Current Perspectives on In Vivo Noninvasive Tracking of Extracellular Vesicles with Molecular Imaging

Fluorescent, phosphorescent, magnetic resonance contrast and radioactive tracer labelling of extracellular vesicles

This review focusses on the significance of fluorescent, phosphorescent labelling and tracking of extracellular vesicles (EVs) for unravelling their biology, pathophysiology, and potential diagnostic and therapeutic uses. Various labeling strategies, such as lipid membrane, surface protein, luminal, nucleic acid, radionuclide, quantum dot labels, and metal complex-based stains, are evaluated for visualizing and characterizing EVs. Direct labelling with fluorescent lipophilic dyes is simple but generally lacks specificity, while surface protein labelling offers selectivity but may affect EV-cell interactions. Luminal and nucleic acid labelling strategies have their own advantages and challenges. Each labelling approach has strengths and weaknesses, which require a suitable probe and technique based on research goals, but new tetranuclear polypyridylruthenium(II) complexes as phosphorescent probes have strong phosphorescence, selective staining, and stability. Future research should prioritize the design of novel fluorescent probes and labelling platforms that can significantly enhance the efficiency, accuracy, and specificity of EV labeling, while preserving their composition and functionality. It is crucial to reduce false positive signals and explore the potential of multimodal imaging techniques to gain comprehensive insights into EVs.

Most recent advances and applications of extracellular vesicles in tackling neurological challenges

Over the past few decades, there has been a notable increase in the global burden of central nervous system (CNS) diseases. Despite advances in technology and therapeutic options, neurological and neurodegenerative disorders persist as significant challenges in treatment and cure. Recently, there has been a remarkable surge of interest in extracellular vesicles (EVs) as pivotal mediators of intercellular communication. As carriers of molecular cargo, EVs demonstrate the ability to traverse the blood-brain barrier, enabling bidirectional communication. As a result, they have garnered attention as potential biomarkers and therapeutic agents, whether in their natural form or after being engineered for use in the CNS. This review article aims to provide a comprehensive introduction to EVs, encompassing various aspects such as their diverse isolation methods, characterization, handling, storage, and different routes for EV administration. Additionally, it underscores the recent advances in their potential applications in neurodegenerative disorder therapeutics. By exploring their unique capabilities, this study sheds light on the promising future of EVs in clinical research. It considers the inherent challenges and limitations of these emerging applications while incorporating the most recent updates in the field.

Challenges and future scope of exosomes in the treatment of cardiovascular diseases

Exosomes are nanosized vesicles that carry biologically diverse molecules for intercellular communication. Researchers have been trying to engineer exosomes for therapeutic purposes by using different approaches to deliver biologically active molecules to the various target cells efficiently. Recent technological advances may allow the biodistribution and pharmacokinetics of exosomes to be modified to meet scientific needs with respect to specific diseases. However, it is essential to determine an exosome's optimal dosage and potential side effects before its clinical use. Significant breakthroughs have been made in recent decades concerning exosome labelling and imaging techniques. These tools provide in situ monitoring of exosome biodistribution and pharmacokinetics and pinpoint targetability. However, because exosomes are nanometres in size and vary significantly in contents, a deeper understanding is required to ensure accurate monitoring before they can be applied in clinical settings. Different research groups have established different approaches to elucidate the roles of exosomes and visualize their spatial properties. This review covers current and emerging strategies for in vivo and in vitro exosome imaging and tracking for potential studies.

Molecular imaging-guided extracellular vesicle-based drug delivery for precise cancer management: Current status and future perspectives

Extracellular vesicles (EVs), the mediators of intercellular communication, have attracted the attention of researchers for the important roles they play in cancer treatment. Compared with other inorganic nano-materials, EVs possess the advantages of higher biocompatibility, better physiochemical stability, easier surface modification, and excellent biosafety. They can be used as an advanced drug delivery system with an improved therapeutic index for various therapeutic agents. Engineered EV-based imaging and therapeutic agents (engineered EVs) have emerged as useful tools in targeted cancer diagnosis and therapy. Non-invasive tracing of engineered EVs contributes to a better evaluation of their functions in cancer progression, in vivo dynamic biodistribution, therapeutic response, and drug-loading efficiency. Recent advances in real-time molecular imaging (MI), and innovative EV labeling strategies have led to the development of novel tools that can evaluate the pharmacokinetics of engineered EVs in cancer management, which may accelerate further clinical translation of novel EV-based drug delivery platforms. Herein, we review the latest advances in EVs, their characteristics, and current examples of EV-based targeted drug delivery for cancer. Then, we discuss the prominent applications of MI for tracing both natural and engineered EVs. Finally, we discuss the current challenges and considerations of EVs in targeted cancer treatment and the limitations of different MI modalities. In the coming decades, EV-based therapeutic applications for cancer with improved drug loading and targeting abilities will be developed, and better anti-cancer effects of drug delivery nanoplatform will be achieved.

Extracellular Vesicles in Hepatobiliary Health and Disease

Extracellular vesicles (EVs) are membrane-bound nanoparticles released by cells and are an important means of intercellular communication in physiological and pathological states. We provide an overview of recent advances in the understanding of EV biogenesis, cargo selection, recipient cell effects, and key considerations in isolation and characterization techniques. Studies on the physiological role of EVs have relied on cell-based model systems due to technical limitations of studying endogenous nanoparticles in vivo . Several recent studies have elucidated the mechanistic role of EVs in liver diseases, including nonalcoholic fatty liver disease, viral hepatitis, cholestatic liver disease, alcohol-associated liver disease, acute liver injury, and liver cancers. Employing disease models and human samples, the biogenesis of lipotoxic EVs downstream of endoplasmic reticulum stress and microvesicles via intracellular activation stress signaling are discussed in detail. The diverse cargoes of EVs including proteins, lipids, and nucleic acids can be enriched in a disease-specific manner. By carrying diverse cargo, EVs can directly confer pathogenic potential, for example, recruitment and activation of monocyte-derived macrophages in NASH and tumorigenicity and chemoresistance in hepatocellular carcinoma. We discuss the pathogenic role of EVs cargoes and the signaling pathways activated by EVs in recipient cells. We review the literature that EVs can serve as biomarkers in hepatobiliary diseases. Further, we describe novel approaches to engineer EVs to deliver regulatory signals to specific cell types, and thus use them as therapeutic shuttles in liver diseases. Lastly, we identify key lacunae and future directions in this promising field of discovery and development. © 2023 American Physiological Society. Compr Physiol 13:4631-4658, 2023.

Extracellular Vesicles and Intercellular Communication: Challenges for In Vivo Molecular Imaging and Tracking

Extracellular vesicles (EVs) are a heterogeneous class of cell-derived membrane vesicles released by various cell types that serve as mediators of intercellular signaling. When released into circulation, EVs may convey their cargo and serve as intermediaries for intracellular communication, reaching nearby cells and possibly also distant organs. In cardiovascular biology, EVs released by activated or apoptotic endothelial cells (EC-EVs) disseminate biological information at short and long distances, contributing to the development and progression of cardiovascular disease and related disorders. The significance of EC-EVs as mediators of cell-cell communication has advanced, but a thorough knowledge of the role that intercommunication plays in healthy and vascular disease is still lacking. Most data on EVs derive from in vitro studies, but there are still little reliable data available on biodistribution and specific homing EVs in vivo tissues. Molecular imaging techniques for EVs are crucial to monitoring in vivo biodistribution and the homing of EVs and their communication networks both in basal and pathological circumstances. This narrative review provides an overview of EC-EVs, trying to highlight their role as messengers of cell-cell interaction in vascular homeostasis and disease, and describes emerging applications of various imaging modalities for EVs visualization in vivo.

