Local Fas/APO-1 (CD95) ligand-mediated tumor cell killing in vivo

Mechano-inhibition of endocytosis sensitizes cancer cells to Fas-induced Apoptosis

The transmembrane death receptor Fas transduces apoptotic signals upon binding its ligand, FasL. Although Fas is highly expressed in cancer cells, insufficient cell surface Fas expression desensitizes cancer cells to Fas-induced apoptosis. Here, we show that the increase in Fas microaggregate formation on the plasma membrane in response to the inhibition of endocytosis sensitizes cancer cells to Fas-induced apoptosis. We used a clinically accessible Rho-kinase inhibitor, fasudil, that reduces endocytosis dynamics by increasing plasma membrane tension. In combination with exogenous soluble FasL (sFasL), fasudil promoted cancer cell apoptosis, but this collaborative effect was substantially weaker in nonmalignant cells. The combination of sFasL and fasudil prevented glioblastoma cell growth in embryonic stem cell-derived brain organoids and induced tumor regression in a xenograft mouse model. Our results demonstrate that sFasL has strong potential for apoptosis-directed cancer therapy when Fas microaggregate formation is augmented by mechano-inhibition of endocytosis.

TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

Destabilizing the genome as a therapeutic strategy to enhance response to immune checkpoint blockade: a systematic review of clinical trials evidence from solid and hematological tumors

Background: Genomic instability is increased alterations in the genome during cell division and is common among most cancer cells. Genome instability enhances the risk of initial carcinogenic transformation, generating new clones of tumor cells, and increases tumor heterogeneity. Although genome instability contributes to malignancy, it is also an "Achilles' heel" that constitutes a therapeutically-exploitable weakness-when sufficiently advanced, it can intrinsically reduce tumor cell survival by creating DNA damage and mutation events that overwhelm the capacity of cancer cells to repair those lesions. Furthermore, it can contribute to extrinsic survival-reducing events by generating mutations that encode new immunogenic antigens capable of being recognized by the immune system, particularly when anti-tumor immunity is boosted by immunotherapy drugs. Here, we describe how genome-destabilization can induce immune activation in cancer patients and systematically review the induction of genome instability exploited clinically, in combination with immune checkpoint blockade. Methods: We performed a systematic review of clinical trials that exploited the combination approach to successfully treat cancers patients. We systematically searched PubMed, Cochrane Central Register of Controlled Trials, Clinicaltrials.gov, and publication from the reference list of related articles. The most relevant inclusion criteria were peer-reviewed clinical trials published in English. Results: We identified 1,490 studies, among those 164 were clinical trials. A total of 37 clinical trials satisfied the inclusion criteria and were included in the study. The main outcome measurements were overall survival and progression-free survival. The majority of the clinical trials (30 out of 37) showed a significant improvement in patient outcome. Conclusion: The majority of the included clinical trials reported the efficacy of the concept of targeting DNA repair pathway, in combination with immune checkpoint inhibitors, to create a "ring of synergy" to treat cancer with rational combinations.

CRISPR/Cas9-mediated abrogation of CD95L/CD95 signaling-induced glioma cell growth and immunosuppression increases survival in murine glioma models

PURPOSE

Glioblastoma is the most common brain tumor in adults and is virtually incurable. Therefore, new therapeutic strategies are urgently needed. Over the last decade, multiple growth-promoting functions have been attributed to CD95, a prototypic death receptor well characterized as an apoptosis mediator upon CD95L engagement. Strategic targeting of non-apoptotic or apoptotic CD95 signaling may hold anti-glioblastoma potential. Due to its antithetic nature, understanding the constitutive role of CD95 signaling in glioblastoma is indispensable.

METHODS

We abrogated constitutive Cd95 and Cd95l gene expression by CRISPR/Cas9 in murine glioma models and characterized the consequences of gene deletion in vitro and in vivo.

RESULTS

Expression of canonical CD95 but not CD95L was identified in mouse glioma cells in vitro. Instead, a soluble isoform-encoding non-canonical Cd95l transcript variant was detected. In vivo, an upregulation of the membrane-bound canonical CD95L form was revealed. Cd95 or Cd95l gene deletion decreased cell growth in vitro. The growth-supporting role of constitutive CD95 signaling was validated by Cd95 re-transfection, which rescued growth. In vivo, Cd95 or Cd95l gene deletion prolonged survival involving tumor-intrinsic and immunological mechanisms in the SMA-497 model. In the GL-261 model, that expresses no CD95, only CD95L gene deletion prolonged survival, involving a tumor-intrinsic mechanism.

CONCLUSION

Non-canonical CD95L/CD95 interactions are growth-promoting in murine glioma models, and glioma growth and immunosuppression may be simultaneously counteracted by Cd95l gene silencing.

Comparative Immunology and Immunotherapy of Canine Osteosarcoma

Approximately 800 people are diagnosed with osteosarcoma (OSA) per year in the USA. Although 70% of patients with localized OSA are cured with multiagent chemotherapy and surgical resection, the prognosis for patients with metastatic or relapsed disease is guarded. The small number of patients diagnosed annually contributes to an incomplete understanding of disease pathogenesis, and challenges in performing appropriately powered clinical trials and detecting correlative biomarkers of response. While mouse models of OSA are becoming increasingly sophisticated, they generally fail to accurately recapitulate tumor heterogeneity, tumor microenvironment (TME), systemic immune dysfunction, and the clinical features of tumor recurrence, metastases, and chemoresistance, which influence outcome. Pet dogs spontaneously develop OSA with an incidence that is 30-50 times higher than humans. Canine OSA parallels the human disease in its clinical presentation, biological behavior, genetic complexity, and therapeutic management. However, despite therapy, most dogs die from metastatic disease within 1 year of diagnosis. Since OSA occurs in immune-competent dogs, immune factors that sculpt tumor immunogenicity and influence responses to immune modulation are in effect. In both species, immune modulation has shown beneficial effects on patient outcome and work is now underway to identify the most effective immunotherapies, combination of immunotherapies, and correlative biomarkers that will further improve clinical response. In this chapter, the immune landscape of canine OSA and the immunotherapeutic strategies used to modulate antitumor immunity in dogs with the disease will be reviewed. From this immunological viewpoint, the value of employing dogs with spontaneous OSA to accelerate and inform the translation of immunotherapies into the human clinic will be underscored.

Toxicology and Pharmacokinetic Studies in Mice and Nonhuman Primates of the Nontoxic, Efficient, Targeted Hexameric FasL: CTLA4-FasL

Cytotoxic T-lymphocyte antigen 4 (CTLA4)-FasL, a homo-hexameric signal converter protein, is capable of inducing robust apoptosis in malignant cells of the B-cell lineage expressing its cognate B7 and Fas targets, while sparing nonmalignant ones. This fusion protein's striking proapoptotic efficacy stems from its complementary abilities to coordinately activate apoptotic signals and abrogate antiapoptotic ones. A limiting factor in translating FasL or Fas receptor agonists into the clinic has been lethal hepatotoxicity. Here, we establish CTLA4-FasL's in vivo efficacy in multiple murine and xenograft models, for both systemic and subcutaneous tumors. Significantly, good laboratory practice (GLP) toxicology studies in mice indicate that CTLA4-FasL given repeatedly at doses up to five times the effective dose was well-tolerated and resulted in no significant adverse events. An equivalent single dose of CTLA4-FasL administered to nonhuman primates was also well-tolerated, albeit with a moderate dose-dependent leukopenia that was completely reversible. Interestingly, monkey peripheral blood mononuclear cells were more sensitive to CTLA4-FasL-induced apoptosis when tested in vitro. In both species, there was short-term elevation in serum levels of IL6, IL2, and IFNγ, although this was not associated with clinical signs of proinflammatory cytokine release, and further, this cytokine elevation could be completely prevented by dexamethasone premedication. Liver toxicity was not observed in either species, as confirmed by serum liver enzyme levels and histopathologic assessment. In conclusion, CTLA4-FasL emerges from animal model studies as an effective and safe agent for targeted FasL-mediated treatment of B7-expressing aggressive B-cell lymphomas.

