NF-kappaB inhibition triggers death of imatinib-sensitive and imatinib-resistant chronic myeloid leukemia cells including T315I Bcr-Abl mutants

Molecular determinants of the response of cancer cells towards geldanamycin and its derivatives

Geldanamycin is an ansamycin-derivative of a benzoquinone isolated from Streptomyces hygroscopicus. It inhibits tyrosine kinases and heat shock protein 90 (HSP90). Geldanamycin and 11 derivatives were subjected to molecular docking to HSP90, and 17-desmethoxy-17-N,N-dimethylamino-geldanamycin (17-DMAG) was the compound with the highest binding affinity (-7.73 ± 0.12 kcal/mol) and the lowest inhibition constant (2.16 ± 0.49 μM). Therefore, 17-DMAG was selected for further experiments in comparison to geldanamycin. Multidrug resistance (MDR) represents a major problem for successful cancer therapy. We tested geldanamycin and 17-DMAG against various drug-resistant cancer cell lines. Although geldanamycin and 17-DMAG inhibited the proliferation in all cell lines tested, multidrug-resistant P-glycoprotein-overexpressing CEM/ADR5000 cells were cross-resistant, ΔEGFR-overexpressing tumor cells and p53 knockout cells were sensitive to these two compounds. COMPARE and hierarchical cluster analyses were performed, and 60 genes were identified to predict the sensitivity or resistance of 59 NCI tumor cell lines towards geldanamycin and 17-DMAG. The distribution of cell lines according to their mRNA expression profiles indicated sensitivity or resistance to both compounds with statistical significance. Moreover, bioinformatic tools were used to study possible mechanisms of action of geldanamycin and 17-DMAG. Galaxy Cistrome analyses were carried out to predict transcription factor binding motifs in the promoter regions of the candidate genes. Interestingly, the NF-ĸB DNA binding motif (Rel) was identified as the top transcription factor. Furthermore, these 60 genes were subjected to Ingenuity Pathway Analysis (IPA) to study the signaling pathway interactions of these genes. Interestingly, IPA also revealed the NF-ĸB pathway as the top network among these genes. Finally, NF-ĸB reporter assays confirmed the bioinformatic prediction, and both geldanamycin and 17-DMAG significantly inhibited NF-κB activity after exposure for 24 h. In conclusion, geldanamycin and 17-DMAG exhibited cytotoxic activity against different tumor cell lines. Their activity was not restricted to HSP90 but indicated an involvement of the NF-KB pathway.

Eliminating chronic myeloid leukemia stem cells by IRAK1/4 inhibitors

Leukemia stem cells (LSCs) in chronic myeloid leukemia (CML) are quiescent, insensitive to BCR-ABL1 tyrosine kinase inhibitors (TKIs) and responsible for CML relapse. Therefore, eradicating quiescent CML LSCs is a major goal in CML therapy. Here, using a G₀ marker (G₀M), we narrow down CML LSCs as G₀M- and CD27- double positive cells among the conventional CML LSCs. Whole transcriptome analysis reveals NF-κB activation via inflammatory signals in imatinib-insensitive quiescent CML LSCs. Blocking NF-κB signals by inhibitors of interleukin-1 receptor-associated kinase 1/4 (IRAK1/4 inhibitors) together with imatinib eliminates mouse and human CML LSCs. Intriguingly, IRAK1/4 inhibitors attenuate PD-L1 expression on CML LSCs, and blocking PD-L1 together with imatinib also effectively eliminates CML LSCs in the presence of T cell immunity. Thus, IRAK1/4 inhibitors can eliminate CML LSCs through inhibiting NF-κB activity and reducing PD-L1 expression. Collectively, the combination of TKIs and IRAK1/4 inhibitors is an attractive strategy to achieve a radical cure of CML.

Proteasome 26S subunit, non-ATPases 1 (PSMD1) and 3 (PSMD3), play an oncogenic role in chronic myeloid leukemia by stabilizing nuclear factor-kappa B

Tyrosine kinase inhibitors (TKIs) targeting BCR-ABL1 have revolutionized therapy for chronic myeloid leukemia (CML), paving the way for clinical development in other diseases. Despite success, targeting leukemic stem cells and overcoming drug resistance remain challenges for curative cancer therapy. To identify drivers of kinase-independent TKI resistance in CML, we performed genome-wide expression analyses on TKI-resistant versus sensitive CML cell lines, revealing a nuclear factor-kappa B (NF-κB) expression signature. Nucleocytoplasmic fractionation and luciferase reporter assays confirmed increased NF-κB activity in the nucleus of TKI-resistant versus sensitive CML cell lines and CD34+ patient samples. Two genes that were upregulated in TKI-resistant CML cells were proteasome 26S subunit, non-ATPases 1 (PSMD1) and 3 (PSMD3), both members of the 19S regulatory complex in the 26S proteasome. PSMD1 and PSMD3 were also identified as survival-critical genes in a published small hairpin RNA library screen of TKI resistance. We observed markedly higher levels of PSMD1 and PSMD3 mRNA in CML patients who had progressed to the blast phase compared with the chronic phase of the disease. Knockdown of PSMD1 or PSMD3 protein correlated with reduced survival and increased apoptosis in CML cells, but not in normal cord blood CD34+ progenitors. Luciferase reporter assays and immunoblot analyses demonstrated that PSMD1 and PSMD3 promote NF-κB protein expression in CML, and that signal transducer and activator of transcription 3 (STAT3) further activates NF-κB in scenarios of TKI resistance. Our data identify NF-κB as a transcriptional driver in TKI resistance, and implicate PSMD1 and PSMD3 as plausible therapeutic targets worthy of future investigation in CML and possibly other malignancies.

miR-181d/RBP2/NF-κB p65 Feedback Regulation Promotes Chronic Myeloid Leukemia Blast Crisis

Background

Chronic myeloid leukemia (CML) is a malignant clonal proliferative disease. Once it progresses into the phase of blast crisis (CML-BP), the curative effect is poor, and the fatality rate is extremely high. Therefore, it is urgent to explore the molecular mechanisms of blast crisis and identify new therapeutic targets.