Protein corona and exosomes: new challenges and prospects

Recent advances in extracellular vesicle (EVs) detection and isolation methods have led to the development of novel therapeutic modalities. Among different types of EVs, exosomes (Exos) can transfer different signaling biomolecules and exhibit several superior features compared to whole-cell-based therapies. Therapeutic factors are normally loaded into the Exo lumen or attached to their surface for improving the on-target delivery rate and regenerative outcomes. Despite these advantages, there are several limitations in the application of Exos in in vivo conditions. It was suggested that a set of proteins and other biological compounds are adsorbed around Exos in aqueous phases and constitute an external layer named protein corona (PC). Studies have shown that PC can affect the physicochemical properties of synthetic and natural nanoparticles (NPs) after introduction in biofluids. Likewise, PC is generated around EVs, especially Exos in in vivo conditions. This review article is a preliminary attempt to address the interfering effects of PC on Exo bioactivity and therapeutic effects. Video Abstract.

Osteosarcoma-Derived Exosomes as Potential PET Imaging Nanocarriers for Lung Metastasis

Lung metastases represent the most adverse clinical factor and rank as the leading cause of osteosarcoma-related death. Nearly 80% of patients present lung micrometastasis at diagnosis not detected with current clinical tools. Herein, an exosome (EX)-based imaging tool is developed for lung micrometastasis by positron emission tomography (PET) using osteosarcoma-derived EXs as natural nanocarriers of the positron-emitter copper-64 (⁶⁴ Cu). Exosomes are isolated from metastatic osteosarcoma cells and functionalized with the macrocyclic chelator NODAGA for complexation with ⁶⁴ Cu. Surface functionalization has no effect on the physicochemical properties of EXs, or affinity for donor cells and endows them with favorable pharmacokinetics for in vivo studies. Whole-body PET/magnetic resonance imaging (MRI) images in xenografted models show a specific accumulation of ⁶⁴ Cu-NODAGA-EXs in metastatic lesions as small as 2-3 mm or in a primary tumor, demonstrating the exquisite tropism of EXs for homotypic donor cells. The targetability for lung metastasis is also observed by optical imaging using indocyanine green (ICG)-labeled EXs and D-luciferin-loaded EXs. These findings show that tumor-derived EXs hold great potential as targeted imaging agents for the noninvasive detection of small lung metastasis by PET. This represents a step forward in the biomedical application of EXs in imaging diagnosis with increased translational potential.

Bio-distribution and longevity of mesenchymal stromal cell derived membrane particles

Vesicle-based medicines hold great promise for therapy development but essential knowledge on the bio-distribution and longevity of vesicles after administration is lacking. We generated vesicles from the membranes of human mesenchymal stromal cells (MSC) and we demonstrated earlier that these so-called membrane particles (MP) mediate immunomodulatory and regenerative responses in target cells. In the present study we examined the bio-distribution and longevity of MP after intravenous administration in mice. While most vesicle tracking methods are based on imaging techniques, which require labeling of vesicles and can only detect dense accumulations of vesicles, we used proteomics analysis to detect the presence of MP-derived proteins in multiple organs and tissues. MP proteins were mainly present in plasma and leukocytes at 1 h after injection, indicating that MP - in contrast to whole MSC - do not accumulate in the lungs upon first passage but remain in circulation. After 24 h, MP proteins were still present in plasma but were most abundant in the liver. RNA sequencing of livers demonstrated that MP impact liver function and in particular induce metabolic pathways. These data provide a clear view of the bio-distribution and longevity of MP, which is likely extrapolatable to other types of vesicles, and demonstrate that MP circulate for up to 24 h and may be a tool for targeting the liver.

In Vivo Imaging for the Visualization of Extracellular Vesicle-Based Tumor Therapy

Extracellular vesicles (EVs) exhibiting versatile biological functions provide promising prospects as natural therapeutic agents and drug delivery vehicles. For future clinical translation, revealing the fate of EVs in vivo, especially their accumulation at lesion sites, is very important. The continuous development of in vivo imaging technology has made it possible to track the real‐time distribution of EVs. This article reviews the applications of mammal‐, plant‐, and bacteria‐derived EVs in tumor therapy, the labeling methods of EVs for in vivo imaging, the advantages and disadvantages of different imaging techniques, and possible improvements for future work.

PAI/MRI Visualization of Tumor Derived Cellular Microvesicles with Endogenous Biopolymer Nanoparticles Modification

Background

Tumor derived cellular microvesicles (TDMVs), as excellent drug delivery vehicles in vivo, play an important role in the treatment of cancers. However, it is difficult to obtain intuitional biodistribution behavior and internalization mechanisms of TDMVs in vivo. Thus, it is very urgent and important to establish a stable and reliable visualization technology to track the biological behavior and function of TDMVs. As an endogenous biopolymer, melanin possesses natural biocompatibility and biodegradability, and various biological imaging could be realized by modifying it. Therefore, melanin-based nanoparticles are excellent candidates for in vivo visualization of TDMVs.

Methods

In this work, the biodistribution and metabolic behavior of TDMVs were visualized by dual-modality imaging with PAI and MRI after incubation with gadolinium ion-chelated melanin nanoparticles.

Results

In this study, MRI and PAI dual-modality imaging of the in vivo distribution behavior of TDMVs was achieved with the help of MNP-Gd. The good targeting ability of TDMVs at the homologous tumor site was observed, and their distribution and metabolism behavior in the whole body were studied at the meantime. The results indicated that TDMVs preferentially accumulated in syngeneic tumor sites and liver regions after intravenous injection and were eventually metabolized by the kidneys over time.

Conclusion

This work proposed a novel dual-modal imaging strategy for the visualization of TDMVs, which is of great significance for further understanding the biological mechanisms of extracellular vesicles.

Non-Invasive imaging of extracellular vesicles: Quo vaditis in vivo?

Extracellular vesicles (EVs) are lipid-bilayer delimited vesicles released by nearly all cell types that serve as mediators of intercellular signalling. Recent evidence has shown that EVs play a key role in many normal as well as pathological cellular processes. EVs can be exploited as disease biomarkers and also as targeted, cell-free therapeutic delivery and signalling vehicles for use in regenerative medicine and other clinical settings. Despite this potential, much remains unknown about the in vivo biodistribution and pharmacokinetic profiles of EVs after administration into living subjects. The ability to non-invasively image exogeneous EVs, especially in larger animals, will allow a better understanding of their in vivo homing and retention patterns, blood and tissue half-life, and excretion pathways, all of which are needed to advance clinical diagnostic and/or therapeutic applications of EVs. We present the current state-of-the-art methods for labeling EVs with various diagnostic contrast agents and tracers and the respective imaging modalities that can be used for their in vivo visualization: magnetic resonance imaging (MRI), X-ray computed tomography (CT) imaging, magnetic particle imaging (MPI), single-photon emission computed tomography (SPECT), positron emission tomography (PET), and optical imaging (fluorescence and bioluminescence imaging). We review here the strengths and weaknesses of each of these EV imaging approaches, with special emphasis on clinical translation.

