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

Abstract

The biodistribution of extracellular vesicles (EVs) is a fundamental question in the field of circulating biomarkers, which has recently gained attention. Despite the capabilities of nuclear imaging methods such as single photon emission computed tomography (SPECT), radioisotope labeling of EVs and the use of the aforementioned methods for in vivo studies hardly can be found in the literature. In this paper we describe a novel method for the radioisotope labeling of erythrocyte-derived EVs using the 99m Tctricarbonyl complex. Moreover, the capability of the developed labeling method for in vivo biodistribution studies is demonstrated in a mouse model. We found that the intravenously administered, According to our data, only a minor fraction of the radioactive label became detached from the EVs.

Advances in Analysis of Biodistribution of Exosomes by Molecular Imaging

“…This implies that UC is still the general method used to isolate exosomes in most academic settings, although the method is not ideal for the mass production of exosomes for the development of therapeutics. SEC was reported in only one publication [82]. In a few studies, precipitation with commercial kits was used to isolate exosomes.…”

“…To avoid this, methods based on the gel filtration (GF) principle are possible alternatives to conventional SEC. Commercial GF columns are already available to remove free probes by simple centrifugation without a significant increase in the sample volume [44,74,82,97]. Precipitation methods were also used to remove free probes.…”

Preclinical translation of exosomes derived from mesenchymal stem/stromal cells

“…54 Radiolabeling of exosomes presents an alternative imaging strategy; however, few published reports have investigated the biodistribution of postinserted radiolabeled EVs. 55,56 An alternative labeling method of engineering MEX with Cre-recombinase in Lox reporter mice has been reported, but it remains unclear whether such engineering methods modulate the functions of the resulting vesicles. 48,57,58 Taken together, the field could benefit from continued investigation of the MEX pharmacokinetics that take these factors into account.…”

Extracellular vesicles in the tumor microenvironment: Therapeutic resistance, clinical biomarkers, and targeting strategies

“…Although MRI can provide anatomical images of high resolution, this technique is limited by its lower sensitivity relative to other molecular imaging approaches . Being able to emit positrons or γ‐rays, radionuclides are detectable even when located deep in tissues, thus can be used to label EVs by embedding into their membrane . In contrast to optical EV‐imaging methods, which have inherent limitations in signal penetrating and low effectiveness in clinical application, nuclear imaging (NI) is a more promising option with enhanced safety and flexible in vivo depth, as exemplified by radioiodine 99m Tc and several other radionuclides currently exploited in clinics (Table ).…”