Exosome-mediated transfer of microRNAs within the tumor microenvironment and neuroblastoma resistance to chemotherapy

Novel mesenchymal stem cell delivery system as targeted therapy against neuroblastoma using the TH-MYCN mouse model

PURPOSE

Mesenchymal stem cells (MSCs) are reported to migrate toward damaged tissues or tumors. We previously reported the in vivo short-term (1 day) tumor-homing effect of xenogeneic human MSCs (hMSCs) using the TH-MYCN mouse neuroblastoma model (MYCN-TgM). In this study, we analyzed the long-term tumor-homing effect of allogeneic mouse MSCs (mMSCs) and explored the antitumor effect and drug delivery function of mMSCs.

METHODS

mMSCs were administered intraperitoneally (i.p.) to MYCN-TgM and traced by an in vivo imaging system (IVIS). We administered green fluorescent protein (GFP)-transduced mMSCs into MYCN-TgM i.p. and examined the cell survival by immunohistochemistry. We also administered interferon beta-transduced mMSCs (mMSCs-IFN-β) to MYCN-TgM i.p. and measured the concentration of IFN-β in the tumor and organs by an enzyme-linked immunosorbent assay (ELISA). The survival curves of MYCN-TgM administered every week was analyzed.

RESULTS

The IVIS revealed the accumulation of fluorescence was observed in the tumor both in vivo and after excision. Immunohistochemistry using anti-GFP antibody revealed that the mMSCs existed within the tumor until 14 days but not in the organs. The ELISA showed increased concentrations of IFN-β only in the tumors, with the values gradually diminishing over 14 days. The mMSCs-IFN-β group survived significantly longer than the control group (p < 0.03), while the mMSCs-alone group did not show a survival advantage.

CONCLUSIONS

Allogeneic mMSCs showed a homing ability for mouse neuroblastoma and existed within the tumor for as long as two weeks. This may be a candidate drug delivery vehicle for antitumor agents against neuroblastoma.

miR-15a-5p, miR-15b-5p, and miR-16-5p inhibit tumor progression by directly targeting MYCN in neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid malignancy in children. Despite current aggressive treatment regimens, the prognosis for high-risk NB patients remains poor, with the survival of less than 40%. Amplification/stabilization of MYCN oncogene, in NB is associated with a high risk of recurrence. Thus, there is an urgent need for novel therapeutics. The deregulated expression of microRNA (miR) is reported in NB; nonetheless, its effect on MYCN regulation is poorly understood. First, we identified that miR-15a-5p, miR-15b-5p, and miR-16-5p (hereafter miR-15a, miR-15b or miR-16) were down-regulated in patient-derived xenografts (PDX) with high MYCN expression. MiR targeting sequences on MYCN mRNA were predicted using online databases such as TargetScan and miR database. The R2 database, containing 105 NB patients, showed an inverse correlation between MYCN mRNA and deleted in lymphocytic leukemia (DLEU) 2, a host gene of miR-15. Moreover, overexpression of miR-15a, miR-15b or miR-16 significantly reduced the levels of MYCN mRNA and N-Myc protein. Conversely, inhibiting miR dramatically enhanced MYCN mRNA and N-Myc protein levels, as well as increasing mRNA half-life in NB cells. By performing immunoprecipitation assays of argonaute-2 (Ago2), a core component of the RNA-induced silencing complex, we showed that miR-15a, miR-15b and miR-16 interact with MYCN mRNA. Luciferase reporter assays showed that miR-15a, miR-15b and miR-16 bind with 3'UTR of MYCN mRNA, resulting in MYCN suppression. Moreover, induced expression of miR-15a, miR-15b and miR-16 significantly reduced the proliferation, migration, and invasion of NB cells. Finally, transplanting miR-15a-, miR-15b- and miR-16-expressing NB cells into NSG mice repressed tumor formation and MYCN expression. These data suggest that miR-15a, miR-15b and miR-16 exert a tumor-suppressive function in NB by targeting MYCN. Therefore, these miRs could be considered as potential targets for NB treatment.

MicroRNA-A Tumor Trojan Horse for Tumor-Associated Macrophages

MicroRNAs (miRs) significantly contribute to the regulation of gene expression, by virtue of their ability to interact with a broad, yet specific set of target genes. MiRs are produced and released by almost every cell type and play an important role in horizontal gene regulation in the tumor microenvironment (TME). In the TME, both tumor and stroma cells cross-communicate via diverse factors including miRs, which are taking central stage as a therapeutic target of anti-tumor therapy. One of the immune escape strategies adopted by tumor cells is to release miRs as a Trojan horse to hijack circulating or tumor-localized monocytes/macrophages to tune them for pro-tumoral functions. On the other hand, macrophage-derived miRs exert anti-tumor functions. The transfer of miRs from host to recipient cells depends on the supramolecular structure and composition of miR carriers, which determine the distinct uptake mechanism by recipient cells. In this review, we provide a recent update on the miR-mediated crosstalk between tumor cells and macrophages and their mode of uptake in the TME.

Natural Killer Cell-Derived Vesicular miRNAs: A New Anticancer Approach?

Natural killer (NK) cells are cytotoxic lymphocytes targeting virus-infected cells and cancer cells. Specific pro- and antikilling signals modulate the overall ability of NK cells to kill cancer cells, however, several immune-escape mechanisms can be enacted by cancer cells to avoid NK-mediated killing. Recently, increasing evidence has shown that extracellular vesicles (EV) released by NK cells carry proteins and miRNAs able to exert an antitumoral effect, even within a highly immune-suppressive tumor microenvironment. These recent findings suggest a possible use of NK-derived EVs as anticancer agents and propel the development of new strategies to enrich EVs with the most effective anticancer cargo as a promising new anticancer approach.

Exploring the key communicator role of exosomes in cancer microenvironment through proteomics

There have been many attempts to fully understand the mechanism of cancer behavior. Yet, how cancers develop and metastasize still remain elusive. Emerging concepts of cancer biology in recent years have focused on the communication of cancer with its microenvironment, since cancer cannot grow and live alone. Cancer needs to communicate with other cells for survival, and thus they secrete various messengers, including exosomes that contain many proteins, miRNAs, mRNAs, etc., for construction of the tumor microenvironment. Moreover, these intercellular communications between cancer and its microenvironment, including stromal cells or distant cells, can promote tumor growth, metastasis, and escape from immune surveillance. In this review, we summarized the role of proteins in the exosome as communicators between cancer and its microenvironment. Consequently, we present cancer specific exosome proteins and their unique roles in the interaction between cancer and its microenvironment. Clinically, these exosomes might provide useful biomarkers for cancer diagnosis and therapeutic tools for cancer treatment.

