Indirect modulation of sensitivity to 5-fluorouracil by microRNA-96 in human colorectal cancer cells

The Critical Function of microRNAs in Developing Resistance against 5- Fluorouracil in Cancer Cells

Although there have been significant advancements in cancer treatment, resistance and recurrence in patients make it one of the leading causes of death worldwide. 5-fluorouracil (5-FU), an antimetabolite agent, is widely used in treating a broad range of human malignancies. The cytotoxic effects of 5-FU are mediated by the inhibition of thymidylate synthase (TYMS/TS), resulting in the suppression of essential biosynthetic activity, as well as the misincorporation of its metabolites into RNA and DNA. Despite its huge benefits in cancer therapy, the application of 5-FU in the clinic is restricted due to the occurrence of drug resistance. MicroRNAs (miRNAs) are small, non-coding RNAs that act as negative regulators in many gene expression processes. Research has shown that changes in miRNA play a role in cancer progression and drug resistance. This review examines the role of miRNAs in 5-FU drug resistance in cancers.

Double-edged sword role of miRNA-633 and miRNA-181 in human cancers

Understanding the function and mode of operation of microRNAs (miRNAs) in cancer is of growing interest. The short non-coding RNAs known as miRNAs, which target mRNA in multicellular organisms, are described as controlling essential cellular processes. The miR-181 family and miR-633 are well-known miRNAs that play a key role in the development and metastasis of tumor cells. They may facilitate either tumor-suppressive or oncogenic function in malignant cells, according to mounting evidence. Metastatic cells that are closely linked to cancer cell migration, invasion, and angiogenesis can be identified by abnormal levels of miR-181 and miR-633. Numerous studies have demonstrated their capacity to control drug resistance, cell growth, apoptosis, and the epithelial-mesenchymal transition (EMT) and metastasis process. Interestingly, the levels of miR-181 and miR-633 and their potential target genes in the basic cellular process can vary depending on the type of cancer cells and their gene expression profile. Such miRNAs' interactions with other non-coding RNAs such as long non-coding RNAs and circular RNAs can influence tumor behaviors. Herein, we concentrated on the multifaceted roles of miR-181 and miR-633 and potential targets in human tumorigenesis, ranging from cell growth and metastasis to drug resistance.

Role of Nanotechnology in Overcoming the Multidrug Resistance in Cancer Therapy: A Review

Cancer is one of the leading causes of morbidity and mortality around the globe and is likely to become the major cause of global death in the coming years. As per World Health Organization (WHO) report, every year there are over 10 and 9 million new cases and deaths from this disease. Chemotherapy, radiotherapy, and surgery are the three basic approaches to treating cancer. These approaches are aiming at eradicating all cancer cells with minimum off-target effects on other cell types. Most drugs have serious adverse effects due to the lack of target selectivity. On the other hand, resistance to already available drugs has emerged as a major obstacle in cancer chemotherapy, allowing cancer to proliferate irrespective of the chemotherapeutic agent. Consequently, it leads to multidrug resistance (MDR), a growing concern in the scientific community. To overcome this problem, in recent years, nanotechnology-based drug therapies have been explored and have shown great promise in overcoming resistance, with most nano-based drugs being explored at the clinical level. Through this review, we try to explain various mechanisms involved in multidrug resistance in cancer and the role nanotechnology has played in overcoming or reversing this resistance.

Perspectives of using microRNA-loaded nanocarriers for epigenetic reprogramming of drug resistant colorectal cancers

Epigenetic regulation by microRNAs (miRs) demonstrated a promising therapeutic potential of these molecules to regulate genetic activity in different cancers, including colorectal cancers (CRCs). The RNA-based therapy does not change genetic codes in tumor cells but can silence oncogenes and/or reactivate inhibited tumor suppressor genes. In many cancers, specific miRs were shown to promote or stop tumor progression. Among confirmed and powerful epigenetic regulators of colon carcinogenesis and development of resistance are onco-miRs, which include let-7, miR-21, miR-22, miR-23a, miR-27a, miR-34, miR-92, miR-96, miR-125b, miR-135b, miR-182, miR-200c, miR-203, miR-221, miR-421, miR-451, and others. Moreover, various tumor-suppressor miRs (miR-15b-5b, miR-18a, miR-20b, miR-22, miR-96, miR-139-5p, miR-145, miR-149, miR-197, miR-199b, miR-203, miR-214, miR-218, miR-320, miR-375-3p, miR-409-3p, miR-450b-5p, miR-494, miR-577, miR-874, and others) were found silenced in drug-resistant CRCs. Re-expression of tumor suppressor miR is complicated by the chemical nature of miRs that are not long-lasting compounds and require protection from the enzymatic degradation. Several recent studies explored application of miRs using nanocarrier complexes. This study critically describes the most successfully tested nanoparticle complexes used for intracellular delivery of nuclear acids and miRs, including micelles, liposomes, inorganic and polymeric NPs, dendrimers, and aptamers. Nanocarriers shield incorporated miRs and improve the agent stability in circulation. Attachment of antibodies and/or specific peptide or ligands facilitates cell-targeted miR delivery. Addressing in vivo challenges, a broad spectrum of non-toxic materials has been tested and indicated reliable advantages of lipid-based (lipoplexes) and polymer-based liposomes. Recent cutting-edge developments indicated that lipid-based complexes with multiple cargo, including several miRs, are the most effective approach to eradicate drug-resistant tumors. Focusing on CRC-specific miRs, this review provides a guidance and insights towards the most promising direction to achieve dramatic reduction in tumor growth and metastasis using miR-nanocarrier complexes.

