Caspase-dependent and -independent cell death of Jurkat human leukemia cells induced by novel synthetic ceramide analogs

Antineoplastic Agents Targeting Sphingolipid Pathways

Emerging studies in the enigmatic area of bioactive lipids have made many exciting new discoveries in recent years. Once thought to play a strictly structural role in cellular function, it has since been determined that sphingolipids and their metabolites perform a vast variety of cellular functions beyond what was previously believed. Of utmost importance is their role in cellular signaling, for it is now well understood that select sphingolipids serve as bioactive molecules that play critical roles in both cancer cell death and survival, as well as other cellular responses such as chronic inflammation, protection from intestinal pathogens, and intrinsic protection from intestinal contents, each of which are associated with oncogenesis. Importantly, it has been demonstrated time and time again that many different tumors display dysregulation of sphingolipid metabolism, and the exact profile of said dysregulation has been proven to be useful in determining not only the presence of a tumor, but also the susceptibility to various chemotherapeutic drugs, as well as the metastasizing characteristics of the malignancies. Since these discoveries surfaced it has become apparent that the understanding of sphingolipid metabolism and profile will likely become of great importance in the clinic for both chemotherapy and diagnostics of cancer. The goal of this paper is to provide a comprehensive review of the current state of chemotherapeutic agents that target sphingolipid metabolism that are undergoing clinical trials. Additionally, we will formulate questions involving the use of sphingolipid metabolism as chemotherapeutic targets in need of further research.

Fludarabine-resistance associates with ceramide metabolism and leukemia stem cell development in chronic lymphocytic leukemia

Fludarabine (flu) -containing regimens such as flu, cyclophosphamide and rituximab have been established as one of the standard first line therapy in medically-fit chronic lymphocytic leukemia (CLL) patients. Therefore, flu-refractory (primary flu-insensitivity or flu-caused relapse) remains a major problem causing treatment failure for CLL patients. We isolated the peripheral blood mononuclear cells (PBMCs) from CLL patients and treated with flu to find flu-refractory cases, and established flu-resistant clonal cells to study molecular mechanism of flu-resistance. By comparing parental MEC-2 cells, a human CLL cell line, we found that flu-resistant clonal cells were significantly increased lethal dose 50 of flu concentration, and up-regulated expression of P-glycoprotein, a drug-resistant marker, glucosylceramide synthase (GCS), an enzyme that can convert ceramide to glucosylceramide, and CD34, a leukemia stem cell marker. Overexpression of GCS leads to promptly elimination of cellular ceramide levels and accumulation of glucosylceramide, which reduces apoptosis and promotes survival and proliferation of flu-resistant clonal cells. Furthermore, we demonstrated that the accumulation of glucosylceramide can be blocked by PDMP to restore flu-sensitivity in flu-resistant clonal cells. We also found that elevating glucosylceramide levels in flu-resistant clonal cells was associated with up-regulation of GCS and CD34 expression. Importantly, overexpression of GCS or CD34 was also determined in flu-refractory PBMCs. Our results show that flu-resistance is associated with the alteration of ceramide metabolism and the development of leukemia stem cell-like cells. The flu-resistance can be reversed by GCS inhibition as a novel strategy for overcoming drug resistance.

The Ayurvedic plant Bacopa monnieri inhibits inflammatory pathways in the brain

ETHNOPHARMACOLOGICAL RELEVANCE

Bacopa monnieri (L) Wettst (common name, bacopa) is a medicinal plant used in Ayurveda, the traditional system of medicine of India, as a nootropic. It is considered to be a "medhya rasayana", an herb that sharpens the mind and the intellect. Bacopa is an important ingredient in many Ayurvedic herbal formulations designed to treat conditions such as memory loss, anxiety, poor cognition and loss of concentration. It has also been used in Ayurveda to treat inflammatory conditions such as arthritis. In modern biomedical studies, bacopa has been shown in animal models to inhibit the release of the pro-inflammatory cytokines TNF-α and IL-6. However, less is known regarding the anti-inflammatory activity of Bacopa in the brain.

