Exosomes mediate drug resistance transfer in MCF-7 breast cancer cells and a probable mechanism is delivery of P-glycoprotein

Cisplatin induces the release of extracellular vesicles from ovarian cancer cells that can induce invasiveness and drug resistance in bystander cells

Ovarian cancer has a poor overall survival that is partly caused by resistance to drugs such as cisplatin. Resistance can be acquired as a result of changes to the tumour or due to altered interactions within the tumour microenvironment. Extracellular vesicles (EVs), small lipid-bound vesicles that are loaded with macromolecular cargo and released by cells, are emerging as mediators of communication in the tumour microenvironment. We previously showed that EVs mediate the bystander effect, a phenomenon in which stressed cells can communicate with neighbouring naive cells leading to various effects including DNA damage; however, the role of EVs released following cisplatin treatment has not been tested. Here we show that treatment of cells with cisplatin led to the release of EVs that could induce invasion and increased resistance when taken up by bystander cells. This coincided with changes in p38 and JNK signalling, suggesting that these pathways may be involved in mediating the effects. We also show that EV uptake inhibitors could prevent this EV-mediated adaptive response and thus sensitize cells in vitro to the effects of cisplatin. Our results suggest that preventing pro-tumourigenic EV cross-talk during chemotherapy is a potential therapeutic target for improving outcome in ovarian cancer patients.This article is part of the discussion meeting issue 'Extracellular vesicles and the tumour microenvironment'.

Modelling the propagation of a dynamical signature in gene expression mediated by the transport of extracellular microRNAs

Extracellular microRNAs (miRNAs) carried by exosomes can play a key role in cell-to-cell communication. Deregulation of miRNA expression and exosome secretion have been related to pathological conditions such as cancer. While it is known that circulating miRNAs can alter gene expression in recipient cells, it remains unclear how significant the dynamical impact of these extracellular miRNAs is. To shed light on this issue, we propose a model for the spatio-temporal evolution of the protein expression in a cell tissue altered by abnormal miRNA expression in a donor cell. This results in a nonhomogeneous cellular response in the tissue, which we quantify by studying the range of action of the donor cell on the surrounding cells. Key model parameters that control the range of action are identified. Based on a model for a heterogeneous cell population, we show that the dynamics of gene expression in the tissue is robust to random changes of the parameter values. Furthermore, we study the propagation of gene expression oscillations in a tissue induced by extracellular miRNAs. In the donor cell, the miRNA inhibits its own transcription which can give rise to local oscillations in gene expression. The resulting oscillations of the concentration of extracellular miRNA induce oscillations of the protein concentration in recipient cells. We analyse the nonmonotonic spatial evolution of the oscillation amplitude of the protein concentration in the tissue which may have implications for the propagation of oscillations in biological rhythms such as the circadian clock.

Advances of exosome in the development of ovarian cancer and its diagnostic and therapeutic prospect

Ovarian cancer is the leading cause of female gynecological cancer mortality. Most patients with ovarian cancer are diagnosed with advanced stage because of lack of early symptoms, physical signs, and sensitive tumor biomarkers. The standard treatment includes cytoreductive surgery and platinum-based chemotherapy (usually platinum combined with paclitaxel). Despite that postoperative adjuvant chemotherapy prolongs survival time, most patients go through relapse within 6–12 months after the treatment. Thus, elucidating the molecular mechanism in cancer development is essential to promote early diagnosis and novel treatments. The role of exosome has been highlighted in multiple research fields in recent years. Exosome has been described as nano-sized vesicle secreted by multiple mammalian cell types, carrying cargos like proteins, miRNAs, mRNAs, and lipids. It participates in the formation of tumor microenvironment and the development of tumorigenesis and drug resistance in ovarian cancer. Meanwhile, it may also play a pivotal role in diagnosis, efficacy evaluation, and prognosis. Besides, studies show that exosome and its processed products have promising value in ovarian cancer treatment. The aim of the current review is to describe the characteristics of exosome in ovarian cancer, especially focusing on its role in immune modulation and drug resistance, hoping to provide new information on its implications in cancer diagnosis and treatment.

PALINA: A phase II safety study of palbociclib in combination with letrozole or fulvestrant in African American women with hormone receptor positive HER2 negative advanced breast cancer

Palbociclib has been shown to be a highly effective therapy in hormone receptor positive metastatic breast cancer when used in combination with letrozole or fulvestrant. Grade 3/4 neutropenia is a common side effect although febrile neutropenia is relatively uncommon. Insufficient data exist to describe the hematological safety of palbociclib in African American women (AAW) known to have a high incidence of benign ethnic neutropenia (BEN). PALOMA 1, 2 and 3, the initial phase II/III studies that led to the U.S. Food and Drug Administration (FDA) approval of palbociclib in metastatic breast cancer, only included participants with baseline absolute neutrophil count (ANC) of 1500/mm³ or higher. African American women (AAW) were underrepresented in the PALOMA trials and this may be partially explained by strict requirements for minimal ANC ≥1500/mm³. The ANC of 1500/mm³ for initiation of treatment in those with BEN has been previously challenged. In this study, we propose to lower the ANC cutoff for enrollment to 1000/mm³. PALINA (NCT02692755) is a phase II, single arm, multicenter clinical trial that will enroll 35 patients. The primary endpoint is to assess the proportion of patients who complete therapy without the development of febrile neutropenia or treatment discontinuation due to neutropenia. The secondary endpoints include number of patients who required dose delays or dose reductions in palbociclib attributed to neutropenia, rate of grade 3/4 neutropenia, clinical benefit rate at 24 weeks, the association between metabolite and exosomal signature with disease response and the association between baseline ANC prior to cancer diagnosis and the Duffy Null polymorphism (SNP rs2814778) with hematological safety. PALINA will provide important information about the hematologic safety of palbociclib in AAW with advanced breast cancer.

Exosome-mediated gefitinib resistance in lung cancer HCC827 cells via delivery of miR-21

Acquired resistance to gefitinib remains a major challenge in cancer treatment. In the present study, the effect of exosomes on the transmission of gefitinib resistance from gefitinib-resistant HCC827 lung cancer cells (H827R) to their gefitinib-sensitive counterparts and the potential underlying mechanisms by which this occurs was investigated. Exosomes were obtained from the cell supernatant using ultracentrifugation and the ExoQuick-TC exosome precipitation solution. Drug resistance was assessed by flow cytometry, apoptosis assays and cell counting kit-8 assays. The expression of microRNA (miR)-21 was analyzed by reverse transcription-quantitative polymerase chain reaction. Exosomes released by H827R cells (R/exo) may decrease the sensitivity of the human NSCLC HCC827 cell line to gefitinib. The results indicated that miR-21 expression was increased in R/exo and R/exo-treated H827S cells. However, miR-21 inhibition abrogated exosome-mediated drug resistance. Phosphorylated-protein kinase B (p-Akt), which is downstream of miR-21, was downregulated following gefitinib treatment; however, R/exo pretreatment elevated p-Akt levels and promoted the activation of Akt. By contrast, miR-21 inhibition reduced p-Akt expression. Therefore, the induction of miR-21 via exosomes and the activation of Akt may be mechanisms by which exosomes mediate the transfer of drug resistance.