Quantitative Biodistribution and Pharmacokinetics Study of GMP-Grade Exosomes Labeled with 89Zr Radioisotope in Mice and Rats

For the successful clinical advancement of exosome therapeutics, the biodistribution and pharmacokinetic profile of exogenous exosomes in various animal models must be determined. Compared with fluorescence or bioluminescence imaging, radionuclide imaging confers multiple advantages for the in vivo tracking of biomolecular therapeutics because of its excellent sensitivity for deep tissue imaging and potential for quantitative measurement. Herein, we assessed the quantitative biodistribution and pharmacokinetics of good manufacturing practice-grade therapeutic exosomes labeled with zirconium-89 (⁸⁹Zr) after systemic intravenous administration in mice and rats. Quantitative biodistribution analysis by positron emission tomography/computed tomography and gamma counting in mice and rats revealed that the total ⁸⁹Zr signals in the organs were lower in rats than in mice, suggesting a higher excretion rate of exosomes in rats. A prolonged ⁸⁹Zr signal for up to 7 days in most organs indicated that substantial amounts of exosomes were taken up by the parenchymal cells in those organs, highlighting the therapeutic potential of exosomes for the intracellular delivery of therapeutics. Exosomes were mainly distributed in the liver and to a lesser extent in the spleen, while a moderately distributed in the kidney, lung, stomach, intestine, urinary bladder, brain, and heart. Exosomes were rapidly cleared from the blood circulation, with a rate greater than that of free ⁸⁹Zr, indicating that exosomes might be rapidly taken up by cells and tissues.

In vivo visualization of murine melanoma cells B16-derived exosomes through magnetic resonance imaging

BACKGROUND

Numerous studies demonstrated that exosomes play a powerful role in mediating intercellular communication to induce a pro-tumoral environment to promote tumor progression, including pre-metastatic niche formation and metastasis. Noninvasive imaging could determine the in vivo kinetics of exosomes in real time to provide better understanding of the mechanisms of the tumor formation, progression and metastasis. Magnetic resonance imaging (MRI) is an ideal technique which provides excellent anatomical resolution, intrinsic soft tissue contrast, unlimited penetration depth and no radiation exposure.

METHODS

A fusion protein composed of ferritin heavy chain (FTH1) and lactadherin was designed for visualizing exosomes through MRI. FTH1 was served as MRI reporter protein and lactadherin is a membrane-associated protein that is distributed on exosome surface. The characterizations of labeled exosomes were validated through transmission electron microscopy, western blot, nanoparticle tracking analysis and finally visualized in vitro and in vivo through MRI.

RESULTS

MR imaging showed that the labeled exosomes are able to be visualized in vitro and in vivo. Verification of the characterizations of exosomes observed no significant difference between labeled and unlabeled exosomes.

CONCLUSION

The proposed FTH1 labeling method was useful for visualizing exosomes through MRI.

GENERAL SIGNIFICANCE

The present study first reported a novel self-label method for imaging labeled exosomes of tumor cells in vivo through MR with cell endogenous MRI reporter protein. It may be further used as a tool to enhance understanding the role of exosomes in various pathophysiological conditions.

Extracellular vesicles in pharmacology: Novel approaches in diagnostics and therapy

Exosomes are nano-sized lipid vesicles that are produced by all eukaryotic cells, and they typically range in size from 30 to 150 nm. Exosomes were discovered almost 40 years ago; however, the last two decades have attracted considerable attention due to exosomes' inherent abilities to shuttle nucleic acids, lipids and proteins between cells, along with their natural affinity to exosome target cells. From a pharmaceutical perspective, exosomes are regarded as naturally produced nanoparticle drug delivery vehicles. The application of exosomes as a means of drug delivery offers critical advantages compared to other nanoparticulate drug delivery systems, such as liposomes and polymeric nanoparticles. These advantages are due to the exosomes' intrinsic features, such as low immunogenicity, biocompatibility, stability, and their ability to overcome biological barriers. Herein, we outline the structure and origin of exosomes, as well as their biological functions. We also touch upon recent advances in exosome labeling, imaging and drug loading. Finally, we discuss exosomes in targeted drug delivery and clinical trial development.

Exosomes derived from olfactory ensheathing cells provided neuroprotection for spinal cord injury by switching the phenotype of macrophages/microglia

Transplantation of olfactory ensheathing cells (OECs) has been demonstrated to be beneficial for spinal cord injury (SCI) by modulating neuroinflammation, supporting neuronal survival and promoting angiogenesis. Besides OECs, the conditioned medium (CM) from OECs has also been proved to have therapeutic effects for SCI, indicating that the bioactive substances secreted by OECs are essential for its protective effects. Nevertheless, there is still little information regarding the underlying mechanisms. Considering that exosomes are crucial for intercellular communication and could be secreted by different types of cells, we speculated that the therapeutic potential of OECs for SCI might be partially based on their exosomes. To examine whether OECs could secret exosomes, we isolated exosomes by polyethylene glycol‐based method, and identified them by electron microscopy study, nanoparticle tracking analysis (NTA) and western blotting. In view of phagocytic ability of microglia and its distinct roles in microenvironment regulation after SCI, we then focused the effects of OECs‐derived exosomes (OECs‐Exo) on microglial phenotypic regulation. We found that the extracted OECs‐Exo could be engulfed by microglia and partially reverse the LPS‐induced pro‐inflammatory polarization through inhibiting NF‐κB and c‐Jun signaling pathways in vitro. Furthermore, OECs‐Exo were found to inhibit the polarization of pro‐inflammatory macrophages/microglia while increased the numbers of anti‐inflammatory cells after SCI. Considering that the neuronal injury is closely related to the activation state of macrophages/microglia, co‐culture of microglia and neurons were performed. Neuronal death induced by LPS‐treated microglia could be significantly alleviated when microglia treated by LPS plus OECs‐Exo in vitro. After SCI, NeuN‐immunostaining and axonal tract‐tracing were performed to assess neuronal survival and axon preservation. Our data showed that the OECs‐Exo promoted the neuronal survival and axon preservation, and facilitated functional recovery after SCI. Our findings provide a promising therapeutic strategy for SCI based on exosome‐immunomodulation.

[In vivo imaging: An essential tool to better understand the biology of extracellular vesicles]

Extracellular vesicles are involved in an increasing number of physiopathological processes and represent promising clinical tools for the diagnosis and treatment of various diseases. Their small size has long hindered in situ studies, which has limited their in vivo characterization and clinical use. Imaging approaches now allow the monitoring of extracellular vesicles in different animal models, in real time and at the single vesicle scale. The zebrafish appears in particular to be a relevant model organism to explore the biology of extracellular vesicles in vivo and to evaluate their therapeutic potential in preclinical studies.

Extracellular Vesicles Protect the Neonatal Lung from Hyperoxic Injury through the Epigenetic and Transcriptomic Reprogramming of Myeloid Cells

Rationale: Mesenchymal stem/stromal cell (MSC)-small extracellular vesicle (MEx) treatment has shown promise in experimental models of neonatal lung injury. The molecular mechanisms by which MEx afford beneficial effects remain incompletely understood. Objectives: To investigate the therapeutic mechanism of action through assessment of MEx biodistribution and impact on immune cell phenotypic heterogeneity. Methods: MEx were isolated from the conditioned medium of human umbilical cord Wharton's jelly-derived MSCs. Newborn mice were exposed to hyperoxia (HYRX, 75% O2) from birth and returned to room air at Postnatal Day 14 (PN14). Mice received either a bolus intravenous MEx dose at PN4 or bone marrow-derived myeloid cells (BMDMy) pretreated with MEx. Animals were killed at PN4, PN7, PN14, or PN28 to characterize MEx biodistribution or for assessment of pulmonary parameters. The therapeutic role of MEx-educated BMDMy was determined in vitro and in vivo. Measurements and Main Results: MEx therapy ameliorated core histological features of HYRX-induced neonatal lung injury. Biodistribution and mass cytometry studies demonstrated that MEx localize in the lung and interact with myeloid cells. MEx restored the apportion of alveolar macrophages in the HYRX-injured lung and concomitantly suppressed inflammatory cytokine production. In vitro and ex vivo studies revealed that MEx promoted an immunosuppressive BMDMy phenotype. Functional assays demonstrated that the immunosuppressive actions of BMDMy are driven by phenotypically and epigenetically reprogrammed monocytes. Adoptive transfer of MEx-educated BMDMy, but not naive BMDMy, restored alveolar architecture, blunted fibrosis and pulmonary vascular remodeling, and improved exercise capacity. Conclusions: MEx ameliorate hyperoxia-induced neonatal lung injury though epigenetic and phenotypic reprogramming of myeloid cells.

