Suppressing miRNA-15a/-16 expression by interleukin-6 enhances drug-resistance in myeloma cells

MicroRNA-15a/16-1 cluster located at chromosome 13q14 is down-regulated but displays different expression pattern and prognostic significance in multiple myeloma

MiRNA-15a/16-1 cluster located at chromosome 13q14 has been confirmed to regulate critical genes associated with cell proliferation, apoptosis and drug resistance in multiple myeloma (MM). However, little is known about their expression pattern and prognostic value in MM patients. In this study, we have analyzed the expression levels of miR-15a/16-1 in 117 MM patients (90 newly diagnosed, 11 relapsed and 16 remission patients) and 19 health donors (HDs) by quantitative real-time PCR. Our results indicated that the expression levels of miR-15a and 16-1 were down-regulated in newly diagnosed MM patients as compared to HDs (P = 0.025; P < 0.001) and independent of del(13q14). Downregulation of miR-15a was significantly associated with disease progression and poor prognosis while miR-16-1 seemed to be a good diagnostic marker to distinguish MM from HDs with area under the curve (AUC) of 0.864, sensitivity of 100% and specificity of 73%. Furthermore, patients with miR-15a < 2.35 (low expression group) had significantly shorter PFS (P < 0.001) and OS (P < 0.001). After adjustment of the established prognostic variables including del(13q), del(17p), amp(1q21) and high risk genetic abnormality, low miR-15a expression (<2.35) was still a powerful independent predictor for PFS (P = 0.008) and OS (P = 0.038). In addition, miR-15a combined with high β2-MG and high risk genetic abnormality can further identify the high-risk subpopulations. Therefore, our data suggest that the expression patterns of miR-15a/16-1 are different in MM patients, and miR-15a seems to be linked with disease progression and prognosis while miR-16-1 acts as a valuable diagnostic marker.

MiR-15a/16 regulates the growth of myeloma cells, angiogenesis and antitumor immunity by inhibiting Bcl-2, VEGF-A and IL-17 expression in multiple myeloma

miRNAs have been reported to be involved in the pathogenesis of many cancers. In this article, we investigated the role and the mechanisms of miR-15a/16 in the pathogenesis of multiple myeloma (MM). We found that miR-15a/16 was down-regulated in bone marrow-derived mononuclear cells (BM-MNCs) of newly diagnosed patients with MM and the downregulation of miR-15a/16 was correlated with International Staging System (ISS) stage. We then demonstrated miR-15a/16 inhibited myeloma cells proliferation, and increased apoptosis rate of U266 cells by suppressing the expression of anti-apoptosis protein Bcl-2. We also found miR-15a/16 could decrease VEGF-A and IL-17 levels in the supernatant of myeloma cells. These results indicate that miR-15a/16 may function as a tumor suppressor in MM through multiple regulatory mechanisms and they may be potential targets for the therapy of MM.

MicroRNAs: Novel Crossroads between Myeloma Cells and the Bone Marrow Microenvironment

Multiple myeloma (MM) is a hematologic malignancy of differentiated plasma cells that accumulate in the bone marrow, where a complex microenvironment made by different cell types supports proliferation, survival, and drug resistance of tumor cells. MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression at posttranscriptional level. Emerging evidence indicates that miRNAs are aberrantly expressed or functionally deregulated in MM cells as the result of multiple genetic or epigenetic mechanisms and that also the tumor microenvironment regulates MM cell functions by miRNAs. Consistently, modulation of miRNA levels in MM cells has been demonstrated to impair their functional interaction with the bone marrow microenvironment and to produce significant antitumor activity even able to overcome the protective bone marrow milieu. This review will describe the most recent findings on miRNA function in the context of MM bone marrow microenvironment, focusing on the therapeutic potential of miRNA-based approaches.

