Noninvasive imaging of radiolabeled exosome-mimetic nanovesicle using 99mTc-HMPAO

Abstract

Exosomes known as nano-sized extracellular vesicles attracted recent interests due to their potential usefulness in drug delivery. Amid remarkable advances in biomedical applications of exosomes, it is crucial to understand in vivo distribution and behavior of exosomes. Here, we developed a simple method for radiolabeling of macrophage-derived exosome-mimetic nanovesicles (ENVs) with 99mTc-HMPAO under physiologic conditions and monitored in vivo distribution of 99mTc-HMPAO-ENVs using SPECT/CT in living mice. ENVs were produced from the mouse RAW264.7 macrophage cell line and labeled with 99mTc-HMPAO for 1 hr incubation, followed by removal of free 99mTc-HMPAO. SPECT/CT images were serially acquired after intravenous injection to BALB/c mouse. When ENVs were labeled with 99mTc-HMPAO, the radiochemical purity of 99mTc-HMPAO-ENVs was higher than 90% and the expression of exosome specific protein (CD63) did not change in 99mTc-HMPAO-ENVs. 99mTc-HMPAO-ENVs showed high serum stability (90%) which was similar to that in phosphate buffered saline until 5 hr. SPECT/CT images of the mice injected with 99mTc-HMPAO-ENVs exhibited higher uptake in liver and no uptake in brain, whereas mice injected with 99mTc-HMPAO showed high brain uptake until 5 hr. Our noninvasive imaging of radiolabeled-ENVs promises better understanding of the in vivo behavior of exosomes for upcoming biomedical application.

Radiolabeling of Extracellular Vesicles with 99mTc for Quantitative In Vivo Imaging Studies

“…The radioactivity detected in the bladder (3% of the injected radioactivity), originates from the free Tc-HMPAO method is challenging due to the low radiochemical yield of the method at low EV concentrations 34 .…”

“…34 The in vivo biodistribution of ENVs used as model system for real EVs was investigated using SPECT/CT. Although this method can be used in principle to label real EVs, the low labeling efficiency of the HMPAO method at low concentrations in the case of liposomes might hinder the successful labeling of EVs.…”

Modularized Extracellular Vesicles: The Dawn of Prospective Personalized and Precision Medicine

“…Although EVMs exhibit characteristics extremely similar to Exos,53, 54, 124 the actual identity of EVMs needs to be clarified by further investigation.…”

“…Furthermore, it has gradually been revealed that EVMs show similar properties to EVs;53, 54 therefore, the method of producing EVMs might be a much more effective way to manufacture modularized EVs.…”

Translational radionanomedicine: a clinical perspective

“…In addition, distribution of properties of nanoparticles means that samples of nanoparticles are inhomogeneous to a certain extent. Radiolabeling procedures could affect the variability of properties of nanoparticles because simple procedures can make aggregated nanoparticles (76). Furthermore, radiolabeled nanoparticles could be slightly different from unlabeled nanoparticles because radiolabelling procedures could alter the nanoparticles to some extent.…”