In silico Analysis of Single Nucleotide Polymorphisms Associated with MicroRNA Regulating 5-fluorouracil Resistance in Colorectal Cancer

Background:

Due to the broad influence and reversible nature of microRNA (miRNA) on the expression and regulation of target genes, researchers suggest that miRNAs and single nucleotide polymorphisms (SNPs) in miRNA genes interfere with 5-fluorouracil (5-FU) drug resistance in colorectal cancer chemotherapy.

Methods:

Computational assessment and cataloging of miRNA gene polymorphisms that target mRNA transcripts directly or indirectly through regulation of 5-FU chemoresistance in CRC were screened out by applying various universally accessible datasets such as miRNA SNP3.0 software.

Results:

1255 SNPs in 85 miRNAs affecting 5-FU resistance (retrieved from literature) were detected. Computational analysis showed that 167 from 1255 SNPs alter microRNA expression levels leading to inadequate response to 5-FU resistance in CRC. Among these 167 SNPs, 39 were located in the seed region of 25/85 miRNA and were more critical than other SNPs. Has-miR-320a-5p with 4 SNP in seed region was miRNA with the most number of SNPs. On the other hand, it has been identified that proteoglycan in cancer, adherents junction, ECM-receptor interaction, Hippo signaling pathway, TGF-beta signaling cascade, biosynthesis of fatty acid, and fatty acid metabolism were the most important pathways targeted by these 85 predicted miRNAs.

Conclusion:

Our data suggest 39 SNPs in the seed region of 25 miRNAs as catalog in miRNA genes that control the 5-FU resistance in CRC. These data also identify the most important pathways regulated by miRNA.

MicroRNA and Alternative mRNA Splicing Events in Cancer Drug Response/Resistance: Potent Therapeutic Targets

Cancer is a multifaceted disease that involves several molecular mechanisms including changes in gene expression. Two important processes altered in cancer that lead to changes in gene expression include altered microRNA (miRNA) expression and aberrant splicing events. MiRNAs are short non-coding RNAs that play a central role in regulating RNA silencing and gene expression. Alternative splicing increases the diversity of the proteome by producing several different spliced mRNAs from a single gene for translation. MiRNA expression and alternative splicing events are rigorously regulated processes. Dysregulation of miRNA and splicing events promote carcinogenesis and drug resistance in cancers including breast, cervical, prostate, colorectal, ovarian and leukemia. Alternative splicing may change the target mRNA 3'UTR binding site. This alteration can affect the produced protein and may ultimately affect the drug affinity of target proteins, eventually leading to drug resistance. Drug resistance can be caused by intrinsic and extrinsic factors. The interplay between miRNA and alternative splicing is largely due to splicing resulting in altered 3'UTR targeted binding of miRNAs. This can result in the altered targeting of these isoforms and altered drug targets and drug resistance. Furthermore, the increasing prevalence of cancer drug resistance poses a substantial challenge in the management of the disease. Henceforth, molecular alterations have become highly attractive drug targets to reverse the aberrant effects of miRNAs and splicing events that promote malignancy and drug resistance. While the miRNA-mRNA splicing interplay in cancer drug resistance remains largely to be elucidated, this review focuses on miRNA and alternative mRNA splicing (AS) events in breast, cervical, prostate, colorectal and ovarian cancer, as well as leukemia, and the role these events play in drug resistance. MiRNA induced cancer drug resistance; alternative mRNA splicing (AS) in cancer drug resistance; the interplay between AS and miRNA in chemoresistance will be discussed. Despite this great potential, the interplay between aberrant splicing events and miRNA is understudied but holds great potential in deciphering miRNA-mediated drug resistance.

The emerging roles of E3 ubiquitin ligases in ovarian cancer chemoresistance

Epithelial cancer of the ovary exhibits the highest mortality rate of all gynecological malignancies in women today, since the disease is often diagnosed in advanced stages. While the treatment of cancer with specific chemical agents or drugs is the favored treatment regimen, chemotherapy resistance greatly impedes successful ovarian cancer chemotherapy. Thus, chemoresistance becomes one of the most critical clinical issues confronted when treating patients with ovarian cancer. Convincing evidence hints that dysregulation of E3 ubiquitin ligases is a key factor in the development and maintenance of ovarian cancer chemoresistance. This review outlines recent advancement in our understanding of the emerging roles of E3 ubiquitin ligases in ovarian cancer chemoresistance. We also highlight currently available inhibitors targeting E3 ligase activities and discuss their potential for clinical applications in treating chemoresistant ovarian cancer patients.

Tumor Suppressor Protein p53 and Inhibitor of Apoptosis Proteins in Colorectal Cancer-A Promising Signaling Network for Therapeutic Interventions

Simple Summary

Tumor suppressor 53 (p53) is a multifunctional protein that regulates cell cycle, DNA repair, apoptosis and metabolic pathways. In colorectal cancer (CRC), mutations of the gene occur in 60% of patients and are associated with a more aggressive tumor phenotype and resistance to anti-cancer therapy. In addition, inhibitor of apoptosis (IAP) proteins are distinguished biomarkers overexpressed in CRC that impact on a diverse set of signaling pathways associated with the regulation of apoptosis/autophagy, cell migration, cell cycle and DNA damage response. As these mechanisms are further firmly controlled by p53, a transcriptional and post-translational regulation of IAPs by p53 is expected to occur in cancer cells. Here, we aim to review the molecular regulatory mechanisms between IAPs and p53 and discuss the therapeutic potential of targeting their interrelationship by multimodal treatment options.

