Promyelocytic Leukemia Cell Line NB4 Research Articles

Targeting inhibition of TCTP could inhibit proliferation and induce apoptosis in AML cells

Translationally controlled tumor protein (TCTP) is a highly conserved multifunctional protein, which participates in many important physiological processes. Recently, the roles of TCTP in cell proliferation and apoptosis, especially its close relationship with various tumors, have attracted widespread attention. In this study, we found that the protein level of TCTP was significantly reduced in acute promyelocytic leukemia cell line NB4 transfected with retinoic acid-induced gene G (RIG-G). The RIG-G was found in our previous work as a key mediator of anti-proliferative activity in retinoid/interferon-related pathways. Here, we tried to further explore the function of TCTP in the development of acute myeloid leukemia (AML) from different levels. Our results showed that inhibiting TCTP expression could attenuate AML cells proliferation and induce apoptosis both in AML cell lines and in xenograft of NOD-SCID mice. In addition, either compared with patients in complete remission or non-leukemia patients, we detected that the expression of TCTP was generally high in the fresh bone marrow of AML patients, suggesting that there was a certain correlation between TCTP and AML disease progression. Taken together, our study revealed the role of TCTP in AML development, and provided a potential target for AML treatment.

Mechanism of Proliferation and Apoptosis of Acute Promyelocytic Leukemia Cell Line NB4 Induced by TPA

To investigate the effect of phorbol-12-myristate-13-ace-tate (TPA) on the proliferation and apoptosis of acute promyelocytic leukemia cell line NB4 and its molecular mechanism. The effect of different concentrations of TPA on the proliferation of NB4 cells at different time points was detected by CCK-8 assay. The morphological changes of NB4 cells were observed by Wright-Giemsa staining. The cell cycle and apoptosis of NB4 cells after TPA treatment were detected by flow cytometry. The mRNA expressions of NB4 cells after TPA treatment were analyzed by high-throughput microarray analysis and real-time quantitative PCR. Western blot was used to detect the protein expression of CDKN1A, CDKN1B, CCND1, MYC, Bax, Bcl-2, c-Caspase 3, c-Caspase 9, PIK3R6, AKT and p-AKT. Compared with the control group, TPA could inhibit the proliferation of NB4 cells, induce the cells to become mature granulocyte-monocyte differentiation, and also induce cell G1 phase arrest and apoptosis. Differentially expressed mRNAs were significantly enriched in PI3K/AKT pathway. TPA treatment could increase the mRNA levels of CCND1, CCNA1, and CDKN1A, while decrease the mRNA level of MYC. It could also up-regulate the protein levels of CDKN1A, CDKN1B, CCND1, Bax, c-Caspase 3, c-Caspase 9, and PIK3R6, while down-regulate MYC, Bcl-2, and p-AKT in NB4 cells. TPA induces NB4 cell cycle arrest in G1 phase and promotes its apoptosis by regulating PIK3/AKT signaling pathway.

Activity of Free and Liposomal Antimony Trioxide in the Acute Promyelocytic Leukemia Cell Line NB4.

Antimony is a chemical element used in the therapy of parasitic diseases with a promising anticancer potential. The aim of this study was to evaluate in vitro activity of free or liposomal vesicle-packed antimony trioxide (AT or LAT) in the t(15;17)(q22;q21) translocation-positive acute promyelocytic leukemia (APL) cell line NB4. Cytotoxicity was analysed with trypan blue exclusion, the MTT assay and neutral red exclusion assay; cell proliferation with PicoGreen®; and reactive oxygen species (ROS) production with DCFDA. Liposomal particles did not change the pH of the cell culture medium and entered the cells. Both formulations resulted in a time- and concentration-dependent cytotoxicity and production of ROS. LAT showed higher toxicity at lower concentrations compared to AT. LAT may be used to decrease drug dosage and maintain high anti-tumoral effects on APL cells.

The synthesis and cytotoxic activity of derivatives of 4β-hydroxywithanolide E

4β-Hydroxywithanolide E, which can be obtained in large amounts from the Physalis genus, possessed anti-proliferative effects on a variety of human cancer cell lines. For discussing its anti-tumor structure-activity relationship, a series of 4β-hydroxywithanolide E derivatives (1–17) were synthesized and evaluated for their antitumor activity in vitro towards acute promyelocytic leukemia NB4 cell line by the Alarma blue assay. Cytotoxicity data revealed that the enone structure and C-4 hydroxyl substituents of ring A, together with the side chain (C-20–C-28) play an important effect on the cytotoxicity.

