RESEARCH ARTICLE – Pharmaceutics, Drug Delivery and Pharmaceutical Technology
Quantitative Analysis of Tissue Distribution of the B16BL6-Derived Exosomes Using a Streptavidin-Lactadherin Fusion Protein and Iodine-125-Labeled Biotin Derivative After Intravenous Injection in Mice

https://doi.org/10.1002/jps.24251Get rights and content

ABSTRACT

We previously succeeded in the visualization of tissue distribution of B16BL6 cells-derived exosomes by labeling with Gaussia luciferase (gLuc)-LA, a fusion protein of gLuc (a reporter protein) and lactadherin (LA; an exosome-tropic protein). However, total amount of B16BL6-derived exosomes delivered to each organ could not be evaluated because of the reduction of luminescent signal from gLuc-LA. The aim of the present study was to quantitatively evaluate the tissue distribution of B16BL6-derived exosomes. To this end, we labeled B16BL6-derived exosomes with iodine-125 (125I) based on streptavidin (SAV)-biotin system. A plasmid vector encoding fusion protein, SAV-LA, was constructed, and B16BL6 cells were transfected with the plasmid to obtain SAV-LA-coupled exosomes. SAV-LA-coupled exosomes were incubated with (3-125I-iodobenzoyl) norbiotinamide (125I-IBB) to obtain 1251-labeled B16BL6 exosomes. After intravenous injection of 125I-labeled B16BL6 exosomes into mice, radioactivity quickly disappeared from the blood circulation. At 4 h, 28%, 1.6%, and 7% of the injected radioactivity/organ was detected in the liver, spleen, and lung, respectively. These results indicate that 125 I-labeling of exosomes using SAV-biotin system is a useful method to quantitatively evaluate the amount of exogenously administered exosomes delivered to each organ and that the liver is the major organ in the clearance of exogenously administered B16BL6-derived exosomes.

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INTRODUCTION

Exosomes are small membrane vesicles that are secreted from various kinds of cells.1 It has been recently revealed that exosomes play key roles in various biological events, such as inflammation and tumor metastasis, because exosomes work as intercellular communication tools by transporting their components, including proteins and nucleic acids, to the cells receiving the exosomes.2., 3., 4., 5. Besides their biological roles, exosomes are attractive candidate vesicles for the delivery of these

Plasmid DNA

The cDNAs of SAV and murine LA were obtained as described in previous reports.12., 14. SAV-LA was constructed by replacing the epidermal growth factor-like domain of LA with SAV. The following primers were used for polymerase chain reaction: SAV (forward) 5′-GGATAGATCTCAGCATGCA GGTCTCCCGT-GTGCTGGCCGCGCTGTGCGGC ATGCTACTCTGCGCCT CTGGCCTCTTCGCCGGTGACCC CTCCAAGGACTC-3′, (reverse) 5′-TCCATGCCCAGCTGT GTAGAACAACCCTGCTGA ACGGCGTCGAGCG-3′ and LA (forward) 5′-TGTTCTACACA GCTGGGCATGGA-3', (reverse)

Modification of Exosomes with SAV-LA

Figure 1a shows the schematic diagram of LA and SAV-LA. Figure 1b shows the SAV concentration in each sample collected during the exosome purification steps. The SAV concentrations in the lysate and exosome fractions were approximately 118 and 42 nM, respectively. The SAV concentrations in the culture medium and UC supernatant fractions were below the detection limit (2 nM). As shown in Figure 1c, TEM observation revealed that biotin-coated gold nanoparticles were bound to the surface of the

DISCUSSION

Results obtained from the in vitro binding assay demonstrated that the exosomes collected from B16BL6 cells transfected with SAV-LA-expressing pDNA possessed binding capacity of SAV to biotin (Figs. 1b and 3). Moreover, TEM observation visualized the binding of SAV-LA-coupled exosomes to biotin-coated gold nanoparticles (Fig. 1c). As the molecules displayed on the outside of the exosomes are exposed to blood components, the reliability of the in vivo analysis based on the radioactivity would be

CONCLUSION

We demonstrated that 125I-labeled B16BL6 exosomes developed by SAV—biotin system is a useful method to obtain quantitative information about the pharmacokinetics of exogenously administered B16BL6-derived exosomes, which will be helpful for the development of exosome-based delivery systems.

ACKNOWLEDGMENTS

This work was partly supported by a Grant-in-Aid for Scientific Research (B) and a Grant-in-Aid for Exploratory Research from the Japan Society for the Promotion of Science (JSPS).

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