Circ_0000260 Regulates the Development and Deterioration of Gastric Adenocarcinoma with Cisplatin Resistance by Upregulating MMP11 via Targeting MiR-129-5p

CircUGGT2 facilitates progression and cisplatin resistance of bladder cancer through nonhomologous end-joining pathway

The development of resistance to cisplatin (CDDP) in bladder cancer presents a notable obstacle, with indications pointing to the substantial role of circular RNAs (circRNAs) in this resistance. Nevertheless, the precise mechanisms through which circRNAs govern resistance are not yet fully understood. Our findings demonstrate that circUGGT2 is significantly upregulated in bladder cancer, facilitating cancer cell migration and invasion. Additionally, our analysis of eighty patient outcomes revealed a negative correlation between circUGGT2 expression levels and prognosis. Using circRNA pull-down assays, mass spectrometry analyses, and RNA Immunoprecipitation (RIP), it was shown that circUGGT2 interacts with the KU heterodimer, consisting of KU70 and KU80. Both KU70 and KU80 are critical components of the non-homologous end joining (NHEJ) pathway, which plays a role in CDDP resistance. Flow cytometry was utilized in this study to illustrate the impact of circUGGT2 on the sensitivity of bladder cancer cell lines to CDDP through its interaction with KU70 and KU80. Additionally, a reduction in the levels of DNA repair factors associated with the NHEJ pathway, such as KU70, KU80, DNA-PKcs, and XRCC4, was observed in chromatin of bladder cancer cells following circUGGT2 knockdown post-CDDP treatment, while the levels of DNA repair factors in total cellular proteins remained constant. Thus, the promotion of CDDP resistance by circUGGT2 is attributed to its facilitation of repair factor recruitment to DNA breaks via interaction with the KU heterodimer. Furthermore, our study demonstrated that knockdown of circUGGT2 resulted in reduced levels of γH2AX, a marker of DNA damage response, in CDDP-treated bladder cancer cells, implicating circUGGT2 in the NHEJ pathway for DNA repair.

Emerging roles of circular RNAs in tumorigenesis, progression, and treatment of gastric cancer

With an estimated one million new cases reported annually, gastric cancer (GC) ranks as the fifth most diagnosed malignancy worldwide. The early detection of GC remains a major challenge, and the prognosis worsens either when patients develop resistance to chemotherapy or radiotherapy or when the cancer metastasizes. The precise pathogenesis underlying GC is not well understood, which further complicates its treatment. Circular RNAs (circRNAs), a recently discovered class of noncoding RNAs that originate from parental genes through "back-splicing", have been shown to play a key role in various biological processes in both eukaryotes and prokaryotes. CircRNAs have been linked to cardiovascular diseases, diabetes, hypertension, Alzheimer's disease, and the occurrence and progression of tumors. Prior studies have established that circRNAs play a crucial role in GC, impacting tumorigenesis, diagnosis, progression, and therapy resistance. This review aims to summarize how circRNAs contribute to GC tumorigenesis and progression, examine their roles in the development of drug resistance, discuss their potential as biotechnological drugs, and summarize their response to therapeutic drugs and microorganism in GC.

Extracellular vesicles in gastric cancer: role of exosomal lncRNA and microRNA as diagnostic and therapeutic targets

Extracellular vesicles (EVs), including exosomes, play a crucial role in intercellular communication and have emerged as important mediators in the development and progression of gastric cancer. This review discusses the current understanding of the role of EVs, particularly exosomal lncRNA and microRNA, in gastric cancer and their potential as diagnostic and therapeutic targets. Exosomes are small membrane-bound particles secreted by both cancer cells and stromal cells within the tumor microenvironment. They contain various ncRNA and biomolecules, which can be transferred to recipient cells to promote tumor growth and metastasis. In this review, we highlighted the importance of exosomal lncRNA and microRNA in gastric cancer. Exosomal lncRNAs have been shown to regulate gene expression by interacting with transcription factors or chromatin-modifying enzymes, which regulate gene expression by binding to target mRNAs. We also discuss the potential use of exosomal lncRNAs and microRNAs as diagnostic biomarkers for gastric cancer. Exosomes can be isolated from various bodily fluids, including blood, urine, and saliva. They contain specific molecules that reflect the molecular characteristics of the tumor, making them promising candidates for non-invasive diagnostic tests. Finally, the potential of targeting exosomal lncRNAs and microRNAs as a therapeutic strategy for gastric cancer were reviewed as wee. Inhibition of specific molecules within exosomes has been shown to suppress tumor growth and metastasis in preclinical models. In conclusion, this review article provides an overview of the current understanding of the role of exosomal lncRNA and microRNA in gastric cancer. We suggest that further research into these molecules could lead to new diagnostic tools and therapeutic strategies for this deadly disease.