Exosome: emerging biomarker in breast cancer

Exosomes are nano-sized membrane vesicles released by a variety of cell types, and are thought to play important roles in intercellular communications. In breast cancer, through horizontal transfer of various bioactive molecules, such as proteins and mRNAs, exosomes are emerging as local and systemic cell-to-cell mediators of oncogenic information and play an important role on cancer progression. This review outlines the current knowledge and concepts concerning the exosomes involvement in breast cancer pathogenesis (including tumor initiation, invasion and metastasis, angiogenesis, immune system modulation and tumor microenvironment) and cancer therapy resistance. Moreover, the potential use of exosomes as promising diagnostic and therapeutic biomarkers in breast cancer are also discussed.

Ovarian cancer-derived extracellular vesicles affect normal human fibroblast behavior

It has become clear that non-tumor cells in the microenvironment, especially fibroblasts, actively participate in tumor progression. Fibroblasts conditioned by tumor cells become "activated" and, as such, are identified as CAFs (cancer-associated fibroblasts). These CAFs remodel the tumor stroma to make it more favourable for cancer progression. The aim of this work was to verify whether EVs (extracellular vesicles - whose role as mediators of information between tumor and stromal cells is well known) released from human ovarian cancer cells were able to activate fibroblasts. EVs isolated from SKOV3 (more aggressive) and CABA I (less aggressive) cells were administered to fibroblasts. The consequent activation was supported by morphological and molecular changes in treated fibroblasts; XTT assays, zymographies, wound healing tests and invasion assays also highlighted higher proliferation, motility, invasiveness and enzyme expression. The secretome of these "activated" fibroblasts was, in turn, able to modulate the responses (proliferation, motility and invasion) of fibroblasts, and of tumor and endothelial cells. These findings support the idea that ovarian cancer cells can modulate fibroblast behaviour through the release of EVs, activating them to a CAFs-like state; the latter are able, in turn, to stimulate the surrounding cells. EVs from SKOV3 rather than from CABA I seem to be more efficient in some processes.

Roles of Extracellular Vesicles in Metastatic Breast Cancer

Cells can secrete extracellular vesicles (EVs) to communicate with neighboring or distant cells by EVs which are composed of a lipid bilayer containing transmembrane proteins and enclosing cytosolic proteins, lipids, and nucleic acids. Breast Cancer is the most frequently diagnosed malignancy with more than 1 million new cases each year and ranks the leading cause of cancer mortality in women worldwide. In this review, we will discuss recent progresses of the roles and mechanisms of cancer-derived EVs in metastatic breast cancer, with a special attention on tumor microenvironment construction, progression, and chemo/radiotherapy responses. This review also covers EV roles as biomarker and therapeutic target in clinical application.

The multifaceted role of exosomes in cancer progression: diagnostic and therapeutic implications [corrected]

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.

Comparative analysis of microRNA expression profiles between A549, A549/DDP and their respective exosomes

Exosomes were reported to transport bioactive molecules and influence the biology behavior of recipient cells. In order to study the role of exosomal microRNAs in the mechanism of cisplatin resistance to lung cancer cells, we analyzed the expression profiles of microRNAs in A549, A549/DDP cells and their exosomes by microarray. The results showed that a certain proportion of microRNAs were co-expressed in the cells and exosomes. Linear regression analysis showed that the expression of microRNAs in A549 and A549/DDP cells were strongly correlated with those in their respective exosomes. The expression level of 5 microRNAs (miR-197-5p, miR-4443, miR-642a-3p, miR-27b-3p and miR-100-5p) with the most differential expression were verified by qRT-PCR. The results were consistent with those of the microarray. Target gene prediction and pathway analysis discovered that the microRNAs in the intersections may participate in drug resistance. And the prediction of their association with diseases found that most of these microRNAs was associated with lung cancer. We could draw a preliminary conclusion that microRNAs in exosomes may be involved in the drug resistance of lung cancer cells to cisplatin.

Cytokine-mediated therapeutic resistance in breast cancer

Therapeutic resistance leading to tumor relapse is a major challenge in breast cancer (BCa) treatment. Numerous factors involved in multiple mechanisms promote the development of tumor chemo/radio-resistance. Cytokines/chemokines are important inflammatory factors and highly related to tumorigenesis, metastasis and tumors responses to treatment. A large number of studies have demonstrated that the network of cytokines activates multiple cell signaling pathways to promote tumor cell survival, proliferation, invasion, and migration. Particularly in BCa, cytokines-enhanced the epithelial-mesenchymal transition (EMT) process plays a pivotal role in the progression of metastatic phenotypes and resistance to the traditional chemo/radio-therapy. Virtually, therapeutic resistance is not entirely determined by tumor cell intrinsic characteristics but also dependent upon synchronized effects by numerous of local microenvironmental factors. Emerging evidence highlighted that exosomes secreted from various types of cells promote intercellular communication by transferring bioactive molecules including miRNAs and cytokines, suggesting that exosomes are essential for sustentation of tumor progression and therapeutic resistance within the tumor microenvironment. In this review, we discuss the mechanisms by which cytokines promote therapeutic resistance of BCa and suggest a potential approach for improving BCa therapeutics by inhibition of exosome function.

Can hi-jacking hypoxia inhibit extracellular vesicles in cancer?

Increasing evidence indicates that extracellular vesicles (EVs) are key players in undesirable cell-cell communication in cancer. However, the release of EVs is not unique to cancer cells; normal cells release EVs to perform physiological roles. Thus, selective inhibition of EV release from cancer cells is desirable. Hypoxia contributes to tumour development and aggressiveness. EV quantities and thus undesirable communications are substantially increased in hypoxia. Targeting hypoxia could selectively inhibit EV release from tumour cells without disturbing physiologically relevant EVs. The unfavourable association between hypoxia and EV release is evident in multiple tumour types; therefore, targeting hypoxia could have a broad therapeutic benefit.

Functional miRNAs in breast cancer drug resistance

Owing to improved early surveillance and advanced therapy strategies, the current death rate due to breast cancer has decreased; nevertheless, drug resistance and relapse remain obstacles on the path to successful systematic treatment. Multiple mechanisms responsible for drug resistance have been elucidated, and miRNAs seem to play a major part in almost every aspect of cancer progression, including tumorigenesis, metastasis, and drug resistance. In recent years, exosomes have emerged as novel modes of intercellular signaling vehicles, initiating cell–cell communication through their fusion with target cell membranes, delivering functional molecules including miRNAs and proteins. This review particularly focuses on enumerating functional miRNAs involved in breast cancer drug resistance as well as their targets and related mechanisms. Subsequently, we discuss the prospects and challenges of miRNA function in drug resistance and highlight valuable approaches for the investigation of the role of exosomal miRNAs in breast cancer progression and drug resistance.

