Involvement of microRNA-451 in resistance of the MCF-7 breast cancer cells to chemotherapeutic drug doxorubicin

Fas signaling promotes chemoresistance in gastrointestinal cancer by up-regulating P-glycoprotein

Fas signaling promotes metastasis of gastrointestinal (GI) cancer cells by inducing epithelial-mesenchymal transition (EMT), and EMT acquisition has been found to cause cancer chemoresistance. Here, we demonstrated that the response to chemotherapy of GI cancer patients with higher expression of FasL was significantly worse than patients with lower expression. Fas-induced activation of the ERK1/2-MAPK pathway decreased the sensitivity of GI cancer cells to chemotherapeutic agents and promoted the expression of P-glycoprotein (P-gp). FasL promoted chemoresistance of GI cancer cell via upregulation of P-gp by increasing β-catenin and decreasing miR-145. β-catenin promoted P-gp gene transcription by binding with P-gp promoter while miR-145 suppressed P-gp expression by interacting with the mRNA 3'UTR of P-gp. Immunostaining and qRT-PCR analysis of human GI cancer samples revealed a positive association among FasL, β-catenin, and P-gp, but a negative correlation between miR-145 and FasL or P-gp. Altogether, our results showed Fas signaling could promote chemoresistance in GI cancer through modulation of P-gp expression by β-catenin and miR-145. Our findings suggest that Fas signaling-based cancer therapies should be administered cautiously, as activation of this pathway may not only lead to apoptosis but also induce chemoresistance.

The Role of MicroRNAs in the Chemoresistance of Breast Cancer

Preclinical Research Breast cancer is the most prevalent malignancy in women with more than 1.3 million new cases every year worldwide. Chemotherapy is a critical therapeutic strategy for breast cancer, while chemoresistance remains a major obstacle to treatment success. In the past two decades, significant progress has been achieved in understanding drug resistance in breast cancer, involving drug efflux, alterations in DNA repair pathways, suppression of apoptosis as well as epithelial-mesenchymal transition, and cancer stem cells. However, more effective therapeutic targets and novel biomarkers are still urgently needed to improve the overall survival and refine the therapeutic strategy for breast cancer patients. MicroRNAs (miRNAs) play crucial roles in cellular processes, such as cell differentiation, proliferation, and apoptosis. The recent discovery of miRNAs in malignancy has provided new directions for research on mechanisms underlying response to chemotherapy. Furthermore, several studies have documented that selected miRNAs, such as miR-200c and miR-34a, may influence response to chemotherapy in several tumor types, including breast cancer. The use of miRNAs as therapeutic targets to overcome chemoresistance is currently under investigation. In this review, we summarize the roles of miRNAs in chemoresistance through multiple molecular mechanisms, and highlight the potential diagnostic and therapeutic applications of miRNAs in overcoming breast cancer chemoresistance.

Serum miRNA expression in patients with esophageal squamous cell carcinoma

The aim of the present study was to investigate the feasibility and value of serum microRNAs (miRNAs/miRs) as biological markers for the prediction of the behavior and prognosis of esophageal squamous cell cancer (ESCC). The differential expression of serum miRNA was detected by an miRNA microarray of 9 patients with ESCC and 9 healthy volunteers. The result of the miRNA microarray was validated in serum samples of 69 patients with ESCC and 14 healthy volunteers by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The association between serum miRNA expression and tumor-node-metastasis (TNM) stage was analyzed. A total of 10 serum-specific miRNAs were identified from the patients with ESCC. Through PCR verification, the expression levels of miR-129, miR-451 and miR-365 were consistent with the microarray results validated by RT-qPCR, and the difference was statistically significant compared with the healthy volunteers (P=0.007, P=0.007 and P<0.001, respectively). Multivariate logistic regression analysis showed that miR-365 could serve as potential diagnostic marker for ESCC; the area under the receiver operating characteristic curve was 0.831, with a sensitivity of 80.56% and a specificity of 86.7%, but its expression did not differ significantly among the different TNM stages (stage I-II vs. III, P=0.052; stage III vs. IV, P=0.069). The expression level of miRNA-129 differed significantly among the different stages (stage I-II vs. III, P=0.002; stage III vs. IV, P=0.042), while the expression level of miR-451 did not differ significantly between stage III and IV (P=0.308). In conclusion, serum microRNAs are novel biomarkers for ESCC, and miRNA-365 and miRNA-129 can be used for the early prediction of cancer and the prediction of clinical stage, respectively.

MicroRNA-induced drug resistance in gastric cancer

Drug resistance remains one of the major reasons of therapy failure in gastric cancer patients. Although the mechanisms of anticancer drug resistance have been broadly investigated, they have not been completely understood. Accumulating reports have recently highlighted the involvement of endogenous non-coding RNAs, known as microRNAs, in the evolution of cancer cell drug resistance. MiRNAs have been characterized as major regulators of crucial genes implicated in the chemoresistance phenotype of gastric cancer cells. MiRNA-based therapy in the future may provide a new strategy to overcome drug resistance. This review summarizes the current knowledge on the role of miRNAs in regulating drug resistance in gastric cancer and their potential to develop targeted therapies and personalized treatment for managing drug resistant gastric cancers.

Comparative Aspects of Molecular Mechanisms of Drug Resistance through ABC Transporters and Other Related Molecules in Canine Lymphoma

The most important causes of treatment failure in canine lymphoma include intrinsic or acquired drug resistance. Thus, elucidation of molecular mechanisms of drug resistance is essential for the establishment of better treatment alternatives for lymphoma patients. The overexpression of drug transporters is one of the most intensively studied mechanisms of drug resistance in many tumors. In canine lymphoma, it has also been shown that the overexpression of drug efflux pumps such as P-glycoprotein is associated with drug-resistant phenotypes. Canine lymphoma has many pathological similarities to human non-Hodgkin’s lymphoma, and they also share similar molecular mechanisms of drug resistance. We have previously demonstrated the association of the overexpression of drug transporters with drug resistance and indicated some molecular mechanisms of the regulation of these transporters’ expressions in canine and human lymphoid tumor cells. However, it has also been indicated that other known or novel drug resistance factors should be explored to overcome drug resistance in lymphoma. In this review, we summarize the recent findings on the molecular mechanisms of drug resistance and possible strategies to develop better treatment modalities for canine lymphoma from the comparative aspects with human lymphoid tumors.

