FasL gene therapy: a new therapeutic modality for head and neck cancer

CD95/Fas ligand induced toxicity

The role of CD95/Fas ligand (CD95L/FasL) in the induction of CD95-mediated extrinsic apoptosis is well characterized. Trimerized, membrane-bound CD95L ligates the CD95 receptor activating downstream signaling resulting in the execution of cells by caspase proteins. However, the expression of CD95L has been reported to induce cell death in contexts in which this pathway is unlikely to be activated, such as in cell autonomous activation induced cell death (AICD) and in CD95-resistant cancer cell lines. Recent data suggests that the CD95L mRNA exerts toxicity through death induced by survival gene elimination (DISE). DISE results from the targeting of networks of survival genes by toxic short RNA (sRNA)s in the RNA-induced silencing complex (RISC). CD95L mRNA contributes to this death directly, through the processing of its mRNA into toxic sRNAs that are loaded into the RISC, and indirectly, by promoting the loading of other toxic sRNAs. Interestingly, CD95L is not the only mRNA that is processed and loaded into the RISC. Protein-coding mRNAs involved in protein translation are also selectively loaded. We propose a model in which networks of mRNA-derived sRNAs modulate DISE, with networks of genes providing non-toxic RISC substrate sRNAs that protect against DISE, and opposing networks of stress-activated genes that produce toxic RISC substrate sRNAs that promote DISE.

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

Apoptosis-Inducing TNF Superfamily Ligands for Cancer Therapy

Cancer is a complex disease with apoptosis evasion as one of its hallmarks; therefore, apoptosis induction in transformed cells seems a promising approach as a cancer treatment. TNF apoptosis-inducing ligands, which are naturally present in the body and possess tumoricidal activity, are attractive candidates. The most studied proteins are TNF-α, FasL, and TNF-related apoptosis-inducing ligand (TRAIL). Over the years, different recombinant TNF family-derived apoptosis-inducing ligands and agonists have been designed. Their stability, specificity, and half-life have been improved because most of the TNF ligands have the disadvantages of having a short half-life and affinity to more than one receptor. Here, we review the outlook on apoptosis-inducing ligands as cancer treatments in diverse preclinical and clinical stages and summarize strategies of overcoming their natural limitations to improve their effectiveness.

Genomic variants in Fas-mediated apoptosis pathway predict a poor response to Platinum-based Chemotherapy for Chinese Gastric Cancer Patients

Platinum-based adjuvant chemotherapy is very common for gastric cancer (GC) patients, but the chemotherapy sensitivity is very heterogeneous. The genomic variants and the gene-gene interactions involved in Fas-mediated apoptosis pathway including Fas (FAS 1377 G > A and 670 A > G), FasL (FASL 844 C > T) and caspase-8 (CASP8 -652 6N ins > del or I > D), may paly vital roles in the response to platinum-based treatment. In our investigation, 662 stage II-III postoperative GC patients were enrolled between 1998 and 2006. 261 patients accepted platinum-based regimens and the remaining 401 were not. The log rank tests, Kaplan Meier plots, Pearson chi-square tests, Student t-tests and Cox regression analyses were performed. For the chemotherapy cohort, FAS 1377 G > A or FAS 670 A > G variants alone was related with inferior survival, and a greater than additive effect was identified when patients simultaneously carrying FAS 1377 GA and FAS 670 GA genotypes. But the poor response was neutralized when patients simultaneously carrying FASL 844 C > T or CASP8 -652 6N ins > del mutations. Our study suggested that FAS 1377 G > A and FAS 670 A > G variants may serve as potential biomarkers to predict the response to platinum-based adjuvant chemotherapy, and the gene-gene interactions involved in Fas-mediated apoptosis pathway may enhance or neutralize the chemosensitivity.

