c-FLIP mediates resistance of Hodgkin/Reed-Sternberg cells to death receptor-induced apoptosis

EX527, a sirtuins 1 inhibitor, sensitizes T-cell leukemia to death receptor-mediated apoptosis by downregulating cellular FLICE inhibitory protein

Death receptor-mediated extrinsic apoptosis system had been developed as a promising therapeutic strategy in clinical oncology, such as TRAIL therapy. However, multiple studies have demonstrated that TRAIL resistance is the biggest problem for disappointing clinical trials despite preclinical success. Targeting cellular FLICE inhibitory protein (cFLIP) is one strategy of combinatorial therapies to overcome resistance to DR-mediated apoptosis due to its negative regulator of extrinsic apoptosis. E × 527 (Selisistat) is a specific inhibitor of SIRT1 activity with safe and well tolerance in clinical trials. Here, we show that E × 527 could strengthen significantly activation of rhFasL-mediated apoptotic signaling pathway and increased apoptotic rate of T leukemia cells with high expression of cFLIP. Mechanically, Inhibition of SIRT1 by E × 527 increased polyubiquitination level of cFLIP via increasing acetylation of Ku70, which could promote proteosomal degradation of cFLIP protein. It implied that combinatorial therapies of E × 527 plus TRAIL may have a potential as a novel clinical application for TRAIL-resistant hematologic malignancies.

CD30 protects EBV-positive diffuse large B-cell lymphoma cells against mitochondrial dysfunction through BNIP3-mediated mitophagy

Epstein-Barr virus (EBV) positive diffuse large B-cell lymphoma (EBV+ DLBCL) predicts poor prognosis and CD30 expression aggravates the worse consequences. Here, we reported that CD30 positivity was an independent prognostic indicator in EBV+ DLBCL patients in a retrospective cohort study. We harnessed CRISPR/Cas9 editing to engineer the first loss-of-function models of CD30 deficiency to identify that CD30 was critical for EBV+ DLBCL growth and survival. We established a pathway that EBV infection mediated CD30 expression through EBV-encoded latent membrane protein 1 (LMP1), which involved NF-κB signaling. CRISPR CD30 knockout significantly repressed BCL2 interacting protein 3 (BNIP3) expression and co-IP assay indicated a binding between CD30 and BNIP3. Moreover, silencing of CD30 induced mitochondrial dysfunction and suppressed mitophagy, resulting in the accumulation of damaged mitochondria by depressing BNIP3 expression. Additionally, CRISPR BNIP3 knockout caused proliferation defects and increased sensitivity to apoptosis. All the findings reveal a strong relationship between mitophagy and adverse prognosis of EBV+ DLBCL and discover a new regulatory mechanism of BNIP3-mediated mitophagy, which may help develop effective treatment regimens with anti-CD30 antibody brentuximab vedotin to improve the prognosis of CD30+ EBV+ DLBCL patients.

The Identification of New c-FLIP Inhibitors for Restoring Apoptosis in TRAIL-Resistant Cancer Cells

The catalytically inactive caspase-8-homologous protein, c-FLIP, is a potent antiapoptotic protein highly expressed in various types of cancers. c-FLIP competes with caspase-8 for binding to the adaptor protein FADD (Fas-Associated Death Domain) following death receptors' (DRs) activation via the ligands of the TNF-R family. As a consequence, the extrinsic apoptotic signaling pathway involving DRs is inhibited. The inhibition of c-FLIP activity in tumor cells might enhance DR-mediated apoptosis and overcome immune and anticancer drug resistance. Based on an in silico approach, the aim of this work was to identify new small inhibitory molecules able to bind selectively to c-FLIP and block its anti-apoptotic activity. Using a homology 3D model of c-FLIP, an in silico screening of 1880 compounds from the NCI database (National Cancer Institute) was performed. Nine molecules were selected for in vitro assays, based on their binding affinity to c-FLIP and their high selectivity compared to caspase-8. These molecules selectively bind to the Death Effector Domain 2 (DED2) of c-FLIP. We have tested in vitro the inhibitory effect of these nine molecules using the human lung cancer cell line H1703, overexpressing c-FLIP. Our results showed that six of these newly identified compounds efficiently prevent FADD/c-FLIP interactions in a molecular pull-down assay, as well as in a DISC immunoprecipitation assay. The overexpression of c-FLIP in H1703 prevents TRAIL-mediated apoptosis; however, a combination of TRAIL with these selected molecules significantly restored TRAIL-induced cell death by rescuing caspase cleavage and activation. Altogether, our findings indicate that new inhibitory chemical molecules efficiently prevent c-FLIP recruitment into the DISC complex, thus restoring the caspase-8-dependent apoptotic cascade. These results pave the way to design new c-FLIP inhibitory molecules that may serve as anticancer agents in tumors overexpressing c-FLIP.

Hodgkin Lymphoma: A Special Microenvironment

Classical Hodgkin's lymphoma (cHL) is one of the most particular lymphomas for the few tumor cells surrounded by an inflammatory microenvironment. Reed-Sternberg (RS) and Hodgkin (H) cells reprogram and evade antitumor mechanisms of the normal cells present in the microenvironment. The cells of microenvironment are essential for growth and survival of the RS/H cells and are recruited through the effect of cytokines/chemokines. We summarize recent advances in gene expression profiling (GEP) analysis applied to study microenvironment component in cHL. We also describe the main therapies that target not only the neoplastic cells but also the cellular components of the background.

Essential role of the linear ubiquitin chain assembly complex and TAK1 kinase in A20 mutant Hodgkin lymphoma

More than 70% of Epstein-Barr virus (EBV)-negative Hodgkin lymphoma (HL) cases display inactivation of TNFAIP3 (A20), a ubiquitin-editing protein that regulates nonproteolytic protein ubiquitination, indicating the significance of protein ubiquitination in HL pathogenesis. However, the precise mechanistic roles of A20 and the ubiquitination system remain largely unknown in this disease. Here, we performed high-throughput CRISPR screening using a ubiquitin regulator-focused single-guide RNA library in HL lines carrying either wild-type or mutant A20. Our CRISPR screening highlights the essential oncogenic role of the linear ubiquitin chain assembly complex (LUBAC) in HL lines, which overlaps with A20 inactivation status. Mechanistically, LUBAC promotes IKK/NF-κB activity and NEMO linear ubiquitination in A20 mutant HL cells, which is required for prosurvival genes and immunosuppressive molecule expression. As a tumor suppressor, A20 directly inhibits IKK activation and HL cell survival via its C-terminal linear-ubiquitin binding ZF7. Clinically, LUBAC activity is consistently elevated in most primary HL cases, and this is correlated with high NF-κB activity and low A20 expression. To further understand the complete mechanism of NF-κB activation in A20 mutant HL, we performed a specifically designed CD83-based NF-κB CRISPR screen which led us to identify TAK1 kinase as a major mediator for NF-κB activation in cells dependent on LUBAC, where the LUBAC-A20 axis regulates TAK1 and IKK complex formation. Finally, TAK1 inhibitor Takinib shows promising activity against HL in vitro and in a xenograft mouse model. Altogether, these findings provide strong support that targeting LUBAC or TAK1 could be attractive therapeutic strategies in A20 mutant HL.

