Distinct and targetable role of calcium-sensing receptor in leukaemia

Haematopoietic stem cells (HSC) reside in the bone marrow microenvironment (BMM), where they respond to extracellular calcium [eCa2+] via the G-protein coupled calcium-sensing receptor (CaSR). Here we show that a calcium gradient exists in this BMM, and that [eCa2+] and response to [eCa2+] differ between leukaemias. CaSR influences the location of MLL-AF9+ acute myeloid leukaemia (AML) cells within this niche and differentially impacts MLL-AF9+ AML versus BCR-ABL1+ leukaemias. Deficiency of CaSR reduces AML leukaemic stem cells (LSC) 6.5-fold. CaSR interacts with filamin A, a crosslinker of actin filaments, affects stemness-associated factors and modulates pERK, β-catenin and c-MYC signaling and intracellular levels of [Ca2+] in MLL-AF9+ AML cells. Combination treatment of cytarabine plus CaSR-inhibition in various models may be superior to cytarabine alone. Our studies suggest CaSR to be a differential and targetable factor in leukaemia progression influencing self-renewal of AML LSC via [eCa2+] cues from the BMM.

The age of the bone marrow microenvironment influences B-cell acute lymphoblastic leukemia progression via CXCR5-CXCL13

B-cell acute lymphoblastic leukemia (B-ALL) occurs most commonly in children, whereas chronic myeloid leukemia is more frequent in adults. The myeloid bias of hematopoiesis in elderly individuals has been considered causative, but the age of the bone marrow microenvironment (BMM) may be contributory. Using various murine models of B-ALL in young vs old mice, we recapitulated B-ALL preponderance in children vs adults. We showed differential effects of young vs old BM macrophages on B-ALL cell function. Molecular profiling using RNA- and ATAC-sequencing revealed pronounced differences in young vs old BMM-derived macrophages and enrichment for gene sets associated with inflammation. In concordance with the role of C-X-C motif chemokine (CXCL) 13 for disease-associated B-cell chemoattraction, we found CXCL13 to be highly expressed in young macrophages on a translational compared with a transcriptional level. Inhibition of CXCL13 in BM macrophages impaired leukemia cell migration and decreased the proliferation of cocultured B-ALL cells, whereas recombinant CXCL13 increased pAKT and B-ALL cell expansion. Pretreatment of B-ALL-initiating cells with CXCL13 accelerated B-ALL progression. Deficiency of Cxcr5, the receptor for CXCL13, on B-ALL-initiating cells prolonged murine survival, whereas high expression of CXCR5 in pediatric B-ALL may predict central nervous system relapse. CXCL13 staining was increased in bone sections from pediatric compared with adult patients with B-ALL. Taken together, our study shows that the age of the BMM and, in particular, BM macrophages influence the leukemia phenotype. The CXCR5-CXCL13 axis may act as prognostic marker and an attractive novel target for the treatment of B-ALL.

Chronic Myeloid Leukemia: A Model Disease of the Past, Present and Future

Chronic myeloid leukemia (CML) has been a "model disease" with a long history. Beginning with the first discovery of leukemia and the description of the Philadelphia Chromosome and ending with the current goal of achieving treatment-free remission after targeted therapies, we describe here the journey of CML, focusing on molecular pathways relating to signaling, metabolism and the bone marrow microenvironment. We highlight current strategies for combination therapies aimed at eradicating the CML stem cell; hopefully the final destination of this long voyage.

Specific, targetable interactions with the microenvironment influence imatinib-resistant chronic myeloid leukemia

Therapy resistance in leukemia may be due to cancer cell-intrinsic and/or -extrinsic mechanisms. Mutations within BCR-ABL1, the oncogene giving rise to chronic myeloid leukemia (CML), lead to resistance to tyrosine kinase inhibitors (TKI), and some are associated with clinically more aggressive disease and worse outcome. Using the retroviral transduction/transplantation model of CML and human cell lines we faithfully recapitulate accelerated disease course in TKI resistance. We show in various models, that murine and human imatinib-resistant leukemia cells positive for the oncogene BCR-ABL1T315I differ from BCR-ABL1 native (BCR-ABL1) cells with regards to niche location and specific niche interactions. We implicate a pathway via integrin β3, integrin-linked kinase (ILK) and its role in deposition of the extracellular matrix (ECM) protein fibronectin as causative of these differences. We demonstrate a trend towards a reduced BCR-ABL1T315I+ tumor burden and significantly prolonged survival of mice with BCR-ABL1T315I+ CML treated with fibronectin or an ILK inhibitor in xenogeneic and syngeneic murine transplantation models, respectively. These data suggest that interactions with ECM proteins via the integrin β3/ILK-mediated signaling pathway in BCR-ABL1T315I+ cells differentially and specifically influence leukemia progression. Niche targeting via modulation of the ECM may be a feasible therapeutic approach to consider in this setting.