Identification and characterization of isocitrate dehydrogenase 1 (IDH1) as a functional target of marine natural product grincamycin B.

Grincamycins (GCNs) are a class of angucycline glycosides isolated from actinomycete Streptomyces strains that have potent antitumor activities, but their antitumor mechanisms remain unknown. In this study, we tried to identify the cellular target of grincamycin B (GCNB), one of most dominant and active secondary metabolites, using a combined strategy. We showed that GCNB-selective-induced apoptosis of human acute promyelocytic leukemia (APL) cell line NB4 through increase of ER stress and intracellular reactive oxygen species (ROS) accumulation. Using a strategy of combining phenotype, transcriptomics and protein microarray approaches, we identified that isocitrate dehydrogenase 1(IDH1) was the putative target of GCNB, and confirmed that GCNs were a subset of selective inhibitors targeting both wild-type and mutant IDH1 in vitro. It is well-known that IDH1 converts isocitrate to 2-oxoglutarate (2-OG), maintaining intracellular 2-OG homeostasis. IDH1 and its mutant as the target of GCN B were validated in NB4 cells and zebrafish model. Knockdown of IDH1 in NB4 cells caused the similar phenotype as GCN B treatment, and supplementation of N-acetylcysteine partially rescued the apoptosis caused by IDH1 interference in NB4 cells. In zebrafish model, GCN B effectively restored myeloid abnormality caused by overexpression of mutant IDH1(R132C). Taken together, we demonstrate that IDH1 is one of the antitumor targets of GCNs, suggesting wild-type IDH1 may be a potential target for hematological malignancies intervention in the future.

Folic acid modified lipid-bilayer coated mesoporous silica nanoparticles co-loading paclitaxel and tanshinone IIA for the treatment of acute promyelocytic leukemia

In this work, paclitaxel (Ptx) combined with tanshinone IIA (TanIIA) was found to show synergistic effect on inducing apoptosis of human acute promyelocytic leukemia (APL) cell line NB4, and the anti-tumor effect was strongest when its molar ratio was 1:1. To enhance the efficacy and reduce side effects, an active targeting drug delivery system with mesoporous silica nanoparticles (MSNs) coated with folic acid (FA) modified PEGylated lipid-bilayer (LB) membrane (FA-LB-MSNs) was established for co-loading drugs. The drug loadings of Ptx and TanIIA in FA-LB-MSNs were 5.5% and 1.8%, respectively. Compared with the uncoated MSNs, the FA-LB-MSNs showed a sustained drug release, and Ptx and TanIIA released synchronously from the carriers. By means of biological adhesion between FA and its receptors, the uptake of FA-LB-MSNs by NB4 cells was significantly higher than that of uncoated preparations, and Ptx combined with TanIIA had strong synergistic effect to enhance the apoptosis and differentiation of NB4 cells. The results of pharmacodynamics in vivo showed that the FA-LB-MSNs targeted tumor in nude mice more effectively than the compared formulations without FA modification. The Ptx and TanIIA-loaded FA-LB-MSNs group showed significantly better effects on inducing apoptosis and inhibiting tumor growth than the reference groups, which agreed with the results of anti-tumor experiments in vitro. Furthermore, no toxicity was observed to the heart, liver, spleen, lung and kidney of the tumor-bearing animals, indicating good biocompatibility of the prepared novel nanocarriers. This study confirmed the synergistic therapeutic effect of Ptx and TanIIA on APL, and the superior of FA-LB-MSNs as co-loaded nanocarriers for active targeted therapy of tumors.

