Constitutive expression of c-FLIP in Hodgkin and Reed-Sternberg cells

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.

Apoptosis-related gene expression profile in chronic myeloid leukemia patients after imatinib mesylate and dasatinib therapy

BACKGROUND/AIMS

We investigated the effects of tyrosine kinase inhibitors (TKIs) on the expression of apoptosis-related genes (BCL-2 and death receptor family members) in chronic myeloid leukemia (CML) patients.

METHODS

Peripheral blood mononuclear cells from 32 healthy subjects and 26 CML patients were evaluated before and after treatment with imatinib mesylate (IM) and dasatinib (DAS) by quantitative PCR.

RESULTS

Anti-apoptotic genes (c-FLIP and MCL-1) were overexpressed and the pro-apoptotic BIK was reduced in CML patients. Expression of BMF, A1, c-FLIP, MCL-1, CIAP-2 and CIAP-1 was modulated by DAS. In IM-resistant patients, expression of A1, c-FLIP, CIAP-1 and MCL-1 was upregulated, and BCL-2, CIAP-2, BAK, BAX, BIK and FASL expression was downregulated.

CONCLUSION

Taken together, our results point out that, in CML, DAS interferes with the apoptotic machinery regulation. In addition, the data suggest that apoptosis-related gene expression profiles are associated with primary resistance to IM.

Cellular FLICE-like inhibitory protein long form (c-FLIPL) overexpression is related to cervical cancer progression

Cervical cancer is a leading cause of cancer deaths in women worldwide and infection by high-risk human papillomavirus types is a precursor event. The cellular FLICE-like inhibitory protein (c-FLIP) has been found to be overexpressed in several types of cancers and could be associated with cervical cancer progression because of its ability to inhibit the apoptotic process. To detect c-FLIP expression in cervical cancer, an immunohistochemical staining was performed, using tissue microarrays, on a series of 536 archival biopsy samples, including normal cervical tissues, low-grade and high-grade squamous intraepithelial lesions, and squamous cervical carcinomas. The epithelium in the normal cervix and low-grade squamous intraepithelial lesions mainly stained negatively for c-FLIP, whereas high-grade intraepithelial lesions and cancer samples showed an elevated expression of c-FLIP. A direct association was observed between the increasing grade of the lesion and the intensity of c-FLIP staining, in which the frequency of intense c-FLIP expression increased from 12.5% in the normal tissue to 82.1% in the cervical cancer tissue. An increased expression of c-FLIP may be an important factor in the progression of cervical cancer. This finding could aid in identifying patients with preneoplastic lesions at greater risk of developing cervical cancer. c-FLIP expression in cervical tissue may be a potential cervical cancer progression marker.

Non-Hodgkin's B-cell lymphoma: advances in molecular strategies targeting drug resistance

Non-Hodgkin's lymphoma (NHL) is a heterogeneous class of cancers displaying a diverse range of biological phenotypes, clinical behaviours and prognoses. Standard treatments for B-cell NHL are anthracycline-based combinatorial chemotherapy regimens composed of cyclophosphamide, doxorubicin, vincristine and prednisolone. Even though complete response rates of 40-50% with chemotherapy can be attained, a substantial proportion of patients relapse, resulting in 3-year overall survival rates of about 30%. Relapsed lymphomas are refractory to subsequent treatments with the initial chemotherapy regimen and can exhibit cross-resistance to a wide variety of anticancer drugs. The emergence of acquired chemoresistance thus poses a challenge in the clinic preventing the successful treatment and cure of disseminated B-cell lymphomas. Gene-expression analyses have increased our understanding of the molecular basis of chemotherapy resistance and identified rational targets for drug interventions to prevent and treat relapsed/refractory diffuse large B-cell lymphoma. Acquisition of drug resistance in lymphoma is in part driven by the inherent genetic heterogeneity and instability of the tumour cells. Due to the genetic heterogeneity of B-cell NHL, many different pathways leading to drug resistance have been identified. Successful treatment of chemoresistant NHL will thus require the rational design of combinatorial drugs targeting multiple pathways specific to different subtypes of B-cell NHL as well as the development of personalized approaches to address patient-to-patient genetic heterogeneity. This review highlights the new insights into the molecular basis of chemorefractory B-cell NHL that are facilitating the rational design of novel strategies to overcome drug resistance.

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.

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: ).

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.

The side population, as a precursor of Hodgkin and Reed-Sternberg cells and a target for nuclear factor-κB inhibitors in Hodgkin's lymphoma

Although disturbed cytokinesis of mononuclear Hodgkin (H) cells is thought to generate Reed-Sternberg (RS) cells, differentiation of Hodgkin's lymphoma (HL) cells is not fully understood. Recent studies indicate that cells found in a side population (SP) share characteristics of cancer stem cells. In this study we identified an SP in the HL cell lines, KMH2 and L428. This SP almost entirely consists of distinct small mononuclear cells, whereas the non-SP is a mixture of relatively large cells with H or RS cell-like morphology. Culture of the small mononuclear cells in the SP from KMH2 generated a non-SP. Single cell culture of the SP cells generated large cells with H or RS cell-like morphology. We found that CD30 overexpression and constitutive nuclear factor-κB (NF-κB) activity, both of which are characteristics of HL cells, are shared between the SP and non-SP cells for both KMH2 and L428. Inhibition of NF-κB induced apoptosis in both fractions, whereas the SP cells were resistant to a conventional chemotherapeutic agent doxorubicin. The results show that HL cell lines contain an SP, that is enriched for distinct small mononuclear cells and generates larger cells with H and RS cell-like morphology. The results also stress the significance of NF-κB inhibition for eradication of HL cells.

Inhibiting the inhibitors: retro-inverso Smac peptides

Resistance against apoptosis-inducing anti-cancer drugs remains a severe problem in therapy. One reason is the overexpression of inhibitors of apoptosis proteins (IAPs), a group of proteins responsible for the prevention of apoptosis induction by inactivation of initiator caspases. The natural inhibitor of the IAPs is the protein Smac, which impedes the binding to the caspases. Although Smac is a potent inhibitor, Smac peptides are not very stable in vivo and thus not applicable in therapy. Bioinformatical methods were applied to design Smac-derived peptides to break the therapy resistance in IAP high-expressing tumor cells. The exchange of amino acids in the Smac peptides AVPI and AVPF against unnatural amino acids leads to an improvement of the apoptosis sensitivity. The variety of Smac peptides was filtered by computational docking. Moreover, Smac-derived peptides with sufficient binding to the IAPs were tested in IAP-expressing Hodgkin Lymphoma cell lines.

Developing curcumin into a viable therapeutic for lymphoma

BACKGROUND

Emerging evidence suggests that natural plant ingredients have played an important role in the healthcare of many countries. Several of these natural plant products possess therapeutic potential for various diseases including cancer. Curcumin is the pigment of turmeric, a well-known chemopreventive agent that has been shown to suppress the proliferation of a wide variety of tumor cells, including lymphoma. Curcumin has been shown to have cancer chemopreventive potential against a variety of tumors via targeting key survival pathways that are aberrantly activated in cancer cells.