CD95/Fas ligand mRNA is toxic to cells

CD95/Fas ligand binds to the death receptor CD95 to induce apoptosis in sensitive cells. We previously reported that CD95L mRNA is enriched in sequences that, when converted to si/shRNAs, kill all cancer cells by targeting critical survival genes (Putzbach et al., 2017). We now report expression of full-length CD95L mRNA itself is highly toxic to cells and induces a similar form of cell death. We demonstrate that small (s)RNAs derived from CD95L are loaded into the RNA induced silencing complex (RISC) which is required for the toxicity and processing of CD95L mRNA into sRNAs is independent of both Dicer and Drosha. We provide evidence that in addition to the CD95L transgene a number of endogenous protein coding genes involved in regulating protein translation, particularly under low miRNA conditions, can be processed to sRNAs and loaded into the RISC suggesting a new level of cell fate regulation involving RNAi.

Targeted nonviral gene therapy in prostate cancer

Prostate cancer is the second-most widespread cancer in men worldwide. Treatment choices are limited to prostatectomy, hormonal therapy, and radiotherapy, which commonly have deleterious side effects and vary in their efficacy, depending on the stage of the disease. Among novel experimental strategies, gene therapy holds great promise for the treatment of prostate cancer. However, its use is currently limited by the lack of delivery systems able to selectively deliver the therapeutic genes to the tumors after intravenous administration without major drawbacks. To remediate this problem, a wide range of nonviral delivery approaches have been developed to specifically deliver DNA-based therapeutic agents to their site of action. This review provides an overview of the various nonviral delivery strategies and gene therapy concepts used to deliver therapeutic DNA to prostate cancer cells, and focuses on recent therapeutic advances made so far.

Early growth response 3 inhibits growth of hepatocellular carcinoma cells via upregulation of Fas ligand

Hepatocellular carcinoma (HCC) is a prevalent malignancy with aggressive biological behavior and poor prognosis. Early growth response 3 (EGR3) is a zinc finger transcription factor, and has been studied primarily in the context of neurodevelopment, autoimmunity, inflammation and angiogenesis. Accumulating evidence indicates that EGR3 is a novel suppressor gene of tumor initiation and progression in certain cancer events, but little work has been carried out in exploring the relationship between EGR3 and HCC growth. The purpose of this study was to investigate the possible effects of EGR3 on cell proliferation and apoptosis in HCC, and determine the underlying mechanisms. Here, we observed that EGR3 expression was frequently downregulated in HCC tissues and cell lines. Ectopic expression of EGR3 contributed to cell proliferation inhibition and apoptosis induction in HCC cells in vitro. Furthermore, the expression of Fas ligand (FasL) was significantly enhanced following upregulation of EGR3 in HCC cells, accompanied by an obvious increase of pro-apoptotic Bak and cell cycle inhibitor p21 expression. Based on nude mouse models, we demonstrated that ectopic expression of EGR3 markedly restricted tumor growth, and the expression of FasL was significantly increased in the xenograft tumor tissues which exhibited high EGR3 expression. We further established a co-transfection in HCC cells with EGR3 overexpression plasmid and FasL siRNA. We found that silencing of FasL gene impeded the anti-proliferative and pro-apoptotic effects, as well as the increase of Bak and p21 expression, suggesting an essential role of FasL in EGR3-mediated growth suppression in HCC cells. Collectively, in conclusion, EGR3 contributes to cell growth inhibition via upregulation of FasL in HCC.

Targeting acid ceramidase sensitises head and neck cancer to cisplatin

BACKGROUND

Acid ceramidase (AC), a key enzyme in ceramide metabolism, plays a role in cancer progression and resistance to therapy. However, the role of AC in head and neck cancer (HNC) has not been addressed. Here, we investigate the effect of AC inhibition on the response to cisplatin-based chemotherapy for HNC.

METHODS

AC protein and messenger RNA (mRNA) expression were examined in primary tumours and paired normal tissues, and in HNC cell lines. The effects of genetic and pharmacological AC inhibition using small hairpin RNA (shRNA) and N-oleoyl-ethanolamine (NOE), alone and in combination with cisplatin, were assessed in human HNC cells by measuring cell viability, cell cycle progression, apoptosis, mRNA, and protein expression, and in preclinical tumour xenograft mouse models.