Fas/FasL signaling is critical for the survival of exhausted antigen-specific CD8+ T cells during tumor immune response

Antigen (Ag)-specific activated CD8⁺ T cells are critical for tumor elimination but become exhausted, and thus, dysfunctional during immune response against the tumor due to chronic antigen stimulation. The signaling of immune checkpoint receptors is known to be a critical component in this exhaustion; however, the fate of these exhausted CD8⁺ T cells remains unclear. Therefore, to elucidate this, we followed the fate of Ag-specific CD8⁺ T cells by directly visualizing them using MHC class I tetramers coupled with ovoalubumin_257-264 in C57BL/6 mice inoculated with EG.7. We found that the number of generated Ag-specific activated CD8⁺ T cells decreased via apoptosis during a prolonged tumor immune response. However, the number of Ag-specific CD8⁺ T cells was significantly higher in Fas ligand (FasL)-dysfunctional gld mice than in control mice, resulting in suppressed tumor growth. In contrast, the enforced expression of Bcl-2 failed to rescue apoptosis of the exhausted CD8⁺ T cells following EG.7 inoculation. These results suggest that Fas/FasL signaling is critical for the survival of exhausted CD8⁺ T cells during the tumor immune response.

Antipancreatic cancer effect of DNT cells and the underlying mechanism

OBJECTIVES

This study aimed to explore double-negative T (DNT) cell cytotoxicity to pancreatic cancer and the effect of the Fas (CD95, APO-1)/FasL (CD178) signaling pathway on this process.

METHODS

DNT cells from the peripheral blood of healthy volunteers were expanded in vitro. The inhibitory effect of DNT cells on pancreatic cancer cells was investigated using a CCK-8 assay and nude mouse tumor model. A mechanistic study was performed using pathway blocking assays.

RESULTS

DNT cells were amplified in vitro with >90% purity, and the growth of pancreatic cancer in vitro was significantly inhibited by DNT cells. After coculture with DNT cells, Fas, caspase-8 and cleaved caspase-8 showed increased expression in pancreatic cancer cells. When blocking agent decoy receptor 3 (DcR3) was added, the antitumor effect of DNT cells and the expression of Fas, caspase-8 and cleaved caspase-8 were reduced in pancreatic cancer cells. In the nude mouse tumor model, the tumor volume and weight were lower in the DNT cell group and gemcitabine group than in the blank control group. Additionally, the expression of Fas, caspase-8 and cleaved caspase-8 was higher in the DNT cell group than in the blank control group. Moreover, DNT cells promoted apoptosis in cancer cells and animal model tissues.

CONCLUSION

DNT cells inhibited the growth of pancreatic cancer, and the Fas/FasL signaling pathway was involved in this process.

Tumour-targeting bacteria engineered to fight cancer

Recent advances in targeted therapy and immunotherapy have once again raised the hope that a cure might be within reach for many cancer types. Yet, most late-stage cancers are either insensitive to the therapies to begin with or develop resistance later. Therapy with live tumour-targeting bacteria provides a unique option to meet these challenges. Compared with most other therapeutics, the effectiveness of tumour-targeting bacteria is not directly affected by the 'genetic makeup' of a tumour. Bacteria initiate their direct antitumour effects from deep within the tumour, followed by innate and adaptive antitumour immune responses. As microscopic 'robotic factories', bacterial vectors can be reprogrammed following simple genetic rules or sophisticated synthetic bioengineering principles to produce and deliver anticancer agents on the basis of clinical needs. Therapeutic approaches using live tumour-targeting bacteria can either be applied as a monotherapy or complement other anticancer therapies to achieve better clinical outcomes. In this Review, we summarize the potential benefits and challenges of this approach. We discuss how live bacteria selectively induce tumour regression and provide examples to illustrate different ways to engineer bacteria for improved safety and efficacy. Finally, we share our experience and insights on oncology clinical trials with tumour-targeting bacteria, including a discussion of the regulatory issues.

A versatile pretargeting approach for tumour-selective delivery and activation of TNF superfamily members

TNFR superfamily (TNFRSF) members have important immunoregulatory functions and are of clear interest for cancer immunotherapy. Various TNFRSF agonists have been clinically evaluated, but have met with limited efficacy and/or toxicity. Recent insights indicate that 'first-generation' TNFRSF agonists lack efficacy as they do not effectively cross-link their corresponding receptor. Reversely, ubiquitous TNFRSF receptor(s) cross-linking by CD40 and Fas agonistic antibodies resulted in dose-limiting liver toxicity. To overcome these issues, we developed a novel pretargeting strategy exploiting recombinant fusion proteins in which a soluble form of TRAIL, FasL or CD40L is genetically fused to a high-affinity anti-fluorescein scFv antibody fragment (scFvFITC). Fusion proteins scFvFITC:sTRAIL and scFvFITC:sFasL induced potent target antigen-restricted apoptosis in a panel of cancer lines and in primary patient-derived cancer cells, but only when pretargeted with a relevant FITC-labelled antitumour antibody. In a similar pretargeting setting, fusion protein scFvFITC:sCD40L promoted tumour-directed maturation of immature monocyte-derived dendritic cells (iDCs). This novel tumour-selective pretargeting approach may be used to improve efficacy and/or reduce possible off-target toxicity of TNFSF ligands for cancer immunotherapy.

Subtype-Specific Radiation Response and Therapeutic Effect of FAS Death Receptor Modulation in Human Breast Cancer

Breast cancer is the most common malignancy diagnosed among women and represents a heterogeneous group of subtypes. Radiation therapy is a critical component of treatment for breast cancer patients. However, little is known about radiation response among these intrinsic subtypes. In previous studies, we identified a significant induction of FAS after irradiation in biologically favorable breast cancer patients and breast cancer cell lines. Here, we expanded our study and investigated radiation response in a mouse model of breast cancer. MCF7 (luminal), HCC1954 (HER2⁺) or SUM159 (basal) cells were implanted orthotopically into the dorsal mammary fat pad of nude mice. These mice were then treated with different doses of radiation to assess tumor growth control. We further investigated the therapeutic effect of FAS modulation by silencing FAS in radiation-responsive tumors and injecting FAS agonist antibody into radiation-resistant tumors. Exposure to radiation inhibited MCF7, and to a lesser extent HCC1954 tumor growth in a dose-dependent manner. In contrast, SUM159 tumors were resistant to radiation. The estimated TCD₅₀ values were 19.3 Gy for MCF7 and 44.9 Gy for SUM159. Radiation induced FAS expression in MCF7 tumors, but not SUM159 tumors. We found that silencing of FAS did not negatively impact radiation response in MCF7 tumors, possibly due to compensation by other apoptotic pathways. On the other hand, FAS activating antibody in combination with radiation treatment delayed SUM159 and HCC1954 tumor growth. However, it did not reach statistical significance compared to radiation treatment alone. Our results suggest that there is intrinsic variation in radiation response among breast cancer subtypes. FAS activation concurrent with radiation slows tumor growth in the radiation-resistant subtypes, but the effect was not significant. Alternative subtype-specific modulators of radiation response are under investigation.