Role of Reactive Oxygen Species in GDC-0152-Induced Apoptosis and Autophagy of NB4 cells

To investigate the effect of reactive oxygen species (ROS) on GDC-0152-induced apoptosis and autophagy of acute promyelocytic leukemia cell line NB4. Different concentrations of GDC-0152 combined with Z-VAD-FMK was applied to NB4 cells. Cell proliferation was detected by CCK8 method. Apoptosis rate, autophagy and ROS level were detected by flow cytometry. The autophagy was observed by Cyto-ID staining fluorescence microscopy, and flow cytometry were used to detect the fluorescence expression. The expression of autophagy-related protein LC3B was detected by Western blot. GDC-0152 increased proliferation inhibition rate and apoptosis rate in NB4 cells (P＜0.05); GDC-0152 induced increase of ROS level of NB4 cells; GDC-0152 increased autophagy of NB4 cells that was found by Cyto-ID staining fluorescence microscopy and flow cytometry (P＜0.05). Western blot showed that GDC-0152 increased LC3B expression in NB4 cells and promoted the conversion of LC3BI to LC3BII; as compared with GDC-0152 (100 ng/ml), GDC-0152 (100 ng/ml) combined with ROS inhibitor YCG063 (10 μmol/L) decreased apoptosis and autophagy (P＜0.05). GDC-0152 inhibits cell proliferation by inducing apoptosis and autophagy of NB4 cells. ROS can promote GDC-0152-induced apoptosis and autophagy of NB4 cells.

Inducible Expression of Mutant ELANE Correlates with Disruption of Differentiation Program, but Not the Unfolded Protein Response

Background. Severe congenital neutropenia (SCN) is characterized by a critical reduction in absolute neutrophil count (ANC < 500/μl), which renders the affected individual vulnerable to recurrent, life-threatening infections. A majority of SCN cases arise due to germline mutations in the neutrophil elastase gene (ELANE). Treatment with high dose granulocyte colony stimulating factor (GCSF) increases the number of neutrophils and eliminates the risk of infection. SCN patients are at a significantly high risk of developing myelodysplastic syndrome (MDS) or acute myelogenous leukemia (AML). About 70% of the MDS/AML cases report somatic mutations in the GCSF receptor gene (CSF3R), suggesting a correlation between GCSF treatment and development of MDS/AML. The current favored mechanism for ELANE mutations promoting SCN is induction of an unfolded protein response (UPR), triggering death of neutrophil precursors resulting in neutropenia. However multiple studies of UPR activation reported a requirement of treatment with chemical UPR inducers such as tunicamycin or bortezomib to observe significant changes. The mechanism of mutant ELANE-mediated neutrophil deficit thus remains elusive. In addition, the ability of G-CSF to alleviate neutropenia and its role in progression from SCN to MDS/AML is still a confounding factor in G-CSF therapy for SCN cases. Methods.We created a doxycycline inducible expression system of ELANE, consisting of wild type (wt) and point mutation (G185R) variant associated with SCN, in the murine myeloblast cell line 32D and the human promyelocytic leukemia cell line NB4. We determined the effect of mutant ELANE expression on cell proliferation (Trypan blue exclusion), survival (Trypan blue exclusion, AnnexinV-PI staining) and differentiation (Wright-Giemsa staining, CD11b expression). Underlying molecular changes were investigated using immunoblotting and qPCR based gene expression analysis. Results . Induction of wt or mutant ELANEexpression with doxycycline did not have any detrimental effects on cell proliferation and survival. However, a partial block in differentiation with an accumulation of myeloid progenitors was observed in cells expression mutant ELANE. Profiling of gene expression for markers of differentiation identified reduced expression of key transcriptional factors (Cebpa, Cebpe, Cebpb, Cebpd, Gfi1, Spi1) coupled with reduced levels of other markers of differentiation (e.g., Mpo, Ltf). Increased transcript levels were also observed in some cell cycle genes (Pola1, Ccnd1). We did not observe an increase in expression of UPR genes upon mutant ELANEinduction. Conclusion.Our data demonstrate that expression of mutant ELANE promotes an aberrant differentiation gene expression profile that leads to a partial block in differentiation. In addition, our data also suggest that mutant ELANE expression does not promote UPR. We also show a concomitant upregulation of cell proliferation genes upon mutant ELANE expression. This detour from a differentiation profile may indicate pre-leukemic underpinnings for G-CSF treatment in SCN. Disclosures No relevant conflicts of interest to declare.

Preliminary results indicate resveratrol affects proliferation and apoptosis of leukemia cells by regulating PTEN/PI3K/AKT pathway.

