Inhibition of acid ceramidase regulates MHC class II antigen presentation and suppression of autoimmune arthritis

The bioactive sphingolipid ceramide affects immune responses although its effect on antigen (Ag) processing and delivery by HLA class II to CD4+T-cells remains unclear. Therefore, we examined the actions of a novel cell-permeable acid ceramidase (AC) inhibitor [(1R,2R) N myristoylamino-(4'-nitrophenyl)-propandiol-1,3] on antigen presentation and inflammatory cytokine production by Ag-presenting cells (APCs) such as B-cells, macrophages, and dendritic cells. We found that AC inhibition in APCs perturbed Ag-processing and presentation via HLA-DR4 (MHC class II) proteins as measured by coculture assay and T-cell production of IL-2. Mass spectral analyses showed that B13 treatment significantly raised levels of four types of ceramides in human B-cells. B13 treatment did not alter Ag internalization and class II protein expression, but significantly inhibited lysosomal cysteinyl cathepsins (B, S and L) and thiol-reductase (GILT), HLA class II Ag-processing, and generation of functional class II-peptide complexes. Ex vivo Ag presentation assays showed that inhibition of AC impaired primary and recall CD4+T-cell responses and cytokine production in response against type II collagen. Further, B13 delayed onset and reduced severity of inflamed joints and cytokine production in the collagen-induced arthritis mouse model in vivo. These findings suggest that inhibition of AC in APCs may dysregulate endolysosomal proteases and HLA class II-associated self-antigen presentation to CD4+T-cells, attenuating inflammatory cytokine production and suppressing host autoimmune responses.

Tamoxifen is a candidate first-in-class inhibitor of acid ceramidase that reduces amitotic division in polyploid giant cancer cells-Unrecognized players in tumorigenesis

Polyploid giant cancer cells (PGCC) represent a poorly understood, small subpopulation of tumor cells that are increasingly being recognized for their critical role in therapy resistance, metastasis, and cancer recurrence. PGCC have the potential to generate progeny through primitive or cleavage-like division, which allows them to evade antimitotic insults. We recently demonstrated that the sphingolipid enzyme acid ceramidase (ASAH1) is required for this process. Since specific ASAH1 inhibitors are not clinically available, we investigated whether tamoxifen, which interferes with ASAH1 function via off-target effects, has a potential clinical benefit independent of estrogen signaling. Our results show that tamoxifen inhibits generation of PGCC offspring in prostate cancer, glioblastoma, and melanoma cells. Analysis of two state-level cancer registries revealed that tamoxifen improves survival outcomes for second, nonbreast cancers that develop in women with early stage breast cancer. Our results suggest that tamoxifen may have a clinical benefit in a variety of cancers that is independent of estrogen signaling and could be due to its inhibition of acid ceramidase. Thus the distinct application of tamoxifen as potentially a first-in-class therapeutic that inhibits the generation of PGCC offspring should be considered in future clinical trials.

Genetic and pharmacological inhibition of acid ceramidase prevents asymmetric cell division by neosis

Radiation treatment failure or relapse after initial response to chemotherapy presents significant clinical challenges in cancer patients. Escape from initial courses of treatment can involve reactivation of embryonic developmental stages, with the formation of polynuclear giant cancer cells (PGCCs). This strategy of dedifferentiation can insulate cancer cells from a variety of treatments and allows a residual subpopulation to reestablish tumors after treatment. Using radiation or docetaxel chemotherapy, we generated PGCCs from prostate cancer cells. Here, we show that expression of acid ceramidase (ASAH1), an enzyme in the sphingolipid pathway linked to therapy resistance and poor outcomes, is elevated in PGCCs. Targeting ASAH1 with shRNA or treatment with the ASAH1 inhibitor, LCL-521, did not impair the formation of PGCCs, but prevented the formation of PGCC progeny that arise through an asymmetric cell division called neosis. Similar results were obtained in lung cancer cells that had been exposed to radiation or cisplatin chemotherapy as stressors. In summary, our data suggest that endoreplication occurs independent of ASAH1 while neosis is ASAH1-dependent in both prostate and lung cancer cells. Because ASAH1 knockout is embryonic lethal but not deleterious to adult animals, targeting this enzyme has the potential to be highly specific to cells undergoing the dedifferentiation process to escape cancer treatments. Pharmacological inhibition of ASAH1 is a potentially powerful strategy to eliminate cells that could otherwise serve as seed populations for recurrence.

Abstract A070: Targeting N-myristoyltransferase 1 inhibits prostate cancer progression

N-myristoyltransferase (NMT) facilitates co/post-translational myristoylation of several oncogenic proteins, regulating their functions in tumor progression. N-myristoyltransferase (NMT), which has been shown to be upregulated in a variety of cancers, is overexpressed in androgen-independent prostate cancer cells. We demonstrate that genetically, ablation of NMT1 inhibited proliferation of prostate cancer cells, tumor growth, and suppressed myristoylation profile of prostate cancer cells. Screening a panel of myristoyl-CoA analogs against purified human NMT1 protein leads to identifying the B13 as an inhibitor for NMT1. B13 significantly suppressed prostate cancer cell proliferation, migration, and invasion by cell cycle arrest, and inhibited the growth of prostate xenograft tumors with minimal pathologic effect on major organs in vivo. Structure activity relationship based optimization of B13 led to LCL204, which showed better inhibitory properties towards NMT1. We demonstrate that targeting protein myristoylation is a potential therapeutic approach to inhibit prostate tumor progression.

Citation Format: Omar Alsaidan, Sungjin Kim, Octavia Goodwin, Qianjin Li, Aiping Bai, Alicja Bielawska, George Zheng, Iryna Lebedyeva, Thomas Albers, James S. Norris, Scott D. Pegan, Houjian Cai. Targeting N-myristoyltransferase 1 inhibits prostate cancer progression [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A070.