The role of circulating miRNAs in multiple myeloma

Multiple myeloma (MM) is a common malignant hematological disease. Dysregulation of microRNAs (miRNAs) in MM cells and bone marrow microenviroment has important impacts on the initiation and progression of MM and drug resistance in MM cells. Recently, it was reported that MM patient serum and plasma contained sufficiently stable miRNA signatures, and circulating miRNAs could be identified and measured accurately from body fluid. Compared to conventional diagnostic parameters, the circulating miRNA profile is appropriate for the diagnosis of MM and estimates patient progression and therapeutic outcome with higher specificity and sensitivity. In this review, we mainly focus on the potential of circulating miRNAs as diagnostic, prognostic, and predictive biomarkers for MM and summarize the general strategies and methodologies for identification and measurement of circulating miRNAs in various cancers. Furthermore, we discuss the correlation between circulating miRNAs and the cytogenetic abnormalities and biochemical parameters assessed in multiple myeloma.

Downregulated miR-33b is a novel predictor associated with disease progression and poor prognosis in multiple myeloma

MiRNAs located at chromosome fragile sites play important roles in regulating critical genes associated with myeloma pathogenesis, disease progression and drug resistance. Our previous results have identified miR-33b (located in chromosome 17p) was one of the dysregulated miRNAs in the sera of newly diagnosed MM patients. However, little is known about its expression pattern in myeloma tumor cells and its prognostic value in MM patients. In the present study, we investigated the expression pattern of miR-33b in 58 newly diagnosed, 11 relapsed, 12 remission MM patients and 18 health donors by quantitative real-time PCR. Our results showed the expression of miR-33b was obviously down-regulated in newly diagnosed and relapsed MM patients compared to remission patients and health donors (p<0.001). Moreover, patients with del(13q), del(17p), t(4;14) and high-risk genetic abnormalities have lower expression levels of miR-33b compared to patients without those of abnormalities (p=0.032, 0.018, 0.034, 0.005). Survival analysis showed patients with miR-33b low expression had significantly shortened PFS (p=0.016) and OS (p=0.033) and might be associated with drug resistance to bortezomib-based treatment. Our data suggest that down-regulated miR-33b might be a novel predictor associated with disease progression and poor prognosis in MM.

Drug resistance in multiple myeloma: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective therapeutic protocols, multiple myeloma still tends to be a hard-to-treat hematologic cancer. This hallmark of the disease is in fact a sequel to drug resistant phenotypes persisting initially or emerging in the course of treatment. Furthermore, the heterogeneous nature of multiple myeloma makes treating patients with the same drug challenging because finding a drugable oncogenic process common to all patients is not yet feasible, while our current knowledge of genetic/epigenetic basis of multiple myeloma pathogenesis is outstanding. Nonetheless, bone marrow microenvironment components are well known as playing critical roles in myeloma tumor cell survival and environment-mediated drug resistance happening most possibly in all myeloma patients. Generally speaking, however; real mechanisms underlying drug resistance in multiple myeloma are not completely understood. The present review will discuss the latest findings and concepts in this regard. It reviews the association of important chromosomal translocations, oncogenes (e.g. TP53) mutations and deranged signaling pathways (e.g. NFκB) with drug response in clinical and experimental investigations. It will also highlight how bone marrow microenvironment signals (Wnt, Notch) and myeloma cancer stem cells could contribute to drug resistance in multiple myeloma.

In vivo multimodality imaging of miRNA-16 iron nanoparticle reversing drug resistance to chemotherapy in a mouse gastric cancer model

miRNA-16 (miR16) plays an important role in modulating the drug resistance of SGC7901 cell lines to adriamycin (ADR). A variety of viral carriers have been designed for miRNA delivery. However, the safety concerns are currently perceived as hampering the clinical application of viral vector-based therapy. Herein a type of magnetic nanoparticles (MNPs) was designed and synthesized using poly(ethylene glycol) (PEG)-coated Fe₃O₄ nanoparticles as a miRNA delivery system for the purpose of reducing drug resistance of gastric cancer cells by enforcing miR16 expression in SGC7901/ADR cells. The MNPs with good biocompatibility were synthesized by thermal decomposition, and then conjugated with miRNA via electrostatic interaction producing miR16/MNPs. After co-culture with miR16/MNPs, ADR-induced apoptosis of SGC7901/ADR was examined by MTT and TUNEL. miR16/MNPs treatment significantly increased cell apoptosis in vitro. SGC7901/ADR(fluc) tumor-bearing nude mice under ADR therapy were treated with miR16/MNPs by tail vein injection for in vivo study. After intraperitoneal injection of ADR, tumor volume measurement and fluorescence imaging were performed to for the death of SGC7901/ADR cells in vivo. Results showed that miR16/MNPs were able to significantly suppress SGC7901/ADR tumor growth, probably through increasing SGC7901/ADR cells' sensitivity to ADR. Our results suggest the efficient delivery of miR16 by MNPs as a novel therapeutic strategy for drug resistant tumor treatment.