MicroRNA-421 confers paclitaxel resistance by binding to the KEAP1 3'UTR and predicts poor survival in non-small cell lung cancer

MicroRNAs regulate post-transcriptional gene expression and play important roles in multiple cellular processes. In this study, we found that miR-421 suppresses kelch-like ECH-associated protein 1(KEAP1) expression by targeting its 3'-untranslated region (3'UTR). A Q-PCR assay demonstrated that miR-421 is overexpressed in non-small cell lung cancer (NSCLC), especially in A549 cells. Consistently, the level of miR-421 was higher in clinical blood samples from lung cancer patients than in those from normal healthy donors, suggesting that miR-421 is an important lung cancer biomarker. Interestingly, overexpression of miR-421 reduced the level of KEAP1 expression, which further promoted lung cancer cell migration and invasion, as well as inhibited cell apoptosis both in vivo and in vitro. Furthermore, knockdown of miR-421 expression with an antisense morpholino oligonucleotide (AMO) increased ROS levels and treatment sensitivity to paclitaxel in vitro and in vivo, indicating that high miR-421 expression may at least partly account for paclitaxel tolerance in lung cancer patients. To find the upstream regulator of miR-421, one of the candidates, β-catenin, was knocked out via the CRISPR/Cas9 method in A549 cells. Our data showed that inhibiting β-catenin reduced miR-421 levels in A549 cells. In addition, β-catenin upregulation enhanced miR-421 expression, indicating that β-catenin regulates the expression of miR-421 in lung cancer. Taken together, our findings reveal the critical role of miR-421 in paclitaxel drug resistance and its upstream and downstream regulatory mechanisms. Therefore, miR-421 may serve as a potential molecular therapeutic target in lung cancer, and AMOs may be a potential treatment strategy.

Exosomal miR-21 regulates the TETs/PTENp1/PTEN pathway to promote hepatocellular carcinoma growth

Background

As an important means of communication, exosomes play an important role in the development of hepatocellular carcinoma (HCC).

Methods

Bioinformatics analysis, dual-luciferase reporter assays, methylation-specific quantitative PCR, and ChIP-PCR analysis were used to gain insight into the underlying mechanism of miR-21 in HCC.

Results

The detection of miRNAs in exosomes of HCC showed that miR-21 expression in exosomes was positively correlated with the expression level of miR-21 in cells and negatively correlated with the expression of its target genes PTEN, PTENp1 and TETs. HCC cell-derived exosomes could increase miR-21 and p-Akt expression in HCC cells and downregulate the expression of PTEN, PTENp1 and TETs. MiR-21 inhibitors or PTENp1 overexpression vectors could weaken the effect of the abovementioned exosomes and simultaneously weaken their role in promoting cell proliferation and migration and inhibiting apoptosis. Further studies showed that miR-21 not only directly regulated the expression of PTEN, PTENp1 and TETs but also increased the methylation level of the PTENp1 promoter by regulating the expression of TETs, thereby inhibiting the expression of PTENp1 and further downregulating the expression of PTEN.

Conclusions

Exosomal miR-21 can regulate the expression of the tumor suppressor genes PTEN and PTENp1 in various ways and affect the growth of HCC cells.

Extracellular vesicles as a novel source of biomarkers in liquid biopsies for monitoring cancer progression and drug resistance

Cancer-derived extracellular vesicles (EVs) have been detected in the bloodstream and other biofluids of cancer patients. They carry various tumor-derived molecules such as mutated DNA and RNA fragments, oncoproteins as well as miRNA and protein signatures associated with various phenotypes. The molecular cargo of EVs partially reflects the intracellular status of their cellular origin, however various sorting mechanisms lead to the enrichment or depletion of EVs in specific nucleic acids, proteins or lipids. It is becoming increasingly clear that cancer-derived EVs act in a paracrine and systemic manner to promote cancer progression by transferring aggressive phenotypic traits and drug-resistant phenotypes to other cancer cells, modulating the anti-tumor immune response, as well as contributing to remodeling the tumor microenvironment and formation of pre-metastatic niches. These findings have raised the idea that cancer-derived EVs may serve as analytes in liquid biopsies for real-time monitoring of tumor burden and drug resistance. In this review, we have summarized recent longitudinal clinical studies describing promising EV-associated biomarkers for cancer progression and tracking cancer evolution as well as pre-clinical and clinical evidence on the relevance of EVs for monitoring the emergence or progression of drug resistance. Furthermore, we outlined the state-of-the-art in the development and commercialization of EV-based biomarkers and discussed the scientific and technological challenges that need to be met in order to translate EV research into clinically applicable tools for precision medicine.

Exosomal miR-196a-1 promotes gastric cancer cell invasion and metastasis by targeting SFRP1

Aim: To investigate the role of exosomal miRNAs on gastric cancer (GC) metastasis. Materials & methods: miRNA expression profiles of exosomes with distinct invasion potentials were analyzed using miRNA microarray and validated by quantitative real-time PCR. In vitro and in vivo experiments assessed the role of exosomal miR-196a-1 in GC's metastasis. Results: High expression level of exosomal miR-196a-1 expression was significantly associated with poor survival in GC. Exosomes that contained miR-196a-1 were secreted from high-invasive GC cells. Ectopic miR-196a-1 expression promoted invasion of low-invasive GC cells by targeting SFRP1. Conclusion: miR-196a-1 was delivered from high-invasive GC into low-invasive GC cells via exosomes and promoted metastasis to the liver in vitro and in vivo.

The role of microRNA in the resistance to treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second most common cause of cancer-related death with a limited efficacy of treatment for intermediate and advanced stages of the disease. Several therapeutic approaches such as trans-arterial chemoembolization (TACE) with anthracyclines, cisplatin and multikinase inhibitor sorafenib have been appealing choices of treatments yet failed to reach a satisfactory outcome mainly due to the numerous mechanisms that influence patient's response. MicroRNAs (miRNAs) are key regulators of many intracellular processes related to drug resistance. This phenomenon has been linked to the modulation of several complex pathways, ranging from the loss of ability of drug accumulation, protective mechanism of autophagy, adaptive mechanism of cancer cells towards the drugs-induced environment, decrease DNA damage and suppression of downstream events that transduce its signal into apoptosis. We summarize the recent findings on the involvement of miRNAs in various drug resistance-related mechanisms in the development of resistance to anthracyclines, cisplatin and sorafenib therapies. Furthermore, we describe the possible application of miRNAs as circulating biomarkers predicting therapy response in HCC. Thus, the undeniable potential and paramount role of miRNA in drug resistance may eventually lead to improved clinical strategies and outcomes for HCC patients.

Exosomal microRNAs from Longitudinal Liquid Biopsies for the Prediction of Response to Induction Chemotherapy in High-Risk Neuroblastoma Patients: A Proof of Concept SIOPEN Study

Despite intensive treatment, 50% of children with high-risk neuroblastoma (HR-NB) succumb to their disease. Progression through current trials evaluating the efficacy of new treatments for children with HR disease usually depends on an inadequate response to induction chemotherapy, assessed using imaging modalities. In this study, we sought to identify circulating biomarkers that might be detected in a simple blood sample to predict patient response to induction chemotherapy. Since exosomes released by tumor cells can drive tumor growth and chemoresistance, we tested the hypothesis that exosomal microRNA (exo-miRNAs) in blood might predict response to induction chemotherapy. The exo-miRNAs expression profile in plasma samples collected from children treated in HR-NBL-1/SIOPEN before and after induction chemotherapy was compared to identify a three exo-miRs signature that could discriminate between poor and good responders. Exo-miRNAs expression also provided a chemoresistance index predicting the good or poor prognosis of HR-NB patients.