FINDINGS

AC overexpression was observed in four of six primary tumour tissues and six of nine HNC cell lines. Cisplatin sensitivity was significantly decreased by AC overexpression and significantly increased by AC downregulation in HNC cells (P<0.01). NOE or AC shRNA-mediated AC inhibition enhanced cisplatin-induced HNC cell death by increasing ceramide production and activating pro-apoptotic proteins, and these effects were abrogated by PUMA small interfering RNA transfection. AC inhibition promoted cisplatin-induced apoptosis of HNC cells in vitro and in vivo.

INTERPRETATIONS

AC overexpression is associated with cisplatin sensitivity, suggesting its potential role as a chemotherapeutic target for HNC. Genetic or pharmacological AC inhibition promotes cisplatin cytotoxicity in HNC cells.

Efficient nonviral gene therapy with FasL and Del1 fragments in mice

BACKGROUND

The expression of FasL in cancer cells is currently being explored as a potential cancer therapy. Because high levels of FasL are necessary for effective treatment, current methods typically rely on the use of highly efficient viral vectors. However, because viral vector-based gene therapy is associated with certain risks, the development of effective nonviral routes for gene delivery would be useful. The present study aimed to improve FasL gene therapy with a nonviral vector by taking advantage of the E3 and C1 domains of Del1 protein, which induces apoptosis and localizes to the extracellular matrix.

METHODS

Mouse explanted tumors derived from a human oral squamous cell carcinoma cell line, SCCKN, were treated with plasmids encoding FasL (pFasL), E3C1 (pE3C1), and a fusion of FasL and E3C1 (pFasL-E3C1). The plasmids were injected locally every 7 days along with a transfection reagent, Jet-PEI (PolyPlus-transfection, San Marcos, CA, USA).

RESULTS

All mice treated with a negative control plasmid or pFasL died within 49 days. By contrast, 83% of mice treated with pFasL-E3C1 survived longer than 49 days. Histochemical studies revealed that the fusion protein is localized to the stroma and induces apoptosis in stromal cells and adjacent parenchymal cells.

CONCLUSIONS

The results obtained in the present study suggest that the protein deposition-based approach described, which makes use of the E3 and C1 domains of Del1, could comprise a novel method for cancer gene therapy with nonviral vectors.

Functional polymorphisms in FAS and FASL contribute to risk of squamous cell carcinoma of the larynx and hypopharynx in a Chinese population

Accumulating evidences indicate that the functional FAS-1377G>A, -670A>G and FASL-844T>C polymorphisms affect the risk of several kinds of cancers. However, their roles in the development of larynx and hypopharynx squamous cell carcinoma (SCC) were still unknown in the Chinese. In the current study, we examined whether these functional genetic variants were associated with the risk of larynx and hypopharynx squamous SCC in a Han Chinese population. The FAS and FASL polymorphisms were genotyped in 300 patients with laryngeal and hypopharyngeal SCC and 300 control subjects by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). Logistic regression analysis revealed that subjects carrying the FASL-844CT or TT genotype had a significantly decreased risk of developing laryngeal and hypopharyngeal SCC [odds ratio (OR)=0.69; 95% confidence interval (CI)=0.51-0.93; P=0.016; or, OR=0.41; 95% CI=0.20-0.86; P=0.009] compared with those carrying the CC genotype. Joint gene-smoking and gene-drinking effects were also observed, with the OR of CC genotype for smokers or drinkers were 5.15 (95%CI=3.24-8.97) or 12.52 (95%CI=7.31-22.47), respectively. Therefore, the FASL-844T>C polymorphism is associated with genetic susceptibility of developing laryngeal and hypopharyngeal SCC in a Han Chinese population.

A novel dual signaling axis for NSP 5a3a induced apoptosis in head and neck carcinoma

NSP 5a3a is a novel structural protein found to be over-expressed in certain cancer cell lines in-vitro such as Hela, Saos-2, and MCF-7 while barely detectable levels in normal body tissues except for Testis. This particular isoform has been known to interact with cyto- nuclear proteins B23, known to be involved in multi-faceted cellular processes such as cell division, apoptosis, ribosome biogenesis, and rRNA processing, as well as with hnRNP-L, known to be involved with RNA metabolism and rRNA processing. A previous preliminary investigation of NSP 5a3a as a potential target in Head and Neck Carcinoma revealed a novel p73 dependent mechanism through which NSP 5a3a induced apoptosis in Head and Neck cell lines when over-expressed in-vitro. Our present investigation further elucidated a novel dual axis signaling point by which NSP 5a3a induces apoptosis in Head and Neck cell line HN30 through p73-DAXX and TRAF2-TRADD. Interestingly, this novel mechanism appears independent of canonical caspases involved in the intrinsic mitochondrial pathway as well as those in the death receptor pathway thru TRAF2 and TRADD.