Circular RNA circLRCH3 promotes oxaliplatin resistance in gastric cancer through the modulation of the miR-383-5p/FGF7 axis

BACKGROUND

Gastric cancer (GC) is a common malignant tumor of the digestive system. Circular RNAs (circRNAs) play a vital role in tumorigenesis and chemoresistance. The current study aimed to explore the possible role and mechanism of circRNA leucine rich repeats and calponin homology domain containing 3 (circLRCH3) in GC chemoresistance.

METHODS

The levels of circLRCH3, microRNA-383-5p (miR-383-5p) and fibroblast growth factor 7 (FGF7) were determined by quantitative real-time PCR or Western blot. Cell Counting Kit-8 (CCK-8) assay was utilized to evaluate cell survival rate and proliferation ability. Colony formation, transwell and flow cytometry assays were used to assess cell proliferation, migration, invasion and apoptosis. The expression of multidrug resistance proteins was detected by Western blot. The binding relationship between miR-383-5p and circLRCH3/FGF7 was verified by dual-luciferase reporter assay or RNA immunoprecipitation assay. Xenograft assay was conducted to analyze the role of circLRCH3 in OXA resistance in vivo.

RESULTS

CircLRCH3 and FGF7 levels were up-regulated, while miR-383-5p level was reduced in OXA-resistant GC tissues and cells. Depletion of circLRCH3 attenuated the resistance of OXA-resistant cells to OXA. CircLRCH3 silence reduced OXA resistance by regulating miR-383-5p. Besides, miR-383-5p elevated OXA sensitivity of GC cells by repressing FGF7. Moreover, the deletion of circLRCH3 increased OXA sensitivity in vivo.

CONCLUSIONS

Knockdown of circLRCH3 alleviated OXA resistance of GC by modulating the miR-383-5p/FGF7 axis, which provided a promising therapeutic target for GC chemoresistance.

Circ_0003356 suppresses gastric cancer growth through targeting the miR-668-3p/SOCS3 axis

BACKGROUND

Circular RNAs (circRNAs) have attracted extensive attention as therapeutic targets in gastric cancer (GC). Circ_0003356 is known to be downregulated in GC tissues, but its cellular function and mechanisms remain undefined.

AIM

To investigate the role of circ_0003356 in GC at the molecular and cellular level.

METHODS

Circ_0003356, miR-668-3p, and SOCS3 expression were assessed via quantitative real time-polymerase chain reaction (qRT-PCR). Wound healing, EdU, CCK-8, flow cytometry and transwell assays were used to analyze the migration, proliferation, viability, apoptosis and invasion of GC cells. The subcellular localization of circ_0003356 was monitored using fluorescence in situ hybridization. The interaction of circ_0003356 with miR-668-3p was confirmed using RIP-qRT-PCR, RNA pull-down, and dual luciferase reporter assays. We observed protein levels of genes via western blot. We injected AGS cells into the upper back of mice and performed immunohistochemistry staining for examining E-cadherin, N-cadherin, Ki67, and SOCS3 expressions. TUNEL staining was performed for the assessment of apoptosis in mouse tumor tissues.

RESULTS

Circ_0003356 and SOCS3 expression was downregulated in GC cells, whilst miR-668-3p was upregulated. Exogenous circ_0003356 expression and miR-668-3p silencing suppressed the migration, viability, proliferation, epithelial to mesenchy-mal transition (EMT) and invasion of GC cells and enhanced apoptosis. Circ_0003356 overexpression impaired tumor growth in xenograft mice. Targeting of miR-668-3p by circ_0003356 was confirmed through binding assays and SOCS3 was identified as a downstream target of miR-668-3p. The impacts of circ_0003356 on cell proliferation, apoptosis, migration, invasion and EMT were reversed by miR-668-3p up-regulation or SOCS3 down-regulation in GC cells.

