Theranostic nanoparticles: Investigation of superparamagnetic iron oxide nanoparticles intrinsically labeled with Zirconium-89 and Actinium-225.

Superparamagnetic iron oxide nanoparticles (SPIONs) are of interest for use as drug delivery vehicles due to their magnetic properties, tunable surface chemistry, and potential for use in magnetic resonance imaging and hyperthermia studies. Additionally, their high affinity for metals allows for radiolabeling radiometals for nuclear medicine applications like nano-theranostics. Herein, we report the synthesis of 225Ac-labeled and 89Zr-labeled PEG-SPIONs. Actinium-225 showed preferential leaching during surface modification compared to zirconium-89, suggesting that it was predominantly bound in surface sites, while zirconium-89 was located at the internal lattice sites. The biodistribution of unmodified 89Zr-labeled SPIONs and surface-modified 89Zr-labeled PEG-SPIONs were compared using PET/MRI which showed rapid blood clearance due to liver uptake. Overall, the reported nanoparticles are promising for applications in targeted alpha therapy.