miRNAs for the detection of multidrug resistance: overview and perspectives

Evaluation of P-glycoprotein-targeting circulating microRNAs as peripheral biomarkers for medically intractable epilepsy

Background

Early diagnosis of medically intractable epilepsy is challenging in clinical work. P-glycoprotein (P-gp) is one of the most important multidrug efflux transporters, which has been demonstrated to contribute to the drug resistance of intractable epilepsy. The present study was aimed to explore the diagnostic value of microRNAs (miRNAs) targeting P-gp for medically intractable epilepsy.

Methods

Thirty-six patients with intractable epilepsy and 36 epilepsy patients responsive to anti-epilepsy drugs, who visited Jinshan Hospital of Fudan University from September 2014 to September 2016, were enrolled in this study. Clinical information of the patients was obtained by retrospectively reviewing medical records. MiRNAs with differential serum expression between the two groups of patients were detected by microarray assay. Meanwhile, miRNAs that were confirmed to regulate P-gp in vitro by western blot were selected for further validation. In the validation phase, reverse transcription quantitative PCR (RT-qPCR) was conducted to confirm the differential expression of the candidate miRNAs in the epilepsy cohorts. Receiver operating characteristic (ROC) curve analysis was carried out to evaluate the diagnostic value of the miRNAs for intractable epilepsy.

Results

Three miRNAs including miR-6514-3p, miR-6076-5p, and miR-6855-3p were identified to be candidate miRNAs by microarray assay. The results of western blotting validated that miR-146a-5p and miR-138-5p could regulate P-gp expression in vitro, so they were included in the candidate miRNAs for further validation. In the validation phase, the results of RT-qPCR indicated that compared with drug-responsive patients, the patients with intractable epilepsy showed decreased level of miR-138-5p and increased level of miR-146a-5p. The results of ROC curve analysis indicated that miR-138-5p (AUC = 0.877) and miR-146a-5p (AUC = 0.866) had high diagnostic value for intractable epilepsy. In addition, the miR-panel composed of miR-138-5p and miR-146a-5p showed higher diagnostic value (AUC = 0.926) than the miRNAs selected by microarray assay.

Conclusions

Our results indicated that the dysregulated miR-138-5p and miR-146a-5p which target P-gp expression have high potential as peripheral biomarkers for medically intractable epilepsy.

Predictive Biomarkers for a Personalized Approach in Resectable Pancreatic Cancer

The mainstay treatment for patients with immediate resectable pancreatic cancer remains upfront surgery, which represents the only potentially curative strategy. Nevertheless, the majority of patients surgically resected for pancreatic cancer experiences disease relapse, even when a combination adjuvant therapy is offered. Therefore, aiming at improving disease free survival and overall survival of these patients, there is an increasing interest in evaluating the activity and efficacy of neoadjuvant and perioperative treatments. In this view, it is of utmost importance to find biomarkers able to select patients who may benefit from a preoperative therapy rather than upfront surgical resection. Defined genomic alterations and a dynamic inflammatory microenvironment are the major culprits for disease recurrence and resistance to chemotherapeutic treatments in pancreatic cancer patients. Signal transduction pathways or tumor immune microenvironment could predict early recurrence and response to chemotherapy. In the last decade, distinct molecular subtypes of pancreatic cancer have been described, laying the bases to a tailored therapeutic approach, started firstly in the treatment of advanced disease. Patients with homologous repair deficiency, in particular with mutant germline BRCA genes, represent the first subgroup demonstrating to benefit from specific therapies. A fraction of patients with pancreatic cancer could take advantage of genome sequencing with the aim of identifying possible targetable mutations. These genomic driven strategies could be even more relevant in a potentially curative setting. In this review, we outline putative predictive markers that could help in the next future in tailoring the best therapeutic strategy for pancreatic cancer patients with a potentially curable disease.

