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Theranostics 2020; 10(1):218-230. doi:10.7150/thno.38198 This issue Cite

Research Paper

Mononuclear phagocyte system blockade improves therapeutic exosome delivery to the myocardium

Zhuo Wan^1#, Lianbi Zhao^2#, Fan Lu^3#, Xiaotong Gao¹, Yan Dong¹, Yingxin Zhao¹, Mengying Wei³, Guodong Yang³, Changyang Xing^2✉, Li Liu^1✉

1. Department of Hematology, Tangdu Hospital, Fourth Military Medical University, Xi'an, 710038, People's Republic of China.
2. Department of Ultrasound Medicine, Tangdu Hospital, Fourth Military Medical University, Xi'an, 710038, People's Republic of China.
3. State Key Laboratory of Cancer Biology, Department of Biochemistry and Molecular Biology, Fourth Military Medical University, Xi'an, 710032, People's Republic of China.
# These authors contributed equally to this work.

✉ Corresponding authors: Li Liu (liuli1com.cn) and Changyang Xing (xcycrazycom).

Abstract

Rationale: Exosomes are emerging as a promising drug delivery carrier. However, rapid uptake of exosomes by the mononuclear phagocyte system (MPS) remains an obstacle for drug delivery into other targeted organs, including the heart. We hypothesized that prior blocking of uptake of exosomes by the MPS would improve their delivery to the targeted organs.

Methods: Exosomes were isolated from the cell culture medium. Fluorescence-labeled exosomes were tracked in vitro and in vivo by fluorescence imaging. The expression of clathrin heavy chain (Cltc), cavolin1, Pak1 and Rhoa, known genes for endocytosis, were profiled in various cell lines and organs by qPCR. The knockdown efficiency of siRNA against Cltc was analyzed by Western blotting. Exosome^control and exosome^blocking were constructed by encapsulating isolated exosomes with siControl or siClathrin via electroporation, while exosome^therapeutic was constructed by encapsulating isolated exosomes with miR-21a. Doxorubicin-induced cardiotoxicity model was used to verify the therapeutic efficiency of the exosome-based miR-21a delivery by echocardiography.

Results: Exosomes were preferentially accumulated in the liver and spleen, mainly due to the presence of abundant macrophages. Besides the well-known phagocytic effect, efficient endocytosis also contributes to the uptake of exosomes by macrophages. Cltc was found to be highly expressed in the macrophages compared with other endocytosis-associated genes. Accordingly, knockdown of Cltc significantly decreased the uptake of exosomes by macrophages in vitro and in vivo. Moreover, prior injection of exosome^blocking strikingly improved the delivery efficiency of exosomes to organs other than spleen and liver. Consistently, compared with the direct injection of exosome^therapeutic, prior injection of exosome^blocking produced a much better therapeutic effect on cardiac function in the doxorubicin-induced cardiotoxicity mouse model.

Conclusions: Prior blocking of endocytosis of exosomes by macrophages with exosome^blocking successfully and efficiently improves the distribution of following exosome^therapeutic in targeted organs, like the heart. The established two-step exosome delivery strategy (blocking the uptake of exosomes first followed by delivery of therapeutic exosomes) would be a promising method for gene therapy.

Keywords: Exosomes, targeted delivery, blocking, clathrin, doxorubicin-induced cardiotoxicity

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