The Inhibitor of Apoptosis Protein Livin Confers Resistance to Fas-Mediated Immune Cytotoxicity in Refractory Lymphoma

Death receptor Fas-mediated apoptosis not only eliminates nonspecific and autoreactive B cells but also plays a major role in antitumor immunity. However, the possible mechanisms underlying impairment of Fas-mediated induction of apoptosis during lymphomagenesis remain unknown. In this study, we employed our developed syngeneic lymphoma model to demonstrate that downregulation of Fas is required for both lymphoma development and lymphoma cell survival to evade immune cytotoxicity. CD40 signal activation significantly restored Fas expression and thereby induced apoptosis after Fas ligand treatment in both mouse and human lymphoma cells. Nevertheless, certain human lymphoma cell lines were found to be resistant to Fas-mediated apoptosis, with Livin (melanoma inhibitor of apoptosis protein; ML-IAP) identified as a driver of such resistance. High expression of Livin and low expression of Fas were associated with poor prognosis in patients with aggressive non-Hodgkin's lymphoma. Livin expression was tightly driven by bromodomain and extraterminal (BET) proteins BRD4 and BRD2, suggesting that Livin expression is epigenetically regulated in refractory lymphoma cells to protect them from Fas-mediated apoptosis. Accordingly, the combination of CD40-mediated Fas restoration with targeting of the BET proteins-Livin axis may serve as a promising immunotherapeutic strategy for refractory B-cell lymphoma. SIGNIFICANCE: These findings yield insights into identifying risk factors in refractory lymphoma and provide a promising therapy for tumors resistant to Fas-mediated antitumor immunity. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/20/4439/F1.large.jpg.

Efficient recruitment of c-FLIPL to the death-inducing signaling complex leads to Fas resistance in natural killer-cell lymphoma

Activation‐induced cell death (AICD) mediated by the Fas/Fas ligand (FasL) system plays a key role in regulating immune response. Although normal natural killer (NK) cells use this system for their homeostasis, malignant NK cells seem to disrupt the process. Extranodal NK/T‐cell lymphoma, nasal type (ENKL) is a rare but fatal disease, for which novel therapeutic targets need to be identified. We confirmed that ENKL‐derived NK cell lines NK‐YS and Hank1, and primary lymphoma cells expressed procaspase‐8/FADD‐like interleukin‐1β‐converting enzyme (FLICE) modulator and cellular FLICE‐inhibitory protein (c‐FLIP), along with Fas and FasL. Compared with Fas‐sensitive Jurkat cells, NK‐YS and Hank1 showed resistance to Fas‐mediated apoptosis in spite of the same expression levels of c‐FLIP and the death‐inducing signaling complex (DISC) formation. Unexpectedly, the long isoform of c‐FLIP (c‐FLIP_L) was coimmunoprecipitated with Fas predominantly in both ENKL‐derived NK cell lines after Fas ligation. Indeed, c‐FLIP_L was more sufficiently recruited to the DISC in both ENKL‐derived NK cell lines than in Jurkat cells after Fas ligation. Knockdown of c‐FLIP_L per se enhanced autonomous cell death and restored the sensitivity to Fas in both NK‐YS and Hank1 cells. Although ENKL cells are primed for AICD, they constitutively express and efficiently utilize c‐FLIP_L, which prevents their Fas‐mediated apoptosis. Our results show that c‐FLIP_L could be a promising therapeutic target against ENKL.

Immune and Inflammatory Cells of the Tumor Microenvironment Represent Novel Therapeutic Targets in Classical Hodgkin Lymphoma

Classical Hodgkin Lymphoma (cHL) is a B-cell malignancy that, typically, responds well to standard therapies. However, patients who relapse after standard regimens or are refractory to induction therapy have a dismal outcome. The implementation of novel therapies such as the anti-CD30 monoclonal antibody Brentuximab Vedotin and immune checkpoint inhibitors has provided curative options for many of these patients. Nonetheless, responses are rarely durable, emphasizing the need for new agents. cHL is characterized by a unique microenvironment in which cellular and humoral components interact to promote tumor survival and dissemination. Knowledge of the complex composition of cHL microenvironment is constantly evolving; in particular, there is growing interest in certain cell subsets such as tumor-associated macrophages, myeloid-derived suppressor cells and neutrophils, all of which have a relevant role in the pathogenesis of the disease. The unique biology of the cHL microenvironment has provided opportunities to develop new drugs, many of which are currently being tested in preclinical and clinical settings. In this review, we will summarize novel insights in the crosstalk between tumor cells and non-malignant inflammatory cells. In addition, we will discuss the relevance of tumor-microenvironment interactions as potential therapeutic targets.

c-FLIP and CD95 signaling are essential for survival of renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most-prominent tumor type of kidney cancers. Resistance of renal cell carcinoma (RCC) against tumor therapy is often owing to apoptosis resistance, e.g., by overexpression of anti-apoptotic proteins. However, little is known about the role of the apoptosis inhibitor c-FLIP and its potential impact on death receptor-induced apoptosis in ccRCC cells. In this study, we demonstrate that c-FLIP is crucial for resistance against CD95L-induced apoptosis in four ccRCC cell lines. Strikingly, downregulation of c-FLIP expression by short hairpin RNA (shRNA)interference led to spontaneous caspase activation and apoptotic cell death. Of note, knockdown of all c-FLIP splice variants was required to induce apoptosis. Stimulation of ccRCC cells with CD95L induced NF-κB and MAP kinase survival pathways as revealed by phosphorylation of RelA/p65 and Erk1/2. Interestingly, CD95L surface expression was high in all cell lines analyzed, and CD95 but not TNF-R1 clustered at cell contact sites. Downstream of CD95, inhibition of the NF-κB pathway led to spontaneous cell death. Surprisingly, knockdown experiments revealed that c-FLIP inhibits NF-κB activation in the context of CD95 signaling. Thus, c-FLIP inhibits apoptosis and dampens NF-κB downstream of CD95 but allows NF-κB activation to a level sufficient for ccRCC cell survival. In summary, we demonstrate a complex CD95-FLIP-NF-κB-signaling circuit, in which CD95-CD95L interactions mediate a paracrine survival signal in ccRCC cells with c-FLIP and NF-κB both being required for inhibiting cell death and ensuring survival. Our findings might lead to novel therapeutic approaches of RCC by circumventing apoptosis resistance.

Formation of the Immunosuppressive Microenvironment of Classic Hodgkin Lymphoma and Therapeutic Approaches to Counter It

Classic Hodgkin lymphoma (cHL) is characterized by a few tumor cells surrounded by a protective, immunosuppressive tumor microenvironment composed of normal cells that are an active part of the disease. Hodgkin and Reed-Sternberg (HRS) cells evade the immune system through a variety of different mechanisms. They evade antitumor effector T cells and natural killer cells and promote T cell exhaustion. Using cytokines and extracellular vesicles, they recruit normal cells, induce their proliferation and "educate" (i.e. reprogram) them to become immunosuppressive and protumorigenic. Therefore, alternative treatment strategies are being developed to target not only tumor cells but also the tumor microenvironment. Here we summarize current knowledge on the ability of HRS cells to build their microenvironment and to educate normal cells to become immunosuppressive. We also describe therapeutic strategies to counteract formation of the tumor microenvironment and related processes leading to T cell exhaustion and repolarization of immunosuppressive tumor-associated macrophages.