Interdiction of Sphingolipid Metabolism Revisited: Focus on Prostate Cancer

Sphingolipid metabolism is known to play a role in cell death, survival, and therapy resistance in cancer. Sphingolipids, particularly dihydroceramide and ceramide, are associated with antiproliferative or cell death responses, respectively, and are central to effective cancer therapy. Within the last decade, strides have been made in elucidating many intricacies of sphingolipid metabolism. New information has emerged on the mechanisms by which sphingolipid metabolism is dysregulated during malignancy and how cancer cells survive and/or escape therapeutic interventions. This chapter focuses on three main themes: (1) sphingolipid enzymes that are dysregulated in cancer, particularly in prostate cancer; (2) inhibitors of sphingolipid metabolism that antagonize prosurvival responses; and (3) sphingolipid-driven escape mechanisms that allow cancer cells to evade therapies. We explore clinical and preclinical approaches to interdict sphingolipid metabolism and provide a rationale for combining strategies to drive the generation of antiproliferative ceramides with prevention of ceramide clearance.

Blocking Myristoylation of Src Inhibits Its Kinase Activity and Suppresses Prostate Cancer Progression

Protein N-myristoylation enables localization to membranes and helps maintain protein conformation and function. N-myristoyltransferases (NMT) catalyze co- or posttranslational myristoylation of Src family kinases and other oncogenic proteins, thereby regulating their function. In this study, we provide genetic and pharmacologic evidence that inhibiting the N-myristoyltransferase NMT1 suppresses cell-cycle progression, proliferation, and malignant growth of prostate cancer cells. Loss of myristoylation abolished the tumorigenic potential of Src and its synergy with androgen receptor in mediating tumor invasion. We identified the myristoyl-CoA analogue B13 as a small-molecule inhibitor of NMT1 enzymatic activity. B13 exposure blocked Src myristoylation and Src localization to the cytoplasmic membrane, attenuating Src-mediated oncogenic signaling. B13 exerted its anti-invasive and antitumor effects against prostate cancer cells, with minimal toxic side-effects in vivo Structural optimization based on structure-activity relationships enabled the chemical synthesis of LCL204, with enhanced inhibitory potency against NMT1. Collectively, our results offer a preclinical proof of concept for the use of protein myristoylation inhibitors as a strategy to block prostate cancer progression. Cancer Res; 77(24); 6950-62. ©2017 AACR.

Acid Ceramidase Deficiency is characterized by a unique plasma cytokine and ceramide profile that is altered by therapy

Acid Ceramidase Deficiency (Farber disease, FD) is an ultra-rare Lysosomal Storage Disorder that is poorly understood and often misdiagnosed as Juvenile Idiopathic Arthritis (JIA). Hallmarks of FD are accumulation of ceramides, widespread macrophage infiltration, splenomegaly, and lymphocytosis. The cytokines involved in this abnormal hematopoietic state are unknown. There are dozens of ceramide species and derivatives, but the specific ones that accumulate in FD have not been investigated. We used a multiplex assay to analyze cytokines and mass spectrometry to analyze ceramides in plasma from patients and mice with FD, controls, Farber patients treated by hematopoietic stem cell transplantation (HSCT), JIA patients, and patients with Gaucher disease. KC, MIP-1α, and MCP-1 were sequentially upregulated in plasma from FD mice. MCP-1, IL-10, IL-6, IL-12, and VEGF levels were elevated in plasma from Farber patients but not in control or JIA patients. C16-Ceramide (C16-Cer) and dhC16-Cer were upregulated in plasma from FD mice. a-OH-C18-Cer, dhC12-Cer, dhC24:1-Cer, and C22:1-Cer-1P accumulated in plasma from patients with FD. Most cytokines and only a-OH-C18-Cer returned to baseline levels in HSCT-treated Farber patients. Sphingosines were not altered. Chitotriosidase activity was also relatively low. A unique cytokine and ceramide profile was seen in the plasma of Farber patients that was not observed in plasma from HSCT-treated Farber patients, JIA patients, or Gaucher patients. The cytokine profile can potentially be used to prevent misdiagnosis of Farber as JIA and to monitor the response to treatment. Further understanding of why these signaling molecules and lipids are elevated can lead to better understanding of the etiology and pathophysiology of FD and inform development of future treatments.

The functional effects of acid ceramidase over-expression in prostate cancer progression and resistance to chemotherapy

Among the many processes regulating cell death, ceramide signaling is a vital component. We previously determined that acid ceramidase (AC) is upregulated in 60% of primary prostate cancer (PCa) tissues, suggesting that AC may play a role in tumor development. In order to determine the significance of AC elevation, stable clones of DU145 cells with AC overexpression (AC-EGFP) were generated. Compared to controls (EGFP), AC-EGFP cells exhibited enhanced cell proliferation and migration. Subcutaneous injection of AC-EGFP cells into Nu/Nu mice resulted in larger tumor volumes compared to EGFP controls. Moreover, using the MTS viability assay, AC-EGFP cells were more resistant to cell death induced by doxorubicin, cisplatin, etoposide, gemcitabine or C6-ceramide. Conversely, knock down of AC using siRNA, sensitized AC-EGFP cells to these drugs. In addition, mass spectroscopic analysis of sphingolipids indicated that long chain ceramide levels were decreased in AC-EGFP cells treated with either doxorubicin or etoposide. In conclusion, this study implicates AC as a critical regulator of PCa progression by affecting not only tumor cell proliferation and migration but also responses to drug therapy, suggesting AC as a potential therapeutic target in advanced PCa.

CD95 Rapidly Clusters in Cells of Diverse Origins

We have shown that CD95-mediated cell death requires a clustering of the receptor in distinct sphingolipid-rich domains of the cell membrane (Grassme et al., 2000, Cremesti et al., 2000). These domains form in response to acid sphingomyelinase (ASM)-induced ceramide generation. However, recent studies challenged the finding of early CD95 clustering (Algeciras-Schimnich et al., 2002). Here, six independent groups tested clustering of CD95 in diverse cell type including primary cells ex vivo and established cell lines. The studies show clustering of CD95 within seconds to minutes in all cell types tested by the different groups. In addition, clustering of CD95 was detected after stimulation of cells using three agonistic anti-CD95 antibodies (CH11, APO-1-3 and JO2), CD95 ligand and stimuli that induce an upregulation and activation of the endogenous CD95/CD95 ligand system. The data confirm our previous studies and suggest rapid, i.e., within seconds to minutes, CD95 clustering as a general phenomenon occurring in many cell types.