METHODS

This review discusses therapeutic potential of curcumin in malignancies of lymphoma as well as therapeutic implications of the recent advances in the field.

RESULTS/CONCLUSION

Dietary-compound curcumin hardwires to multiple cellular processes. Suppression of cell proliferation, induction of apoptosis, and inhibition of metastasis are considered to be the major mechanisms underlying its anticancer properties.

Expression and biological significance of c-FLIP in human hepatocellular carcinomas

BACKGROUND

c-FLIP can be considered as a tumor-progression factor in regard to its anti-apoptotic functions. In the present study, we intended to investigate the expression of c-FLIP in human HCC tissues, and its relation with drug-induced cell apoptosis through the specific inhibition of c-FLIP expression by siRNA in 7721 cells.

METHODS

c-FLIP expression was quantified immunohistochemically in HCC tissues(eighty-six cases), and corresponding noncancerous tissues (fifty-seven cases). Patients with HCC were followed up for cancer recurrence. Then, the c-FLIP gene was silenced with specific siRNA in 7721 HCC cells. c-FLIP expression was detected by RT-PCR, Western Blot and immunocytochemical staining. The cellular viability and cell apoptosis were assayed in vitro with cells treated with doxorubicin.

RESULTS

Positive immunostaining was detected for c-FLIP in 83.72% (72/86) human HCC tissues, 14.81% (4/27) hepatic cirrhosis, 11.11% (2/18) hepatic hemangioma tissues, and absent in normal hepatic tissues. The overexpression(more than 50%) of c-FLIP in HCC adversely affected the recurrence-free survival. Through c-FLIP gene silencing with siRNA, the expressions of c-FLIP mRNA and protein were remarkably down-regulated in 7721 HCC cells. And doxorubicin showed apparent inhibition on cell proliferations, and induced more apoptosis.

CONCLUSION

These results indicate that c-FLIP is frequently expressed in human HCCs, and its overexpression implied a lesser probability of recurrence-free survival. The specific silencing of c-FLIP gene can apparently up-regulate drug-induced HCC cell apoptosis, and may have therapeutic potential for the treatment of human HCC.

Involvement of FLIP in 2-methoxyestradiol-induced tumor regression in transgenic adenocarcinoma of mouse prostate model

PURPOSE

The purpose of this study is to investigate whether Fas-associated death domain interleukin-1 converting enzyme like inhibitory protein (FLIP) inhibition is a therapeutic target associated with 2-methoxyestradiol (2-ME2)-mediated tumor regression.

EXPERIMENTAL DESIGN

Expression and levels of FLIP were analyzed using (a) real-time PCR and immunoblot analysis in androgen-independent PC-3 cells treated with the newly formulated 2-ME2 and (b) immunohistochemistry in different Gleason pattern human prostate tumors. Transient transfections and chromatin immunoprecipitation (ChIP) assays were used to identify the transcription factors that regulate FLIP. Involvement of FLIP in 2-ME2-induced tumor regression was evaluated in transgenic adenocarcinoma mouse prostate (TRAMP) mice.

RESULTS

High Gleason pattern (5+5) human prostate tumors exhibit significant increase in FLIP compared with low Gleason pattern 3+3 (P=or<0.04). 2-ME2 reduced the levels and promoter activity of FLIP (P=0.001) in PC-3 cells. Transient expression assays show sequences between -503/+242 being sufficient for 2-ME2-induced inhibition of FLIP promoter activity. Cotransfection experiments show that overexpression of Sp1 activated, whereas Sp3 inhibited, Sp1 transactivation of FLIP promoter activity (P=0.0001). 2-ME2 treatment reduced binding of Sp1 to the FLIP promoter as evidenced by ChIP. Further, levels of FLIP associated with Fas or FADD decreased, whereas cleavage of caspase-8, levels of Bid, and apoptosis increased in response to 2-ME2 treatment in PC-3 cells. Administration of 2-ME2 regressed established prostate tumors in TRAMP mice that were associated with reduced expression of FLIP and Sp1.

CONCLUSION

Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

C/EBPalpha or C/EBPalpha oncoproteins regulate the intrinsic and extrinsic apoptotic pathways by direct interaction with NF-kappaB p50 bound to the bcl-2 and FLIP gene promoters

CCAAT/enhancer-binding protein alpha (C/EBPalpha) is mutated in 10% of acute myeloid leukemias, resulting in either a truncated protein or an altered leucine zipper (C/EBPalphaLZ) that prevents DNA binding. C/EBPalpha induces bcl-2 in cooperation with nuclear factor-kappaB (NF-kappaB) p50 to inhibit apoptosis. We now demonstrate that C/EBPalpha or a C/EBPalphaLZ oncoprotein binds the bcl-2 P2 promoter in chromatin immunoprecipitation assays and induces the promoter dependent on the integrity of a kappaB site. C/EBPalpha expressed as a transgene in B cells binds and activates the bcl-2 promoter, but not in nfkb1-/- mice lacking NF-kappaB p50. Bcl-2 is central to the intrinsic apoptotic pathway, whereas FLICE inhibitory protein (FLIP) modulates caspase-8, the initiator caspase of the extrinsic pathway. C/EBPalpha and C/EBPalphaLZ also bind the FLIP promoter and induce its expression dependent upon NF-kappaB p50. Moreover, induction of FLIP by C/EBPalpha protects splenocytes from Fas ligand-induced apoptosis, but only if p50 is present. We also demonstrate the direct interaction between bacterially produced C/EBPalpha and NF-kappaB p50, mediated by the C/EBPalpha basic region. These findings indicate that C/EBPalpha or its oncoproteins activate the bcl-2 and FLIP genes by tethering to their promoters through bound NF-kappaB p50. Targeting their interaction may favor apoptosis of transformed cells.

Biologic features of Hodgkin lymphoma and the development of biologic prognostic factors in Hodgkin lymphoma: tumor and microenvironment

Classical Hodgkin lymphoma is now recognised as a B-cell lymphoma. Improved therapy has increased cure rates dramatically; however, relapse and death still occurs in a minority of patients. Much has been learned about the biology of Hodgkin and Reed Sternberg cells and their interactions with the microenvironment, which has informed studies exploring biologic markers that may improve upon clinical prognostic models. This manuscript reviews recent advances in our understanding of the pathobiology of cHL with an emphasis on biologic prognostic markers.