A p53-dependent tumor suppressor network is induced by selective miR-125a-5p inhibition in multiple myeloma cells

The analysis of deregulated microRNAs (miRNAs) is emerging as a novel approach to disclose the regulation of tumor suppressor or tumor promoting pathways in tumor cells. Targeting aberrantly expressed miRNAs is therefore a promising strategy for cancer treatment. By miRNA profiling of primary plasma cells from multiple myeloma (MM) patients, we previously reported increased miR-125a-5p levels associated to specific molecular subgroups. On these premises, we aimed at investigating the biological effects triggered by miR-125a-5p modulation in MM cells. Expression of p53 pathway-related genes was down-regulated in MM cells transfected with miR-125a-5p mimics. Luciferase reporter assays confirmed specific p53 targeting at 3'UTR level by miR-125a-5p mimics. Interestingly, bone marrow stromal cells (BMSCs) affected the miR-125a-5p/p53 axis, since adhesion of MM cells to BMSCs strongly up-regulated miR-125a-5p levels, while reduced p53 expression. Moreover, ectopic miR-125a-5p reduced, while miR-125-5p inhibitors promoted, the expression of tumor suppressor miR-192 and miR-194, transcriptionally regulated by p53. Lentiviral-mediated stable inhibition of miR-125a-5p expression in wild-type p53 MM cells dampened cell growth, increased apoptosis and reduced cell migration. Importantly, inhibition of in vitro MM cell proliferation and migration was also achieved by synthetic miR-125a-5p inhibitors and was potentiated by the co-expression of miR-192 or miR-194. Taken together, our data indicate that miR-125a-5p antagonism results in the activation of p53 pathway in MM cells, underlying the crucial role of this miRNA in the biopathology of MM and providing the molecular rationale for the combinatory use of miR-125a inhibitors and miR-192 or miR-194 mimics for MM treatment.

Low serum miR-19a expression as a novel poor prognostic indicator in multiple myeloma

Multiple myeloma (MM) is the second most common hematologic malignancy characterized by the clonal expansion of plasma cells. Despite continuing advances, novel biomarkers are needed for diagnosis and prognosis of MM. In our study, we characterized the diagnostic and prognostic potential of circulating microRNAs (miRNAs) in MM. Serum miRNA levels were analyzed in 108 newly diagnosed symptomatic MM patients and 56 healthy donors (HDs). Our analysis identified 95 dysregulated miRNAs in newly diagnosed MM patients. Of the 95 dysregulated miRNAs, dysregulation of miR-19a, miR-92a, miR-214-3p, miR-135b-5p, miR-4254, miR-3658 and miR-33b was confirmed by quantitative reverse transcription PCR (RT-qPCR). Receiver operating characteristic analysis revealed that a combination of miR-19a and miR-4254 can distinguish MM from HD with a sensitivity of 91.7% and specificity of 90.5%. Decreased expression of miR-19a was positively correlated with international staging system advancement, del(13q14) and 1q21 amplification. Furthermore, downregulation of miR-19a resulted in significantly decreased progression-free survival (PFS) and overall survival (OS). Our analysis indicated that the poor prognostic correlation of miR-19a expression was independent of genetic abnormalities in MM. Multivariate analysis revealed that miR-19a was a significant predictor of shortened PFS and OS. Interestingly, although miR-19a levels portend a poor prognosis, patients with low miR-19a levels had an improved response to bortezomib compared to those with high miR-19a profile. Patients with downregulated miR-19a experienced a significantly extended survival upon bortezomib-based therapy. These data demonstrate that the expression patterns of serum microRNAs are altered in MM, and miR-19a levels are a valuable prognostic marker to identify high-risk MM.

