Exosomes in cancer development and clinical applications

Exosomes participate in cancer progression and metastasis by transferring bioactive molecules between cancer and various cells in the local and distant microenvironments. Such intercellular cross‐talk results in changes in multiple cellular and biological functions in recipient cells. Several hallmarks of cancer have reportedly been impacted by this exosome‐mediated cell‐to‐cell communication, including modulating immune responses, reprogramming stromal cells, remodeling the architecture of the extracellular matrix, or even endowing cancer cells with characteristics of drug resistance. Selectively, loading specific oncogenic molecules into exosomes highlights exosomes as potential diagnostic biomarkers as well as therapeutic targets. In addition, exosome‐based drug delivery strategies in preclinical and clinical trials have been shown to dramatically decrease cancer development. In the present review, we summarize the significant aspects of exosomes in cancer development that can provide novel strategies for potential clinical applications.     

Exosomes enriched in stemness/metastatic-related mRNAS promote oncogenic potential in breast cancer

Cancer cells efficiently transfer exosome contents (essentially mRNAs and microRNAs) to other cell types, modifying immune responses, cell growth, angiogenesis and metastasis. Here we analyzed the exosomes release by breast tumor cells with different capacities of stemness/metastasis based on CXCR4 expression, and evaluated their capacity to generate oncogenic features in recipient cells. Breast cancer cells overexpressing CXCR4 showed an increase in stemness-related markers, and in proliferation, migration and invasion capacities. Furthermore, recipient cells treated with exosomes from CXCR4-cells showed increased in the same abilities. Moreover, inoculation of CXCR4-cell-derived exosomes in immunocompromised mice stimulated primary tumor growth and metastatic potential. Comparison of nucleic acids contained into exosomes isolated from patients revealed a “stemness and metastatic” signature in exosomes of patients with worse prognosis. Finally, our data supported the view that cancer cells with stem-like properties show concomitant metastatic behavior, and their exosomes stimulate tumor progression and metastasis. Exosomes-derived nucleic acids from plasma of breast cancer patients are suitable markers in the prognosis of such patients.     

The versatile role of exosomes in cancer progression: diagnostic and therapeutic implications

Background

Recent advances in cancer biology have highlighted the relevance of exosomes and nanovesicles as carriers of genetic and biological messages between cancer cells and their immediate and/or distant environments. It has been found that these molecular cues may play significant roles in cancer progression and metastasis. Cancer cells secrete exosomes containing diverse molecules that can be transferred to recipient cells and/or vice versa to induce a plethora of biological processes, including angiogenesis, metastasis formation, therapeutic resistance, epithelial-mesenchymal transition and epigenetic/stemness (re)programming. While exosomes interact with cells within the tumour microenvironment to promote tumour growth, these vesicles can also facilitate the process of distant metastasis by mediating the formation of pre-metastatic niches. Next to their tumour promoting effects, exosomes have been found to serve as potential tools for cancer diagnosis and therapy. The ease of isolating exosomes and their content from different body fluids has led to the identification of diagnostic and prognostic biomarker signatures, as well as to predictive biomarker signatures for therapeutic responses. Exosomes can also be used as cargos to deliver therapeutic anti-cancer drugs, and they can be engineered to serve as vaccines for immunotherapy. Additionally, it has been found that inhibition of exosome secretion, and thus the transfer of oncogenic molecules, holds promise for inhibiting tumour growth. Here we provide recent information on the diverse roles of exosomes in various cellular and systemic processes governing cancer progression, and discuss novel strategies to halt this progression using exosome-based targeted therapies and methods to inhibit exosome secretion and the transfer of pro-tumorigenic molecules.

Conclusions

This review highlights the important role of exosomes in cancer progression and its implications for (non-invasive) diagnostics and the development of novel therapeutic strategies, as well as its current and future applications in clinical trials.

     

Progression of Exosome-Mediated Chemotherapy Resistance in Cancer

Chemotherapy plays an important role in controlling cancer progression, but the long-term use of chemotherapeutic agents can lead to drug resistance and eventually treatment failure. Therefore, elucidation of the mechanism of drug resistance is the key to solve the problem of chemotherapy resistance. In recent years, exosomes derived from tumor cells have received extensive attention from researchers. In this paper, we reviewed the role and mechanism of exosome-mediated tumor drug resistance in recent years, summarized the related studies of exosome and chemotherapy drug resistance, and focused on several different ways by which exosomes participate in tumor drug resistance. It includes the transporters of non-coding RNAs (ncRNAs), active proteins, stromal cell-derived exosomes and exosomes that directly mediate the efflux of drug molecules. Our review suggests that exosomes can play a role in the treatment of tumor drug resistance by inhibiting the secretion of exosomes, providing a new idea for the prevention and treatment of tumor chemotherapy drug resistance.     

