Exosomal circRNAs as novel cancer biomarkers: Challenges and opportunities

Exosomal circular RNAs in tumor microenvironment: An emphasis on signaling pathways and clinical opportunities

Exosomes can regulate the malignant progression of tumors by carrying a variety of genetic information and transmitting it to target cells. Recent studies indicate that exosomal circular RNAs (circRNAs) regulate multiple biological processes in carcinogenesis, such as tumor growth, metastasis, epithelial-mesenchymal transition, drug resistance, autophagy, metabolism, angiogenesis, and immune escape. In the tumor microenvironment (TME), exosomal circRNAs can be transferred among tumor cells, endothelial cells, cancer-associated fibroblasts, immune cells, and microbiota, affecting tumor initiation and progression. Due to the high stability and widespread presence of exosomal circRNAs, they hold promise as biomarkers for tumor diagnosis and prognosis prediction in blood and urine. In addition, designing nanoparticles targeting exosomal circRNAs and utilizing exosomal circRNAs derived from immune cells or stem cells provide new strategies for cancer therapy. In this review, we examined the crucial role of exosomal circRNAs in regulating tumor-related signaling pathways and summarized the transmission of exosomal circRNAs between various types of cells and their impact on the TME. Finally, our review highlights the potential of exosomal circRNAs as diagnostic and prognostic prediction biomarkers, as well as suggesting new strategies for clinical therapy.

Exosomal LncRNAs and CircRNAs in lung cancer: Emerging regulators and potential therapeutic targets

Lung cancer remains one of the most prevalent and lethal malignancies globally, characterized by high incidence and mortality rates among all cancers. The delayed diagnosis of lung cancer at intermediate to advanced stages frequently leads to suboptimal treatment outcomes. To improve the management of this disease, it is imperative to identify new, highly sensitive prognostic and diagnostic biomarkers. Exosomes, extracellular vesicles with a lipid-bilayer structure and a size range of 30-150 nm, are pivotal in intercellular communication and play significant roles in lung cancer progression. Non-coding RNAs (ncRNAs), including long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), are highly prevalent within exosomes and play a crucial role in various pathophysiological processes mediated by these extracellular vesicles. Beyond their established functions in miRNA and protein sequestration, these ncRNAs are involved in regulating translation and interactions within exosomes. Numerous studies have highlighted the importance of exosomal lncRNAs and circRNAs in influencing epithelial-mesenchymal transition (EMT), angiogenesis, proliferation, invasion, migration, and metastasis in lung cancer. Due to their unique functional characteristics, these molecules are promising therapeutic targets and biomarkers for diagnosis and prognosis. This review provides a succinct summary of the formation of exosomal lncRNAs and circRNAs, clarifies their biological roles, and thoroughly explains the mechanisms by which they participate in the progression of lung cancer. Finally, we discuss the potential clinical applications and challenges associated with exosomal lncRNAs and circRNAs in lung cancer.

Circular RNAs in human diseases

Circular RNAs (circRNAs) are a unique class of RNA molecules formed through back-splicing rather than linear splicing. As an emerging field in molecular biology, circRNAs have garnered significant attention due to their distinct structure and potential functional implications. A comprehensive understanding of circRNAs' functions and potential clinical applications remains elusive despite accumulating evidence of their involvement in disease pathogenesis. Recent research highlights their significant roles in various human diseases, but comprehensive reviews on their functions and applications remain scarce. This review provides an in-depth examination of circRNAs, focusing first on their involvement in non-neoplastic diseases such as respiratory, endocrine, metabolic, musculoskeletal, cardiovascular, and renal disorders. We then explore their roles in tumors, with particular emphasis on exosomal circular RNAs, which are crucial for cancer initiation, progression, and resistance to treatment. By detailing their biogenesis, functions, and impact on disease mechanisms, this review underscores the potential of circRNAs as diagnostic biomarkers and therapeutic targets. The review not only enhances our understanding of circRNAs' roles in specific diseases and tumor types but also highlights their potential as novel diagnostic and therapeutic tools, thereby paving the way for future clinical investigations and potential therapeutic interventions.

Prospects for the clinical application of exosomal circular RNA in squamous cell carcinoma

Squamous cell carcinoma (SCC) is a prevalent malignancy affecting multiple organs in the human body, including the oral cavity, esophagus, cervix, and skin. Given its significant incidence and mortality rates, researchers are actively seeking effective diagnostic and therapeutic strategies. In recent years, exosomes and their molecular cargo, particularly circular RNA (circRNA), have emerged as promising areas of investigation in SCC research. Exosomes are small vesicles released into the extracellular environment by cells that contain biomolecules that reflect the physiological state of the cell of origin. CircRNAs, known for their unique covalently closed loop structure and stability, have garnered special attention in oncology and are closely associated with tumorigenesis, progression, metastasis, and drug resistance. Interestingly, exosomal circRNAs have been identified as ideal biomarkers for noninvasive cancer diagnosis and prognosis assessment. This article reviews the progress in research on exosomal circRNAs, focusing on their expression patterns, functions, and potential applications as biomarkers in SCC, aiming to provide new insights and strategies for the diagnosis and treatment of SCC.

Exploring the evolving roles and clinical significance of circRNAs in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) represents the predominant malignancies in the head and neck region, and has limited therapeutic alternatives. Circular RNAs (circRNAs), a substantial category of non-coding RNA molecules, exert influential roles in human disease development and progression, employing various mechanisms such as microRNA sponging, interaction with RNA-binding proteins, and translational capabilities. Accumulating evidence highlights the differential expression of numerous circRNAs in HNSCC, and numerous dysregulated circRNAs underscore their crucial involvement in malignant advancement and resistance to treatment. This review aims to comprehensively outline the characteristics, biogenesis, and mechanisms of circRNAs, elucidating their functional significance in HNSCC. In addition, we delve into the clinical implications of circRNAs, considering their potential as biomarkers or targets for diagnosis, prognosis, and therapeutic applications in HNSCC. The discussion extends to exploring future challenges in the clinical translation of circRNAs, emphasizing the need for further research.