Acid ceramidase promotes nuclear export of PTEN through sphingosine 1-phosphate mediated Akt signaling

The tumor suppressor PTEN is now understood to regulate cellular processes at the cytoplasmic membrane, where it classically regulates PI3K signaling, as well as in the nucleus where multiple roles in controlling cell cycle and genome stability have been elucidated. Mechanisms that dictate nuclear import and, less extensively, nuclear export of PTEN have been described, however the relevance of these processes in disease states, particularly cancer, remain largely unknown. We investigated the impact of acid ceramidase on the nuclear-cytoplasmic trafficking of PTEN. Immunohistochemical analysis of a human prostate tissue microarray revealed that nuclear PTEN was lost in patients whose tumors had elevated acid ceramidase. We found that acid ceramidase promotes a reduction in nuclear PTEN that is dependent upon sphingosine 1-phosphate-mediated activation of Akt. We were further able to show that sphingosine 1-phosphate promotes formation of a complex between Crm1 and PTEN, and that leptomycin B prevents acid ceramidase and sphingosine 1-phosphate mediated loss of nuclear PTEN, suggesting an active exportin-mediated event. To investigate whether the tumor promoting aspects of acid ceramidase in prostate cancer depend upon its ability to export PTEN from the nucleus, we used enforced nuclear expression of PTEN to study docetaxel-induced apoptosis and cell killing, proliferation, and xenoengraftment. Interestingly, while acid ceramidase was able to protect cells expressing wild type PTEN from docetaxel, promote proliferation and xenoengraftment, acid ceramidase had no impact in cells expressing PTEN-NLS. These findings suggest that acid ceramidase, through sphingosine 1-phosphate, promotes nuclear export of PTEN as a means of promoting tumor formation, cell proliferation, and resistance to therapy.

Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse

Escape of prostate cancer (PCa) cells from ionizing radiation-induced (IR-induced) killing leads to disease progression and cancer relapse. The influence of sphingolipids, such as ceramide and its metabolite sphingosine 1-phosphate, on signal transduction pathways under cell stress is important to survival adaptation responses. In this study, we demonstrate that ceramide-deacylating enzyme acid ceramidase (AC) was preferentially upregulated in irradiated PCa cells. Radiation-induced AC gene transactivation by activator protein 1 (AP-1) binding on the proximal promoter was sensitive to inhibition of de novo ceramide biosynthesis, as demonstrated by promoter reporter and ChIP-qPCR analyses. Our data indicate that a protective feedback mechanism mitigates the apoptotic effect of IR-induced ceramide generation. We found that deregulation of c-Jun induced marked radiosensitization in vivo and in vitro, which was rescued by ectopic AC overexpression. AC overexpression in PCa clonogens that survived a fractionated 80-Gy IR course was associated with increased radioresistance and proliferation, suggesting a role for AC in radiotherapy failure and relapse. Immunohistochemical analysis of human PCa tissues revealed higher levels of AC after radiotherapy failure than those in therapy-naive PCa, prostatic intraepithelial neoplasia, or benign tissues. Addition of an AC inhibitor to an animal model of xenograft irradiation produced radiosensitization and prevention of relapse. These data indicate that AC is a potentially tractable target for adjuvant radiotherapy.

LCL124, a cationic analog of ceramide, selectively induces pancreatic cancer cell death by accumulating in mitochondria

Treatment of pancreatic cancer that cannot be surgically resected currently relies on minimally beneficial cytotoxic chemotherapy with gemcitabine. As the fourth leading cause of cancer-related death in the United States with dismal survival statistics, pancreatic cancer demands new and more effective treatment approaches. Resistance to gemcitabine is nearly universal and appears to involve defects in the intrinsic/mitochondrial apoptotic pathway. The bioactive sphingolipid ceramide is a critical mediator of apoptosis initiated by a number of therapeutic modalities. It is noteworthy that insufficient ceramide accumulation has been linked to gemcitabine resistance in multiple cancer types, including pancreatic cancer. Taking advantage of the fact that cancer cells frequently have more negatively charged mitochondria, we investigated a means to circumvent resistance to gemcitabine by targeting delivery of a cationic ceramide (l-t-C6-CCPS [LCL124: ((2S,3S,4E)-2-N-[6'-(1″-pyridinium)-hexanoyl-sphingosine bromide)]) to cancer cell mitochondria. LCL124 was effective in initiating apoptosis by causing mitochondrial depolarization in pancreatic cancer cells but demonstrated significantly less activity against nonmalignant pancreatic ductal epithelial cells. Furthermore, we demonstrate that the mitochondrial membrane potentials of the cancer cells were more negative than nonmalignant cells and that dissipation of this potential abrogated cell killing by LCL124, establishing that the effectiveness of this compound is potential-dependent. LCL124 selectively accumulated in and inhibited the growth of xenografts in vivo, confirming the tumor selectivity and therapeutic potential of cationic ceramides in pancreatic cancer. It is noteworthy that gemcitabine-resistant pancreatic cancer cells became more sensitive to subsequent treatment with LCL124, suggesting that this compound may be a uniquely suited to overcome gemcitabine resistance in pancreatic cancer.

Differential expression of epithelial and mesenchymal proteins in a panel of prostate cancer cell lines

PURPOSE

Epithelial to mesenchymal transition is an important process that results in increased cell migration, invasion and metastasis of many carcinomas. During epithelial to mesenchymal transition epithelial cells down-regulate cell-cell adhesion molecules (ie E-cadherin), up-regulate mesenchymal proteins (ie N-cadherin and cadherin-11), alter polarity, reorganize the cytoskeleton and become isolated. In combination this leads to greater motility. We investigated the role of E-cadherin and the associated catenin-protein complex in regulating epithelial to mesenchymal transition in prostate cancer progression.

MATERIALS AND METHODS

The relative invasion index of prostate cancer cells was assessed by MTT based in vitro invasion assay. Immunoprecipitation and Western blot were done to determine cadherin-complex formation, and catenin and cadherin protein expression.

RESULTS

Restoration of E-cadherin expression in nonE-cadherin expressing prostate cancer cells decreased invasive potential. However, in vitro invasive potential was tightly regulated by the interaction of cadherin proteins with the catenin complex. E and N-cadherin, cadherin-11, and the catenin proteins α, β, γ and p120 are important for the downstream signaling associated with epithelial to mesenchymal transition in tumor cells.