CONCLUSION

Circ_0003356 impaired GC development through its interaction with the miR-668-3p/SOCS3 axis.

Regulatory mechanisms and clinical applications of tumor-driven exosomal circRNAs in cancers

Malignant tumors seriously affect people's survival and prognosis. Exosomes, as vesicle structures widely existing in human tissues and body fluids, are involved in cell-to-cell transmission. Tumor-derived exosomes were secreted from tumors and involved in the development of carcinogenesis. Circular RNA (circRNA), a novel member of endogenous noncoding RNAs, is widespread in human and play a vital role in many physiological or pathological processes. Tumor-driven exosomal circRNAs are often involved in tumorigenesis and development including the proliferation, invasion, migration and chemo-or-radiotherapy sensitivity of tumor cell by multiple regulatory mechanisms. In this review, we will elaborate the roles and functions of tumor-driven exosomal circRNAs in cancers which may be used as potential cancer biomarkers and novel therapeutic targets.

The critical role of circular RNAs in drug resistance in gastrointestinal cancers

Nowadays, drug resistance (DR) in gastrointestinal (GI) cancers, as the main reason for cancer-related mortality worldwide, has become a serious problem in the management of patients. Several mechanisms have been proposed for resistance to anticancer drugs, including altered transport and metabolism of drugs, mutation of drug targets, altered DNA repair system, inhibited apoptosis and autophagy, cancer stem cells, tumor heterogeneity, and epithelial-mesenchymal transition. Compelling evidence has revealed that genetic and epigenetic factors are strongly linked to DR. Non-coding RNA (ncRNA) interferences are the most crucial epigenetic alterations explored so far, and among these ncRNAs, circular RNAs (circRNAs) are the most emerging members known to have unique properties. Due to the absence of 5' and 3' ends in these novel RNAs, the two ends are covalently bonded together and are generated from pre-mRNA in a process known as back-splicing, which makes them more stable than other RNAs. As far as the unique structure and function of circRNAs is concerned, they are implicated in proliferation, migration, invasion, angiogenesis, metastasis, and DR. A clear understanding of the molecular mechanisms responsible for circRNAs-mediated DR in the GI cancers will open a new window to the management of GI cancers. Hence, in the present review, we will describe briefly the biogenesis, multiple features, and different biological functions of circRNAs. Then, we will summarize current mechanisms of DR, and finally, discuss molecular mechanisms through which circRNAs regulate DR development in esophageal cancer, pancreatic cancer, gastric cancer, colorectal cancer, and hepatocellular carcinoma.

Exosomal circular RNAs: A chief culprit in cancer chemotherapy resistance

Chemotherapy is one of the primary treatments for malignant tumors. However, the acquired drug resistance hinders clinical efficacy and leads to treatment failure in most patients. Exosomes are cell-derived vesicles with a diameter of 30-150 nm carrying and delivering substances such as DNAs, RNAs, lipids, and proteins for cellular communication in tumor development. Circular RNAs (circRNAs) present covalently closed-loop RNA structures, which regulate tumor cell proliferation, apoptosis, and metastasis by controlling different genes and signaling pathways. CircRNAs are abundant and stably expressed in exosomes. Recent studies have shown that they play critical roles in chemotherapy resistance in various cancers. In this review, we summarized the origin of exosomes and discussed the regulation mechanism of exosomal circRNAs in cancer drug resistance.

CircRNA: A new class of targets for gastric cancer drug resistance therapy

Gastric cancer (GC) is one of the most common malignancies worldwide. Patients with advanced GC need palliative care to ensure survival. This includes the use of chemotherapy agents, such as cisplatin, 5-fluorouracil, oxaliplatin, paclitaxel, and pemetrexed, as well as targeted agents. However, the emergence of drug resistance evidence in poor patient outcomes and poor prognosis is a motivation to determine the specific mechanism of drug resistance. Interestingly, circular RNAs (circRNAs) play an important part in the carcinogenesis and progression of GC and are involved in GC drug resistance. This review systematically summarizes the functions and mechanisms of circRNAs underlying GC drug resistance, especially chemoresistance. It also emphasizes that circRNAs can serve as promising targets for improving drug resistance and therapeutic efficacy.

