fluorine
atoms and advantageous properties as 19F MRI tracers. Furthermore,
in this pilot study, we modified these polymers by introducing a redox-responsive
monomer. As a result, our polymers changed their physicochemical properties
once exposed to an oxidative environment. Reactive oxygen species
(ROS)-responsive polymers were prepared by incorporating small amounts
(0.9–4.5 mol %) of the N-[2-(ferrocenylcarboxamido)ethyl]acrylamide
(FcCEA) monomer, which is hydrophobic and diamagnetic in the reduced
electroneutral (Fe(II), ferrocene) state but hydrophilic and paramagnetic
in the oxidized (Fe(III), ferrocenium cation) state. This property
can be useful for theranostic purposes (therapy and diagnostic purposes),
especially, in terms of ROS-responsive drug-delivery systems. In the
reduced state, these nanoparticles remain self-assembled with the
encapsulated drug but release the drug upon oxidation in ROS-rich
tumors or inflamed tissues.