Exosome‐transmitted p120‐catenin suppresses hepatocellular carcinoma progression via STAT3 pathways

Hepatocellular carcinoma (HCC) is a fatal disease with increasing morbidity and poor prognosis due to surgical recurrence and metastasis. Moreover, the molecular mechanism of HCC progression remains unclear. Although the role of p120‐catenin (p120ctn) in liver cancer is well studied, the effects of secreted p120ctn transported by exosomes are less understood. Here, we show that p120ctn in exosomes secreted from liver cancer cells suppresses HCC cell proliferation and metastasis and expansion of liver cancer stem cells (CSCs). Mechanically, exosome p120ctn inhibits HCC cell progression via the STAT3 pathway, and the STAT3 inhibitor S3I‐201 abolishes the observed effects on growth, metastasis, and self‐renewal ability between exosome p120ctn‐treated HCC cells and control cells. Taken together, we propose that p120ctn‐containing exosomes derived from cancer cells inhibit the progression of liver cancer and may offer a new therapeutic strategy.     

The role of exosomes in metastasis and progression of melanoma

The mechanisms of melanoma metastasis have been the subject of extensive research for decades. Improved diagnostic and therapeutic strategies are of increasing importance for the treatment of melanoma due to its high burden of mortality in the advanced stages of the disease. Intercellular communication is a critical event for the progression of cancer. Collective evidence suggests that exosomes, small extracellular membrane vesicles released by the cells, are important facilitators of intercellular communication between the cells and the surrounding environment. Although the emerging field of exosomes is rapidly gaining traction in the scientific community, there is limited knowledge regarding the role of exosomes in melanoma. This review discusses the multifaceted role of melanoma-derived exosomes in promoting the process of metastasis by modulating the invasive and angiogenic capacity of malignant cells. The future implications of exosome research and the therapeutic potential of exosomes are also discussed.     

外泌体在癌症诊治中的作用与机制

外泌体是一种新型的癌症生物标志物，它由所有体液中各种活细胞分泌的双层纳米囊泡构成，含有丰富的蛋白质、DNA、mRNA和非编码RNA。目前外泌体被认为是细胞间通讯的另一种机制，参与细胞间交换蛋白质、脂质和遗传物质。越来越多的研究表明，外泌体在肿瘤的发生、生长、进展、转移、耐药性和免疫逃逸中发挥重要作用。在本文中，我们根据外泌体生物学的最新进展，详细阐述了外泌体影响肿瘤之间通信的具体机制，并报道了外泌体可能成为癌症诊断中有前途的生物标志物，并代表癌症治疗的新靶点。     

Role of stem cell derived exosomes in tumor biology

Exosomes are nano‐scale messengers loaded with bio‐molecular cargo of RNA, DNA, and Proteins. As a master regulator of cellular signaling, stem cell (both normal, and cancer stem cells) secreted exosome orchestrate various autocrine and paracrine functions which alter tumor micro‐environment, growth and progression. Exosomes secreted by one of the two important stem cell phenotypes in cancers a) Mesenchymal stem cells, and b) Cancer stem cells not only promote cancerous growth but also impart therapy resistance in cancer cells. In tumors, normal or mesenchymal stem cell (MSCs) derived exosomes (MSC‐exo) modulate tumor hallmarks by delivering unique miRNA species to neighboring cells and help in tumor progression. Apart from regulating tumor cell fate, MSC‐exo are also capable of inducing physiological processes, for example, angiogenesis, metastasis and so forth. Similarly, cancer stem cells (CSCs) derived exosomes (CSC‐exo) contain stemness‐specific proteins, self‐renewal promoting regulatory miRNAs, and survival factors. CSC‐exo specific cargo maintains tumor heterogeneity and alters tumor progression. In this review we critically discuss the importance of stem cell specific exosomes in tumor cell signaling pathways with their role in tumor biology.     