Large and small extracellular vesicles released by glioma cells in vitro and in vivo

Tumour cells release diverse populations of extracellular vesicles (EVs) ranging in size, molecular cargo, and function. We sought to characterize mRNA and protein content of EV subpopulations released by human glioblastoma (GBM) cells expressing a mutant form of epidermal growth factor receptor (U87EGFRvIII) in vitro and in vivo with respect to size, morphology and the presence of tumour cargo. The two EV subpopulations purified from GBM U87EGFRvIII cancer cells, non-cancer human umbilical vein endothelial cells (HUVEC; control) and serum of U87EGFRvIII glioma-bearing mice using differential centrifugation (EVs that sediment at 10,000 × g or 100,000 × g are termed large EVs and small EVs, respectively) were characterized using transmission electron microscopy (TEM), confocal microscopy, nanoparticle tracking analysis (NTA), flow cytometry, immunofluorescence (IF), quantitative-polymerase chain reaction (qPCR), droplet digital polymerase chain reaction (ddPCR) and micro-nuclear magnetic resonance (μNMR). We report that both U87EGFRvIII and HUVEC release a similar number of small EVs, but U87EGFRvIII glioma cells alone release a higher number of large EVs compared to non-cancer HUVEC. The EGFRvIII mRNA from the two EV subpopulations from U87EGFRvIII glioma cells was comparable, while the EGFR protein (wild type + vIII) levels are significantly higher in large EVs. Similarly, EGFRvIII mRNA in large and small EVs isolated from the serum of U87EGFRvIII glioma-bearing mice is comparable, while the EGFR protein (wild type + vIII) levels are significantly higher in large EVs. Here we report for the first time a direct comparison of large and small EVs released by glioma U87EGFRvIII cells and from serum of U87EGFRvIII glioma-bearing mice. Both large and small EVs contain tumour-specific EGFRvIII mRNA and proteins and combining these platforms may be beneficial in detecting rare mutant events in circulating biofluids.

Large oncosomes overexpressing integrin alpha-V promote prostate cancer adhesion and invasion via AKT activation

BACKGROUND

Molecular markers for prostate cancer (PCa) are required to improve the early definition of patient outcomes. Atypically large extracellular vesicles (EVs), referred as "Large Oncosomes" (LO), have been identified in highly migratory and invasive PCa cells. We recently developed and characterized the DU145R80 subline, selected from parental DU145 cells as resistant to inhibitors of mevalonate pathway. DU145R80 showed different proteomic profile compared to parental DU145 cells, along with altered cytoskeleton dynamics and a more aggressive phenotype.

METHODS

Immunofluorescence staining and western blotting were used to identify blebbing and EVs protein cargo. EVs, purified by gradient ultra-centrifugations, were analyzed by tunable resistive pulse sensing and multi-parametric flow cytometry approach coupled with high-resolution imaging technologies. LO functional effects were tested in vitro by adhesion and invasion assays and in vivo xenograft model in nude mice. Xenograft and patient tumor tissues were analyzed by immunohistochemistry.

RESULTS

We found spontaneous blebbing and increased shedding of LO from DU145R80 compared to DU145 cells. LO from DU145R80, compared to those from DU145, carried increased amounts of key-molecules involved in PCa progression including integrin alpha V (αV-integrin). By incubating DU145 cells with DU145R80-derived LO we demonstrated that αV-integrin on LO surface was functionally involved in the increased adhesion and invasion of recipient cells, via AKT. Indeed either the pre-incubation of LO with an αV-integrin blocking antibody, or a specific AKT inhibition in recipient cells are able to revert the LO-induced functional effects. Moreover, DU145R80-derived LO also increased DU145 tumor engraftment in a mice model. Finally, we identified αV-integrin positive LO-like structures in tumor xenografts as well as in PCa patient tissues. Increased αV-integrin tumor expression correlated with high Gleason score and lymph node status.

CONCLUSIONS

Overall, this study is the first to demonstrate the critical role of αV-integrin positive LO in PCa aggressive features, adding new insights in biological function of these large EVs and suggesting their potential use as PCa prognostic markers.