Methods

The expression levels of miR-181d, RBP2 and NF-κB p65 were assessed in 42 newly diagnosed CML-CP patients and 15 CML-BP patients. Quantitative real-time PCR, Western blots, and cell proliferation assay were used to characterize the changes induced by overexpression or inhibition of miR-181d, RBP2 or p65. Luciferase reporter assay and ChIP assay was conducted to establish functional association between miR-181d, RBP2 and p65. Inhibition of miR-181d expression and its consequences in tumor growth was demonstrated in vivo models.

Results

We found that miR-181d was overexpressed in CML-BP, which promoted leukemia cell proliferation. Histone demethylase RBP2 was identified as a direct target of miR-181d which downregulated RBP2 expression. Moreover, RBP2 inhibited transcriptional expression of NF-κB subunit, p65 by binding to its promoter and demethylating the tri/dimethylated H3K4 region in the p65 promoter locus. In turn, p65 directly bound to miR-181d promoter and upregulated its expression. Therefore, RBP2 inhibition resulting from miR-181d overexpression led to p65 upregulation which further forwarded miR-181d expression. This miR-181d/RBP2/p65 feedback regulation caused sustained NF-κB activation, which contributed to the development of CML-BP.

Conclusions

Taken together, the miR-181d/RBP2/p65 feedback regulation promoted CML-BP and miR-181d may serve as a potential therapeutic target of CML-BP.

Inhibition of cystathionine β-synthase promotes apoptosis and reduces cell proliferation in chronic myeloid leukemia

Increased endogenous hydrogen sulfide (H₂S) level by cystathionine β-synthase (CBS) has been shown to closely relate tumorigenesis. H₂S promotes angiogenesis, stimulates bioenergy metabolism and inhibits selective phosphatases. However, the role of CBS and H₂S in chronic myeloid leukemia (CML) remains elusive. In this study, we found that CBS and H₂S levels were increased in the bone marrow mononuclear cells of pediatric CML patients, as well as in the CML-derived K562 cells and CBS expression levels were correlated with different disease phases. Inhibition of CBS reduced the proliferation of the CML primary bone marrow mononuclear cells and induced growth inhibition, apoptosis, cell cycle arrest, and migration suppression in K562 cells and tumor xenografts. The knockdown of CBS expression by shRNA and inhibiting CBS activity by AOAA decreased the endogenous H₂S levels, promoted mitochondrial-related apoptosis and inhibited the NF-κB-mediated gene expression. Our study suggests that inhibition of CBS induces cell apoptosis, as well as limits cell proliferation and migration, a potential target for the treatment of chronic myeloid leukemia.

Acetylshikonin induces apoptosis of human leukemia cell line K562 by inducing S phase cell cycle arrest, modulating ROS accumulation, depleting Bcr-Abl and blocking NF-κB signaling

Acetylshikonin, a natural naphthoquinone derivative compound from Lithospermum erythrorhyzon, has been reported to kill bacteria, suppress inflammation, and inhibit tumor growth. However, the effect of acetylshikonin on human chronic myelocytic leukemia (CML) cells apoptosis and its detailed mechanisms remains unknown. The purpose of the present study was to investigate whether acetylshikonin could inhibit proliferation or induce apoptosis of the K562 cells, and whether by regulating the NF-κB signaling pathway to suppress the development of CML. K562 cells were treated with serial diluted acetylshikonin at different concentrations. Our data showed that K562 cell growth was significantly inhibited by acetylshikonin with an IC50 of 2.03 μM at 24 h and 1.13 μM at 48 h, with increased cell cycle arrest in S-phase. The results of annexin V-FITC/PI and AO/EB staining showed that acetylshikonin induced cell apoptosis in a dose-dependent manner. K562 cells treated with acetylshikonin underwent massive apoptosis accompanied by a rapid generation of reactive oxygen species (ROS). Scavenging the ROS completely blocked the induction of apoptosis following acetylshikonin treatment. The levels of the pro-apoptotic proteins Bax, cleaved caspase-9, cleaved PARP and cleaved caspase-3 increased with increased concentrations of acetylshikonin, while the level of the anti-apoptotic protein Bcl-2 was downregulated. The levels of Cyt C and AIF, which are characteristic proteins of the mitochondria-regulated intrinsic apoptotic pathway, also increased in the cytosol after acetylshikonin treatment. However, the mitochondrial fraction of Cyt C and AIF were decreased under acetylshikonin treatment. In addition, acetylshikonin decreased Bcr-Abl expression and inhibited its downstream signaling. Acetylshikonin could lead to a blockage of the NF-κB signaling pathway via decreasing nuclear NF-κB P65 and increasing cytoplasmic NF-κB P65. Moreover, acetylshikonin significantly inhibited the phosphorylation of IkBα and IKKα/β in K562 cells. These results demonstrated that acetylshikonin significantly inhibited K562 cell growth and induced cell apoptosis through the mitochondria-regulated intrinsic apoptotic pathway. The mechanisms may involve the modulating ROS accumulation, inhibition of NF-κB and BCR-ABL expression. The inhibition of BCR-ABL expression and the inactivation of the NF-κB signaling pathway caused by acetylshikonin treatment resulted in K562 cell apoptosis. Together, our results indicate that acetylshikonin could serve as a potential therapeutic agent for the future treatment of CML.

