DHMEQ, a new NF-kappaB inhibitor, induces apoptosis and enhances fludarabine effects on chronic lymphocytic leukemia cells.

Chronic lymphocytic leukemia (CLL) is a low-grade lymphoid malignancy incurable with conventional modalities of chemotherapy. Strong and constitutive nuclear factor kappa B (NF-kappaB) activation is a characteristic of CLL cells. We examined the effects of a new NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), on CLL cells. Dehydroxymethylepoxyquinomicin completely abrogated constitutive NF-kappaB activity and induced apoptosis of CLL cells. Apoptosis induced by DHMEQ was accompanied by downregulation of NF-kappaB-dependent antiapoptotic genes: c-IAP, Bfl-1, Bcl-X(L) and c-FLIP. Dehydroxymethylepoxyquinomicin also inhibited NF-kappaB induced by CD40 and enhanced fludarabine-mediated apoptosis of CLL cells. Results of this study suggest that inhibition of constitutive and inducible NF-kappaB by DHMEQ in combination with fludarabine is a promising strategy for the treatment of CLL.     

Targeting NF-kappaB and induction of apoptosis by novel NF-kappaB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ) in Burkitt lymphoma cells

A new NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), inhibited proliferation and induced apoptosis in human Burkitt lymphoma, HS-Sultan and Daudi cell lines. The activation of caspase-3 and the cleavage of caspase substrate PARP were observed after treatment with DHMEQ. The induction of apoptosis by DHMEQ was prevented by the pretreatment of Burkitt lymphoma cells with pan-caspase inhibitor, z-VAD-FMK. The expression of anti-apoptotic factors such as IAP-1 and XIAP was suppressed by DHMEQ. Phosphorylation of ERK and JNK was induced by DHMEQ. In conclusion, these results demonstrate that NF-kappaB might be an ideal target to develop for new anti-cancer drugs for Burkitt lymphoma.     

Growth suppression and apoptosis induction in synovial sarcoma cell lines by a novel NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ)

Synovial sarcoma is a relatively common soft tissue sarcoma with an aggressive clinical course. Although surgery is currently the first treatment modality, improvement of adjuvant chemotherapy is deemed essential to improve the clinical outcome. Nuclear factor-kappaB (NF-kappaB) is constitutively activated in various cancer cells and has emerged as a potential therapeutic molecular target; however, the possible involvement of NF-kappaB in the pathology of sarcomas remains to be clarified. Herein we examined the effects of a novel NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ) on two synovial sarcoma-derived cell lines, HS-SY-II and SYO-1. The growth of both cell lines was completely inhibited by DHMEQ and apoptosis was induced at 10 microg/ml. Additionally, we found that DHMEQ showed additive effects when used in combination with other cytotoxic agents. These observations indicate that inhibition of NF-kappaB activity may serve as a potential therapeutic target for synovial sarcoma.     

Transient inhibition of NF-κB by DHMEQ induces cell death of primary effusion lymphoma without HHV-8 reactivation

Primary effusion lymphoma (PEL) is a refractory malignancy caused by human herpes virus 8 (HHV-8) in immunocompromised individuals. The tumor cells of PEL are characterized by constitutive NF-κB activation. Dehydroxymethylepoxyquinomicin (DHMEQ) is a new NF-κB inhibitor and is effective on various tumor cells with constitutively activated NF-κB. Thus, in search for a new therapeutic modality of PEL, we examined the effect of DHMEQ on PEL cells. We confirmed constitutive activation of NF-κB with subcomponents of p50 and p65 in PEL cell lines. DHMEQ quickly and transiently abrogated NF-κB activation and reduced the cell viability in dose- and time-dependent manners, inducing apoptosis through activation of both mitochondrial and membrane pathways. Array analysis revealed that DHMEQ down-regulated expression levels of NF-κB target genes, such as interleukin-6 (IL6), Myc , chemokine (C-C motif) receptor 5 ( CCR5 ) and NF-κB1, whereas it up-regulated expression levels of some genes involved in apoptosis, and cell cycle arrest. DHMEQ did not reactivate HHV-8 lytic genes, indicating that NF-κB inhibition by DHMEQ did not induce virus replication. DHEMQ rescued CB-17 SCID mice xenografted with PEL cells, reducing the gross appearance of effusion. Thus, DHMEQ transiently abrogated the NF-κB activation, irreversibly triggering the apoptosis cascade without HHV-8 reactivation. In addition, DHMEQ could rescue the PEL-xenograft mice. Therefore, we suggest DHMEQ as a promising candidate for molecular target therapy of the PEL. ( Cancer Sci 2009; 100: 737–746)     