Abstract

Despite recent advances in the treatment of colorectal cancer (CRC), patient’s individual response and clinical follow-up vary considerably with tumor intrinsic factors to contribute to an enhanced malignancy and therapy resistance. Among these markers, upregulation of members of the inhibitor of apoptosis protein (IAP) family effects on tumorigenesis and radiation- and chemo-resistance by multiple pathways, covering a hampered induction of apoptosis/autophagy, regulation of cell cycle progression and DNA damage response. These mechanisms are tightly controlled by the tumor suppressor p53 and thus transcriptional and post-translational regulation of IAPs by p53 is expected to occur in malignant cells. By this, cellular IAP1/2, X-linked IAP, Survivin, BRUCE and LIVIN expression/activity, as well as their intracellular localization is controlled by p53 in a direct or indirect manner via modulating a multitude of mechanisms. These cover, among others, transcriptional repression and the signal transducer and activator of transcription (STAT)3 pathway. In addition, p53 mutations contribute to deregulated IAP expression and resistance to therapy. This review aims at highlighting the mechanistic and clinical importance of IAP regulation by p53 in CRC and describing potential therapeutic strategies based on this interrelationship.

Flavonoid display ability to target microRNAs in cancer pathogenesis

MicroRNAs (miRNAs) are non-coding, conserved, single-stranded nucleotide sequences involved in physiological and developmental processes. Recent evidence suggests an association between miRNAs' deregulation with initiation, promotion, progression, and drug resistance in cancer cells. Besides, miRNAs are known to regulate the epithelial-mesenchymal transition, angiogenesis, autophagy, and senescence in different cancer types. Previous reports proposed that apart from the antioxidant potential, flavonoids play an essential role in miRNAs modulation associated with changes in cancer-related proteins, tumor suppressor genes, and oncogenes. Thus, flavonoids can suppress proliferation, help in the development of drug sensitivity, suppress metastasis and angiogenesis by modulating miRNAs expression. In the present review, we summarize the role of miRNAs in cancer, drug resistance, and the chemopreventive potential of flavonoids mediated by miRNAs. The potential of flavonoids to modulate miRNAs expression in different cancer types demonstrate their selectivity and importance as regulators of carcinogenesis. Flavonoids as chemopreventive agents targeting miRNAs are extensively studied in vitro, in vivo, and pre-clinical studies, but their efficiency in targeting miRNAs in clinical studies is less investigated. The evidence presented in this review highlights the potential of flavonoids in cancer prevention/treatment by regulating miRNAs, although further investigations are required to validate and establish their clinical usefulness.

MicroRNA, Diabetes Mellitus and Colorectal Cancer

Diabetes mellitus (DM) is an endocrinological disorder that is due to either the pancreas not producing enough insulin, or the body does not respond appropriately to insulin. There are many complications of DM such as retinopathy, nephropathy, and peripheral neuropathy. In addition to these complications, DM was reported to be associated with different cancers. In this review, we discuss the association between DM and colorectal cancer (CRC). CRC is the third most commonly diagnosed cancer worldwide that mostly affects older people, however, its incidence and mortality are rising among young people. We discuss the relationship between DM and CRC based on their common microRNA (miRNA) biomarkers. miRNAs are non-coding RNAs playing important functions in cell differentiation, development, regulation of cell cycle, and apoptosis. miRNAs can inhibit cell proliferation and induce apoptosis in CRC cells. miRNAs also can improve glucose tolerance and insulin sensitivity. Therefore, investigating the common miRNA biomarkers of both DM and CRC can shed a light on how these two diseases are correlated and more understanding of the link between these two diseases can help the prevention of both DM and CRC.

microRNA-96 promotes occurrence and progression of colorectal cancer via regulation of the AMPKα2-FTO-m6A/MYC axis

BACKGROUND

Colorectal cancer (CRC) is one of the frequently occurred malignancies in the world. To date, several onco-microRNAs (miRNAs or miRs), including miR-96, have been identified in the pathogenesis of CRC. In the present study, we aimed to corroborate the oncogenic effect of miR-96 on CRC and to identify the specific mechanisms related to AMPKα2/FTO/m6A/MYC.

METHODS

RT-qPCR and Western blot analysis were performed to examine the expression pattern of miR-96, AMPKα2, FTO and MYC in the clinical CRC tissues and cells. The relationship between miR-96 and AMPKα2 was then predicted using in silico analysis and identified by dual-luciferase reporter assay. Gain- or loss-of-function approaches were manipulated to evaluate the modulatory effects of miR-96, AMPKα2, FTO and MYC on cell growth, cycle progression and apoptosis. The mechanism of FTO-mediated m6A modification of MYC was analyzed via Me-RIP and PAR-CLIP analysis. The mediatory effects of miR-96 antagomir on cancerogenesis were validated in vivo.

RESULTS

miR-96, FTO and MYC were upregulated, while AMPKα2 was downregulated in CRC tissues and cells. miR-96 could down-regulate AMPKα2, which led to increased expression of FTO and subsequent upregulated expression of MYC via blocking its m6A modification. This mechanism was involved in the pro-proliferative and anti-apoptotic roles of miR-96 in CRC cells. Besides, down-regulation of miR-96 exerted inhibitory effect on tumor growth in vivo.

