MicroRNAs of bone marrow mesenchymal stem cell-derived exosomes regulate acute myeloid leukemia cell proliferation and apoptosis.

BACKGROUND: Acute myeloid leukemia (AML) is a malignant hematological disease, originating from hematopoiesis stem cell differentiation obstruction and clonal proliferation. New reagents or biologicals for the treatment of AML are urgently needed, and exosomes have been identified as candidate biomarkers for disease diagnosis and prognosis. This study aimed to investigate the effects of exosomes from bone marrow mesenchymal stem cells (BMSCs) on AML cells as well as the underlying microRNA (miRNA)-mediated mechanisms. METHODS: Exosomes were isolated using a precipitation method, followed by validation using marker protein expression and nanoparticle tracking analysis. Differentially expressed miRNAs were identified by deep RNA sequencing and confirmed by quantitative real-time polymerase chain reaction (qPCR). Cell proliferation was assessed by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt method, and cell cycle progression and apoptosis were detected by flow cytometry. Functional gene expression was analyzed by qPCR and Western blotting (WB). Significant differences were determined using Student's t test or analysis of variance. RESULTS: BMSCs-derived exosomes effectively suppressed cell proliferation (both P < 0.0001 at 10 and 20 µg/mL) and cell cycle progression (P < 0.01 at G0-G1 stage), and also significantly enhanced cell apoptosis (P < 0.001) in KG-1a cells. There were 1167 differentially expressed miRNAs obtained from BMSCs-derived exosomes compared with KG-1a cell-derived exosomes (P < 0.05). Knockdown of hsa-miR-124-5p in BMSCs abrogated the effects of BMSCs-derived exosomes in regulating KG-1a such as the change in cell proliferation (both P < 0.0001 vs. normal KG-1a cell [NC] at 48 and 72 h). KG-1a cells treated with BMSCs-derived exosomes suppressed expression of structural maintenance of chromosomes 4 (P < 0.001 vs. NC by qPCR and P < 0.0001 vs. NC by WB), which is associated with the progression of various cancers. This BMSCs-derived exosomes effect was significantly reversed with knockdown of hsa-miR-124-5p (P < 0.0001 vs. NC by WB). CONCLUSIONS: BMSCs-derived exosomes suppress cell proliferation and cycle progression and promote cell apoptosis in KG-1a cells, likely acting through hsa-miR-124-5p. Our study establishes a basis for a BMSCs-derived exosomes-based AML treatment.

PIM-1 kinase inhibitor SMI-4a exerts antitumor effects in chronic myeloid leukemia cells by enhancing the activity of glycogen synthase kinase 3ß.

The development of targeted tyrosine kinase inhibitors (TKIs) has succeeded in altering the course of chronic myeloid leukemia (CML). However, a number of patients have failed to respond or experienced disease relapse following TKI treatment. Proviral integration site for moloney murine leukemia virus­1 (PIM­1) is a serine/threonine kinase that participates in regulating apoptosis, cell cycle, signal transduction and transcriptional pathways, which are associated with tumor progression, and poor prognosis. SMI­4a is a selective PIM­1 kinase inhibitor that inhibits PIM­1 kinase activity in vivo and in vitro. The present study aimed to explore the mechanism underlying the antitumor effect of SMI­4a in K562 and imatinib­resistant K562 (K562/G) cell lines. It was demonstrated that SMI­4a inhibited the proliferation of K562 and K562/G cells using a WST­8 assay. The Annexin V­propidium iodide assay demonstrated that SMI­4a induced apoptosis of K562 and K562/G cells in a dose­, and time­dependent manner. Furthermore, Hoechst 33342 staining was used to verify the apoptosis rate. The clone formation assay revealed that SMI­4a significantly inhibited the colony formation capacity of K562 and K562/G cells. Western blot analysis demonstrated that SMI­4a decreased phosphorylated (p)­Ser9­glycogen synthase kinase (GSK) 3ß/pGSK3ß and inhibited the translocation of ß­catenin. In addition, the downstream gene expression of apoptosis regulator Bax and poly(ADP­ribose) polymerase­1 was upregulated, and apoptosis regulator Bcl­2 and Myc proto­oncogene protein expression levels were downregulated. Immunofluorescence results demonstrated changes in the expression level of ß­catenin in the plasma and nucleus. The results of the present study suggest that SMI­4a is an effective drug to use in combination with current chemotherapeutics for the treatment of imatinib-resistant CML.

Celecoxib exerts antitumor effects in HL-60 acute leukemia cells and inhibits autophagy by affecting lysosome function.

Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, has been demonstrated to exert antitumor activity in a variety of cancer cells. The underlying mechanism involves inhibition of cell cycle progression and induction of apoptosis. Besides, celecoxib has also been found to induce autophagy in some solid tumor cells. The aim of this study was to investigate the effect of celecoxib on cell proliferation in HL-60 human acute leukemia cells and to explore the potential mechanism. HL-60 cells were exposed to various concentrations of celecoxib and cell viability was evaluated by the MTT assay. Apoptosis was analyzed with flow cytometry and the amount of autophagosome was evaluated by LysoTracker probe labelling. The expression of apoptosis- and autophagy-related proteins was assayed by Western blot and LysoSensor probe labelling was used to detect the effect of celecoxib on the lysosomal functions. The results of this study indicated that celecoxib inhibited cell proliferation in a time- and dose-dependent fashion. The flow cytometry analysis showed that celecoxib induced apoptosis at low concentrations and mainly cell necrosis at high concentrations. The Western blot test confirmed the induction of apoptosis by the upregulation of apoptosis-related proteins cleaved caspase-3 and cleaved PARP. Furthermore, this study demonstrated that celecoxib prevented the autophagic flux by inhibiting lysosome function; the fluorescence intensity of the LysoTracker probe and the level of autophagy-related proteins LC3-II and p62 were increased, but the fluorescence intensity of the LysoSensor probe was weakened. These findings show that celecoxib is an autophagy suppresser and has antitumor effects in HL-60 cells by inducing cell apoptosis and necrosis.

Zoledronic acid overcomes adriamycin resistance in acute myeloid leukemia cells by promoting apoptosis.

Zoledronic acid (ZOL), a nitrogen­containing bisphosphonate, is widely used in metastatic bone disease. Previous studies indicate that ZOL has marked anti­leukemia activity, however, the underlying mechanism of action remains to be elucidated. The present study aimed to explore the mechanism of the anti­leukemia effect of ZOL in leukemia cells. It was observed that ZOL inhibited the proliferation of HL­60 and adriamycin­resistant HL­60 (HL­60/A) cells using a WST­8 assay. An Annexin V­propidium iodide indicated that ZOL induced apoptosis of the two cell types in a dose­ and time­dependent manner. Hoechst 33342 staining was also used to verify the levels of apoptosis. The colony formation assay demonstrated that ZOL significantly inhibited colony formation capacity in acute myeloid leukemia (AML) cells. This was achieved by the induction of S­phase cell cycle arrest, downregulation of B­cell lymphoma 2 (Bcl­2) and upregulation of Bcl­2 associated X protein and cleaved poly (ADP­ribose) polymerase. The results indicate that ZOL inhibited cell proliferation by inducing apoptosis via the mitochondrial apoptotic pathway and this anti­leukemic activity appeared notably enhanced in HL­60/A cells. As ZOL is already available for clinical use, these results indicate that it may be an effective addition to the chemotherapeutic strategies for AML.