Leprosy drug clofazimine activates peroxisome proliferator-activated receptor-γ and synergizes with imatinib to inhibit chronic myeloid leukemia cells

Leukemia stem cells contribute to drug-resistance and relapse in chronic myeloid leukemia (CML) and BCR-ABL1 inhibitor monotherapy fails to eliminate these cells, thereby necessitating alternate therapeutic strategies for patients CML. The peroxisome proliferator-activated receptor-γ (PPARγ) agonist pioglitazone downregulates signal transducer and activator of transcription 5 (STAT5) and in combination with imatinib induces complete molecular response in imatinib-refractory patients by eroding leukemia stem cells. Thiazolidinediones such as pioglitazone are, however, associated with severe side effects. To identify alternate therapeutic strategies for CML we screened Food and Drug Administration-approved drugs in K562 cells and identified the leprosy drug clofazimine as an inhibitor of viability of these cells. Here we show that clofazimine induced apoptosis of blood mononuclear cells derived from patients with CML, with a particularly robust effect in imatinib-resistant cells. Clofazimine also induced apoptosis of CD34⁺38^- progenitors and quiescent CD34⁺ cells from CML patients but not of hematopoietic progenitor cells from healthy donors. Mechanistic evaluation revealed that clofazimine, via physical interaction with PPARγ, induced nuclear factor kB-p65 proteasomal degradation, which led to sequential myeloblastoma oncoprotein and peroxiredoxin 1 downregulation and concomitant induction of reactive oxygen species-mediated apoptosis. Clofazimine also suppressed STAT5 expression and consequently downregulated stem cell maintenance factors hypoxia-inducible factor-1α and -2α and Cbp/P300 interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2). Combining imatinib with clofazimine caused a far superior synergy than that with pioglitazone, with clofazimine reducing the half maximal inhibitory concentration (IC₅₀) of imatinib by >4 logs and remarkably eroding quiescent CD34⁺ cells. In a K562 xenograft study clofazimine and imatinib co-treatment showed more robust efficacy than the individual treatments. We propose clinical evaluation of clofazimine in imatinib-refractory CML.

Repurposing of Bromocriptine for Cancer Therapy

Bromocriptine is an ergot alkaloid and dopamine D₂ receptor agonist used to treat Parkinson's disease, acromegaly, hyperprolactinemia, and galactorrhea, and more recently diabetes mellitus. The drug is also active against pituitary hormone-dependent tumors (prolactinomas and growth-hormone producing adenomas). We investigated, whether bromocriptine also inhibits hormone-independent and multidrug-resistant (MDR) tumors. We found that bromocriptine was cytotoxic towards drug-sensitive CCRF-CEM, multidrug-resistant CEM/ADR5000 leukemic cells as well as wild-type or multidrug-resistant ABCB5-transfected HEK293 cell lines, but not sensitive or BCRP-transfected multidrug-resistant MDA-MB-231 breast cancer cells. Bromocriptine strongly bound to NF-κB pathway proteins as shown by molecular docking and interacted more strongly with DNA-bound NF-κB than free NF-κB, indicating that bromocriptine may inhibit NF-κB binding to DNA. Furthermore, bromocriptine decreased NF-κB activity by a SEAP-driven NF-κB reporter cell assay. The expression of MDR-conferring ABC-transporters (ABCB1, ABCB5, ABCC1, and ABCG2) and other resistance-mediating factors (EGFR, mutated TP53, and IκB) did not correlate with cellular response to bromocriptine in a panel of 60 NCI cell lines. There was no correlation between cellular response to bromocriptine and anticancer drugs usually involved in MDR (e.g., anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and others). COMPARE analysis of microarray-based mRNA expression in these cell lines revealed that genes from various functional groups such as ribosomal proteins, transcription, translation, DNA repair, DNA damage, protein folding, mitochondrial respiratory chain, and chemokines correlated with cellular response to bromocriptine. Our results indicate that bromocriptine inhibited drug-resistant tumor cells with different resistance mechanisms in a hormone-independent manner. As refractory and otherwise drug-resistant tumors represent a major challenge to successful cancer chemotherapy, bromocriptine may be considered for repurposing in cancer therapy.

The BCR-ABL/NF-κB signal transduction network: a long lasting relationship in Philadelphia positive Leukemias

The Nuclear Factor-kappa B (NF-κB) family of transcription factors plays a key role in cancer pathogenesis due to the ability to promote cellular proliferation and survival, to induce resistance to chemotherapy and to mediate invasion and metastasis. NF-κB is recruited through different mechanisms involving either canonical (RelA/p50) or non-canonical pathways (RelB/p50 or RelB/p52), which transduce the signals originated from growth-factors, cytokines, oncogenic stress and DNA damage, bacterial and viral products or other stimuli. The pharmacological inhibition of the NF-κB pathway has clearly been associated with significant clinical activity in different cancers. Almost 20 years ago, NF-κB was described as an essential modulator of BCR-ABL signaling in Chronic Myeloid Leukemia and Philadelphia-positive Acute Lymphoblastic Leukemia. This review summarizes the role of NF-κB in BCR-ABL-mediated leukemogenesis and provides new insights on the long lasting BCR-ABL/NF-κB connection.

NF-κB in Hematological Malignancies

NF-κB (Nuclear Factor Κ-light-chain-enhancer of activated B cells) transcription factors are critical regulators of immunity, stress response, apoptosis, and differentiation. Molecular defects promoting the constitutive activation of canonical and non-canonical NF-κB signaling pathways contribute to many diseases, including cancer, diabetes, chronic inflammation, and autoimmunity. In the present review, we focus our attention on the mechanisms of NF-κB deregulation in hematological malignancies. Key positive regulators of NF-κB signaling can act as oncogenes that are often prone to chromosomal translocation, amplifications, or activating mutations. Negative regulators of NF-κB have tumor suppressor functions, and are frequently inactivated either by genomic deletions or point mutations. NF-κB activation in tumoral cells is also driven by the microenvironment or chronic signaling that does not rely on genetic alterations.