Simultaneous isolation and preconcentration of exosomes by ion concentration polarization

Exosomes carry microRNA biomarkers, occur in higher abundance in cancerous patients than in healthy ones, and because they are present in most biofluids, including blood and urine, these can be obtained noninvasively. Standard laboratory techniques to isolate exosomes are expensive, time consuming, provide poor purity, and recover on the order of 25% of the available exosomes. We present a new microfluidic technique to simultaneously isolate exosomes and preconcentrate them by electrophoresis using a high transverse local electric field generated by ion-depleting ion-selective membrane. We use pressure-driven flow to deliver an exosome sample to a microfluidic chip such that the transverse electric field forces them out of the cross flow and into an agarose gel which filters out unwanted cellular debris while the ion-selective membrane concentrates the exosomes through an enrichment effect. We efficiently isolated exosomes from 1× PBS buffer, cell culture media, and blood serum. Using flow rates from 150 to 200 μL/h and field strengths of 100 V/cm, we consistently captured between 60 and 80% of exosomes from buffer, cell culture media, and blood serum as confirmed by both fluorescence spectroscopy and nanoparticle tracking analysis. Our microfluidic chip maintained this recovery rate for more than 20 min with a concentration factor of 15 for 10 min of isolation.

Periostin is identified as a putative metastatic marker in breast cancer-derived exosomes

Breast cancer (BrCa) is the most frequent cancer type in women and a leading cause of cancer related deaths in the world. Despite the decrease in mortality due to better diagnostics and palliative care, there is a lack of prognostic markers of metastasis. Recently, the exploitation of liquid biopsies and in particular of the extracellular vesicles has shown promise in the identification of such prognostic markers. In this study we compared the proteomic content of exosomes derived from metastatic and non-metastatic human (MCF7 and MDA-MB-231) and mouse (67NR and 4T1) cell lines. We found significant differences not only in the amount of secreted exosomes but most importantly in the protein content of exosomes secreted from metastatic versus non-metastatic ones. We identified periostin as a protein that is enriched in exosomes secreted by metastatic cells and validated its presence in a pilot cohort of breast cancer patient samples with localized disease or lymph node (LN) metastasis.

MicroRNA expression profiles of drug-resistance breast cancer cells and their exosomes

Exosomes have been shown to transmit drug resistance through delivering miRNAs. We aimed to explore their roles in breast cancer. Three resistant sublines were established by exposing parental MDA-MB-231 cell line to docetaxel, epirubicin and vinorelbine, respectively. Preneoadjuvant chemotherapy biopsies and paired surgically-resected specimens embedded in paraffin from 23 breast cancer patients were collected. MiRNA expression profiles of the cell lines and their exosomes were evaluated using microarray. The result showed that most miRNAs in exosomes had a lower expression level than that in cells, however, some miRNAs expressed higher in exosomes than in cells, suggesting a number of miRNAs is concentrated in exosomes. Among the dysregulated miRNAs, 22 miRNAs were consistently up-regulated in exosomes and their cells of origin. We further found that 12 of the 22 miRNAs were significantly up-regulated after preneoadjuvant chemotherapy. Further study of the role of these 12 miRNAs in acquisition of drug resistance is needed to clarify their contribution to chemoresistance.

Exosomes promote cetuximab resistance via the PTEN/Akt pathway in colon cancer cells

Cetuximab is widely used in patients with metastatic colon cancer expressing wildtype KRAS. However, acquired drug resistance limits its clinical efficacy. Exosomes are nanosized vesicles secreted by various cell types. Tumor cell-derived exosomes participate in many biological processes, including tumor invasion, metastasis, and drug resistance. In this study, exosomes derived from cetuximab-resistant RKO colon cancer cells induced cetuximab resistance in cetuximab-sensitive Caco-2 cells. Meanwhile, exosomes from RKO and Caco-2 cells showed different levels of phosphatase and tensin homolog (PTEN) and phosphor-Akt. Furthermore, reduced PTEN and increased phosphorylated Akt levels were found in Caco-2 cells after exposure to RKO cell-derived exosomes. Moreover, an Akt inhibitor prevented RKO cell-derived exosome-induced drug resistance in Caco-2 cells. These findings provide novel evidence that exosomes derived from cetuximab-resistant cells could induce cetuximab resistance in cetuximab-sensitive cells, by downregulating PTEN and increasing phosphorylated Akt levels.

Mechanisms of Drug Resistance in Cancer: The Role of Extracellular Vesicles

Drug resistance remains a major barrier to the successful treatment of cancer. The mechanisms by which therapeutic resistance arises are multifactorial. Recent evidence has shown that extracellular vesicles (EVs) play a role in mediating drug resistance. EVs are small vesicles carrying a variety of macromolecular cargo released by cells into the extracellular space and can be taken up into recipient cells, resulting in transfer of cellular material. EVs can mediate drug resistance by several mechanisms. They can serve as a pathway for sequestration of cytotoxic drugs, reducing the effective concentration at target sites. They can act as decoys carrying membrane proteins and capturing monoclonal antibodies intended to target receptors at the cell surface. EVs from resistant tumor cells can deliver mRNA, miRNA, long noncoding RNA, and protein inducing resistance in sensitive cells. This provides a new model for how resistance that arises can then spread through a heterogeneous tumor. EVs also mediate cross-talk between cancer cells and stromal cells in the tumor microenvironment, leading to tumor progression and acquisition of therapeutic resistance. In this review, we will describe what is known about how EVs can induce drug resistance, and discuss the ways in which EVs could be used as therapeutic targets or diagnostic markers for managing cancer treatment. While further characterization of the vesiculome and the mechanisms of EV function are still required, EVs offer an exciting opportunity in the fight against cancer.

Extracellular vesicles as emerging targets in cancer: Recent development from bench to bedside

Extracellular vesicles (EVs) have emerged as important players of cancer initiation and progression through cell-cell communication. They have been recognized as critical mediators of extracellular communications, which promote transformation, growth invasion, and drug-resistance of cancer cells. Interestingly, the secretion and uptake of EVs are regulated in a more controlled manner than previously anticipated. EVs are classified into three groups, (i) exosomes, (ii) microvesicles (MVs), and (iii) apoptotic bodies (ABs), based on their sizes and origins, and novel technologies to isolate and distinguish these EVs are evolving. The biologically functional molecules harbored in these EVs, including nucleic acids, lipids, and proteins, have been shown to induce key signaling pathways in both tumor and tumor microenvironment (TME) cells for exacerbating tumor development. While tumor cell-derived EVs are capable of reprogramming stromal cells to generate a proper tumor cell niche, stromal-derived EVs profoundly affect the growth, resistance, and stem cell properties of tumor cells. This review summarizes and discusses these reciprocal communications through EVs in different types of cancers. Further understanding of the pathophysiological roles of different EVs in tumor progression is expected to lead to the discovery of novel biomarkers in liquid biopsy and development of tumor specific therapeutics. This review will also discuss the translational aspects of EVs and therapeutic opportunities of utilizing EVs in different cancer types.