Anti-Fas Antibody Conjugated Nanoparticles Enhancing the Antitumor Effect of Camptothecin by Activating the Fas-FasL Apoptotic Pathway

Emerging evidence suggest that the introduction of Fas ligand (FasL) can enhance the Fas-dependent apoptosis and induce durable immune responses against tumor. However, selective triggering of apoptosis in tumor cells while sparing normal cells remains a great challenge for the application of FasL-based therapeutic strategies. Herein, smart nanoparticles (NPs) with a sandwich structure were fabricated. These NPs consist of a matrix metalloproteinase (MMP) cleavable PEG outer layer, an anti-Fas antibody middle layer, and a camptothecin (CPT)-loaded inner core. They could accumulate at a tumor site by the enhanced permeability and retention (EPR) effect. The removable PEG layer protects the cytotoxic anti-Fas antibody from premature contact with normal tissues, thus avoiding the unexpected lethal side effect before they reach the tumor site. Due to the high level of MMP expressed by tumor cells inside the tumor tissue, these NPs would shed their PEG layers, resulting in the exposure of anti-Fas antibody to bind the Fas receptor and triggering the apoptosis of tumor cells. Results of Western blot confirmed that these NPs could mimic the function of activated cytotoxic lymphocyte (CTL) to activate the Fas-FasL apoptosis pathway of tumor cells. With the aid of CPT payload, these anti-Fas antibody conjugated NPs achieved a high tumor inhibition in the B16 allograft tumor animal model. The design of these NPs provides a method for delivering cytotoxic ligand to targeting tissue, which may be valuable in cancer therapy.

Potent and tumor specific: arming bacteria with therapeutic proteins

Bacteria are perfect vessels for targeted cancer therapy. Conventional chemotherapy is limited by passive diffusion, and systemic administration causes severe side effects. Bacteria can overcome these obstacles by delivering therapeutic proteins specifically to tumors. Bacteria have been modified to produce proteins that directly kill cells, induce apoptosis via signaling pathways, and stimulate the immune system. These three modes of bacterial treatment have all been shown to reduce tumor growth in animal models. Bacteria have also been designed to convert nontoxic prodrugs to active therapeutic compounds. The ease of genetic manipulation enables creation of arrays of bacteria that release many new protein drugs. This versatility will allow targeting of multiple cancer pathways and will establish a platform for individualized cancer medicine.

Cumulus cells accelerate oocyte aging by releasing soluble Fas ligand in mice

Although previous studies have suggested that cumulus cells (CCs) accelerate oocyte aging by secreting soluble and heat-sensitive paracrine factors, the factors involved are not well characterized. Because Fas-mediated apoptosis represents a major pathway in induction of apoptosis in various cells, we proposed that CCs facilitate oocyte aging by releasing soluble Fas ligand (sFasL). In this study, we reported that when the aging of freshly ovulated mouse oocytes were studied in vitro, both the apoptotic rates of CCs and the amount of CCs produced sFasL increased significantly with the culture time. We found that oocytes expressed stable levels of Fas receptors up to 24 h of in vitro aging. Moreover, culture of cumulus-denuded oocytes in CCs-conditioned CZB medium (CM), in CZB supplemented with recombinant sFasL, or in CM containing sFasL neutralizing antibodies all showed that sFasL impaired the developmental potential of the oocytes whereas facilitating activation and fragmentation of aging oocytes. Furthermore, CCs from the FasL-defective gld mice did not accelerate oocyte aging due to the lack of functional FasL. In conclusion, we propose that CCs surrounding aging oocytes released sFasL in an apoptosis-related manner, and the released sFasL accelerated oocyte aging by binding to Fas receptors.

Targeting of the tumor necrosis factor receptor superfamily for cancer immunotherapy

The tumor necrosis factor (TNF) ligand and cognate TNF receptor superfamilies constitute an important regulatory axis that is pivotal for immune homeostasis and correct execution of immune responses. TNF ligands and receptors are involved in diverse biological processes ranging from the selective induction of cell death in potentially dangerous and superfluous cells to providing costimulatory signals that help mount an effective immune response. This diverse and important regulatory role in immunity has sparked great interest in the development of TNFL/TNFR-targeted cancer immunotherapeutics. In this review, I will discuss the biology of the most prominent proapoptotic and co-stimulatory TNF ligands and review their current status in cancer immunotherapy.

The "go or grow" potential of gliomas is linked to the neuropeptide processing enzyme carboxypeptidase E and mediated by metabolic stress

Glioblastoma (GBM), the most common malignant brain tumor, is among the most lethal neoplasms, with a median survival of approximately 1 year. Prognosis is poor since GBMs possess a strong migratory and highly invasive potential, making complete surgical resection impossible. Reduced expression of carboxypeptidase E (CPE), a neuropeptide-processing enzyme, in a cell death-resistant glioma cell line and lower CPE expression levels in the cohort of GBM samples of The Cancer Genome Atlas compared to normal brain control specimens prompted us to analyze the function of CPE as a putative tumor suppressor gene. In our samples, CPE was also reduced in GBM compared to normal brain with the strongest loss in cells surrounding hypoxic tumor areas as well as in most glioma cell lines and primary glioma cells. In our cohort of glioma patients, loss of CPE predominantly occurred in glioblastomas and was associated with worse prognosis. In glioma cells, CPE overexpression was significantly reduced, whereas knockdown or inhibition enhanced glioma cell migration and invasion. The decreased migratory potential following CPE overexpression was paralleled by altered cellular morphology, promoting a transition to focal adhesions and associated stress fibers. In contrast to the decreased migration, high CPE levels were associated with higher proliferative rates. As microenvironmental regulation cues, we identified CPE as being downregulated upon hypoxia or glucose deprivation. Our findings indicate an oxygen- and nutrition-dependent anti-migratory, but pro-proliferative role of CPE in gliomas with prognostic impact for patient survival, thereby contributing to the understanding of the "go or grow" hypothesis in gliomas.

Targeting the Fas/FasL signaling pathway in cancer therapy

INTRODUCTION

The Fas/FasL system plays a significant role in tumorigenesis. Research has shown that its impairment in cancer cells may lead to apoptosis resistance and contribute to tumor progression. Thus, the development of effective therapies targeting the Fas/FasL system may play an important role in the fight against cancer.

AREAS COVERED

In this review the recent literature on targeting the Fas/FasL system for therapeutic exploitation at different levels is reviewed. Promising pre-clinical approaches and various exceptions are highlighted. The potential of combined therapies is also explored, whereby tumor sensitivity to Fas-mediated apoptosis is restored, before an effective targeted therapy is employed.

EXPERT OPINION

The success of the Fas/FasL system targeting for therapeutics will require a better understanding of the alterations conferring resistance, in order to use the most appropriate sensitizing chemotherapeutic or radiotherapeutic agents in combination with effective targeted therapies.