Novel strategies for targeting leukemia stem cells: sounding the death knell for blood cancer

BACKGROUND

Cancer stem cells (CSCs), also known as tumor-initiating cells (TICs), are characterized by high self-renewal and multi-lineage differentiation capacities. CSCs are thought to play indispensable roles in the initiation, progression and metastasis of many types of cancer. Leukemias are thought to be initiated and maintained by a specific sub-type of CSC, the leukemia stem cell (LSC). An important feature of LSCs is their resistance to standard therapy, which may lead to relapse. Increasing efforts are aimed at developing novel therapeutic strategies that selectively target LSCs, while sparing their normal counterparts and, thus, minimizing adverse treatment-associated side-effects. These LSC targeting therapies aim to eradicate LSCs through affecting mechanisms that control their survival, self-renewal, differentiation, proliferation and cell cycle progression. Some LSC targeting therapies have already been proven successful in pre-clinical studies and they are now being tested in clinical studies, mainly in combination with conventional treatment regimens.

CONCLUSIONS

A growing body of evidence indicates that the selective targeting of LSCs represents a promising approach to improve disease outcome. Beyond doubt, the CSC hypothesis has added a new dimension to the area of anticancer research, thereby paving the way for shaping a new trend in cancer therapy.

Regulatory network analysis of microRNAs and genes in imatinib-resistant chronic myeloid leukemia

Targeted therapy in the form of selective breakpoint cluster region-abelson (BCR/ABL) tyrosine kinase inhibitor (imatinib mesylate) has successfully been introduced in the treatment of the chronic myeloid leukemia (CML). However, acquired resistance against imatinib mesylate (IM) has been reported in nearly half of patients and has been recognized as major issue in clinical practice. Multiple resistance genes and microRNAs (miRNAs) are thought to be involved in the IM resistance process. These resistance genes and miRNAs tend to interact with each other through a regulatory network. Therefore, it is crucial to study the impact of these interactions in the IM resistance process. The present study focused on miRNA and gene network analysis in order to elucidate the role of interacting elements and to understand their functional contribution in therapeutic failure. Unlike previous studies which were centered only on genes or miRNAs, the prime focus of the present study was on relationships. To this end, three regulatory networks including differentially expressed, related, and global networks were constructed and analyzed in search of similarities and differences. Regulatory associations between miRNAs and their target genes, transcription factors and miRNAs, as well as miRNAs and their host genes were also macroscopically investigated. Certain key pathways in the three networks, especially in the differentially expressed network, were featured. The differentially expressed network emerged as a fault map of IM-resistant CML. Theoretically, the IM resistance process could be prevented by correcting the included errors. The present network-based approach to study resistance miRNAs and genes might help in understanding the molecular mechanisms of IM resistance in CML as well as in the improvement of CML therapy.

Non genomic loss of function of tumor suppressors in CML: BCR-ABL promotes IκBα mediated p53 nuclear exclusion

Tumor suppressor function can be modulated by subtle variation of expression levels, proper cellular compartmentalization and post-translational modifications, such as phosphorylation, acetylation and sumoylation. The non-genomic loss of function of tumor suppressors offers a challenging therapeutic opportunity. The reactivation of a tumor suppressor could indeed promote selective apoptosis of cancer cells without affecting normal cells. The identification of mechanisms that affect tumor suppressor functions is therefore essential. In this work, we show that BCR-ABL promotes the accumulation of the NFKBIA gene product, IκBα, in the cytosol through physical interaction and stabilization of the protein. Furthermore, BCR-ABL/IκBα complex acts as a scaffold protein favoring p53 nuclear exclusion. We therefore identify a novel BCR-ABL/IκBα/p53 network, whereby BCR-ABL functionally inactivates a key tumor suppressor.

Pharmacogenomics of Scopoletin in Tumor Cells

Drug resistance and the severe side effects of chemotherapy necessitate the development of novel anticancer drugs. Natural products are a valuable source for drug development. Scopoletin is a coumarin compound, which can be found in several Artemisia species and other plant genera. Microarray-based RNA expression profiling of the NCI cell line panel showed that cellular response of scopoletin did not correlate to the expression of ATP-binding cassette (ABC) transporters as classical drug resistance mechanisms (ABCB1, ABCB5, ABCC1, ABCG2). This was also true for the expression of the oncogene EGFR and the mutational status of the tumor suppressor gene, TP53. However, mutations in the RAS oncogenes and the slow proliferative activity in terms of cell doubling times significantly correlated with scopoletin resistance. COMPARE and hierarchical cluster analyses of transcriptome-wide mRNA expression resulted in a set of 40 genes, which all harbored binding motifs in their promoter sequences for the transcription factor, NF-κB, which is known to be associated with drug resistance. RAS mutations, slow proliferative activity, and NF-κB may hamper its effectiveness. By in silico molecular docking studies, we found that scopoletin bound to NF-κB and its regulator IκB. Scopoletin activated NF-κB in a SEAP-driven NF-κB reporter cell line, indicating that NF-κB might be a resistance factor for scopoletin. In conclusion, scopoletin might serve as lead compound for drug development because of its favorable activity against tumor cells with ABC-transporter expression, although NF-κB activation may be considered as resistance factor for this compound. Further investigations are warranted to explore the full therapeutic potential of this natural product.

Use of deferasirox, an iron chelator, to overcome imatinib resistance of chronic myeloid leukemia cells

BACKGROUND/AIMS

The treatment of chronic myeloid leukemia (CML) has achieved impressive success since the development of the Bcr-Abl tyrosine kinase inhibitor, imatinib mesylate. Nevertheless, resistance to imatinib has been observed, and a substantial number of patients need alternative treatment strategies.

METHODS

We have evaluated the effects of deferasirox, an orally active iron chelator, and imatinib on K562 and KU812 human CML cell lines. Imatinib-resistant CML cell lines were created by exposing cells to gradually increasing concentrations of imatinib.