MiR-873-5p: A Potential Molecular Marker for Cancer Diagnosis and Prognosis

miR-873 is a microRNA located on chromosome 9p21.1. miR-873-5p and miR-873-3p are the two main members of the miR-873 family. Most studies focus on miR-873-5p, and there are a few studies on miR-873-3p. The expression level of miR-873-5p was down-regulated in 14 cancers and up-regulated in 4 cancers. miR-873-5p has many targeted genes, which have unique molecular functions such as catalytic activity, transcription regulation, and binding. miR-873-5p affects cancer development through the PIK3/AKT/mTOR, Wnt/β-Catenin, NF-κβ, and MEK/ERK signaling pathways. In addition, the target genes of miR-873-5p are closely related to the proliferation, apoptosis, migration, invasion, cell cycle, cell stemness, and glycolysis of cancer cells. The target genes of miR-873-5p are also related to the efficacy of several anti-cancer drugs. Currently, in cancer, the expression of miR-873-5p is regulated by a variety of epigenetic factors. This review summarizes the role and mechanism of miR-873-5p in human tumors shows the potential value of miR-873-5p as a molecular marker for cancer diagnosis and prognosis.

The Role of Circulating MicroRNAs in Patients with Early-Stage Pancreatic Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is increasing in incidence and is still associated with a high rate of mortality. Only a minority of patients are diagnosed in the early stage. Radical surgery is the only potential curative procedure. However, radicality is reached in 20% of patients operated on. Despite the multidisciplinary approach in resectable tumors, early tumor recurrences are common. Options on how to select optimal candidates for resection remain limited. Nevertheless, accumulating evidence shows an important role of circulating non-coding plasma and serum microRNAs (miRNAs), which physiologically regulate the function of a target protein. miRNAs also play a crucial role in carcinogenesis. In PDAC patients, the expression levels of certain miRNAs vary and may modulate the function of oncogenes or tumor suppressor genes. As they can be detected in a patient's blood, they have the potential to become promising non-invasive diagnostic and prognostic biomarkers. Moreover, they may also serve as markers of chemoresistance. Thus, miRNAs could be useful for early and accurate diagnosis, prognostic stratification, and individual treatment planning. In this review, we summarize the latest findings on miRNAs in PDAC patients, focusing on their potential use in the early stage of the disease.

miR-485's anti-drug resistant epilepsy effects by regulating SV2A/PSD-95 and targeting ABCC1 and neuronal signaling-transduction proteins in hippocampus of rats

AIM

Drug-resistant epilepsy (DRE), most subsequently developing refractory epilepsy, causes a significant burden to the society. microRNAs have been demonstrated as key regulators and therapeutic targets in epilepsy. Accordingly, the aim of the present study was to test whether miR-485 could be a potential target for DRE.

METHODS AND RESULTS

An in vivo DRE model was developed in Sprague-Dawley rats by lithium chloride-pilocarpine and screened by antiepileptic drugs. We found that miR-485-5p in hippocampus was significant downregulated at early stage and recovered to normal level at late stage of DRE. Overexpression of miR-485-5p in dentate gyrus (DG) of hippocampus in DRE rats could significantly decrease the frequency of seizures and the numbers of epileptiform spikes of hippocampal DG neuron, and could specifically decrease SV2A expression without affecting PSD-95 expression in DG. Furthermore, miR-485-5p overexpression could significantly downregulate the expression of efflux transporter related to multidrug resistance (ABCC1) in hippocampus at late stage of DRE. Finally, a specific expression pattern of neuronal signaling-transduction proteins (LRP4, MDM4, p53, and TMBIM1) for DRE was observed, and miR-485-5p overexpression could modulate these proteins' expression levels toward normal in hippocampus both at early and late stage of DRE.

CONCLUSION

Collectively, these results suggest that miR-485 was a potential target for anti-DRE, and this effects might be partially via miR-485-5p/homeostatic-synaptic plasticity-molecule axis and/or targeting efflux transporter (ABCC1) and other neuronal signaling-transduction proteins (LRP4, MDM4, p53, and TMBIM1).

MiRNAs directly targeting the key intermediates of biological pathways in pancreatic cancer

Pancreatic Cancer (PC) is a severe form of malignancy all over the world. Delayed diagnosis and chemoresistance are the major factors contributing to its poor prognosis and high mortality rate. The genetic and epigenetic regulations of biological pathways further complicate the progression and chemotherapy response to this cancer. MicroRNAs (MiRNAs) involvement has been observed in all types of cancers including PC. The understanding and categorization of miRNAs according to their specific targets are very important to develop early diagnostic and therapeutic interventions. The current review, emphasizing recent research findings, has categorized miRNAs that directly target the potential onco-factors that act as central converging signal-nodes in five major cancer-related pathways i.e., MAPK/ERK, JAK/STAT, Wnt/β-catenin, AKT/mTOR, and TGFβ in PC. The therapeutic perspectives of miRNAs in PC have also been discussed. This will help to understand the interplay of various miRNAs within foremost signaling pathways and develop a multifactorial approach to treat difficult-to-treat PC.