PTEN-PI3K/AKT signaling pathway is widely involved in the regulation of cell proliferation, cell cycle, apoptosis, and invasion. Resveratrol (Resv) is a natural botanical ingredient involved in several biological activities. It is still unclear in terms of whether Resv may exert anti-leukemia effects by regulating the PTEN-PI3K/AKT pathway. This study investigated the effect of Resv on leukemia cell proliferation and apoptosis by regulating PTEN-PI3K/AKT pathway. Human normal peripheral blood PBMC cells, and human acute promyelocytic leukemia (APL) cell line NB-4 and HL-60 cells were cultured in vitro. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to detect Phosphatase and tensin homolog (PTEN) mRNA expression. Western blot was adopted to test PTEN protein expression. HL-60 and NB-4 cells were treated with 0, 5, 10, and 20 μM Resv, respectively. Cell proliferation was analyzed by cell counting kit8 (CCK-8) assay. The level of caspase-3 was measured by Western blot. HL-60 cells were divided into control group, 20 μM Resv treatment group, and Resv+PTEN inhibitor SF1670 group. Cell apoptosis was determined by flow cytometry. Cell proliferation was assessed by EdU staining. Compared with peripheral blood mononuclear cell (PBMC), PTEN mRNA and protein levels were significantly decreased in NB-4 and HL-60 cells. Resv significantly inhibited the proliferation activity in HL-60 and NB-4 cells, and increased the activity of caspase-3. Resv treatment up-regulated the expression of PTEN and reduced the expression of p-AKT protein in HL-60 cells. However, Resv treatment markedly suppressed the proliferation of HL-60 and induced apoptosis. SF1670 treatment in the presence of Resv significantly antagonized the down-regulation of p-AKT protein expression induced by Resv, resulting in decreased apoptosis and enhanced cell proliferation. Resv can up-regulate PTEN expression and inhibit the activity of PI3K/AKT pathway to play an anti-leukemia effect through suppressing cell proliferation and inducing apoptosis.

Indole itself and its novel derivative affect PML cells proliferation via controlling the expression of cell cycle genes

Recently the role of indole and pyran rings in carcinogenesis has been well studied. Here we studied the effects and the possible mechanisms of the action of basal indole (I3A) and its novel indole derivative (C19H15F3N2O) on inhibition of proliferation cells in acute promyelocytic leukemia NB4 cell line by examining the expression of cell cycle genes. We treated NB4 cells with concentration of C19H15F3N2O for 24-72 h. The MTT and PI/Annexin V examinations were employed for assessment of the proliferation and apoptosis of NB4 cells. Both of Cyclin D and P21 were detected by the Real-time PCR. The western blotting analysis was also performed to show the protein levels for P21. A difference was regarded significant if p-value was less than 0.05. MTT assay showed that 15.12-1000 µg/mL C19H15F3N2O caused a time and concentration-dependent inhibition of NB4 cell proliferation. Exposure to higher concentrations of C19H15F3N2O resulted in significantly increased apoptosis rate in NB4 cells. RT PCR showed that C19H15F3N2O has up-regulated the expression of P21 and down-regulated the expression of Cyclin D. Western blotting experiments also demonstrated that the P21 expression in C19H15F3N2O treated cells has significantly increased, where compared with either untreated control cells or I3A treated cells. This newly (C19H15F3N2O) was able to inhibit NB4 cells proliferation and causes apoptosis of these cells more than I3A, and these effects are probably facilitated via cell cycle arrest. C19H15F3N2O might probably be introduced as a promising organic therapeutic reagent against APL.

Effects of EGCG on Proliferation, Cell Cycle and DAPK1 Gene Methylation of Acute Promyelocytic Leukemia NB4 Cell Line

To investigate the effects of epigallocatechin-3-gallate (EGCG) on proliferation and cell cycle of acute promyelocytic leukemia NB4 cell line and to clarify the molecular mechanism. NB4 cells were treated with 0,50,75,100 and 125µmol/L of EGCG for 24, 48, 72 and 96 h, respectively. The proliferation level of NB4 cells was measured by CCK-8 assay. The cell cycle progression of NB4 cells was assayed by flow cytometry. The mRNA expression levels of DNMT1, DNMT3a and DAPK1 were detected by RT-PCR. The methylation status of gene was tested by methylation specific PCR, and the expression level of DAPK1 protein was detected by Western blot. The proliferation and cell cycle progression of NB4 cells treated with EGCG were inhibited and showed the characteristic of time-dependent and dose-dependent manner. The expression level of DAPK1 and DNMT3a decreased in NB4 cells treated with EGCG. The expression level of DAPK increased in NB4 cells treated with EGCG, while the methylation of DAPK1 gene decreased. EGCG inhibits the proliferation and cell cycle progression of NB4 cells by inhibiting the expression of DNMT1 and DNMT3a and down-regulating the methylation status of DAPK1 gene.