Caspase-8: A Novel Target to Overcome Resistance to Chemotherapy in Glioblastoma

Caspase-8 was originally identified as a central player of programmed cell death triggered by death receptor stimulation. In that context, its activity is tightly regulated through several mechanisms, with the best established being the expression of FLICE-like inhibitory protein (FLIP) family proteins and the Src-dependent phosphorylation of Caspase-8 on Tyr380. Loss of apoptotic signaling is a hallmark of cancer and indeed Caspase-8 expression is often lost in tumors. This event may account not only for cancer progression but also for cancer resistance to radiotherapy and chemotherapy. Intriguingly, other tumors, such as glioblastoma, preferentially retain Caspase-8 expression, and high levels of Caspase-8 expression may correlate with a worse prognosis, suggesting that in this context this protease loses its apoptotic activity and gains additional functions. Using different cellular systems, it has been clearly shown that in cancer Caspase-8 can exhibit non-canonical functions, including promotion of cell adhesion, migration, and DNA repair. Intriguingly, in glioblastoma models, Caspase-8 can promote NF-κB-dependent expression of several cytokines, angiogenesis, and in vitro and in vivo tumorigenesis. Overall, these observations suggest that some cancer cells may hijack Caspase-8 function which in turn promote cancer progression and resistance to therapy. Here we aim to highlight the multiple functions of Caspase-8 and to discuss whether the molecular mechanisms that modulate the balance between those functions may be targeted to dismantle the aberrant activity of Caspase-8 and to restore its canonical apoptotic functionality.

Acquired Natural Killer Cell Dysfunction in the Tumor Microenvironment of Classic Hodgkin Lymphoma

An understanding of interactions within the tumor microenvironment (TME) of classic Hodgkin lymphoma (cHL) has helped pave the way to novel immunotherapies that have enabled dormant and tumor-tolerant immune cells to be reactivated. The immunosuppressive nature of the TME in cHL specifically inhibits the proliferation and activity of natural killer (NK) cells, which contributes to tumor immune-escape mechanisms. This deficiency of NK cells begins at the tumor site and progresses systemically in patients with advanced disease or adverse prognostic factors. Several facets of cHL account for this effect on NK cells. Locally, malignant Reed-Sternberg cells and cells from the TME express ligands for inhibitory receptors on NK cells, including HLA-E, HLA-G, and programmed death-ligand 1. The secretion of chemokines and cytokines, including soluble IL-2 receptor (sCD25), Transforming Growth Factor-β, IL-10, CXCL9, and CXCL10, mediates the systemic immunosuppression. This review also discusses the potential reversibility of quantitative and functional NK cell deficiencies in cHL that are likely to lead to novel treatments.

Invariant Natural Killer T Cells in Immune Regulation of Blood Cancers: Harnessing Their Potential in Immunotherapies

Invariant natural killer T (iNKT) cells are a unique innate T lymphocyte population that possess cytolytic properties and profound immunoregulatory activities. iNKT cells play an important role in the immune surveillance of blood cancers. They predominantly recognize glycolipid antigens presented on CD1d, but their activation and cytolytic activities are not confined to CD1d expressing cells. iNKT cell stimulation and subsequent production of immunomodulatory cytokines serve to enhance the overall antitumor immune response. Crucially, the activation of iNKT cells in cancer often precedes the activation and priming of other immune effector cells, such as NK cells and T cells, thereby influencing the generation and outcome of the antitumor immune response. Blood cancers can evade or dampen iNKT cell responses by downregulating expression of recognition receptors or by actively suppressing or diverting iNKT cell functions. This review will discuss literature on iNKT cell activity and associated dysregulation in blood cancers as well as highlight some of the strategies designed to harness and enhance iNKT cell functions against blood cancers.

Increased cFLIP expression in thymic epithelial tumors blocks autophagy via NF-κB signalling

The anti-apoptotic cellular FLICE-like inhibitory protein cFLIP plays a pivotal role in normal tissues homoeostasis and the development of many tumors, but its role in normal thymus (NT), thymomas and thymic carcinomas (TC) is largely unknown.

Expression, regulation and function of cFLIP were analyzed in biopsies of NT, thymomas, thymic squamous cell carcinomas (TSCC), thymic epithelial cells (TECs) derived thereof and in the TC line 1889c by qRT-PCR, western blot, shRNA techniques, and functional assays addressing survival, senescence and autophagy. More than 90% of thymomas and TSCCs showed increased cFLIP expression compared to NT. cFLIP expression declined with age in NTs but not in thymomas. During short term culture cFLIP expression levels declined significantly slower in neoplastic than non-neoplastic primary TECs. Down-regulation of cFLIP by shRNA or NF-κB inhibition accelerated senescence and induced autophagy and cell death in neoplastic TECs.

The results suggest a role of cFLIP in the involution of normal thymus and the development of thymomas and TSCC. Since increased expression of cFLIP is a known tumor escape mechanism, it may serve as tissue-based biomarker in future clinical trials, including immune checkpoint inhibitor trials in the commonly PD-L1^high thymomas and TCs.

Rocaglamide breaks TRAIL-resistance in human multiple myeloma and acute T-cell leukemia in vivo in a mouse xenogtraft model

Multiple myeloma (MM) is an incurable malignancy by the presently known therapies. TRAIL is a promising anticancer agent that virtually not shows any toxicity to normal cells. We have recently carried out clinical trials with a human circularly permuted TRAIL, CPT, against MM saw a partial response in approximate 20-30% of patients. In the current study, we investigated the cause of CPT resistance and revealed that the majority of the MM patients express elevated levels of c-FLIP. Knockdown of c-FLIP expression by siRNA alone was sufficient to increase CPT-mediated apoptosis in a CPT-resistant human MM cell line U266. To overcome CPT resistance, we investigated the combination of CPT with Rocaglamides(s) in MM which has been shown to inhibit c-FLIP expression in vitro. We show that Rocaglamide(s) overcomes CPT resistance in U266 in vitro and significant increases in anti-tumor efficacies of CPT in mice xenografted with U266. Similar results were also obtained in mice xenografted with the CPT-resistant human acute T-cell leukemia cell line Molt-4. Our study suggests that the combination of Rocaglamide(s) with CPT may provide a more efficient treatment against myeloma and leukemia.

A roadmap of constitutive NF-κB activity in Hodgkin lymphoma: Dominant roles of p50 and p52 revealed by genome-wide analyses

Background

NF-κB is widely involved in lymphoid malignancies; however, the functional roles and specific transcriptomes of NF-κB dimers with distinct subunit compositions have been unclear.

Methods

Using combined ChIP-sequencing and microarray analyses, we determined the cistromes and target gene signatures of canonical and non-canonical NF-κB species in Hodgkin lymphoma (HL) cells.

Results

We found that the various NF-κB subunits are recruited to regions with redundant κB motifs in a large number of genes. Yet canonical and non-canonical NF-κB dimers up- and downregulate gene sets that are both distinct and overlapping, and are associated with diverse biological functions. p50 and p52 are formed through NIK-dependent p105 and p100 precursor processing in HL cells and are the predominant DNA binding subunits. Logistic regression analyses of combinations of the p50, p52, RelA, and RelB subunits in binding regions that have been assigned to genes they regulate reveal a cross-contribution of p52 and p50 to canonical and non-canonical transcriptomes. These analyses also indicate that the subunit occupancy pattern of NF-κB binding regions and their distance from the genes they regulate are determinants of gene activation versus repression. The pathway-specific signatures of activated and repressed genes distinguish HL from other NF-κB-associated lymphoid malignancies and inversely correlate with gene expression patterns in normal germinal center B cells, which are presumed to be the precursors of HL cells.