Role of exosomes in the communication and treatment between OSCC and normal cells

Oral squamous cell carcinoma (OSCC) is a prevalent cancer that needs new therapeutic targets due to the poor postoperative prognosis in patients. Exosomes are currently one of important research areas owing to their unique properties. Exosomes are capable of acting as drug transporters, as well as facilitating interactions between OSCC and normal cells. Exosomes can be detected in body fluids such as blood, urine, cerebrospinal fluid, and bile. When exosomes are released from donor cells, they can carry various bioactive molecules to recipient cells, where these molecules participate in biological processes. This review highlights the mechanisms of exosome transfer between normal and OSCC cells. Exosomes isolated from donor OSCC cells can carry circular RNAs (circRNAs), long non-coding RNAs (lncRNAs), and microRNAs (miRNAs) and play a role in signaling processes in the recipient OSCC cells, human umbilical vein endothelial cells, and macrophages. Exosomes secreted by carcinoma-associated fibroblasts, macrophages, and stem cells can also enter the recipient OSCC cells and modulate signaling events in these cells. Exosomes isolated from OSCC plasma, serum, and saliva are also associated with OSCC prognosis. Furthermore, while exosomes were shown to be associated with chemotherapy resistance in OSCC, they can also be used for drug delivery during OSCC treatment. In this paper, we reviewed the molecular mechanisms and functions of exosomes from different cell sources in OSCC cells, providing a basis for diagnosis and prognosis prediction in OSCC patients, and offering guidance for the design of molecular targets carried by exosomes in OSCC.

Identification of a lncRNA/circRNA-miRNA-mRNA network in Nasopharyngeal Carcinoma by deep sequencing and bioinformatics analysis

Background: Accumulating evidence indicates that non-coding RNAs (ncRNA), including long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), can function as competitive endogenous RNAs (ceRNAs) by binding to microRNAs (miRNAs) and regulating host gene expression at the transcriptional or post-transcriptional level. Dysregulation in ceRNA network regulation has been implicated in the occurrence and development of cancer. However, the lncRNA/circRNA-miRNA-mRNA regulatory network is still lacking in nasopharyngeal carcinoma (NPC). Methods: Differentially expressed genes (DEGs) were obtained from our previous sequencing data and Gene Expression Omnibus (GEO). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) were used to explore the biological functions of these common DEGs. Through a series of bioinformatic analyses, the lncRNA/circRNA-miRNA-mRNA network was established. In additional, the external data GSE102349 was used to test the prognostic value of the hub mRNAs through the Kaplan-Meier method. Results: We successfully constructed a lncRNA/circRNA-miRNA-mRNA network in NPC, consisting of 16 lncRNAs, 6 miRNAs, 3 circRNAs and 10 mRNAs and found that three genes (TOP2A, ZWINT, TTK) were significantly associated with overall survival time (OS) in patients. Conclusion: The regulatory network revealed in this study may help comprehensively elucidate the ceRNA mechanisms driving NPC, and provide novel candidate biomarkers for evaluating the prognosis of NPC.

Regulatory mechanism and promising clinical application of exosomal circular RNA in gastric cancer

Gastric cancer (GC) is one of the most common malignancies worldwide and the leading cause of cancer-related deaths. Exosomes are nanoscale extracellular vesicles secreted by a variety of cells and play an important role in cellular communication and epigenetics by transporting bioactive substances in the tumor microenvironment (TME). Circular RNA (circRNA) is a type of non-coding RNA (ncRNA) with a specific structure, which is widely enriched in exosomes and is involved in various pathophysiological processes mediated by exosomes. Exosomal circRNAs play a critical role in the development of GC by regulating epithelial-mesenchymal transition (EMT), angiogenesis, proliferation, invasion, migration, and metastasis of GC. Given the biological characteristics of exosomal circRNAs, they have more significant diagnostic sensitivity and specificity in the clinic and may become biomarkers for GC diagnosis and prognosis. In this review, we briefly describe the biogenesis of exosomes and circRNAs and their biological functions, comprehensively summarize the mechanisms of exosomal circRNAs in the development of GC and chemotherapy resistance, and finally, we discuss the potential clinical application value and challenges of exosomal circRNAs in GC.

Exosomal circCOL1A1 promotes angiogenesis via recruiting EIF4A3 protein and activating Smad2/3 pathway in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the third frequently diagnosed cancer with high incidence and mortality rate worldwide. Our previous report has demonstrated that circCOL1A1 (hsa_circ_0044556) functions as an oncogene in CRC, and Gene Ontology (GO) analysis has also revealed the strong association between circCOL1A1 and angiogenesis. However, the mechanism of circCOL1A1 or exosomal circCOL1A1 in CRC angiogenesis remains elusive.

METHODS

Purified exosomes from CRC cells were characterized by nanoparticle tracking analyzing, electron microscopy and western blot. qRT-PCR, immunohistochemistry or western blot were employed to test the expression of circCOL1A1, EIF4A3, Smad pathway and angiogenic markers. Cell proliferation of HUVECs was monitored by CCK-8 assay. The migratory and angiogenic capabilities of HUVECs were detected by wound healing and tube formation assay, respectively. Bioinformatics analysis, RNA immunoprecipitation (RIP), RNA pull-down and FISH assays were used to detect the interactions among circCOL1A1, EIF4A3 and Smad2/3 mRNA. The in vitro findings were verified in xenograft model.