Optimization of 5-arylidene barbiturates as potent, selective, reversible LSD1 inhibitors for the treatment of acute promyelocytic leukemia

Histone lysine specific demethylase 1 (LSD1) is overexpressed in diverse hematologic disorders and recognized as a promising target for blood medicines. In this study, molecular docking-based virtual screening united with bioevaluation was utilized to identify novel skeleton of 5-arylidene barbiturate as small-molecule inhibitors of LSD1. Among the synthesized derivatives, 12a exhibited reversible and potent inhibition (IC50 = 0.41 μM) and high selectivity over the MAO-A and MAO-B. Notably, 12a strongly induced differentiation effect on acute promyelocytic leukemia NB4 cell line and distinctly escalated the methylation level on histone 3 lysine 4 (H3K4). Our findings indicate that 5-arylidene barbiturate may represent a new skeleton of LSD1 inhibitors and 12a deserve as a promising agent for the further research.

Sorafenib inhibited cell growth through the MEK/ERK signaling pathway in acute promyelocytic leukemia cells.

The present study assessed the mechanism underlying the effect of sorafenib on the proliferation and apoptosis of the acute promyelocytic leukemia (APL) cell line NB4. NB4 cells were treated with different concentrations of sorafenib (0, 1.5, 3, 6, and 12 µM) for 24, 48 and 72 h. Cell proliferation, cell cycle, and apoptosis were analyzed using an MTT assay and flow cytometry analysis, respectively. Reverse transcription-semi-quantitative polymerase chain reaction and western blot analysis were performed to assess the expression of caspase-3, caspase-8, myeloid cell leukemia (MCL)1, cyclin D1, mitogen-activated protein kinase (MEK), phosphorylated (P)-MEK, extracellular signal-regulated kinase (ERK) and P-ERK. The results of the MTT assay demonstrated that, compared with untreated cells, the proliferation of sorafenib-treated NB4 cells was inhibited dose- and time-dependently. Furthermore, cell cycle arrest was induced in the G0/G1 phase and cell apoptosis was promoted in a dose-dependent manner in sorafenib-treated NB4 cells compared with untreated cells. In addition, the expression of the proapoptotic molecules caspase-3 and caspase-8 was significantly upregulated, and the expression of the antiapoptotic molecule MCL1 and the cell cycle-associated cyclin D1 was downregulated in sorafenib-treated NB4 cells compared with untreated cells. Furthermore, the phosphorylation of MEK and ERK was inhibited in sorafenib-treated NB4 cells compared with untreated cells. Sorafenib may inhibit proliferation and induce cell cycle arrest and apoptosis in APL cells. The underlying mechanisms of such effects may be associated with alterations to the expression of apoptosis-associated and cell cycle-associated molecules via MEK/ERK signaling pathway inhibition.

Identification of an IRF-1 splicing transcript in APL cells sharing similar transactivation activity of the full length one

Interferon regulatory factor-1 (IRF-1) is a member of the interferon regulatory factor family. It acts as a transcriptional activator and plays a critical role in antiviral defense, immune response, cell growth regulation, apoptosis and cell differentiation. Deletions, mutations or aberrant splicing of IRF-1 would result in its functional inactivation, and closely related to the tumorigenesis. In this work, we identified an IRF-1 splicing transcript (IRF-1-s) in all-trans retinoic acid (ATRA)-treated acute promyelocytic leukemia (APL) cell line NB4 cells. It lost the exon 8 and 9 of the full length IRF-1, expressed in numerous cell types and could be induced to expression by ATRA in NB4 cells. It turned out similar biological activity as full length IRF-1 to enhance the transcription of interferon stimulated response element (ISRE)-containing target genes. Identification of IRF-1-s in NB4 cells would be benefit for our further exploring the signaling pathway of ATRA and interferons, as well as the mechanisms of differentiation of APL cells.