CONCLUSIONS

Restoration of epithelial specific proteins, such as E-cadherin, in tumor cells can inhibit invasion. However, invasion is a complex process regulated not only by E and N-cadherin but also by catenin-complex proteins. The complex signaling process associated with tumor invasion warrants further investigation since crosstalk between overlapping signaling pathways is involved in regulating prostate cancer invasion, metastasis and progression.

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.

Genome characterization of the oleaginous fungus Mortierella alpina

Mortierella alpina is an oleaginous fungus which can produce lipids accounting for up to 50% of its dry weight in the form of triacylglycerols. It is used commercially for the production of arachidonic acid. Using a combination of high throughput sequencing and lipid profiling, we have assembled the M. alpina genome, mapped its lipogenesis pathway and determined its major lipid species. The 38.38 Mb M. alpina genome shows a high degree of gene duplications. Approximately 50% of its 12,796 gene models, and 60% of genes in the predicted lipogenesis pathway, belong to multigene families. Notably, M. alpina has 18 lipase genes, of which 11 contain the class 2 lipase domain and may share a similar function. M. alpina's fatty acid synthase is a single polypeptide containing all of the catalytic domains required for fatty acid synthesis from acetyl-CoA and malonyl-CoA, whereas in many fungi this enzyme is comprised of two polypeptides. Major lipids were profiled to confirm the products predicted in the lipogenesis pathway. M. alpina produces a complex mixture of glycerolipids, glycerophospholipids and sphingolipids. In contrast, only two major sterol lipids, desmosterol and 24(28)-methylene-cholesterol, were detected. Phylogenetic analysis based on genes involved in lipid metabolism suggests that oleaginous fungi may have acquired their lipogenic capacity during evolution after the divergence of Ascomycota, Basidiomycota, Chytridiomycota and Mucoromycota. Our study provides the first draft genome and comprehensive lipid profile for M. alpina, and lays the foundation for possible genetic engineering of M. alpina to produce higher levels and diverse contents of dietary lipids.

Abstract 2497: Induction of AP-1 activity by ceramide results in ASAH1 upregulation: A mechanism of prostate cancer cell radioresistance

Background: Although radiation therapy is a mainstay of treatment for localized prostatic disease, the escape of a subset of tumor cells from ionizing radiation (IR)-induced killing may lead to disease relapse and progression. The metabolic balance between the pro-apoptotic sphingolipid, ceramide, and its anti-apoptotic metabolites has been characterized as a critical mediator of cell death under conditions of cell stress, including IR exposure. While the lysosomal ceramide-metabolizing enzyme, acid ceramidase (ASAH1), is constitutively expressed in all human tissues, ASAH1 has been found to be over-expressed in cancer cells exposed to IR. The goal of this study was to examine the biological impact of and possible mechanism for altered ASAH1 expression observed in irradiated prostate cancer cells. Methods: Sphingolipid expression was measured by LC-MS. Ceramidase activities were assessed by thin layer chromatography. ASAH1 mRNA and protein expression in cell lines were measured by qPCR and western blot, respectively. Transcription activity was assessed using a luciferase reporter driven by the 1.5kb proximal promoter region of ASAH1. AP-1 promoter occupancy was determined by chromatin immunoprecipitation (ChIP)-qPCR. Post-irradiative cell growth was determined by clonogenic survival assay. Results: IR induced nearly two-fold expression of ceramide, and between three- and four-fold expression of its metabolites, sphingosine and sphingosine-1-phosphate. Enzyme activity assays demonstrated specific increase of acid, but not neutral or alkaline, ceramidase in the irradiated prostate cancer cells, suggesting a prominent role for ASAH1 in IR-induced sphingolipid metabolism. Consistent with increased mRNA and protein levels, luciferase-promoter-reporter assay confirmed that ASAH1 regulation occurs at least in part at the transcriptional level. Interestingly, inhibition of de novo and salvage pathways of ceramide biogenesis abrogated IR-induced ASAH1 upregulation, implicating the involvement of ceramide in IR-induced ASAH1 overexpression. Through studies using protein-DNA binding arrays and ChIP-qPCR, we identified AP-1 as a direct, ceramide-sensitive transcription factor of ASAH1 in irradiated cells. Expression of a dominant negative mutant of c-Jun, a central component of the AP-1 complex, was able to abrogate IR-induced ASAH1 overexpression. Since ASAH1 silencing by shRNA sensitized prostate cancer cells to IR-induced cell killing, here we also observed radiosensitization by expression of the c-Jun dominant negative construct, which was rescued in part by forced overexpression of an ASAH1 transgene. Conclusion: The reported studies demonstrate that IR programs an unexpected phenotype of radiation resistance through ASAH1 upregulation mediated by ceramide-sensitive AP-1 activation. This study was supported in part by NIH/NCI P01 CA097132.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2497. doi:10.1158/1538-7445.AM2011-2497

Autophagy is increased in prostate cancer cells overexpressing acid ceramidase and enhances resistance to C6 ceramide

Acid ceramidase (AC) overexpression has been observed in prostate cancer cell lines and primary tumors, and contributes to resistance to chemotherapy and radiation. The consequence of AC overexpression is the ability to convert ceramide, which is often produced as a proapoptotic response to stress, to sphingosine, which can then be converted to the prosurvival molecule sphingosine-1-phosphate. In addition to their ability to metabolize ceramide produced in response to stress, we show here that prostate cancer cell lines overexpressing AC also have increased lysosomal density and increased levels of autophagy. Furthermore, pretreatment with 3-methyladenine restores sensitivity of these cells to treatment with C(6) ceramide. We also observed increased expression of the lysosomal stabilizing protein KIF5B and increased sensitivity to the lysosomotropic agent LCL385. Thus, we conclude that AC overexpression increases autophagy in prostate cancer cells, and that increased autophagy enhances resistance to ceramide.

Targeting sphingolipid metabolism in head and neck cancer: rational therapeutic potentials

IMPORTANCE OF THE FIELD

Ceramide accumulation has been shown to be a conserved mechanism of apoptosis initiation in normal physiological processes as well as in response to cancer treatments. Therefore, it is unsurprising that many cancers develop aberrations of sphingolipid metabolism that prevent the accumulation of ceramide, whether by reduction of ceramide generation or by enhanced ceramide catabolism, particularly dangerous when catabolism leads to generation of pro-tumor sphingosine-1-phosphate and ceramide-1-phosphate. Numerous studies have now implicated dysregulation of sphingolipid metabolism in head and neck cancers.