Biologic sequelae of c-Jun NH(2)-terminal kinase (JNK) activation in multiple myeloma cell lines

Although c-Jun NH(2)-terminal kinase (JNK) is activated by treatment with therapeutic agents, the biologic sequelae of inhibiting constitutive activation of JNK has not yet been clarified. In this study, we examine the biologic effect of JNK inhibition in multiple myeloma (MM) cell lines. JNK-specific inhibitor SP600125 induces growth inhibition via induction of G1 or G2/M arrest in U266 and MM.1S multiple myeloma cell lines, respectively. Neither exogenous IL-6 nor insulin-like growth factor-1 (IGF-1) overcome SP600125-induced growth inhibition, and IL-6 enhances SP600125-induced G2/M phase in MM.1S cells. Induction of growth arrest is mediated by upregulation of p27(Kip1), without alteration of p53 and JNK protein expression. Importantly, SP600125 inhibits growth of MM cells adherent to bone marrow stromal cells (BMSCs). SP600125 induces NF-kappaB activation in a dose-dependent fashion, associated with phosphorylation of IkappaB kinase alpha (IKKalpha) and degradation of IkappaBalpha. In contrast, SP600125 does not affect phosphorylation of STAT3, Akt, and/or ERK. IKK-specific inhibitor PS-1145 inhibits SP600125-induced NF-kappaB activation and blocks the protective effect of SP600125 against apoptosis. Our data therefore demonstrate for the first time that inhibiting JNK activity induces growth arrest and activates NF-kappaB in MM cells.     

Multiple myeloma: lusting for NF-kappaB

Multiple myeloma (MM) is a late-stage B cell malignancy that has received much attention recently because of its therapeutic susceptibility to proteasome inhibitors. Two papers in this issue of Cancer Cell show that primary MM samples and MM cell lines frequently have mutations in genes encoding regulators and effectors of NF-kappaB signaling, and that these mutations lead to chronic NF-kappaB target gene expression, which is required for the viability of these MM tumor cells. These results reveal the molecular basis for constitutive NF-kappaB activity in many MMs and further validate the NF-kappaB signaling pathway as an appropriate target for MM therapy.     

Molecular mechanisms of constitutive NF-kappaB/Rel activation in Hodgkin/Reed-Sternberg cells

A common characteristic of malignant cells derived from patients with Hodgkin's disease (HD) is a high level of constitutive nuclear NF-kappaB/Rel activity, which stimulates proliferation and confers resistance to apoptosis. We have analysed the mechanisms that account for NF-kappaB activation in a panel of Hodgkin/Reed-Sternberg (H-RS) cell lines. Whereas two cell lines (L428 and KMH-2) expressed inactive IkappaBalpha, no significant changes in NF-kappaB or IkappaB expression were seen in other H-RS cells (L591, L1236 and HDLM-2). Constitutive NF-kappaB was susceptible to inhibition by recombinant IkappaBalpha, suggesting that neither mutations in the NF-kappaB genes nor posttranslational modifications of NF-kappaB were involved. Endogenous IkappaBalpha was bound to p65 and displayed a very short half-life. IkappaBalpha degradation could be blocked by inhibitors of the NF-kappaB activating pathway. Proteasomal inhibition caused an accumulation of phosphorylated IkappaBalpha and a reduction of NF-kappaB activity in HDLM-2 and L1236 cells. By in vitro kinase assays we demonstrate constitutive IkappaB kinase (IKK) activity in H-RS cells, indicating ongoing signal transduction. Furthermore, H-RS cells secrete one or more factor(s) that were able to trigger NF-kappaB activation. We conclude that aberrant activation of IKK's, and in some cases defective IkappaBs, lead to constitutive nuclear NF-kappaB activity, which in turn results in a growth advantage of Hodgkin's disease tumor cells.     

