Synthesis of Water-soluble chitosan-g-PEO and its application for preparation of superparamagnetic iron oxide nanoparticles in aqueous media

Fluorescent dye labeled iron oxide/silica core/shell nanoparticle as a multimodal imaging probe

PURPOSE

To develop an MRI/optical multimodal imaging probe based on dye-conjugated iron oxide/silica core/shell nanoparticle, and investigate the distance-dependent fluorescence quenching through careful control of the distance between the iron oxide core and fluorescent dyes.

METHODS

Different size of core/shell nanoparticles were prepared by varying the silica shell width. PEGylation on the surface of silica shell was followed to improve the stability of particles in the physiological condition. In vitro cytotoxicity was evaluated by the MTT assay on a HeLa cell line and in vivo imaging of subcutaneous SCC7 xenografted mice was performed using MRI/optical imaging modalities.

RESULTS

Diameter and ζ-potential of the nanoparticles were measured, and TEM images demonstrated the mono-disperse nature of the particles. Quenching efficiency of the dyes on the surface was nearly 100% in the smallest nanoparticle, while almost no quenching effect was observed for the largest nanoparticle. In vitro cytotoxicity showed nearly 90% cell viability at 0.15 Fe mg/mL, a comparable concentration for clinical use. The tumor area was significantly darkened after the nanoparticle injection due to the high transverse relaxivity value of the nanoparticles. Fluorescence signal was affected by the particle size due to the distance-dependent quenching/dequenching behaviour.

Synthesis and characterization of folic acid modified water-soluble chitosan derivatives for folate-receptor-mediated targeting

Three chemical modification methods of carboxymethylation, quaternization and hydroxypropylation were used to synthesize water-soluble chitosan derivatives. In order to study the feasibility of these chitosan derivatives as backbones of nuclear imaging agents, folic acid (FA) and Technetium-99m were introduced onto the water-soluble chitosan chains. The bifunctional chelating agent 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was conjugated to the folate grafted chitosan derivatives for chelating with radionuclides such as (64)Cu and (68)Ga. The structures of these new ligands were characterized with multiple methods. The solubility and stability of the (99m)Tc-complexes were both favorable. Further study of their radiochemical and biological properties will be performed to evaluate the usefulness of these water-soluble chitosan derivatives for nuclear imaging agent design.

Development of MRI/NIRF 'activatable' multimodal imaging probe based on iron oxide nanoparticles

A fabrication method of Cy5.5-MMP substrate and PEG conjugated iron oxide nanoparticles with thin silica coating (PCM-CS) and its potential as an 'activatable' dual imaging probe for tumor imaging is described in this report. PCM-CS showed an intensity-averaged diameter of 43.1 ± 6.3 nm by dynamic light scattering without any noticeable aggregation over 7 days. Fluorescence of Cy5.5 on the surface of nanoparticles was fully quenched and the quenching efficiency was 97.2%. PCM-CS showed protease specific fluorescence recovery in vitro caused from the specific peptide cleavage by MMP-2 and the probe displayed the sensitivity on 0.5 nM or less enzyme concentration. Tumor was successfully visualized by NIRF and MRI in vivo by intravenously injected PCM-CS. NIRF signal of tumor was gradually increased up to 12h post injection and the intensity of tumor was about 3-4 times higher than normal tissue. NIRF signal at MMP-2 inhibitor treated tumor was clearly lower than tumor without inhibitor due to the insufficient peptide cleavage. NIRF signal at excised tumor was 5-10 times stronger than other organs. Noticeable darkening in magnetic resonance image was observed at the tumor region and the image was gradually darkened at 12h post injection of PCM-CS. The maximum signal difference between tumor region and healthy muscle was 34%.