RESULTS

Co-treatment of cells with deferasirox and imatinib induced a synergistic dose-dependent inhibition of proliferation of both CML cell lines. Cell cycle analysis showed an accumulation of cells in the subG1 phase. Western blot analysis of apoptotic proteins showed that co-treatment with deferasirox and imatinib induced an increased expression of apoptotic proteins. These tendencies were clearly identified in imatinib-resistant CML cell lines. The results also showed that co-treatment with deferasirox and imatinib reduced the expression of BcrAbl, phosphorylated Bcr-Abl, nuclear factor-κB (NF-κB) and β-catenin.

CONCLUSIONS

We observed synergistic effects of deferasirox and imatinib on both imatinib-resistant and imatinib-sensitive cell lines. These effects were due to induction of apoptosis and cell cycle arrest by down-regulated expression of NF-κB and β-catenin levels. Based on these results, we suggest that a combination treatment of deferasirox and imatinib could be considered as an alternative treatment option for imatinib-resistant CML.

Knock-down of CIAPIN1 sensitizes K562 chronic myeloid leukemia cells to Imatinib by regulation of cell cycle and apoptosis-associated members via NF-κB and ERK5 signaling pathway

CIAPIN1 (cytokine-induced apoptosis inhibitor 1) was recently identified as an essential downstream effector of the Ras signaling pathway. However, its potential role in regulating myeloid leukemia cells sensitivity to Imatinib remains unclear. In this study, we found depletion of CIAPIN1 inhibited proliferation and triggered more apoptosis of K562CML (chronic myeloid leukemia) cells with or without Imatinib treatment. Meanwhile, CIAPIN1 depletion decreased ERK5 phosphorylation and NF-κB activity. Importantly, treating CIAPIN1-depleted K562 cells with ERK5 signaling pathway specific inhibitor, XMD8-92, further inhibited proliferation and promoted apoptosis with or without Imatinib treatment. Treatment with the NF-κB specific inhibitor, Bay 11-7082, induced nearly the same inhibition of proliferation and promotion of apoptosis conferred by CIAPIN1 depletion as was observed with XMD8-92 treatment. Further, XMD8-92 and Bay 11-7082 synergistically inhibited proliferation and promoted apoptosis of CIAPIN1-depleted K562 cells with or without Imatinib treatment. The nude mice transplantation model was also performed to confirm the enhanced sensitivity of CIAPIN1-depleted K562 cells to Imatinib. Thus, our results provided a potential management by which CIAPIN1 knock-down might have a crucial impact on enhancing sensitivity of K562 cells to Imatinib in the therapeutic approaches, indicating that CIAPIN1 knock-down might serve as a combination with chemotherapeutical agents in leukemia diseases therapy.

Inhibition of Ras-mediated signaling pathways in CML stem cells

BACKGROUND

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by the presence of the BCR-ABL1 oncoprotein in cells with a hematopoietic stem cell (HSC) origin. BCR-ABL1 tyrosine kinase activity leads to constitutive activation of Ras, which in turn acts as a branch point to initiate multiple downstream signaling pathways governing proliferation, self-renewal, differentiation and apoptosis. As aberrant regulation of these cellular processes causes transformation and disease progression particularly in advanced stages of CML, investigation of these signaling pathways may uncover new therapeutic targets for the selective eradication of CML stem cells. Transcription factors play a crucial role in unbalancing the Ras signaling network and have recently been investigated as potential modulators in this regard. In this review, we first briefly summarize the Ras-associated molecular pathways that are involved in the regulation of CML stem cell properties. Next we discuss the relevance of Ras-associated transcription factors as nuclear targets in combination treatment strategies for CML.

CONCLUSIONS

A closer investigation of the influence of Ras-mediated signaling pathways on CML progression to blast crisis is warranted to uncover new directions for targeted therapies, particularly in cases that are resistant to current tyrosine kinase inhibitors.

Prognostic value of the expression of phosphatase and tensin homolog and CD44 in elderly patients with refractory acute myeloid leukemia

The leukemic stem cell marker CD44, has been reported to have prognostic significance in hematological malignancies. The present study therefore aimed to evaluate whether the expression levels of CD44 and the associated pathway components are associated with the survival rate of elderly patients with refractory acute myeloid leukemia (AML). A total of 20 elderly patients diagnosed with refractory AML were divided into two groups, following induction chemotherapy: Complete remission (CR, n=9) and non-remission (NR. n=11). Bone marrow biopsy specimens were collected, expression levels of CD44, phosphatase and tensin homolog (PTEN), mammalian target of rapamycin (mTOR) and nuclear factor-κB (NF-κB) were analyzed by immunohistochemistry and the captured images were analyzed in a blinded manner using Image Pro Plus software, version 6.0. The overall survival rates (OS) of the patients were then analyzed with log rank, and the correlation between CD44, PTEN, mTOR and NF-κB expression levels and patients survival rates were statistically analyzed using Pearson's method. Significant differences were observed between the CR and NR groups for PTEN (P=0.025) and CD44 (P=0.020) expression levels. Positive CD44 expression was significantly correlated with poor overall survival, with a hazard ratio of 6.281 (95% CI, 1.78-22.12; P=0.0042). The mean OS was 4.00 months for patients that demonstrated positive CD44 expression, compared with 9.27 months for patients that demonstrated negative CD44 expression. A tendency towards reduced survival rates was also observed in patients negative for PTEN expression, when compared with that of PTEN-positive patients. The mean OS was 4.81 months in PTEN-negative patients vs. 8.8 months in PTEN-positive patients, with a hazard ratio of 2.689 (95%CI, 0.89-8.08; P=0.078). Patients that exhibited PTEN-positive and CD44-negative expression, survived significantly longer than patients that demonstrated PTEN-negative and CD44-positive expression (mean OS, 9.86 vs 2.67 months; hazard ratio=0.037; 95% CI, 0.006-0.222, P=0.0006). The expression levels of NF-κB and mTOR were slightly increased in the NR group compared with those of the CR group, although no significant differences were identified. PTEN and CD44 expression levels demonstrated trends towards negative correlation. In conclusion, the expression levels of CD44 and PTEN may be useful markers to predict the prognosis of elderly patients with refractory AML.