Conclusions

We provide insights that are relevant for lymphomas with constitutive NF-κB activation and generally for the decoding of the mechanisms of differential gene regulation through canonical and non-canonical NF-κB signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0280-5) contains supplementary material, which is available to authorized users.

Brentuximab: a major advance in treatment of CD30-positive malignancies

Antibody-directed therapies allow greater selectivity in targeting of tumor associated antigens and spare normal cells. Brentuximab vedotin is an anti-CD30 antibody–drug conjugate. It has demonstrated impressive activity in the treatment of refractory and or relapsed Hodgkin's lymphoma, anaplastic large cell lymphoma and other CD30+ lymphoid malignancies. Several ongoing trials are testing the potential use of brentuximab vedotin for treatment of various CD30+ and CD30- malignancies in the setting of high-risk untreated disease. It is being tested in combination with chemotherapy, and testing in combination with immune therapy is also planned. CD30 plays a pivotal role in immune regulation and is also an attractive new target for intervention in the setting of select auto-immune diseases, as well as graft versus host disease.

RIP1 Cleavage in the Kinase Domain Regulates TRAIL-Induced NF-κB Activation and Lymphoma Survival

Although TRAIL is considered a potential anticancer agent, it enhances tumor progression by activating NF-κB in apoptosis-resistant cells. Cellular FLICE-like inhibitory protein (cFLIP) overexpression and caspase-8 activation have been implicated in TRAIL-induced NF-κB activation; however, the underlying mechanisms are unknown. Here, we report that caspase-8-dependent cleavage of RIP1 in the kinase domain (KD) and intermediate domain (ID) determines the activation state of the NF-κB pathway in response to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) treatment. In apoptosis-sensitive cells, caspase-8 cleaves RIP1 in the KD and ID immediately after the recruitment of RIP1 to the receptor complex, impairing IκB kinase (IKK) recruitment and NF-κB activation. In apoptosis-resistant cells, cFLIP restricts caspase-8 activity, resulting in limited RIP1 cleavage and generation of a KD-cleaved fragment capable of activating NF-κB but not apoptosis. Notably, depletion of the cytoplasmic pool of TRAF2 and cIAP1 in lymphomas by CD40 ligation inhibits basal RIP1 ubiquitination but does not prompt cell death, due to CD40L-induced cFLIP expression and limited RIP1 cleavage. Inhibition of RIP1 cleavage at the KD suppresses NF-κB activation and cell survival even in cFLIP-overexpressing lymphomas. Importantly, RIP1 is constitutively cleaved in human and mouse lymphomas, suggesting that cFLIP-mediated and caspase-8-dependent limited cleavage of RIP1 is a new layer of mechanism that promotes NF-κB activation and lymphoma survival.

Lymphoma: immune evasion strategies

While the cellular origin of lymphoma is often characterized by chromosomal translocations and other genetic aberrations, its growth and development into a malignant neoplasm is highly dependent upon its ability to escape natural host defenses. Neoplastic cells interact with a variety of non-malignant cells in the tumor milieu to create an immunosuppressive microenvironment. The resulting functional impairment and dysregulation of tumor-associated immune cells not only allows for passive growth of the malignancy but may even provide active growth signals upon which the tumor subsequently becomes dependent. In the past decade, the success of immune checkpoint blockade and adoptive cell transfer for relapsed or refractory lymphomas has validated immunotherapy as a possible treatment cornerstone. Here, we review the mechanisms by which lymphomas have been found to evade and even reprogram the immune system, including alterations in surface molecules, recruitment of immunosuppressive subpopulations, and secretion of anti-inflammatory factors. A fundamental understanding of the immune evasion strategies utilized by lymphomas may lead to better prognostic markers and guide the development of targeted interventions that are both safer and more effective than current standards of care.

Immune evasion strategies of molluscum contagiosum virus

Molluscum contagiosum virus (MCV) is the causative agent of molluscum contagiosum (MC), the third most common viral skin infection in children, and one of the five most prevalent skin diseases worldwide. No FDA-approved treatments, vaccines, or commercially available rapid diagnostics for MCV are available. This review discusses several aspects of this medically important virus including: physical properties of MCV, MCV pathogenesis, MCV replication, and immune responses to MCV infection. Sequencing of the MCV genome revealed novel immune evasion molecules which are highlighted here. Special attention is given to the MCV MC159 and MC160 proteins. These proteins are FLIPs with homologs in gamma herpesviruses and in the cell. They are of great interest because each protein regulates apoptosis, NF-κB, and IRF3. However, the mechanism that each protein uses to impart its effects is different. It is important to elucidate how MCV inhibits immune responses; this knowledge contributes to our understanding of viral pathogenesis and also provides new insights into how the immune system neutralizes virus infections.

Brentuximab vedotin

Brentuximab vedotin is an anti-CD30 antibody-drug conjugate with proven efficacy in patients with CD30(+) malignancies, including classical Hodgkin lymphoma and anaplastic large cell lymphoma. Promising activity has also been seen in other lymphomas that express CD30. Because of its acceptable toxicity profile and significant clinical efficacy, single-agent brentuximab vedotin is an approved treatment for relapsed patients with these diseases. Brentuximab vedotin has safely been combined with chemotherapy and is now being compared with standard treatments in randomized trials.

Molecular mechanisms and anti-cancer aspects of the medicinal phytochemicals rocaglamides (=flavaglines)

Rocaglamides (= flavaglines) are potent natural anti-cancer phytochemicals that inhibit cancer growth at nanomolar concentrations by the following mechanisms: (1) inhibition of translation initiation via inhibition of phosphorylation of the mRNA cap-binding eukaryotic translation initiation factor eIF4E and stabilization of RNA-binding of the translation initiation factor eIF4A in the eIF4F complex; (2) blocking cell cycle progression by activation of the ATM/ATR-Chk1/Chk2 checkpoint pathway; (3) inactivation of the heat shock factor 1 (HSF1) leading to up-regulation of thioredoxin-interacting protein (TXNIP) and consequent reduction of glucose uptake and (4) induction of apoptosis through activation of the MAPK p38 and JNK and inhibition of the Ras-CRaf-MEK-ERK signaling pathway. Besides the anti-cancer activities, rocaglamides are also shown to protect primary cells from chemotherapy-induced cell death and alleviate inflammation- and drug-induced injury in neuronal tissues. This review will focus on the recently discovered molecular mechanisms of the actions of rocaglamides and highlights the benefits of using rocaglamides in cancer treatment.

Parthenolide Sensitizes Human Colorectal Cancer Cells to Tumor Necrosis Factor-related Apoptosis-inducing Ligand through Mitochondrial and Caspase Dependent Pathway

BACKGROUND/AIMS

Combination therapy utilizing tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in conjunction with other anticancer agents, is a promising strategy to overcome TRAIL resistance in malignant cells. Recently, parthenolide (PT) has proved to be a promising anticancer agent, and several studies have explored its use in combination therapy. Here, we investigated the molecular mechanisms by which PT sensitizes colorectal cancer (CRC) cells to TRAIL-induced apoptosis.

METHODS

HT-29 cells (TRAIL-resistant) were treated with PT and/or TRAIL for 24 hours. The inhibitory effect on proliferation was detected using the 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Annexin V staining, cell cycle analysis, and Hoechst 33258 staining were used to assess apoptotic cell death. Activation of an apoptotic pathway was confirmed by Western blot.