Efficient growth suppression and apoptosis in human laryngeal carcinoma cell line HEP-2 induced by an adeno-associated virus expressing human FAS ligand

BACKGROUND

Apoptosis induced by Fas/FasL system has been proposed as a gene therapy methold for various cancers.

METHODS

We used adeno-associated virus-expressing enhanced green fluorescent protein (EGFP)-human FasL (AAV-EGFP-hFasL) to deliver FasL into Hep-2 cells, cytotoxicity was detected by MTS assay , apoptosis was confirmed by flow cytometry. We also treated the xenograft of Hep-2 tumor in nude mice with intratumoral injection of AAV-EGFP-hFasL. The size of the xenograft, the apoptosis in the xenograft, and the survival rate of the inoculated mice were then evaluated.

RESULTS

Hep-2 cells infected with AAV-EGFP-hFasL showed increased apoptosis rate and killing effect compared with AAV-EGFP-infected cells. In addition intratumoral injections of AAV-EGFP-hFasL into Hep-2 xenografts induced significant growth suppression of tumors.

CONCLUSION

Our findings suggest that the introduction of FasL into head and neck squamous cell carcinoma may induce significant apoptosis, and adeno-associated virus may be a useful vehicle for gene therapy.

Potential for modulation of the fas apoptotic pathway by epidermal growth factor in sarcomas

One important mechanism by which cancer cells parasitize their host is by escaping apoptosis. Thus, selectively facilitating apoptosis is a therapeutic mechanism by which oncotherapy may prove highly advantageous. One major apoptotic pathway is mediated by Fas ligand (FasL). The death-inducing signaling Ccmplex (DISC) and subsequent death-domain aggregations are created when FasL is bound by its receptor thereby enabling programmed cell death. Conceptually, if a better understanding of the Fas pathway can be garnered, an oncoselective prodeath therapeutic approach can be tailored. Herein, we propose that EGF and CTGF play essential roles in the regulation of the Fas apoptotic pathway in sarcomas. Tumor and in vitro data suggest viable cells counter the prodeath signal induced by FasL by activating EGF, which in turn induces prosurvival CTGF. The prosurvival attributes of CTGF ultimately predominate over the death-inducing FasL. Cells destined for elimination inhibit this prosurvival response via a presently undefined pathway. This scenario represents a novel role for EGF and CTGF as regulators of the Fas pathway in sarcomas.

Fas ligand gene transfer effectively induces apoptosis in head and neck cancer cells

CONCLUSION

Fas ligand (FasL) gene therapy may provide a new efficient therapeutic model for head and neck squamous cell cancer (HNSCC). Acid ceramidase (AC) may not play an important role in the sensitivity of HNSCC cell lines to Fas-induced apoptosis.

OBJECTIVES

The aims of this study were to investigate the efficacy of FasL gene therapy for HNSCC in vitro and to determine whether the expression of AC in different kinds of HNSCC cell lines is related to the sensitivity of HNSCC cell lines to Fas-mediated apoptotic induction.

METHODS

Three HNSCC cell lines (Hep-2, MMSI, and SCCVII) were transfected with pEGFP-FasL, a plasmid containing a modified human FasL gene fused to enhanced green fluorescent protein (GFP). pEGFP-C1, a plasmid containing the GFP gene alone, was used as a control. Cell death was observed by fluorescence imaging and quantified using a tetrazolium-based (MTS) assay. SCCVII cells were analyzed by flow cytometry to determine the presence of apoptotic induction. Hep-2 and MMSI cells were evaluated by quantitative real-time PCR to evaluate the expression of AC.