Alginate encapsulated cells secreting Fas-ligand reduce lymphoma carcinogenicity

Fas ligand (CD95L/APO-1) is considered as a potent anti-tumor agent due to its mediated cell death properties. We have designed a polymeric microencapsulation system, which encapsulates soluble FasL secreting cells. The encapsulated cells continuously release soluble FasL (sFasL) at the tumor site, while the device protects the encapsulated cells from the host immune system. The potential and efficacy of this system are demonstrated in vitro and in vivo for tumor inhibition. Polymeric microcapsules composed of Alginate Poly-l-lysine were optimized to encapsulate L5 secreting sFasL cells. The expression and anti-tumor activities of the sFasL were confirmed in vitro and tumor inhibition was studied in vivo in SCID mice bearing subcutaneous lymphoma tumors. In vitro, sFasL secreted by the encapsulated L5-sFasL cells was biologically active, inhibited proliferation and induced apoptotic cell death in Fas sensitive tumor cells. Mice injected with encapsulated L5-sFasL cells on the day of tumor injection or 10 days after tumor injection showed significant reduction in tumor volume, of 87% and 95%, respectively. Our findings show that encapsulated cells expressing sFasL can be used as a local device and efficiently suppress malignant Fas sensitive tumors with no side effects.

Mechanisms Conferring Resistance to Pro-Apoptotic Cancer Gene Therapy

Recently, we have described a novel approach to the treatment of cancer that employs a series of vectors that encode surface expressed chimeric proteins in which the cytoplasmic death domain of Fas is fused in-frame to the extracellular domain of one of a number of cell surface receptors that recognize and bind various ligands that are differentially expressed within the tumor microenvironment. Although the majority of tumor cells transduced with such vectors are killed in the presence of the corresponding cognate ligand, a small percentage survive and in vivo may go on to repopulate a treated tumor. In order to understand the mechanisms employed by tumors to escape the cytotoxic effects of pro-apoptotic signals triggered via Fas, we isolated a large number of 293 tumor cell clones that survive following transfection with a plasmid vector encoding Flk-1/Fas, a chimeric receptor that induces tumor cell death in the presence of the pro-angiogenic cytokine VEGF. Characterization of Flk-1/Fas-positive clones revealed that while survival can most often be attributed simply to the down-regulation of VEGF ligand expression, in cells that express both receptor and ligand, other proteins involved in the regulation of apoptosis may be targeted. Specifically, a Flk-1/Fas-positive, VEGF-positive clone was identified in which expression of APAF-1 was almost completely abrogated.

S-nitrosylation of the death receptor fas promotes fas ligand-mediated apoptosis in cancer cells

BACKGROUND & AIMS

Fas belongs to the family of tumor necrosis factor receptors which induce apoptosis. Many cancer cells express Fas but do not undergo Fas-mediated apoptosis. Nitric oxide reverses this resistance by increasing levels of Fas at the plasma membrane. We studied the mechanisms by which NO affects Fas function.

METHODS

Colon and mammary cancer cell lines were incubated with the NO donor glyceryl trinitrate or lipid A; S-nitrosylation of Fas was monitored using the biotin switch assay. Fas constructs that contained mutations at cysteine residues that prevent S-nitrosylation were used to investigate the involvement of S-nitrosylation in Fas-mediated cell death. Apoptosis was monitored according to morphologic criteria.

RESULTS

NO induced S-nitrosylation of cysteine residues 199 and 304 in the cytoplasmic part of Fas. In cancer cells that overexpressed wild-type Fas, S-nitrosylation induced Fas recruitment to lipid rafts and sensitized the cells to Fas ligand. In cells that expressed a mutant form of Fas in which cysteine 304 was replaced by valine residue, NO-mediated translocation of Fas to lipid rafts was affected and the death-inducing signal complex and synergistic effect of glyceryl trinitrate-Fas ligand were inhibited significantly. These effects were not observed in cells that expressed Fas with a mutation at cysteine 199.

CONCLUSIONS

We identified post-translational modifications (S-nitrosylation of cysteine residues 199 and 304) in the cytoplasmic domain of Fas. S-nitrosylation at cysteine 304 promotes redistribution of Fas to lipid rafts, formation of the death-inducing signal complex, and induction of cell death.

Human toxin-based recombinant immunotoxins/chimeric proteins as a drug delivery system for targeted treatment of human diseases

INTRODUCTION

The development of specific immunosuppressive reagents remains the major goal in the treatment of human diseases. One such approach is the use of recombinant immunotoxins/chimeric proteins, composed of targeting and killing moieties, fused at the cDNA level. Most of these 'magic bullets' use bacterial or plant toxins to induce cell death. These toxins are extremely potent, but they also cause severe toxicity and systemic side effects that limit the maximal doses given to patients. Moreover, being of non-human origin, they are highly immunogenic, and the resulting neutralizing antibody production impairs their efficacy.

AREAS COVERED

This review describes recombinant immunotoxins/chimeric proteins composed of the classical delivering, cell-targeting molecules, fused to highly cytotoxic human proteins capable of generating an intense apoptotic response within the target cell. This review focuses on the new 'Human Killing Moieties' of these targeted proteins and describes recent progress in the development of these promising molecules.

EXPERT OPINION

Human toxin-based immunotoxins/chimeric proteins for the targeted delivery of drugs are still in their early stages of development. However, they are certain to advance in the very near future to become an extra weapon in the everlasting war against human diseases, mainly cancer.

Targeting apoptosis pathways in glioblastoma

The treatment of glioblastoma remains a major challenge for clinicians since these highly aggressive brain tumors are relatively resistant towards radio- and chemotherapy. The pathways that control apoptosis are altered in glioblastoma cells leading to resistance towards apoptotic stimuli in general. In this review we describe the alterations affecting the p53 pathway, the BCL-2 protein family, the inhibitor of apoptosis proteins and several growth factor pathways involved in the regulation of programmed cell death and define possible targets for new therapies within these apoptotic pathways in glioblastomas. Moreover, we review strategies to target death receptor pathways, most notably to render the glioblastoma cells more susceptible towards this approach without enhancing toxicity in general. Most of the strategies targeting apoptosis in glioblastomas presented here are in a pre-clinical stage of development, however, they all share the ultimative goal to improve the outcome for glioblastoma patients.

APO010, a synthetic hexameric CD95 ligand, induces human glioma cell death in vitro and in vivo

Death receptor targeting has emerged as one of the promising novel approaches of cancer therapy. The activation of one such prototypic death receptor, CD95 (Fas/APO-1), has remained controversial because CD95 agonistic molecules have exhibited either too strong toxicity or too little activity. The natural CD95 ligand (CD95L) is a cytokine, which needs to trimerize to mediate a cell death signal. Mega-Fas-Ligand, now referred to as APO010, is a synthetic hexameric CD95 agonist that exhibits strong antitumor activity in various tumor models. Here, we studied the effects of APO010 in human glioma models in vitro and in vivo. Compared with a cross-linked soluble CD95L or a CD95-agonistic antibody, APO010 exhibited superior activity in glioma cell lines expressing CD95 and triggered caspase-dependent cell death. APO010 reduced glioma cell viability in synergy when combined with temozolomide. The locoregional administration of APO010 induced glioma cell death in vivo and prolonged the survival of tumor-bearing mice. A further exploration of APO010 as a novel antiglioma agent is warranted.

Enhancing melanoma treatment with resveratrol

BACKGROUND

Resveratrol (RESV) is a naturally occurring compound that possesses anti-cancer capabilities. The goal of this study was to evaluate the potential of RESV as an adjunct to chemotherapy in melanoma treatment.