CONCLUSIONS

Taken together, miR-96 antagomir could potentially retard the cancerogenesis in CRC via AMPKα2-dependent inhibition of FTO and blocking FTO-mediated m6A modification of MYC, highlighting novel mechanisms associated with colorectal cancerogenesis.

Molecular determinants of response to 5-fluorouracil-based chemotherapy in colorectal cancer: The undisputable role of micro-ribonucleic acids

5-flurouracil (5-FU)-based chemotherapy is the main pharmacological therapy for advanced colorectal cancer (CRC). Despite significant progress in the treatment of CRC during the last decades, 5-FU drug resistance remains the most important cause of failure in CRC therapy. Resistance to 5-FU is a complex and multistep process. Different mechanisms including microsatellite instability, increased expression level of key enzyme thymidylate synthase and its polymorphism, increased level of 5-FU-activating enzymes and mutation of TP53 are proposed as the main determinants of resistance to 5-FU in CRC cells. Recently, micro-ribonucleic acids (miRNA) and their alterations were found to have a crucial role in 5-FU resistance. In this regard, the miRNA-mediated mechanisms of 5-FU drug resistance reside among the new fields of pharmacogenetics of CRC drug response that has not been completely discovered. Identification of the biological markers that are related to response to 5-FU-based chemotherapy is an emerging field of precision medicine. This approach will have an important role in defining those patients who are most likely to benefit from 5-FU-based chemotherapy in the future. Thereby, the identification of 5-FU drug resistance mechanisms is an essential step to predict and eventually overcome resistance. In the present comprehensive review, we will summarize the latest knowledge regarding the molecular determinants of response to 5-FU-based chemotherapy in CRC by emphasizing the role of miRNAs.

Molecular mechanisms and clinical implications of miRNAs in drug resistance of colorectal cancer

Systemic chemotherapy is identified as a curative approach to prolong the survival time of patients with colorectal cancer (CRC). Although great progress in therapeutic approaches has been achieved during the last decades, drug resistance still extensively persists and serves as a major hurdle to effective anticancer therapy for CRC. The mechanism of multidrug resistance remains unclear. Recently, mounting evidence suggests that a great number of microRNAs (miRNAs) may contribute to drug resistance in CRC. Certain of these miRNAs may thus be used as promising biomarkers for predicting drug response to chemotherapy or serve as potential targets to develop personalized therapy for patients with CRC. This review mainly summarizes recent advances in miRNAs and the molecular mechanisms underlying miRNA-mediated chemoresistance in CRC. We also discuss the potential role of drug resistance-related miRNAs as potential biomarkers (diagnostic and prognostic value) and envisage the future orientation and challenges in translating the findings on miRNA-mediated chemoresistance of CRC into clinical applications.

MicroRNAs and Apoptosis in Colorectal Cancer

Colorectal cancer (CRC) is the third leading cause of cancer death in the world, and its incidence is rising in developing countries. Treatment with 5-Fluorouracil (5-FU) is known to improve survival in CRC patients. Most anti-cancer therapies trigger apoptosis induction to eliminate malignant cells. However, de-regulated apoptotic signaling allows cancer cells to escape this signaling, leading to therapeutic resistance. Treatment resistance is a major challenge in the development of effective therapies. The microRNAs (miRNAs) play important roles in CRC treatment resistance and CRC progression and apoptosis. This review discusses the role of miRNAs in contributing to the promotion or inhibition of apoptosis in CRC and the role of miRNAs in modulating treatment resistance in CRC cells.

Mechanisms of Multidrug Resistance in Cancer Chemotherapy

Cancer is one of the main causes of death worldwide. Despite the significant development of methods of cancer healing during the past decades, chemotherapy still remains the main method for cancer treatment. Depending on the mechanism of action, commonly used chemotherapeutic agents can be divided into several classes (antimetabolites, alkylating agents, mitotic spindle inhibitors, topoisomerase inhibitors, and others). Multidrug resistance (MDR) is responsible for over 90% of deaths in cancer patients receiving traditional chemotherapeutics or novel targeted drugs. The mechanisms of MDR include elevated metabolism of xenobiotics, enhanced efflux of drugs, growth factors, increased DNA repair capacity, and genetic factors (gene mutations, amplifications, and epigenetic alterations). Rapidly increasing numbers of biomedical studies are focused on designing chemotherapeutics that are able to evade or reverse MDR. The aim of this review is not only to demonstrate the latest data on the mechanisms of cellular resistance to anticancer agents currently used in clinical treatment but also to present the mechanisms of action of novel potential antitumor drugs which have been designed to overcome these resistance mechanisms. Better understanding of the mechanisms of MDR and targets of novel chemotherapy agents should provide guidance for future research concerning new effective strategies in cancer treatment.

Identification of Differently Expressed Genes Associated With Prognosis and Growth in Colon Adenocarcinoma Based on Integrated Bioinformatics Analysis

Latest statistics showed that the morbidity and mortality of colon adenocarcinoma (COAD) ranked fourth and fifth, respectively, around the world. COAD was a heterogeneous disease, and the high rates of recurrence, metastasis, and drug resistance still posed great challenges for treatment, which needs to further develop therapeutic and prognostic targets. In this study, we got the top 3,075 differentially expressed genes (DEGs) and 1,613 potential prognostic genes by GEPIA 2 and identified 1,166 fitness genes in COAD based on genome-scale CRISPR-Cas9 knockout (GeCKO) screening data. Excluding the genes already reported in the literatures, a total of nine DEGs overlapping with prognostic and fitness genes were further analyzed. High expression of CCT6A, RHOQ, and RRP12 promoted COAD cell growth and were relative to lower survival rate of COAD patients, while high expression of UTP18, DDOST, YRDC, ACTG1, RFT1, and NLE1 also promoted COAD cell growth, but were relative to higher survival rate. In addition, CCT6A, UTP18, YRDC, RRP12, RFT1, NLE1, as well as DDOST were essential genes across pan-cancer including COAD cells, and ACTG1 and RHOQ were less essential genes in cancer cells. In a word, we discovered nine novel potential genes that could serve as anticancer targets and prognostic markers in COAD and its subtypes.