AREAS COVERED IN THIS REVIEW

This review highlights the importance of sphingolipid metabolism and brings sphingolipid metabolism to the forefront in the investigation of novel therapies for head and neck cancer. It reviews sphingolipid-centric therapies under investigation in preclinical and clinical trials of cancers of the head and neck.

WHAT THE READER WILL GAIN

The roles of sphingolipids and sphingolipid metabolism in cancer are reviewed and the reader will be brought up to date with discoveries in the field of sphingolipid metabolism in head and neck cancer.

TAKE HOME MESSAGE

As treatments for head and neck cancers are currently limited, the potential of targeting sphingolipid metabolism should be taken into consideration as we seek novel ways to combat this group of tumors.

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.

Ceramide plays a prominent role in MDA-7/IL-24-induced cancer-specific apoptosis

Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) uniquely displays broad cancer-specific apoptosis-inducing activity through induction of endoplasmic reticulum (ER) stress. We hypothesize that ceramide, a promoter of apoptosis, might contribute to mda-7/IL-24 induction of apoptosis. Ad.mda-7-infected tumor cells, but not normal cells, showed increased ceramide accumulation. Infection with Ad.mda-7 induced a marked increase in various ceramides (C16, C24, C24:1) selectively in prostate cancer cells. Inhibiting the enzyme serine palmitoyltransferase (SPT) using the potent SPT inhibitor myriocin (ISP1), impaired mda-7/IL-24-induced apoptosis and ceramide production, suggesting that ceramide formation caused by Ad.mda-7 occurs through de novo synthesis of ceramide and that ceramide is required for mda-7/IL-24-induced cell death. Fumonisin B1 (FB1) elevated ceramide formation as well as apoptosis induced by Ad.mda-7, suggesting that ceramide formation may also occur through the salvage pathway. Additionally, Ad.mda-7 infection enhanced expression of acid sphingomyelinase (ASMase) with a concomitant increase in ASMase activity and decreased sphingomyelin in cancer cells. ASMase silencing by RNA interference inhibited the decreased cell viability and ceramide formation after Ad.mda-7 infection. Ad.mda-7 activated protein phosphatase 2A (PP2A) and promoted dephosphorylation of the anti-apoptotic molecule BCL-2, a downstream ceramide-mediated pathway of mda-7/IL-24 action. Pretreatment of cells with FB1 or ISP-1 abolished the induction of ER stress markers (BiP/GRP78, GADD153 and pospho-eIF2alpha) triggered by Ad.mda-7 infection indicating that ceramide mediates ER stress induction by Ad.mda-7. Additionally, recombinant MDA-7/IL-24 protein induced cancer-specific production of ceramide. These studies define ceramide as a key mediator of an ER stress pathway that may underlie mda-7/IL-24 induction of cancer-specific killing.

Acid ceramidase upregulation in prostate cancer: role in tumor development and implications for therapy

Bioactive sphingolipids, such as ceramide, sphingosine and sphingosine-1-phosphate are known bio-effector molecules which play important roles in various aspects of cancer biology including cell proliferation, growth arrest, apoptosis, metastasis, senescence and inflammation. Therefore, enzymes involved in ceramide metabolism are gaining recognition as being critical regulators of cancer cell growth and/or survival. We previously observed that the ceramide metabolizing enzyme, acid ceramidase (AC) is upregulated in tumor tissues. Studies have now concluded that this creates a dysfunctional ceramide pathway, which is responsible for tumor progression and resistance to chemotherapy and radiation. This suggests that development of small-molecule drugs that inhibit AC enzyme activity is a promising approach for improving standard cancer therapy and patient's clinical outcomes.

Angiography postclipping and coiling of cerebral aneurysms

Postclipping cerebral angiography is generally not practised in the UK. The International Subarachnoid Trial (ISAT) data show that coiling compared favourably with clipping in the early posttreatment phase. We present a 4-year, single unit experience comparing cerebral angiography at 6 months postclipping and postcoiling, defining the proportion of aneurysms in either group, which were incompletely excluded from the cerebral circulation after treatment. There were 4 'dog-ear' remnants (4.6%) in the clipping group of 86 aneurysms, one of which required further surgery. Thirty-one out of 82 (37.8%) coiled aneurysms that underwent check angiography were inadequately excluded from the cerebral circulation at 6 months. Of these, to date, four patients have undergone re-coiling. Although the immediate complications of coiling may be less than those of clipping (ISAT), it seems that the degree and permanence of exclusion of an aneurysm from the cerebral circulation may be more secure with surgery. In summary, the rates of incomplete aneurysmal exclusion from the cerebral circulation, the requirement for reintervention and the requirement for continuing surveillance were all higher in the coiled population than in the clipped population.

How much can be concluded from the International Subarachnoid Aneurysm Trial (ISAT)?

Recently published data from the International Subarachnoid Aneurysm Trial (ISAT) shows that for patients enrolled in the trial there is a 7.4% reduction in the incidence of death or dependency at 1 year if they undergo coiling, rather than clipping. Furthermore, extrapolation of longer-term follow-up data for patient mortality appears to suggest that this advantage will be maintained in the longer term. Based on a reassessment of the published data, the authors note: (1) the incidence of rebleeding following treatment is approximately three times higher in the coiled group (p<0.001); (2) the need for aneurysm retreatment is likely to be higher in the coiled group; (3) trends in longer-term mortality data are not a reliable basis for predicting future outcomes of the trial; (4) trends in longer-term morbidity data are more reliable and suggest that the advantage of coiling diminishes with time; (5) The absence of up-to-date published rates of aneurysm retreatment and of longer-term rates of death or dependence makes ISAT extremely hard to interpret. It is far from clear that the early advantage of coiling will be maintained in the future and, hence, longer follow-up is required. Treatment of aneurysms is a continually evolving field and there is currently no other major source of information concerning management of aneurysms. For these reasons the authors recommend the instigation of a national aneurysm registry to prospectively collect data.