MicroRNA biogenesis and cellular proliferation

Given the fundamental roles of microRNAs (miRNAs) in physiological, developmental, and pathologic processes, we hypothesized that genes involved in miRNA biogenesis contribute to human complex traits. For 13 such genes, we evaluated the relationship between transcription and 2 classes of complex traits, namely cellular growth and sensitivity to various chemotherapeutic agents in a set of lymphoblastoid cell lines. We found a highly significant correlation between argonaute RNA-induced silencing complex catalytic component 2 (AGO2) expression and cellular growth rate (Bonferroni-adjusted P < 0.05), and report additional miRNA biogenesis genes with suggestive associations with either cellular growth rate or chemotherapeutic sensitivity. AGO2 expression was found to be correlated with multiple drug sensitivity phenotypes. Furthermore, small interfering RNA knockdown of AGO2 resulted in cellular growth inhibition in an ovarian cancer cell line (OVCAR-3), supporting the role of this miRNA biogenesis gene in cell proliferation in cancer cells. Expression quantitative trait loci mapping indicated that genetic variation (in the form of both single-nucleotide polymorphisms and copy number variations) that may regulate the expression of AGO2 can have downstream effects on cellular growth-dependent complex phenotypes.

Chemoresistance, cancer stem cells, and miRNA influences: the case for neuroblastoma

Neuroblastoma is a type of cancer that develops most often in infants and children under the age of five years. Neuroblastoma originates within the peripheral sympathetic ganglia, with 30% of the cases developing within the adrenal medulla, although it can also occur within other regions of the body such as nerve tissue in the spinal cord, neck, chest, abdomen, and pelvis. MicroRNAs (miRNAs) regulate cellular pathways, differentiation, apoptosis, and stem cell maintenance. Such miRNAs regulate genes involved in cellular processes. Consequently, they are implicated in the regulation of a spectrum of signaling pathways within the cell. In essence, the role of miRNAs in the development of cancer is of utmost importance for the understanding of dysfunctional cellular pathways that lead to the conversion of normal cells into cancer cells. This review focuses on highlighting the recent, important implications of miRNAs within the context of neuroblastoma basic research efforts, particularly concerning miRNA influences on cancer stem cell pathology and chemoresistance pathology for this condition, together with development of translational medicine approaches for novel diagnostic tools and therapies for this neuroblastoma.

miR-451a Inhibited Cell Proliferation and Enhanced Tamoxifen Sensitive in Breast Cancer via Macrophage Migration Inhibitory Factor

This study aims to investigate the regulative effects of microRNA-451a (miR-451a) on cell proliferation and sensitivity to tamoxifen in breast cancer cells. In cell culture experiments, the lentiviral vectors of pHBLV-miR-451a and pHBLV-miR-451a sponge were constructed and used to transfect MCF-7 and LCC2 cells. The transfection efficiency was tested by fluorescent observation, and cell lines with stable over- or downregulated expression of miR-451a were established. The expression of miR-451a and the target gene macrophage migration inhibitory factor (MIF) were detected by real-time reverse transcriptase polymerase chain reaction and/or western blot. Moreover, MTT assay, colony formation, and Transwell invasion assays were also performed. Data showed that the recombinant lentiviral vectors were constructed correctly, and the virus titer was 1 × 10(8) CFU/mL. The stable transfected cells were obtained. Overexpression of miR-451a downregulated MIF expression in mRNA and protein levels and inhibited cell proliferation, colony formation, and invasion of breast cancer cells. Downregulation of miR-451a upregulated MIF expression and increased breast cancer cell growth, invasion, and tamoxifen sensitivity. In summary, the miR-451a/MIF pathway may play important roles in the biological properties of breast cancer cells and may be a potential therapeutic target for breast cancer.

miR-494 promotes cell proliferation, migration and invasion, and increased sorafenib resistance in hepatocellular carcinoma by targeting PTEN

MicroRNA-494 (miR-494) acts as an oncomiR and is involved in tumor development, progression and metastasis, and confers resistance to chemotherapeutic drugs by targeting a number of molecules in several human cancers. However, the function and underlying molecular mechanism of miR-494 in hepatocellular carcinoma (HCC) has not been totally elucidated. In the present study, we determined the role played by miR-494 in HCC tissues and HCC cell lines using quantitative RT-PCR (RT-qPCR). The results showed that, miR-494 was significantly upregulated in HCC tissues and HCC cell lines. Additionally, a high miR-494 expression positively correlated with tumor differentiation (P<0.01), TNM stage (P<0.01) and lymph node metastasis (P<0.01). Luciferase reporter assays confirmed that miR-494 binds to the 3'-untranslated region (3'-UTR) of the phosphatase and tensin homolog (PTEN) mRNA and represses its translation. Functional analyses indicated that the upregulation of miR-494 promoted cell viability, migration and invasion, decreased cell apoptosis and cell cycle arrest at G1 stage, and conferred sorafenib resistance to HCC cell lines. Underexpression of PTEN by siRNA significantly attenuated the inhibitory effects of anti-miR-494 on the proliferation, migration and invasion of liver cancer cells. Mechanistic investigations revealed that miR-494 suppressed the expression of PTEN but increased the expression of PI3K and p-Akt, which contribute to the promotion of proliferation, migration and invasion, and increased sorafenib resistance to HCC cell lines. These findings suggested that miR-494 is a potential candidate for HCC therapeutics.

MiR-130a and MiR-374a Function as Novel Regulators of Cisplatin Resistance in Human Ovarian Cancer A2780 Cells

Chemoresistance remains a major obstacle to effective treatment in patients with ovarian cancer, and recently increasing evidences suggest that miRNAs are involved in drug-resistance. In this study, we investigated the role of miRNAs in regulating cisplatin resistance in ovarian cancer cell line and analyzed their possible mechanisms. We profiled miRNAs differentially expressed in cisplatin-resistant human ovarian cancer cell line A2780/DDP compared with parental A2780 cells using microarray. Four abnormally expressed miRNAs were selected (miR-146a,-130a, -374a and miR-182) for further studies. Their expression were verified by qRT-PCR. MiRNA mimics or inhibitor were transfected into A2780 and A2780/DDP cells and then drug sensitivity was analyzed by MTS array. RT-PCR and Western blot were carried out to examine the alteration of MDR1, PTEN gene expression. A total of 32 miRNAs were found to be differentially expressed in A2780/DDP cells. Among them, miR-146a was down-regulated and miR-130a,-374a,-182 were upregulated in A2780/DDP cells, which was verified by RT-PCR. MiR-130a and miR-374a mimics decreased the sensitivity of A2780 cells to cisplatin, reversely, their inhibitors could resensitize A2780/DDP cells. Furthermore, overexpression of miR-130a could increase the MDR1 mRNA and P-gp levels in A2780 and A2780/DDP cells, whereas knockdown of miR-130a could inhibit MDR1 gene expression and upregulate the PTEN protein expression .In a conclusion, the deregulation of miR-374a and miR-130a may be involved in the development and regulation of cisplatin resistance in ovarian cancer cells. This role of miR-130a may be achieved by regulating the MDR1 and PTEN gene expression.