RESULTS

Transfection of pEGFP-FasL plasmid was shown to be able to induce cell death, the sensitivity of Fas-mediated apoptosis in HNSCC was different, and the level of AC did not correlate with the sensitivity of HNSCC cells to Fas-induced apoptosis.

Targeting Fas in osteoresorptive disorders

IMPORTANCE OF THE FIELD

Fas receptor is a mediator of the external apoptotic pathway in many cells and tissues. It is proposed that Fas receptor mediates osteoresorptive effects of estrogen deficiency and local/systemic inflammation.

AREAS COVERED IN THIS REVIEW

This review covers the past two decades of research on the expression and function of the Fas-Fas ligand system on bone cells, involvement in the pathogenesis of osteoresorption and potential therapeutic modulation.

WHAT THE READER WILL GAIN

We review the structure, biological function and intracellular signaling pathways of the Fas-Fas ligand system emphasizing the role of the non-apoptotic signaling pathways in bone cells, particularly osteoblast differentiation. We also present data on the in vitro expression and function of the Fas-Fas ligand system on osteoblast/osteoclast lineage cells, animal and human studies confirming its involvement in osteoresorptive disorders and potential therapeutic approaches to modulate its function.

TAKE HOME MESSAGE

Tissue specific therapeutic approaches need to be established to modify the Fas-Fas ligand system in osteoresorptive disorders as systemic targeting has many side effects. The most promising approach would be to target Fas signaling molecules coupled with osteoblast/osteoclast differentiation pathways, but a precise definition of these targets is still needed.

Survival signalling and apoptosis resistance in glioblastomas: opportunities for targeted therapeutics

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults and one of the most aggressive cancers in man. Despite technological advances in surgical management, combined regimens of radiotherapy with new generation chemotherapy, the median survival for these patients is 14.6 months. This is largely due to a highly deregulated tumour genome with opportunistic deletion of tumour suppressor genes, amplification and/or mutational hyper-activation of receptor tyrosine kinase receptors. The net result of these genetic changes is augmented survival pathways and systematic defects in the apoptosis signalling machinery. The only randomised, controlled phase II trial conducted targeting the epidermal growth factor receptor (EGFR) signalling with the small molecule inhibitor, erlotinib, has showed no therapeutic benefit. Survival signalling and apoptosis resistance in GBMs can be viewed as two sides of the same coin. Targeting increased survival is unlikely to be efficacious without at the same time targeting apoptosis resistance. We have critically reviewed the literature regarding survival and apoptosis signalling in GBM, and highlighted experimental, preclinical and recent clinical trials attempting to target these pathways. Combined therapies simultaneously targeting apoptosis and survival signalling defects might shift the balance from tumour growth stasis to cytotoxic therapeutic responses that might be associated with greater therapeutic benefits.

Role of CXC chemokine ligand 13 in oral squamous cell carcinoma associated osteolysis in athymic mice

Oral squamous cell carcinomas (OSCC) are malignant tumors with a potent activity of local bone invasion; however, the molecular mechanisms of tumor osteolysis are unclear. In this study, we identified high level expression of chemokine ligand, CXCL13 and RANK ligand (RANKL) in OSCC cells (SCC1, SCC12 and SCC14a). OSCC cell-conditioned media (20%) induced osteoclast differentiation which was inhibited by OPG in peripheral blood monocyte cultures indicating that OSCC cells produce soluble RANKL. Recombinant hCXCL13 (10 ng/ml) significantly enhanced RANKL-stimulated osteoclast differentiation in these cultures. Trans-well migration assay identified that CXCL13 induces chemotaxis of peripheral blood monocytes in vitro which was inhibited by addition of anti-CXCR5 receptor antibody. Zymogram analysis of conditioned media from OSCC cells revealed matrix metalloproteinase-9 (MMP-9) activity. Interestingly, CXCL13 treatment to OSCC cells induced CXCR5 and MMP-9 expression suggesting an autocrine regulatory function in OSCC cells. To examine the OSCC tumor cell bone invasion/osteolysis, we established an in vivo model for OSCC by subcutaneous injection of OSCC cells onto the surface of calvaria in NCr-nu/nu athymic mice, which developed tumors in 4-5 weeks. muCT analysis revealed numerous osteolytic lesions in calvaria from OSCC tumor-bearing mice. Histochemical staining of calvarial sections from these mice revealed a significant increase in the numbers of TRAP-positive osteoclasts at the tumor-bone interface. Immunohistochemical analysis confirmed CXCL13 and MMP-9 expression in tumor cells. Thus, our data implicate a functional role for CXCL13 in bone invasion and may be a potential therapeutic target to prevent osteolysis associated with OSCC tumors in vivo.