AIM OF THE STUDY

The current study examines the ability of Bacopa to inhibit the release of pro-inflammatory cytokines from microglial cells, the immune cells of the brain that participate in inflammation in the CNS. The effect of Bacopa on signaling enzymes associated with CNS inflammatory pathways was also studied.

MATERIALS AND METHODS

Various extracts of Bacopa were prepared and examined in the N9 microglial cell line in order to determine if they inhibited the release of the proinflammatory cytokines TNF-α and IL-6. Extracts were also tested in cell free assays as inhibitors of caspase-1 and matrix metalloproteinase-3 (enzymes associated with inflammation) and caspase-3, which has been shown to cleave protein Tau, an early event in the development of Alzheimer's disease.

RESULTS

The tea, infusion, and alkaloid extracts of bacopa, as well as Bacoside A significantly inhibited the release of TNF-α and IL-6 from activated N9 microglial cells in vitro. In addition, the tea, infusion, and alkaloid extracts of Bacopa effectively inhibited caspase 1 and 3, and matrix metalloproteinase-3 in the cell free assay.

CONCLUSIONS

Bacopa inhibits the release of inflammatory cytokines from microglial cells and inhibits enzymes associated with inflammation in the brain. Thus, Bacopa can limit inflammation in the CNS, and offers a promising source of novel therapeutics for the treatment of many CNS disorders.

Ceramide as a Target of Marine Triterpene Glycosides for Treatment of Human Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous myeloid clonal disorder exhibiting the accumulation of immature myeloid progenitors in the bone marrow and peripheral blood. Standard AML therapy requires intensive combination chemotherapy, which leads to significant treatment-related toxicity. The search for new, low toxic marine agents, inducing the generation of ceramide in leukemic cells is a new approach to improve the therapy of leukemia. This review focuses on the metabolism of sphingolipids, the role of ceramide in treating leukemia, and the antitumor activity, related to ceramide metabolism, of some marine metabolites, particularly stichoposides, triterpene glycosides extracted from sea cucumbers of the family Stichopodiidae.

Inhibitors of Ceramidases

The topic of ceramidases has experienced an enormous boost during the last few years. Ceramidases catalyze the degradation of ceramide to sphingosine and fatty acids. Ceramide is not only the central hub of sphingolipid biosynthesis and degradation, it is also a key molecule in sphingolipid signaling, promoting differentiation or apoptosis. Acid ceramidase inhibition sensitizes certain types of cancer to chemo- and radio-therapy and this is suggestive of a role of acid ceramidase inhibitors as chemo-sensitizers which can act synergistically with chemo-therapeutic drugs. In this review, we summarize the development of ceramide analogues as first-generation ceramidase inhibitors together with data on their activity in cells and disease models. Furthermore, we describe the recent developments that have led to highly potent second-generation ceramidase inhibitors that act at nanomolar concentrations. In the third part, various assays of ceramidases are described and their relevance for accurately measuring ceramidase activities and for the development of novel inhibitors is highlighted. Besides potential clinical implications, the recent improvements in ceramidase inhibition and assaying may help to better understand the mechanisms of ceramide biology.

Bioactive Secondary Metabolites from Acid Mine Waste Extremophiles

The extremophilic microbes of the Berkeley Pit Lake are a valuable source of new and interesting secondary metabolites. It is of particular interest that these acidophilic microbes produce small molecule inhibitors of pathways associated with low pH and high Eh. These same small molecules also inhibit molecular pathways induced by reactive oxygen species (ROS) and inflammation in mammalian cells. Low pH is a hallmark of inflammation and high Eh is one of ROS, so the suitability of this collection as a source of bioactive metabolites is actually quite biorational. Compound isolation was guided by inhibition of caspase-1 and matrix metalloproteinase-3, and active compounds were sent to the National Cancer Institute-Developmental Therapeutics Program and Memorial Sloan Kettering Cancer center for evaluation as either antiproliferative or cytotoxic agents.