Crosstalk between microRNA30a/b/c/d/e-5p and the canonical Wnt pathway: implications for multiple myeloma therapy

Dysregulation of transcription via the Wnt/β-catenin signaling pathway underlies the pathogenesis of a wide variety of frequent human cancers. These include epithelial carcinomas such as colorectal cancer and hematologic malignancies such as multiple myeloma. Thus, the Wnt/β-catenin in pathway potentially offers an attractive target for cancer therapy. This approach, however, has thus far proved challenging because the pathway plays a number of critical roles in physiologic homeostasis, [corrected] and because drugs that broadly target the pathway have unacceptable side effects. miRNAs function as regulators of gene expression and have also been implicated in the pathogenesis of multiple myeloma and other human cancers, offering the promise of novel therapeutic approaches if they can be applied effectively in vivo. Because BCL9 is a critical transcriptional coactivator of β-catenin that is aberrantly expressed in many human cancers but is of low abundance in normal tissues, [corrected] the Wnt/β-catenin/BCL9 complex has emerged as a promising and most likely relatively safe therapeutic target in cancers with dysregulated Wnt/β-catenin activity. This review discusses recent advances in the biology of Wnt inhibitors and the appealing possibility of a functional link between BCL9 and miRNA30a/b/c/d/e-5p that could be exploited for multiple myeloma therapy.

MicroRNA: important player in the pathobiology of multiple myeloma

Recent studies have revealed a pivotal role played by a class of small, noncoding RNAs, microRNA (miRNA), in multiple myeloma (MM), a plasma cell (PC) malignancy causing significant morbidity and mortality. Deregulated miRNA expression in patient's PCs and plasma has been associated with tumor progression, molecular subtypes, clinical staging, prognosis, and drug response in MM. A number of important oncogenic and tumor suppressor miRNAs have been discovered to regulate important genes and pathways such as p53 and IL6-JAK-STAT signaling. miRNAs may also form complex regulatory circuitry with genetic and epigenetic machineries, the deregulation of which could lead to malignant transformation and progression. The translational potential of miRNAs in the clinic is being increasingly recognized that they could represent novel biomarkers and therapeutic targets. This review comprehensively summarizes current progress in delineating the roles of miRNAs in MM pathobiology and management.

Micro-RNAs, New performers in multiple myeloma bone marrow microenvironment

The established interaction between multiple myeloma cells and bone marrow microenvironment components provides malignant cells with various survival, growth and drug resistance signals. As a new concept, identification of miRNAs and their related gene/protein targets, signaling molecules and pathways in the context of bone marrow microenvironment will help understanding more deeply the pathogenesis of the disease and possible mechanisms underlying environment-induced drug resistance. Recent studies suggest that bone marrow stromal cells can modulate some miRNAs (miR-21, miR-15a/16) in multiple myeloma cells through direct adhesion, cytokine secretion or transfer of miRNA-containing exosomes, however; the specific miRNA targets are not clear. In spite of a remarkable progress in understanding myeloma biology and therapy, the disease persists to be hard to treat. This review will discuss the most recent findings on miRNAs expression and function in the context of bone marrow microenvironment highlighting the miRNAs as potential therapeutic targets in multiple myeloma.

Aberrant microRNA expression in multiple myeloma

Multiple myeloma (MM) is a devastating disease with a complex biology, and in spite of improved survivability by novel treatment strategies over the last decade, MM is still incurable by current therapy. MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression at a post-transcriptional level. More than half of all protein coding genes are estimated to be controlled by miRNAs, and their expression is frequently deregulated in many diseases, including cancer. Recent studies have reported aberrant miRNA expression patterns in MM, and the function of individual miRNAs in MM has been investigated in detail in cell culture and animal models. Here, we review the current knowledge on the role of miRNAs in MM pathogenesis and discuss their potential as prognostic biomarkers and targets for treatment.