Exosomal MiRNAs in Pediatric Cancers

MicroRNAs (miRNAs) have generated great attention in oncology as they play a fundamental role in the regulation of gene expression and their aberrant expression is present in almost all types of tumors including pediatric ones. The discovery that miRNAs can be transported by exosomes, which are vesicles of 40–120 nm involved in cellular communication, that are produced by different cell types, and that are present in different biological fluids, has opened the possibility of using exosomal miRNAs as biomarkers. The possibility to diagnose and monitor the progression and response to drugs through molecules that can be easily isolated from biological fluids represents a particularly important aspect in the pediatric context where invasive techniques are often used. In recent years, the idea of liquid biopsy as well as studies on the possible role of exosomal miRNAs as biomarkers have developed greatly. In this review, we report an overview of all the evidences acquired in recent years on the identification of exosomal microRNAs with biomarker potential in pediatric cancers. We discuss the following herein: neuroblastoma, hepatoblastoma, sarcomas (osteosarcoma, Ewing’s sarcoma and rhabdoid tumors, and non-rhabdomyosarcoma soft tissue sarcoma), brain tumors, lymphomas, and leukemias.

Circulating miRNA Profiling in Plasma Samples of Ovarian Cancer Patients

Ovarian cancer is one of the most common cancer types in women characterized by a high mortality rate due to lack of early diagnosis. Circulating miRNAs besides being important regulators of cancer development could be potential biomarkers to aid diagnosis. We performed the circulating miRNA expression analysis in plasma samples obtained from ovarian cancer patients stratified into FIGO I, FIGO III, and FIGO IV stages and from healthy females using the NanoString quantitative assay. Forty-five miRNAs were differentially expressed, out of these 17 miRNAs showed significantly different expression between controls and patients, 28 were expressed only in patients, among them 19 were expressed only in FIGO I patients. Differentially expressed miRNAs were ranked by the network-based analysis to assess their importance. Target genes of the differentially expressed miRNAs were identified then functional annotation of the target genes by the GO and KEGG-based enrichment analysis was carried out. A general and an ovary-specific protein–protein interaction network was constructed from target genes. Results of our network and the functional enrichment analysis suggest that besides HSP90AA1, MYC, SP1, BRCA1, RB1, CFTR, STAT3, E2F1, ERBB2, EZH2, and MET genes, additional genes which are enriched in cell cycle regulation, FOXO, TP53, PI-3AKT, AMPK, TGFβ, ERBB signaling pathways and in the regulation of gene expression, proliferation, cellular response to hypoxia, and negative regulation of the apoptotic process, the GO terms have central importance in ovarian cancer development. The aberrantly expressed miRNAs might be considered as potential biomarkers for the diagnosis of ovarian cancer after validation of these results in a larger cohort of ovarian cancer patients.

Surveillance of Tumour Development: The Relationship Between Tumour-Associated RNAs and Ribonucleases

Tumour progression is accompanied by rapid cell proliferation, loss of differentiation, the reprogramming of energy metabolism, loss of adhesion, escape of immune surveillance, induction of angiogenesis, and metastasis. Both coding and regulatory RNAs expressed by tumour cells and circulating in the blood are involved in all stages of tumour progression. Among the important tumour-associated RNAs are intracellular coding RNAs that determine the routes of metabolic pathways, cell cycle control, angiogenesis, adhesion, apoptosis and pathways responsible for transformation, and intracellular and extracellular non-coding RNAs involved in regulation of the expression of their proto-oncogenic and oncosuppressing mRNAs. Considering the diversity/variability of biological functions of RNAs, it becomes evident that extracellular RNAs represent important regulators of cell-to-cell communication and intracellular cascades that maintain cell proliferation and differentiation. In connection with the elucidation of such an important role for RNA, a surge in interest in RNA-degrading enzymes has increased. Natural ribonucleases (RNases) participate in various cellular processes including miRNA biogenesis, RNA decay and degradation that has determined their principal role in the sustention of RNA homeostasis in cells. Findings were obtained on the contribution of some endogenous ribonucleases in the maintenance of normal cell RNA homeostasis, which thus prevents cell transformation. These findings directed attention to exogenous ribonucleases as tools to compensate for the malfunction of endogenous ones. Recently a number of proteins with ribonuclease activity were discovered whose intracellular function remains unknown. Thus, the comprehensive investigation of physiological roles of RNases is still required. In this review we focused on the control mechanisms of cell transformation by endogenous ribonucleases, and the possibility of replacing malfunctioning enzymes with exogenous ones.

Cancer drug resistance: A fleet to conquer

Cancer is a disease that claims millions of lives each year across the world. Despite advancement in technologies and therapeutics for treating the disease, these modes are often found to turn ineffective during the course of treatment. The resistance against drugs in cancer patients stems from multiple factors, which constitute genetic heterogeneity like gene mutations, tumor microenvironment, exosomes, miRNAs, high rate of drug efflux from cells, and so on. This review attempts to collate all such known and reported factors that influence cancer drug resistance and may help researchers with information that might be useful in developing better therapeutics in near future to enable better management of several cancers across the world.

Decrypting noncoding RNA interactions, structures, and functional networks

The world of noncoding RNAs (ncRNAs) is composed of an enormous and growing number of transcripts, ranging in length from tens of bases to tens of kilobases, involved in all biological processes and altered in expression and/or function in many types of human disorders. The premise of this review is the concept that ncRNAs, like many large proteins, have a multidomain architecture that organizes them spatially and functionally. As ncRNAs are beginning to be imprecisely classified into functional families, we review here how their structural properties might inform their functions with focus on structural architecture-function relationships. We will describe the properties of "interactor elements" (IEs) involved in direct physical interaction with nucleic acids, proteins, or lipids and of "structural elements" (SEs) directing their wiring within the "ncRNA interactor networks" through the emergence of secondary and/or tertiary structures. We suggest that spectrums of "letters" (ncRNA elements) are assembled into "words" (ncRNA domains) that are further organized into "phrases" (complete ncRNA structures) with functional meaning (signaling output) through complex "sentences" (the ncRNA interactor networks). This semiotic analogy can guide the exploitation of ncRNAs as new therapeutic targets through the development of IE-blockers and/or SE-lockers that will change the interactor partners' spectrum of proteins, RNAs, DNAs, or lipids and consequently influence disease phenotypes.

Drug-resistant endothelial cells facilitate progression, EMT and chemoresistance in nasopharyngeal carcinoma via exosomes

Recent antitumor drug development has included investigation of a wide variety of anti-angiogenesis therapies. Because cancer cells in tumors require new blood vessels to grow and spread, they stimulate capillary proliferation from existing vessels as well as new vessel formation from endothelial precursor cells. Our previous findings suggested that drug resistance in mouse endothelial cells supported tumor growth, but the relationship between endothelial cells (ECs) and nasopharyngeal carcinoma (NPC) cells remained unclear. Exosomes are small membrane vesicles that are released by several cell types, including human microvascular ECs (HMECs). Exosomes carrying membrane and cytoplasmic constituents have been described as participants in a novel mechanism of cell-to-cell communication. In the present study, we investigated the mechanisms underlying the interactions between HMECs and NPC cells. We found that drug-resistant HMECs secreted small heterogeneous 40-100 nm vesicles, defined as exosomes. Co-incubation of NPC cells with doxorubicin-resistant (R-DOX) HMEC-derived exosomes resulted in promotion of their proliferation, migration, and chemoresistance, as well as changes in the expression of epithelial-mesenchymal transition (EMT) markers. These effects were significantly inhibited by treatment with GW4869 (an exosome inhibitor). We also found that GW4869 inhibited the stimulation of drug-resistant HMECs on NPC progression by modulating EMT in vivo. These data suggest that exosomes participate in a novel mechanism by which drug-resistant ECs enhance NPC progression.