RESULTS

Treatment with TRAIL alone inhibited the proliferation of HCT 116 cells in a dose-dependent manner, whereas proliferation was not affected in HT-29 cells. Combination PT and TRAIL treatment significantly inhibited cell growth and induced apoptosis of HT-29 cells. We observed that the synergistic effect was associated with misregulation of B-cell lymphoma 2 (Bcl-2) family members, release of cytochrome C to the cytosol, activation of caspases, and increased levels of p53.

CONCLUSION

Combination therapy using PT and TRAIL might offer an effetive strategy to overcome TRAIL resistance in certain CRC cells.

Immunologic pathomechanism of Hodgkin's lymphoma

Hodgkin's lymphoma is a lymphoid malignancy of the immune system. The pathognomonic Hodgkin and Reed-Sternberg cells (HRS) are derived mainly from monoclonal, preapoptotic B cells, and they carry rearranged, somatically mutated immunoglobulin heavy chains. In an appropriate microenvironment, HRS cells escape from apoptosis by several mechanisms, including single mutations, aberrant signaling pathways. Eventually, weakened immune surveillance leads to uncontrolled, disproportional B cell proliferation. This review summarizes the latest findings on the pathogenesis of Hodgkin lymphoma, with a special emphasis on immunologic processes, and depicts current and future immunotherapeutic regimens, which improve treatment outcomes and reduce late toxicities.

Targeting the Anti-Apoptotic Protein c-FLIP for Cancer Therapy

Cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) is a major resistance factor and critical anti-apoptotic regulator that inhibits tumor necrosis factor-alpha (TNF-alpha), Fas-L, and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis as well as chemotherapy-triggered apoptosis in malignant cells. c-FLIP is expressed as long (c-FLIP(L)), short (c-FLIP(S)), and c-FLIP(R) splice variants in human cells. c-FLIP binds to FADD and/or caspase-8 or -10 in a ligand-dependent and-independent fashion, which in turn prevents death-inducing signaling complex (DISC) formation and subsequent activation of the caspase cascade. Moreover, c-FLIP(L) and c-FLIP(S) are known to have multifunctional roles in various signaling pathways, as well as activating and/or upregulating several cytoprotective signaling molecules. Upregulation of c-FLIP has been found in various tumor types, and its downregulation has been shown to restore apoptosis triggered by cytokines and various chemotherapeutic agents. Hence, c-FLIP is an important target for cancer therapy. For example, small interfering RNAs (siRNAs) that specifically knockdown the expression of c-FLIP(L) in diverse human cancer cell lines augmented TRAIL-induced DISC recruitment and increased the efficacy of chemotherapeutic agents, thereby enhancing effector caspase stimulation and apoptosis. Moreover, small molecules causing degradation of c-FLIP as well as decreasing mRNA and protein levels of c-FLIP(L) and c-FLIP(S) splice variants have been found, and efforts are underway to develop other c-FLIP-targeted cancer therapies. This review focuses on (1) the functional role of c-FLIP splice variants in preventing apoptosis and inducing cytokine and drug resistance; (2) the molecular mechanisms that regulate c-FLIP expression; and (3) strategies to inhibit c-FLIP expression and function.

The microenvironment in classical Hodgkin lymphoma: an actively shaped and essential tumor component

Classical Hodgkin lymphoma (cHL) is characterized by a minority of tumor cells derived from germinal center B-cells and a vast majority of non-malignant reactive cells. The tumor cells show a loss of B-cell phenotype including lack of the B-cell receptor, which makes the tumor cells vulnerable to apoptosis. To overcome this threat, tumor cells and their precursors depend on anti-apoptotic and growth stimulating factors that are obtained via triggering of multiple membrane receptors. In addition, tumor cells shape the environment by producing a wide variety of chemokines and cytokines. These factors alter the composition of the microenvironment and modulate the nature and effectiveness of the infiltrating cells. The attracted cells enhance the pro-survival and growth stimulating signals for the tumor cells. To escape from an effective anti-tumor response tumor cells avoid recognition by T and NK cells, by downregulation of HLA molecules and modulating NK and T-cell receptors. In addition, the tumor cells produce immune suppressive cytokines that inhibit cytotoxic responses. In this review the relevance of the microenvironment in the pathogenesis of cHL will be discussed.

Apoptotic and proliferative characteristics of proliferation centers in lymph node sections of patients with chronic lymphocytic leukemia

We have analyzed the immunohistochemical expression of a wide range of molecules along with the proliferation rate separately in the proliferation centers (PCs) and in the rest of the tumor area, in lymph node or spleen sections of patients with chronic lymphocytic leukemia (CLL). Fas, FasL and c-FLIP were observed both within and outside the PCs in all cases. However, only the difference in FasL expression between the PCs and the non-PC areas attained statistical significance. Median survivin expression in the PCs was higher compared to the non-PC areas. Cleaved caspase 3 was expressed at very low levels both within and outside PCs, while BCL-2 protein was expressed at high levels in all cases in both tumor compartments. Multivariate analysis demonstrated that concurrent overexpression of Fas/FasL/c-FLIP in the PCs was correlated with worse outcome for progression-free survival as well as for overall survival.

c-FLIP does not correlate with response to immunochemotherapy treatment and outcome of patients with nodal diffuse large B-cell lymphoma

Cellular FLICE-inhibitory protein (c-FLIP) is a critical anti-apoptotic regulator that inhibits apoptosis-inducing ligand, (TRAIL)-induced apoptosis as well as chemotherapy-triggered apoptosis in malignant cells. The present study was designed to investigate the clinical and prognostic significance of c-FLIP expression in patients with nodal diffuse large B-cell lymphoma (DLBCL) treated with immunochemotherapy.

METHODS

We have analyzed lymph node biopsy specimens, obtained from 60 patients with newly diagnosed nodal DLBCL treated with immunochemotherapy (R-CHOP or R-EPOCH). The expression of c-FLIP was analyzed using the standard imunohistochemical method on formalin-fixed and routinely processed paraffin-embedded lymph node specimens and evaluated semi quantitavely as a percentage of tumor cells.

RESULTS

c-FLIP immunoexpression (>50% positive tumor cells) has been found in 28 (46.7%) patients, and observed as cytoplasmic staining. There was not significant difference in c-FLIP immunoexpression between GCB and non-GCB subtype of DLBCL (P=0.639). Besides, c-FLIP immunoexpression had no significant association with IPI, "bulky" disease, extranodal localization, haemoglobin, Ki-67 immunoexpression or other clinico-pathological parameters. c-FLIP positivity has no significant influence on therapy response and survival in patients with DLBCL (P=0.562 and P=0.093, respectively). Patients with c-FLIP overexpression did not relapse more often that patients without expression of this apoptotic protein (P=0.365).

CONCLUSION

Our results suggest that c-FLIP immunoexpression can not be used as a prognostic factor in patients with nodal DLBCL treated with immunochemotherapy.