A review of ceramide analogs as potential anticancer agents

Ceramide serves as a central mediator in sphingolipid metabolism and signaling pathways, regulating many fundamental cellular responses. It is referred to as a 'tumor suppressor lipid', since it powerfully potentiates signaling events that drive apoptosis, cell cycle arrest, and autophagic responses. In the typical cancer cell, ceramide levels and signaling are usually suppressed by overexpression of ceramide-metabolizing enzymes or downregulation of ceramide-generating enzymes. However, chemotherapeutic drugs as well as radiotherapy increase intracellular ceramide levels, while exogenously treating cancer cells with short-chain ceramides leads to anticancer effects. All evidence currently points to the fact that the upregulation of ceramide levels is a promising anticancer strategy. In this review, we exhibit many anticancer ceramide analogs as downstream receptor agonists and ceramide-metabolizing enzyme inhibitors.

Cytotoxic activity and quantitative structure activity relationships of arylpropyl sulfonamides

B13 is a ceramide analogue and apoptosis inducer with potent cytotoxic activity. A series of arylpropyl sulfonamide analogues of B13 were evaluated for their cytotoxicity using MTT assays in prostate cancer PC-3 and leukemia HL-60 cell lines. Some compounds (4, 9, 13, 14, 15, and 20) showed stronger activities than B13 in both tumor cell lines, and compound (15) gave the most potent activity with IC₅₀ values of 29.2 and 20.7 µM, for PC-3and HL-60 cells, respectively. Three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis was performed to build highly reliable and predictive CoMSIA models with cross-validated q² values of 0.816 and 0.702, respectively. Our results suggest that long alkyl chains and a 1R, 2R configuration of the propyl group are important for the cytotoxic activities of arylpropyl sulfonamides. Moreover, the introduction of small hydrophobic groups in the phenyl ring and sulfonamide group could increase biological activity.

Calcium and mitochondrial metabolism in ceramide-induced cardiomyocyte death

Ceramides are important intermediates in the biosynthesis and degradation of sphingolipids that regulate numerous cellular processes, including cell cycle progression, cell growth, differentiation and death. In cardiomyocytes, ceramides induce apoptosis by decreasing mitochondrial membrane potential and promoting cytochrome-c release. Ca(2+) overload is a common feature of all types of cell death. The aim of this study was to determine the effect of ceramides on cytoplasmic Ca(2+) levels, mitochondrial function and cardiomyocyte death. Our data show that C2-ceramide induces apoptosis and necrosis in cultured cardiomyocytes by a mechanism involving increased Ca(2+) influx, mitochondrial network fragmentation and loss of the mitochondrial Ca(2+) buffer capacity. These biochemical events increase cytosolic Ca(2+) levels and trigger cardiomyocyte death via the activation of calpains.

Novel 3-hydroxy vinylboronates influence sphingolipid metabolism, cause apoptosis in Jurkat cells and prevent tumor development in nude mice

A series of novel 3-hydroxy vinylboronates which share structural similarities with sphingolipids were synthesized and tested in vitro and in vivo as anticancer agents. The molecules reduced cancer cell survival in vitro by influencing their sphingolipid metabolism. In a cancer model in nude mice the lead compound E7 prevented the development of tumor as long as the treatment period continued. Moreover, it delayed tumor growth after the treatment was finished.

Caspase-1 inhibitors from an extremophilic fungus that target specific leukemia cell lines

Berkeley Pit Lake, Butte, Montana, is a 540 m deep abandoned open-pit copper mine filled with over 140 billion liters of acidic, metal-sulfate-contaminated water. This harsh environment has yielded several microorganisms that produce interesting biologically active compounds. Several polyketide metabolites including the new berkazaphilones A (1) and B (2) and octadienoic acid derivatives berkedienoic acid (13) and berkedienolactone (15), as well as previously reported azaphilone 4, vermistatin (6), dihydrovermistatin (7), penisimplicissin (8), aldehyde 9, and methylparaconic acid (11), were isolated from a culture broth of Penicillium rubrum taken from a depth of 270 m. The structures of these compounds were deduced by interpretation of spectroscopic data. The compounds were isolated either for their inhibition of the signal transduction enzyme caspase-1 or because of their structural similarity to these inhibitors. Selected compounds were further evaluated for their ability to inhibit interleukin-1β production by inflammasomes in induced THP-1 cells. Berkazaphilones B (2) and C (4) and vermistatin analogue penisimplicissin (8) exhibited selective activity against leukemia cancer cell lines in the National Cancer Institute 60 human cell line assay.