Mononuclear phagocytes in head and neck squamous cell carcinoma

The head and neck squamous cell carcinoma microenvironments contain many immune cells and their secretory products. Many of these cells belong to the mononuclear phagocyte system. The aim of this review is to study the interactions between mononuclear phagocytes and head and neck squamous cell carcinoma tissue. The role of inflammation in tumours and the cytokine interleukin-6 will be highlighted. Future therapy strategies in the treatment of head and neck cancer might be directed towards mononuclear phagocytes and their cytokine production.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

The Del1 deposition domain can immobilize 3alpha-hydroxysteroid dehydrogenase in the extracellular matrix without interfering with enzymatic activity

Developing methods that result in targeting of therapeutic molecules in gene therapies to target tissues has importance, as targeting can increase efficacy and decrease off target-side-effects. Work from my laboratory previously showed that the extracellular matrix protein Del1 is organized in the extracellular matrix (ECM) via the Del1 deposition domain (DDD). In this work, a fusion protein with DDD was made to assay the ability to immobilize an enzyme without disrupting enzymatic function. A prostatic cancer-derived cell line LNCap that grows in an androgen-dependent manner was used with 3α-hydroxysteroid dehydrogenase (3 αHD), which catalyzes dihydrotestosterone (DHT). Plasmids encoding a 3αHD:DDD fusion were generated and transfected into cultured cells. The effects of 3αHD immobilized in the ECM by the DDD were evaluated by monitoring growth of LNCap cells and DHT concentrations. It was demonstrated that the DDD could immobilize an enzyme in the ECM without interfering with function.

Identifying fragilities in biochemical networks: robust performance analysis of Fas signaling-induced apoptosis

Proper control of apoptotic signaling is critical to immune response and development in multicellular organisms. Two tools from control engineering are applied to a mathematical model of Fas ligand signaling-induced apoptosis. Structured singular value analysis determines the volume in parameter space within which the system parameters may exist and still maintain efficacious signaling, but is limited to linear behaviors. Sensitivity analysis can be applied to nonlinear systems but is difficult to relate to performance criteria. Thus, structured singular value analysis is used to quantify performance during apoptosis rejection, ensuring that the system remains sensitive but not overly so to apoptotic stimuli. Sensitivity analysis is applied when the system has switched to the death-inducing, apoptotic steady state to determine parameters significant to maintaining the bistability. The analyses reveal that the magnitude of the death signal is fragile to perturbations in degradation parameters (failures in the ubiquitin/proteasome mechanism) while the timing of signal expression can be tuned by manipulating local parameters. Simultaneous parameter uncertainty highlights apoptotic fragility to disturbances in the ubiquitin/proteasome system. Sensitivity analysis reveals that the robust signaling characteristics of the apoptotic network is due to network architecture, and the apoptotic signaling threshold is best manipulated by interactions upstream of the apoptosome.