Current theranostic approaches for metastatic cancers through hypoxia-induced exosomal packaged cargo

Tumour cells exhibit numerous defence mechanisms against various therapeutic strategies and help in developing drug resistance. These defence strategies help cancer cells prevent their elimination from an organism and prosper at a specific location. In recent times it's been observed that there is a significant contribution of secreted extracellular vesicles (EVs) from such tumorigenic sites in the development and prognosis of cancer. Amongst the various types of EVs, exosomes behave like biological carriers, play a crucial role in transporting the content between different cells, and had such an underrated defence mode by getting induced due to the hypoxia secreted highly specialised double-membrane structures. These small structure vesicles play a critical part in regulating local microenvironment and intracellular communications, cited by many research studies. Exosomes are a potential carrier of several cargo biomolecules like proteins, lipids, miRNAs, mRNAs etc., facilitating better communication within the microenvironment of cancer cells, enhancing the metastatic rate along with cancer progression. Several studies have extensively researched elucidating exosomes mediated radiation-induced bystander effects: multidrug resistance, epithelial-mesenchymal transition, and help cancer cells escape from the immune system apart from playing a critical role in angiogenesis too. Due to its natural tendency to carry different biomolecules, it can also be used to haul chemical drugs and efficiently deliver the drug molecules to the targeted site of cancer. The current review aims to explore the vivid role of hypoxia-induced exosomes in tumour progression along with its application and challenges in cancer therapeutics.

Extracellular vesicles as a new hope for diagnosis and therapeutic intervention for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer with a high mortality rate. Early diagnosis and treatment before tumor progression into an advanced stage is ideal. The current diagnosis of HCC is mainly based on imaging modalities such as ultrasound, computed tomography, and magnetic resonance imaging. These methods have some limitations including diagnosis in the case of very small tumors with atypical imaging patterns. Extracellular vesicles (EVs) are nanosized vesicles which have been shown to act as an important vector for cell-to-cell communication. In the past decade, EVs have been investigated with regard to their roles in HCC formation. Since these EVs contain biomolecular cargo such as nucleic acid, lipids, and proteins, it has been proposed that they could be a potential source of tumor biomarkers and a vector for therapeutic cargo. In this review, reports on the roles of HCC-derived EVs in tumorigenesis, and clinical investigations using circulating EVs as a biomarker for HCC and their potential diagnostic roles have been comprehensively summarized and discussed. In addition, findings from in vitro and in vivo reports investigating the potential roles of EVs as therapeutic interventions are also presented. These findings regarding the potential benefits of EVs will encourage further investigations and may allow us to devise novel strategies using EVs in the early diagnosis as well as for treatment of HCC in the future.

Cancer Patient Tissueoid with Self-Homing Nano-Targeting of Metabolic Inhibitor

The current paradigm of cancer medicine focuses on patient- and/or cancer-specific treatments, which has led to continuous progress in the development of patient representatives (e.g., organoids) and cancer-targeting carriers for drug screening. As breakthrough concepts, i) living cancer tissues convey intact profiles of patient-specific microenvironmental signatures. ii) The growth mechanisms of cancer mass with intense cell-cell interactions can be harnessed to develop self-homing nano-targeting by using cancer cell-derived nanovesicles (CaNVs). Hence, a tissueoid model of ovarian cancer (OC) is developed by culturing OC patient tissues in a 3D gel chip, whose microchannel networks enable perfusion to maintain tissue viability. A novel model of systemic cancer responses is approached by xenografting OC tissueoids into ischaemic hindlimbs in nude mice. CaNVs are produced to carry general chemotherapeutics or new drugs under pre/clinical studies that target the BRCA mutation or energy metabolism, thereby increasing the test scope. This pioneer study cross-validates drug responses from the OC clinic, tissueoid, and animal model by demonstrating the alignment of results in drug type-specific efficiency, BRCA mutation-dependent drug efficiency, and metabolism inhibition-based anti-cancer effects. Hence, this study provides a directional foundation to accelerate the discovery of patient-specific drugs with CaNV application towards future precision medicine.

Bacterial Extracellular Vesicles in Gastrointestinal Tract Cancer: An Unexplored Territory

Bacterial extracellular vesicles are membrane-enclosed, lipid bi-layer nanostructures that carry different classes of biomolecules, such as nucleic acids, lipids, proteins, and diverse types of small molecular metabolites, as their cargo. Almost all of the bacteria in the gut secrete extracellular vesicles to assist them in competition, survival, material exchange, host immune modulation, infection, and invasion. The role of gut microbiota in the development, progression, and pathogenesis of gastrointestinal tract (GIT) cancer has been well documented. However, the possible involvement of bacterial extracellular vesicles (bEVs) in GIT cancer pathophysiology has not been given due attention. Studies have illustrated the ability of bEVs to cross physiological barriers, selectively accumulate near tumor cells, and possibly alter the tumor microenvironment (TME). A systematic search of original published works related to bacterial extracellular vesicles on gastrointestinal cancer was performed for this review. The current systemic review outlines the possible impact of gut microbiota derived bEVs in GIT cancer in light of present-day understanding. The necessity of using advanced sequencing technologies, such as genetic, proteomic, and metabolomic investigation methodologies, to facilitate an understanding of the interrelationship between cancer-associated bacterial vesicles and gastrointestinal cancer is also emphasized. We further discuss the clinical and pharmaceutical potential of bEVs, along with future efforts needed to understand the mechanism of interaction of bEVs in GIT cancer pathogenesis.

SnRNA sequencing defines signaling by RBC-derived extracellular vesicles in the murine heart

In a unique model of fluorescent based mapping of EV recipient cells, RBC-EVs were found to signal to cardiac cells and regulate gene expression in a model of ischemic heart failure.

Extracellular vesicles (EVs) mediate intercellular signaling by transferring their cargo to recipient cells, but the functional consequences of signaling are not fully appreciated. RBC-derived EVs are abundant in circulation and have been implicated in regulating immune responses. Here, we use a transgenic mouse model for fluorescence-based mapping of RBC-EV recipient cells to assess the role of this intercellular signaling mechanism in heart disease. Using fluorescent-based mapping, we detected an increase in RBC-EV–targeted cardiomyocytes in a murine model of ischemic heart failure. Single cell nuclear RNA sequencing of the heart revealed a complex landscape of cardiac cells targeted by RBC-EVs, with enrichment of genes implicated in cell proliferation and stress signaling pathways compared with non-targeted cells. Correspondingly, cardiomyocytes targeted by RBC-EVs more frequently express cellular markers of DNA synthesis, suggesting the functional significance of EV-mediated signaling. In conclusion, our mouse model for mapping of EV-recipient cells reveals a complex cellular network of RBC-EV–mediated intercellular communication in ischemic heart failure and suggests a functional role for this mode of intercellular signaling.

Diagnostic and Therapeutic Potential of Extracellular Vesicles

Extracellular vesicles (EVs) are naturally phospholipid enclosed nanovesicles released by many cells in the body. They are stable in circulation, have low immunogenicity, and act as carriers for functionally active biological molecules. They interact with target organs and bind to the receptors. Their target specificity is important to use EVs as noninvasive diagnostic and prognostic tools. EVs play a vital role in normal physiology and cellular communication. They are known to protect their cargo from degradation, which makes them important drug carriers for targeted drug delivery. Using EVs with markers and tracking their path in systemic circulation can be revolutionary in using them as diagnostic tools. We will discuss the scope of this in this paper. Although there are limitations in EVs isolation and storage, their high biocompatibility will fuel more innovations to overcome these challenges.