Protein and chemotherapy profiling of extracellular vesicles harvested from therapeutic induced senescent triple negative breast cancer cells

Triple negative breast cancer (TNBC) is an aggressive subtype with relatively poor clinical outcomes and limited treatment options. Chemotherapy, while killing cancer cells, can result in the generation of highly chemoresistant therapeutic induced senescent (TIS) cells that potentially form stem cell niches resulting in metastases. Intriguingly, senescent cells release significantly more extracellular vesicles (EVs) than non-senescent cells. Our aim was to profile EVs harvested from TIS TNBC cells compared with control cells to identify a potential mechanism by which TIS TNBC cells maintain survival in the face of chemotherapy. TIS was induced and confirmed in Cal51 TNBC cells using the chemotherapeutic paclitaxel (PTX) (Taxol). Mass spectrometry (MS) analysis of EVs harvested from TIS compared with control Cal51 cells was performed using Ingenuity Pathway Analysis and InnateDB programs. We demonstrate that TIS Cal51 cells treated with 75 nM PTX for 7 days became senescent (senescence-associated β-galactosidase (SA-β-Gal) positive, Ki67-negative, increased p21 and p16, G2/M cell cycle arrest) and released significantly more EVs (P=0.0002) and exosomes (P=0.0007) than non-senescent control cells. Moreover, TIS cells displayed an increased expression of the multidrug resistance protein 1/p-glycoprotein. MS analysis demonstrated that EVs derived from senescent Cal51 cells contained 142 proteins with a significant increased fold change compared with control EVs. Key proteins included ATPases, annexins, tubulins, integrins, Rabs and insoluble senescence-associated secretory phenotype (SASP) factors. A fluorescent analogue of PTX (Flutax-2) allowed appreciation of the removal of chemotherapy in EVs from senescent cells. Treatment of TIS cells with the exosome biogenesis inhibitor GW4869 resulted in reduced SA-β-Gal staining (P=0.04). In summary, this study demonstrates that TIS cells release significantly more EVs compared with control cells, containing chemotherapy and key proteins involved in cell proliferation, ATP depletion, apoptosis and the SASP. These findings may partially explain why cancer senescent cells remain viable despite chemotherapeutic challenge.

Elevated levels of extracellular vesicles are associated with therapy failure and disease progression in breast cancer patients undergoing neoadjuvant chemotherapy

Extracellular vesicles (EVs) have been discussed as a diagnostic tool for minimal residual disease (MRD) evaluation in breast cancer (BC) in addition to the analysis of circulating tumor cells (CTCs). Therefore, we investigated circulating EV levels as surrogate markers for disease monitoring and prediction of prognosis in primary, non-metastatic, locally advanced BC patients. EVs were enriched from blood samples of BC patients before and after neoadjuvant chemotherapy (NACT) and from healthy females. EV marker expression analysis was performed and EV sizes and concentrations were determined by nanoparticle tracking analysis. The results were associated with disease status, outcome and CTC presence, evaluated by gene expression analysis after enrichment. We demonstrated that i) the EV concentration was 40-fold higher in BC patients compared to healthy females, ii) the EV concentration increased during therapy, iii) an increased EV concentration pre-NACT was associated with therapy failure and iv) an elevated EV concentration post-NACT was associated with a reduced three-year progression-free and overall survival. Of note, residual stem cell-like and/or resistant CTCs after therapy were associated with a lower EV concentration post-NACT. Our study highlights that the concentration of EVs within BC blood samples may serve as a complementary parameter reflecting the status of MRD as well as therapy and disease outcome in parallel with CTC investigation.

Exosomes as mediators of platinum resistance in ovarian cancer

Exosomes have been implicated in the cell-cell transfer of oncogenic proteins and genetic material. We speculated this may be one mechanism by which an intrinsically platinum-resistant population of epithelial ovarian cancer (EOC) cells imparts its influence on surrounding tumor cells. To explore this possibility we utilized a platinum-sensitive cell line, A2780 and exosomes derived from its resistant subclones, and an unselected, platinum-resistant EOC line, OVCAR10. A2780 cells demonstrate a ~2-fold increase in viability upon treatment with carboplatin when pre-exposed to exosomes from platinum-resistant cells as compared to controls. This coincided with increased epithelial to mesenchymal transition (EMT). DNA sequencing of EOC cell lines revealed previously unreported somatic mutations in the Mothers Against Decapentaplegic Homolog 4 (SMAD4) within platinum-resistant cells. A2780 cells engineered to exogenously express these SMAD4 mutations demonstrate up-regulation of EMT markers following carboplatin treatment, are more resistant to carboplatin, and release exosomes which impart a ~1.7-fold increase in resistance in naive A2780 recipient cells as compared to controls. These studies provide the first evidence that acquired SMAD4 mutations enhance the chemo-resistance profile of EOC and present a novel mechanism in which exchange of tumor-derived exosomes perpetuates an EMT phenotype, leading to the development of subpopulations of platinum-refractory cells.

Chemoresistance in cancer cells: exosomes as potential regulators of therapeutic tumor heterogeneity

Drug resistance in cancer cells remains a fundamental challenge. Be it nontargeted or targeted drugs, the presence of intrinsic or acquired cancer cell resistance remains a great obstacle in chemotherapy. Conventionally, a spectrum of cellular mechanisms defines drug resistance including overexpression of antiapoptotic proteins and drug efflux pumps, mutations in target and synergistic activation of prosurvival pathways in tumor cells. In addition to these well-studied routes, exosome-induced chemoresistance is emerging as a novel mechanism. Mechanistically, exosomes impart resistance by direct drug export, transport of drug efflux pumps and miRNAs exchange among cells. Moreover, exosome signaling creates ‘therapeutic tumor heterogeneity’ and favorably condition tumor microenvironment. Here, we discuss exosomes’ role in chemoresistance and possibilities of developing novel therapeutic strategies.

Autocrine mechanisms of cancer chemoresistance

An ever-increasing number of studies highlight the role of cancer secretome in the modification of tumour microenvironment and in the acquisition of cancer cell resistance to therapeutic drugs. The knowledge of the mechanisms underlying the relationship between cancer cell-secreted factors and chemoresistance is becoming fundamental for the identification of novel anticancer therapeutic strategies overcoming drug resistance and novel prognostic secreted biomarkers. In this review, we summarize the novel findings concerning the regulation of secreted molecules by cancer cells compromising drug sensitivity. In particular, we highlight data from available literature describing the involvement of cancer cell-secreted molecules determining chemoresistance in an autocrine manner, including: i) growth factors; ii) glycoproteins; iii) inflammatory cytokines; iv) enzymes and chaperones; and v) tumor-derived exosomes.