Short hairpin RNA targeting c-FLIP sensitizes human cervical adenocarcinoma Hela cells to chemotherapy and radiotherapy

c-FLIP inhibits caspase-8 activation and cell apoptosis mediated by death receptors. The present study aims at determining the effects of c-FLIP targeted vector-based short hairpin RNA (shRNA) on cell growth and evaluating its modulation of responsiveness to drugs and radiotherapy in cervical adenocarcinoma Hela cells. cFLIP expression of the cells transfected with shRNA against c-FLIP was significantly down-regulated after 72 h. c-FLIP silencing markedly suppressed cell proliferation and increased cell apoptosis. The activation of caspase-8 and caspase-3 was induced with shRNA targeting cFLIP with the passage of time after transfection. Furthermore, Vector-based shRNA against c-FLIP subsequently increased the sensitivity to cisplatin, iritican and Co60 radiotherapy by about 4- to 6-folds in Hela cells. Our data suggest that vector-based shRNA effectively inhibited c-FLIP expression, enhanced the expression level of caspase-8 and caspase-3 to induce cell apoptosis, probably with the higher efficacy in combination therapies with conventional chemotherapy and radiotherapy in cervical adenocarcinoma.

Caspase-8 and its inhibitors in RCCs in vivo: the prominent role of ARC

Activation of the initiator-caspase, caspase-8 is under tight control of multiple antiapoptotic regulators including ARC, cFlip(S), cFlip(L) and PED/PEA-15. Since there is little data regarding the expression of caspase-8 and its antiapoptotic regulators in human tumours in vivo, we analysed their expression in renal cell carcinomas (RCCs) to identify which of these genes might be crucial for the well known impaired apoptosis and--as a result--resistance towards chemotherapy and ionizing radiation of RCCs. Caspase-8, cFlip(S), cFlip(L) and PED/PEA-15 mRNA expression was significantly increased only in early stages of RCCs compared to non-neoplastic renal tissue. In contrast, ARC mRNA expression was significantly increased in RCCs of all stages without differences between the tumour stages and grades. Importantly, the relative mRNA expression ratio between ARC and caspase-8 was significantly increased during carcinogenesis and tumour progression. In contrast, the relative mRNA expression ratio between cFlip(S), cFlip(L) or PED/PEA-15 and caspase-8 remained constant during all tumour stages. In conclusion, our analysis revealed that ARC is the only caspase-8 inhibiting regulator being constantly overexpressed in RCCs. Furthermore, the balance between antiapoptotic ARC and proapoptotic caspase-8 is the only one to be disturbed during carcinogenesis and tumour progression of RCCs. This inhibition of Caspase-8 might therefore be one example for the multiple antiapoptotic functions of ARC in RCCs possibly contributing to the marked resistance of RCCs towards radio- and chemotherapy and reflects a shift of gene expression towards a more antiapoptotic context in RCCs.

Curcumin induces cell-arrest and apoptosis in association with the inhibition of constitutively active NF-kappaB and STAT3 pathways in Hodgkin's lymphoma cells

Although treatment of Hodgkin's lymphoma (HL) with a multi-drug approach has been very successful, its toxicity becomes evident after several years as secondary malignancies and cardiovascular disease. Therefore, the current goal in HL treatment is to find new therapies that specifically target the deregulated signaling cascades, such as NF-kappaB and STAT3, which cause Hodgkin and Reed-Sternberg (H-RS) cell proliferation and resistance of apoptosis. Based on the above information, we investigated the capacity of curcumin to inhibit NF-kappaB and STAT3 in H-RS cells, characterizing the functional consequences. Curcumin is incorporated into H-RS cells and acts inhibiting both NF-kappaB and STAT3 activation, leading to a decreased expression of proteins involved in cell proliferation and apoptosis, e.g. Bcl-2, Bcl-xL, cFLIP, XIAP, c-IAP1, survivin, c-myc and cyclin D1. Interestingly, curcumin caused cell cycle arrest in G2-M and a significant reduction (80-97%) in H-RS cell viability. Furthermore, curcumin triggered cell death by apoptosis, as evidenced by the activation of caspase-3 and caspase-9, changes in nuclear morphology and phosphatidylserine translocation. The above findings provide a mechanistic rationale for the potential use of curcumin as a therapeutic agent for patients with HL.

FLIP as an anti-cancer therapeutic target

Suppression of apoptosis is one of the hallmarks of carcinogenesis. Tumor cells endure apoptotic pressure by overexpressing several antiapoptotic proteins, and FLICE inhibitory protein (FLIP) is one of the important antiapoptotic proteins that have been shown to be overexpressed in various primary tumor cells. FLIP has two death-effector domains in tandem, mimicking the prodomain of procaspase-8. It is recruited to Fadd in death-inducing signaling complex, thereby preventing the activation of procaspase-8. To date, three isoforms of human cytosolic FLIP (c-FLIP) and six viral homologs (v-FLIP) have been identified. Recently, the crystal structure of v-FLIP MC159 was determined for the first time as an atomic-detail FLIP structure, which revealed that two death effector domains are packed tightly against each other mainly through conserved hydrophobic interactions. The overexpression of c-FLIP in tumor cells has been shown to be the determinant of the tumor's resistance to death ligands such as FasL and TRAIL. It has also been shown that the down-regulation of c-FLIP results in sensitizing resistant tumor cells. Therefore, the agents directly targeting c-FLIP at mRNA and protein levels are expected to be developed in near future and tested for the potential as a new class of anti-cancer drugs.

Bortezomib induces caspase-dependent apoptosis in Hodgkin lymphoma cell lines and is associated with reduced c-FLIP expression: A gene expression profiling study with implications for potential combination therapies

The Hodgkin cells and Reed-Sternberg cells (HRS) of classical Hodgkin lymphoma (CHL) are derived from germinal center B cells. The pathogenesis of CHL is unclear but constitutive activation of NFkappaB may contribute. Proteasome inhibition aimed at inhibiting NFkappaB has been shown to result in apoptosis in HRS cells. Here we investigated the effects of bortezomib, a proteasome inhibitor, in HRS cells with a combination of functional assays and gene expression profiling (GEP). Exposure of KMH2 and L428 cells to bortezomib resulted in inhibition of proliferation and induction of apoptosis. Gene expression analysis of KMH2 cells by oligonucleotide cDNA microarrays showed that a limited set of genes were differentially expressed involving several key cellular pathways including cell cycle and apoptosis. Among them, the caspase 8 inhibitor cFLIP was down-regulated and confirmed by Q-PCR. Given the evidence that cFLIP in HRS cells contribute to cells' insensitive to death receptor-mediated apoptosis, we combined bortezomib and TRAIL. This combination caused further down-regulation of cFLIP protein and increased apoptosis in CHL cells demonstrated by PARP p85 immunohistochemistry and immunoblotting. Such apoptotic effects were inhibited by caspase inhibitor z-VAD-FMK, confirming the pro-apoptotic effects of bortezomib and TRAIL are caspase-dependent. Bortezomib has no detectable effect on expression of TRAIL receptor DR4/DR5 in these two cell lines. Tissue microarray analysis of primary Hodgkin lymphomas displayed that 82% cases (95/116) expressed cFLIP in Reed-Sternberg cells. The discovery of apoptotic pathways that can be manipulated by proteasome inhibition provides rationale for the combination of bortezomib and agents such as TRAIL in CHL treatment.