RESULTS

CRC cell-derived exosomal circCOL1A1 promoted angiogenesis of HUVECs via recruiting EIF4A3. EIF4A3 was elevated in CRC tissues, and it stimulated angiogenesis of HUVECs through directly binding and stabilizing Smad2/3 mRNA. Moreover, exosomal circCOL1A1 promoted angiogenesis via inducing Smad2/3 signaling pathway in vitro, and it also accelerated tumor growth and angiogenesis in vivo.

CONCLUSION

CRC cell-derived exosomal circCOL1A1 promoted angiogenesis via recruiting EIF4A3 and activating Smad2/3 signaling.

Exosomal non-coding RNAs in angiogenesis: Functions, mechanisms and potential clinical applications

Exosomes are extracellular vesicles that can be produced by most cells. Exosomes act as important intermediaries in intercellular communication, and participate in a variety of biological activities between cells. Non-coding RNAs (ncRNAs) usually refer to RNAs that do not encode proteins. Although ncRNAs have no protein-coding capacity, they are able to regulate gene expression at multiple levels. Angiogenesis is the formation of new blood vessels from pre-existing vessels, which is an important physiological process. However, abnormal angiogenesis could induce many diseases such as atherosclerosis, diabetic retinopathy and cancer. Many studies have shown that ncRNAs can stably exist in exosomes and play a wide range of physiological and pathological roles including regulation of angiogenesis. In brief, some specific ncRNAs can be enriched in exosomes secreted by cells and absorbed by recipient cells through the exosome pathway, thus activating relevant signaling pathways in target cells and playing a role in regulating angiogenesis. In this review, we describe the physiological and pathological functions of exosomal ncRNAs in angiogenesis, summarize their role in angiogenesis-related diseases, and illustrate potential clinical applications like novel drug therapy strategies and diagnostic markers in exosome research as inspiration for future investigations.

Exosome-delivered circRPS5 inhibits the progression of melanoma via regulating the miR-151a/NPTX1 axis

BACKGROUND

Circular RNAs (circRNAs) have been reported to exert critical functions in tumorigenesis and development. However, the underlying mechanism by which circRNAs regulate melanoma progression remain to be elucidated.

METHODS

The differentially expressed circRNAs were first identified by circRNA-seq, and circRNAs were validated via qRT-PCR and Sanger sequencing. Then, the impact of circRPS5, miR-151a and NPTX1 expression on the progression of melanoma cell were determined by gain- and loss-of-function assays. The relationship between circRPS5, miR-151a, and NPTX1 was predicted by StarBase website and authenticated by luciferase reporter assay. The melanoma cells-derived exosomes were characterized using nanoparticle tracking analysis (NTA) and western blot.

RESULTS

CircRPS5 was significantly downregulated in melanoma tissues and cell lines. Functionally, circRPS5 suppressed the proliferation, migration, and invasion of melanoma cells, and induced cell cycle arrest and apoptosis in vitro. Mechanistically, circRPS5 harbor miR-151a, acting as miRNA sponge, and then miR-151a targeted the 3'-UTR of NPTX1. Finally, circRPS5 was mainly incorporated into exosomes to inhibit the progression of melanoma cells.

CONCLUSIONS

This finding reveal circRPS5 suppressed the progression of melanoma through miR-151a/NPTX1 pathway, and may provide a promising therapeutic strategies for melanoma.

CircRNAs in colorectal cancer: potential biomarkers and therapeutic targets

Globally, colorectal cancer (CRC) is the third most prevalent cancer and the second leading cause of cancer-related deaths. Circular RNAs (circRNAs) are single-stranded RNA with covalently closed-loop structures and are highly stable, conserved, and abundantly expressed in various organs and tissues. Recent research found abnormal circRNA expression in CRC patients' blood/serum, cells, CRC tissues, and exosomes. Furthermore, mounting data demonstrated that circRNAs are crucial to the development of CRC. CircRNAs have been shown to exert biological functions by acting as microRNA sponges, RNA-binding protein sponges, regulators of gene splicing and transcription, and protein/peptide translators. These characteristics make circRNAs potential markers for CRC diagnosis and prognosis, potential therapeutic targets, and circRNA-based therapies. However, further studies are still necessary to improve the understanding of the roles and biological mechanisms of circRNAs in the development of CRC. In this review, up-to-date research on the role of circRNAs in CRC was examined, focusing on their potential application in CRC diagnosis and targeted therapy, which would advance the knowledge of the functions of circRNAs in the development and progression of CRC.

Diagnostic accuracy of circulating exosomal circRNAs in malignances: A meta-analysis and systematic review

BACKGROUND

Pathogenesis of malignant tumors are often accompanied by aberrant expression of circular RNAs (circRNAs), indicating the potential diagnostic value of circRNAs in tumors. CircRNAs have been found to be enriched, stable and ubiquitous in serum and plasma exosomes. The study aims at evaluating the diagnostic performance of circulating (plasma and serum) exosomal circRNA in different types of cancer by synthesis of published data.

METHODS

A comprehensive literature search was conducted in PubMed, Embase, Medline and the Web of Science databases to identify potentially eligible studies published before April 2021. We conducted the meta-analysis following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses recommendations.

RESULTS

Eleven articles comprising 21 studies were included, and a total of 1609 cases and 1498 controls were evaluated. Six types of cancer were involved in these studies, including lung cancer, hepatocellular carcinoma, colorectal cancer, gastric cancer, multiple myeloma and osteosarcoma. The pooled sensitivity and specificity were 0.72 (95% confidence interval [CI], 0.62-0.81) and 0.83 (95% CI, 0.78-0.88), respectively. Summary receiver operating characteristic curve was constructed and the pooled value of area under curve was 0.86 (95% CI, 0.83-0.89), indicating a favorable diagnostic efficacy of circulating exosomal circRNAs in malignancies.