METHODS

The in vitro and in vivo cytotoxic activity of RESV with or without chemotherapy was tested using cellular assays and a xenograft model. Two Duke melanoma cell lines (DM738, DM443) were used for both in vivo and in vitro experiments, and two nonmalignant human fibroblast lines (NHDF, HS68) were used for in vitro cellular assays. Xenografts were randomized to treatment arms and tumors measured to evaluate response. Results were analyzed using a Student's t-test and ANOVA. Western blots were performed on in vivo tissue.

RESULTS

In vitro RESV significantly decreased melanoma cell viability in all lines tested (all P < 0.0001). Treatment of fibroblast cell lines revealed that RESV selectively spared NHDF and HS68 cells compared with its cytotoxic effects on melanoma cells (P < 0.0001). Treatment of malignant cells with 50 μM RESV and temozolomide (TMZ) for 72 h significantly enhanced cytotoxicity compared with treatment with TMZ alone (P < 0.0001). In vivo, however, there was no significant difference between any treatment arms (P = 0.65).

CONCLUSION

RESV shows promise as a novel therapeutic in the management of melanoma for its selective anti-tumor activity in vitro. Translating in vitro results to in vivo models has proven difficult. Barriers thought to prevent such translation are identified, and a rationale for overcoming them is discussed.

Therapeutic effects of the Sp1 inhibitor mithramycin A in glioblastoma

Mithramycin A (MitA) is a chemotherapeutic compound which has been used in the therapy of several types of cancer. For experimental cancer it has been shown that MitA mediates the expression of genes involved in tumor progression such as genes involved in immunosurveillance, cell motility or cell death. MitA works synergistically with Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and with antiangiogenic agents. We were therefore interested in analyzing whether MitA might be a suitable agent for glioma therapy. We demonstrate herein that the cell death sensitizing effects of MitA are cell line specific, independent of the endogenous status of the tumor suppressor p53 as well as of the endogenous expression of X-linked inhibitor of apoptosis (XIAP) or basal sensitivity towards death ligand-induced cell death. In glioma cells, MitA reduced the secretion and activity of the migration-involved matrix metalloproteinases (MMP), diminished vascular endothelial growth factor (VEGF), and increased recepteur d'origine nantais (RON) kinase messenger RNA (mRNA), paralleled by a significant reduction of glioma cell migration. In contrast to other cancer types, in glioma cells MitA did not alter the expression of the immunorelevant genes major histocompatibility complex I class related (MIC)-A, MIC-B or UL16 binding proteins (ULBP). We conclude that, whereas MitA-mediated reduction of XIAP expression and sensitization to Apo2L/TRAIL are cell line specific, its antimigratory effects are more general and might be the result of altered expression of MMP, VEGF, and/or RON kinase. Therefore, MitA might be a potential agent to reduce glioma cell migration.

SC68896, a novel small molecule proteasome inhibitor, exerts antiglioma activity in vitro and in vivo

PURPOSE

Glioblastomas are among the most lethal neoplasms, with a median survival of <1 year. Modulation of the proteasome function has emerged as a novel approach to cancer pharmacotherapy. Here, we characterized the antitumor properties of SC68896, a novel small molecule proteasome inhibitor.

EXPERIMENTAL DESIGN

Different tumor cell lines were tested by crystal violet staining for sensitivity to SC68896, given alone or in combination with death ligands. The molecular mechanisms mediating SC68896-induced cell death and changes in cell cycle progression were assessed by immunoblot and flow cytometry. An orthotopic human glioma xenograft model in nude mice was used to examine the in vivo activity of SC68896.

RESULTS

SC68896 inhibits the proliferation of cell lines of different types of cancer, including malignant glioma. Exposure of LNT-229 glioma cells to SC68896 results in a concentration- and time-dependent inhibition of the proteasome, with a consequent accumulation of p21 and p27 proteins, cell cycle arrest, caspase cleavage, and induction of apoptosis. Using RNA interference, we show that the effect of SC68896 on glioma cells is facilitated by wild-type p53. SC68896 sensitizes glioma cells to tumor necrosis factor-related apoptosis-inducing ligand and CD95 ligand and up-regulates the cell surface expression of the tumor necrosis factor-related apoptosis-inducing ligand receptor cell death receptors 4 and 5, which may contribute to this sensitization. Intracerebral glioma-bearing nude mice treated either i.p. or intratumorally with SC68896 experience prolonged survival.

CONCLUSIONS

SC68896 is the first proteasome inhibitor that exerts antiglioma activity in vivo. It may represent a novel prototype agent for the treatment of malignant gliomas and warrants clinical evaluation.

Humanized immunotoxins: a new generation of immunotoxins for targeted cancer therapy

Chemotherapy, radiation, and surgery are the conventional treatment modalities for cancer. The success achieved with these approaches has been limited due to several factors like chemoresistance to drugs, non-specificity leading to peripheral toxicity, and non-resectable tumors. To combat these problems, the concept of targeted therapy using immunotoxins was developed. Immunotoxins are chimeric proteins with a cell-selective ligand chemically linked or genetically fused to a toxin moiety and can target cancer cells overexpressing tumor-associated antigens, membrane receptors, or carbohydrate antigens. Ligands for these receptors or monoclonal antibodies or single chain variable fragments directed against these antigens are fused with bacterial or plant toxins and are made use of as immunotoxins. Pseudomonas exotoxin, anthrax toxin, and diphtheria toxin are the commonly used bacterial toxins. Ricin, saporin, gelonin, and poke weed antiviral protein are the plant toxins utilized in immunotoxin constructs. Several such fusion proteins are in clinical trials, and denileukin difitox is a FDA-approved fusion protein. In spite of the promise shown by bacterial- and plant toxin-based chimeric proteins, their clinical application is hampered by several factors like immunogenicity of the toxin moiety and non-specific toxicity leading to vascular leak syndrome. In order to overcome these problems, a novel generation of immunotoxins in which the cytotoxic moiety is an endogenous protein of human origin like proapoptotic protein or RNase has been developed. This review summarizes the advances in this new class of fusion protein and the future directions to be explored.

Defects in the regulatory clearance mechanisms favor the breakdown of self-tolerance during spontaneous autoimmune orchitis

We identified aberrations leading to spontaneous autoimmune orchitis (AIO) in mink, a seasonal breeder and natural model for autoimmunity. This study provides evidence favoring the view that a malfunction of the clearance mechanisms for apoptotic cell debris arising from imbalances in phagocyte receptors or cytokines acting on Sertoli cells constitutes a major factor leading to breakdown of self-tolerance during spontaneous AIO. Serum anti-sperm antibody titers measured by ELISA reflected spermatogenic activity without causing immune inflammatory responses. Orchitic mink showed excess antibody production accompanied by spermatogenic arrest, testicular leukocyte infiltration, and infertility. AIO serum labeled the postacrosomal region, the mid and end piece of mink sperm, whereas normal mink serum did not. Normal serum labeled plasma membranes, whereas AIO serum reacted with germ cell nuclei. Western blot analyses revealed that AIO serum reacted specifically to a 23- and 50-kDa protein. The number of apostain-labeled apoptotic cells was significantly higher in orchitic compared with normal tubules. However, apoptosis levels measured by ELISA in seminiferous tubular fractions (STf) were not significantly different in normal and orchitic tubules. The levels of CD36, TNF-alpha, TNF-alpha RI, IL-6, and Fas but not Fas-ligand (L), and ATP-binding cassette transporter ABCA1 were changed in AIO STf. TNF-alpha and IL-6 serum levels were increased during AIO. Fas localized to germ cells, Sertoli cells, and the lamina propria of the tubules and Fas-L, to germ cells. Fas colocalized with Fas-L in residual bodies in normal testis and in giant cells and infiltrating leukocytes in orchitic tubules.