Contribution of the Epstein Barr virus to the molecular pathogenesis of Hodgkin lymphoma

Although the morphology of the pathognomonic Reed-Sternberg cells of Hodgkin lymphoma (HL) was described over a century ago, it was not until recently that their origin from B lymphocytes was recognised. The demonstration that a proportion of cases of HL harbour the Epstein-Barr virus (EBV) and that its genome is monoclonal in these tumours suggests that the virus contributes to the development of HL in some cases. This review summarises current knowledge of the pathogenesis of HL with particular emphasis on the association with EBV.

Critical role for Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein in anoikis resistance and distant tumor formation

BACKGROUND

Normal epithelial cells undergo anoikis, or apoptosis on loss of anchorage to the extracellular matrix, by initiating the death receptor pathway of caspase activation. However, malignant epithelial cells with metastatic potential resist anoikis and can survive in an anchorage-independent fashion. We hypothesized that c-Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein (FLIP), an endogenous inhibitor of death receptor signaling, may suppress anoikis.

METHODS

We assessed viability and apoptosis of PPC-1 prostate cancer cells cultured in adherent and suspension conditions using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt and Annexin V staining assays. Expression of the death receptor Fas and activation of caspase 8 were measured using flow cytometry. Expression of Fas ligand was measured by reverse transcription-polymerase chain reaction. FLIP protein expression was measured by immunoblotting. Small-molecule inhibitors of FLIP (including the death receptor sensitizer 5809354) and small-interfering (si) RNA directed against FLIP were used to assess the effects of FLIP inhibition on anoikis of prostate cancer cells in vitro and in vivo. All statistical tests were two-sided.

RESULTS

PPC-1 cells cultured in suspension resisted anoikis, despite increased expression of Fas (0 versus 8 hours, mean relative percent expression = 100% versus 135%, difference = 35%, 95% confidence interval [CI] = 10% to 61%; P = .02) and Fas L (0 versus 24 hours, mean relative percent expression = 100% versus 208%, difference = 108%, 95% CI = 18% to 197%; P = .02). Knockdown of FLIP expression by siRNA or treatment with 5809354 sensitized prostate cancer cells to anoikis (control siRNA versus FLIP siRNA at 10 nM, mean relative percent viability = 95% versus 51%, difference = 44%, 95% CI = 34% to 54%; P<.001; control versus 5809354 at 20 microM, mean relative percent viability = 96% versus 52%, difference = 44%, 95% CI = 13% to 75%; P = .015). Inhibition of FLIP expression specifically activated caspase 8 in PPC-1 cells grown in suspension but not adherent conditions and decreased the metastatic potential of circulating PPC-1 cells in vivo.

CONCLUSIONS

FLIP may be a suppressor of anoikis and therefore a possible target for antimetastatic therapeutic strategies.

c-FLIP expression in colorectal carcinomas: association with Fas/FasL expression and prognostic implications

AIMS

Disruption of apoptotic cell death has been implicated in tumour aggressiveness in colonic carcinogenesis. The Fas-Fas ligand (FasL) system is involved in the execution of apoptosis induced by the immune system. c-FLIP protein constitutes an inhibitor of Fas and other (TRAIL) death receptor-mediated apoptosis. The aim of this study was to investigate the simultaneous expression of Fas, FasL and c-FLIP in relation to standard clinicopathological parameters and patients' outcome in colorectal cancer.

METHODS AND RESULTS

Levels of Fas, FasL and c-FLIP protein expression were quantified immunohistochemically in paraffin-embedded tissues from 90 patients. Immunopositivity was detected for Fas, FasL and c-FLIP in 71%, 35.5% and 68.8% of cases, respectively. Concurrent expression of Fas/FasL was seen in 28 samples (31%), of which 24 (85.7%) also displayed c-FLIP positivity (P = 0.04). c-FLIP overexpression (> 10%) tended to prevail marginally in higher stage tumours (P = 0.09). Additionally, FasL and c-FLIP adversely affected survival on both univariate (P = 0.001 and P = 0.0024, respectively) and multivariate analysis [hazard ratio (HR) 3.491, P = 0.005 and HR 2.960, P = 0.036, respectively].

CONCLUSIONS

The frequent expression and coexpression of Fas, FasL and c-FLIP in colorectal carcinoma implicates c-FLIP as an inhibitor of the Fas-FasL-induced death pathway in these tumours. Moreover, c-FLIP conveys independent prognostic information in the presence of classical prognosticators.

The relationship between c-FLIP expression and human papillomavirus E2 gene disruption in cervical carcinogenesis

OBJECTIVE

Human papillomavirus (HPV) is the essential causative factor in cervical carcinogenesis, and apoptosis inhibition is one of the key features of HPV-induced malignant transformation. This study is to investigate the possible cause-effect association between high-risk HPV and cellular FLICE-like inhibitory protein (c-FLIP), an important apoptosis regulator, during cervical carcinogenesis.

METHODS

A series of 80 archival samples, including 20 squamous cervical carcinomas (SCC) 54 cervical intraepithelial neoplasia (CIN) lesions and 6 normal cervical tissues, were subjected for c-FLIP immunohistochemical staining and HPV HC-II analysis. Typing HPV-16 infection was analyzed by the polymerase chain reaction (PCR), and its status was assessed with the integrity and disruption of the HPV-16 E2 gene, which was amplified in three overlapping fragments.

RESULTS

The types of HR-HPV infection and E2 disruption were associated closely with cervical lesion severity. There was a significant relationship between lesion grade and c-FLIP expression level. c-FLIP overexpression was also closely associated with HR-HPV infection and its integration status. Multivariate regression analysis revealed c-FLIP as a strong independent predictor for CIN, with 100% PPV, and showed 90.9% PPV in detecting HR-HPV, and remained a significance factor to rule out which case has no HR-HPV integration, with a 94.7% sensitivity and a 90.0% NPV.

CONCLUSIONS

The present data approved that c-FLIP overexpression is related significantly to the presence of HR-HPV infection and its integration status during progression of cervical squamous cell cancer and confirmed the role of c-FLIP as an early marker of cervical carcinogenesis.