Acid ceramidase upregulation in prostate cancer cells confers resistance to radiation: AC inhibition, a potential radiosensitizer

Radiation resistance in a subset of prostate tumors remains a challenge to prostate cancer radiotherapy. The current study on the effects of radiation on prostate cancer cells reveals that radiation programs an unpredicted resistance mechanism by upregulating acid ceramidase (AC). Irradiated cells demonstrated limited changes of ceramide levels while elevating levels of sphingosine and sphingosine-1-phosphate. By genetically downregulating AC with small interfering RNA (siRNA), we observed radiosensitization of cells using clonogenic and cytotoxicity assays. Conversely, AC overexpression further decreased sensitivity to radiation. We also observed that radiation-induced AC upregulation was sufficient to create cross-resistance to chemotherapy as demonstrated by decreased sensitivity to Taxol and C(6) ceramide compared to controls. Lower levels of caspase 3/7 activity were detected in cells pretreated with radiation, also indicating increased resistance. Finally, utilization of the small molecule AC inhibitor, LCL385, sensitized PPC-1 cells to radiation and significantly decreased tumor xenograft growth. These data suggest a new mechanism of cancer cell resistance to radiation, through upregulation of AC that is, in part, mediated by application of the therapy itself. An improved understanding of radiotherapy and the application of combination therapy achieved in this study offer new opportunities for the modulation of radiation effects in the treatment of cancer.

Molecular targeting of acid ceramidase: implications to cancer therapy

Increasingly recognized as bioactive molecules, sphingolipids have been studied in a variety of disease models. The impact of sphingolipids on cancer research facilitated the entry of sphingolipid analogues and enzyme modulators into clinical trials. Owing to its ability to regulate two bioactive sphingolipids, ceramide and sphingosine-1-phosphate, acid ceramidase (AC) emerges as an attractive target for drug development within the sphingolipid metabolic pathway. Indeed, there is extensive evidence supporting a pivotal role for AC in lipid metabolism and cancer biology. In this article, we review the current knowledge of the biochemical properties of AC, its relevance to tumor promotion, and its molecular targeting approaches.

Novel analogs of D-e-MAPP and B13. Part 1: synthesis and evaluation as potential anticancer agents

A series of novel isosteric analogs of the ceramidase inhibitors, (1S,2R)-N-myristoylamino-phenylpropanol-1 (d-e-MAPP) and (1R,2R)-N-myristoylamino-4'-nitro-phenylpropandiol-1,3 (B13), with modified targeting and physicochemical properties were designed, synthesized, and evaluated as potential anticancer agents. When MCF7 cells were treated with the analogs, results indicated that the new analogs were of equal or greater potency compared to the parent compounds. Their activity was predominantly defined by the nature of the modification of the N-acyl hydrophobic interfaces: N-acyl analogs (class A), urea analogs (class B), N-alkyl analogs (class C, lysosomotropic agents), and omega-cationic-N-acyl analogs (class D, mitochondriotropic agents). The most potent compounds belonged to either class D, the aromatic ceramidoids, or to class C, the aromatic N-alkylaminoalcohols. Representative analogs selected from this study were also evaluated by the National Cancer Institute In Vitro Anticancer Drug Discovery Screen. Again, results showed a similar class-dependent activity. In general, the active analogs were non-selectively broad spectrum and had promising activity against all cancer cell lines. However, some active analogs of the d-e-MAPP family were selective against different types of cancer. Compounds LCL85, LCL120, LCL385, LCL284, and LCL204 were identified to be promising lead compounds for therapeutic development.

Novel analogs of D-e-MAPP and B13. Part 2: signature effects on bioactive sphingolipids

Novel isosteric analogs of the ceramidase inhibitors (1S,2R)-N-myristoylamino-phenylpropanol-1 (d-e-MAPP) and (1R,2R)-N-myristoylamino-4'-nitro-phenylpropandiol-1,3 (B13) with modified targeting and physicochemical properties were developed and evaluated for their effects on endogenous bioactive sphingolipids: ceramide, sphingosine, and sphingosine 1-phosphate (Cer, Sph, and S1P) in MCF7 cells as determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). Time- and dose-response studies on the effects of these compounds on Cer species and Sph levels, combined with structure-activity relationship (SAR) data, revealed 4 distinct classes of analogs which were predominantly defined by modifications of the N-acyl-hydrophobic interfaces: N-acyl-analogs (class A), urea-analogs (class B), N-alkyl-analogs (class C), and omega-cationic-N-acyl analogs (class D). Signature patterns recognized for two of the classes correspond to the cellular compartment of action of the new analogs, with class D acting as mitochondriotropic agents and class C compounds acting as lysosomotropic agents. The neutral agents, classes A and B, do not have this compartmental preference. Moreover, we observed a close correlation between the selective increase of C(16)-, C(14)-, and C(18)-Cers and inhibitory effects on MCF7 cell growth. The results are discussed in the context of compartmentally targeted regulators of Sph, Cer species, and S1P in cancer cell death, emphasizing the role of C(16)-Cer. These novel analogs should be useful in cell-based studies as specific regulators of Cer-Sph-S1P inter-metabolism, in vitro enzymatic studies, and for therapeutic development.

Tissue-specific shRNA delivery: a novel approach for gene therapy in cancer

A novel tissue-specific shRNA delivery system has been developed using cre-lox technology. Conditionally silenced pSico vector containing oligonucleotides of CD44shRNA and tissue-specific promoter-driven Cre-recombinase expression vector are packaged into transferrin-coated nanoparticles that can deliver shRNA into specific tumors. This system has strong potential in cancer therapy.

Specific isoforms of p73 control the induction of cell death induced by the viral proteins, E1A or apoptin

A member of the p53 family, p73, has several isoforms and differentially regulates transcription of genes involved in the control of the cell cycle and apoptosis. We have previously shown efficient and p53-independent, tumor-specific cell death induced by the viral proteins E1A and Apoptin. Here, we demonstrate that the induction of apoptosis by these viral proteins involves activation of TAp73. Both E1A and Apoptin induced expression of endogenous TAp73 and the p53/p73 BH3-only pro-apoptotic target, PUMA, independently of the p53 function. Furthermore, exogenous expression of TAp73 isoforms, particularly TAp73beta, sensitized cells to killing by both E1A and Apoptin, while expression of DeltaNp73alpha blocked this activity. Besides, knockout of the p73 regulator, c-Abl, attenuated E1A-induced apoptosis. In accordance with the role of p73 in apoptosis induced by these viral proteins, overexpression of TAp73beta strongly induced apoptosis in p53-deficient cancer cells in vitro and in HNSCC xenografts. Using a doxycycline-inducible system, we provide evidence for target selectivity and significant differences in protein stability for specific p73 isoforms, suggesting a diverse and pivotal role for p73 in response to various genotoxic agents. Collectively, our data show that in the absence of the p53 function, viral proteins E1A and Apoptin utilize the p73 pathway to induce efficient tumor cell death.