DNA methylation and chromatin modifiers in colorectal cancer

Colorectal carcinogenesis is a multistep process involving the accumulation of genetic alterations over time that ultimately leads to disease progression and metastasis. Binding of transcription factors to gene promoter regions alone cannot explain the complex regulation pattern of gene expression during this process. It is the chromatin structure that allows for a high grade of regulatory flexibility for gene expression. Posttranslational modifications on histone proteins such as acetylation, methylation, or phosphorylation determine the accessibility of transcription factors to DNA. DNA methylation, a chemical modification of DNA that modulates chromatin structure and gene transcription acts in concert with these chromatin conformation alterations. Another epigenetic mechanism regulating gene expression is represented by small non-coding RNAs. Only very recently epigenetic alterations have been included in molecular subtype classification of colorectal cancer (CRC). In this chapter, we will provide examples of the different epigenetic players, focus on their role for epithelial-mesenchymal transition and metastatic processes and discuss their prognostic value in CRC.

The role and mechanisms of action of microRNAs in cancer drug resistance

MicroRNAs (miRNAs) are small non-coding RNAs with a length of about 19–25 nt, which can regulate various target genes and are thus involved in the regulation of a variety of biological and pathological processes, including the formation and development of cancer. Drug resistance in cancer chemotherapy is one of the main obstacles to curing this malignant disease. Statistical data indicate that over 90% of the mortality of patients with cancer is related to drug resistance. Drug resistance of cancer chemotherapy can be caused by many mechanisms, such as decreased antitumor drug uptake, modified drug targets, altered cell cycle checkpoints, or increased DNA damage repair, among others. In recent years, many studies have shown that miRNAs are involved in the drug resistance of tumor cells by targeting drug-resistance-related genes or influencing genes related to cell proliferation, cell cycle, and apoptosis. A single miRNA often targets a number of genes, and its regulatory effect is tissue-specific. In this review, we emphasize the miRNAs that are involved in the regulation of drug resistance among different cancers and probe the mechanisms of the deregulated expression of miRNAs. The molecular targets of miRNAs and their underlying signaling pathways are also explored comprehensively. A holistic understanding of the functions of miRNAs in drug resistance will help us develop better strategies to regulate them efficiently and will finally pave the way toward better translation of miRNAs into clinics, developing them into a promising approach in cancer therapy.

Epigenetic Regulation by lncRNAs: An Overview Focused on UCA1 in Colorectal Cancer

Colorectal cancers have become the second leading cause of cancer-related deaths. In particular, acquired chemoresistance and metastatic lesions occurring in colorectal cancer are a major challenge for chemotherapy treatment. Accumulating evidence shows that long non-coding (lncRNAs) are involved in the initiation, progression, and metastasis of cancer. We here discuss the epigenetic mechanisms through which lncRNAs regulate gene expression in cancer cells. In the second part of this review, we focus on the role of lncRNA Urothelial Cancer Associated 1 (UCA1) to integrate research in different types of cancer in order to decipher its putative function and mechanism of regulation in colorectal cancer cells. UCA1 is highly expressed in cancer cells and mediates transcriptional regulation on an epigenetic level through the interaction with chromatin modifiers, by direct regulation via chromatin looping and/or by sponging the action of a diversity of miRNAs. Furthermore, we discuss the role of UCA1 in the regulation of cell cycle progression and its relation to chemoresistance in colorectal cancer cells.

The Dual Role of MicroRNAs in Colorectal Cancer Progression

Colorectal cancer (CRC) is responsible for one of the major cancer incidence and mortality worldwide. It is well known that MicroRNAs (miRNAs) play vital roles in maintaining the cell development and other physiological processes, as well as, the aberrant expression of numerous miRNAs involved in CRC progression. MiRNAs are a class of small, endogenous, non-coding, single-stranded RNAs that bind to the 3’-untranslated region (3′-UTR) complementary sequences of their target mRNA, resulting in mRNA degradation or inhibition of its translation as a post-transcriptional regulators. Moreover, miRNAs also can target the long non-coding RNA (lncRNA) to regulate the expression of its target genes involved in proliferation and metastasis of CRC. The functions of these dysregulated miRNAs appear to be context specific, with evidence of having a dual role in both oncogenes and tumor suppression depending on the cellular environment in which they are expressed. Therefore, the unique expression profiles of miRNAs relate to the diagnosis, prognosis, and therapeutic outcome in CRC. In this review, we focused on several oncogenic and tumor-suppressive miRNAs specific to CRC, and assess their functions to uncover the molecular mechanisms of tumor initiation and progression in CRC. These data promised that miRNAs can be used as early detection biomarkers and potential therapeutic target in CRC patients.