Talazoparib nanoparticles for overcoming multidrug resistance in triple-negative breast cancer

Herein, we investigated efflux pumps-mediated talazoparib-resistance in the treatment of triple-negative breast cancer (TNBC). Furthermore, we produced a novel talazoparib-solid lipid nanoparticles (SLNs) and then explored in vitro therapeutic efficacy of talazoparib-SLNs to overcome talazoparib-resistance in TNBC cells. Talazoparib-SLNs formulation was produced and then characterized. Calcein and Rho-123 were used to analyze the functional activity of drug efflux pumps in these cells. Additionally, RT-PCR, western blot and immunofluorescence analysis were used to detect the messenger RNA, and protein expression level, and cellular localization of the multidrug resistance (MDR1), breast cancer resistance protein (BCRP), and MRP1. We found that talazoparib efflux was mediated by BCRP and MRP1 pumps in TNBC cells. Talazoparib-SLNs could significantly enhance therapeutic efficacy of talazoparib. Furthermore, talazoparib-SLNs were more effective in the suppression of MDR1, BCRP, and MRP1 gene and protein expression levels than talazoparib. Consequently, this study suggests that talazoparib-SLNs formulation represents a promising therapeutic carrier to reverse MDR-mediated resistance in TNBC.

miRNA and Gene Expression in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains a challenging disease that is mostly diagnosed late in the course of the illness. Unlike other cancers in which measurable successes have been achieved with traditional chemotherapy, targeted therapy, and, recently, immunotherapy, PDAC has proved to be poorly responsive to these treatments, with only marginal to modest incremental benefits using conventional cytotoxic therapy. There is, therefore, a great unmet need to develop better therapies based on improved understanding of biology and identification of predictive and prognostic biomarkers that would guide therapy. miRNAs are small noncoding RNAs that regulate the expression of some key genes by targeting their 3'-untranslated mRNA region. Aberrant expression of miRNAs has been linked to the development of various malignancies, including PDAC. A series of miRNAs have been identified as potential tools for early diagnosis, prediction of treatment response, and prognosis of patients with PDAC. In this review, we present a summary of the miRNAs that have been studied in PDAC in the context of disease biology.

MicroRNA-298 Reverses Multidrug Resistance to Antiepileptic Drugs by Suppressing MDR1/P-gp Expression in vitro

P-glycoprotein (P-gp), a critical multidrug transporter, recognizes and transports various antiepileptic drugs (AEDs) through the blood-brain barrier (BBB). This may decrease the concentrations of AEDs in brain tissues and cause multidrug resistance (MDR) in patients with refractory epilepsy. Compelling evidence indicates that microRNAs (miRNAs) modulate MDR in various cancers by regulating P-gp expression. Furthermore, a previous study showed that miR-298 mediates MDR in breast cancer cells by downregulating P-gp expression. Based on the therapeutic results obtained from tumor cells, we aimed to determine whether miR-298 reverses MDR to AEDs by regulating P-gp expression in the BBB. We first established different drug-resistant cell lines, including PHT-resistant HBMECs (human brain microvascular endothelial cells) and doxorubicin (DOX)-resistant U87-MG (human malignant glioma) cells, by inducing P-gp overexpression. Quantitative real-time PCR (qRT-PCR) analysis revealed reduced expression of miR-298 in both HBMEC/PHT and U87-MG/DOX cells, and the luciferase reporter assay identified the direct binding of miR-298 to the 3′-untranslated region (3′-UTR) of P-gp. Moreover, ectopic expression of miR-298 downregulated P-gp expression at the mRNA and protein levels, thereby increasing the intracellular accumulation of AEDs in drug-resistant HBMEC/PHT and U87-MG/DOX cells. Thus, our findings suggest that miR-298 reverses MDR to AEDs by inhibiting P-gp expression, suggesting a potential target for overcoming MDR in refractory epilepsy.