The effects of microRNA on the absorption, distribution, metabolism and excretion of drugs

The importance of genetic factors (e.g. sequence variation) in the absorption, distribution, metabolism, excretion (ADME) and overall efficacy of therapeutic agents is well established. Our ability to identify, interpret and utilize these factors is the subject of much clinical investigation and therapeutic development. However, drug ADME and efficacy are also heavily influenced by epigenetic factors such as DNA/histone methylation and non-coding RNAs [especially microRNAs (miRNAs)]. Results from studies using tools, such as in silico miRNA target prediction, in vitro functional assays, nucleic acid profiling/sequencing and high-throughput proteomics, are rapidly expanding our knowledge of these factors and their effects on drug metabolism. Although these studies reveal a complex regulation of drug ADME, an increased understanding of the molecular interplay between the genome, epigenome and transcriptome has the potential to provide practically useful strategies to facilitate drug development, optimize therapeutic efficacy, circumvent adverse effects, yield novel diagnostics and ultimately become an integral component of personalized medicine.

Has‑miR‑125a and 125b are induced by treatment with cisplatin in nasopharyngeal carcinoma and inhibit apoptosis in a p53‑dependent manner by targeting p53 mRNA

MicroRNA (miRNA) is a class of non‑coding RNA, which targets mRNAs of interest and suppresses its expression by degradation or translational inhibition. miRNA (miR)‑125a and miR‑125b were previously demonstrated to translationally and transcriptionally inhibit the expression of p53. The observed downregulation of the protein level of p53 in cisplatin‑treated patients with nasopharyngeal carcinoma (NPC) indicates the association between cisplatin resistance, miR‑125a and miR‑125b. In the present study, through the detection of the expression levels of miR‑125a and miR‑125b, a significant upregulation of these miRs was demonstrated in cisplatin‑treated patients with NPC. As a consequence, the protein expression level of p53 decreased notably. To confirm the induction of miR‑125a and miR‑125b by treatment with cisplatin, a cisplatin‑resistant TW03 cell model (TW03/DDP) was constructed. As expected, in the TW03/DDP cells, the expression levels of miR‑125a and miR‑125b were upregulated, and this caused downregulation of p53. Ectopic expression of these miRNAs in the TW03 cell model sensitized TW03 to cisplatin by decreasing the protein expression levels of p53, whereas ectopic expression in the antisense oligos of these microRNAs demonstrated the opposite effect. In addition, the present demonstrated that the cisplatin‑induced expression of miR‑125a and miR‑125b inhibited cisplatin‑induced apoptosis in the TW03 cells by decreasing the protein expression levels of p53. Taken together, the present study revealed for the first time, to the best of our knowledge, that induction of the expression of miR‑125a and miR‑125b by treatment with cisplatin resulted in resistance to the cisplatin drug in the NPC cells.

miR-520h is crucial for DAPK2 regulation and breast cancer progression

MicroRNAs (miRNAs) are small RNAs that suppress gene expression by their interaction with 3'untranslated region of specific target mRNAs. Although the dysregulation of miRNAs has been identified in human cancer, only a few of these miRNAs have been functionally documented in breast cancer. Thus, defining the important miRNA and functional target involved in chemoresistance is an urgent need for human breast cancer treatment. In this study, we, for the first time, identified a key role of miRNA 520h (miR-520h) in drug resistance. Through protecting cells from paclitaxel-induced apoptosis, expression of miR-520h promoted the drug resistance of human breast cancer cells. Bioinformatics prediction, compensatory mutation and functional validation further confirmed the essential role of miR-520h-suppressed Death-associated protein kinase 2 (DAPK2) expression, as restoring DAPK2 abolished miR-520h-promoted drug resistance, and knockdown of DAPK2 mitigated cell death caused by the depletion of miR-520h. Furthermore, we observed that higher level of miR-520h is associated with poor prognosis and lymph node metastasis in human breast cancer patients. These results show that miR-520h is not only an independent prognostic factor, but is also a potential functional target for future applications in cancer therapeutics.

Circadian disruption-induced microRNAome deregulation in rat mammary gland tissues

Breast cancer is the most common malignancy affecting women worldwide, and evidence is mounting that circadian-disruption-induced breast cancer is a warranted concern. Although studies on the role of epigenetics have provided valuable insights, and although epigenetics has been increasingly recognized in the etiology of breast cancer, relatively few studies have investigated the epigenetic link between circadian disruption (CD) and breast cancer. Using a proven photoperiod-shifting paradigm, differing degrees of CD, various tissue-extraction time points, and Illumina sequencing, we investigated the effect of CD on miRNA expression in the mammary tissues of a rodent model system. To our knowledge, our results are the first to illustrate CD-induced changes in miRNA expressions in mammary tissues. Furthermore, it is likely that these miRNA expression changes exhibit varying time frames of plasticity linked to both the degree of CD and length of reentrainment, and that the expression changes are influenced by the light and dark phases of the 24-hour circadian cycle. Of the differentially expressed miRNAs identified in the present study, all but one have been linked to breast cancer, and many have predicted circadian-relevant targets that play a role in breast cancer development. Based on the analysis of protein levels in the same tissues, we also propose that the initiation and development of CD-induced breast cancer may be linked to an interconnected web of increased NF-κB activity and increased levels of Tudor-SN, STAT3, and BCL6, with aberrant CD-induced downregulation of miR-127 and miR-146b potentially contributing to this dynamic. This study provides direct evidence that CD induces changes in miRNA levels in mammary tissues with potentially malignant consequences, thus indicating that the role of miRNAs in CD-induced breast cancer should not be dismissed.

[Advances in tumor chemo-resistance regulated by MicroRNA]

Chemotherapy is one of the primary treatment for malignant tumors. Tumor multidrug resistance (MDR) is a major cause of clinical failure of chemotherapy; however the mechanisms of chemo-resistance have not been fully elucidated. Recently, microRNA is one of the new hotspots in life science. MicroRNA regulates the expression of genes and plays roles a series of life events by post-transcriptional regulations, including cell proliferation, apoptosis, fat metabolism, nervous development, hormone secretion, tumor vessels generation, stem cell differentiation, tumor cell invasion and metastasis, and other physiological and pathological processes. Recent studies show that microRNA regulates the expression of multiple genes with high efficiency and specificity. The abnormal regulation of target genes by microRNA is responsible for tumor chemo-resistance, this may be an important component of the complexity of the regulation of chemo-resistance. Therefore, the study of microRNA and tumor drug resistance has profound practical significance. In this review, recent studies of tumor drug resistance, regulation of tumor drug resistance by microRNA, and microRNA as a potential target for tumor drug resistance therapy are reviewed.

The Roles of MicroRNAs in Breast Cancer

MicroRNAs (miRNAs) constitute a large family of small, approximately 20–22 nucleotide, non-coding RNAs that regulate the expression of target genes, mainly at the post-transcriptional level. Accumulating lines of evidence have indicated that miRNAs play important roles in the maintenance of biological homeostasis and that aberrant expression levels of miRNAs are associated with the onset of many diseases, including cancer. In various cancers, miRNAs play important roles in tumor initiation, drug resistance and metastasis. Recent studies reported that miRNAs could also be secreted via small endosome-derived vesicles called exosomes, which are derived from multiple cell types, including dendritic cells, lymphocytes, and tumor cells. Exosomal miRNAs play an important role in cell-to-cell communication and have been investigated as prognostic and diagnostic biomarkers. In this review, we summarize the major findings related to the functions of miRNAs in breast cancer, which is the most frequent cancer in women, and discuss the potential clinical uses of miRNAs, including their roles as therapeutic targets and diagnostic markers.