Vitamin K antagonism impairs the bone marrow microenvironment and hematopoiesis

Vitamin K antagonists (VKAs) have been used in 1% of the world's population for prophylaxis or treatment of thromboembolic events for 64 years. Impairment of osteoblast function and osteoporosis has been described in patients receiving VKAs. Given the involvement of cells of the bone marrow microenvironment (BMM), such as mesenchymal stem cells (MSCs) and macrophages, as well as other factors such as the extracellular matrix for the maintenance of normal hematopoietic stem cells (HSCs), we investigated a possible effect of VKAs on hematopoiesis via the BMM. Using various transplantation and in vitro assays, we show here that VKAs alter parameters of bone physiology and reduce functional HSCs 8-fold. We implicate impairment of the functional, secreted, vitamin K-dependent, γ-carboxylated form of periostin by macrophages and, to a lesser extent, MSCs of the BMM and integrin β3-AKT signaling in HSCs as at least partly causative of this effect, with VKAs not being directly toxic to HSCs. In patients, VKA use associates with modestly reduced leukocyte and monocyte counts, albeit within the normal reference range. VKAs decrease human HSC engraftment in immunosuppressed mice. Following published examples that alteration of the BMM can lead to hematological malignancies in mice, we describe, without providing a causal link, that the odds of VKA use are higher in patients with vs without a diagnosis of myelodysplastic syndrome (MDS). These results demonstrate that VKA treatment impairs HSC function via impairment of the BMM and the periostin/integrin β3 axis, possibly associating with increased MDS risk.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Large extracellular vesicles carry most of the tumour DNA circulating in prostate cancer patient plasma

Cancer-derived extracellular vesicles (EVs) are membrane-enclosed structures of highly variable size. EVs contain a myriad of substances (proteins, lipid, RNA, DNA) that provide a reservoir of circulating molecules, thus offering a good source of biomarkers. We demonstrate here that large EVs (L-EV) (large oncosomes) isolated from prostate cancer (PCa) cells and patient plasma are an EV population that is enriched in chromosomal DNA, including large fragments up to 2 million base pair long. While L-EVs and small EVs (S-EV) (exosomes) isolated from the same cells contained similar amounts of protein, the DNA was more abundant in L-EV, despite S-EVs being more numerous. Consistent with in vitro observations, the abundance of DNA in L-EV obtained from PCa patient plasma was variable but frequently high. Conversely, negligible amounts of DNA were present in the S-EVs from the same patients. Controlled experimental conditions, with spike-ins of L-EVs and S-EVs from cancer cells in human plasma from healthy subjects, showed that circulating DNA is almost exclusively enclosed in L-EVs. Whole genome sequencing revealed that the DNA in L-EVs reflects genetic aberrations of the cell of origin, including copy number variations of genes frequently altered in metastatic PCa (i.e. MYC, AKT1, PTK2, KLF10 and PTEN). These results demonstrate that L-EV-derived DNA reflects the genomic make-up of the tumour of origin. They also support the conclusion that L-EVs are the fraction of plasma EVs with DNA content that should be interrogated for tumour-derived genomic alterations.

Abstract 4056: Immune regulation by miR-1227 LO

Immunotherapy offers great promise for the treatment of prostate cancer; however prostate cancer often acquires mechanisms to dampen the tumoricidal immune response. Understanding how prostate cancer dampens the immune system will facilitate the generation of more effective immunotherapies. Here we investigate how large oncosomes (LO)-mediated transfer of miR-1227 to immune cells modulates the immune response.