Zebrafish as a preclinical model for Extracellular Vesicle-based therapeutic development

Extracellular Vesicles (EVs) are released during various pathophysiological processes and reflect the state of their cell of origin. Once released, they can propagate through biological fluids, target cells, deliver their content and elicit functional responses. These specific features would allow their harnessing as biomarkers, drug nano-vehicles and therapeutic intrinsic modulators. However, the further development of their potential therapeutic application is hampered by the lack of knowledge about how EVs behave in vivo. Recent advances in the field of imaging EVs in vivo now allow live-tracking of endogenous and exogenous EV in various model organisms at high spatiotemporal resolution to define their distribution, half-life and fate. This review highlights current imaging tools available to image EVs in vivo and how live imaging especially in the zebrafish embryo can bring further insights into the characterization of EVs dynamics, biodistribution and functions to potentiate their development for therapeutic applications.

Engineered exosomes: desirable target-tracking characteristics for cerebrovascular and neurodegenerative disease therapies

As extracellular vesicles secreted by cells, exosomes are intercellular signalosomes for cell communication and pharmacological effectors. Because of their special properties, including low toxicity and immunogenicity, biodegradability, ability to encapsulate endogenous biologically active molecules and cross the blood-brain barrier (BBB), exosomes have great therapeutic potential in cerebrovascular and neurodegenerative diseases. However, the poor targeting ability of natural exosomes greatly reduces the therapeutic effect. Using engineering technology, exosomes can obtain active targeting ability to accumulate in specific cell types and tissues by attaching targeting units to the membrane surface or loading them into cavities. In this review, we outline the improved targeting functions of bioengineered exosomes, tracing and imaging techniques, administration methods, internalization in the BBB, and therapeutic effects of exosomes in cerebrovascular and neurodegenerative diseases and further evaluate the clinical opportunities and challenges in this research field.

Extracellular vesicles as a drug delivery system: A systematic review of preclinical studies

During the past decades, extracellular vesicles (EVs) have emerged as an attractive drug delivery system. Here, we assess their pre-clinical applications, in the form of a systematic review. For each study published in the past decade, disease models, animal species, EV donor cell types, active pharmaceutical ingredients (APIs), EV surface modifications, API loading methods, EV size and charge, estimation of EV purity, presence of biodistribution studies and administration routes were quantitatively analyzed in a defined and reproducible way. We have interpreted the trends we observe over the past decade, to define the niches where to apply EVs for drug delivery in the future and to provide a basis for regulatory guidelines.

Profiling of Extracellular Small RNAs Highlights a Strong Bias towards Non-Vesicular Secretion

The extracellular environment consists of a plethora of molecules, including extracellular miRNA that can be secreted in association with extracellular vesicles (EVs) or soluble protein complexes (non-EVs). Yet, interest in therapeutic short RNA carriers lies mainly in EVs, the vehicles conveying the great majority of the biological activity. Here, by overexpressing miRNA and shRNA sequences in parent cells and using size exclusion liquid chromatography (SEC) to separate the secretome into EV and non-EV fractions, we saw that >98% of overexpressed miRNA was secreted within the non-EV fraction. Furthermore, small RNA sequencing studies of native miRNA transcripts revealed that although the abundance of miRNAs in EVs, non-EVs and parent cells correlated well (R2 = 0.69-0.87), quantitatively an outstanding 96.2-99.9% of total miRNA was secreted in the non-EV fraction. Nevertheless, though EVs contained only a fraction of secreted miRNAs, these molecules were stable at 37 °C in a serum-containing environment, indicating that if sufficient miRNA loading is achieved, EVs can remain delivery-competent for a prolonged period of time. This study suggests that the passive endogenous EV loading strategy might be a relatively wasteful way of loading miRNA to EVs, and active miRNA loading approaches are needed for developing advanced EV miRNA therapies in the future.

Using single-vesicle technologies to unravel the heterogeneity of extracellular vesicles

Extracellular vesicles (EVs) are heterogeneous lipid containers with a complex molecular cargo comprising several populations with unique roles in biological processes. These vesicles are closely associated with specific physiological features, which makes them invaluable in the detection and monitoring of various diseases. EVs play a key role in pathophysiological processes by actively triggering genetic or metabolic responses. However, the heterogeneity of their structure and composition hinders their application in medical diagnosis and therapies. This diversity makes it difficult to establish their exact physiological roles, and the functions and composition of different EV (sub)populations. Ensemble averaging approaches currently employed for EV characterization, such as western blotting or 'omics' technologies, tend to obscure rather than reveal these heterogeneities. Recent developments in single-vesicle analysis have made it possible to overcome these limitations and have facilitated the development of practical clinical applications. In this review, we discuss the benefits and challenges inherent to the current methods for the analysis of single vesicles and review the contribution of these approaches to the understanding of EV biology. We describe the contributions of these recent technological advances to the characterization and phenotyping of EVs, examination of the role of EVs in cell-to-cell communication pathways and the identification and validation of EVs as disease biomarkers. Finally, we discuss the potential of innovative single-vesicle imaging and analysis methodologies using microfluidic devices, which promise to deliver rapid and effective basic and practical applications for minimally invasive prognosis systems.

Potential Use of Exosomes as Diagnostic Biomarkers and in Targeted Drug Delivery: Progress in Clinical and Preclinical Applications

Exosomes are cell-derived vesicles containing heterogeneous active biomolecules such as proteins, lipids, mRNAs, receptors, immune regulatory molecules, and nucleic acids. They typically range in size from 30 to 150 nm in diameter. An exosome's surfaces can be bioengineered with antibodies, fluorescent dye, peptides, and tailored for small molecule and large active biologics. Exosomes have enormous potential as a drug delivery vehicle due to enhanced biocompatibility, excellent payload capability, and reduced immunogenicity compared to alternative polymeric-based carriers. Because of active targeting and specificity, exosomes are capable of delivering their cargo to exosome-recipient cells. Additionally, exosomes can potentially act as early stage disease diagnostic tools as the exosome carries various protein biomarkers associated with a specific disease. In this review, we summarize recent progress on exosome composition, biological characterization, and isolation techniques. Finally, we outline the exosome's clinical applications and preclinical advancement to provide an outlook on the importance of exosomes for use in targeted drug delivery, biomarker study, and vaccine development.

Prognostic and Predictive Biomarkers in Non-Small Cell Lung Cancer Patients on Immunotherapy-The Role of Liquid Biopsy in Unraveling the Puzzle

In the last decade, immunotherapy has been one of the most important advances in the non-small cell lung cancer (NSCLC) treatment landscape. Nevertheless, only a subset of NSCLC patients benefits from it. Currently, the only Food and Drug Administration (FDA) approved diagnostic test for first-line immunotherapy in metastatic NSCLC patients uses tissue biopsies to determine the programmed death ligand 1 (PD-L1) status. However, obtaining tumor tissue is not always feasible and puts the patient at risk. Liquid biopsy, which refers to the tumor-derived material present in body fluids, offers an alternative approach. This less invasive technique gives real-time information on the tumor characteristics. This review addresses different promising liquid biopsy based biomarkers in NSCLC patients that enable the selection of patients who benefit from immunotherapy and the monitoring of patients during this therapy. The challenges and the opportunities of blood-based biomarkers such as cell-free DNA (cfDNA), circulating tumor cells (CTCs), exosomes, epigenetic signatures, microRNAs (miRNAs) and the T cell repertoire will be addressed. This review also focuses on the less-studied feces-based and breath-based biomarkers.

