Exploiting a novel miR-519c-HuR-ABCG2 regulatory pathway to overcome chemoresistance in colorectal cancer. Exp Cell Res. 2015;338:222-231. [PMID: 26386386 DOI: 10.1016/j.yexcr.2015.09.011]

Fluorescence-Guided Spatial Drug Screening in 3D Colorectal Cancer Spheroids

The limited recapitulation of critical cancer features in 2D cultures causes poor translatability of preclinical results from in vitro assays to in vivo tumor models. This contributes to slow drug development with a low success rate. 3D cultures better recapitulate the tumor microenvironment, enabling more accurate predictions when screening drug candidates and improving the development of chemotherapeutics. Platinum (Pt) (IV) compounds are promising prodrugs designed to reduce the severe systemic toxicity of widely used Food and Drug Administration (FDA)-approved Pt(II) drugs such as cisplatin. Here, this work presents spatiotemporal evaluations in 3D colorectal cancer (CRC) spheroids of mitochondria-targeting Pt(IV) complexes. CRC spheroids provide a greater pathophysiological recapitulation of in vivo tumors than 2D cultures by a marked upregulation of the ABCG2 chemoresistance marker expression. Furthermore, new 3D-staining protocols are introduced to evaluate the real-time decrease in mitochondria membrane potential (ΔΨ) in CRC spheroids, and a Pt-sensing dye to quantify the Pt mitochondrial accumulation. Finally, this work demonstrates a correlation between in vitro results and the efficacy of the compounds in vivo. Overall, the CRC spheroids represent a fast and cost-effective model to assess the behavior of Pt compounds in vitro and predict their translational potential in CRC treatment.

Aptamer-functionalized nanomaterials (AFNs) for therapeutic management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents one of the deadliest cancers globally, making the search for more effective diagnostic and therapeutic approaches particularly crucial. Aptamer-functionalized nanomaterials (AFNs), an innovative nanotechnology, have paved new pathways for the targeted diagnosis and treatment of HCC. Initially, we outline the epidemiological background of HCC and the current therapeutic challenges. Subsequently, we explore in detail how AFNs enhance diagnostic and therapeutic efficiency and reduce side effects through the specific targeting of HCC cells and the optimization of drug delivery. Furthermore, we address the challenges faced by AFNs in clinical applications and future research directions, with a particular focus on enhancing their biocompatibility and assessing long-term effects. In summary, AFNs represent an avant-garde therapeutic approach, opening new avenues and possibilities for the diagnosis and treatment of HCC.

Utilizing non-coding RNA-mediated regulation of ATP binding cassette (ABC) transporters to overcome multidrug resistance to cancer chemotherapy

Multidrug resistance (MDR) is one of the primary factors that produces treatment failure in patients receiving cancer chemotherapy. MDR is a complex multifactorial phenomenon, characterized by a decrease or abrogation of the efficacy of a wide spectrum of anticancer drugs that are structurally and mechanistically distinct. The overexpression of the ATP-binding cassette (ABC) transporters, notably ABCG2 and ABCB1, are one of the primary mediators of MDR in cancer cells, which promotes the efflux of certain chemotherapeutic drugs from cancer cells, thereby decreasing or abolishing their therapeutic efficacy. A number of studies have suggested that non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), play a pivotal role in mediating the upregulation of ABC transporters in certain MDR cancer cells. This review will provide updated information about the induction of ABC transporters due to the aberrant regulation of ncRNAs in cancer cells. We will also discuss the measurement and biological profile of circulating ncRNAs in various body fluids as potential biomarkers for predicting the response of cancer patients to chemotherapy. Sequence variations, such as alternative polyadenylation of mRNA and single nucleotide polymorphism (SNPs) at miRNA target sites, which may indicate the interaction of miRNA-mediated gene regulation with genetic variations to modulate the MDR phenotype, will be reviewed. Finally, we will highlight novel strategies that could be used to modulate ncRNAs and circumvent ABC transporter-mediated MDR.

RNA binding proteins in cancer chemotherapeutic drug resistance

Drug resistance has been a major obstacle in the quest for a cancer cure. Many chemotherapeutic treatments fail to overcome chemoresistance, resulting in tumor remission. The exact process that leads to drug resistance in many cancers has not been fully explored or understood. However, the discovery of RNA binding proteins (RBPs) has provided insight into various pathways and post-transcriptional gene modifications involved in drug tolerance. RBPs are evolutionarily conserved proteins, and their abnormal gene expression has been associated with cancer progression. Additionally, RBPs are aberrantly expressed in numerous neoplasms. RBPs have also been implicated in maintaining cancer stemness, epithelial-to-mesenchymal transition, and other processes. In this review, we aim to provide an overview of RBP-mediated mechanisms of drug resistance and their implications in cancer malignancy. We discuss in detail the role of major RBPs and their correlation with noncoding RNAs (ncRNAs) that are associated with the inhibition of chemosensitivity. Understanding and exploring the pathways of RBP-mediated chemoresistance will contribute to the development of improved cancer diagnosis and treatment strategies.

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.

Epigenetic modulations in cancer: predictive biomarkers and potential targets for overcoming the resistance to topoisomerase I inhibitors

INTRODUCTION

Altered epigenetic map is frequently observed in cancer and recent investigations have demonstrated a pertinent role of epigenetic modifications in the response to many anticancer drugs including the DNA damaging agents. Topoisomerase I (Top I) is a well-known nuclear enzyme that is critical for DNA function and cell survival and its inhibition causes DNA strand breaks and cell cycle arrest. Inhibitors of human Top I have proven to be a prosperous chemotherapeutic treatment for a vast number of cancer patients. While the treatment is efficacious in many cases, resistance and altered cellular response remain major therapeutic issues.

AREAS COVERED

This review highlights the evidence available till date on the influence of different epigenetic modifications on the response to Top I inhibitors as well as the implications of targeting epigenetic alterations for improving the efficacy and safety of Top I inhibitors.

EXPERT OPINION

The field of epigenetic research is steadily growing. With its assistance, we could gain better understanding on how drug response and resistance work. Epigenetics can evolve as possible biomarkers and predictors of response to many medications including Top I inhibitors, and could have significant clinical implications that necessitate deeper attention.HIGHLIGHTSEpigenetic alterations, including DNA methylation and histone modifications, play a pertinent role in the response to several anticancer treatments, including DNA damaging agents like Top I inhibitors.Although camptothecin derivatives are used clinically as Top I inhibitors for management of cancer, certain types of cancer have inherent and or acquired resistance that limit the curative potential of them.Epigenetic modifications like DNA hypomethylation can either increase or decrease sensitivity to Top I inhibitors by different mechanisms.The combination of Top I inhibitors with the inhibitors of histone modifying enzymes can result in enhanced cytotoxic effects and sensitization of resistant cells to Top I inhibitors.MicroRNAs were found to directly influence the expression of Top I and other proteins in cancer cells resulting in positive or negative alteration of the response to Top I inhibitors.lncRNAs and their genetic polymorphisms have been found to be associated with Top I function and the response to its inhibitors.Clinical trials of epigenetic drugs in combination with Top I inhibitors are plentiful and some of them showed potentially promising outcomes.