Extracellular vesicle (EV)-encapsulated miRNAs are being increasingly recognized for playing a key role in cancer progression and immune modulation. miR-1227 is a poorly characterized miRNA that is enriched in EV secreted by prostate cancer cells in comparison to non-malignant prostate epithelial cells. miR-1227 expression is increased in migratory glioblastoma cells in comparison to non-migratory glioblastoma cells, and in radiation resistant esophageal cells and colorectal cancer stromal cells indicating that miR-1227 is upregulated in different cancer types. However, the role of miR-1227 in cancer is poorly understood. We demonstrate here that EV obtained from prostate cancer cells overexpressing miR-1227, induce the migration of prostate cancer cells and fibroblasts. A comparative analysis between different EV subtypes indicates that miR-1227 is enriched in LO, a class of EV that are secreted by highly invasive amoeboid-migrating cells. We also show that LO carry more RNA than the more widely studied exosomes indicating that LO may be a more robust source of EV-encapsulated miRNA. RNA sequencing from miR-1227 stably expressing prostate cancer cells and 5 different in silico miRNA target prediction methods were used to identify putative miR-1227 targets. IPA pathway analysis from these predicted targets highlighted several functions related to the immune system, including T cell homeostasis, T cell development, and development of Th17 cells. A more in-depth analysis of the 51 genes involved in T cell homeostasis showed enrichment of genes associated with Th17 and Th1 T cell differentiation. Alterations in Th17 and Th1 differentiation modulates T cell cytokine secretion, which are important mediators of cancer growth and progression. Transient transfection of miR-1227 in immune cells altered the cytokine expression profile, resulting in the upregulation of several cytokines that promote cancer growth including CCL5 and IL6. We tested whether LO can be taken up by activated T cells to directly modulate cytokine secretion. To determine whether miR-1227 can be functionally transferred to recipient cells via LO we isolated LO from prostate cancer cells stably expressing miR-1227 using ultracentrifugation followed by density gradient purification. The isolated LO were used to treat immune cells to show that LO-encapsulated miR-1227 alters cytokine profiles. These results indicate that LO-encapsulated miR-1227 may be involved in cancer immune modulation through targeting specific genes involved in T-cell differentiation.

Citation Format: Andrew R. Chin, Dolores Di Vizio, Valentina R. Minciacchi, Mariana Sobreiro, Cristiana Spinelli. Immune regulation by miR-1227 LO [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4056.

MYC Mediates Large Oncosome-Induced Fibroblast Reprogramming in Prostate Cancer

Communication between cancer cells and the tumor microenvironment results in the modulation of complex signaling networks that facilitate tumor progression. Here, we describe a new mechanism of intercellular communication originating from large oncosomes (LO), which are cancer cell-derived, atypically large (1-10 μm) extracellular vesicles (EV). We demonstrate that, in the context of prostate cancer, LO harbor sustained AKT1 kinase activity, nominating them as active signaling platforms. Active AKT1 was detected in circulating EV from the plasma of metastatic prostate cancer patients and was LO specific. LO internalization induced reprogramming of human normal prostate fibroblasts as reflected by high levels of α-SMA, IL6, and MMP9. In turn, LO-reprogrammed normal prostate fibroblasts stimulated endothelial tube formation in vitro and promoted tumor growth in mice. Activation of stromal MYC was critical for this reprogramming and for the sustained cellular responses elicited by LO, both in vitro and in vivo in an AKT1-dependent manner. Inhibition of LO internalization prevented activation of MYC and impaired the tumor-supporting properties of fibroblasts. Overall, our data show that prostate cancer-derived LO powerfully promote establishment of a tumor-supportive environment by inducing a novel reprogramming of the stroma. This mechanism offers potential alternative options for patient treatment. Cancer Res; 77(9); 2306-17. ©2017 AACR.

High-throughput sequencing of two populations of extracellular vesicles provides an mRNA signature that can be detected in the circulation of breast cancer patients

Extracellular vesicles (EVs) contain a wide range of RNA types with a reported prevalence of non-coding RNA. To date a comprehensive characterization of the protein coding transcripts in EVs is still lacking. We performed RNA-Sequencing (RNA-Seq) of 2 EV populations and identified a small fraction of transcripts that were expressed at significantly different levels in large oncosomes and exosomes, suggesting they may mediate specialized functions. However, these 2 EV populations exhibited a common mRNA signature that, in comparison to their donor cells, was significantly enriched in mRNAs encoding E2F transcriptional targets and histone proteins. These mRNAs are primarily expressed in the S-phase of the cell cycle, suggesting that they may be packaged into EVs during S-phase. In silico analysis using subcellular compartment transcriptome data from the ENCODE cell line compendium revealed that EV mRNAs originate from a cytoplasmic RNA pool. The EV signature was independently identified in plasma of patients with breast cancer by RNA-Seq. Furthermore, several transcripts differentially expressed in EVs from patients versus controls mirrored differential expression between normal and breast cancer tissues. Altogether, this largest high-throughput profiling of EV mRNA demonstrates that EVs carry tumor-specific alterations and can be interrogated as a source of cancer-derived cargo.