Down-regulation of miRNA-452 is associated with adriamycin-resistance in breast cancer cells

Adriamycin (ADR) is an important chemotherapeutic agent frequently used in treatment of breast cancer. However, resistance to ADR results in treatment failure in many patients. Recent studies have indicated that microRNAs (miRNAs) may play an important role in such drug-resistance. In the present study, microRNA-452 (miR-452) was found to be significantly down-regulated in adriamycin-resistant MCF-7 cells (MCF-7/ADR) compared with the parental MCF-7 cells by miRNA microarray and real-time quantitative PCR (RT-qPCR). MiR-452 mimics and inhibitors partially changed the adriamycin-resistance of breast cancer cells, as also confirmed by apoptosis assay. In exploring the potential mechanisms of miR-452 in the adriamycin-resistance of breast cancer cells, bioinformatics analysis, RT-qPCR and Western blotting showed that dysregulation of miR-452 played an important role in the acquired adriamycin-resistance of breast cancer, maybe at least in part via targeting insulin-like growth factor-1 receptor (IGF-1R).

Mechanisms of endocrine resistance in breast cancer: an overview of the proposed roles of noncoding RNA

Endocrine therapies such as tamoxifen and aromatase inhibitors are the standard treatment options for estrogen receptor-positive breast cancer patients. However, resistance to these agents has become a major clinical obstacle. Potential mechanisms of resistance to endocrine therapies have been identified, often involving enhanced growth factor signaling and changes in the expression or action of the estrogen receptor, but few studies have addressed the role of noncoding RNA (ncRNA). Two important types of ncRNA include microRNA (miRNA) and long noncoding RNA (lncRNA). miRNAs are small RNA molecules that regulate gene expression via translational inhibition or degradation of mRNA transcripts, while lncRNAs are larger RNA molecules that have been shown to play a role in multiple cellular maintenance functions such as protein scaffolding, chromatin looping, and regulation of mRNA stability. Both miRNA and lncRNA have recently impacted the field of breast cancer research as important pieces in the mechanistic puzzle of the genes and pathways involved in breast cancer development and progression. This review serves as an overview of the roles of miRNA and lncRNA in breast cancer progression and the development of endocrine resistance. Ideally, future experiments in the field should include identification of ncRNAs that could be potential therapeutic targets in endocrine-resistant tumors, as well as ncRNA biomarkers that facilitate more tumor-specific treatment options for endocrine-resistant breast cancer patients.

Regulation of multidrug resistance proteins by genistein in a hepatocarcinoma cell line: impact on sorafenib cytotoxicity

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide. Sorafenib is the only drug available that improves the overall survival of HCC patients. P-glycoprotein (P-gp), Multidrug resistance-associated proteins 2 and 3 (MRP2 and 3) and Breast cancer resistance protein (BCRP) are efflux pumps that play a key role in cancer chemoresistance. Their modulation by dietary compounds may affect the intracellular accumulation and therapeutic efficacy of drugs that are substrates of these transporters. Genistein (GNT) is a phytoestrogen abundant in soybean that exerts its genomic effects through Estrogen-Receptors and Pregnane-X-Receptor (PXR), which are involved in the regulation of the above-mentioned transporters. We evaluated the effect of GNT on the expression and activity of P-gp, MRP2, MRP3 and BCRP in HCC-derived HepG2 cells. GNT (at 1.0 and 10 μM) increased P-gp and MRP2 protein expression and activity, correlating well with an increased resistance to sorafenib cytotoxicity as detected by the methylthiazole tetrazolium (MTT) assay. GNT induced P-gp and MRP2 mRNA expression at 10 but not at 1.0 μM concentration suggesting a different pattern of regulation depending on the concentration. Induction of both transporters by 1.0 μM GNT was prevented by cycloheximide, suggesting translational regulation. Downregulation of expression of the miR-379 by GNT could be associated with translational regulation of MRP2. Silencing of PXR abolished P-gp induction by GNT (at 1.0 and 10 μM) and MRP2 induction by GNT (only at 10 μM), suggesting partial mediation of GNT effects by PXR. Taken together, the data suggest the possibility of nutrient-drug interactions leading to enhanced chemoresistance in HCC when GNT is ingested with soy rich diets or dietary supplements.

Modulation of microRNAs by phytochemicals in cancer: underlying mechanisms and translational significance

MicroRNAs (miRNAs) are small, endogenous noncoding RNAs that regulate a variety of biological processes such as differentiation, development, and survival. Recent studies suggest that miRNAs are dysregulated in cancer and play critical roles in cancer initiation, progression, and chemoresistance. Therefore, exploitation of miRNAs as targets for cancer prevention and therapy could be a promising approach. Extensive evidence suggests that many naturally occurring phytochemicals regulate the expression of numerous miRNAs involved in the pathobiology of cancer. Therefore, an understanding of the regulation of miRNAs by phytochemicals in cancer, their underlying molecular mechanisms, and functional consequences on tumor pathophysiology may be useful in formulating novel strategies to combat this devastating disease. These aspects are discussed in this review paper with an objective of highlighting the significance of these observations from the translational standpoint.

DNA/RNA chimera templates improve the emission intensity and target the accessibility of silver nanocluster-based sensors for human microRNA detection

In recent years microRNAs (miRNAs) have been established as important biomarkers in a variety of diseases including cancer, diabetes, cardiovascular disease, aging, Alzheimer's disease, asthma, autoimmune disease and liver diseases. As a consequence, a variety of monitoring methods for miRNAs have been developed, including a fast and simple method for miRNA detection by exploitation of the unique photoluminescence of DNA-templated silver nanoclusters (DNA/AgNCs). To increase the versatility of the AgNC-based method, we have adopted DNA/RNA chimera templates for AgNC-based probes, allowing response from several human miRNAs which are hardly detectable with DNA-based probes. Here, we demonstrate in detail the power of DNA/RNA chimera/AgNC probes in detecting two human miRNAs, let-7a and miR-200c. The DNA/RNA chimera-based probes are highly efficient to determine the level of miRNAs in several human cell lines.