Circular RNA circ_0005667 promotes cisplatin resistance of endometrial carcinoma cells by regulating IGF2BP1 through miR-145-5p

BACKGROUND

Circular RNA (circRNA) plays a significant role in cisplatin (DDP) resistance. The purpose of this study was to explore the role of circ_0005667 in DDP resistance of endometrial carcinoma (EC) cells.

METHODS

The expression of circular RNA circ_0005667, microRNA-145-5p (miR-145-5p) and insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) in DDP-sensitive and DDP-resistant EC tissues and EC cells was determined by quantitative real-time PCR (qRT-PCR). The expression of apoptosis-related proteins, drug resistance-related proteins and IGF2BP1 proteins were detected by western blot. The half-maximal inhibitory concentration (IC50) of DDP was determined using a cell counting kit-8 (CCK-8) assay. For functional assays, cell proliferation, migration, invasion and cell apoptosis were determined using 5-ethynyl-2'-deoxyuridine (EdU) assay, wound healing assay, transwell assay and flow cytometry assay, respectively. The binding relationship between miR-145-5p and circ_0005667 or IGF2BP1 was verified by dual-luciferase reporter assay. A xenograft experiment was applied to clarify the functional role of circ_0005667 in vivo.

RESULTS

Levels of circ_0005667 and IGF2BP1 were markedly increased, whereas miR-145-5p was downregulated in DDP-resistant EC tissues and cells. The circ_0005667 deficiency could enhance DDP sensitivity, inhibit cell proliferation, migration and invasion and promote cell apoptosis in DDP-resistant EC cells in vitro. Mechanistically, circ_0005667 modulated IGF2BP1 expression through sponging miR-145-5p. In addition, miR-145-5p depletion attenuated circ_0005667 silencing-induced effects in EC cells. The regulation of miR-145-5p in DDP resistance involved low IGF2BP1 expression. In vivo experiments revealed that circ_0005667 silencing could improve the sensitivity of the tumor to DDP.

CONCLUSION

Circ_0005667 enhanced DDP resistance in EC by elevating IGF2BP1 through sponging miR-145-5p.

Current evidence on circRNAs as potential theranostic markers for detecting chemoresistance in breast cancer: a systematic review and meta‑analysis

This study assessed the value of circRNAs (circular RNAs) as prognostic markers in BC (breast cancer). We searched pertinent studies on the PubMed, Embase, and Web of Science online databases published according to PRISMA guidelines. A random-effects model for meta-analysis was used to assess the combined effect size of the HRs (hazard ratios) of the included studies. The heterogeneity test used Cochran's Q-test and I² statistics. Thirty of the 520 trials retrieved were included in the systematic review. A total of 11 chemotherapeutic agents were used in the included studies. A total of 30 studies on 30 circRNAs were included in the systematic review. Of the 30 relevant circRNAs, 28 were upregulated and two were downregulated in breast cancer versus normal samples, and both were associated with increased drug resistance. Nine of 30 studies were used for the meta-analysis. The results of the meta-analysis showed that the groups with circRNA upregulation and circRNA downregulation showed the same prognostic risk (HR = 1.37, 95% Cl: 0.80-2.36, I² = 63.7%). The results of subgroup analysis showed that both upregulated circRNAs (HR = 2.24, 95% Cl: 1.34-3.75, I² = 0%) and downregulated circRNAs (HR = 0.61, 95% Cl: 0.45-0.83, I² = 0%) were associated with poor BC prognosis. Collectively, the results of all relevant articles collected indicated that circRNAs showed good potential as possible clinical biomarkers of chemoresistance in BC patients.