IkappaBalpha independent induction of NF-kappaB and its inhibition by DHMEQ in Hodgkin/Reed-Sternberg cells

Constitutive nuclear factor kappaB (NF-kappaB) activation characterizes Hodgkin/Reed-Sternberg (H-RS) cells. Blocking constitutive NF-kappaB has been shown to be a potential strategy to treat Hodgkin lymphoma (HL). Here, for the first time we show that although constitutive NF-kappaB level of H-RS cell lines is very high, topoisomerase inhibitors further enhance NF-kappaB activation through IkappaB kinase activation in not only H-RS cell lines with wild-type IkappaBalpha, but also in those with IkappaBalpha mutations and lacking wild-type IkappaBalpha. Thus, both constitutive and inducible NF-kappaB are potential targets to treat HL. We also present the data that indicate the involvement of IkappaBbeta in NF-kappaB induction by topoisomerase inhibitors. A new NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ) inhibited constitutive NF-kappaB activity and induced apoptosis of H-RS cell lines. DHMEQ also inhibited the growth of H-RS cells without significant systemic toxicity in a NOD/SCID/gammac(null) (NOG) mice model. DHMEQ and topoisomerase inhibitors revealed enhancement of apoptosis of H-RS cells by blocking inducible NF-kappaB. Results of this study suggest that both constitutive and inducible NF-kappaB are molecular targets of DHMEQ in the treatment of HL. The results also indicate that IkappaBbeta is involved in NF-kappaB activation in H-RS cells and IkappaBbeta substitutes for IkappaBalpha in H-RS cells lacking wild-type IkappaBalpha.

NF-κB–independent down-regulation of XIAP by bortezomib sensitizes HL B cells against cytotoxic drugs

The proteasome inhibitor bortezomib has been shown to possess promising antitumor activity and significant efficacy against a variety of malignancies. Different studies demonstrated that bortezomib breaks the chemoresistance in different tumor cells basically by altering nuclear factor–κB (NF-κB) activity. NF-κB has been shown to be constitutively active in most primary Hodgkin-Reed-Sternberg (H-RS) cells in lymph node sections and in Hodgkin lymphoma (HL) cell lines and was suggested to be a central molecular switch in apoptosis resistance in HL. Here we report a bimodal effect of bortezomib in HL cells. Whereas high-dose bortezomib induced direct cytotoxicity that correlated with decreased NF-κB activity, low-dose bortezomib sensitized HL cells against a variety of cytotoxic drugs without altering NF-κB action. Strikingly, bortezomib induced marked XIAP down-regulation at the posttranslational level that was independent of the NF-κB status. Similarly, RNA interference (RNAi)–mediated XIAP down-regulation generated susceptibility to cytostatic agents. The results identify XIAP as an NF-κB–independent target of bortezomib action that controls the chemoresistant phenotype of HL cells.

Troglitazone sensitizes tumor cells to TRAIL-induced apoptosis via down-regulation of FLIP and Survivin

Induction of apoptosis by the death ligand TRAIL might be a promising therapeutic approach in cancer therapy. However, since not all tumor cells are sensitive to TRAIL, there is a need for the development of strategies to overcome TRAIL-resistance. The results of the present study show that the anti-diabetic drug troglitazone sensitizes human glioma and neuroblastoma cells to TRAIL-induced apoptosis. This process is accompanied by a substantial increase of active caspase 8 and active caspase 3, but it is independent of troglitazone's effects on the nuclear receptor PPAR-gamma. Troglitazone induces a pronounced reduction in protein expression levels of the anti-apoptotic FLICE-inhibitory protein (FLIP) without affecting FLIP mRNA levels. Further, protein and mRNA expression levels of the anti-apoptotic protein Survivin significantly decrease upon treatment with troglitazone. Moreover, sensitization to TRAIL is partly accompanied by an up-regulation of the TRAIL receptor, TRAIL-R2. A combined treatment with troglitazone and TRAIL might be a promising experimental therapy because troglitazone sensitizes tumor cells to TRAIL-induced apoptosis via various mechanisms, thereby minimizing the risk of acquired tumor cell resistance.

XIAP targeting sensitizes Hodgkin lymphoma cells for cytolytic T-cell attack

The immunosurveillance of Hodgkin lymphoma (HL) by cytotoxic T lymphocytes (CTLs) is insufficient, and the clinical experience with adoptive transfer of CTLs is limited. We have previously reported that defects in mitochondrial apoptotic pathways and elevated XIAP expression confer resistance to different apoptotic stimuli in HL cells. Here, we aimed to develop molecular strategies to overcome the resistance of HL cells against CTL-mediated killing via granzyme B (grzB). In HL cells, grzB-induced mitochondrial release of proapoptotic Smac is blocked, which results in complete abrogation of cytotoxicity mediated by CTLs. Cytosolic expression of recombinant mature Smac enhanced caspase activity induced by grzB and restored the apoptotic response of HL cells. Similarly, down-regulation of XIAP by RNA interference markedly enhanced the susceptibility of HL cells for CTL-mediated cytotoxicity. XIAP gene knockdown sensitized HL cells for killing by antigen-specific CTLs redirected by grafting with a chimeric anti-CD30scFv-CD3zeta immunoreceptor. The results suggest that XIAP targeting by Smac agonists or XIAP-siRNA can be used as a synergistic strategy for cellular immunotherapy of Hodgkin lymphoma.

Pathobiology of Classical Hodgkin Lymphoma

The World Health Organization has acknowledged the malignant nature of classical Hodgkin lymphoma (cHL), which encompasses four histological subtypes. The diagnosis of cHL is based on the detection of malignant Hodgkin and Reed-Sternberg cells (HRSC) confirmed by immunophenotyping and the detection of growth patterns specific to each histological subtype. The pathologic HRSC arise from germinal center or immediate postgerminal cells that lack detectable immunoglobulin/B-cell antigen receptor expression, with a consequent loss of B-cell identity; very few cHL cases are of T-cell origin. To escape apoptosis, which normally occurs in B cells with nonfunctioning antigen receptor machinery, HRSC develop concurrent antiapoptotic mechanisms by activation of nuclear factor-kappaB or are rescued by Epstein-Barr virus infection. HRSC are characterized by a variable and inconstant immunophenotype, with a remarkable loss of lineage-specific cell antigens and expression of antigens of other cell lineages. The master plan of B-cell identity in HRSC is disturbed not only at the immunoglobulin expression level, but also at the transcriptional factor level. HRSC are further characterized by profound cell cycle deregulation with futile replication, multinucleation and poly- and aneuploidy. Here, we review pathobiological aspects of cHL with respect to lymphomagenesis and routine diagnostics.