Exosomes and their role in tumorigenesis and anticancer drug resistance

Exosomes are a class of extracellular vesicles ranging in size from 40 to 100 nm, which are secreted by both cancer cells and multiple stromal cells in the tumor microenvironment. Following their secretion, exosomes partake in endocrine, paracrine and autocrine signaling. Internalization of exosomes by tumor cells influences several cellular pathways which alter cancer cell physiology. Tumor-derived exosomes secreted by cancer or stromal cells can also confer anticancer drug-resistant traits upon cancer cells. These exosomes promote chemoresistance by transferring their cargo which includes nucleic acids, proteins, and metabolites to cancer cells or act as a decoy for immunotherapeutic targets. Depletion of exosomes can reverse some of the detrimental effects on tumor metabolism and restore drug sensitivity to chemotherapeutic treatment. Herein we discuss various approaches that have been developed to deplete exosomes for therapeutic purposes. The natural composition, low immunogenicity and cytotoxicity of exosomes, along with their ability to specifically target tumor cells, render them an appealing platform for drug delivery. The ability of exosomes to mediate autocrine and paracrine signaling in target cells, along with their natural structure and low immunogenicity render them an attractive vehicle for the delivery of anticancer drugs to tumors.

Screening miRNAs associated with resistance gemcitabine from exosomes in A549 lung cancer cells

Purpose

To establish a gemcitabine-resistant lung adenocarcinoma cell line, A549/G+, and to screen the differences of miRNA expression in exosomes from A549 and A549/G+ cells.

Methods

A549 cells were exposed in gemcitabine until they were resistant to gemcitabine, and extracted exosomes from A549 and A549/G+. The RNAs from exosomes were subjected to miRNA expression microarray experiments.

Results

After 39 weeks of continuous induction, we induced drug resistance in A549 cells. The resistance index was 6. Via GeneChip miRNA 4.0 analysis, there were 446 differential miRNAs between A549 and A549/G+. Target gene prediction and pathway analysis discovered the microRNAs in the intersections may participate in drug resistance.

Conclusion

These differential miRNAs help to do in-depth research to elucidate the mechanism of resistance to gemcitabine in non-small cell lung cancer.

Drug resistance and combating drug resistance in cancer

Cancer is the second leading cause of death in the US. Current major treatments for cancer management include surgery, cytotoxic chemotherapy, targeted therapy, radiation therapy, endocrine therapy and immunotherapy. Despite the endeavors and achievements made in treating cancers during the past decades, resistance to classical chemotherapeutic agents and/or novel targeted drugs continues to be a major problem in cancer therapies. Drug resistance, either existing before treatment (intrinsic) or generated after therapy (acquired), is responsible for most relapses of cancer, one of the major causes of death of the disease. Heterogeneity among patients and tumors, and the versatility of cancer to circumvent therapies make drug resistance more challenging to deal with. Better understanding the mechanisms of drug resistance is required to provide guidance to future cancer treatment and achieve better outcomes. In this review, intrinsic and acquired resistance will be discussed. In addition, new discoveries in mechanisms of drug resistance will be reviewed. Particularly, we will highlight roles of ATP in drug resistance by discussing recent findings of exceptionally high levels of intratumoral extracellular ATP as well as intracellular ATP internalized from extracellular environment. The complexity of drug resistance development suggests that combinational and personalized therapies, which should take ATP into consideration, might provide better strategies and improved efficacy for fighting drug resistance in cancer.

Exosomal hsa-miR199a-3p Promotes Proliferation and Migration in Neuroblastoma

Neuroblastoma (NB) is the most common pediatric extra-cranial solid tumor with heterogeneous characteristics, and the prognosis of patients with high-risk NB is usually poor. Discovery of novel biomarkers for early detection and investigation of the underlying mechanisms governing invasion and metastasis of NB are urgently needed. Recently, exosomal microRNAs (miRNAs) have been shown to play vital regulatory or communication roles in the process of various types of cancers. However, the roles and mechanisms of exosomal miRNAs in NB remain unknown. Thus, the present study aims to investigate the detailed functions of tumor-derived exosomal miRNAs in progression and migration of NB in vivo and in vitro. By examining different exosomal miRNA expression profiles in the plasma of NB patients, we identified that the expression of hsa-miR199a-3p from exosomes was significantly upregulated, which was correlated with the severity of NB patients. Furthermore, we confirmed that exosomal hsa-miR199a-3p could facilitate proliferation and migration of NB via regulating NEDD4 expression. In summary, our data, for the first time, revealed that exosomal hsa-miR199a-3p could promote tumor proliferation and migration via decreasing NEDD4 expression in NB, suggesting that exosomal hsa-miR199a-3p may be applicated as a fast, easy, and non-invasive detection biomarker and contribute to the development of novel therapeutic strategies for NB in the future.

The Interaction Between Two Worlds: MicroRNAs and Toll-Like Receptors

MicroRNAs (miRNAs) are critical mediators of posttranscriptional regulation via their targeting of the imperfect antisense complementary regions of coding and non-coding transcripts. Recently, researchers have shown that miRNAs play roles in many aspects of regulation of immune cell function by targeting of inflammation-associated genes, including Toll-like receptors (TLRs). Besides this indirect regulatory role of miRNAs, they can also act as physiological ligands of specific TLRs and initiate the signaling cascade of immune response. In this review, we summarize the potential roles of miRNAs in regulation of TLR gene expression and TLR signaling, with a focus on the ability of miRNAs bind to TLRs.

Basics and applications of tumor-derived extracellular vesicles

Extracellular vesicle (EV)-mediated intercellular communication acts as a critical culprit in cancer development. The selective packaging of oncogenic molecules renders tumor-derived EVs capable of altering the tumor microenvironment and thereby modulating cancer developments that may contribute to drug resistance and cancer recurrence. Moreover, the molecular and functional characteristics of cancer through its development and posttreatment evolve over time. Tumor-derived EVs are profoundly involved in this process and can, therefore, provide valuable real-time information to reflect dynamic changes occurring within the body. Because they bear unique molecular profiles or signatures, tumor-derived EVs have been highlighted as valuable diagnostic and predictive biomarkers as well as novel therapeutic targets. In addition, the use of an advanced EV-based drug delivery system for cancer therapeutics has recently been emphasized in both basic and clinical studies. In this review, we highlight comprehensive aspects of tumor-derived EVs in oncogenic processes and their potential clinical applications.