Induction of endoplasmic reticulum stress by sorafenib and activation of NF-κB by lestaurtinib as a novel resistance mechanism in Hodgkin lymphoma cell lines

Hodgkin-Reed/Sternberg (HRS) cells of classical Hodgkin lymphoma show aberrant expression and activation of several receptor tyrosine kinases (RTK) in the majority of cases. Therefore, we tested whether tyrosine kinase inhibitors (TKI) already in clinical use or late stages of clinical trials have antiproliferative effects on HRS cell lines and evaluated the targets, affected signaling pathways, and mechanisms of cell death and resistance. Sorafenib and lestaurtinib had antiproliferative effects on HRS cell lines at concentrations achievable in patients. Sorafenib inhibited platelet-derived growth factor receptor (PDGFR) α, TRKA and RON, caused decreases in total and phosphorylated amounts of several signaling molecules, and provoked caspase-3-independent cell death, most likely due to endoplasmic reticulum stress as indicated by upregulation of GADD34 and GADD153 and phosphorylation of PERK. Lestaurtinib inhibited TRKA, PDGFRα, RON, and JAK2 and had only a cytostatic effect. Besides deactivation, lestaurtinib also caused activation of signaling pathways. It caused increases in CD30L and TRAIL expression, and CD30L/CD30 signaling likely led to the observed concomitant activation of extracellular signal-regulated kinase 1/2 and the alternative NF-κB pathway. These data disclose the possible use of sorafenib for the treatment of Hodgkin lymphoma and highlight NF-κB activation as a potential novel mechanism of resistance toward TKIs.

Predictive value of Sp1/Sp3/FLIP signature for prostate cancer recurrence

Prediction of prostate cancer prognosis is challenging and predictive biomarkers of recurrence remain elusive. Although prostate specific antigen (PSA) has high sensitivity (90%) at a PSA level of 4.0 ng/mL, its low specificity leads to many false positive results and considerable overtreatment of patients and its performance at lower ranges is poor. Given the histopathological and molecular heterogeneity of prostate cancer, we propose that a panel of markers will be a better tool than a single marker. We tested a panel of markers composed of the anti-apoptotic protein FLIP and its transcriptional regulators Sp1 and Sp3 using prostate tissues from 64 patients with recurrent and non-recurrent cancer who underwent radical prostatectomy as primary treatment for prostate cancer and were followed with PSA measurements for at least 5 years. Immunohistochemical staining for Sp1, Sp3, and FLIP was performed on these tissues and scored based on the proportion and intensity of staining. The predictive value of the FLIP/Sp1/Sp3 signature for clinical outcome (recurrence vs. non-recurrence) was explored with logistic regression, and combinations of FLIP/Sp1/Sp3 and Gleason score were analyzed with a stepwise (backward and forward) logistic model. The discrimination of the markers was identified by sensitivity-specificity analysis and the diagnostic value of FLIP/Sp1/Sp3 was determined using area under the curve (AUC) for receiver operator characteristic curves. The AUCs for FLIP, Sp1, Sp3, and Gleason score for predicting PSA failure and non-failure were 0.71, 0.66, 0.68, and 0.76, respectively. However, this increased to 0.93 when combined. Thus, the “biomarker signature” of FLIP/Sp1/Sp3 combined with Gleason score predicted disease recurrence and stratified patients who are likely to benefit from more aggressive treatment.

Activated T cell exosomes promote tumor invasion via Fas signaling pathway

Activated T cells release bioactive Fas ligand (FasL) in exosomes, which subsequently induce self-apoptosis of T cells. However, their potential effects on cell apoptosis in tumors are still unknown. In this study, we purified exosomes expressing FasL from activated CD8(+) T cell from OT-I mice and found that activated T cell exosomes had little effect on apoptosis and proliferation of tumor cells but promoted the invasion of B16 and 3LL cancer cells in vitro via the Fas/FasL pathway. Activated T cell exosomes increased the amount of cellular FLICE inhibitory proteins and subsequently activated the ERK and NF-κB pathways, which subsequently increased MMP9 expression in the B16 murine melanoma cells. In a tumor-invasive model in vivo, we observed that the activated T cell exosomes promoted the migration of B16 tumor cells to lung. Interestingly, pretreatment with FasL mAb significantly reduced the migration of B16 tumor cells to lung. Furthermore, CD8 and FasL double-positive exosomes from tumor mice, but not normal mice, also increased the expression of MMP9 and promoted the invasive ability of B16 murine melanoma and 3LL lung cancer cells. In conclusion, our results indicate that activated T cell exosomes promote melanoma and lung cancer cell metastasis by increasing the expression of MMP9 via Fas signaling, revealing a new mechanism of tumor immune escape.

A New Player in the Development of TRAIL Based Therapies for Hepatocarcinoma Treatment: ATM Kinase

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. HCCs are genetically and phenotypically heterogeneous tumors characterized by very poor prognosis, mainly due to the lack, at present, of effective therapeutic options, as these tumors are rarely suitable for radiotherapy and often resistant to chemotherapy protocols. In the last years, agonists targeting the Tumor Necrosis Factor Related Apoptosis Inducing Ligand (TRAIL) death receptor, has been investigated as a valuable promise for cancer therapy, based on their selectivity for malignant cells and low toxicity for healthy cells. However, many cancer models display resistance to death receptor induced apoptosis, pointing to the requirement for the development of combined therapeutic approaches aimed to selectively sensitize cancer cells to TRAIL. Recently, we identified ATM kinase as a novel modulator of the ability of chemotherapeutic agents to enhance TRAIL sensitivity. Here, we review the biological determinants of HCC responsiveness to TRAIL and provide an exhaustive and updated analysis of the molecular mechanisms exploited for combined therapy in this context. The role of ATM kinase as potential novel predictive biomarker for combined therapeutic approaches based on TRAIL and chemotherapeutic drugs will be closely discussed.

Analysis of NF-κB Pathway Proteins in Pediatric Hodgkin Lymphoma: Correlations with EBV Status and Clinical Outcome-A Children's Oncology Group Study

Constitutively active nuclear factor-κB (NF-κB) is integral to the survival of Hodgkin/Reed-Sternberg cells (H/RS) in Hodgkin Lymphoma (HL). To investigate NF-κB pathway proteins in pediatric HL, we utilized a tissue microarray compiled from 102 children enrolled in the Children's Oncology Group intermediate-risk clinical trial AHOD0031 (56 male, 78 Caucasian, median age 15y (range 1-20y), 85 nodular sclerosing subtype, 23 Epstein Barr virus (EBV) positive, 24 refractory/relapsed disease). We examined the intensity, localization, and pathway correlations of NF-κB pathway proteins (Rel-A/p65, Rel-B, c-Rel, NF-κB1, NF-κB2, IκB-α, IKK-α, IKK-β, IKK-γ/NEMO, NIK, A20), as well as their associations with EBV status and clinical outcome. NF-κB pathway proteins were overexpressed in pediatric HL patients compared to controls. Patients with EBV-tumors, or with rapid early therapy response, had tightly coordinated regulation of NF-κB pathway proteins, whereas patients with EBV+ tumors, or slow early therapy response, had little coordinated NF-κB pathway regulation. High NIK expression was associated with a slow response to therapy and decreased EFS. Elevated Rel-B, NIK and the NF-κB inhibitor A20 were associated with decreased EFS in multivariate analysis. These studies suggest a pivotal role for the NF-κB pathway in therapy response and patient survival (clinicaltrials.gov identifier: ).