Emerging roles of circular RNAs in gastric cancer metastasis and drug resistance

Gastric cancer (GC) is an aggressive malignancy with a high mortality rate and poor prognosis, primarily caused by metastatic lesions. Improved understanding of GC metastasis at the molecular level yields meaningful insights into potential biomarkers and therapeutic targets. Covalently closed circular RNAs (circRNAs) have emerged as crucial regulators in diverse human cancers including GC. Furthermore, accumulating evidence has demonstrated that circRNAs exhibit the dysregulated patterns in GC and have emerged as crucial regulators in GC invasion and metastasis. However, systematic knowledge regarding the involvement of circRNAs in metastatic GC remains obscure. In this review, we outline the functional circRNAs related to GC metastasis and drug resistance and discuss their underlying mechanisms, providing a comprehensive delineation of circRNA functions on metastatic GC and shedding new light on future therapeutic interventions for GC metastases.

Mechanism underlying circRNA dysregulation in the TME of digestive system cancer

Circular RNAs (circRNAs) are a new series of noncoding RNAs (ncRNAs) that have been reported to be expressed in eukaryotic cells and have a variety of biological functions in the regulation of cancer pathogenesis and progression. The TME, as a microscopic ecological environment, consists of a variety of cells, including tumor cells, immune cells and other normal cells, ECM and a large number of signaling molecules. The crosstalk between circRNAs and the TME plays a complicated role in affecting the malignant behaviors of digestive system cancers. Herein, we summarize the mechanisms underlying aberrant circRNA expression in the TME of the digestive system cancers, including immune surveillance, angiogenesis, EMT, and ECM remodelling. The regulation of the TME by circRNA is expected to be a new therapeutic method.

Small Extracellular Vesicles and Their Involvement in Cancer Resistance: An Up-to-Date Review

In recent years, tremendous progress has been made in understanding the roles of extracellular vesicles (EVs) in cancer. Thanks to advancements in molecular biology, it has been found that the fraction of EVs called exosomes or small EVs (sEVs) modulates the sensitivity of cancer cells to chemotherapeutic agents by delivering molecularly active non-coding RNAs (ncRNAs). An in-depth analysis shows that two main molecular mechanisms are involved in exosomal modified chemoresistance: (1) translational repression of anti-oncogenes by exosomal microRNAs (miRs) and (2) lack of translational repression of oncogenes by sponging of miRs through long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). At the cellular level, these processes increase the proliferation and survival of cancer cells and improve their ability to metastasize and resist apoptosis. In addition, studies in animal models have shown enhancing tumor size under the influence of exosomal ncRNAs. Ultimately, exosomal ncRNAs are responsible for clinically significant chemotherapy failures in patients with different types of cancer. Preliminary data have also revealed that exosomal ncRNAs can overcome chemotherapeutic agent resistance, but the results are thoroughly fragmented. This review presents how exosomes modulate the response of cancer cells to chemotherapeutic agents. Understanding how exosomes interfere with chemoresistance may become a milestone in developing new therapeutic options, but more data are still required.

Advances in the Study of CircRNAs in Tumor Drug Resistance

Recent studies have revealed that circRNAs can affect tumor DNA damage and repair, apoptosis, proliferation, and invasion and influence the transport of intratumor substances by acting as miRNA sponges and transcriptional regulators and binding to proteins in a variety of ways. However, research on the role of circRNAs in cancer radiotherapy and chemoresistance is still in its early stages. Chemotherapy is a common approach to oncology treatment, but the development of tumor resistance limits the overall clinical efficacy of chemotherapy for cancer patients. The current study suggests that circRNAs have a facilitative or inhibitory effect on the development of resistance to conventional chemotherapy in a variety of tumors, suggesting that circRNAs may serve as a new direction for the study of antitumor drug resistance. In this review, we will briefly discuss the biological features of circRNAs and summarize the recent progression of the involvement of circRNAs in the development and pathogenesis of cancer chemoresistance.