Injured liver-released miRNA-122 elicits acute pulmonary inflammation via activating alveolar macrophage TLR7 signaling pathway

Hepatic injury is often accompanied by pulmonary inflammation and tissue damage, but the underlying mechanism is not fully elucidated. Here we identify hepatic miR-122 as a mediator of pulmonary inflammation induced by various liver injuries. Analyses of acute and chronic liver injury mouse models confirm that liver dysfunction can cause pulmonary inflammation and tissue damage. Injured livers release large amounts of miR-122 in an exosome-independent manner into the circulation compared with normal livers. Circulating miR-122 is then preferentially transported to mouse lungs and taken up by alveolar macrophages, in which it binds Toll-like receptor 7 (TLR7) and activates inflammatory responses. Depleting miR-122 in mouse liver or plasma largely abolishes liver injury-induced pulmonary inflammation and tissue damage. Furthermore, alveolar macrophage activation by miR-122 is blocked by mutating the TLR7-binding GU-rich sequence on miR-122 or knocking out macrophage TLR7. Our findings reveal a causative role of hepatic miR-122 in liver injury-induced pulmonary dysfunction.

Extracellular miRNAs as activators of innate immune receptors

Since the discovery of the existence of microRNAs (miRNAs) in body fluids, the fascinating hypothesis that extracellular miRNAs may play a role in cell-to-cell signalling started to make its own way. In this review, we summarize the current knowledge that supports the role of miRNAs in the regulation of the immune response by an unconventional mechanism based on the activation of intracellular innate immune sensors of nucleic acids, namely the Toll-like receptors (TLRs). Such a mechanism of action has been now described to amplify and influence the pathogenesis of several inflammation-dependent pathological conditions, including cancer growth and metastasis, neurodegeneration, autoimmunity and cardiovascular diseases. The available data suggest that we have only begun to touch upon a complex system that is likely to involve many receptors and molecules. These findings may help to understand the pathogenesis of immune-mediated diseases and provide the basis for the identification of new potential therapeutic targets.

MicroRNAs and Long Non-Coding RNAs and Their Hormone-Like Activities in Cancer

Hormones are messengers circulating in the body that interact with specific receptors on the cell membrane or inside the cells and regulate, at a distal site, the activities of specific target organs. The definition of hormone has evolved in the last years. Hormones are considered in the context of cell–cell communication and mechanisms of cellular signaling. The best-known mechanisms of this kind are chemical receptor-mediated events, the cell–cell direct interactions through synapses, and, more recently, the extracellular vesicle (EV) transfer between cells. Recently, it has been extensively demonstrated that EVs are used as a way of communication between cells and that they are transporters of specific messenger signals including non-coding RNAs (ncRNAs) such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Circulating ncRNAs in body fluids and extracellular fluid compartments may have endocrine hormone-like effects because they can act at a distance from secreting cells with widespread consequences within the recipient cells. Here, we discuss and report examples of the potential role of miRNAs and lncRNAs as mediator for intercellular communication with a hormone-like mechanism in cancer.

Extracellular vesicles derived from natural killer cells use multiple cytotoxic proteins and killing mechanisms to target cancer cells

Extracellular vesicles (EVs) are secreted membrane vesicles, which play complex physiological and pathological functions in intercellular communication. Recently, we isolated natural killer (NK) cell-derived EVs (NK-EVs) from ex vivo expansion of NK cell cultures. The isolated NK-EVs contained cytotoxic proteins and several activated caspases, and they induced apoptosis in target cells. In this report, the protein levels of cytotoxic proteins from NK-EV isolates were analysed by ELISA. The mean values of perforin (PFN, 550 ng/mL), granzyme A (GzmA, 185 ng/mL), granzyme B (GzmB, 23.4 ng/mL), granulysin (GNLY, 56 ng/mL), and FasL (2.5 ng/mL) were obtained from >60 isolations using dot plots. The correlation between cytotoxicity and cytotoxic protein levels was examined by linear regression. PFN, GzmA, GzmB, GNLY all had a positive, moderate correlation with cytotoxicity, suggesting that there is not a single cytotoxic protein dominantly involved in killing and that all of these proteins may contribute to cytotoxicity. To further explore the possible killing mechanisms, cells were treated with NK-EVs, proteins extracted and lysates assessed by Western blotting. The levels of Gzm A substrates, SET and HMG2, were diminished in targeted cells, indicating that GzmA may induce a caspase-independent death pathway. Also, cytochrome C was released from mitochondria, a central hallmark of caspase-dependent death pathways. In addition, several ER-associated proteins were altered, suggesting that NK-EVs may induce ER stress resulting in cell death. Our results indicate that multiple killing mechanisms are activated by NK-derived EVs, including caspase-independent and -dependent cell death pathways, which can mediate cytotoxicity against cancer cells. Abbreviations: NK: natural killer cells; aNK: activated NK cells; EV: extracellular vesicles; ER: endoplasmic reticulum; ALL: acute lymphoblastic leukaemia; FBS: foetal bovine serum. GzmA: granzyme A; GzmB: granzyme B; GNLY: granulysin; PFN: perforin.

Exosome-derived miR-339-5p mediates radiosensitivity by targeting Cdc25A in locally advanced esophageal squamous cell carcinoma

Cancer cells associated with radioresistance are likely to give rise to local recurrence and distant metastatic relapse. However, it remains unclear whether specific miRNAs have direct roles in radioresistance and/or prognosis. In this study, we find that miR-339-5p promotes radiosensitivity, and is downregulated in radioresistant subpopulations of esophageal cancer cells. Notably, miR-339-5p was selectively secreted into blood via exosomes, and that higher serum miR-339-5p levels were positively associated with radiotherapy sensitivity and good survival. Moreover, miR-339-5p expression was downregulated in the T3/T4 stage compared with T1/T2 stage in esophageal squamous cell carcinoma (ESCC) patients (P = 0.04), and low miR-339-5p expression in tissue was significantly associated with poor overall survival (P = 0.036) and disease-free survival (P = 0.037). Overexpression of miR-339-5p enhanced radiosensitivity in vitro and in vivo. Mechanistically, miR-339-5p enhances radiosensitivity by targeting Cdc25A, and is transcriptionally regulated by Runx3. Correlations were observed between miR-339-5p levels and Cdc25A/Runx3 levels in tissue samples. Intriguingly, combined analysis of miR-339-5p expression with Runx3 increased the separation of the survival curves obtained for either gene alone in the TCGA datasets (P = 0.009). Overall, exosome-derived miR-339-5p mediates radiosensitivity through downregulation of Cdc25A, and predicts pathological response to preoperative radiotherapy in locally advanced ESCC, suggesting it could be a promising non-invasive biomarker for facilitating personalized treatments.

The role of exosomal noncoding RNAs in cancer

Extracellular vesicles (EVs) membranes enclose nanosized vesicles with a size range of 30-150 nm and are plentiful in our body in both physiological and pathological conditions. Exosomes, a type of EV, are important mediators of intracellular communication among tumor cells, immune cells, and stromal cells. They can shuttle bioactive molecules, such as proteins, lipids, RNA, and DNA; however, the precise function of EVs remains largely unknown. In recent years, tumor-associated cargo in exosomes has been a hot topic in research, especially with respect to noncoding RNAs (ncRNAs). Herein, we review the role of exosomal ncRNAs, including miRNAs and long noncoding RNAs, in tumor biological processes. Clinically, exosomal ncRNAs may eventually become novel biomarkers and therapeutic targets in cancer progression.