Targeting cellular FLICE-like inhibitory protein as a novel approach to the treatment of Hodgkin's lymphoma

Hodgkin's lymphoma is one of the most common lymphoid cancers, particularly among young adults. Although there have been dramatic improvements in the treatment of Hodgkin's lymphoma, leading to high cure rates in some groups, current combination chemotherapy regimes are associated with significant secondary complications in long-term survivors. Furthermore, although a proportion of patients with Hodgkin's lymphoma will be cured, there still remains a significant rate of relapse and also a smaller proportion of poor responders who will go on to die of their disease. Therefore, developments in the treatment of Hodgkin's lymphoma must be directed at improving cure rates and reducing the burden of secondary complications. In recent years, the underlying pathogenesis of Hodgkin's lymphoma has become better understood. In particular, it is emerging that a key pathogenic event in Hodgkin's lymphoma is protection from Fas-induced cell death. Recent studies by the authors' group, and others, have demonstrated that this is, in part, due to the expression by Hodgkin/Reed-Sternberg cells of the cellular Fas-associated death domain-like IL-1 converting enzyme (FLICE)-like inhibitory protein molecule, a potent inhibitor of Fas-induced death. In this review, the role of cellular FLICE-like inhibitory protein in the pathogenesis of Hodgkin's lymphoma will be explored and also the possibility of targeting this molecule in order to provide an alternative and potentially safe approach to the treatment of Hodgkin's lymphoma will be investigated.

Epstein-Barr virus, cytokines, and inflammation: a cocktail for the pathogenesis of Hodgkin's lymphoma?

The association between chronic inflammation and cancer has been known for well over a century. However, direct evidence detailing the role of inflammation in carcinogenesis has been slow in forthcoming. A number of recent studies suggest that the gaps in our understanding of the molecular pathways bridging the link between inflammation and cancer are slowly beginning to close and that this relationship is more deep-rooted than had been previously believed. This review addresses the link between inflammation and Hodgkin's lymphoma (HL), a malignancy which has many features reminiscent of chronic inflammation. The role of Epstein-Barr virus (EBV) in the pathogenesis of HL is discussed, along with an outline of our current understanding of the cellular nature and development of Reed-Sternberg cells, the malignant cells of HL. The involvement of cytokines and chemokines as orchestrators of inflammation and vehicles for chemical cross-talk between the malignant cells and the reactive inflammatory infiltrate forms a major part of the review. It is suggested that chronic inflammation, triggered by factors such as EBV, is likely to contribute to tumor cell proliferation, progression, and inhibition of apoptosis. Furthermore, it is proposed that the pro-inflammatory transcription factor NF-kappaB plays a central role in many of these processes.

cFLIP expression correlates with tumour progression and patient outcome in non-Hodgkin lymphomas of low grade of malignancy

The present study investigated whether the expression of cellular Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (cFLIP) conveys prognostic information in non-Hodgkin lymphomas (NHLs). cFLIP expression was quantified by immunohistochemistry and immunofluorescence in biopsy specimens from 86 NHL patients for whom clinical information was available. NHL malignancy was graded as high/intermediate or low according to the World Health Organization Classification of Lymphoid Neoplasms. cFLIP was positive in 23 of 45 high-/intermediate-grade NHLs and in 25 of 41 low-grade NHLs. Negative expression of cFLIP was associated with the presence of apoptotic cells in the tumour mass, regardless of the histotype and of the malignancy grade. In NHLs positive for cFLIP, 11 of 23 (48%) high-/intermediate-grade cases and 18 of 25 (72%) low-grade cases showed a bad outcome. In NHLs negative for cFLIP, only four of 22 (18%) high-/intermediate-grade patients and 12 of 16 (75%) low-grade patients achieved complete remission. All these correlations were statistically significant. The correlation of cFLIP expression with clinical outcome was independent of therapy, whether or not it included anti-CD20 antibody (Rituximab). The present findings strongly indicate that cFLIP is a reliable predictor of tumour progression and clinical prognosis in NHLs of low grade of malignancy.

The role of cellular flice inhibitory protein (c-FLIP) in the pathogenesis and treatment of cancer

Protection from death receptor (DR)-mediated apoptosis has been proposed as an important step in the development of malignancy, enabling tumour cells not only to survive and escape antitumour immune responses, but also to develop resistance to chemotherapy or other cancer treatments. An important regulator of DR-induced death is the cellular FADD-like IL-1beta-converting enzyme inhibitory protein (c-FLIP) which, when overexpressed, can protect tumour cells from apoptosis. This review focuses on the role of c-FLIP as a tumour progression factor, with particular emphasis on recent work from the authors' laboratory concerning the contribution of c-FLIP to the pathogenesis of Hodgkin's lymphoma. The possibility of targeting c-FLIP as an approach to the treatment of cancer and, in particular, Hodgkin's lymphoma is discussed.

cIAP2 is highly expressed in Hodgkin–Reed–Sternberg cells and inhibits apoptosis by interfering with constitutively active caspase-3

In this study, the expression of activated caspase-3 by the tumor cells of classical Hodgkin lymphoma (cHL), the Hodgkin-Reed-Sternberg (HRS) cells, is confirmed. This raises the question why caspase-3 does not kill HRS cells. There are only a few molecules, which are able to directly inhibit caspase-3. One of them is cIAP2. We show that cIAP2 is expressed in the HRS cells in 20 of 23 cHL cases by in situ hybridization. Suppression experiments with cIAP2 antisense RNA show that down-regulation of cIAP2 significantly reduces apoptosis resistance in cHL cell lines. cIAP2 overexpression appears to be unique for HRS cells since the tumor cells of non-Hodgkin lymphomas are nearly cIAP2-negative. We demonstrate that cIAP2 is inducible by CD30 stimulation in cHL cell lines of T-cell origin and anaplastic large cell lymphoma cell lines, whereas cHL cell lines of B-cell origin constitutively express cIAP2. Inhibition of cIAP2 expression by cIAP2 antisense RNA decreases resistance to apoptosis. The results indicate that cIAP2 contributes to the apoptosis resistance of HRS cells, mainly by inhibiting effector caspases. According to these findings, a therapeutical application of inhibitors of apoptosis proteins antagonists in cHL appears promising.

Inhibition of Nuclear Translocation of Nuclear Factor-κB Despite Lack of Functional IκBα Protein Overcomes Multiple Defects in Apoptosis Signaling in Human B-Cell Malignancies

PURPOSE

Defective apoptosis signaling is a typical feature of classic Hodgkin's lymphoma, multiple myeloma, and activated B-cell-like diffuse large B-cell lymphoma. In these malignancies, the transcription factor nuclear factor-kappaB (NF-kappaB) is a critical mediator of apoptosis resistance and oncogenic growth, making it an attractive therapeutic target. Here, we sought to determine how to overcome apoptosis resistance experimentally in these malignancies by targeting NF-kappaB.

EXPERIMENTAL DESIGN

We investigated the effect of different inhibitors of NF-kappaB on classic Hodgkin's lymphoma, multiple myeloma, and activated B-cell-like diffuse large B-cell lymphoma cell lines harboring different molecular defects in apoptosis signaling both quantitatively and qualitatively.