Inhibition of tumor growth using salmonella expressing Fas ligand

Intravenous administration of bacteria leads to their accumulation in tumors and to sporadic tumor regression. We therefore explored the hypothesis that Salmonella typhimurium engineered to express the proapoptotic cytokine Fas ligand (FasL) would exhibit enhanced antitumor activity. Immunocompetent mice carrying tumors derived from syngeneic murine D2F2 breast carcinoma or CT-26 colon carcinoma cells were treated intravenously with FasL-expressing S. typhimurium or with phosphate-buffered saline (PBS; control). Treatment with FasL-expressing S. typhimurium inhibited growth of primary tumors by an average of 59% for D2F2 tumors and 82% for CT-26 tumors (eg, at 25 days after initial treatment, mean volume of PBS-treated CT-26 colon carcinomas = 1385 mm(3) and of S. typhimurium FasL-treated CT-26 tumors = 243 mm(3), difference = 1142 mm(3), 95% confidence interval = 800 mm(3) to 1484 mm(3), P < .001). Pulmonary D2F2 metastases (as measured by lung weight) were reduced by 34% in S. typhimurium FasL-treated mice compared with PBS-treated mice. FasL-expressing S. typhimurium had similar effects on growth of murine B16 melanoma tumors in wild-type mice but not in lpr/lpr mice, which lack Fas, or in mice with disrupted host inflammatory responses. Antitumor activity was achieved without overt toxicity. These preclinical results raise the possibility that using attenuated S. typhimurium to deliver FasL to tumors may be an effective and well-tolerated therapeutic strategy for some cancers.

DEK is a poly(ADP-ribose) acceptor in apoptosis and mediates resistance to genotoxic stress

DEK is a nuclear phosphoprotein implicated in oncogenesis and autoimmunity and a major component of metazoan chromatin. The intracellular cues that control the binding of DEK to DNA and its pleiotropic functions in DNA- and RNA-dependent processes have remained mainly elusive so far. Our recent finding that the phosphorylation status of DEK is altered during death receptor-mediated apoptosis suggested a potential involvement of DEK in stress signaling. In this study, we show that in cells committed to die, a portion of the cellular DEK pool is extensively posttranslationally modified by phosphorylation and poly(ADP-ribosyl)ation. Through interference with DEK expression, we further show that DEK promotes the repair of DNA lesions and protects cells from genotoxic agents that typically trigger poly(ADP-ribose) polymerase activation. The posttranslational modification of DEK during apoptosis is accompanied by the removal of the protein from chromatin and its release into the extracellular space. Released modified DEK is recognized by autoantibodies present in the synovial fluids of patients affected by juvenile rheumatoid arthritis/juvenile idiopathic arthritis. These findings point to a crucial role of poly(ADP-ribosyl)ation in shaping DEK's autoantigenic properties and in its function as a promoter of cell survival.

A novel p53 rescue compound induces p53-dependent growth arrest and sensitises glioma cells to Apo2L/TRAIL-induced apoptosis

Reactivation of mutant p53 in tumours is a promising strategy for cancer therapy. Here we characterise the novel p53 rescue compound P53R3 that restores sequence-specific DNA binding of the endogenously expressed p53(R175H) and p53(R273H) mutants in gel-shift assays. Overexpression of the paradigmatic p53 mutants p53(R175H), p53(R248W) and p53(R273H) in the p53 null glioma cell line LN-308 reveals that P53R3 induces p53-dependent antiproliferative effects with much higher specificity and over a wider range of concentrations than the previously described p53 rescue drug p53 reactivation and induction of massive apoptosis (PRIMA-1). Furthermore, P53R3 enhances recruitment of endogenous p53 to several target promoters in glioma cells bearing mutant (T98G) and wild-type (LNT-229) p53 and induces mRNA expression of numerous p53 target genes in a p53-dependent manner. Interestingly, P53R3 strongly enhances the mRNA, total protein and cell surface expression of the death receptor death receptor 5 (DR5) whereas CD95 and TNF receptor 1 levels are unaffected. Accordingly, P53R3 does not sensitise for CD95 ligand- or tumour necrosis factor alpha-induced cell death, but displays synergy with Apo2L.0 in 9 of 12 glioma cell lines. Both DR5 surface induction and synergy with Apo2L.0 are sensitive to siRNA-mediated downregulation of p53. Thus this new p53 rescue compound may open up novel perspectives for the treatment of cancers currently considered resistant to the therapeutic induction of apoptosis.

Dendritic cells trigger tumor cell death by a nitric oxide-dependent mechanism

Dendritic cells (DCs) are well known for their capacity to induce adaptive antitumor immune response through Ag presentation and tumor-specific T cell activation. Recent findings reveal that besides this role, DCs may display additional antitumor effects. In this study, we provide evidence that LPS- or IFN-gamma-activated rat bone marrow-derived dendritic cells (BMDCs) display killing properties against tumor cells. These cytotoxic BMDCs exhibit a mature DC phenotype, produce high amounts of IL-12, IL-6, and TNF-alpha, and retain their phagocytic properties. BMDC-mediated tumor cell killing requires cell-cell contact and depends on NO production, but not on perforin/granzyme or on death receptors. Furthermore, dead tumor cells do not exhibit characteristics of apoptosis. Thus, intratumoral LPS injections induce an increase of inducible NO synthase expression in tumor-infiltrating DCs associated with a significant arrest of tumor growth. Altogether, these results suggest that LPS-activated BMDCs represent powerful tumoricidal cells which enforce their potential as anticancer cellular vaccines.

Fas Ligand Delivery by a Prostate-Restricted Replicative Adenovirus Enhances Safety and Antitumor Efficacy

PURPOSE

Recent studies showed that Fas ligand (FasL) induced apoptosis in tumor cells and suppressed the immune response in several types of tumors. However, the toxicity of FasL limited further administration. This study delivered FasL in prostate cancer cells using an improved prostate-restricted replicative adenovirus (PRRA), thereby improving the antitumor effect while decreasing systemic toxicity.

EXPERIMENTAL DESIGN

We designed a FasL-armed PRRA, called AdIU3, by placing adenoviral E1a and E4 genes, FasL cDNA, and E1b gene under the control of two individual PSES enhancers. Tissue-specific viral replication and FasL expression were analyzed, and the tumor killing effect of AdIU3 was investigated both in vitro and in vivo using androgen-independent CWR22rv s.c. models via local administration and bone models via systemic administration. The safety of systemic administration of AdIU3 was evaluated. AdCMVFasL, in which FasL was controlled by a universal cytomegalovirus (CMV) promoter, was used as a control.

RESULTS

AdIU3 enhanced FasL expression in prostate-specific antigen (PSA)/prostate-specific membrane antigen (PSMA)-positive cells but not in PSA/PMSA-negative cells. It induced apoptosis and killed PSA/PMSA-positive prostate cancer cells but spared normal human fibroblasts, hepatocytes, and negative cells. The increase in killing activity was confirmed to result in part from a bystander killing effect. Furthermore, AdIU3 was more effective than a plain PRRA in inhibiting the growth of androgen-independent prostate cancer xenografts and bone tumor formation. Importantly, systemic administration of AdIU3 resulted in undetectable toxicity, whereas the same doses of AdCMVFasL killed all mice due to multiviscera failure in 16 h.