CONCLUSIONS

In conclusion, our study evaluated the diagnostic power of circulating exosomal circRNAs in 6 types of cancer by synthesis of published data comprising 21 studies from eleven articles. The pooled analysis provided the evidence supporting circulating exosomal circRNAs as a promising noninvasive diagnostic biomarkers for malignancies.

CircRNAs in tumor immunity and immunotherapy: Perspectives from innate and adaptive immunity

Tumor immunotherapy is a new therapeutic approach that has been evolving in the last decade and has dramatically changed the treatment options for cancer. Circular RNAs (circRNAs) are non-coding RNAs (ncRNAs) with high stability, tissue-specific and cell-specific expression. There is growing evidence that circRNAs are involved in the regulation of both adaptive and innate immunity. They play important roles in tumor immunotherapy by affecting macrophage, NK and T cell function. The high stability and tissue specificity make them ideal candidate biomarkers for therapeutic effects. CircRNAs also represent one of promising targets or adjuvant for immunotherapy. Investigations in this field progress rapidly and provide essential support for the diagnosis, prognosis and treatment guidance of cancers in the future. In this review, we summarize the role of circRNAs on tumor immunity from the viewpoint of innate and adaptive immunity, and explore the role of circRNAs in tumor immunotherapy.

Altered non-coding RNA profiles of seminal plasma extracellular vesicles of men with poor semen quality undergoing in vitro fertilization treatment

BACKGROUND

Currently, the precise mechanisms that underline male infertility are still unclear. Accumulating data implicate non-coding RNA cargo of seminal plasma extracellular vesicles due to their association with poor semen quality and higher expression levels relative to vesicle-free seminal plasma.

METHOD

We assessed sperm-free seminal plasma extracellular vesicle non-coding RNA profiles from 91 semen samples collected from male participants of couples seeking infertility treatment. Men were classified into two groups (poor, n = 32; normal, n = 59) based on World Health Organization semen cutoffs. Small RNA sequencing reads were mapped to standard biotype-specific transcriptomes in the order micro RNA > transfer RNA > piwi-interacting RNA > ribosomal RNA  > ribosomal RNA > circular RNA > long non-coding RNA using STAR. Differential expression of normalized non-coding RNA read counts between the two groups was conducted by EdgeR (Fold change ≥1.5 and (false discovery rate [FDR] < 0.05).

RESULT

Small RNA sequencing identified a wide variety of seminal plasma extracellular vesicle non-coding RNA biotypes including micro RNA, ribosomal RNAs, piwi-interacting RNAs, transfer RNA, long non-coding RNAs as well as circular RNAs, and fragments associated with pseudogenes, and nonsense-mediated decay. The expression levels of 57 seminal plasma extracellular vesicle non-coding RNAs (micro RNA: 6, piwi-interacting RNA: 4, ribosomal RNA: 6, circular RNA: 34, and long non-coding RNA: 7) were altered in men with poor semen quality relative to normal semen parameters, many (60%) of which were circular RNA species. Ontology analysis of differentially expressed micro RNAs and circular RNAs showed enrichment in functional terms related to cellular communication and early development.

CONCLUSION

This is the first study to generate comprehensive seminal plasma extracellular vesicle non-coding RNA profiles in a clinical setting and to determine the differences between men with normal and abnormal semen parameters. Thus, our study suggests that seminal plasma extracellular vesicle non-coding RNAs may represent novel biomarkers of male reproductive phenotypes.

The Crosstalk and Clinical Implications of CircRNAs and Glucose Metabolism in Gastrointestinal Cancers

The majority of glucose in tumor cells is converted to lactate despite the presence of sufficient oxygen and functional mitochondria, a phenomenon known as the "Warburg effect" or "aerobic glycolysis". Aerobic glycolysis supplies large amounts of ATP, raw material for macromolecule synthesis, and also lactate, thereby contributing to cancer progression and immunosuppression. Increased aerobic glycolysis has been identified as a key hallmark of cancer. Circular RNAs (circRNAs) are a type of endogenous single-stranded RNAs characterized by covalently circular structures. Accumulating evidence suggests that circRNAs influence the glycolytic phenotype of various cancers. In gastrointestinal (GI) cancers, circRNAs are related to glucose metabolism by regulating specific glycolysis-associated enzymes and transporters as well as some pivotal signaling pathways. Here, we provide a comprehensive review of glucose-metabolism-associated circRNAs in GI cancers. Furthermore, we also discuss the potential clinical prospects of glycolysis-associated circRNAs as diagnostic and prognostic biomarkers and therapeutic targets in GI cancers.

Exploring the potential of exosomes in diagnosis and drug delivery for pancreatic ductal adenocarcinoma

Pancreatic cancer (PC) is a cancer of the digestive system, and pancreatic ductal adenocarcinoma (PDAC) accounts for approximately 90% of all PC cases. Exosomes derived from PDAC (PDAC-exosomes) promote PDAC development and metastasis. Exosomes are nanoscale vesicles secreted by most cells, which can carry biologically active molecules and mediate communication and cargo transportation among cells. Recent studies have focused on transforming exosomes into good drug delivery systems (DDSs) to improve the clinical treatment of PDAC. This review considers PDAC as the main research object to introduce the role of PDAC-exosomes in PDAC development and metastasis. This review focuses on the following two themes: (a) the great potential of PDAC-exosomes as new diagnostic markers for PDAC, and (b) the transformation of exosomes into potential DDSs.