Microglia-Derived Microvesicles Affect Microglia Phenotype in Glioma

Extracellular-released vesicles (EVs), such as microvesicles (MV) and exosomes (Exo) provide a new type of inter-cellular communication, directly transferring a ready to use box of information, consisting of proteins, lipids and nucleic acids. In the nervous system, EVs participate to neuron-glial cross-talk, a bidirectional communication important to preserve brain homeostasis and, when dysfunctional, involved in several CNS diseases. We investigated whether microglia-derived EVs could be used to transfer a protective phenotype to dysfunctional microglia in the context of a brain tumor. When MV, isolated from microglia stimulated with LPS/IFNγ were brain injected in glioma-bearing mice, we observed a phenotype switch of tumor associated myeloid cells (TAMs) and a reduction of tumor size. Our findings indicate that the MV cargo, which contains upregulated transcripts for several inflammation-related genes, can transfer information in the brain of glioma bearing mice modifying microglial gene expression, reducing neuronal death and glioma invasion, thus promoting the recovery of brain homeostasis.

Microvesicles expressing adenosinergic ectoenzymes and their potential role in modulating bone marrow infiltration by neuroblastoma cells

Metastatic diffusion of Neuroblastoma (NB) cells in the bone marrow (BM) represents the most negative prognostic factors for NB patients. Multiple immune escape mechanisms are postulated as responsible. Our working hypothesis is that adenosine (ADO), an immunosuppressive molecule along with the ectoenzymatic pathways (CD39-CD73 and CD38-CD203a/PC-1-CD73) controlling its production, are involved in the dynamics of NB cells in the BM. The results indicate that ectonucleotidases are expressed by i) NB cell lines, ii) metastatic NB cells isolated from NB patients' BM, iii) microvesicles (MV) derived from both NB cell types and iv) resident BM cell populations. BM infiltration by NB cells increased CD203a/PC-1 and CD73 expression on lymphoid and myeloid cells, respectively. Expressions of ectoenzymes and GD2 (NB-associated marker) were higher on MV from NB patients' BM than in controls. Moreover, CD203a/PC-1 expression on BM-derived MV provide a basis for distinguishing NB patients with high or low BM infiltration. ADO production and consumption of related by-products were significantly higher when assessed on NB patients' MV than those from controls. MV isolated from NB patients' BM significantly downregulated in vitro T cell proliferation. Lastly, NB patients with worse prognosis are identified by a high percentage of CD38⁺ or CD73⁺ MV in the BM. In conclusion, ectonucleotidases are present and functional on NB cells, as well as in NB-infiltrated BM and in MV derived from BM. It is reasonable that MV are involved in BM infiltration by NB cells. Therefore, targeting these molecules may widen the therapeutic armamentarium for metastatic NB patients.

The emerging roles of macrophages in cancer metastasis and response to chemotherapy

Macrophages represent a heterogeneous group of cells, capable of carrying out distinct functions in a variety of organs and tissues. Even within individual tissues, their functions can vary with location. Tumor-associated macrophages (TAMs) specialize into three major subtypes that carry out multiple tasks simultaneously. This is especially true in the context of metastasis, where TAMs establish most of the cellular and molecular prerequisites for successful cancer cell dissemination and seeding to the secondary site. Perivascular TAMs operate in the perivascular niche, where they promote tumor angiogenesis and aid in the assembly of intravasation sites called tumor microenvironment of metastasis (TMEM). Streaming TAMs co-migrate with tumor cells (irrespective of the perivascular niche) and promote matrix remodeling, tumor cell invasiveness, and an immunosuppressive local microenvironment. Premetastatic TAMs are recruited to the premetastatic niche, where they can assist in tumor cell extravasation, seeding, and metastatic colonization. The dynamic interplay between TAMs and tumor cells can also modify the ability of the latter to resist cytotoxic chemotherapy (a phenotype known as environment-mediated drug resistance) and induce chemotherapy-mediated pro-metastatic microenvironmental changes. These observations suggest that future therapeutics should be designed to target TAMs with the aim of suppressing the metastatic potential of tumors and rendering chemotherapy more efficient.

Differential Exosomic Proteomic Patterns and Their Influence in Resveratrol Sensitivities of Glioblastoma Cells

Glioblastoma multiforme (GBM) is the commonest primary brain malignancy with extremely poor prognosis. Resveratrol posseses anti-cancer effects, while GBM cells respond differently to it due to certain unknown reason(s). Because the tumor-derived exosomes are supposed to influence chemosensitivity, the exosomic proteins released from resveratrol-sensitive U251 and resveratrol-resistant glioblastoma LN428 cells are profiled before (N/Exo) and after drug treatment (Res/Exo) by label-free liquid chromatography-mass spectrometry (LC-MS). The therapeutic implications of the proteomic findings are estimated by gene ontology enrichment analysis (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG)-based bioinformatic analyses and further elucidated by exosome co-incubating. The results reveal that U251/N/Exo but not U251/Res/Exo enhances resveratrol sensitivity of resveratrol-resistant LN428 cells. The resveratrol sensitive properties of U251 cells are not altered by either LN428/N/Exo or LN428/Res/Exo. U251/N/Exo contains higher levels of chromatin silencing and epidermis development proteins, while U251/Res/Exo has more oxygen transport and G protein-coupled receptor. Both of LN428/N/Exo and LN428/Res/Exo are rich in the proteins related with nucleosome assembly, microtubule-based process and chromatin silencing. In conclusion, U251/N/Exo sensitizes LN428 cells to resveratrol via delivering drug sensitizing signals, suggesting the presence of additional factor(s) that may determine the resveratrol sensitivities of glioblastoma cells.

Current Progresses of Exosomes as Cancer Diagnostic and Prognostic Biomarkers

Cancer related exosomes are nano-size membrane vesicles that play important roles in tumor microenvironment. Emerging evidence indicates that exosomes can load unique cargoes, including proteins and nucleic acids that reflect the condition of tumor. Therefore, exosomes are being used as diagnostic and prognostic biomarkers for various cancers. In this review, we describe the current progresses of cancer related exosomes, including their biogenesis, molecular contents, biological functions, sources where they are derived from, and methods for their detection. We will also discuss the current exosomal biomarkers and the utilization of them for early diagnosis and prognostics in cancer.

Hepatocellular carcinoma-derived exosomal miRNA-21 contributes to tumor progression by converting hepatocyte stellate cells to cancer-associated fibroblasts

BACKGROUND

Hepatocellular carcinoma (HCC) remains a global challenge due to its high morbidity and mortality rates as well as poor response to treatment. The communication between tumor-derived elements and stroma plays a critical role in facilitating cancer progression of HCC. Exosomes are small extracellular vesicles (EVs) that are released from the cells upon fusion of multivesicular bodies with the plasma membrane. There is emerging evidence indicating that exosomes play a central role in cell-to-cell communication. Much attention has been paid to exosomes since they are found to transport bioactive proteins, messenger RNA (mRNAs) and microRNA (miRNAs) that can be transferred in active form to adjacent cells or to distant organs. However, the mechanisms underlying such cancer progression remain largely unexplored.