High content, quantitative AFM analysis of the scalable biomechanical properties of extracellular vesicles

Extracellular vesicles (EVs) are studied extensively as natural biomolecular shuttles and for their diagnostic and therapeutic potential. This exponential rise in interest has highlighted the need for highly robust and reproducible approaches for EV characterisation. Here we optimise quantitative nanomechanical tools and demonstrate the advantages of EV population screening by atomic force microscopy (AFM). Our high-content informatics analytical tools are made available for use by the EV community for widespread, standardised determination of structural stability. Ultracentrifugation (UC) and sonication, the common mechanical techniques used for EV isolation and loading respectively, are used to demonstrate the utility of optimised PeakForce-Quantitative Nano Mechanics (PF-QNM) analysis. EVs produced at an industrial scale exhibited biochemical and biomechanical alterations after exposure to these common techniques. UC resulted in slight increases in physical dimensions, and decreased EV adhesion concurrent with a decrease in CD63 content. Sonicated EVs exhibited significantly reduced levels of CD81, a decrease in size, increased Young's modulus and decreased adhesive force. These biomechanical and biochemical changes highlight the effect of EV sample preparation techniques on critical properties linked to EV cellular uptake and biological function. PF-QNM offers significant additional information about the structural information of EVs following their purification and downstream processing, and the analytical tools will ensure consistency of analysis of AFM data by the EV community, as this technique continues to become more widely implemented.

Radiolabeled HER2-directed exosomes exhibit improved cell targeting and specificity

Aim: Here, we established a reliable strategy for generation and characterization of targeted radiolabeled exosomes for the detection of HER2-positive cells quantitatively. Materials & methods: Targeted exosomes (T-exos) were radiolabeled by two different radiotracers, [^99mTc]Tc-HMPAO or [¹¹¹In]In-oxine. The labeling efficiency and stability were assessed using exosome exclusive spin columns. HER2-positive and -negative cells were treated with [¹¹¹In]In-oxine-exosomes after 3 and 24 h. Results: [¹¹¹In]In-oxine labeling did not change the binding ability and general features of the exosomes. With [¹¹¹In]In-oxine, 70% labeling efficiency and 78% radiochemical stability over 24 h were achieved. [¹¹¹In]In-oxine-T-exos showed greater uptake by HER2-positive cells compared with untargeted exosomes. Conclusion: [¹¹¹In]In-oxine-T-exos could potentially be used as an effective imaging tool for HER2 expression.

Radioiodine labeling and in vivo trafficking of extracellular vesicles

Biodistribution and role of extracellular vesicles (EVs) are still largely unknown. Reliable tracking methods for EVs are needed. In this study, nuclear imaging using radioiodine were developed and applied for tracking EVs derived from cell lines. EVs were obtained from supernatant of thyroid cancer cell (Cal62) and natural killer cells (NK92-MI) using sequential ultracentrifuges. Sulfosuccinimidyl-3-(4-hydroxypheynyl) propionate were labeled to membrane of Cal62 and NK92-MI cell derived EVs, then the EVs were labeled with radioiodine (I-131 and I-125) using pre-coated iodination tubes (RI-EVs). In vivo gamma camera images were obtained after intravenous injection of the RI-EVs, and ex vivo biodistribution study was also performed. EVs were labeled with radioiodine and radiochemical purity of the RI-EV was more than 98%. Results of nanoparticle tracking analysis and electron microscopy showed that there was no significant difference in EVs before and after the radioiodine labeling. After intravenous injection of RI-EVs to mice, gamma camera imaging well visualized the real-time biodistribution of the RI-EVs. RI-EVs were mainly visualized at liver, spleen, and lung. Nuclear imaging system of EVs derived from thyroid cancer and NK cells using radioiodine labeling of the EVs was established. Thus, this system might be helpful for in vivo tracking of EVs.

Human fibroblast-derived extracellular vesicles promote hair growth in cultured human hair follicles

Hair loss is a prevalent medical condition affecting both genders. In this study, we investigate the effects of a specific class of extracellular vesicles (EVs), namely human normal fibroblast-derived EVs (hFB-EVs), on human dermal papilla (DP) and outer root sheath (ORS) cells and examine the molecular mechanisms responsible for hair growth in hair follicles (HFs). We find that Wnt3a, which maintains the hair-generating activity of DP cells, is enriched and more strongly associated with hFB-EVs than with fibroblasts. Furthermore, hFB-EV-associated Wnt3a mediated receptor activation in cultured DP cells, leading to an increase in β-catenin in the cytoplasm and its translocation into the nucleus, thereby elevating expression of the target genes Axin2 and Lef1. Additionally, hFB-EVs promoted the migration, proliferation, and differentiation of ORS cells and elongation of the hair shaft in human HFs. These findings revealed a novel mechanism by which hFB-EVs influence hair growth.

New approaches in extracellular vesicle engineering for improving the efficacy of anti-cancer therapies

Cancer is a disease that evolves continuously with unpredictable outcomes. Although conventional chemotherapy can display significant antitumor effects, the lack of specificity and poor bioavailability remain major concerns in cancer therapy. Moreover, with the advent of novel anti-cancer gene therapies, there is an urgent need for drug delivery vectors capable of bypassing cellular barriers and efficiently transferring therapeutic cargo to recipient cells. A number of drug delivery systems have been proposed to overcome these limitations, but their successful clinical translation has been hampered by the onset of unexpected side effects and associated toxicities. The application of extracellular vesicles (EVs), a class of naturally released, cell-derived particles, as drug delivery vectors presents a breakthrough in nanomedicine, taking into account their biocompatibility and natural role in intercellular communication. Combining the advantageous intrinsic properties of EVs with surface functionalization and the encapsulation of drugs allows for a new class of engineered EVs that serve as effective therapeutic carriers. Here, we describe the various successful approaches involving the application of engineered EVs as bio-derived drug delivery vectors in cancer therapy. The latest and most effective strategies of engineering EVs to improve drug loading, stealth properties and tumour targeting capabilities of EVs are debated. Finally, current obstacles and future perspectives of smart engineered EVs are discussed.

'Golden' exosomes as delivery vehicles to target tumors and overcome intratumoral barriers: in vivo tracking in a model for head and neck cancer

Exosomes are promising vectors for anti-tumor therapy, due to their biocompatibility, low immunogenicity, and innate ability to interact with target cells. However, promoting clinical application of exosome-based therapeutics requires elucidation of key issues, including exosome biodistribution, tumor targeting and accumulation, and the ability to overcome tumor barriers that limit the penetration of various nano-carriers and drugs. Here, we examined these parameters in exosomes derived from mesenchymal stem cells (MSC-exo) and from the A431 squamous cell carcinoma line (A431-exo), which both have potential use in cancer therapy. Using our novel technique combining gold nanoparticle (GNP) labeling of exosomes and non-invasive computed tomography imaging (CT), we longitudinally and quantitatively tracked the two intravenously-injected exosome types in A431 tumor-bearing mice. CT imaging up to 48 h and subsequent ex vivo analysis revealed tumor homing abilities of both exosome types, yet there was significantly higher tumor accumulation of MSC-exo as compared to A431-exo. Moreover, MSC-exo demonstrated the ability to penetrate the tumor and distribute throughout its bulk, while non-encapsulated GNPs remained concentrated at the tumor periphery. Histological analysis showed penetration of MSC-exo not only into the tumor tissue, but also into tumor cell cytoplasm. While the proportion of biodistribution between organs at 48 h was similar for both exosome types, more rapid clearance was indicated for A431-exo. Thus, our findings demonstrate an effect of exosome type on tumor targeting abilities and biodistribution, and suggest that MSC-exo may have superior abilities for tumor-targeted therapy.