Cytotoxicities and Quantitative Structure Activity Relationships of B13 Sulfonamides in HT-29 and A549 Cells

B13 analogues are being considered as therapeutic agents for cancer cells, since B13 is a ceramide analogue and inhibits ceramidase to promote apoptosis in cancer cells. B13 sulfonamides are assumed to have biological activity similar to B13, since they are made by bioisosterically substituting the carboxyl moiety of B13 with sulfone group. Twenty B13 sulfonamides were evaluated for their in vitro cytotoxicities against human colon cancer HT-29 and lung cancer A549 cell lines using MTT assays. Replacement of the amide group with a sulfonamide group increased cytotoxicity in both cancer cell lines. The sulfonamides with long alkyl chains exhibited activities two to three times more potent than that of B13 and compound (15) had the most potent activity with IC₅₀ values of 27 and 28.7µM for HT-29 and A549, respectively. The comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were used to carry out QSAR molecular modeling of these compounds. The predictive CoMSIA models for HT-29 and A549 gave cross-validated q2 values of 0.703 and 0.830, respectively. From graphical analysis of these models, we suppose that the stereochemistry of 1,3-propandiol is not important for activity and that introduction of a sulfonamide group and long alkyl chains into B13 can increase cytotoxicity.

Ordering of ceramide formation and caspase-9 activation in CD95L-induced Jurkat leukemia T cell apoptosis

Ceramide, a biologically active sphingolipid in cell death signaling, accumulates upon CD95L treatment, concomitantly to apoptosis induction in Jurkat leukemia T cells. Herein, we show that ceramide did not increase in caspase-8 and -10-doubly deficient Jurkat cells in response to CD95L, indicating that apical caspases are essential for CD95L-triggered ceramide formation. Jurkat cells are typically defined as type 2 cells, which require the activation of the mitochondrial pathway for efficient apoptosis induction in response to CD95L. Caspase-9-deficient Jurkat cells significantly resisted CD95L-induced apoptosis, despite ceramide accumulation. Knock-down of sphingomyelin synthase 1, which metabolizes ceramide to sphingomyelin, enhanced (i) CD95L-triggered ceramide production, (ii) cytochrome c release from the mitochondria and (iii) caspase-9 activation. Exogenous ceramide-induced caspase-3 activation and apoptosis were impaired in caspase-9-deficient Jurkat cells. Conversely, caspase-9 re-expression in caspase-9-deficient Jurkat cells restored caspase-3 activation and apoptosis upon exogenous ceramide treatment. Collectively, our data provide genetic evidence that CD95L-triggered endogenous ceramide increase in Jurkat leukemia T cells (i) is not a mere consequence of cell death and occurs mainly in a caspase-9-independent manner, (ii) is likely involved in the pro-apoptotic mitochondrial pathway leading to caspase-9 activation.

Control of metabolism and signaling of simple bioactive sphingolipids: Implications in disease

Simple bioactive sphingolipids include ceramide, sphingosine and their phosphorylated forms sphingosine 1-phosphate and ceramide 1-phosphate. These molecules are crucial regulators of cell functions. In particular, they play important roles in the regulation of angiogenesis, apoptosis, cell proliferation, differentiation, migration, and inflammation. Decoding the mechanisms by which these cellular functions are regulated requires detailed understanding of the signaling pathways that are implicated in these processes. Most importantly, the development of inhibitors of the enzymes involved in their metabolism may be crucial for establishing new therapeutic strategies for treatment of disease.