The role of c-FLIP splice variants in urothelial tumours

Deregulation of apoptosis is common in cancer and is often caused by overexpression of anti-apoptotic proteins in tumour cells. One important regulator of apoptosis is the cellular FLICE-inhibitory protein (c-FLIP), which is overexpressed, for example, in melanoma and Hodgkin's lymphoma cells. Here, we addressed the question whether deregulated c-FLIP expression in urothelial carcinoma impinges on the ability of death ligands to induce apoptosis. In particular, we investigated the role of the c-FLIP splice variants c-FLIP(long) (c-FLIP(L)) and c-FLIP(short) (c-FLIP(S)), which can have opposing functions. We observed diminished expression of the c-FLIP(L) isoform in urothelial carcinoma tissues as well as in established carcinoma cell lines compared with normal urothelial tissues and cells, whereas c-FLIP(S) was unchanged. Overexpression and RNA interference studies in urothelial cell lines nevertheless demonstrated that c-FLIP remained a crucial factor conferring resistance towards induction of apoptosis by death ligands CD95L and TRAIL. Isoform-specific RNA interference showed c-FLIP(L) to be of particular importance. Thus, urothelial carcinoma cells appear to fine-tune c-FLIP expression to a level sufficient for protection against activation of apoptosis by the extrinsic pathway. Therefore, targeting c-FLIP, and especially the c-FLIP(L) isoform, may facilitate apoptosis-based therapies of bladder cancer in otherwise resistant tumours.

Rocaglamide and a XIAP inhibitor cooperatively sensitize TRAIL-mediated apoptosis in Hodgkin's lymphomas

Although most of the patients with Hodgkin's lymphoma (HL) can be cured by the current regimen of high-dose multiagent chemotherapy, the treatment causes high risks of later toxicities including secondary malignancies. Therefore, new rational strategies are needed for HL treatment. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent due to its tumor selectivity and its lack of toxicity for normal cells. Unfortunately, many cancers remain resistant to TRAIL including HL. HL is characterized by enhanced expression of cellular caspase-8 (FLICE)-inhibitory protein (c-FLIP) and X-linked inhibitor of apoptosis (XIAP), which block receptor-mediated apoptosis by inhibiting caspase-8 and caspase-3, respectively. We have recently discovered the herbal compound Rocaglamide, which breaks TRAIL-resistance in acute T cell leukemia through inhibition of c-FLIP expression. We have also shown that small molecule XIAP inhibitors can sensitize TRAIL-mediated apoptosis in several resistant tumors. However, whether targeting XIAP or c-FLIP is also a suitable strategy to prime HL cells for TRAIL-induced apoptosis has not yet been investigated. In our study, we show that Rocaglamide suppresses c-FLIP expression in HL cells in a dose- and time-dependent manner. However, downregulation of c-FLIP alone was not sufficient to sensitize TRAIL-induced apoptosis in HL cells. Similarly, treatment of HL cells with a small molecule XIAP inhibitor resulted in a moderate induction of apoptosis. However, inhibition of XIAP alone was also not sufficient to enhance TRAIL-induced cell death. Synergistic increase in TRAIL-mediated killing of HL cells was only obtained by combination of Rocaglamide and XIAP inhibitors. Our study demonstrates that targeting both c-FLIP and XIAP are necessary for an efficient treatment of HL.

Nonsteroidal anti-inflammatory drugs induce apoptosis in cutaneous T-cell lymphoma cells and enhance their sensitivity for TNF-related apoptosis-inducing ligand

Cutaneous T-cell lymphomas (CTCL) form a heterogeneous group of non-Hodgkin's lymphomas of the skin. In previous studies, we had characterized CTCL cells as resistant to the death ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which correlated to pronounced expression of the caspase-8/-10 inhibitor c-FLIP. For identification of proapoptotic strategies in CTCL cells and for overcoming their death ligand resistance, we investigated the effects of nonsteroidal anti-inflammatory drugs (NSAIDs) such as acetylsalicylic acid, sodium salicylate, and diclofenac (DF). These drugs strongly enhanced apoptosis, as well as decreased CTCL cell proliferation and vitality, and DF furthermore sensitized for TRAIL-induced apoptosis. Full activation of the caspase cascade (caspase-3, -8, -9) and decreased mitochondrial membrane potential were characteristic for NSAID treatment, whereas cytochrome c release was seen only for DF. Downregulation of Mcl-1 and enhanced surface expression of TRAIL were seen in response to NSAIDs. Most characteristic for apoptosis induction was the downregulation of c-FLIP. In agreement with the critical role of c-FLIP for apoptosis deficiency of CTCL cells, its overexpression decreased NSAID-mediated apoptosis and its downregulation by small hairpin RNA-enhanced apoptosis. The study provides a rationale for the use of NSAIDs as a new therapeutic option for CTCL patients. Supporting this concept, ex vivo lymphoma cells of CTCL patients also revealed significant sensitivity for NSAID treatment.

Carbon monoxide inhibits Fas activating antibody-induced apoptosis in endothelial cells

Background

The extrinsic apoptotic pathway initiates when a death ligand, such as the Fas ligand, interacts with its cell surface receptor (ie., Fas/CD95), forming a death-inducing signaling complex (DISC). The Fas-dependent apoptotic pathway has been implicated in several models of lung or vascular injury. Carbon monoxide, an enzymatic product of heme oxygenase-1, exerts antiapoptotic effects at low concentration in vitro and in vivo.

Methods

Using mouse lung endothelial cells (MLEC), we examined the antiapoptotic potential of carbon monoxide against apoptosis induced by the Fas/CD95-activating antibody (Jo2). Carbon monoxide was applied to cell cultures in vitro. The expression and/or activation of apoptosis-related proteins and signaling intermediates were determined using Western Immunoblot and co-immunoprecipitation assays. Cell death was monitored by lactate dehydrogenase (LDH) release assays. Statistical significance was determined by student T-test and a value of P < 0.05 was considered significant.

Results

Treatment of MLEC with Fas-activating antibody (Jo2) induced cell death associated with the formation of the DISC, and activation of caspases (-8, -9, and -3), as well as the pro-apoptotic Bcl-2 family protein Bax. Exposure of MLEC to carbon monoxide inhibited Jo2-induced cell death, which correlated with the inhibition of DISC formation, cleavage of caspases-8, -9, and -3, and Bax activation. Carbon monoxide inhibited the phosphorylation of the Fas-associated death domain-containing protein, as well as its association with the DISC. Furthermore, carbon monoxide induced the expression of the antiapoptotic protein FLIP and increased its association with the DISC.

CO-dependent cytoprotection against Fas mediated apoptosis in MLEC depended in part on activation of ERK1/2-dependent signaling.

Conclusions

Carbon monoxide has been proposed as a potential therapy for lung and other diseases based in part on its antiapoptotic effects in endothelial cells. In vitro, carbon monoxide may inhibit both Fas/caspase-8 and Bax-dependent apoptotic signaling pathways induced by Fas-activating antibody in endothelial cells. Strategies to block Fas-dependent apoptotic pathways may be useful in development of therapies for lung or vascular disorders.

Expression of heat shock proteins in classical Hodgkin lymphoma: correlation with apoptotic pathways and prognostic significance

AIMS

Heat shock proteins (HSPs), known to inhibit apoptosis and promote cellular survival, are overexpressed in many tumours. We analysed the expression of relevant HSPs and heat shock factor 1 (HSF1) in classical Hodgkin lymphoma (cHL) and their relationship with caspase signalling pathways and patient outcome.