MIR600HG sponges miR-125a-5p to regulate glycometabolism and cisplatin resistance of oral squamous cell carcinoma cells via mediating RNF44

There is increasing evidence that dysregulated long non-coding RNA (lncRNA) is implicated in tumorigenesis and progression. We aim to explore the role of lncRNA MIR600HG in glycometabolism and cisplatin (DDP) resistance of oral squamous cell carcinoma (OSCC) cells via regulating microRNA-125a-5p (miR-125a-5p) and RING finger 44 (RNF44). Expression of MIR600HG, miR-125a-5p, and RNF44 in OSCC clinical samples, cell lines, and DDP-resistant OSCC cells (SCC-9/DDP) was determined. In SCC-9 cells, proliferation, IC50 value of DDP, migration, invasion, and apoptosis were detected; in SCC-9/DDP cells, proliferation, IC50 value of DDP, apoptosis, glucose consumption, and production of lactic acid and ATP were evaluated. The interaction of MR600HG, miR-125a-5p, and RNF44 was verified. MIR600HG and RNF44 were upregulated while miR-125a-5p was downregulated in OSCC tissues and cell lines, and also in SCC-9/DDP cells. In SCC-9 cells, MIR600HG overexpression improved cell growth, metastasis, and inhibited cell susceptibility to DDP; in SCC-9/DDP cells, silencing of MIR600HG promoted apoptosis, improved DDP sensitivity, and inhibited cell glycolysis. Downregulation of miR-125a-5p showed the opposite effect to downregulation of MIR600HG. MIR600HG bound to miR-125a-5p and miR-125a-5p targeted RNF44. Downregulation of miR-125a-5p reversed the improvement of DDP sensitivity and the inhibition of cell glycolysis by downregulated MIR600HG on SCC-9/DDP cells. Downregulating RNF44 reversed the promotion of DDP resistance and cell glycolysis of SCC-9/DDP cells mediated by downregulation of miR-125a-5p. Collectively, our study addresses that MIR600HG downregulation elevates miR-125a-5p and reduces RNF44 expression, thereby improving DDP sensitivity and inhibiting glycolysis in DDP-resistant OSCC cells.

Liquid biopsy at the frontier of detection, prognosis and progression monitoring in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide and a leading cause of carcinogenic death. To date, surgical resection is regarded as the gold standard by the operator for clinical decisions. Because conventional tissue biopsy is invasive and only a small sample can sometimes be obtained, it is unable to represent the heterogeneity of tumor or dynamically monitor tumor progression. Therefore, there is an urgent need to find a new minimally invasive or noninvasive diagnostic strategy to detect CRC at an early stage and monitor CRC recurrence. Over the past years, a new diagnostic concept called “liquid biopsy” has gained much attention. Liquid biopsy is noninvasive, allowing repeated analysis and real-time monitoring of tumor recurrence, metastasis or therapeutic responses. With the advanced development of new molecular techniques in CRC, circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), exosomes, and tumor-educated platelet (TEP) detection have achieved interesting and inspiring results as the most prominent liquid biopsy markers. In this review, we focused on some clinical applications of CTCs, ctDNA, exosomes and TEPs and discuss promising future applications to solve unmet clinical needs in CRC patients.

Circ_0058063 contributes to cisplatin-resistance of bladder cancer cells by upregulating B2M through acting as RNA sponges for miR-335-5p

Bladder cancer (BC) is one of the most common malignant tumors of the urinary system, and cisplatin (CDDP) is a critical chemical drug for the treatment of BC. However, CDDP-resistance seriously limits the therapeutic efficacy of this drug for clinical utilization. Thus, identification of pivotal molecule targets that regulate CDDP-resistance in BC become urgent and necessary. In this study, we firstly identified a novel BC-associated circular RNA circ_0058063 that participates in the regulation of CDDP-resistance in BC. Specifically, circ_0058063 was significantly overexpressed in CDDP-resistant tissue and cells, in contrast with the corresponding CDDP-sensitive counterparts. Further loss-of-function experiments validated that downregulation of circ_0058063 suppressed cell proliferation and tumor growth, whereas induced cell apoptosis in the CDDP-resistant BC cells in vitro and in vivo. In addition, we disclosed that circ_0058063 acts as a sponge for miR-335-5p to positively regulate B2M expression, and further rescuing experiments verified that the enhancing effects of sh-circ_0058063 on CDDP-sensitivity in the CDDP-resistant BC cells were abrogated by silencing miR-335-5p. Taken together, our results demonstrated that circ_0058063 contributed to CDDP resistance of bladder cancer cells via sponging miR-335-5p, and B2M might be the downstream effector gene. This study firstly evidenced that targeting circ_0058063 might be an effective strategy to improve CDDP-sensitivity in BC.