Recent advances microRNAs and metabolic reprogramming in colorectal cancer research

Colorectal cancer (CRC) is a cancer with the highest incidence and mortality. Alteration of gene expression is the main pathophysiological mechanism of CRC, which results in disturbed signaling pathways and cellular metabolic processes. MicroRNAs are involved in almost all pathophysiological processes and are correlative with colorectal cancer metabolism, proliferation, and chemotherapy resistance. Metabolic reprogramming, an important feature of cancer, is strongly correlative with the development and prognosis of cancers, including colorectal cancer. MicroRNAs can target enzymes involved in metabolic processes, thus playing a regulatory role in tumor metabolism. The disorder of the signaling pathway is another characteristic of tumor, which induces the occurrence and proliferation of tumors, and is closely correlative with the prognosis and chemotherapy resistance of tumor patients. MicroRNAs can target the components of the signaling pathways to regulate their transduction. Understanding the function of microRNAs in the occurrence and proliferation of CRC provides novel insights into the optimal treatment strategies, prognosis, and development of diagnosis in CRC. This article reviews the relationship between CRC and microRNA expression and hopes to provide new options for the diagnosis and treatment of CRC.

Resistance to TOP-1 Inhibitors: Good Old Drugs Still Can Surprise Us

Irinotecan (SN-38) is a potent and broad-spectrum anticancer drug that targets DNA topoisomerase I (Top1). It exerts its cytotoxic effects by binding to the Top1-DNA complex and preventing the re-ligation of the DNA strand, leading to the formation of lethal DNA breaks. Following the initial response to irinotecan, secondary resistance is acquired relatively rapidly, compromising its efficacy. There are several mechanisms contributing to the resistance, which affect the irinotecan metabolism or the target protein. In addition, we have demonstrated a major resistance mechanism associated with the elimination of hundreds of thousands of Top1 binding sites on DNA that can arise from the repair of prior Top1-dependent DNA cleavages. Here, we outline the major mechanisms of irinotecan resistance and highlight recent advancements in the field. We discuss the impact of resistance mechanisms on clinical outcomes and the potential strategies to overcome resistance to irinotecan. The elucidation of the underlying mechanisms of irinotecan resistance can provide valuable insights for the development of effective therapeutic strategies.

Relationship between HuR and tumor drug resistance

Human resistance protein R (HuR), also known as embryonic lethal abnormal visual-like protein (ELAVL1), is an RNA-binding protein widely expressed in vivo that affects the mRNA stability of targeted and is involved in post-transcriptional regulation. Recent studies have shown that HuR is aberrantly expressed in different human cancers and is an essential factor in poor clinical prognosis. The role of HuR in numerous tumors suggests that it could be a new target for tumor therapy and as a marker for efficacy and prognostic assessment. This review focuses on the relationship between HuR and drug resistance in different tumors and briefly describes the structure, function, and inhibitors of HuR. We summarize the mechanisms by which HuR causes tumor resistance and the molecular targets affected.

Inhibiting lncRNA NEAT1 facilitates the sensitization of melanoma cells to cisplatin through modulating the miR-519c-3p-MeCP2 axis

Cutaneous melanoma is an aggressive human malignancy, leading to high mortality worldwide. In addition to surgery, radiotherapy and chemotherapy are routine approaches to treat melanoma at late or metastatic stage. However, a group of melanoma patients developed chemoresistance, which ultimately limited the efficiency of chemotherapy. LncRNA NEAT1 (Nuclear-enriched abundant transcript 1) is frequently overexpressed in various cancers. Currently, the precise roles and underlying mechanisms of NEAT1 in chemoresistant melanoma remain unclear. This study reports NEAT1 was significantly upregulated in melanoma tumor specimens and cell lines. Blocking NEAT1 effectively sensitized melanoma cells to cisplatin (CDDP), a frequently used first-line anticancer agent. From the established cisplatin resistant melanoma cell line (SK-MEL-5 CDDP Res), we detected significantly upregulated NEAT1 expression and downregulated miR-519c-3p expression compared with those from SK-MEL-5 parental cells. Subsequently, expression of miR-519c-3p was remarkedly attenuated in melanoma tumors and cell lines. Bioinformatics analysis, RNA pull-down assay and luciferase assay consistently demonstrated that NEAT1 sponged miR-519c-3p to downregulate its expression in melanoma cells. Moreover, we identified the methyl CpG binding protein 2 (MeCP2), which is positively associated with cisplatin resistance in melanoma, was a direct target of miR-519c-3p in melanoma cells. Restoration of MeCP2 rescued the miR-519c-3p-promoted cisplatin sensitization. Finally, we showed restoration of miR-519c-3p in NEAT1-overexpressing SK-MEL-5 CDDP Res cells successfully overrode the NEAT1-promoted cisplatin resistance in melanoma from in vitro and in vivo results. In summary, our results unveiled biological roles and molecular mechanisms of the noncoding RNA-mediated cisplatin resistance in melanoma, suggesting blocking the NEAT1-miR-519c-3p-MeCP2 axis as a therapeutic strategy against chemoresistant melanoma.

Recent Advances in Novel Recombinant RNAs for Studying Post-transcriptional Gene Regulation in Drug Metabolism and Disposition

Drug-metabolizing enzymes and transporters are major determinants of the absorption, disposition, metabolism, and excretion (ADME) of drugs, and changes in ADME gene expression or function may alter the pharmacokinetics/ pharmacodynamics (PK/PD) and further influence drug safety and therapeutic outcomes. ADME gene functions are controlled by diverse factors, such as genetic polymorphism, transcriptional regulation, and coadministered medications. MicroRNAs (miRNAs) are a superfamily of regulatory small noncoding RNAs that are transcribed from the genome to regulate target gene expression at the post-transcriptional level. The roles of miRNAs in controlling ADME gene expression have been demonstrated, and such miRNAs may consequently influence cellular drug metabolism and disposition capacity. Several types of miRNA mimics and small interfering RNA (siRNA) reagents have been developed and widely used for ADME research. In this review article, we first provide a brief introduction to the mechanistic actions of miRNAs in post-transcriptional gene regulation of drug-metabolizing enzymes, transporters, and transcription factors. After summarizing conventional small RNA production methods, we highlight the latest advances in novel recombinant RNA technologies and applications of the resultant bioengineered RNA (BioRNA) agents to ADME studies. BioRNAs produced in living cells are not only powerful tools for general biological and biomedical research but also potential therapeutic agents amenable to clinical investigations.

ELAVL1 promotes prostate cancer progression by interacting with other m6A regulators

N6-Methyladenosine (m6A) imbalance is an important factor in the occurrence and development of prostate cancer (PCa). Many m6A regulators have been found to be significantly dysregulated in PCa. ELAVL1 is an m6A binding protein that can promote the occurrence and development of tumors in an m6A-dependent manner. In this study, we found that most m6A regulators were significantly dysregulated in PCa, and some m6A regulators were associated with the progression-free interval. Mutations and copy number variations of these m6A regulators can alter their expression. However, ELAVL1 mutations were not found in PCa. Nevertheless, ELAVL1 upregulation was closely related to PCa proliferation. High ELAVL1 expression was also related to RNA metabolism. Further experiments showed that ELAVL1 interacted with other m6A regulators and that several m6A regulatory mRNAs have m6A sites that can be recognized by ELAVL1. Additionally, protein–protein interactions occur between ELAVL1 and other m6A regulators. Finally, we found that the dysregulation of ELAVL1 expression occurred in almost all tumors, and interactions between ELAVL1 and other m6A regulators also existed in almost all tumors. In summary, ELAVL1 is an important molecule in the development of PCa, and its interactions with other m6A regulators may play important roles in PCa progression.