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

Numerous studies have proved that cell-nonautonomous regulation of neoplastic cells is a distinctive and essential characteristic of tumorigenesis. Two way communications between the tumor and the stroma, or within the tumor significantly influence disease progression and modify treatment responses. In the tumor microenvironment (TME), malignant cells utilize paracrine signaling initiated by adjacent stromal cells to acquire resistance against multiple types of anticancer therapies, wherein extracellular vesicles (EVs) substantially promote such events. EVs are nanoscaled particles enclosed by phospholipid bilayers, and can mediate intercellular communications between cancerous cells and the adjacent microenvironment to accelerate pathological proceeding. Here we review the most recent studies of EV biology and focus on key cell lineages of the TME and their EV cargoes that are biologically active and responsible for cancer resistance, including proteins, RNAs, and other potentially essential components. Since EVs are emerging as novel but critical elements in establishing and maintaining hallmarks of human cancer, timely and insightful understanding of their molecular properties and functional mechanisms would pave the road for clinical diagnosis, prognosis, and effective targeting in the global landscape of precision medicine. Further, we address the potential of EVs as promising biomarkers in cancer clinics and summarize the technical improvements in EV preparation, analysis, and imaging. We highlight the practical issues that should be exercised with caution to guide the development of targeting agents and therapeutic methodologies to minimize cancer resistance driven by EVs, thereby allowing to effectively control the early steps of disease exacerbation.

HFE genotype affects exosome phenotype in cancer

Neuroblastoma is the third most common childhood cancer, and timely diagnosis and sensitive therapeutic monitoring remain major challenges. Tumor progression and recurrence is common with little understanding of mechanisms. A major recent focus in cancer biology is the impact of exosomes on metastatic behavior and the tumor microenvironment. Exosomes have been demonstrated to contribute to the oncogenic effect on the surrounding tumor environment and also mediate resistance to therapy. The effect of genotype on exosomal phenotype has not yet been explored. We interrogated exosomes from human neuroblastoma cells that express wild-type or mutant forms of the HFE gene. HFE, one of the most common autosomal recessive polymorphisms in the Caucasian population, originally associated with hemochromatosis, has also been associated with increased tumor burden, therapeutic resistance boost, and negative impact on patient survival. Herein, we demonstrate that changes in genotype cause major differences in the molecular and functional properties of exosomes; specifically, HFE mutant derived exosomes have increased expression of proteins relating to invasion, angiogenesis, and cancer therapeutic resistance. HFE mutant derived exosomes were also shown to transfer this cargo to recipient cells and cause an increased oncogenic functionality in those recipient cells.

Cisplatin-resistant lung cancer cell-derived exosomes increase cisplatin resistance of recipient cells in exosomal miR-100-5p-dependent manner

Exosomes derived from lung cancer cells confer cisplatin (DDP) resistance to other cancer cells. However, the underlying mechanism is still unknown. A549 resistance to DDP (A549/DDP) was established. Microarray was used to analyze microRNA (miRNA) expression profiles of A549 cells, A549/DDP cells, A549 exosomes, and A549/DDP exosomes. There was a strong correlation of miRNA profiles between exosomes and their maternal cells. A total of 11 miRNAs were significantly upregulated both in A549/DDP cells compared with A549 cells and in exosomes derived from A549/DDP cells in contrast to exosomes from A549 cells. A total of 31 downregulated miRNAs were also observed. miR-100–5p was the most prominent decreased miRNA in DDP-resistant exosomes compared with the corresponding sensitive ones. Downregulated miR-100–5p was proved to be involved in DDP resistance in A549 cells, and mammalian target of rapamycin (mTOR) expression was reverse regulated by miR-100–5p. Exosomes confer recipient cells’ resistance to DDP in an exosomal miR-100–5p-dependent manner with mTOR as its potential target both in vitro and in vivo. Exosomes from DDP-resistant lung cancer cells A549 can alter other lung cancer cells’ sensitivity to DDP in exosomal miR-100–5p-dependent manner. Our study provides new insights into the molecular mechanism of DDP resistance in lung cancer.

Predictive role of GSTP1-containing exosomes in chemotherapy-resistant breast cancer

Anthracycline/taxane-based chemotherapy regimens are usually used as neoadjuvant chemotherapies to decrease tumour size and prevent metastasis of advanced breast cancer. However, patients have a high risk of developing chemo-resistance during treatment through still unknown mechanisms. Glutathione S-transferase P1 (GSTP1), which belongs to the family of phase II metabolic enzymes, has been reported to function in detoxifying several anti-cancer drugs by conjugating them with glutathione. Previous studies have identified GSTP1 as a predictor of prognosis and chemo-resistance in breast cancer patients, but the mechanisms governing GSTP1-dependent drug resistance are still unclear. We have found that GSTP1 expression is much higher in adriamycin-resistant cells and their corresponding exosomes. The role of GSTP1-containing exosomes in conferring drug resistance was analysed through cell apoptosis and immunofluorescence staining assays. Furthermore, we analysed 42 cases of paired breast cancer tissues collected before and after anthracycline/taxane-based neoadjuvant chemotherapy by immunohistochemistry. Higher GSTP1 expression was shown in the progressive disease (PD)/stable disease (SD) group than in the partial response (PR)/complete response (CR) group both in the samples collected before and after the chemotherapy treatment. Interestingly, GSTP1 partly re-localized from the cell nucleus to the cytoplasm upon treatment, and similar results were obtained for the exosomal marker Tumour susceptibility gene 101 protein (TSG101), which also increased in the cytoplasm after chemotherapy. After analysing the serum exosomes of 30 patients treated with anthracycline/taxane-based neoadjuvant chemotherapy, we discovered that the levels of GSTP1 in exosomes from patients in the PD/SD group were significantly higher than those in the PR/CR group. Here, for the first time, we investigated a novel role for GSTP1-containing exosomes and their capability to transfer drug resistance and evaluated their clinical use in predicting chemo-resistance.

UCH-L1-containing exosomes mediate chemotherapeutic resistance transfer in breast cancer

BACKGROUND

Chemotherapy resistance has become a serious challenge in the treatment of breast cancer. Previous studies showed cells can transfer proteins, including those responsible for drug resistance to adjacent cells via exosomes.

METHODS

The switches of drug resistance via exosomes transfer were assessed by CellTiter-Blue Viability assay, flow cytometry, and immunostaining analysis. Relative protein levels of Ubiquitin carboxyl terminal hydrolase-L1 (UCH-L1), P-glycoprotein (P-gp), extracellular-signal regulated protein kinase1/2 (ERK1/2), and phospho-extracellular-signal regulated protein kinase1/2 (p-ERK1/2) were measured by Western blot. Immunohistochemistry was performed on 93 breast cancer samples to assess the associations of UCH-L1 levels with immunofluorescence value of UCH-L1 in circulating exosomes.