RESULTS

The cyclopentenone prostaglandin, 15-deoxy-Delta12,14-prostaglandin J(2), a known inhibitor of NF-kappaB, induced caspase-dependent apoptosis; it restored mitochondrial apoptotic signaling by down-regulation of X-linked inhibitor of apoptosis protein and heat shock protein 27 and led to breakdown of the mitochondrial membrane potential and, finally, cleavage of caspase-3 irrespective of IkappaBalpha mutational status. Surprisingly, 15-deoxy-Delta12,14-prostaglandin J(2) and the IkappaB kinase inhibitor curcumin both reduced nuclear levels of p65 in cell lines lacking IkappaBalpha, suggesting that inhibition of nuclear translocation of NF-kappaB can occur in the absence of IkappaBalpha. Finally, a synthetic peptide that specifically abrogates the assembly of the IkappaB kinase complex killed IkappaBalpha-defective cells by induction of apoptosis, paralleled by reduction of nuclear NF-kappaB.

CONCLUSIONS

These results show that molecular defects in apoptotic signaling, such as IkappaBalpha mutations, can be circumvented by targeting NF-kappaB through inhibition of the IkappaB kinase complex followed by induction of apoptosis in classic Hodgkin's lymphoma, multiple myeloma, and activated B-cell-like diffuse large B-cell lymphoma. Thus, targeting IkappaB kinases may represent an attractive therapeutic approach against these malignancies regardless of the mutational status of IkappaBalpha.

Molecular pathogenesis of Hodgkin's lymphoma

According to the WHO classification, Hodgkin's lymphoma (HL) is subdivided into a classical variant and a nodular lymphocyte predominant variant which are characterized by the presence of Hodgkin's and Reed-Sternberg (H-RS) cells or lymphocytic and histiocytic (L&H) cells, respectively. This article reviews genetic characteristics and transcriptional changes of H-RS and L&H cells, including recent knowledge about transforming mechanisms and signaling pathways that contribute to the antiapoptotic phenotype displayed by H-RS and L&H cells. We also discuss major cellular and molecular mediators contributing to the establishment and maintenance of a reactive background in HL-affected tissues. We believe that an in-depth understanding of the pathogenesis of HL will eventually lead to the development of novel biologically based therapeutic strategies in the near future.

Expression of cellular FLICE/caspase-8 inhibitory protein is associated with malignant potential in endometrial carcinoma

This study aimed to investigate the expression of cellular Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE)/caspase-8 inhibitory protein (c-FLIP) in endometrial carcinoma and its possible implications. c-FLIP protein was detected in 42 endometrial carcinoma tissues and in 22 normal proliferative endometrial tissues by immunohistochemistry. In addition, c-FLIP messenger ribonucleic acid (mRNA) was evaluated in 20 endometrial carcinomas and in 18 normal proliferative endometria by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) using SYBR Green I(TM). The relationship between c-FLIP protein level and tumor cell proliferation and that between c-FLIP protein level and clinicopathologic parameters of patients with endometrial carcinoma was analyzed. c-FLIP protein expression was significantly higher in neoplastic tissues than in normal tissues (P < 0.01), and similar result was obtained from RT-PCR analysis of c-FLIP mRNA (P < 0.01). Furthermore, c-FLIP protein was significantly associated with proliferating cell nuclear antigen-labeling index (P < 0.01), clinical stage (P < 0.05), the presence of invasion to > 1/2 myometrium (P < 0.05), and lymph node metastasis (P < 0.01). Multivariate analysis of variance also confirmed the association of c-FLIP with clinical stage (P < 0.05) and with lymph node metastasis (P < 0.05), while its association with myometrial invasion was marginal (P = 0.059). It is concluded that c-FLIP might contribute to the carcinogenesis and aggressiveness of endometrial carcinoma and might be a useful prognostic factor in the tumor.

The fully human anti-CD30 antibody 5F11 activates NF-κB and sensitizes lymphoma cells to bortezomib-induced apoptosis

5F11, a fully human monoclonal antibody directed against CD30, effectively induces killing of CD30-expressing lymphoma cell lines in vitro and in animal models. A recently conducted phase 1/2 study shows that 5F11 is well tolerated in heavily pretreated patients with relapsed and refractory CD30+ lymphoma and has some clinical activity. In the present study, we demonstrate that 5F11 activates nuclear factor κB (NF-κB) and the anti-apoptotic protein cellular FLICE (Fas-associating protein with death domain-like interleukin-1β-converting enzyme) inhibitory protein (c-flip) in Hodgkin lymphoma (HD)-derived cell lines, which might cause apoptosis resistance, thus limiting the clinical use of 5F11. To overcome this resistance, we combined 5F11 with the proteasome inhibitor bortezomib, which has been shown to suppress NF-κB activity. This combination revealed a synergistic cytotoxic effect in vitro and in a human HD xenograft model provided that 5F11 precedes bortezomib treatment. We conclude that initial 5F11-mediated NF-κB signaling sensitizes the tumor cells to bortezomib-induced cell death. These data suggest a therapeutic value of this combination for HD patients. (Blood. 2005;106:1839-1842)

FLIP is frequently expressed in endometrial carcinoma and has a role in resistance to TRAIL-induced apoptosis

The FLICE-inhibitory protein (FLIP) plays a key role in the regulation of apoptosis triggered by death ligands. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce apoptosis in some types of tumor but not in others. To assess the possible role of FLIP in apoptosis resistance in endometrial carcinoma, we performed an immunohistochemical study on a tissue microarray composed of 95 endometrial carcinomas. We found positive signals in 43% of the cases, as well as a significant difference in FLIP expression between stage I and II tumors. Moreover, we observed that endometrial carcinoma cell lines Ishikawa and KLE did not undergo apoptosis after TRAIL treatment. Cotreatment of these cells with the inhibitor of transcription actinomycin D resulted in a dramatic decrease in cell viability and induced activation of caspase-8. These events coincided with downregulation of FLIP mRNA and protein. Inhibitors of caspase-8 or overexpression of FLIP completely blocked apoptosis induced by actinomycin D plus TRAIL cotreatment. More importantly, downregulation of endogenous FLIP expression by specific siRNAs sensitized endometrial carcinoma cells to TRAIL-induced apoptosis in the absence of actinomycin D. Taken together, our results suggest for the first time a critical role for FLIP in the regulation apoptosis triggered by TRAIL in endometrial carcinoma cells.