The Detection of Exosomal PD-L1 in Peripheral Blood

Peripheral blood is a source for liquid biopsy, which can meet the requirements of pretreatment disease typing to determine precise targeted therapy and monitoring of posttreatment minimal residual disease monitoring. Compared with ctDNA and CTC, exosomes have a higher concentration, good biostability, biocompatibility, low immunogenicity, and low toxicity in peripheral blood. Tumors generally secrete a large amounts of exosomes, which have potential pathophysiological roles in tumor progression. With the continuous improvement of liquid biopsy technology, many researchers have found that exosomes are the key for tumor PD-L1 to exert its role, which may be the mechanism that leads to PD-L1 and/or PD-1 inhibitor therapy resistance. Namely, tumor-derived exosomes may mediate systemic immunosuppression against PD-1 or PD-L1 inhibitor therapy, endogenous tumor cell-derived exosomal PD-L1, and tumor microenvironment-derived exosomes. Induction of PD-L1 by exosomes may be a crucial mechanisms of exosome-mediated antitumor immune tolerance. This article reviews the relationship between the detection of peripheral blood exosomal PD-L1 and tumor progression and the mechanism of exosomal PD-L1 in tumor immunotherapy.

Unraveling the significance of exosomal circRNAs in cancer therapeutic resistance

Exosomes are nanoscale extracellular vesicles secreted by a variety of cells, affecting the physiological and pathological homeostasis. They carry various cargoes including proteins, lipids, DNA, and RNA and have emerged as critical mediators of intercellular communication. During cell-cell communication, they can internalize either by autologous or heterologous recipient cells, which activate different signaling pathways, facilitating malignant progression of cancer. Among different types of cargoes in exosomes, the endogenous non-coding RNAs, such as circular RNAs (or circRNAs), have gained tremendous attention for their high stability and concentration, playing promising functional roles in cancer chemotherapeutic response by regulating the targeted gene expression. In this review, we primarily described the emerging evidence demonstrating the important roles of circular RNAs derived from exosomes in the regulation of cancer-associated signaling pathways that were involved in cancer research and therapeutic interventions. Additionally, the relevant profiles of exosomal circRNAs and their biological implications have been discussed, which is under investigation for their potential effect on the control of cancer therapeutic resistance.

Exosomes in Genitourinary Cancers: Emerging Mediators of Drug Resistance and Promising Biomarkers

Drug resistance presents a major obstacle in the treatment of genitourinary cancers. Exosomes as the medium of intercellular communication serve important biological functions and play essential roles in pathological processes, including drug response. Through the transfer of bioactive cargoes, exosomes can modulate drug resistance via multiple mechanisms. This review attempts to elucidate the mechanisms of exosomal cargoes with reference to tumor drug resistance, their role in genitourinary cancers, and their potential clinical applications as candidate biomarkers in liquid biopsy.

Functions of exosomal non-coding RNAs to the infection with Mycobacterium tuberculosis

Tuberculosis (TB) is a major infectious disease induced by Mycobacterium tuberculosis (M. tb) which causes the world's dominant fatal bacterial contagious disease. Increasing studies have indicated that exosomes may be a novel option for the diagnosis and treatment of TB. Exosomes are nanovesicles (30-150 nm) containing lipids, proteins and non-coding RNAs (ncRNAs) released from various cells, and can transfer their cargos and communicate between cells. Furthermore, exosomal ncRNAs exhibit diagnosis potential in bacterial infections, including TB. Additionally, differential exosomal ncRNAs regulate the physiological and pathological functions of M. tb-infected cells and act as diagnostic markers for TB. This current review explored the potential biological roles and the diagnostic application prospects of exosomal ncRNAs, and included recent information on their pathogenic and therapeutic functions in TB.

The importance of regulatory pathway mediated by Circ0001955 in colorectal cancer

INTRODUCTION

Colorectal cancer (CRC) has become one of the most common cancers in recent years. Given the importance that non-coding RNAs have recently acquired in various diseases including cancers, we decided to design this study to evaluate the expression levels of circ0001955/miR-145-5p/ONECUT2 axis in CRC.

METHODS

After bioinformatics analysis of GEO datasets related to CRC, a putative circ0001955/ miR-145-5p/ ONECUT2 pathway was assumed. Then, the expression levels of these genes were measured in 50 CRC samples and adjacent tissues by qRT- PCR. Also, correlation coefficients, receiver operating characteristic (ROC) curves, and correlation between circ0001955 levels with clinicopathological parameters of patients were analyzed.

RESULTS

Circ0001955 and ONECUT2 were considerably up-regulated, while the expression level of miR-145-5p was decreased in CRC samples compared with adjacent tissues (p < 0.05). Moreover, statistically significant correlations were observed between expression levels of circ0001955, miR-145-5p, and ONECUT2. We did not find any significant correlation between circ0001955 expression and clinicopathological parameters.

CONCLUSION

Our study showed that circ0001955 is dysregulated in CRC. This finding can open a new window for researchers for a better understanding of the potential pathways involved in CRC pathogenesis and, consequently, to find new treatment pathways.

A Review and In Silico Analysis of Tissue and Exosomal Circular RNAs: Opportunities and Challenges in Thyroid Cancer

Simple Summary

Thyroid cancer is the most common endocrine neoplasm. Recently, knowledge of the molecular genetic changes of thyroid cancer has dramatically improved. Understanding the roles of these molecular changes in thyroid cancer tumorigenesis and progression is essential in developing a successful treatment strategy and improving disease outcomes. As a family of non-coding RNAs, circular RNAs (circRNAs) have been involved in several aspects of the physiological and pathological processes of the cells. The roles of circRNAs in cancer development and progress are evident. In the current review, we aimed to explore the clinical potential of circRNAs as potential diagnostic, prognostic, and therapeutic targets in thyroid cancer. Furthermore, screening the genome-wide circRNAs and performing functional enrichment analyses for all associated dysregulated circRNAs in thyroid cancer have been done. Given the unique advantages circRNAs have, such as superior stability, higher abundance, and presence in different body fluids, this family of non-coding RNAs could be promising diagnostic and prognostic biomarkers and potential therapeutic targets for thyroid cancer.

