Standardization of DMSA ligand exchange reaction​ to achieve uniformly coated iron oxide nanoparticles and their application for cancer imaging

Introduction: Since the interactions of iron oxide nanoparticles (IONPs) with physiological environments are mediated by their surface coating, the quality and reproducibility of the IONPs' surface is a crucial parameter... [ view full abstract ]

Introduction:

Since the interactions of iron oxide nanoparticles (IONPs) with physiological environments are mediated by their surface coating, the quality and reproducibility of the IONPs' surface is a crucial parameter for their successful biomedical application and clinical potential translatability. Within the surface coating reactions, the oleic acid /dimercaptosuccinic acid (DMSA) ligand exchange is one of the most widely used. However, this surface coating reaction has not been yet fully characterized and optimized.  As consequence, the potential biological activity of  DMSA-coated IONPs further modified with bioactive compounds will be highly unpredictable.  

Methods:

We produced and characterized DMSA-coated IONPs of 10 nm core . By means of chemical strategies, we elucidated the mechanistic aspects hampering the reproducibility of OA/DMSA ligand exchange reaction. Hence, we designed a novel protocol accessing monodisperse IONPs with controlled and reproducible DMSA-surrounding shell (n=4). Then, we fully characterized the produced lots and demonstrated the viability of our strategy compared with untreated DMSA-IONPs. To assess their biomedical potential, we PEGylated (via EDC chemistry) and labeled with a fluorophore (via thiol-maleimide 'click' reaction) the treated DMSA-IONPs, finally accessing a dual contrast agent promoting optical and magnetic resonance imaging (OI/MRI). As control, the same procedure was repeated using untreated DMSA-IONPs. Both set of particles were compared by confocal laser scanner microscopy (CLSM). Finally, the ability of treated IONPs as dual contrast agent has been assessed in the diagnostic OI/MRI imaging of an orthotopic mice model of human breast cancer (n=4). The satisfactory imaging results were also confirmed by immunohistochemistry.

Results and Discussion:

Herein, we elucidate the mechanistic aspects of OA/DMSA ligand exchange on IONPs  and present a standardized protocol that enables controlled and reproducible DMSA shell grafting. The physical-chemical characterizations confirmed our hypothesis. The as-prepared DMSA-IONPs were successfully PEGylated and labeled, showing by CLSM a fluorescence intensity almost one order of magnitud higher than the untreated ones. As contrast agent, these extravasate into the tumor's interstitium by enhanced permeability and retention effect (EPR) enabling a T₂ signal decrease around 20% (n=4) and optical tracking. 

In sum, the standardization of IONPs multifunctional coating as theranostic agents for biomedical application has been achieved.