Resistance to Fas-mediated apoptosis is restored by cycloheximide through the downregulation of cellular FLIPL in NK/T-cell lymphoma

Extranodal NK/T-cell lymphoma (NKTL), nasal type, is a highly aggressive neoplasm and is strongly associated with Epstein-Barr virus (EBV). In this study, we demonstrate that EBV-positive NKTL cell lines, namely, Hank-1, NK-YS, and NK-L, are resistant to Fas-mediated apoptosis induced by anti-Fas antibodies despite high levels of Fas surface expression and no mutation in the Fas gene. Fas stimulation of Hank-1 and NK-YS cells showed little processing of caspase 8, caspase 3, or bid, although the proximal signaling molecules of the death-inducing signaling complex, namely, Fas, Fas-associated protein with a death domain, caspase 8, and bid were present in these cells. Consistent with previous reports on the hypermethylation of death associated protein (DAP) kinase in NKTLs, the promoter of DAP kinase was methylated and its mRNA not detected in Hank-1 cells. However, the restoration of DAP kinase expression by 5-aza-2'-deoxycytidine did not sensitize Hank-1 to Fas-mediated apoptosis, indicating that DAP kinase deficiency does not contribute to resistance to Fas-mediated apoptosis. Since etoposide-induced apoptosis involved caspase 3 activation in Hank-1 and NK-YS cells, the caspase 3-dependent apoptotic machinery appears to be intact. Interestingly, cotreatment of Hank-1 with cycloheximide, a protein synthesis inhibitor, markedly sensitized cells to Fas-mediated apoptosis along with caspase 8 activation and c-FLIP(L) (cellular FLICE inhibitory protein long form) downregulation. Moreover, immunohistochemistry on paraffin-embedded tissue revealed c-FLIP expression in 39% (14 of 36) of NKTL patients. Taken together, these findings indicate that c-FLIP(L)-mediated resistance to Fas contributes to the development and progression of NKTLs. This study also suggests that agents capable of downregulating c-FLIP(L) could be used to treat NKTL.

STAT3 is essential for Hodgkin lymphoma cell proliferation and is a target of tyrphostin AG17 which confers sensitization for apoptosis

Classical Hodgkin lymphoma (cHL) is a distinct malignancy of the immune system. Despite the progress made in the understanding of the biology of cHL, the transforming events remain to be elucidated. Recently, we demonstrated that the Janus kinase inhibitor AG490 blocked cellular proliferation and STAT3 phosphorylation in cHL. To explore the potential of constitutively activated STAT3 as a drug target and its role in cHL pathogenesis, different cHL cell lines were analyzed. Treatment of cHL cells by the protein tyrosine kinase inhibitor AG17 was associated with inhibition of cellular proliferation and cell cycle arrest. AG17 treatment was accompanied by decreased levels of STAT3 phosphorylation, whereas NF-kappaB and p38/SAPK2 signaling were not inhibited. Incubation with AG17 or AG490 sensitized cHL cells to CD95/Fas/Apo-1 or staurosporine-mediated apoptosis. Coincubation of tyrphostins with staurosporine was accompanied by rapid complete inhibition of STAT3 phosphorylation. RNA interference directed against STAT3 in L428 and L1236 cHL cells demonstrated that STAT3 is essential for cell proliferation of these cHL cells. In conclusion, these findings support the concept that STAT3 signaling is important in the pathogenesis of cHL and tyrphostins are agents for developing new therapeutic strategies.

From Hodgkin disease to Hodgkin lymphoma: biologic insights and therapeutic potential

Reclassification of Hodgkin disease as Hodgkin lymphoma (HL) represents a milestone in the lymphoma field, awarding recent insights in the molecular biology of Hodgkin and Reed-Sternberg (H-RS) cells and their environment. This review summarizes antiapoptotic and proproliferative pathways involved in the pathogenesis of this disease with the ultimate goal of translating laboratory knowledge into clinical decision making. The focus is on potential targets and novel drugs, which are discussed in the context of the complex biology of HL. Considering that HL patients are more likely to die from acute and late treatment-related toxicities than from HL itself, the introduction of targeted, biologically based therapies for HL patients with palliative and eventually curative intention might be justified. (Blood. 2005;105:4553-4560)

Rapid turnover of c-FLIPshort is determined by its unique C-terminal tail

The caspase-8 inhibitor c-FLIP exists as two splice variants, c-FLIP(L) and c-FLIP(S), with distinct roles in death receptor signaling. The mechanisms determining their turnover have not been established. We found that in differentiating K562 erythroleukemia cells both c-FLIP isoforms were inducibly degraded by the proteasome, but c-FLIP(S) was more prone to ubiquitylation and had a considerably shorter half-life. Analysis of the c-FLIP(S)-specific ubiquitylation revealed two lysines, 192 and 195, C-terminal to the death effector domains, as principal ubiquitin acceptors in c-FLIP(S) but not in c-FLIP(L). Furthermore the c-FLIP(S)-specific tail of 19 amino acids, adjacent to the two target lysines, was demonstrated to be the key element determining the isoform-specific instability of c-FLIP(S). Molecular modeling in combination with site-directed mutagenesis demonstrated that the C-terminal tail is required for correct positioning and subsequent ubiquitylation of the target lysines. Because the antiapoptotic operation of c-FLIP(S) was not affected by the tail deletion, the antiapoptotic activity and ubiquitin-mediated degradation of c-FLIP(S) are functionally and structurally independent processes. The presence of a small destabilizing sequence in c-FLIP(S) constitutes an important determinant of c-FLIP(S)/c-FLIP(L) ratios by allowing differential degradation of c-FLIP isoforms. The conformation-based predisposition of c-FLIP(S) to ubiquitin-mediated degradation introduces a novel concept to the regulation of the death-inducing signaling complex.

Expression of cellular FLICE-inhibitory protein and its association with p53 mutation in colon cancer

AIM: To investigate the expression of cellular FLICE (Fas associated death domain-like IL-1beta-converting enzyme)-inhibitory protein (c-FLIP) and its association with p53 mutation in colon cancer.

METHODS: Immunohistochemical staining of c-FLIP and mutant p53 by using specific antibodies was performed by the standard streptavidin-peroxidase technique for 45 colon cancer tissue samples with matched normal tissues. Semi-quantitative reverse transcriptional (RT)-PCR was used to measure c-FLIP mRNA levels. t-test statistical method was used in data analyses.

RESULTS: c-FLIP mRNA was expressed in all colon cancer tissues and its level (0.63±0.12) was significantly higher than that in normal tissues (0.38±0.10, P<0.01). Immuno-histochemically, c-FLIP protein was also expressed in all colon cancers (45/45) and 71.1% (32/45) showed an intense immunostaining, in contrast, 93.3% (42/45) of normal colonic mucosa showed positive staining and none of them immunostained intensely. The quantity of c-FLIP protein was significantly higher in cancer tissues than in normal mucosa (7.04±1.20 vs 5.21±0.86, P<0.01). Positive staining of mutant p53 protein was found in 60% (27/45) colon cancers. c-FLIP mRNA level was decreased in p53 positive group compared with p53 negative cancer tissues (0.59±0.13 vs 0.69±0.14, P<0.01), but c-FLIP protein had a significantly higher level in p53 positive cancer tissues than in negative ones (7.57±1.30 vs 6.25±1.27, P<0.01).

CONCLUSION: c-FLIP is specially overexpressed in colon cancers and it might contribute to carcinogenesis of normal colonic mucosa. p53 may exert transcriptional upregulation effects on c-FLIP gene and more potent effects on promoting the degradation of c-FLIP protein.