Therapeutic application of exosomes in ischaemic stroke

Ischaemic stroke is a leading cause of long-term disability in the world, with limited effective treatments. Increasing evidence demonstrates that exosomes are involved in ischaemic pathology and exhibit restorative therapeutic effects by mediating cell–cell communication. The potential of exosome therapy for ischaemic stroke has been actively investigated in the past decade. In this review, we mainly discuss the current knowledge of therapeutic applications of exosomes from different cell types, different exosomal administration routes, and current advances of exosome tracking and targeting in ischaemic stroke. We also briefly summarised the pathology of ischaemic stroke, exosome biogenesis, exosome profile changes after stroke as well as registered clinical trials of exosome-based therapy.

The use of hydrogel-delivered extracellular vesicles in recovery of motor function in stroke: a testable experimental hypothesis for clinical translation including behavioral and neuroimaging assessment approaches

Neural tissue engineering, nanotechnology and neuroregeneration are diverse biomedical disciplines that have been working together in recent decades to solve the complex problems linked to central nervous system (CNS) repair. It is known that the CNS demonstrates a very limited regenerative capacity because of a microenvironment that impedes effective regenerative processes, making development of CNS therapeutics challenging. Given the high prevalence of CNS conditions such as stroke that damage the brain and place a severe burden on afflicted individuals and on society, it is of utmost significance to explore the optimum methodologies for finding treatments that could be applied to humans for restoration of function to pre-injury levels. Extracellular vesicles (EVs), also known as exosomes, when derived from mesenchymal stem cells, are one of the most promising approaches that have been attempted thus far, as EVs deliver factors that stimulate recovery by acting at the nanoscale level on intercellular communication while avoiding the risks linked to stem cell transplantation. At the same time, advances in tissue engineering and regenerative medicine have offered the potential of using hydrogels as bio-scaffolds in order to provide the stroma required for neural repair to occur, as well as the release of biomolecules facilitating or inducing the reparative processes. This review introduces a novel experimental hypothesis regarding the benefits that could be offered if EVs were to be combined with biocompatible injectable hydrogels. The rationale behind this hypothesis is presented, analyzing how a hydrogel might prolong the retention of EVs and maximize the localized benefit to the brain. This sustained delivery of EVs would be coupled with essential guidance cues and structural support from the hydrogel until neural tissue remodeling and regeneration occur. Finally, the importance of including non-human primate models in the clinical translation pipeline, as well as the added benefit of multi-modal neuroimaging analysis to establish non-invasive, in vivo, quantifiable imaging-based biomarkers for CNS repair are discussed, aiming for more effective and safe clinical translation of such regenerative therapies to humans.

Delivery Efficacy Differences of Intravenous and Intraperitoneal Injection of Exosomes: Perspectives from Tracking Dye Labeled and MiRNA Encapsulated Exosomes

BACKGROUND

Exosomes are cell-derived nanovesicles that play vital roles in intercellular communication. Recently, exosomes are recognized as promising drug delivery vehicles. Up till now, how the in vivo distribution of exosomes is affected by different administration routes has not been fully understood.

METHODS

In the present study, in vivo distribution of exosomes following intravenous and intraperitoneal injection approaches was systemically analyzed by tracking the fluorescence-labeled exosomes and qPCR analysis of C. elegans specific miRNA abundance delivered by exosomes in different organs.

RESULTS

The results showed that exosomes administered through tail vein were mostly taken up by the liver, spleen and lungs while exosomes injected intraperitoneally were more dispersedly distributed. Besides the liver, spleen, and lungs, intraperitoneal injection effectively delivered exosomes into the visceral adipose tissue, making it a promising strategy for obesity therapy. Moreover, the results from fluorescence tracking and qPCR were slightly different, which could be explained by systemic errors.

CONCLUSION

Together, our study reveals that different administration routes cause a significant differential in vivo distribution of exosomes, suggesting that optimization of the delivery route is prerequisite to obtain rational delivery efficiency in detailed organs.

Extracellular vesicles derived from fibroblasts promote wound healing by optimizing fibroblast and endothelial cellular functions

Extracellular vesicles (EVs) have been exhibited as promising candidates for delivering endogenous therapeutic cargos for regenerative therapies. Fibroblasts could be candidate source cells for EVs, to investigate their therapeutic effects in wound healing. Here we demonstrated the isolation and characterization of fibroblast-derived (L929 cell line) EVs (L929-EVs). Furthermore, L929-EVs treatment showed pro-wound healing effects in vitro by enhancing proliferation, migration, and scarless wound healing related genes in fibroblast cells. L929-EVs treatment also enhanced the migration and tube formation of endothelial cells. The combination of L929-EVs with fibrin glue accelerated wound healing in the mouse skin wound model by enhancing collagen formation, collagen maturation, and blood vessels in the wounded skin. The role of fibroblast-derived EVs in wound healing could be an important phenomenon, and fibroblast-derived EVs could be harnessed for wound healing therapies.

Imaging as a tool to accelerate the translation of extracellular vesicle-based therapies for central nervous system diseases

Extracellular vesicles (EVs) are natural and diverse lipid bilayer-enclosed particles originating from various cellular components and containing an abundance of cargoes. Due to their unique properties, EVs have gained considerable interest as therapeutic agents for a variety of diseases, including central nervous system (CNS) disorders. Their therapeutic value depends on cell origin but can be further enhanced by enrichment of cargo when used as drug carriers. Therefore, there has been significant effort directed toward introducing them to clinical practice. However, it is essential to avoid the failures we have seen with whole-cell therapy, in particular for the treatment of the CNS. Successful launching of clinical studies is contingent upon the understanding of the biodistribution of EVs, including their uptake and clearance from organs and specific homing into the region of interest. A multitude of noninvasive imaging methods has been explored in vitro to investigate the spatio-temporal dynamics of EVs administered in vivo. However, only a few studies have been performed to track the delivery of EVs, especially delivery to the brain, which is the most therapeutically challenging organ. We focus here on the use of advanced imaging techniques as an essential tool to facilitate the acceleration of clinical translation of EV-based therapeutics, especially in the CNS arena. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

In Vivo Tracking of Extracellular Vesicles by Nuclear Imaging: Advances in Radiolabeling Strategies

Extracellular vesicles (EVs) are naturally secreted vesicles that have attracted a large amount of interest in nanomedicine in recent years due to their innate biocompatibility, high stability, low immunogenicity, and important role in cell-to-cell communication during pathological processes. Their versatile nature holds great potential to improve the treatment of several diseases through their use as imaging biomarkers, therapeutic agents, and drug-delivery vehicles. However, the clinical translation of EV-based approaches requires a better understanding of their in vivo behavior. Several imaging technologies have been used for the non-invasive in vivo tracking of EVs, with a particular emphasis on nuclear imaging due to its high sensitivity, unlimited penetration depth and accurate quantification. In this article, we will review the biological function and inherent characteristics of EVs and provide an overview of molecular imaging modalities used for their in vivo monitoring, with a special focus on nuclear imaging. The advantages of radionuclide-based imaging modalities make them a promising tool to validate the use of EVs in the clinical setting, as they have the potential to characterize in vivo the pharmacokinetics and biological behavior of the vesicles. Furthermore, we will discuss the current methods available for radiolabeling EVs, such as covalent binding, encapsulation or intraluminal labeling and membrane radiolabeling, reporting the advantages and drawbacks of each radiolabeling approach.

Locally Applied Stem Cell Exosome-Scaffold Attenuates Nerve Injury-Induced Pain in Rats

Purpose

Nerve injury-induced pain is difficult to treat. In this study, we developed an alginate scaffold with human umbilical cord mesenchymal stem cell exosomes (EX-SC) to treat nerve injury-induced pain.

