Expression and significance of miR-21 in multiple myeloma patients

MicroRNAs as a Potential New Preventive Approach in the Transition from Asymptomatic to Symptomatic Multiple Myeloma Disease

Simple Summary

Multiple myeloma (MM) is the second most common haematologic malignancy, and it remains an incurable disease despite the advances of novel therapies. It is characterised by a multistep process that arises from a pre-malignant asymptomatic status-defined monoclonal gammopathy of undetermined significance (MGUS), evolves to a middle stage named smouldering myeloma phase (SMM), and culminates in the active disease (MM). Identification of early and non-invasive markers of the disease progression is currently an active field of investigation. In this review, we discuss the role and significance of microRNAs (miRNAs) as potential diagnostic biomarkers to predict the clinical transition from MGUS/SMM status to MM.

Abstract

Multiple myeloma (MM) is a hematological malignancy characterised by proliferation of clonal plasma cells (PCs) within the bone marrow (BM). Myelomagenesis is a multi-step process which goes from an asymptomatic phase, defined as monoclonal gammopathy of undetermined significance (MGUS), to a smouldering myeloma (SMM) stage, to a final active MM disease, characterised by hypercalcemia, renal failure, bone lesions anemia, and higher risk of infections. Overall, microRNAs (miRNAs) have shown to significantly impact on MM tumorigenesis, as a result of miRNA-dependent modulation of genes involved in pathways known to be crucial for MM pathogenesis and disease progression. We aim to revise the literature related to the role of miRNAs as potential diagnostic and prognostic biomarkers, thus highlighting their key role as novel players within the field of MM and related premalignant conditions.

Identification of MicroRNAs With In Vivo Efficacy in Multiple Myeloma-related Xenograft Models

BACKGROUND/AIM

Multiple myeloma is a B-cell neoplasm, which can spread within the marrow of the bones forming many small tumors. In advanced disease, multiple myeloma can spread to the blood as plasma cell leukemia. In some cases, a localized tumor known as plasmacytoma is found within a single bone. Despite the approval of several agents such as melphalan, corticosteroids, proteasome inhibitors, thalidomide-based immuno-modulatory agents, histone deacetylase inhibitors, a nuclear export inhibitor and monoclonal antibodies daratuzumab and elatuzumab, the disease presently remains uncurable.

MATERIALS AND METHODS

In order to define new targets and treatment modalities we searched the literature for microRNAs, which increase or inhibit in vivo efficacy in multiple-myeloma-related xenograft models.

RESULTS AND CONCLUSION

We identified six up-regulated and twelve down-regulated miRs, which deserve further preclinical validation.

Molecular Mechanisms of Bortezomib Action: Novel Evidence for the miRNA-mRNA Interaction Involvement

Bortezomib is an anti-tumor agent, which inhibits 26S proteasome degrading ubiquitinated proteins. While apoptotic transcription-associated activation in response to bortezomib has been suggested, mechanisms related to its influence on post-transcriptional gene silencing mediated regulation by non-coding RNAs remain not fully elucidated. In the present study, we examined changes in global gene and miRNA expression and analyzed the identified miRNA-mRNA interactions after bortezomib exposure in human neuroblastoma cells to define pathways affected by this agent in this type of cells. Cell viability assays were performed to assess cytotoxicity of bortezomib. Global gene and miRNA expression profiles of neuroblastoma cells after 24-h incubation with bortezomib were determined using genome-wide RNA and miRNA microarray technology. Obtained results were then confirmed by qRT-PCR and Western blot. Further bioinformatical analysis was performed to identify affected biological processes and pathways. In total, 719 genes and 28 miRNAs were downregulated, and 319 genes and 61 miRNAs were upregulated in neuroblastoma cells treated with bortezomib. Possible interactions between dysregulated miRNA/mRNA, which could be linked to bortezomib-induced neurotoxicity, affect neurogenesis, cellular calcium transport, and neuron death. Bortezomib might exert toxic effects on neuroblastoma cells and regulate miRNA-mRNA interactions influencing vital cellular functions. Further studies on the role of specific miRNA-mRNA interactions are needed to elucidate mechanisms of bortezomib action.

Profiling of circulating exosomal miRNAs in patients with Waldenström Macroglobulinemia

Waldenström Macroglobulinemia (WM) is a low-grade B-cell lymphoma characterized by disease progression from IgM MGUS to asymptomatic and then symptomatic disease states. We profiled exosomes from the peripheral blood of patients with WM at different stages (30 smoldering/asymptomatic WM, 44 symptomatic WM samples and 10 healthy controls) to define their role as potential biomarkers of disease progression. In this study, we showed that circulating exosomes and their miRNA content represent unique markers of the tumor and its microenvironment. We observed similar levels of miRNAs in exosomes from patients with asymptomatic (smoldering) and symptomatic WM, suggesting that environmental and clonal changes occur in patients at early stages of disease progression before symptoms occur. Moreover, we identified a small group of miRNAs whose expression correlated directly or inversely with the disease status of patients, notably the known tumor suppressor miRNAs let-7d and the oncogene miR-21 as well as miR-192 and miR-320b. The study of these miRNAs’ specific effect in WM cells could help us gain further insights on the mechanisms underlying WM pathogenesis and reveal their potential as novel therapeutic targets for this disease.

Gambogenic Acid Exerts Antitumor Activity in Hypoxic Multiple Myeloma Cells by Regulation of miR-21

Hypoxia is an inseparable component of the bone marrow (BM) microenvironment, accounting for aggressive tumor behavior and poor prognosis of multiple myeloma (MM). Gambogenic acid (GNA) has proven to be an attractive option for treatment of tumors due to its tumor suppressive activity. Herein, we found that GNA exhibits remarkable apoptotic activity against MM cells even under hypoxia. MicroRNA-21 (miR-21) has been found over-expressed in MM patients and associated with the occurrence and development of MM. Direct studies have shown that there is a functional link between hypoxia and miR-21 expression in multiple types of tumors. In the current study, we found that hypoxia increased miR-21 expression in U266 cells and miR-21 induced by hypoxia was associated with concurrent reductions in its target PTEN. After treatment with GNA, miR-21 expression in hypoxic U266 cells was strikingly downregulated in a dose-dependent manner. Besides, we identified that regulation of miR-21/PTEN by GNA under hypoxia is related with inhibition of HIF-1α accumulation and STAT3 phosphorylation. Furthermore, in vivo study revealed that intravenous GNA injection could significantly suppress tumor growth and the miR-21/PTEN pathway is involved in GNA's anti-tumor effects. Taken together, all these results indicated that GNA could be a highly potent therapeutic for human MM.