Soluble factors released by activated cytotoxic T lymphocytes interfere with death receptor pathways in neuroblastoma

Neuroblastoma (NB) is often described as an unfavorable target for both HLA-restricted and death receptor-mediated elimination by cytotoxic T lymphocytes (CTLs) due to low or absent HLA class I and caspase-8 expression. We investigated the effects of soluble factors released by CTLs activated by TCR triggering (named as activated supernatant; AS) on the levels and composition of cell surface molecules involved in HLA-restricted and HLA-independent NB cell recognition (surface immune phenotype). Using a panel of long-term propagated NB cell lines and freshly isolated primary human NB cells, we analyzed surface expression of the (1) cognate receptors for TNFalpha, Fas and TRAIL; (2) HLA class I and II heterodimers; (3) adhesion molecules; (4) the intracellular expression and activation of caspase-8, as well as (5) the susceptibility of NB cells to death receptor-mediated killing prior to and after exposure to AS. The exposure of NB cells to soluble factors released by activated CTLs skewed the surface immune phenotype of both long term cultured and primary NB cells, induced the expression and activation of caspase-8 and increased the susceptibility of tumor cells to lysis by TRAIL and Fas-agonistic antibody. Blocking experiments identified IFNgamma and TNFalpha as main factors responsible for modulating the surface antigens of NB cells by AS. Our data suggest that recruitment of CTLs activated on third party targets into the vicinity of the NB tumor mass, may override the "silent" immune phenotype of NB cells via the action of soluble factors.

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.

Multifaceted targeting in cancer: the recent cell death players meet the usual oncogene suspects

Recent complicated advances towards the blueprinting of the altered molecular networks that lie behind cancer development have paved the way for targeted therapy in cancer. This directed a significant part of the research community to the development of specialized targeted agents, many of which are already available or in clinical trials. The prospect of patient-tailored therapeutic strategies, although very close to becoming a reality also raises the level of complexity of the therapeutic approach. This review summarizes the functions, in vivo expression patterns and aberrations of factors presently targeted or representing potential targets by therapeutic agents, focusing on those implicated in death receptor-induced apoptosis. The authors overview the regulation of these factors and death receptor-induced apoptosis by classical oncogenes (e.g., RAS, MYC, HER2) and their effectors/regulators, most of which are also being targeted. In addition, the importance of orthologic systemic approaches in future patient-tailored therapies are discussed.

Role of acid ceramidase in resistance to FasL: therapeutic approaches based on acid ceramidase inhibitors and FasL gene therapy

Head and neck squamous cell cancers (HNSCC) are particularly aggressive and are resistant to many forms of treatment. Ceramide metabolism has been shown to play an important role in cancer progression and cancer resistance to therapy in many tumor models, including HNSCC. Here, we study the role of the ceramide-metabolizing enzyme acid ceramidase (AC) in therapeutic responses in HNSCC. First, we show that AC is over-expressed in 70% of head and neck squamous cell tumors compared with normal tissues, suggesting that this enzyme may play an important role in facilitating HNSCC growth. Next, comparison of three HNSCC cell lines with low, medium, and high levels of AC reveals an inverse correlation between the levels of AC and their response to exogenous C-6-ceramide. Furthermore, over-expression of AC in SCC-1 cells increased resistance to Fas-induced cell killing. Conversely, down-regulation of AC using specific AC small interfering RNA (siRNA) sensitized the SCC-1 cancer cell line to Fas-induced apoptosis. Finally, we show that the AC inhibitor LCL 204 can sensitize HNSCC cell lines to Fas-induced apoptosis both in vitro and in a xenograft model in vivo, suggesting that the combination of FasL gene therapy and LCL 204 may become a new treatment option for advanced-stage head and neck cancer.

Combined therapeutic use of AdGFPFasL and small molecule inhibitors of ceramide metabolism in prostate and head and neck cancers: a status report

As of January 2005, there were 1020 gene therapy clinical trials ongoing worldwide with 675 or 66.2% devoted to cancer gene therapy. The majority are occurring in the US and Europe (http://www.wiley.co.uk/genetherapy/clinical/). At the present time, to our knowledge there are no trials that employ gene delivery of Fas Ligand (FasL). As an important note, and in contrast to somatic cell therapy trials, there are no reported deaths due to therapeutic vector administration in any cancer gene therapy trial. That said, from our studies and from the published literature, the issue of gene delivery remains the major obstacle to successfully employing gene therapy for cancer treatment. Numerous laboratories are studying this with many different approaches. My co-workers and I have focused on the delivery issue by using various approaches that address tumor targeting and transgene expression. In addition, we are focusing on enhancing tumor cell killing via the bystander effect and through use of small molecules to enhance bystander activity.