Materials and Methods

The scaffold was prepared and characterized for its physical traits and biocompatibility. In vitro studies of PC12 and HEK293 cells were used to evaluate the neuroprotective and neurotrophic effects of exosomes. Right L5/6 spinal nerve ligation (SNL) was performed in Sprague-Dawley rats to induce mechanical allodynia and thermal hyperalgesia, evaluated by von Frey hair and radiant heat tests. The EX-SC was wrapped around ligated L5/6 spinal nerves for treatment. Western blotting and immunofluorescence staining were used to evaluate neuron/glial activation, cytokines and neurotrophic factor of affected dorsal root ganglion (DRG).

Results

In cell culture assay, the exosomes induce neurite outgrowth of PC12 cells and protect PC12 and HEK293 cells against formaldehyde acid treatment. On post-ligation day 21, rats receiving EX-SC had significantly higher median (interquartile range) withdrawal threshold and latency [14.1 (13.7-15.5) g, 14.2 (13.7-15.3) s] than saline-SC-treated rats [2.1 (1.7-3.0) g, 2.0 (1.8-2.4) s, P=0.02 and 0.002]. The EX-SC also attenuated SNL-induced up-regulation of c-Fos, GFAP, Iba1, TNF-α and IL-1β, while enhancing the level of IL-10 and GDNF, in the ipsilateral L5/6 DRG. After implantation for 21 days, the EX-SC enhanced the expression of myelin basic protein and IL-10 in injured L5/6 axons.

Conclusion

We demonstrate the EX-SC possesses antinociceptive, anti-inflammation and pro-neurotrophic effects in the SNL pain model. It could be a promising therapeutic alternative for nerve injury-induced pain.

Exosomes in disease and regeneration: biological functions, diagnostics, and beneficial effects

Exosomes are a subtype of extracellular vesicles. They range from 30 to 150 nm in diameter and originate from intraluminal vesicles. Exosomes were first identified as the mechanism for releasing unnecessary molecules from reticulocytes as they matured to red blood cells. Since then, exosomes have been shown to be secreted by a broad spectrum of cells and play an important role in the cardiovascular system. Different stimuli are associated with increased exosome release and result in different exosome content. The release of harmful DNA and other molecules via exosomes has been proposed as a mechanism to maintain cellular homeostasis. Because exosomes contain parent cell-specific proteins on the membrane and in the cargo that is delivered to recipient cells, exosomes are potential diagnostic biomarkers of various types of diseases, including cardiovascular disease. As exosomes are readily taken up by other cells, stem cell-derived exosomes have been recognized as a potential cell-free regenerative therapy to repair not only the injured heart but other tissues as well. The objective of this review is to provide an overview of the biological functions of exosomes in heart disease and tissue regeneration. Therefore, state-of-the-art methods for exosome isolation and characterization, as well as approaches to assess exosome functional properties, are reviewed. Investigation of exosomes provides a new approach to the study of disease and biological processes. Exosomes provide a potential "liquid biopsy," as they are present in most, if not all, biological fluids that are released by a wide range of cell types.

Small but Fierce: Tracking the Role of Extracellular Vesicles in Glioblastoma Progression and Therapeutic Resistance

Glioblastoma is the most common and aggressive brain tumor in adults. Most patients die within a year and long-term survival remains rare, owing to a combination of rapid progression/degeneration, lack of successful treatments, and high recurrence rates. Extracellular vesicles are cell-derived membranous structures involved in numerous physiological and pathological processes. In the context of cancer, these biological nanoparticles play an important role in intercellular communication, allowing cancer cells to exchange information with each other, the tumor microenvironment as well as distant cells. Here, light is shed on the role of extracellular vesicles in glioblastoma heterogeneity, tumor microenvironment interactions, and therapeutic resistance, and an overview on means to track their release, uptake, and cargo delivery is provided.

Palmitoylated mNeonGreen Protein as a Tool for Visualization and Uptake Studies of Extracellular Vesicles

Extracellular vesicles (EVs) are membranous nanoparticles released by cells as vital mediators of intercellular communication. As such, EVs have become an attractive target for pathogens and cancer cells, which can take control over their cargo composition, as well as their trafficking, shaping the pathogenesis. Despite almost four decades of research on EVs, the number of specific and efficient EV labeling methods is limited, and there is still no universal method for the visualization of their transport in living cells. Lipophilic dyes that non-specifically intercalate into the EVs membranes may diffuse to other membranes, leading to the misinterpretation of the results. Here, we propose a palmitoylated fluorescent mNeonGreen (palmNG) protein as an alternative to chemical dyes for EVs visualization. The Branchiostoma lanceolatum-derived mNeonGreen is a brighter, more stable, and less sensitive to laser-induced bleaching alternative to green fluorescent protein (GFP), which makes it a more potent tag in a variety of fluorescence-based techniques. A palmNG-expressing stable human melanoma cell line was generated using retrovirus gene transfer and cell sorting. This protein partially localizes to cellular membranes, and can be detected inside size-exclusion (SEC)-purified EVs. With the use of flow cytometry and fluorescent confocal microscopy, we performed qualitative and quantitative analyses of palmNG-EVs uptake in recipient human hepatoma cells, in comparison to PKH67-labeled vesicles. Our findings confirm that membrane-embedded mNeonGreen can be successfully applied as a tool in EVs transfer and uptake studies.

Current Perspectives on Clinical Use of Exosomes as a Personalized Contrast Media and Theranostics

An appropriate combination of biomarkers and imaging technologies will become standard practice in the future. Because the incidence of and mortality from cancers is rising, the further study of new approaches for the early detection and precise characterization of tumors is essential. Extracellular vesicles (EVs), including exosomes, prove to have great potential when it comes to diagnosis and targeted therapy. Due to their natural ability to pass through biological barriers, depending on their origin, EVs can accumulate at defined sites, including tumors, preferentially. This manuscript discusses the difficulties and simplicities of processing cell-derived materials, packaging diverse groups of agents in EVs, and activating the biological complex. Developing exosome-based diagnostic techniques to detect disease precisely and early as well as treat disease marks a new era of personalized radiology and nuclear medicine. As circulating drug delivery vehicles for novel therapeutic modalities, EVs offer a new platform for cancer theranostic.

Identification of Lymphatic and Hematogenous Routes of Rapidly Labeled Radioactive and Fluorescent Exosomes through Highly Sensitive Multimodal Imaging

There has been considerable interest in the clinical use of exosomes as delivery vehicles for treatments as well as for promising diagnostic biomarkers, but the physiological distribution of exosomes must be further elucidated to validate their efficacy and safety. Here, we aimed to develop novel methods to monitor exosome biodistribution in vivo using positron emission tomography (PET) and optical imaging. Exosomes were isolated from cultured mouse breast cancer cells and labeled for PET and optical imaging. In mice, radiolabeled and fluorescently labeled exosomes were injected both via lymphatic and hematogenous metastatic routes. PET and fluorescence images were obtained and quantified. Radioactivity and fluorescence intensity of ex vivo organs were measured. PET signals from exosomes in the lymphatic metastatic route were observed in the draining sentinel lymph nodes. Immunohistochemistry revealed greater exosome uptake in brachial and axillary versus inguinal lymph nodes. Following administration through the hematogenous metastasis pathway, accumulation of exosomes was clearly observed in the lungs, liver, and spleen. Exosomes from tumor cells were successfully labeled with ⁶⁴Cu (or ⁶⁸Ga) and fluorescence and were visualized via PET and optical imaging, suggesting that this simultaneous and rapid labeling method could provide valuable information for further exosome translational research and clinical applications.