Large oncosomes contain distinct protein cargo and represent a separate functional class of tumor-derived extracellular vesicles

Large oncosomes (LO) are atypically large (1-10μm diameter) cancer-derived extracellular vesicles (EVs), originating from the shedding of membrane blebs and associated with advanced disease. We report that 25% of the proteins, identified by a quantitative proteomics analysis, are differentially represented in large and nano-sized EVs from prostate cancer cells. Proteins enriched in large EVs included enzymes involved in glucose, glutamine and amino acid metabolism, all metabolic processes relevant to cancer. Glutamine metabolism was altered in cancer cells exposed to large EVs, an effect that was not observed upon treatment with exosomes. Large EVs exhibited discrete buoyant densities in iodixanol (OptiPrep^TM) gradients. Fluorescent microscopy of large EVs revealed an appearance consistent with LO morphology, indicating that these structures can be categorized as LO. Among the proteins enriched in LO, cytokeratin 18 (CK18) was one of the most abundant (within the top 5^th percentile) and was used to develop an assay to detect LO in the circulation and tissues of mice and patients with prostate cancer. These observations indicate that LO represent a discrete EV type that may play a distinct role in tumor progression and that may be a source of cancer-specific markers.

Abstract 4154: Large oncosomes derived from the aggressive prostate cancer sub-line, DU145R80, can modify the biological behavior of the parental DU145 cells

We have recently established a zoledronic acid-resistant prostate cancer cell line, DU145R80,which exhibits higher invasive capability compared to parental DU145 cells, and epithelial-to-mesenchymal transition (EMT)[Milone MR, Cell Death Dis. 2013]. To investigate the mechanism by which the cells become invasive, we compared DU145R80 and DU145 cells by a proteomic approach, unveiling a signaling network that links the interior of the nucleus to changes in cytoskeleton dynamics and to the extracellular matrix, dictating prostate cancer aggressiveness [Milone MR Oncotarget 2014].Cytoskeletal modifications allow cells to gain a more migratory/invasive behavior and to interact with the surrounding microenvironment triggering different kind of biological phenomena, including the formation of large oncosomes (LO), a bioactive class of extracellular vesicles (EVs) [Di Vizio D, Cancer Res. 2009]. In this study, we found a higher amount of spontaneously shed LO along with an increased gelatinase activity from DU145R80 cells compared to the parental counterpart. By applying low speed and discontinuous gradient ultracentrifugation to both DU145 and DU145R80 cell media, we obtained a pure preparation of LO, floating at a 1.15 g/mL density fraction and positive for LO markers such as as Cav-1, Ck18, GAPDH. Moreover, we treated DU145 parental cells with pure preparations of LO from either DU145 or DU145R80 cells and performed an invasion assay, showing that LO from the resistant, aggressive DU145R80 cell line increase the invading ability of DU145. Treatment of DU145 cells with LO originating from the parental cell line itself did not result in increased invasinevess, suggesting a specific role for EVs from aggressive cells. In addition, in order to investigate LO content, we focused our attention on a cell surface glycoprotein, CUB domain-containing protein 1 (CDCP-1), putatively linked to the network of proteins identified in DU145R80 cells and whose role in cancer is still under debate. Our results demonstrate that CDCP-1 expression is significantly reduced in DU145R80 compared to DU145 cells, suggesting a tumor-protective role for the protein in prostate cancer. We also observed, for the first time, that the CDCP-1 expression pattern displayed by both cell lines was reflected in their derived LO. These data intriguingly suggest that CDCP-1 may change its expression pattern upon modifications in tumor cells properties, playing a different role in different stages of cancer development. Overall, these findings highlight LO as a new biological component in the development of aggressive features by prostate cancer cells, connecting molecular alterations to changes in the ability to interact with the surrounding environment, and suggested new prognostic markers and/or therapeutical targets.

Citation Format: Chiara Ciardiello, Valentina R. Minciacchi, Mariana Reis-Sobreiro, Maria R. Milone, Biagio Pucci, Rita Lombardi, Francesca Bruzzese, Dolores Di Vizio, Alfredo Budillon. Large oncosomes derived from the aggressive prostate cancer sub-line, DU145R80, can modify the biological behavior of the parental DU145 cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4154. doi:10.1158/1538-7445.AM2015-4154

Extracellular vesicles in cancer: exosomes, microvesicles and the emerging role of large oncosomes

Since their first description, extracellular vesicles (EVs) have been the topic of avid study in a variety of physiologic contexts and are now thought to play an important role in cancer. The state of knowledge on biogenesis, molecular content and horizontal communication of diverse types of cancer EVs has expanded considerably in recent years. As a consequence, a plethora of information about EV composition and molecular function has emerged, along with the notion that cancer cells rely on these particles to invade tissues and propagate oncogenic signals at distance. The number of in vivo studies, designed to achieve a deeper understanding of the extent to which EV biology can be applied to clinically relevant settings, is rapidly growing. This review summarizes recent studies on cancer-derived EV functions, with an overview about biogenesis and molecular cargo of exosomes, microvesicles and large oncosomes. We also discuss current challenges and emerging technologies that might improve EV detection in various biological systems. Further studies on the functional role of EVs in specific steps of cancer formation and progression will expand our understanding of the diversity of paracrine signaling mechanisms in malignant growth.

