Incorporation of Targeting Biomolecule Improves Interpolymer Complex-Superparamagnetic Iron Oxide Nanoparticles Attachment to and Activation of T2 MR Signals in M2 Macrophages

Abstract

Introduction: Inflammatory diseases are the leading cause of death in the world, accounting for 3 out of 5 deaths. Despite the abundance of diagnostic tools for detection, most screening and diagnostic methods are indirect and insufficient as they are unable to reliably discriminate between high-risk or low-risk stages of inflammatory diseases. Previously, we showed that the selective activation of interpolymer complexed superparamagnetic iron oxide nanoparticles (IPC-SPIOs) under oxidative conditions can be detected by a change in T2 magnetic resonance (MR) contrast. In this work, IPC-SPIOs were further modified by incorporating mannose as a targeting biomolecule to enhance nanoparticle delivery to M2 macrophages at inflammatory sites. Methods: Uncoated SPIOs were synthesized via coprecipitation from a mixture of FeCl2 and FeCl3, PEGylated by adsorbing PEG 300 kDa (40 mg/mL in water) to SPIOs (3 mg/mL in water) over 24 hours, and complexed by mixing 0.25 mg/mL aqueous poly(gallol) with 2 mg/mL PEG-SPIOs and adding 1 M of phosphate buffer in a 9:9:2 ratio. Mannose-PEG attachment was accomplished conducting a second complexation of mannose-PEG to IPC-SPIOs. M2 macrophages were treated with 150, 100, and 75 µg/mL of IPC-SPIOs and mannose-IPC-SPIOs to investigate activation of T2 MRI signals. Results and Discussion: Surface modification resulted in a slight reduction in ROS scavenging capacity; however, nanoparticle uptake by M2 macrophages increased by over 50%. The higher uptake did not cause a reduction in cellular viability. In fact, mannose-IPC-SPIOs induced significant T2 MR contrast in M2 macrophages compared to IPC-SPIOs and nanoparticles exposed to M1 macrophages. M2 macrophages activated over 30% of mannose-IPC-SPIOs after 6 hours of exposure compared to M1 macrophages and untargeted M2 macrophages. These findings demonstrated that mannose-IPC-SPIOs specifically targeted M2 macrophages and scavenged cellular ROS to activate T2 MR signal, which can be used to detect inflammation.