Abstract
Extracellular vesicles (EVs) are currently being considered as promising drug delivery vehicles. EVs are naturally occurring vesicles that exhibit many characteristics favorable to serve as drug delivery vehicles. In addition, EVs have inherent properties for treatment of cancers and other diseases. For research and clinical translation of use of EVs as drug delivery vehicles, in vivo tracking of EVs is essential. The latest molecular imaging techniques enable the tracking of EVs in living animals. However, each molecular imaging technique has its certain advantages and limitations for the in vivo imaging of EVs; therefore, understanding the molecular imaging techniques is essential to select the most appropriate imaging technology to achieve the desired imaging goal. In this review, we summarize the characteristics of EVs as drug delivery vehicles and the molecular imaging techniques used in visualizing and monitoring EVs in in vivo environments. Furthermore, we provide a perceptual vision of EVs as drug delivery vehicles and in vivo monitoring of EVs using molecular imaging technologies.
Highlights
A recent study compared the dye-based direct labeling with the Renilla luciferase (Rluc)-based indirect labeling of Extracellular vesicles (EVs) derived from thyroid cancer cells
This study revealed that labeling with the dye can affect the normal distribution of EVs in an animal model; EV organotropism, which occurs due to the integrins present in the EV membrane, could be influenced by the dye attached onto the EV surface membrane, leading to different in vivo distribution (Gangadaran et al, 2017b)
EVs have become an enthusiastic subject as drug delivery vehicles
Summary
Extracellular vesicles (EVs) are naturally occurring nanovesicles released by different types of cells, including reticulocytes (Johnstone et al, 1991), platelets (Brisson et al, 2017), mesenchymal stem cells (Rajendran et al, 2017), T cells (Karlsson et al, 2001; Ludwig et al, 2017), B lymphocytes (Raposo et al, 1996), NK cells (Shoae-Hassani et al, 2017; Zhu et al, 2017), dendritic cells (DCs) (Lu et al, 2017), and some tumor cells (Aharon et al, 2017; Baumgart et al, 2017; Schillaci et al, 2017); these nanovesicles can be detected in human biological fluids (Cappello et al, 2017). The use of EVs as systems to deliver therapeutic materials has been widely studied (Table 1), the effectiveness of EV-based therapy depends on the targetability of EVs to tumor or another desired cell in vivo. Non-invasive imaging modalities might provide clear view on the in vivo distribution of EVs and provide accurate targetability of EVs to the desired cell/tissue and would be useful in the development of EVs as drug delivery vehicles.
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