The role of microRNAs in 5-FU resistance of colorectal cancer: Possible mechanisms

Colorectal cancer (CRC) is one of the most common cancers globally. Despite recent advances in therapeutic approaches, this cancer continues to have a poor prognosis, particularly when diagnosed late. 5-Fluorouracil (5-FU) has been commonly prescribed for patients with CRC, but resistance to 5-FU is one of the main reasons for failure in the treatment of this condition. Recently, microRNAs (miRNAs) have been established as a means of modifying the signaling pathways involved in initiation and progression of CRC and their role as oncogene or tumor suppressor have been investigated in various studies. Moreover, miRNAs through various mechanisms play an important role in inducing tumor resistance or sensitivity to anticancer drugs. Detecting and targeting these mechanisms may be a new therapeutic approach. This review summarizes the current knowledge about the potential roles of miRNAs in 5-FU resistance, with particular emphasis on molecular mechanism involved.

The Network of Non-coding RNAs in Cancer Drug Resistance

Non-coding RNAs (ncRNAs) have been implicated in most cellular functions. The disruption of their function through somatic mutations, genomic imprinting, transcriptional and post-transcriptional regulation, plays an ever-increasing role in cancer development. ncRNAs, including notorious microRNAs, have been thus proposed to function as tumor suppressors or oncogenes, often in a context-dependent fashion. In parallel, ncRNAs with altered expression in cancer have been reported to exert a key role in determining drug sensitivity or restoring drug responsiveness in resistant cells. Acquisition of resistance to anti-cancer drugs is a major hindrance to effective chemotherapy and is one of the most important causes of relapse and mortality in cancer patients. For these reasons, non-coding RNAs have become recent focuses as prognostic agents and modifiers of chemo-sensitivity. This review starts with a brief outline of the role of most studied non-coding RNAs in cancer and then highlights the modulation of cancer drug resistance via known ncRNAs based mechanisms. We identified from literature 388 ncRNA-drugs interactions and analyzed them using an unsupervised approach. Essentially, we performed a network analysis of the non-coding RNAs with direct relations with cancer drugs. Within such a machine-learning framework we detected the most representative ncRNAs-drug associations and groups. We finally discussed the higher integration of the drug-ncRNA clusters with the goal of disentangling effectors from downstream effects and further clarify the involvement of ncRNAs in the cellular mechanisms underlying resistance to cancer treatments.

Non-Coding RNAs and Resistance to Anticancer Drugs in Gastrointestinal Tumors

Non-coding RNAs are important regulators of gene expression and transcription. It is well established that impaired non-coding RNA expression especially the one of long non-coding RNAs and microRNAs is involved in a number of pathological conditions including cancer. Non-coding RNAs are responsible for the development of resistance to anticancer treatments as they regulate drug resistance-related genes, affect intracellular drug concentrations, induce alternative signaling pathways, alter drug efficiency via blocking cell cycle regulation, and DNA damage response. Furthermore, they can prevent therapeutic-induced cell death and promote epithelial-mesenchymal transition (EMT) and elicit non-cell autonomous mechanisms of resistance. In this review, we summarize the role of non-coding RNAs for different mechanisms resulting in drug resistance (e.g., drug transport, drug metabolism, cell cycle regulation, regulation of apoptotic pathways, cancer stem cells, and EMT) in the context of gastrointestinal cancers.

Role of microRNAs in the resistance of colorectal cancer to chemoradiotherapy

Colorectal cancer (CRC) is among the main tumor-related causes of death worldwide. The fact that the majority of the patients develop resistance to chemoradiotherapy (CRT) is a major obstacle for the treatment of CRC. In order to develop more effective treatment strategies, it is crucial to elucidate the mechanisms underlying the development of resistance to CRT. Several studies have recently indicated the regulatory effects of microRNAs (miRNAs) in response to antitumor agents. For example, miR-34a attenuates the chemoresistance of colon cancer to 5-FU by inhibiting E2F3 and SIRT1. The miR-34a mimic MRX34 is the first synthetic miRNA to have been entered into clinical trials. miR-21 prevents tumor cell stemness, invasion and drug resistance, which are required for the development of CRC. These findings suggest that miRNAs represent a focus in the research of novel cancer treatments aimed at sensitizing cancer cells to chemotherapeutic drugs. The aim of the present study was to review the functions of miRNAs and investigate the roles of miRNAs in CRC radioresistance or chemoresistance. Furthermore, the potential of including miRNAs in therapeutic strategies and using them as molecular biomarkers for predicting radiosensitivity and chemosensitivity was discussed.

Microfluidic co-culture of pancreatic tumor spheroids with stellate cells as a novel 3D model for investigation of stroma-mediated cell motility and drug resistance

BACKGROUND

Pancreatic stellate cells (PSCs), a major component of the tumor microenvironment in pancreatic cancer, play roles in cancer progression as well as drug resistance. Culturing various cells in microfluidic (microchannel) devices has proven to be a useful in studying cellular interactions and drug sensitivity. Here we present a microchannel plate-based co-culture model that integrates tumor spheroids with PSCs in a three-dimensional (3D) collagen matrix to mimic the tumor microenvironment in vivo by recapitulating epithelial-mesenchymal transition and chemoresistance.

METHODS

A 7-channel microchannel plate was prepared using poly-dimethylsiloxane (PDMS) via soft lithography. PANC-1, a human pancreatic cancer cell line, and PSCs, each within a designated channel of the microchannel plate, were cultured embedded in type I collagen. Expression of EMT-related markers and factors was analyzed using immunofluorescent staining or Proteome analysis. Changes in viability following exposure to gemcitabine and paclitaxel were measured using Live/Dead assay.