MicroRNAs, Tristetraprolin Family Members and HuR: A Complex Interplay Controlling Cancer-Related Processes

Simple Summary

AU-rich Element Binding Proteins (AUBPs) represent important post-transcriptional regulators of gene expression by regulating mRNA decay and/or translation. Importantly, AUBPs can interfere with microRNA-dependent regulation by (i) competing with the same binding sites on mRNA targets, (ii) sequestering miRNAs, thereby preventing their binding to their specific targets or (iii) promoting miRNA-dependent regulation. These data highlight a new paradigm where both miRNA and RNA binding proteins form a complex regulatory network involved in physiological and pathological processes. However, this interplay is still poorly considered, and our current models do not integrate this level of complexity, thus potentially giving misleading interpretations regarding the role of these regulators in human cancers. This review summarizes the current knowledge regarding the crosstalks existing between HuR, tristetraprolin family members and microRNA-dependent regulation.

Abstract

MicroRNAs represent the most characterized post-transcriptional regulators of gene expression. Their altered expression importantly contributes to the development of a wide range of metabolic and inflammatory diseases but also cancers. Accordingly, a myriad of studies has suggested novel therapeutic approaches aiming at inhibiting or restoring the expression of miRNAs in human diseases. However, the influence of other trans-acting factors, such as long-noncoding RNAs or RNA-Binding-Proteins, which compete, interfere, or cooperate with miRNAs-dependent functions, indicate that this regulatory mechanism is much more complex than initially thought, thus questioning the current models considering individuals regulators. In this review, we discuss the interplay existing between miRNAs and the AU-Rich Element Binding Proteins (AUBPs), HuR and tristetraprolin family members (TTP, BRF1 and BRF2), which importantly control the fate of mRNA and whose alterations have also been associated with the development of a wide range of chronic disorders and cancers. Deciphering the interplay between these proteins and miRNAs represents an important challenge to fully characterize the post-transcriptional regulation of pro-tumorigenic processes and design new and efficient therapeutic approaches.

The role of human antigen R (HuR) in modulating proliferation, senescence and radiosensitivity of skin cells

The skin is the largest outermost organ of the human body. It is vulnerable to various damages, such as ionizing radiation. Exploration of proliferation, senescence and radiosensitivity of skin cells contributes to the development of medical and cosmetic countermeasures against skin aging and toward injury protection. Human antigen R (HuR) is one of the most widely studied RNA-binding proteins and serves an important role in stabilization of mRNA and regulation of the expression of the target genes. To investigate the role of HuR in modulating proliferation, senescence and radiosensitivity of skin cells, the present study performed an in vitro study using lentivirus-mediated overexpression or silencing of HuR in human keratinocyte HaCaT cells and human skin fibroblast WS1 cells. The results indicated that overexpression of HuR promoted proliferation, whereas downregulation of HuR inhibited proliferation of HaCaT and WS1 cells. Overexpression of HuR reduced apoptosis and senescence in skin cells. RNA-Seq of skin cells with HuR overexpression or knockdown identified 77 mRNAs positively or negatively correlated with HuR expression levels. In addition, silencing of HuR induced a significant increase in radiogenic reactive oxygen species after irradiation. Overexpression of HuR increased radiotolerance of HaCaT and WS1 cells. RNA immunoprecipitation coupled with RNA-Seq identified 14 mRNAs interacting with HuR upon radiation exposure. Overall, the findings of the present study illustrated the key role of HuR in modulating proliferation, senescence and radiosensitivity of skin cells providing a new therapeutic strategy for cosmetic treatments and to combat skin injury.

miRNAs as cornerstones in colorectal cancer pathogenesis and resistance to therapy: A spotlight on signaling pathways interplay - A review

Colorectal cancer (CRC) is the world's third most prevalent cancer and the main cause of cancer-related mortality. A lot of work has been put into improving CRC patients' clinical care, including the development of more effective methods and wide biomarkers variety for prognostic, and diagnostic purposes. MicroRNAs (miRNAs) regulate a variety of cellular processes and play a significant role in the CRC progression and spread via controlling their target gene expression by translation inhibition or mRNA degradation. Consequently, dysregulation and disruption in their function, miRNAs are linked to CRC malignant pathogenesis by controlling several cellular processes involved in the CRC. These cellular processes include increased proliferative and invasive capacity, cell cycle aberration, evasion of apoptosis, enhanced EMT, promotion of angiogenesis and metastasis, and decreased sensitivity to major treatments. The miRNAs control cellular processes in CRC via regulation of pathways such as Wnt/β-catenin signaling, PTEN/AKT/mTOR axis, KRAS, TGFb signaling, VEGFR, EGFR, and P53. Hence, the goal of this review was to review miRNA biogenesis and present an updated summary of oncogenic and tumor suppressor (TS) miRNAs and their potential implication in CRC pathogenesis and responses to chemotherapy and radiotherapy. We also summarise the biological importance and clinical applications of miRNAs in the CRC.

Cellular irinotecan resistance in colorectal cancer and overcoming irinotecan refractoriness through various combination trials including DNA methyltransferase inhibitors: a review

Treatment with pharmacological drugs for colorectal cancer (CRC) remains unsatisfactory. A major cause of failure in pharmacotherapy is the resistance of colon cancer cells to the drugs, creating an urgent issue. In this review, we summarize previous studies on the resistance of CRC cells to irinotecan and discuss possible reasons for refractoriness. Our review presents the following five major causes of irinotecan resistance in human CRC: (1) cellular irinotecan resistance is induced mainly through the increased expression of the drug efflux transporter, ABCG2; (2) cellular irinotecan resistance is also induced in association with a nuclear receptor, pregnane/steroid X receptor (PXR/SXR), which is enriched in the CYP3A4 gene enhancer region in CRC cells by exposing the cells to SN-38; (3) irinotecan-resistant cells possess either reduced DNA topoisomerase I (Top1) expression at both the mRNA and protein levels or Top1 missense mutations; (4) alterations in the tumor microenvironment lead to drug resistance through intercellular vesicle-mediated transmission of miRNAs; and (5) CRC stem cells are the most difficult targets to successfully treat CRC. In the clinical setting, CRC gradually develops resistance to initially effective irinotecan-based therapy. To solve this problem, several clinical trials, such as irinotecan plus cetuximab vs. cetuximab monotherapy, have been conducted. Another clinical trial on irinotecan plus guadecitabine, a DNA-methyltransferase inhibitor, has also been conducted.