Pharmacogenomic Characterization of Cytotoxic Compounds from Salvia officinalis in Cancer Cells

Salvia officinalis is used as a dietary supplement with diverse medicinal activity (e.g. antidiabetic and antiatherosclerotic effects). The plant also exerts profound cytotoxicity toward cancer cells. Here, we investigated possible modes of action to explain its activity toward drug-resistant tumor cells. Log10IC50 values of two constituents of S. officinalis (ursolic acid, pomolic acid) were correlated to the expression of ATP-binding cassette (ABC) transporters (P-glycoprotein/ABCB1/MDR1, MRP1/ABCC1, BCRP/ABCG2) and epidermal growth factor receptor (EGFR) or mutations in RAS oncogenes and the tumor suppressor gene TP53 of the NCI panel of cell lines. Gene expression profiles predicting sensitivity and resistance of tumor cells to these compounds were determined by microarray-based mRNA expressions, COMPARE, and hierarchical cluster analyses. Furthermore, the binding of both plant acids to key molecules of the NF-κB pathway (NF-κB, I-κB, NEMO) was analyzed by molecular docking. Neither expression nor mutation of ABC transporters, oncogenes, or tumor suppressor genes correlated with log10IC50 values for ursolic acid or pomolic acid. In microarray analyses, many genes involved in signal transduction processes correlated with cellular responsiveness to these compounds. Molecular docking indicated that the two plant acids strongly bound to target proteins of the NF-κB pathway with even lower free binding energies than the known NF-κB inhibitor MG-132. They interacted more strongly with DNA-bound NF-κB than free NF-κB, pointing to inhibition of DNA binding by these compounds. In conclusion, the lack of cross-resistance to classical drug resistance mechanisms (ABC-transporters, oncogenes, tumor suppressors) may indicate a promising role of the both plant acids for cancer chemotherapy. Genes involved in signal transduction may contribute to the sensitivity or resistance of tumor cells to ursolic and pomolic acids. Ursolic and pomolic acid may target different steps of the NF-κB pathway to inhibit NF-κB-mediated functions.

IKK-dependent activation of NF-κB contributes to myeloid and lymphoid leukemogenesis by BCR-ABL1

The product of the Ph chromosome, the BCR-ABL1 tyrosine kinase activates diverse signaling pathways in leukemic cells from patients with chronic myeloid leukemia (CML) and Ph(+) B-cell acute lymphoblastic leukemia (B-ALL). Previous studies showed that nuclear factor κB (NF-κB) is activated in BCR-ABL1-expressing cells, but the mechanism of activation and importance of NF-κB to the pathogenesis of BCR-ABL1-positive myeloid and lymphoid leukemias are unknown. Coexpression of BCR-ABL1 and a superrepressor mutant of inhibitory NF-κB α (IκBαSR) blocked nuclear p65/RelA expression and inhibited the proliferation of Ba/F3 cells and primary BCR-ABL1-transformed B lymphoblasts without affecting cell survival. In retroviral mouse models of CML and B-ALL, coexpression of IκBαSR attenuated leukemogenesis, prolonged survival, and reduced myeloid leukemic stem cells. Coexpression of dominant-negative mutants of IκB kinase α (IKKα)/IKK1 or IKKβ/IKK2 also inhibited lymphoid and myeloid leukemogenesis by BCR-ABL1. Blockade of NF-κB decreased expression of the NF-κB targets c-MYC and BCL-X and increased the sensitivity of BCR-ABL1-transformed lymphoblasts to ABL1 kinase inhibitors. These results demonstrate that NF-κB is activated through the canonical IKK pathway and plays distinct roles in the pathogenesis of myeloid and lymphoid leukemias induced by BCR-ABL1, validating NF-κB and IKKs as targets for therapy of Ph(+) leukemias.

Pharmacologic IKK/NF-κB inhibition causes antigen presenting cells to undergo TNFα dependent ROS-mediated programmed cell death

Monocyte-derived antigen presenting cells (APC) are central mediators of the innate and adaptive immune response in inflammatory diseases. As such, APC are appropriate targets for therapeutic intervention to ameliorate certain diseases. APC differentiation, activation and functions are regulated by the NF-κB family of transcription factors. Herein, we examined the effect of NF-κB inhibition, via suppression of the IκB Kinase (IKK) complex, on APC function. Murine bone marrow-derived macrophages and dendritic cells (DC), as well as macrophage and DC lines, underwent rapid programmed cell death (PCD) after treatment with several IKK/NF-κB inhibitors through a TNFα-dependent mechanism. PCD was induced proximally by reactive oxygen species (ROS) formation, which causes a loss of mitochondrial membrane potential and activation of a caspase signaling cascade. NF-κB-inhibition-induced PCD of APC may be a key mechanism through which therapeutic targeting of NF-κB reduces inflammatory pathologies.

The role of inflammation in leukaemia

Acute leukaemias are a group of malignancies characterised by the invasion of the bone marrow by immature haematopoietic precursors and differentiation arrest at various maturation steps. Multiplicity of intrinsic and extrinsic factors influences the transformation and progression of leukaemia. The intrinsic factors encompass genetic alterations of cellular pathways leading to the activation of, among others, inflammatory pathways (such as nuclear factor kappa B). The extrinsic components include, among others, the inflammatory pathways activated by the bone marrow microenvironment and include chemokines, cytokines and adhesion molecules. In this chapter, we review the role of inflammatory processes in the transformation, survival and proliferation of leukaemias, particularly the role of nuclear factor kappa B and its downstream signalling in leukaemias and the novel therapeutic strategies that exploit potentially unique properties of inflammatory signalling that offer interesting options for future therapeutic interventions.

