Investigation of nanostar-labeled mesenchymal stem cells for in vivo cell tracking in osteoarthritis using optoacoustic imaging

Abstract

Background & Aim This project aims to investigate gold nanostar (NS)-labeled mesenchymal stem/stromal cells (MSCs) for in vivo cell tracking using optoacoustic imaging (OAI) for the treatment of osteoarthritis (OA). OAI, specifically multi-spectral optoacoustic tomography (MSOT) has demonstrated excellent resolution at increasing depths. To further enhance depth penetration and sensitivity, a novel gold nanoparticle – the NS has been developed. This NS will also be used to permit tracking of MSCs in vivo. Different nanostar surface coatings have been investigated for their uptake and effects on MSC characteristics: methoxy (NS-OMe) and carboxyl (NS-COOH). SPIONs (superparamagnetic iron oxide nanoparticles) have also been used to functionalize the NS (NS-SPIONs) and permit dual OAI and magnetic resonance imaging. In order to permit labeling and tracking of MSC-derived extracellular vesicles (EVs), conjugation of an antibody to the NS has also been performed using available carboxyl groups. The aims of this project are to optimize MSC labeling and to investigate MSC phenotype post-labeling. Methods, Results & Conclusion Methods Methods to investigate uptake of NS included transmission electron microscopy (TEM), Image Stream X analysis (ISX) and MSOT. Viability, tri-lineage differentiation and surface immunophenotype assays were used to assess MSC characteristics post -labeling. In vivo imaging of NS in the knee joint was performed using MSOT. Results NS-OMe were efficiently internalized by MSCs and had no effects on MSCs characteristics. NS-COOH demonstrated inefficient cellular internalization. ISX was used to quantify the uptake of NS conjugated to an antibody and validated these initial findings as only 20% of MSCs contained NS-COOH conjugated to an antibody. NS-SPIONs were also investigated and demonstrated efficient internalization by MSCs. NS-SPIONS will be further investigated to identify the optimal labeling concentration for MSOT detection. Finally, preliminary work has explored the capacity of MSOT to detect NS in vivo. An enhanced optoacoustic signal in the knee joint following an intra-articular injection of NS was shown as indicated by the white arrows in figure 1. Conclusion MSC uptake and internalization of NS is variable in response to different NS surface coatings. NS-OMe demonstrated the most efficient uptake by cells while NS-COOH was least efficient. The uptake of NS-SPIONs has been found to be optimal and future work will determine the optimal concentration for MSOT detection.