Exosomes Derived from Irradiated Esophageal Carcinoma-Infiltrating T Cells Promote Metastasis by Inducing the Epithelial–Mesenchymal Transition in Esophageal Cancer Cells

Exosomes are nanovesicles derived from tumor and normal cells that are detectable in human biological fluids, such as plasma, and cell culture supernatants. The function of exosome secretion from “normal” cells is unclear. Although numerous studies have investigated exosomes derived from hematopoietic cells, little is known regarding exosomes fromT cells, even though these cells play significant roles in innate and acquired immunity. A CCK-8 assay was used to examine the ability of exosomes to inhibit TE13 cell proliferation. In vitro invasion and wound healing assays were conducted to explore the effects of exosomes on TE13 cell migration and invasion. A Western blottinganalys is was performed to investigate the effects of exosomes on the expression of the EMT-related moleculesβ-catenin, NF-κB and snail. This study aimed to investigate the effects of exosomes from irradiated T cells on the human esophageal squamous cell carcinoma (ESCC) cell line TE13 and revealed that exosomes inhibit the proliferation but promote the metastasis of TE13 cells in a dose-and time-dependent manner. Furthermore, exosomes significantly increased the expression of β-catenin, NF-κB and snail in TE13 cells. The results of this study suggest an important role for T cell-derived exosomes in the progression of esophageal carcinoma: T cell-derived exosomes promote esophageal cancer metastasis, likely by promoting the EMT through the upregulation of β-catenin and the NF-κB/snail pathway. Moreover, this study supports the use of exosomes as a nearly perfect example of biomimetic nanovesicles that could be utilized in future therapeutic strategies against various diseases, including cancer.     

Regulation of exosome release from mammary epithelial and breast cancer cells – A new regulatory pathway

PurposeExosomes are small 50–100 nm sized extracellular vesicles released from normal and tumour cells and are a source of a new intercellular communication pathway. Tumour exosomes promote tumour growth and progression. What regulates the release and homoeostatic levels of exosomes, in cancer, in body fluids remains undefined.MethodsWe utilised a human mammary epithelial cell line (HMEC B42) and a breast cancer cell line derived from it (B42 clone 16) to investigate exosome production and regulation. Exosome numbers were quantified using a Nanosight LM10 and measured in culture supernatants in the absence and presence of exosomes in the medium. Concentrated suspensions of exosomes from the normal mammary epithelial cells, the breast cancer cells and bladder cancer cells were used. The interaction of exosomes with tumour cells was also investigated using fluorescently labelled exosomes.ResultsExosome release from normal human mammary epithelial cells and breast cancer cells is regulated by the presence of exosomes, derived from their own cells, in the extracellular environment of the cells. Exosomes from normal mammary epithelial cells also inhibit exosome secretion by breast cancer cells, which occurs in a tissue specific manner. Labelled exosomes from mammary epithelial cells are internalised into the tumour cells implicating a dynamic equilibrium and suggesting a mechanism for feedback control.ConclusionsThese data suggest a previously unknown novel feedback regulatory mechanism for controlling exosome release, which may highlight a new therapeutic approach to controlling the deleterious effects of tumour exosomes. This regulatory mechanism is likely to be generic to other tumours.     

Induction of myeloid‐derived suppressor cells by tumor exosomes

Myeloid‐derived suppressor cells (MDSCs) promote tumor progression. The mechanisms of MDSC development during tumor growth remain unknown. Tumor exosomes (T‐exosomes) have been implicated to play a role in immune regulation, however the role of exosomes in the induction of MDSCs is unclear. Our previous work demonstrated that exosomes isolated from tumor cells are taken up by bone marrow myeloid cells. Here, we extend those findings showing that exosomes isolated from T‐exosomes switch the differentiation pathway of these myeloid cells to the MDSC pathway (CD11b⁺Gr‐1⁺). The resulting cells exhibit MDSC phenotypic and functional characteristics including promotion of tumor growth. Furthermore, we demonstrated that in vivo MDSC mediated promotion of tumor progression is dependent on T‐exosome prostaglandin E2 (PGE2) and TGF‐β molecules. T‐exosomes can induce the accumulation of MDSCs expressing Cox2, IL‐6, VEGF, and arginase‐1. Antibodies against exosomal PGE2 and TGF‐β block the activity of these exosomes on MDSC induction and therefore attenuate MDSC‐mediated tumor‐promoting ability. Exosomal PGE2 and TGF‐β are enriched in T‐exosomes when compared with exosomes isolated from the supernatants of cultured tumor cells (C‐exosomes). The tumor microenvironment has an effect on the potency of T‐exosome mediated induction of MDSCs by regulating the sorting and the amount of exosomal PGE2 and TGF‐β available. Together, these findings lend themselves to developing specific targetable therapeutic strategies to reduce or eliminate MDSC‐induced immunosuppression and hence enhance host antitumor immunotherapy efficacy. © 2008 Wiley‐Liss, Inc.     