The Emerging Roles of Circular RNAs in the Chemoresistance of Gastrointestinal Cancer

Gastrointestinal (GI) cancer represents a major global health problem due to its aggressive characteristics and poor prognosis. Despite the progress achieved in the development of treatment regimens, the clinical outcomes and therapeutic responses of patients with GI cancer remain unsatisfactory. Chemoresistance arising throughout the clinical intervention is undoubtedly a critical barrier for the successful treatment of GI cancer. However, the precise mechanisms associated with chemoresistance in GI cancer remain unclear. In the past decade, accumulating evidence has indicated that circular RNAs (circRNAs) play a key role in regulating cancer progression and chemoresistance. Notably, circRNAs function as molecular sponges that sequester microRNAs (miRNAs) and/or proteins, and thus indirectly control the expression of specific genes, which eventually promote or suppress drug resistance in GI cancer. Therefore, circRNAs may represent potential therapeutic targets for overcoming drug resistance in patients with GI cancer. This review comprehensively summarizes the regulatory roles of circRNAs in the development of chemoresistance in different GI cancers, including colorectal cancer, gastric cancer and esophageal cancer, as well as deciphers the underlying mechanisms and key molecules involved. Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies against GI cancer.

Exosomes and Exosomal circRNAs: The Rising Stars in the Progression, Diagnosis and Prognosis of Gastric Cancer

Gastric cancer (GC) is a common malignant tumor affecting human health, with occult onset and poor prognosis. Exosomes are extracellular vesicles secreted by almost all cells, which can reflect the state of source cells or tissues. It is reported that exosomes are involved in almost all processes of GC. Exosomes provided a window to understand changes in cell or tissue states by carrying active components such as circular RNAs (circRNAs). CircRNAs are a naturally occurring class of endogenous noncoding RNAs and abnormal expression during the occurrence and development of GC. Exosomal circRNAs are those circRNAs stably existing in exosomes and having high clinical values as novel potential diagnosis and prognosis biomarkers of GC, which have the characteristics of abnormal expression, tissue specificity and development stage specificity. Herein, we briefly summarize the functions and roles and the current research progress of exosomes and exosomal circRNAs in GC with a focus on the potential application for GC progression, diagnosis and prognosis. We also prospected the clinical application of exosomes and exosomal circRNAs in the future.

The role of miR-129-5p in cancer: a novel therapeutic target

MiRNA-129-5p belongs to the microRNA-129 (miRNA-129) family. MiRNA-129-5p is expressed in many tissues and organs of the human body, and it regulates a wide range of biological functions. The abnormal expression of miRNA-129-5p is related to the occurrence and development of a variety of malignant tumors. MiRNA-129-5p plays an important role in the tumorigenesis process and functions by promoting or inhibiting tumors. However, the role of miRNA-129-5p in cancer remains controversial. This article reviews the different biological functions of miRNA-129-5p in cancer and provides ideas for research in this field to guide the development of targeted therapies and drugs for malignant tumors.

Research Progress on the Functions and Mechanism of circRNA in Cisplatin Resistance in Tumors

Cisplatin is a common chemotherapeutic drug that has been used to treat of numerous tumors, including testicular, lung, bladder, ovarian, liver and head and neck cancers. Although clinical chemotherapy based on cisplatin has shown a remarkable therapeutic effect, the resistance to cisplatin becomes increasingly obvious as a patient uses it for a prolonged period. It not only affects the prognosis of these tumors, but also causes the recurrence of cancer and decreases the overall survival rate. The development of cisplatin resistance involves several mechanisms, including DNA damage repair, ATP-binding cassette (ABC) transporter, autophagy, cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), and other related signaling pathways. Interestingly, these mechanisms have been found to be influenced by circular RNAs (circRNAs) to regulate tumor proliferation, invasion, chemosensitivity, and other biological behaviors in the tumor microenvironment (TME). In recent years, circRNAs in cisplatin resistance in tumors, especially lung cancer and gastric cancer, have gradually drawn peoples' attention. This review summarizes recent studies on the functions and mechanisms of circRNAs in cisplatin resistance. We emphasize that circRNA can be used as a promising target gene to improve drug resistance and therapeutic efficacy.