METHODS AND RESULTS

Using tissue microarrays (TMAs), most cases showed strong immunohistochemical expression of HSPs [10, 27, 40, 60, 70, 90, 110, HO1, cell division cycle 37 homolog (CDC37) and HSF1, which points to cHL as a potential candidate to stress-response inhibitors. Active caspases 3, 8 and 9 were detected in 55.1%, 55.4% and 96.2% of cases although cleaved poly (ADP-ribose) polymerase (PARP) was observed in only 16.1%, suggesting an improper functioning of apoptosis. Statistical analysis showed associations of HSP70 with active caspase 3 (P = 0.000); HSP40 with active caspase 9 (P = 0.031) and p53 (P = 0.003); HO1 with p53 (P = 0.006) and p21 (P = 0.005); and p53 with p21 (P = 0.015).

CONCLUSIONS

Correlations between the expression of apoptotic markers and HSPs may suggest a role for the latter in modulating apoptosis in cHL, mainly through the HSP70-HSP40 system, and in the stabilization of p53. Survival analyses showed that absence of active caspase 8 and HO1 had a negative impact in patient outcome.

In vitro and in vivo characterisation of a novel c-FLIP-targeted antisense phosphorothioate oligonucleotide

Previous studies have suggested that the caspase 8 inhibitor FLIP is a promising anti-cancer therapeutic target. In this study, we characterised a novel FLIP-targeted antisense phosphorothioate oligonucleotide (AS PTO). FLIP AS and control PTOs were assessed in vitro in transient transfection experiments and in vivo using xenograft models in Balb/c nude mice. FLIP expression was assessed by QPCR and Western. Apoptosis induction was determined by flow cytometry and Western. Of 5 sequences generated, one potently down-regulated FLIP. AS PTO-mediated down-regulation of FLIP resulted in caspase 8 activation and apoptosis induction in non-small cell lung (NSCLC) cells but not in normal lung cells. Similar results were observed in colorectal and prostate cancer cells. Furthermore, the FLIP AS PTO sensitized cancer cells but not normal lung cells to apoptosis induced by rTRAIL. Moreover, the FLIP AS PTO enhanced chemotherapy-induced apoptosis in NSCLC cells. Importantly, compared to a control non-targeted PTO, intra-peritoneal delivery of FLIP AS PTO inhibited the growth of NSCLC xenografts and enhanced the in vivo antitumour effects of cisplatin. We have identified a novel FLIP-targeted AS PTO that has in vitro and in vivo activity and which therefore has potential for further pre-clinical development.

NF-κB as a potential therapeutic target in myelodysplastic syndromes and acute myeloid leukemia

IMPORTANCE OF THE FIELD

The inactive NF-κB-inhibitor of NF-κB (IκB) complex is activated by stimuli including pro-inflammatory cytokines, mitogens, growth factors and stress-inducing agents. The release of NF-κB facilitates its translocation to the nucleus, where it promotes cell survival by initiating transcription of genes encoding stress-response enzymes, cell-adhesion molecules, pro-inflammatory cytokines and anti-apoptotic proteins. NF-κB and associated regulatory factors (IκB kinase subunits and bcl-3) are implicated in hematological and solid tumour malignancies. NF-κB appears to be involved in cell proliferation control, apoptosis control, angiogenesis promotion and possibly regulation of diffusion of metastases. There are several reports that inhibition of NF-κB as a therapeutic target may have a role in tumour cell death or growth inhibition.

AREA COVERED IN THIS REVIEW

We review data about inhibition of NF-κB in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). We describe the molecular mechanisms underlying NF-κB deregulation in these haematological malignancies.

WHAT THE READER WILL GAIN

Constitutive activation of NF-κB in the nucleus has been reported in some varieties of MDS/AML. The in vitro and in vivo results of NF-κB inhibition in myeloid malignancies are highlighted.

TAKE HOME MESSAGE

NF-κB selective inhibitory drugs may be useful, either as single agents or associated with conventional chemotherapy.

Targeting c-FLIP in cancer

Cellular-FLICE inhibitory protein (c-FLIP) is a key anti-apoptotic regulator that inhibits cell death mediated by the death receptors Fas, DR4, DR5, and TNF-R1. Three splice variants of c-FLIP function at the DISC level by blocking the processing and activation of procaspase-8 and -10. Overexpression of c-FLIP has been identified in many different tumour types, and its downregulation in vitro has been shown to restore apoptosis mediated by CD95L and TRAIL. c-FLIP therefore represents a promising target for cancer therapy. This review focuses on the molecular mechanisms that control c-FLIP expression and current research into inhibitors of the protein. Increasing evidence supports the investigation of c-FLIP as a therapeutic target to restore an apoptotic response in cancer cells.

KLF4 is a tumor suppressor in B-cell non-Hodgkin lymphoma and in classic Hodgkin lymphoma

The transcription factor KLF4 may act both as an oncogene and a tumor suppressor in a tissue-depending manner. In T- and pre-B-cell lymphoma, KLF4 was found to act as tumor suppressor. We found the KLF4 promoter methylated in B-cell lymphoma cell lines and in primary cases of B-cell lymphomas, namely, follicular lymphoma, diffuse large B-cell lymphoma, Burkitt lymphoma, and in classic Hodgkin lymphoma (cHL) cases. Promoter hypermethylation was associated with silencing of KLF4 expression. Conditional overexpression of KLF4 in Burkitt lymphoma cell lines moderately retarded proliferation, via cell-cycle arrest in G(0)/G(1). In the cHL cell lines, KLF4 induced massive cell death that could partially be inhibited with Z-VAD.fmk. A quantitative reverse-transcribed polymerase chain reaction array revealed KLF4 target genes, including the proapoptotic gene BAK1. Using an shRNA-mediated knock-down approach, we found that BAK1 is largely responsible for KLF4-induced apoptosis. In addition, we found that KLF4 negatively regulates CXCL10, CD86, and MSC/ABF-1 genes. These genes are specifically up-regulated in HRS cells of cHL and known to be involved in establishing the cHL phenotype. We conclude that epigenetic silencing of KLF4 in B-cell lymphomas and particularly in cHL may favor lymphoma survival by loosening cell-cycle control and protecting from apoptosis.

Enhanced death ligand-induced apoptosis in cutaneous SCC cells by treatment with diclofenac/hyaluronic acid correlates with downregulation of c-FLIP

Actinic keratosis (AK) occurs on sun-exposed skin and may progress to invasive squamous cell carcinoma (SCC). As for its topical treatment, diclofenac/hyaluronic acid (HA) has been recently approved. The NSAID diclofenac is an inhibitor of COX-2; however, its mode of action in cutaneous epithelial cancer cells is largely unknown. Here, the effects of diclofenac/HA were investigated in relation to death ligand-mediated apoptosis (TNF-alpha, TRAIL, and CD95 activation). Whereas diclofenac/HA only moderately induced apoptosis by itself, it resulted in pronounced enhancement of death ligand-mediated apoptosis in sensitive SCC cell lines (3/4). Apoptosis was associated with activation of initiator caspases of the extrinsic pathway (caspase-8/caspase-10). Furthermore, death ligand and diclofenac/HA-mediated apoptosis were blocked by the same caspase inhibitors, indicating related pathways. The proapoptotic effects of diclofenac/HA appeared independent of the p53 pathway. Also, upregulation of death receptors appeared less important; however, strong downregulation of c-FLIP isoforms was seen after diclofenac/HA treatment. The crucial role of c-FLIP was proven through overexpression and knockdown experiments. Thus, induction of apoptosis appears to be highly characteristic of the mode of action of diclofenac/HA, and the therapeutic effect may be related to sensitization of neoplastic keratinocytes for death ligand-induced apoptosis.