Reduction of GPSM3 expression akin to the arthritis-protective SNP rs204989 differentially affects migration in a neutrophil model.

G Protein Signaling Modulator-3 (GPSM3) is a leukocyte-specific regulator of G protein-coupled receptors (GPCRs), which binds inactivated Gαi·GDP subunits and precludes their reassociation with Gβγ subunits. GPSM3 deficiency protects mice from inflammatory arthritis and, in humans, GPSM3 single nucleotide polymorphisms (SNPs) are inversely associated with the risk of rheumatoid arthritis development; recently, these polymorphisms were linked to one particular SNP (rs204989) that decreases GPSM3 transcript abundance. However, the precise role of GPSM3 in leukocyte biology is unknown. Here we show that GPSM3 is induced in the human promyelocytic leukemia NB4 cell line following retinoic acid treatment, which differentiates this cell line into a model of neutrophil physiology (NB4*). Reducing GPSM3 expression in NB4* cells, akin to the effect ascribed to the rs204989 C>T transition, disrupts cellular migration toward leukotriene B4 (LTB4) and (to a lesser extent) interleukin-8 (a.k.a. IL-8 or CXCL8), but not migration toward formylated peptides (fMLP). As the chemoattractants LTB4 and CXCL8 are involved in recruitment of neutrophils to the arthritic joint, our results suggest that the arthritis-protective GPSM3 SNP rs204989 may act to decrease neutrophil chemoattractant responsiveness.

Delphinidin induces cytotoxicity and potentiates cytocidal effect in combination with arsenite in an acute promyelocytic leukemia NB4 cell line.

The effects of delphinidin were investigated by focusing on growth inhibition, cell cycle arrest and apoptosis induction in the human acute promyelocytic leukemia (APL) NB4 cell line. Delphinidin exhibited a dose- and time-dependent cytotoxic effect against NB4 cells. Almost no cell cycle arrest, but an apparent increase in the percentage of sub-G1 cells was observed in delphinidin-treated cells. The activation of caspase-8 and -9 was observed as early as 1-h post-exposure to delphinidin, followed by the activation of caspase-3 from 3-h post-exposure. A substantial decrease in the expression level of Bid was also observed as early as 1-h post-exposure. A modest decrease in the mitochondrial membrane potential (ΔΨm) was observed at 3-h post-exposure, followed by a substantial time-dependent decrease in ΔΨm in treated cells. Delphinidin exerted more potent cytotoxicity against NB4 cells than normal peripheral blood mononuclear cells (PBMNCs). In addition, delphinidin in combination with an arsenic derivative arsenite (As(III)), which has demonstrated marked efficacy in patients with APL, achieved an enhanced cytocidal effect against NB4 cells, but lesser on PBMNCs. Treatment of NB4 cells with As(III) plus delphinidin did not increase, but decreased slightly, intracellular arsenic accumulation (As[i]) as compared to that treated with As(III) alone. These results suggested that delphinidin selectively sensitized NB4 cells to As(III), resulting in the enhancement of As(III) cytotoxicity by strengthening intrinsic/extrinsic pathway-mediated apoptosis induction, rather than affecting the As[i] levels. These observations may offer a rationale for the use of delphinidin to improve the clinical efficacy of As(III).

The antileukemia roles of PP242 alone or in combination with daunorubicin in acute leukemia.