Abstract 4868: Large oncosomes are internalized and functionally modulate transcription factors in recipient cells

Background and Objective: We recently reported that rapidly migratory, “amoeboid” prostate cancer (PCa) cells shed large (1-10µm diameter), bioactive extracellular vesicles (EV), termed large oncosomes (LO), whose abundance correlates with tumor aggressiveness (Di Vizio et al., Cancer Res. 2009; Di Vizio et al. Am J Pathol. 2012). Increasing evidence supports an important role for EVs in mechanisms of communication between cancer cells and the surrounding microenvironment. EVs can activate signal transduction as well as transfer biomolecules to recipient cells, processes that may promote oncogenesis and/or enhance tumor progression. The aim of this study was to investigate the molecular mechanisms of LO internalization into recipient cells and LO-mediated intercellular communication. Results: LO stimulated the migration of tumor and endothelial cells and contained active MMP2 and MMP9, key proteases involved in tumor cell invasion. Quantitative LC-MS/MS SILAC analysis of LO and exosomes demonstrated enrichment of specific proteins in LO in comparison with exosomes. Fluorescently labeled-LO were internalized into recipient cells and maintained their stability as discrete microvesicles that were localized in the perinuclear space at early time points and into the nucleus at later times. Because of this transfer of LO to the nuclear compartment, we investigated whether exposure to LO altered the activity of transcription factors in recipient cells, hypothesizing a possible novel mechanism of LO-mediated intracellular communication. Interestingly, the degree of internalization, as quantitatively assessed by flow cytometry, varied among different recipient cells, including benign and cancer prostate epithelial cells, immortalized myofibroblasts, cancer associated fibroblasts and endothelial cells. These results suggest cell-specific affinities for target cells and, perhaps, finely regulated mechanisms underlying LO-internalization. Moreover selective inhibition of pathways important in EV internalization indicated that the LO enter cells through an active endocytic process, rather than passively fusing with the plasma membrane of recipient cells. Internalization of LO resulted in altered expression of transcription factors. Conclusions: Our results show for the first time that internalization of intact LO might be necessary for their biological activity in recipient cells. These findings also suggest that the functional role of LO in the tumor microenvironment might be mediated by modulation of transcription factors.

Citation Format: Valentina R. Minciacchi, Matteo Morello, Sungyong You, Wei Yang, Mariana Sobreiro, Cristiana Spinelli, Mandana Zandian, Mirja Rotinen, Samantha Morley, Rosalyn Adam, Michael R. Freeman, Dolores Di Vizio. Large oncosomes are internalized and functionally modulate transcription factors in recipient cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4868. doi:10.1158/1538-7445.AM2014-4868

Large oncosomes mediate intercellular transfer of functional microRNA

Prostate cancer cells release atypically large extracellular vesicles (EVs), termed large oncosomes, which may play a role in the tumor microenvironment by transporting bioactive molecules across tissue spaces and through the blood stream. In this study, we applied a novel method for selective isolation of large oncosomes applicable to human platelet-poor plasma, where the presence of caveolin-1-positive large oncosomes identified patients with metastatic disease. This procedure was also used to validate results of a miRNA array performed on heterogeneous populations of EVs isolated from tumorigenic RWPE-2 prostate cells and from isogenic non-tumorigenic RWPE-1 cells. The results showed that distinct classes of miRNAs are expressed at higher levels in EVs derived from the tumorigenic cells in comparison to their non-tumorigenic counterpart. Large oncosomes enhanced migration of cancer-associated fibroblasts (CAFs), an effect that was increased by miR-1227, a miRNA abundant in large oncosomes produced by RWPE-2 cells. Our findings suggest that large oncosomes in the circulation report metastatic disease in patients with prostate cancer, and that this class of EV harbors functional molecules that may play a role in conditioning the tumor microenvironment.