Clinical relevance of ceramide metabolism in the pathogenesis of human head and neck squamous cell carcinoma (HNSCC): attenuation of C(18)-ceramide in HNSCC tumors correlates with lymphovascular invasion and nodal metastasis

It has been documented previously that defects in the generation of C(18)-ceramide, a product of ceramide synthase 1 (CerS1), also known as longevity assurance gene 1 (hLASS1), play important roles in the pathogenesis and/or progression of HNSCC. However, whether altered levels of ceramide generation in HNSCC tumors have any clinical relevance remains unknown. In this study, the levels of endogenous ceramides were measured in tumor tissues of 45 HNSCC patients as compared to their normal tissues using high-pressure liquid chromatography/mass spectrometry (LC/MS), and then possible link between ceramide levels and the clinical parameters of HNSCC were examined. The data showed that the levels of C(16)-, C(24)-, C(24:1)-ceramides were significantly elevated in the majority of tumor tissues compared to their normal tissues, while the levels of only C(18)-ceramide were significantly decreased in HNSCC tumors, especially in tumor tissues of male patients. Importantly, it was also shown here that decreased C(18)-ceramide levels in HNSCC tumor tissues were significantly associated with the higher incidences of lymphovascular invasion, and pathologic nodal metastasis. Importantly, attenuation of C(18)-ceramide was also positively linked to the higher overall stages of the primary HNSCC tumors. Therefore, these data suggest, for the first time, that the defects in the generation/accumulation of C(18)-ceramide might have important clinical roles in HNSCC, especially in lymphovascular invasion and nodal disease.

Recent Advances and Current Challenges in Tumor Immunology and Immunotherapy

Despite advances in animal studies, where the cure of the majority of mice with pre-established (albeit early-stage) tumors has become almost standard, human clinical trials have been much less successful. Here we describe some of the most recent advances in the specialist field of tumor immunology and immunotherapy, highlighting salient work to identify key problem areas and potential solutions. We make particular note of recent developments in adoptive therapy; whole-cell, DNA, and peptide vaccines; and antibody therapy. We also describe the revival of interest in regulatory T cells and conclude by detailing the need for clinical trial read-out autonomy and methods to predict which patients will respond to a particular treatment.

Lysosomotropic acid ceramidase inhibitor induces apoptosis in prostate cancer cells

PURPOSE

Alterations in ceramide metabolism have been reported in prostate cancer (PCa), resulting in escape of cancer cells from ceramide-induced apoptosis. Specifically, increased expression of lysosomal acid ceramidase (AC) has been shown in some primary PCa tissues and in several PCa cell lines. To determine if this represents a novel therapeutic target, we designed and synthesized LCL204, a lysosomotropic analog of B13, a previously reported inhibitor of AC METHODS: Prostate cancer cell lines were treated with LCL204 for varying times and concentrations. Effects of treatment on cytotoxicity, sphingolipid content, and apoptotic markers were assessed.

RESULTS

Treatment of DU145 PCa cells resulted in increased ceramide and decreased sphingosine levels. Interestingly, LCL204 caused degradation of AC in a cathepsin-dependent manner. We also observed rapid destabilization of lysosomes and the release of lysosomal proteases into the cytosol following treatment with LCL204. Combined, these events resulted in mitochondria depolarization and executioner caspase activation, ultimately ending in apoptosis

CONCLUSIONS

These results provide evidence that treatment with molecules such as LCL204, which restore ceramide levels in PCa cells may serve as a new viable treatment option for PCa.

HLA Class II Protein Expression in Prostate Cancer Cells (48.22)

Prostate cancer is the second most commonly diagnosed cancer in men. Presently, there is no effective treatment for patients who develop recurrence, or for those who have metastatic disease at the time of diagnosis. Recent evidence suggests that reduced expressions of target protein antigens as well as HLA molecules are the predominant immune escape mechanisms of malignant prostate tumors. The purpose of this study was to investigate the prospect of antigen specific immunotherapy against prostate cancer via the HLA class II pathway of immune recognition. Here, we show for the first time that prostate cancer cells express functional HLA class II proteins that are recognized by T cells. We also show that prostate cancer cells can be induced with IFN-γ to express high levels of class II proteins as well as an enzyme, lysosomal thiol reductase (GILT), that may facilitate enhanced class II antigen presentation and CD4+ T cell recognition. Select prostate tumors can be transduced with HLA class II molecules resulting in efficiently presented antigenic peptides that also stimulate CD4+ T cells. These data suggest that prostate cancer cells can be targeted via the HLA class II pathway, and that genetically manipulated prostate tumor cells can be employed for direct antigen presentation, and CD4+ T cell mediated tumor therapy.

International Society for Cell and Gene Therapy of Cancer: 2005 meeting in Shenzhen, China

The 2005 International Society for Cell and Gene Therapy of Cancer (ISCGT) Congress was held in Shenzhen, China (www.iscgtchina2005.com) from December 9th-11th 2005. Here, we describe a representation of the most seminal presentations providing an overview of the progress in the field of cancer gene therapy including the successful introduction of the first approved gene therapy drug.