CUEDC2 sensitizes chronic myeloid leukemic cells to imatinib treatment

CUEDC2, a newly reported protein, has been found to be ubiquitously expressed in human tissues and repress NF-κB activity. To study the role of CUEDC2 in chronic myeloid leukemia (CML), we explored the function of CUEDC2 in CML cells through using the CML cell line K562 and its imatinib resistant cells K562/G01. K562 cells expressed a relatively higher level of CUEDC2 compared to K562/G01 cells. Knockdown of CUEDC2 in K562 cells resulted in decreased cell apoptosis after imatinib treatment; when CUEDC2 was overexpressed in K562/G01 cells, imatinib induced more cell apoptosis. By analyzing the activity of NF-κB, the results indicated a negative association between the expression of CUEDC2 and NF-κB signaling pathway in these CML cells. Our data suggested that the expression level of CUEDC2 has an inverse correlation with imatinib resistance and activity of NF-κB signaling pathway in CML cells, CUEDC2 could regulate imatinib sensitivity in CML cells at least partially through NF-κB signaling pathway.

Molecular biology of chronic myeloid leukemia

Detailed information on the crystal structure of the pharmacologically targeted domains of the BCR-ABL molecule and on its intracellular signaling, which are potentially involved in growth, anti-apoptosis, metabolism and stemness, has made the study of chronic myeloid leukemia the most successful field in tumor biology. However, we now face the issue of drug resistance due to deregulation in the quality control of both DNA and protein. BCR-ABL is basically a misfolded protein with intrinsically disordered regions, which not only produces endoplasmic reticulum stress followed by unfolded protein response in some settings, but also conformational plasticity that may affect the structure of the whole molecule. The intercellular signaling derived from the leukemic cell microenvironment may influence the intracellular responses that take place in a manner both dependent on and independent of BCR-ABL tyrosine kinase activity.

The Interface between BCR-ABL-Dependent and -Independent Resistance Signaling Pathways in Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is a clonal hematopoietic disorder characterized by the presence of the Philadelphia chromosome which resulted from the reciprocal translocation between chromosomes 9 and 22. The pathogenesis of CML involves the constitutive activation of the BCR-ABL tyrosine kinase, which governs malignant disease by activating multiple signal transduction pathways. The BCR-ABL kinase inhibitor, imatinib, is the front-line treatment for CML, but the emergence of imatinib resistance and other tyrosine kinase inhibitors (TKIs) has called attention for additional resistance mechanisms and has led to the search for alternative drug treatments. In this paper, we discuss our current understanding of mechanisms, related or unrelated to BCR-ABL, which have been shown to account for chemoresistance and treatment failure. We focus on the potential role of the influx and efflux transporters, the inhibitor of apoptosis proteins, and transcription factor-mediated signals as feasible molecular targets to overcome the development of TKIs resistance in CML.

Effect of RNAi-induced down regulation of nuclear factor kappa-B p65 on acute monocytic leukemia THP-1 cells in vitro and vivo

NF-κB p65 is found constitutively active in acute monocytic leukemia, and has been considered an important factor for poor prognosis. Therefore, develop specifically target p65 inhibitors will be substantial interest. Until now, although several p65 inhibitors are currently in preclinical and clinical development, none of them are targeting. In this study, siRNA targeting p65 was introduced into the acute monocytic leukemia cell line THP-1 and THP-1 xenograft tumors in nude mice, and then, we measured p65 mRNA and protein levels by real-time RT-PCR and Western blotting, and levels of related protein cyclin D1, Bc1-2, and SMRT by Western blotting. We also investigated the cell cycle and apoptosis via FCM, and cell proliferation by Cell Counting Kit-8 assay. We found that p65 siRNA could effectively reduce the p65 mRNA and protein expression, arrest cells in G0/G1 phase, inhibit the proliferation and increase the apoptosis of THP-1 cells, and intratumoral injection of p65 siRNA could suppress tumor growth in nude mice. We also found that when down regulation of p65, the expression of cyclin D1 and Bc1-2 decreased, and the expression of SMRT increased in vitro and vivo. All these findings suggest that NF-κB p65 maybe an attractive candidate for the therapeutic targeting of acute monocytic leukemia.

Inhibition of IGF-1 signalling enhances the apoptotic effect of AS602868, an IKK2 inhibitor, in multiple myeloma cell lines

Multiple myeloma (MM) is a B cell neoplasm characterized by bone marrow infiltration with malignant plasma cells. IGF-1 signalling has been explored as a therapeutic target in this disease. We analyzed the effect of the IKK2 inhibitor AS602868, in combination with a monoclonal antibody targeting IGF-1 receptor (anti-IGF-1R) in human MM cell lines. We found that anti-IGF-1R potentiated the apoptotic effect of AS602868 in LP1 and RPMI8226 MM cell lines which express high levels of IGF-1R. Anti-IGF-1R enhanced the inhibitory effect of AS602868 on NF-κB pathway signalling and potentiated the disruption of mitochondrial membrane potential caused by AS602868. These results support the role of IGF-1 signalling in MM and suggest that inhibition of this pathway could sensitize MM cells to NF-κB inhibitors.

Novel IkB kinase inhibitors for treatment of nuclear factor-kB-related diseases

INTRODUCTION

NF-kB is a key regulator of inflammation and immunity in cancer development. The IkB kinase (IKK) is a multisubunit complex containing catalytic subunits termed IKK-α, -β and -γ. It is well known that many pro-inflammatory stimuli require the IKK-β subunit for NF-kB activation.

AREAS COVERED

NF-kB affects the progression of inflammation-related diseases,such as myocardial ischemia, bronchial asthma, arthritis, cancer and other diseases. We review the characteristics and effects of these inhibitors on inflammatory and other diseases.

EXPERT OPINION

Various synthesized IKK inhibitors have been developed and they will be used clinically in the near future.