MicroRNA-195 chemosensitizes colon cancer cells to the chemotherapeutic drug doxorubicin by targeting the first binding site of BCL2L2 mRNA

The mechanisms underlying doxorubicin (Dox) resistance in colon cancer cells are not fully understood. MicroRNA (miRNA) play important roles in tumorigenesis and drug resistance. However, the relationship between miRNA and Dox resistance in colon cancer cells has not been previously explored. In this study, we utilized microRNA array and real-time PCR to verify that miR-127, miR-195, miR-22, miR-137 were significantly down-regulated, while miR-21, miR-592 were up-regulated in both HT29/DOX and LOVO/DOX cell lines. In vitro cell viability assay showed that knockdown of miR-195 in HT29 and LOVO cells caused a marked inhibition of Dox-induced cytotoxicity. Moreover, we explored that miR-195 is involved in repression of BCL2L2 expression through targeting its 3'-untranslated region, especially the first binding site within its mRNA. Furthermore, down-regulation of miR-195 conferred DOX resistance in parental cells and reduced cell apoptosis activity, while over-expression of miR-195 sensitized resistant cells to DOX and enhanced cell apoptosis activity, all of which can be partly rescued by BCL2L2 siRNA and cDNA expression. These results may have implications for therapeutic strategies aiming to overcome colon cancer cell resistance to Dox.

Epigenetic Regulation of miRNAs and Breast Cancer Stem Cells

MicroRNAs have emerged as important targets of chemopreventive strategies in breast cancer. We have found that miRNAs are dysregulated at an early stage in breast cancer, in non-malignant Ductal Carcinoma In Situ. Many dietary chemoprevention agents can act by epigenetically activating miRNA-signaling pathways involved in tumor cell proliferation and invasive progression. In addition, many miRNAs activated via chemopreventive strategies target cancer stem cell signaling and prevent tumor progression or relapse. Specifically, we have found that miRNAs regulate DCIS stem cells, which may play important roles in breast cancer progression to invasive disease. We have shown that chemopreventive agents can directly inhibit DCIS stem cells and block tumor formation in vivo, via activation of tumor suppressor miRNAs.

MDR1 will play a key role in pharmacokinetic changes under hypoxia at high altitude and its potential regulatory networks

Some newest studies indicated that drug transports may play the key role in pharmacokinetics changes under hypoxia at high altitude; MDR1 is now known to affect the disposition of many administered drugs and make a major contribution to absorption, distribution, metabolism, excretion. Different expression of MDR1 is frequently found in different normal tissues and tumor cells; it is important to better understand how MDR1 is regulated under hypoxia, which seems to be a complex and highly controlled process. Several signaling pathways and transcription factors have been described as being involved in the regulation of MDR1 expression, such as MAPK/ERK, nuclear factor-kappaB, hypoxia-inducible factor-1a, pregnane × receptor, constitutive androstane receptor and microRNA. Recently, researches have been increasingly appreciating long non-coding RNAs (lncRNAs) as an integral component of gene regulatory networks. lncRNAs play crucial roles in various biological processes ranging from epigenetic gene regulation, transcriptional control, post-transcriptional regulation, pre-mRNA processing and nuclear organization. A last recent research showed that H19 gene non-coding RNA is believed to induce P-glycoprotein expression under hypoxia.

Cellular communication via microparticles: role in transfer of multidrug resistance in cancer

Multidrug resistance (MDR) continues to be a major impediment to the successful treatment of cancer. The two efflux transporters, P-glycoprotein (P-gp) and MRP1 are major contributors to cancer MDR clinically. The upregulation of P-gp leading to MDR was initially understood to occur via pre- and post-transcriptional mechanisms only. However, we demonstrated that microparticles mediate the intercellular exchange and trafficking of bioactive material, including functional P-gp and selected modulatory miRNAs. This exchange of P-gp leads to the dissemination of MDR within a cancer cell population. These findings have significant implications in understanding the cellular basis governing the intercellular acquisition of deleterious traits in cancers, serving to substantially advance our understanding of the molecular basis of the emergence of MDR in cancer clinically.

Combination of microRNA therapeutics with small-molecule anticancer drugs: mechanism of action and co-delivery nanocarriers

MicroRNAs (miRNAs) regulate multiple molecular pathways vital for the hallmarks of cancer with a high degree of biochemical specificity and potency. By restoring tumor suppressive miRNAs or ablating oncomiRs, miRNA-based therapies can sensitize cancer cells to conventional cytotoxins and the molecularly targeted drugs by promoting apoptosis and autophagy, reverting epithelial-to-mesenchymal transition, suppressing tumor angiogenesis, and downregulating efflux transporters. The development of miRNA-based therapeutics in combination with small-molecule anticancer drugs provides an unprecedented opportunity to counteract chemoresistance and improve treatment outcome in a broad range of human cancers. This review summarizes the mechanisms and advantages for the combination therapies involving miRNAs and small-molecule drugs, as well as the recent advances in the co-delivery nanocarriers for these agents.

A summary for molecular regulations of miRNAs in breast cancer

BACKGROUND

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer-related death among women worldwide. MicroRNAs (miRNAs) are naturally-occurring, non-coding small RNA molecules that can modulate protein coding-genes, which makes it contributing to nearly all the physiological and pathological processes. Progression of breast cancer and resistance to endocrine therapies have been attributed to the possibility of hormone-responsive miRNAs involved in the regulation of certain signaling pathways.

METHODOLOGY

This review introduces better understanding of miRNAs to provide promising advances for treatment. miRNAs have multiple targets, and they were found to regulate different signaling pathways; consequently it is important to characterize their mechanisms of action and their cellular targets in order to introduce miRNAs as novel and promising therapies.

RESULTS

This review summarizes the molecular mechanisms of miRNAs in TGF-beta signaling, apoptosis, metastasis, cell cycle, ER-signaling, and drug resistance.

CONCLUSION

Finally, miRNAs will be introduced as promising molecules to be used in the fight against breast cancer and its developed drug resistance.

MicroRNAs in colorectal cancer: small molecules with big functions

Colorectal cancer (CRC) is the third most lethal malignancy, with pathogenesis intricately dependent upon microRNAs (miRNAs). miRNAs are short, non-protein coding RNAs, targeting the 3'-untranslated regions (3'-UTR) of certain mRNAs. They usually serve as tumor suppressors or oncogenes, and participate in tumor phenotype maintenance. Therefore, miRNAs consequently regulate CRC carcinogenesis and other biological functions, including apoptosis, development, angiogenesis, migration, and proliferation. Due to its differential expression and distinct stability, miRNAs are regarded as molecular biomarkers (for diagnosis/prognosis) and therapeutic targets for CRC. Recently, a remarkable number of miRNAs have been discovered with implications via incompletely understood mechanisms in CRC. As further study of relevant miRNAs continues, it is hopeful that novel miRNA-based therapeutic strategies may be available for CRC patients in the future.

MicroRNAs and their relevance to ABC transporters

MicroRNAs (miRNAs) are small noncoding RNAs, which regulate the expression of their target genes post-transcriptionally by RNA interference. They are involved in almost all cellular processes, including proliferation, differentiation, apoptosis, cell survival and the maintenance of tissue specificity. Recent findings also suggest that efflux pumps of the ABC (ATP-binding cassette) transporter family are subject to miRNA-mediated gene regulation. Moreover, it seems that ABC transporters are embedded in a concerted and miRNA-guided network of concurrently regulated proteins that mediate altered drug transport and cell survival in changing environmental conditions. In this review, we summarize recent findings of miRNAs interacting with ABC transporters, which have been connected with drug distribution as well as with drug resistance. Additionally, we specify findings of complex miRNA-protein pathways conferring increased drug export and cell survival.