Abstract

Thyroid cancer (TC) is the most common endocrine tumor. The genetic and epigenetic molecular alterations of TC have become more evident in recent years. However, a deeper understanding of the roles these molecular changes play in TC tumorigenesis and progression is essential in developing a successful treatment strategy and improving patients’ prognoses. Circular RNAs (circRNAs), a family of non-coding RNAs, have been implicated in several aspects of carcinogenesis in multiple cancers, including TC. In the current review, we aimed to explore the clinical potential of circRNAs as putative diagnostic, prognostic, and therapeutic targets in TC. The current analyses, including genome-wide circRNA screening and functional enrichment for all deregulated circRNA expression signatures, show that circRNAs display atypical contributions, such as sponging for microRNAs, regulating transcription and translation processes, and decoying for proteins. Given their exceptional clinical advantages, such as higher stability, wider abundance, and occurrence in several body fluids, circRNAs are promising prognostic and theranostic biomarkers for TC.

The Application of Liquid Biopsy Techniques in High-Risk Population for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors of the digestive system and has a 5-year overall survival rate of 14.1%. Many HCC patients are diagnosed at an advanced stage, and thus early screening is essential for reducing the mortality of HCC. In addition to commonly used detection indicators such as serum alpha-fetoprotein (AFP), lens culinaris agglutinin-reactive fraction of alpha-fetoprotein (AFP-L3) and abnormal prothrombin (protein induced by vitamin K absence II, PIVKA-II), liquid biopsy techniques have been demonstrated to have diagnostic value in HCC detection. Compared with invasive procedures, liquid biopsy can detect circulatory metabolites of malignant neoplasms. Liquid biopsy techniques can detect circulating tumor cells, circulating tumor DNA, circulating RNA and exosomes and have been used in the early screening, diagnosis and prognostic evaluation of HCC. This paper reviews the molecular biological characteristics and application of different liquid biopsy techniques, and aim to highlight promising biomarkers that may be feasible options for early-stage HCC evaluation to improve early screening in populations at high risk for HCC.

Nucleic acids and proteins carried by exosomes from various sources: Potential role in liver diseases

Exosomes are extracellular membrane-encapsulated vesicles that are released into the extracellular space or biological fluids by many cell types through exocytosis. As a newly identified form of intercellular signal communication, exosomes mediate various pathological and physiological processes by exchanging various active substances between cells. The incidence and mortality of liver diseases is increasing worldwide. Therefore, we reviewed recent studies evaluating the role of exosomes from various sources in the diagnosis and treatment of liver diseases.

Identifying potential microRNA biomarkers for colon cancer and colorectal cancer through bound nuclear norm regularization

Colon cancer and colorectal cancer are two common cancer-related deaths worldwide. Identification of potential biomarkers for the two cancers can help us to evaluate their initiation, progression and therapeutic response. In this study, we propose a new microRNA-disease association identification method, BNNRMDA, to discover potential microRNA biomarkers for the two cancers. BNNRMDA better combines disease semantic similarity and Gaussian Association Profile Kernel (GAPK) similarity, microRNA function similarity and GAPK similarity, and the bound nuclear norm regularization model. Compared to other five classical microRNA-disease association identification methods (MIDPE, MIDP, RLSMDA, GRNMF, AND LPLNS), BNNRMDA obtains the highest AUC of 0.9071, demonstrating its strong microRNA-disease association identification performance. BNNRMDA is applied to discover possible microRNA biomarkers for colon cancer and colorectal cancer. The results show that all 73 known microRNAs associated with colon cancer in the HMDD database have the highest association scores with colon cancer and are ranked as top 73. Among 137 known microRNAs associated with colorectal cancer in the HMDD database, 129 microRNAs have the highest association scores with colorectal cancer and are ranked as top 129. In addition, we predict that hsa-miR-103a could be a potential biomarker of colon cancer and hsa-mir-193b and hsa-mir-7days could be potential biomarkers of colorectal cancer.

Exosomics in oral cancer diagnosis, prognosis, and therapeutics - An emergent and imperative non-invasive natural nanoparticle-based approach

Exosomes- the natural nanoparticles belonging to heterogeneous vesicles are released via nearly all sorts of cells, including tumour cells, to oprate intercellular communication. Selective packaging of exosomes amid nucleic acids, phospholipids, and proteins makes them ideal for intercellular communications occurring among different cells. The existence of exosomes has been validated in various biofluids, including saliva. Being non-invasive and in direct contact with oral malignant cells, saliva establishes itself as a preeminent source of early cancer biomarkers. In context, the role and providence of both recipient and donor secreting cells are persuaded through exosomal cargo.Several studies have emphasized the influence of exosomal contents in different stages of cancer development, reconciling interactions between tumour cells and their surrounding niche. More explicitly, a transformation of exosomal contents such as nucleic acids, lipids, and proteins can endorse tumour progression and help ascertain a secluded pre-metastatic niche crammed with substances that errand cancer cell proliferation,angiogenesis, metastasis, and drug resistance. The blooming field of exosomes has directed the evolution of high-end isolation and characterization techniques along with the development of an entirely new field- exosomics that comprises complete analysis of exosomal cargo in various physiological conditions, including oral cancer. Researchers have discovered multiple pathways involved in exosome biogenesis to understand numerous events associated with cancer progression. Tissue-specific packaging of exosomes makes them a novel source of prognostic and diagnostic biomarkers and potential therapeutic targets. The extent of the current review confers the contemporary perception of the versatile task of exosomes, especially salivary exosomes, as potential biomarkers in the progression and diagnosis as well as therapeutics of oral cancers and their potential employment in clinical applications.