RESULT

The Adriamycin-resistant human breast cancer cells (MCF7/ADM) secreted exosomes carrying UCH-L1 and P-gp proteins into the extracellular microenvironment then integrated into Adriamycin-sensitive human breast cancer cells (MCF7/WT) in a time-dependent manner, transferring the chemoresistance phenotype. Notably, in blood samples from patients with breast cancer, the level of exosomes carrying UCH-L1 before chemotherapy was significantly negatively correlated with prognosis.

CONCLUSION

Our study demonstrated that UCH-L1-containing exosomes can transfer chemoresistance to recipient cells and these exosomes may be useful as non-invasive diagnostic biomarkers for detection of chemoresitance in breast cancer patients, achieving more effective and individualized chemotherapy.

Tumor Microenvironment Modulation via Gold Nanoparticles Targeting Malicious Exosomes: Implications for Cancer Diagnostics and Therapy

Exosomes are nanovesicles formed in the endosomal pathway with an important role in paracrine and autocrine cell communication. Exosomes secreted by cancer cells, malicious exosomes, have important roles in tumor microenvironment maturation and cancer progression. The knowledge of the role of exosomes in tumorigenesis prompted a new era in cancer diagnostics and therapy, taking advantage of the use of circulating exosomes as tumor biomarkers due to their stability in body fluids and targeting malignant exosomes’ release and/or uptake to inhibit or delay tumor development. In recent years, nanotechnology has paved the way for the development of a plethora of new diagnostic and therapeutic platforms, fostering theranostics. The unique physical and chemical properties of gold nanoparticles (AuNPs) make them suitable vehicles to pursuit this goal. AuNPs’ properties such as ease of synthesis with the desired shape and size, high surface:volume ratio, and the possibility of engineering their surface as desired, potentiate AuNPs’ role in nanotheranostics, allowing the use of the same formulation for exosome detection and restraining the effect of malicious exosomes in cancer progression.

Exosomes in tumor microenvironment: novel transporters and biomarkers

Tumor microenvironment (TME) plays an integral part in the biology of cancer, participating in tumor initiation, progression, and response to therapy. Exosome is an important part of TME. Exosomes are small vesicles formed in vesicular bodies with a diameter of 30-100 nm and a classic "cup" or "dish" morphology. They can contain microRNAs, mRNAs, DNA fragments and proteins, which are shuttled from a donor cell to recipient cells. Exosomes secreted from tumor cells are called tumor-derived (TD) exosomes. There is emerging evidence that TD exosomes can construct a fertile environment to support tumor proliferation, angiogenesis, invasion and premetastatic niche preparation. TD exosomes also may facilitate tumor growth and metastasis by inhibiting immune surveillance and by increasing chemoresistance via removal of chemotherapeutic drugs. Therefore, TD-exosomes might be potential targets for therapeutic interventions via their modification or removal. For example, exosomes can serve as specific delivery vehicles to tumors of drugs, small molecules, or agents of prevention and gene therapy. Furthermore, the biomarkers detected in exosomes of biological fluids imply a potential for exosomes in the early detection and diagnosis, prediction of therapeutic efficacy, and determining prognosis of cancer. Although exosomes may serve as cancer biomarkers and aid in the treatment of cancer, we have a long way to go before we can further enhance the anti-tumor therapy of exosomes and develop exosome-based cancer diagnostic and therapeutic strategies.

From pathogenesis to clinical application: insights into exosomes as transfer vectors in cancer

Exosomes are nanoscale extracellular membrane vesicles that are created by the fusion of an intracellular multivesicular body with the cell membrane. They are widely distributed in serum, urine, saliva and other biological fluids. As important transfer vectors for intercellular communication and genetic material, exosomes can stimulate target cells directly via receptor-mediated interactions or via the transfer of various bioactive molecules, such as cell membrane receptors, proteins, mRNAs and microRNAs, thus exerting their biological functions. This review focuses on the biological characteristics of exosomes, as well as their role and underlying mechanisms of action in the evolution of tumor formation, metastasis, drug resistance and other malignant behaviors. Additionally, this review emphasizes the potential applications of exosomes in the treatment of tumors. Further research may provide new ideas and methods to establish effective, exosome-based strategies for the early diagnosis and treatment of tumors.

Tumor-derived exosomes in cancer progression and treatment failure

Exosomes have diameter within the range of 30-100 nm and spherical to cup-shaped nanoparticles with specific surface molecular characteristics, such as CD9 and CD63. These vesicles are present in nearly all human body fluids, including blood plasma/serum, saliva, breast milk, cerebrospinal fluid, urine, semen, and particularly enriched in tumor microenvironment. Exosomes contain multiple proteins, DNA, mRNA, miRNA, long non-coding RNA, and even genetic materials of viruses/prions. These materials are biochemically and functionally distinct and can be transferred to a recipient cell where they regulate protein expression and signaling pathways. Recently, exosomes are demonstrated to have a close relationship with tumor development and metastasis. Exosomes influence therapeutic effect in cancer patients. In this review, we describe the biogenesis, composition, and function of exosomes. The mechanism on how tumor-derived exosomes contribute to cancer progression and clinical treatment failure is also described, with special focus on their potential applications in cancer therapy.

From glioblastoma to endothelial cells through extracellular vesicles: messages for angiogenesis

Glioblastoma has one of the highest mortality rates among cancers, and it is the most common and malignant form of brain cancer. Among the typical features of glioblastoma tumors, there is an aberrant vascularization: all gliomas are among the most vascularized/angiogenic tumors. In recent years, it has become clear that glioblastoma cells can secrete extracellular vesicles which are spherical and membrane-enclosed particles released, in vitro or in vivo, by both normal and tumor cells; they are involved in the regulation of both physiological and pathological processes; among the latter, cancer is the most widely studied. Extracellular vesicles from tumor cells convey messages to other tumor cells, but also to normal stromal cells in order to create a microenvironment that supports cancer growth and progression and are implicated in drug resistance, escape from immunosurveillance and from apoptosis, as well as in metastasis formation; they are also involved in angiogenesis stimulation, inducing endothelial cells proliferation, and other pro-angiogenic activities. To this aim, the present paper assesses in detail the extracellular vesicles phenomenon in the human glioblastoma cell line U251 and evaluates extracellular vesicles ability to promote the processes required to achieve the formation of new blood vessels in human brain microvascular endothelial cells, highlighting that they stimulate proliferation, motility, and tube formation in a dose-response manner. Moreover, a molecular characterization shows that extracellular vesicles are fully equipped for angiogenesis stimulation in terms of proteolytic enzymes (gelatinases and plasminogen activators), pro-angiogenic growth factors (VEGF and TGFβ), and the promoting-angiogenic CXCR4 chemokine receptor.