Cell-intrinsic NF-κB activation is critical for the development of natural regulatory T cells in mice

Background

Naturally occurring CD4⁺CD25⁺Foxp3⁺ regulatory T (Treg) cells develop in the thymus and represent a mature T cell subpopulation critically involved in maintaining peripheral tolerance. The differentiation of Treg cells in the thymus requires T cell receptor (TCR)/CD28 stimulation along with cytokine-promoted Foxp3 induction. TCR-mediated nuclear factor kappa B (NF-κB) activation seems to be involved in differentiation of Treg cells because deletion of components of the NF-κB signaling pathway, as well as of NF-κB transcription factors, leads to markedly decreased Treg cell numbers in thymus and periphery.

Methodology/Principal Findings

To investigate if Treg cell-intrinsic NF-κB activation is required for thymic development and peripheral homeostasis of Treg cells we used transgenic (Tg) mice with thymocyte-specific expression of a stable IκBα mutant to inhibit NF-κB activation solely within the T cell lineage. Here we show that Treg cell-intrinsic NF-κB activation is important for the generation of cytokine-responsive Foxp3⁻ thymic Treg precursors and their further differentiation into mature Treg cells. Treg cell development could neither be completely rescued by the addition of exogenous Interleukin 2 (IL-2) nor by the presence of wild-type derived cells in adoptive transfer experiments. However, peripheral NF-κB activation appears to be required for IL-2 production by conventional T cells, thereby participating in Treg cell homeostasis. Moreover, pharmacological NF-κB inhibition via the IκB kinase β (IKKβ) inhibitor AS602868 led to markedly diminished thymic and peripheral Treg cell frequencies.

Conclusion/Significance

Our results indicate that Treg cell-intrinsic NF-κB activation is essential for thymic Treg cell differentiation, and further suggest pharmacological NF-κB inhibition as a potential therapeutic approach for manipulating this process.

Triptolide inhibits the proliferation of cells from lymphocytic leukemic cell lines in association with downregulation of NF-κB activity and miR-16-1*

AIM

To examine the effects of triptolide (TPL) on T-cell leukemia cells and identify their underlying mechanisms.

METHODS

The cytotoxicity of TPL was assessed by MTT assay. Cell apoptosis was determined using annexin V and DAPI staining and analyzed by flow cytometry or fluorescence microscopy. The activation of caspase pathways and the expression of nuclear factor κB (NF-κB) p65 were examined by Western blotting. Differences in microRNA (miRNA) expression in Molt-4 and Jurkat cells before and after TPL treatment were identified using microarrays and real-time RT-PCR, respectively.

RESULTS

TPL 20-160 nmol/L treatment potently inhibited cell growth and induced apoptosis in T-cell lymphocytic leukemia cell lines. Molt-4 and Jurkat cells, however, were more sensitive to TPL than L428 and Raji cells. After 24 h of treatment, bortezomib abrogated the growth of Molt-4 and Jurkat cells with an IC(50) of 15.25 and 24.68 nmol/L, respectively. Using Molt-4 cells, we demonstrated that treatment 20-80 nmol/L inhibited the translocation of NF-κB p65 from the cytoplasm to the nucleus and that phosphorylated NF-κB p65 in nuclear extracts was down-regulated in a dose-dependent manner. Similar results were also seen in Jurkat cells but not in L428 cells, as these cells are resistant to TPL and bortezomib (a NF-κB inhibitor). Twenty-three miRNAs were differentially expressed after TPL treatment. Functional analysis revealed that TPL treatment could inhibit expression of miR-16-1* and that transfection of miR-16-1* led to significantly decreased apoptosis induced by TPL.

CONCLUSION

Our in vitro studies suggest that TPL might be an effective therapeutic agent for treatment of T-cell lymphocytic leukemia and that its cytotoxic effects could be associated with inhibition of NF-κB and down-regulation of miR-16-1*.

Pristimerin induces apoptosis in imatinib-resistant chronic myelogenous leukemia cells harboring T315I mutation by blocking NF-kappaB signaling and depleting Bcr-Abl

Background

Chronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl. Bcr-Abl-T315I is the notorious point mutation that causes resistance to imatinib and the second generation tyrosine kinase inhibitors, leading to poor prognosis. CML blasts have constitutive p65 (RelA NF-κB) transcriptional activity, and NF-κB may be a potential target for molecular therapies in CML that may also be effective against CML cells with Bcr-Abl-T315I.

Results

In this report, we discovered that pristimerin, a quinonemethide triterpenoid isolated from Celastraceae and Hippocrateaceae, inhibited growth and induced apoptosis in CML cells, including the cells harboring Bcr-Abl-T315I mutation. Additionally, pristimerin inhibited the growth of imatinib-resistant Bcr-Abl-T315I xenografts in nude mice. Pristimerin blocked the TNFα-induced IκBα phosphorylation, translocation of p65, and expression of NF-κB-regulated genes. Pristimerin inhibited two steps in NF-κB signaling: TAK1→IKK and IKK→IκBα. Pristimerin potently inhibited two pairs of CML cell lines (KBM5 versus KBM5-T315I, 32D-Bcr-Abl versus 32D-Bcr-Abl-T315I) and primary cells from a CML patient with acquired resistance to imatinib. The mRNA and protein levels of Bcr-Abl in imatinib-sensitive (KBM5) or imatinib-resistant (KBM5-T315I) CML cells were reduced after pristimerin treatment. Further, inactivation of Bcr-Abl by imatinib pretreatment did not abrogate the TNFα-induced NF-κB activation while silencing p65 by siRNA did not affect the levels of Bcr-Abl, both results together indicating that NF-κB inactivation and Bcr-Abl inhibition may be parallel independent pathways.

Conclusion

To our knowledge, this is the first report to show that pristimerin is effective in vitro and in vivo against CML cells, including those with the T315I mutation. The mechanisms may involve inhibition of NF-κB and Bcr-Abl. We concluded that pristimerin could be a lead compound for further drug development to overcome imatinib resistance in CML patients.