Expression and clinical value of circRNAs in serum extracellular vesicles for gastric cancer

Objective

At present, there are still no effective diagnosis methods for gastric cancer (GC). Increasing evidences indicate that Extracellular Vesicle circular RNAs (EV circRNAs) play a crucial role in several diseases. However, their correlations with GC are not clarified. This study aims to investigate the expression profile of serum EV circRNAs in GC and evaluate its potential clinical value.

Methods

High-throughput RNA sequencing (RNA-seq) was used to assess circRNA expression profiles between 4 patients with GC and 4 healthy controls. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were employed to determine the biological functions of differentially expressed (DE) circRNAs. A circRNA-miRNA-mRNA network was constructed using bioinformatics tools. Reverse transcription-quantitative polymerase chain reaction (RT-q)PCR was used to validate the dysregulated circRNAs. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic value of circRNAs for GC.

Results

A total of 4692 circRNAs were detected in the serum EVs of healthy controls and patients with GC, most of which were novel (98%) and intergenic (52%). 7 circRNAs were upregulated and 4 circRNAs were downregulated (|log₂Fold Change| > 2, P < 0.05). GO and KEGG pathway enrichment analyses revealed that DE circRNAs were primarily involved in glutathione metabolism, protein folding, and drug metabolism-cytochrome P450. Of these, 3 circRNAs (Chr10q11, Chr1p11, and Chr7q11) were identified to be significantly overexpressed in patients with GC compared with healthy controls using RT-qPCR. The combination of 3 EV circRNAs and carcinoembryonic antigen (CEA) produced an area under the curve (AUC) of 0.866 (95%CI: 0.803-0.915) with a sensitivity and specificity of 80.4% and 81.8%, respectively. Additionally, the expression levels of 3 EV circRNAs were significantly correlated with tumor size, lymph node metastasis, and TNM stage. The circRNA-miRNA-mRNA network showed that the 3 identified circRNAs were predicted to interact with 13 miRNAs and 91 mRNAs.

Conclusion

Our results illustrate that the panel of EV circRNAs in serum are aberrantly expressed and may act as the suitable biomarkers for gastric cancer.

Plasma Exosomal hsa_circ_0015286 as a Potential Diagnostic and Prognostic Biomarker for Gastric Cancer

Circular RNA (circRNA) is stable and abundant in exosomes as a potential biomarker for the diagnosis and prognosis of tumor. In this study, cancer specific exosomal circRNAs were identified through circRNA microarray, and 58 circRNAs were significantly upregulated in cancer cells derived exosomes. Then 60 patients with newly diagnosed gastric cancer (GC), 30 chronic gastritis patients and 30 healthy subjects were enrolled for further clinical validation. We detected that hsa_circ_0015286 was remarkably highly expressed in GC tissue, plasma and cancer cells compared with normal controls. Results of ROC curve analysis showed that the area under curve (AUC) of hsa_circ_0015286, CEA and CA 19-9 was 0.778, 0.673, and 0.665, respectively. The combined detection of three indicators had the highest AUC (0.843). Exosomal hsa_circ_0015286 expression was closely associated with tumor size, TNM stage and lymph node metastasis. The expression level of exosomal hsa_circ_0015286 in GC patients decreased significantly after surgery. Overall survival of patients with low hsa_circ_0015286 expression was longer than those with high expression. Our data demonstrated that exosomal hsa_circ_0015286 might be a promising noninvasive biomarker for the diagnosis and prognosis evaluation of GC.

Circulating Noncoding RNAs in Pituitary Neuroendocrine Tumors-Two Sides of the Same Coin

Pituitary neuroendocrine tumors (PitNET) are common intracranial neoplasms. While in case of hormone secreting tumors pituitary hormone measurements can be used for monitoring the disease, in non-functional tumors there is a need to discover non-invasive biomarkers. Non-coding RNAs (ncRNAs) are popular biomarker candidates due to their stability and tissue specificity. Among ncRNAs, miRNAs, lncRNAs and circRNAs have been investigated the most in pituitary tumor tissues and in circulation. However, it is still not known whether ncRNAs are originated from the pituitary, or whether they are casually involved in the pathophysiology. Additionally, there is strong diversity among different studies reporting ncRNAs in PitNET. Therefore, to provide an overview of the discrepancies between published studies and to uncover the reasons why despite encouraging experimental data application of ncRNAs in clinical routine has not yet taken hold, in this review available data are summarized on circulating ncRNAs in PitNET. The data on circulating miRNAs, lncRNAs and circRNAs are organized according to different PitNET subtypes. Biological (physiological and pathophysiological) factors behind intra- and interindividual variability and technical aspects of detecting these markers, including preanalytical and analytical parameters, sample acquisition (venipuncture) and type, storage, nucleic acid extraction, quantification and normalization, which reveal the two sides of the same coin are discussed.

The Biological Functions and Clinical Values of Exosomal Circular RNAs in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) exacts a heavy disease burden and is currently the second most common cause of cancer-related deaths worldwide. HCC usually lacks obvious symptoms in the early stage, and most HCC patients are diagnosed at advanced stages with poor prognosis. Circular RNAs (circRNAs) are single-stranded RNAs that form covalently closed loops and are stable in exosomes. Exosomes are known as important messengers of the cross-talk between tumor and immune cells. Accumulating studies have demonstrated the promoter or suppressor roles of exosomal circRNAs in the carcinogenesis, progression, and metastasis of HCC. In this review, we summarized the current studies on the biological functions and diagnostic and prognostic values of exosomal circRNAs in HCC progression.