METHODS

Exosomes were isolated by differential ultracentrifugation from conditioned medium of HCC cells and identified by electron microscopy and Western blotting analysis. Hepatic stellate cells (HSCs) were treated with different concentrations of exosomes, and the activation of HSCs was analyzed by Western blotting analysis, wound healing, migration assay, Edu assay, CCK-8 assay and flow cytometry. Moreover, the different miRNA levels of exosomes were tested by real-time quantitative PCR (RT-PCR). The angiogenic ability of activated HSCs was analyzed by qRT-PCR, CCK-8 assay and tube formation assay. In addition, the abnormal lipid metabolism of activated HSCs was analyzed by Western blotting analysis and Oil Red staining. Finally, the relationship between serum exosomal miRNA-21 and prognosis of HCC patients was evaluated.

RESULTS

We showed that HCC cells exhibited a great capacity to convert normal HSCs to cancer-associated fibroblasts (CAFs). Moreover, our data revealed that HCC cells secreted exosomal miRNA-21 that directly targeted PTEN, leading to activation of PDK1/AKT signaling in HSCs. Activated CAFs further promoted cancer progression by secreting angiogenic cytokines, including VEGF, MMP2, MMP9, bFGF and TGF-β. Clinical data indicated that high level of serum exosomal miRNA-21 was correlated with greater activation of CAFs and higher vessel density in HCC patients.

CONCLUSIONS

Intercellular crosstalk between tumor cells and HSCs was mediated by tumor-derived exosomes that controlled progression of HCC. Our findings provided potential targets for prevention and treatment of live cancer.

Natural Killer-Derived Exosomal miR-186 Inhibits Neuroblastoma Growth and Immune Escape Mechanisms

In neuroblastoma, the interplay between immune cells of the tumor microenvironment and cancer cells contributes to immune escape mechanisms and drug resistance. In this study, we show that natural killer (NK) cell-derived exosomes carrying the tumor suppressor microRNA (miR)-186 exhibit cytotoxicity against MYCN-amplified neuroblastoma cell lines. The cytotoxic potential of these exosomes was partly dependent upon expression of miR-186. miR-186 was downregulated in high-risk neuroblastoma patients, and its low expression represented a poor prognostic factor that directly correlated with NK activation markers (i.e., NKG2D and DNAM-1). Expression of MYCN, AURKA, TGFBR1, and TGFBR2 was directly inhibited by miR-186. Targeted delivery of miR-186 to MYCN-amplified neuroblastoma or NK cells resulted in inhibition of neuroblastoma tumorigenic potential and prevented the TGFβ1-dependent inhibition of NK cells. Altogether, these data support the investigation of a miR-186-containing nanoparticle formulation to prevent tumor growth and TGFβ1-dependent immune escape in high-risk neuroblastoma patients as well as the inclusion of ex vivo-derived NK exosomes as a potential therapeutic option alongside NK cell-based immunotherapy.Significance: These findings highlight the therapeutic potential of NK cell-derived exosomes containing the tumor suppressor miR-186 that inhibits growth, spreading, and TGFβ-dependent immune escape mechanisms in neuroblastoma.

Exosomes as drug carriers for clinical application

Exosomes are nanoscale vesicles shed from all cell types and play a major role in communication and transportation of materials between cells due to their ability to transfer proteins and nucleic acids from one cell to another. Analogous in size and function to synthetic nanoparticles, exosomes offer many advantages, rendering them the most promising candidates for targeted drug or gene delivery vehicles. Exosomes can also induce chemoresistance or radioresistance of tumor cells. Studies about the related mechanisms help overcome cancer therapy resistance to some extent. In this review, we focus on the application of exosomes as nanocarriers and the current status of the application of exosomes to cancer therapy.

MicroRNAs, Regulatory Messengers Inside and Outside Cancer Cells

MicroRNAs (miRNAs) are a class of short non-coding RNAs (ncRNAs) with typical sequence lengths of 19-25 nucleotides and extraordinary abilities to regulate gene expression. Because miRNAs regulate multiple important biological functions of the cell (proliferation, migration, invasion, apoptosis, differentiation, and drug resistance), their expression is highly controlled. Genetic and epigenetic alterations frequently found in cancer cells can cause aberrant expression of miRNAs and, consequently, of their target genes. The tumor microenvironment can also affect miRNA expression through soluble factors (e.g., cytokines and growth factors) secreted by either tumor cells or non-tumor cells (such as immune and stromal cells). Furthermore, like hormones, miRNAs can be secreted and regulate gene expression in recipient cells. Altered expression levels of miRNAs in cancer cells determine the acquisition of fundamental biological capabilities (hallmarks of cancer) responsible for the development and progression of the disease.

Tumor-derived microRNAs induce myeloid suppressor cells and predict immunotherapy resistance in melanoma

The accrual of myeloid-derived suppressor cells (MDSCs) represents a major obstacle to effective immunotherapy in cancer patients, but the mechanisms underlying this process in the human setting remain elusive. Here, we describe a set of microRNAs (miR-146a, miR-155, miR-125b, miR-100, let-7e, miR-125a, miR-146b, miR-99b) that are associated with MDSCs and resistance to treatment with immune checkpoint inhibitors in melanoma patients. The miRs were identified by transcriptional analyses as being responsible for the conversion of monocytes into MDSCs (CD14+HLA-DRneg cells) mediated by melanoma extracellular vesicles (EVs) and were shown to recreate MDSC features upon transfection. In melanoma patients, these miRs were increased in circulating CD14+ monocytes, plasma, and tumor samples, where they correlated with the myeloid cell infiltrate. In plasma, their baseline levels clustered with the clinical efficacy of CTLA-4 or programmed cell death protein 1 (PD-1) blockade. Hence, MDSC-related miRs represent an indicator of MDSC activity in cancer patients and a potential blood marker of a poor immunotherapy outcome.

Exosome mediated multidrug resistance in cancer

Extracellular vesicles (EVs), named as exosomes, were recently found to play important roles in cell-cell communication by transducing various biochemical and genetic information. Exosomes, secreted from either tumor cells or stromal cells including immune cells, can eventually remodel tumor environment to promote tumor progression such as metastasis and multidrug resistance (MDR). Therefore, the detection or targeting of biochemical and genetic cargos like proteins, lipids, metabolites and various types of RNAs or DNAs are believed to be valuable for the diagnosis and treatment of human cancer. In this review, we will summarize recent progresses in the research of exosomes especially its biological and clinical relevance to MDR. By doing so, we hope it could be valuable for the prevention, detection and intervention of MDR which is one of the major challenges for the clinical management of human cancers.