RESULTS

PANC-1 cells formed 3D tumor spheroids within 5 days and the number of spheroids increased when co-cultured with PSCs. Culture conditions were optimized for PANC-1 cells and PSCs, and their appropriate interaction was confirmed by reciprocal activation shown as increased cell motility. PSCs under co-culture showed an increased expression of α-SMA. Expression of EMT-related markers, such as vimentin and TGF-β, was higher in co-cultured PANC-1 spheroids compared to that in mono-cultured spheroids; as was the expression of many other EMT-related factors including TIMP1 and IL-8. Following gemcitabine exposure, no significant changes in survival were observed. When paclitaxel was combined with gemcitabine, a growth inhibitory advantage was prominent in tumor spheroids, which was accompanied by significant cytotoxicity in PSCs.

CONCLUSIONS

We demonstrated that cancer cells grown as tumor spheroids in a 3D collagen matrix and PSCs co-cultured in sub-millimeter proximity participate in mutual interactions that induce EMT and drug resistance in a microchannel plate. Microfluidic co-culture of pancreatic tumor spheroids with PSCs may serve as a useful model for studying EMT and drug resistance in a clinically relevant manner.

Insights into the involvement of noncoding RNAs in 5-fluorouracil drug resistance

5-Fluorouracil is a classic chemotherapeutic drug that is widely used to treat various cancers. However, patients often exhibit primary or acquired drug resistance during treatment with 5-fluorouracil chemotherapy. 5-Fluorouracil resistance is a multifactorial event that involves abnormal enzyme metabolism, transport deregulation, cell cycle disorders, apoptosis resistance, and mismatch repair deficiency. Despite advancements in bioresearch technologies in the past several decades, the molecular mechanisms of 5-fluorouracil resistance have not been completely clarified. Recently, microarray analyses have shown that noncoding RNAs (i.e. microRNAs and long noncoding RNAs) play a vital role in 5-fluorouracil resistance in multiple cancer cell lines. These noncoding RNAs can function as oncogenes or tumor suppressors, contributing to 5-fluorouracil drug resistance. In this review, we discuss the effects of microRNAs on 5-fluorouracil sensitivity via targeting of metabolic enzymes, the cell cycle, apoptosis, autophagy, the epithelial–mesenchymal transition, and cancer stem cells. In particular, we focus on summarizing current knowledge on the molecular mechanisms through which long noncoding RNAs mediate 5-fluorouracil drug resistance. Moreover, we describe the specific microRNAs that may function as markers for prediction of chemotherapeutic response to 5-fluorouracil. This review will help to improve the current understanding of how to reverse 5-fluorouracil resistance and may facilitate the establishment of new strategies for alleviating drug resistance in the future.

Influence of microRNAs and Long Non-Coding RNAs in Cancer Chemoresistance

Innate and acquired chemoresistance exhibited by most tumours exposed to conventional chemotherapeutic agents account for the majority of relapse cases in cancer patients. Such chemoresistance phenotypes are of a multi-factorial nature from multiple key molecular players. The discovery of the RNA interference pathway in 1998 and the widespread gene regulatory influences exerted by microRNAs (miRNAs) and other non-coding RNAs have certainly expanded the level of intricacy present for the development of any single physiological phenotype, including cancer chemoresistance. This review article focuses on the latest research efforts in identifying and validating specific key molecular players from the two main families of non-coding RNAs, namely miRNAs and long non-coding RNAs (lncRNAs), having direct or indirect influences in the development of cancer drug resistance properties and how such knowledge can be utilised for novel theranostics in oncology.

Gambogic acid potentiates the chemosensitivity of colorectal cancer cells to 5-fluorouracil by inhibiting proliferation and inducing apoptosis

Chemotherapy using 5-fluorouracil (5-FU) for colorectal cancer (CRC) has low specificity and response rates, leading to severe side effects. Gambogic acid (GA), a traditional Chinese medicine, has multi-targeted anticancer effects, including growth inhibition and apoptosis induction. However, it is unclear whether a combination of 5-FU and GA has synergistic anticancer effects in CRC cells. In this study, SW480 and HCT116 human CRC cells and human intestinal epithelial cells (IECs) were treated with different concentrations of 5-FU, GA or 5-FU+GA. A Cell Counting kit-8 assay was conducted to quantify cell proliferation. The combination index (CI) was calculated and the median-effect principle was applied to analyze the interaction between 5-FU and GA. Flow cytometry was used to determine the percentage of cells undergoing apoptosis. Reverse transcription-quantitative polymerase chain reaction and western blotting were applied to measure P53, survivin and thymidylate synthase (TS) mRNA and protein levels. It was found that 5-FU+GA more pronouncedly inhibited cell growth and induced apoptosis, compared with either monotherapy. CI values <1 indicated the synergistic effects of the drugs. 5-FU+GA further decreased P53, survivin and TS mRNA and protein levels in the two CRC cell lines compared with single drugs, whereas increased P53 protein levels were observed in HCT116 cells. Moreover, 5-FU+GA did not increase cytotoxicity to IECs. These results demonstrate that GA enhances the anticancer effects of 5-FU on CRC cells. Combined treatment with 5-FU and GA is effective and safe for CRC cells, and may become a promising chemotherapy treatment.