An Introspective Update on the Influence of miRNAs in Breast Carcinoma and Neuroblastoma Chemoresistance

Chemoresistance to conventional cytotoxic drugs may occur in any type of cancer and this can either be inherent or develop through time. Studies have linked this acquired resistance to the abnormal expression of microRNAs (miRNAs) that normally silence genes. At abnormal levels, miRNAs can either gain ability to silence tumour suppressor genes or else lose ability to silence oncogenes. miRNAs can also affect pathways that are involved in drug metabolism, such as drug efflux pumps, resulting in a resistant phenotype. The scope of this review is to provide an introspective analysis on the specific niches of breast carcinoma and neuroblastoma research.

The expression and function of miRNA-451 in osteosarcoma

MicroRNA-451 has been proven down-regulated in many human malignancies and correlated with tumor progression. However, its expression and clinical significance in osteosarcoma is still unclear. Thus, the aim of this study was to explore the effects of miR-451 in osteosarcoma tumorigenesis and development. The expression level of miR-451 was quantified by quantitative real-time reverse-transcriptase-polymerase chain reaction in primary osteosarcoma tissues and osteosarcoma cell lines. MTT, flow cytometric, and scratch migration assay were used to test the proliferation, apoptosis, and migration of miR-451 transfection osteosarcoma cells, and a mouse model was used to investigate tumorigenesis. The expression levels of miR-451 in osteosarcoma tissues were significantly lower than those in corresponding noncancerous bone tissues (P < 0.001). In addition, miR-451 down-regulation more frequently occurred in osteosarcoma specimens with advanced clinical stage (P < 0.001), positive distant metastasis (P = 0.015), and poor response to neoadjuvant chemotherapy (P < 0.001). Univariate and multivariate analysis identified low miR-451 expression as an unfavorable prognostic factor for both overall and disease-free survival. After miR-451 transfection, cell proliferation, migration, and tumorigenesis in the osteosarcoma cells were significantly inhibited and cell apoptosis was increased. These findings indicate that miR-451 may act not only as a novel diagnostic and prognostic marker, but also as a potential target for molecular therapy of osteosarcoma.

MiR-222 targeted PUMA to improve sensitization of UM1 cells to cisplatin

microRNAs have been shown to play critical roles in regulating the chemosensitivity of cancer cells. As a member of the oncogenic miRNAs (oncomiRs), miR-222 has been reported to drive the oncogenesis of many types of malignancies. However, little is known concerning the specific role of miR-222 in human oral squamous cell carcinoma (OSCC). The present study explored the role and mechanism of miR-222 in increasing the expression of p53 up-regulated modulator of apoptosis (PUMA) and enhancing the sensitivity of OSCC to cisplatin (CDDP). Results showed that antisense (As)-miR-222 inhibits the expression of miR-222. In contrast, PUMA was dramaticallyup-regulated. IC₅₀ values were significantly decreased in cells treated with As-miR-222 combined with CDDP, to a greater extent than in cells treated with CDDP alone. Furthermore, As-miR-222 enhanced apoptosis and inhibited the invasiveness of UM1 cells. Analysis of the above data suggested that, in UM1 cells, there might be a regulatory loop between miR-222 and PUMA, and that miR-222 inhibition increased the chemosensitivity to CDDP. These findings demonstrated that down-regulation of miR-222 could enhance the chemosensitivity of human OSCC cells to CDDP, and that the combination of As-miR-222 and CDDP could be an effective therapeutic strategy by boosting the expression of PUMA for controlling the growth of OSCC.

Targeting of miR34a-NOTCH1 axis reduced breast cancer stemness and chemoresistance

Human breast cancers include cancer stem cell populations as well as nontumorigenic cancer cells. Breast cancer stem cells have self-renewal capability and are resistant to conventional chemotherapy. miRNAs regulate the expression of many target genes; therefore, dysregulation of miRNAs has been associated with the pathogenesis of human diseases, including cancer. However, a role for miRNA dysregulation in stemness and drug resistance has yet to be identified. Members of the miR34 family are reportedly tumor-suppressor miRNAs and are associated with various human cancers. Our results confirm that miR34a expression was downregulated in MCF7/ADR cells compared with MCF7 cells. We hypothesized that this reduction was due to the p53 (TP53) mutation in MCF7/ADR cells. In this study, we found that primary and mature miR34a were suppressed by treatment with p53 RNAi or the dominant-negative p53 mutant in MCF7 cells. Ectopic miR34a expression reduced cancer stem cell properties and increased sensitivity to doxorubicin treatment by directly targeting NOTCH1. Furthermore, tumors from nude mice treated with miR34a were significantly smaller compared with those of mice treated with control lentivirus. Our research suggests that the ectopic expression of miR34a represents a novel therapeutic approach in chemoresistant breast cancer treatment.

MicroRNA-106a confers cisplatin resistance in non-small cell lung cancer A549 cells by targeting adenosine triphosphatase-binding cassette A1

MicroRNAs (miRNAs) have been discovered to have pivotal roles in regulating the drug resistance of various types of human cancer, including cisplatin (DDP) resistance in non-small cell lung cancer (NSCLC). Fewer studies have explored the roles of miR-106a in NSCLC-cell resistance to DDP and its precise molecular mechanism has remained elusive. In the present study, whether miR-106a was able to mediate resistance of the lung cancer cell line A549 to DDP was investigated. Reverse transcription quantitative polymerase chain reaction was used to analyze miR-106a mRNA expression levels. miR-106a expression levels were upregulated in the DDP-resistant cell line A549/DDP compared with its parental cell line, A549. miR-106a-transfection induced DDP-resistance in A549 cells, while repression of miR-106a by anti-miR-106a in A549/DDP resulted in enhanced DDP cytotoxicity. Furthermore, it was discovered that the mechanism of miR-106a-induced DDP resistance involved the expression of adenosine triphosphatase-binding cassette, sub-family A, member 1 (ABCA1), as indicated by transfection of cells with short interfering RNA-ABCA1. The results of the present study suggested a novel mechanism underlying DDP-resistance in NSCLC.

miRNA27a is a biomarker for predicting chemosensitivity and prognosis in metastatic or recurrent gastric cancer