Dual role of NF-kappaB in apoptosis of THP-1 cells during treatment with etoposide and lipopolysaccharide

One of the mechanisms repressing apoptosis in tumor cells can involve the expression of anti-apoptotic NF-kappaB target genes. In this study, we demonstrated that a potent NF-kappaB inhibitor, Nalpha-tosyl-L-lysinyl chloromethyl ketone (TLCK), inhibits apoptosis of THP-1 cells triggered by etoposide (VP16), and actinomycin D (ACT D) or cycloheximide inhibits apoptosis. However, persistent activation of NF-kappaB by lipopolysaccharide (LPS) led to the survival of leukemic cells against VP16-induced apoptosis. Thus, the molecular events (Bax/X-chromosome-linked IAP (XIAP)) occurring downstream of NF-kappaB activation during VP16 and/or LPS stimulation may become important to understand the multiple effects of NF-kappaB.     

Evidence for radiosensitizing by gliotoxin in HL-60 cells: implications for a role of NF-kappaB independent mechanisms

Radioresistance markedly impairs the efficacy of tumor radiotherapy and may involve antiapoptotic signal transduction pathways that prevent radiation-induced cell death. A common cellular response to genotoxic stress induced by radiation is the activation of the nuclear factor kappa B (NF-kappaB). NF-kappaB activation in turn can lead to an inhibition of radiation-induced apoptotic cell death. Thus, inhibition of NF-kappaB activation is commonly regarded as an important strategy to abolish radioresistance. Among other compounds, the fungal metabolite gliotoxin (GT) has been reported to be a highly selective inhibitor of NF-kappaB activation. Indeed, low doses of GT were sufficient to significantly enhance radiation-induced apoptosis in HL-60 cells. However, this effect turned out to be largely independent of NF-kappaB activation since radiation of HL-60 cells with clinically relevant doses of radiation induced only a marginal increase in NF-kappaB activity, and selective inhibition of NF-kappaB by SN50 did not result in a marked enhancement of GT-induced apoptosis. GT induced activation of JNKs, cytochrome c release from the mitochondria and potently stimulated the caspase cascade inducing cleavage of caspases -9, -8, -7 and -3. Furthermore, cleavage of the antiapoptotic protein X-linked IAP and downregulation of the G2/M-specific IAP-family member survivin were observed during GT-induced apoptosis. Finally, the radiation-induced G2/M arrest was markedly reduced in GT-treated cells most likely due to the rapid induction of apoptosis. Our data demonstrate that various other pathways apart from the NF-kappaB signaling complex can sensitize tumor cells to radiation and propose a novel mechanism for radiosensitization by GT, the interference with the G2/M checkpoint that is important for repair of radiation-induced DNA damage in p53-deficient tumor cells.     

Antitumor effects of the novel NF-kappaB inhibitor dehydroxymethyl-epoxyquinomicin on human hepatic cancer cells: analysis of synergy with cisplatin and of possible correlation with inhibition of pro-survival genes and IL-6 production