Regulation of Drug Transport Proteins-From Mechanisms to Clinical Impact: A White Paper on Behalf of the International Transporter Consortium

Membrane transport proteins are involved in the absorption, disposition, efficacy, and/or toxicity of many drugs. Numerous mechanisms (e.g., nuclear receptors, epigenetic gene regulation, microRNAs, alternative splicing, post‐translational modifications, and trafficking) regulate transport protein levels, localization, and function. Various factors associated with disease, medications, and dietary constituents, for example, may alter the regulation and activity of transport proteins in the intestine, liver, kidneys, brain, lungs, placenta, and other important sites, such as tumor tissue. This white paper reviews key mechanisms and regulatory factors that alter the function of clinically relevant transport proteins involved in drug disposition. Current considerations with in vitro and in vivo models that are used to investigate transporter regulation are discussed, including strengths, limitations, and the inherent challenges in predicting the impact of changes due to regulation of one transporter on compensatory pathways and overall drug disposition. In addition, translation and scaling of in vitro observations to in vivo outcomes are considered. The importance of incorporating altered transporter regulation in modeling and simulation approaches to predict the clinical impact on drug disposition is also discussed. Regulation of transporters is highly complex and, therefore, identification of knowledge gaps will aid in directing future research to expand our understanding of clinically relevant molecular mechanisms of transporter regulation. This information is critical to the development of tools and approaches to improve therapeutic outcomes by predicting more accurately the impact of regulation‐mediated changes in transporter function on drug disposition and response.

MicroRNAs and drug resistance in colorectal cancer with special focus on 5-fluorouracil

Colorectal cancer is globally one of the most common cancers in all age groups. The current chemotherapy combinations for colorectal cancer treatment include 5-fluorouracil-based regimens; however, drug resistance remains one of the main reasons for chemotherapy failure and disease recurrence. Many studies have determined colorectal cancer chemoresistance mechanisms such as drug efflux, cell cycle arrest, DNA damage repair, apoptosis, autophagy, vital enzymes, epigenetic, epithelial-mesenchymal transition, stem cells, and immune system suppression. Several microRNAs affect drug resistance by regulating the drug resistance-related target genes in colorectal cancer. These drug resistance-related miRNAs may be used as promising biomarkers for predicting drug response or as potential therapeutic targets for treating patients with colorectal cancer. This work reviews and discuss the role of selected microRNAs in 5-fluorouracil resistance and their molecular mechanisms in colorectal cancer.

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.

The role of non-coding RNAs in chemotherapy for gastrointestinal cancers

Gastrointestinal (GI) cancers, including colorectal, gastric, hepatic, esophageal, and pancreatic tumors, are responsible for large numbers of deaths around the world. Chemotherapy is the most common approach used to treat advanced GI cancer. However, chemoresistance has emerged as a critical challenge that prevents successful tumor elimination, leading to metastasis and recurrence. Chemoresistance mechanisms are complex, and many factors and pathways are involved. Among these factors, non-coding RNAs (ncRNAs) are critical regulators of GI tumor development and subsequently can induce resistance to chemotherapy. This occurs because ncRNAs can target multiple signaling pathways, affect downstream genes, and modulate proliferation, apoptosis, tumor cell migration, and autophagy. ncRNAs can also induce cancer stem cell features and affect the epithelial-mesenchymal transition. Thus, ncRNAs could possibly act as new targets in chemotherapy combinations to treat GI cancer and to predict treatment response.

Gastrointestinal cancer drug resistance: the role of exosomal miRNAs

Resistance of gastrointestinal (GI) cancer cells to therapeutic agents are one of the major problems in treating this type of cancer. Although the exact mechanism of drug resistance has not yet been fully elucidated, various factors have been identified as contributing factors involved in this process. Several studies have revealed the role of exosomes, especially exosomal microRNAs (miRNAs), in GI tumorigenesis, invasion, angiogenesis, and drug resistance. Exosomes, a type of small extracellular vesicles (EVs), are originated from endosomes and are released into the extracellular environment and body fluids by different cell types. Exosomes mediate cell-cell communication by transferring different cargos, including miRNAs, between parent and recipient cells. Therefore, identifying these exosomal miRNAs and their functions in GI cancers might provide new clues to further explore the secret of this process and thus help in drug-resistance management. This review article will discuss the roles of exosomal miRNAs and their mechanisms of action in drug resistance of different types of GI cancer cells (e.g., stomach, esophagus, liver, pancreas, and colon) to therapeutic agents.

Multidrug efflux transporter ABCG2: expression and regulation

The adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) was originally discovered in a multidrug-resistant breast cancer cell line. Studies in the past have expanded the understanding of its role in physiology, disease pathology and drug resistance. With a widely distributed expression across different cell types, ABCG2 plays a central role in ATP-dependent efflux of a vast range of endogenous and exogenous molecules, thereby maintaining cellular homeostasis and providing tissue protection against xenobiotic insults. However, ABCG2 expression is subjected to alterations under various pathophysiological conditions such as inflammation, infection, tissue injury, disease pathology and in response to xenobiotics and endobiotics. These changes may interfere with the bioavailability of therapeutic substrate drugs conferring drug resistance and in certain cases worsen the pathophysiological state aggravating its severity. Considering the crucial role of ABCG2 in normal physiology, therapeutic interventions directly targeting the transporter function may produce serious side effects. Therefore, modulation of transporter regulation instead of inhibiting the transporter itself will allow subtle changes in ABCG2 activity. This requires a thorough comprehension of diverse factors and complex signaling pathways (Kinases, Wnt/β-catenin, Sonic hedgehog) operating at multiple regulatory levels dictating ABCG2 expression and activity. This review features a background on the physiological role of transporter, factors that modulate ABCG2 levels and highlights various signaling pathways, molecular mechanisms and genetic polymorphisms in ABCG2 regulation. This understanding will aid in identifying potential molecular targets for therapeutic interventions to overcome ABCG2-mediated multidrug resistance (MDR) and to manage ABCG2-related pathophysiology.

RUNX1 regulates the proliferation and chemoresistance of colorectal cancer through the Hedgehog signaling pathway

Background: Chemoresistance is one of the main causes of recurrence in colorectal cancer (CRC) patients and leads to a poor prognosis. To characterize RUNX1 expression in colorectal cancer (CRC) and elucidate its mechanistic involvement in the tumor biology of this disease.

Methods: The expression of RUNX1 in CRC and normal tissues was detected by bioinformatics analysis. Cell proliferation was measured by CCK-8 and clonogenic assays. In vivo tumor progression was assessed with a xenograft mouse model. Cell drug sensitivity tests and flow cytometry were performed to analyze CRC cell chemoresistance. RUNX1, key molecules of the Hedgehog signaling pathway, and ABCG2 were detected by qRT-PCR and Western blotting.

Results: RUNX1 expression is upregulated in CRC tissues. RUNX1 enhanced CRC cell resistance to 5-fluorouracil (5-FU), promoted proliferation, and inhibited 5-FU-induced apoptosis. Mechanistically, RUNX1 can activate the Hedgehog signaling pathway and promote the expression of ABCG2 in CRC cells.