PP242 is a novel dual mammalian target of rapamycin (mTOR) inhibitor that simultaneously inhibits mTORC1 and mTORC2, and its antileukemia effect has been sufficiently investigated here. The human acute leukemia cell lines and primary blasts were treated with PP242 alone or in combination with daunorubicin (DNR). Cell proliferation was examined using an MTT assay. The phosphorylation expression of the Akt/mTORC1/eIF4E signaling pathway was assessed by western blot analysis. The assembly of the eIF4F translation initiation complex was examined using a 7-methyl-guanosine cap affinity assay. PP242 significantly induced cytotoxicity in human acute leukemia cells, especially in combination with DNR. The phosphorylation levels of eIF4E (p-eIF4E) at Ser209 influence the antileukemia roles of PP242. As expected, the antiproliferative effects of PP242 on leukemia cells with low p-eIF4E expression, such as the acute promyelocytic leukemia NB4 cell line and AML-M3 primary blasts, were poor. Surprisingly, the effects of PP242 in leukemia cells with high p-eIF4E expression, such as the acute myelomonocytic leukemia THP-1 cell line and M4-M5 primary blasts, were also weak. In contrast, PP242 exerted a significant antiproliferative effect in the Ph+ acute lymphoblastic leukemia SUP-B15 cell line and the mantle cell lymphoma JEKO-1 cell line, which had intermediate p-eIF4E levels. PP242 inhibited the translation of the antiapoptotic protein Mcl-1 by downregulating the Akt/mTORC1/eIF4E signaling pathway. More importantly, DNR activated the Akt/mTORC1/eIF4E signaling pathway, whereas PP242 effectively eliminated this deleterious side effect of DNR and synergistically enhanced the anticancer ability of DNR treatment. PP242, especially in combination with DNR, exerts significant antileukemia effects.

Changes of Apolipoprotein M Gene Expression During the Cell Differentiation and Apoptosis Induced by Simvastatin in Combination with All-Trans Retinoic Acid in Human Promyelocytic Leukemia Cell Line NB4.

We examined the effect of simvastatin (SV) alone and in combination with all-trans retinoic acid (ATRA) on proliferation, differentiation, apoptosis and apolipoprotein M (apoM) expression in the human promyelocytic leukemia cell line NB4. The NB4 cells were incubated with 10μM Simvastatin (10SV) and 0.5μM ATRA alone or in combination, taking NB4 cells without any treatment as normal controls. The cells of different groups were collected at 24, 48 and 72h post-incubation for further detection. Their morphological changes were observed after Wright stain. MTT method was used to assay the growth inhibition rate and flow cytometry to detect CD11b expression level and the early stage apoptosis ratio. Real-time quantitative reverse transcriptase-polymerase chain reaction was used to detect the apoM gene expression levels. As expected 0.5μM ATRA did not affect proliferation or apoptosis, strongly induced differentiation and decreased apoM expression.10SV inhibited proliferation, increased apoptosis, induced differentiation and increased apoM expression in a time-dependent manner. The addition of ATRA to SV did not increase the effect of SV on proliferation and apoptosis, but increased the effect of SV on differentiation. And completely abrogated the effect of SV on apoM expression. Together these results show that SV has anti-leukemic properties by itself and that combined therapy may have a place in the current anti-leukemic arsenal.

Mechanisms of resistance to apoptosis in the human acute promyelocytic leukemia cell line NB4.

Current frontline therapies have improved overall survival in acute promyelocytic leukemia (APL) patients to exceptional rates; however, relapse is still a problem among high-risk and old patients. Therefore, the development of better and safer therapies continues to be a goal in the treatment of this disease. In the present work, we examined three different pathways that hinder cell death in the APL cell line NB4, shedding light on the mechanisms that underlie resistance to apoptosis in these cells and that might help provide them with a proliferative advantage. We found that the proteasome inhibitor MG-132 specifically induces in NB4 cells an Nrf2-mediated antioxidant response which counteracts mitochondria-dependent apoptosis induced by the lipophilic cation dequalinium. More importantly, we also demonstrated that high basal autophagy levels and the gain-of-function of mutant p53 are intrinsic mechanisms of resistance to apoptosis in this cell line. According to our results, the pharmacological inhibition of autophagy and p53 mutants are useful tools to explore resistance to apoptosis in APL and other types of cancer and could be the bases of new therapeutic approaches that improve the efficiency and allow dose reduction of the current treatments.

A small-molecule targeting the microRNA binding domain of argonaute 2 improves the retinoic acid differentiation response of the acute promyelocytic leukemia cell line NB4.

Argonaute proteins are pivotal regulators of gene expression mediating miRNAs function. Modulating their activity would be extremely useful to elucidate the processes governing small-RNAs-guided gene silencing. We report the identification of a chemical compound able to compete with Argonaute 2 miRNAs binding, and we demonstrate that this functional inhibition determines effects similar to Argonaute 2 shRNA-mediated down-regulation, favoring granulocytic differentiation of the acute promyelocytic leukemia cell line NB4 in response to retinoic acid.