We tested the novel NF-kappaB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ) in the hepatic cancer (HCC) HepG2, HA22T/VGH and HuH-6 cells. The sensitivity to the cell growth inhibitory and apoptotic effects of the agent increased along with the levels of constitutively activated NF-kappaB, which were low in HepG2 and higher in HA22T/VGH and HuH-6. In HA22T/VGH, DHMEQ exhibited synergy with cisplatin. In the same cells, DHMEQ exerted dose-dependent decreases in the nuclear levels of activated NF-kappaB and attenuated NF-kappaB activation by cisplatin. It down-regulated Bcl-XL mRNA in a dose-dependent manner and up-regulated that of Bcl-XS. It also decreased interleukin 6 (IL-6), NAIP and, after 16 h of exposure to the higher concentration tested (10 microg/ml), c-IAP-1 mRNA levels. At 10 microg/ml it caused significant increase in Bax, XIAP, cyclin D1 and beta-catenin mRNAs. The combination of DHMEQ with cisplatin produced unexpected significant decrease in c-IAP-2 and Bcl-XS mRNAs as well as additive decrease (IL-6, NAIP and, after 16 h, Bcl-XL) or increase (XIAP at 8 h) in gene expression. HA22T/VGH produce IL-6; in agreement with the results on mRNA, DHMEQ inhibited such a process. HA22T/VGH lack the IL-6 receptor alpha chain, ruling out that in these cells the antitumor effects of DHMEQ may be attributed to an interference with a growth stimulatory autocrine loop based on IL-6. However, the use of DHMEQ in HCC might be beneficial to contrast the adverse systemic effects of the released cytokine.     

Ligand-independent signaling by overexpressed CD30 drives NF-kappaB activation in Hodgkin-Reed-Sternberg cells

Overexpression of CD30 and constitutive NF-kappaB activation characterizes tumor cells of Hodgkin's disease (HD), Hodgkin and Reed-Sternberg (H-RS) cells. We report that in H-RS cells overexpression of CD30 leads to self-aggregation, recruitment of TRAF2 and TRAF5, and NF-kappaB activation, independent of CD30 ligand. CD30 and TRAF proteins co-localized in H-RS cell lines and in lymph nodes of HD. An adenovirus-vector carrying a decoy CD30 lacking the cytoplasmic region or a dominant negative IkappaBalpha mutant blocks NF-kappaB activation, down regulates IL-13 expression and induces apoptosis. Thus, in H-RS cells, ligand-independent activation of CD30 signaling drives NF-kappaB activation and this leads to constitutive cytokine expression, which provides a molecular basis for HD. Inhibition of NF-kappaB activation by adenovirus vector-mediated gene transfer may provide a novel strategy of cell- and target molecule-specific therapy for patients with HD.     

Inhibition of cellular adhesion in human umbilical vein endothelial cells by NF-kappaB inhibitor DHMEQ under flow

We previously designed and synthesized DHMEQ as an inhibitor of NF-kappaB. In the present study, we looked into the effect of DHMEQ on the cell adhesion in human umbilical vein endothelial cells (HUVEC) under flow. We used freshly prepared HUVEC and human mononuclear cells throughout the experiment. DHMEQ inhibited TNF-alpha-, IL-1beta-, and LPS-induced NF-kappaB activation in HUVEC. It also inhibited TNF-alpha-induced expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. DHMEQ also inhibited TNF-alpha-induced mononuclear cell-HUVEC adhesion. The effect of DHMEQ was more prominent when the cells were under shear stress. DHMEQ inhibited the adhesion between HUVEC and HT-29 colon cancer cells more clearly under the flow condition than under the static condition of the culture medium. These results suggest that DHMEQ, being a unique inhibitor of NF-kappaB, may be effective in suppressing atherosclerosis and metastasis by inhibiting the expression of adhesion molecules.     

The NPM-ALK oncoprotein abrogates CD30 signaling and constitutive NF-kappaB activation in anaplastic large cell lymphoma

NPM-ALK characterizes anaplastic large cell lymphoma (ALCL), as does the high expression of CD30, a feature shared with H-RS cells of classic Hodgkin's lymphoma. In H-RS cells, ligand-independent signaling by overexpressed CD30 drives constitutive NF-kappaB activation, which is absent in ALCL cells. Here we show that NPM-ALK impedes CD30 signaling and NF-kappaB activation, dependent on both ALK kinase activity and the N-terminal NPM domain. NPM-ALK transduction into H-RS cell lines abrogates recruitment and aggregation of TRAF proteins, inducing an ALCL-like morphology and phenotype. TRAF2 associates with NPM-ALK at a consensus binding motif located in the kinase domain. Thus, NPM-ALK abrogates CD30-driven NF-kappaB activation and can also induce an ALCL phenotype, distinguishing ALCL cells from H-RS cells of T cell origin.