Macrophage-secreted Exosomes Delivering miRNA-21 Inhibitor can Regulate BGC-823 Cell Proliferation

Exosomes, membranous nanovesicles, naturally carry bio-macromolecules or miRNA and play impoetantroles in tumor pathogenesis. Here, we showed that macrophages cell-derived exosomes can function as vehiclesto deliver exogenous miR-21 inhibitor into BGC-823 gastric cancer cells. Exosomes loaded with miR-21inhibitorsignificantly increased miR-21 levels in BGC-823, but miR-21inhibitor loaded in exosomes exerted an oppositeeffect. miRNA transfected with exosomes had less cellular toxicity to host cells compared to conventionaltransfection methods. The miR-21inhibitor loaded exosomes promoted the migration ability and reducedapoptosis of BGC-823 gastric cancer cells. These observations indicate that miR-21 acts as a tumor promoterby targeting the PDCD4 gene and preventing apoptosis of gastric cancer cells through inhibition of PDCD4expression. Furthermore, exosome -mediated miR-21 inhibitor delivery resulted in functionally more efficientinhibition and less cellular toxicity compared to conventional transfection methods. Similar approaches could beuseful in modification of target biomolecules in vitro and in vivo. These findings contribute to our understandingof the functions of miR-21 and exosomes as a carrier for therapy of gastric cancer.     

外泌体miRNAs在乳腺癌肿瘤微环境中的研究进展

乳腺癌是全球女性最常发生的恶性肿瘤,患者死亡的主要原因是复发、转移和耐药性的出现。研究已经证明,外泌体介导癌细胞与肿瘤微环境之间的信息交流,外泌体携带的miRNAs通过差异表达于乳腺癌细胞,在微环境中影响癌基因表达的调控,介导乳腺癌细胞的信号通路,调节癌细胞周期进程以及重塑肿瘤相关成纤维细胞等,从而促进乳腺癌的发生、发展和转移;另外外泌体介导中和、药物外排和免疫系统抑制三种主要机制导致耐药性。未来,各种类型乳腺癌中差异表达的miRNAs有望成为临床诊断和预后的相关生物标志物,及抗肿瘤治疗的新靶点。     

PDL1-positive exosomes suppress antitumor immunity by inducing tumor-specific CD8+ T cell exhaustion during metastasis

Metastasis is the main cause of death in individuals with cancer. Immune checkpoint blockade (ICB) can potentially reverse CD8⁺ cytotoxic T lymphocytes (CTLs) dysfunction, leading to significant remission in multiple cancers. However, the mechanism underlying the development of CTL exhaustion during metastatic progression remains unclear. Here, we established an experimental pulmonary metastasis model with melanoma cells and discovered a critical role for melanoma-released exosomes in metastasis. Using genetic knockdown of nSMase2 and Rab27a, 2 key enzymes for exosome secretion, we showed that high levels of effector-like tumor-specific CD8⁺ T cells with transitory exhaustion, instead of terminal exhaustion, were observed in mice without exosomes; these cells showed limited inhibitory receptors and strong proliferation and cytotoxicity. Mechanistically, the immunosuppression of exosomes depends on exogenous PD-L1, which can be largely rescued by pretreatment with antibody blockade. Notably, we also found that exosomal PD-L1 acts as a promising predictive biomarker for ICB therapies during metastasis. Together, our findings suggest that exosomal PD-L1 may be a potential immunotherapy target, suggesting a new curative therapy for tumor metastasis.     

Exosomes mediate intercellular transfer of non–autonomous tolerance to proteasome inhibitors in mixed‐lineage leukemia

Proteasome inhibitors significantly improve cancer outcomes, but their use is eventually followed by proteasome inhibitor resistance and relapse. Current understanding of proteasome inhibitor resistance is limited to cell‐autonomous mechanisms; whether non–autonomous mechanisms can be implicated in the development of proteasome inhibitor resistance is unclear. Here, we show that proteasome inhibitor tolerance can be transmitted non–autonomously through exosome‐mediated intercellular interactions. We revealed that reversible proteasome inhibitor resistance can be transmitted from cells under therapy stress to naïve sensitive cells through exosome‐mediated cell cycle arrest and enhanced stemness in mixed‐lineage leukemia cells. Integrated multi‐omics analysis using the Tied Diffusion through Interacting Events algorithm identified several candidate exosomal proteins that may serve as predictors for proteasome inhibitor resistance and potential therapeutic targets for treating refractory mixed‐lineage leukemia. Furthermore, inhibiting the secretion of exosomes is a promising strategy for reversing proteasome inhibitor resistance in vivo, which provides a novel proof of principle for the treatment of other refractory or relapsed cancers.     