CONCLUSIONS

AdIU3 decreased the toxicity of FasL by controlling its expression with PSES, with greatly enhanced prostate cancer antitumor efficacy. The results suggested that toxic antitumor factors can be delivered safely by a PRRA.

Synergistic effects of combined cytotoxic and apoptosis-inducing drugs on Tenon's capsule fibroblasts in vitro and in vivo

BACKGROUND

Highly toxic antimetabolites have gained access to routine clinical use to modulate and reduce the amount of postoperative scarring following glaucomatous filtering procedures. It could be speculated that by combining two different antiproliferative substances with different mechanisms of action total amounts of the substances could be decreased and side effects reduced.

METHODS

Twenty-two substances were tested that had antiproliferative effects by acting cytotoxically, inhibiting growth factors, or inducing apoptosis. With combinations of each two substances, cell culture experiments using 3T3 and human Tenon's capsule fibroblasts were performed evaluating cell toxicity, proliferation and migration, the extent of free radicals, and the amount of apoptosis (TUNEL, electron microscopy). The five most potent combinations were used in an animal experiment with rabbits performing filtering procedures. The extent of episcleral scarring was evaluated by histopathology.

RESULTS

The results of the various assays revealed consistently strong effects in 5 of the 462 combinations. Of these five combinations, two were highly effective in the rabbit model. Substances with strong effects when applied in combination included staurosporine, mitomycin, and CD95L.

CONCLUSIONS

We found synergistic effects in assays that evaluated different aspects of cell function. The amount of scarring in an animal experiment was inhibited to a level comparable with a high single dose of mitomycin. Combination therapy of two antiproliferative acting substances may be a promising concept.

Hypophosphorylation of the architectural chromatin protein DEK in death-receptor-induced apoptosis revealed by the isotope coded protein label proteomic platform

During apoptosis nuclear morphology changes dramatically due to alterations of chromatin architecture and cleavage of structural nuclear proteins. To characterize early events in apoptotic nuclear dismantling we have performed a proteomic study of apoptotic nuclei. To this end we have combined a cell-free apoptosis system with a proteomic platform based on the differential isotopic labeling of primary amines with N-nicotinoyloxy-succinimide. We exploited the ability of this system to produce nuclei arrested at different stages of apoptosis to analyze proteome alterations which occur prior to or at a low level of caspase activation. We show that the majority of proteins affected at the onset of apoptosis are involved in chromatin architecture and RNA metabolism. Among them is DEK, an architectural chromatin protein which is linked to autoimmune disorders. The proteomic analysis points to the occurrence of multiple PTMs in early apoptotic nuclei. This is confirmed by showing that the level of phosphorylation of DEK is decreased following apoptosis induction. These results suggest the unexpected existence of an early crosstalk between cytoplasm and nucleus during apoptosis. They further establish a previously unrecognized link between DEK and cell death, which will prove useful in the elucidation of the physiological function of this protein.

TRAIL receptor-mediated JNK activation and Bim phosphorylation critically regulate Fas-mediated liver damage and lethality

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family with potent apoptosis-inducing properties in tumor cells. In particular, TRAIL strongly synergizes with conventional chemotherapeutic drugs to induce tumor cell death. Thus, TRAIL has been proposed as a promising future cancer therapy. Little, however, is known regarding what the role of TRAIL is in normal untransformed cells and whether therapeutic administration of TRAIL, alone or in combination with other apoptotic triggers, may cause tissue damage. In this study, we investigated the role of TRAIL in Fas-induced (CD95/Apo-1-induced) hepatocyte apoptosis and liver damage. While TRAIL alone failed to induce apoptosis in isolated murine hepatocytes, it strongly amplified Fas-induced cell death. Importantly, endogenous TRAIL was found to critically regulate anti-Fas antibody-induced hepatocyte apoptosis, liver damage, and associated lethality in vivo. TRAIL enhanced anti-Fas-induced hepatocyte apoptosis through the activation of JNK and its downstream substrate, the proapoptotic Bcl-2 homolog Bim. Consistently, TRAIL- and Bim-deficient mice and wild-type mice treated with a JNK inhibitor were protected against anti-Fas-induced liver damage. We conclude that TRAIL and Bim are important response modifiers of hepatocyte apoptosis and identify liver damage and lethality as a possible risk of TRAIL-based tumor therapy.

Secretory expression of synthetic human Fas ligand extracellular domain gene in Pichia pastoris: influences of tag addition and N-glycosylation site deletion, and development of a purification method

Human Fas ligand is a medically important membrane glycoprotein that induces the apoptosis of harmful cells. A new secretory expression and purification method was devised for the production of a large amount of recombinant human Fas ligand extracellular domain (hFasLECD) by Pichia pastoris. The expression plasmid containing a synthetic hFasLECD gene designed using yeast optimal codons was constructed for the secretion of hFasLECD. The secreted product exhibited the specific binding activity toward soluble human Fas receptor extracellular domain-human IgG(1)-Fc domain fusion protein, and the receptor-ligand complex was immunoprecipitated by Protein A conjugated agarose-gel beads. The influences of the N- and C- terminal addition of FLAG/(His)(6) tag spaced by pentaglycine sequence and the sequentially accumulative deletions of N-glycosylation sites within hFasLECD were investigated. The secretion of functional hFasLECD was retained after the N-terminal tagging and the deletion of either single or double N-glycosylation sites. As judged from SDS-PAGE analysis of the culture supernatant, the N-terminal addition of FLAG-(Gly)(5) tag and the deletion of single N-glycosylation site via N184Q mutation increased the secretion level of the product. In contrast, the C-terminal tagged genes and all N-glycosylation sites deleted gene failed to direct the secretion of functional hFasLECD. The secreted products in the culture medium were purified using a cation-exchange chromatography and a gel-filtration chromatography. The purified hFasLECDs existed as trimers composed of a mixture of monomer species in different glycosylation states. Approximately five milligram of functional N-terminal FLAG-(Gly)(5) tagged hFasLECD N184Q mutant was obtained from one liter culture supernatant.

Frequency and resistance of CD95 (Fas/Apo-1) gene-transfected tumor cells to CD95-mediated apoptosis by the elimination and methylation of integrated DNA

It is important for more effective gene therapies to clarify the mechanisms by which cDNA integrated into cells can maintain or lose its function in vivo. We evaluated genetic and epigenetic events leading to alternation of the introduced CD95 (Fas/Apo-1) gene as a model of gene therapy. Solid tumors formed by CD95 cDNA-transfected hepatoma cells (F6b) were almost completely cured by a single treatment of anti-CD95 monoclonal antibody (mAb) but recurred in gld/gld lpr/lpr mice after initial complete response. Recurred tumors were resistant to repeated mAb treatment. The ratio of resistant cells in tumors was estimated as 4.2 cells per 10(6) cells. The CD95-resistant tumor contained CD95-vanished and CD95-decreased cells. CD95-vanished cells were due to the deletion of CD95cDNA. However, CD95-decreased cells retained CD95cDNA, which was highly methylated when determined with methylation-dependent enzymes and a demethylation reagent, indicating that DNA methylation was responsible for the reduced CD95 expression and resistance to mAb. CD95-decreased cells reduced the CD95 expression further but did not delete cDNA after a second in vivo treatment with anti-CD95 mAb, suggesting that the elimination of cDNA is not induced after its methylation and that cells containing methylated genes became more resistant by further methylation. Thus, the elimination and methylation of integrated cDNA appear to occur through different mechanisms. Our study of resistant tumor cells, which arose by both mutational and epigenetic modifications of the introduced CD95 plasmid, provides important and fundamental information about the fate of introduced cDNA, augmenting the efficiency of gene therapy.

