Development of a Multimodal Imaging Probe for Lymph Node Targeting Using Specific Amphiphile Encapsulation Technology on Iron Oxide Nanoparticles

Abstract

Introduction: Multimodal imaging probes could provide synergistic effect through combining the benefits and supplementing the weaknesses from each imaging system. Nanoparticle is a good carrier and imaging probe itself and surface modification using huge surface area make it possible for multifunctional application. The aim of this study is to develop a multimodal iron oxide nanoparticle using an encapsulation method with specific amphiphiles (1). Methods: Specific amphiphiles were synthesized by conjugating stearylamine with SCN-Bn-NOTA and SCN-Bn-Mannose. Mannose-containing nanoparticle was designed for imaging lymph nodes (2). NOTA is an excellent chelating agent for 68Ga labeling (3). Iron oxide nanoparticles were encapsulated with prepared solution containing polysorbate 60 and functionalized amphiphiles by vigorous mixing and sonication. Reaction mixture was purified using size exclusion column and concentrated with centrifugal filter. Concentration of the final material was measured by colorimetric analysis at 457 nm. Size distribution was analysed using a DLS instrument. Stability was evaluated under various conditions (0.9, 1.8, 3.6% NaCl solution, rt, 1, 3, 24 h

human serum, 37°C, 2 h). Phantom study was performed for estimation of T2-weighted MR (3.0 T) signal of the final probes and was compared with that of commercialized iron oxide-based probes (Feridex®). In vivo study was performed for 60 min dynamic imaging after s.c. injection of 68Ga labeled probe to the left footpad of a mouse (12.0 MBq/10 µL) and follow up with T2-weighted MRI imaging for 30 min. Microscopic histopathologic examination of popliteal lymph nodes after prussian blue staining was performed. Results: The size distribution of NOTA-IO-Man was 10.1±1.5 nm with high encapsulation recovery ratio (92.0%). No significant aggregation or degradation was found under various harsh conditions. The radiochemical purity of 68Ga-NOTA-IO-Man was >99% and was stable in human serum for 120 min and no size transition (10.1±1.5 nm, P=.29) was observed. The calculated relaxivity coefficient (r2) of mM-1s-1 was 449.9 which was higher than Feridex® (180.38). The specificity of 68Ga-NOTA-IO-Man was confirmed showing both PET/CT and MRI signal at the same site. The tissue section of left popliteal lymph node resulted in a distinctive blue pigment demonstrating the existence of ferric iron. Conclusions: In this study, we developed lymph node targeting PET/MRI dual-modality imaging probes successfully using facile encapsulation method.