Down-regulation of miR-210-3p encourages chemotherapy resistance of renal cell carcinoma via modulating ABCC1

Background

ATP-binding cassette transporter super-family including ABCC1 and MDR-1 were involved in multi-drug resistance (MDR) of renal cell carcinoma (RCC) patients. Several miRNAs were confirmed to promote the MDR and the survival of tumor cells.

Methods

The RCC cell lines Caki-2 with vinblastine-resistant (Caki-2/VBL) or doxorubicin-resistant (Caki-2/DOX) were constructed, respectively. The expressions of miR-210-3p, ABCC1 and MDR-1 protein were determined by qRT-PCR and Western blot assays. The viability of RCC cells was assessed by MTT assay. The regulatory relationship between miR-210-3p and ABCC1 was analyzed by Dual Luciferase assay. The effect of miR-210-3p in vivo was investigated with a tumor xenograft model in mice.

Results

MiR-210-3p expression was observed to significantly decrease in Caki-2/VBL and Caki-2/DOX cells. Meanwhile, ABCC1 and MDR-1 were significantly increased in Caki-2/VBL and Caki-2/DOX cells. ABCC1 was a novel target of miR-210-3p and negatively regulated by miR-210-3p. And miR-210-3p improved drug-sensitivity of RCC cells. Down-regulation of ABCC1 could reverse the effect of miR-210-3p knockdown on the drug-resistance and the level of MDR-1 in drug-sensitive RCC cells.

Conclusion

We confirmed that down-regulation of miR-210-3p increased ABCC1 expression, thereby enhancing the MRP-1-mediated multidrug resistance of RCC cells.

miR-1266 Contributes to Pancreatic Cancer Progression and Chemoresistance by the STAT3 and NF-κB Signaling Pathways

Pancreatic cancer is characterized by chemoresistance after several cycles of chemotherapy, which is a major issue responsible for treatment failure of pancreatic cancer. Therefore, it is necessary to explore the specific mechanism underlying chemotherapeutic resistance to overcome this issue. Here we report that miR-1266 is dramatically elevated and correlates with poor survival and chemotherapy response in pancreatic cancer patients. Upregulation of miR-1266 enhanced the chemoresistance of pancreatic cancer cells to gemcitabine (GEM) in vitro and in vivo; conversely, inhibition of miR-1266 yielded the opposite effect. Importantly, silencing of miR-1266 restored the sensitivity of pancreatic cancer cells to GEM in a dose-dependent manner in vivo. Furthermore, our results demonstrate that miR-1266 promotes resistance of pancreatic cancer cells to GEM by targeting multiple negative regulators of the STAT3 and NF-κB pathways, including SOCS3, PTPN11, ITCH, and TNIP1, leading to constitutive activation of STAT3 and NF-κB signaling. Thus, our findings clarify a novel mechanism by which miR-1266 induces chemotherapeutic resistance in pancreatic cancer, indicating that miR-1266 may be used as chemotherapeutic response indicator. Antagomir-1266 as a chemotherapeutic sensitizer, in combination with GEM, may serve as a rational regimen in the treatment of chemotherapy-resistant pancreatic cancer.

Regulation of drug resistance and metastasis of gastric cancer cells via the microRNA647-ANK2 axis

Due to a lack of effective methods for early diagnosis, the majority of patients with gastric cancer (GC) are diagnosed during the late stages of the disease, which are often accompanied by metastasis. For these patients, despite being considered an important therapeutic modality in the treatment of cancer, chemotherapy is usually not effective due to multidrug resistance (MDR). The expression levels of MDR/metastasis-associated genes are regulated by numerous microRNAs (miRNAs/miRs). The expression of miR-647 in GC tissues and SGC7901/VCR cell line (drug resistance to vincristine) was detected by qRT-PCR. The effect of overexpression of miR-647 on drug resistance was evaluated by measuring the half maximal inhibitory concentration (IC₅₀) value of SGC-7901/VCR to vincristine and tumor growth in vivo. Moreover, drug-induced cell apoptosis and cell cycle were evaluated by flow cytometry, as well as the ability of cell migration and invasiveness detected by wound healing and transwell assay. Furthermore, underlying targets of miR-647 were predicted by TargetScan and MicroRNA; meanwhile, the expression of ANK2, FAK, MMP2, MMP12,CD44,SNAIL1 were observed by qRT-PCR and western blot analysis. The present study established that the expression levels of miR-647 were downregulated in GC tissues from patients with metastasis and in the vincristine-resistant SGC7901 (SGC-7901/VCR) GC cell line. The IC₅₀ value for vincristine was significantly decreased, whereas the proportion of cells in G₀/G₁ phase and the drug-induced apoptotic rate were significantly increased following upregulation of miR-647. Furthermore, the results demonstrated that miR-647 overexpression led to decreased migration and invasion of SGC-7901/VCR cells. Overexpression of miR-647 was also demonstrated to sensitize tumors to chemotherapy in vivo. In addition, miR-647 overexpression was able to reduce the expression levels of ankyrin-B, focal adhesion kinase, matrix metalloproteinase (MMP)2, MMP12, cluster of differentiation 44 and snail family transcriptional repressor 1. In conclusion, these findings demonstrated that miR-647 may function as a novel target to ameliorate drug resistance and metastasis of GC cells.