Immunohistochemical detection of CD 95 (Fas) & Fas ligand (Fas-L) in plasma cells of multiple myeloma and its correlation with survival

Multiple myeloma (MM) is a malignant disease resulting from an uncontrolled proliferation of a neoplastic plasma cell clone in the bone marrow, which might also be induced by the loss of control on apoptosis. Fas ligand (Fas-L), a member of the tumor necrosis factor family, induces apoptosis mediated via its transmembrane death receptor Fas (Apo-1/CD95) antigen. In the present study, immunostaining was performed on the initial diagnostic bone marrow biopsies of 36 MM patients (1 stage I, 5 stage II, 30 stage III), to evaluate the distribution of Fas receptor and Fas-L on malignant plasma cells. Both Fas and Fas-L were positive in 13 cases and negative in 3, whereas 10 cases were Fas-negative, Fas-L-positive and 10 were Fas-positive, Fas-L-negative. Although no association was found between the expression of Fas receptor or Fas-L and overall survival, Fas-L positivity was significantly associated with a shorter event-free survival (p = 0.0335). In this study, it has been shown that the expression of Fas-L, in malignant plasma cells of myeloma patients significantly shortens the event-free survival, indicating that the defect in apoptosis might be associated with disease progression in MM.

A novel antiapoptotic mechanism based on interference of Fas signaling by CD44 variant isoforms

There is growing evidence that one of the central common characteristics of tumor and inflammatory cells is their resistance to programmed cell death. This feature results in the accumulation of harmful cells, which are mostly refractory to Fas (FAS, APO-1)-mediated apoptosis. A molecule found on these cells is the transmembrane receptor CD44 with its variant isoforms (CD44v). The establishment of transfectants expressing different CD44v isoforms allowed us to demonstrate that the CD44v6 and CD44v9 isoforms exhibit an antiapoptotic effect and can block Fas-mediated apoptosis. Moreover, we observed that CD44v6 and CD44v9 colocalize and interact with Fas. Importantly, an anti-CD44v6 antibody can abolish the antiapoptotic effect of CD44v6. These results are the first to show that CD44v isoforms interfere with Fas signaling. Our findings improve the understanding of the pathogenesis of cancer and autoimmunity and open new strategies to treat such disorders.

FasL (CD95L/APO-1L) resistance of neurons mediated by phosphatidylinositol 3-kinase-Akt/protein kinase B-dependent expression of lifeguard/neuronal membrane protein 35

The contribution of Fas (CD95/APO-1) to cell death mechanisms of differentiated neurons is controversially discussed. Rat cerebellar granule neurons (CGNs) express high levels of Fas in vitro but are resistant to FasL (CD95L/APO-1L/CD178)-induced apoptosis. We here show that this resistance was mediated by a phosphatidylinositol 3-kinase (PI 3-kinase)-Akt/protein kinase B (PKB)-dependent expression of lifeguard (LFG)/neuronal membrane protein 35. Reduction of endogenous LFG expression by antisense oligonucleotides or small interfering RNA lead to increased sensitivity of CGNs to FasL-induced cell death and caspase-8 cleavage. The inhibition of PI 3-kinase activity sensitized CGNs to FasL-induced caspase-8 and caspase-3 processing and caspase-dependent fodrin cleavage. Pharmacological inhibition of PI 3-kinase, overexpression of the inhibitory protein IkappaB, or cotransfection of an LFG reporter plasmid with dominant-negative Akt/PKB inhibited LFG reporter activity, whereas overexpression of constitutively active Akt/PKB increased LFG reporter activity. Overexpression of LFG in CGNs interfered with the sensitization to FasL by PI 3-kinase inhibitors. In contrast to CGNs, 12 glioma cell lines, which are sensitive to FasL, did not express LFG. Gene transfer of LFG into these FasL-susceptible glioma cells protected against FasL-induced apoptosis. These results demonstrate that LFG mediated the FasL resistance of CGNs and that, under certain circumstances, e.g., inhibition of the PI 3-kinase-Akt/PKB pathway, CGNs were sensitized to FasL.

CD7-restricted activation of Fas-mediated apoptosis: a novel therapeutic approach for acute T-cell leukemia

Agonistic anti-Fas antibodies and multimeric recombinant Fas ligand (FasL) preparations show high tumoricidal activity against leukemic cells, but are unsuitable for clinical application due to unacceptable systemic toxicity. Consequently, new antileukemia strategies based on Fas activation have to meet the criterion of strictly localized action at the tumor-cell surface. Recent insight into the FasL/Fas system has revealed that soluble homotrimeric FasL (sFasL) is in fact nontoxic to normal cells, but also lacks tumoricidal activity. We report on a novel fusion protein, designated scFvCD7:sFasL, that is designed to have leukemia-restricted activity. ScFvCD7:sFasL consists of sFasL genetically linked to a high-affinity single-chain fragment of variable regions (scFv) antibody fragment specific for the T-cell leukemia-associated antigen CD7. Soluble homotrimeric scFvCD7:sFasL is inactive and acquires tumoricidal activity only after specific binding to tumor cell-surface-expressed CD7. Treatment of T-cell acute lymphoblastic leukemia (T-ALL) cell lines and patient-derived T-ALL, peripheral T-cell lymphoma (PTCL), and CD7-positive acute myeloid leukemia (AML) cells with homotrimeric scFvCD7:sFasL revealed potent CD7-restricted induction of apoptosis that was augmented by conventional drugs, farnesyl transferase inhibitor L-744832, and the proteasome inhibitor bortezomib (Velcade; Millenium, Cambridge, MA). Importantly, identical treatment did not affect normal human peripheral-blood lymphocytes (PBLs) and endothelial cells, with only moderate apoptosis in interleukin-2 (IL-2)/CD3-activated T cells. CD7-restricted activation of Fas in T-cell leukemic cells by scFvCD7:sFasL revitalizes interest in the applicability of Fas signaling in leukemia therapy.

BCL-xL: time-dependent dissociation between modulation of apoptosis and invasiveness in human malignant glioma cells

Conditionally BCL-xL-overexpressing LNT-229 Tet-On glioma cell clones were generated to investigate whether the 'antiapoptosis phenotype' and the 'motility phenotype' mediated by BCL-2 family proteins in glioma cells could be separated. BCL-xL induction led to an immediate and concentration-dependent protection of LNT-229 cells from apoptosis. BCL-xL induction for up to 3 days did not result in altered invasiveness. In contrast, long-term BCL-xL induction for 21 days resulted in increased transforming growth factor-beta2 expression, and in metalloproteinase-2 and -14 dependent, but integrin independent, increased invasiveness. Withdrawal of doxycycline (Dox) abolished the protection from apoptosis whereas the 'invasion phenotype' remained stable. Dox stimulation of BCL-xL-inducible LNT-229 cells conferred infiltrative growth to BCL-xL-positive glioma cells in vivo and reduced the survival of tumor-bearing mice. These data allow to dissect a direct antiapoptotic action of BCL-xL from an indirect effect, presumably mediated by altered gene expression, which modifies tumor cell invasiveness in vitro and in vivo.