Role of exosomes in the immune microenvironment of ovarian cancer

Exosomes are excretory vesicles that can deliver a variety of bioactive cargo molecules to the extracellular environment. Accumulating evidence demonstrates exosome participation in intercellular communication, immune response, inflammatory response and they even play an essential role in affecting the tumor immune microenvironment. The role of exosomes in the immune microenvironment of ovarian cancer is mainly divided into suppression and stimulation. On one hand exosomes can stimulate the innate and adaptive immune systems by activating dendritic cells (DCs), natural killer cells and T cells, allowing these immune cells exert an antitumorigenic effect. On the other hand, ovarian cancer-derived exosomes initiate cross-talk with immunosuppressive effector cells, which subsequently cause immune evasion; one of the hallmarks of cancer. Exosomes induce the polarization of macrophages in M2 phenotype and induce apoptosis of lymphocytes and DCs. Exosomes further activate additional immunosuppressive effector cells (myeloid-derived suppressor cells and regulatory T cells) that induce fibroblasts to differentiate into cancer-associated fibroblasts. Exosomes also induce the tumorigenicity of mesenchymal stem cells to exert additional immune suppression. Furthermore, besides mediating the intercellular communication, exosomes carry microRNAs (miRNAs), proteins and lipids to the tumor microenvironment, which collectively promotes ovarian cancer cells to proliferate, invade and tumors to metastasize. Studying proteins, lipids and miRNAs carried by exosomes could potentially be used as an early diagnostic marker of ovarian cancer for designing treatment strategies.     

外泌体在恶性肿瘤放疗中的研究进展

外泌体是细胞分泌的直径在30~120 nm的具有生物学活性的盘状囊泡,参与恶性肿瘤的侵袭、转移及多药耐药等诸多方面。在放射治疗领域,目前已证实放射线所引起的肿瘤细胞外泌体分泌的变化,可影响细胞间的通讯作用,同时增加肿瘤细胞的放射线抗性。本文就外泌体在恶性肿瘤放疗中的研究进展作一综述。     

Increased T‐helper 17 cell differentiation mediated by exosome‐mediated microRNA‐451 redistribution in gastric cancer infiltrated T cells

MicroRNA (miR)‐451 is a cell metabolism‐related miRNA that can mediate cell energy‐consuming models by several targets. As miR‐451 can promote mechanistic target of rapamycin (mTOR) activity, and increased mTOR activity is related to increased differentiation of T‐helper 17 (Th17) cells, we sought to investigate whether miR‐451 can redistribute from cancer cells to infiltrated T cells and enhance the distribution of Th17 cells through mTOR. Real‐time PCR was used for detecting expression of miR‐451 in gastric cancer, tumor infiltrated T cells and exosomes, and distribution of Th17 was evaluated by both flow cytometry and immunohistochemistry (IHC). Immunofluorescence staining was used in monitoring the exosome‐enveloped miR‐451 from cancer cells to T cells with different treatments, and signaling pathway change was analyzed by western blot. miR‐451 decreased significantly in gastric cancer (GC) tissues but increased in infiltrated T cells and exosomes; tumor miR‐451 was negatively related to infiltrated T cells and exosome miR‐451. Exosome miR‐451 can not only serve as an indicator for poor prognosis of post‐operation GC patients but is also related to increased Th17 distribution in gastric cancer. miR‐451 can redistribute from cancer cells to T cells with low glucose treatment. Decreased 5′ AMP‐activated protein kinase (AMPK) and increased mTOR activity was investigated in miR‐451 redistributed T cells and the Th17 polarized differentiation of these T cells were also increased. Exosome miR‐451 derived from tumor tissues can serve as an indicator for poor prognosis and redistribution of miR‐451 from cancer cells to infiltrated T cells in low glucose treatment can enhance Th17 differentiation by enhancing mTOR activity.     

肿瘤微环境中外泌体功能研究进展

细胞外囊泡是一种十分重要的细胞间通讯的方式，尤其是外泌体在生理、病理过程中的调控作用越来越受到研究人员的关注。而在肿瘤微环境中，肿瘤细胞、免疫细胞、基质细胞都是外泌体的主要来源，外泌体中包裹的大量生物活性分子，对下游靶细胞的表型分化、生理功能、代谢状态有着重要的作用。探究肿瘤微环境中外泌体的调控作用，对进一步认识肿瘤发生、进展、转移、耐药、免疫逃逸等过程有着十分重要的意义，并且可作为肿瘤患者早期诊断和预后评价的重要指标。本文将主要介绍外泌体在肿瘤微环境中的作用。