Circ_0000520 contributes to triple-negative breast cancer progression through mediating the miR-1296/ZFX axis

Background

Triple‐negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with a high incidence of local recurrence and metastasis. Circular RNAs (circRNAs) are implicated in the pathomechanism of TNBC. Here, we investigated the function of circ_0000520 in TNBC and its associated mechanism.

Methods

Reverse transcription quantitative polymerase chain reaction (RT‐qPCR) and Western blot assay were used to measure RNA and protein expression. Cell proliferation was analyzed by cell counting kit‐8 (CCK8) assay, flow cytometry and colony formation assay. Cell apoptosis was assessed by flow cytometry. Cell migration ability was analyzed by transwell migration and wound healing assays. Transwell invasion assay was conducted to analyze the invasion ability. Dual‐luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and RNA‐pulldown assay were performed to verify the interaction between microRNA‐1296 (miR‐1296) and circ_0000520 or zinc finger protein X‐linked (ZFX). Xenograft mice model was established to analyze the role of circ_0000520 in xenograft tumor growth in vivo.

Results

Circ_0000520 expression was upregulated in TNBC tissues and cell lines. Circ_0000520 knockdown suppressed the proliferation, migration, and invasion whereas induced the apoptosis of TNBC cells. miR‐1296 was verified as a target of circ_0000520, and circ_0000520 silencing‐mediated suppressive effects on the malignant potential of TNBC cells were partly overturned by miR‐1296 knockdown. miR‐1296 interacted with the 3′ untranslated region (3′UTR) of ZFX, and ZFX overexpression partly reversed miR‐1296 overexpression‐mediated effects in TNBC cells. Circ_0000520 absence reduced ZFX expression by upregulating miR‐1296 in TNBC cells. Circ_0000520 silencing suppressed xenograft tumor growth in vivo.

Conclusions

Circ_0000520 contributed to TNBC development by binding to miR‐1296 to induce ZFX expression.

Role of Exosomal Non-coding RNAs in Gastric Cancer: Biological Functions and Potential Clinical Applications

Gastric cancer (GC) is one of the most common fatal cancers worldwide. The communication between GC and other cells in the GC microenvironment directly affects GC progression. Recently, exosomes have been revealed as new players in intercellular communication. They play an important role in human health and diseases, including cancer, owing to their ability to carry various bioactive molecules, including non-coding RNAs (ncRNAs). NcRNAs, including micro RNAs, long non-coding RNAs, and circular RNAs, play a significant role in various pathophysiological processes, especially cancer. Increasing evidence has shown that exosomal ncRNAs are involved in the regulation of tumor proliferation, invasion, metastasis, angiogenesis, immune regulation, and treatment resistance in GC. In addition, exosomal ncRNAs have promising potential as diagnostic and prognostic markers for GC. Considering the biocompatibility of exosomes, they can also be used as biological carriers for targeted therapy. This review summarizes the current research progress on exosomal ncRNAs in gastric cancer, focusing on their biological role in GC and their potential as new biomarkers for GC and therapeutics. Our review provides insight into the mechanisms involved in GC progression, which may provide a new point cut for the discovery of new diagnostic markers and therapeutic strategies.

The role and application of small extracellular vesicles in gastric cancer

Gastric cancer (GC) is a common tumour that affects humans worldwide, is highly malignant and has a poor prognosis. Small extracellular vesicles (sEVs), especially exosomes, are nanoscale vesicles released by various cells that deliver bioactive molecules to recipient cells, affecting their biological characteristics, changing the tumour microenvironment and producing long-distance effects. In recent years, many studies have clarified the mechanisms by which sEVs function with regard to the initiation, progression, angiogenesis, metastasis and chemoresistance of GC. These molecules can function as mediators of cell-cell communication in the tumour microenvironment and might affect the efficacy of immunotherapy. Due to their unique physiochemical characteristics, sEVs show potential as effective antitumour vaccines as well as drug carriers. In this review, we summarize the roles of sEVs in GC and highlight the clinical application prospects in the future.