Downregulation of miR-874-3p promotes chemotherapeutic resistance in colorectal cancer via inactivation of the Hippo signaling pathway

Overcoming resistance to chemotherapy is an arduous challenge in the treatment of colorectal cancer (CRC), particularly since the underlying molecular mechanisms remain obscure. In the present study, we reported that miR-874-3p was markedly downregulated in CRC tissues compared with that in adjacent normal colorectal epithelial tissues. Upregulation of miR-874-3p attenuated the chemoresistance of CRC cells to 5-fluorouracil (5-FU) in vitro and in vivo. Conversely, inhibition of miR-874-3p yielded an opposite effect. Furthermore, our results demonstrated that miR-874-3p directly inhibited the expression of transcriptional co-activators YAP and TAZ of the Hippo signaling pathway, resulting in the inactivation of the TEAD transcription. Thus, our findings clarify a novel mechanism by which miR-874-3p restores chemotherapeutic sensitivity of CRC to 5-FU, indicating that offering miR-874-3p mimics in combination with 5-FU may serve as a new therapeutic strategy to circumvent the chemoresistance in CRC.

Role of miR-27a, miR-181a and miR-20b in gastric cancer hypoxia-induced chemoresistance

Despite the search for new therapeutic strategies for gastric cancer (GC), there is much evidence of progression due to resistance to chemotherapy. Multidrug resistance (MDR) is the ability of cancer cells to survive after exposure to chemotherapeutic agents. The involvement of miRNAs in the development of MDR has been well described but miRNAs able to modulate the sensitivity to chemotherapy by regulating hypoxia signaling pathways have not yet been fully addressed in GC. Our aim was to analyze miR-20b, miR-27a and miR-181a expression with respect to (epirubicin/oxaliplatin/capecitabine (EOX)) chemotherapy regimen in a set of GC patients, in order to investigate whether miRNAs deregulation may influence GC MDR also via hypoxia signaling modulation. Cancer biopsy were obtained from 21 untreated HER2 negative advanced GC patients, retrospectively analyzed. All patients received a first-line chemotherapy (EOX) regimen. MirWalk database was used to identify miR-27a, miR-181a and miR-20b target genes. The expression of miRNAs and of HIPK2, HIF1A and MDR1 genes were detected by real-time PCR. HIPK2 localization was assessed by immunohistochemistry. Our data showed the down-regulation of miR-20b, miR-27a, miR-181a concomitantly to higher levels of MDR1, HIF1A and HIPK2 genes in GC patients with a progressive disease respect to those with a disease control rate. Moreover, immunohistochemistry assay highlighted a higher cytoplasmic HIPK2 staining, suggesting a different role for it. We showed that aberrant expression of miR-20b, miR27a and miR-181a was associated with chemotherapeutic response in GC through HIF1A, MDR1 and HIPK2 genes modulation, suggesting a possible novel therapeutic strategy.

MicroRNA-21 as a prognostic biomarker in patients with pancreatic cancer - A systematic review and meta-analysis

OBJECTIVES

The aim of this systematic review and meta-analysis is to summarize the current knowledge regarding microRNA-21 and to evaluate its prognostic impact in patients with pancreatic cancer.

METHODS

We conducted an electronic literature search to identify all published studies in PubMed/MEDLINE, Scopus and Google Scholar databases from 2000 until August 2016.