Conclusions: Our study demonstrated that RUNX1 promotes CRC proliferation and chemoresistance by activating the Hedgehog signaling pathway and ABCG2 expression.

microRNAs: Small molecules with a large impact on colorectal cancer

Colorectal cancer (CRC) accounts for one of the main cancer-related mortality and morbidity worldwide. The molecular mechanisms of CRC development have been broadly investigated and, over the last decade, it has become evident that aberrant transcription of microRNAs (miRNAs), a class of small, noncoding RNA molecules, has a significant role in the inception and promotion of CRC. In the involved tissues of CRC, the transcription profile of miRNAs is modulated, and their expression templates are related with prognosis, diagnosis, and treatment outcomes. Here, in the current review, we attempted to discuss the latest information regarding the aberrantly expressed miRNAs in CRC and the advantages of utilizing miRNAs as biomarkers for early diagnosis and prognosis of CRC as well as potential therapeutic application. The effect of miRNAs involved in various signaling pathways, primarily p53, EGFR, Wnt, and TGF-β pathways, was clarified.

Role of multidrug resistance-associated proteins in cancer therapeutics: past, present, and future perspectives

Cancer, a major public health problem, is one of the world's top leading causes of death. Common treatments for cancer include cytotoxic chemotherapy, surgery, targeted drugs, endocrine therapy, and immunotherapy. However, despite the outstanding achievements in cancer therapies during the last years, resistance to conventional chemotherapeutic agents and new targeted drugs is still the major challenge. In the present review, we explain the different mechanisms involved in cancer therapy and the detailed outlines of cancer drug resistance regarding multidrug resistance-associated proteins (MRPs) and their role in treatment failures by common chemotherapeutic agents. Further, different modulators of MRPs are presented. Finally, we outlined the models used to analyze MRP transporters and proposed a future impact that may set up a base or pave the way for many researchers to investigate the cancer MRP further.

MicroRNAs' role in the environment-related non-communicable diseases and link to multidrug resistance, regulation, or alteration

The discovery of microRNAs (miRNAs) 20 years ago has advocated a new era of "small molecular genetics." About 2000 miRNAs are present that regulate one third of the genome. MiRNA dysregulated expression arising as a response to our environment insult or stress or changes may contribute to several diseases, namely non-communicable diseases, including tumor growth. Their presence in body fluids, reflecting level alteration in various cancers, merit circulating miRNAs as the "next-generation biomarkers" for early-stage tumor diagnosis and/or prognosis. Herein, we performed a comprehensive literature search focusing on the origin, biosynthesis, and role of miRNAs and summarized the foremost studies centering on miR value as non-invasive biomarkers in different environment-related non-communicable diseases, including various cancer types. Moreover, during chemotherapy, many miRNAs were linked to multidrug resistance, via modulating numerous, environment triggered or not, biological processes and/or pathways that will be highlighted as well.

Nanoplatform-based natural products co-delivery system to surmount cancer multidrug-resistant

The emergence of multidrug resistance (MDR) in malignant tumors is the primary reason for invalid chemotherapy. Antitumor drugs are often adversely affected by the MDR of tumor cells. Treatments using conventional drugs, which have specific drug targets, hardly regulate the complex signaling pathway of MDR cells because of the complex formation mechanism of MDR. However, natural products have positive advantages, such as high efficiency, low toxicity, and ability to target multiple mechanism pathways associated with MDR. Natural products, as MDR reversal agents, synergize with chemotherapeutics and enhance the sensitivity of tumor cells to chemotherapeutics, and the co-delivery of natural products and antitumor drugs with nanocarriers maximizes the synergistic effects against MDR in tumor cells. This review summarizes the molecular mechanisms of MDR, the advantages of natural products combined with chemotherapeutics in offsetting complicated MDR mechanisms, and the types and mechanisms of natural products that are potential MDR reversal modulators. Meanwhile, aiming at the low bioavailability of cocktail combined natural products and chemotherapeutic in vivo, the advantages of nanoplatform-based co-delivery system and recent research developments are illustrated on the basis of our previous research. Finally, prospective horizons are analyzed, which are expected to considerably improve the nano-co-delivery of natural products and chemotherapeutic systems for MDR reversal in cancer.

Nucleolin-Targeting AS1411 Aptamer-Modified Micelle for the Co-Delivery of Doxorubicin and miR-519c to Improve the Therapeutic Efficacy in Hepatocellular Carcinoma Treatment

BACKGROUND

Multidrug resistance (MDR) has emerged to be a major hindrance in cancer therapy, which contributes to the reduced sensitivity of cancer cells toward chemotherapeutic drugs mainly owing to the over-expression of drug efflux transporters. The combination of gene therapy and chemotherapy has been considered as a potential approach to improve the anti-cancer efficacy by reversing the MDR effect.

MATERIALS AND METHODS

The AS1411 aptamer-functionalized micelles were constructed through an emulsion/solvent evaporation strategy for the simultaneous co-delivery of doxorubicin and miR-519c. The therapeutic efficacy and related mechanism of micelles were explored based on the in vitro and in vivo active targeting ability and the suppression of MDR, using hepatocellular carcinoma cell line HepG2 as a model.

RESULTS

The micelle was demonstrated to possess favorable cellular uptake and tumor penetration ability by specifically recognizing the nucleolin in an AS1411 aptamer-dependent manner. Further, the intracellular accumulation of doxorubicin was significantly improved due to the suppression of ABCG2-mediated drug efflux by miR-519c, resulting in the efficient inhibition of tumor growth.

CONCLUSION

The micelle-mediated co-delivery of doxorubicin and miR-519c provided a promising strategy to obtain ideal anti-cancer efficacy through the active targeting function and the reversion of MDR.

The role of non-coding RNAs in ABC transporters regulation and their clinical implications of multidrug resistance in cancer

INTRODUCTION

Multi-drug resistance (MDR) is a hindrance toward the successful treatment of cancers. The primary mechanism that gives rise to acquired chemoresistance is the overexpression of adenosine triphosphate-binding cassette (ABC) transporters. The dysregulation of non-coding RNAs (ncRNAs) is a widely concerned reason contributing to this phenotype.

AREAS COVERED

In this review, we describe the role of intracellular and exosomal ncRNAs including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) in ABC transporters-induced tumor MDR. Meanwhile, we will introduce the potential therapeutic strategies which reverse MDR in terms of reducing the expression of ABC transporters via targeting ncRNAs, like nucleic acid delivery with nanoparticles as well as miRNAs-targeted small molecular compounds.

EXPERT OPINION

The dysregulated ncRNAs-mediated overexpression of ABC transporters in chemo-resistant cancer is not negligible. Finding out the underlying mechanism may provide a theoretical basis for clinical therapy of cancer MDR, and the emergence of new approaches for gene therapy targeting ncRNAs to suppress ABC transporters makes reversing cancer MDR possible despite its clinical application requires further investigations. Also, the discovered ncRNAs regulating ABC transporters in chemo-resistant cancers are just a tip of the iceberg of the genetic transcripts, especially for circRNAs, which justify more concern.Abbreviations: MDR, multi-drug resistance; ABC, adenosine triphosphate-binding cassette; NcRNAs, non-coding RNAs; MiRNAs, microRNAs; LncRNAs, long non-coding RNAs; CircRNAs, circular RNAs; CeRNAs, competing endogenous RNAs; 3'UTR, 3'-untranslated regions; SLC, solute carrier; ABCB1/MDR1, ABC subfamily B member 1; ABCG2/BCRP, ABC subfamily G member 2; ABCCs/MRPs, ABC subfamily C 1 to 12; DLL1: Delta-like protein 1; DTX, docetaxel; DOX/ADM/ADR, doxorubicin/adriamycin; PTX, paclitaxel; VBL, vinblastine; VCR, vincristine; MTX, methotrexate; CDDP/DDP, cisplatin/cis-diaminedichloroplatinum; OXA/L-OHP, oxaliplatin; TMZ, temozolomide; 5-FU, 5-fluorouracil; MTA, pemetrexed; NSCLC, non-small cell lung carcinoma; HCC, hepatocellular carcinoma; CRC, colorectal carcinoma; RB, retinoblastoma; RCC, renal cell carcinoma; OS, osteosarcoma; PDAC, pancreatic ductal adenocarcinoma; TNBC, triple-negative breast cancer.