Intercellular Transfer of Cancer Drug Resistance Traits by Extracellular Vesicles

Extracellular vesicles (EVs) are nanosized particles (100-1000 nm) enclosed by a phospholipid bilayer that have been described as important mediators of intercellular communication. The role of EVs in oncobiology has been extensively studied, including their contribution to the horizontal transfer of drug resistance from drug-resistant to drug-sensitive cancer cells. This review focuses on the EVs cargo responsible for this intercellular transfer of drug resistance; namely, drug-efflux pumps, miRNAs, long noncoding RNAs (lncRNAs), and other mediators. Additionally, the known molecular mechanisms and features of this transfer are discussed. This is an emerging area of research and we highlight topics that need to be further studied to fully understand and counteract the intercellular transfer of drug resistance mediated by EVs.

Role of long non-coding RNA in tumor drug resistance

Chemotherapy has been extensively used in tumor treatment, including either systemic or local treatment. Miserably, in many kinds of cancers, chemotherapy is gradually insensitive. The mechanisms of tumor drug resistance have been widely explored, yet have not been fully characterized. With several studies in the development of drug resistance, recent works have highlighted the involvement of non-coding RNAs in tumor development. A growing number of long non-coding RNAs (lncRNAs) have been identified as transcripts of larger than 200 nucleotides in length, which have low coding potential, but potentially coding small peptides with 50-70 amino acids. Despite so often being branded as transcriptional noise, it is becoming increasingly clear that a large number of lncRNAs are crucial molecular regulators of the processes of tumor involving the initiation and progression of human tumor. More recently, accumulating evidence is revealing an important role of lncRNA in tumor drug resistance and lncRNA expression profiling can be correlated with the evolution of tumor drug resistance. The long non-coding-RNA-mediated form of drug resistance brings yet another mechanism of drug resistance. So, exploiting the newly emerging knowledge of lncRNAs for the development of new therapeutic applications to overcome human tumor drug resistance will be significant.

Plasmalogen enrichment in exosomes secreted by a nematode parasite versus those derived from its mouse host: implications for exosome stability and biology

Extracellular vesicles (EVs) mediate communication between cells and organisms across all 3 kingdoms of life. Several reports have demonstrated that EVs can transfer molecules between phylogenetically diverse species and can be used by parasites to alter the properties of the host environment. Whilst the concept of vesicle secretion and uptake is broad reaching, the molecular composition of these complexes is expected to be diverse based on the physiology and environmental niche of different organisms. Exosomes are one class of EVs originally defined based on their endocytic origin, as these derive from multivesicular bodies that then fuse with the plasma membrane releasing them into the extracellular environment. The term exosome has also been used to describe any small EVs recovered by high-speed ultracentrifugation, irrespective of origin since this is not always well characterized. Here, we use comparative global lipidomic analysis to examine the composition of EVs, which we term exosomes, that are secreted by the gastrointestinal nematode, Heligmosomoides polygyrus, in relation to exosomes secreted by cells of its murine host. Ultra-performance liquid chromatography – tandem mass spectrometry (UPLC-MS/MS) analysis reveals a 9- to 62-fold enrichment of plasmalogens, as well as other classes of ether glycerophospholipids, along with a relative lack of cholesterol and sphingomyelin (SM) in the nematode exosomes compared with those secreted by murine cells. Biophysical analyses of the membrane dynamics of these exosomes demonstrate increased rigidity in those from the nematode, and parallel studies with synthetic vesicles support a role of plasmalogens in stabilizing the membrane structure. These results suggest that nematodes can maintain exosome membrane structure and integrity through increased plasmalogens, compensating for diminished levels of other lipids, including cholesterol and SM. This work also illuminates the prevalence of plasmalogens in some EVs, which has not been widely reported and could have implications for the biochemical or immunomodulatory properties of EVs. Further comparative analyses such as those described here will shed light on diversity in the molecular properties of EVs that enable them to function in cross-species communication.

A Single-Cell Assay for Time Lapse Studies of Exosome Secretion and Cell Behaviors

To understand the inhomogeneity of cells in biological systems, there is a growing demand on the capability of characterizing the properties of individual single cells. Since single-cell studies require continuous monitoring of the cell behaviors, an effective single-cell assay that can support time lapsed studies in a high throughput manner is desired. Most currently available single-cell technologies cannot provide proper environments to sustain cell growth and, proliferation of single cells and convenient, noninvasive tests of single-cell behaviors from molecular markers. Here, a highly versatile single-cell assay is presented that can accommodate different cellular types, enable easy and efficient single-cell loading and culturing, and be suitable for the study of effects of in vitro environmental factors in combination with drug screening. One salient feature of the assay is the noninvasive collection and surveying of single-cell secretions at different time points, producing unprecedented insight of single-cell behaviors based on the biomarker signals from individual cells under given perturbations. Above all, the acquired information is quantitative, for example, measured by the number of exosomes each single-cell secretes for a given time period. Therefore, our single-cell assay provides a convenient, low-cost, and enabling tool for quantitative, time lapsed studies of single-cell properties.

Transferring intercellular signals and traits between cancer cells: extracellular vesicles as "homing pigeons"

Extracellular vesicles are cell-derived vesicles, which can transport various cargos out of cells. From their cell of origin, the content molecules (proteins, non-coding RNAs including miRNAs, DNA and others) can be delivered to neighboring or distant cells and as such extracellular vesicles can be regarded as vehicles of intercellular communication or "homing pigeons". Extracellular vesicle shuttling is able to actively modulate the tumor microenvironment and can partake in tumor dissemination. In various diseases, including cancer, levels of extracellular vesicle secretion are altered resulting in different amounts and/or profiles of detectable vesicular cargo molecules and these distinct content profiles are currently being evaluated as biomarkers. Apart from their potential as blood-derived containers of specific biomarkers, the transfer of extracellular vesicles to surrounding cells also appears to be involved in the propagation of phenotypic traits. These interesting properties have put extracellular vesicles into the focus of many recent studies.Here we review findings on the involvement of extracellular vesicles in transferring traits of cancer cells to their surroundings and briefly discuss new data on oncosomes, a larger type of vesicle. A pressing issue in cancer treatment is rapidly evolving resistance to many initially efficient drug therapies. Studies investigating the role of extracellular vesicles in this phenomenon together with a summary of the technical challenges that this field is still facing, are also presented. Finally, emerging areas of research such as the analysis of the lipid composition on extracellular vesicles and cutting-edge techniques to visualise the trafficking of extracellular vesicles are discussed.

The biological significance and clinical applications of exosomes in ovarian cancer

Exosomes are nano-sized (20-100nm) vesicles released by a variety of cells and are generated within the endosomal system or at the plasma membrane. There is emerging evidence that exosomes play a key role in intercellular communication in ovarian and other cancers. The protein and microRNA content of exosomes has been implicated in various intracellular processes that mediate oncogenesis, tumor spread, and drug resistance. Exosomes may prime distant tissue sites for reception of future metastases and their release can be mediated by the tumor microenvironment (e.g., hypoxia). Ovarian cancer-derived exosomes have unique features that could be leveraged for use as biomarkers to facilitate improved detection and treatment of the disease. Further, exosomes have the potential to serve as targets and/or drug delivery vehicles in the treatment of ovarian cancer. In this review we discuss the biological and clinical significance of exosomes relevant to the progression, detection, and treatment of ovarian cancer.