The role of circRNAs in the regulation of myocardial angiogenesis in coronary heart disease

During myocardial ischemia, timely reperfusion is critical to limit infarct area and the overall loss of cardiac contractile function. New treatment strategies need to be developed for patients who are neither able to receive interventional treatment nor suitable for surgical blood transport reconstruction surgery. Therapeutic angiogenesis is a promising approach that can be used to guide new treatment strategies. The goal of these therapies is to form new blood vessels or promote the maturation of existing vasculature systems, bypassing blocked arteries to maintain organ perfusion, thereby relieving symptoms and preventing the remodeling of bad organs. Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), have been attracted much attention for their roles in various physiological and pathological processes. There is growing evidence that ncRNAs, especially circRNAs, play an important role in the regulation of cardiomyopathy angiogenesis due to its diversity of functions. Therefore, this article reviews the role and mechanisms of circRNA in myocardial angiogenesis to better understand the role of circRNAs in myocardial angiogenesis, which may provide useful insights and new revelations for the research field of identifying diagnostic markers and therapeutic approaches for the treatment of coronary artery disease.

A modular microfluidic platform for serial enrichment and harvest of pure extracellular vesicles

A modular microfluidic platform is developed to enrich EVs on micron-sized carrier beads immobilized with EV-specific antibodies, based on affinity capture, and elute pure EVs from the carrier beads in a high throughput.

Emerging role of exosomes as biomarkers in cancer treatment and diagnosis

Cancer is a leading cause of death worldwide and cancer incidence and mortality are rapidly growing. These massive amounts of cancer patients require rapid diagnosis and efficient treatment strategies. However, the currently utilized methods are invasive and cost-effective. Recently, the effective roles of exosomes as promising diagnostic, prognostic, and predictive biomarkers have been revealed. Exosomes are membrane-bound extracellular vesicles containing RNAs, DNAs, and proteins, and are present in a wide array of body fluids. Exosomal cargos have shown the potential to detect various types of cancers at early stages with high sensitivity and specificity. They can also delivery therapeutic agents efficiently. In this article, an overview of recent advances in the research of exosomal biomarkers and their applications in cancer diagnosis and treatment has been provided. Furthermore, the advantages and challenges of exosomes as liquid biopsy targets are discussed and the clinical implications of using exosomal miRNAs have been revealed.

Urinary extracellular vesicles: Assessment of pre-analytical variables and development of a quality control with focus on transcriptomic biomarker research

Urinary extracellular vesicles (uEV) are a topical source of non-invasive biomarkers for health and diseases of the urogenital system. However, several challenges have become evident in the standardization of uEV pipelines from collection of urine to biomarker analysis. Here, we studied the effect of pre-analytical variables and developed means of quality control for uEV isolates to be used in transcriptomic biomarker research. We included urine samples from healthy controls and individuals with type 1 or type 2 diabetes and normo-, micro- or macroalbuminuria and isolated uEV by ultracentrifugation. We studied the effect of storage temperature (-20°C vs. -80°C), time (up to 4 years) and storage format (urine or isolated uEV) on quality of uEV by nanoparticle tracking analysis, electron microscopy, Western blotting and qPCR. Urinary EV RNA was compared in terms of quantity, quality, and by mRNA or miRNA sequencing. To study the stability of miRNA levels in samples isolated by different methods, we created and tested a list of miRNAs commonly enriched in uEV isolates. uEV and their transcriptome were preserved in urine or as isolated uEV even after long-term storage at -80°C. However, storage at -20°C degraded particularly the GC-rich part of the transcriptome and EV protein markers. Transcriptome was preserved in RNA samples extracted with and without DNAse, but read distributions still showed some differences in e.g. intergenic and intronic reads. MiRNAs commonly enriched in uEV isolates were stable and concordant between different EV isolation methods. Analysis of never frozen uEV helped to identify surface characteristics of particles by EM. In addition to uEV, qPCR assays demonstrated that uEV isolates commonly contained polyoma viruses. Based on our results, we present recommendations how to store and handle uEV isolates for transcriptomics studies that may help to expedite standardization of the EV biomarker field.

Genomic Landscape of Liquid Biopsy for Hepatocellular Carcinoma Personalized Medicine

Hepatocellular carcinoma (HCC) is the sixth most frequently diagnosed cancer and the third leading cause of cancer-related deaths worldwide. Advanced-stage HCC patients have poor survival rates and this requires the discovery of novel clear biomarkers for HCC early diagnosis and prognosis, identifying risk factors, distinguishing HCC from non-HCC liver diseases, and assessment of treatment response. Liquid biopsy has emerged as a novel minimally invasive approach to enable monitoring tumor progression, metastasis, and recurrence. Since the liquid biopsy analysis has relatively high specificity and low sensitivity in cancer early detection, there is a risk of bias. Next-generation sequencing (NGS) technologies provide accurate and comprehensive gene expression and mutational profiling of liquid biopsies including cell-free circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), and genomic components of extracellular vesicles (EVs) including micro-RNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). Since HCC is a highly heterogeneous cancer, HCC patients can display various genomic, epigenomic, and transcriptomic patterns and exhibit varying sensitivity to treatment options. Identification of individual variabilities in genomic signatures in liquid biopsy has the potential to greatly enhance precision oncology capabilities. In this review, we highlight and critically discuss the latest progress in characterizing the genomic landscape of liquid biopsy, which can advance HCC personalized medicine.