Targeting CD47/TNFAIP8 by miR-155 overcomes drug resistance and inhibits tumor growth through induction of phagocytosis and apoptosis in multiple myeloma.

The mechanisms of drug resistance in multiple myeloma are poorly understood. Here we show that CD47, an integrin-associated receptor, is significantly upregulated in drug resistant myeloma cells in comparison with parental cells, and that high expression of CD47 detected by immunohistochemistry is associated with shorter progression free and overall survivals in multiple myeloma patients. We show that miR-155 is expressed at low levels in drug resistant myeloma cells and is a direct regulator of CD47 through its 3'UTR. Furthermore, low miR-155 levels are associated with advanced stages of disease. MiR-155 overexpression suppressed CD47 expression on myeloma cell surface, leading to induction of phagocytosis of myeloma cells by macrophages and inhibition of tumor growth. MiR-155 overexpression also re-sensitized drug-resistant myeloma cells to bortezomib leading to cell death through targeting TNFAIP8, a negative mediator of apoptosis in vitro and in vivo. Thus, miR-155 mimics may serve as a promising new therapeutic modality by promoting phagocytosis and inducing apoptosis in patients with refractory/relapsed multiple myeloma.

MARCKS inhibition cooperates with autophagy antagonists to potentiate the effect of standard therapy against drug-resistant multiple myeloma.

Overexpression of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) is implicated in drug resistance and progression of multiple myeloma (MM). The basis for MARCKS induction and impact on MM are not known. Here we show that microRNA-34a (miR-34a), regulates MARCKS translation and is under-expressed in drug-resistant MM cells, leading to increased MARCKS protein level. Over-expression of miR-34a reduces MARCKS expression and sensitizes resistant cells to anti-myeloma drugs. A MARCKS peptide inhibitor (MPS) exerts a dose dependent cytotoxic effect on drug-resistant MM cells with minimal cytotoxicity to normal hematopoietic cells. MPS synergizes with the proteasomal-inhibitor bortezomib to effectively kill drug-resistant MM cells both in vitro and in a xenograft model of MM. While MARCKS inhibition killed MM cells, it also enhanced a pro-survival autophagic pathway that sustained growth following MARCKS inhibition. In accordance, combined treatment with MARCKS antagonists, bortezomib and the autophagy inhibitor, chloroquine, significantly diminished tumor growth in drug-resistant MM cell lines as well as primary MM cells. This study uncovers a mechanism of drug resistance involving miR-34a-MARCKS autoregulatory loop and provides a framework for a potentially new therapeutic strategy to overcome drug resistance in multiple myeloma.

EZH2 as a therapeutic target for multiple myeloma and other haematological malignancies.

Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that is of great interest in human cancer. It has been shown to have a dual nature, as it can act as a gene repressor or activator. Studies have highlighted the various roles of EZH2 in the pathophysiology of multiple myeloma (MM). It was also shown to have a role in the development of drug resistance in MM. There are several ongoing clinical trials of EZH2 inhibitors in haematological malignancies. Pre-clinical studies have provided a rationale for the therapeutic relevance of EZH2 inhibitors in MM. This paper reviews the evidence supporting the role of EZH2 in MM pathophysiology and drug resistance, with an emphasis on interactions between EZH2 and microRNAs, as well as the prognostic significance of EZH2 expression in MM. Furthermore, results from the pre-clinical studies of EZH2 inhibition in MM and currently available interim results from clinical trials of EZH2 inhibitors in haematological malignancies are presented. Preliminary data exploring anticipated mechanisms of resistance to EZH2 inhibitors are also reviewed. There is therefore strong evidence to support the relevance of targeting EZH2 for the treatment of MM.

Dysregulation of EZH2/miR-138 axis contributes to drug resistance in multiple myeloma by downregulating RBPMS.

EZH2 is highly expressed in multiple myeloma (MM). However, the molecular mechanisms underlying EZH2 overexpression and its role in drug resistance of MM remain undefined. Here we show that EZH2 is upregulated in drug-resistant MM cells and its aberrant overexpression is associated with poor prognosis of MM patients. Overexpression of EZH2 in parental MM cells renders them resistant to anti-myeloma drugs and suppression of EZH2 displays the opposite effects. Using miRNA target scan algorithms, we identify miR-138 as a regulator of EZH2, which is conversely repressed by EZH2-induced H3K27 trimethylation in MM-resistant cell lines and primary tumor cells. Analysis of ChIP-seq dataset and H3K27me3 ChIP reveals that RBPMS is a direct and functionally relevant target of EZH2. RBPMS silencing confers resistance to MM cells and restoration of RBPMS by miR-138 overexpression re-sensitizes the resistant cells to drug. Importantly, in vivo delivery of miR-138 mimics or pharmacological inhibitor of EZH2 in combination with a proteasome inhibitor, bortezomib, induces significant regression of tumors in xenograft model. This study establishes EZH2/miR-138 axis as a potential therapeutic target for MM.

Re-evaluation of acute erythroid leukemia according to the 2016 WHO classification.

In the recent update of WHO classification, the definition of myeloid neoplasms with erythroid predominance has been modified shifting the main criteria for calculating blast percentage from non-erythroid cells (NEC) to all nucleated marrow cells (ANC). Thus, the cases previously classified as erythroid/myeloid subtype of acute erythroid leukemia (AEL) based on the 2008 WHO will now be categorized either as myelodysplastic syndrome with excess blasts (MDS-EB) or acute myeloid leukemia, not otherwise specified (AML-NOS). However, the clinical significance of this new classification has not been demonstrated. Thus, we reviewed a leukemia database and reclassified 38 cases previously diagnosed as AEL, erythroid/myeloid subtype, with the consideration of 2016 revision criteria. Twenty seven (71%) of them had >20% blasts in NEC but less than 20% blasts in ANC, and 11 (29%) had >20% in both NEC and ANC. There was no significant difference in overall survivals (OS) among AEL, MDS-EB, and AML-NOS (non-erythroid predominance, NEP). However, AML with myelodysplasia-related changes showed significant shorter OS than AEL, MDS-EB and AML-NOS (NEP). Our results indicate that in myeloid neoplasm with erythroid predominance, patients with >20% blasts, of either NEC or ANC, share similar clinical laboratory features and survival outcomes with AML-NOS.

High IKZF1/3 protein expression is a favorable prognostic factor for survival of relapsed/refractory multiple myeloma patients treated with lenalidomide.

The aim of this study is to assess nucleoprotein expression of IKZF1/3 in patients with relapsed/refractory multiple myeloma (MM) who received lenalidomide-based therapy and correlated them with their clinical outcomes. A total of 50 patients diagnosed with MM were entered in the study with the median follow-up of 86.4 months. By immunohistochemistry (IHC), IKZF1 and IKZF3 were expressed in 72 and 58% of the cases, respectively. IKZF1 and IKZF3 expressions were associated with longer median progression free survival (P = 0.0029 and P < 0.0001) and overall survival (P = 0.0014 and P < 0.0001). IKZF3 expression also appears predicted a favorable response to the lenalidomide-based therapy.