MicroRNA-Based Therapeutics for Drug-Resistant Colorectal Cancer

Although therapeutic approaches for patients with colorectal cancer (CRC) have improved in the past decades, the problem of drug resistance still persists and acts as a major obstacle for effective therapy. Many studies have shown that drug resistance is related to reduced drug uptake, modification of drug targets, and/or transformation of cell cycle checkpoints. A growing body of evidence indicates that several microRNAs (miRNAs) may contribute to the drug resistance to chemotherapy, targeted therapy, and immunotherapy by regulating the drug resistance-related target genes in CRC. These drug resistance-related miRNAs may be used as promising biomarkers for predicting drug response or as potential therapeutic targets for treating patients with CRC. In this review, we summarized the recent discoveries regarding anti-cancer drug-related miRNAs and their molecular mechanisms in CRC. Furthermore, we discussed the challenges associated with the clinical application of miRNAs as biomarkers for the diagnosis of drug-resistant patients and as therapeutic targets for CRC treatment.

The oncogenic and tumor suppressive roles of RNA-binding proteins in human cancers

Posttranscriptional regulation is a mechanism for the cells to control gene regulation at the RNA level. In this process, RNA-binding proteins (RBPs) play central roles and orchestrate the function of RNA molecules in multiple steps. Accumulating evidence has shown that the aberrant regulation of RBPs makes  contributions to the initiation and progression of tumorigenesis via numerous mechanisms such as genetic changes, epigenetic alterations, and noncoding RNA-mediated regulations. In this article, we review the effects caused by RBPs and their functional diversity in the malignant transformation of cancer cells that occurs through the involvement of these proteins in various stages of RNA regulation including alternative splicing, stability, polyadenylation, localization, and translation. Besides this, we review the various interactions between RBPs and other crucial posttranscriptional regulators such as microRNAs and long noncoding RNAs in the pathogenesis of cancer. Finally, we discuss the potential approaches for targeting RBPs in human cancers.

Hypoxia, endoplasmic reticulum stress and chemoresistance: dangerous liaisons

Solid tumors often grow in a micro-environment characterized by < 2% O₂ tension. This condition, together with the aberrant activation of specific oncogenic patwhays, increases the amount and activity of the hypoxia-inducible factor-1α (HIF-1α), a transcription factor that controls up to 200 genes involved in neoangiogenesis, metabolic rewiring, invasion and drug resistance. Hypoxia also induces endoplasmic reticulum (ER) stress, a condition that triggers cell death, if cells are irreversibly damaged, or cell survival, if the stress is mild.Hypoxia and chronic ER stress both induce chemoresistance. In this review we discuss the multiple and interconnected circuitries that link hypoxic environment, chronic ER stress and chemoresistance. We suggest that hypoxia and ER stress train and select the cells more adapted to survive in unfavorable conditions, by activating pleiotropic mechanisms including apoptosis inhibition, metabolic rewiring, anti-oxidant defences, drugs efflux. This adaptative process unequivocally expands clones that acquire resistance to chemotherapy.We believe that pharmacological inhibitors of HIF-1α and modulators of ER stress, although characterized by low specificty and anti-cancer efficacy when used as single agents, may be repurposed as chemosensitizers against hypoxic and chemorefractory tumors in the next future.

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.

The significance of microRNA deregulation in colorectal cancer development and the clinical uses as a diagnostic and prognostic biomarker and therapeutic agent

Colorectal cancer (CRC) is one of the most widely recognized and deadly malignancies worldwide. Although death rates have declined over the previous decade, mainly because of enhanced screening or potential treatment alternatives, CRC remains the third leading cause of cancer-related mortality globally, with an estimated incidence of over 1 million new cases and approximately 600 000 deaths estimated yearly. Therefore, many scientific efforts are put into the development of new diagnostic biomarkers for CRC. MicroRNAs (miRNAs), one of the epigenetics categories, have demonstrated significant roles in carcinogenesis and progression through regulating epithelial-mesenchymal transition (EMT), oncogenic signaling pathways, and metastasis. Dysregulation of miRNAs expression has been reported in many cancers, including CRC. The expression profile of miRNAs is reproducibly altered in CRC, and their expression patterns are associated with diagnosis, prognosis, and therapeutic outcomes in CRC. Recently, many studies were conducted on the dysregulation of miRNAs as a diagnostic and prognostic biomarker in CRC. Among them, some miRNAs, which include miR-21, miR-34 family, miR-155, miR-224, and miR-378, have been more studied in CRC with more prominent roles in diagnosis, prognosis, and therapy. In the present review, we summarized the latest information regarding the dysregulated miRNAs in CRC and the advantages of using miRNAs as a biomarker for CRC diagnosis, treatment, and their function in different signaling pathways involved in CRC progression. Moreover, we described the translation of miRNA research to potential therapeutic applications in the management of CRC in clinical settings.

MicroRNAs and colorectal cancer chemoresistance: New solution for old problem

BACKGROUND

Colorectal cancer (CRC) is one of the most common gastrointestinal malignancies with a significant mortality rate. Despite the great advances in cancer treatment in the last few decades, effective treatment of CRC is still under challenge. One of the main problems associated with CRC treatment is the resistance of cancer cells to chemotherapy drugs.

METHODS

Many studies have been carried out to identify CRC chemoresistance mechanisms, and shed light on the role of ATP-binding cassette transporters (ABC transporters), enzymes as thymidylate synthase, some signaling pathways, and cancer stem cells (CSC) in chemoresistance and failed CRC chemotherapies. Other studies have also been recently carried out to find solutions to overcome chemoresistance. Some of these studies have identified the role of miRNAs in chemoresistance of the CRC cells and the effective use of these micro-molecules to CRC treatment.

RESULTS

Considering the results of these studies, more focus on miRNAs likely leads to a proper solution to overcome CRC chemoresistance.

CONCLUSION

The current study has reviewed the related literature while discussing the efficacy of miRNAs as potential clinical tools for overcoming CRC chemoresistance and reviewing the most important chemoresistance mechanisms in CRC cells.