RESULTS

A total of 17 studies involving 1471 patients met the inclusion criteria for the quantitative synthesis. The microRNA-21 upregulation was significantly associated with poorer overall survival, disease-free survival, and progression-free survival. The subgroup analysis revealed that microRNA-21 overexpression has a significant higher prognostic value for patients who receive adjuvant chemotherapy. Increased microRNA-21 was associated with a statistically significant higher rate of metastatic lymph nodes and poorly differentiated tumors.

CONCLUSIONS

MicroRNA-21 upregulation in pancreatic cancer is associated with a significantly poorer overall survival, disease-free survival, and progression-free survival. MicroRNA-21 may be a useful prognostic biomarker, allowing stratification for chemotherapy administration, and being a component of precision medicine in patients with pancreatic cancer.

The underlying mechanisms of non-coding RNAs in the chemoresistance of pancreatic cancer

Pancreatic cancer, which is often asymptomatic, is currently one of the most common causes of cancer-related death. This phenomenon is most likely due to a lack of early diagnosis, a high metastasis rate and a disappointing chemotherapy outcome. Thus, improving treatment outcomes by overcoming chemotherapy resistance may be a useful strategy in pancreatic cancer. Various underlying mechanisms involved in the chemoresistance of pancreatic cancer have been investigated. Notably, non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), play a pivotal role in regulating sensitivity to chemotherapy in pancreatic cancer. In this review, we highlight recent evidence regarding the role of miRNAs and lncRNAs in the chemoresistance of pancreatic cancer, including their expression levels, targets, biological functions and the regulation of chemoresistance, and discuss the potential clinical application of miRNAs and lncRNAs in the treatment of pancreatic cancer.

MicroRNA-100 and microRNA-21 as markers of survival and chemotherapy response in pancreatic ductal adenocarcinoma UICC stage II

Background

Pancreatic ductal adenocarcinoma (PDAC) remains a highly chemoresistant tumor entity for which no reliable molecular targets exist to predict or influence the success of chemotherapy. Recently, we identified a panel of microRNAs associated with induced gemcitabine chemoresistance in human PDAC cell lines. This clinical study evaluates these microRNAs and associated molecular markers as prognostic markers of outcome in 98 PDAC patients Union Internationale Contre le Cancer (UICC) stage II undergoing curative surgery with adjuvant gemcitabine chemotherapy. The primary end points of this study are recurrence-free survival and overall survival.

Results

Poor response to chemotherapy was significantly correlated to overexpression of microRNA-21 (p = 0.029), microRNA-99a (p = 0.037), microRNA-100 (p = 0.028), and microRNA-210 (p = 0.021) in tissue samples of PDAC patients UICC stage II. Upregulation of these microRNAs was associated with a significantly shorter overall survival and recurrence-free survival (p < 0.05). Overexpression of phosphatase and tensin homolog (PTEN) (p = 0.039) and low expression of multidrug resistance (MDR)-1 (p = 0.043) and breast cancer resistance protein (BCRP)-1 (p = 0.038) were significantly correlated to improved response to adjuvant chemotherapy. Adjuvant gemcitabine treatment (p < 0.0001) and low tumor grading (p = 0.047) were correlated to better outcome. MicroRNA-100, microRNA-21, and its targets PTEN and MDR-1 were independent factors of survival in multivariate analysis.

Conclusions

Multivariate survival analyses identified microRNA-21 and microRNA-100 as unfavorable prognostic factors in resected and adjuvant treated PDAC UICC stage II patients.

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.

Molecular mechanisms underlying the role of microRNAs in the chemoresistance of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an extremely severe disease where the mortality and incidence rates are almost identical. This is mainly due to late diagnosis and limited response to current treatments. The tumor macroenvironment/microenvironment have been frequently reported as the major contributors to chemoresistance in PDAC, preventing the drugs from reaching their intended site of action (i.e., the malignant duct cells). However, the recent discovery of microRNAs (miRNAs) has provided new directions for research on mechanisms underlying response to chemotherapy. Due to their tissue-/disease-specific expression and high stability in tissues and biofluids, miRNAs represent new promising diagnostic and prognostic/predictive biomarkers and therapeutic targets. Furthermore, several studies have documented that selected miRNAs, such as miR-21 and miR-34a, may influence response to chemotherapy in several tumor types, including PDAC. In this review, we summarize the current knowledge on the role of miRNAs in PDAC and recent advances in understanding their role in chemoresistance through multiple molecular mechanisms.