We previously identified five miRNAs (miR-1, miR-20a, miR-27a, miR-34a, and miR-423-5p) that are up-regulated in gastric cancer. The goal of this study was to investigate the value of these miRNAs as potential biomarkers for predicting chemosensitivity and prognosis in metastatic or recurrent gastric cancer patients who received first-line chemotherapy. A total of 82 patients with metastatic or recurrent GC receiving first-line chemotherapy were included in our study. The expression levels of the five miRNAs were evaluated using hydrolysis probe-based stem-loop quantitative reverse transcription polymerase chain reaction (qRT-PCR) in individual samples before first-line chemotherapy. Patients receiving first-line chemotherapy with fluoropyrimidine combined with oxaliplatin or paclitaxel were chosen for the chemosensitivity analysis. The relationships between expression of the five-miRNAs and clinicopathological parameters, response to chemotherapy and prognosis were analyzed statistically. Patients with higher miRNA1 expression levels tended to have a higher rate of liver metastasis, and higher miRNA34a expression levels occurred more frequently in males (P = 0.022). The expression of the remaining three miRNAs showed no obvious relationship to any of the clinicopathological features. The partial response rates of the patients with high miRNA1 expression and low miRNA1 expression were 11.1% and 23.1%, respectively (P = 0.048). Similar results were observed for miRNA27a (the partial response rate was 7.7% vs. 25.9%, P = 0.018). Patients with up-regulated miRNA27a expression had a significantly worse overall survival (OS) than patients with lower miRNA27a expression (P = 0.024). In patients with MRGC, miRNA27a is a potential biomarker for predicting resistance to fluoropyrimidine-based chemotherapy and a novel prognostic marker for gastric cancer.

MicroRNAs: Promising chemoresistance biomarkers in gastric cancer with diagnostic and therapeutic potential

Gastric cancer (GC) is the fourth most common cancer worldwide and ranks second in global cancer mortality statistics. Perioperative chemotherapy plays an important role in the management and treatment of advanced stage disease. However, response to chemotherapy varies widely, with some patients presenting no or only minor response to treatment. Hence, chemotherapy resistance is a major clinical problem that impacts on outcome. Unfortunately, to date there are no reliable biomarkers available that predict response to chemotherapy before the start of the treatment, or that allow modification of chemotherapy resistance. MicroRNAs (miRNAs) could provide an answer to this problem. miRNAs are involved in the initiation and progression of a variety of cancer types, and there is evidence that miRNAs impact on resistance towards chemotherapeutic drugs as well. This current review aims to provide an overview about the potential clinical applicability of miRNAs as biomarkers for chemoresistance in GC. The authors focus in this context on the potential of miRNAs to predict sensitivity towards different chemotherapeutics, and on the potential of miRNAs to modulate sensitivity and resistance towards chemotherapy in GC.

Regulation of BGC-823 cell sensitivity to adriamycin via miRNA-135a-5p

MicroRNAs (miRNAs) play an important role in the genesis and development of gastric cancer. In the present study, we determined whether miRNA-135a-5p expression was increased in gastric cancer compared with adjacent non-tumor tissues using 20 pairs of gastric cancer and para-carcinoma tissue samples which were assessed via microarray and bioinformatics analysis, and western blotting. The protein content detection showed that miRNA‑135a-5p expression was inversely correlated with AP-2α. Bioinformatics analysis revealed that AP-2α contains a putative miRNA-135a-5p target, which was confirmed as a direct target using the 3'-UTR luciferase reporter system. Additionally, an increase and decrease of miRNA-135a-5p inhi-bited or impaired adriamycin-induced apoptosis in BGC-823 cells (p<0.05, compared with the group without gene intervention), respectively. Luciferase reporter experiments confirmed that AP-2α bound to the BCL-2 promoter and affected its transcription. Therefore, miRNA-135a-5p increased BCL-2 via AP-2α and consequently enhanced cell resistance to apoptosis. This newly identified miRNA-135a-5p-AP-2α-BCL-2 pathway provides insight for the treatment of gastric cancer and solution for insensitivity of gastric cancer to chemotherapy drugs.

Serum miR-19a predicts resistance to FOLFOX chemotherapy in advanced colorectal cancer cases

BACKGROUND

Colorectal cancer is the fourth most common cancer worldwide and the second leading cause of cancer-related death. FOLFOX is the most common regimen used in the first-line chemotherapy in advanced colorectal cancer, but only half of the patients respond to this regimen and we have almost no clue in predicting resistance in such first-line application.

METHODS

To explore the potential molecular biomarkers predicting the resistance of FOLFOX regimen as the first-line treatment in advanced colorectal cancer, we screened microRNAs in serum samples from drug-responsive and drug-resistant patients by microarrays. Then differential microRNA expression was further validated in an independent population by reverse transcription and quantitative real- time PCR.

RESULTS

62 microRNAs expressing differentially with fold-change >2 were screened out by microarray analysis. Among them, 5 (miR-221, miR-222, miR-122, miR-19a, miR-144) were chosen for further validation in an independent population (N=72). Our results indicated serum miR-19a to be significantly up-regulated in resistance-phase serum (p=0.009). The ROC curve analysis showed that the sensitivity of serum miR-19a to discriminate the resistant patients from the response ones was 66.7%, and the specificity was 63.9% when the AUC was 0.679. We additionally observed serum miR-19a had a complementary value for cancer embryonic antigen (CEA). Stratified analysis further revealed that serum miR-19a predicted both intrinsic and acquired drug resistance.

CONCLUSIONS

Our findings confirmed aberrant expression of serum miR-19a in FOLFOX chemotherapy resistance patients, suggesting serum miR-19a could be a potential molecular biomarker for predicting and monitoring resistance to first-line FOLFOX chemotherapy regimens in advanced colorectal cancer patients.

MiR-451 increases radiosensitivity of nasopharyngeal carcinoma cells by targeting ras-related protein 14 (RAB14)

Radioresistance severely impedes the treatment of nasopharyngeal carcinoma (NPC). Recent evidence has shown that the abnormal expression of microRNAs (miRNAs) contributes to radiosensitivity. The aim of this study, therefore, was to investigate whether expression of the miRNAs correlated with radiosensitivity in the context of NPC. Quantitative reverse transcription polymerase chain reaction (RT-PCR) was used to quantify miR-451 expression in two representative NPC cell lines. The role of miR-451 in NPC radiosensitivity was analyzed using a colony formation assay and an immunofluorescence assay with overexpression of miR-451 in NPC cells. Luciferase reporter assays, RT-PCR, and Western blot were performed to confirm the target of miR-451. High levels of miR-451 expression enhanced radiosensitivity in NPC cells by inhibiting the repair of irradiation-induced double-strand breaks (DSBs) and increasing apoptosis. The results also demonstrated that miR-451 directly targeted ras-related protein 14 (RAB14). Downregulation of RAB14 partially replicated the miR-451-mediated DSBs induced by ionizing radiation (IR). MiR-451 could be a potential target for enhancing radiosensitivity of NPC cells by targeting RAB14.

Targeting the microRNA-regulating DNA damage/repair pathways in cancer

INTRODUCTION

Maintenance of genome stability requires the integrity of the DNA repair machinery. DNA damage response (DDR) determines cell fate and regulates the expression of microRNAs (miRNAs), which in turn may also regulate important components of the DNA repair machinery.