5-Fluorouracil resistance mechanisms in colorectal cancer: From classical pathways to promising processes

Colorectal cancer (CRC) is a public health problem. It is the third most common cancer in the world, with nearly 1.8 million new cases diagnosed in 2018. The only curative treatment is surgery, especially for early tumor stages. When there is locoregional or distant invasion, chemotherapy can be introduced, in particular 5-fluorouracil (5-FU). However, the disease can become tolerant to these pharmaceutical treatments: resistance emerges, leading to early tumor recurrence. Different mechanisms can explain this 5-FU resistance. Some are disease-specific, whereas others, such as drug efflux, are evolutionarily conserved. These mechanisms are numerous and complex and can occur simultaneously in cells exposed to 5-FU. In this review, we construct a global outline of different mechanisms from disruption of 5-FU-metabolic enzymes and classic cellular processes (apoptosis, autophagy, glucose metabolism, oxidative stress, respiration, and cell cycle perturbation) to drug transporters and epithelial-mesenchymal transition induction. Particular interest is directed to tumor microenvironment function as well as epigenetic alterations and miRNA dysregulation, which are the more promising processes that will be the subject of much research in the future.

The RNA Binding Protein HuR: A Promising Drug Target for Anticancer Therapy

The stability of mRNA is one of the key factors governing the regulation of eukaryotic gene expression and function. Human antigen R (HuR) is an RNA-binding protein that regulates the stability, translation, and nucleus-to-cytoplasm shuttling of its target mRNAs. While HuR is normally localized within the nucleus, it has been shown that HuR binds mRNAs in the nucleus and then escorts the mRNAs to the cytoplasm where HuR protects them from degradation. It contains several RNA recognition motifs, which specifically bind to adenylate and uridylate-rich regions within the 3'-untranslated region of the target mRNA to mediate its effect. Many of the HuR target mRNAs encode proteins important for cell growth, tumorigenesis, angiogenesis, tumor inflammation, invasion and metastasis. HuR overexpression is known to correlate well with high-grade malignancy and poor prognosis in many tumor types. Thus, HuR has emerged as an attractive drug target for cancer therapy. Novel small molecule HuR inhibitors have been identified by high throughput screening and new formulations for targeted delivery of HuR siRNA to tumor cells have been developed with promising anticancer activity. This review summarizes the significant role of HuR in cancer development, progression, and poor treatment response. We will discuss the potential and challenges of targeting HuR therapeutically.

The RNA-Binding Protein HuR in Digestive System Tumors

Human antigen R (HuR) is a member of the Hu family of RNA-binding proteins. This molecule, which was first described in tumors nearly two decades ago, has recently received much attention in tumor-related research because it regulates the expression of many tumor-associated molecules through posttranscriptional regulatory mechanisms, thereby affecting biological characteristics. It is suggested that HuR might be a novel therapeutic target and a marker for therapeutic response and prognostic assessment. Increasing evidence supports that HuR also plays critical roles in the development, therapy, and prognosis of digestive system tumors. Herein, we review the relationships between HuR and digestive system tumors, demonstrating the importance of HuR in digestive system tumor diagnosis.

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.

PLOD2 increases resistance of gastric cancer cells to 5-fluorouracil by upregulating BCRP and inhibiting apoptosis

Background: Gastric cancer (GC) is one of the most common cancers, and it is the third most common cause of cancer-related mortality worldwide. Fluorouracil (5-FU)-based chemotherapy is frequently used for the treatment of advanced GC. However, a substantial proportion of patients eventually experience refractory disease due to drug resistance. PLOD2 was reported to increase invasion and migration in several GC cell lines, but the roles of PLOD2 in chemoresistance are still unclear. The present study aimed to determine whether PLOD2 could confer 5-FU resistance in GC.

Methods: The expression of PLOD2 in GC cell lines was assessed by Western blotting. The cells were transfected by lentiviral transduction. The IC50 values were determined by the CCK-8 assay. The migration and invasion abilities of cells were analyzed by the Transwell assay. The proportion of apoptotic cells was assessed by flow cytometry. The protein levels of P-gp (MDR1), MRP1, BCRP (ABCG2), Bax and Bcl2 were analyzed by Western blotting. Furthermore, tumor xenograft models in nude mice were established to test tumor growth and weight.

Result: The knockdown of PLOD2 in BGC823 cells significantly decreased the IC50 values of 5-FU. It also contributed to reducing the cell migration and invasion and promoting the apoptosis of GC cells. The opposite results appeared in PLOD2-overexpressing MGC803 GC cells. In vivo experiments showed that the knockdown of PLOD2 increased the growth inhibition of transplanted tumors in nude mice in response to 5-FU. Our mechanistic studies revealed that PLOD2-overexpressing cells appear to be resistant to the therapeutic characteristics of 5-FU in GC cells by upregulating BCRP and that PLOD2 confers resistance to 5-FU-induced apoptosis in GC cells by affecting the expression of Bax and Bcl2.

Conclusion: PLOD2 contributed to increasing resistance of gastric cancer cells to 5-fluorouracil by upregulating BCRP and inhibiting apoptosis.

HuR Reduces Radiation-Induced DNA Damage by Enhancing Expression of ARID1A

Tumor suppressor ARID1A, a subunit of the chromatin remodeling complex SWI/SNF, regulates cell cycle progression, interacts with the tumor suppressor TP53, and prevents genomic instability. In addition, ARID1A has been shown to foster resistance to cancer therapy. By promoting non-homologous end joining (NHEJ), ARID1A enhances DNA repair. Consequently, ARID1A has been proposed as a promising therapeutic target to sensitize cancer cells to chemotherapy and radiation. Here, we report that ARID1A is regulated by human antigen R (HuR), an RNA-binding protein that is highly expressed in a wide range of cancers and enables resistance to chemotherapy and radiation. Our results indicate that HuR binds ARID1A mRNA, thereby increasing its stability in breast cancer cells. We further find that ARID1A expression suppresses the accumulation of DNA double-strand breaks (DSBs) caused by radiation and can rescue the loss of radioresistance triggered by HuR inhibition, suggesting that ARID1A plays an important role in HuR-driven resistance to radiation. Taken together, our work shows that HuR and ARID1A form an important regulatory axis in radiation resistance that can be targeted to improve radiotherapy in breast cancer patients.

Epigenetic Biomarkers in Colorectal Cancer Patients Receiving Adjuvant or Neoadjuvant Therapy: A Systematic Review of Epidemiological Studies

Colorectal cancer (CRC) represents the third-most common cancer worldwide and one of the main challenges for public health. Despite great strides in the application of neoadjuvant and adjuvant therapies for rectal and colon cancer patients, each of these treatments is still associated with certain adverse effects and different response rates. Thus, there is an urgent need for identifying novel potential biomarkers that might guide personalized treatments for specific subgroups of patients. However, until now, there are no biomarkers to predict the manifestation of adverse effects and the response to treatment in CRC patients. Herein, we provide a systematic review of epidemiological studies investigating epigenetic biomarkers in CRC patients receiving neoadjuvant or adjuvant therapy, and their potential role for the prediction of outcomes and response to treatment. With this aim in mind, we identified several epigenetic markers in CRC patients who received surgery with adjuvant or neoadjuvant therapy. However, none of them currently has the robustness to be translated into the clinical setting. Thus, more efforts and further large-size prospective studies and/or trials should be encouraged to develop epigenetic biomarker panels for personalized prevention and medicine in CRC cancer.