Cytotoxicity and apoptosis enhancement in brain tumor cells upon coadministration of paclitaxel and ceramide in nanoemulsion formulations

The objective of this study was to examine augmentation of therapeutic activity in human glioblastoma cells with combination of paclitaxel (PTX) and the apoptotic signaling molecule, C(6)-ceramide (CER), when administered in novel oil-in-water nanoemulsions. The nanoemulsions were formulated with pine-nut oil, which has high concentrations of essential polyunsaturated fatty acid (PUFA). Drug-containing nanoemulsions were characterized for particle size, surface charge, and the particle morphology was examined with transmission electron microscopy (TEM). Epi-fluorescent microscopy was used to analyze nanoemulsion-encapsulated rhodamine-labeled PTX and NBD-labeled CER uptake and distribution in U-118 human glioblastoma cells. Cell viability was assessed with the MTS (formazan) assay, while apoptotic activity of PTX and CER was evaluated with caspase-3/7 activation and flow cytometry. Nanoemulsion formulations with the oil droplet size of approximately 200 nm in diameter were prepared with PTX, CER, and combination of the two agents. When administered to U-118 cells, significant enhancement in cytotoxicity was observed with combination of PTX and CER as compared to administration of individual agents. The increase in cytotoxicity correlated with enhancement in apoptotic activity in cells treated with combination of PTX and CER. The results of these studies show that oil-in-water nanoemulsions can be designed with combination therapy for enhancement of cytotoxic effect in brain tumor cells. In addition, PTX and CER can be used together to augment therapeutic activity, especially in aggressive tumor models such as glioblastoma.

Chemical tools to investigate sphingolipid metabolism and functions

Sphingolipids comprise an important group of biomolecules, some of which have been shown to play important roles in the regulation of many cell functions. From a structural standpoint, they all share a long 2-amino-1,3-diol chain, which can be either saturated (sphinganine), hydroxylated at C4 (phytosphingosine), or unsaturated at C4 (sphingosine) as in most mammalian cells. N-acylation of sphingosine leads to ceramide, a key intermediate in sphingolipid metabolism that can be enzymatically modified at the C1-OH position to other biologically important sphingolipids, such as sphingomyelin or glycosphingolipids. In addition, both ceramide and sphingosine can be phosphorylated at C1-OH to give ceramide-1-phosphate and sphingosine-1-phosphate, respectively. To better understand the biological and biophysical roles of sphingolipids, many efforts have been made to design synthetic analogues as chemical tools able to unravel their structure-activity relationships, and to alter their cellular levels. This last approach has been thoroughly studied by the development of specific inhibitors of some key enzymes that play an important role in biosynthesis or metabolism of these intriguing lipids. With the above premises in mind, the aim of this review is to collect, in a systematic way, the recent efforts described in the literature leading to the development of new chemical entities specifically designed to achieve the above goals.

Ceramide-induced formation of ROS and ATP depletion trigger necrosis in lymphoid cells

In lymphocytes, Fas activation leads to both apoptosis and necrosis, whereby the latter form of cell death is linked to delayed production of endogenous ceramide and is mimicked by exogenous administration of long- and short-chain ceramides. Here molecular events associated with noncanonical necrotic cell death downstream of ceramide were investigated in A20 B lymphoma and Jurkat T cells. Cell-permeable, C6-ceramide (C6), but not dihydro-C6-ceramide (DH-C6), induced necrosis in a time- and dose-dependent fashion. Rapid formation of reactive oxygen species (ROS) within 30 min of C6 addition detected by a dihydrorhodamine fluorescence assay, as well as by electron spin resonance, was accompanied by loss of mitochondrial membrane potential. The presence of N-acetylcysteine or ROS scavengers like Tiron, but not Trolox, attenuated ceramide-induced necrosis. Alternatively, adenovirus-mediated expression of catalase in A20 cells also attenuated cell necrosis but not apoptosis. Necrotic cell death observed following C6 exposure was associated with a pronounced decrease in ATP levels and Tiron significantly delayed ATP depletion in both A20 and Jurkat cells. Thus, apoptotic and necrotic death induced by ceramide in lymphocytes occurs via distinct mechanisms. Furthermore, ceramide-induced necrotic cell death is linked here to loss of mitochondrial membrane potential, production of ROS, and intracellular ATP depletion.

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.