AREAS COVERED

In this review, we describe the bidirectional connection between miRNAs and DDR and their link with important biological functions such as, DNA repair, cell cycle and apoptosis in cancer. Furthermore, we highlight the potential implications of recent findings on miRNA/DDR in determining chemotherapy response in cancer patients, and the use of these biomarkers for novel potential therapeutic approaches.

EXPERT OPINION

Defects in the DDR and deregulation of miRNAs are important hallmarks of human cancer. A full understanding of the mechanisms underlying the connection between miRNAs and DDR/DNA repair pathways will positively impact our knowledge on human tumor biology and on different responses to distinct drugs. Specific miRNAs interact with distinct DDR components and are promising targets for enhancing the effects of, and/or to overcome the resistance to, conventional chemotherapeutic agents. Finally, the development of innovative tools to deliver miRNA-targeting oligonucleotides may represents novel types of cancer interventions in clinic.

MicroRNA expression profile of bromocriptine-resistant prolactinomas

MicroRNAs (miRNA) have been implicated in the resistance of tumors to chemotherapy. However, little is known about miRNA expression in bromocriptine-resistant prolactinomas. In this study, 23 prolactinoma samples were classified as bromocriptine-sensitive or -resistant according to the clinical definition of bromocriptine resistance, and their miRNA expression profiles were determined using Solexa sequencing. We found 41 miRNAs that were differentially expressed between the two groups, and 12 of these were validated by stem-loop qRT-PCR. Hsa-mir-93, hsa-mir-17, hsa-mir-22*, hsa-mir-126*, hsa-mir-142-3p, hsa-mir-144*, hsa-mir-486-5p, hsa-mir-451, and hsa-mir-92a were up-regulated and hsa-mir-30a, hsa-mir-382, and hsa-mir-136 were down-regulated in bromocriptine-resistant prolactinomas in comparison with bromocriptine-sensitive prolactinomas. Furthermore, silencing of mir-93 significantly increased the sensitivity of MMQ cells to dopamine agonist treatment. Mir-93 directly affected p21 expression in MMQ cells by targeting the 3'-UTR. Our study is the first to identify a miRNA expression profile associated with bromocriptine-resistant prolactinoma.

Enforced expression of miR-101 enhances cisplatin sensitivity in human bladder cancer cells by modulating the cyclooxygenase-2 pathway

Alterations in microRNA (miRNA) expression have been shown to be involved in the tumor response to chemotherapy. However, the possible role of miR‑101 in cisplatin sensitivity in human bladder cancer cells remains unclear. In this study, quantitative polymerase chain reaction and western blotting were utilized to determine the expression profiles of miR‑101 and cyclooxygenase‑2 (COX‑2) in human bladder cancer cells. The effect of miR‑101 and small interfering RNA (siRNA) against COX‑2 on cell viability was evaluated using MTT assays, and apoptosis levels were determined using fluorescence‑activated cell sorting analysis of Annexin V/propidium iodide‑stained cells. Luciferase reporter plasmids were constructed to confirm direct targeting. This study found that the expression of miR‑101 was downregulated in the cisplatin‑resistant cell line T24/CDDP as compared with that in the parental line, T24. Furthermore, overexpression of miR‑101 significantly increased the anti‑proliferative effects and apoptosis induced by cisplatin, whereas knockdown of miR‑101 significantly decreased the anti‑proliferative effects and apoptosis induced by cisplatin. In addition, downregulation of miR‑101 induced cell survival and cisplatin resistance through the upregulation of COX‑2 expression. Luciferase gene reporter assays confirmed that COX‑2 was a direct target gene of miR‑101. Inhibition of COX‑2 using COX‑2 siRNA abrogated the cisplatin resistance induced by miR‑101 downregulation. These results suggest that miR‑101 may provide a novel mechanism for understanding cisplatin resistance in bladder cancer by modulating the COX‑2 pathway.

MicroRNAs as key regulators of xenobiotic biotransformation and drug response

In the last decade, microRNAs have emerged as key factors that negatively regulate mRNA expression. It has been estimated that more than 50% of protein-coding genes are under microRNA control and each microRNA is predicted to repress several mRNA targets. In this respect, it is recognized that microRNAs play a vital role in various cellular and molecular processes and that, depending on the biological pathways in which they intervene, distorted expression of microRNAs can have serious consequences. It has recently been shown that specific microRNA species are also correlated with toxic responses induced by xenobiotics. Since the latter are primarily linked to the extent of detoxification in the liver by phase I and phase II biotransformation enzymes and influx and efflux drug transporters, the regulation of the mRNA levels of this particular set of genes through microRNAs is of great importance for the overall toxicological outcome. Consequently, in this paper, an overview of the current knowledge with respect to the complex interplay between microRNAs and the expression of biotransformation enzymes and drug transporters in the liver is provided. Nuclear receptors and transcription factors, known to be involved in the transcriptional regulation of these genes, are also discussed.

Barriers to drug delivery in solid tumors

Over the last decade, significant progress has been made in the field of drug delivery. The advent of engineered nanoparticles has allowed us to circumvent the initial limitations to drug delivery such as pharmacokinetics and solubility. However, in spite of significant advances to tumor targeting, an effective treatment strategy for malignant tumors still remains elusive. Tumors possess distinct physiological features which allow them to resist traditional treatment approaches. This combined with the complexity of the biological system presents significant hurdles to the site-specific delivery of therapeutic drugs. One of the key features of engineered nanoparticles is that these can be tailored to execute specific functions. With this review, we hope to provide the reader with a clear understanding and knowledge of biological barriers and the methods to exploit these characteristics to design multifunctional nanocarriers, effect useful dosing regimens and subsequently improve therapeutic outcomes in the clinic.

MicroRNAs in the diagnosis and prognosis of breast cancer and their therapeutic potential (review)

MicroRNAs (miRNAs) are non-coding single-stranded RNAs in eukaryotes and are involved in the regulation of the post-transcriptional expression of specific genes. Studies have demonstrated that miRNAs play important roles in regulating diverse physiological events such as cell proliferation, differentiation and embryo development. In recent decades, considerable attention has been given to the relationship between miRNA and the pathology of cancers, particularly breast cancer. A large number of miRNAs have been shown to be involved in the pathophysiology of breast cancer. Studies have revealed that some miRNAs might regulate the oncogenesis and growth of breast cancer by acting on breast tumor-initiating cells or other downstream targets. Studies have also demonstrated that some miRNAs act as suppressors of metastasis or promoters of breast cancer. Additionally, certain miRNAs are involved in cancer tissue angiogenesis (one of the most important mechanisms of tumor growth and metastasis). Clinical evidence indicates that some miRNAs can be used as diagnostic and prognostic biomarkers for breast cancer due to their significantly increased or decreased expression in cancer tissue. Moreover, certain miRNAs may have therapeutic potential for targeting ER-α/HER, breast tumor-initiating cells and metastasis as well as multidrug resistance. In this review, we discuss the relationship between miRNAs and the pathogenesis of breast cancer as well as the progress of current research on the miRNA-specific diagnosis, prognosis and treatment of breast cancer.