Involvement of sphingolipids in apoptin-induced cell killing

The potential anti-tumor agent Apoptin activates apoptosis in many human cancers and transformed cell lines, but is believed to be less potent in primary cells. Although caspase 3 is activated during apoptin-induced apoptosis, the mechanism of tumor cell killing remains elusive. We now show that apoptin-mediated cell death involves modulation of the sphingomyelin-ceramide pathway. Treating cells with Ad-GFPApoptin resulted in increased ceramide accumulation and enhanced expression of acid sphingomyelinase (ASMase) with a concomitant increase in ASMase activity and decreased sphingomyelin. Using confocal microscopy, ASMase, normally present in the endosomal/lysosomal compartment, was observed to translocate to the cell's periphery. Cotreatment of Ad-GFPApoptin-infected cells with the ASMase inhibitor desipramine (2.5 muM) attenuated (30%; P<0.01) apoptin-induced cell death. Apoptin was also able to induce a significant decline in sphingosine content by inhibition of ceramide deacylation through down-regulation of acid ceramidase at the protein level. Supporting the role of ceramide in apoptin action, treatment of cells with the combination of an exogenous cell-permeable ceramide analog (C6-ceramide) and Ad-GFPApoptin infection yielded a significant increase (P<0.01) in apoptosis over either treatment modality alone. Together, these data suggest that apoptin modulates ceramide/sphingolipid metabolism as part of its mechanism of action.

New insights on the use of desipramine as an inhibitor for acid ceramidase

Treatment of different cancer cell lines with desipramine induced a time- and dose-dependent downregulation of acid ceramidase. Desipramine's effect on acid ceramidase appeared specific for amphiphilic agents (desipramine, chlorpromazine, and chloroquine) but not other lysomotropic agents such as ammonium chloride and bafilomycin A1, and was not transcriptionally regulated. The cathepsin B/L inhibitor, CA074ME, but not the cathepsin D inhibitor, pepstatin A, blocked desipramine's effect on acid ceramidase. Desipramine led to a more pronounced downregulation of sphingosine compared to ceramide suggesting acid ceramidase inhibition is important to desipramine's mechanism of action. This study reveals a new mechanism of action for desipramine.

Modulation of ceramide metabolism enhances viral protein apoptin's cytotoxicity in prostate cancer

Despite local and systemic therapies, the National Cancer Institute estimates that prostate cancer will cause over 30,000 deaths in 2006. This suggests that additional therapeutic approaches are needed. The chicken anemia viral protein Apoptin causes tumor-selective apoptosis in human tumor lines independent of p53 and Bcl-2 status. Tet-regulated expression of Apoptin from an adenoviral vector showed cytotoxicity in DU145, PC-3, and LNCaP tumor cells regardless of expression of p53, Bcl-2, Bcl-xL, Bax, survivin, FLIP(S), XIAP, or CIAP. Apoptin expression caused an increase in the tumor suppressor lipid ceramide, which regulates the cellular stress response. Interestingly, 10 of 15 primary prostate cancers examined by Western blotting overexpressed acid ceramidase (AC), suggesting that ceramide deacylation might serve to negate elevated levels of ceramide, creating a more antiapoptotic phenotype. This was confirmed in AC-overexpressing cells in which we observed decreased sensitivity to apoptosis following treatment with Apoptin. Addition of the AC inhibitor LCL204, in combination with Apoptin, augmented cell killing. This effect was also demonstrated in vivo in that Apoptin and LCL204 cotreatment significantly reduced tumor growth in DU145 xenografts (P<0.05). Taken together, our data demonstrated that Apoptin is a promising therapeutic agent for prostate cancer and that its function is improved when combined with acid ceramidase inhibitors.

Acid Ceramidase but Not Acid Sphingomyelinase Is Required for Tumor Necrosis Factor-α-induced PGE2 Production

Sphingolipids are well established effectors of signal transduction downstream of the tumor necrosis factor (TNF) receptor. In a previous study, we showed that the sphingosine kinase/sphingosine 1-phosphate (S1P) pathway couples TNF receptor to induction of the cyclooxygenase 2 gene and prostaglandin synthesis (Pettus, B. J., Bielawski, J., Porcelli, A. M., Reames, D. L., Johnson, K. R., Morrow, J., Chalfant, C. E., Obeid, L. M., and Hannun, Y. A. (2003) FASEB J. 17, 1411-1421). In this study, the requirement for acid sphingomyelinase and sphingomyelin metabolites in the TNFalpha/prostaglandin E(2) (PGE(2)) pathway was investigated. The amphiphilic compound desipramine, a frequently employed inhibitor of acid sphingomyelinase (ASMase), blocked PGE(2) production. However, the action of desipramine was independent of its action on ASMase, since neither genetic loss of ASMase (Niemann-Pick fibroblasts) nor knockdown of ASMase using RNA interference affected TNFalpha-induced PGE(2) synthesis. Further investigations revealed that desipramine down-regulated acid ceramidase (AC), but not sphingosine kinase, at the protein level. This resulted in a time-dependent drop in sphingosine and S1P levels. Moreover, exogenous administration of either sphingosine or S1P rescued PGE(2) biosynthesis after desipramine treatment. Interestingly, knockdown of endogenous AC by RNA interference attenuated cyclooxygenase 2 induction by TNFalpha and subsequent PGE(2) biosynthesis. Taken together, these results define a novel role for AC in the TNFalpha/PGE(2) pathway. In addition, the results of this study warrant careful reconsideration of desipramine as a specific inhibitor for ASMase.

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.

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

In this study, we investigated the in vitro and in vivo efficacy of Fas ligand (FasL) gene therapy for the treatment of head and neck cancer. Three head and neck squamous cell carcinoma (HNSCC) cell lines (SCC-1, SCC-12, and SCC-14a) were treated with the Fas agonist CH-11, a monoclonal antibody to the Fas receptor, or with a replication-incompetent adenovirus (AdGFPFasL) expressing a modified murine Fas ligand gene fused to green fluorescent protein (GFP). A replication-incompetent adenovirus containing the GFP gene alone was used as a control for viral transduction toxicity (AdGFP). Cell death was quantified using a tetrazolium-based (MTS) assay. Cells were analyzed by flow cytometry to determine the expression of adenoviral and Fas receptors on the surface of the cells. Our results showed that the head and neck cancer cell lines are resistant to cell death induction when treated with the anti-Fas monoclonal antibody CH-11. This resistance can be overcome with AdGFPFasL, which was able to induce cell death in all three cell lines. Apoptosis induction was demonstrated using Western blotting by evaluating poly(ADP-ribose) polymerase, and caspase 9 cleavages. In addition, intratumoral injections of AdGFPFasL into SCC-14a xenografts induced significant growth suppression of tumors, indicating that FasL gene therapy may provide a new efficient therapeutic modality for HNSCC that is worthy of a clinical trial.