Modulation of Intracellular Ceramide Using Polymeric Nanoparticles to Overcome Multidrug Resistance in Cancer

Although multidrug resistance (MDR) is known to develop through a variety of molecular mechanisms within the tumor cell, many tend to converge toward the alteration of apoptotic signaling. The enzyme glucosylceramide synthase (GCS), responsible for bioactivation of the proapoptotic mediator ceramide to a nonfunctional moiety glucosylceramide, is overexpressed in many MDR tumor types and has been implicated in cell survival in the presence of chemotherapy. The purpose of this study was to investigate the therapeutic strategy of coadministering ceramide with paclitaxel, a commonly used chemotherapeutic agent, in an attempt to restore apoptotic signaling and overcome MDR in the human ovarian cancer cell line SKOV3. Poly(ethylene oxide)-modified poly(epsilon-caprolactone) (PEO-PCL) nanoparticles were used to encapsulate and deliver the therapeutic agents for enhanced efficacy. Results show that indeed the cotherapy eradicates the complete population of MDR cancer cells when they are treated at their IC(50) dose of paclitaxel. More interestingly, when the cotherapy was combined with the properties of nanoparticle drug delivery, the MDR cells can be resensitized to a dose of paclitaxel near the IC(50) of non-MDR (drug sensitive) cells, indicating a 100-fold increase in chemosensitization via this approach. Molecular analysis of activity verified the hypothesis that the efficacy of this therapeutic approach is indeed due to a restoration in apoptotic signaling, although the beneficial properties of PEO-PCL nanoparticle delivery seemed to enhance the therapeutic success even further, showing the promising potential for the clinical use of this therapeutic strategy to overcome MDR.

Synthesis of a Novel Ceramide Analogue and its Use in a High-Throughput Fluorogenic Assay for Ceramidases

Several investigations have shown that acid ceramidase inhibitors are potential antiproliferative and cytostatic drugs for cancer chemotherapy. The combinatorial chemistry approach for the discovery of acid ceramidase inhibitors requires the availability of a high-throughput enzyme assay. The synthesis of a novel fluorogenic ceramidase substrate, and its processing both in vitro and in cultured cells in a microtiter plate layout, are reported in this article. This coumarinic substrate was hydrolyzed in vitro (rat liver lysosomes) with Km and Vmax values of 113 microM and 3.6 pmol min-1 mg-1, respectively. Similarly, hydrolysis occurred in intact cultured cells that overexpressed acidic ceramidase. The assay was validated for the identification and characterization of acidic ceramidase inhibitors by using several alpha-ketoamide ceramide analogues, whose inhibitory activity had been previously described.

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.

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.

Design, synthesis and activity as acid ceramidase inhibitors of 2-oxooctanoyl and N-oleoylethanolamine analogues

The synthesis of novel N-acylethanolamines and their use as inhibitors of the aCDase is reported here. The compounds are either 2-oxooctanamides or oleamides of sphingosine analogs featuring a 3-hydroxy-4,5-hexadecenyl tail replaced by ether or thioether moieties. It appears that, within the 2-oxooctanamide family, the C3-OH group of the sphingosine molecule is required for inhibition both in vitro and in cultured cells. Furthermore, although the (E)-4 double bond is not essential for inhibitory activity, the (E) configuration is required, since the analogue with a (Z)-4 unsaturation was not inhibitory. None of the oleamides inhibited the aCDase in vitro. Conversely, with the exception of N-oleoylethanolamine and its analogs with S-decyl and S-hexadecyl substituents, all the synthesized oleamides inhibited the aCDase in cultured cells, although with a relatively low potency. We conclude that novel aCDase inhibitors can evolve from N-acylation of sphingoid bases with electron deficient-acyl groups. In contrast, chemical modification of the N-oleoylsphingosine backbone does not seem to offer an appropriate strategy to obtain aCDase inhibitors.

Sphingolipids as modulators of cancer cell death: potential therapeutic targets

Through modifications in the fine membrane structure, cell-cell or cell-matrix interactions, and/or modulation of intracellular signaling pathways, sphingolipids can affect the tumorigenic potential of numerous cell types. Whereas ceramide and its metabolites have been described as regulators of cell growth and apoptosis, these lipids as well as other sphingolipid molecules can modulate the ability of malignant cells to grow and resist anticancer treatments, and their susceptibility to non-apoptotic cell deaths. This review summarizes our current knowledge on the properties of sphingolipids in the regulation of cancer cell death and tumor development. It also provides an update on the potential perspectives of manipulating sphingolipid metabolism and using sphingolipid analogues in anticancer therapy.