Immunosuppressive circuits in tumor microenvironment and their influence on cancer treatment efficacy

It has been for long conceived that hallmarks of cancer were intrinsic genetic features driving tumor development, proliferation, and progression, and that targeting such cell-autonomous pathways could be sufficient to achieve therapeutic cancer control. Clinical ex vivo data demonstrated that treatment efficacy often relied on the contribution of host immune responses, hence introducing the concept of tumor microenvironment (TME), namely the existence, along with tumor cells, of non-tumor components that could significantly influence tumor growth and survival. Among the complex network of TME-driving forces, immunity plays a key role and the balance between antitumor and protumor immune responses is a major driver in contrasting or promoting cancer spreading. TME is usually a very immunosuppressed milieu because of a vast array of local alterations contrasting antitumor adaptive immunity, where metabolic changes contribute to cancer dissemination by impairing T cell infiltration and favoring the accrual and activation of regulatory cells. Subcellular structures known as extracellular vesicles then help spreading immunosuppression at systemic levels by distributing genetic and protein tumor repertoire in distant tissues. A major improvement in the knowledge of TME is now pointing the attention back to tumor cells; indeed, recent findings are showing how oncogenic pathways and specific mutations in tumor cells can actually dictate the nature and the function of immune infiltrate. As our information on the reciprocal interactions regulating TME increases, finding a strategy to interfere with TME crosstalk becomes more complex and challenging. Nevertheless, TME interactions represent a promising field for the discovery of novel biomarkers and therapeutic targets for improving treatment efficacy in cancer.

Paclitaxel‑resistant gastric cancer MGC‑803 cells promote epithelial‑to‑mesenchymal transition and chemoresistance in paclitaxel‑sensitive cells via exosomal delivery of miR‑155‑5p

Paclitaxel is a first-line chemotherapeutic agent for gastric cancer; however, resistance limits its effectiveness. Investigation into the underlying mechanisms of paclitaxel resistance is urgently required. In the present study, a paclitaxel-resistant gastric cancer cell line (MGC-803R) was generated with a morphological phenotype of epithelial-to-mesenchymal transition (EMT) and increased expression levels of microRNA (miR)-155-5p. MGC-803R cell-derived exosomes were effectively taken up by paclitaxel-sensitive MGC-803S cells, which exhibited EMT and chemoresistance phenotypes. miR-155-5p was enriched in MGC-803R-exosomes and could be delivered into MGC-803S cells. miR-155-5p overexpression in MGC-803S cells via transfection with mimics resulted in similar phenotypic effects as treatment with MGC-803R exosome and increased miR-155-5p content in MGC-803S exosomes, which then capable of inducing the malignant phenotype in the sensitive cells. GATA binding protein 3 (GATA3) and tumor protein p53-inducible nuclear protein 1 (TP53INP1) were identified as targets of miR-155-5p. Exosomal miR-155-5p inhibited these targets by directly targeting their 3′ untranslated regions. Knockdown of miR-155-5p was observed to reverse the EMT and chemoresistant phenotypes of MGC-803R cells, potentially via GATA3 and TP53INP1 upregulation, which inhibited MGC-803R-exosomes from inducing the malignant phenotype. These results demonstrated that exosomal delivery of miR-155-5p may induce EMT and chemoresistant phenotypes from paclitaxel-resistant gastric cancer cells to the sensitive cells, which may be mediated by GATA3 and TP53INP1 suppression. Targeting miR-155-5p may thus be a promising strategy to overcome paclitaxel resistance in gastric cancer.

Exosomes derived from HBV-associated liver cancer promote chemoresistance by upregulating chaperone-mediated autophagy

Liver cancer, which is the second leading cause of tumor-associated mortality, is of great concern worldwide due to its resistance to chemotherapeutic drugs. Transcatheter arterial chemoembolization (TACE) has previously been used as a treatment for unresectable liver tumors in China; however, the response to TACE treatment differs between patients. It has been reported that hepatitis B virus (HBV)-as sociated tumors are less sensitive to TACE treatment compared with non-HBV-associated liver cancer. Previous studies have demonstrated that exosomes serve a crucial role in hepatic carcinoma chemoresistance. We therefore hypothesized that HBV may modulate chemosensitivity via exosomes. The aim of the present study was to investigate how exosomes affect chemoresistance by assessing their role in chaperone-mediated autophagy (CMA)-dependent chemoresistance in HBV-associated liver cancer. Iconography data from HBV-positive and HBV-negative patients with hepatic carcinoma receiving TACE treatment were assessed, and it was revealed that the tumor volume was decreased in the patients with non-HBV-associated liver cancer compared with that in the patients with HBV-associated tumors following TACE therapy. Furthermore, it was revealed that exosomes from HBV-infected liver cancer cells were able to downregulate cell apoptosis when treated with oxaliplatin compared with exosomes from normal HepG2 cells. Furthermore, the results demonstrated that HBV-associated exosomes modulate cell death via activating the CMA pathway, and its key molecule, lysosome-associated membrane protein (Lamp2a), was also upregulated. Lamp2a-knockdown was also found to reverse anti-apoptotic effects in liver cancer. Taken together, the results of the present study suggest that chemoresistance in patients with HBV-associated hepatic tumors may be mediated by exosomes, and thus may provide a basis for the development of novel treatment strategies for chemoresistant liver cancer.

Effect of exosomal miRNA on cancer biology and clinical applications

Exosomes, extracellular vesicles with diameters ranging from 30 to 150 nm, are widely present in various body fluids. Recently, microRNAs (miRNAs) have been identified in exosomes, the biogenesis, release, and uptake of which may involve the endosomal sorting complex required for transport (ESCRT complex) and relevant proteins. After release, exosomes are taken up by neighboring or distant cells, and the miRNAs contained within modulate such processes as interfering with tumor immunity and the microenvironment, possibly facilitating tumor growth, invasion, metastasis, angiogenesis and drug resistance. Therefore, exosomal miRNAs have a significant function in regulating cancer progression. Here, we briefly review recent findings regarding tumor-derived exosomes, including RNA sorting and delivering mechanism. We then describe the intercommunication occurring between different cells via exosomal miRNAs in tumor microenvironmnt, with impacts on tumor proliferation, vascularization, metastasis and other biological characteristics. Finally, we highlight the potential role of these molecules as biomarkers in cancer diagnosis and prognosis and tumor resistance to therapeutics.

Exosome-mediated transfer of lncRUNX2-AS1 from multiple myeloma cells to MSCs contributes to osteogenesis

Multiple myeloma (MM) is characterized by the decreased osteogenic potential of mesenchymal stem cells (MSCs). Communication between cancer cells and cancer stromal cells is a driving factor in tumor progression. Understanding the myeloma-stroma interactions is critical to the development of effective strategies that can reverse bone diseases. Here we identified that bioactive lncRNA RUNX2-AS1 in myeloma cells could be packed into exosomes and transmitted to MSCs, thus repressing the osteogenesis of MSCs. RUNX2-AS1, which arises from the antisense strand of RUNX2, was enriched in MSCs derived from MM patients (MM-MSCs). RUNX2-AS1 was capable of forming an RNA duplex with RUNX2 pre-mRNA at overlapping regions and this duplex transcriptionally repressed RUNX2 expression by reducing the splicing efficiency, resulting in decreased osteogenic potential of MSCs. In vivo mouse models, administered an inhibitor of exosome secretion, GW4869, was found to be effective in preventing bone loss, sustained by both bone formation and anticatabolic activities. Therefore, exosomal lncRNA RUNX2-AS1 may serve as a potential therapeutic target for bone lesions in MM. In summary, our results indicated a key role of exosomal lncRUNX2-AS1 in transferring from MM cells to MSCs in osteogenic differentiation, through a unique exosomal lncRUNX2-AS1/RUNX2 pathway.