Implications of Extracellular Vesicle Transfer on Cellular Heterogeneity in Cancer: What Are the Potential Clinical Ramifications?

The functional and phenotypic heterogeneity of tumor cells represents one of the greatest challenges in the successful treatment of cancer patients, because it increases the risk that certain individual tumor cells possess the ability to, for example, metastasize or to tolerate cytotoxic drugs. This heterogeneity in cellular behavior is driven by genetic and epigenetic changes and environmental differences. Recent studies suggest that an additional layer of complexity of tumor heterogeneity exists, based on the ability of cells to share functional biomolecules through local and systemic transfer of extracellular vesicles (EV), with profound effects on cellular behavior. The transfer of functional biomolecules between various populations of tumor cells and between tumor cells and nontumor cells has large consequences for both the tumor cells and the microenvironment that support the cellular behavior of tumor cells, and therefore for the clinical outcome of cancer. Here, we discuss the latest findings on EV transfer and the potential implications of EV-mediated local and systemic transmission of phenotypic behavior, particularly in the context of tumor heterogeneity, metastatic disease, and treatment response. Cancer Res; 76(8); 2071-5. ©2016 AACR.

Extracellular vesicles in breast cancer drug resistance and their clinical application

Drug resistance currently represents a daunting challenge in the treatment of breast cancer patients. With an increased understanding of the underlying mechanisms of drug resistance, the role of extracellular vesicles (EVs) in the development of chemo-insensitivity attracts extensive attention. EVs are membrane-limited, cell type-dependent vesicles that are secreted by normal or malignant cells. EVs comprise various types of contents, including genetic cargoes, proteins, and specific lipids. The characteristics of the contents determine their specific functions in not only physiological but also pathological conditions. It has been demonstrated that miRNAs and proteins in EVs are strongly correlated with breast cancer drug resistance. Additionally, they may exert an influence on de novo and acquired resistance bioprocesses. With the advances in extraction and detection technologies, EVs have also been employed to precisely diagnose and predict the outcome of therapy in breast cancer. On the other hand, they can also be exploited as efficient delivery system in future anticancer applications. In this paper, we summarized relative mechanisms concerning the relationship between EVs and breast cancer drug resistance, and then, we provide up-to-date research advances in the clinical application of EVs.

Cancer Exosomes as Mediators of Drug Resistance

In the last decades, several studies demonstrated that the tumor microenvironment is a critical determinant not only of tumor progression and metastasis, but also of resistance to therapy. Exosomes are small membrane vesicles of endocytic origin, which contain mRNAs, DNA fragments, and proteins, and are released by many different cell types, including cancer cells. Mounting evidence has shown that cancer-derived exosomes contribute to the recruitment and reprogramming of constituents associated with the tumor microenvironment. Understanding how exosomes and the tumor microenvironment impact drug resistance will allow novel and better strategies to overcome drug resistance and treat cancer. Here, we describe a technique for exosome purification from cell culture, and fresh and frozen plasma, and further analysis by electron microscopy, NanoSight microscope, and Western blot.

Localization of MRP-1 to the outer mitochondrial membrane by the chaperone protein HSP90β

Overexpression of plasma membrane multidrug resistance-associated protein 1 (MRP-1) in Ewing's sarcoma (ES) predicts poor outcome. MRP-1 is also expressed in mitochondria, and we have examined the submitochondrial localization of MRP-1 and investigated the mechanism of MRP-1 transport and role of this organelle in the response to doxorubicin. The mitochondrial localization of MRP-1 was examined in ES cell lines by differential centrifugation and membrane solubilization by digitonin. Whether MRP-1 is chaperoned by heat shock proteins (HSPs) was investigated by immunoprecipitation, immunofluorescence microscopy, and HSP knockout using small hairpin RNA and inhibitors (apoptozole, 17-AAG, and NVPAUY). The effect of disrupting mitochondrial MRP-1-dependent efflux activity on the cytotoxic effect of doxorubicin was investigated by counting viable cell number. Mitochondrial MRP-1 is glycosylated and localized to the outer mitochondrial membrane, where it is coexpressed with HSP90. MRP-1 binds to both HSP90 and HSP70, although only inhibition of HSP90β decreases expression of MRP-1 in the mitochondria. Disruption of mitochondrial MRP-1-dependent efflux significantly increases the cytotoxic effect of doxorubicin (combination index, <0.9). For the first time, we have demonstrated that mitochondrial MRP-1 is expressed in the outer mitochondrial membrane and is a client protein of HSP90β, where it may play a role in the doxorubicin-induced resistance of ES.-Roundhill, E., Turnbull, D., Burchill, S. Localization of MRP-1 to the outer mitochondrial membrane by the chaperone protein HSP90β.

Breast Cancer-Derived Extracellular Vesicles: Characterization and Contribution to the Metastatic Phenotype

The study of extracellular vesicles (EVs) in cancer progression is a complex and rapidly evolving field. Whole categories of cellular interactions in cancer which were originally presumed to be due solely to soluble secreted molecules have now evolved to include membrane-enclosed extracellular vesicles (EVs), which include both exosomes and shed microvesicles (MVs), and can contain many of the same molecules as those secreted in soluble form but many different molecules as well. EVs released by cancer cells can transfer mRNA, miRNA, and proteins to different recipient cells within the tumor microenvironment, in both an autocrine and paracrine manner, causing a significant impact on signaling pathways, mRNA transcription, and protein expression. The transfer of EVs to target cells, in turn, supports cancer growth, immunosuppression, and metastasis formation. This review focuses exclusively on breast cancer EVs with an emphasis on breast cancer-derived exosomes, keeping in mind that breast cancer-derived EVs share some common physical properties with EVs of other cancers.

The Emerging Role of Extracellular Vesicle-Mediated Drug Resistance in Cancers: Implications in Advanced Prostate Cancer

Emerging evidence has shown that the extracellular vesicles (EVs) regulate various biological processes and can control cell proliferation and survival, as well as being involved in normal cell development and diseases such as cancers. In cancer treatment, development of acquired drug resistance phenotype is a serious issue. Recently it has been shown that the presence of multidrug resistance proteins such as Pgp-1 and enrichment of the lipid ceramide in EVs could have a role in mediating drug resistance. EVs could also mediate multidrug resistance through uptake of drugs in vesicles and thus limit the bioavailability of drugs to treat cancer cells. In this review, we discussed the emerging evidence of the role EVs play in mediating drug resistance in cancers and in particular the role of EVs mediating drug resistance in advanced prostate cancer. The role of EV-associated multidrug resistance proteins, miRNA, mRNA, and lipid as well as the potential interaction(s) among these factors was probed. Lastly, we provide an overview of the current available treatments for advanced prostate cancer, considering where EVs may mediate the development of resistance against these drugs.