Mini-pillar array for hydrogel-supported 3D culture and high-content histologic analysis of human tumor spheroids

Three-dimensional (3D) cancer cell culture models mimic the complex 3D organization and microenvironment of human solid tumor tissue and are thus considered as highly predictive models representing avascular tumor regions. Confocal laser scanning microscopy is useful for monitoring drug penetration and therapeutic responses in 3D tumor models; however, photonic attenuation at increasing imaging depths and limited penetration of common fluorescence tracers are significant technical challenges to imaging. Immunohistological staining would be a good alternative, but the preparation of tissue sections from rather fragile spheroids through fixing and embedding procedures is challenging. Here we introduce a novel 3 × 3 mini-pillar array chip that can be utilized for 3D cell culturing and sectioning for high-content histologic analysis. The mini-pillar array chip facilitated the generation of 3D spheroids of human cancer cells within hydrogels such as alginate, collagen, and Matrigel. As expected, visualization of the 3D distribution of calcein AM and doxorubicin by optical sectioning was limited by photonic attenuation and dye penetration. The integrity of the 3D microtissue section was confirmed by immunostaining on paraffin sections and cryo-sections. The applicability of the mini-pillar array for drug activity evaluation was tested by measuring viability changes in spheroids exposed to anti-cancer agents, 5-fluorouracil and tirapazamine. Thus, our novel mini-pillar array platform can potentially promote high-content histologic analysis of 3D cultures and can be further optimized for field-specific needs.

MicroRNA-874 inhibits growth, induces apoptosis and reverses chemoresistance in colorectal cancer by targeting X-linked inhibitor of apoptosis protein

MicroRNA-874 (miR-874) is downregulated and acts as a tumor suppressor in several types of cancers, whereas the biological function of miR-874 in colorectal cancer (CRC) remains unclear. The aims of the present study were to investigate the clinical significance, biological effects, and the underlying mechanisms of miR-874 in CRC. Reverse transcription-quantitative PCR (RT-qPCR) was used to detect miR-874 expression in CRC cell lines and tissue samples. MTT and colony formation assays and flow cytometry were performed to analyze the effects of miR-874 expression on growth, apoptosis and the chemoresistance of CRC cells. Regulation of putative miR-874 targets was determined by dual-luciferase reporter assays. RT-qPCR and western blot assays were performed to detected the levels of X-linked inhibitor of apoptosis protein (XIAP) mRNA and protein expression. It was found that expression of miR-874 was downregulated in CRC tissues and cell lines, and its expression was significantly negatively correlated with TNM stage and lymph node metastasis of the CRC patients. Functional assays revealed that restoration of miR-874 inhibited proliferation, reduced colony formation, enhanced apoptosis, as well as decreased the 5-fluorouracil (5-FU) resistance of the CRC cells. Through luciferase activity assay, RT-qPCR and western blot analysis, XIAP was shown to be a direct target of miR-874. In addition, XIAP expression was significantly increased in the CRC tissues and cell lines, and was inversely correlated with miR-874 expression. Importantly, downregulation of XIAP in CRC cells had an effect similar to that of miR-874 overexpression. Taken together, these data showed that miR-874 inhibits growth, increases apoptosis and enhances chemosensitivity in CRC cells by targeting XIAP, suggesting that miR-874 may be a potential molecular target for the treatment of human CRC.

CCL21 Facilitates Chemoresistance and Cancer Stem Cell-Like Properties of Colorectal Cancer Cells through AKT/GSK-3β/Snail Signals

Some evidence indicated that chemoresistance associates with the acquisition of cancer stem-like properties. Recent studies suggested that chemokines can promote the chemoresistance and stem cell properties in various cancer cells, while the underling mechanism is still not completely illustrated. In our study, we found that CCL21 can upregulate the expression of P-glycoprotein (P-gp) and stem cell property markers such as Bmi-1, Nanog, and OCT-4 in colorectal cancer (CRC) HCT116 cells and then improve the cell survival rate and mammosphere formation. Our results suggested that Snail was crucial for CCL21-mediated chemoresistance and cancer stem cell property in CRC cells. Further, we observed that CCL21 treatment increased the protein but not mRNA levels of Snail, which suggested that CCL21 upregulates Snail via posttranscriptional ways. The downstream signals AKT/GSK-3β mediated CCL21 induced the upregulation of Snail due to the fact that CCL21 treatment can obviously phosphorylate both AKT and GSK-3β. The inhibitor of PI3K/Akt, LY294002 significantly abolished CCL21 induced chemoresistance and mammosphere formation of HCT116 cells. Collectively, our results in the present study revealed that CCL21 can facilitate chemoresistance and stem cell property of CRC cells via the upregulation of P-gp, Bmi-1, Nanog, and OCT-4 through AKT/GSK-3β/Snail signals, which suggested a potential therapeutic approach to CRC patients.

MicroRNAs predict and modulate responses to chemotherapy in colorectal cancer

Colorectal cancer (CRC) is the fourth leading cause of cancer-related death globally. Chemotherapy regimens consisting of 5-fluorouracil (5-FU) in combination with either oxaliplatin or irinotecan are the first-line options for treatment of metastatic CRC. However, primary or acquired resistance to these chemotherapeutics is a major clinical challenge. MicroRNAs (miRNAs) are a group of small non-coding RNAs that regulate gene expression post-transcriptionally. miRNAs play important roles in many cancer-related processes, including cell proliferation, apoptosis and invasion, and their dysregulation is implicated in colorectal tumourigenesis. Pertinent to chemotherapy, increasing evidence has revealed that miRNAs can be directly linked to chemosensitivity in CRC. In this review, we summarize current evidence concerning the role of miRNAs in prediction and modulation of cellular responses to 5-FU, oxaliplatin and irinotecan in CRC. We also discuss the possible targets and intracellular pathways involved in these processes.