MicroRNA-519c-3p promotes tumor growth and metastasis of hepatocellular carcinoma by targeting BTG3

Tumor recurrence and metastasis after surgical resection are the major causes for the cancer-related death of hepatocellular carcinoma (HCC). Thus, better understanding the mechanisms involved in tumor progression will benefit to improve HCC treatment. Accumulating evidence demonstrates that microRNAs (miRNAs) play critical roles in the development and progression of HCC. However, the function of miR-519c-3p in HCC and its related mechanism remain unexplored. Here, we reported that miR-519c-3p was strongly overexpressed in HCC tissues, which was significantly correlated with poor prognosis and clinicopathological features including tumor size ≥5 cm, vascular invasion and advanced tumor-node-metastasis (TNM) stages (III + IV). Furthermore, the elevated levels of miR-519c-3p were observed in HCC cell lines. Subsequently, gain- or loss-of-function assays demonstrated that miR-519c-3p promoted HCC cell proliferation, migration as well as invasion in vitro, and facilitated the growth and metastasis of HCC cells in vivo. Mechanistically, B-cell translocation gene 3 (BTG3) was identified as a direct downstream target of miR-519c-3p. The level of BTG3 mRNA was downregulated in HCC and negatively correlated with miR-519c-3p expression. Western blotting confirmed that BTG3 was negatively regulated by miR-519c-3p in HCC cells. Luciferase reporter assays illustrated the direct interaction between miR-519c-3p and the 3'UTR of BTG3 mRNA. Recuse experiments demonstrated that BTG3 mediated the promoting effects of miR-519c-3p on the proliferation and motility of HCC cells. Collectively, our results suggest that miR-519c-3p functions as a tumor promotor in regulating the growth and metastasis of HCC by targeting BTG3, and potentially serves as a novel therapeutic target for HCC.

Inhibition of Caspase-2 Translation by the mRNA Binding Protein HuR: A Novel Path of Therapy Resistance in Colon Carcinoma Cells?

An increased expression and cytoplasmic abundance of the ubiquitous RNA binding protein human antigen R (HuR) is critically implicated in the dysregulated control of post- transcriptional gene expression during colorectal cancer development and is frequently associated with a high grade of malignancy and therapy resistance. Regardless of the fact that HuR elicits a broad cell survival program by increasing the stability of mRNAs coding for prominent anti-apoptotic factors, recent data suggest that HuR is critically involved in the regulation of translation, particularly, in the internal ribosome entry site (IRES) controlled translation of cell death regulatory proteins. Accordingly, data from human colon carcinoma cells revealed that HuR maintains constitutively reduced protein and activity levels of caspase-2 through negative interference with IRES-mediated translation. This review covers recent advances in the understanding of mechanisms underlying HuR's modulatory activity on IRES-triggered translation. With respect to the unique regulatory features of caspase-2 and its multiple roles (e.g., in DNA-damage-induced apoptosis, cell cycle regulation and maintenance of genomic stability), the pathophysiological consequences of negative caspase-2 regulation by HuR and its impact on therapy resistance of colorectal cancers will be discussed in detail. The negative HuR-caspase-2 axis may offer a novel target for tumor sensitizing therapies.

Development of precision medicine approaches based on inter-individual variability of BCRP/ABCG2

Precision medicine is a rapidly-developing modality of medicine in human healthcare. Based on each patient׳s unique characteristics, more accurate dosages and drug selection can be made to achieve better therapeutic efficacy and less adverse reactions in precision medicine. A patient׳s individual parameters that affect drug transporter action can be used to develop a precision medicine guidance, due to the fact that therapeutic efficacy and adverse reactions of drugs can both be affected by expression and function of drug transporters on the cell membrane surface. The purpose of this review is to summarize unique characteristics of human breast cancer resistant protein (BCRP) and the genetic variability in the BCRP encoded gene ABCG2 in the development of precision medicine. Inter-individual variability of BCRP/ABCG2 can impact choices and outcomes of drug treatment for several diseases, including cancer chemotherapy. Several factors have been implicated in expression and function of BCRP, including genetic, epigenetic, physiologic, pathologic, and environmental factors. Understanding the roles of these factors in controlling expression and function of BCRP is critical for the development of precision medicine based on BCRP-mediated drug transport.

ABC Transporters: Regulation and Association with Multidrug Resistance in Hepatocellular Carcinoma and Colorectal Carcinoma

For most cancers, the treatment of choice is still chemotherapy despite its severe adverse effects, systemic toxicity and limited efficacy due to the development of multidrug resistance (MDR). MDR leads to chemotherapy failure generally associated with a decrease in drug concentration inside cancer cells, frequently due to the overexpression of ABC transporters such as P-glycoprotein (P-gp/MDR1/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2), which limits the efficacy of chemotherapeutic drugs. The aim of this review is to compile information about transcriptional and post-transcriptional regulation of ABC transporters and discuss their role in mediating MDR in cancer cells. This review also focuses on drug resistance by ABC efflux transporters in cancer cells, particularly hepatocellular carcinoma (HCC) and colorectal carcinoma (CRC) cells. Some aspects of the chemotherapy failure and future directions to overcome this problem are also discussed.

Current Evidence on miRNAs as Potential Theranostic Markers for Detecting Chemoresistance in Colorectal Cancer: A Systematic Review and Meta-Analysis of Preclinical and Clinical Studies

BACKGROUND

Findings from observational clinical studies examining the relationship between biomarker expression and theranosis in colorectal cancer (CRC) have been conflicting.

OBJECTIVE

We conducted this systematic review and meta-analysis to summarise the existing evidence to demonstrate the involvement of microRNAs (miRNAs) in chemoresistance and sensitivity in CRC through drug genetic pathways.

METHODS

Using PRISMA guidelines, we systematically searched PubMed and Science Direct for relevant studies that took place between 2012 and 2017. A random-effects model of meta-analysis was applied to evaluate the pooled effect size of hazard ratios (HRs) across the included studies. Cochran's Q test and the I² statistic were used to detect heterogeneity. A funnel plot was used to assess potential publication bias.

RESULTS

Of the 4700 studies found, 39 studies comprising 2822 patients with CRC met the inclusion criteria. The included studies used one or a combination of 14 chemotherapy drugs, including 5-fluorouracil and oxaliplatin. Of the 60 miRNAs, 28 were associated with chemosensitivity, 20 with chemoresistance, and one with differential expression and radiosensitivity; ten miRNAs were not associated with any impact on chemotherapy. The results outline the importance of 34 drug-regulatory pathways of chemoresistance and sensitivity in CRC. The mean effect size was 0.689 (95% confidence interval 0.428-1.110), indicating that the expression of miRNAs decreased the likelihood of death by about 32%.

CONCLUSION

Studies have consistently shown that multiple miRNAs could act as clinical predictors of chemoresistance and sensitivity. An inclusion of supplementary miRNA estimation in CRC routine practice needs to be considered to evaluate the efficacy of chemotherapy after confirming our findings with large-scale prospective cohort studies.

PROSPERO REGISTRATION NUMBER

CRD42017082196.

Emerging targets in cancer drug resistance

Drug resistance is a complex phenomenon that frequently develops as a failure to chemotherapy during cancer treatment. Malignant cells increasingly generate resistance to various chemotherapeutic drugs through distinct mechanisms and pathways. Understanding the molecular mechanisms involved in drug resistance remains an important area of research for identification of precise targets and drug discovery to improve therapeutic outcomes. This review highlights the role of some recent emerging targets and pathways which play critical role in driving drug resistance.